The age of the universe

摘要

The big bang theory is a remarkably simple theory built on two pillars: the theory of general relativity and the assumption that the universe is isotropic and homogeneous on large scales. This theory has had a number of important successes: it can explain the observed expansion of the universe; The thermal micro- wave background radiation; the observed abundances of deu- terium, helium, and lithium; and the rapid evolution seen in distant galaxies (see refs. 1 and 2 for recent reviews).