The cosmological constant and the time of its dominance

Abstract

We explore a model in which the cosmological constant $Λ$ and the density contrast at the time of recombination $σ_{rec}$ are random variables, whose range and {\it 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 $σ_{rec}$, and find that it is peaked near the observationally suggested values, for a wide class of {\it a priori} distributions.