Published online by Cambridge University Press: 05 March 2013
With the completion of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, it is interesting to form the dimensionless quantity H 0 t 0 by multiplying the Hubble Constant by the age of the Universe. In a matter dominated decelerating Universe with a density exceeding 0·26 of the critical value, H 0 t 0 < 1; in an accelerating Universe with the same Ω m = 0·26, but dominated by vacuum energy with Ω V ≥ 1 – Ω m , H 0 t 0 ≥ 1. If the first globular clusters formed 109 years after the Big Bang, then with 95% confidence H 0 t 0 =1·0 ± 0·3. The classical Einstein–de Sitter cosmological model has H 0 t 0 = ⅔.