ST ScI Preprint #1381

The Cosmological Constant and the Time of Its Dominance

We explore a model in which the cosmological constant and the density contrast at the time of recombination _rec are random variables, whose range and a priori probabilities are determined by the laws of physics. (Such models arise naturally in the framework of inflationary cosmology.) Based on the assumption that we are typical observers, we show that the order of magnitude coincidence among the three timescales: the time of galaxy formation, the time when the cosmological constant starts to dominate the cosmic energy density, and the present age of the universe, finds a natural explanation. We also discuss the probability distribution for _rec. Assuming a power law a priori distribution _rec^- we find that for >3 the most probable values of _rec are near the observationally suggested values, whereas for <3 the typical _rec would be too large. This may be used to place constraints on inflationary models (or on any alternative theory of initial conditions).