The Theoretical Framework

Abstract

The observational evidence discussed in Chap. 2, particularly the isotropy of the Cosmic Microwave Background Radiation, indicates that the natural starting point for the construction of cosmological models is to assume that, to first approximation, the Universe is isotropic and homogeneous at the present epoch. This is precisely what Einstein assumed in developing his static model of 1917, the first fully selfconsistent model of the Universe, derived long before the large-scale isotropy of our Universe was established (Einstein, 1917). Likewise, Friedman’s discovery of what were to become the standard models for the large-scale dynamics of the Universe predated the discovery of the expansion of the Universe. The Friedman models were based upon expanding solutions of Einstein’s equations, following clues provided by de Sitter and Lanczos.