Hideki Yukawa

JAPANESE PHYSICIST
1907–1981

Japanese physicist Hideki Yukawa, recipient of the 1949 Nobel Prize in physics, "for his prediction of the existence of mesons on the basis of theoretical work on nuclear forces."

Hideki Ogawa (he changed his surname upon marrying Sumi Yukawa) was born on January 23, 1907, in Tokyo. A year thereafter his family moved to Kyoto, where he was raised and attended school. The fifth of seven children of Takuji and Koyuki Ogawa, Hideki came from a family of scholars. Although not inclined to science as he grew up, Hideki happened upon some books on modern physics while in high school and soon found quantum mechanics (which was still a rapidly developing field at the time) very intriguing. As a result of that interest, he entered Kyoto University to study physics in 1926. He received his M.S. from that institution in 1929 and a Ph.D. from Osaka University in 1938.

In the 1930s the English physicist James Chadwick had discovered the neutron, and scientists were struggling to determine how protons and neutrons interacted inside a nucleus. A theory known as quantum electrodynamics explains electricity and magnetism by assuming that the force is caused by the interaction of photons with charged particles. Scientists tried to create a similar theory of nuclear forces based on the interaction of protons and neutrons with some particle analogous to photons. Yukawa developed a theory for the interaction of massive force carriers, the so-called Yukawa potential, and predicted that, since the nuclear force only acts over distances of 10 ⁻¹⁵ meters (3.281 × 10 ⁻¹⁴ feet), these unknown force carriers should have a mass about two hundred times as heavy as an electron. Yukawa published his theory in 1935, but since such a particle was unknown at the time, his results were largely ignored.

This situation changed in 1937 when a new particle was discovered in a cosmic-ray experiment. It had the correct mass, and Yukawa's theory was thought to be vindicated as a consequence. However, the details of the theory did not correspond with the measured properties of this particle. In a confusing cosmic coincidence, it turned out that particle was a muon (a heavier electronlike particle), and it was not until 1947 that the pion (as the force carrier came to be known) was discovered. Finally, all the pieces of the theory of nuclear force fell into place, and in 1949 Yukawa received the Nobel Prize in physics.

Yukawa had left Osaka in 1948 to work in the United States. However, in 1953 he returned home to Kyoto to become director of a new interuniversity research institute housed in an academic building named for him. He retired from this position in 1970 and died in Kyoto on September 8, 1981.

SEE ALSO Chadwick, James .

Michael J. Fosmire

Bibliography

Kemmer, N. (1983). "Hideki Yukawa." Biographical Memoirs of Fellows of the Royal Society 27: 661–676.

Yukawa, Hideki (1982). Tabibito: The Traveler , tr. L. Brown and R. Yoshida. Singapore: World Scientific.