Introduction to Cosmology

Einstein’s general relativity is a satisfactory theory of gravitation, and it provides a space-time structure whenever the matter distribution is given. Thus, if the average distribution of matter in the universe is put into Einstein’s field equations, the average space-time structure of the whole universe may be deduced. This is a very interesting exercise, and it is part of the subject of cosmology. Cosmology is the study of the dynamical structure of the universe and seeks to answer questions regarding the origin, the evolution, and the future behavior of the universe as a whole. Historically, after establishing his General Theory of Relativity in 1916, Einstein promptly applied his theory to problems in cosmology and published his first paper on relativistic cosmology in 1917. At that time, cosmology was the only field in which the significance of general relativity could be fully manifested.

In this chapter and in the following chapters, we will be studying cosmology. Cosmologists piece together the observed information about the universe into a selfconsistent theory or model that describes the nature, origin, and evolution of the universe.