Foundations of Modern Cosmology

Abstract

Modern theoretical cosmology is essentially based on Einstein's theory of general relativity, with which this chapter starts. His original relativistic model of 1917 was closed and static, and made use of the so-called cosmological constant. The static nature of the universe, whether in Einstein's model or the one proposed by Willem de Sitter, had a paradigmatic status in early relativistic cosmology. However, the paradigm broke down in the early 1930s when Hubble's observations were combined with the theoretical works of Friedmann and Georges Lemaître. From that time onward, the expanding universe became part of mainstream cosmology. However, in the 1930s there was not yet a settled framework of cosmology, a science where unorthodox theories flourished and where mathematical reasoning dominated over physical considerations.