Radiation backgrounds and their cosmological implications

Abstract

The information content of radiation backgrounds at wavelengths ranging from radio waves to gamma rays is reviewed, within the context of the standard big bang cosmology. It is shown that the various backgrounds provide useful inputs and constraints on the physical features of the universe such as the existence and growth of large scale inhomogeneities like galaxies, clusters and superclusters, the overall density of the universe, the photon to baryon ratio and the extent of antimatter in the universe, etc. It is argued that there are questions posed by the data which may require rethinking of some aspects of standard cosmology.