Big bang nucleosynthesis

In the first thousand seconds of its evolution the Universe was a primordial nuclear reactor synthesizing the light nuclides D, He-3, He-4 and Li-7. These messengers from the Big Bang provide a unique window in the early, hot, dense Universe, offering the opportunity fort tests of the standard models of particle physics and of cosmology. A new, statistically coherent comparison of the primordial abundances of these nuclides inferred from increasingly accurate observational data with those predicted by standard models hints at a possible crisis. The case for this emerging crisis is presented and several paths towards ameliorating it are explored.