Feynman invented diagrams that physicists still use

Person: Richard Feynman
Lived: 1918–1988
Field: Physics
From: American

The story

Calculations in particle physics involve long, intricate integrals describing every way particles can collide, exchange energy and transform. In the 1940s quantum electrodynamics, the theory of how light and charged particles interact, was also plagued by infinite answers. Keeping track of the terms was a daunting task that only a few specialists could manage.

Richard Feynman, then a young professor at Cornell University, introduced a new tool in 1948. In his pictorial scheme, lines represent particles and the points where they meet represent interactions. Each diagram corresponds to a precise mathematical term, so physicists could draw the possible processes and then translate them directly into calculations. The diagrams grew out of his path integral approach to quantum mechanics, which he had begun in his doctoral thesis at Princeton under John Archibald Wheeler. A key insight, which drew on an interpretation first proposed by the Swiss physicist Ernst Stueckelberg, was that a positron, the antimatter twin of the electron, could be treated as an electron moving backwards in time.

The idea did not catch on at once. When Feynman first showed the diagrams at the Pocono Conference in 1948, they puzzled his audience, and Paul Dirac, Edward Teller and Niels Bohr all raised objections. Freeman Dyson was convinced that Feynman's approach was easier to understand, and his 1949 paper added rules showing how to use it. Papers using Feynman diagrams began to appear in 1950 and soon became the norm, and students learned the powerful new tool.

The diagrams became central to Feynman's share of the 1965 Nobel Prize in Physics. The Nobel committee's summary notes that in 1948 he helped create a new quantum electrodynamics by introducing these graphic representations, which make interaction probabilities easier to calculate. Computer programs were later written to evaluate the diagrams, allowing physicists to make predictions of very high precision.

Feynman diagrams are now used far beyond their original field, including in solid-state physics. The physicist Frank Wilczek wrote that the calculations behind his own 2004 Nobel Prize would have been literally unthinkable without them. Feynman was so fond of his invention that in 1975 he bought a van and had it painted with Feynman diagrams.

Why it matters

Feynman diagrams made complex particle calculations manageable and are used every day in research from particle colliders to condensed matter physics.