ASTRON 1101 Lecture 36: Astronomy 11.30.16
30 Nov 2016
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Document Summary
Big bang theory: the universe began expanding a finite time ago from a very dense, very hot initial state. How hot and how dense was it initially. The idea of a universe expanding from an initial dense state was quite radical when it was first proposed by friedmann and lemaitre. The big bang theory became the standard cosmological theory because it was supported by observational evidence. Evidence for the big bang theory: the night sky is dark. If we lived in an infinitely large, eternally old universe filled with stars, the night sky would be bright. Light from stars at a distance greater than ~c/h0 ~ 14. 4 billion light years ~ 4400 mpc simply hasn"t had time to reach us. Evidence for the big bang theory: the oldest stars have an age < 1/h0. The age of a globular cluster of stars is known from its main sequence turnoff; the oldest globular clusters have t = 13 gyr.
