Hideki Yukawa
Yukawa, Hideki (1907-1981) was a Japanese theoretical physicist who won the 1949 Nobel Prize in physics for a theory he published in 1935. Yukawa was the first Japanese to receive a Nobel Prize.
Theoretical physicists are scientists who develop the laws and theories of physics and predict outcomes. Experimental physicists perform carefully designed experiments and then compare their results to what was predicted to happen. Yukawa's theory predicted the existence of the subatomic particles now known as mesons. In 1947, British physicist Cecil Frank Powell and his colleagues discovered the meson.
Yukawa was born Hideki Ogawa in Tokyo on Jan. 23, 1907. A year after his birth, the family moved to Kyoto, where his father, Takuji Ogawa, became a professor of geology at Kyoto University. His mother was Koyuki Ogawa. Hideki had several brothers who also became university professors. Ogawa studied Chinese classics and learned to read Kanji characters. He also became interested in modern physics after he found books on relativity and quantum mechanics. After teaching himself some German, he read works by German theoretical physicist Max Karl Ernst Ludwig Planck .
After Ogawa graduated from high school in 1926, he entered Kyoto Imperial University to major in physics. He received a master's degree in 1929. From that point on, he investigated theoretical physics, particularly the theory of elementary particles. Electrons and several other subatomic particles are elementary particles— that is, they are not made up of smaller units of matter. Protons and neutrons are composite particles. They are made up of elementary particles called quarks.
According to a Japanese tradition, Ogawa was adopted into his wife Sumi Yukawa's family after their marriage in 1932, and he took his wife's family name, becoming Hideki Yukawa. Yukawa taught at Kyoto Imperial University and at Osaka University, where he earned his doctorate in physics in 1938. In 1939, he became a professor of physics at Kyoto Imperial University.
In 1935, a few months after announcing his theory, Yukawa published his paper “On the Interaction of Elementary Particles.” His paper contained a series of equations that predicted the existence of a new basic particle of subatomic matter, which became known as the meson. This work brought Yukawa to the attention of physicists internationally.
Scientists studying the atom at that time were puzzled by how the nucleus holds together. At Osaka University, Yukawa pondered the same question: Why doesn't the nucleus of an atom split apart? The nucleus was known to contain closely packed, positively charged protons. Since positive electric charges should repel each other, why did the protons stay together? Yukawa theorized that protons and neutrons in the nucleus attract one another by exchanging mesons.
After Yukawa predicted the existence of mesons in 1935, British physicist Cecil Frank Powell and his colleagues observed charged pi mesons in 1947, confirming Yukawa's prediction.
A meson is any of about 150 kinds of unstable subatomic particles. Meson comes from a Greek word meaning middle. Mesons were given this name because the first ones found were heavier than an electron but lighter than a proton. However, physicists later discovered that most mesons are heavier than a proton.
A meson is unstable because of its composition. It consists of one quark and one antiquark. An antiquark is a particle of antimatter. An antiparticle has the same mass, or amount of matter, as its corresponding particle, but carries an opposite charge. When a particle of matter and a particle of its antimatter opposite meet, they completely destroy each other. A meson's quark and antiquark can avoid meeting for only a tiny fraction of a second.
Mesons differ in the types of quarks and antiquarks they are made of and in the motions of those particles within the meson. The lightest meson is the pi meson, also known as a pion. It comes in three varieties, with electric charges of 11, 21, and 0. The charged pions are the longest-lived mesons, with an average lifetime of 26 nanoseconds. One nanosecond is one-billionth of a second. The mass of a pi meson is about one-seventh the mass of a proton. The heaviest mesons observed, the upsilons, are more than 10 times as heavy as a proton.
Mesons are produced when stable particles, such as protons, collide at high speeds. The collision converts part of the kinetic energy —energy of motion—of the particles into a quark and an antiquark. Such collisions often occur when a cosmic ray from space strikes a particle in the earth's atmosphere. Mesons are also produced in machines called particle accelerators.
The Royal Swedish Academy awarded Yukawa the Nobel Prize in physics in 1949 “for his prediction of the existence of mesons on the basis of theoretical work on nuclear forces.” Powell received the 1950 Nobel Prize in physics, in part for his discoveries concerning mesons.
From 1948 to 1949, Yukawa was a visiting professor at the Institute for Advanced Study in Princeton, New Jersey. He then taught at Columbia University in New York City. He served as director of the Research Institute for Fundamental Physics, now the Yukawa Institute for Fundamental Physics, at Kyoto University from 1953 to 1970.
In 1955, Yukawa became 1 of 11 eminent scientists who put their names on a document that came to be called the Russell-Einstein manifesto. It was written by American scientist Albert Einstein and British philosopher and mathematician Bertrand Russell. The Russell-Einstein manifesto called upon the scientists of the world, no matter what their political persuasion, to meet and discuss the threat to civilization posed by nuclear weapons. The United States had dropped the first atomic bombs on Hiroshima and Nagasaki in 1945 and, in 1952, had tested the first hydrogen bomb at Bikini Atoll in the Pacific Ocean. By 1955, fears were growing about the destructive power of such weapons and the long-term effects of nuclear radiation.
The other signers were physicists Max Born of Germany, Percy Williams Bridgman and Leopold Infeld of the United States, Frédéric Joliot-Curie of France, Cecil Powell and Joseph Rotblat of the United Kingdom, and chemists Paul Hermann Muller of Switzerland and Linus Carl Pauling of the United States. Yukawa also became active in international conferences at which scientists discussed disarmament.
Yukawa was a member of the Japan Academy and the Japan Physical Society. He won the Imperial Prize of the Japan Academy in 1940, the Order of Cultural Merit in 1943, and the Japanese government's Order of the Rising Sun in 1977. Kyoto University established the Research Institute for Fundamental Physics, now the Yukawa Institute for Fundamental Physics, to commemorate Yukawa's receipt of the Nobel Prize.
He was also a foreign member of the American National Academy of Sciences, the American Physical Society, the Royal Society of London, and the Russian Academy of Sciences. Yukawa also received honorary doctorates from several universities. He won the M. V. Lomonosov Gold Medal of the Russian Academy of Sciences and the Order of Merit of the Federal Republic of Germany in 1964.
Yukawa wrote Introduction to Quantum Mechanics (1946) and Introduction to the Theory of Elementary Particles (1948), both in Japanese. In 1946, he founded the journal Progress of Theoretical Physics, written in English, which he also edited. Besides his scientific writings, he also published his reflections on philosophy in Creativity and Intuition: A Physicist Looks at East and West (1973). He studied the works of Asian philosophers such as Taoist philosophers Laozi and Zhuangzi. Yukawa died in 1981 in Kyoto.