Sin-itiro Tomonaga

The Japanese physicist Sin-itiro Tomonaga (1906-1979) is best known for his fundamental contributions to quantum electrodynamics.

The oldest son of a philosopher and university professor, Sin-itiro Tomonaga was born on March 31, 1906, in Tokyo. After obtaining his degree from Kyoto University in 1929, he spent 3 years as a research student in Kajuro Tomaki's laboratory at the university and then became a research student under Yoshio Nishina in the Science Research Institute in Tokyo. Tomonaga remained there until 1940, with the exception of some time spent in 1939 at the University of Leipzig with Werner Heisenberg.

In 1940 Tomonaga married Rijo, by whom he had three children. In 1941, he became professor of physics at the Tokyo University of Science and Literature (which after the war became part of the Tokyo University of Education).

During the war years, while working in complete isolation from other physicists, Tomonaga made the contributions to quantum electrodynamics for which he shared the Nobel Prize of 1965 with Julian Schwinger of Harvard University and Richard Feynman of the California Institute of Technology. The achievement of these physicists must be understood in the context of the general development of physics since 1925-1926, when quantum mechanics was discovered and elaborated by Heisenberg, Erwin Schrödinger, Paul Dirac, Max Born, and others. Although this elegant theory had been developed specifically to understand the structure of the atom, it was soon generalized by Heisenberg, Wolfgang Pauli, Dirac, and Enrico Fermi to include an explanation of radiation processes and of processes, like the Compton effect, involving the interaction of radiation and matter. The resulting theory—quantum electrodynamics—agreed qualitatively with experiment but refused to yield precise agreement. Most physicists of the 1930s took this to mean that there was something fundamentally wrong with the theory. "Tomonaga, Schwinger, and Feynman, " wrote F. J. Dyson in Science (1965), "rescued the theory without making any radical innovations. Their victory was a victory of conservation. They kept the physical basis of the theory [the postulation of only electrons, positrons, and photons] precisely as it had been laid down by Dirac, and only changed the mathematical superstructure. By polishing and refining with great skill the mathematical formalism, they were able to show that the theory does in fact give meaningful predictions for all observable quantities."

The remarkable thing, as Dyson pointed out, was that, although certain experiments had played a decisive role in Schwinger's and Feynman's thinking, Tomonaga had reached an essentially identical insight on the basis of theoretical considerations alone. He had published those conclusions in Japanese in 1943, but his papers were not translated into English until 1948—until Schwinger and Feynman had been able to direct their efforts away from war-related researches and had independently achieved essentially the same results.

After the war Tomonaga received many honors for his work. Besides the 1965 Nobel Prize, he received the Japan Academy Prize in 1948, the Order of Culture (Japan) in 1952, and the Lomonosov Medal from the USSR in 1964. He was professor of physics at Tokyo University of Education from 1949 to 1969, and served as president of the institution from 1956 until 1962. In 1963, he became director of the university's Institute of Optical Research. He was also president of the Science Council of Japan from 1963 to 1969. He retired from the Tokyo University of Education in 1969, and served as Professor Emeritus until his death in Tokyo on July 8, 1979.

Further Reading on Sin-itiro Tomonaga

The Nobel Foundation's annual volume Les Prix Nobel 1965 (1966) has, in English, a brief biography of Tomonaga and his personal recollections of the development of quantum electrodynamics. Some background material is in Henry A. Boorse and Lloyd Motz, eds., The World of the Atom (2 vols., 1966).