Cosmic background radiation is an electromagnetic radiation from the Big Bang. The origin of this radiation depends on the region of the spectrum that is observed. One component is the cosmic microwave background. This component is redshifted photons that have freely streamed from an epoch when the Universe became transparent for the first time to radiation. Its discovery and detailed observations of its properties are considered one of the major conformations of the Big Bang. The discovery (by chance in 1965) of the cosmic background radiation suggests that the early universe was dominated by a radiation field, a field of extremely high temperature and pressure.
The Sunyaev-Zel'dovich effect shows the phenomena of radiant cosmic background radiation interacting with "electron" clouds distorting the spectrum of the radiation.
There is also background radiation in the infrared, x-rays, etc., with different causes, and they can sometimes be resolved into an individual source. See cosmic infrared background and X-ray background. See also cosmic neutrino background and extragalactic background light.
1931: The term microwave first appears in print: "When trials with wavelengths as low as 18 cm were made known, there was undisguised surprise that the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1"
1946: Robert Dicke predicts a microwave background radiation temperature of 20 K (ref: Helge Kragh)
1946: Robert Dicke predicts a microwave background radiation temperature of "less that 20 K"[clarification needed] but later revised to 45 K (ref: Stephen G. Brush).
1949: Ralph Alpher and Robert Herman re-re-estimate Gamow's estimate at 28 K.
1960s: Robert Dicke re-estimates a MBR (microwave background radiation) temperature of 40 K (ref: Helge Kragh).
1965: Arno Penzias and Robert Woodrow Wilson measure the temperature to be approximately 3 K. Robert Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson interpret this radiation as a signature of the Big Bang.