ABSTRACT

It is a reasonable assumption that, on the scales that are relevant to a description of the development of the present universe, of all the interactions only gravity plays a role. All other interactions are neutralized by the existence of opposite charges in the neighbourhood and have an influence only on the detailed course of the initial phase of the development of the universe. The currently accepted theory of gravitation is Einstein’s general theory of relativity. This is not a gauge theory: gravitation is interpreted purely geometrically as the curvature of four-dimensional spacetime. For a detailed introduction to general relativity see [Wei72, Mis73, Sex87]. While general relativity was being developed (1917), the accepted model was that of a stationary universe. In 1922 Friedman examined non-stationary solutions of Einstein’s field equations. Almost all models based on expansion contain an initial singularity of infinitely high density. From this the universe developed via an explosion (the Big Bang). An expanding universe was experimentally confirmed when Hubble discovered galactic redshifts in 1929 [Hub29] and interpreted their velocity of recession as a consequence of this explosion. With the discovery of the cosmic microwave background in 1964 [Pen65], which is interpreted as the echo of the Big Bang, the Big Bang model was finally established in preference to competing models, such as the steady-state model. The proportions of the light elements could also be predicted correctly over 10 orders of magnitude within this model (see section 13.8). All this has resulted in the Big Bang model being today known as the standard model of cosmology. For further literature see [Boe88, Gut89, Kol90, Kol93, Nar93, Pee93, Pee95, Kla97, Bot98a, Pea98, Ber99,Ric01,Dol02].