Effects of Very Long Wavelength Primordial Gravitational Radiation

The Universe may contain gravitational waves with wavelength 1–10 Mpc, of primordial origin, associated with the initial irregularities that give rise to galaxies and clusters. If their energy density pa were comparable with the‘ critical density’ |\, c\, (\, 2\, \, 10^-29\, g\, cm^-3) |, these waves would have interesting effects on the apparent dynamics of groups of galaxies. In a canonical ‘ big bang ’ model, which is assumed initially smooth except for small perturbations, we expect ρG ⪡ ρc. However a ‘chaotic universe’ which resembles a Friedmann model only for redshifts ≲ 1000 could lead to | G\, \, c|. It is argued that such a model is compatible with present observations, and that it suggests a new interpretation of the microwave background.