UC San Diego

We discuss how Yp, the observationally inferred primordial 4He abundance, becomes a stringent test of both the standard homogeneous and inhomogeneous big bang models. We argue that the standard procedure of extrapolating the straight line fit to the 4He data to obtain the zero metallicity intercept is inappropriate and places inordinate weight on high-metallicity points. Extrapolating lower metallicity data versus JV, we obtain Yp = 0.220 ± 0.010. At face value, this result just precludes the standard model with three light neutrinos and places severe constraints on inhomogeneous models. However, systematic errors are potentially large, and therefore no definitive conclusion can be reached at this time.