Sin-Itiro Tomonaga
1906-1979
Japanese Physicist
Apioneer in the field of quantum electrodynamics, Sin-Itiro Tomonaga developed a theory about subatomic particles that resolved earlier difficulties encountered by physicists seeking to bring together principles of quantum mechanics and special relativity. He shared the 1965 Nobel Prize for Physics with Richard Feynman (1918-1988) and Julian Schwinger (1918-1994).
Tomonaga was born in Tokyo on March 31, 1906, to Sanjuro and Hide Tomonaga. His father became a professor of philosophy at Kyoto Imperial University when Tomonaga was a boy, and the family moved to Kyoto. Later Tomonaga enrolled in Kyoto's renowned Third High School, and there he studied alongside Hideki Yukawa (1907-1981), who would later become Japan's first Nobel Prize winner (also in physics) in 1949. Both men later majored in physics at Kyoto Imperial University, earning their bachelor's degrees in 1929, and both remained as research assistants to physicist Kajuro Tamaki.
In 1932 Tomonaga took a job as research assistant to Yoshio Nishina at the Institute of Physical and Chemical Research in Tokyo. Five years later, he went to the University of Leipzig in Germany, where he studied under the great Werner Heisenberg (1901-1976). At Leipzig Tomonaga wrote his dissertation, on the atomic nucleus, and in 1939 earned his Ph.D. from Kyoto Imperial.
Tomonaga married Ryoko Sekiguchi, daughter of the director of the Tokyo Metropolitan Observatory, in 1940. The couple later had two sons, Atsushi and Makoto, and a daughter, Shigeko. In 1941 Tomonaga became professor of physics at Bunrika University (now Tokyo University of Education), and during this period conducted some of his most important research.
Quantum electrodynamics (QED) had emerged in the 1920s, as physicists sought answers from both quantum mechanics and relativity theory as a means of explaining the behavior of particles and their interaction with energy. English physicist Paul Dirac (1902-1984) had developed a theory of QED that initially seemed effective in explaining these questions, but in time Dirac's theory ran into difficulties. Among these was the fact that, according to Dirac's predictions, particles under certain circumstances would have infinite mass and infinite electrical charge—which was clearly impossible.
Tomonaga, however, was convinced that he could resolve the "divergence difficulties" Dirac had encountered. Using a mathematical technique called renormalization, he was able to demonstrate that although a particle could theoretically assume infinite mass and charge, this would never occur in the real world. He published a paper on his findings in 1943, but because of World War II, this information did not reach the scientific community at large until 1947. Around the same time, Schwinger and Feynman, working at the California Institute of Technology (Cal Tech), published similar findings. In 1965 the three physicists shared the Nobel Prize in recognition of their independently derived solutions to the "divergence difficulties" problem.
In 1949 Tomonaga accepted an invitation to go to the Institute of Advanced Studies (IAS) in Princeton, New Jersey, as a visiting scholar. Two years later he returned to Tokyo as director of the Institute for Scientific Research, and in 1955 he helped establish the Institute for Nuclear Studies at the University of Tokyo. A year later, he became president of the university.
In addition to the Nobel Prize, Tomonaga received the Japan Academy Prize in 1948, the Order of Culture of Japan in 1952, and the Lomonosov Medal of the Soviet Academy of Sciences in 1964. He retired in 1962, but shortly afterward became president of the Science Council of Japan and director of the Institute for Optical Research. Tomonaga held these posts until 1969. He died in Tokyo on July 8, 1979.
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