Einstein’sCosmos

PUBLISHEDTITLESINTHEGREATDISCOVERIESSERIES

DavidFosterWallace:EverythingandMore:ACompactHistoryof

SherwinB.Nuland:TheDoctors’Plague:Germs,ChildbedFever,andtheStrangeStoryofIgnácSemmelweisMichioKaku:Einstein’sCosmos:HowAlbertEinstein’sVisionTransformedOurUnderstandingofSpaceandTime

BarbaraGoldsmith:ObsessiveGenius:TheInnerWorldofMarieCurieRebeccaGoldstein:Incompleteness:TheProofandParadoxofKurtGodel

FORTHCOMINGTITLES

GeorgeJohnsononHubbleandtheMeasurementoftheUniverseDaniel

MendelsohnonArchimedesandtheScienceoftheAncientGreeksRichardReevesonRutherfordandtheAtom

MadisonSmarttBellonLavoisierandModernChemistryDavidLeavittonAlanTuringandtheComputer

WilliamT.VollmanonCopernicusandtheCopernicanRevolutionDavidQuammenonDarwinandEvolution

GENERALEDITORS:EDWINBARBERANDJESSECOHEN

BYMICHIOKAKU

BeyondEinstein

HyperspaceVisions

Einstein’sCosmos

ParallelWorlds

MICHIOKAKU

Einstein’sCosmos

HowAlbertEinstein’sVisionTransformedOurUnderstandingofSpaceandTime

W.W.NORTON&COMPANYNEWYORK•LONDON

ThisbookisdedicatedtoMichelleandAlyson.

Contents

Preface:ANewLookattheLegacyofAlbertEinsteinAcknowledgments

PartI.FirstPicture:RacingaLightBeam

CHAPTER1PhysicsbeforeEinsteinCHAPTER2TheEarlyYearsCHAPTER3SpecialRelativityandthe“MiracleYear”

PartII.SecondPicture:WarpedSpace-Time

CHAPTER4GeneralRelativityand“theHappiestThoughtofMyLife”CHAPTER5TheNewCopernicusCHAPTER6TheBigBangandBlackHoles

PartIII.TheUnfinishedPicture:TheUnifiedFieldTheory

CHAPTER7UnificationandtheQuantumChallengeCHAPTER8War,Peace,andE=mc2CHAPTER9Einstein’sPropheticLegacy

Notes

Bibliography

PREFACE

ANewLookattheLegacyofAlbertEinstein

Genius.Absent-mindedprofessor.Thefatherofrelativity.Themythicalfigureof Albert Einstein—hair flaming in the wind, sockless, wearing an oversizedsweatshirt, puffing on his pipe, oblivious to his surroundings—is etchedindelibly on ourminds. “Apop icon on a parwithElvis Presley andMarilynMonroe,he stares enigmatically frompostcards,magazinecovers,Tshirts, andlarger-than-lifeposters.ABeverlyHillsagentmarketshis image for televisioncommercials.Hewouldhavehateditall,”writesbiographerDenisBrian.Einstein is among the greatest scientists of all time, a towering figurewho

ranks alongside Isaac Newton for his contributions. Not surprisingly, TimemagazinevotedhimthePersonoftheCentury.Manyhistorianshaveplacedhimamongthehundredmostinfluentialpeopleofthelastthousandyears.Givenhisplaceinhistory,thereareseveralreasonsfortryingtomakeafresh

newefforttore-examinehislife.First,histheoriesaresodeepandprofoundthatthepredictionshemadedecadesagoarestilldominating theheadlines,so it isvitalthatwetrytounderstandtherootsofthesetheories.Asanewgenerationofinstruments that were inconceivable in the 1920s (e.g., satellites, lasers,supercomputers, nanotechnology, gravity wave detectors) probe the outerreaches of the cosmos and the interior of the atom, Einstein’s predictions arewinningNobelPrizes forotherscientists.Even thecrumbsoffEinstein’s tableareopeningupnewvistasforscience.The1993NobelPrize,forexample,wentto two physicists who indirectly confirmed the existence of gravity waves,predictedbyEinsteinin1916,byanalyzingthemotionofdoubleneutronstarsintheheavens.Also,the2001NobelPrizewenttothreephysicistswhoconfirmedtheexistenceofBose-Einsteincondensates,anewstateofmatterexistingnearabsolutezerothatEinsteinpredictedin1924.Other predictions are now being verified. Black holes, once considered a

bizarre aspect of Einstein’s theory, have now been identified by the HubbleSpaceTelescopeandtheVeryLargeArrayRadioTelescope.EinsteinringsandEinsteinlensesnotonlyhavebeenconfirmedbutalsoarekeytoolsastronomersusetomeasureinvisibleobjectsinouterspace.EvenEinstein’s“mistakes”arebeingrecognizedasprofoundcontributionsto

ourknowledgeoftheuniverse.In2001,astronomersfoundconvincingevidencethat the “cosmological constant,” thought to be Einstein’s greatest blunder,actually contains the largest concentration of energy in the universe and willdetermine the ultimate fate of the cosmos itself. So experimentally, there hasbeena“renaissance”inEinstein’slegacyasmoreevidencepilesupverifyinghispredictions.Second, physicists are re-evaluating his legacy and especially his thinking

process.While recent biographies haveminutely examined his private life forclues to theoriginsofhis theories,physicistsarebecoming increasinglyawarethatEinstein’stheoriesarebasednotsomuchonarcanemathematics(letalonehis love life!) but simple and elegant physical pictures. Einstein would oftencommentthatifanewtheorywasnotbasedonaphysicalimagesimpleenoughforachildtounderstand,itwasprobablyworthless.In thisbook, therefore, thesepictures, theseproductsofEinstein’s scientific

imagination, become a formal organizing principle aroundwhich his thinkingprocessandhisgreatestachievementsaredescribed.PartIusesthepicturethatEinsteinfirstthoughtofwhenhewassixteenyears

old:whatalightbeamwouldlooklikeifhecouldracealongsideit.Thispicture,inturn,wasprobablyinspiredbyachildren’sbookthatheread.Byvisualizingwhat happens if he were to race a light beam, Einstein isolated the keycontradiction between the two great theories of the time, Newton’s theory offorcesandMaxwell’stheoryoffieldsandlight.Intheprocessofresolvingthisparadox,heknewthatoneofthesetwogreattheories—Newton’s,asitturnsout—must fall. In some sense, all of special relativity (which would eventuallyunlockthesecretofthestarsandnuclearenergy)iscontainedinthispicture.InPartII,weareintroducedtoanotherpicture:Einsteinimaginedplanetsas

marblesrollingaroundacurvedsurfacecenteredatthesun,asanillustrationoftheideathatgravityoriginatesfromthebendingofspaceandtime.Byreplacingthe forcesofNewtonwith thecurvatureofasmoothsurface,Einsteingaveanentirely fresh, revolutionary picture of gravity. In this new framework, the“forces”ofNewtonwereanillusioncausedbythebendingofspaceitself.Theconsequences of this simple picturewould eventually give us black holes, thebigbang,andtheultimatefateoftheuniverseitself.PartIIIdoesn’thaveapicture—thissectionismoreaboutthefailuretocome

upwithanimageguidinghis“unifiedfieldtheory,”onethatwouldhavegivenEinsteinawaytoformulatethecrowningachievementoftwothousandyearsofinvestigation into the laws ofmatter and energy. Einstein’s intuition began tofalter,asalmostnothingwasknowninhis timeabout theforces thatgovernedthenucleusandsubatomicparticles.

Thisunfinishedunifiedfieldtheoryandhisthirty-yearsearchfora“theoryofeverything”wasbynomeansafailure—althoughthishasbeenrecognizedonlyrecently.Hiscontemporariessawitasafool’schase.ThephysicistandEinsteinbiographer Abraham Pais lamented, “In the remaining 30 years of his life heremained active in research but his fame would be undiminished, if notenhanced,hadhegone fishing instead.” Inotherwords,his legacymighthavebeenevengreaterifhehadleftphysicsin1925ratherthan1955.In the last decade, however, with the coming of a new theory called

“superstring theory” or “M-theory,” physicists have been re-evaluatingEinstein’slaterworkandhislegacy,asthesearchfortheunifiedfieldtheoryhasassumed center stage in theworld of physics.The race to attain the theory ofeverything has become the ultimate goal of a whole generation of young,ambitiousscientists.Unification,once thought tobe thefinalburialgroundforthecareersofagingphysicists,isnowthedominantthemeintheoreticalphysics.Inthisbook,Ihopetogiveanew,refreshinglookatthepioneeringworkof

Einstein,perhapsevenamoreaccurateportrayalofhisenduringlegacyasseenfrom the vantage point of simple physical pictures.His insights, in turn, havefueledthecurrentgenerationofrevolutionarynewexperimentsbeingconductedinouterspaceandinadvancedphysics laboratoriesandaredrivingthe intensesearch to fulfill hismost cherished dream, a theory of everything. This is theapproachtohislifeandhisworkthatIthinkhewouldhavelikedthebest.

AcknowledgmentsIwouldliketothankthehospitalityofthestaffatPrincetonUniversityLibrary,wheresomeof theresearchfor thisbookwascarriedout.The librarycontainscopiesofallofEinstein’smanuscriptsandoriginalmaterials.Iwouldalsoliketothank Professors V. P. Nair and Daniel Greenberger of City College of NewYork for reading themanuscriptandmakinghelpfulandcriticalcomments. Inaddition,conversationswithFredJerome,whoobtainedEinstein’svoluminousFBIfile,wereveryuseful.IamalsogratefultoEdwinBarberforhissupportandencouragement, and to JesseCohen formaking invaluable editorial commentsandchangesthathavegreatlystrengthenedthemanuscriptandgivenitfocus.IamalsodeeplyindebtedtoStuartKrichevsky,whohasrepresentedmanyofmybooksonscienceforalltheseyears.

PARTI

FIRSTPICTURE

RacingaLightBeam

CHAPTER1

PhysicsbeforeEinsteinA journalist once asked Albert Einstein, the greatest scientific genius sinceIsaacNewton,toexplainhisformulaforsuccess.Thegreatthinkerthoughtforasecondandthenreplied,“IfAissuccess,IshouldsaytheformulaisA=X+Y+Z,XbeingworkandYbeingplay.”AndwhatisZ,askedthejournalist?“Keepingyourmouthshut,”hereplied.What physicists, kings and queens, and the public found endearingwas his

humanity,hisgenerosity,andhiswit,whetherhewaschampioningthecauseofworldpeaceorprobingthemysteriesoftheuniverse.Evenchildrenwouldflocktoseethegrandoldmanofphysicswalkthestreets

ofPrinceton,andhewouldreturnthefavorbywigglinghisearsbackat them.Einsteinlikedtochatwithaparticularfive-year-oldboywhowouldaccompanythegreatthinkeronhiswalkstotheInstituteforAdvancedStudy.Onedaywhilethey were strolling, Einstein suddenly burst out in laughter. When the boy’smotheraskedhimwhattheytalkedabout,hersonreplied,“IaskedEinsteinifhehadgone to thebathroom today.”Themotherwashorrified,but thenEinsteinreplied,“I’mgladtohavesomeoneaskmeaquestionIcananswer.”AsphysicistJeremyBernsteinoncesaid,“Everyonewhohadrealcontactwith

Einsteincameawaywithanoverwhelmingsenseofthenobilityoftheman.Thephrasethatrecursagainandagainishis‘humanity,’…thesimple,lovablequalityofhischaracter.”Einstein, who was equally gracious to beggars, children, and royalty alike,

was also generous to his predecessors in the illustrious pantheon of science.Although scientists, like all creative individuals, can be notoriously jealous oftheirrivalsandengageinpettysquabbles,Einsteinwentoutofhiswaytotracethe origins of the ideas he pioneered back to the giants of physics, includingIsaacNewton and James ClerkMaxwell, pictures ofwhomwere prominentlydisplayedonhisdeskandwalls.Infact,theworkofNewtononmechanicsandgravityandofMaxwellonlightformedthetwopillarsofscienceattheturnofthe twentieth century. Remarkably, almost the sum total of all physical

knowledge at that time was embodied in the achievements of these twophysicists.It’seasytoforgetthatbeforeNewton,themotionofobjectsonEarthandin

theheavenswasalmost totallyunexplained,withmanybelievingthatourfateswere determined by themalevolent designs of spirits and demons.Witchcraft,sorcery,andsuperstitionwereheatedlydebatedevenatthemostlearnedcentersoflearninginEurope.Scienceasweknowitdidnotexist.GreekphilosophersandChristiantheologians,inparticular,wrotethatobjects

moved because they acted out of human-like desires and emotions. To thefollowersofAristotle,objects inmotioneventually sloweddownbecause theygot“tired.”Objectsfelltothefloorbecausethey“longed”tobeunitedwiththeearth,theywrote.Themanwhowouldintroduceorderintothischaoticworldofspiritswasina

sense the opposite ofEinstein in temperament andpersonality.WhileEinsteinwas always generous with his time and quick with a one-liner to delight thepress, Newton was notoriously reclusive, with a tendency toward paranoia.Deeply suspicious of others, he had bitter, long-standing feuds with otherscientistsoverpriority.Hisreticencewaslegendary:whenhewasamemberoftheBritishParliamentduringthe1689–90session,theonlyrecordedincidentofhisspeakingbeforetheaugustbodywaswhenhefeltadraftandaskedanushertoclosethewindow.AccordingtobiographerRichardS.Westfall,Newtonwasa“torturedman,anextremelyneuroticpersonalitywhoteeteredalways,atleastthroughmiddleage,onthevergeofbreakdown.”But in matters of science, Newton and Einstein were true masters, sharing

many key characteristics. Both could obsessively spendweeks andmonths inintenseconcentrationtothepointofphysicalexhaustionandcollapse.Andbothhadtheabilitytovisualizeinasimplepicturethesecretsoftheuniverse.In1666,whenNewtonwastwenty-threeyearsold,hebanishedthespiritsthat

hauntedtheAristotelianworldbyintroducinganewmechanicsbasedonforces.Newton proposed three laws ofmotion in which objectsmoved because theywere being pushed or pulled by forces that could be accuratelymeasured andexpressedbysimpleequations.Insteadofspeculatingonthedesiresofobjectsasthey moved, Newton could compute the trajectory of everything from fallingleaves,soaringrockets,cannonballs,andcloudsbyaddinguptheforcesactingonthem.Thiswasnotmerelyanacademicquestion,becauseithelpedtolaythefoundation for the Industrial Revolution, where the power of steam enginesdriving huge locomotives and ships created new empires. Bridges, dams, andtoweringskyscraperscouldnowbebuiltwithgreatconfidence,sincethestresseson every brick or beam could be computed. So great was the victory of

Newton’s theory of forces that he was justly lionized during his lifetime,promptingAlexanderPopetoacclaim:

NatureandNature’slawslayhidinnight,Godsaid,LetNewtonbe!andallwaslight.

Newtonappliedhistheoryofforcestotheuniverseitselfbyproposinganew

theory of gravity. He liked to tell the story of how he returned to the familyestateinWoolsthorpeinLincolnshireaftertheblackplagueforcedtheclosingofCambridgeUniversity.Oneday,ashesawanapplefalloffatreeonhisestate,heaskedhimselfthefatefulquestion:ifanapplefalls,thendoesthemoonalsofall?CanthegravitationalforceactingonanappleonEarthbe thesameforcethat guides themotion of heavenly bodies?Thiswas heresy, since the planetswere supposed to lie on fixed spheres that obeyed perfect, celestial laws, incontrast to the laws of sin and redemption that governed thewickedways ofhumanity.Inaflashofinsight,Newtonrealizedhecouldunifybothearthlyandheavenly

physicsintoonepicture.Theforcethatpulledanappletothegroundmustbethesameforcethatreachedouttothemoonandguideditspath.Hestumbleduponanewvisionofgravity.Heimaginedhimselfsittingonamountaintopthrowingarock.By throwing the rockfasterandfaster,he realized thathecould throwitfartherandfarther.Butthenhemadethefatefulleap:whathappensifyouthrowtherocksofastthatitneverreturns?Herealizedthatarock,fallingcontinuallyunder gravity, would not hit the earth but would circle around it, eventuallyreturningtoitsownerandhittinghimonthebackofhishead.Inthisnewview,hereplacedtherockwiththemoon,whichwasconstantlyfallingbutneverhitthe ground because, like the rock, it moved completely around the earth in acircular orbit. The moon was not resting on a celestial sphere, as the churchthought,butwascontinuallyinfreefalllikearockorapple,guidedbytheforceofgravity.Thiswasthefirstexplanationofthemotionofthesolarsystem.Two decades later, in 1682, all of London was terrified and amazed by a

brilliantcometthatwaslightingupthenightsky.Newtoncarefullytrackedthemotionofthecometwithareflectingtelescope(oneofhisinventions)andfoundthatitsmotionfithisequationsperfectlyifitwasassumedtobeinfreefallandacted on by gravity. With the amateur astronomer Edmund Halley, he couldpredictpreciselywhenthecomet(laterknownasHalley’scomet)wouldreturn,the first prediction made on the motion of comets. The laws of gravity thatNewton used to calculate themotion ofHalley’s comet and themoon are thesame ones NASA uses today to guide its space probes with breathtaking

accuracypastUranusandNeptune.According to Newton, these forces act instantaneously. For example, if the

sunwere to suddenlydisappear,Newtonbelieved the earthwouldbe instantlythrownoutofitsorbitandwouldfreezeindeepspace.Everyoneintheuniversewould know that the sun had just disappeared at that precise instant of time.Thus, it’spossibletosynchronizeallwatchessotheybeatuniformlyanywhereintheuniverse.AsecondonEarthhasthesamelengthasasecondonMarsandJupiter.Like time,space isalsoabsolute.MetersticksonEarthhave thesamelengthasmetersticksonMarsandJupiter.Metersticksdonotchangeinlengthanywhereintheuniverse.Secondsandmetersarethereforethesamenomatterwherewejourneyinspace.Newton thus based his ideas on the commonsense notion ofabsolute space

andtime.ToNewton,spaceandtimeformedanabsolutereferenceframeagainstwhichwecanjudgethemotionofallobjects.Ifwearetravelingonatrain,forexample,webelievethatthetrainismovingandtheearthisstill.However,aftergazingatthetreespassingourwindows,wecanspeculatethatperhapsthetrainis actually at rest, and the trees are being sent past our windows. Sinceeverything in the train seems motionless, we can ask the question, which isreallymoving, the trainor the trees?ToNewton, thisabsolutereferenceframecoulddeterminetheanswer.Newton’slawsremainedthefoundationforphysicsfornearlytwocenturies.

Then,inthelatenineteenthcentury,asnewinventionssuchasthetelegraphandthe light bulb were revolutionizing the great cities of Europe, the study ofelectricity brought about a whole new concept in science. To explain themysteriousforcesofelectricityandmagnetism,JamesClerkMaxwell,aScottishphysicistatCambridgeUniversityworkinginthe1860s,developedatheoryoflightnotbasedonNewtonianforces,butonanewconceptcalledfields.Einsteinwrote that the field concept “is the most profound and the most fruitful thatphysicshasexperiencedsinceNewton.”Thesefieldscanbevisualizedbysprinklingironfilingsoverasheetofpaper.

Place a magnet beneath the sheet of paper, and the filings will magicallyrearrange themselves intoa spiderweb–likepattern,with lines spreading fromthe North Pole to the South Pole. Surrounding any magnet, therefore, is amagneticfield,aninvisiblearrayoflinesofforcepenetratingallofspace.Electricity creates fields aswell.At science fairs, children laughwhen their

hairsstandonendastheytouchasourceofstaticelectricity.Thehairstraceouttheinvisibleelectricfieldlinesemanatingfromthesource.These fields, however, are quite different from the forces introduced by

Newton.Forces,saidNewton,actinstantlyoverallspace,sothatadisturbance

inonepart of theuniversewouldbe felt instantly throughout all theuniverse.Maxwell’s brilliant observation was that magnetic and electric effects do nottravel instantaneously, like Newtonian forces, but take time and move at adefinitevelocity.HisbiographerMartinGoldmanwrites,“Theideaofthe timeofmagneticaction…seemstohavestruckMaxwelllikeaboltoutoftheblue.”Maxwellshowed,forexample,thatifoneshookamagnet,itwouldtaketimefornearbyironfilingstomove.Imaginea spiderwebvibrating in thewind.Adisturbance like thewindon

onepartofthewebcausesaripplethatspreadsthroughouttheentireweb.Fieldsand spider webs, unlike forces, allow for vibrations that travel at a definitespeed.Maxwellthensetouttocalculatethespeedofthesemagneticandelectriceffects. Inoneof thegreatestbreakthroughsof thenineteenthcentury,heusedthisideatosolvethemysteryoflight.Maxwell knew from the earlier work ofMichael Faraday and others that a

movingmagneticfieldcancreateanelectricfield,andviceversa.Thegeneratorsand motors that electrify our world are direct consequences of this dialectic.(This principle is used to light up our homes. For example, in a dam, fallingwaterspinsawheel,which in turnspinsamagnet.Themovingmagnetic fieldpushes the electrons in awire,which then travel in a high-voltagewire to thewall sockets in our living rooms.Similarly, in an electric vacuumcleaner, theelectricityflowingfromourwallsocketscreatesamagneticfieldthatforcesthebladesofthemotortospin.)The genius of Maxwell was to put the two effects together. If a changing

magnetic fieldcancreateanelectric fieldandviceversa, thenperhapsbothofthem can form a cyclical motion, with electric fields and magnetic fieldscontinuallyfeedingoffeachotherandturningintoeachother.Maxwellquicklyrealized that this cyclical pattern would create a moving train of electric andmagnetic fields, allvibrating inunison, each turning into theother inanever-endingwave.Thenhecalculatedthespeedofthiswave.To his astonishment, he found that it was the speed of light. Further, in

perhaps themostrevolutionarystatementof thenineteenthcentury,heclaimedthatthiswaslight.Maxwellthenannouncedpropheticallytohiscolleagues,“Wecan scarcely avoid the conclusion that light consists of the transverseundulations of the same medium which is the cause of electric and magneticphenomenon.” After puzzling over the nature of light formillennia, scientistsfinally understood its deepest secrets. Unlike Newton’s forces, which wereinstantaneous,thesefieldstraveledatadefinitespeed:thespeedoflight.Maxwell’sworkwas codified in eight difficult partial differential equations

(knownas“Maxwell’sequations”),whicheveryelectricalengineerandphysicist

hashadtomemorizeforthepastcenturyandahalf.(Today,onecanbuyaT-shirt containing all eight equations in their full glory.TheT-shirt prefaces theequationsby stating, “In thebeginning,God said…,”andendsby saying, “…andtherewaslight.”)Bytheendofthenineteenthcentury,sogreatweretheexperimentalsuccesses

of Newton andMaxwell that some physicists confidently predicted that thesetwogreatpillarsofsciencehadansweredallthebasicquestionsoftheuniverse.When Max Planck (founder of the quantum theory) asked his advisor aboutbecomingaphysicist,hewastoldtoswitchfieldsbecausephysicswasbasicallyfinished. There was nothing really new to be discovered, he was told. Thesethoughts were echoed by the great nineteenth-century physicist Lord Kelvin,whoproclaimed thatphysicswasessentiallycomplete, except for a fewminor“clouds”onthehorizonthatcouldnotbeexplained.But thedeficienciesof theNewtonianworldwerebecomingmoreandmore

glaring each year. Discoveries like Marie Curie’s isolation of radium andradioactivity were rocking the world of science and catching the publicimagination.Evenafewouncesofthisrare,luminoussubstancecouldsomehowlightupadarkenedroom.Shealsoshowedthatseeminglyunlimitedquantitiesofenergycouldcomefromanunknownsourcedeepinsidetheatom,indefianceofthelawofconservationofenergy,whichstatesthatenergycannotbecreatedordestroyed.Thesesmall“clouds,”however,wouldsoonspawnthegreattwinrevolutionsofthetwentiethcentury,relativityandthequantumtheoryBut what seemed most embarrassing was that any attempt to merge

Newtonian mechanics with Maxwell’s theory failed. Maxwell’s theoryconfirmedthefactthatlightwasawave,butthisleftopenthequestion,whatiswaving? Scientists knew that light can travel in a vacuum (in fact travelingmillionsoflight-yearsfromdistantstarsthroughthevacuumofouterspace),butsinceavacuumbydefinitionis“nothing,”thislefttheparadoxthatnothingwaswaving!Newtonian physicists tried to answer this question by postulating that light

consistedofwavesvibratinginaninvisible“aether,”astationarygasthatfilledup the universe. The aether was supposed to be the absolute reference frameuponwhichonecouldmeasureallvelocities.Askepticmightsaythatsincetheearthmovedaroundthesun,andthesunmovedaroundthegalaxy,thenitwasimpossibletotellwhichwasreallymoving.Newtonianphysicistsansweredthisbystatingthatthesolarsystemwasmovingwithrespecttothestationaryaether,soonecoulddeterminewhichwasreallymoving.However, the aether began to assume more and more magical and bizarre

properties. For example, physicists knew that waves travel faster in a denser

medium.Thus,soundvibrationscantravelfasterinwaterthaninair.However,since light traveledata fantasticvelocity (186,000milespersecond), itmeantthattheaethermustbeincrediblydensetotransmitlight.Buthowcouldthisbe,sincetheaetherwasalsosupposedtobelighterthanair?Withtime,theaetherbecame almost a mystical substance: it was absolutely stationary, weightless,invisible, with zero viscosity, yet stronger than steel and undetectable by anyinstrument.By1900,thedeficienciesofNewtonianmechanicswerebecomingharderand

harder to explain. Theworldwas now ready for a revolution, butwhowouldlead it? Although other physicists were well aware of the holes in the aethertheory, they timidly tried to patch them up within a Newtonian framework.Einstein,withnothingtolose,wasabletostrikeattheheartoftheproblem:thatNewton’sforcesandMaxwell’sfieldswereincompatible.Oneofthetwopillarsof science must fall.When one of these pillars finally fell, it would overturnmore than two hundred years of physics andwould revolutionize thewayweview the universe and reality itself. Newtonian physics would be toppled byEinsteinwithapicturethatevenachildcouldunderstand.

CHAPTER2

TheEarlyYearsThemanwhowouldforeverreshapeourconceptionoftheuniversewasbornonMarch14,1879, in the small cityofUlm,Germany.HermannandPaulineKochEinsteinweredistressedthattheirson’sheadwasmisshapen,andprayedthathewasnotmentallydamaged.Einstein’s parents weremiddle-class secularized Jews struggling to provide

fortheirgrowingfamily.Paulinewasthedaughterofarelativelywealthyman:her father,JuliusDerzbacher (whochangedhisname toKoch),establishedhisfortuneby leavinghis jobasabakerandentering thegrain trade.PaulinewastheculturedoneintheEinsteinfamily,insistingthatherchildrentakeupmusicand starting youngAlbert on his lifelong love affairwith the violin.HermannEinstein, in contrast to his father-in-law, had a lackluster business career,originallystarting in thefeatherbedbusiness.HisbrotherJakobconvincedhimto switch to the new electrochemical industry. The inventions of Faraday,Maxwell, andThomasEdison, allofwhichharnessed thepowerofelectricity,were now lighting up cities around the world, and Hermann saw a futurebuilding dynamos and electric lighting. The business would prove precarious,however, leading to periodic financial crises and bankruptcies and forcing thefamilytorelocateseveraltimesduringAlbert’schildhood,includingtoMunichayearafterhisbirth.TheyoungEinsteinwaslateinlearninghowtospeak,solatethathisparents

feared that hemight be retarded.Butwhen he finally did speak, he did so incomplete sentences.Still, evenasanine-year-old,hecouldnot talkverywell.His only siblingwashis sisterMaja, twoyears younger thanAlbert. (At first,youngAlbertwaspuzzledbythenewpresenceinthehousehold.Oneofhisfirstphraseswas, “Butwhere are thewheels?”)Being the younger sister toAlbertwas no joy, since he had a nasty tendency to throw objects at her head. Shewouldlaterlament,“Asoundskullisneededtobethesisterofathinker.”Contrarytomyth,Einsteinwasagoodstudentinschool,buthewasonlygood

in the areas he cared about, such as mathematics and science. The Germanschool system encouraged students to give short answers based on rote

memorization—otherwise, they might be punished by painful slaps to theknuckles.YoungAlbert,however,spokeslowly,hesitantly,choosinghiswordscarefully.Hewasfarfrombeingtheperfectstudent,chafingunderasuffocating,authoritativesystemthatcrushedcreativityandimagination,replacingthemwithmind-numbing drills. When his father asked the headmaster what professionyoungAlbert shouldpursue,he replied, “Itdoesn’tmatter; he’ll nevermakeasuccessofanything.”Einstein’s demeanor established itself early. He was dreamy, often lost in

thoughtorreading.HisclassmatesusedtotaunthimbycallinghimBiedermeier,which translates loosely as “nerd.” A friend would remember, “Classmatesregarded Albert as a freak because he showed no interest in sports. Teachersthought himdull-witted because of his failure to learn by rote andhis strangebehavior.”Atageten,AlbertenteredtheLuitpoldGymnasiuminMunich,wherehismost excruciatingordealwas learning classicalGreek.Hewould sit in hischair,smilingblanklytohidehisboredom.Atonepointhisseventh-gradeGreekteacher,HerrJosephDegenhart,toldAlberttohisfacethatitwouldbebetterifhe simplywerenot there.WhenEinsteinprotested that hedidnothingwrong,theteacherrepliedbluntly,“Yes,thatistrue.Butyousitthereinthebackrowandsmile,andthatviolatesthefeelingofrespectwhichateacherneedsfromhisclass.”Even decades later, Einstein would bitterly nurse the scars left by the

authoritarianmethodsof theday:“It is, in fact,nothingshortofamiracle thatthe modern methods of instruction have not yet entirely strangled the holycuriosityofinquiry;forthisdelicatelittleplant,asidefromstimulations,standsmainlyinneedoffreedom.”Einstein’sinterestinsciencestartedearly,beginningwithhisencounterwith

magnetism,whichhecalledhis“firstmiracle.”Hewasgivenacompassbyhisfatherandwasendlesslyfascinatedbythefactthatinvisibleforcescouldmakeobjectsmove.Hefondlyremembered,“AwonderofsuchnatureIexperiencedasachildof4or5years,whenmyfathershowedmeacompassneedle….Icanstill remember…that this experiencemadeadeepand lasting impressionuponme.Somethingdeeplyhiddenhadtobebehindthings.”When he was about eleven, however, his life took an unexpected turn: he

becamedevoutlyreligious.Adistant relativewouldcomeby to tutorAlbert inthe Jewish faith, and he latched onto it in a surprisingly enthusiastic, almostfanaticalway.HerefusedtoeatporkandevencomposedseveralsongsinpraiseofGod,which he sang on hisway to school. This period of intense religiousfervordidnot last long,however.Thefurtherhedelvedintoreligious loreanddoctrine, themorehe realized that theworldsof scienceand religioncollided,

withmanyofthemiraclesfoundinreligioustextsviolatingthelawsofscience.“ThroughthereadingofpopularbooksIsoonreachedtheconvictionthatmuchinthestoriesoftheBiblecouldnotbetrue,”heconcluded.Justasabruptlyashepickedreligionup,hedropped it.His religiousphase,

however, would have a profound effect on his later views. His reversalrepresented his first rejection of unthinking authority, one of the lifelonghallmarksofhispersonality.NeveragainwouldEinsteinunquestioninglyacceptauthority figures as the finalword.Although he concluded that one could notreconcilethereligiouslorefoundintheBiblewithscience,healsodecidedthattheuniversecontainedwholerealmsthatwerejustbeyondthereachofscience,andthatoneshouldhaveprofoundappreciationforthelimitationsofscienceandhumanthought.His early interest in compasses, science, and religion, however,might have

witheredhadyoungAlbertnotfoundacaringmentortohonehisideas.In1889,apoorPolishmedicalstudentnamedMaxTalmudwasstudyinginMunichandateweeklydinnersattheEinsteinhouse.ItwasTalmudwhointroducedEinsteinto the wonders of science beyond the dry, rote memorization of his classes.Years later, Talmud would fondly write, “In all these years I never saw himreading any light literature.Nor did I ever see him in the company of schoolmatesorotherboysofhisage.Hisonlydiversionwasmusic,healreadyplayedMozart and Beethoven sonatas, accompanied by his mother.” Talmud gaveEinsteinabookongeometry,whichhedevoureddayandnight.Einsteincalledthis his “secondmiracle.”Hewouldwrite, “At the ageof 12, I experienced asecondwonderofatotallydifferentnature:inalittlebookwithEuclideanplanegeometry.”Hecalledithis“holygeometrybook,”whichhetreatedashisnewBible.Hereat last,Einsteinmadecontactwith the realmofpure thought.Without

expensive laboratories or equipment, he could explore universal truth, limitedonlyby thepowerof thehumanmind.Mathematics,observedhis sisterMaja,becameanendlesssourceofpleasuretoAlbert,especiallyifintriguingpuzzlesand mysteries were involved. He bragged to his sister that he had found anindependentproofofthePythagoreantheoremaboutrighttriangles.Einstein’s mathematical readings did not stop there; eventually he taught

himselfcalculus,surprisinghis tutor.Talmudwouldadmit,“Soon theflightofhismathematicalgeniuswassohighthatIcouldnolongerfollow….Thereafter,philosophywasoften the subjectofour conversations. I recommended thathereadKant.”Talmud’sexposureofyoungAlberttotheworldofImmanuelKantand his Critique of Pure Reason nourished Einstein’s lifelong interest inphilosophy. He began to ponder the eternal questions facing all philosophers,

suchastheoriginofethics,theexistenceofGod,andthenatureofwars.Kant,inparticular,heldunorthodoxviews,evencastingdoubtabout theexistenceofGod.Hepokedfunatthepompousworldofclassicalphilosophy,where“thereis usually a great deal of wind.” (Or, as the Roman orator Cicero once said,“There isnothing soabsurd that it hasnotbeen saidbyaphilosopher.”)Kantalso wrote that world government was the way to end wars, a position thatEinsteinwouldholdfortherestofhislife.Atonepoint,Einsteinwassomovedby themusings ofKant that he even considered becoming a philosopher.Hisfather, who wanted a more practical profession for his son, dismissed this as“philosophicalnonsense.”Fortunately, because of his father’s electrochemical business, there were

plenty of electric dynamos, motors, and gadgets lying around the factory tonourishhiscuriosityandstimulatehisinterestinscience.(HermannEinsteinwasworkingtogetthecontractforanambitiousprojectwithhisbrotherJakob,theelectrification of the city center ofMunich.Hermann dreamed of being at theforefront of this historic undertaking. If he landed the project, it wouldmeanfinancialstabilityaswellasalargeexpansionofhiselectricfactory.)Beingsurroundedbyhugeelectromagneticcontraptionsnodoubtawakenedin

Albert an intuitiveunderstandingofelectricityandmagnetism. Inparticular, itprobablysharpenedhisremarkableabilitytodevelopgraphic,physicalpicturesthat would describe the laws of nature with uncanny accuracy. While otherscientistsoftenburiedtheirheadsinobscuremathematics,Einsteinsawthelawsofphysics as clear as simple images.Perhaps thiskeen abilitydates from thishappyperiodoftime,whenhecouldsimplylookatthegadgetssurroundinghisfather’sfactoryandponderthelawsofelectricityandmagnetism.Thistrait,theability to see everything in terms of physical pictures, would mark one ofEinstein’sgreatcharacteristicsasaphysicist.At age fifteen, Einstein’s education was disrupted by the family’s periodic

financialproblems.Hermann,generous toa fault,wasalwayshelping those infinancial trouble; he wasn’t tough-minded like most successful businessmen.(Albertwouldlaterinherit thissamegenerosityofspirit.)Hiscompany,failingtolandthecontracttolightupMunich,wentbankrupt.Pauline’swealthyfamily,nowlivinginGenoa,Italy,offeredtocometoHermann’saidbybackinganewcompany.Therewasacatch,however.TheyinsistedthathemovehisfamilytoItaly(inpartsotheycouldkeepa tightreinonhisfreewheeling,overgenerousimpulses). The family moved toMilan, close to a new factory in Pavia. Notwantingtofurtherinterrupthisson’seducation,HermannleftAlbertwithsomedistantrelativesinMunich.All alone,Albertwasmiserable, trapped in a boarding school he hated and

facingmilitarydutyinthedreadedPrussianarmy.Histeachersdislikedhim,andthefeelingwasmutual.Hewasapparentlyabouttobeexpelledfromschool.Onan impulse, Einstein decided to reunite with his family. He arranged for hisfamilydoctortowriteamedicalnoteexcusinghimfromschool,statingthathemightsufferabreakdownunlessherejoinedhisfamily.Hethenmadethesolojourney to Italy, eventually winding up totally unexpected on his parents’doorstep.HermannandPaulinewereperplexedaboutwhattodowiththeirson,adraft-

dodging, high school dropoutwith no skills, no profession, and no future.Hewould get into long arguments with his father, who wanted him to pursue apractical profession like electrical engineering, while Albert preferred to talkaboutbeingaphilosopher.Eventually, theycompromised, andAlbertdeclaredhe would attend the famed Zurich Polytechnic Institute in Switzerland, eventhoughhewastwoyearsyoungerthanmoststudentstakingtheentranceexam.OneadvantagewasthatthePolytechnicdidnotrequireahighschooldiploma,justapassinggradeonitstoughentranceexamination.Unfortunately, Einstein flunked the entrance exam. He failed the French,

chemistry,andbiologyportions,buthedidsoexceptionallywellinthemathandphysicssectionsthatheimpressedAlbinHerzog,theprincipal,whopromisedtoadmithim the followingyear,withoutAlberthaving to take thedreadedexamagain. The head of the physics department, Heinrich Weber, even offered toallow Einstein to audit his physics classes when he was in Zurich. Herzogrecommended that Einstein spend the interim year attending a high school inAarau, just thirtyminuteswestofZurich.ThereAlbertbecamea lodgerat thehouse of the high school’s director, Jost Winteler, establishing a lifelongfriendshipbetweentheEinsteinfamilyandtheWintelers.(Infact,Majawouldlater marry Winteler’s son, Paul, and Einstein’s friend Michele Besso wouldmarrytheeldestdaughter,Anna.)Einsteinenjoyed the relaxed, liberalatmosphereof theschool.Here,hewas

relatively freeof theoppressive, authoritarian rulesof theGerman system.HeenjoyedthegenerosityoftheSwiss,whocherishedtoleranceandindependenceofspirit.Einsteinwouldfondlyrecall,“IlovetheSwissbecause,byandlarge,they are more humane than the other people among whom I have lived.”Remembering all the bad memories of his years in German schools, he alsodecided to renounce his German citizenship, a surprising step for a mereteenager.Hewouldremainstatelessforfiveyears(untilheeventuallybecameaSwisscitizen).Albert,flourishinginthisfreeratmosphere,begantoshedhisimageasashy,

nervous, withdrawn loner, to become outgoing and gregarious, someone who

was easy to talk to andwhomade loyal friends.Maja, in particular, began tonotice a new change in her older brother as he blossomed into a mature,independent thinker.Einstein’s personalitywouldpass through several distinctphases throughout his life, the first being his bookish, withdrawn, introvertedphase. In Italy and especially Switzerland, he was entering his second phase:something of an impudent, cocky, sure-of-himself bohemian, always full ofcleverquips.Hecouldmakepeoplehowlwithhispuns.Nothingwouldpleasehimmorethantellingasillyjokethatwouldsendhisfriendsrollinginhelplesslaughter.Some called him the “cheeky Swabian.” One fellow student, Hans Byland,

captured Einstein’s emerging personality: “Whoever approached him wascaptivatedbyhissuperiorpersonality.Amockingtraitaroundthefleshymouthwithitsprotrudinglowerlipdidnotencouragethephilistinetotanglewithhim.Unconfined by conventional restrictions, he confronted the world spirit as alaughingphilosopher,andhiswittysarcasmmercilesslycastigatedallvanityandartificiality.”By all accounts, this “laughing philosopher” was also growing up to be

popular with the girls. He was a wisecracking flirt, but girls also found himsensitive,easytoconfidein,andsympathetic.Onefriendaskedhimforadviceinloveconcerningherboyfriend.Anotheraskedhimtosignherautographbook,inwhichheinscribedapieceofsillydoggerel.Hisviolinplayingalsoendearedhimtomanyandputhimindemandatdinnerparties.Lettersfromthatperiodshow that he was quite popular with women’s groups who needed strings toaccompanythepiano.“Manyayoungorelderlywomanwasenchantednotonlybyhisviolinplaying,butalsobyhisappearance,whichsuggestedapassionateLatin virtuoso rather than a stolid student of the sciences,” wrote biographerAlbrechtFolsing.One girl in particular captured his attention. Only sixteen, Einstein fell

passionatelyinlovewithoneofJostWinteler’sdaughters,Marie,whowastwoyears older. (In fact, all the keywomen in his lifewould be older than he, atendencyalsosharedbybothhissons.)Kind,sensitive, talented,Mariewishedtobecomeateacherlikeherfather.AlbertandMarietooklongwalkstogether,often bird watching, a favorite hobby of the Winteler family. He alsoaccompaniedherwithhisviolinwhilesheplayedthepiano.Albertconfessedtoherhistruelove:“Belovedsweetheart…Ihavenow,my

angel, had to learn the full meaning of nostalgia and longing. But love givesmuch more happiness than longing gives pain. I only now realize howindispensable my dear little sunshine has become to my happiness.” Mariereturned Albert’s affections and even wrote to Einstein’s mother, who wrote

backapprovingly.TheWintelersandtheEinsteins,infact,halfexpectedtoseeawedding announcement from the two lovebirds. Marie, however, felt a bitinadequatewhen speaking about sciencewith her sweetheart, and thought thiscould be a problem in a relationshipwith such an intense, focused boyfriend.She realized that shewouldhave to compete forEinstein’s affectionswithhisfirsttruelove:physics.WhatconsumedEinstein’sattentionswasnotonlyhisgrowingaffection for

Marie but also a fascinationwith themysteries of light and electricity. In thesummer of 1895, he wrote an independent essay about light and the aether,entitled“AnInvestigationoftheStateoftheAetherinaMagneticField,”whichhesenttohisfavoriteuncle,CaesarKoch,inBelgium.Onlyfivepageslong,itwas his very first scientific paper, arguing that the mysterious force calledmagnetism thatmesmerized him as a child could be viewed as some kind ofdisturbance in the aether. Years earlier, Talmud had introduced Einstein toAaronBernstein’sPopularBooksonNaturalScience.Einsteinwouldwritethatitwas“aworkwhichIreadwithbreathlessattention.”Thisbookwouldhaveafatefulimpactonhim,becausetheauthorincludedadiscussiononthemysteriesofelectricity.Bernsteinaskedthereadertotakeafancifulrideinsideatelegraphwire,racingalongsideanelectricsignalatfantasticspeeds.At the age of sixteen, Einstein had a daydream that led him to an insight

whichwouldlaterchangethecourseofhumanhistory.Perhapsrememberingthefanciful ride taken in Bernstein’s book, Einstein imagined himself runningalongside a light beam and asked himself a fateful question:What would thelightbeam look like?LikeNewtonvisualizing throwinga rockuntil itorbitedtheearthlikethemoon,Einstein’sattempttoimaginesuchalightbeamwouldyielddeepandsurprisingresults.In the Newtonian world, you can catch up to anything if you move fast

enough. A speeding car, for example, can race alongside a train. If you peerinside the train, you can see the passengers reading their newspapers anddrinkingtheircoffeeasiftheyweresittingintheirlivingrooms.Althoughtheymight be hurtling at great speed, they look perfectly stationary as we ridealongsideatthesamespeedinthecar.Similarly, imagine a police car catching up to a speeding motorist. As the

policecaracceleratesandpullsupalongsidethecar,thepoliceofficercanlookintothecarandwavetothepassenger,askinghimtopullover.Totheofficer,themotorist in thecarappearsat rest,althoughboth thepoliceofficerand themotoristmaybetravelingatahundredmilesanhour.Physicistsknewthatlightconsistedofwaves,soEinsteinreasonedthatifyou

couldrunalongsidealightbeam,thenthelightbeamshouldbeperfectlyatrest.

Thismeansthatthelightbeam,asseenbytherunner,wouldlooklikeafrozenwave,astillphotographofawave.Itwouldnotoscillateintime.TotheyoungEinstein,however,thisdidnotmakeanysense.Nowherehadanyoneeverseenafrozenwave; there was no such description of one in the scientific literature.Light,toEinstein,wasspecial.Youcouldnotcatchuptoalightbeam.Frozenlightdidnotexist.Hedidnotunderstand it then,butheaccidentally stumbledupononeof the

greatest scientific observations of the century, leading up to the principle ofrelativity.Hewould laterwrite that “such a principle resulted from a paradoxuponwhich Ihadalreadyhitat theageof sixteen: If Ipursueabeamof lightwiththevelocityc(velocityoflightinavacuum),Ishouldobservesuchabeamoflight…atrest.However,thereseemstobenosuchthing,whetheronthebasisofexperienceoraccordingtoMaxwell’sequations.”Itwaspreciselyhisabilitytoisolatethekeyprinciplesbehindanyphenomena

andzeroinontheessentialpicturethatputEinsteinonthebrinkofmountingascientific revolution. Unlike lesser scientists who often got lost in themathematics, Einstein thought in terms of simple physical pictures—speedingtrains, falling elevators, rockets, and moving clocks. These pictures wouldunerringly guide him through the greatest ideas of the twentieth century. Hewrote, “All physical theories, their mathematical expression notwithstanding,ought to lend themselves to so simple a description that even a child couldunderstand.”In the fall of 1895, Einstein finally entered the Polytechnic and began an

entirelynewphaseinhislife.Forthefirsttime,hethought,hewouldbeexposedto the latest developments in physics that were being debated across thecontinent. He knew that revolutionary winds were blowing in the world ofphysics. Scores of new experiments were being performed, seemingly indefianceofthelawsofIsaacNewtonandclassicalphysics.At the Polytechnic, Einstein wanted to learn new theories about light,

especially Maxwell’s equations, which he would later write were the “mostfascinating subject at the time Iwas a student.”WhenEinstein finally learnedMaxwell’sequations,hecouldanswer thequestion thatwascontinuallyonhismind. As he suspected, he found that there were no solutions of Maxwell’sequationsinwhichlightwasfrozenintime.Butthenhediscoveredmore.Tohissurprise,hefoundthat inMaxwell’s theory, lightbeamsalways traveledat thesamevelocity,nomatterhowfastyoumoved.Hereatlastwasthefinalanswerto theriddle:youcouldnevercatchup toa lightbeambecause italwaysspedawayfromyouatthesamespeed.This,inturn,violatedeverythinghiscommonsensetoldhimabouttheworld.Itwouldtakehimseveralmoreyearstounravel

the paradoxes from that key observation, that light always travels at the samevelocity.These revolutionary times demanded revolutionary new theories, and new,

daring leaders. Unfortunately, Einstein did not find these leaders at thePolytechnic. His teachers preferred to dwell on classical physics, promptingEinstein to cut his classes and spend most of his time in the laboratory orlearning about new theories by himself. His professors viewed these repeatedabsences from class as chronic laziness; once again Einstein’s teachersunderestimatedhim.AmongtheteachersatthePolytechnicwasphysicsprofessorHeinrichWeber,

the samepersonwhohadbeen impressedwithEinsteinandoffered to lethimaudit his classes after he failed the entrance exam. He had even promisedEinstein a job as his assistant after graduation. Over time, however, WeberbegantoresentEinstein’simpatienceanddisregardforauthority.Eventually,theprofessor withdrew his support for Einstein, saying, “You are a smart boy,Einstein,averysmartboy.Butyouhaveonegreatfault:youdonotletyourselfbetoldanything.”PhysicsinstructorJeanPernetalsowasnotfondofEinstein.Hewas insultedwhenEinstein once threw the labmanual for oneofPernet’sclasses into the garbage without even looking at it. But Pernet’s assistantdefended Einstein, stating that although unorthodox, Einstein’s solutionswerealwaysright.PernetneverthelessconfrontedEinstein:“You’reenthusiastic,buthopelessatphysics.Foryourowngood,you should switch to somethingelse,medicinemaybe,literature,orlaw.”Once,becauseEinsteinhadtornupthelabinstructions,heaccidentallycausedanexplosion that severely injuredhis righthand, requiring stitches to close the wound. His relations with Pernet haddegeneratedsobadlythatPernetgaveEinsteina“1,”thelowestpossiblegrade,inhiscourse.MathematicsprofessorHermannMinkowskievencalledEinsteina“lazydog.”In contrast to his professors’ disdain, the friends Einstein made in Zurich

wouldstandloyallybyhimfortherestofhislife.Therewereonlyfivestudentsin his physics class that year, and he got to know them all. One wasMarcelGrossman, a student ofmathematicswho took careful,meticulousnotes of allthelectures.Hisnotesweresogood, infact, thatEinsteinfrequentlyborrowedthem rather than go to class, often getting better scores on the exams thanGrossman himself. (Even today, Grossman’s notes are preserved at theuniversity.)GrossmanconfidedtoEinstein’smotherthat“somethingverygreat”wouldsomedayhappentoEinstein.But one person who caught Einstein’s attention was another student in his

class,MilevaMaric,awomanfromSerbia.Itwasraretofindaphysicsstudent

fromtheBalkans,evenrarertofindawoman.Milevawasaformidablepersonwhodecidedbyherself togo toSwitzerlandbecause itwas theonlyGerman-speaking country admitting women to the university. She was only the fifthwomantobeacceptedtostudyphysicsatthePolytechnic.Einsteinhadmethismatch,awomanwhocouldspeak the languageofhis first love.He foundherirresistible and quickly broke off his relationship with Marie Winteler. HedaydreamedthatheandMilevawouldbecomeprofessorsofphysicsandmakegreatdiscoveriestogether.Soon, theywerehelplesslyinlove.Whentheywereseparatedduringvacations,theywouldexchangelong,torridloveletters,callingeachotherbyahostoffondnicknames,suchas“Johnny”and“Dollie.”Einsteinwouldwriteherpoemsaswellasexhortationsofhislove:“IcangoanywhereIwant—but I belongnowhere, and Imiss your two little arms and theglowingmouthfullof tendernessandkisses.”EinsteinandMilevaexchangedover430letters, preserved by one of their sons. (Ironically, although they lived in nearpoverty,justonestepaheadofthebillcollectors,someoftheselettersrecentlyfetched$400,000atanauction.)Einstein’sfriendscouldnotunderstandwhathesawinMileva.WhileEinstein

wasoutgoingwithaquicksenseofhumor,Mileva,fouryearsolder,wasmuchdarker. She was moody, intensely private, and distrustful of others. She alsowalkedwithanoticeablelimpduetoacongenitalproblem(onelegwasshorterthantheother),whichfurtherisolatedherfromothers.FriendswhisperedbehindherbackaboutthepeculiarbehaviorofhersisterZorka,whoactedstrangelyandwouldlaterbecomeinstitutionalizedasaschizophrenic.But,mostimportant,hersocialstatuswasquestionable.WhereastheSwissmightsometimeslookdownonJews,JewsinturnsometimeslookeddownonsouthernEuropeans,especiallyfromtheBalkans.Mileva,inturn,hadnoillusionsaboutEinstein.Hisbrilliancewaslegendary,

as well as his irreverent attitude toward authority. She knew that he hadrenouncedhisGermancitizenshipandheldunpopularviewsconcerningwarandpeace.Shewouldwrite,“MysweethearthasaverywickedtongueandisaJewintothebargain.”Einstein’s growing involvement with Mileva, however, was opening up a

seismicchasmwithhisparents.Hismother,whohadlookedapprovinglyonhisrelationshipwithMarie, thoroughly dislikedMileva, regarding her as beneathAlbertandsomeonewhowouldbringruintohimandtheirreputation.Shewassimply too old, too sick, too unfeminine, too gloomy, and too Serbian. “ThisMiss Maric is causing me the bitterest hours of my life,” she confided to afriend.“Ifitwereinmypower,Iwouldmakeeverypossibleefforttobanishherfromourhorizon.Ireallydislikeher.ButIhavelostallinfluencewithAlbert.”

Shewouldwarnhim,“Bythetimeyou’re30,she’llbeanoldwitch.”ButEinsteinwasdetermined to seeMileva, even if itmeantcausingadeep

ruptureinhisclose-knitfamily.Once,whenEinstein’smotherwasvisitingherson,sheasked,“What’stobecomeofher?”WhenEinsteinreplied,“Mywife,”she suddenly threw herself on the bed, sobbing uncontrollably. His motheraccusedhimofdestroyinghisfutureforawoman“whocannotgainentrancetoa good family.” Eventually, facing the fierce opposition from his parents,Einstein would have to shelve any thoughts of marriage to Mileva until hefinishedschoolandgotawell-payingjob.In1900,whenEinsteinfinallygraduatedfromthePolytechnicwithadegree

inphysicsandmathematics,his lucksoured. Itwasassumed thathewouldbegivenanassistantship.Thiswasthenorm,especiallysincehehadpassedallhisexams and had done well in school. But because Professor Weber hadwithdrawn his job offer, Einstein was the only one in his class denied anassistantship—adeliberate slap in the face.Once sococky,he suddenly foundhimselfinuncertaincircumstances,especiallyasfinancialsupportfromawell-to-doauntinGenoadriedupwithhisgraduation.Unaware of the depth ofWeber’s intense antipathy, Einstein foolishly gave

Weber’snameasareference,notrealizingthat thiswouldfurthersabotagehisfuture. Reluctantly, he began to realize that this error probably doomed hiscareerevenbeforeitstarted.Hewouldlamentbitterly,“Iwouldhavefound[ajob]longagoifWeberhadnotplayedadishonestgamewithme.Allthesame,Ileavenostoneunturnedanddonotgiveupmysenseofhumor….Godcreatedthedonkeyandgavehimathickhide.”Meanwhile, Einstein also applied for Swiss citizenship, but this was

impossible until he could prove he was employed. His world was collapsingswiftly. The thought of having to play the violin on the street like a beggarcrossedhismind.His father, realizing his son’s desperate plight, wrote a letter to Professor

WilhelmOstwaldofLeipzig,pleadingwithhimtogivehissonanassistantship.(Ostwaldneverevenrespondedtothisletter.Ironically,adecadelaterOstwaldwouldbe thefirstperson tonominateEinsteinfor theNobelPrize inphysics.)Einstein would note how unfair the world suddenly became: “By the mereexistenceofhisstomach,everyonewascondemnedtoparticipateinthatchase.”Hewrotesadly,“Iamnothingbutaburdentomyrelatives….ItwouldsurelybebetterifIdidnotliveatall.”Tomakemattersworse,justatthistimehisfather’sbusinessonceagainwent

bankrupt.Infact,hisfatherspentallofhiswife’sinheritanceandwasdeeplyindebttoherfamily.Lackinganyfinancialsupport,Einsteinhadnochoicebutto

find themostmenial teachingpositionavailable.Desperate,hebegan tocombthenewspapers foranyhintofa job.Atonepoint,healmostgaveuphopeofever becoming a physicist and seriously considered working for an insurancecompany.In 1901, he found a job teaching mathematics at theWinterthur Technical

School.Somehow,betweenexhaustingteachingduties,hewasable tosqueezeenoughtimetowritehisfirstpublishedpaper,“DeductionsfromthePhenomenaofCapillarity,”whichEinsteinhimselfrealizedwasnotearthshaking.Thenextyear,hetookatemporarytutoringpositionataboardingschoolinSchaffhausen.Truetoform,hecouldnotgetalongwiththeauthoritariandirectoroftheschool,JakobNuesch,andwassummarilyfired.(ThedirectorwassoinflamedthatheevenaccusedEinsteinoffomentingarevolution.)Einsteinwasbeginningtothinkthathewouldspendtherestofhislifeforced

toekeoutamenialexistencetutoringindifferentstudentsandscouringtheadsinnewspapers.HisfriendFriedrichAdlerwouldrecallthatatthistimeAlbertwasclosetostarvation.Hewasacompletefailure.Stillherefusedtoaskhisrelativesforahandout.Thenhefacedtwomoresetbacks.First,Milevaflunkedherfinalexams at the Polytechnic for the second time.Thismeant that her career as aphysicistwasessentiallyfinished.Noonewouldeveracceptherintoagraduateprogram with her dismal record. Painfully disheartened, she lost interest inphysics. Their romantic dreams of exploring the universe together were over.Andthen,inNovember1901,whenMilevawasbackhome,hereceivedaletterfromhertellinghimthatshewaspregnant!Einstein, despite his lack of prospects,was still thrilled at the possibility of

becomingafather.BeingseparatedfromMilevawastorture,buttheyfuriouslyexchangedletters,almostdaily.OnFebruary4,1902,hefinallylearnedhewasafatherofababygirl,bornatMileva’sparents’homeinNoviSadandchristenedLieserl.Excited,Einsteinwantedtoknoweverythingabouther.HeevenpleadedwithMileva topleasesendaphotoorasketchofher.Mysteriously,noone issure what happened to the child. The last mention of her is in a letter fromSeptember 1903, which stated that she was suffering from scarlet fever.Historians believe that she most likely died of the disease or that she waseventuallygivenupforadoption.Justwhenhisfortunesappearedasiftheycouldnotsinkanylower,Einstein

receivedword from an unexpected source. His good friendMarcel GrossmanhadbeenabletosecureajobforhimasaminorcivilservantattheBernPatentOffice. From that lowly position, Einstein would change the world. (To keepalivehisfadinghopesofonedaybecomingaprofessor,hepersuadedProfessorAlfredKleiner of theUniversity ofZurich to be his Ph.D. advisor during this

period.)On June 23, 1902, Einstein began work at the patent office as a technical

expert, third class,with a paltry salary. In hindsight, therewere at least threehiddenadvantagestoworkingatthisoffice.First,hisjobforcedhimtofindthebasicphysicalprinciplesthatunderlayanyinvention.Duringtheday,hehonedhis considerable physical instincts by stripping away unnecessary details andisolatingtheessentialingredientofeachpatentandthenwritingupareport.Hisreportswereso longondetailandanalysis thathewrote tohis friends thathewas making a living “pissing ink.” Second, many of the patent applicationsconcerned electromechanical devices, so his ample experience visualizing theinnerworkingsofdynamosandelectricmotorsfromhisfather’sfactorywasagreathelp.Andlast,itfreedhimfromdistractionsandgavehimtimetoponderdeepquestionsabout lightandmotion.Often,hecouldfinish thedetailsofhisworkquickly,leavinghourstofallbackonthedaydreamsthatdoggedhimsincehis youth. In hiswork and especially at night, he returned to his physics.Thequiet atmosphere of the patent office suited him. He called it his “worldlymonastery.”Einstein had barely settled into his new job at the patent office when he

learned thathis fatherwasdyingofheartdisease. InOctoberhehad todepartimmediately for Milan. On his deathbed, Hermann finally gave Albert hisblessingtomarryMileva.ThedeathleftAlbertwithanoverpoweringsensethathe had disappointed his father and family, a feeling thatwould staywith himforever.Hissecretary,HelenDukas,wrote,“Manyyears later,hestill recalledvividly his shattering sense of loss. Indeed on one occasion hewrote that hisfather’s death was the deepest shock he had ever experienced.” Maja, inparticular,bitterlynotedthat“sadfatedidnotpermit[herfather]eventosuspectthattwoyearslaterhissonwouldlaythefoundationofhisfuturegreatnessandfame.”In January of 1903, Einstein finally felt secure enough tomarryMileva.A

yearlater,theirsonHanswasborn.Einsteinsettleddowntothelifeofalowlycivil servant in Bern, a husband, and a father. His friend David Reichinsteinvividly remembered visitingEinstein during this period: “The door of the flatwas open to allow the floor, which had just been scrubbed, and thewashing,hungup in thehall, to dry. I enteredEinstein’s room.Withonehand, hewasstoically rocking abassinet inwhich therewas a child. Inhismouth,Einsteinhadabad,averybadcigar,andintheotherhand,anopenbook.Thestovewassmokinghorribly.”To raise some extra money, he put an ad in the local newspaper, offering

“privatelessonsinmathematicsandphysics.”Itwasthefirstrecordedmention

of Einstein’s name in any newspaper. Maurice Solovine, a Jewish Romanianstudent of philosophy, was the first student to answer the ad. To his delight,EinsteinfoundthatSolovinewasanexcellentsoundingboardforhismanyideasabout space, time, and light. To prevent himself from becoming dangerouslyisolated from themaincurrents inphysics,hehitupon the ideaof forminganinformal study group, which Einstein mockingly called the “OlympianAcademy,”todebatethegreatissuesoftheday.Inhindsight, thedays spentwith the academygroupwereperhaps themost

joyous inEinstein’s life.Decades later, tearswouldcome tohiseyeswhenherecalled thevibrant, audaciousclaims theymadeas theyvoraciouslydevouredall the major scientific works of the day. Their spirited debates and raucousdiscussions filled the coffeehouses and beer halls of Zurich, and anythingseemedpossible.Theywouldfondlyswear,“ThesewordsofEpicurusappliedtous:‘Whatabeautifulthingjoyouspovertyis!’”In particular, they poured over the controversial work of Ernst Mach, a

Viennesephysicistandphilosopherwhowassomethingofagadfly,challenginganyphysicistwhospokeofthingsthatwerebeyondoursenses.Machspelledouthistheoriesinaninfluentialbook,TheScienceofMechanics.Hechallengedtheidea of atoms, which he thought were hopelessly beyond the realm ofmeasurement. What most riveted Einstein’s attention, however, was Mach’sscathing criticism of the aether and absolute motion. ToMach, the imposingedificeofNewtonianmechanicswasbasedonsand,astheconceptsofabsolutespaceandabsolutetimecouldneverbemeasured.Hebelievedrelativemotionscouldbemeasured,butabsolutemotionscouldnot.Noonehadeverfoundthemysticalabsolutereferenceframethatcoulddeterminethemotionoftheplanetsand the stars, and no one had ever found even the slightest experimentalevidencefortheaethereither.One seriesof experiments that indicateda fatalweakness in thisNewtonian

picturehadbeenperformed in1887byAlbertMichelsonandEdwardMorley,whohadsetouttogivethebestpossiblemeasurementofthepropertiesofthisinvisible aether. They reasoned that the earthmoveswithin this sea of aether,creating an “aether wind,” and hence the speed of light should change,dependingonthedirectiontheearthtook.Think,forexample,ofrunningwiththewind.Ifyouruninthesamedirection

asthewind,thenyoufeelyourselfbeingpushedalongwiththewind.Withthewindatyourback,youtravelatafasterspeed,andinfactyourspeedhasbeenincreased by the speed of the wind. If you run into the wind, then you slowdown;yourspeed isnowdecreasedby thespeedof thewind.Similarly ifyourun sideways, 90 degrees to thewind, you are blown off to the sidewith yet

another speed. The point is that your speed changes depending on whichdirectionyourunwithrespecttothewind.MichelsonandMorleydevisedacleverexperimentwherebyasinglebeamof

light is split into two distinct beams, each shot in different directions at rightanglestoeachother.Mirrorsreflectedthebeamsbacktothesource,andthenthetwo beams were allowed to mix and interfere with each other. The wholeapparatuswascarefullyplacedonabedofliquidmercury,sothatitcouldrotatefreely,anditwassodelicatethatiteasilypickedupthemotionofpassinghorsecarriages. According to the aether theory, the two beams should travel atdifferentspeeds.Onebeam,forexample,wouldmovealongthedirectionoftheearth’smotionintheaether,andtheotherbeamwouldmoveat90degreestotheaetherwind.Thus,whentheyreturnedbacktothesource,theyshouldbeoutofphasewitheachother.Much to their astonishment,Michelson andMorley found that the speed of

lightwasidenticalforalllightbeams,nomatterinwhichdirectiontheapparatuspointed.Thiswasdeeplydisturbing,foritmeantthattherewasnoaetherwindatall,andthespeedoflightneverchanged,evenastheyrotatedtheirapparatusinalldirections.This left physicists with two equally unpleasant choices. One was that the

earthmightbeperfectlystationarywithrespecttotheaether.Thischoiceseemedto violate everything known about astronomy since the original work ofCopernicus,whofoundthat therewasnothingspecialaboutthelocationoftheearth in the universe. Second, one might abandon the aether theory andNewtonianmechanicsalongwithit.Heroiceffortsweremadetosalvagetheaethertheory.Thecloseststeptoward

aresolutiontothispuzzlewasfoundbytheDutchphysicistHendrikLorentzandtheIrishphysicistGeorgeFitzGerald.Theyreasonedthattheearth,initsmotionthrough the aether,was actually physically compressedby the aetherwind, sothat allmeter sticks in theMichelson-Morley experimentwere shrunken. Theaether, which already had near mystical properties of being invisible,noncompressible, extremely dense, and so on, now had onemore property: itcould mechanically compress atoms by passing through them. This wouldconvenientlyexplainthenegativeresult.Inthispicture,thespeedoflightdidinfactchange,butyoucouldnevermeasureitbecauseeverytimeyoutriedusingameterstick,thevelocityoflightwouldindeedchangeandthemeterstickswouldshrinkinthedirectionoftheaetherwindbypreciselytherightamount.Lorentz and FitzGerald independently calculated the amount of shrinkage,

yielding what is now called the “Lorentz-FitzGerald contraction.” NeitherLorentznorFitzGeraldwereespeciallypleasedwiththisresult;itwassimplya

quickfix,awayofpatchingupNewtonianmechanics,but itwasthebest theycould do.Notmanyphysicists liked theLorentz-FitzGerald contraction either,sinceitsmackedofbeinganadhocprinciple,thrownintopropupthesaggingfortunesof the aether theory.ToEinstein, the ideaof the aether,with its nearmiraculousproperties, seemed artificial and contrived.Earlier,Copernicushaddestroyedtheearth-centeredsolarsystemofPtolemy,whichrequiredtheplanetsto move in extremely complex circular motions called “epicycles.” WithOccam’s Razor, Copernicus sliced away the blizzard of epicycles needed topatchupthePtolemaicsystemandputthesunatthecenterofthesolarsystem.LikeCopernicus,EinsteinwoulduseOccam’sRazortosliceawaythemany

pretensions of the aether theory. And he would do this by using a children’spicture.

CHAPTER3

SpecialRelativityandthe“MiracleYear”IntriguedbyMach’s criticismsofNewton’s theory,Einsteinwentback to thepicture that had haunted him since he was sixteen, running alongside a lightbeam.HereturnedtothecuriousbutimportantdiscoverythathemadewhileatthePolytechnic, that inMaxwell’s theory the speed of lightwas the same, nomatterhowyoumeasuredit.Foryears,hepuzzledoverhowthiscouldpossiblyhappen,becauseinaNewtonian,commonsenseworldyoucanalwayscatchuptoaspeedingobject.Imagineagainthepoliceofficerchasingafteraspeedingmotorist.Ifhedrives

fastenough,theofficerknowsthathecancatchuptothemotorist.Anyonewhohas ever gotten a ticket for speeding knows that. But if we now replace thespeedingmotoristwithalightbeam,andanobserverwitnessesthewholething,then the observer concludes that the officer is speeding just behind the lightbeam,travelingalmostasfastaslight.Weareconfidentthattheofficerknowsheistravelingneckandneckwiththelightbeam.Butlater,whenweinterviewhim,wehearastrangetale.Heclaimsthatinsteadofridingalongsidethelightbeamaswejustwitnessed,itspedawayfromhim,leavinghiminthedust.Hesaysthatnomatterhowmuchhegunnedhisengines,thelightbeamspedawayatpreciselythesamevelocity.Infact,heswearsthathecouldnotevenmakeadentincatchinguptothelightbeam.Nomatterhowfasthetraveled,thelightbeam traveled away from him at the speed of light, as if he were stationaryinsteadofspeedinginapolicecar.Butwhenyou insist thatyousaw thepoliceofficer speedingneckandneck

withthelightbeam,withinahairsbreadthofcatchingupto it,hesaysyouarecrazy; he never even got close. To Einstein, this was the central, naggingmystery:Howwasitpossiblefortwopeopletoseethesameeventinsuchtotallydifferentways? If the speedof lightwas really a constant of nature, thenhowcouldawitnessclaimthattheofficerwasneckandneckwiththelightbeam,yettheofficerswearsthatheneverevengotclose?EinsteinhadrealizedearlierthattheNewtonianpicture(wherevelocitiescan

beaddedandsubtracted)andtheMaxwellianpicture(where thespeedof light

was a constant) were in total contradiction. Newtonian theory was a self-containedsystem,restingonafewassumptions.Ifonlyoneoftheseassumptionswerechanged, itwouldunravel theentire theory in the sameway that a loosethread can unravel a sweater. That thread would be Einstein’s daydream ofracingalightbeam.OnedayaroundMayof1905,EinsteinwenttovisithisgoodfriendMichele

Besso,whoalsoworkedatthepatentoffice,andlaidoutthedimensionsoftheproblemthathadpuzzledhimforadecade.UsingBessoashisfavoritesoundingboard for ideas, Einstein presented the issue: Newtonian mechanics andMaxwell’sequations, thetwopillarsofphysics,wereincompatible.Oneortheother was wrong.Whichever theory proved to be correct, the final resolutionwouldrequireavastreorganizationofallofphysics.Hewentoverandovertheparadox of racing a light beam. Einsteinwould later recall, “The germ of thespecial relativity theorywas already present in that paradox.” They talked forhours, discussing every aspect of the problem, includingNewton’s concept ofabsolute space and time,which seemed to violateMaxwell’s constancy of thespeed of light. Eventually, totally exhausted, Einstein announced that he wasdefeatedandwouldgiveuptheentirequest.Itwasnouse;hehadfailed.AlthoughEinsteinwasdepressed,histhoughtswerestillchurninginhismind

whenhereturnedhomethatnight.Inparticular,herememberedridinginastreetcarinBernandlookingbackatthefamousclocktowerthatdominatedthecity.Hethenimaginedwhatwouldhappenifhisstreetcarracedawayfromtheclocktower at the speed of light. He quickly realized that the clock would appearstopped,sincelightcouldnotcatchuptothestreetcar,buthisownclockinthestreetcarwouldbeatnormally.Thenitsuddenlyhithim,thekeytotheentireproblem.Einsteinrecalled,“A

stormbroke loose inmymind.”Theanswerwassimpleandelegant: timecanbeat at different rates throughout the universe, depending on how fast youmoved. Imagine clocks scattered at different points in space, each oneannouncingadifferenttime,eachonetickingatadifferentrate.OnesecondonEarthwas not the same length as one second on themoon or one second onJupiter. In fact, the faster you moved, the more time slowed down. (Einsteinonce joked that in relativity theory, he placed a clock at every point in theuniverse, each one running at a different rate, but in real life he didn’t haveenoughmoneytobuyevenone.)Thismeantthateventsthatweresimultaneousin one frame were not necessarily simultaneous in another frame, as Newtonthought.Hehadfinallytappedinto“God’sthoughts.”Hewouldrecallexcitedly,“Thesolutioncametomesuddenlywiththethoughtthatourconceptsandlawsofspaceandtimecanonlyclaimvalidityinsofarastheystandinaclearrelation

toourexperiences….Bya revisionof theconceptofsimultaneity intoamoremalleableform,Ithusarrivedatthetheoryofrelativity.”For example, remember that in the paradox of the speeding motorist, the

policeofficerwastravelingneckandneckwiththespeedinglightbeam,whiletheofficerhimselfclaimedthatthelightbeamwasspeedingawayfromhimatprecisely the speed of light, nomatter howmuch he gunned his engines. Theonlywaytoreconcilethesetwopicturesistohavethebrainoftheofficerslowdown.Timeslowsdownfor thepoliceman. Ifwecouldhaveseen theofficer’swristwatchfromtheroadside,wewouldhaveseenthatitnearlystoppedandthathisfacialexpressionswerefrozenintime.Thus,fromourpointofview,wesawhimspeedingneckandneckwiththelightbeam,buthisclocks(andhisbrain)were nearly stopped.Whenwe interviewed the officer later,we found that heperceivedthelightbeamtobespeedingaway,onlybecausehisbrainandclockswererunningmuchslower.To complete his theory, Einstein also incorporated the Lorentz-FitzGerald

contraction,exceptthatitwasspaceitselfthatwascontracted,nottheatoms,asLorentzandFitzGeraldthought.(Thecombinedeffectofspacecontractionandtime dilation is today called the “Lorentz transformation.”) Thus, he coulddispense entirelywith the aether theory.Summarizing thepath thathe took torelativity,hewouldwrite,“IowemoretoMaxwellthantoanyone.”Apparently,although he was dimly aware of the Michelson-Morley experiment, theinspiration for relativity did not come from the aetherwind, but directly fromMaxwell’sequations.Thedayafterthisrevelation,EinsteinwentbacktoBesso’shomeand,without

even saying hello, he blurted out, “Thank you, I’ve completely solved theproblem.”Hewouldproudlyrecall,“Ananalysisoftheconceptoftimewasmysolution.Timecannotbeabsolutelydefined,andthereisaninseparablerelationbetweentimeandsignalvelocity.”Forthenextsixweeks,hefuriouslyworkedouteverymathematicaldetailofhisbrilliant insight, leading toapaper that isarguablyoneofthemostimportantscientificpapersofalltime.Accordingtohisson,hethenwentstraighttobedfortwoweeksaftergivingthepapertoMilevatocheckforanymathematicalerrors.Thefinalpaper,“OntheElectrodynamicsof Moving Bodies,” was scribbled on thirty-one handwritten pages, but itchangedworldhistory.In the paper, he does not acknowledge any other physicist; he only gives

thanks toMicheleBesso. (Einsteinwas aware of Lorentz’s earlywork on thesubject, but not the Lorentz contraction itself, which Einstein foundindependently.) It was finally published in Annalen der Physik in September1905, in volume 17. In fact, Einsteinwould publish three of his pathbreaking

papersinthatfamousvolume17.HiscolleagueMaxBornhaswritten,volume17is“oneof themostremarkablevolumes in thewholescientific literature. ItcontainsthreepapersbyEinstein,eachdealingwithadifferentsubjectandeachtoday acknowledged to be a masterpiece.” (Copies of that famous volumerecentlysoldfor$15,000atanauctionin1994.)Withalmostbreathtakingsweep,Einsteinbeganhispaperbyproclaimingthat

his theoriesworkednot just for light,butwere truthsabout theuniverse itself.Remarkably, he derived all his work from two simple postulates applying toinertialframes(i.e.,objectsthatmovewithconstantvelocitywithrespecttoeachother):

1. Thelawsofphysicsarethesameinallinertialframes.2. Thespeedoflightisaconstantinallinertialframes.

Thesetwodeceptivelysimpleprinciplesmarkthemostprofoundinsightsinto

thenatureof theuniversesinceNewton’swork.Fromthem,onecanderiveanentirelynewpictureofspaceandtime.First, in onemasterful stroke,Einstein elegantly proved that if the speed of

light was indeed a constant of nature, then themost general solutionwas theLorentz transformation. He then showed thatMaxwell’s equations did indeedrespect that principle. Last, he showed that velocities add in a peculiar way.Although Newton, observing the motion of sailing ships, concluded thatvelocitiescouldaddwithoutlimit,Einsteinconcludedthatthespeedoflightwastheultimatevelocityintheuniverse.Imagine,forthemoment,thatyouareinarocket speeding at 90% the speedof light away fromEarth.Now fire abulletinside the rocket that is also going at 90% the speed of light. According toNewtonianphysics,thebulletshouldbegoingat180%thespeedoflight, thusexceeding light velocity. But Einstein showed that because meter sticks areshorteningandtimeisslowingdown,thesumofthesevelocitiesisactuallycloseto99%thespeedoflight.Infact,Einsteincouldshowthatnomatterhowhardyou tried, you could never boost yourself beyond the speed of light. Lightvelocitywastheultimatespeedlimitintheuniverse.We never see these bizarre distortions in our experience because we never

travel near the speed of light. For everyday velocities, Newton’s laws areperfectly fine. This is the fundamental reason why it took over two hundredyearstodiscoverthefirstcorrectiontoNewton’slaws.Butnowimaginethatthe

speedof light isonly20milesperhour.Ifacarweretogodownthestreet, itmight look compressed in the direction of motion, being squeezed like anaccordion down to perhaps 1 inch in length, for example, although its heightwouldremainthesame.Becausethepassengersinthecararecompresseddownto1inch,wemightexpectthemtoyellandscreamastheirbonesarecrushed.Infact,thepassengersseenothingwrong,sinceeverythinginsidethecar,includingtheatomsintheirbodies,issqueezedaswell.Asthecarslowsdowntoastop,itwouldslowlyexpandfrom1inchtoabout

10feet,andthepassengerswouldwalkoutasifnothinghappened.Whoisreallycompressed?Youor thecar?Accordingtorelativity,youcannot tell,sincetheconceptoflengthhasnoabsolutemeaning.Inretrospect,onecansee thatotherscametantalizinglyclose todiscovering

relativity. Lorentz and FitzGerald obtained the same contraction, but they hadthe totally wrong understanding of the result, thinking it was anelectromechanicaldeformationoftheatoms,ratherthanasubtletransformationof space and time itself. Henri Poincaré, recognized as the greatest Frenchmathematician of his time, came close. He understood that the speed of lightmust be a constant in all inertial frames, and even showed that Maxwell’sequationsretainedthesameformunderaLorentz transformation.However,hetoorefusedtoabandontheNewtonianframeworkoftheaetherandthoughtthatthesedistortionswerestrictlyaphenomenonofelectricityandmagnetism.Einsteinthenpushedfurtherandmadethenextfatefulleap.Hewroteasmall

paper,almostafootnote,latein1905thatwouldchangeworldhistory.Ifmetersticks and clocks became distorted the faster youmoved, then everything youcanmeasurewithmetersticksandclocksmustalsochange,includingmatterandenergy. In fact,matter and energy could change into eachother.For example,Einsteincouldshowthatthemassofanobjectincreasedthefasteritmoved.(Itsmass would in fact become infinite if you hit the speed of light—which isimpossible,whichproves theunattainabilityof the speedof light.)Thismeantthat the energyofmotionwas somehowbeing transformed into increasing themass of the object. Thus, matter and energy are interchangeable. If youcalculatedpreciselyhowmuchenergywasbeingconvertedintomass,inafewsimple lines you could show that E=mc2, the most celebrated equation of alltime.Since the speedof lightwas a fantastically large number, and its squarewas even larger, thismeant that even a tiny amount ofmatter could release afabulous amount of energy. A few teaspoons of matter, for example, has theenergyofseveralhydrogenbombs.Infact,apieceofmatterthesizeofahousemightbeenoughtocracktheearthinhalf.Einstein’sformulawasnotsimplyanacademicexercise,becausehebelieved

thatitmightexplainacuriousfactdiscoveredbyMarieCurie,thatjustanounceof radium emitted 4,000 calories of heat per hour indefinitely, seeminglyviolatingthefirstlawofthermodynamics(whichstatesthatthetotalamountofenergy is always constant or conserved).He concluded that there should be aslightdecreaseinitsmassasradiumradiatedawayenergy(anamounttoosmalltobemeasuredusingtheequipmentof1905).“Theideaisamusingandenticing;butwhethertheAlmightyislaughingatitandisleadingmeupthegardenpath—that Icannotknow,”hewrote.Heconcluded thatadirectverificationofhisconjecture “for the time being probably lies beyond the realm of possibleexperience.”Whyhadn’tthisuntappedenergybeennoticedbefore?Hecomparedthistoa

fabulouslyrichmanwhokepthiswealthsecretbyneverspendingacent.BaneshHoffman, a former student, wrote, “Imagine the audacity of such a

step…. Every clod of earth, every feather, every speck of dust becoming aprodigiousreservoirofuntappedenergy.Therewasnowayofverifyingthisatthetime.Yetinpresentinghisequationin1907Einsteinspokeofitasthemostimportantconsequenceofhistheoryofrelativity.Hisextraordinaryabilitytoseefar ahead is shown by the fact that his equationwas not verified…until sometwenty-fiveyearslater.”Once again, the relativity principle forced a major revision in classical

physics.Before,physicistsbelievedin theconservationofenergy, thefirst lawof thermodynamics,which states that the total amount of energy cannever becreatedordestroyed.Now,physicistsconsideredthetotalcombinedamountofmatterandenergyasbeingconserved.Einstein’s restless mind tackled yet another problem that same year, the

photoelectric effect.HeinrichHertz,back in1887,noticed that if a lightbeamstruck a metal, under certain circumstances a small electric current could becreated.This is the same principle that underliesmuch ofmodern electronics.Solarcellsconvertordinarysunlightintoelectricalpower,whichcanbeusedtoenergize our calculators. TV cameras take light beams from the subject andconvertthemintoelectriccurrents,whicheventuallywinduponourTVscreen.However,attheturnofthecentury,thiswasstillatotalmystery.Somehow,

the lightbeamwasknockingelectronsoutof themetal,buthow?Newtonhadbelieved that light consisted of tiny particles that he called “corpuscles,” butphysicistswereconvincedthatlightwasawave,andaccordingtoclassicalwavetheory its energywas independentof its frequency.Forexample, although redand green light have different frequencies, they should have the same energy,andhence,when theyhit a pieceofmetal, the energyof the ejected electronsshould be the same as well. Similarly, classical wave theory said that if one

turneduptheintensityofthelightbeambyaddingmorelamps,thentheenergyoftheejectedelectronsshouldincrease.TheworkofPhilippLenard,however,demonstratedthat theenergyof theejectedelectronswasstrictlydependentonthefrequencyorcolorofthelightbeam,notitsintensity,whichwasoppositethepredictionofthewavetheory.Einsteinsoughttoexplainthephotoelectriceffectbyusingthenew“quantum

theory”recentlydiscoveredbyMaxPlanckinBerlinin1900.Planckmadeoneof themost radical departures from classical physics by assuming that energywas not a smooth quantity, like a liquid, but occurred in definite, discretepackets, called “quanta.” The energy of each quantumwas proportional to itsfrequency. The proportionality constant was a new constant of nature, nowcalled “Planck’s constant.” One reason why the world of the atom and thequantum seems so bizarre is the fact that Planck’s constant is a very smallnumber.Einsteinreasonedthatifenergyoccurredindiscretepackets,thenlightitselfmustbequantized.(Einstein’spacketof“lightquanta”waslaterchristenedthe “photon,” a particle of light, by chemist Gilbert Lewis in 1926.) Einsteinreasonedthatiftheenergyofthephotonwasproportionaltoitsfrequency,thentheenergyof theejectedelectronshouldalsobeproportional to its frequency,contrarytoclassicalphysics.(It’samusingtonotethatonthepopularTVseriesStarTrek,thecrewoftheEnterprisefires“photontorpedoes”atitsenemies.Inreality,thesimplestlauncherofphotontorpedoesisaflashlight.)Einstein’s new picture, a quantum theory of light,made a direct prediction

thatcouldbetestedexperimentally.Byturningupthefrequencyoftheincominglightbeam,oneshouldbeabletomeasureasmoothriseinthevoltagegeneratedin themetal. This historic paper (whichwould eventuallywin him theNobelPrizeinphysics)waspublishedonJune9,1905,withthetitle“OnaHeuristicPointofViewConcerningtheProductionandTransformationofLight.”Withit,thephotonwasborn,aswellasthequantumtheoryoflight.In yet another article written during the “miracle year” of 1905, Einstein

tackled the problem of the atom.Although the atomic theorywas remarkablysuccessful indetermining thepropertiesofgasesandchemical reactions, therewasnodirect proofof their existence, asMach andother criticswere fondofpointingout.Einsteinreasonedthatonemightbeabletoprovetheexistenceofatomsbynoticingtheireffectonsmallparticlesinaliquid.“Brownianmotion,”for example, refers to tiny, randommotions of small particles suspended in aliquid.Thispropertywasdiscoveredin1828bythebotanistRobertBrown,whoobserved tiny pollen grains under a microscope exhibiting strange randommotions.Atfirst,hethoughtthatthesezigzagmovementswerelikethemotionofmale spermcells.Buthe found that this strangeaberrantbehaviorwasalso

exhibitedbytinygrainsofglassandgranite.Some had speculated that Brownian motion might be due to the random

impacts ofmolecules, but no one could formulate a reasonable theory of this.Einstein,however,tookthenextdecisivestep.Hereasonedthatalthoughatomswere too small to be observed, one could estimate their size and behavior bycalculatingtheircumulativeimpactonlargeobjects.Ifoneseriouslybelievedinthe theory of atoms, then the atomic theory should be able to calculate thephysicaldimensionsofatomsbyanalyzingBrownianmotion.Byassumingthatthe random collisions of trillions upon trillions of molecules of water werecausingrandommotionsofadustparticle,hewasabletocomputethesizeandweight of atoms, thereby giving experimental evidence of the existence ofatoms.It was nothing short of amazing that by peering into a simple microscope,

Einsteincouldcalculate thatagramofhydrogencontained3.03×1023 atoms,which is close to thecorrectvalue.The titlewas“On theMovementofSmallParticles Suspended in Stationary Liquids Required by the Molecular-KineticTheory of Heat” (July 18). This simple paper, in effect, gave the firstexperimental proof of the existence of atoms. (Ironically, just a year afterEinsteincalculatedthesizeofatoms,thephysicistLudwigBoltzmann,whohadpioneered the theory of atoms, committed suicide, in part because of theincessant ridiculehe received for advancing the atomic theory.)AfterEinsteinwrotethesefourhistoricpapers,healsosubmittedanearlierpaperofhis,onthesize ofmolecules, to his advisor, ProfessorAlfredKleiner, as his dissertation.Thatnight,hegotdrunkwithMileva.At first,hisdissertationwas refused.ButonJanuary15,1906,Einsteinwas

finallygrantedaPh.D.fromtheUniversityofZurich.HecouldnowcallhimselfDr.Einstein.ThebirthofthenewphysicsalltookplaceattheEinsteinresidenceonKramgasse49inBern.(Today,itiscalledthe“EinsteinHouse.”Asyougazethroughitsbeautifulbaywindowfacingthestreet,youcanreadaplaquewhichstatesthatthroughthiswindow,thetheoryofrelativitywascreated.Ontheotherwall,youcanseeapictureoftheatomicbomb.)Thus,1905wastrulyanannusmirabilisinthehistoryofscience.Ifweareto

find another comparable miracle year, we would have to look back to 1666,when Isaac Newton, twenty-three years old, hit upon the universal law ofgravitation,theintegralanddifferentialcalculus,thebinomialtheorem,andhistheoryofcolor.Einsteinhadfinishedtheyear1905layingdownthephotontheory,providing

evidencefor theexistenceofatoms,andtopplingtheframeworkofNewtonianphysics, each of them worthy of international acclaim. He was disappointed,

however,inthedeafeningsilencethatensued.Hiswork,itseemed,wastotallyignored.Disheartened,Einsteinwentabouthispersonallife,raisinghischildandtoiling by himself at the patent office. Perhaps the thought of pioneering newworldsinphysicswasallapipedream.In early 1906, however, the first glimmer of response riveted Einstein’s

attention.Hegotjustasingleletter,butitwasfromperhapsthemostimportantphysicist of the time, Max Planck, who immediately understood the radicalimplications of Einstein’s work.What drew Planck to the theory of relativitywasthatitelevatedaquantity,thespeedoflight,intoafundamentalconstantofnature.Planck’sconstant,forexample,demarcatedtheclassicalworldfromthesubatomicworldofthequantum.Weareshieldedfromthestrangepropertiesofatoms because of the smallness of Planck’s constant. Similarly, felt Planck,Einsteinwasraising thespeedof light intoanewconstantofnature.Wewereshieldedfromtheequallybizarreworldofcosmicphysicsbythehugevalueofthespeedoflight.In Planck’s mind, these two constants, Planck’s constant and the speed of

light,laiddownthelimitsofcommonsenseandNewtonianphysics.WecannotseethefundamentallyweirdnatureofphysicalrealitybecauseofthesmallnessofPlanck’sconstantandtheimmensityofthespeedoflight.Ifrelativityandthequantumtheoryviolatedcommonsense,itwasonlybecauseweliveourentirelifeinatinycorneroftheuniverse,inashelteredworldwherevelocitiesarelowcompared to the speed of light and objects are so large we never encounterPlanck’sconstant.Nature,however,doesnotcareaboutourcommonsense,butcreatedauniversebasedonsubatomicparticlesthatroutinelygonearthespeedoflightandobeyPlanck’sformula.Inthesummerof1906,Plancksenthisassistant,MaxvonLaue,tomeetthis

obscure civil servantwho appeared out of nowhere to challenge the legacy ofIsaacNewton.Theywere supposed tomeet in thewaiting roomof the patentofficebutcomicallywalkedrightpasteachotherbecausevonLaueexpectedtoseeanimposing,authoritativefigure.WhenEinsteinfinallyintroducedhimself,von Laue was surprised to find someone completely different, a surprisinglyyoung and casually dressed civil servant. They became lifelong friends.(However,vonLaueknewabadcigarwhenhesawone.WhenEinsteinofferedhim a cigar, von Laue discretely threw it into the Aare River when Einsteinwasn’tlookingastheytalkedandcrossedabridge.)With the blessing ofMax Planck, the work of Einstein gradually began to

attract the attention of other physicists. Ironically, one of Einstein’s oldprofessors at thePolytechnic,whohadcalledhima“lazydog” for cuttinghisclasses, took a particular interest in the work of his former student. The

mathematicianHermannMinkowskiplungedaheadanddevelopedtheequationsofrelativityevenfurther,tryingtoreformulateEinstein’sobservationthatspaceturns into time and vice versa the faster you move. Minkowski put this intomathematical language and concluded that space and time formed a four-dimensionalunity.Suddenly,everyonewastalkingaboutthefourthdimension.For example, on amap, two coordinates (length andwidth) are required to

locateanypoint. Ifyouadda thirddimension,height, thenyoucanlocateanyobjectinspace,fromthetipofyournosetotheendsoftheuniverse.Thevisibleworld around us is thus three-dimensional. Writers like H. G. Wells hadconjecturedthatperhapstimecouldbeviewedasafourthdimension,suchthatanyeventcouldbe locatedbygiving its three-dimensionalcoordinatesand thetimeatwhichitoccurs.Thus,ifyouwanttomeetsomeoneinNewYorkCity,youmightsay,“Meetmeatthecornerof42ndStreetandFifthAvenue,onthetwentiethfloor,atnoon.”Fournumbersuniquelyspecifytheevent.ButWells’sfourth dimension was only an idea without any mathematical or physicalcontent.Minkowski then rewrote Einstein’s equations to reveal this beautiful four-

dimensional structure, forever linking space and time into a four-dimensionalfabric. Minkowski wrote, “From now on, space and time separately havevanished into the merest shadows, and only a kind of union of the two willpreserveanyindependentreality.”At first,Einsteinwasnot impressed. In fact,heevenwrotederisively, “The

mainthingisthecontent,notthemathematics.Withmathematics,youcanproveanything.” Einstein believed that at the core of relativity lay basic physicalprinciples,notprettybutmeaningless four-dimensionalmathematics,whichhecalled “superfluous erudition.”Tohim, the essential thingwas tohave a clearandsimplepicture(e.g., trains, fallingelevators, rockets),and themathematicswouldcomelater.Infact,atthispointhethoughtthatmathematicsrepresentedonlythebookkeepingnecessarytotrackwhatwashappeninginthepicture.Einsteinwouldwrite,halfinjest,“Sincethemathematicianshaveattackedthe

relativity theory, I myself no longer understand it anymore.” With time,however, he began to appreciate the full power ofMinkowski’s work and itsdeep philosophical implications.WhatMinkowski had shownwas that it waspossible to unify two seemingly different concepts by using the power ofsymmetry.Spaceandtimewerenowtobeviewedasdifferentstatesofthesameobject.Similarly,energyandmatter,aswellaselectricityandmagnetism,couldberelatedvia thefourthdimension.Unification throughsymmetrybecameoneofEinstein’sguidingprinciplesfortherestofhislife.Thinkofasnowflake,forexample.Ifyourotatethesnowflakeby60degrees,

the snowflake remains the same. Mathematically, we say that objects thatmaintain their formafter a rotation are called “covariant.”Minkowski showedthat Einstein’s equations, like a snowflake, remain covariant when space andtimearerotatedasfour-dimensionalobjects.In other words, a new principle of physics was being born, and it further

refinedtheworkofEinstein:TheequationsofphysicsmustbeLorentzcovariant(i.e.,maintain the same form under a Lorentz transformation). Einsteinwouldlater admit that without the four-dimensional mathematics of Minkowski,relativity“mighthaveremainedstuckinitsdiapers.”Whatwasremarkablewasthat this new four-dimensional physics allowed physicists to compress all theequations of relativity into a remarkably compact form. For example, everyelectrical engineering student and physicist, when first studying Maxwell’sseries of eight partial differential equations, finds that they are fiendishlydifficult. But Minkowski’s new mathematics collapsed Maxwell’s equationsdown to just two. (In fact, one can prove using four-dimensionalmathematicsthatMaxwell’s equations are the simplest possible equations describing light.)For the first time, physicists appreciated the power of symmetry in theirequations.Whenaphysicisttalksabout“beautyandelegance”inphysics,whatheorsheoftenreallymeansisthatsymmetryallowsonetounifyalargenumberofdiversephenomenaandconceptsintoaremarkablycompactform.Themorebeautiful an equation is, the more symmetry it possesses, and the morephenomenaitcanexplainintheshortestamountofspace.Thus, the power of symmetry allows us to unify disparate pieces into their

harmonious,integralwhole.Rotationsofasnowflake,forexample,allowustoseetheunitythatexistsbetweeneachpointonthesnowflake.Rotatinginfour-dimensional space unifies the concept of space and time, turning one into theotherasthevelocityisincreased.Thisbeautiful,elegantconcept,thatsymmetryunifiesseeminglydissimilarentities intoapleasing,harmoniouswhole,guidedEinsteinforthenextfiftyyears.Paradoxically,assoonasEinsteincompleted the theoryofspecial relativity,

hebegantoloseinterest,preferringtocontemplateanother,deeperquestion,theproblemofgravityandacceleration,whichseemedbeyondthereachofspecialrelativity.Einsteinhadgivenbirthtorelativitytheory,butlikeanylovingparent,heimmediatelyrealizeditspotentialfaultsandtriedtocorrectthem.(Morewillbesaidaboutthislater.)Meanwhile,experimentalevidencebegantoconfirmsomeofhisideas,raising

hisvisibilitywithinthephysicscommunity.TheMichelson-Morleyexperimentwasrepeated,eachtimeyieldingthesamenegativeresultandcastingdoubtonthe entire aether theory. Meanwhile, experiments on the photoelectric effect

confirmedEinstein’sequations.Furthermore,in1908experimentsonhigh-speedelectrons seemed to prove that themass of the electron increased the faster itmoved.Buoyedbytheexperimentalsuccessesslowlypilingupforhistheories,heapplied for a lectureship (privatdozent)positionat thenearbyUniversityofBern.Thispositionwasbelowthatofaprofessor,but itoffered theadvantagethat he could simultaneously continue with his job at the patent office. Hesubmittedhisrelativitythesisaswellasotherpublishedworks.Atfirst,hewasrejected by the department head, Aime Foster, who declared that relativitytheorywasincomprehensible.Hissecondtrywassuccessful.In1908,withevidencemountingthatEinsteinhadmademajorbreakthroughs

in physics, hewas seriously considered for amore prestigious position at theUniversity of Zurich. He faced stiff competition, however, from an oldacquaintance,FriedrichAdler.BothtopcandidatesforthepositionwereJewish,which was a handicap, but Adler was the son of the founder of the AustrianSocialDemocraticParty,towhichmanyfacultymembersweresympathetic,soit appeared as if Einstein would be passed over for the position. It wassurprising,therefore,thatAdlerhimselfarguedstronglyforEinsteintotaketheposition.HewasashrewdobserverofcharacterandsizedupEinsteincorrectly.HewroteeloquentlyofEinstein’soutstandingabilitiesasaphysicist,butnoted,“As a student he was treated contemptuously by the professors….He has nounderstanding of how to get on with important people.” Due to Adler’sextraordinary self-sacrifice, Einstein was awarded the position and began hismeteoricclimbuptheacademicladder.HenowreturnedtoZurich,butthistimeasaprofessor,notasafailed,unemployedphysicistandmisfit.WhenhefoundanapartmentinZurich,hewasdelightedtolearnthatAdlerlivedonefloorjustbelowhis,andtheybecamegoodfriends.In1909,Einsteingavehismaidenlectureathisfirstmajorphysicsconference

inSalzburg,wheremanyluminaries,includingMaxPlanck,wereinattendance.Inhistalk,“TheDevelopmentofOurViewsontheNatureandConstitutionofRadiation,” he forcefully brought the equation E=mc2 to the world. Einstein,used to scrimping on funds for his lunch, marveled at the opulence of thisconference.He recalled, “The festivities ended in theHotelNational,with themostopulentbanquetIhaveeverattendedinmylife.ItencouragedmetosaytotheGenevanpatriciansittingnexttome:DoyouknowwhatCalvinwouldhavedonehadhebeenhere?…Hewouldhaveerectedanenormousstakeandhadusburntforsinfulextravagance.Themanneveraddressedanotherwordtome.”Einstein’stalkwasthefirsttimeinhistorythatanyonehadclearlypresented

the concept of “duality” in physics, the concept that light can have dualproperties,eitherasawave,asMaxwellhadsuggestedinthepreviouscentury,

orasaparticle,asNewtonhadsuggested.Whetheronesawlightasaparticleorasawavedependedontheexperiment.Forlow-energyexperiments,wherethewavelength of the light beam is large, thewave picturewasmore useful. Forhigh-energy beams, where the wavelength of light is extremely small, theparticlepicturewasmoresuitable.Thisconcept(whichdecadeslaterwouldbeattributed to Danish physicist Niels Bohr) proved to be a fundamentalobservationofthenatureofmatterandenergyandoneoftherichestsourcesofresearchonthequantumtheory.Althoughnowaprofessor,Einstein remained justasbohemianasever.One

student vividly recalled his maiden lecture at the University of Zurich: “Heappeared inclass insomewhatshabbyattire,wearingpants thatwere tooshortandcarryingwithhimaslipofpaperthesizeofavisitingcardonwhichhehadsketchedhislecturenotes.”In1910,Einstein’ssecondson,Eduard,wasborn.Einstein,ever therestless

wanderer, was already looking for a new position, apparently because someprofessors wanted to remove him from the university. The next year, he wasofferedapositionattheGermanUniversityofPrague’sInstituteofTheoreticalPhysics at an increased salary. Ironically, his office was next to an insaneasylum. Pondering themysteries of physics, he oftenwondered if the inmateswerethesaneones.Thatsameyear,1911,alsomarkedthemeetingoftheFirstSolvayConference

in Brussels, funded by a wealthy Belgian industrialist, Ernest Solvay, whichwould highlight thework of theworld’s leading scientists. Thiswas themostimportantconferenceofitstime,anditgaveEinsteinachancetomeetthegiantsof physics and exchange ideas with them. HemetMarie Curie, the two-timeNobel laureate,andformeda lifelongrelationship.The theoryofrelativityandhisphotontheorywerethecenterofattention.Thethemeoftheconferencewas“TheTheoryofRadiationandtheQuanta.”One question debated at the conference was the famous “twin paradox.”

Einstein had already made mention of the strange paradoxes concerning theslowing down of time. The twin paradox was proposed by physicist PaulLangevin,whoannouncedasimplethoughtexperimentthatprobedsomeoftheseeming contradictions in relativity theory. (At the time, the newspaperswerefilled with lurid stories about Langevin, who was unhappily married andinvolved in a scandalous romance with Marie Curie, a widow.) LangevinconsideredtwotwinslivingonEarth.Onetwinistransportednearthespeedoflight and then returns back to Earth. Fifty years, say,may have transpired onEarth,butsincetimeslowsdownontherocket,therockettwinhasagedbyonlytenyears.When the twins finallymeet, there isamismatch in theirages,with

therockettwinbeingfortyyearsyounger.Nowview the situation from thepointofviewof the rocket twin.Fromhis

perspective,heisatrest,anditisEarththathasblastedoff,sotheearthtwin’sclocksbecomeslower.When the two twinsfinallymeet, theearth twinshouldbe younger, not the rocket twin. But since motions should be relative, thequestion is, which twin is really younger? Since the two situations seemsymmetrical, thispuzzleeven today remainsa thorn in thesideofanystudentwhohastriedtotacklerelativity.Theresolutionof thepuzzle,asEinsteinpointedout, is that therocket twin,

nottheearthtwin,hasaccelerated.Therockethastoslowdown,stop,andthenreverse,whichclearlycausesgreatstressontherockettwin.Inotherwords,thesituationsarenotsymmetricalbecauseaccelerations,whicharenotcoveredbytheassumptionsbehindspecialrelativity,onlyoccurfortherockettwin,whoisreallyyounger.(However, the situation becomes more puzzling if the rocket twin never

returns.Inthisscenario,eachseesbytelescopetheothertwinslowingdownintime. Since the situations are now perfectly symmetrical, then each twin isconvinced that theotherone isyounger.Likewise,each twin isconvinced thattheotheriscompressed.Sowhichtwinisyoungerandthinner?Asparadoxicalas it seems, in relativity theory it is possible to have two twins, each youngerthantheother,eachthinnerthantheother.Thesimplestwaytodeterminewhoisreally thinner or younger in all these paradoxes is to bring the two twinstogether, which requires yanking one of the twins around, which in turndetermineswhichtwinis“really”moving.Althoughthesemind-bendingparadoxeswereindirectlyresolvedinEinstein’s

favor at the atomic levelwith studies of cosmic rays and atom smashers, thiseffectissosmallthatitwasnotdirectlyseeninthelaboratoryuntil1971,whenairplanescarryingatomicclocksweresentintotheairatgreatspeeds.Becausetheseatomicclockscanmeasurethepassingoftimewithastronomicalprecision,scientists,bycomparing the twoclocks, couldverify that timebeat slower thefasteryoumoved,exactlyasEinsteinhadpredicted.)Anotherparadoxinvolvestwoobjects,eachshorterthantheother.Imaginea

big-gamehuntertryingtotrapatigerabout10feetlongwithacagethatisonly1footwide.Normally,thisisimpossible.Nowimaginethatthetigerismovingsofastthatitshrinkstoonly1foot,sothecagecandropandcapturethetiger.Asthetigerscreechestoahalt,itexpands.Ifthecageismadeofwebbing,thetiger breaks the webbing. If the cage is made of concrete, the poor tiger iscrushedtodeath.Butnowlookatthesituationfromthepointofviewofthetiger.Ifthetigeris

atrest,thecageisnowmovingandhasshrunkdowntoonlyone-tenthofafoot.Howcanacagethatsmallcatchatiger10feetlong?Theansweristhatasthecagedrops,itshrinksinthedirectionofmotion,soitbecomesaparallelogram,asquashedsquare.The twoendsof thecage thereforedonotnecessarilyhit thetiger simultaneously. What is simultaneous to the big-game hunter is notsimultaneoustothetiger.Ifthecageismadeofwebbing,thenthefrontpartofthe cage hits the tiger’s nose first and begins to rip. As the cage drops, itcontinuestoripalongthetiger’sbody,untilthebackendofthecagefinallyhitsthetail.Ifthecageismadeofconcrete,thenthetiger’snoseiscrushedfirst.Asthecagedescends,itcontinuestocrushthelengthofthetiger’sbody,untilthebackendofthecagefinallycapturesthetail.These paradoxes even seized the public’s imagination, with the following

limerickrunninginthehumormagazinePunch:

ThereoncewasayoungladynamedBrightWhocouldtravelmuchfasterthanlightShesetoutoneday,inarelativewayAndcamebackthepreviousnight.

By this time, his good friend Marcel Grossman was a professor at the

Polytechnic,andhesoundedoutEinsteintoseeifhewantedapositionathisoldschool,thistimeasafullprofessor.LettersofrecommendationspokeofEinsteinin the highest terms. Marie Curie wrote that “mathematical physicists areunanimousinconsideringhisworkasbeingofthefirstrank.”So,justsixteenmonthsafterarrivinginPrague,hereturnedtoZurichandthe

old Polytechnic. Returning to the Polytechnic (since 1911 called the SwissFederal Institute of Technology, or ETH), this time as a famous professor,marked a personal victory for Einstein. He left the university with his nameclouded indisgrace,withprofessors likeWeberactivelysabotaginghiscareer.Hereturnedastheleaderofthenewrevolutioninphysics.Thatyear,hereceivedhis first nomination for the Nobel Prize in physics. His ideas were stillconsideredtooradicalfortheSwedishacademy,andthereweredissidentvoicesamong Nobel laureates who wanted to sabotage his nomination. In 1912, theNobel Prize did not go toEinstein, but toNilsGustafDalén, for hiswork onimproving lighthouses. (Ironically, lighthouses today have been made largelyobsolete by the introduction of the global positioning satellite system, whichdependscruciallyonEinstein’stheoryofrelativity.)Within another year, Einstein’s reputation was growing so rapidly that he

begantogetinquiriesfromBerlin.MaxPlanckwaseagertocapturethisrising

star in physics, and Germany was the unquestioned leader of the world’sresearch in physics, the crown jewel of German research being in Berlin.Einstein hesitated at first, since he had renounced hisGerman citizenship andstillnursedsomebittermemoriesfromhisyouth,buttheofferwastootempting.In1913,EinsteinwaselectedtothePrussianAcademyofSciencesandlater

offeredapositioninBerlinattheuniversity.HewouldbemadedirectoroftheKaiserWilhelmInstituteforPhysics.Butbeyondthetitles,whichmeantlittletohim,whatmade the offer especially attractivewas the fact that therewere noteaching obligations. (Although Einstein was a popular lecturer among thestudents, noted for treating his students with respect and kindness, teachingdetractedfromhismaininterest,generalrelativity.)In1914,EinsteinarrivedinBerlintomeetthefaculty.Hefeltabitnervousas

they looked him over. Einstein would write, “The gentlemen in Berlin aregambling on me as if I were a prize hen. As for myself, I don’t even knowwhether I’m going to lay another egg.” The thirty-five-year-old rebel, withstrange politics and stranger attire, soon had to adjust to the stiff, upper-crustways of the Prussian Academy of Sciences, where members addressed eachother as “Privy Councillor” or “Your Excellency.” Einstein would muse, “Itseems that most members confine themselves to displaying a peacock-likegrandeurinwriting;otherwisetheyarequitehuman.”Einstein’striumphantmarchfromthepatentofficeinBerntothetopranksof

German researchwas not without its personal toll. As his fame began to risewithinthescientificcommunity,hispersonallifebegantounravel.ThesewereEinstein’s most productive years, bearing fruit that would eventually reshapehumanhistory,andalmost impossibledemandswerebeingplacedonhis time,estranginghimfromhiswifeandchildren.EinsteinwrotethatlivingwithMilevawaslikelivinginacemetery,andwhen

alonehetriedtoavoidbeinginthesameroomwithher.Hisfriendssplitonthequestionofwhowasmainlytoblame.ManybelievedthatMilevawasbecomingincreasinglyisolatedandresentfulofherfamoushusband.EvenMileva’sfriendswere distressed that she had aged considerably in those years and had let herappearance deteriorate noticeably. She was becoming increasingly shrill andcold,jealousevenofthetimehespentwithhiscolleagues.WhenshediscoveredaletterofcongratulationssenttoEinsteinbyAnnaSchmid(whoknewEinsteinduring his brief time in Aarau and had since married), she blew her top,precipitatingperhapsoneoftheangriestriftsintheiralreadyshakymarriage.On the other hand, others believed that Einstein was hardly the perfect

husband,constantlyontheroad,leavingMilevatoraisetwochildrenmainlybyherself.Travelattheturnofthecenturywasnotoriouslydifficult,andextensive

travels were taking him away for days and weeks. Like passing ships in thenight,whenhewashome,theywouldonlymeetbrieflyatnightfordinnerorthetheater.Hewas so immersed in the abstractworldofmathematics thathehadlittle emotional energy to connect with his wife. Worse, the more shecomplainedtohimabouthisabsences, themorehewithdrewintotheworldofphysics.Itisprobablysafetosaythatthereissometruthinbothallegationsanditis

pointless to assign blame. In retrospect, it was probably inevitable that themarriage would experience enormous strains. Perhaps their friends were rightyearsagowhentheysaidthatthetwowereincompatible.ButthefinalbreakwasprecipitatedbyhisacceptanceoftheofferfromBerlin.

MilevawasreluctantaboutgoingtoBerlin.PerhapsbeingaSlavinthecenterofa Teutonic culture was too intimidating to her; more importantly, many ofEinstein’s relatives lived inBerlin, andMileva fearedbeingunder their harsh,disapprovinggaze. Itwasnosecret thather in-lawshatedher.At first,MilevaandthechildrenmadethetriptoBerlinwithEinstein,butthensuddenlysheleftfor Zurich, taking the children with her. They would never be united again.Einstein,who cherished his childrenmore than anyone,was devastated. Fromthat point on, hewas forced tomaintain a long-distance relationshipwith hissons,makingthegruelingten-hourtripfromBerlintoZurichforvisits.(WhenMileva was eventually awarded custody of the children, Einstein’s secretary,HelenDukas,wrotethathecriedallthewayhome.)Butwhatprobablyalsoprecipitatedtherupturewasthegrowingpresenceofa

certain cousin of Einstein’s in Berlin. He would confess, “I live a verywithdrawnlifebutnota lonelyone, thankstothecareofafemalecousinwhoactuallydrewmetoBerlininthefirstplace.”ElsaLowenthalwasadoublecousin;hermotherandEinstein’smotherwere

sisters,and theirgrandfatherswerebrothers.Shewasdivorced, livingwithhertwodaughters,Margot and Ilse, just upstairs fromherparents (Einstein’s auntand uncle). She and Einstein met briefly in 1912 when he visited Berlin. Bythen,Einsteinhadapparentlydecided thathismarriage toMilevawas finishedandthatdivorcewasinevitable.However,hefearedtherepercussionsadivorcewouldhaveonhisyoungsons.Ever since they were children, Elsa had taken a liking to Einstein. She

confessedtohavingfalleninlovewithhimasachildwhensheheardhimplayMozart. But what apparentlymost attracted her was his rising stardom in theacademicworld,hisrespectbyphysicistsaroundtheworld.Infact,shemadeitnosecret thatshe loved tobask in this fame.LikeMileva,shewasolder, fouryearsolderthanEinstein.Butthatiswheretheresemblanceended.Infact,they

were like polar opposites. Einstein, in fleeing Mileva, was apparently goingoverboard in the other direction. While Mileva was often uncaring of herappearance and looked continually harassed, Elsa was highly bourgeois andconsciousofclassranking.Shewasalwaystryingtocultivateacquaintancesinintellectual circles in Berlin and would proudly show off Einstein to all herfriendsinhighsociety.UnlikeMileva,whowaslaconic,withdrawn,andmoody,Elsa was a social butterfly, fluttering between dinner parties and theateropenings.AndunlikeMileva,whogaveup trying to reformherhusband,Elsawasmoreofamother,continuallycorrectinghismannerswhiledevotingherfullenergiestohelpinghimfulfillhisdestiny.ARussianjournalistlatersummedupthe relationship between Einstein and Elsa: “She is all love for her greathusband, always ready to shield him from the harsh intrusions of life and toensure thepeaceofmindnecessary forhisgreat ideas tomature.She is filledwith the realization of his great purpose as a thinker and with the tenderestfeelings of companion, wife, and mother towards a remarkable, exquisite,grown-upchild.”After Mileva stormed out of Berlin in 1915, taking the children with her,

EinsteinandElsagotevencloser.WhatconsumedEinsteinduringthisimportantperiod,however,wasnotlove,buttheuniverseitself.

PARTII

SECONDPICTURE

WarpedSpace-Time

CHAPTER4

GeneralRelativityand“theHappiestThoughtofMyLife”Einsteinwasstillnotsatisfied.Hewasalreadyrankedamongthetopphysicistsofhistime,yethewasrestless.Herealizedthattherewereatleasttwoglaringholesinhistheoryofrelativity.First,itwasbasedentirelyoninertialmotions.Innature,however,almostnothing is inertial.Everything is ina stateofconstantacceleration: the jostlingof trains, thezigzagsof falling leaves, the rotationoftheeartharoundthesun,themotionofheavenlybodies.Relativitytheoryfailedtoaccountforeventhecommonestaccelerationfoundontheearth.Second,thetheorysaidnothingaboutgravity.Itmadethesweepingclaimthat

itwasauniversalsymmetryofnature,applyingtoallsectorsoftheuniverse,yetgravity seemed beyond its reach. This was also quite embarrassing, becausegravity is everywhere. The deficiencies of relativity were obvious. Since thespeedoflightwastheultimatespeedoftheuniverse,relativitytheorysaidthatitwouldtakeeightminutesforanydisturbanceonthesuntoreachtheearth.This,however, contradicted Newton’s theory of gravity, which stated thatgravitational effects were instantaneous. (The speed of Newton’s gravity wasinfinite, since the speed of light does not appear anywhere in Newton’sequations.) Einstein therefore needed to completely overhaul Newton’sequationstoincorporatethespeedoflight.In short, Einstein realized the immensity of the problemof generalizing his

relativitytheorytoincludeaccelerationsandgravity.Hebegantocallhisearliertheoryof1905the“specialtheoryofrelativity,”todifferentiateitfromthemorepowerful “general theory of relativity” that was needed to describe gravity.WhenhetoldMaxPlanckofhisambitiousprogram,Planckwarnedhim,“Asanolder friend, I must advise you against it for in the first place you will notsucceed, and even if you succeed, no one will believe you.” But Planck alsorealizedtheimportanceoftheproblemwhenhesaid,“Ifyouaresuccessful,youwillbecalledthenextCopernicus.”The key insight into a new theory of gravity took placewhileEinsteinwas

still slavingoverpatent applications as a lowlycivil servantback in1907.Hewouldrecall,“IwassittinginachairinthepatentofficeatBernwhenallofa

sudden, a thought occurred tome: If a person falls freely, hewill not feel hisownweight.Iwasstartled.Thissimplethoughtmadeadeepimpressiononme.Itimpelledmetowardatheoryofgravitation.”Inaninstant,Einsteinrealizedthatifhehadfallenoveroffhischair,hewould

bemomentarilyweightless.Forexample,ifyouareinanelevatorandthecablesuddenlybreaks,youwouldbeinfreefall;youwouldfallatthesamerateastheelevatorfloor.Sincebothyouandtheelevatorarenowfallingatthesamespeed,it would appear that you are weightless, floating in air. Similarly, Einsteinrealizedthatifhefelloveroffhischair,hewouldbeinfreefallandtheeffectofgravity would be canceled perfectly by his acceleration, making him appearweightless.This concept is an old one. Itwas known toGalileo,who in an apocryphal

storydroppeda small rockanda largecannonball from theLeaningTowerofPisa.HewasthefirsttoshowthatallobjectsonEarthaccelerateatpreciselythesamerateundergravity(32feetpersecondsquared).Newtonalsoknewthisfactwhenherealized that theplanetsand themoonwereactually inastateoffreefallintheirorbitaroundthesunortheearth.Everyastronautwhohaseverbeenshotintoouterspacealsorealizesthatgravitycanbecanceledbyacceleration.Ina rocket ship, everything inside, including the floor, the instruments, and you,fallsatthesamerate.Thus,whenyoulookaround,everythingisfloating.Yourfeetdriftabovethefloor,givingtheillusionthatgravityhasvanished,becausethefloorisfallingalongwithyourbody.Andifanastronauttakesaspacewalkoutsidetheship,heorshedoesnotsuddenlydroptotheearth,butinsteadfloatsgentlyalongsidetherocketbecauseboththerocketandtheastronautarefallinginunisonevenas theyorbit theearth. (Gravityhasnotactuallydisappeared inouter space, as many science books erroneously claim. The sun’s gravity ispowerful enough to whip the planet Pluto in its orbit billions of miles fromEarth.Gravityhasnotdisappeared;ithasjustbeencanceledbythefallingoftherocketshipbeneathyourfeet.)Thisiscalledthe“equivalenceprinciple,”inwhichallmassesfallatthesame

rate under gravity (more precisely, the inertial mass is the same as thegravitationalmass).Thiswas indeedanold idea, almost a curiosity toGalileoandNewton, but in the hands of a seasoned physicist like Einstein, it was tobecomethefoundationofanewrelativistictheoryofgravity.EinsteinwentonegiantstepfurtherthanGalileoorNewton.Heformulatedhisnextpostulate,thepostulatebehindgeneralrelativity:Thelawsofphysicsinanacceleratingframeoragravitatingframeareindistinguishable.Remarkably,thissimplestatement,inthehandsofEinstein,becamethebasisofatheorythatwouldgiveuswarpedspace,blackholes,andthecreationoftheuniverse.

After this brilliant insight of 1907 in the patent office, it took years forEinstein’s new theory of gravity to gestate. A new picture of gravity wasemerging from theequivalenceprinciple,but itwouldn’tbeuntil1911 thathebegan to publish the fruits of his thoughts. The first consequence of theequivalenceprincipleisthefactthatlightmustbendundergravity.Theideathatgravitymightinfluencelightbeamsisanoldone,datingbackatleasttothetimeof Isaac Newton. In his book Opticks, he asked whether or not gravity caninfluence starlight: “Do not Bodies act upon light at a Distance, and by theirAction bend its Rays; and is not this Action strongest at the least Distance?”Unfortunately,giventhetechnologyoftheseventeenthcentury,hecouldgivenoanswer.But now Einstein, after more than two hundred years, returned to this

question.Considerturningonaflashlightinsidearocketshipthatisacceleratinginouterspace.Becausetherocketisacceleratingupward,thelightbeamdroopsdownward.Nowinvoke theequivalenceprinciple.Since thephysics inside thespaceship must be indistinguishable from the physics on Earth, it means thatgravity must also bend light. In a few brief steps, Einstein was led to a newphysical phenomenon, the bending of light due to gravity. He immediatelyrealizedthatsuchaneffectwascalculable.Thelargestgravitationalfieldinthesolarsystemisgeneratedbythesun,so

Einstein asked himself whether the sun was sufficient to bend starlight fromdistant stars. This could be tested by taking two photographs of the samecollectionof stars in the sky at twodifferent seasons.The first photoof thesestars would be taken at night when starlight is undisturbed; the second photowouldbetakenseveralmonthslaterwhenthesunispositioneddirectlyinfrontof thissamecollectionofstars.Bycomparing the twophotographs,onemightbeabletomeasurehowthestarshaveshiftedslightlyinthesun’svicinityduetothesun’sgravity.Becausethesunoverwhelmsthelightcomingfromthestars,anyexperimentonthebendingofstarlightwouldhavetobeperformedduringasolar eclipse, when the moon blocks out the light from the sun and the starsbecome visible during the daytime. Einstein reasoned that photographs of thedayskytakenduringaneclipse,comparedtophotographstakenofthesameskyatnight,shouldshowaslightdistortioninthelocationofthestarsinthevicinityof thesun.(Thepresenceof themoonalsobendsstarlightabitbecauseof themoon’s gravity, but this is a very tiny amount compared to the bending ofstarlightcausedbythesun,whichismuchlarger.Thus,thebendingofstarlightduringaneclipseisnotaffectedbythepresenceofthemoon.)Theequivalenceprinciplecouldhelphimtocalculatetheapproximatemotion

of light beams as they were pulled by gravity, but it still did not tell him

anything about gravity itself.Whatwas lackingwas a field theory of gravity.RecallthatMaxwell’sequationsdescribeagenuinefieldtheory,inwhichlinesof force are like a spider web that could vibrate and support waves travelingalongthelinesofforce.Einsteinsoughtagravitationalfieldwhoselinesofforcecouldsupportgravitationalvibrationsthattraveledatthespeedoflight.Around1912,afteryearsofconcentratedthought,heslowlybegantorealize

that he needed to overhaul our understanding of space and time; to do sorequired newgeometries beyond those inherited from the ancientGreeks.Thekeyobservationthatsenthimontheroadtocurvedspace-timewasaparadox,sometimes referred to as “Ehrenfest’s paradox,” that his friend Paul EhrenfestonceposedtoEinstein.Considerasimplemerry-go-roundoraspinningdisk.Atrest,weknowthatitscircumferenceisequaltoptimesthediameter.Oncethemerry-go-roundissetintomotion,however,theouterrimtravelsfasterthantheinteriorandhence,accordingtorelativity,shouldshrinkmorethantheinterior,distorting the shapeof themerry-go-round.Thismeans that the circumferencehasshrunkandisnowless thanp times thediameter; that is, thesurface isnolongerflat.Spaceiscurved.Thesurfaceofthemerry-go-roundcanbecomparedtotheareawithintheArcticCircle.WecanmeasurethediameteroftheArcticCirclebywalkingfromonepointonthecircle,directlyacrosstheNorthPole,totheoppositepointonthecircle.ThenwecanmeasurethecircumferenceoftheArcticCircle.Ifwecomparethetwo,wealsofindthatthecircumferenceislessthanptimesthediameterbecausetheearth’ssurfaceiscurved.Butforthelasttwo thousand years, physicists and mathematicians relied on Euclideangeometry,whichisbasedonflatsurfaces.Whatwouldhappeniftheyimaginedageometrybasedoncurvedsurfaces?Oncewe realize that space can be curved, a startling new picture emerges.

Thinkofaheavyrockplacedonabed.Therock,ofcourse,will sink into thebed. Now shoot a tiny marble over the bed. The marble will not move in astraightlinebutinacurvedlinearoundtherock.Therearetwowaystoanalyzethis effect. From a distance, a Newtonian may say that there is a mysterious“force”thatemanatesfromtherocktothemarble,forcingthemarbletochangeits path. This force, although invisible, reaches out and pulls on the marble.However,arelativistmayseeanentirelydifferentpicture.Toarelativistlookingat the bed close up, there is no force that pulls the marble. There is just thedepression in thebed,whichdictates themotionof themarble.As themarblemoves, the surfaceof thebed“pushes” themarbleuntil itmoves in a circularmotion.Nowreplacetherockwiththesun,themarblewiththeearth,andthebedwith

spaceandtime.Newtonwouldsaythataninvisibleforcecalled“gravity”pulls

theeartharoundthesun.Einsteinwouldreplythatthereisnogravitationalpullatall.Theearthisdeflectedaroundthesunbecausethecurvatureofspaceitselfispushingtheearth.Inasense,gravitydoesnotpull,butspacepushes.Inthispicture,Einsteincouldexplainwhyitwouldtakeeightminutesforany

disturbanceonthesuntoreachtheearth.Forexample, ifwesuddenlyremovethe rock, the bed will spring back to normal, creating ripples that travel at adefinite speedacross thebed.Similarly, if the sunwere todisappear, itwouldcreateashockwaveofwarpedspacethatwouldtravelatthespeedoflight.Thispicturewassosimpleandelegantthathecouldexplaintheessentialideatohissecond son, Eduard,who asked himwhy hewas so famous. Einstein replied,“When a blind beetle crawls over the surface of a curved branch, it doesn’tnotice that the track it has covered is indeed curved. I was lucky enough tonoticewhatthebeetledidn’tnotice.”Newton, in his landmark Philosophiae Naturalis Principia Mathematica,

confessedthathewasunabletoexplaintheoriginofthismysteriouspull,whichactedinstantlythroughouttheuniverse.Hecoinedhisfamousphrasehypothesesnon fingo (I frame no hypotheses) because of his inability to explain wheregravitycamefrom.WithEinstein,weseethatgravityiscausedbythebendingof space and time. “Force” is now revealed to be an illusion, a by-product ofgeometry. In this picture, the reasonwhywe are standing on the earth is notbecause the earth’s gravity pulls us down. According to Einstein, there is nogravitationalpull.Theearthwarpsthespace-timecontinuumaroundourbodies,sospaceitselfpushesusdowntothefloor.Thus,itisthepresenceofmatterthatwarps space around it, giving us the illusion that there is a gravitational forcepullingonneighboringobjects.This bending, of course, is invisible, and from a distance,Newton’s picture

appears to be correct. Think of ants walking on a crumpled sheet of paper.Tryingtofollowastraightline,theyfindthattheyareconstantlybeingtuggedtotheleftandrightastheywalkoverthefoldsinthepaper.Totheants,itappearsas if there is amysterious force pulling them in both directions. However, tosomeonelookingdownontheants, it isobviousthat thereisnoforce, thereisjust thebendingof thepaperpushingontheants,whichgives the illusionthatthere is a force.Recall thatNewton thought of space and time as an absolutereference frame for all motions. However, to Einstein, space and time couldassume a dynamic role. If space is curved, then anyonemoving on this stagewould think thatmysterious forceswere acting on their bodies, pushing themonewayortheother.Bycomparingspace-timetoafabric thatcanstretchandbend,Einsteinwas

forced to study themathematics of curved surfaces.Hequickly foundhimself

buriedinamorassofmathematics,unabletofindtherighttoolstoanalyzehisnewpictureofgravity.Insomesense,Einstein,whooncescornedmathematicsas “superfluous erudition,”was now paying for the years inwhich he cut themathematicscoursesatthePolytechnic.In desperation, he turned to his friend, Marcel Grossman. “Grossman, you

musthelpmeorelseI’llgocrazy!”Einsteinconfessed,“NeverinmylifehaveItormentedmyselfanythinglikethis,andthatIhavebecomeimbuedwithagreatrespect for mathematics, the more subtle parts of which I had previouslyregardedassheerluxury!Comparedtothisproblemtheoriginalrelativitytheoryischild’splay.”When Grossman reviewed the mathematical literature, he found that,

ironicallyenough, thebasicmathematics thatEinsteinneededhad indeedbeentaughtat thePolytechnic. In thegeometryofBernhardRiemann,developed in1854,Einstein finally found themathematics powerful enough to describe thebendingofspace-time.(Yearslater,whenlookingbackathowdifficultitwastomaster newmathematics, Einstein noted to some junior high school students,“Donotworryaboutyourdifficultiesinmathematics;Icanassureyouthatminearestillgreater.”)Before Riemann, mathematics was based on Euclidean geometry, the

geometryofflatsurfaces.Schoolchildrenforthousandsofyearshadbeengrilledinthetime-honoredtheoremsofGreekgeometry,wherethesumoftheinteriorangles of a triangle equals 180 degrees, and parallel lines never meet. Twomathematicians, the Russian Nicolai Lobachevsky and the Austro-HungarianJános Bolyai, came extremely close to developing a non-Euclidean geometry,thatis,inwhichthesumoftheanglesofatrianglecanbemoreorlessthan180degrees.Butthetheoryofnon-Euclideangeometrywasfinallydevelopedbythe“prince of mathematics,” Carl Friedrich Gauss, and especially his student,Riemann. (Gauss suspected that Euclid’s theory might be incorrect even onphysical grounds.He had his assistants shine light beams from atop theHarzMountains,tryingtoexperimentallycalculatethesumoftheanglesofatriangleformedby threemountain-tops.Unfortunately, he got a negative result.Gausswasalsosuchapoliticallycautiousindividualthatheneverpublishedhisworkon this sensitive subject, fearing the ire of conservatives who swore byEuclideangeometry.)Riemann discovered entirely new worlds of mathematics—the geometry of

curved surfaces in any dimension, not just two or three spatial dimensions.Einstein was convinced these higher geometries would yield a more accuratedescription of the universe. For the first time, the mathematical language of“differential geometry” was working its way into the world of physics.

Differentialgeometry,ortensorcalculus,themathematicsofcurvedsurfacesinany dimension, was once considered to be the most “useless” branch ofmathematics,devoidofanyphysicalcontent.Suddenly,itwastransformedintothelanguageoftheuniverseitself.In most biographies, Einstein’s theory of general relativity is presented as

fully developed in 1915, as if he unerringly found the theory fully formed bymagic. However, only in the last decades have some of Einstein’s “lostnotebooks”beenanalyzed,andtheyfillinthemanymissinggapsbetween1912and 1915. Now it is possible to construct, sometimes month by month, thecrucial evolution of one of the greatest theories of all time. In particular, hewantedtogeneralizethenotionofcovariance.Specialrelativity,aswesaw,wasbased on the idea ofLorentz covariance, that is, that the equations of physicsretain the same formunder aLorentz transformation.NowEinsteinwanted togeneralizethistoallpossibleaccelerationsandtransformations,notjustinertialones.Inotherwords,hewantedequationsthatretainedthesameformnomatterwhat frameof referencewasused,whether itwasacceleratingormovingwithconstantvelocity.Eachframeofreferencein turnrequiresacoordinatesystemtomeasure the three dimensions of space and the time.WhatEinstein desiredwas a theory that retained its form no matter which distance and timecoordinateswereusedtomeasuretheframe.Thisledhimtohisfamedprincipleofgeneralcovariance:theequationsofphysicsmustbegenerallycovariant(i.e.,theymustmaintainthesameformunderanarbitrarychangeofcoordinates).Forexample,thinkofthrowingafishingnetoveratabletop.Thefishingnet

representsanarbitrarycoordinatesystem,andtheareaofthetabletoprepresentssomething that remains the same under any distortion of the fishing net. Nomatterhowwetwistorcurlupthefishingnet,theareaofthetabletopremainsthesame.In 1912, aware that Riemann’s mathematics was the correct language for

gravitation, and guided by the law of general covariance, Einstein searchedwithin Riemannian geometry for objects that are generally covariant.Surprisingly,therewereonlytwocovariantobjectsavailabletohim:thevolumeof a curved space and the curvature (called the “Ricci curvature”) of such aspace.Thiswasof immensehelp:by severely restricting thepossiblebuildingblocksusedtoconstructatheoryofgravity,theprincipleofgeneralcovarianceledEinsteintoformulatetheessentiallycorrecttheoryin1912,afteronlyafewmonthsofexaminingRiemann’swork,basedontheRiccicurvature.Forsomereason,however,hethrewawaythecorrecttheoryof1912andbegantopursueanincorrectidea.Preciselywhyheabandonedthecorrecttheorywasamysterytohistoriansuntilrecently,whenthelostnotebookswerediscovered.Thatyear,

when he essentially constructed the correct theory of gravity out of the Riccicurvature,hemadeacrucialmistake.Hethoughtthatthiscorrecttheoryviolatedwhat is known as “Mach’s principle.”One particular version of this principlepostulates that the presence of matter and energy in the universe uniquelydetermines the gravitational field surrounding it. Once you fix a certainconfigurationofplanetsandstars,thenthegravitationsurroundingtheseplanetsand stars is fixed. Think, for example, of throwing a pebble into a pond. Thelarger thepebble, thegreater therippleson thepond.Thus,onceweknowtheprecisesizeofthepebble,thedistortionofthepondcanbeuniquelydetermined.Likewise, if we know the mass of the sun, we can uniquely determine thegravitationalfieldsurroundingthesun.ThisiswhereEinsteinmadehismistake.Hethoughtthatthetheorybasedon

theRiccicurvatureviolatedMach’sprinciplebecausethepresenceofmatterandenergydidnotuniquelyspecify thegravitational fieldsurrounding it.WithhisfriendMarcelGrossman,hetriedtodevelopamoremodesttheory,onethatwascovariant just under rotations (but not general accelerations). Because heabandonedtheprincipleofcovariance,however,therewasnoclearpathtoguidehim, and he spent three frustrating years wandering in the wilderness of theEinstein-Grossmantheory,whichwasneitherelegantnoruseful—forinstance,itfailed to yield Newton’s equations for small gravitational fields. AlthoughEinsteinhadperhapsthebestphysical instinctsofanyoneonEarth,heignoredthem.While groping for the final equations, Einstein focused on three key

experimentsthatmightprovehisideasconcerningcurvedspaceandgravity:thebending of starlight during an eclipse, the red shift, and the perihelion ofMercury.In1911,evenbeforehisworkoncurvedspace,EinsteinheldouthopethatanexpeditioncouldbesenttoSiberiaduringthesolareclipseofAugust21,1914,tofindthebendingofstarlightbythesun.TheastronomerErwinFinlayFreundlichwastoinvestigatethiseclipse.And

Einsteinwassoconvincedofthecorrectnessofhisworkthatatfirstheofferedtofundtheambitiousprojectoutofhisownpocket.“Ifeverythingfails,I’llpayfor the thing out ofmy own slight savings, at least the first 2,000marks,” hewrote. Eventually, a wealthy industrialist agreed to provide the funding.Freundlich left for Siberia a month before the solar eclipse, but GermanydeclaredwaronRussia,andheandhisassistantwere takenprisonerand theirequipmentwasconfiscated. (Inhindsight,perhaps itwas fortunate forEinsteinthat the 1914 expedition was unsuccessful. If the experiment had beenperformed,theresultswouldnot,ofcourse,haveagreedwiththevaluepredictedby Einstein’s incorrect theory, and his entire program might have been

disgraced.)Next, Einstein calculated how gravitywould affect the frequency of a light

beam.Ifarocketislaunchedfromtheearthandsentintoouterspace,thegravityoftheearthactslikeadrag,pullingtherocketback.Energyisthereforelostastherocketstrugglesagainstthepullofgravity.Similarly,Einsteinreasonedthatiflightwereemittedfromthesun,thengravitywouldalsoactasadragonthelightbeam,making it loseenergy.The lightbeamwillnotchange invelocity,butthefrequencyofthewavewilldropasitlosesenergystrugglingagainstthesun’s gravity. Thus, yellow light from the sunwill decrease in frequency andbecomeredderasthelightbeamleavesthesun’sgravitationalpull.Gravitationalredshift,however,isanextremelysmalleffect,andEinsteinhadnoillusionthatitwould be tested in the laboratory any time soon. (In fact itwould take fourmoredecadesbeforegravitationalredshiftcouldbeseeninthelaboratory.)Last, he set out to solve an age-old problem: why the orbit of Mercury

wobbles and deviates slightly from Newton’s laws. Normally, the planetsexecute perfect ellipses in their journeys around the sun, except for slightdisturbances caused by the gravity of nearby planets, which results in atrajectoryresemblingthepetalsofadaisy.TheorbitofMercury,however,evenaftersubtractingthe interferencecausedbynearbyplanets,showedasmallbutdistinct deviation fromNewton’s laws.This deviation, called the “perihelion,”was first observed in 1859 by astronomerUrbain Leverrier, who calculated atiny shift of 43.5 seconds of arc per century that could not be explained byNewton’s laws. (The fact that there were apparent discrepancies in Newton’slawsofmotionwasnotnew.Intheearly1800s,whenastronomerswerepuzzledbya similarwobblingof theorbit ofUranus, they faceda stark choice: eitherabandonthelawsofmotionorpostulatethattherewasanotherunknownplanettuggingontheorbitofUranus.Physicistsbreathedasighofreliefwhenin1846,a new planet, christened Neptune, was discovered just where Newton’s lawspredicteditshouldbe.)But Mercury was the remaining puzzle. Rather than discard Newton,

astronomers in time-honored traditionpostulated theexistenceofanewplanetcalled “Vulcan,” circling the sun within the orbit of Mercury. In repeatedsearches of the night sky, however, astronomers could find no experimentalevidenceforsuchaplanet.Einstein was prepared to accept the more radical interpretation: perhaps

Newton’s laws themselveswere incorrect,orat least incomplete. InNovember1915,afterwastingthreeyearsontheEinstein-Grossmantheory,hewentbacktotheRiccicurvature,whichhehaddiscardedbackin1912,andspottedhiskeymistake.(EinsteinhaddroppedtheRiccicurvaturebecauseityieldedmorethan

one gravitational field generated by a piece ofmatter, in seeming violation ofMach’sprinciple.Butthen,becauseofgeneralcovariance,henowrealizedthatthese gravitational fields were actually mathematically equivalent and yieldedthe same physical result. This impressed upon Einstein the power of generalcovariance: not only did it severely restrict the possible theories of gravity, italsoyieldeduniquephysical resultsbecausemanygravitational solutionswereequivalent.)InperhapsthegreatestmentalconcentrationofEinstein’slife,hethenslaved

away at his final equation, shutting out all distractions and working himselfmercilessly to see if he could derive the perihelion of Mercury. His lostnotebooksshowthathewouldrepeatedlyproposeasolutionandthenruthlesslycheck to see that it reproduced Newton’s old theory in the limit of smallgravitationalfields.This taskwasextremelytedious,sincehis tensorequationsconsistedoftendistinctequations,ratherthanthesingleequationofNewton.Ifitfailed, thenhewouldtryanothersolutiontoseeif thatreproducedNewton’sequation.Thisexhaustive,almostHerculean taskwas finallycompleted in lateNovember 1915, leaving Einstein totally drained. After a long tediouscalculationwithhisoldtheoryof1912,hefoundthatitpredictedthedeviationinMercury’sorbittobe42.9secondsofarcpercentury,wellwithinacceptableexperimentallimits.Einsteinwasshockedbeyondbelief.Thiswasexhilarating,thefirstsolidexperimentalevidencethathisnewtheorywascorrect.“Forsomedays, Iwasbeyondmyselfwith excitement,”he recalled. “Myboldestdreamshavenowcometrue.”Thedreamofalifetime,tofindtherelativisticequationsforgravity,wasrealized.WhatthrilledEinsteinwasthatthroughtheabstractphysicalandmathematical

principle of general covariance, he could derive a solid, decisive experimentalresult: “Imaginemy joyover the practicability of general covariance andoverthe result that the equations correctly yield the perihelion movement ofMercury.”Withthenewtheory,hethenrecalculatedthebendingofstarlightbythesun.Theadditionofcurvedspacetohistheorymeantthatthisfinalanswerwas1.7secondsofarc,twicehisoriginalvalue(about1/2000thofadegree).Hewasconvincedthatthetheorywassosimple,elegant,andpowerfulthatno

physicist could escape its hypnotic spell. “Hardly anyone who has trulyunderstood itwillbeable toescape thecharmof this theory,”hewouldwrite.“The theory isof incomparablebeauty.”Miraculously, theprincipleofgeneralcovariancewassopowerfulatoolthatthefinalequation,whichwoulddescribethe structure of the universe itself, was only 1 inch long. (Physicists todaymarvelthatanequationsoshortcanreproducethecreationandevolutionoftheuniverse.PhysicistVictorWeisskopflikenedthatsenseofwondertothestoryof

a peasantwho saw a tractor for the first time in his life.After examining thetractorandpeeringunderthehood,heasksinbewilderment,“Butwhereisthehorse?”)The only thing to mar Einstein’s triumph was a minor priority fight with

David Hilbert, perhaps the world’s greatest living mathematician. While thetheorywasinitslast,finalstepsbeforecompletion,Einsteinhadgivenaseriesof six two-hour lectures at Göttingen for Hilbert. Einstein still lacked certainmathematical tools (called the “Bianchi identities”) that prevented him fromderiving his equations from a simple form, called the “action.” Later, Hilbertfilled in the final step in the calculation, wrote down the action, and thenpublished the final result by himself, just six days ahead of Einstein. Einsteinwasnotpleased.Infact,hebelievedthatHilberthadtriedtostealthetheoryofgeneralrelativitybyfillinginthefinalstepandtakingcredit.Eventually,theriftbetweenEinstein andHilbert healed, butEinstein becamewary of sharing hisresults too freely. (Today, theactionbywhichonederivesgeneral relativity isknown as the “Einstein-Hilbert action.”Hilbertwas probably led to finish thelast tiny piece of Einstein’s theory because, as he often said, “physics is tooimportant to be left to the physicists” that is, physicists probably were notmathematicallyskilledenoughtoprobenature.Thisviewapparentlywassharedby other mathematicians. The mathematician Felix Klein would grumble thatEinsteinwas not innately amathematician, butworked under the influence ofobscure physical-philosophical impulses. That is probably the essentialdifference between mathematicians and physicists and why the former haveconsistentlyfailedtofindnewlawsofphysics.Mathematiciansdealexclusivelywithscoresofsmall,self-consistentdomains,likeisolatedprovinces.Physicists,however, deal with a handful of simple physical principles that may requiremany mathematical systems to solve. Although the language of nature ismathematics, the driving force behind nature seems to be these physicalprinciples,forexample,relativityandthequantumtheory.)NewsofEinstein’snewtheoryofgravitywasinterruptedbytheoutbreakof

war. In 1914, the assassination of the heir to the Austro-Hungarian thronetouched off the greatest bloodletting of its time, drawing the British, Austro-Hungarian,Russian,andPrussianempiresintoacatastrophicconflictthatwoulddoom tens of millions of young men. Almost overnight, quiet, distinguishedprofessors at German universities became bloodthirsty nationalists. Nearly theentire faculty at the University of Berlin was swept up by the war fever anddevotedalltheirenergiestothewareffort.InsupportoftheKaiser,ninety-threeprominentintellectualssignedthenotorious“ManifestototheCivilizedWorld,”which called for all people to rally around theKaiser and ominously declared

that the German people must defy “Russian hordes allied with Mongols andNegroesunleashedagainstthewhiterace.”ThemanifestojustifiedtheGermaninvasion of Belgium and proudly proclaimed, “The German Army and theGerman people are one. This awareness now binds seventy million Germanswithout distinction of education, class, or party.” Even Einstein’s benefactor,MaxPlanck,signedthemanifesto,asdidsuchdistinguishedindividualsasFelixKlein and physicists Wilhelm Roentgen (the discoverer of X-rays), WaltherNernst,andWilhelmOstwald.Einstein, a confirmedpacifist, refused to sign themanifesto.GeorgNicolai,

Elsa’s physician, was a prominent anti-war activist and asked one hundredintellectuals to sign a counter-manifesto. Because of the overwhelming warhysteriagrippingGermany,onlyfouractuallydidsignit,amongthemEinstein.Einstein could only shake his head in disbelief, writing, “Unbelievable whatEuropehasunleashedinitsfolly.”Headdedsadly,“Atsuchatimeasthisonerealizeswhatasorryspeciesofanimalonebelongsto.”In1916,Einstein’sworldwasrockedonceagain,thistimebytheastonishing

news that his close idealistic friend, Friedrich Adler, the same physicist whogenerously gave up a potential professorship at the University of Zurich inEinstein’s favor,hadassassinated theAustrianprimeminister,CountKarlvonStürgkh, in a crowded Vienna restaurant, shouting, “Down with tyranny!Wewant peace!” The entire country was riveted by the news that the son of thefounderoftheAustrianSocialDemocratshadcommittedanunspeakableactofmurderagainstthenation.Adlerwasimmediatelysenttoprison,wherehefacedapossibledeathsentence.Whileawaitinghistrial,Adlerreturnedtohisfavoritepastime,physics,andbeganwritinga longessaythatwascriticalofEinstein’stheoryofrelativity.Infact,inthemidstofalltheturmoilhehadcreatedbytheassassination and its potential consequences, he preoccupied himself with theideathathehadfoundacrucialerrorinrelativity!Adler’s fatherViktor seized upon the only possible defense available to his

son.Realizingthatmentalillnessraninthefamily,Viktorstatedthathissonwasmentally deranged, andpleaded for leniency.As proof of hismadness,Viktorpointed to the fact thathissonwas trying todisproveEinstein’swell-acceptedtheoryofrelativity.Einsteinofferedtobeacharacterwitness,buthewasnevercalled.ThoughthecourtoriginallyfoundAdlerguiltyandsentencedhimtodeathby

hanging,thesentencewaslaterchangedtolifeimprisonmentasaresultofpleasonhisbehalfbyEinsteinandothers.(Ironically,withthesubsequentcollapseofthe government after World War I, Adler was freed in 1918 and was evenelected to theAustrianNationalAssembly, becomingoneof themost popular

figuresinthelabormovement.)The war and the great mental effort necessary to create general relativity

inevitably took a toll on Einstein’s health, which was always precarious. Hefinallycollapsedinpainin1917,sufferingfromanearbreakdown.SoweakenedwashebyhisHerculeanmentalfeatthathewasunabletoleavehisapartment.Hisweightplummeteddangerouslyby56poundsinjusttwomonths.Becomingashellofhisformerself,hefeltthathewasdyingofcancer,butwasdiagnosedwithastomachulcer.Thephysicianrecommendedcompleterestandachangeindiet.During thisperiod,Elsabecameaconstantcompanion,nursing theailingEinsteinslowlybacktohealth.HegrewmuchclosertoElsaandherdaughtersaswell,especiallyafterhemovedintoanapartmentnexttohers.InJune1919,EinsteinfinallymarriedElsa.Withverydefiniteideasofwhata

distinguished professor should dress like, she helped to usher in his transitionfrom a bohemian, bachelor professor to an elegant, domesticated husband,perhaps preparing him for the next development in his life as he emerged aheroicfigureontheworldstage.

CHAPTER5

TheNewCopernicusEinstein, recovering from the disruption and chaos ofWorldWar I, eagerlyawaited the analysis of the next solar eclipse, to take place onMay29, 1919.OneBritishscientist,ArthurEddington,waskeenlyinterestedinperformingthedecisive experiment to test Einstein’s theory. Eddington was secretary of theRoyalAstronomicalSocietyinEnglandandwasequallyateasewithperformingastronomical observations by telescope and delving into the mathematics ofgeneral relativity.He also had another reason for performing the solar eclipseexperiment: he was a Quaker, and his pacifist beliefs prevented him fromfightingwiththeBritisharmyduringWorldWarI.Infact,hewasfullypreparedto go to prison rather than be inducted into the military. The officials ofCambridgeUniversityfearedascandalifoneofitsyoungstarswenttojailasaconscientious objector, so they were able to negotiate a deferment from thegovernment,onthestipulationthatheperformacivicduty,specifically,leadinganexpeditiontoobservethesolareclipseof1919andtestEinstein’stheory.Sonowitwashisofficialpatrioticdutyforthewarefforttoleadtheexpeditiontotestgeneralrelativity.ArthurEddingtonsetupcampattheislandofPrincipe,intheGulfofGuinea,

offthecoastofWestAfrica,andanotherteam,ledbyAndrewCrommelin,setsail to Sobral in northern Brazil. Bad weather conditions, with rain cloudsblocking out the sun, almost ruined the entire experiment. But the cloudsmiraculouslypartedjustenoughforphotographstobetakenofthestarsat1:30intheafternoon.Itwouldbemonths,however,before the teamscould return toEnglandand

carefullyanalyzetheirdata.WhenEddingtonfinallycomparedhisphotographswithotherphotographs taken inEngland severalmonths earlierwith the sametelescope,hefoundanaveragedeflectionof1.61arcseconds,whiletheSobralteamdeterminedavalueof1.98arcseconds.Takinganaverage,theycalculated1.79arcseconds,whichconfirmedEinstein’spredictionof1.74arcsecondstowithin experimental error. Eddington would later fondly recall that verifyingEinstein’stheorywasthegreatestmomentinhislife.

On September 22, 1919, Einstein finally received a cable from HendrikLorentz, informing him of the fantastic news. Einstein excitedly wrote to hismother, “DearMother—Good news today. H. A. Lorentz cabled me that theEnglish expedition really has proved the deflection of light by the sun.”MaxPlanckapparentlystayedupallnighttoseeifthesolareclipsedatawouldverifygeneralrelativity.Einsteinjokedlater,“Ifhehadreallyunderstoodthegeneraltheoryofrelativity,hewouldhavegonetobedthewayIdid.”Although thescientificcommunitywasnowbuzzingwith thestartlingnews

ofEinstein’snewtheoryofgravity,thefirestormdidnotbreakpubliclyuntilajoint meeting of the Royal Society and the Royal Astronomical Society inLondononNovember6,1919.Einsteinwassuddenlytransformedfromasenior,distinguishedprofessorofphysicsinBerlintoaworldfigure,aworthysuccessortoIsaacNewton.Atthatmeeting,philosopherAlfredWhiteheadnoted,“TherewasanatmosphereoftenseinterestthatwasexactlythatofaGreekdrama.”SirFrankDysonwasthefirsttospeak.Hesaid,“AftercarefulstudyoftheplatesIam prepared to say that there can be no doubt that they confirm Einstein’sprediction. A very definite result has been obtained that light is deflected inaccordancewithEinstein’s lawofgravity.”TheNobel laureate J. J.Thomson,president of the Royal Society, said solemnly, this is “one of the greatestachievements in the history of human thought. It is not the discovery of anoutlyingislandbutofawholecontinentofnewscientificideas.Itisthegreatestdiscovery in connection with gravitation since Newton enunciated hisprinciples.”Accordingtolegend,asEddingtonlefttheassembly,anotherscientiststopped

him and asked, “There’s a rumor that only three people in the entire worldunderstand Einstein’s theory. Youmust be one of them.” Eddington stood insilence,sothescientistsaid,“Don’tbemodestEddington.”Eddingtonshrugged,andsaid,“Notatall.Iwaswonderingwhothethirdmightbe.”The next day, the Times of London splashed the headline: “Revolution in

Science—New Theory of the Universe—Newton’s Ideas Overthrown—Momentous Pronouncement—Space ‘Warped.’” (Eddingtonwrote to Einstein,“All England is talking about your theory…. For scientific relations betweenEngland and Germany, this is the best thing that could have happened.” TheLondon newspapers also noted, approvingly, that Einstein did not sign theinfamous manifesto of ninety-three German intellectuals that had infuriatedBritishintellectuals.)Eddington, in fact,would serve asEinstein’smainproponent andkeeper of

theflameintheEnglish-speakingworld,defendinggeneralrelativityagainstallchallengers. Like Thomas Huxley in the previous century, who served as

“Darwin’s bulldog” to promote the heretical theory of evolution to a deeplyreligiousVictorianEngland,Eddingtonwouldusethefullforceofhisscientificreputation and considerable debating skills to promote relativity. This strangeunionbetweentwopacifists,aQuakerandaJew,helpedtobringrelativitytotheEnglish-speakingpeople.So suddenly did this story burst on theworldmedia thatmany newspapers

werecaughtoffguard,scramblingtofindanyonewithaknowledgeofphysics.TheNewYorkTimeshurriedlysentitsgolfexpert,HenryCrouch,tocoverthisfast-breaking story, adding numerous errors in the process. TheManchesterGuardian sent itsmusic critic to cover the story. Later, theTimes of Londonasked Einstein to elaborate on his new theory in an article. To illustrate therelativity principle, he wrote in theTimes: “Today in Germany I am called aGermanmanof science,and inEngland IamrepresentedasaSwiss Jew. If Icometoberegardedasabêtenoire,thedescriptionswillbereversed,andIshallbecome a Swiss Jew for the Germans and a German man of science for theEnglish.”Soon,hundredsofnewspaperswereclamoringforanexclusiveinterviewwith

this certified genius, this successor to Copernicus and Newton. Einstein wasbesieged by reporters eager to make their deadlines. It seemed that everynewspaper in theworldwascarrying this storyon its frontpages.Perhaps thepublic, exhaustedby the carnage and senseless savageryofWorldWar I,wasreadyforamythicfigurewhotappedintotheirdeepestmythsandlegendsaboutthe stars in the heavens, whose mystery has forever been in their dreams.Einstein,moreover,hadredefinedtheimageofgeniusitself.Insteadofanalooffigure,thepublicwasdelightedthatthismessengerfromthestarswasayoungBeethoven, completewith flaming hair and rumpled clothes,who couldwise-crackwiththepressandthrillthecrowdswithlearnedone-linersandquips.Hewrotetohisfriends,“Atpresent,everycoachmanandeverywaiterargues

aboutwhether or not the relativity theory is correct.Aperson’s conviction onthis point depends on the political party he belongs to.”But after the noveltywore off, he began to see the down side to this publicity. “Since the flood ofnewspaper articles,” he wrote, “I have been so swamped with questions,invitations,challenges,thatIdreamIamburninginHellandthepostmanistheDevil eternally roaring at me, throwing new bundles of letters at my headbecause I have not answered the old ones.” He concluded, “This world is acuriousmadhouse”withhimatthecenterofthis“relativitycircus,”ashecalledit.Helamented,“Ifeelnowsomethinglikeawhore.EverybodywantstoknowwhatIamdoing.”Curiosityseekers,cranks,circuspromoters,allclamoredforapiece of Albert Einstein. The Berliner Illustrite Zeitung detailed some of the

problemsfacedbythesuddenlyfamousscientist,whodeclinedagenerousofferfrom the London Palladium booking agent to include him on a bill withcomedians,tightropewalkers,andfireeaters.Einsteincouldalwayspolitelysayno to offers thatwouldmakehim into a curiosity, but he could donothing topreventbabiesandevencigarbrandsfrombeingnamedafterhim.AnythingasmomentousasEinstein’sdiscovery inevitably invitedarmiesof

skepticstomountacounterattack.TheskepticswereledbytheNewYorkTimes.AfterrecoveringfromtheinitialshockofbeingscoopedbytheBritishpress,itseditors kidded the British people for being so gullible, for being so quick toacceptthetheoriesofEinstein.TheNewYorkTimeswrotethattheBritish“seemtohavebeen seizedwith something like intellectual panicwhen theyheardofphotographicverificationof theEinstein theory….Theyare slowly recoveringas they realize that the sun still rises—apparently—in the east.” WhatparticularlyirkedtheeditorsinNewYorkandarousedtheirsuspicionwasthatsoveryfewpeopleintheworldcouldmakeanysenseofthetheory.Theeditorswailedthatthiswasborderingonbeingun-Americanandundemocratic.Wastheworldbeingdupedbyapracticaljoker?In the academic world, the skeptics were legitimized by a Columbia

Universityprofessorofcelestialmechanics,CharlesLanePoor.Hemistakenlyled thechargeby stating, “The supposedastronomicalproofsof the theory, ascited and claimed by Einstein, do not exist.” Poor compared the author ofrelativitytheorytothecharactersofLewisCarroll:“Ihavereadvariousarticleson the fourth dimension, the relativity theory of Einstein, and otherpsychologicalspeculationon theconstitutionof theuniverse;andafter readingthemIfeelasSenatorBrandegeefeltafteracelebrateddinnerinWashington.‘Ifeel,’hesaid,‘asifIhadbeenwanderingwithAliceinWonderlandandhadteawith theMadHatter.’” EngineerGeorge FrancisGillette fumed that relativitywas “cross-eyed physics…utterly mad…the moronic brain child of mentalcolic…thenadirofpuredrivel…andvoodoononsense.By1940,relativitywillbe considered a joke.Einstein is alreadydeadandburied alongsideAnderson,Grimm, and the Mad Hatter.” Ironically, the only reason why historians stillremember these individuals is their futile tirades against relativity theory. It isthe hallmark of good science that physics is not determined by a popularitycontestorbyNewYorkTimeseditorials,butbycarefulexperimentation.AsMaxPlanck once said, referring to the ferocious criticism that he once facedwhenproposinghisquantumtheory,“Anewscientifictruthdoesnotasaruleprevailbecause itsopponentsdeclare themselvespersuadedorconvinced,butbecausethe opponents gradually die out and the younger generation is made familiarwith the truth from the start.” Einstein himself once remarked, “Great spirits

havealwaysencounteredviolentoppositionfrommediocreminds.”Unfortunately, the adulation of Einstein in the press stimulated the hatred,

jealousy,andbigotryofthegrowingarmyofhisdetractors.ThemostnotorioushaterofJewsinthephysicsestablishmentwasPhilippLenard,theNobelPrize–winning physicist who had established the basic frequency dependence of thephotoelectric effect, a result thatwas finally explainedbyEinstein’s theory ofthelightquantum,thephoton.MilevahadevenattendedLenard’slectureswhenshe visited Heidelberg. In lurid publications, he decried that Einstein was a“Jewishfraud”andthatrelativity“couldhavebeenpredictedfromthestart—ifracetheoryhadbeenmorewidespread—sinceEinsteinwasaJew.”Eventually,he became a leading member of what was called the Anti-relativity League,devotedtopurging“Jewishphysics”fromGermanyandestablishingthepurityofAryanphysics.Lenardwasbynomeansalonewithinthephysicsworld.Hewas joined by many in the German scientific establishment, including NobellaureateJohannesStarkandHansGeiger(inventoroftheGeigercounter).In August 1920, this virulent group of detractors booked Berlin’s huge

Philharmonic Hall strictly for the purpose of denouncing relativity theory.Remarkably,Einsteinwasintheaudience.Hebravedanonstopseriesofangryspeakerswhodenouncedhimasapublicityhound,plagiarist, andcharlatan tohisface.Thenextmonth,therewasyetanothersuchconfrontation,thistimeatameeting of the Society of German Scientists in Bad Nauheim. Armed policewere present to guard the hall’s entrance and dampen any demonstration orviolence.EinsteinwasjeeredandhooteddownwhenhetriedtoanswersomeofLenard’sinflammatorycharges.NewsofthisraucousexchangehitthepapersinLondon, and the people ofBritain became alarmedby rumors thatGermany’sgreatscientistwasbeinghoundedoutofGermany.TheGermanForeignOfficerepresentativeinLondon,toquellsuchrumors,saiditwouldbecatastrophicforGerman science if Einstein left, and that “we should not drive away such aman…whomwecanuseineffectiveculturalpropaganda.”InApril of 1921,with invitations pouring in from all corners of theworld,

Einsteindecidedtousehisnewcelebritytopromotenotonlyrelativitybutalsohis other causes, which now included peace and Zionism. He had finallyrediscovered his Jewish roots. In long conversations with his friend KurtBlumenfeld, he began to fully appreciate the deep suffering inflicted on theJewishpeople throughout thecenturies.Blumenfeld,hewrote,wasresponsiblefor “making me conscious of my Jewish soul.” ChaimWeizmann, a leadingZionist, focusedon the ideaof usingEinstein as amagnet to attract funds forHebrewUniversity inJerusalem.Theplan involvedsendingEinsteinona tourthroughtheheartlandofAmerica.

AssoonasEinstein’sshipdocked inNewYorkHarbor,hewasmobbedbyreporterseager foraglimpseofhim.Crowds lined thestreetsofNewYork toview his motorcade and cheered when he waved back from his open-toppedlimousine.“It’sliketheBarnumcircus!”Elsasaid,assomeonethrewabouquetather.Einsteinmused,“TheladiesofNewYorkwanttohaveanewstyleeveryyear.Thisyear thefashionisrelativity.”Headded,“DoIhavesomethingofacharlatanorahypnotistaboutmethatdrawspeoplelikeacircusclown?”As expected, Einstein aroused intense interest among the public and

galvanized the Zionist cause. Well-wishers, curiosity seekers, and Jewishadmirers packed every auditorium he spoke in. A mob of eight thousandsqueezed into the Sixty-ninth Regiment Armory in Manhattan while threethousand had to be turned away, eagerly awaiting a glimpse of the genius.Einstein’s receptionatCityCollegeofNewYorkwasoneof thehighlightsofthe trip. Isidor Isaac Rabi, who would later win a Nobel Prize, took copiousnotes of Einstein’s lecture andmarveled that Einstein, unlike other physicists,possessedacrowd-pleasingcharisma.(Eventoday,apictureoftheentirestudentbody of City College of New York crowding around Einstein hangs in thechairman’sofficeattheschool.)AfterleavingNewYork,Einstein’stripthroughtheUnitedStateswaslikea

whistle-stop tour, passing through several major cities. In Cleveland, threethousandpeoplemobbedhim.Heescaped“frompossiblyseriousinjuryonlybystrenuouseffortsbyasquadofJewishwarveteranswhofoughtthepeopleoffintheirmadeffortstoseehim.”InWashington,hemetwithPresidentWarrenG.Harding.Unfortunately, they could not communicate, since Einstein spoke noEnglish and Harding did not speak German or French. (In all, Einstein’swhirlwind tour netted almost a million dollars, $250,000 alone from a singledinner at the Waldorf Astoria Hotel speaking before eight hundred Jewishdoctors.)His travels in America not only introduced millions of Americans to the

mystery of space and time, but also reaffirmed Einstein’s deep and heartfeltcommitment to the Jewish cause. Growing up in a comfortable, middle-classEuropeanfamily,hehadnodirectcontactwiththesufferingofpoorJewsfromaroundtheworld.“ItwasthefirsttimeinmylifethatIsawJewsenmasse,”henoted.“NotuntilIwasinAmericadidIdiscovertheJewishpeople.IhadseenmanyJews,butneither inBerlinnorelsewhere inGermanyhad IencounteredtheJewishpeople.TheJewishpeopleIsawinAmericacamefromRussia,fromPoland,orgenerallyfromeasternEurope.”After the United States, Einstein went to England, where he met the

ArchbishopofCanterbury.Tothereliefoftheclergy,Einsteinassuredhimthat

relativitytheorywouldnotunderminepeople’smoraleandbeliefinreligion.Helunchedat theRothschildsandmet thegreatclassicalphysicistLordRayleigh,whosaidtoEinstein,“Ifyourtheoriesaresound,Iunderstand…thatevents,say,of theNormanConquest have not yet occurred.”When hewas introduced toLordHaldaneandhisdaughter, she faintedat thesightofhim.Later,EinsteinpaidhomagetoIsaacNewtonbygazingathistombinEngland’smosthallowedground, Westminster Abbey, and laying a wreath. In March 1922, EinsteinreceivedaninvitationtospeakattheCollègedeFrance,wherehewasmobbedby the Parisian press and followed by huge crowds. One journalist remarked,“He has become the great fashion. Academics, politicians, artists, policemen,cab drivers, and pickpockets know when Einstein lectures. Tout Paris knowseverythingandtellsmorethanitknowsaboutEinstein.”Controversysurroundedthetripassomescientists,stillnursingthewoundsfromWorldWarI,boycottedhistalk,usingtheexcusethattheycouldnotattendbecauseGermanywasnotamember of the League of Nations. (In response, a Paris paper gibed, “If aGermanwere to discover a cure for cancer or tuberculosis,would these thirtyacademics have to wait until Germany became a member of the League ofNationstouseit?”)Einstein’sreturntoGermany,however,wasmarredbythepoliticalinstability

of postwar Berlin. Ominously, it had become the season for politicalassassinations. In 1919, the socialist leaders Rosa Luxemburg and KarlLiebknechthadbeenkilled.InApril1922,WaltherRathenau,aJewishphysicistandcolleagueofEinsteinwhohadrisentobecometheGermanforeignminister,was assassinated by submachine guns as he rode in his car.A fewdays later,MaximilianHarden, another prominent Jew,was severelywounded in anotherassassinationattempt.A day of national mourning was declared, with theaters, schools, and

universitiesclosingtohonorRathenau.AmillionpeoplestoodsilentlyneartheParliament building where the funeral services were being held. However,Philipp Lenard refused to cancel his classes at the Physics Institute inHeidelberg.(Previously,hehadevenadvocatedkillingRathenau.Onthedayofnationalmourning, a group ofworkers tried to persuade Lenard to cancel hisclasses, but were drenched with water thrown from the second floor of hisbuilding.TheworkersthenbrokeintotheinstituteanddraggedLenardout.Theywereabouttothrowhimintotheriverwhenthepoliceintervened.)That year, a young German, Rudolph Leibus, was charged in Berlin with

offeringarewardforthemurderofEinsteinandotherintellectuals,sayingthat“it was a patriotic duty to shoot these leaders of pacifist sentiment.” He wasfound guilty by the courts but fined only sixteen dollars. (Einstein took these

threatsseriously,bothfromanti-Semitesaswellasderangedindividuals.Once,amentally unbalancedRussian immigrant,EugeniaDickson,wrote a series ofmenacingletterstoEinstein,ravingthathewasanimpostermasqueradingastherealEinstein, and stormed intoEinstein’s house trying to kill him.But beforethis crazedwoman could attack Einstein, Elsa struggledwith her at the door,managingtosubdueherandcallthepolice.)Einstein,facingthisdangeroustideofanti-Semitism,tooktheopportunityto

launch another world tour, this time to the Orient. The philosopher andmathematicianBertrandRussellwasonaspeakingtourinJapanandwasaskedbyhishoststonominatesomeofthemostillustriouspeopleofthetimetospeakinJapan.HeimmediatelynominatedLeninandEinstein.SinceLenin,ofcourse,was unavailable, the invitationwent toEinstein.He accepted it and began hisodysseyinJanuary1923.“Lifeislikeridingabicycle.Tokeepyourbalanceyoumustkeepmoving,”hewrote.While en route to Japan and China, Einstein received a message from

Stockholmthatmanythoughtwaslongoverdue.ThetelegramconfirmedthathehadwontheNobelPrizeinphysics.Buthewontheprizenotfortherelativitytheory, his crowning achievement, but for the photoelectric effect. WhenEinsteinfinallydeliveredhisNobelPrizespeechthenextyear,intypicalfashionheshockedtheaudiencebynotspeakingaboutthephotoelectriceffectatall,aseveryoneexpected,butaboutrelativity.WhattooksolongforEinstein,byfarthemostvisibleandrespectedfigurein

physics,towintheNobelPrize?Ironically,hehadbeenrejectedeighttimesbytheNobelPrizeCommittee, from1910 to1921.During thatperiod,numerousexperiments had been conducted to verify the correctness of relativity. SvenHedin, amember of theNobel nominating committee, later confessed that theproblem was Lenard, who had great influence over other judges, includingHedin.TheNobelPrize–winningphysicistRobertMillikanalsorecalledthattheNobelnominating committee, split on thequestionof relativity, finallygave acommittee member the task of evaluating the theory: “He spent all his timestudyingEinstein’stheoryofrelativity.Hecouldn’tunderstandit.Didn’tdaretogive the prize and run the risk of learning later that the theory of relativity isinvalid.”Aspromised,Einsteinsent theNobelPrizemoneytoMilevaaspartof their

divorce settlement ($32,000 in 1923 dollars). She would eventually use themoneytopurchasethreeapartmenthousesinZurich.Bythe1920sand1930s,Einsteinhademergedasagiantontheworldstage.

Newspapers clamored for interviews, his face smiled from film newsreels, hewas flooded with requests beseeching him to speak, and journalists would

breathlesslyprinteverytrivialtidbitfromhislife.EinsteinquippedthathewaslikeKingMidas,excepteverythinghetouchedturnedintoanewspaperheadline.NewYorkUniversity’sClassof1930,askedtonametheworld’smostpopularfigure,choseCharlesLindberghfirst,andAlbertEinsteinsecond,outrankingallof Hollywood’s movie stars. Everywhere Einstein went, his mere presencewouldsparkhugecrowds.Forexample,fourthousandpeoplestartedanearriottryingtocrashafilmexplainingrelativityat theAmericanMuseumofNaturalHistoryinNewYork.AgroupofindustrialistsevenbankrolledthebuildingoftheEinsteinTowerinPotsdam,Germany,afuturistic-lookingsolarobservatoryfinishedin1924thathousedatelescopeinatower54feethigh.Einsteinwassomuchindemandfromartistsandphotographersthatwantedtocapturethefaceofgeniusthathelistedhisjobdescriptionas“artists’model.”This time, however, he did not make the mistake he made with Mileva,

neglectingherwhilehewasonworldtours.ToElsa’sdelight,hetookheralongtogreetcelebrities,royalty,andthepowerful.Elsa,inturn,adoredherhusbandand gloried in his world fame. She was “gentle, warm, motherly, andprototypicallybourgeois,[and]lovedtotakecareofherAlbertle.”In1930,EinsteinmadehissecondtriumphanttriptotheUnitedStates.Onhis

visittoSanDiego,thehumoristWillRogersnotedaboutEinstein,“Heatewitheverybody, talkedwitheverybody,posed foreverybody thathadany film left,attendedeveryluncheon,everydinner,everymovieopening,everymarriageandtwo-thirds of the divorces. In fact, he made himself such a good fellow thatnobody had the nerve to ask what his theory was.” He visited the CaliforniaInstituteofTechnologyandtheobservatoryatMt.Wilson,meetingastronomerEdwinHubble,whohadverifiedsomeofEinstein’stheoriesabouttheuniverse.He also visited Hollywood and received a glittering reception worthy of asuperstar.In1931,heandElsaattendedtheworldpremierofCharlieChaplin’sfilmCityLights.Thecrowdsstrained tocatcha fleetingglimpseof theworld-famous scientist surrounded by Hollywood royalty. At the opening, as theaudiencewildlycheeredChaplinandEinstein,Chaplin remarked, “Thepeopleapplaudmebecauseeveryoneunderstandsme,andtheyapplaudyoubecausenoone understands you.” Einstein, bewildered by the frenzy that celebrities cangenerate,askedwhatitallmeant.Chaplinwiselyreplied,“Nothing.”(WhenhevisitedNewYork’sfamedRiversideChurch,hesawhisfaceonastained-glasswindow portraying the world’s great philosophers, leaders, and scientists. Hequipped,“IcouldhaveimaginedtheywouldmakeaJewishsaintoutofme,butIneverthoughtIwouldbecomeaProtestantone!”)Einsteinwasalsosoughtoutforhisthoughtsonphilosophyandreligion.His

meeting with a fellow Nobel laureate, Indian mystic Rabindranath Tagore, in

1930 attracted considerable press attention. They made quite a pair, withEinstein’s flamingwhitehairandTagore’sequally imposing longwhitebeard.One journalist remarked,“Itwas interesting to see them together—Tagore, thepoetwiththeheadofathinker,andEinstein,thethinkerwiththeheadofapoet.Itseemedtoanobserverasthoughtwoplanetswereengagedinachat.”EversincehereadKantasachild,Einsteinbecamesuspiciousoftraditional

philosophy, which he often thought degenerated into pompous but ultimatelysimplistichocuspocus.Hewrote,“Isnotallofphilosophyasifwritteninhoney?Itlookswonderfulwhenonecontemplatesit,butwhenonelooksagainitisallgone. Onlymush remains.” Tagore and Einstein clashed over the question ofwhether theworld can exist independently of human existence.While Tagoreheld themystical belief that humanexistencewas essential to reality,Einsteinreplied, “The world, considered from the physical aspect, does existindependently of human consciousness.” Although they disagreed on thequestion of physical reality, they found a bitmore agreement on questions ofreligionandmorality.Intheareaofethics,Einsteinbelievedthatmoralitywasdefinedbyhumanity,notbyGod.“Morality isof thehighest importance—butforus,notGod,”Einsteinobserved.“Idonotbelieve in the immoralityof theindividual, and I consider ethics to be an exclusively human concernwith nosuperhumanauthoritybehindit.”Although skeptical about traditional philosophy, he also had the deepest

respectforthemysteriesposedbyreligion,especiallythenatureofexistence.Hewould write, “Science without religion is lame, religion without science isblind.”Hewouldalsoattributethisappreciationofmysteryasthesourceofallscience: “all the fine speculations in the realm of science spring from a deepreligiousfeeling.”Einsteinwrote,“Themostbeautifulanddeepestexperienceaman can have is the sense of themysterious. It is the underlying principle ofreligionaswellasofallseriousendeavorinartandscience.”Heconcluded,“Ifsomething is in me which can be called religious, then it is the unboundedadmirationforthestructureoftheworldsofarassciencecanrevealit.”Perhapshismostelegantandexplicitstatementaboutreligionwaswrittenin1929:“I’mnot an atheist and I don’t think I can call myself a pantheist. We are in theposition of a little child entering a huge library filled with books in manydifferentlanguages.Thechildknowssomeonemusthavewrittenthosebooks.Itdoes not know how. It does not understand the languages in which they arewritten.Thechilddimlysuspectsamysteriousorder in thearrangementof thebooksbutdoesn’tknowwhatit is.That,itseemstome,istheattitudeofeventhemost intelligent humanbeing towardGod.We see a universemarvelouslyarrangedandobeyingcertain laws,butonlydimlyunderstand these laws.Our

limitedmindscannotgraspthemysteriousforcethatmovestheconstellations.IamfascinatedbySpinoza’spantheism,butadmireevenmorehiscontributionstomodernthoughtbecauseheis thefirstphilosophertodealwiththesoulandbodyasone,nottwoseparatethings.”EinsteinwouldoftenmakeadistinctionbetweentwotypesofGods,whichare

oftenconfusedindiscussionsaboutreligion.First,thereisthepersonalGod,theGod that answers prayers, parts thewaters, andperformsmiracles.This is theGodof theBible, theGodof intervention.Then there is theGod thatEinsteinbelieved in, theGod of Spinoza, theGod that created the simple and elegantlawsthatgoverntheuniverse.Even in themidst of thismedia circus,Einsteinmiraculously never lost his

focus and devoted his efforts to probing these laws of the universe.While ontransatlantic ships or long train rides, he had the discipline to shut outdistractionsandconcentrateonhiswork.AndwhatintriguedEinsteinduringthisperiod was the ability of his equations to solve the structure of the universeitself.

CHAPTER6

TheBigBangandBlackHolesDid the universe have a beginning? Is the universe finite or infinite?Will ithaveanend?Ashebegan toaskwhathis theorymightsayabout thecosmos,Einstein,likeNewtonbeforehim,encounteredthesamekindsofquestionsthathadpuzzledphysicistscenturiesearlier.In 1692, five years after Newton completed his masterpiece, Philosophiae

NaturalisPrincipiaMathematica,he receiveda letter fromaminister,RichardBentley, that perplexed him. Bentley pointed out that if gravity was strictlyattractive,andneverrepulsive,thenanystaticcollectionofstarswillnecessarilycollapse in on itself. This simple but potent observation was puzzling, as theuniverse seemed stable enough, yet his universal gravitation would, givenenoughtime,collapsetheentireuniverse!Bentleywasisolatingakeyproblemfaced by any cosmology in which gravity was an attractive force: a finiteuniversemustnecessarilybeunstableanddynamic.After pondering this disturbing question, Newton wrote a letter back to

Bentley,stating that theuniverse, toavoid thiscollapse,must thereforeconsistof an infinite, uniformcollectionof stars. If theuniversewere indeed infinite,theneverystarwouldbepulledevenlyinalldirections,andhencetheuniversecould be stable even if gravity was strictly attractive. Newton wrote, “If thematterwasevenlydisposedthroughoutaninfinitespace,itcouldneverconveneintoonemass…andthusmightthesunandfixedstarsbeformed.”But if onemade that assumption, then there arose another, deeper problem,

knownas“Olbers’paradox.”Itasks,quitesimply,whythenightskyisblack.Iftheuniverseisindeedinfinite,static,anduniform,theneverywherewelook,oureyesshouldseeastarintheheavens.Thus,thereshouldbeaninfiniteamountofstarlighthittingoureyesfromalldirections,andthenightskyshouldbewhite,notblack.Soiftheuniversewasuniformandfinite,itwouldcollapse,butifitwereinfinite,theskyshouldbeonfire!Over two hundred years later, Einstein faced the same problems, but in

disguisedform.In1915,theuniversewasacomfortableplace,thoughttoconsistof a static, solitary galaxy, theMilkyWay. This bright swath of light cutting

across thenight sky consistedofbillionsof stars.ButwhenEinsteinbegan tosolvehisequations,hefoundsomethingdisturbingandunexpected.Heassumedthattheuniversewasfilledwithauniformgas,whichapproximatedthestarsanddustclouds.Muchtohisconsternation,hefoundthathisuniversewasdynamic,that it preferred to expand or contract and was never stable. In fact, he soonfound himself in the quicksand of cosmological questions that have puzzledphilosophers and physicists like Newton for ages. Finite universes are neverstableundergravity.Einstein,forcedtoconfrontacontractingorexpandingdynamicuniverselike

Newton, was still not ready to throw out the prevailing picture of a timeless,staticuniverse.Einstein therevolutionarywasstillnotrevolutionaryenoughtoaccept that theuniversewasexpandingorhadabeginning.Hissolutionwasaratherfeebleone.In1917,heintroducedwhatmightbecalleda“fudgefactor”intohisequations, the“cosmologicalconstant.”This factorpositeda repulsiveantigravitythatbalancedtheattractiveforceofgravity.Theuniversewasmadestaticbyfiat.Toperformthissleightofhand,Einsteinrealizedthatgeneralcovariance,the

main guidingmathematical principle behind general relativity, allows for twopossible general covariant objects: the Ricci curvature (which forms thefoundationofgeneral relativity)and thevolumeof spacetime. Itwas thereforepossibletoaddasecondtermtohisequationsthatwasconsistentwithgeneralcovarianceandproportional to thevolumeof theuniverse. Inotherwords, thecosmologicalconstantassignedanenergytoemptyspace.Thisantigravityterm,nowcalled“darkenergy,”istheenergyofthepurevacuum.Itcanpushgalaxiesapart or bring them together. Einstein chose the value of the cosmologicalconstant precisely to counteract the contraction caused by gravity, so theuniverse became static. He was unhappy with this, as it smacked of amathematical swindle, but he had no choice if he wanted to preserve a staticuniverse. (Itwould take another eighty years before astronomers finally foundevidence for the cosmological constant, which is now believed to be thedominantsourceofenergyintheuniverse.)The puzzle deepened in the next few years asmore solutions to Einstein’s

equationswere discovered. In 1917,Willem de Sitter, a Dutch physicist, sawthatitwaspossibletofindastrangesolutiontoEinstein’sequations:auniversethat was empty of all matter yet still expanded! All that was neededwas thecosmological constant, the energy of the vacuum, to drive an expandinguniverse.Thiswasunsettling toEinstein,who still believed, likeMachbeforehim,thatthenatureofspacetimeshouldbedeterminedbythemattercontentoftheuniverse.Herewasauniversethatexpandedwithoutanymatterwhatsoever,

needingonlydarkenergytopropelitselfforward.ThefinalradicalstepsweretakenbyAlexanderFriedmannin1922andbya

Belgian priest, Georges Lemaître, in 1927, who showed that an expandinguniverse emerges naturally from Einstein’s equations. Friedmann obtained asolution of Einstein’s equations beginning with a homogeneous, isotropicuniverse in which the radius expands or contracts. (Unfortunately, Friedmanndied in 1925 of typhoid fever in Leningrad before he could elaborate on hissolution.)IntheFriedmann-Lemaîtrepicture,therearethreepossiblesolutions,dependingonthedensityoftheuniverse.Ifthedensityoftheuniverseislargerthanacertaincriticalvalue,thentheexpansionoftheuniversewilleventuallybereversedbygravity,andtheuniversewillbegintocontract.(Thecriticaldensityis roughly ten hydrogen atoms per cubic yard.) In this universe, the overallcurvatureispositive(byanalogy,aspherehaspositivecurvature).Ifthedensityoftheuniverseissmallerthanthecriticalvalue,thenthereisnotenoughgravitytoreversetheexpansionoftheuniverse,soitexpandsindefinitely.(Eventually,theuniverseapproachesnearabsolutezerointemperatureasitexpandstowardwhatiscalledthe“bigfreeze.”)Inthisuniverse,theoverallcurvatureisnegative(byanalogy,asaddleoratrumpethornhasnegativecurvature).Last,thereisthepossibilitythattheuniversewillbebalancedrightatthecriticalvalue(inwhichcase itwill still expand indefinitely). In thisuniverse, thecurvature iszero, sothe universe is flat. Thus, the fate of the universe could be determined, inprinciple,bysimplymeasuringitsaveragedensity.Progress in thisdirectionwasconfusing, sincenow therewereat least three

cosmological models about how the universe should evolve (Einstein’s, deSitter’s,andFriedmann-Lemaître’s).Thematter resteduntil1929,when itwasfinallysettledbytheastronomerEdwinHubble,whoseresultsweretoshakethefoundations of astronomy.He first demolished the one-galaxy universe theorybydemonstratingthepresenceofothergalaxiesfarbeyondtheMilkyWay.(Theuniverse, far from being a comfortable collection of a hundred billion starscontained in a single galaxy, now contained billions of galaxies, each onecontainingbillionsofstars.Injustoneyear,theuniversesuddenlyexploded.)Hefoundthat therewerepotentiallybillionsofothergalaxies,and that theclosestone was Andromeda, about two million light-years from Earth. (The word“galaxy,” in fact, comes from the Greek word for “milk,” since the GreeksthoughtthattheMilkyWaygalaxywasmilkspilledbythegodsacrossthenightsky.)ThisshockingrevelationalonewouldhaveguaranteedHubble’sfameamong

thegiantsofastronomy.ButHubblewentfurther.In1928,hemadeafatefultriptoHollandwherehemetdeSitter,whoclaimedthatEinstein’sgeneralrelativity

predictedanexpandinguniversewithasimplerelationshipbetweenredshiftanddistance. The farther a galaxywas fromEarth, the faster it would bemovingaway. (This red shift is slightly different from the red shift considered byEinsteinbackin1915.ThisredshiftiscausedbygalaxiesrecedingfromEarthinanexpandinguniverse.Ifayellowstar,forexample,movesawayfromus,thespeedofthelightbeamremainsconstantbutitswavelengthgets“stretched,”sothat thecolorof theyellowstarreddens.Similarly, ifayellowstarapproachesEarth, its wavelength is shrunken, squeezed like an accordion, and its colorbecomesbluish.)When Hubble returned to the observatory at Mt. Wilson, he began a

systematic determination of the red shift of these galaxies to see if thiscorrelationheldup.Heknewthatbackin1912,VestoMelvinSlipherhadshownthatsomedistantnebulaewererecedingfromEarth,creatingaredshift.Hubblenow systematically calculated the red shift coming from distant galaxies anddiscovered that these galaxies were receding from Earth—in other words, theuniversewasexpandingatafantasticrate.Hethendiscoveredthathisdatacouldfit the conjecture made by de Sitter. This is now called “Hubble’s law”: thefasteragalaxyisrecedingfromEarth,thefartheritis(andviceversa).Plotted on a curve, graphing distance versus velocity, Hubble found a near

straight line, as predicted by general relativity, whose slope is now called“Hubble’sconstant.”Hubble,inturn,wascurioustoknowhowhisresultswouldfit intoEinstein’s. (Unfortunately,Einstein’smodel hadmatter but nomotion,anddeSitter’suniversehadmotionbutnomatter.Hisresultsdidseemtoagreewith the work of Friedmann and Lemaître, which possessed both matter andmotion.)In1930,EinsteinmadethepilgrimagetotheMt.Wilsonobservatory,where hemetHubble for the first time. (When the astronomers there proudlyboastedthattheirmammoth100-inchtelescope,thebiggestintheworldatthattime,coulddeterminethestructureoftheuniverse,Elsawasnotimpressed.Shesaid, “My husband does that on the back of an old envelope.”) As Hubbleexplained the painstaking results he found from analyzing scores of galaxies,eachonerecedingfromtheMilkyWay,Einsteinadmittedthatthecosmologicalconstant was the greatest blunder of his life. The cosmological constant,introduced by Einstein to artificially create a static universe, was nowdispensable.Theuniversedidexpandashefoundadecadeearlier.Furthermore, Einstein’s equations gave perhaps the simplest derivation of

Hubble’s law. Assume the universe is a balloon that is expanding, with thegalaxiesrepresentedastinydotspaintedontheballoon.Toanantsittingonanyone of these dots, it appears as if every other dot is moving away from it.Likewise,thefartheradotisawayfromtheant,thefasteritismovingaway,as

inHubble’slaw.Thus,Einstein’sequationsgavenewinsightsintosuchancientquestionslike,isthereanendtotheuniverse?Iftheuniverseendswithawall,thenwecanaskthequestion,whatliesbeyondthewall?Columbusmighthaveanswered that question by considering the shape of the earth. In threedimensions, the earth is finite (being just a ball floating in space), but in twodimensions,itappearsinfinite(ifonegoesaroundandarounditscircumference)soanyonewalkingonthesurfaceoftheearthwillneverfindtheend.Thus,theearth is both finite and infinite at the same time, depending on the number ofdimensionsonemeasures.Likewise,onemightstatethattheuniverseisinfiniteinthreedimensions.Thereisnobrickwallinspacethatrepresentstheendoftheuniverse; a rocket sent into space will never collide with some cosmic wall.However, there is the possibility that the universe might be finite in fourdimensions. (If it were a four-dimensional ball, or hypersphere, you mightconceivablytravelcompletelyaroundtheuniverseandcomebacktowhereyoustarted. In thisuniverse, the farthestobjectyoucanseewitha telescope is thebackofyourhead.)If the universe is expanding at a certain rate, then one can reverse the

expansionandcalculate theroughtimeatwhichtheexpansionfirstoriginated.Inotherwords,notonlydid theuniversehaveabeginning,butalsoonecouldcalculateitsage.(In2003,satellitedatashowedthattheuniverseis13.7billionyears old.) In 1931, Lemaître postulated a specific origin to the universe, asuper-hot genesis. If one tookEinstein’s equations to their logical conclusion,theyshowedthattherewasacataclysmicorigintotheuniverse.In1949,cosmologistFredHoylechristenedthisthe“bigbang”theoryduring

adiscussiononBBCradio.Becausehewaspushinga rival theory, the legendgot started that he coined the name “big bang” as an insult (although he laterdeniedthatstory).However,itshouldbepointedoutthatthenameisacompletemisnomer.Itwasnotbig,andtherewasnobang.Theuniversestartedoutasaninfinitesimally small “singularity.”And therewas nobangor explosion in theconventional sense, since it was the expansion of space itself that pushed thestarsapart.Not only did Einstein’s theory of general relativity introduce entirely

unexpectedconceptssuchastheexpandinguniverseandthebigbang,butalsoitintroduced another concept that has intrigued astronomers ever since: blackholes.In1916, justoneyearafterhepublishedhis theoryofgeneralrelativity,Einstein was astonished to receive word that a physicist, Karl Schwarzschild,had solved his equations exactly for the case of a single pointlike star.Previously,Einstein had only used approximations to the equations of generalrelativity because theywere so complex. Schwarzschild delighted Einstein by

finding an exact solution, with no approximations whatsoever. AlthoughSchwarzschild was director of the Astrophysical Observatory in Potsdam, hevolunteered to serveGermany on the Russian front. Remarkably, as a soldierdodging shells bursting overhead, he managed against all odds to work onphysics.NotonlydidhecalculatethetrajectoryofartilleryshellsfortheGermanarmy,healsocalculatedthemostelegant,exactsolutionofEinstein’sequations.Today, this is called the “Schwarzschild solution.” (Unfortunately, he neverlived long enough to enjoy the fame that his solution generated. One of thebrighteststarsemerginginthisnewfieldofrelativity,Schwarzschilddiedattheageofforty-two,justafewmonthsafterhispaperswerepublished,fromarareskindisease hepickedupwhile fightingon theRussian front, awaste for theworldofscience.EinsteindeliveredamovingeulogyforSchwarzschild,whosedeathonlyre-enforcedEinstein’shatredofthesenselessnessofwar.)The Schwarzschild solution, which created quite a sensation in scientific

circles, also had strange consequences. Schwarzschild found that extremelyclosetothispointlikestar,gravitywassointensethatevenlightitselfcouldnotescape, so the star became invisible! This was a sticky problem not only forEinstein’s theory of gravity but also for theNewtonian theory.Back in 1783,JohnMichell,rectorofThornhillinEngland,posedthequestionwhetherastarcould become so massive that even light could not escape. His calculations,usingonlyNewtonianlaws,couldnotbetrustedbecausenooneknewpreciselywhat the speed of light was, but his conclusions were hard to dismiss. Inprinciple, a star could become somassive that its lightwould orbit around it.Thirteen years later, in his famous book Exposition du système du monde,mathematicianPierre-SimonLaplacealsoaskedwhetherthese“darkstars”werepossible(butprobablyfoundthespeculationsowildthathedeleteditfromthethirdedition).Centurieslater,thequestionofdarkstarscameupagain,thankstoSchwarzschild.He found that therewas a “magic circle” surrounding the star,nowcalledthe“eventhorizon,”atwhichmind-bendingdistortionsofspacetimeoccur.Schwarzschilddemonstrated thatanyoneunfortunateenough to fallpastthis event horizonwould never return. (Youwould have to go faster than thespeed of light to escape, which is impossible.) In fact, from inside the eventhorizon, nothing can escape, not even a light beam. Light emitted from thispointlikestarwouldsimplyorbitaroundthestarforever.Fromtheoutside, thestarwouldappearshroudedindarkness.One could use the Schwarzschild solution to calculate how much ordinary

matter had to be compressed to reach this magic circle, called the“Schwarzschildradius,”atwhichpointthestarwouldcompletelycollapse.Forthesun,theSchwarzschildradiuswas3kilometers,orlessthan2miles.Forthe

earth, itwas less thanacentimeter. (Since thiscompressionfactorwasbeyondphysicalcomprehensioninthe1910s,physicistsassumedthatnoonewouldeverencountersuchafantasticobject.)But themoreEinsteinstudiedthepropertiesof these stars, later christened “black holes” by physicist John Wheeler, thestranger theybecame.Forexample, ifyoufell intoablackhole, itwouldonlytake a fraction of a second to fall through the event horizon. As you brieflysailed past it, you would see light orbiting the black hole that was capturedperhapsaeons—perhapsbillionsofyears—ago.Thefinalmillisecondwouldnotbeaverypleasantone.Thegravitationalforceswouldbesogreatthattheatomsof your bodywould be crushed. Death would be inevitable and horrible. Butobserverswatchingthiscosmicdeathtakeplacefromasafedistancewouldseean entirely different picture. The light emitted from your body would bestretchedbygravity,soitwouldappearasifyouwerefrozenintime.Totherestoftheuniverse,youwouldstillbehoveringovertheblackhole,motionless.Thesestars,infact,weresofantasticthatmostphysiciststhoughttheycould

neverbefoundintheuniverse.Eddington,forexample,said,“Thereshouldbealaw of Nature to prevent a star from behaving in this absurd way.” In 1939,Einsteintriedtoshowmathematicallythatsuchablackholewasimpossible.Hebeganby studyinga star in formation, that is, a collectionofparticles circlingaround in space, gradually pulled in by their gravitational force. Einstein’scalculation showed that this circling collection of particles would graduallycollapse, butwouldonly comewithin1.5 times theSchwarzschild radius, andhenceablackholecouldneverform.Although this calculation seemed airtight, what Einstein apparently missed

was the possibility of an implosion ofmatter in the star itself, created by thecrushingeffectofthegravitationalforceoverwhelmingallthenuclearforcesinmatter. This more detailed calculation was published in 1939 by J. RobertOppenheimerandhisstudentHartlandSnyder.Insteadofassumingacollectionofparticlescirclinginspace,theyassumedastaticstar,largeenoughsothatitsmassive gravity could overwhelm the quantum forces inside the star. Forexample, a neutron star consists of a large ball of neutrons about the size ofManhattan(20milesacross)makingupagiganticnucleus.Whatkeepsthisballof neutrons fromcollapsing is theFermi force,which preventsmore than oneparticlewithcertainquantumnumbers(e.g.,spin)frombeinginthesamestate.Ifthegravitationalforceislargeenough,thenonecanovercometheFermiforceandtherebysqueezethestartowithintheSchwarzschildradius,atwhichpointnothingknowntosciencecanpreventacompletecollapse.However,itwouldbeanother three decades or so before neutron stars were found and black holeswerediscovered,somostofthepapersonthemind-bendingpropertiesofblack

holeswereconsideredhighlyspeculative.Although Einstein was still rather skeptical about black holes, he was

confident that one day yet another of his predictions would come true: thediscoveryofgravitywaves.Aswehaveseen,oneofthetriumphsofMaxwell’sequationswas the prediction that vibrating electric andmagnetic fieldswouldcreatea travelingwavethatcouldbeobserved.Likewise,Einsteinwonderedifhis equationsallowed forgravitywaves. InaNewtonianworld,gravitywavescannot exist, since the “force” of gravity acts instantaneously throughout theuniverse,touchingallobjectssimultaneously.Butingeneralrelativity,insomesense,gravitywaveshavetoexist,asvibrationsofthegravitationalfieldcannotexceedthespeedoflight.Thus,acataclysmicevent,suchasthecollisionoftwoblackholes,willreleaseashockwaveofgravity,agravitywave,travelingatthespeedoflight.Asearlyas1916,Einsteinwasabletoshowthatwithsuitableapproximations,

hisequationsdidyieldwavelikemotionsofgravity.Thesewavesspreadacrossthe fabric of spacetimewith the speedof light, as expected. In 1937,with hisstudentNathanRosen,hewasabletofindanexactsolutionofhisequationsthatgave gravity waves, with no approximations whatsoever. Gravity waves werenowafirmpredictionofgeneralrelativity.Einsteindespaired,however,ofeverbeingabletowitnesssuchanevent.Calculationsshowedthatitwasfarbeyondthe experimental capabilities of scientists at that time. (It would take almosteightyyears,sinceEinsteinfirstdiscoveredgravitywaves inhisequations, fortheNobelPrizetobeawardedtophysicistswhofoundthefirstindirectevidencefor gravity waves. The first gravity waves may be directly detected perhapsninetyyearsafterhisfirstprediction.Thesegravitywaves, in turn,maybe theultimatemeansbywhichtoprobethebigbangitselfandfindtheunifiedfieldtheory.)In1936,aCzechengineer,RudiMandl,approachedEinsteinwithyetanother

ideaconcerningthestrangepropertiesofspaceandtime,askingwhethergravityfromanearbystarcouldbeusedasalenstomagnifythelightfromdistantstars,in the sameway that glass lenses can be used tomagnify light. Einstein hadconsideredthispossibilitybackin1912,but,proddedbyMandl,calculatedthatthe lenswould create a ringlikepattern to anobserver onEarth.For example,considerlightfromafarawaygalaxypassingbyanearbygalaxy.Thegravityofthenearbygalaxymightsplit thelight inhalf,witheachhalfgoingaroundthegalaxy in opposite directions. When the light beams pass the nearby galaxycompletely, they rejoin. From the earth, onewould see these light beams as aringoflight,anopticalillusioncreatedbythebendingoflightaroundthenearbygalaxy.However,Einsteinconcludedthat“thereisnotmuchhopeofobserving

thisphenomenondirectly.”Infact,hewrotethatthiswork“isoflittlevalue,butitmakesthepoorguy[Mandl]happy.”Onceagain,Einsteinwassofaraheadofhis time that itwould takeanothersixtyyearsbeforeEinstein lensesandringswould be found and eventually become indispensable tools by whichastronomersprobethecosmos.As successful and far-reaching as general relativity was, it did not prepare

Einsteininthemid-1920sforthefightofhislife,todeviseaunifiedfieldtheorytounitethelawsofphysicswhilesimultaneouslydoingbattlewiththe“demon,”thequantumtheory.

PARTIII

THEUNFINISHEDPICTURE

TheUnifiedFieldTheory

CHAPTER7

UnificationandtheQuantumChallengeIn1905,almostassoonasEinsteinworkedoutthespecialtheoryofrelativity,hebegantoloseinterestinitbecausehesethissightsonbiggergame:generalrelativity.In1915,thepatternrepeateditself.Assoonashefinishedformulatinghis theory of gravity, he began to shift his focus to an even more ambitiousproject: the unified field theory,whichwould unify his theory of gravitywithMaxwell’stheoryofelectromagnetism.Itwassupposedtobehismasterpiece,aswell as the summation of science’s two-thousand-year investigation into thenatureofgravityand light. Itwouldgivehim theability to “read theMindofGod.”Einsteinwasnotthefirsttosuggestarelationshipbetweenelectromagnetism

andgravity.MichaelFaraday,workingattheRoyalInstitutioninLondoninthenineteenth century, performed some of the first experiments to probe therelationship between these two pervasive forces.Hewould, for example, dropmagnets fromtheLondonBridgeandsee if their rateofdescentdifferedfromthat of ordinary rocks. If magnetism interacted with gravity, perhaps themagnetic field might act as a drag on gravity, making the magnets fall at adifferentrate.Hewouldalsodroppiecesofmetalfromthetopofalectureroomto a cushion on the floor, trying to see if the descent could induce an electriccurrentinthemetal.Allhisexperimentsproducednegativeresults.However,henoted, “They do not shake my strong feeling of the existence of a relationbetweengravity andelectricity, though theygivenoproof that sucha relationexists.”Furthermore,Riemann,whofoundedthetheoryofcurvedspaceinanydimension, believed strongly that both gravity and electromagnetism could bereduced to purely geometric arguments. Unfortunately, he did not have anyphysicalpictureorfieldequations,sohisideaswentnowhere.Einstein once summarized his attitude toward unification by comparing

marble and wood. Marble, thought Einstein, described the beautiful world ofgeometry,inwhichsurfaceswarpedsmoothlyandcontinuously.Theuniverseofstars and galaxies played out their cosmic game on the beautiful marble ofspace-time.Wood,on theotherhand, represented the chaoticworldofmatter,

withitsjungleofsubatomicparticles,itsnonsensicalrulesforthequantum.Thiswood, like gnarled vines, grows in unpredictable and random ways. Newparticles being discovered in the atom made the theory of matter quite ugly.Einstein saw the defect in his equations. The fatal flaw was that wooddetermined the structure of themarble. The amount of bending of space-timewasdeterminedbytheamountofwoodatanypoint.Thus,toEinstein,hisstrategywasclear:tocreateatheoryofpuremarble,to

eliminate thewoodby reformulating it solely in terms ofmarble. If thewooditself couldbe shown tobemadeofmarble, thenhewouldhavea theory thatwaspurelygeometric.Forexample,apointparticleisinfinitelytiny,havingnoextension in space. In field theory, a point particle is represented by a“singularity,”apointwherethefieldstrengthgoestoinfinity.Einsteinwantedtoreplace thissingularitywithasmoothdeformationofspaceandtime.Imagine,forexample,akinkorknotinarope.Fromadistance,thekinkmaylooklikeaparticle, but close-up the kink or knot is nothing but a wrinkle in the rope.Similarly,Einsteinwantedtocreateatheorythatwaspurelygeometricandhadnosingularitieswhatsoever.Subatomicparticles,liketheelectron,wouldemergeas kinks or as some kind of small wrinkle on the surface of space-time. Thefundamental problem, however, was that he lacked a concrete symmetry andprinciplethatcouldunifyelectromagnetismandgravity.Aswesawearlier,thekey to Einstein’s thinking was unification through symmetry. With specialrelativity,hehadthepicturethatguidedhimconstantly,runningnexttoalightbeam.Thispicture revealed the fundamental contradictionbetweenNewtonianmechanicsandMaxwell’s fields.From this,hewasable toextractaprinciple,theconstancyofthespeedoflight.Last,hewasabletoformulatethesymmetrythatunifiedspaceandtime,theLorentztransformations.Similarly,withgeneralrelativity,hehadapicture,thatgravitywascausedby

the warping of space and time. This picture exposed the fundamentalcontradictionbetweenNewton’sgravity(wheregravitytraveledinstantaneously)and relativity (where nothing can go faster than light). From the picture, heextractedaprinciple,theequivalenceprinciple,thatacceleratingandgravitatingframes obeyed the same laws of physics. Last, he was able to formulate thegeneralized symmetry that described accelerations and gravity, which wasgeneralcovariance.TheproblemfacingEinsteinnowwastrulydaunting,becausehewasworking

atleastfiftyyearsaheadofhistime.Inthe1920s,whenhebeganworkontheunified field theory, the only established forces were the gravitational andelectromagnetic forces. The nucleus of the atom had only been discovered in1911byErnestRutherford,andtheforcethatheldittogetherwasstillshrouded

inmystery.Butwithoutanunderstandingofthenuclearforces,Einsteinlackedacrucialpartofthepuzzle.Furthermore,noexperimentorobservationexposedacontradiction between gravity and electromagnetism that would be the hookEinsteincouldgrabonto.HermannWeyl,amathematicianwhowasinspiredbyEinstein’ssearchfora

unifiedfieldtheory,madethefirstseriousattemptin1918.Atfirst,Einsteinwasvery impressed. “It is a masterful symphony,” he wrote. Weyl expandedEinstein’s old theory of gravity by adding theMaxwell field directly into theequations.Thenhedemanded that theequationsbecovariantunderevenmoresymmetriesthanEinstein’soriginaltheory,includingscaletransformations(i.e.,transformations that expand or contract all distances).However, Einstein soonfoundsomestrangeanomalies in the theory.Forexample, ifyou traveled inacircle and came back to your original point, you would find that you wereshorterbuthadthesameshape.Inotherwords,lengthswerenotpreserved.(InEinstein’stheory,lengthscouldalsochange,buttheyremainedthesameifyoucameback towhereyoustarted.)Timewouldalsobeshifted inaclosedpath,butthiswouldviolateourunderstandingofthephysicalworld.Forexample,itmeantthatifvibratingatomsweremovedaroundacompletecircle,theywouldbe vibrating at a different frequency when they came back. AlthoughWeyl’stheoryseemedingenious,ithadtobeabandonedbecauseitdidnotfitthedata.(Inhindsight,wecan see that theWeyl theoryhad toomuch symmetry.Scaleinvariance is apparently a symmetry that nature does not use to describe ourvisibleuniverse.)In 1923, Arthur Eddington also caught the bug. Inspired byWeyl’s work,

Eddington (andmanyothersafterhim) triedhishandataunified field theory.LikeEinstein,hecreatedatheorybasedontheRiccicurvature,buttheconceptofdistancedidnotappearintheequations.Inotherwords,itwasimpossibletodefinemetersorsecondsinhis theory; the theorywas“pre-geometrical.”Onlyinthelaststepwoulddistancefinallyappearasaconsequenceofhisequations.ElectromagnetismwassupposedtoemergeasapieceoftheRiccicurvature.ThephysicistWolfgangPauli did not like this theory at all, stating that it had “nosignificance for physics.” Einstein also panned it, thinking it had no physicalcontent.ButwhatreallyrockedEinsteintothecorewasapaperthathesawin1921,

written by an obscure mathematician, Theodr Kaluza, from the University ofKönigsberg.Kaluzasuggested thatEinstein,whohadpioneered theconceptofthefourthdimension,addyetanotherdimensiontohisequations.Kaluzabeganby reformulating Einstein’s own general relativity in five dimensions (fourdimensionsofspaceandonedimensionoftime).Thistakesnoworkatall,since

Einstein’sequationscouldeasilybeformulatedinanydimension.Then,inafewlines,Kaluzashowedthatifthefifthdimensionisseparatedfromtheotherfour,Einstein’sequationsemerged,alongwithMaxwell’sequations!Inotherwords,Maxwell’s equations, the horrible set of eight partial differential equationsmemorizedbyeveryengineerandphysicist,canbereducedtowaves travelingon the fifth dimension. To put it another way,Maxwell’s theory was alreadyhiddeninsideEinstein’stheoryifrelativitywereextendedtofivedimensions.EinsteinwassurprisedbythesheeraudacityandbeautyofKaluza’swork.He

wrote Kaluza, “The idea of achieving [unification] by means of a five-dimensionalcylinderworldneverdawnedonme….Atfirstglance,Ilikedyourideaenormously.”Afewweekslater,afterstudyingthetheory,hewrote,“Theformalunityofyourtheoryisstartling.”In1926,themathematicianOskarKleingeneralized Kaluza’s work and speculated that the fifth dimension wasunobservable because itwas small andpossibly linked to the quantum theory.Kaluza and Klein were thus proposing an entirely different approach tounification. To them, electromagnetism was nothing but vibrations ripplingalongthesurfaceofasmallfifthdimension.For example, if we think of fish living in a shallow pond, swimming just

below the lily pads, the fish might conclude that their universe was two-dimensional. They can move forward and backward, left and right, but theconceptof“up”intothethirddimensionwouldbealientothem.Iftheiruniversewastwo-dimensional,thenhowmighttheybecomeawareofamysteriousthirddimension? Imagine that it rains one day. Tiny ripples in the third dimensionmovealongthesurfaceofthepond,andtheyareclearlyvisibletothefish.Asthese ripplesmovealong the surface, the fishmight conclude that therewasamysterious force thatcould illuminate theiruniverse.Similarly, in thispicture,wearethefish.Weconductouraffairsinthreespatialdimensions,unawarethatthere could be higher dimensions existing just beyond our senses. The onlydirectcontactthatwemighthavewiththeunseenfifthdimensionislight,nowviewedasripplestravelingalongthefifthdimension.TherewasareasonwhytheKaluza-Kleintheoryworkedsowell.Recallthat

unification through symmetrywasoneofEinstein’sgreat strategies that led torelativity.IntheKaluza-Kleintheory,electromagnetismandgravitywereunitedbecauseofanewsymmetry,five-dimensionalgeneralcovariance.Althoughthispicture was immediately appealing, unifying gravity and electromagnetism byintroducinganotherdimension,therewasstill thenaggingquestion,wherewasthis fifth dimension? No experiment has ever, even to this day, picked upevidenceofanyhigherdimensionofspacebeyondlength,width,andheight.Ifthesehigherdimensionsexist,thentheymustbeextremelysmall,muchsmaller

thananatom.Forexample,weknowthatifwereleasechlorinegasintoaroom,itsatomscanslowlypermeateall thenooksandcranniesofany roomwithoutdisappearing into somemysterious extra dimension.We know, therefore, thatanyhiddendimensionmustbesmallerthananyatom.Inthisnewtheory,ifonemakes the fifth dimension smaller than an atom, then it is consistent with alllaboratorymeasurements, which have never detected the presence of the fifthdimension.KaluzaandKleinassumedthatthefifthdimensionwas“curledup”intoasmallball,toosmalltobeexperimentallyobserved.AlthoughtheKaluza-Kleintheorywasafresh,intriguingapproachtounifying

electromagnetismwithgravity,Einsteineventuallyhaddoubts.Thethoughtthatthe fifth dimensionmight not exist, that itmight be amathematical fiction ormirage,botheredhim.Also,hehadproblemsfindingsubatomicparticlesintheKaluza-Klein theory.Hisgoalwastoderive theelectronfromhisgravitationalfieldequations,andtryashecould,hecouldfindnosuchsolution.(Inhindsight,thiswasatremendousmissedopportunityforphysics.IfphysicistshadtakentheKaluza-Klein theorymore seriously, theymight have addedmore dimensionsbeyond five. As we increase the number of dimensions, Maxwell’s fieldincreases in number into what are called “Yang-Mills fields.” Klein actuallydiscovered theYang-Mills fields in the late1930s,buthisworkwas forgottenbecauseofthechaosofWorldWarII.Itwouldtakealmosttwodecadesbeforetheywererediscovered,inthemid-1950s.TheseYang-Millsfieldsnowformthefoundation of the current theory of the nuclear force.Almost all of subatomicphysicsisformulatedintermsofthem.Afteranothertwentyyears,theKaluza-Klein theorywould be resurrected in the form of a new theory, string theory,nowconsideredtheleadingcandidateforaunifiedfieldtheory.)Einstein hedged his bets. If the Kaluza-Klein theory failed, then he would

have to explore a different avenue toward the unified field theory.His choicewastoinvestigategeometriesbeyondRiemanniangeometry.Heconsultedmanymathematicians,anditbecamequicklyobviousthatthiswasatotallyopenfield.In fact, at Einstein’s urging, many mathematicians began to look into “post-Riemannian” geometries, or the “theory of connections,” to help him explorenew possible universes. New geometries involving “torsion” and “twistedspaces”were soon developed as a consequence. (These abstract spaceswouldhave no application to physics for another seventy years, until the arrival ofsuperstringtheory.)Workingonpost-Riemanniangeometrieswasanightmare,however.Einstein

had no guiding physical principle to help him through the thicket of abstractequations.Previously,heusedtheequivalenceprincipleandgeneralcovarianceascompasses.Bothwerefirmlyrootedinexperimentaldata.Hehadalsorelied

on physical pictures to show him the way. With the unified field theory,however,hehadnoguidingphysicalprincipleorpicture.SocuriouswastheworldaboutEinstein’sworkthataprogressreporthegave

on the unified field theory to the PrussianAcademywas reported to theNewYork Times,which even published parts of Einstein’s paper. Soon, therewerehundredsofreportersswarmingoutsidehishome,hopingforaglimpseofhim.Eddingtonwrote,“YoumaybeamusedtohearthatoneofourgreatdepartmentstoresinLondon(Selfridges)haspostedonitswindowyourpaper(thesixpagespastedupsidebyside)sothatpassers-bycanreaditallthrough.Largecrowdsgatheraroundtoreadit.”Einstein,however,wouldhavetradedalltheadulationandpraiseintheworldforasimplephysicalpicturetoguidehispath.Gradually,otherphysicistsbegantohintthatEinsteinwasonthewrongtrack

and that his physical intuition was failing him. One critic was his friend andcolleagueWolfgangPauli,oneoftheearlypioneersofthequantumtheory,whowas famous in scientific circles for his unsparing wit. He once said of amisguidedphysicspaper,“Itisnotevenwrong.”Toacolleaguewhosepaperhehadreviewed,hesaid,“Idonotmindifyouthinkslowly,butIdoobjectwhenyoupublishmorequicklythanyouthink.”Afterheheardaconfused,incoherentseminar, hewould say, “What you saidwas so confusing that one cannot tellwhetheritwasnonsenseornot.”WhenfellowphysicistscomplainedthatPauliwastoocritical,hewouldreply,“Somepeoplehaveverysensitivecorns,andtheonlywaytolivewiththemistosteponthesecornsuntiltheyareusedtoit.”Hisimpressionoftheunifiedfieldtheorywasreflectedbyhisfamouscommentthatwhat God has torn asunder, let no man put together. (Ironically, later Pauliwould also catch the bug and propose his own version of the unified fieldtheory.)Pauli’sviewwouldhavebeenendorsedbymanyofhisfellowphysicists,who

grewincreasinglypreoccupiedwiththequantumtheory,theothergreattheoryofthetwentiethcentury.Thequantumtheorystandsasoneofthemostsuccessfulphysical theories of all time. It has had unparalleled success explaining themysterious world of the atom, and by doing so has unleashed the power oflasers,modernelectronics,computers,andnanotechnology.Ironically,however,the quantum theory is based on a foundation of sand. In the atomic world,electronsseeminglyappearintwoplacesatthesametime,jumpbetweenorbitswithout warning, and disappear into the ghostly world between existence andnonexistence. As Einstein remarked as early as 1912, “The more success thequantumtheoryhas,thesillieritlooks.”Some of the bizarre features of the quantumworld were made apparent in

1924,whenEinsteinreceivedacuriousletterfromanobscureIndianphysicist,

SatyendraNathBose,whose papers on statistical physicswere so strange thattheywere flatly rejected for publication. Bosewas proposing an extension ofEinstein’s earlierwork on statisticalmechanics, searching for a fully quantummechanical treatment of a gas, treating the atoms as quantum objects. Just asEinsteinhadextendedPlanck’sworktoatheoryoflight,BosewashintingthatonecouldextendEinstein’sworkintoafullyquantumtheoryofatomsinagas.Einstein,amasterofthesubject,foundthatthoughBosehadmadeanumberofmistakes, making assumptions that could not be justified, his final answerappeared to be correct. Einstein was not only intrigued by the paper, hetranslateditintoGermanandsubmitteditforpublication.He then extendedBose’swork andwrote a paper of his own, applying the

resulttoextremelycoldmatterthathoversjustabovethetemperatureofabsolutezero.BoseandEinsteinfoundacuriousfactaboutthequantumworld:allatomsareindistinguishable;thatis,youcannotputalabeloneachatom,asBoltzmannandMaxwellhadthought.Whilerocksandtreesandotherordinarymattercanbe labeled and given names, in the quantumworld all atoms of hydrogen areidentical in any experiment; there are no green or blue or yellow hydrogenatoms.Einsteinthenfoundthatifacollectionofatomsweresupercooledtonearabsolute zero,where all atomicmovement almost ceases, all the atomswouldfalldowntothelowestenergystate,creatingasingle“superatom.”Theseatomswouldcondenseintothesamequantumstate,behavingessentiallylikeasinglegigantic atom. He was proposing an entirely new state of matter, never seenbefore onEarth.However, before the atoms could tumble down to the lowestenergy state, the temperatureswould have to be fantastically small,much toosmall to be experimentally observed, about a millionth of a degree aboveabsolute zero. (At these extremely low temperatures, the atoms vibrate inlockstep,andsubtlequantumeffectsonlyseenat the levelof individualatomsnowbecomedistributedthroughouttheentirecondensate.Likethespectatorsatafootballgamewhoform“humanwaves”thatsweepacrossthestandsastheystandupanddowninunison,theatomsina“Bose-Einsteincondensate”actasifeverythingisvibratinginunison.)ButEinsteindespairedofeverobservingthisBose-Einsteincondensationinhislifetime,sincethetechnologyofthe1920sdidnotpermitexperimentsneartemperaturesofabsolutezero.(Infact,Einsteinwassoaheadofhistimethatitwouldbeaboutseventyyearsbeforethatpredictioncouldbetested.)InadditiontoBose-Einsteincondensation,Einsteinwasinterestedinwhether

hisprincipleofdualitycouldbeapplied tomatteraswellas light. Inhis1909lecture, Einstein had showed that there was a dual nature to light, that it cansimultaneously have both particle and wavelike properties. Although it was a

heretical idea, it was supported fully by experimental results. Inspired by thedualityprograminitiatedbyEinstein,ayounggraduatestudent,PrinceLouisdeBroglie, then speculated in 1923 that evenmatter itself can have both particleandwavelikeproperties.Thiswasabold,revolutionaryconcept,sinceitwasadeep-seatedprejudicethatmatterconsistedofparticles.StimulatedbyEinstein’swork on duality, deBroglie could explain away some of themysteries of theatombyintroducingtheconceptthatmatterhadwavelikeproperties.EinsteinlikedtheaudacityofdeBroglie’s“matterwaves”andpromotedhis

theory. (De Broglie would eventually be awarded the Nobel Prize for thisseminalidea.)Butifmatterhadwavelikeproperties,thenwhatwastheequationthat the waves obeyed? Classical physicists had plenty of experience writingdowntheequationsofoceanwavesandsoundwaves,soanAustrianphysicist,Erwin Schrödinger, was inspired to write down the equation of these matterwaves.WhileSchrödinger,awell-knownladies’man,wasstayingwithoneofhis innumerable girlfriends in theVillaHerwig inArosaduring theChristmasholidays in 1925, he managed to divert himself long enough to formulate anequation that would soon be known as one of the most celebrated in all ofquantum physics, the Schrödinger wave equation. Schrödinger’s biographer,WalterMoore,wrote,“Like thedark ladywhoinspiredShakespeare’ssonnets,the lady of Arosa may remain forever mysterious.”(Unfortunately, becauseSchrödingerhadsomanygirlfriendsandloversinhislife,aswellasillegitimatechildren,itisimpossibletodeterminepreciselywhoservedasthemuseforthishistoric equation.) Over the next several months, in a remarkable series ofpapers,Schrödinger showed that themysterious rules foundbyNielsBohr forthehydrogenatomweresimpleconsequencesofhisequation.Forthefirsttime,physicistshadadetailedpictureoftheinterioroftheatom,bywhichonecould,in principle, calculate the properties ofmore complex atoms, evenmolecules.Withinmonths,thenewquantumtheorybecameasteamroller,obliteratingmanyof themost puzzlingquestions about the atomicworld, answering thegreatestmysteriesthathadstumpedscientistssincetheGreeks.Thedanceofelectronsasthey moved between orbits, releasing pulses of light or binding moleculestogether, suddenly became calculable, a matter of solving standard partialdifferentialequations.Oneyoungbrashquantumphysicist,PaulAdrianMauriceDirac, even boasted that all of chemistry could be explained as solutions ofSchrödinger’sequation,reducingchemistrytoappliedphysics.ThusEinstein,whowasthefatherofthe“oldquantumtheory”ofthephoton,

becamethegodfatherofthe“newquantumtheory,”basedontheseSchrödingerwaves. (Today, when high school chemistry students have to memorize thefunny football-shaped “orbitals” that surround the nucleus,with strange labels

and “quantum numbers,” they are actually memorizing the solutions to theSchrödinger wave equation.) The breakthroughs in quantum physics nowaccelerated enormously. Realizing that the Schrödinger equation did notincorporate relativity, just two years later Dirac generalized the Schrödingerequation toa fully relativistic theoryofelectrons,andonceagain theworldofphysics was dazzled. While Schrödinger’s celebrated equation wasnonrelativisticandonlyappliedtoelectronsmovingatslowvelocitiescomparedto light, Dirac’s electrons obeyed the full Einstein symmetry. Furthermore,Dirac’s equation could automatically explain some obscure properties of theelectron, including something called “spin.” It was known from earlierexperiments by Otto Stern and Walter Gerlach that the electron acted like aspinningtopinamagneticfield,withangularmomentumgivenby1/2(inunitsofPlanck’sconstant).TheDiracelectronyieldedpreciselythespin1/2givenbytheStern-Gerlachexperiment.(TheMaxwellfield,representingthephoton,hasspin1,andEinstein’sgravitywaveshavespin2.WithDirac’swork,itbecameclear that the spin of a subatomic particle would be one of its importantproperties.)ThenDiracwentonestepfurther.Bylookingattheenergyoftheseelectrons,

hefoundthatEinsteinhadoverlookedasolutiontohisownequations.Usually,when taking the square root of a number, we introduce both positive andnegative solutions. For example, the square root of 4 can be either plus 2 orminus 2. Because Einstein ignored a square root in his equations, his famousequationE=mc2was not quite correct. The correct equationwasE= ±mc2.This extra minus sign, argued Dirac, made possible a new kind of mirroruniverse,oneinwhichparticlescouldexistwithanewformof“antimatter.”(Strangely, justa fewyearsearlier in1925,Einsteinhimselfhadentertained

theideaofantimatterwhenheshowedthatbyreversingthesignoftheelectroncharge in a relativistic equation, one can get identical equations if one alsoreversestheorientationofspace.Heshowedthatforeveryparticleofacertainmass,theremustexistanotherparticlewithoppositechargebutidenticalmass.Relativitytheorynotonlygaveusthefourthdimension,itwasnowgivingusaparallel world of antimatter. However, Einstein, never one to quibble overpriority,graciouslyneverchallengedDirac.)Atfirst,theradicalideasofDiracmetwithfierceskepticism.Theideaofan

entire universe of mirror particles that arose fromE = ±mc2 seemed like anoutlandish idea. Quantum physicistWernerHeisenberg (whowithNiels Bohrhad independently found a formulation of the quantum theory equivalent toSchrödinger’s)wrote,“Thesaddestchapterofmodernphysicsisandremainsthe

Dirac theory…. I regard theDirac theory…as learned trashwhich no one cantake seriously.” However, physicists had to swallow their pride when theantielectron,orpositron,was finallydiscovered in1932, forwhichDirac laterreceived the Nobel Prize. Heisenberg finally admitted, “I think that thisdiscoveryofantimatterwasperhapsthebiggestjumpofallthebigjumpsinourcentury.” Once again, the theory of relativity yielded unexpected riches, thistimegivingusanentirelynewuniversemadeofantimatter.(It seems strange that Schrödinger andDirac, who developed the twomost

importantwave functions in thequantum theory,were suchpolar opposites intheir personalities.While Schrödingerwas always accompanied by some ladyfriend,Diracwaspainfullyshywithwomenandwasamanofremarkablyfewwords.AfterDirac’sdeath, theBritish,honoringhiscontributions to theworldof physics, had the relativistic Dirac equation engraved into stone inWestminsterAbbey,notfarfromNewton’sgrave.)Soon,physicistsateveryinstituteonthisplanetstruggledtolearnthestrange,

beautiful properties of the Schrödinger and Dirac equations. However, for alltheir undeniable successes, quantum physicists still had to grapple with atroubling philosophical question: if matter is a wave, then precisely what iswaving? This is the same question that had haunted thewave theory of light,whichgavebirthtotheincorrecttheoryoftheaether.ASchrödingerwaveislikeanoceanwaveandeventuallyspreadsoutifleftbyitself.Withenoughtime,thewave function eventually dissipates over the entire universe. But this violatedeverything that physicists knew about electrons. Subatomic particles werebelievedtobepointlikeobjectsthatmadedefinite,jetlikestreakswhichcouldbephotographedonfilm.Thus,althoughthesequantumwaveshadnearmiraculoussuccess in describing the hydrogen atom, it did not seem possible that theSchrödingerwavecoulddescribeanelectronmovinginfreespace.Infact,iftheSchrödingerwave really representedanelectron, itwouldslowlydissipateandtheuniversewoulddissolve.Somethingwas terriblywrong. Finally, Einstein’s lifelong friendMaxBorn

proposedoneof themost controversial solutions to thispuzzle. In1926,Borntookthedecisivestep,claimingthat theSchrödingerwavedidnotdescribetheelectronatall,butonlytheprobabilityoffindingtheelectron.Hedeclaredthat“the motion of particles follows probability laws, but probability itselfpropagatesinconformitywiththelawsofcausality.”Inthisnewpicture,matterindeedconsistedofparticles,notwaves.Themarkingscapturedonphotographicplates are the tracks left by pointlike particles, not waves. But the chance offindingtheparticleatanygivenpointwasgivenbyawave.(Moreprecisely,theabsolutesquareoftheSchrödingerwaverepresentstheprobabilityoffindingthe

particle at a specific point in space and time.) Thus, it did not matter if theSchrödinger wave spread out over time. It simply meant that if you left anelectronby itself, over time itwouldwander aroundandyouwouldnotknowprecisely where it was. All the paradoxes were now solved: the Schrödingerwavewasnottheparticleitself,butrepresentedthechanceoffindingit.WernerHeisenbergtookthisonestepfurther.Hehadagonizedendlesslywith

Bohroverthepuzzlesofprobabilityinfestingthisnewtheory,oftengettingintoheatedargumentswithhisoldercolleague.Oneday,afterafrustratingnightofgrapplingwiththequestionofprobabilities,hetookalongstrolldownFaelledPark,behindhisuniversity, constantlyaskinghimselfhow itwaspossible thatonecouldnotknowthepreciselocationofanelectron.Howcanthelocationofanelectronbeuncertain,asclaimedbyBorn,ifyoucansimplymeasurewhereitis?Then, itsuddenlyhithim.Everythingbecameclear. Inorder toknowwhere

anelectronwas,youhadtolookatit.Thismeantshiningalightbeamatit.Butthephotonsinthelightbeamwouldcollidewiththeelectron,makingitspositionuncertain. In other words, the act of observation necessarily introduceduncertainty.He reformulated thisquestion into anewprincipleofphysics, theuncertaintyprinciple,whichstates thatonecannotdetermineboth the locationandthevelocityofaparticleat thesametime. (Moreprecisely, theproductofthe uncertainty in position and momentum must be greater than or equal toPlanck’sconstantdividedby4p).Thiswasnotjustaby-productofthecrudenessof our instruments; it was a fundamental law of nature. Even God could notknowboththeprecisepositionandmomentumofanelectron.Thiswas thedecisivemomentwhen thequantum theoryplunged intodeep,

totallyunchartedwaters.Uptothen,onecouldarguethatquantumphenomenawerestatistical,representingtheaveragemotionsoftrillionsofelectrons.Now,even the motions of a single electron could not be definitively determined.Einstein was horrified. He almost felt betrayed, knowing that his good friendMaxBornwasabandoningdeterminism,oneofthemostcherishedideasinallofclassical physics. Determinism states, in essence, that you can determine thefuture ifyouknoweverythingabout thepresent.Forexample,Newton’sgreatcontributiontophysicswasthathecouldpredictthemotionofcomets,moons,andplanetsviahis lawsofmotiononceheknew thepresent stateof the solarsystem. For centuries, physicists had marveled at the precision of Newton’slaws, that they could predict the position of celestial bodies, in principle,millionsofyearsintothefuture.Infact,uptothattime,allofsciencewasbasedondeterminism;that is,ascientistcanpredict theoutcomeofanexperimentifthe scientist knows the position and velocities of all particles. Followers of

Newtonsummarized thisbeliefbycomparing theuniverse toagiganticclock.GodwoundupthisclockatthebeginningoftimeandithasbeensteadilytickingeversinceaccordingtoNewton’slawsofmotion.Ifyouknewthepositionandvelocity of every atom in the universe, then you can, via Newton’s laws ofmotion, calculate the subsequent evolution of the universe with infiniteprecision.However,theuncertaintyprinciplenegatedallofthis,statingthatitisimpossibletopredictthefuturestateoftheuniverse.Givenauraniumatom,forexample,onecouldnevercalculatewhenitwilldecay,onlythelikelihoodofitsdoing so. In fact, evenGod or a deity did not knowwhen the uranium atomwoulddecay.In December 1926, responding to Born’s paper, Einstein wrote, “Quantum

mechanicscalls for agreatdealof respect.But some innervoice tellsme thatthis is not the true Jacob. The theory offers a lot, but it hardly brings us anycloser to theOldMan’s secret. Formy part, at least I am convinced that Hedoesn’t throw dice.” When commenting on Heisenberg’s theory, Einsteinremarked,“Heisenberghaslaidabigquantumegg.InGöttingentheybelieveinit(Idon’t).”Schrödingerhimselfdislikedthisideaintensely.Heoncesaidthatifhisequationrepresentedonlyprobabilities,thenheregrettedhavinganythingtodo with it. Einstein chimed in that he would have become a “cobbler oremployeeinagaminghouse,”ifhehadknownthatthequantumrevolutionhehelpedtoinitiatewouldintroducechanceintophysics.Physicistswerebeginning todivide into twocamps.Einstein ledone camp,

whichstillclungtoabeliefindeterminism,anideathatdatedbacktoNewtonhimself and had guided physicists for centuries. Schrödinger and de Brogliewereallies.Theother,muchlargercampwasledbyNielsBohr,whobelievedinuncertaintyandchampionedanewversionofcausality,basedonaveragesandprobabilities.BohrandEinstein,insomesense,werepolaroppositesinotherways.While

Einstein as a child shunned sports and was glued to books on geometry andphilosophy,BohrwasrenownedthroughoutDenmarkasasoccerstar.WhereasEinstein spoke forcefully and dynamically, wrote almost lyrically, and couldexchangebanterwithjournalistsaswellasroyalty,Bohrwasstiff,hadahorriblemumble,was often inarticulate and inaudible, andwould often repeat a singleword endlessly when engrossed in thought. While Einstein could effortlesslywrite elegant andbeautiful prose,Bohrwasparalyzedwhenhehad towrite apaper.Asahighschool student,hewoulddictateallhispapers tohismother.After he married, he would dictate them to his wife (even interrupting hishoneymoon to dictate one long and important paper). He would sometimesinvolvehisentirelaboratoryinrewritinghispapers,onceoverahundredtimes,

completely disrupting thework. (Wolfgang Pauli, once asked to visit Bohr inCopenhagen, replied, “If the last proof is sent away, then Iwill come.”)Bothwere, however, obsessed with their first love, physics. Bohr, in fact, wouldscribble equations on the goal post of a soccer game if he had an inspiration.Bothwouldalsosharpentheir thoughtsbyusingothersassoundingboardsfortheirideas.(Strangely,Bohrcouldonlyfunctionifhehadassistantsaroundhimto bounce off ideas.Without an assistantwhose ear he could borrow, hewashelpless.)The showdown finally came at the Sixth Solvay Conference in Brussels in

1930. What was at stake was nothing less than the nature of reality itself.Einstein hammered incessantly atBohr,who reeled under the constant attacksbutmanagedtoablydefendhispositions.Finally,Einsteinpresentedanelegant“thought experiment” which, he thought, would demolish the “demon,” theuncertaintyprinciple:Imagineaboxcontainingradiation.Thereisaholeintheboxwith a shutter.When the shutter is opened briefly, it can release a singlephotonfromthebox.Thus,wecanmeasurewithgreatcertaintytheprecisetimeatwhichthephotonwasemitted.Muchlater,theboxcanbeweighed.Becauseofthereleaseofthephoton,theboxweighsless.Becauseoftheequivalenceofmatterandenergy,wecannowtellhowmuchtotalenergytheboxcontains,alsoto great accuracy. Thus, we now know both the total energy and the time ofopeningoftheshuttertoarbitraryaccuracy,withoutanyuncertainty,andhencetheuncertaintyprincipleiswrong.Einsteinthoughthehadfinallyfoundthetooltodemolishthenewquantumtheory.PaulEhrenfest,oneoftheparticipantstothisconferenceandawitnesstothis

fiercebattle,wouldwrite,“ToBohr,thiswasaheavyblow.Atthemomenthesaw no solution. He was extremely unhappy all through the evening, walkedfromone person to another, trying to persuade themall that this could not betrue,because ifEwas right thiswouldmean theendofphysics.Buthecouldthinkofnorefutation.Iwillneverforgetthesightofthetwoopponentsleavingthe university club. Einstein, a majestic figure, walking calmly with a faintironical smile,andBohr trottingalongbyhis side,extremelyupset.”Whenhetalked to Ehrenfest later that evening, all Bohr couldmumble was one word,over and over again: “Einstein…Einstein…Einstein.” But after an intense,sleeplessnight,BohrfinallyfoundthedefectinEinstein’sargument,andheusedEinstein’s own theory of relativity to defeat him.Bohr noted that because theboxweighed less thanbefore, itwould rise slightly in the earth’s gravity.Butaccording to general relativity, time speeds up as gravity getsweaker (so thattimebeatsfasteronthemoon,forexample).Thus,anyminusculeuncertaintyinmeasuring the time of the shutter would be translated into an uncertainty in

measuring thepositionof thebox.Youcannot, therefore,measure thepositionoftheboxwithabsolutecertainty.Furthermore,anyuncertaintyintheweightoftheboxwillbereflectedinanuncertaintyinitsenergyandalsoitsmomentum,andhenceyoucannotknowthemomentumof theboxwithabsolutecertainty.When everything is put together, the two uncertainties identified byBohr, theuncertainty inposition anduncertainty inmomentum, agreepreciselywith theuncertaintyprinciple.Bohrhadsuccessfullydefendedthequantumtheory.WhenEinstein complained that “God does not play dice with the world,” Bohrreportedlyfiredback,“StoptellingGodwhattodo.”Ultimately, Einstein had to admit that Bohr had successfully refuted his

arguments.Einsteinwouldwrite,“Iamconvincedthat this theoryundoubtedlycontainsapieceofdefinitivetruth.”CommentingonthehistoricBohr-Einsteindebate,JohnWheelersaiditwas“thegreatestdebateinintellectualhistorythatIknowabout.Inthirtyyears,Ineverheardofadebatebetweentwogreatermenover a longer period of time on a deeper issue with deeper consequences forunderstandingthisstrangeworldofours.”Schrödinger,whoalsohatedthisnewinterpretationofhisequations,proposed

his celebrated problem of the cat to poke holes into the uncertainty principle.Schrödingerwrote about quantummechanics: “I don’t like it, and I’m sorry Ihadanythingtodowithit.”Themostridiculousproblem,hewrote,wasthatofacat sealed in a box, inside which there is a bottle of hydrocyanic acid, apoisonous gas, connected to a hammer, triggered by a Geiger counter that isconnected to a piece of radioactive substance. There is no question thatradioactivedecayisaquantumeffect.Iftheuraniumdoesnotdecay,thenthecatisalive.But if anatomdecays, itwill setoff thecounter, trigger thehammer,breaktheglass,andkillthecat.Butaccordingtothequantumtheory,wecannotpredict when the uranium atom will decay. In principle, it may exist in bothstatessimultaneously,bothintactanddecayed.Butiftheuraniumatomcanexistsimultaneouslyinbothstates, thenitmeansthatthecatmustalsoexist inbothstates.Sothequestionis,isthecatdeadoralive?Normally, this isasillyquestion.Even ifwecannotopen thebox,common

sense tellsus that thecat iseitherdeadoralive.Onecannotbebothdeadandalivesimultaneously;thiswouldviolateeverythingweknowabouttheuniverseand physical reality.However, the quantum theory gives us a strange answer.Thefinalanswer is,wedon’treallyknow.Beforeyouopenthebox, thecat isrepresentedbyawave, andwaves canadd, likenumbers.Wehave to add thewavefunctionofadeadcattothatofalivecat.Thus,thecatisneitherdeadnoralivebeforeyouopenthebox.Sealedinsidethebox,allyoucansayisthattherearewavesthatrepresentthecatbeingbothdeadandaliveatthesametime.

Once we finally open the box, we can make a measurement and see forourselves if the cat is dead or alive. Themeasurement process, by an outsideobserver, allows us to “collapse” thewave function and determine the precisestate of the cat. Then we know if the cat is dead or alive. The key is themeasurementprocessbyanoutsideobserver;byshiningalightinsidethebox,thewave function has collapsed and the object suddenly assumes a definitivestate.In other words, the process of observation determines the final state of an

object.TheweaknessofBohr’sCopenhageninterpretation lies in thequestion,do objects really exist before you make a measurement? To Einstein andSchrödinger,allthisseemedpreposterous.Fortherestofhislife,Einsteinwouldgrapplewith thesedeepphilosophicalquestions(whicheventodayarestill thesubjectofintensedebate).Several upsetting aspects of this puzzle shook Einstein to the core. First,

beforeameasurementismade,weexistasthesumofallpossibleuniverses.Wecannotsayforcertainifwearedeadoralive,orwhetherdinosaursarestillalive,orwhether the earthwas destroyed billions of years ago.All events, before ameasurement ismade, are possible.Second, itwould seem that theprocess ofobservationcreatesreality!Thus,wehaveanewtwist to theoldphilosophicalpuzzleofwhetheratreereallyfallsintheforestifnoonehearsit.ANewtonianwouldarguethatthetreecanfall,independentofobservation.ButsomeonefromtheCopenhagen schoolwould say that the tree can exist in all possible states(fallen,upright,sapling,mature,burnt,rotten,etc.)untilitisobserved,atwhichpointitsuddenlyspringsintoexistence.Thusthequantumtheoryaddsatotallyunexpectedinterpretation:observingthetreedeterminesthestateofthetree,thatis,whetheritfellornot.Einstein,fromhisdaysatthepatentoffice,alwayshadanuncannyknackfor

isolating the essence of any problem. Hewould, therefore, ask visitors to hishome the followingquestion: “Does themoon exist because amouse looks atit?” If the Copenhagen school is correct, then yes, in some sense the moonspringsintoexistencewhenamouseobservesit,andthemoon’swavefunctioncollapses.Overthedecades,anumberof“solutions”havebeenofferedtothecatproblem,noneof them totally satisfactory.Althoughalmostnoonechallengesthevalidityofquantummechanicsitself,thesequestionsstillremainassomeofthegreatestphilosophicalchallengesinallofphysics.“I have thought a hundred times asmuch about the quantumproblems as I

have about general relativity theory,” wrote Einstein about how he endlesslygrappledwiththefoundationsofthequantumtheory.Aftermuchdeepthought,Einstein fired back with what he thought was the definitive critique of the

quantum theory. In1933,withhis studentsBorisPodolskyandNathanRosen,heproposedanovelexperiment thateven today iscausingheadaches tomanyquantum physicists as well as philosophers. The “EPR experiment” may nothave demolished quantum theory, as Einstein had hoped it would, but itsucceededinprovingthatthequantumtheory,whichwasalreadyprettybizarre,getsweirderandweirder.Supposethatanatomemitstwoelectronsinoppositedirections. Each electron is spinning like a top, pointing either up or down.Supposefurtherthattheyarespinninginoppositeways,sothetotalspiniszero,although you don’t know which way they are spinning. For example, oneelectronmaybespinningup,whiletheotherisspinningdown.Ifyouwaitlongenough, these electrons could be separated by billions of miles. Before anymeasurementismade,youdon’tknowthespinsoftheelectrons.Now suppose that you finally measure the spin of one electron. It is, for

example,foundtobespinningup.Theninstantly,youknowthespinoftheotherelectron,althoughitismanylight-yearsaway—sinceitsspinistheoppositeofitspartner,itmustbespinningdown.Thismeansthatameasurementinonepartoftheuniverseinstantlydeterminedthestateofanelectronontheothersideofthe universe, seemingly in violation of special relativity. Einstein called this“spookyaction-at-a-distance.”Thephilosophical implicationsof thisare ratherstartling. It means that some atoms in our body may be connected with aninvisiblewebtoatomsontheothersideoftheuniverse,suchthatmotionsinourbody can instantly affect the state of atoms billions of light-years away, inseeming violation of special relativity. Einstein disliked this idea, because itmeant that the universe was nonlocal; that is, events here on Earth instantlyaffecteventsontheothersideoftheuniverse,travelingfasterthanlight.Onhearingofthisnewobjectiontoquantummechanics,Schrödingerwroteto

Einstein, “I was very happy that in that paper…you have evidently caughtdogmatic quantummechanics by the coat-tails.”Hearing of the latestEinsteinpaper,Bohr’scolleagueLeonRosenfeldwrote,“Wedroppedeverything;wehadtoclearupsuchamisunderstandingatonce.Bohr,ingreatexcitement,instantlybegandictatingthedraftofarejoinder.”TheCopenhagenschoolwithstoodthechallenge,butataprice:Bohrhad to

concedetoEinsteinthatthequantumuniversewasindeednonlocal(i.e.,eventsin one part of the universe can instantly affect another part of the universe).Everything in the universe is somehow meshed together in a cosmic“entanglement.”SotheEPRexperimentdidnotdisprovequantummechanics;itonly revealedhowcrazy it really is. (Over theyears, thisexperimenthasbeenmisunderstood,withscoresofspeculationsthatonecouldbuildEPRfaster-than-light radio, or that we can send signals back in time, or that we can use this

effectfortelepathy.)TheEPRexperimentdidnotnegaterelativity,however.Inthissense,Einstein

hadthelastlaugh.NousefulinformationcanbetransmittedfasterthanlightviatheEPRexperiment.Forexample,youcannotsendMorsecodefasterthanlightvia the EPR apparatus. Physicist John Bell used this example to explain theproblem.He described amathematician called Bertlmannwho alwayswore apinksockandagreensock.Ifyouknewthatonefoothadthegreensock,youknew immediately that the other sockwas pink.Yet no signalwent fromonefoot to theother. Inotherwords,knowingsomething isentirelydifferent fromsendingthatknowledge.There isaworldofdifferencebetweenthepossessionofinformationanditstransmission.Bythelate1920s,therewerenowtwotoweringbranchesofphysics:relativity

and the quantum theory. The sum total of all human knowledge about thephysical universe could be summarized by these two theories. One theory,relativity,gaveusatheoryoftheverylarge,atheoryofthebigbangandblackholes.Theothertheory,thequantumtheory,gaveusatheoryoftheverysmall,the bizarre world of the atom. Although the quantum theory was based oncounterintuitiveideas,noonecoulddisputeitsstunningexperimentalsuccesses.NobelPrizeswerepracticallyflyingoffthewallforyoungphysicistswillingtoapply thequantum theory.Einsteinwas too seasoned a physicist to ignore thebreakthroughs being made almost daily in the quantum theory. He did notdispute the experimental successes of it. Quantum mechanics was the “mostsuccessfulphysicaltheoryofourperiod,”hewouldadmit.NeitherdidEinsteinimpedethedevelopmentofquantummechanics,asalesserphysicistmighthave.(In1929,Einstein recommended thatSchrödinger andHeisenberg share in theNobelPrize.)InsteadEinsteinshiftedstrategies.Hewouldnolongerattackthetheory as being incorrect.His new strategywas to absorb the quantum theoryintohisunifiedfield theory.When thearmyofcritics inBohr’scampaccusedhimofignoringthequantumworld,hefiredbackthathisrealgoalwasnothingshortofcosmicinscope:toswallowupthequantumtheoryinitsentiretyinhisnewtheory.Einsteinusedananalogydrawnfromhisownwork.Relativitydidnotprove thatNewtonian theorywascompletelywrong; itonlyshowed that itwasincomplete,thatitcouldbesubsumedintoalargertheory.Thus,Newtonianmechanics is quite valid in its own particular domain: the realm of smallvelocities and large objects. Similarly, Einstein believed that the quantumtheory’s bizarre assumptions about cats being dead and alive simultaneouslycould be explained in a higher theory. In this respect, legions of Einstein’sbiographershavemissedthepoint.Einstein’sgoalwasnottoprovethequantumtheory incorrect, as many of his critics have claimed. He has too often been

painted as the last dinosaur of classical physics, the aging rebel who foundhimselfbecoming thevoiceof reaction.Einstein’s truegoalwas toexpose thequantumtheory’sincompletenessandtousetheunifiedfieldtheorytocompleteit.Infact,oneofthecriteriafortheunifiedfieldtheorywasthatitreproducetheuncertaintyprincipleinsomeapproximation.Einstein’sstrategywastousegeneralrelativityandhisunifiedfieldtheoryto

explaintheoriginofmatteritself,toconstructmatteroutofgeometry.In1935,EinsteinandNathanRoseninvestigatedanovelwayinwhichquantumparticlessuch as the electron would emerge naturally as a consequence of his theoryratherthanasfundamentalobjects.Inthisway,hehopedtoderivethequantumtheorywithouteverhaving to face theproblemofprobabilitiesandchance. Inmosttheories,elementaryparticlesemergeassingularities,thatis,regionswherethe equations blow up. Think of Newton’s equations, for example, where theforceisgivenbytheinversesquareofthedistancebetweentwoobjects.Whenthis distance goes to zero, the force of gravity goes to infinity, giving us asingularity.BecauseEinsteinwantedtoderivethequantumtheoryfromadeepertheory, he reasoned that he needed a theory totally free of singularities.(Examplesof this exist in simplequantum theories.Theyare called “solitons”andresemblekinksinspace;thatis,theyaresmooth,notsingular,andtheycanbounceoffeachotherandmaintaintheirsameshape.)Einstein andRosen proposed a novelway to achieve such a solution. They

startedwith two Schwarzschild black holes, defined on two parallel sheets ofpaper.Byusingscissors,onecouldcutouteachblackholesingularityandgluethe two sheets back together. Thus, one obtains a smooth, singularity-freesolution, which Einstein thought might represent a subatomic particle. Thus,quantum particles can be viewed as tiny black holes. (This idea was actuallyrevivedinstringtheorysixtyyearslater,wheretherearemathematicalrelationsthatcanturnsubatomicparticlesintoblackholesandviceversa.)This “Einstein-Rosen bridge,” however, can be viewed in another way. It

represents the first mention in the scientific literature of a “wormhole” thatconnectstwouniverses.Wormholesareshortcutsthroughspaceandtime,likeagateway or portal that connects two parallel sheets of paper. The concept ofwormholeswasintroducedtothepublicbyCharlesDodgson(otherwiseknownasLewisCarroll),theOxfordmathematicianand,mostfamously,theauthorofAliceinWonderlandandThroughtheLookingGlass.WhenAliceputsherhandthrough the LookingGlass, she is in effect entering a kind of Einstein-Rosenbridge connecting two universes—the strange world of Wonderland and thecountrysideofOxford.Itwasrealized,ofcourse, thatanyonewhofell throughanEinstein-Rosenbridgewouldbecrushedtodeathbytheintensegravitational

force, enough to rip their atoms apart. Passage through the wormhole to aparalleluniversewasimpossibleiftheblackholewasstationary.(Itwouldtakeanothersixtyyearsbeforetheconceptofwormholeswouldoccupyakeyroleinphysics.)Eventually,Einsteingaveupthisidea,inpartbecausehecouldnotexplainthe

richness of the subatomicworld.He could not entirely explain all the curiouspropertiesof“wood”intermsof“marble.”Thereweresimplytoomanyfeaturesof subatomic particles (e.g., mass, spin, charge, quantum numbers, etc.) thatfailedtoemergefromhisequations.Hisgoalwastofindthepicturethatwouldreveal the unified field theory in all its splendor, but one crucial problemwasthatnotenoughwasknownatthattimeaboutthepropertiesofthenuclearforce.Einsteinwasworkingdecadesbeforedatafrompowerfulatomsmasherswouldclarifythenatureofsubatomicmatter.Asaresult,thepicturenevercame.

CHAPTER8

War,Peace,andE=mc2Inthe1930s,withtheworldcaughtinthevicelikegripoftheGreatDepression,chaoswasonceagainstalkingthestreetsofGermany.Withthecollapseofthecurrency,hard-working,middle-classcitizenssuddenly found their life savingswiped out almost overnight. The rising Nazi Party fed upon the misery andgrievances of theGerman people, focusing their anger at themost convenientscapegoat, the Jews. Soon, with the backing of powerful industrialists, theybecamethestrongestforceintheReichstag.Einstein,whohadresistedtheanti-Semites for years, realized that this time the situation was life-threatening.Although a pacifist, he was also realistic, adjusting his views in light of themeteoric rise of theNazi Party. “Thismeans that I am opposed to the use offorce under any circumstances except when confronted by an enemy whopursues the destruction of life as an end in itself,” he wrote. This flexibilitywouldbeputtothetest.In 1931, a book called One Hundred Authorities against Einstein was

published, containing all kinds of anti-Semitic slander directed against thefamousphysicist.“ThepurposeofthispublicationistoopposetheterroroftheEinsteinianswithanaccountof thestrengthof theiropposition,” thedocumentfumed. Einstein later quipped that they did not really need one hundredauthorities todestroy relativity. If itwere incorrect,onesmall factwouldhavebeen sufficient. InDecember1932,Einstein, unable to resist the rising tideofNazism, leftGermany forgood.He toldElsa to lookat theircountryhouse inCaputhandsaidsadly,“Turnaround,youwillneverseeitagain.”Thesituationdeteriorated dramatically on January 30, 1933, when the Nazis, already thelargest block in the Parliament, finally seized power, and Adolf Hitler wasappointedaschancellorofGermany.TheNazisconfiscatedEinstein’spropertyand his bank account, leaving him officially penniless, and took over hischerishedCaputhvacationhouse, claiming tohave foundadangerousweaponthere.(Itwaslaterfoundtobeabreadknife.TheCaputhhousewasusedduringthe Third Reich by theNazi BundDeutschesMädel, the “League of GermanGirls”).OnMay10,theNazisheldapublicburningofbannedbooks,Einstein’s

worksamongthem.Thatyear,EinsteinwrotetotheBelgianpeople,whowereundertheshadowofGermany:“Undertoday’sconditions,ifIwereaBelgian,Iwouldnotrefusemilitaryservice.”Hisremarkswerecarriedbytheinternationalmedia and earned him immediate scorn from bothNazis and fellow pacifists,manyofwhombelievedthattheonlywaytoconfrontHitlerwaswithpeacefulmeans.Einstein,realizingthetruedepthsofthebrutalityoftheNaziregime,wasunmoved: “The antimilitarists are falling on me as on a wicked renegade….thosefellowssimplywearblinders.”ForcedtofleeGermany,Einsteintheworldtravelerwasonceagainaperson

withoutahome.Onhis trip toEnglandin1933,hestoppedbytoseeWinstonChurchill at his estate. Under “address” in Churchill’s guest book, Einsteinwrote,“None.”NownearthetopoftheNazi’shatelist,hehadtobecarefulofhispersonalsecurity.AGermanmagazinelistingtheenemiesoftheNaziregimeshowedEinstein’spictureonthefrontcoverwiththecaption,“Notyethanged.”Anti-SemiteswereproudtosaythatiftheycoulddriveEinsteinoutofGermany,they could drive all Jewish scientists out.Meanwhile, theNazis passed a newlaw requiring the dismissal of all Jewish officials, which was an immediatedisaster for German physics. Nine Nobel laureates had to leave Germanybecause of the new civil service law, and seventeen hundred facultymembersweredismissedinthefirstyear,causingavasthemorrhagingofGermanscienceandtechnology.ThemassexodusoutofNazi-controlledEuropewasstaggering,virtuallydepletingthecreamofthescientificelite.Max Planck, ever the conciliator, refused all efforts by his colleagues to

oppose Hitler publicly. He preferred to use private channels and even metpersonallywithHitler inMay 1933,making one last final plea to prevent thecollapseofGermanscience.Planckwouldwrite,“Ihadhopedtoconvincehimthat he was doing enormous damage…by expelling our Jewish colleagues; toshowhowsenselessandutterlyimmoralitwastovictimizemenwhohadalwaysthought of themselves as Germans, and who had offered up their lives forGermany like everyone else.”At thatmeeting,Hitler said that he hadnothingagainstJews,buttheywereallCommunists.WhenPlancktriedtoreply,Hitlershoutedback tohim,“Peoplesay that Igetattacksofnervousweakness,but Ihavenervesofsteel!”HethenslappedhiskneeandcontinuedhistiradeagainstJews. Planck would regret, “I failed to make myself understood…. There issimplynolanguageinwhichonecantalktosuchmen.”Einstein’sJewishcolleaguesallfledGermanyfortheirlives.LeoSzilardleft

withhislifesavingsstuffedinhisshoes.FritzHaberfledGermanyin1933forPalestine. (Ironically, as a loyal German scientist he had helped to developpoisongasfortheGermanarmy,producingthenotoriousZyklonBgas.Later,

his own gas was used to kill many members of his family at the Auschwitzconcentration camp.)ErwinSchrödinger,whowasnot Jewish,was also sweptup by the hysteria. On March 31, 1933, when the Nazis declared a nationalboycottofallJewishstores,hehappenedtobeinfrontofBerlin’slargeJewishdepartment store, Wertheim’s, when he suddenly witnessed gangs of stormtrooperswithNazi swastikas beating up Jewish shopkeepers as the police andthecrowdstoodbyandlaughed.Schrödingerwasincensedandwentuptooneofthestormtroopersandberatedhim.Thenthestormtroopersturnedandbegantobeathiminstead.Hecouldhavebeenseriouslyhurtbythisferociousbeating,butayoungphysicistwearingaNaziswastikainstantlyrecognizedSchrödingerand was able to get him to safety. Badly shaken, Schrödinger would leaveGermanyforEnglandandIreland.In1943, theNazisoccupiedDenmark,andBohr,whowaspart Jewish,was

targetedforextinction.HemanagedtoescapejustonestepaheadoftheGestapovia neutral Sweden and then fly to Britain, although he almost died ofsuffocationon theplanebecauseofan ill-fittingoxygenmask.Planck, a loyalpatriotwhoneverleftGermany,alsosufferedhorribly.Hissonwasarrestedfortrying to assassinate Hitler, for which he was tortured by the Nazis and laterexecuted.Einstein, although in exile, was besieged with job offers from around the

world.LeadinguniversitiesinEngland,Spain,andFrancewishedtocapturethisworld-famous figure. Previously, he had been a guest professor at PrincetonUniversity. He had spent hiswinters in Princeton and his summers in Berlin.AbrahamFlexner,representinganewinstitutetobeformedatPrinceton,largelywith a five-million-dollar fund from the Bamberger fortune, had met severaltimeswithEinsteinandapproachedhimabout thepossibilityofmoving to thenew institute.What appealed toEinsteinwas the fact thathewouldbe free totravelandfreeofteachingduties.Althoughhewasapopularlecturer,regularlybreaking up audiences with his antics and enchanting royalty with amusinganecdotes,teachingandlecturingdutiesweretakingtimeawayfromhisbelovedphysics.OnecolleaguewarnedEinsteinthatcomingpermanentlytotheUnitedStates

was like “committing suicide.”TheUnitedStates, before the sudden influxofJewish scientists fleeing Nazi Germany, was considered a quiet backwater ofscience,withalmostnoinstitutionsofhigherlearningcapableofcompetingwithEurope’s.Defendinghischoice,EinsteinwrotetoQueenElizabethofBelgium,“Princeton is a wonderful little spot…a quaint ceremonious village of punydemigodsonstilts.ByignoringcertainspecialconventionsIhavebeenabletocreateformyselfanatmosphereconducivetostudyandfreeofdistraction.”The

newsthatEinsteinhadsettledintheUnitedStateswasheardaroundtheworld.The“popeofphysics”hadleftEurope.ThenewVaticanwouldbetheInstituteforAdvancedStudyatPrinceton.WhenEinsteinwasshownhisofficeforthefirsttime,hewasaskedwhathe

needed.Besidesadeskandachair,hesaidheneededa“largewastebasket…soIcanthrowawayallmymistakes.”(TheinstitutealsoapparentlymadeanoffertoErwinSchrödinger.Butthelatter,itissaid,whowasoftenaccompaniedbyhiswife andmistress andpracticed an “openmarriage”with a long list of lovers,foundtheatmospheretoostiflingandconservative.)TheAmericanpeoplewerefascinatedbythenewarrivalinNewJersey,whoinstantlybecamethecountry’smostfamousscientist.Soon,hewasafamiliarfiguretoall.TwoEuropeans,onabet,sentaletterto“Dr.Einstein,America,”toseeifitwouldreachhim.Itdid.The1930swerehardonEinsteinpersonally. It seemedas ifhisworst fears

about his sonEduard (fondly nicknamedTedel)were confirmedwhenEduardfinally suffered a nervous breakdown in 1930 after a failed romance with anolderwoman.HewastakentotheBurghozlipsychiatrichospitalinZurich,thesame hospital where Mileva’s sister had been institutionalized. Diagnosed asschizophrenic,hewasnevertoleavethecareofaninstitutionfortherestofhislifeexceptforshortvisits.Einstein,whoalwayssuspectedthatoneofhissonsmight inheritmentalproblemsfromhiswife,blamed“graveheredity.”“Ihaveseenitcoming,slowlybutirresistibly,eversinceTedel’syouth,”hewrotesadly.In 1933, his close friend Paul Ehrenfest, who helped to stimulate the earlydevelopment of general relativity but suffered from depression, eventuallycommittedsuicide,shootingandkillinghisyoungmentallyretardedson in theprocess.Afteraprolonged,painfulillness,Elsa,whohadbeenwithEinsteinforabout

twentyyears,diedin1936.Accordingtofriends,Einsteinwas“utterlyashenandshaken.”Herdeath“severed thestrongest tiehehadwithahumanbeing.”Hetookithardbutmanagedtoslowlyrecuperate.Hewouldwrite,“Ihavegotusedextremelywelltolifehere.Ilivelikeabearinmyden….Thebearishnesshasbeenfurtherenhancedbythedeathofmywomancomrade,whowasbetterwithotherpeoplethanIam.”AfterElsa’sdeath,hewouldlivewithhissisterMaja,whohadfledtheNazis;

hisstepdaughterMargot;andhissecretary,HelenDukas.Hehadstartedthefinalphaseofhislife.Duringthe1930sand1940sheagedrapidly,andwithoutElsato constantly harp about his appearance, the dashing, charismatic figure whodazzled kings and queens in his tuxedo reverted back into the old, bohemianways of his youth.He now became thewhite-haired figure rememberedmostdearly by the public, the sage of Princeton,whowould good-humoredly greet

bothchildrenandroyaltyalike.For Einstein, however, there was no rest.While at Princeton, he faced yet

anotherchallenge,thequesttobuildanatomicbomb.Backin1905,Einsteinhadspeculated that his theory might be able to explain how a small amount ofradiumcouldglowferociouslyinthedark,itsatomsreleasinglargequantitiesofpowerwithoutapparentlimit.Infact,theamountofenergylockedinthenucleuscould easily be a hundredmillion times greater than that stored in a chemicalweapon.By1920,Einsteinhadgrasped theenormouspractical implicationsofthe energy locked in the nucleus of the atom when he wrote, “It might bepossible,anditisnotevenimprobable,thatnovelsourcesofenergyofenormouseffectivenesswillbeopenedup,butthisideahasnodirectsupportfromthefactsknown tous so far. It isverydifficult tomakeprophecies,but it iswithin therealmofthepossible.”In1921,heevenspeculatedthatatsomepointfarinthefuture, the current economy, based on coal, might eventually be replaced bynuclear energy.But he also clearly understood two enormous problems. First,this cosmic fire could be used to forge an atomic bomb, with horribleconsequences for humanity.Hewrote prophetically, “All bombardments sincetheinventionoffirearmsputtogetherwouldbeharmlesschild’splaycomparedtoitsdestructiveeffects.”Healsowrotethatanatomicbombcouldbeusedtounleash nuclear terrorism and even a nuclear war: “Assuming that it werepossibletoeffectthatimmenseenergyrelease,weshouldmerelyfindourselvesinanagecomparedtowhichourcoal-blackpresentwouldseemgolden.”Last, andmost important, he realized the enormous challenge in producing

such a weapon. In fact, he doubted that it was doable in his lifetime. Thepractical problems of taking the terrible power locked in a single atom andmagnifying it trillionsof timeswasbeyondanythingpossible in the1920s.Hewrotethatitwasasdifficult“asfiringatbirdsinthedark,inaneighborhoodthathasfewbirds.”Einstein realized that thekeymightbe tosomehowmultiply thepowerofa

single atom. If one could take the energy of an atom and then trigger thesubsequent release of energy from nearby atoms, then one might be able tomagnifythisnuclearenergy.Hehintedthatachainreactionmighthappenif“theraysreleased…areinturnabletoproducethesameeffects.”Butinthe1920s,hehadnoideahowsuchachainreactionmightbeproduced.Others,ofcourse,alsotoyed with the idea of nuclear energy, not to benefit humanity, but formalevolent reasons. InApril 1924,PaulHarteck andWilhelmGroth informedtheGermanArmyOrdinanceDepartment that“thecountry thatexploits it firstwillhaveanincalculableadvantageovertheothers.”Theproblemofreleasingthisenergyisasfollows:Thenucleusoftheatomis

positivelychargedandhencerepelsotherpositivecharges.Thus,thenucleusisprotected against any random collisions that might unlock its nearly limitlessenergy. ErnestRutherford,whose pioneeringwork led to the discovery of thenucleus of the atom, dismissed the atomic bomb, stating that “anyone whoexpects a source of power from the transformation of these atoms is talkingmoonshine.” This stalemate was broken dramatically in 1932 when JamesChadwickdiscoveredanewparticle,theneutron,apartneroftheprotoninthenucleus that is neutral in charge. If one could fire a beam of neutrons at thenucleus, then the neutron, undeterred by the electric field around the nucleus,might be able to shatter it, releasing nuclear energy. The thought occurred tophysicists:abeamoftheseneutronsmighteffortlesslysplittheatomandtriggeranatomicbomb.WhileEinsteinhaddoubtsaboutthepossibilityofanatomicbomb,keyevents

leading to nuclear fission were accelerating. In 1938, Otto Hahn and FritzStrassmannoftheKaiserWilhelmInstituteforPhysicsinBerlinelectrifiedtheworldofphysicsbysplittingtheuraniumnucleus.Theyfoundtracesofbariumafter bombarding uranium with neutrons, which indicated that the uraniumnucleus split in half, creating barium in the process. Lise Meitner, a Jewishscientist and colleagueofHahnwhohad fled theNazis, andher nephewOttoFrisch provided the missing theoretical basis to Hahn’s result. Their resultsshowed that the debris left over from the processweighed a bit less than theoriginaluraniumnucleus.Itseemedasifmasswasdisappearinginthisreaction.The splitting of the uranium atom also released 200million electron volts ofenergy,whichapparentlyappearedoutofnowhere.Wheredidthemissingmassgo, andwhere did this energymysteriously come from?Meitner realized thatEinstein’sequationE=mc2heldthekeytothispuzzle.Ifonetookthemissingmassandmultiplieditbyc2,thenonefound200millionelectronvolts,preciselyaccording toEinstein’s theory.Bohr,when toldof this startlingverificationofEinstein’s equation, immediately grasped the significance of this result. Heslappedhisforeheadandexclaimed,“Oh,whatfoolsweallhavebeen!”InMarchof1939,EinsteintoldtheNewYorkTimesthattheresultssofar“do

not justify the assumption of a practical utilization of the atomic energiesreleasedintheprocess….However,thereisnosinglephysicistwithsoulsopoorwho would allow this to affect his interest in this highly important subject.”Ironically,thatverysamemonth,EnricoFermiandFrédéricJoliot-Curie(MarieCurie’sson-in-law)discoveredthattwoneutronscanbereleasedbythesplittingoftheuraniumnucleus.Thiswasastaggeringresult.If thesetwoneutronscangoontosplittwootheruraniumnuclei,thenthiswouldresultinfourneutrons,

then eight, then sixteen, then thirty-two, ad infinitum, until the unimaginablepowerofthenuclearforcewasreleasedinachainreaction.Withinafractionofa second, the splitting of a single uranium atom could trigger the splitting oftrillionsupontrillionsofotheruraniumatoms,releasingunimaginablequantitiesof nuclear energy. Fermi, looking out his window in Columbia University,musedgrimly thatasingleatomicbombcoulddestroyall thathecouldseeofNewYorkCity.Theracewason.Alarmedat the rapidspeedofevents,Szilardwasworried

thattheGermans,whowereleadersinatomicphysics,wouldbethefirsttobuildanatomicbomb. In1939,SzilardandEugeneWignerdrove toLongIsland tovisitEinsteintosignaletterthatwouldbegiventoPresidentRoosevelt.Thefateful letter,oneof themost important inworldhistory,began,“Some

recentworkbyE.FermiandL.Szilard,whichhasbeencommunicatedtomeinmanuscript, leadsme toexpect that theelementuraniummaybe turned intoanewand important sourceof energy in the immediate future.”Ominously, theletter noted that Hitler had invaded Czechoslovakia and had sealed off theBohemianpitchblendemines,arichsourceofuraniumore.Andthentheletterwarned,“Asinglebombofthistype,carriedbyboatorexplodedinaport,mightwell destroy thewhole portwith some of the surrounding territory.However,such bombsmight verywell prove to be too heavy for transportation by air.”Alexander Sachs, a Roosevelt advisor, was given the letter to pass onto thepresident.WhenSachsaskedRooseveltifheunderstoodtheextremegravityofthe letter,Roosevelt replied,“Alex.Whatyouareafter is tosee that theNazisdon’tblowusup.”HeturnedtoGeneralE.M.Watsonandsaid,“Thisrequiresaction.”Only six thousanddollarswasapproved for thewholeyear’s researchon uranium.However, interest in the atomic bombwas given a sudden boostwhen the secret Frisch-Peierls report reachedWashington in the fall of 1941.British scientists,working independently, confirmed all the details outlinedbyEinstein, and on December 6, 1941, the Manhattan Engineering Project wassecretlysetup.UnderthedirectionofJ.RobertOppenheimer,whohadworkedonEinstein’s

theory of black holes, hundreds of the world’s top scientists were secretlycontactedandthenshippedouttoLosAlamosinthedesertofNewMexico.Ateverymajoruniversity,scientistslikeHansBethe,EnricoFermi,EdwardTeller,and Eugene Wigner quietly left after receiving a tap on the shoulder. (Noteveryonewaspleasedbytheintenseinterestintheatomicbomb.LiseMeitner,whosework helped to trigger the project, staunchly refused to be part of anyworkonthebomb.ShewastheonlyprominentAlliednuclearscientisttorefusethe call to join the group at Los Alamos. “I will have nothing to do with a

bomb!” she stated flatly. Years later, when Hollywood scriptwriters tried toglamorizeherinthefilmTheBeginningoftheEnd,asthewomanwhobravelysmuggledouttheblueprintforthebombasshefledNaziGermany,shereplied,“I would rather walk naked down Broadway” than be part of this fanciful,scurrilouseffort.)Einsteinwas aware that all his close colleagues at Princetonwere suddenly

disappearing, leaving amysteriousmailing address in Santa Fe,NewMexico.Einsteinhimself,though,wasnevergiventhetapontheshoulderandsatouttheentirewaratPrinceton.Thereasonforthishasbeenrevealedindeclassifiedwardocuments.VannevarBush, the chief of theOffice ofScientificResearch andDevelopmentandRoosevelt’s trustedadvisor,wrote, “Iwishverymuch that Icouldplacethewholethingbeforehim[Einstein]…butthisisutterlyimpossibleinviewoftheattitudeofpeoplehereinWashingtonwhohavestudiedhiswholehistory.”FBIandarmyintelligenceconcludedthatEinsteincouldnotbetrusted:“In view of his radical background, this office would not recommend theemploymentofDr.Einstein,onmattersofasecretnature,withoutaverycarefulinvestigation,asitseemsunlikelythatamanofhisbackgroundcould,insuchashort time, become a loyal American citizen.” Apparently, the FBI did notrealizethatEinsteinwasalreadywellawareoftheprojectandinfacthadhelpedtosetitintomotioninthefirstplace.Einstein’sFBI file, recentlydeclassified, runs1,427pages. J.EdgarHoover

had targetedEinstein as being either aCommunist spy or a dupe at best. Theagency carefully screened every piece of gossip about him and filed it away.Ironically,theFBIwascuriouslynegligentinconfrontingEinsteinhimself,asifthey feared him. Instead, agents preferred to interview and harass thosesurroundinghim.Asaresult,theFBIbecamearepositoryofhundredsoflettersfrom every crank and paranoid. In particular, they filed away reports thatEinsteinwasworkingonsomekindofdeathray.InMay1943,anavylieutenantcalledonEinstein,askinghimifhewouldbewilling toworkonweaponsandhighexplosivesfortheU.S.Navy.“Hefeltverybadaboutbeingneglected.Hehadnotbeenapproachedbyanyonetodoanywarwork,”wrotethelieutenant.Einstein, always quick with a quip, remarked that he was now in the navywithouthavingtogetahaircut.TheintenseAlliedefforttobuildanatomicbombwasstimulatedbyfearsof

theGermanbomb.Inreality,theGermanwareffortwasbadlyunderstaffedandunderfunded.WernerHeisenberg,German’sgreatestquantumphysicist,wasputinchargeof a teamof scientists toworkon theGermanproject. In the fallof1942,whenGermanscientistsrealizedthatitwouldtakeanotherthreeyearsofstrenuouseffort toproduceanatomicbomb,AlbertSpeer, theNaziarmaments

minister,decidedtotemporarilyshelvetheproject.Speermadeastrategicerror,assuming that Germany would win the war in three years, making the bombunnecessary. Nevertheless, he continued funding research on nuclear-poweredsubmarines.Heisenbergwashamperedbyotherproblems.Hitlerdeclared thatordinance

development would proceed only on weapons that promised results in sixmonths, an impossible deadline. In addition to a lack of funding, Germanlaboratories were under attack by Allied forces. In 1942, a commando squadsuccessfullyblewupHeisenberg’sheavy-waterfactoryinVemork,Norway.IncontrasttoFermi’sdecisiontobuildacarbon-basedreactor,theGermanschoseto build a heavy-water reactor that could use natural uranium, which wasplentiful, rather than the extremely rare uranium-235. In 1943, the Allies hitBerlinhardwithsaturationbombing,forcingHeisenbergtomovehislaboratory.TheKaiserWilhelm Institute for Physicswas evacuated toHechingen, in thehills south of Stuttgart. Heisenberg had to build Germany’s reactor in a rockcellar in nearby Haigerloch. Under intense pressure and bombing, they neversucceededinsustainingachainreaction.Meanwhile, physicists in the Manhattan Project were rushing to process

enough plutonium and uranium for four atomic bombs. They were doingcalculations rightup to the timeof the fatefuldetonation inAlamogordo,NewMexico.The firstbomb,basedonplutonium-239,wasdetonated inJuly1945.AfterthedecisiveAlliedvictoryovertheNazis,manyphysiciststhoughtthatthebombwouldbeunnecessaryagainsttheremainingenemy,Japan.Somebelievedthat a demonstration atomic bomb should be detonated on a deserted island,witnessed by a delegation of Japanese officials, to warn the Japanese thatsurrenderwasinevitable.OthersevendraftedalettertoPresidentHarryTrumanaskinghimnottodropthebombonJapan.Unfortunately,thisletterwasneverdelivered.One scientist, JosephRotblatt, even resigned from the atomicbombproject, stating that hisworkwas finished and that the bomb should never beusedagainstJapan.(HewouldlaterwintheNobelPrizeforpeace.)Nevertheless, thedecisionwasmadetodropnotone,but twoatomicbombs

on Japan in August 1945. Einstein was vacationing at Saranac Lake in NewYork.ThatweekHelenDukasheardthenewsontheradio.Sherecalledthatthereport“saidanewkindofbombhasbeendroppedonJapan.AndthenIknewwhat it was because I knew about the Szilard thing in a vague way…. AsProfessorEinsteincamedowntotea,Itoldhim,andhesaid,‘Oh,Weh’[OhmyGod].”In1946,Einsteinmade thecoverofTime.Ominously, this time therewasa

nuclearfireballeruptingbehindhim.Theworldsuddenlyrealizedthat thenext

war,WorldWar III,might be foughtwith atomicbombs.But,Einsteinnoted,becausenuclearweaponsmightsendcivilizationbackthousandsofyears,WorldWarIVwouldbefoughtwithrocks.Thatyear,EinsteinbecamechairmanoftheEmergencyCommitteeofAtomicScientists,perhapsthefirstmajoranti-nuclearorganization,anduseditasaplatformtoargueagainstthecontinuedbuildingofnuclear weapons—and to advocate one of his cherished causes, worldgovernment.Meanwhile,amidst thestormunleashedby theatomicandhydrogenbombs,

Einsteinmaintainedhispeaceandsanitybyreturningstubbornlytohisphysics.In the 1940s, pioneering work was still being done in the areas he helped tofound,includingcosmologyandtheunifiedfieldtheory.Thiswastobehislastandfinalattemptto“readthemindofGod.”After the war, Schrödinger and Einstein maintained a lively transatlantic

correspondence.Almostalone,thesetwofathersofthequantumtheoryresistedthetideofquantummechanicsandfocusedonthequestforunification.In1946,Schrödingerconfessed toEinstein,“Youareafterbiggame.Youareona lionhunt, while I am speaking of rabbits.” Encouraged by Einstein, Schrödingercontinued his hot pursuit of a particular type of unified field theory, called“affine field theory.” Soon, Schrödinger completed his own theory, whichconvincedhimthathefinallyaccomplishedwhatEinsteinhadfailedtoachieve,the unification of light and gravity. He marveled that his new theory was a“miracle,”a“totallyunhopedforgiftfromGod.”Working in Ireland, Schrödinger had felt isolated from the mainstream of

physics,being reduced toacollegeadministratorandahas-been.NowhewasconvincedthathisnewtheorymightwinhimasecondNobelPrize.Hurriedly,hecalledamajorpressconference.Ireland’sprimeminister,EamonDeValera,andothers showedup to listen tohispresentation.Whena reporteraskedhimhowconfidenthewasabouthistheory,hesaid,“IbelieveIamright.Ishalllookanawfulfool if Iamwrong.”However,EinsteinquicklysawthatSchrödingerhad pursued a theory that he himself had discarded years earlier.As physicistFreemanDysonwrote,thetrailleadingtotheunifiedfieldtheoryislitteredwiththecorpsesoffailedattempts.Undaunted, Einstein kept working on the unified field theory, largely in

isolation from the rest of the physics community. Lacking a guiding physicalprinciple, he would try to find beauty and elegance in his equations. AsmathematicianG.H.Hardyoncesaid,“Mathematicalpatternslikethoseofthepaintersor thepoetsmustbebeautiful.The ideas, like thecolorsor thewordsmust fit together in a harmonious way. Beauty is the first test. There is nopermanent place for ugly mathematics.” But lacking something like an

equivalence principle for the unified field theory, Einstein was left without aguidingstar.Helamentedthefactthatotherphysicistsdidnotseetheworldashedid,butheneverlostanysleepoverthis.Hewouldwrite,“Ihavebecomealonelyoldfellow.Akindofpatriarchalfigurewhoisknownchieflybecausehedoesnotwearsocksandisdisplayedonvariousoccasionsasanoddity.ButinmyworkIammorefanaticalthaneverandIreallyentertainthehopethatIhavesolvedmyold problemsof the unity of the physical field. It is, however, likebeinginanairshipinwhichonecancruisearoundinthecloudsbutcannotseeclearlyhowonecanreturntoreality,i.e.toearth.”Einstein realized that byworking on his unified field theory rather than the

quantum theory, he was isolated from the main avenues of research at theinstitute. “I must seem like an ostrich who forever buries its head in therelativistic sand in order not to face the evil quanta,” he lamented. Over theyears,otherphysicistswouldwhisper thathewasover thehill andbehind thetimes,butthisdidnotbotherhim.“Iamgenerallyregardedasasortofpetrifiedobject,renderedblindanddeafbytheyears.Ifindthisrolenottoodistasteful,asitcorrespondsverywellwithmytemperament,”hewrote.In 1949, on his seventieth birthday, a special celebration was held in

Einstein’shonorattheinstitute.Scoresofphysicistscametopraisethegreatestscientistoftheirtimeandcontributearticlesforabookinhishonor.However,fromthetoneofsomespeakersandinterviewswiththepress,itbecameapparentthatsomeofthemtookEinsteintotaskforhispositiononthequantumtheory.Einsteinpartisanswerenothappywiththis,butEinsteintookitgood-naturedly.Afamilyfriend,ThomasBucky,notedthat“OppenheimermadefunofEinsteinin a magazine article with such statements as, ‘He’s old. Nobody pays anyattentiontohimanymore.’Weweremadderthanallhellaboutit.ButEinsteinwasnotmadatall.Hejustdidn’tbelieveitandlaterOppenheimerdeniedhehadsaidit.”ThatwasEinstein’smanner,totakehiscriticswithagrainofsalt.Whenthe

bookinhishonorcameout,hewroteingoodhumor,“Thisisnotajubileebookforme,butanimpeachment.”Hewasaseasonedenoughscientisttoknowthatnewideaswerehardtocomeby,andthathewasnotproducingideaslikehedidinhisyouth.Ashewouldwrite,“Anythingreallynewisinventedonlyinone’syouth.Lateronebecomesmoreexperienced,morefamous—andmorestupid.”What kept him going, however, were the clues he saw everywhere that

unification was one of the grand schemes of the universe. He would write,“Nature shows us only the tail of the lion. But I do not doubt that the lionbelongs to it even though he cannot at once reveal himself because of hisenormous size.”Everyday,whenhewokeup, hewould askhimself a simple

question: IfhewereGod,howwouldhecreate theuniverse?In fact,givenalltheconstraintsnecessarytocreateauniverse,heaskedhimselfanotherquestion:DidGodhaveanychoice?Ashegazedattheuniverse,everythinghesawtoldhim thatunificationwas thegreatest theme innature, thatGodcouldnothavecreated a universe that made gravity, electricity, and magnetism as separateentities.Whathelacked,asheknew,wasaguidingprinciple,aphysicalpicturethatwouldlightthewaytotheunifiedfieldtheory.Nonecame.Withspecialrelativitythepicturewasasixteen-year-oldyouthracingaftera

lightbeam.Withgeneralrelativity,itwasamanleaningbackinhischair,aboutto fall, or marbles rolling on curved space. However, with the unified fieldtheory,hehadnosuchguidance.Einsteinwasfamousforhisstatement,“SubtleistheLord,butmaliciousheisnot.”Afterhestruggledforsomanydecadesonthe problemof unification, he admitted to his assistantValentineBargman, “Ihavesecondthoughts.MaybeGodismalicious.”Although the quest for a unified field theory was known to be the hardest

probleminallofphysics,itwasalsothemostglamorousandseducedlegionsofphysicists. It is ironic, for example, that Wolfgang Pauli, one of Einstein’sseverest critics of the unified field theory, would eventually catch the bughimself. In the late 1950s, both Heisenberg and Pauli were increasinglyinterestedinaversionof theunifiedfield theorythat theyclaimedcouldsolvetheproblemsthatstumpedEinsteinfor thirtyyears. Infact,writesPais,“From1954 to theendofhis life,Heisenberg (d.1976)was immersed in attempts atderivingallofparticlephysicsfromafundamentalnon-linearwaveequation.”In1958, Pauli visited Columbia University and gave a presentation on theHeisenberg-Pauliversionof theunified field theory.Theaudience,needless tosay,was skeptical.NielsBohr,whowas in the audience, finally stoodup andsaid,“Weinthebackareconvincedyourtheoryiscrazy.Butwhatdividesusiswhetheryourtheoryiscrazyenough.”Physicist Jeremy Bernstein, also in the audience, remarked, “It was an

uncannyencounterof twogiantsofmodernphysics. Ikeptwonderingwhat inthe world a non-physicist visitor would have made of it.” Eventually, Paulibecamedisillusionedwiththetheory,believingithadtoomanyflaws.Whenhiscollaborator insisted on plunging ahead with the theory, Pauli wrote toHeisenberg and enclosed a blank sheet of paper, stating that if his theorywasreally the unified field theory, then this blank sheet of paper was a work byTitian.Althoughprogressintheunifiedfieldtheorywasslowandpainful,therewere

plenty of other interesting breakthroughs that kept Einstein busy. One of thestrangestwastimemachines.

ToNewton,timewaslikeanarrow.Oncefired,itunerringlyflewinastraightline,neverdeviatingfromitspath.Onesecondontheearthwasonesecondinouterspace.Timewasabsoluteandbeatuniformlythroughtheentireuniverseatthesamerate.Eventscould takeplacesimultaneously throughout theuniverse.However,Einsteinintroducedtheconceptofrelativetime,soonesecondontheearth was not one second on the moon. Time was like Old Man River,meandering its way past planets and stars, slowing down as it went byneighboringheavenlybodies.Thequestion that themathematicianKurtGödelnowraisedwas,cantheriveroftimehavewhirlpoolsandturnbackonitself?Orcan it fork into two rivers,creatingaparalleluniverse?Einsteinwas forced toconfront thisquestion in1949whenGödel,Einstein’sneighborat the instituteand arguably the greatest mathematical logician of the century, showed thatEinstein’sequationsallowedfor time travel.Gödelstartedwithauniverse thatwas filledwithagasand rotating. Ifonestartedoff ina rocket shipandwentaroundtheentireuniverse,thenonemightarriveontheearthbeforeoneleft!Inotherwords, time travelwould be a natural phenomenon inGödel’s universe,whereonewouldroutinelytravelbackintimeduringatriparoundtheuniverse.This shook Einstein. So far, every time people tried to find solutions to

Einstein’s equations, they found solutions that seemed to fit the data. TheperihelionofMercury,theredshift,thebendingofstarlight,thegravityofastar,andsoon,allfitexperimentaldataverynicely.Now,hisequationsweregivingsolutionsthatchallengedallourbeliefsabouttime.Iftimetravelwereroutinelypossible,thenhistorycouldneverbewritten.Thepast,likeshiftingsands,couldbechangedanytimesomeoneenteredhisorhertimemachine.Worse,onemightdestroytheuniverseitselfbycreatingatimeparadox.Whatifyouwentbackintimeandshotyourparentsbeforeyouwereborn?Thiswasproblematic,becausehowcouldyoubeborninthefirstplaceifyoujustkilledyourparents?Timemachinesviolatedcausality,whichwasacherishedprincipleofphysics.

Einsteinwas not happywith the quantum theory precisely because it replacedcausality with probabilities. Now, Gödel was eliminating causality entirely!After much consideration, Einstein finally dismissed Gödel’s solution bypointingoutthatitdidnotfittheobservationaldata:theuniversewasexpanding,notrotating,sotimetravel,at leastforthetimebeing,couldbedismissed.Butthisleftopenthepossibilitythatiftheuniverserotatedinsteadofexpanded,thentime travel would be routine. It would, however, take another five decadesbefore the concept of time travel would be revived into a major field ofinvestigation.The1940swasalsoaturbulenttimeincosmology.GeorgeGamow,whowas

Einstein’s liaison with the U.S. Navy during the war, was less interested in

designingexplosivesthanaskingquestionsaboutthebiggestexplosionofall,thebig bang. Gamow would ask himself several questions that would turncosmologyupsidedown.Hetookthebigbangtheorytoits logicalconclusion.Heshrewdlyspeculatedthatiftheuniversewasindeedborninafieryexplosion,thenitshouldbepossibletodetecttheleftoverheatfromtheearlyfireball.Thereshouldbean“echoofcreation” from thebigbang itself.Heused theworkofBoltzmann and Planck, who showed that the color of a hot object shouldcorrelate with its temperature since both are different forms of energy. Forexample, ifanobject is redhot, itmeans that its temperature isapproximately3,000degreesCelsius.Ifanobjectisyellowhot(likeoursun),thenitisroughly6,000 degrees Celsius (which is the temperature of the surface of our sun).Similarly, our own bodies are warm, so we can calculate the “color” of ourbodies, which correlates to infrared radiation. (Army night-vision goggles areeffective because they detect the infrared radiation emitted from our warmbodies.)ArguingthattheBigBanghappenedbillionsofyearsago,twomembersof Gamow’s group, Robert Herman and Ralph Alpher, calculated as early as1948 that the afterglow of the Big Bang should be 5 degrees above absolutezero,whichisremarkablyclosetothecorrectvalue.Thisradiationcorrespondsto microwave radiation. Therefore, the “color of creation” is microwaveradiation.(Thismicrowaveradiation,whichwaseventuallyfounddecadeslaterand determined to correspond to 2.7 degrees above absolute zero, wouldcompletelyrevolutionizethefieldofcosmology.)AlthoughhewasrelativelyisolatedatPrinceton,Einsteinlivedtoseetheday

whenhistheoryofgeneralrelativitywasspawningrichnewavenuesofresearchin cosmology, black holes, gravity waves, and other areas. However, the lastyears of his lifewere also filledwith sorrows. In1948, he receivedword thatMileva,afteralong,hardlifecaringfortheirmentallyillson,hadpassedaway,apparentlyofastrokeduringatantrumofEduard’s.(Later,85,000francsincashwas found stuffed in her bed, apparently the lastmoney left from her Zurichapartments. Itwasused tohelppay forEduard’s long-termcare.) In1951,hisdearsisterMajadied.In1952,ChaimWeizmann,themanwhohadorganizedEinstein’striumphant

tour of America in 1921, passed away after being president of Israel.Unexpectedly, Israel’s premier, David Ben-Gurion, then offered Einstein thepresidencyofIsrael.Althoughitwasquiteanhonor,hehadtodecline.In1955,EinsteinreceivedwordthatMicheleBesso,whohadhelpedEinstein

refinehisideasonspecialrelativity,haddied.InalettertoBesso’sson,Einsteinwrotemovingly,“WhatIadmiredmostaboutMichelewasthefactthathewasable to live so many years with one woman, not only in peace but also in

constantunity,somethingIhavelamentablyfailedattwice….Soinquittingthisstrange world he has once again preceded me by a little. That doesn’t meananything.For thoseofuswhobelieve inphysics, thisseparationbetweenpast,present,andfutureisonlyanillusion,howevertenacious.”That year, with his health failing, he said, “It is tasteless to prolong life

artificially.Ihavedonemyshare;itistimetogo.Iwilldoitelegantly.”Einsteinfinally died on April 18, 1955, of a burst aneurysm. After his death, thecartoonist Herblock published in the Washington Post a moving cartoondepictingtheearth,asseenfromouterspace,withalargesignthatread,“AlbertEinstein livedhere.”Thatnight,newspapersaroundtheworldflashedover thewireservicesaphotographofEinstein’sdesk.Onitwasthemanuscriptforhisgreatestunfinishedtheory,theunifiedfieldtheory.

CHAPTER9

Einstein’sPropheticLegacyMost biographers uniformly ignore the last thirty years of Einstein’s life,considering it almost an embarrassment unworthy of a genius, a stain on hisotherwise sterling history. However, scientific developments in the last fewdecadeshavegivenusanentirelynewlookintoEinstein’slegacy.Becausehisworkwassofundamental,reshapingtheveryfoundationsofhumanknowledge,his impact continues to reverberate throughout physics. Many of the seedsplanted by Einstein are now germinating in the twenty-first century, mainlybecauseourinstrumentssuchasspacetelescopes,X-rayspaceobservatories,andlasers are now powerful and sensitive enough to verify a variety of hispredictionsmadedecadesago.Infact,crumbsthathavetumbledoffEinstein’splatearenowwinningNobel

Prizes for other scientists. Furthermore, with the rise of superstring theory,Einstein’sconceptofunificationofall forces,once thesubjectofderisionandderogatorycomments, isnowassumingcenterstagein theworldof theoreticalphysics. This chapter discusses new developments in three areas whereEinstein’s enduring legacy continues to dominate the world of physics: thequantumtheory,generalrelativityandcosmology,andtheunifiedfieldtheory.WhenEinstein firstwrotehispaperonBose-Einsteincondensation in1924,

hedidnotbelieve that this curiousphenomenonwouldbediscoveredanytimesoon.Onewouldhavetocoolmaterialsdowntonearabsolutezerobeforeallthequantumstatescouldcollapseintoagiantsuperatom.In 1995, Eric A. Cornell from the National Institute of Standards and

Technology and Carl E.Weiman of the University of Colorado did just that,producingapureBose-Einsteincondensateof2,000rubidiumatomsattwenty-billionths of a degree above absolute zero. In addition,Wolfgang Ketterle ofMIT independently produced Bose-Einstein condensates with enough sodiumatoms to do important experiments on them, such as proving that these atomsdisplayedinterferencepatternsconsistentwithatomsthatwerecoordinatedwitheachother.Inotherwords, theyactedlikethesuperatompredictedbyEinsteinoverseventyyearsearlier.

Since the initial announcement, discoveries in this fast-moving field havecome rapidly. In1997,Ketterle andhis colleagues atMITcreated theworld’sfirst “atom laser” using Bose-Einstein condensates.What gives laser light itsmarvelousproperties is the fact that thephotonsmarch inunisonand lockstepwitheachother,whileordinarylightischaoticandincoherent.Sincematteralsohaswavelikeproperties,physicistsspeculatedthatbeamsofatomscouldalsobemade to “lase” as well, but the lack of Bose-Einstein condensates hinderedprogress in this direction. These physicists accomplished their feat by firstcooling down a collection of atoms until they condensed. Then they hit thecondensatewithalaserbeam,whichturnedtheatomsintoasynchronizedbeam.In 2001, Cornell, Weiman, and Ketterle were awarded the Nobel Prize in

physics.TheNobelPrizecommitteecited them“for theachievementofBose-Einsteincondensationindilutegasesofalkaliatoms,andforearlyfundamentalstudiesofthepropertiesofthecondensates.”ThepracticalapplicationsofBose-Einsteincondensatesarejustbeingrealized.Thesebeamsofatomiclaserscouldprovevaluable in the futurewhenapplied tonanotechnology.Theymayallowthemanipulationofindividualatomsandthecreationoflayersofatomicfilmsforsemiconductorsincomputersofthefuture.In addition to atomic lasers, some physicists have speculated that quantum

computers (computers that compute on individual atoms) could be based onBose-Einstein condensates, which could eventually replace silicon-basedcomputers.Othershavespeculatedthatdarkmatter,inpart,couldbecomposedofBose-Einsteincondensates.Ifso,thenthisobscurestateofmattercouldmakeupmostoftheuniverse.Einstein’s contributionshavealso forcedquantumphysicists to rethink their

devotion to the original Copenhagen interpretation of the theory. Back in the1930s and 1940s,when quantum physicistswere snickering behind Einstein’sback,itwaseasytoignorethisgiantofphysicsbecausesomanydiscoveriesinquantumphysicswerebeingmadealmostdaily.Whohad time tocontemplatethe foundations of the quantum theory when physicists were scrambling tocollectNobelPrizes likeapplespickedoffa tree?Hundredsofcalculationsonthe properties ofmetals, semiconductors, liquids, crystals, and othermaterialscouldnowbeperformed,eachofwhichmightcreateentireindustries.Therewassimply no time to spare.As a consequence, physicists for decades simply gotused to theCopenhagenschool,brushing theunanswereddeeperphilosophicalquestions under the rug. The Bohr-Einstein debates were forgotten. However,nowthatmanyofthe“easy”questionsaboutmatterhavebeenpickedclean,themuch more difficult questions raised by Einstein are still unanswered. Inparticular,scoresofinternationalconferencesaretakingplacearoundtheworld

as physicists re-examine the cat problem mentioned in chapter 7. Now thatexperimentalistscanmanipulate individualatoms, thecatproblemisno longerjust an academic question. In fact, the ultimate fate of computer technology,which accounts for a large fraction of theworld’swealth,may depend on itsresolutionsincecomputersofthefuturemayusetransistorsmadeofindividualatoms.Ofall thealternatives, theCopenhagenschoolofBohr isnowrecognized to

have the leastattractiveanswer to thecatproblem,although therehasbeennoexperimental deviation from Bohr’s original interpretation. The Copenhagenschool postulates that there is a “wall” that separates the commonsense,macroscopicworldoftrees,mountains,andpeoplethatweseearoundus,fromthemysterious,nonintuitivemicroscopicworldofthequantumandwaves.Inthemicroscopicworld,subatomicparticlesexistinanetherstatebetweenexistenceandnonexistence.However,weliveontheothersideofthewall,whereallwavefunctionshavecollapsed, soourmacroscopicuniverseseemsdefiniteandwelldefined. In other words, there is a wall separating the observer from theobserved.Somephysicists,includingNobellaureateEugeneWigner,evenwentfurther.

Thekeyelementofobserving,hestressed,isconsciousness.Ittakesaconsciousobserver tomakeanobservationanddetermine the realityof thecat.Butwhoobserves the observer? The observer must also have another observer (called“Wigner’s friend”) to determine that the observer is alive.But this implies aninfinitechainofobservers,eachoneobservingtheother,eachonedeterminingthatthepreviousobserverisaliveandwell.ToWigner,thismeantthatperhapsthere was a cosmic consciousness that determined the nature of the universeitself!Ashe said, “Thevery studyof the externalworld led to the conclusionthatthecontentoftheconsciousnessistheultimatereality.”Somehavearguedtherefore that this proves the existence of God, some sort of cosmicconsciousness, or that the universe itself was somehow conscious. As Planckonce said, “Science cannot solve the ultimate mystery of Nature. And it isbecauseinthelastanalysisweourselvesarepartofthemysterywearetryingtosolve.”Over the decades, other interpretations have been proposed. In 1957,Hugh

Everett,thenagraduatestudentofphysicistJohnWheeler,proposedperhapsthemostradicalsolutiontothecatproblem,the“manyworlds”theory,statingthatall possible universes exist simultaneously. The cat could indeed be dead andalivesimultaneously,becausetheuniverseitselfhassplitintotwouniverses.Theimplicationsofthisideaarequiteunsettling,becauseitmeansthattheuniverseis constantly bifurcating at each quantum instant, spinning off into infinite

numbers of quantum universes.Wheeler himself, originally enthusiastic abouthis student’s approach, later abandoned it, stating that it carried too much“metaphysical baggage.” For example, imagine a cosmic ray that penetratesWinston Churchill’s mother’s womb, triggering a miscarriage. Thus, onequantumevent separates us froma universe inwhichChurchill never lived torallythepeopleofEnglandandtheworldagainstthemurderousforcesofAdolfHitler. In that parallel universe, perhaps the Nazis won World War II andenslavedmuchoftheworld.Orimagineaworldwhereasolarwind, triggeredbyquantumevents,pushedacometormeteorfromitspath65millionyearsago,so it never hit the Yucatan Peninsula of Mexico and never wiped out thedinosaurs. In that parallel universe, humans never emerged and Manhattan,whereIamnowliving,ispopulatedbyrampagingdinosaurs.Themindissentspinningcontemplatingallpossibleuniverses.Afterdecades

of futile arguing over various interpretations of the quantum theory, in 1965JohnBell,aphysicistatthenuclearlaboratoryatCERNinGeneva,Switzerland,analyzed an experiment that would decisively prove or disprove Einstein’scriticismofthequantumtheory.Thiswouldbetheacidtest.Hewassympatheticto the deep philosophical questions raised by Einstein decades earlier, andproposed a theorem that would finally settle the question. (Bell’s theorem isbasedonre-examiningavariationoftheoldEPRexperimentandanalyzingthecorrelation between the two particlesmoving in opposite directions.)The firstcredibleexperimentwasperformedin1983byAlainAspectattheUniversityofParis,andtheresultsconfirmedthequantummechanicalviewpoint.Einsteinwaswrongabouthiscriticismofthequantumtheory.ButifEinstein’scriticismofthequantumtheorycouldnowberuledout,then

which of the various quantummechanical schools is correct?Most physiciststodaybelieve that theCopenhagen school iswoefully incomplete.Bohr’swallseparating the microscopic world from the macroscopic world does not seemvalid in today’s world, when we can now manipulate individual atoms.“Scanning tunneling microscopes” can in fact displace individual atoms andhavebeenusedtospellout“IBM”andcreateaworkingabacusmadeofatoms.Inaddition,awholenewfieldoftechnology,called“nanotechnology,”hasbeencreatedbasedonthemanipulationofatoms.ExperimentslikeSchrödinger’scatexperimentcannowbeperformedonindividualatoms.Despitethis,thereisstillnosolutiontothecatproblemthatissatisfactoryto

allphysicists.AlmosteightyyearssinceBohrandEinsteinclashedattheSolvayConference, however, some leading physicists, including several Nobellaureates, have converged on the idea of “decoherence” to resolve the catproblem.Decoherencestartswiththefactthatthewavefunctionofacatisquite

complicatedbecause it contains somethingon the order of 1025 atoms, a trulyastronomicalnumber.Hencetheinterferencebetweenthelivecat’swaveandthedead cat’swave is quite intense. Thismeans that the twowave functions cancoexistsimultaneouslyinthesamespacebutcanneverinfluenceeachother.Thetwowavefunctionshave“decohered”fromeachotherandnolongersenseeachother’s presence. In one version of decoherence, wave functions never“collapse,” as claimed byBohr. They simply separate and, for all intents andpurposes,neverinteractagain.Nobel laureate Steven Weinberg compares this to listening to a radio. By

turningadial,wecantunesuccessivelytomanyradiostations.Eachfrequencyhasdecoheredfromtheothers,sothereisnointerferencebetweenstations.Ourroom is simultaneously filled with signals from all radio stations, each oneyieldinganentireworldofinformation,yettheydonotinteractwitheachother.Andourradiotunesintoonlyoneatatime.Decoherencesoundsattractive,since itmeans thatordinarywavetheorycan

beusedtoresolvetheproblemofthecatwithoutresortingtothe“collapse”ofthewave function. In this picture,waves never collapse.However, the logicalconclusions are disturbing. In the final analysis, decoherence implies a “manyworlds”interpretation.Butinsteadofradiostationsthatdonotinterfere,nowwehaveentireuniverses thatdonot interact. Itmay seemstrange,but thismeansthat sitting in the very roomwhere you are reading this book, there exist thewave function of parallel worlds where the Nazis wonWorldWar II, wherepeople speak in strange tongues, where dinosaurs battle in your living room,wherealiencreatureswalktheearth,orwheretheearthneverexistedinthefirstplace.Our“radio”istunedonlytothefamiliarworldwelivein,butwithinthisroomthereexistother“radiostations”whereinsane,bizarreworldscoexistwithours.Wecannot interactwith thesedinosaurs,monsters,andalienswalking inour living rooms because we live on a different “radio” frequency and havedecoheredfromthem.AsNobel laureateRichardFeynmanhassaid,“I thinkIcansafelysaythatnobodyunderstandsquantummechanics.”While Einstein’s critique of the quantum theory helped to sharpen its

developmentbutmaynothavebroughtforthawhollysatisfactorysolutiontoitsparadoxes, his ideas have been vindicated elsewhere, most spectacularly ingeneral relativity. In an era of atomic clocks, lasers, and supercomputers,scientistsaremountingthekindofhigh-precisiontestsofgeneralrelativitythatEinsteincouldonlydreamabout.In1959,forexample,RobertV.PoundandG.A.RebkaofHarvardfinallyconfirmedEinstein’spredictionofgravitationalredshiftinthelaboratory,thatis,thatclocksbeatatdifferentratesinagravitationalfield. They took radioactive cobalt and shot radiation from the basement of

LymanLaboratoryatHarvardtotheroof,74feetabove.Usinganextremelyfinemeasuringdevice(whichusedtheMossbauereffect),theyshowedthatphotonslostenergy(hencewerereducedinfrequency)as theymadethe journeyto thetopof the laboratory. In1977, astronomer JesseGreensteinandhis colleaguesanalyzed the beating of time in a dozenwhite dwarf stars. As expected, theyconfirmedthattimesloweddowninalargegravitationalfield.Thesolareclipseexperimenthasalsobeenredonewithextremeprecisionona

number of occasions. In 1970, astronomers pinpointed the location of twoextremelydistantquasars,3C279and3C273.ThelightfromthesequasarsbentaspredictedbyEinstein’stheory.The introductionof atomic clocks alsohas revolutionized theway inwhich

precision tests can be performed. In 1971, atomic clockswere placed on a jetplane, which was flown both East to West and West to East. These atomicclocks, in turn,were thencomparedwithatomicclocks thatwerestationaryattheNavalObservatoryinWashington,D.C.Byanalyzingtheatomicclocksonthe jets traveling at different velocities (but with constant altitude), scientistscould verify special relativity. Then, by analyzing jets traveling at the samespeedbutdifferent altitude, theycould test thepredictionofgeneral relativity.On both occasions, the results verified Einstein’s predictions, withinexperimentalerror.The launching of space satellites has also revolutionized the way in which

general relativity can be tested. The Hipparcos satellite, launched by theEuropeanSpaceAgency in1989,spent fouryearscalculating thedeflectionofstarlight by the sun, even analyzing stars that are 1,500 times fainter than thestarsintheBigDipper.Indeepspace,thereisnonecessitytowaitforaneclipse,and experiments can be conducted all the time.Without fail, they found thatstarlightbentaccordingtoEinstein’sprediction.Infact,theyfoundthatstarlightfromhalfwayacrosstheskywasbentbythesun.In the twenty-first century, a variety of other precision experiments are

plannedtotesttheprecisionofgeneralrelativity,includingmoreexperimentsondouble stars and even bouncing laser signals off the moon. But the mostinteresting precision tests may come from gravity waves. Einstein predictedgravity waves in 1916. However, he despaired of ever being able to seeconfirmation of these elusive phenomena in his lifetime. The experimentalequipmentoftheearlytwentiethcenturywassimplytooprimitive.Butin1993,theNobelPrizewasawardedtotwophysicists,RussellHulseandJosephTaylor,forindirectlyverifyingtheexistenceofgravitywavesbyexaminingdoublestarsrotatingaroundeachother.TheyexaminedPSR1913+16,adoubleneutronstarabout16,000light-years

from Earth, in which two dead stars orbit each other every seven hours andforty-fiveminutes, releasingcopiousquantitiesofgravitywaves in theirwake.Imagine, for example, stirring a pot ofmolasseswith two spoons, each spoonrotatingaroundtheother.Aseachspoonmovesinthemolasses,itleavesatrailofmolassesinitswake.Similarly,ifwereplacethemolasseswiththefabricofspace-timeandthespoonsbydeadstars,wefindtwostarschasingeachotherinspace,emittingwavesofgravity.Sincethesewavescarryenergy,thetwostarseventuallyloseenergyandgraduallyspiraltogether.Byanalyzingthesignalsofthisdouble-starsystem,onecanexperimentallycalculatetheprecisedecayintheorbit of the double star.As expected fromEinstein’s general relativity theory,the two stars come closer by a millimeter every revolution. Over a year, theseparationof the starsdecreasesbyayard inanorbit that is435,000miles indiameter,which isprecisely thenumber thatcanbecalculated fromEinstein’sequations. In fact, the two starswill completely collapse in 240million yearsowing to the loss of gravity waves. This precision experiment can bereinterpreted as a way in which to test the accuracy of Einstein’s generalrelativity. The numbers are so precise that we can conclude that generalrelativityis99.7%accurate(wellwithinexperimentalerror).Morerecently,thereisintenseinterestinaseriesoffar-reachingexperiments

toobservegravitywavesdirectly.TheLIGO(LaserInterferometerGravitationalWaveObservatory)projectmaysoonbethefirsttoobservegravitationalwaves,perhapsfromblackholescollidinginouterspace.LIGOisaphysicist’sdreamcometrue,thefirstapparatuspowerfulenoughtomeasuregravitywaves.LIGOconsists of three laser facilities in the United States (two in Hanford,Washington, and one in Livingston, Louisiana). It is actually one part of aninternationalconsortium,includingtheFrench-ItaliandetectorcalledVIRGOinPisa, Italy; a Japanese detector called TAMA outside Tokyo; and a British-German detector called GEO600 in Hanover, Germany. Altogether, LIGO’sfinalconstructioncostwillbe$292million(plus$80millionforcommissioningandupgrades),makingitthemostexpensiveprojecteverfundedbytheNationalScienceFoundation.The laser detectors used in LIGO look very much like the device used by

Michelson-Morley at the turn of the century to detect the aetherwind, exceptthatlaserbeamsareusedinsteadofordinarylightbeams.Alaserbeamissplitinto twoseparatebeams thatmoveperpendicular toeachother.Afterhittingamirror, these two beams are then reunited. If a gravity wave were to hit theinterferometer, therewould be a disturbance in the lengths of the paths of thelaser beams, which could be seen as an interference pattern between the twobeams.Tomakesurethatthesignalhittingthelaserapparatusisnotaspurious

one,laserdetectorsarerequiredtobedistributedaroundtheplanetEarth.OnlyahugegravitywavemuchbiggerthanEarthwouldbeabletofirethedetectorsallatonce.Eventually,a seriesof these laserdetectorswillbeplaced inouter spaceby

NASAandtheEuropeanSpaceAgency.Around2010,NASAwilllaunchthreesatellites, called LISA (Laser Interferometry Space Antenna). They will orbitaroundthesunatapproximatelythesamedistanceastheearth’sorbit.Thethreelaserdetectorswill formanequilateral triangle inouter space (about3millionmiles on a side). The system will be so delicate it will be able to detectvibrationsofonepart in abillion trillion (corresponding to a shift that isone-hundredththewidthofasingleatom),allowingscientists todetect theoriginalshockwaves fromthebigbang itself. Ifallgoeswell,LISAshouldbeable topeertowithinthefirsttrillionthofasecondafterthebigbang,makingitperhapsthe most powerful of all cosmological tools to exploring creation. This isessential, because it is believed that LISA may be able to find the firstexperimentaldataontheprecisenatureoftheunifiedfieldtheory,thetheoryofeverything.YetanotherimportanttoolintroducedbyEinsteinwasgravitylenses.Backin

1936, he proved that nearby galaxies can act as gigantic lenses that focus thelightfromdistantobjects.ItwouldtakemanydecadesfortheseEinsteinlensesto be observed. The first breakthrough came in 1979, when astronomersobserved the quasar Q0957+561 and found that space was being warped andactingasalenstoconcentratelight.In 1988, the first observationof anEinstein ringwas from the radio source

MG1131+0456, and about twenty, mostly fragments of rings, have beenobserved since then. In 1997, the first completely circularEinstein ringswereobserved with the Hubble Space Telescope and Britain’s MERLIN (Multi-Element Radio Linked Interferometer Network) radio telescope array. Byanalyzing the distant galaxy 1938+666, they found the characteristic ring thatsurroundedthegalaxy.“Atfirstsight,itlookedartificialandwethoughtitwassome sort of defect in the image, but then we realized we were looking at aperfect Einstein ring!” said Dr. Ian Brown of the University of Manchester.Astronomers in Britain were elated by the discovery, declaring, “It’s a bulls-eye!” The ring is tiny. It is only a second of an arc, or roughly the size of apenny viewed from a distance of two miles. However, it is a verification ofEinstein’spredictionmadedecadesago.One of the greatest explosions in general relativity has been in the area of

cosmology.In1965,twophysicists,RobertWilsonandArnoPenzias,detectedthefaintmicrowaveradiationfromouterspacewiththeirBellLaboratoryHorn

RadioTelescopeinNewJersey.Thetwophysicists,unawareofthepioneeringworkofGamowandhis students, accidentallypickedup thiscosmic radiationfromthebigbangwithoutrealizingit.(Accordingtolegend,theythoughttheywere picking up interference from the bird droppings that littered their radiotelescope. Later, Princeton physicist R. H. Dicke correctly identified thisradiation as Gamow’s microwave background radiation.) Penzias andWilsonwereawardedtheNobelPrizefortheirpioneeringwork.Sincethen,theCOBE(CosmicBackgroundExplorer)satellite,launchedin1989,hasgivenusthemostdetailed picture of this cosmic microwave background radiation, which isremarkablysmooth.WhenphysicistsledbyGeorgeSmootoftheUniversityofCalifornia at Berkeley carefully analyzed any slight ripples in this smoothbackground,theyproducedaremarkablephotographofthebackgroundradiationwhen the universe was only about 400,000 years old. The media mistakenlycalled thispicture the“faceofGod.” (Thisphotograph isnot the faceofGod,butitisa“babypicture”ofthebigbang.)Whatisinterestingaboutthepictureisthattheripplesprobablycorrespondto

tiny quantum fluctuations in the big bang. According to the uncertaintyprinciple,thebigbangcouldnothavebeenaperfectlysmoothexplosion,sincequantumeffectsmusthaveproducedripplesofacertainsize.This,infact,waspreciselywhat theBerkeleygroup found. (In fact, if theyhadnot found theseripples,itwouldhavebeenagreatsetbackfortheuncertaintyprinciple.)Theseripplesnotonlyshowedthattheuncertaintyprincipleappliedtothebirthoftheuniverse,butalsogavescientistsaplausiblemechanismforthecreationofour“lumpyuniverse.”Whenwelookaroundus,weseethatthegalaxiesarefoundin clusters, thereby giving the universe a rough texture. This lumpiness canpossibly be easily explained as the ripples from the original big bang, whichhavebeenstretchedastheuniverseexpanded.Hence,whenweseetheclustersofgalaxiesintheheavens,wemaybepeeringintotheoriginalripplesofthebigbangleftbytheuncertaintyprinciple.ButperhapsthemostspectacularrediscoveryofEinstein’sworkcomesinthe

form of “dark energy.” As we saw earlier, he introduced the concept of thecosmologicalconstant(ortheenergyofthevacuum)in1917inordertopreventtheuniversefromexpanding.(Werecall that thereareonlytwopossible termsallowed by general covariance, the Ricci curvature and the volume of space-time, so the cosmological constant term cannot be easily dismissed.) He latercalledithisgreatestblunderwhenEdwinHubbleshowedthattheuniverseisinfact expanding. Results found in 2000, however, reveal that Einstein wasprobably right after all: the cosmological constant not only exists, but darkenergy probably makes up the largest source of matter/energy in the entire

universe. By analyzing supernovae in distant galaxies, astronomers have beenabletocalculatetherateofexpansionoftheuniverseoverbillionsofyears.Totheirsurprise,theyfoundthattheexpansionoftheuniverse,insteadofslowingdownasmosthadthought,isactuallyspeedingup.Ouruniverseisinarunawaymode andwill eventually expand forever. Thus,we can now predict how ouruniversewilldie.Previously,somecosmologistsbelievedthattheremightbeenoughmatterin

the universe to reverse the cosmic expansion, so that the universe mighteventually contract and a blue shift would be seen in outer space. (PhysicistStephenHawking even believed that timemight reverse itself as the universecontracted and history might repeat itself in a backward fashion. This wouldmeanthatpeoplewouldturnyoungerandjumpintotheirmother’swomb, thatpeoplewoulddivebackwardfromaswimmingpoolandlanddryonthedivingboard,andfryingeggswouldleapintotheirunbrokenshells.Hawking,however,hassinceadmittedhemadeamistake.)Eventually,theuniversewouldimplodeonitself,creatingtheenormousheatofa“bigcrunch.”Othersevenspeculatedthat the universe may then undergo another big bang, thereby creating anoscillatinguniverse.However,allthishasnowbeenruledoutwiththeexperimentalresultthatthe

expansionoftheuniverseisaccelerating.Thesimplestexplanationthatseemstofit the data is to assume that there is an enormous amount of dark energypervading the universewhich acts like antigravity, pushing the galaxies apart.Thegreater the universe becomes, themorevacuumenergy there is,which inturnpushesthegalaxiesevenfartherapart,creatinganacceleratinguniverse.This seems tovindicateoneversionof the“inflationaryuniverse” idea, first

proposedbyMITphysicistAlanGuth,which is amodificationof theoriginalbigbangtheoryofFriedmannandLemaître.Roughly,intheinflationarypicturetherearetwophasestotheexpansion.Thefirstisarapid,exponentialexpansion,whentheuniversewasdominatedbyalargecosmologicalconstant.Eventually,thisexponentialinflationterminates,andtheexpansionslowsdowntoresemblethe conventional expanding universe found by Friedmann and Lemaître. Ifcorrect, thismeans that the universe visible around us is just a pinpoint on amuch larger space-time that represents the true universe. Recent experimentswith balloons high in the atmosphere have also given credible evidence ofinflation by showing that the universe seems to be approximately flat, whichindicateshowbigitreallyis.Wearelikeantssittingonahugeballoon,thinkingthatouruniverseisflatonlybecausewearesosmall.Dark energy also forces us to reappraise our true role and position in the

universe.ItwasCopernicuswhoshowedthattherewasnothingspecialaboutthe

positionofhumansinthesolarsystem.Theexistenceofdarkmattershowsthatthere isnothingspecialabout theatoms thatmakeupourworld,since90%ofthematter in the universe ismade ofmysterious darkmatter.Now, the resultfrom the cosmological constant indicates that dark energy dwarfs darkmatter,which in turn dwarfs the energy of the stars and galaxies. The cosmologicalconstant, once reluctantly introduced by Einstein to stabilize the universe, isprobably by far the largest source of energy in the universe. (In 2003, theWMAPsatelliteverifiedthat4%oftheuniverse’smatterandenergyisfoundinordinary atoms, 23% in some formof unknowndarkmatter, and73%of it indarkenergy.)Anotherstrangepredictionofgeneral relativity is theblackhole,whichwas

consideredsciencefictionwhenSchwarzschildreintroducedtheconceptofdarkstarsback in1916.However, theHubbleSpaceTelescopeand theVeryLargeArrayRadioTelescopehavenowverifiedtheexistenceofoverfiftyblackholes,mainly lurking in the heart of large galaxies. In fact, many astronomers nowbelievethatperhapshalfofallthetrillionsofgalaxiesintheheavenshaveblackholesattheircenter.Einstein realized the problem with identifying these exotic creatures: by

definition, they are invisible since light itself cannot escape, and henceextremelydifficult to see innature.TheHubbleSpaceTelescope,peering intotheheartsofdistantquasarsandgalaxies,hasnowtakenspectacularphotographsof thespinningdisksurrounding theblackholes located in theheartofdistantgalaxies, such as M-87 and NGC-4258. In fact, one can clock some of thismatter revolving around theblackhole at about amillionmiles per hour.ThemostdetailedHubblephotographsshowthatthereisadotattheverycenteroftheblackhole,aboutasinglelight-yearacross,whichispowerfulenoughtospinanentiregalaxyabout100,000light-yearsacross.Afteryearsofspeculation, itwasfinallyshownin2002thatthereisablackholelurkinginourownbackyard,theMilkyWaygalaxy,whichweighs the sameas about2million suns.Thus,ourmoonrevolvesaroundtheearth,theearthrevolvesaroundthesun,andthesunrevolvesaroundablackhole.AccordingtotheworkofMichellandLaplaceintheeighteenthcentury, the

massof a dark star or blackhole is proportional to its radius.Thus, theblackholeat thecenterofourgalaxy is roughlya tenthof the radiusof theorbitofMercury.Itisastonishingthatanobjectthatsmallcanaffectthedynamicsofourentiregalaxy.In2001,astronomersusingtheEinsteinlenseffectannouncedthatawanderingblackholewasdiscoveredmovingwithin theMilkyWaygalaxy.As the blackholemoved, it distorted the surrounding starlight.By tracing themovement of this light distortion, astronomers could calculate its trajectory

acrosstheheavens.(Anywanderingblackholeapproachingtheearthcouldhavecatastrophicconsequences.Itwouldeatuptheentiresolarsystemandnotevenburp.)In 1963, research in black holes received a boost when New Zealand

mathematician Roy Kerr generalized Schwarzschild’s black hole to includespinningblackholes.Sinceeverythingintheuniverseseemstobespinning,andbecauseobjectsspinfasterwhentheycollapse,itwasnaturaltoassumethatanyrealistic black holewould be spinning at a fantastic rate.Much to everyone’ssurprise, Kerr found an exact solution of Einstein’s equations inwhich a starcollapsed into a spinning ring. Gravity would try to collapse the ring, butcentrifugal effects could become sufficiently strong to counteract gravity, andthespinningringwouldbestable.Whatmostpuzzledrelativistswasthatifyoufell through the ring,youwouldnotbecrushed todeath.Gravitywasactuallylargebut finiteat thecenter,soyoucould inprinciplefallstraight through thering,intoanotheruniverse.AjourneythroughtheEinstein-Rosenbridgewouldnotnecessarilybealethalone.Iftheringwerelargeenough,onemightentertheparalleluniversesafely.Physicistsimmediatelybegantopickapartwhatmighthappenifyoufellinto

aKerrblackhole.Anencounterwith suchablackholewouldcertainlybeanunforgettable experience. In principle, itmight give us a shortcut to the stars,transporting us instantly into another part of the galaxy, or perhaps anotheruniverse entirely. As you approached the Kerr black hole, you would passthroughtheeventhorizonsoyouwouldneverbeabletogobacktowhereyoustarted (unless there was another Kerr black hole that connected the paralleluniverse back to our universe,making a roundtrip possible).Also, therewereproblemswith stability.One could show that if you fell through theEinstein-Rosenbridge,thedistortionsofspace-timethatyoucreatedmightforcetheKerrblack hole to close up, making a complete journey through the bridgeimpossible.AsstrangeastheideaofaKerrblackholewas,actingasagatewayorportal

between twouniverses, it couldnotbedismissedonphysicalgroundsbecauseblackholesareindeedspinningveryrapidly.However,itsoonbecameapparentthat theseblackholesnotonly connected twodistant points in space, but alsoconnectedtwotimesaswell,actingastimemachines.When Gödel found the first time travel solution of Einstein’s equations in

1949,itwasconsideredanovelty,anisolatedaberrationoftheequations.Sincethen, however, scores of time travel solutions have now been discovered inEinstein’s equations. For example, it was discovered that an old solution,discoveredbyW.J.vanStockumin1936,actuallyallowedfortimetravel.The

vanStockumsolutionconsistedofan infinitecylinder spinning rapidlyarounditsaxis,likethespinningpolefoundinoldbarbershops.Ifyoujourneyedaroundthespinningcylinder,thenyoumightbeabletoreturntotheoriginalspotbeforeyou left, much like the Gödel solution of 1949. Although this solution isintriguing, theproblemis that thecylinderhas tobe infinite in length.Afinitespinning cylinder will apparently not work. In principle, therefore, both theGödelandthevanStockumsolutioncanberuledoutonphysicalgrounds.In1988,KipThorneandhiscolleaguesatCaltechfoundyetanothersolution

ofEinstein’sequationsthatadmitstimetravelviaawormhole.Theywereabletosolvetheproblemoftheone-waytripthroughtheeventhorizonbyshowingthat a new type ofwormholewas completely transversable. In fact, they havecalculated thata trip throughsucha timemachinemaybeascomfortableasaplaneride.Thekeytoall thesetimemachinesisthematterorenergythatwarpsspace-

time onto itself. To bend time into a pretzel, one needs a fantastic amount ofenergy, far beyond anything known to modern science. For the Thorne timemachine, oneneeds negativematter or negative energy.Noonehas ever seennegativematterbefore.Infact,ifyouhadapieceofitinyourhand,itwouldfallup,notdown.Searchesfornegativematterhaveprovedfruitless.Ifanyexistedontheearthbillionsofyearsago,itwouldhavefallenupintoouterspace,tobelost forever.Negativeenergy,on theotherhand,actuallyexists in the formoftheCasimir effect. Ifwe take two neutral parallelmetal plates,we know thatthey are uncharged and hence are not attracted or repelled toward each other.They should remain at rest.However, in 1948HenrikCasimir demonstrated acuriousquantumeffect,demonstrating that the twoparallelplateswillactuallyattract each other by a small but nonzero force, which has actually beenmeasuredinthelaboratory.ThusaThornetimemachinecanbebuiltasfollows:Taketwosetsofparallel

metalplates.BecauseoftheCasimireffect,theregionbetweeneachsetofplateswill have negative energy. According to Einstein’s theory, the presence ofnegativeenergywillopenuptinyholesorbubblesinspace-time(smallerthanasubatomic particle) inside this region.Now assume, for the sake of argument,that an advancedcivilization far aheadofours can somehowmanipulate theseholes,grabonefromeachpairofplates,andthenstretchthemuntilalongtubeorwormholeconnectsthetwosetsofplates.(Linkingthesetwosetsofparallelplates with a wormhole is far beyond anything possible with today’stechnology.)Nowsendonepairofplatesona rocket that is travelingnear thespeedoflight,sothattimeslowsdownaboardtherocketship.Aswediscussedearlier,clockson the rocket runslower thanclocksonEarth. Ifyou jump into

theholewithin theparallelplates sittingonEarth,youwillbe sucked throughthewormholeconnectingthetwoplatesandfindyourselfontherocketbackinthepast,atadifferentpointinspaceandtime.Since then, the field of timemachines (or more properly “closed time like

curves”) has become a lively area of physics,with scores of papers publishedwith different designs, all of them based on Einstein’s theory. Not everyphysicist hasbeen amused, though.Hawking, for one, didnot like the ideaoftimetravel.Hesaid,tongue-in-cheek,thatiftimetravelwerepossible,wewouldbefloodedwith tourists fromthefuture,whichwedon’tsee. If timemachineswere commonplace, then history would be impossible to write, changinganytimesomeonespunthedialoftheirtimemachine.Hawkinghasdeclaredthathewantstomaketheworldsafeforhistorians.However,inT.H.White’sTheOnce and Future King, there is a society of ants that obeys the dictum,“Everythingnot forbidden iscompulsory.”Physicists take this law toheart, soHawkingwasforcedtopostulatethe“chronologyprotectionconjecture,”whichbans timemachines by fiat. (Hawking has since given up trying to prove thisconjecture. He now maintains that time machines, although theoreticallypossible,arenotpractical.)These time machines apparently obey the laws of physics, as we currently

know them. The trick, of course, is to somehow access these tremendousenergies (availableonly to“sufficientlyadvancedcivilizations”)andshowthatthese wormholes are in fact stable against quantum corrections and don’texplodeorcloseupassoonasyouenterone.Itshouldalsobementionedthattimeparadoxes(suchaskillingyourparents

beforeyouareborn)mightberesolvedwithtimemachines.BecauseEinstein’stheory is based on smooth, curved Riemann surfaces, we do not simplydisappear when we enter the past and create a time paradox. There are twopossibleresolutionsoftimetravelparadoxes.First,iftheriveroftimecanhavewhirlpools, then perhaps we simply fulfill the past when we enter the timemachine.Thismeans that time travel is possible, butwe cannot alter thepast,merelycomplete it. Itwasmeant tobe thatwewouldenter the timemachine.ThisviewisheldbyRussiancosmologistIgorNovikov,whosays,“WecannotsendatimetravelerbacktotheGardenofEdentoaskEvenottopicktheapplefromthetree.”Second,theriveroftimeitselfmayforkintotworivers;thatis,aparalleluniversemayopenup.Thus, ifyoushootyourparentsbeforeyouareborn,youhaveonlykilledpeoplewhoaregeneticallyidentical toyourparentsbutarenotreallyyourparentsatall.Yourownparentsindeedgavebirthtoyouand made your body possible. What has happened is that you have jumpedbetweenouruniverseandanotheruniverse,soalltimeparadoxesareresolved.

ButthetheoryclosesttoEinstein’sheartwashisunifiedfieldtheory.Einsteinremarked to Helen Dukas that perhaps in a hundred years, physicists willunderstandwhathewasdoing.Hewaswrong.Inlessthanfiftyyears,therehasbeen a resurgence of interest in the unified field theory. The quest forunification, once derided by physicists as being hopelessly beyond reach, isperhapsnow tantalizinglywithinourgrasp. It dominates the agendaof almosteverymeetingoftheoreticalphysicists.After two thousandyearsof investigation into thepropertiesofmatter, ever

since Democritus and fellow Greeks asked what the universe was made of,physicshasproducedtwocompetingtheoriesthataretotallyincompatible.Thefirst is the quantum theory, which is incomparable in terms of describing theworld of atoms and subatomic particles. The second is Einstein’s generalrelativity, which has given us breathtaking theories of black holes and theexpanding universe. The ultimate paradox is that these two theories are totalopposites.Theyarebasedondifferentassumptions,differentmathematics,anddifferentphysicalpictures.Thequantumtheory isbasedondiscretepacketsofenergy, called “quanta,” and the dance of subatomic particles. The relativitytheory,however,isbasedonsmoothsurfaces.Physicists today have formulated the most advanced version of quantum

physics,embodiedinsomethingcalledthe“StandardModel,”whichcanexplainsubatomicexperimentaldata.Itis,insomesense,themostsuccessfultheoryinnature,abletodescribethepropertiesofthree(theelectromagneticandtheweakandstrongnuclearforces)of thefourfundamental forces.Assuccessfulas theStandardModelis,thereareglaringtwoproblemswithit.First,itissupremelyugly, perhaps one of the ugliest theories ever proposed in science.The theorysimply ties together theweak, strong,andelectromagnetic forcesbyhand. It’slikeusingScotchtapetoconnectawhale,aardvark,andagiraffetogether,andclaiming that this is the supreme achievement of nature, the end product ofmillions of years of evolution. Up close, the Standard Model consists of abewildering,motleycollectionofsubatomicparticleswithstrangenamesthatdonot make much sense, like quarks, Higgs bosons, Yang-Mills particles, W-bosons, gluons, and neutrinos. Worse, the Standard Model does not mentiongravity at all. In fact, if one tries to graft gravity onto theStandardModel byhand, one finds that the theory blows up. It yields nonsense.All attempts foralmostfiftyyearstograftthequantumtheoryandrelativitytogetherhaveprovedfruitless.Givenallitsaestheticdefects,weconcludethattheonlythinggoingforthe theory is that it is undeniably correct within its experimental domain.Clearly,whatisneededistogobeyondtheStandardModel, tore-examinetheunificationapproachofEinstein.

Afterfiftyyears,theleadingcandidateforatheoryofeverything,onethatcanunify both the quantum theory and general relativity, is something called“superstring theory.” In fact, it is the only game in town because all rivaltheorieshavebeenruledout.AsphysicistStevenWeinbergsaid,“Stringtheoryhasprovidedourfirstplausiblecandidateforafinaltheory.”Weinbergbelievesthat themaps thatguided theancientmarinersallpointed to theexistenceofafabledNorthPole, though itwould takecenturiesbeforeRobertPearyactuallysetfootonitin1909.Similarly,allthediscoveriesmadeinparticlephysicspointto the existence of the “North Pole” of the universe, that is, a unified fieldtheory. Superstring theory can absorb all the good features of the quantumtheoryandrelativityinasurprisinglysimpleway.Superstringtheoryisbasedonthe idea that subatomicparticles canbeviewed as notes on a vibrating string.AlthoughEinsteincomparedmattertowoodbecauseofallitstangledpropertiesand seemingly chaotic nature, superstring theory reduces matter to music.(Einstein,whowasanexcellentviolinist,probablywouldhavelikedthis.)Atonepointinthe1950s,physicistsdespairedofmakingsenseofsubatomic

particles because new ones were being discovered all the time. J. RobertOppenheimer,indisgust,oncesaid,“TheNobelPrizeinPhysicsshouldbegivento the physicist who does not discover a new particle that year.” ThesesubatomicparticlesweregivensomanystrangeGreeknamesthatEnricoFermisaid,“IfIhadknownthattherewouldbesomanyparticleswithGreeknames,Iwouldhavebecomeabotanist rather thanaphysicist.”But in string theory, ifonehadasupermicroscopeandcouldpeerdirectlyintoanelectron,onewouldfindnotapointparticle,butavibratingstring.Whenthesuperstringvibratesinadifferent mode or note, it changes into a different subatomic particle, like aphotonoraneutrino.Inthispicture,thesubatomicparticlesthatweseeinnaturecan be viewed as the lowest octave of the superstring. Thus, the blizzard ofsubatomic particles discovered over the decades are simply notes on thissuperstring.Thelawsofchemistry,whichseemsoconfusingandarbitrary,arethemelodies played out on superstrings.The universe itself is a symphony ofstrings.Andthelawsofphysicsarenothingbutharmoniesofthesuperstring.SuperstringtheorycanalsoencompassallofEinstein’sworkonrelativity.As

the string moves in space-time, it forces the surrounding space around it tocurve, precisely as Einstein had predicted back in 1915. In fact, superstringtheoryisinconsistentunlessitcanmoveinaspace-timeconsistentwithgeneralrelativity. As physicist Edward Witten has said, even if Einstein had neverdiscoveredthe theoryofgeneralrelativity, itmighthavebeenrediscoveredviathe string theory. Witten says, “String theory is extremely attractive becausegravity is forceduponus.Allknownconsistentstring theories includegravity,

sowhilegravityisimpossibleinquantumfieldtheoryaswehaveknownit,it’sobligatoryinstringtheory.”However,stringtheorymakessomeotherquitesurprisingpredictions.Strings

canonlyconsistentlymoveintendimensions(onedimensionof timeandninedimensions of space). In fact, string theory is the only theorywhich fixes thedimensionalityof itsownspace-time.Like theKaluza-Klein theoryof1921, itcanunifygravitywithelectromagnetismbyassumingthathigherdimensionscanvibrate,creatingforcesthatcanspreadthroughoutthreedimensionslikelight.(Ifwe add an eleventh dimension, then string theory allows for the possibility ofmembranesvibratinginhyperspace.Thisiscalled“M-theory,”whichcanabsorbstringtheoryandprovidenewinsightsintothetheoryfromthevantagepointoftheeleventhdimension.)WhatwouldEinsteinthinkofsuperstringtheoryifhewerealivetoday?The

physicistDavidGrosssaid,“Einsteinwouldhavebeenpleasedwiththis,atleastwiththegoal,ifnottherealization….Hewouldhavelikedthefactthatthereisan underlying geometrical principle—which unfortunately, we don’t reallyunderstand.”TheessenceofEinstein’sunified field theory, aswe saw,was tocreatematter (wood)outofgeometry(marble).Grosscommentedon this:“Tobuildmatteritselfoutofgeometry—thatinasenseiswhatstringtheorydoes….[It’s]atheoryofgravityinwhichparticlesofmatteraswellastheotherforcesof nature emerge in the sameway that gravity emerges from geometry.” It isinstructivetogobacktoEinstein’searlyworkontheunifiedfieldtheory,fromthevantagepointofstringtheory.ThekeytoEinstein’sgeniuswasthathewasabletoisolatethekeysymmetriesoftheuniversethatunifythelawsofnature.The symmetry that unifies space and time is the Lorentz transformation, orrotations in four dimensions. The symmetry behind gravity is generalcovariance,orarbitrarycoordinatetransformationsofspace-time.However,onEinstein’sthirdtryatagreatunifyingtheory,hefailed,mainly

because he lacked the symmetry that would unite gravity and light, or unitemarble(geometry)withwood(matter).He,ofcourse,wasacutelyawarethathelacked a fundamental principle that would guide him through the thicket oftensorcalculus.Heoncewrote,“Ibelievethatinordertomakerealprogressonemustagainferretoutsomegeneralprinciplefromnature.”Butthatispreciselywhatthesuperstringprovides.Thesymmetryunderlying

thesuperstringiscalled“supersymmetry,”astrangeandbeautifulsymmetrythatunifies matter with forces. As mentioned earlier, subatomic particles have apropertycalled“spin,”actingasiftheywerespinningtops.Theelectron,proton,neutron, andquarks thatmakeup thematter in theuniverses all have spin 1/2and they are called “fermions,” named after Enrico Fermi, who explored the

propertiesofparticleswithhalf-integralspin.Thequantaofforces,however,arebased on electromagnetism (with spin 1) and gravitation (with spin 2).Noticethattheyhaveintegralspin,andarecalled“bosons”(aftertheworkofBoseandEinstein).Thekeypoint is that ingeneral,matter (wood) ismadeof fermionswithhalf-integral spin,while forces (marble)aremadeofbosonswith integralspin.Supersymmetryunifiesfermionsandbosons.Thisistheessentialpoint,thatsupersymmetryallowsforaunificationofwoodandmarble,asEinsteinwished.In fact, supersymmetry allows for a new type of geometry that has evensurprised the mathematicians, called “superspace,” which makes possible“supermarble.”Inthisnewapproach,wemustgeneralizetheolddimensionsofspace and time to include new fermionic dimensions,which then allowsus tocreatea“superforce”outofwhichallforcesoriginatedattheinstantofcreation.Thus, some physicists have speculated that one must generalize Einstein’s

originalprincipleofgeneralcovariancetoread:theequationsofphysicsmustbesuper covariant (i.e., maintain the same form after a super covarianttransformation).Superstring theoryallowsus to reanalyzeEinstein’soldworkon theunified

fieldtheory,butinanentirelynewlight.Whenwebegintoanalyzethesolutionsto the superstring equations, we encounter many of the bizarre spaces thatEinstein pioneered back in the 1920s and 1930s. As we saw earlier, he wasworkingwithgeneralizationsofRiemannianspace,whichtodaycancorrespondto some spaces found in string theory. Einstein was looking at these bizarrespaces one after the other, in agonizing fashion (including complex spaces,spaceswith“torsion,”“twistedspaces,”“antisymmetricspaces,”etc.),buthegotlostbecausehelackedanyguidingphysicalprincipleorpicturetoleadhimoutofthetangleofmathematics.Thisiswheresupersymmetrycomesin—itactsasanorganizingprinciple that allowsus to analyzemanyof these spaces fromadifferentperspective.But is supersymmetry the symmetry that eluded Einstein for the last three

decadesofhislife?ThekeytoEinstein’sunifiedfieldtheoryisthatitwastobemadeofpuremarble,thatis,puregeometry.Theugly“wood”thatinfestedhisoriginal relativity theory was to be absorbed into geometry. Supersymmetrymightholdthekeytoatheoryofpuremarble.Inthistheory,onecanintroducesomething called “superspace,” in which space itself becomessupersymmetrized. Inotherwords, there is thepossibility that the finalunifiedfieldtheorywillbemadeof“supermarble,”outofanew“supergeometry.”Physicistsnowbelievethatattheinstantofthebigbang,allthesymmetriesof

theworldwereunified, asEinsteinbelieved.The four forceswe see innature(gravity,electromagnetism,andthestrongandweaknuclearforce)wereunified

intoasingle“superforce”attheinstantofcreation,andonlylaterbrokeapartasthe universe cooled. Einstein’s quest for the unified field theory seemedimpossible, only because today we see the four forces of the world horriblybrokenintofourpieces.Ifwecanturnbacktheclock13.7billionyears,totheoriginalbigbang,wewould see the cosmicunityof theuniversedisplayed infullglory,asEinsteinimagined.Wittenclaimsthatstringtheorywillonedaydominatephysicsthesameway

thatquantummechanicsdominatedphysicsforthepasthalf-century.However,there are still many formidable obstacles. The critics of the theory point outsomeof itsweakspots.First, it is impossible to testdirectly.Sincesuperstringtheoryisa theoryof theuniverse, theonlywaytotest it is tore-createthebigbang,thatis,createenergiesinanatomsmasherthatapproximatethebeginningoftheuniverse.Todothiswouldrequireanatomsmasherthesizeofagalaxy.This is out of the question, even for an advanced civilization.However,mostphysicsisdoneindirectly,sotherearehighhopesthattheLargeHadronCollider(LHC) tobebuiltoutsideofGeneva,Switzerland,willhaveenoughenergy toprobe the theory. The LHC, when it is turned on in the near future, willaccelerateprotonstotrillionsofelectronvolts,sufficienttosmashatomsapart.Whenexaminingthedebrisofsuchfantasticcollisions,physicistshopetofindanewkind of particle, the superparticle or “sparticle,”whichwould represent ahigherresonanceoroctaveofthesuperstring.There is even some speculation that darkmattermaybemadeof sparticles.

Forexample,thepartnerofthephoton,calledthe“photino,”isneutralincharge,stable,andhasmass.Iftheuniversewerefilledwithagasofphotinos,wewouldnotbeabletoseeit,butitwouldactverymuchlikedarkmatter.Oneday,ifweeveridentifythetruenatureofdarkmatter,itmayprovideanindirectproofofsuperstringtheory.Yetanotherwaytotestthetheoryindirectlyistoanalyzegravitywavesfrom

thebigbang.WhentheLISAgravitywavedetectorsarelaunchedintospaceinthe next decade, they may eventually pick up gravity waves emitted one-trillionthofasecondaftertheinstantofcreation.Iftheseagreewithpredictionsmadefromthestringtheory,thedatamightconfirmthetheoryonceandforall.M-theorymayalsoexplainsomeofthepuzzlesthatsurroundtheoldKaluza-

Klein universe.Recall that one serious objection to theKaluza-Klein universewasthatthesehigherdimensionscouldnotbeseeninthelaboratory,andinfactmust bemuch smaller than an atom (otherwise, atoms would float into thesehigher dimensions). But M-theory gives us a possible solution to this byassuming that our universe itself is amembrane floating in an infinite eleven-dimensionalhyperspace.Thus,subatomicparticlesandatomswouldbeconfined

toourmembrane (ouruniverse), but gravity, being adistortionof hyperspace,canflowfreelybetweenuniverses.This hypothesis, as strange as itmay seem, can be tested. Ever since Isaac

Newton,physicistshaveknown thatgravitydecreasesas the inverse squareofthedistance. In four spatialdimensions,gravity shoulddecreaseas the inversecubeofthedistance.Thus,bymeasuringtinydeviationsfromaperfectinversesquare law, one may detect the presence of other universes. Recently, it wasconjecturedthat if there isaparalleluniverseonlyamillimeterawayfromouruniverse, it might be compatible with Newtonian gravity and also might bedetectablewiththeLHC.Thisinturnhascreatedacertainamountofexcitementamong physicists, realizing that one aspect of superstring theory might betestablesoon,eitherbylookingforsparticlesorbylookingforparalleluniversesamillimeterfromours.These parallel universes might provide yet another explanation for dark

matter.Ifthereisaparalleluniversenearby,wewillnotbeabletoseeitorfeelit(sincematterisconfinedtoourmembraneuniverse)butwewouldbeabletofeelitsgravity(whichcantravelbetweenuniverses).Tous,thiswouldappearasifinvisiblespacehadsomeformofgravity,muchlikedarkmatter.Infact,somesuperstringtheoristshavespeculatedthatperhapsdarkmattercanbeexplainedasthegravityproducedbyanearbyparalleluniverse.But the real problemof proving the correctness of superstring theory is not

experiment.Wedon’thavetobuildgiganticatomsmashersorspacesatellitestoverifythetheory.Therealproblemispurelytheoretical:ifwearesmartenoughtocompletelysolvethetheory,weshouldbeabletofindallitssolutions,whichshouldincludeouruniverse,withitsstars,galaxies,planets,andpeople.Sofar,nooneonEarth is smart enough to completely solve these equations.Perhapstomorrow,orperhapsdecadesfromnow,someonemayannouncethattheyhavecompletelysolvedthetheory.Atthattime,wewillbeabletotellwhetheritisatheoryofeverything,oratheoryofnothing.Becausestringtheoryissoprecise,withoutanyadjustableparameters,thereisnothinginbetween.WillsuperstringtheoryorM-theoryallowustounifythelawsofnatureintoa

simple,coherentwhole,asEinsteinoncesaid?Atthispoint,itistooearlytosay.We are reminded of Einstein’s words: “The creative principle resides inmathematics. In a certain sense, therefore, I hold it true that pure thought cangraspreality,astheancientsdreamed.”Perhapsayoungreaderofthisbookwillbeinspiredbythisquestforaunificationofallphysicalforcestocompletethisprogram.Sohowshouldwere-evaluateEinstein’struelegacy?Insteadofsayingthathe

shouldhavegonefishingafter1925,perhapsamorefittingtributemightbeas

follows:All physical knowledge at the fundamental level is contained in twopillars of physics, general relativity and the quantum theory.Einsteinwas thefounderofthefirst,wasthegodfatherofthesecond,andpavedthewayforthepossibleunificationofboth.

Notes

Preface

“Apopicononapar…”:Brian,p.436.“Intheremaining30yearsofhislife…”:Pais,EinsteinLivedHere,p.43.

Chapter1.PhysicsbeforeEinstein“IfAissuccess,Ishouldsay…”:Pais,EinsteinLivedHere,p.152.“Everyonewhohadrealcontact…”:French,p.171.“torturedman,anextremelyneurotic…”:Cropper,p.19.“isthemostprofoundandthemostfruitfulthatphysics…”:Ibid.,p.173.“Theideaofthetimeofmagneticaction…”:Ibid.,p.163.“Wecanscarcelyavoidtheconclusion…”:Ibid.,p.164.

Chapter2.TheEarlyYears“Asoundskullisneeded…”:Brian,p.3.“Itdoesn’tmatter;…”:Clark,p.27.“ClassmatesregardedAlbertasafreak…”:Brian,p.3.“Yes,thatistrue….”:Pais,SubtleIstheLord,p.38.“Itis,infact,nothingshort…”:Cropper,p.205.“Awonderofsuchnature…”:Schilpp,p.9.“Throughthereadingofpopularbooks…”:Ibid.,p.5.“InalltheseyearsInever…”:Pais,SubtleIstheLord,p.38.“Attheageof12,…”:Schilpp,p.9.“Soontheflightofhismathematicalgenius…”:Sugimoto,p.14.“philosophicalnonsense…”:Brian,p.7.“IlovetheSwiss…”:Clark,p.65.“Whoeverapproachedhimwascaptivated…”:Folsing,p.39.“Manyayoungorelderlywoman…”:Ibid.,p.44.“Belovedsweetheart…”:Brian,p.12;Folsing,p.42.

“aworkwhichIreadwithbreathlessattention.”:Schilpp,p.15.“suchaprincipleresultedfromaparadoxuponwhich…”:Ibid.,p.53.“All physical theories, their mathematical expression notwithstanding,…”:Calaprice,p.261.“mostfascinatingsubjectatthetime…”:Clark,p.55.“Youareasmartboy,Einstein,…”:Pais,SubtleIstheLord,p.44;Brian,p.31.“You’reenthusiastic,buthopelessatphysics….”:Folsing,p.57.“somethingverygreat”:Sugimoto,p.19.“IcangoanywhereIwant—…”:Folsing,p.71.“Mysweethearthasaverywickedtongue…”:Brian,p.31.“ThisMissMariciscausingme…”:Ibid.,p.47.“Bythetimeyou’re30,she’llbeanoldwitch.”:Ibid.“What’stobecomeofher?”:Ibid.,p.25.“whocannotgainentrancetoagoodfamily.”:Ibid.“Iwouldhavefound[ajob]…”:Thorne,p.69.“Bythemereexistenceofhisstomach,…”:Schilpp,p.3.“Iamnothingbutaburdentomyrelatives…”:Pais,SubtleIstheLord,p.41.“pissingink”:Brian,p.69.“worldlymonastery.”:Ibid.,p.52.“Manyyearslater,hestillrecalled…”:Ibid.,p.53.“sadfatedidnotpermit[herfather]…”:Ibid.“Thedooroftheflatwasopentoallowthefloor,…”:Sugimoto,p.33.“privatelessonsinmathematicsandphysics.”:Ibid.,p.31.“ThesewordsofEpicurusappliedtous:…”:Brian,p.55.

Chapter3.SpecialRelativityandthe“MiracleYear”“Thegermofthespecialrelativitytheory…”:Folsing,p.166.“Astormbrokelooseinmymind.”:Brian,p.61.“Thesolutioncametomesuddenly…”:Ibid.p.63“IowemoretoMaxwellthantoanyone.”:Ibid.,p.152.ManybiographiestraceEinstein’s ideas back to the Michelson-Morley experiment. But as Einsteinhimself made clear on several occasions, this experiment only peripherallyaffectedhis thinking.Hewas led to relativity theoryviaMaxwell’s equations.TheentirethrustofhisoriginalpaperwastoshowthatMaxwell’sequationshada hidden symmetry revealed by his relativity theory, and that this should beelevatedtoauniversalprincipleofphysics.“Thankyou,I’vecompletelysolvedtheproblem.”:Folsing,p.155;Pais,SubtleIstheLord,p.139.

“oneofthemostremarkablevolumesinthewhole…”:Cropper,p.206.“Theideaisamusingandenticing;…”:Folsing,p.196.“forthetimebeing…”:Ibid.,p.197.“Imaginetheaudacityofsuchastep…”:Brian,p.71.“Fromnowon,spaceandtimeseparatelyhavevanished…”:Ibid.,p.72.“Themainthingisthecontent,…”:Ibid.,p.76.“superfluouserudition”:Cropper,p.220.“Sincethemathematicianshaveattackedtherelativity…”:Clark,p.159.“mighthaveremainedstuckinitsdiapers.”:Cropper,p.220.“Asastudenthewastreatedcontemptuouslybytheprofessors…”:Brian,p.73.“ThefestivitiesendedintheHotelNational,…”:Ibid.,p.75.“Heappearedinclassinsomewhatshabbyattire,…”:Cropper,p.215.Anotherparadoxinvolvestwoobjects,eachshorterthantheother.…:Overthedecades, scores of paradoxes have been introduced to illustrate the seeminglybizarrenatureofspecialrelativity.Theyusuallyinvolvetwoframesofreferencetraveling at different speeds that aremaking observations of the same object.Theparadoxesarisebecausetheobserversineachframeseethesameobjectintwo entirely different ways. Almost all of them can be resolved using twoobservations.First,lengthcontractioninoneframehastobebalancedwithtimedilation in the other. If we forget to balance the distortion of space with thedistortionoftime,thentheparadoxesarise.Second,paradoxesariseifweforgettobringthetwoframestogetherattheend.Thefinalresolutionofwhoisreallyyoungerorshortercanbeachievedwhenwebringthetwoobserverstogetherinspace and time and compare them. Unless we bring them together, then it ispossible tohave twoobjectseachshorterandyounger than theother,which isimpossibleinNewtonianphysics.p.82“ThereoncewasayoungladynamedBright…”:Goingfasterthanlightinorder tobreak the timebarrier togobackward in time isnotpossible.Asyouapproachthespeedoflight,yourmassbecomesnearlyinfinite,youaresqueezeduntilyouarealmost infinitely thin,andtimealmoststops.Hence, thespeedoflightistheultimatespeedintheuniverse.However,Idiscusspossibleloopholestothislater,whenIwriteaboutwormholesandEinstein-Rosenbridges.“mathematicalphysicistsareunanimous…”:Sugimoto,p.44.“ThegentlemeninBerlinaregamblingonme…”:Cropper,p.216.“Itseemsthatmostmembers…”:Folsing,p.336.“Iliveaverywithdrawnlife…”:Ibid.,p.332.“Sheisallloveforhergreathusband,…”:Brian,p.151.

Chapter4.GeneralRelativityand“theHappiestThoughtofMy

Life”“Asanolderfriend,Imustadviseyou…”:Pais,SubtleIstheLord,p.239.“Iwassittinginachairinthepatentoffice…”:Ibid.,p.179;Folsing,p.303.“DonotBodiesactuponlightataDistance,…”:Folsing,p.435.“Whenablindbeetlecrawlsoverthesurface…”:Calaprice,p.9.“Grossman,youmusthelpmeorelse…”:Pais,SubtleIstheLord,p.212.“NeverinmylifehaveItormentedmyself…”:Folsing,p.315.“Donotworryaboutyourdifficultiesinmathematics;…”:Calaprice,p.252.Mach’sprinciple:Moreprecisely,Mach’sprinciplestates that the inertiaofanobject,andhenceitsmass,isduetothepresenceofalltheothermassesintheuniverse,e.g.,thedistantstars.MachrestatedanobservationknownasfarbackasNewton,thatthesurfaceofaspinningpailofwaterbecomesdepressed(dueto centripetal forces). The faster the spin, the greater the depression of thesurface.Ifallmotionsarerelative,includingrotations,thenonecanconsiderthepail to be at rest and all the distant stars to rotate around it. Thus, reasonedMach, it was the rotation of the distant stars that caused the stationary pail’ssurface to be depressed.Thus, the presence of the distant stars determines theinertialpropertiesofthepailofwater,includingitsmass.Einsteinmodifiedthislawtomeanthatthegravitationalfieldisuniquelydeterminedbythedistributionofmassesintheuniverse.“Ifeverythingfails,I’llpayforthething…”:Folsing,p.320.EinsteinhaddroppedtheRiccicurvature…:Generalcovariancemeansthattheequationsretainthesameformafterachangeofcoordinates(todaythisiscalleda “gauge transformation”).Einstein did not appreciate in 1912 that thismeantthatthephysicalpredictionsofhistheoryalsoremainedthesameafterachangeof coordinates. Thus, in 1912 he found, to his horror, that his theory gave aninfinitenumberofsolutionsforthegravitationalfieldsurroundingthesun.Butthree years later, he suddenly realized that all of these solutions described thesame physical system, i.e., the sun. Thus, the Ricci curvaturewas a perfectlywell-definedmathematicalobject thatcoulduniquelydescribe thegravitationalfieldaroundastar,accordingtoMach’sprinciple.“Forsomedays,Iwasbeyondmyselfwithexcitement…”:Folsing,p.374.“Imaginemyjoyoverthepracticability…”:Ibid.,p.373.“Hardlyanyonewhohastrulyunderstood…”:Ibid.,p.372.“RussianhordesalliedwithMongolsandNegroesunleashedagainst thewhiterace.”:Brian,p.89.“TheGermanArmy…”:Sugimoto,p.51.“UnbelievablewhatEuropehasunleashedinitsfolly.”:Folsing,p.343.

Thewar and the greatmental effort necessary…:The chaos caused byWorldWarIalmostclosedtheUniversityofBerlinwhenstudentsseizedcontrolofthecampus and the rector. Faculty members immediately called Einstein to helpnegotiatetheirrelease.EinsteininturncalledphysicistMaxBorntohelpmaketheperilous journey tonegotiatewith thestudents.Bornwould laterwrite thatthey traveled“in theBavarianQuarter throughstreets fullofwild-lookingandshouting youthswith red badges….Einsteinwaswell known to be politicallyleftwing, ifnot ‘red’,andwouldbean idealperson tohelpnegotiatewith thestudents”(Brian,p.97).Einsteinwasrecognizedbythestudents,whothengavehimtheirdemands.TheyagreedtolettheirprisonersgofreeifthenewlyelectedSocialDemocraticpresident,FriedrichEbert,consented.EinsteinandBornthenmade the journey to the palace of the Reichschancellor and pleaded with thepresident, who then agreed to authorize the release of the prisoners. Bornrecalled later, “We left the palace in the Reichschancellor in the highest ofspirits, with the feeling of having taken part in a historic event, and hopingindeedthatthetimeofPrussianarrogancewasfinished,thatitwasalloverwiththe Junkers, the hegemony of the aristocrats, the cliques of officials, and themilitary, that now theGerman democracywas victorious.”Einstein andBorn,twotheoreticalphysicistsinterestedinthesecretsoftheatomandtheuniverse,hadapparentlyfoundamorepracticalapplicationfor their talents:saving theiruniversity.

Chapter5.TheNewCopernicus“DearMother—Goodnewstoday…”:Sugimoto,p.57.“Ifhehadreallyunderstood…”:Calaprice,p.97.“Therewasanatmosphereoftenseinterest…”:Parker,p.124.“Aftercarefulstudyoftheplates…”:Ibid.“oneofthegreatestachievementsinthehistoryofhumanthought….”:Clark,p.290;Parker,p.124.“There’sarumor…”:Parker,p.126.“Don’tbemodestEddington…”:Ibid.“RevolutioninScience—NewTheoryoftheUniverse—…”:Folsing,p.445.“AllEnglandistalking…”:Ibid.“TodayinGermanyIamcalledaGermanmanofscience,…”:Ibid.,p.451.“Atpresent,everycoachmanandeverywaiter…”:Ibid.,p.343.“Sincethefloodofnewspaperarticles…”:Cropper,p.217.“Thisworldisacuriousmadhouse…”:Ibid.,p.217.“Ifeelnowsomethinglikeawhore….”:Brian,p.106.

“seem to have been seizedwith something like intellectual panic…”: Ibid., p.102.“Thesupposedastronomicalproofs…”:Ibid.,p.101.“Ihavereadvariousarticlesonthefourthdimension,…”:Ibid.,p.102.“cross-eyedphysics…utterlymad…”:Ibid.,p.103.“Anewscientifictruthdoesnotasaruleprevail…”:Folsing,p.199.“Great spirits have always encountered violent opposition…”: Pais, EinsteinLivedHere,p.219.“couldhavebeenpredictedfromthestart—…”:Sugimoto,p.66.“weshouldnotdriveawaysuchaman…”:Brian,p.113.HehadfinallyrediscoveredhisJewishroots….:ItshouldbepointedoutthathisZionist colleagues often feared that Einstein, famous for speaking his mind,wouldsaythingstheydisapprovedof.Einstein,forexample,oncethought thatthe Jewish homeland should be in Peru, stressing that no one should beunnecessarilydisplacedifJewssettledthere.Heoftenstatedthatfriendshipandmutual respectbetween theJewishandArabpeoplewereabsolutely importantfactorsinanysuccessfulattempttocreateaJewishstateintheMiddleEast.Heoncewrote, “I shouldmuch rather see a reasonable agreementwith theArabsbasedonlivingtogetherinpeacethanthecreationofaJewishstate”(Calaprice,p.135).“makingmeconsciousofmyJewishsoul…”:Brian,p.120.“It’sliketheBarnumcircus!”:Ibid.,p.121.“TheladiesofNewYork…”:Sugimoto,p.74.Amobofeightthousandsqueezed…:Brian,p.123.“frompossiblyseriousinjuryonlybystrenuousefforts…”:Ibid.,p.130.“Itwasthefirsttimeinmylife…”:Pais,EinsteinLivedHere,p.154.“NotuntilIwasinAmericadidIdiscover…”:Folsing,p.505.“Ifyourtheoriesaresound,Iunderstand…”:Brian,p.131.“Hehasbecomethegreatfashion….”:Pais,EinsteinLivedHere,p.152.“IfaGermanweretodiscoveracureforcancer…”:Sugimoto,p.63.Previously,hehadevenadvocatedkillingRathenau.:Ibid.,p.64.“itwasapatrioticdutytoshoot…”:Clark,p.360Once,amentallyunbalancedRussianimmigrant,…:Brian,p.150.“Lifeislikeridingabicycle….”:Ibid.,p.146.“Hespentallhistime…”:Brian,p.144.Bythe1920sand1930s,Einsteinhademergedasagiant…:Einstein,alionofGermansociety,wasconstantlysurroundedbywealthymatronswhoclamoredto hear his wit and wisdom, many of whom would donate generously to hisfavorite causes and charities. Some of them would occasionally send their

personallimousinetopickEinsteinupathissummerhouseinCaputh,toescorthim toa fund-raiserorconcert. Inevitably, rumorswould spreadaboutallegedaffairs.Ifonetracksthesourceoftheserumors,onefindsthattheycomemainlyfrom the recollections of themaid at the summer house, HertaWaldow,whosoldherstorytothepress.Shehadnoproof,however,ofanyextramaritalaffairsand admitted that these society women would invariably personally givechocolates to Elsa when picking up her husband to quell any suspicions ofimpropriety. Furthermore, Konrad Wachsmann, an architect who helped todesign the Caputh summer house, observed the Einstein household andconcludedthattheseliaisonswereperfectlyharmless.Hebelievedthattheywere“almostwithoutexception”platonicinnature,thatEinsteinwasneverunfaithfultoElsawiththesewomen.“gentle,warm,motherly,…”:Cropper,p.217.“Heatewitheverybody,…”:Pais,EinsteinLivedHere,p.184.“Thepeopleapplaudme…”:Sugimoto,p.122.“Icouldhaveimagined…”:Brian,p.205.“Itwasinterestingtoseethemtogether—…”:Calaprice,p.336.“Isnotallofphilosophyasifwritteninhoney?…”:Pais,SubtleIstheLord,p.318.“Theworld,consideredfromthephysicalaspect,…”:Pais,EinsteinLivedHere,p.186.“Moralityisofthehighestimportance—…”:Calaprice,p.293.“Sciencewithoutreligionislame,…”:Pais,EinsteinLivedHere,p.122.“Themostbeautifulanddeepestexperience…”:Ibid.,p.119.“Ifsomethingisinmewhichcanbecalledreligious,…”:Sugimoto,p.113.“I’mnotanatheist…”:Brian,p.186.

Chapter6.TheBigBangandBlackHoles“Ifthematterwasevenly…”:Misneretal.,p.756.“Myhusbanddoesthat…”:Croswell,p.35.“ThereshouldbealawofNature…”:Thorne,p.210.“thereisnotmuchhope…”:Pettersetal.,p.7.“isoflittlevalue,butitmakesthepoorguy[Mandl]happy.”:Ibid.

Chapter7.UnificationandtheQuantumChallenge“Theydonotshakemystrongfeeling…”:Pais,SubtleIstheLord,p.23.“Itisamasterfulsymphony”:Parker,p.209.

“nosignificanceforphysics.”:Pais,SubtleIstheLord,p.343.“Theideaofachieving…”:Ibid.,p.330.“Theformalunityofyourtheoryisstartling.”:Ibid.,p.330.“Youmaybeamusedtohear…”:Pais,EinsteinLivedHere,p.179.“Itisnotevenwrong.”:Cropper,p.257.“Idonotmind…”:Ibid.“Whatyousaid…”:Ibid.“Somepeoplehaveverysensitive…”:Ibid.“Themoresuccess…”:Calaprice,p.231.“LikethedarkladywhoinspiredShakespeare’ssonnets,…”:Moore,p.195.Thisextraminussign,arguedDirac,madepossible…:Becausematterpreferstotumbledowntothelowestenergystate, thismeant thatallelectronsmightfallinto these negative energy states and the universewould collapse. To preventthisdisaster,Diracpostulatedthatallnegativeenergystateswerealreadyfilled.Apassinggammaraymightknockanelectronoutofitsnegativeenergystate,leaving a “hole” or bubble. This hole, predicted Dirac, would behave like anelectronwithpositivecharge,i.e.,antimatter.“Thesaddestchapterofmodernphysics…”:Pais,InwardBound,p.348.“Ithinkthatthisdiscoveryofantimatter…”:Ibid.,p.360“themotionofparticlesfollows…”:Folsing,p.585.“Quantummechanicscallsforagreatdealofrespect….”:Ibid.“Heisenberghaslaidabigquantumegg….”:Brian,p.156.p.165“cobbleroremployeeinagaminghouse”:Ferris,p.290.“Physicistswerebeginningto…:Einsteinmostclearlypresentedhispositionondeterminismanduncertaintyasfollows:“Iamadeterminist,compelledtoactasif freewill existed, because if Iwish to live in a civilized society, Imust actresponsibly.Iknowphilosophicallyamurdererisnotresponsibleforhiscrimes,but I prefer not to take tea with him…. I have no control, primarily thosemysteriousglandsinwhichnaturepreparestheveryessenceoflife.HenryFordmaycall it ishis InnerVoice,Socrates referred to itashisdaemon:eachmanexplainsinhisownwaythefactthatthehumanwillisnotfree….Everythingisdetermined,thebeginningaswellastheend,byforcesoverwhichwehavenocontrol. It is determined for the insect aswell as for the star. Human beings,vegetables, or cosmic dust, we all dance to amysterious time, intoned in thedistancebyaninvisibleplayer”(Brian,p.185).“Ifthelastproofissentaway,thenIwillcome.”:Cropper,p.244.“ToBohr,thiswasaheavyblow….”:Folsing,p.561.“Iamconvincedthatthistheory…”:Ibid.,p.591.“thegreatestdebateinintellectualhistory…”:Brian,p.306.

“Idon’tlikeit,…”:Kaku,Hyperspace,p.280.“Doesthemoonexist…”:Ibid.,p.260.“I have thought a hundred times as much about the quantum problems…”:Calaprice,p.260.“spookyaction-at-a-distance”:Brian,p.281.“Iwasveryhappythatinthatpaper…”:Ibid.“Wedroppedeverything;…”:Folsing,p.698.“most successful physical theory of our period”: Pais,Einstein LivedHere, p.128.

Chapter8.War,Peace,andE=mc2“ThismeansthatIamopposedtotheuseofforce…”:Cropper,p.226.“Thepurposeofthispublicationistooppose…”:Sugimoto,p.127.“Turnaround,youwillneverseeitagain.”:Pais,EinsteinLivedHere,p.190.“Undertoday’sconditions,ifIwereaBelgian,…”:Folsing,p.675.“Theantimilitaristsarefallingonme…”:Ibid.“Ihadhopedtoconvincehim…”:Cropper,p.271.“PeoplesaythatIgetattacksofnervousweakness,…”:Brian,p.247.“Ifailedtomakemyselfunderstood…”:Cropper,p.271.Hecouldhavebeenseriouslyhurtbythisferociousbeating,…:Moore,p.265.“Princetonisawonderfullittlespot…”:Cropper,p.226.“largewastebasket…soIcanthrow…”:Brian,p.251.TwoEuropeans,onabet…:Parker,p.17.“graveheredity”:Folsing,p.672.“Ihaveseenitcoming,…”:Ibid.“utterlyashenandshaken”:Brian,p.297.“severedthestrongesttiehehad…”:Ibid.“Ihavegotusedextremelywell…”:Folsing,p.699.“Itmightbepossible,anditisnotevenimprobable,…”:Ibid.,p.707.“Allbombardmentssince…”:Ibid.,p.708.“Assumingthatitwerepossibletoeffect…”:Ibid.“asfiringatbirdsinthedark,…”:Ibid.,p.709.“theraysreleased…areinturn…”:Ibid.,p.708.“thecountrythatexploitsitfirst…”:Ibid.,p.712.“anyonewhoexpectsasourceofpower…”:Pais,InwardBound,p.436.“Oh,whatfoolsweallhavebeen!”Cropper,p.340.“donotjustifytheassumption…”:Folsing,p.710.“SomerecentworkbyE.FermiandL.Szilard,…”:Ibid.,p.712.

“Thisrequiresaction.”:Ibid.“Iwillhavenothing…”:Cropper,p.342.“Iwouldratherwalknaked…”:Ibid.“IwishverymuchthatIcouldplace…”:Folsing,p.714.“Inviewofhisradicalbackground,…”:Ibid.“Hefeltverybadaboutbeingneglected….”:Ibid.,p.715.“saidanewkindofbombhasbeendroppedonJapan….”:Brian,p.344.In1946,Einsteinmadethecover…:In1948,hehelpeddrafthisMessagetotheIntellectuals,whichstated,“Manhasnotsucceededindevelopingpoliticalandeconomicformsoforganizationwhichwouldguaranteethepeacefulcoexistenceofthenationsoftheworld.Wescientists,whosetragicdestinyhasbeentohelpinmakingthemethodsofannihilationmoregruesomeandmoreeffective,mustconsider itoursolemnand transcendentduty todoall inourpower topreventthese weapons from being used for the brutal purpose for which they wereinvented.What task couldpossiblybemore important to us?What social aimcouldbeclosertoourhearts?”(Sugimoto,p.153).Heclarifiedhisviewonworldgovernmentwhenhesaid,“Theonlysalvationforcivilization…lies in thecreationofworldgovernment,withsecurityofnationsfounded upon law…. As long as sovereign states continue to have separatearmamentsandarmamentssecrets,newworldwarswillbeinevitable”(Folsing,p.721).“Youareafterbiggame….”:Brian,p.350.“IbelieveIamright….”:Ibid.,p.359.“Mathematicalpatternslikethoseof thepaintersor thepoets…”:Weinberg,p.153.“Ihavebecomealonelyoldfellow….”:Brian,p.331.“Imustseemlikeanostrich…”:Pais,SubtleIstheLord,p.465.“Iamgenerallyregardedasasortofpetrifiedobject…”:Ibid.,p.162.“Oppenheimermadefun…”:Brian,p.377.“Thisisnotajubileebookforme,…”:Cropper,p.223.“Anythingreallynewisinvented…”:Ibid.“Natureshowsusonly…”:Calaprice,p.232.“SubtleistheLord,…”Ibid.,p.241.“Ihavesecondthoughts…”:Ibid.“From1954totheendofhislife,…”:Pais,InwardBound,p.585.“Weintheback…”:Kaku,BeyondEinstein,p.11.“Itwasanuncannyencounteroftwogiants…”:Cropper,p.252.“WhatIadmiredmostaboutMichelewasthefact…”:Overbye,p.377.“Itistastelesstoprolonglifeartificially….”:Calaprice,p.63.

Chapter9.Einstein’sPropheticLegacy“Theverystudyoftheexternalworld…”:CreaseandMann,p.67.“Sciencecannotsolvetheultimatemystery…”:Barrow,p.378.Thiswouldbetheacidtest….:Moreprecisely,Belladvocatedre-examiningtheoldEPRexperiment.Inprinciple,onecanmeasuretheanglescreatedbytheaxisof polarization of the pairs of electrons. Bymaking a detailed analysis of thecorrelation between various angles of polarization between the two pairs ofelectrons, Bell was able to construct an inequality, called “Bell’s inequality,”concerning these angles. If quantum mechanics were correct, then one set ofrelationswouldbesatisfied.Ifquantummechanicswereincorrect,thenanotherset of relations would be satisfied. Every time this experiment has beenperformed,thepredictionsofquantummechanicsprovetobecorrect.“IthinkIcansafelysay…”:Barrow,p.144.“At first sight, it looked artificial…”: Petters et al., p. 155;New York Times,March31,1998.“It’sabulls-eye!”:NewYorkTimes,Ibid.“Wecannotsendatimetraveler…”:Hawkingetal.,p.85.“Stringtheoryhasprovidedourfirstplausiblecandidate…”:Weinberg,p.212.“TheNobelPrizeinPhysics…”:Kaku,BeyondEinstein,p.67.“IfIhadknown…”:Ibid.“String theory is extremely attractive because gravity is forced upon us….”:DaviesandBrown,p.95.Itshouldalsobepointedoutthatthelatestversionofstring theory is called “M-theory.” String theory is defined in ten-dimensionalspace (with nine dimensions of space and one dimension of time). However,therearefiveself-consistentstringtheoriesthatcanbewrittenintendimensions,whichhaspuzzledtheoristswhowouldlikeasinglecandidateforaunifiedfieldtheory, not five. Recently, Witten and his colleagues showed that all fivetheoriesareactuallyequivalent ifonedefines the theory ineleven-dimensionalspace (with ten dimensions of space and one dimension of time). In elevendimensions, higherdimensionalmembranes can exist, and some speculate thatouruniversemaybesuchamembrane.Although the introductionofM-theoryhasbeenagreatadvanceforstringtheory,atpresentnooneknowsthepreciseequationsforM-theory.“Einsteinwouldhavebeenpleasedwiththis,…”:Ibid.,p.150.“Ibelievethatinordertomakerealprogress…”:Pais,SubtleIstheLord,p.328.“Thecreativeprincipleresides…”:Kaku,QuantumFieldTheory,p.699.

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TableofContents

Preface:ANewLookattheLegacyofAlbertEinsteinAcknowledgmentsPartI.FirstPicture:RacingaLightBeam

CHAPTER1PhysicsbeforeEinsteinCHAPTER2TheEarlyYearsCHAPTER3SpecialRelativityandthe“MiracleYear”

PartII.SecondPicture:WarpedSpace-Time

CHAPTER 4 General Relativity and “the Happiest Thought of MyLife”CHAPTER5TheNewCopernicusCHAPTER6TheBigBangandBlackHoles

PartIII.TheUnfinishedPicture:TheUnifiedFieldTheory

CHAPTER7UnificationandtheQuantumChallengeCHAPTER8War,Peace,andE=mc2CHAPTER9Einstein’sPropheticLegacyNotesBibliography