The Nobel Prize for Physics has been awarded jointly to John Mather and George Smoot "for their discovery of the black-body form and anisotropy of the cosmic microwave background radiation".
The Big Bang theory predicts this radiation, first registered in 1964, as a relic of the massive explosion that heralded the birth of the Universe. An alternate theory for the origins of the universe - the idea that the universe had always existed in a steady state - had also been proposed.
NASA's COBE satellite was launched in 1989 specifically to investigate the nature of the cosmic microwave background radiation.
Mather and Smoot analysed the data gathered by the satellite and, according to the Royal Swedish Academy of Sciences, this work was instrumental in developing cosmology into a precise science. It further bolstered the Big Bang theory, confirming at least two of its predictions.
After the Big Bang, the Universe was quite hot - around 3000K - and emitting what is known as black-body radiation. This refers to a very specific spectrum of radiation which is dependent solely on the temperature of the body. Over time, the Universe was expected to cool to around 2.7K, just above absolute zero.
With data collected in the first nine minutes of COBE's operation, Mather and Smoot confirmed that the cosmic microwave background radiation did indeed have a black-body form matching that predicted by the theory. This indicated that the radiation is indeed a result of the Big Bang, and therefore that the Universe has not always existed in a steady state.
Further detailed analysis of the data showed there were slight fluctuations in the temperature of the radiation depending on the direction it was measured in. Because of this, it is said to be anisotropic.
This anisotropy is responsible for matter being able to aggregate to form stars, galaxies, planets and, eventually, Nobel laureates.
John Mather works at NASA's Goddard Space Flight Centre, and George Smoot is based in the University of California, Berkeley. ®