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The History and Philosophyof Astronomy
(Lecture 19: Einstein II)
Instructor: Volker BrommTA: Jarrett Johnson
The University of Texas at Austin
Astronomy 350L(Fall 2006)
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Overview: Einsteins Life
Nov. 2
Nov. 7
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Einstein in Berlin: 1914-32
1914: Max Planck secures Einsteins appointment
as professor at the Prussian Academy of Sciences(founded 1700 by Leibniz, German equivalent of Royal Society)
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Berlin 1914: World Center of Science
Einstein becomes part of vibrant scientific community!
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Berlin 1914: Outbreak of WW I
All European nations excited to go to war!
Einstein takes lone pacifist stand!
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General Theory of Relativity (1915-16)
Big Q: What is gravity???
Newton (1687): -- `action-at-a-distance
-- doesnt really answer the question
Einstein (1915): -- principle of equivalence
-- great idea: GRAVITY = ACCELERATION
-- his happiest thought
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General Theory of Relativity (1915-16)
Principle of Equivalence (gravity = acceleration)
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General Theory of Relativity (1915-16)
Principle of Equivalence (gravity = acceleration)
(1g upwards)
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General Theory of Relativity (1915-16)
Big Q: What is gravity???
principle of equivalence: GRAVITY = ACCELERATION
you dont feel effect of gravity in freely falling spaceship(`weightlessness)
it is possible to transform away gravity (locally)!
But: you cant get rid of gravity completely!
tidal forces betray gravity!
globally, gravity is non-uniform!
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General Theory of Relativity (1915-16)
gravity betrayed:
gravity: neighboring particles in free-fall slowlyconverge (experience: `tidal forces)
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General Theory of Relativity (1915-16)
tidal effect of gravity similar to behavior of`straight lines on curved surfaces
Einsteins great idea: gravity is related to curvature ofspace! (surface = 2 dimensional space)
(ants are told to crawl straight ahead!)
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General Theory of Relativity (1915-16)
Principle 1: Matter tells space how to curve
matter creates `dimples in otherwise flat spacetime!
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General Theory of Relativity (1915-16)
Principle 2: Curved space tells matter how to move
particles move through spacetime along paths of
least resistance (technically: `geodesics)!
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General Theory of Relativity (1915-16)
Einsteins Field equations:
a `tensor equation very complicated
(10 coupled non-linear differential equations)
(curvature of space) (matter content)
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Einstein vs Newton
compare views on planetary motion:
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Einstein vs Newton
Old view (Newton): Gravity acts `at-a-distance(i.e., speed of gravitational disturbance = infinity)
New view (Einstein): Gravity acts viagravitational waves (`ripples in spacetime)(i.e., speed of gravitational disturbance = speed of light)
try to detect them with LIGO and LISA!
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LIGO Experiment (Laser Interferometer
Gravitational-wave Observatory) tries to detect gravitational waves
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General Theory of Relativity (1915-16)
- Predict `gravitational redshift(light escaping from massive body becomes redder)
- Predict gravitational bending (deflection) of light!(most famous of the 3 tests; `experimentum crucis)
- Successfully explain anomaly in Mercurys orbit(`perihelion precession)
Einstein proposes 3 classical tests of GR:
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General Theory of Relativity (1915-16)
Gravitational redshift:
Photon climbing out of gravitational well loses energyless energy = lower frequence = redder color!
was successfully measured only in 1960 (Pound & Rebka)
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General Theory of Relativity (1915-16)
Bending of light-rays:
Prediction: Suns gravity deflects light from distant stars!
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General Theory of Relativity (1915-16)
Observe bending of light during Solar eclipse!
Einsteins prediction: Stars shifted by 1.75
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Eddingtons Eclipse Expedition (1919)
Eddingtons observation confirms Einsteins theory!
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After 1919: Einstein the Legend
Einstein becomes world-famous!
travels the globe
hobnobs with high-society
begins to exert significantinfluence in politics
(New York Times)
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1919: Divorce and 2 nd Marriage
marriage with his cousin Elsa Einstein (1919-36)
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Einstein visits America
Einstein at City Hall, New York (1921)
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Einstein visits America
Chaplin to Einstein: People love me, because theyunderstand everything I say, and they love you,because they understand nothing of what you say
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Einsteins Favorite Recreational Spots
his beloved summer house in Caputh (near Berlin)
many famous and powerful visitors
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Einsteins Favorite Recreational Spots
Island of Hiddensee (Germanys Marthas Vineyard)
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Solving Einsteins Equations of GR
1916: Karl Schwarzschild predicts black holes
Karl Schwarzschild (1873-1916)
`Schwarzschild radius
f
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Solving Einsteins Equations of GR
1917: Einstein constructs model of the universethat is eternal and static
begin by postulating `cosmological principle :Universe looks everywhere the same!(homogeneity and isotropy)
today, we knowthis is an excellentapproximation, butin 1917, it was merelyan inspired guess!
S l i Ei i E i f GR
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Solving Einsteins Equations of GR
1917: Einstein constructs model of the universethat is eternal and static
finite but without boundary
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Ei t i `G t t Bl d
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Einsteins Greatest Blunder
The cosmological constant:
cosmological constant (lambda) acts as anti-gravity(physically: very weird stuff, having negative pressure)
(curvature of space) (matter)(cosmological
constant)
S l i g Ei t i E ti f GR
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Solving Einsteins Equations of GR
1922: an expanding universe (GR withoutcosmological constant)
Alexander Friedmann(1888-1925)
Escape from Germany (1932)
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Escape from Germany (1932)
Dec. 10, 1932: Einstein andElsa depart from Berlin fora visit to U.S.
Jan. 30: Hitler comes topower
Einstein (being Jewish)never sets foot into Germanyagain
Einsteins Fa orite Recreational Spots
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Einsteins Favorite Recreational Spots
his beloved summer house in Caputh (near Berlin)
many famous and powerful visitors
Einstein in Princeton (1933 55)
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Einstein in Princeton (1933-55)
professor at newly foundedInstitute for Advanced Study
Einstein in Princeton (1933 55)
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Einstein in Princeton (1933-55)
112 Mercer Street: his private house
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Einstein in Princeton (1933-55)
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Einstein in Princeton (1933-55)
failure to find `unified field theory(i.e., gravity + electromagnetism)!
Einstein and the Bomb
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Einstein and the Bomb
1939: Fellow migr Leo Szilard (Hungary) warnsEinstein of possible Nazi bomb effort
Einstein and the Bomb
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Einstein and the Bomb
Letter to FDR
E warns presidentabout Nazi bomb
setting `Manhattanproject into motion
Einstein and the Bomb
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Einstein and the Bomb
Hiroshima bomb: 1 gram of uranium
Einstein and the Foundation of Israel
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Einstein and the Foundation of Israel
Ben Gurion offers Einstein Presidency of IsraelEinstein declines (1 st Israeli president: Chaim Waizmann)
1955: Journeys End
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: y
dies in Princeton hospital, his body is cremated thesame day, and his ashes scattered at undisclosed place
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