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Dark Energy in the Universe

This article explores the concept of dark energy in the universe and its relation to Einstein's theory of general relativity. It discusses the expansion of the universe, the role of dark energy, and the implications for the future.

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Dark Energy in the Universe

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  1. Dark Energy in the Universe Scott Dodelson October 18,2001

  2. A long time ago in a galaxy far, far away...

  3. Einstein and General Relativity Idea: Matter affects the structure of Space-Time E.g. A massive star attracts nearby objects by distorting space

  4. In 1919, Eddington led expedition to observe solar eclipse ... Leading to confirmation of Einstein's theory ... And widespread adulation ... London Times Nov 8, 1919 The Revolution in Science: Einstein vs. Newton

  5. Expanding Sphere Energy = Kinetic Energy + Gravitational Energy 0 = (½) m v2 - G m M(r)/ r

  6. Einstein's Static Universe How did Einstein make the universe static? 0 = (½) m v2 - G m M(r)/r Introduced dark energy. Ordinary matter: M(r) = constant Dark energy: M(r) ~ r3Negative Pressure Changed the curvature energy to be negative

  7. Aleksandr Aleksandrovich Friedmann Born: June 1888, St. Petersburgh, Russia Died: September 1925, St. Petersburgh Published paper on Bernoulli Numbers at age 17. WWI: Join volunteer aviation detachment.

  8. Used mathematical tools to improve bombing: I have recently had a chance to verify my ideas during a flight over Przemysl; the bombs turned out to be falling almost the way the theory predicts. To have conclusive proof of the theory I'm going to fly again in a few days. Letter from Friedmann, Feb 28, 1915

  9. Expansion of the Universe June 29, 1922: Friedmann introduces the expanding universe, abandoning the dark energy Einstein put in by hand. September 18, 1922: Einstein publishes a comment on Friedmann's paper: result ``seems suspect to me'', ``solutions do not appear compatible'' May 31, 1923: Einstein retracts his criticism: ``My objection rested on a calculational error.''

  10. Edwin Hubble measures expansion in 1929 ...

  11. BUT Naturalness, Inflation Galaxies, clusters, Stats of gal distribution Observers``ArrogantTheorists'' Theorists: ``Ignorant Observers’’ Age Ugly theory … Dark Energy in the Universe !

  12. 1916-1922 No Expansion: Negative Curvature, Dark Energy • 1922-1970 Expansion: Zero Curvature, Matter Only • 1970-1998 Expansion: Positive Curvature/Bad Theorists? Zero Curvature/Bad Observers? Dark Energy?

  13. After billions of years light from the distant supernova reaches Earth

  14. Supernovae are standard candles The apparent brightness of a supernova is therefore a measure of its distance from us. Can get Hubble relation for very distant objects!

  15. Since M remains constant, expansion slows, like a rocket leaving Earth Since M increases with r, universe is driven to expand faster and faster Dark Energy

  16. Fainter -> Far Away -> Scale Factor (redshift)

  17. Geometry Determined by Energy ClosedFlatOpen

  18. Observations of Matter and of Supernovae suggest that The Universe is Flat! Can this be tested?

  19. Probe Geometry with Light Paths q d D

  20. Cosmic Microwave Background Anisotropies Physical size of hot/cold spots is known; measureangular size to get distance to last scattering. The Universe is Flat!

  21. Deep, profound questions remain • What is the dark energy? • How is it related to the rest of physics? • Is it testable? • Could it be useful? • What are the ramifications for the future? Strings? Quintessence? We are thinking .. Large extra dimensions? Cosmological constant?

  22. What should we make of Einstein? The Man of the Century… • Missed the expansion • Almost suppressed it • Blundered into dark energy

  23. Even Einstein’s Greatest Blunder ... teaches us about the importance of tackling big problems. Even though Einstein was wrong, his audacity laid the groundwork for the future.

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