cosmic background radiation

Electromagnetic radiation left over from the original formation of the universe in the Big Bang between 10 and 20 billion years ago. It corresponds to an overall background temperature of 2.73 K (−270.4°C/−454.8°F), or approximately 3°C above absolute zero.

Cosmic background radiation was first detected in 1965 by US physicists Arno Penzias and Robert Wilson, who in 1978 shared the Nobel Prize for Physics for their discovery. In 1992 the US Cosmic Background Explorer satellite detected slight ‘ripples’ in the strength of cosmic background radiation that are believed to mark the first stage in the formation of galaxies. On 30 June 2001, NASA launched the Wilkinson Microwave Anisotropy Probe, which has measured and mapped the temperature of the cosmic background radiation over the entire sky.