Primordial Nucleosynthesis
  The current of status of big bang nucleosynthesis is reviewed and the concordance between theory and observation is examined in detail. It is argued that when using the observational data on he4 and li7, the two isotopes whose abundances are least affected by chemical and stellar evolution, both are completely consistent with BBN theory. In addition, these isotopes determine the value of the baryon-to-photon ratio, $\eta$ to be relatively low, $\eta \approx 1.8 \times 10^{-10}$, which happens to agree with some recent measurements of D/H in quasar absorption systems. These results have far reaching consequences for galactic chemical evolution, the amount of baryonic dark matter in the Universe and on the allowed number of degrees of freedom in the early Universe. 
Keith A. Olive