ASTRO 142 Chapter Notes - Chapter 14: Diffuse Infrared Background Experiment, Cosmic Background Radiation, Black-Body Radiation
Document Summary
The hot big bang model proposes that early on, the matter density and temperature were very high and the universe was opaque; matter and radiation constantly exchanged energy. Thus the universe was in thermal equilibrium in its early stages of existence and would naturally have been filled with blackbody radiation appropriate to its temperature. 380,000 years after the big bang, the universe was so hot that all matter existed as plasma. During this time, photons could not travel undisturbed through the plasma because they interacted constantly with the charged electrons and baryons, in a phenomenon known as. As a result, the universe was opaque: as the universe expanded, cooled, and rarefied, there came a time at which the electrons were captured by atomic nuclei. Since then the universe has been transparent to photons, and the cosmic radiation has traveled unimpeded through space. Occasionally, a few of its photons strike receivers located on a small planet in the.
