Big Bang Nucleosynthesis: Consistency Or Crisis ?

Abstract

The early, hot, dense, expanding Universe was a primordial reactor in which the light nuclides D, 3He, 4He and 7Li were synthesized in astrophysically interesting abundances. The challenge to the standard hot big bang model (Big Bang Nucleosynthesis = BBN) is the comparison between the observed and predicted abundances, the latter which depend only on the universal abundance of nucleons. The current status of observations is reviewed and the inferred primordial abundances are used to confront BBN. This comparison suggests consistency for BBN for a narrow range in the nucleon abundance but, looming on the horizon are some potential crises which will be outlined.