INTERPRETATION OF THE COBE FIRAS CMBR SPECTRUM

The cosmic microwave background spectrum measured by the FIRAS instrum ent on NASA's COBE is indistinguishable from a blackbody, implying str ingent limits on energy release in the early universe later than the t ime t=1 yr after the big bang. We compare the FIRAS data to previous p recise measurements of the cosmic microwave background spectrum and fi nd a reasonable agreement. We discuss the implications of the y<2.5x 10(-5) and mu<3.3x10(-4) 95% confidence limits found by Mather et al . (1994) on many processes occurring after t=1 yr, such as explosive s tructure formation, reionization, and dissipation of small-scale densi ty perturbations. We place limits on models with dust plus Population III stars, or evolving populations of IR galaxies, by directly compari ng the Mather et al, spectrum to the model predictions.