Shoichi Sakata

Theoretical physicist. Born in Tokyo as the eldest son of business magnate Sakata Mikita (1879-1958). After attending Konan Junior and Senior High School in Osaka, he graduated from the Department of Physics, Faculty of Science, Kyoto Imperial University in 1933 (Showa 8). He joined the Nishina Laboratory at the RIKEN Institute, where he worked with Tomonaga Shinichiro on research into electron pair generation. In 1934, he was invited by Yukawa Hideki to move to the newly established Osaka Imperial University, where he served as an assistant and lecturer in the Faculty of Science. In 1939, he returned to Kyoto Imperial University with Yukawa and became a lecturer. In 1942, he moved to Nagoya Imperial University, where he served as a professor and dean of the Faculty of Science.

In 1937, upon hearing a report by Anderson and others that particles with a mass 200 times that of an atom had been discovered in cosmic rays, he worked with Yukawa and others to develop the Yukawa theory of mesons (1935), and in 1939, together with Tanikawa Yasutaka (1916-1987), he announced that neutral mesons become two or three gamma rays in a very short time, and in 1942, together with Tanikawa, Nakamura Seitaro (1913-2007), and Inoue Ken (1921-2004), he announced the "two-meson theory," which distinguishes between the Yukawa (π (pi)) mesons that generate nuclear force and the (μ (mu)) mesons discovered by Anderson. This was proven by experiments in various countries after the Second World War, and he received the Asahi Prize and the Japan Academy Imperial Prize. After moving to Nagoya University, Sakata began researching the limits of applicability of "renormalization theory," beginning with his proposal of the "C meson (condensed meson) theory" (1946), which influenced electromagnetic quantum mechanics and the "renormalization theory" proposed by Tomonaga et al. In 1955, Sakata proposed a composite model for elementary particles (the Sakata model) based on the results of this series of research, which led to new developments in particle physics. Sakata's view of nature as an infinite hierarchy of matter played an important role in the birth of this composite model. Sakata developed this idea through his reading of Engels' "Dialectics of Nature" in his high school days and through his interactions with Taketani Mitsuo, a friend and collaborator from his days at RIKEN.

Furthermore, from his philosophical standpoint, he was actively involved in the democratization of the research system at Nagoya University, the organization of the particle physics group, and international activities such as serving in the Science Council of Japan's Committee on Academic Freedom and Thought, as well as the Pugwash Conferences.

[Takenobu Kobayashi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

理論物理学者。財界人坂田幹太(さかたみきた)（1879―1958）の長男として東京に生まれる。大阪の甲南中学・高校を経て、1933年（昭和8）京都帝国大学理学部物理学科を卒業し、理化学研究所仁科(にしな)研究室に入り、朝永振一郎(ともながしんいちろう)とともに電子対発生の研究に取り組んだ。1934年に湯川秀樹(ゆかわひでき)に招かれ新設まもない大阪帝国大学へ移り理学部助手、講師を務めた。1939年には湯川とともに京都帝国大学へ戻り講師となった。1942年に名古屋帝国大学へ移り同大学教授、理学部長などを務めた。

　1937年にアンダーソンらによって宇宙線中に原子の200倍の質量をもつ粒子が発見されたという報告を聞き、湯川らとともに中間子についての湯川理論（1935）を発展させることに努め、1939年に谷川安孝(たにかわやすたか)（1916―1987）と、中性中間子が非常な短時間で二つあるいは三つのγ(ガンマ)線になることを発表し、さらに1942年には核力を生む湯川（π(パイ)）中間子とアンダーソンが発見した（μ(ミュー)）中間子とを区別する「二中間子論」を谷川、中村誠太郎（1913―2007）、井上健（1921―2004）とともに発表した。これは第二次世界大戦後各国の実験で証明され、朝日賞、日本学士院恩賜賞を受けた。名古屋大学へ移ってからは、電磁量子力学や朝永らによる「くりこみ理論」に影響を与えた「C中間子（凝集中間子）論」の提唱（1946）をはじめとして、「くりこみ理論」の適用限界についての研究に取り組んだ。1955年（昭和30）にこうした一連の研究成果から素粒子に対する複合模型（坂田模型）を提案し、素粒子論の新たな展開を生み出した。またこの複合模型の誕生には、物質の無限の階層性という自然観が重要な役割を果たした。坂田はこの考えを高校時代に読んだエンゲルスの『自然の弁証法』や理研時代からの友人・協力者である武谷三男(たけたにみつお)との交流から実らせた。

　さらにその哲学的立場から、名古屋大学での研究体制の民主化、素粒子論グループの組織化、学術会議「学問と思想の自由委員会」での活動をはじめ、パグウォッシュ会議などの国際的な活動にも精力的に取り組んだ。

［小林武信］

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