The History and Philosophy of Astronomy Lecture 19: Einstein. Presentation

8/9/2019 The History and Philosophy of Astronomy Lecture 19: Einstein. Presentation

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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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Principle of Equivalence (gravity = acceleration)


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Principle of Equivalence (gravity = acceleration)

(1g upwards)


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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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gravity betrayed:

gravity: neighboring particles in free-fall slowlyconverge (experience: `tidal forces)


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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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Principle 1: Matter tells space how to curve

matter creates `dimples in otherwise flat spacetime!


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Principle 2: Curved space tells matter how to move

particles move through spacetime along paths of

least resistance (technically: `geodesics)!


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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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- 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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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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Bending of light-rays:

Prediction: Suns gravity deflects light from distant stars!


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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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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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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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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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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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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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112 Mercer Street: his private house


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failure to find `unified field theory(i.e., gravity + electromagnetism)!

Einstein and the Bomb


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1939: Fellow migr Leo Szilard (Hungary) warnsEinstein of possible Nazi bomb effort



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Letter to FDR

E warns presidentabout Nazi bomb

setting `Manhattanproject into motion



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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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The History and Philosophy of Astronomy Lecture 19: Einstein. Presentation