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Insight Press614Vermont Street, San Francisco, CA 94107
Written and Illustrated by
Lewis Carroll EpsteinCity College o Sam h c i s c o f
The following people played important parts in putting this story together:encouragement educationMichael Scott Robert Pisani
Michael Gatdebled Jonathan KernLouise Ainsworth Gerald Leone
discussions of theory
HatryM John Ehlers David Wall Robert Nason Peter Epstein Danny Epstein Renie Baus David SonnabendAmy McManus
organizing initiation to the world of publication
Robert Head Darllen Flfe Paul Hewilt Ellen BuonRobyn Brode
illustrations editing, design, and production typesetting printing
Chapter 5 i the centerpiece oS s thiswork The chapters p d in8 it relate to its development and those fo110wbg it relate t o application of its perspective.
a b l e of C o n t e n . .
The Prhcfple of RelatfvftyMostly on the historyo ideasabout m o w f Galilee's Dictum ught In the Day of the Ether The Dictum in Jeopardy The Dictum Prevails Summary Question and Answer
38 11 11 14 16
Ether atoms The old aetherChapter 2
The Central ProblemMostly about the s p e d o light f
A Step Backward The Problem Possibilities A Wild Plan
ReviewQuestions and Answers
Inside a physicist's head
viii / TABLE OF CONTENTS
Pandora's BOXMostly about time desgnchroMon and is 6onseqmence-s t
Thought Experiments Synchronized Motion DifFerent Time Desynchronized Motion Space Shrinks Epitome Questions and Answers
3333 34 39 41 42 43
No sideways contraction Playing with time offsets Seeing or measuring?Chapter 4
Measuring the ConseqnencesMostly about how to calculatethe effect exady
'ho Kinds of Speed Slow Time Cosmic Speedometer Question and Answer Light Waves Desynchronized Time Does the photon know the light clock is moving? The aether and who is really moving Ganged clocks Beating the limitChapter 5
63 67 68 69
62 6671 73
The MythMostly abont w y space shrinks, time s l o w and h w y you c n t go laster than light h a'
Good and Bad Myths The Story Out of Body W o Kinds of Time Question and Answer 3D
TABLE OF CONTENTS / i x
In the Beginning What Makes It Shrink? Questions and Answers The Myth Proven A Parting Word Question and Answer The myths of motion Through space and timeChapter 6
The Big BangMostly about the fireban radiation, the edge o f the adverse, and the coarmological principle as applied to the B g Bang cosmology i Genesis 100 Looking Back 101 Age Is Impossible 103 The Ultimate Horizon 104Chapter 7
The Third LegM o s t ,about how speed affects mass
Mass Momentum Punch Out Relative Mass Energy Has Weight Relative momentum ImpedoChapter 8
107 108 110 114 117
Mostly aboat theweight o f energy and what mass is made o f
Equivalent Energy,Equivalent Weight Masserators A Popular Misconception Is Mass Energy? For teachers only E = mc2 by bouncing light from a moving mirror
121 122 127 129
x / TABLE OF CONTENlS
Ea *Mostly about changing the speed o I&ht f
Light Falls Can C Change? Crisis Slow Time Again Curved Spacetime Heavy light How slow?Chapter 1 0
137 138 140 140 141138
Cause o Gravity fMostly about how curved spacetime makes gravity
The Origin of Gravity Surprise! How Fast Can You Fall? A Hole to China 'Ikapped Inside Question and Answer Escape Fashion, Not Shape The floor comes up Galilee's explanation Gravitation by refractionChapter 1 1
Spaee WarpedMostly about how camed spamakes gravity
Bullet Versus Photon The Bump Another Cause The Bump's Effect Questions and Answers Everything Wrinkled Questions and Answers How to draw straight lines on curved surfaces
164 16 6 170 171 175 177 179182
TABLE OF CONTENTS /xi
The Ends of Space and T h eMostly aboat the raptnring and mending o heaven f
Black Hole Worm Holes and Bridges 'Ifrvo Cosmologies Question and Answer
184 193 194 196
Black hole anticipated How to draw infinity
Whilemodwinsleep,atew~creep, in places deep,where
dark &hags keep..
Among all creatP11.e~. hmmsare distfngrrishedby the extent to which they wonder about things that do not immediately affect their subsistence.
m Principle eGallleo's IHctnm
The year Columbus spent discovering the New World, a university sophomore named Copernicus spent discovering mathematics and astronomy. These discoveries and a lifetime of study led Copernicus to the realization that the earth was not only a globe in space, but that the globe MOVED around the sun. However, most thinking people found it impossible to believe that the heavy earth could be in motion, indeed, in perpetual motion. They presented reasoned arguments against Copernicus's theory. Here is one such argument: Suppose the earth does move and suppose you drop a coin directly above your toe. By the time the coin falls to earth the earth will have moved and your foot will be carried with it. So the is coin must m s your toe. But if you drop a coin above your toe it will, in fact, hit your toe.Thus the earth can- Figure 1-1. Ifthe earth was m ' n g , not be moving. then dropped objects would notfall About a century later, while the straight down.
2 / THE PRINCIPLE OF RELATIVITY
first English colonies were being established in North America, Galileo came to the defense of the moving earth idea. Here, in a nutshell, is Galileo's counterargument. Suppose you are flying along smoothly and standing inside an aircraft cabin, even in a supersonic aircraft, and you drop a coin directly above your toe. Sure enough, it hits your toe.* Galileo referred to a ship's cabin rather than an aircraft cabin, but the central idea is that if you are closed inside a box that is moving smoothly, that is, not starting or stopping or jerking or turning but just moving at one speed in one direction, you cannot tell if you are in motion; everything in your box happens as if' you were at rest. That fundamental idea became known as Galilee's Dictum. Moreover, if you open a window in the box and look out and see another box approaching your box, you still can't tell if you are moving. You can't tell if you are moving toward the other box or if the other box is moving toward you. All you know is that there is relative motion between the boxes. In essence, Galileo's Dictum is this: All smooth, linear motions are
Figure 1-2. But dropped objea do falZaaigbt dolOn. nerefme, the earth cannot be in motion.
*The coin hits your toe because if your toe is moving to the right due to the aircraft's motion, so also is the coin moving to the right at the moment it is dropped, since the is joined the lira& Your body just before you drop it.The coin keeps moving to the right after you let go. So the coin follows your toe and hits i t
relative. The universe is full of parl ticles, a l moving in different directions at different speeds. Who is to say which particle is really, absolutely, at rest? Thus you can never say, "The speed of this particle is 900 miles per hour." All you can say is, "The speed of this particle is 900 miles per hour relative to the air, or relative to the moon, or relative to this earthquake wave frontl' This is all very reasonable and the business would be permanently settled here were it not for certain curiosities about light first noted by a keeneyed painter, Franciscus Grimaldi, who was officially employed by the very two popes with whom Galileo had his daculties.
Figure 1-3. Smooth motion in a straight line does not affect what is happening inside the box. You might think that is obvious,yet in the thy of Galileo it was a new idea.
Grimaldi observed that surrounding and even inside the shadow of an opaque object were several rings or fringes. Now, most people had supposed that light was a rain of minute particles. That idea fit well into Galileo's scheme of a world of particles and it explained why light flies in straight lines and why shadows are exact silhouettes of the objects that cast them. But it did not explain Grimaldi's fringes. The artist proposed that light was a fluidlike substance that could flow slightly around and behind objects, and that the fringes resulted from ripples spreading downstream from the edges of an object, just as ripples spread from the edges of a stone
4 / THE PRINCIPLE OF RELATIVITY
Figure 1 4 . If light t3 a rain of little pellets, an object should completely shield the area behind it, as illustrated here. To do tht3 apm'ment,you need a point source of light. 7%esun (or a light bulb) is not a point source. SO the light 13passed though a pinhole; the pinhole is thepoint.
Figure 1-5. But infact, the area behind an object is not completely shieIded. Ifyou look very closely,you willsee it is contaminated with rings of light.
6 / THE PRINCIPLE OF RELATIVITY
Figure 1-6 Note the waves spreading into the shieIded area of quiet water behind the stone.
around which a fast current is flowing. In this way the wave nature of light first came to be suspected. As the theory was subsequently developed, light was taken to be a vibration transmitted through space, rather than a fluid flow through space. (Yet, f