Robert F. Christy, American physicist and astrophysicist (b. 1916)
Robert Frederick Christy (May 14, 1916 – October 3, 2012) was a Canadian-American theoretical physicist and later astrophysicist who was one of the last surviving people to have worked on the Manhattan Project during World War II. He briefly served as acting president of California Institute of Technology (Caltech).

A graduate of the University of British Columbia (UBC) in the 1930s where he studied physics, he followed George Volkoff, who was a year ahead of him, to the University of California, Berkeley, where he was accepted as a graduate student by Robert Oppenheimer, the leading theoretical physicist in the United States at that time. Christy received his doctorate in 1941 and joined the physics department of Illinois Institute of Technology.

In 1942 he joined the Manhattan Project at the University of Chicago, where he was recruited by Enrico Fermi to join the effort to build the first nuclear reactor, having been recommended as a theory resource by Oppenheimer. When Oppenheimer formed the Manhattan Project's Los Alamos Laboratory in 1943, Christy was one of the early recruits to join the Theory Group. Christy is generally credited with the insight that a solid sub-critical mass of plutonium could be explosively compressed into supercriticality, a great simplification of earlier concepts of implosion requiring hollow shells. For this insight the solid-core plutonium model is often referred to as the "Christy pit".

After the war, Christy briefly joined the University of Chicago Physics department before being recruited to join the Caltech faculty in 1946 when Oppenheimer decided it was not practical for him to resume his academic activities. He stayed at Caltech for his academic career, serving as Department Chair, Provost and Acting President. In 1960 Christy turned his attention to astrophysics, creating some of the first practical computation models of stellar operation. For this work Christy was awarded the Eddington Medal of the Royal Astronomical Society in 1967. In the 1980s and 1990s Christy participated in the National Research Council's Committee on Dosimetry, an extended effort to better understand the actual radiation exposure due to the bombs dropped on Japan, and on the basis of that learning, better understand the medical risks of radiation exposure.