New Perspective on Cosmic Coincidence Problems

Cosmological data suggest that we live in an interesting period in the history of the universe when ρ_Λ~ρM~ρR. The occurrence of any epoch with such a ``triple coincidence'' is puzzling, while the question of why we happen to live during this special epoch is the ``Why now?'' problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the ``Why now?'' problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale MEW, and the Planck scale MPl and requires ρ_Λ1/4~MEW²/MPl parametrically. Assuming that the true vacuum energy vanishes, we present a simple model, where a false vacuum energy yields a cosmological constant of this form.