A neutrino-dominated universe?

The hot big bang picture of the origin of the universe successfully explains the cosmic background radiation and the primordial nucleosyntheses. The theory's horizon and flatness problems are solved by bringing in grand unified theories, but the phase transition needed to spontaneously break the grand unified symmetry is also predicted to produce large numbers of magnetic monopoles. The inflationary universe scenario solves this problem, but cannot successfully account for the release of the latent heat associated with the phase transition. The new inflationary universe avoids this problem, is monopole-free, predicts the existence of the large entropy associated with the flatness problem, and predicts the value of the energy density today with an extraordinary degree of accuracy. Considerations of the energy density show that it cannot be explained by baryons. This and other lines of evidence indicate that the universe is dominated by massive neutrinos on increasing scales.