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Lecture 40 Cosmology IV

Lecture 40 Cosmology IV. In spite of all this, there are arguments that Omega must be 1 There is observational evidence that space is Euclidean, not curved “Inflation” (see p634) requires Omega to be 1 If Omega is approximately 1, it is probably exactly 1 (??!!!***).

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Lecture 40 Cosmology IV

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  1. Lecture 40 Cosmology IV • In spite of all this, there are arguments that Omega must be 1 • There is observational evidence that space is Euclidean, not curved • “Inflation” (see p634) requires Omega to be 1 • If Omega is approximately 1, it is probably exactly 1 (??!!!***)

  2. Simply stated: if Omega =1, it stays 1 through the history of the universe. If Omega < 1 or Omega > 1, the value depends on the Cosmic Scale Factor a. Since a has changed enormously (infinitely) throughout the history of the universe, it shouldn’t be anywhere near 1 now if it wasn’t very, very close to 1 early on. So if it is close to 1 now, it is probably exactly 1

  3. Important new piece of information in and about 1997 • If you have a “standard candle”, an object with constant, known M, you can measure how a(t) has changed throughout the history of the universe • Basic idea: expanding universe says light from a source has to “fan out” into a larger volume than in a static universe. Fall-off of intensity is steeper than the inverse square law • The degree of extra “fan out” depends on how a(t) has changed with time

  4. For Omega =1, the fan out is the smallest • For Omega =0.33, it is larger • For Omega = 0, it is larger still, and the maximum for a Friedmann universe

  5. Use cosmological model to calculate m of z

  6. Now need objects to fill up the plot. Real standard candles • Type Ia supernovae….white dwarfs “shoved over the edge” • http://antwrp.gsfc.nasa.gov/apod/ap000312.html

  7. What do the data on Type Ia supernovae show? • http://www-supernova.lbl.gov/public/misc/forrosen/sciencesnpop.pdf • Distant Type Ia supernovae are even fainter than in an empty universe • The scale factor has increased even more than for Omega = 0

  8. Points to the following form for a(t) An accelerating universe How is it possible?

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