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Hidechi YukavaJapanese physicist, member of the USSR Academy of Sciences, Nobel Prize laureate (1949). Predicted the existence of mesons, electron capture, developed the basic principles of meson theory.
Date of Birth: 23.01.1907
Country:  Japan |
Content:
Biography of Hideki Yukawa
Hideki Yukawa, a Japanese physicist, member of the USSR Academy of Sciences, and recipient of the Nobel Prize (1949), predicted the existence of mesons, electron capture, and developed the fundamental principles of meson theory.
Early Life and Education
Hideki Yukawa was born as Hideki Ogawa in Tokyo, Japan. After getting married, he took on his wife's surname and became Hideki Yukawa. He was the fifth of seven children born to Takudzi and Koyuki Ogawa. When he was one year old, his family moved to Kyoto, where his father became a professor of geology at Kyoto Imperial University. Yukawa grew up in a cultural and intellectual atmosphere. His father had a strong interest in archaeology, history, and literature of ancient China and Japan. As a young boy, Yukawa became acquainted with Chinese classics through his paternal grandfather, a philologist. Yukawa attended the Third Middle School in Kyoto, where he developed an interest in literature, philosophy, and mathematics. However, he was particularly drawn to modern physics, which he discovered by reading books on relativity and quantum mechanics available in the school library. He taught himself German to read Max Planck's multi-volume work, which he purchased from a local bookstore.
After graduating from high school in 1926, Yukawa enrolled in Kyoto Imperial University, where he studied physics under an accelerated program. He stood out for conducting high-precision experiments in Kajuro Tamaki's laboratory. In 1929, he obtained a master's degree after writing a dissertation on the properties of Paul A.M. Dirac's equation, which applies the theory of relativity to quantum mechanics in describing atomic particle motion. Yukawa remained in Tamaki's laboratory as an unpaid assistant, but his interest gradually shifted from experimental to theoretical physics. The most exciting work in quantum theory was happening in Europe, and many of its unsolved problems fascinated the young physicist. Although quantum theory was only briefly covered in his university courses, between 1929 and 1932, Yukawa independently studied it by reading the necessary literature. He had conversations with Werner Heisenberg and Dirac when they visited Kyoto, and he also met Yoshi Nishina, who had worked with Niels Bohr in Copenhagen. Yukawa later admitted that Tamaki and Nishina had a decisive influence on his decision to devote himself to theoretical physics, noting his lack of experimental inclination due to his inability to "master the production of ordinary glass laboratory equipment." In 1932, he became a physics lecturer at Kyoto University, a year later at Osaka University, and in 1936, he became an associate professor at Osaka University. It was in Osaka that Yukawa began seriously contemplating the problem that had occupied physicists' minds for the past two decades: why does the atomic nucleus not break apart into pieces? It was already known that the nucleus contained tightly packed positively charged particles (protons). Given that like charges repel each other, and the repulsion force increases rapidly as the distance between the charges decreases, the coupling of protons seemed like a mystery. James Chadwick's discovery of the neutron in 1932, an uncharged particle with a mass almost equal to that of a proton, further complicated matters. The neutron, later recognized as another inhabitant of the nucleus, explained the existence of isotopes, elements with the same number of protons but different numbers of neutrons. However, the problem of proton binding remained, complicated by the need to explain the binding of neutrons to each other and to protons. Gravity, the mutual attraction of all masses, was too weak to have a significant influence on nuclear binding.
Meson Theory
Several prominent physicists, including Heisenberg, proposed their theories of the nucleus, but none of them withstood criticism. It was clear that an unknown nuclear force existed, but it had to be extraordinarily strong and act at short distances. Moreover, quantum physicists had to come to terms with considering known forces as forces acting through the exchange of particles containing units of field energy called quanta. In the case of the electromagnetic field, the photon is such a particle, a quantum of electromagnetic energy. Photons have no rest mass – they either move or do not exist. In 1935, Yukawa proposed that the strong force holding the nucleus together is associated with an exchange particle of large mass. He published a complex but insightful theory that allowed him to calculate the mass (approximately 200 times the mass of an electron) of a hypothetical particle. He also showed that it could not be detected in ordinary nuclear reactions because its large mass is equivalent to very high energy, but it could be searched for in collisions of cosmic rays with atomic nuclei.
Yukawa's article appeared in a Japanese physics journal. Although written in English, it went unnoticed for two years. American physicist Carl D. Anderson discovered the positron in 1932 while studying photographs of tracks obtained from cosmic rays passing through an ionization chamber. (Particles similar to those present in cosmic rays are invisible but ionize the water vapor in the chamber, causing it to condense into visible droplets.) In 1937, apparently unaware of Yukawa's hypothesis, Anderson discovered tracks from an unknown particle with a mass similar to the hypothetical particle Yukawa had predicted. Initially, it was called the mesotron and later the meson (from the Greek "mesos," meaning "middle," because the particle's mass was intermediate between the masses of the electron and the proton). This discovery brought attention to Yukawa's prediction, and Western physicists began investigating possible connections. However, after a few years, they realized that Anderson's particle and Yukawa's particle were different. In particular, the observed meson weakly interacted with the nucleus (Yukawa postulated strong interaction), and its lifetime was more than 100 times longer than the predicted one-hundred-millionth of a second. Some physicists began to suspect that Yukawa had gone down the wrong path.
Yukawa returned to Kyoto Imperial University in 1939. By that time, he had become a well-known theorist, and his presence helped the university's physics department gain international recognition. The Second World War disrupted the connections between Japanese and Western physicists, but Yukawa continued his particle research. In 1942, two of his colleagues, Yasutaka Tanikawa and Soiti Sakata, speculated that there were two types of mesons, a heavier and a lighter one, and that Anderson had discovered the lighter type in cosmic rays at sea level. It seemed that Yukawa's heavier particle could only be detected at high altitudes, where primary cosmic rays first interact with atomic nuclei. The particle would quickly decay into the lighter type of mesons, whose longer lifetimes allowed them to reach lower heights. In 1947, Cecil F. Powell detected Yukawa's particle using an ionization chamber placed at high altitudes. He was likely unaware of Tanikawa and Sakata's work, but he seemed to be aware of the two-meson hypothesis proposed by Robert E. Marshak and Hans A. Bethe in 1947. In 1948, mesons were artificially produced at the University of California, Berkeley.
In light of these discoveries, Yukawa was "vindicated" and received the Nobel Prize in Physics in 1949 "for his prediction of the existence of mesons on the basis of his theoretical work on nuclear forces." Yukawa's particle became known as the pion, and Anderson's lighter particle became known as the mu-meson and later the muon. In fact, pions come in three types: one electrically neutral, one positively charged, and one negatively charged. Muons are nearly identical to electrons except for their large mass. Many other types of mesons have been discovered since then. When Yukawa learned about the award, he was in the United States, having taken a year off from Kyoto University to conduct research at the Institute for Advanced Study in Princeton, New Jersey. After spending a year at the institute, he accepted an invitation from Columbia University to work as a visiting professor. The university funded his stay there starting in 1951, and he was appointed as a professor of physics. In 1953, Yukawa returned to Kyoto University, where he took on the role of director of the Research Institute for Fundamental Physics. Here, he continued his research on quantum physics and elementary particles while also dedicating a lot of time to educating a whole generation of young Japanese physicists until his retirement in 1970.
Starting in 1954, when the United States conducted a hydrogen bomb test that destroyed Bikini Atoll in the Pacific Ocean, Yukawa began publicly speaking out against nuclear weapons "as a scientist, a Japanese, and a representative of all humanity." He was among the signatories of the "Russell-Einstein Manifesto" (named after its author, Bertrand Russell), which called on governments to resolve their conflicts peacefully. Yukawa also participated in conferences where scientists discussed disarmament issues.
Yukawa (then Ogawa) married Sumi Yukawa in 1932. They raised two sons together. In his later years, he returned to his youthful interests and became interested in history, literature, philosophy, and also wrote poetry in Japanese. In addition to his scientific work, he published philosophical reflections. In his book "Creativity and Intuition: A Physicist Looks at East and West" (1973), Yukawa highly praised the influence of Eastern philosophers, especially Lao Tzu and Chuang Tzu, on his own thinking.
In addition to the Nobel Prize, Yukawa was awarded the Imperial Prize of the Japan Academy (1940), the Lomonosov Gold Medal of the USSR Academy of Sciences (1964), the Order of Merit from the Federal Republic of Germany (1967), and the Order of the Rising Sun - a Japanese state award (1977). He was a member of numerous prestigious scientific academies and societies, including the National Academy of Sciences, the Physical Society of Japan, the Royal Society of London, and the USSR Academy of Sciences.
