Shin’ichiro Tomonaga

It’s the birthday of Shin’ichiro Tomonaga (朝永 振一郎), who was born in 1906 in Tokyo. After earning a PhD at Kyoto University, Tomonaga spent two years at the University of Leipzig, where he collaborated with Werner Heisenberg. By the the late 1930s it had become apparent to quantum theorists that they could not calculate an arbitrary encounter between a relativistic particle and an electromagnetic field. The mathematical series that embodied the solution diverged. Having returned to Japan before the outbreak of World War II, Tomonaga discovered in 1948 a method to get rid of the troublesome infinities. Julian Schwinger had independently discovered the same result - for which the two men, along with Richard Feynman, shared the 1965 Nobel physics prize. The theory that they had developed, quantum electrodynamics, was the first to achieve full agreement between quantum mechanics and special relativity. Using it, physicists could calculate the electron’s magnetic moment, the hydrogen atom’s Lamb shift and other tiny but significant effects.

Date in History: 31 March 1906