John Cromwell Mather
active c. 1946, Roanoke, Virginia, United States
American astrophysicist who led the FIRAS team on the COBE satellite measuring the perfect blackbody spectrum of the cosmic microwave background; later project scientist of the James Webb telescope.
Mather earned his PhD at UC Berkeley in 1974, just as the idea of a satellite measuring the microwave background was proposed — he was one of the three authors of the proposal to NASA. He joined NASA Goddard as COBE's study scientist.
Launched in 1989, his FIRAS instrument measured the cosmic microwave background (CMB) spectrum matching a 2.725 K Planck curve to unprecedented precision — the most direct evidence for the Big Bang. He shared the 2006 Nobel with George Smoot and later became senior project scientist of the James Webb Space Telescope.
Nobel-winning work
The cosmic microwave background (CMB) — the 'embers' of the Big Bang — was predicted to have a perfect blackbody spectrum, reflecting the thermal equilibrium of the early universe. Mather designed and ran FIRAS, an interferometer spectrometer comparing the sky to a reference blackbody inside the satellite.
Published in 1990: the CMB spectrum matches a Planck curve at 2.735 ± 0.06 K with errors below 0.03% of peak intensity — 'the most perfect blackbody ever measured in nature'. The result ruled out rival cosmologies and established the CMB as a true thermal relic of the Big Bang; together with the anisotropies found by Smoot's DMR it marks the dawn of precision cosmology.
Workplaces: NASA Goddard Space Flight Center
United States