The end of the age problem, and the case for a cosmological constant revisited

The case for an open universe versus a flat universe with nonzero cosmological constant is reanalyzed, following new globular cluster dating results that now suggest a dramatically reduced lower limit on the age of the universe, which, for example, allow age consistency for a flat matter-dominated universe with a Hubble constant H₀ ≤ 67 km s^-1 Mpc^-1. I incorporate not only the new age data but also updates on baryon abundance constraints and large-scale structure arguments. For the first time, the allowed parameter space for the density of nonrelativistic matter appears larger for an open universe than for a flat universe with cosmological constant, while a flat universe with zero cosmological constant remains strongly disfavored, in spite of the fact that it is now more consistent with the new age constraint. I argue that fundamental theoretical arguments favor a nonzero cosmological constant over an open universe. However, if either case is confirmed, the challenges posed for fundamental physics will be great.