The Big Bang


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The Big Bang

  1. 1. In The Beginning big bang cosmology
  2. 2. Einstein Problem: Gravitational attraction would cause the universe to collapse. Solution: Addition of the cosmological constant to the general theory creates an anti-gravitational effect Result: Preservation of the eternal, static universe.
  3. 3. Modified Field Equation Spacetime MatterConversion Factors Cosmological Constant
  4. 4. Alexander Friedman 1888 - 1925 “On the possibility of a world with constant negative curvature of space” (1924) What happens if the Cosmological Constant (Λ) has different values? What happens if the universe is expanding?
  5. 5. Friedman Equations
  6. 6. Georges Lemaître 1894 - 1966 Suggested that in an expanding universe, galaxies should be retreating at a velocity proportional to their distance from us (1927) Proposed a compact,“primeval atom” or “Cosmic Egg” that exploded, expanded and evolved into the universe as we see it today.
  7. 7. William Herschel 1738 - 1822
  8. 8. Charles Messier 1730 – 1817 Catalog of 103 nebulous and “deep sky” objects (1781)
  9. 9. William Parsons, Earl of Rosse, 1800 - 1867 Able to distinguish between elliptical and spiral-shaped nebulae. Managed to make out individual point sources in some of these nebulae, “Leviathan”
  10. 10. Henrietta Leavitt 1868 – 1921 Studying variable stars and found that brighter ones appeared to have longer periods. Estimating period of variability allowed estimation of their distance
  11. 11. Small Magellanic Cloud
  12. 12. Cepheids in the SMC The Cepheids are huddled together and can be assumed to be relatively close together compared with distance to earth [200,000 light years] Therefore, a Cepheid in this sample that appears twice as bright as another in the sample is twice as intrinsically luminous.
  13. 13. Leavitt, Henrietta S. "1777 Variables in the Magellanic Clouds". Annals of Harvard College Observatory. LX(IV) (1908) 87-110. Period (days) Log Period (days) Brightness
  14. 14. 800x Sun 10,000x Sun
  15. 15. So What? Cepheids are easily identifiable They are relatively plentiful and scattered throughout the universe We can measure intrinsic luminosity from period Need calibration (direct measurement 1913 by Ejnar Hertzsprung)
  16. 16. Stellar Parallax
  17. 17. A “standard candle” Find a Cepheid Measure the period and thus derive the intrinsic luminosity (how bright it is) Measure the apparent luminosity (how bright it appears to be) Work out the distance that accounts for the difference.
  18. 18. Doppler Effect Redshift (objects moving away) Blueshift (objects getting closer)
  19. 19. Edwin Hubble 1889 - 1953 In 1923, found a cepheid in Andromeda and (measuring the distance) found it to lie beyond the Milky Way The nebulae were galaxies and the universe was full of them!
  20. 20. Hubble’s Law - 1929 Linear relationship between a galaxy’s distance and “apparent” recessional velocity Implies universe is expanding First observational support for Lemaître’s prediction in 1927
  21. 21. Hubble’s Law - 1929
  22. 22. A B C D E F G EDC F
  23. 23. Georges Lemaître 1894 - 1966 There was both “creation” and “evolution” of the universe.
  24. 24. Friedmann-Lemaître-Robertson- Walker (FLRW) Model Howard Robinson (US) and Arthur Walker (England) independently explored these ideas in the 1930’s. Offers an exact solution of Einstein's field equations of general relativity Describes a simply connected, homogeneous [same properties in all locations], isotropic [same properties when viewed in any direction from any location], expanding or contracting universe.
  25. 25. The αβγ Paper Ralph Alpher, [Hans Bethe] & George Gamow pictured the early universe as a dense “soup” of protons, neutrons and electrons. Bigger and bigger atoms were built by fusion in the heat of the Big Bang.
  26. 26. The αβγ Paper Success: Model could explain why the universe is currently 90% Hydrogen and 9% Helium. Failure: Model could not explain the formation of elements heavier than Helium.
  27. 27. George Gamow 1904 - 1968 With Alpher & Robert Herman (1948) predicted an “echo” of the Big Bang Alpher & Herman (1949) predicted that the radiation should be in the radio region of the EM spectrum
  28. 28. Fred Hoyle 1915 – 2001 With Thomas Gold & Hermann Bondi proposed the Steady State Model The Universe was indeed expanding but new matter was being formed in the gaps between the galaxies Thus the universe evolves but remains unchanged and eternal
  29. 29. Radio Astronomy Discovery of young galaxies and quasars at the far reaches of the universe Uneven distribution went against Steady State model which claimed the universe should be similar everywhere
  30. 30. Robert Wilson & Arno Penzias “Discovery” of the Cosmic Microwave Background (CMB) radiation as a background noise (1964) Nobel Prize in 1978 Was this sufficient evidence for acceptance of the Big Bang?
  31. 31. Confirms black-body spectrum of CMB as expected Discovery of variations (anisotropies) in the CMB which indicated tiny variations in the density of the early universe
  32. 32. Stephen Hawking The COBE results are “the greatest discovery of the century, if not of all times”.
  33. 33. The Nobel committee stated that COBE can “be regarded as the starting point for cosmology as a precision science.”
  34. 34. High-precision CMB mapping yields age of the universe of 13.73 ± 0.12 billion years
  35. 35. The End Heat Death (Kelvin) Big Rip Big Crunch Big Bounce Multiverse