Type Ia Supernovae, the Hubble Constant, the Cosmological Constant, and the Age of the Universe

The age of the Universe depends on both the present-day Hubble Constant and on the history of cosmic expansion. For decelerating cosmologies such as Omega_m= 1, the dimensionless product H_0,t_0<1 and modestly high values of the Hubble constant H_0 > 70 would be inconsistent with a cosmic age t_0 larger than 12 Gyr. But if Omega_Lambda > 0, then H_0,t_0 can take on a range of values. Evidence from the Hubble diagram for high redshift Type Ia supernovae favors Omega_Lambda~0.7 and H_0,t_0 ~ 1. Then, if H_0 lies in the range 65--73, the age of the Universe, t_0, is 14+/-1.6 Gyr.