Cosmological constant and the time of its dominance - art. no. 023503

We explore a model in which the cosmological constant Lambda and the densit y contrast at the rime of recombination sigma(rec) are random variables, wh ose 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 ord er of magnitude coincidence among the three time scales, 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 sigma(rec). Assuming a power law a priori distribution proportional to sigma(rec)(-alph a) We find that for alpha>3 the most probable values of sigma(rec) are near the observationally suggested values, whereas for alpha<3 the typical sigm a(rec) would be too large. This may be used to place constraints on inflati onary models (orr on any alternative theory of initial conditions).