The Crisis Confronting Standard Big Bang Nucleosynthesis

This manuscript is the written version of the material I attempted to cover at “Critical Dialogues in Cosmology”. My position is that although BBN is inevitable in an expanding universe filled with radiation and baryons, at present there is a conflict between the abundances of the light nuclides predicted by standard, big bang nucleosynthesis (SBBN) and those inferred from current observational data. This challenge to SBBN provides opportunities for astronomy/astrophysics, cosmology and particle physics. Perhaps there are unaccounted-for errors in passing from the observational data to the derived abundances (astronomy/astrophysics). Perhaps there are unaccounted-for systematic corrections in translating the derived abundances from “here and now” to “there and then” (astrophysics/cosmology). Or perhaps the tension between theory and observations is offering us a hint of new physics beyond the standard model (cosmology/particle physics).