Cosmic Background Radiation

The existence of essentially isotropic homogeneous cosmic background radiation with the spectrum of a 3 K blackbody places important limits on cosmological speculations. This radiation has been the subject of intensive experimental investigation for more than a decade. Current research centers around measurements of the spectrum of the cosmic background radiation at submillimeter wavelengths, and measurements of the anisotropy of this radiation from centimeter to submillimeter wavelengths. In this talk we will discuss some of the difficulties of making these measurements and summarize the present status of the field. In 1948, Alpher and Herman [1] reported theoretical investigations of “big bang” cosmological models in an effort to explain the abundance of the chemical elements. They concluded that their model universe was filled with isotropic homogeneous blackbody radiation with a characteristic temperature of a few degrees Kelvin. This radiation was emitted by the ∼ 3,000 K cosmic plasma and has not interacted with matter since the plasma cooled sufficiently to form hydrogen. Because of the subsequent expansion of the universe, this radiation has cooled to the present temperature of ∼ 3 K.