Uncertainty in Newton’s constant and precision predictions of the primordial helium abundance

The current uncertainty in Newton's constant G₍ is of the order of 0. 15%. For values of the baryon to photon ratio consistent with both cosmic microwave background observations and the primordial deuterium abundance, this uncertainty in G₍ corresponds to an uncertainty in the primordial ^4He mass fraction Y₏ of 1. 310^-4. This uncertainty in Y₏ is comparable to the effect from the current uncertainty in the neutron lifetime ₍, which is often treated as the dominant uncertainty in calculations of Y₏. Recent measurements of G₍ seem to be converging within a smaller range; a reduction in the estimated error on G₍ by a factor of 10 would essentially eliminate it as a source of uncertainty in the calculation of the primordial ^4He abundance.