No crisis for big bang nucleosynthesis

Contrary to a recent claim, the inferred primordial abundances of the light elements are quite consistent with the expectations from standard big bang nucleosynthesis when attention is restricted to direct observations rather than results from chemical evolution models. The number of light neutrino (or equivalent particle) species ($N_{\nu }$) can be as high as 4.53 if the nucleon-to-photon ratio ($\eta$) is at its lower limit of 1.65×${10}^{-10\mathrm{}}$, as constrained by the upper bound on the deuterium abundance in high redshift quasar absorption systems. Alternatively, with $N_{\nu }=3\mathrm{}$, $\eta$ can be as high as 8.90×${10}^{-10\mathrm{}}$ if the deuterium abundance is bounded from below by its interstellar value. These conclusions follow from the upward revision of the primordial helium abundance inferred from recent observations of blue compact galaxies, using updated atomic physics inputs.