John C. Mather developed and led the scientific use of the COBE FIRAS instrument to test the radiation spectrum of the cosmic microwave background. Comparing the sky signal against a controlled reference blackbody made the measurement a stringent test of spectral shape.
The measured spectrum closely followed Planck's law at a temperature near 2.7 kelvin, strongly supporting a thermal origin in the early Universe. This result addresses a different observable from angular anisotropy: a nearly perfect blackbody spectrum concerns the distribution over frequency, while a sky map concerns changes with direction.[ref]
Nobel Lecture: From the Big Bang to the Nobel Prize and beyond by John C. Mather. Discussion of FIRAS calibration, blackbody spectrum and cosmological interpretation
Portrait of John C. Mather
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John C. Mather is an American astrophysicist known for his work in the field of cosmology and his significant contributions to our understanding of the universe. He was awarded the Nobel Prize in Physics in 2006, along with George F. Smoot, for their work on the Cosmic Background Explorer Satellite (COBE), which provided critical measurements of the cosmic microwave background radiation.
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