John Gaston "Jack" Fox (March 5, 1916 – July 24, 1980) was an American nuclear physicist. He earned his PhD from Princeton in 1941 and was soon recruited to work on the Manhattan Project. He later moved to Pittsburgh where he spent the rest of his career as a professor of physics at Carnegie Mellon University. He is best known for his work in the 1960s, applying the results of the extinction theorem to the then-current body of experimental evidence relating to both special relativity and emission theory.