Richard Feynman

Richard Phillips Feynman was born in 1918 in Far Rockaway, Queens. His father Melville, a uniform salesman with no formal scientific training, taught the young Feynman to ask why — to demand a mechanism for any phenomenon, never to be satisfied with a name in place of an explanation — and that habit shaped the rest of Feynman's intellectual life. He took his bachelor's at MIT in 1939 and went to Princeton for graduate work under John Archibald Wheeler. The 1942 PhD thesis *The Principle of Least Action in Quantum Mechanics* introduced the path-integral formulation of quantum mechanics: the amplitude for a particle to go from one spacetime point to another is the sum over all possible paths between them, weighted by e^{iS/ℏ} where S is the classical action. The reformulation was equivalent to Schrödinger's wave mechanics but radically more flexible, and it became the foundation for everything Feynman did afterward.

Feynman went directly from Princeton to the Manhattan Project at Los Alamos (1943–1945, T-Division — theoretical calculations of critical mass, with Hans Bethe), then to Cornell (1945–1950) and Caltech (1950 to retirement). At Cornell, between 1947 and 1949, he developed the diagrammatic formulation of quantum electrodynamics that now bears his name: each Feynman diagram represents a term in the perturbative expansion of a quantum-mechanical amplitude, with virtual particles propagating along the lines and interacting at the vertices. The diagrams, the path-integral derivation of the Feynman rules, and the careful treatment of regularisation and renormalisation made calculations that had been intractable in 1947 routine by 1950. Feynman shared the 1965 Nobel Prize for physics with Julian Schwinger (Harvard, who had developed an equivalent operator-based formulation) and Sin-Itiro Tomonaga (Tokyo, who had derived essentially the same results during the war and the Allied bombing).

At Caltech Feynman taught the famous two-year introductory physics course (1961–1963) whose lecture notes, edited by Robert Leighton and Matthew Sands and published as *The Feynman Lectures on Physics*, are still the most-cited physics textbook in print. Volume II, on electromagnetism, derives Maxwell's equations from the photon — a striking inversion of the historical order, and the §12.4 voice anchor of this site. Feynman also did important work on superfluidity, the parton model of hadron structure (1969), and quantum computing (1981). The investigation of the 1986 Challenger disaster — for which he served on the Rogers Commission and gave the famous televised demonstration of the O-ring's loss of resilience in ice water — was the most-watched moment of public-facing physics ever broadcast in the United States. He died in 1988 at Caltech of liposarcoma. *Surely You're Joking, Mr. Feynman!* (1985) remains in print as one of the most popular memoirs by any scientist of the twentieth century.