Feynman Diagrams

Feynman diagrams are a powerful pictorial tool for making calculations in quantum theory. They were invented by the American theoretical physicist Richard Feynman (1918–88) during the late 1940s, in the context of ► quantum electrodynamics (QED), physicists' quantum-mechanical theory of electric and magnetic forces. The diagrams were intended to provide a shorthand for the famously unwieldy mathematics of QED calculations, in which it had become common, since the 1930s, for physicists to mistakenly conflate or omit terms within long series of expressions. Feynman unveiled his new techniques at a private conference in 1948. He also coached a young protégé, Freeman Dyson (born 1923, at that time a graduate student at Cornell University in upstate New York, where Feynman taught), in how to use the diagrams. Feynman and Dyson each published a pair of articles on the new techniques during 1949 [1].

Feynman's own route to the diagrams involved a major re-thinking of quantum mechanics, based on his notion of ► path integrals, which he developed for his dissertation at Princeton University in 1942. Dyson, on the other hand, recognized that the diagrams could be useful for calculations in ► quantum field theory independent of Feynman's particular ideas about path integrals. Well into the 1960s, most applications of Feynman diagrams, and most discussion of them in textbooks, followed Dyson's prescriptions, until Feynman's path integrals entered the mainstream [4,5].