Standard Synthesis

Abstract

One of the two most important observations that indicate a hot past of the universe is the universal distribution of helium and deuterium. Deuterium, in particular, has no chance to escape from the deep interior of stars. It is processed to helium much faster than it is produced through two-proton processes. The presence of deuterium in the interstellar, primordial gas (Fig. 1.7) requires the hypothesis of a synthesis at a time when free neutrons were present in substantial concentration, that is, in the early universe near a temperature corresponding to the difference in rest mass, i.e.kT ≈ (m_nm_p)c². At this temperature, the universe was necessarily dominated by radiation (more precisely, hot matter), and the radiation served not only as the source of gravitation in the Friedmann equation but also as a heat bath. This situation was predicted by Gamow.