Sin-Itiro Tomonaga was a pioneer in the field of quantum electrodynamics, a broad theory that uses principles from quantum mechanics and special relativity to explain a wide variety of physical phenomena. He developed a theory about subatomic particles that was consistent with the relativity theory about the same time that Richard P. Feynman and Julian Schwinger independently reached similar solutions. The three were jointly awarded the 1965 Nobel Prize in physics for their efforts in quantum theory.
Sin-Itiro (also transliterated as Sin-Ichiro) Tomonaga was born in Tokyo on March 31, 1906, to Sanjuro and Hide Tomonaga. When Sin-Itiro was a child, his family moved to Kyoto, where his father had been appointed professor of philosophy at the Kyoto Imperial University. Sin-Itiro enrolled at Kyoto's prestigious Third High School where he was a classmate of Hideki Yukawa , later to become Japan's first Nobel Prize winner (in the field of physics) in 1949. After graduation, Tomonaga and Yukawa both went on to Kyoto Imperial University, where both majored in physics and earned their bachelor's degrees in 1929. The two then stayed on as research assistants to Kajuro Tamaki.
In 1932, Tomonaga and Yukawa finally went their separate ways, with Tomonaga accepting a position as research assistant to Yoshio Nishina at the Institute of Physical and Chemical Research in Tokyo. After five years in this post, Tomonaga traveled to the University of Leipzig where he studied under physicist Werner Heisenberg. While at Leipzig, Tomonaga wrote a paper on the atomic nucleus that earned him a Ph.D. from Kyoto Imperial upon his return to Japan in 1939. In 1941 Tomonaga became professor of physics at Tokyo's Bunrika University (now Tokyo University of Education), a post he held until 1956, when he became president of the university. After leaving Tokyo University in 1962, Tomonaga served as president of the Science Council of Japan and director of the Institute for Optical Research.
Attacks Problems of Quantum Electrodynamics
The topic that dominated Tomonaga's research throughout most of his life was quantum electrodynamics (QED). QED arose during the 1920s when the successes of quantum theory and relativity made it apparent that classical laws of physics were inadequate to explain the behavior of elementary particles. A number of theorists attempted to develop new equations that would take into consideration both quantum mechanics and relativity theory to explain the behavior of particles and their interaction with energy.
By the late 1920s, impressive progress had been made in dealing with this problem, especially as a result of the work of the English physicist Paul Dirac . Dirac's theory successfully predicted the qualitative properties of atomic particles and the way they interacted with energy. Over time, however, it became apparent that Dirac's theory was quantitatively inadequate. Among the most serious problems of the Dirac theory was the prediction that, under certain circumstances, particles would have infinite mass and infinite charge. The physical absurdity of these predictions, commonly known as "divergence difficulties," deeply troubled physicists, many of whom decided that a totally knew approach to QED would be needed.
Success with Quantum Electrodynamics Brings Nobel Prize
Tomonaga, however, took another view. He was convinced that techniques could be found that would allow the retention of Dirac's fundamental approach while resolving the "divergence difficulties" inherent within it. The mathematical technique he used, called renormalization, worked. Tomonaga was eventually able to demonstrate that infinite mass and charge are indeed a fundamental part of the Dirac theory, but that they apply to situations that would never be encountered in the real world.
Tomonaga's fundamental paper on QED was published in Japan in 1943. Because of the war, however, news and translation of the paper did not reach the rest of the world until 1947. At about the same time, similar papers dealing with QED written by Schwinger at Harvard and Feynman at the California Institute of Technology were also being published. When the 1965 Nobel Prize in physics was announced, therefore, it was divided among the three physicists for the independent solutions of the "divergence difficulties" problem.
Tomonaga's prize-winning research had been carried out at Tokyo's Bunrika University of Science and Literature, where he had been appointed professor of physics in 1941. He remained in this post, after the university had been incorporated into the Tokyo University of Education, until 1949. He then accepted an invitation to become a visiting scholar the Institute for Advanced Studies at Princeton, New Jersey. He returned to Tokyo in 1951 to become head of the Institute for Scientific Research. Four years later, he was instrumental in the founding of the Institute for Nuclear Studies at the University of Tokyo and then, in 1956, became president of the university. Upon his retirement in 1962, Tomonaga accepted an offer to become president of the Science Council of Japan and director of the Institute for Optical Research, posts he held until 1969.
Tomonaga was married in 1940 to Ryoko Sekiguchi, daughter of the director of the Tokyo Metropolitan Observatory. They had two sons, Atsushi and Makoto, and a daughter, Shigeko. In addition to the Nobel Prize, Tomonaga was awarded 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. Tomonaga died in Tokyo on July 8, 1979.
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