Julian Seymour Schwinger (February 12, 1918 - July 16, 1994) was an American theoretical physicist. He formulated the theory of renormalization and posited a phenomenon of electron-positron pairs known as the Schwinger effect. He was jointly awarded the Nobel Prize in Physics in 1965 for his work on quantum electrodynamics (QED), along with Richard Feynman and Shinichiro Tomonaga.
Schwinger was born in New York City, attended the City College of New York as an undergraduate, and received his doctorate from Columbia University in 1939 where he studied under I.I. Rabi. He worked at the University of California, Berkeley and was later appointed to a position at Purdue University.
During World War II Schwinger worked at the Radiation Laboratory at MIT, providing theoretical support for the development of radar. He tried applying his knowledge as a Nuclear Physicist to electromagnetic engineering problems, and arrived at results on nuclear scattering. Consequently, Schwinger began to apply his understanding of radiation to quantum physics.
After the war, Schwinger left Purdue for Harvard University, where he taught from 1945 to 1974. He married in 1947. During this time, he developed the concept of renormalization, which explained the Lamb shift in an electron's magnetic field. He also realized, in his study of particle physics, that neutrinos would come in multiple varieties, associated with leptons like the electron and muon, which was experimentally verified in recent years.
Having supervised more than seventy doctoral dissertations, Schwinger is known as one of the most prolific graduate advisors in physics. Three of his students won Nobel prizes: Benjamin Roy Mottelson, Sheldon Glashow and Walter Kohn (in chemistry).
In his later career, displeased with the complexity of other explanations of particle physics experiments, Schwinger developed source theory, which treats gravitons, photons, and other particles uniformly. Schwinger left Harvard in 1974 for a position the University of California, Los Angeles where he continued his work on source theory. Here, he established a legacy of excellent lecturing and mentoring skills.
See also Schwinger model, Schwinger-Dyson equations, Schwinger's variational principle, Rarita-Schwinger action
Schwinger and Feynman
As a famous physicist, Schwinger was often compared to another legendary physicist of his generation, Richard Feynman. Schwinger was more mathematically inclined and heavily favoured mathematical rigour in his way of doing physics, especially in the field of Quantum Field Theory. By contrast, Feynman was more intuitive and this showed in his Feynman diagram approach to the QFT. Schwinger disliked Feynman diagrams to the point of banning them altogether in his class.