A Brief History of Astronomy

Osher Lifelong Learning Institute October 1, 2013

Dick Dahlberg

What Is So Special About Astronomy?

• For 3000 years: Astronomy = Science – From ancient Babylon to Copernicus (15th C.)

• But with a little geometry thrown in.

• The heavens were visible. – There was a pattern to the behavior of the Sun,

Moon, stars, planets. – Was there also a message???

• Creation myths frequently had a cosmic basis.

Astronomy Also The Basis For Many Early Religions

• Tribes and villages with a common set of beliefs were more stable .

• Belief systems (religions?) frequently had a cosmic component.

• There must be some explanation for the locust invasion. – OF COURSE: the planetary alignment was wrong!!!!

Agenda • Ancient Babylon (2nd to 3rd millenia BCE):

– Star maps • Ancient Greeks (3rd to 6th century BCE):

– Remarkable calculations concerning our solar system. • Aristotle (384 to 322 BCE):

– Earth at the center of a perfect and divine Universe. • Ptolemy (60 to 168 CE):

– Added bells and whistles to Aristotle’s mistake. • Copernicus (1473 to 1543):

– Sun centered solar system: Part 1: Simplicity a virtue. • Tycho Brahe (1546 to 1601):

– Refined astronomical data.

Agenda - Continued • Kepler (1571 to 1630):

– Sun centered solar system: Part 2: Orbits are ellipses. • Galileo (1564 to 1642):

– Sun centered solar system : Part 3: More evidence. – The heavens are not perfect and divine.

• Sun spots; Moon craters – Jupiter’s moons; phases of Venus

• Newton (1642 to 1727): – Sun centered solar system: Part 4: The physics.

• Michelson/Morley (1852 to 1931): – Proved there was no ether.

Agenda - Continued • Einstein (1879 to 1955):

– Laid the groundwork for the Big Bang. • Evidence of the Big Bang:

– Lemaitre (1894 to 1966): • Deduced the possibility of a Big Bang from Einstein’s General

Theory of Relativity. – Hubble (1889 to 1953:

• Discovered the red-shift: everything is moving away from everything else.

– Gamow, Alpher and Hoyle (mid 20th Century): • Deduced the abundance of elements from first principles.

– Penzias and Wilson (1964): • Discovered radiation left over from the Big Bang.

Astronomy in Ancient Babylon 2nd and 3rd Millennia BCE

The Babylonian Book

Enuma Anu Enlil Tablet 63: The Venus Tablet: 7th c. BCE .

• Enuma Anu Enlil contained a record of Babylonian astronomical observations. – Star catalogs. – Data on Mercury, Venus, Mars,

Jupiter and Saturn.

• Babylonian data were extensively used by the Greeks and Egyptians.

ANCIENT GREEK SCIENTISTS

The Emergence of Real Scientists Ancient Greeks

Greek Scientists in Raphael’s Painting: Pythagoras Anaxagoras Aristotle Euclid Ptolemy Plato Many other philosophers and

scientists

School of Athens Raphael Fresco (1509), Vatican City

Aristarchus: 310 to 230 BCE • Proposed a sun-

centered solar system. • The Earth rotates on its

axis once a day. – Estimated distance to

the Sun.

Aristarchus Relative Distances: Sun and Moon

• At half-moon, the Moon, Sun and Earth for a right triangle.

• The Moon-Earth-Sun angle can be measured. – 87 degrees by Aristarchus.

• The Sun is 20 times farther than Moon.

• Good science: wrong answer. – The actual multiplier is 400. – The actual angle was close to

90 degrees: hard to measure.

Eratosthenes: 275 to 195 BCE • Greek mathematician and

astronomer. • Determined the

circumference of the Earth

• Determined the diameter of the Moon and its distance from the Earth.

Eratosthenes Circumference of the Earth

Julian Rubin: julianTrubin.com (2011)

• Find a spot where Sun is directly overhead: Syene (Aswan, Egypt)

• Place a pole a known distance from that spot. – Alexandria, 550 miles from Syene..

• Measure the angle between pole and sun’s ray: – 7.2degrees.

• Then: 7.2 / 360 = 550/Circumference. • Circ. = 27,500 miles.

• Radius of the Earth: • L = length of shadow cast at

Alexandria by pole of height H: • L/H = 550/radius

Hipparchus: 190 to 120 BCE • The greatest astronomer in

antiquity. • His quantitative models of the

motions of the Sun and Moon have survived.

• Achievements: – Predicted eclipses. – Distance to Moon: 250,000

miles. – First star catalogue. – Calculated length of year to

within 6.5 minutes.. • Hipparchus’ work was

extensively reported in Ptolemy’s “Almagest”.

The “First Authority”

Aristotle 384 to 322 BCE

Aristotle’s Early Life

• Born in northern Greece. • Aristocratic family.

• At age 18, student at Plato’s Academy.

• At age 42, became head of Royal Society of Macedon. – Alexander the Grea

Aristotle The Pre-Eminent Teacher

Aristotle studied under Plato for 24 years.

Plato and Aristotle From Raphael’s Painting

“School of Athens”

• Founded the Lyceum in 335 BCE (at age 49).

• Studied and taught anatomy, astronomy, geology, physics, rhetoric, theology, philosophy, logic …..(almost everything)

• Sought the general principles of nature. – By observation.

• Wanted to unify all branches of knowledge – Wrote 150 treatises.

• For 2000 years, he defined an educated man.

Aristotle’s Universe • The Universe is divine and perfect. • Heavenly bodies move naturally in perfect circles.

• The circular motions are in harmony with theology: perfect.

• The heavens are a nest of spherical shells with the

Earth at the center • The largest is a Devine Sphere, self-moving, carrying the

fixed stars.

• An “aether” fills the Universe and makes up the stars and planets.

The Earth Centered Universe

Claudius Ptolemy 2nd Century CE Egyptian Astronomer

Claudius Ptolemy Last Great Astronomer of Ancient Times

Early Baroque Artist’s Rendition

• 90 CE to 168 CE. • Roman citizen • Greek ancestry

– Wrote in Greek. • Lived in Alexandria • Ptolemy built on

Aristotle’s Universe.

The “Almagest”:

The “Greatest Compilation”

Picture of George Trebizoud’s Latin Translation of the “Almagest” (15th c..)

• Ptolemy’s major work on astronomy. – Much due to Hipparchus. – Divided into 13 books.

• Goal: write down everything that was known. – Star catalogues.

• Locations for 1022 stars and 48 constellations.

– Tables for computing planetary locations.

Ptolemy’s Universe

• The Earth was at the center (of the Universe).

• Earth did not move

• All motion was in circular paths.

• Universe imagined to be composed of nested spheres.

Ptolemy’s Model Complicated But Accurate

• Epicycles necessary for accuracy. – Accurately gave locations

of planets, stars. – Predicted eclipses.

• Better than initial versions of the sun-centered model.

Ptolemic Model of the Universe

1747 Icelandic Manuscript

1524 Engraving Library of Congress

Comparison Earth-Centered vs. Sun-Centered

Criterion Earth- Centered: Ptolemy

Success Sun-Centered: Early Greek

Success

Common sense

Obvious Good Leap of imagination

Not so good

Awareness of motion

None detected Good None detected Not so good

Stellar parallax None observed

Good None observed Not so good

Planetary predictions

With epicycles Good Not so good

Simplicity Very complex Not so good Naturally simple

Good

What Is the Parallax Effect?

Astronomy 161 Lectures Dept. of Physics and Astronomy University of Tennessee

Ptolemy’s “Ecumene” Map

Map Of the Known World

1482 Johannes Schnitzer Engraving (British Library Board)

• Devised a latitude/longitude grid. – Located the grid

coordinates for 8000 locations on the world map.

• Even though Ptolemy’s estimates of latitude and longitude were wrong by about 15%, his maps were used into the 16th Century.

The Sun Centered Universe: Part 1

Nicholas Copernicus: 1473 to 1543

Nicholas Copernicus Renaissance Astronomer (1473 to 1543)

• Polish mathematician,

astronomer, physician, jurist, diplomat, cleric, artist, poet, economist, and linguist (translated ancient Greek texts into Latin).

• Was a strong Catholic. – Received a doctorate in canon

law . – Did not want to antagonize

the Church. • Church strongly favored the

Ptolemaic model of the Universe. – Biblical references to the

relative positions of Sun and Earth.

Biblical References?

• Psalm 93.1 and Chronicles 16:30: “The world is firmly established , it cannot be moved.”

• Ecclesiastes 1:5: “And the Sun rises and sets and returns to its place”.

Simplicity The Driving Force For Copernicus

• Was familiar with the Sun-centered model of the Ancient Greeks. – Had great respect for Aristotle. – Was a student of Ptolemy’s “Almagest”.

• But simplicity is a virtue.

– William of Occam: 14th Century Franciscan. – Occam’s Rasor: The simplest of two competing theories is probably

the best. • “When you hear hoof beats, think horses not zebras.”

The Starting Point: Seven Axioms

1) The heavenly bodies do not share a common center. 2) The center of the Earth is not the center of the universe.

3) The center of the universe is near the Sun. 4) The distance from Sun to Earth is insignificant compared to the distance

to the stars.

5) The daily apparent motion of the stars is a result of the Earth’s rotation on its own axis.

6) The apparent annual sequence of movements of the Sun is a result of the Earth’s rotation about it.

7) The apparent retrograde motion of some of the planets is the result of our relative position as observer on a moving Earth.

Copernicus’s Seminal Work “On The Revolution Of the Heavenly Spheres”: 1543

Copernicus’s Universe: • Sphere of fixed stars. • Saturn: 30 year orbit. • Jupiter: 12 years. • Mars: 2 years. • Earth. • Venus: 9 months. • Mercury: 80 days.

All orbits circular and uniform around the Sun.

The Phases of Venus Model Comparison

Ptolemaic Earth-Centered Model Venus is between the Earth and Sun Venus always appears as a crescent. Copernican Sun-Centered Model Venus is not always between the Earth and Sun. The full range of phases is seen from the Earth.

Astronomy 161 Lectures Dept. of Physics and Astronomy University of Tennessee

Copernicus’s Work: Small (Initial) Impact Why???

• Copernicus died shortly after publication: Could not promote his ideas. • The Church was against him • Dreadful writing style. • An unauthorized preface was added (during printing) implying that the

major hypothesis was not true. – Apparently Copernicus’s apprentice, Georg Rheticus, and a Lutheran cleric, Andreas

Osiander, added the preface. – Purpose? A mystery.

• AND: The Ptolemaic Model was more accurate

• CONCLUSION: Need more accurate data

Needed: More Astronomical Data

Tycho Brahe: 1546 to 1601 The Scientific Bridge Between

Copernicus and Kepler

Tycho Brahe Danish Scientist (and Character)

• Swashbuckling Danish nobleman • Lost part of his nose in a duel. • Employed a dwarf court jester who sat under the table while they were eating. • Also had a tame elk • Died from too much beer.

• Fell in love with Kirsten Hansen – Daughter of a Lutheran

minister, a commoner. • Danish law:

– When nobleman and commoner live together, and she has the keys to the house, their allegiance is binding in a “morganatic marriage” after 3 years.

• They lived together for 30 years. – Had 8 (legitimate) children.

Initial Interest In Astronomy

• In 1572 (age 26) Brahe witnessed a supernova: Tycho’s Star.

• In 1577 Brahe observed a comet. – Accompanying tail suggested an “elongated” orbit.

• Conventional wisdom at the time:

– Both were atmospheric events. – The universe beyond the Moon’s orbit? Perfect and unchangeable.

• Brahe showed both events were not atmospheric events.

* Aristotle: beware.

Brahe: Professional Astronomer • Brahe became obsessed with the need for more and better astronomical data.

• King Frederick II persuaded Brahe to set up shop in Denmark

• Moved to Prague in 1597.

– At the invitation of HRE Rudolph II. – Established a new observatory.

• Worked there with Kepler until his death in 1601.

• His legacy: a vast amount of accurate astronomical data.

Late Breaking News

• Body exhumed in 2010 to try to determine cause of death: – Burst bladder? Judgment at the time.

• 11 days before death, at a banquet, he should have gone to the toilet but didn’t.

– Kidney failure? – Killed by Kepler? – Poisoned (mercury) by his cousin, Eric Brahe, on orders from

Danish king, Christian IV ? • Tycho was rumored to be having an affair with the King’s mother.

– An accidental overdose of mercury taken by Tycho in medicating a kidney ailment?

– Autopsy will examine hair samples and conduct CT scan of bones.

The Sun Centered Universe: Part 2 Johannes Kepler: 1571 to 1630

Johannes Kepler

1610 Portrait [Artist Unknown]

• German mathematician and astronomer.

– Prof. of Mathematics and Astronomy at age 23.

– Assistant to Tycho Brahe (Prague, 1600 to 1601).

• Devout Lutheran • Believed God created cosmic

harmony through a geometric arrangement of planetary orbits.

• Caught up in Counter Reformation

Kepler’s Goal Harmonize the Copernican Model With The Bible

• God created a certain harmony with respect to planetary orbits. – What was His plan?

• The Sun is the symbol of “God

the Father”. • The Son: the stellar sphere. • The Holy Spirit: the intervening

space.

Kepler’s First Attempt: • Regular polygons: one

inscribed inside and one circumscribed outside a circle (orbit) at definite ratios. • The basis for a model of

the Universe? • Did not fit data too well.

• Instead of regular

polygons , try Platonic Solids.

The Five Platonic Solids • Their elegance and simplicity

suggested an astronomical connection.

• Kepler tried to find a connection between the Platonic Solids and planetary orbits.

“The Cosmographic Mystery” (1595) Second Attempt: 3-D Platonic Solids

• The five Platonic Solids could be uniquely inscribed and circumscribed by spheres. – In a nested arrangement.

• Six known planets: Mercury, Venus,

Earth, Mars, Jupiter and Saturn.

• Order of solids: octahedron (8 faces), icosahedron (20), dodecahedron (12), tetrahedron, (4), hexahedron (6, cube).

• The model did not fit all the data. – Inaccurate data?

• In 1600, Kepler (age 27) went to Prague to work with Tycho Brahe to get more accurate data.

Success At Last The Third Attempt

Kepler’s Depiction of the Geocentric Motion of Mars Through Several Retrograde Cycles [Astronomia Nova (1609) ]

• Using Brahe’s Data, Kepler Analyzed the Orbit of Mars

• By trial and error, Kepler discovered the ellipse.

• The First Law: All planets move in ellipses with the Sun at one focus.

Kepler’s Three Laws

Kepler’s Second Law: University of Tennessee Astronomy 161: The Solar System

• First Law: All planets move in ellipses about the Sun with the Sun at one focus.

• Second Law: Planets sweep out equal areas in equal times.

• Third Law: Square of the orbital period of a planet is proportional to the cube of the semi-major axis (half of the major axis). – P = period – R = radius – P1

2/P22 = R1

3/R23

Kepler’s Major Publications

“A New Astronomy” (1609) • Manuscript was completed in 1605.

• Published in 1609 due to legal disputes with Brahe’s heirs. “The Epitome of Copernican Astronomy” • Kepler’s most Influential Work • Three volumes attempted to explain planetary motions through physical

causes.

Epilogue

• As with Copernicus, Kepler’s work not widely accepted at first. – Circular orbits were sacred.

• The Church rejected his findings. • Kepler could not explain why orbits were

elliptical.

The Sun Centered Universe: Part 3 Galileo Galilei: 1564 to 1642

Galileo: The Father Of Modern Science

Galileo Galilei The first mathematical physicist

• Galileo was deeply religious: • A brilliant and caustic wit. • Chair of Mathematics Dept., Univ.

of Padua, at age 27. • The “Father of Modern Science”:

– Scientific method – Experimentalist and theorist

• Believed the Copernican model of the Universe.

Galileo And the Church

At the Beginning

• Galileo was a devout Catholic.

• Galileo’s friend, Cardinal Barberini, became Pope Urban VIII in 1623.

• The Church was adamantly opposed to the Copernican model: – Psalm 93.1 and Chronicles 16:30: “The world is firmly established , it

cannot be moved.” – Ecclesiastes 1:5: “And the Sun rises and sets and returns to its place”.

• Catholicism was in a 30 years war with the Protestants.

– In no mood to be lenient. • Aristotle was still deeply revered.

– Galileo was reluctant to criticize Aristotle.

Galileo’s Telescope Refracting Telescope: 1608

Photograph of Original Telescope

• Flemish spectacle maker won patent for telescope. – Light enters at the top and is

focused on the eye at the bottom.

• Galileo recognized its

potential.

• Built his own, a “refracting” telescope.

Discovery of Moons of Jupiter: 1610 Composite Sketch of Galilean Moons (NASA Archive)

• The Galilean moons from the top: Io, Europa, Ganymede, Callisto.

• Discovery proved that not all heavenly bodies circled the Earth.

The Phases of Venus

• Venus has only one face toward the

Sun. • “Full” exposure appears small from

Earth. – “New” exposure large. – “New” exposure visible because

of “halo”. • This should have been the end of the

Ptolemaic model.

Galileo And The Church: At the End

• Galileo defended the Sun-centered model from the beginning. – Claimed it was not contrary to Scripture.

• The Inquisition ordered Galileo not to “hold or defend” the

Sun-centered hypothesis. – But Galileo was free to “discuss” the Sun-centered model.

• Galileo began writing a “Dialogue Concerning the Two Chief

World Systems”.

“Dialogue Concerning the Two Chief World Systems”: 1632

• Arguments presented as a dialogue on the issues as opposed to advocacy. – Simplicio: Aristotle (Pope

Urban VIII). – Sagredo: neutral layman. – Salviato: Galileo

• Ptolemaic system subtly ridiculed.

• Copernican system advanced.

Galileo Facing the Inquisition 1857 painting by Cristiano Banti

• Found “vehemently suspect of heresy”.

• Required to “abjure, curse and detest” Sun centered theory.

• Formally sentenced to prison. – Commuted to house

arrest. • “Dialogue” was banned.

Comparison Earth-Centered vs. Sun-Centered

Criterion Earth- Centered: Ptolemy

Success Sun-Centered: Galileo/Kepler

Success

Common sense

Obvious Good Leap of imagination

Not so good

Awareness of motion

None detected Good None detected Not so good

Stellar parallax None observed

Good None observed Not so good

Planetary predictions

With epicycles Good Kepler’s system Good

Phases of Venus

Fails Not so good Natural consequence

Good

Simplicity Very complex Not so good Naturally simple

Good

And In Addition…………….

• The Heavens are not perfect: – Sun spots – Moon craters – Comets – Supernovas

• The moons of Jupiter do not orbit the Earth

• Aristotle’s grip on science finally broken.

The Sun Centered Universe: Part 4 Isaac Newton: 1642 to 1727

The Greatest Scientist?

Newton’s Early Life

Isaac Newton At Age 46 1689 Portrait by Kneller

• Mathematician and physicist. – Possibly the greatest scientist

in history. • Unhappy childhood.

– Born 3 months after death of father.

– Stepfather shunned him. – Raised by grandparents. – Came to hate mother and

stepfather. • Angered by criticism.

– Harsh toward enemies. – Harbored resentment.

• Never married.

Newton’s College Years

Apple tree: Cambridge Univ. Botanical Garden [Descended From Newton’s Tree (?)]

• Entered Cambridge Univ. at age 19. • Spent ages 23 to 25 at family home in

Woolsthorpe. • Due to plague. • Conducted private research. • Major discoveries were made during

this period. • Gravity. • Laws of motion. • Optics. • Calculus

• Prof. of Math. at 27.

Newton’s Theology • An Arian.

• Did not believe Jesus was the Son of God.

• God was the master Creator

Canterbury Cathedral

• Newton believed he was chosen to understand biblical scripture – to find hidden messages. . • Believed in alchemy; the Philosopher’s Stone, ESP, magic, spiritualism, numerology.

• Newton: “Gravity explains the motion of the planets but it cannot explain who set the planets in motion. God governs all things and knows all that is or can be done.”

• The “Principia” concludes with an account of monotheism and an attack on the doctrine of the Trinity.

“Principia Mathematica” (1687) Considered the Most Important Scientific Work Ever Published

• Major portions of work done 1665 to 1667 when at Woolsthorpe.

• Aristotle: Earthly things and heavenly things obey different laws.

• Newton: The same force governs bodies on Earth and in the heavens.

Three Laws of Motion

And the Law of Gravity 1) Law of Inertia: An object at rest

tends to stay at rest and an object in uniform motion tends to stay in motion unless acted upon by an external force.

2) Force = mass x acceleration

3) To every action there is an

equal and opposite reaction.

The Law Gravity: Gravitational force: F =

Gm1m2/r2

A “Thought” Experiment • A dropped ball will fall to the

ground due to gravity.

• Throw the ball horizontally: it will hit the ground farther away.

• Throw it hard enough, with no air, and it will circle the earth and return to the starting point.

• Hence: centripetal motion + gravity = orbit. – The Moon continually falls

toward the Earth

Newton’s Great Synthesis

• Kepler developed 3 laws of planetary motion. – Empirically derived: matched the data obtained

by Brahe. • Kepler did not know why they gave the right answer.

• Newton explained why they worked.

– Showed they applied throughout the Universe.

Newton Developed the Reflecting Telescope

• REFRACTORY TELESCOPES: chromatic aberration problems. – Lens acts like prism. – Newton recognized this.

• Problem solved with a

REFLECTING TELESCOPE. – Invented by a Scot (Gregory),

but improved by Newton.

Most Optical Telescopes are Reflecting

200 Inch Reflecting Telescope on Mt. Palomar

Left: Replica of Newton’s 2nd Reflecting Telescope

Isaac Newton’s Tomb Westminster Abbey

• Alexander Pope: “Nature and Nature’s laws lay hid in

night; God said “Let Newton be” and all

was light.”

• In a 1676 letter to

Robert Hooke, Newton wrote:

“If I have seen further it is by standing on the shoulders of giants.”

Newton: Summary

• Discovered 3 Laws of Motion • Discovered the Law of Gravity. • Asserted that the laws of physics applied

throughout the Universe. – The Earth was not unique.

• Invented a reflecting telescope.

The Speed Of Light

Albert Michelson: 1852 to 1931 The “Failed Experiment”

Albert Michelson

• Born in Poland: to U.S. in 1855.

• U.S. Naval Academy in 1869. – Professor of Physics at Academy

in 1877.

• Conducted first experiments on the speed of light while at the Academy.

• Professor of Physics, Case Western Univ. (Cleveland) in 1883.

• Michelson-Morley experiments in 1887.

• Nobel Prize for Physics in 2007. – First American so honored in

Physics.

The Speed of Light Through the Centuries

• Light faster than thunder. • Empedocles in 450 BCE Ancient Greece: finite. • Aristotle, 4th c. BCE: infinite. • Kepler, 1609: infinite • Galileo, 1632: between two people on distant hills:

– Between 10,000 km/hr. and infinity. • Ole Roemer, Danish astronomer (17th century):

– Analyzed data on eclipses of Jupiter’s moon, Io: • Deduced speed: 190,000 km/sec.

The Speed of Light Through the Centuries Continued

• Michelson at age 27 at U.S. Naval Academy (1878): – Speed of light is 299,910 (+/- 50) km/sec.

• EXACT VALUE: 299.792.458 km/sec. – The length of a meter is defined in this way.

The Concept of Ether [Space “matter”]

• Postulated by Aristotle: – Fills every point in space.

• Newton: endorsed the notion of an “ether”. – Speed of light relative to ether.

• Maxwell: equations showed EM waves traveled at “c” in a vacuum. – Light is a wave. So what is waving??? Something in the ether.

• Michelson-Morley experiments in 1887 showed “ether” did not affect light velocity. – Hence, no ether? – But the idea finally died with Einstein.

Michelson-Morley Strategy

The Earth’s movement around the Sun and the Sun’s movement in space allow light measurements to be made against, with and across the ether.

Experimental Concept The Michelson-Morley Experiment

• Work with monochromatic light.

• Split beam into perpendicular beams. • One beam against the Ether. • One beam across the Ether.

• Reflect the beams back and recombine into one beam. • If they arrive back at different

times, interference. • Expectation: the “cross

wind” time will be less than the “into the wind” time.

Michelson: Summary • Measured the speed of light.

• Proved that an “ether” did not

exist.

• Signaled the beginning of a second (and third?) scientific revolution: relativity and quantum mechanics.

Michelson, Einstein and Morley [California Institute of Technology: 1931]

Einstein credited Michelson with a crucial experiment on the speed of light.

Theory of Relativity

Albert Einstein: 1879 to 1955

Einstein’s Early Childhood and Education

Einstein at age 25

• Born in Ulm, Germany. • Family were non-observant Jews. • In an out of several schools,

Einstein entered Zurich Polytechnic in 1896. • Graduated in 1900 with a

teaching certificate. • Could not find a teaching

position. • Bern Patent Office: 1902 • While at the patent office, he

continued education. • Ph.D. in 1905.

Einstein Escaped From Germany • 1908: Prof. of Physics, Univ. of

Bern.

• 1914 to 1932: Director of the Kaiser Wilhelm Institute for Physics.

• 1933 Hitler’s anti-Jewish programs prompted Einstein to flee to England, then the U.S.

• Institute For Advanced Studies at Princeton until his death.

Einstein Sheds “Pacifism” Wings Takes Up “Preparedness” Sword

Cartoon In Brooklyn Eagle (1933)

1905: A Year To Remember [Einstein’s Age: 26]

• Special Theory of Relativity.. • Equivalence of Mass and Energy: E = mc2

• The Photoelectric Effect: Light travels in quanta (packages of energy).

• Brownian Motion ---------------------------------------------------------------- • And in 1916: The General Theory of Relativity.

Theory of Relativity Important to the History of Astronomy • Special Theory:

– The velocity of light is a constant • Independent of the velocity of the source or observer. • There is no “ether”.

– Nothing can move faster than the speed of light.

• General Theory:

– Gravity is equivalent to the warping of space by celestial bodies – The General Theory led Georges Lamaitre to propose a Big Bang origin for the

Universe.

The Big Bang

The Origin of the Universe?

Overview of the Big Bang The Concept: The Universe emerged from an extremely dense singularity. The initial expansion was very rapid. Since then, space has been steadily expanding carrying galaxies with it, like raisins in a rising loaf of bread. Gnixon: Wikipedia Project

Evidence of the Big Bang: 1) The Red Shift and Hubble’s Law: 1929 2) Abundance of Elements:

Gamow, Alpher and Hoyle: 1948 to 1953

3) Cosmic Microwave Background Radiation: Penzias and Wilson:

1964

The Original Idea: 1927 Georges Lemaitre, Roman Catholic Priest (1894 to 1966)

• Lemaitre was ordained in 1923.

• Educated at Cambridge and Harvard . • Observatory at MIT from 1923 to

1925.

• General Relativity implied a moment of creation: “The primeval atom hypothesis is a cosmogenic hypothesis which pictures the present Universe as a result of the radioactive disintegration of an atom”.

• Lemaitre was rebuffed by Einstein.

• In 1949, this hypothesis had legs and

was called the BIG BANG by Fred Hoyle.

Time Line From the Big Bang • Within the first second, a great expansion took place. * The universe cooled enough so subatomic particles could combine. * Within a few seconds, Hydrogen and Helium nuclei began to form. • Stars began to form after about 300 million years.

– Carbon and other heavy elements were formed in the stars and spread though out the universe by disintegrating stars.

“Recent” History

The Red Shift: Hubble’s Law (1929) Edwin Hubble: American Astronomer (1889 to 1953)

Univ. of Chicago: law and astronomy Ph.D. thesis from Yerkes Observatory:

“Photographic Investigations of Faint Nebulae”.

100 inch Mt. Wilson Telescope Hubble discovered that our galaxy was

not the only galaxy.

The Red Shift: Doppler Effect

• When object moves away ,light wave-length gets longer and the “color” shifts down toward the red.

• HUBBLE’S LAW (1929): “Degree of Doppler shift (Red Shift) increases with increasing distance of galaxies from our own.”

• First observational support of the Big Bang theory.

• The Universe behaves like it is exploding.

George Gamow and Ralph Alpher

• George Gamow: 1904 to 1968. • Russian-born American physicist. • Tried to leave USSR (with wife) in

1932. – By kayak to Turkey: failed.

• Succeeded in 1933: physics conference in Brussels.

• Ralph Alpher: 1921 to 2007. • In 2005, was awarded the National

Medal of Science, the highest scientific honor in the U.S.

Hydrogen To Helium Atom Ratio: 10 to 1

• The starting point was a hot soup of gamma rays, quarks and other elementary particles.

• Between 1 msec and 1 sec, quarks combined to form protons and neutrons.

• After a few seconds, nuclei could be formed: – Hydrogen (H-1) + neutron = Deuterium (H-2) – (H-2) + (H-1) = helium-3 (He-3). – He-3 + He-3 = He-4 plus 2 (H-1)

• Gamow and Alpher calculated that the hydrogen to helium atom ratio should be 10:1.

Atom Ratios In the Universe

• Hydrogen and helium account for 99.9% of all atoms in the universe: universe:

* Hydrogen: 10,000 * Helium: 1,000 * Oxygen: 6 * Carbon 1 * Everything else: < 1 • The Sun converts 584 million tons of hydrogen

into 580 million tons of helium each second.

The Formation of Carbon: 1953 Fred Hoyle: 1915 to 2001

• Hoyle worked at the Cambridge Institute for Astronomy. – Was a rebel; frequently took contrary positions. – Rejected Darwinian evolution:

• Coined the term “Big Bang”, but….

– Rejected the Big Bang theory.

• Seminal work: “Synthesis of the Elements in the Stars” (with other authors): 1957.

Difficult to Form Carbon-12

• It is very difficult to create Carbon by adding nucleons to Helium. • The resulting nuclei are

very unstable.

• Hoyle postulated (1953) that three Helium nuclei combine in a special sequence to give Carbon: – He-4 + He-4 = Beryllium-8 – Be-8 + He-4 = Carbon-12

• For this to happen, the Carbon

nucleus had to have an (as yet) unknown energy level. – Hoyle predicted its existence. – It was found later at Cal Tech.

The Heavier Elements?

• As the hydrogen gradually disappeared, a star would cool.

• Gravity would cause it to contract, generating heat.

• Light nuclei would fuse into the heavy elements.

• As the star got steadily smaller, it would eventually

explode. – “Contaminate” the Universe with heavy stuff.

Cosmic Microwave Background Radiation

• Initially, the nuclear soup was very dense;

– OPAQUE to light.

• After 379,000 years, the universe cooled to about 3000oC. – Atoms had formed and the universe became TRANSPARENT. – Photons could travel unimpeded throughout the universe.

• For the next 13 billion years, the universe continued to expand, and cool, and the

photons continued to fill all space. – The residue of that event is the COSMIC MICROWAVE BACKGROUND

RADIATION.

An Early Estimate of CMBR Alpher and Herman

• In 1948 , Alpher and Robert Herman* calculated that when the Universe became TRANSPARENT the residual radiation moving about the Universe had a “temperature” of about 240 oC below zero.

• As the Universe expanded the temperature of space would decrease further. • Today: about 270oC below zero.

Herman, Gamow, Alpher

* Herman: 1914 to 1997, PhD Physics, Princeton.

The Penzias- Wilson “Experiment”: 1964

• Penzias and Wilson (at Bell Labs)

accidentally measured background radiation corresponding to a black body of about 270 C below zero.

– They had been studying radio waves from space.

– Could not get rid of the “noise” their radio telescopes were picking up.

• This confirmed the predictions of Alpher

and Herman in 1948. • A major confirmation of the Big Bang

theory.

Left: Cosmic Background Explorer (COBE 1989)

Penzias and Wilson

• Arno Penzias: 1933 to ? – Fled (when a boy) from Nazi Germany in 1939. – PhD in Physics from Columbia University.

• Robert Wilson: 1936 to ? – Educated at Cal Tech

• Penzias and Wilson won Nobel Prize in 1978

The Hubble Space Telescope Hubble Space Telescope

Deployed in low earth orbit in 1990. Light from a galaxy 13.2 billion years old was recently seen by the telescope (formed about 480 million years after the Big Bang).

– Earliest galaxy so far seen.

Hubble: Reflecting Telescope Two parabolic mirrors.

Summary: So…What Do (We Think) We Know?

• Initially a soup of sub-atomic particles. • A rapid expansion of the universe took place. • For 379,000 years, gradual cooling: 3000oK. • The Universe became “transparent”. • 8 billion years: the Sun was formed. • Carbon and other heavy elements were formed in the

stars. • Interstellar space continued to cool to -270 C, today.

• AGE OF THE EARTH: 4.54 +/- 1% BILLION YEARS • AGE OF UNIVERSE: 13.73 +/- 0.17 BILLION YEARS

What Are We Worried About?

• The initial expansion: – 100 doublings in 10-35 sec.?

• Universe still expanding? • Dark matter and dark energy? • The boundary between the Universe and …? • What came before t = zero?