John C. Mather (born August 7, 1946, Roanoke, Virginia, U.S.) is an American physicist, who was corecipient, with George F. Smoot, of the 2006 Nobel Prize for Physics for discoveries supporting the big-bang model.
Mather studied physics at Swarthmore University (B.S., 1968) and the University of California at Berkeley (Ph.D., 1974). He later joined the staff of the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center, serving as a senior astrophysicist.
In the 1980s Mather and Smoot were instrumental in developing the Cosmic Background Explorer (COBE) for NASA. The satellite was launched in 1989 and measured cosmic microwave background radiation formed during the early phases of creation of the universe. The resulting data supports the hypothesis that the universe emerged from a state of high temperature and density—the so-called big bang that occurred at least 10 billion years ago.
In 1995 Mather became the senior project scientist for the James Webb Space Telescope, which was launched in 2021. He wrote a book about the COBE project, The Very First Light: The True Inside Story of the Scientific Journey Back to the Dawn of the Universe (1996, revised 2008, with John Boslough).