Born at Yukon in Florida, Smoot was educated at the Massachusetts Institute of Technology where he took his PhD in physics in 1970. He moved to the University of California, Berkeley, in 1971 as a research physicist and in 1974 was appointed team leader for the differential microwave radiometers on board the Cosmic Background Explorer Satellite (COBE).

In 1965 Penzias and Wilson had discovered the cosmic background radiation. Initially it appeared to be perfectly isotropic, exactly the same whatever part of the universe it came from. Theorists found it difficult to account for such uniformity, and experimentalists began to wonder if it really was as uniform as it appeared.

The first disproof of isotropy came in 1977 from observations taken on board a high-flying U2 plane. The dipole anisotropy, as it was called, was small and was connected with the position of the Milky Way. Clearly further work was called for. After a number of delays, COBE was launched in 1989. Three instruments were carried. The differential microwave radiometer would measure differences in radiation from two points in the sky and could pick out differences between them of 1 part in 100,000. Also, a photometer measured the absolute brightness of the sky and searched for diffuse infrared radiation from the early universe. Finally, an interferometer measured the spectrum of the background radiation from 1 centimeter to 100 micrometers.

As the results emerged Smoot saw within the assumed uniformity ‘islands of structure’. A year was spent checking the reliability of the data – prizes were offered to anyone on the team who could identify a significant flaw. Finally the material was checked against a list of all the systematic errors ever noted during the years of preparation. After four papers describing the initial results had been revised more than a hundred times, Smoot was ready to go public.

The results seemed to show that there were bright spots in the universe, 30 millionths of a degree warmer than the average temperature. This was precisely the result predicted by the inflationary model of Alan Guth. It might also be possible, Smoot considered, to find in the ripples in the radiation the galactic clusters that populate the universe. Smoot has published a valuable popular account of the COBE mission in his Wrinkles in Time (1993).