Lee, Tsung Dao (1926-) shared the 1957 Nobel Prize in physics with his longtime collaborator Chen Ning Yang. They proposed that the “conservation of parity,” a basic principle of nuclear physics, did not hold true in some cases.
Parity, in physics, refers to the symmetry between an event and its reflection in a mirror. The idea of parity is a useful tool in quantum mechanics, the field of physics that describes the structure of the atom and the motion of atomic particles. Physicists say that parity is conserved when an event and its mirror image both satisfy identical laws of nature. In this case, an observer cannot tell the difference between the event and its reflection.
Physicists once believed that the conservation of parity was a natural law that applied to all events. But in 1956, the two Chinese-born physicists, Lee and Yang, suggested a number of experiments that proved otherwise. The experiments showed that parity was not conserved in a type of nuclear event called a weak interaction. As a result of the work of Lee and Yang, the principle of the symmetry of space was destroyed, allowing scientists to move into new directions.
Tsung Dao Lee was born on Nov. 25, 1926, in Shanghai, China, to Tsing-Kong Lee, a businessman, and Ming-Chang (Chang) Lee. Lee graduated from high school in 1943. He then attended the National Chekiang University in Kweichow province.
While in college, Lee met Chen Ning Yang, who would share his future Nobel Prize. Lee was so brilliant in physics that he won a scholarship to study at the University of Chicago (UC), in Illinois.
At UC, Lee studied under Nobel Prize-winning physicist Enrico Fermi. Lee's friend Yang also became a graduate student in physics at UC. Lee completed his Ph.D. degree at UC in 1950. His thesis was entitled “Hydrogen Content of White Dwarf Stars.” For several months in 1950, Lee served as research associate at Yerkes Astronomical Observatory, at Williams Bay, Wisconsin, operated by UC.
Lee served as research associate and lecturer in physics at the University of California in Berkeley from 1950 to 1951. Lee and Yang reunited in 1951, when Lee joined the Institute for Advanced Study in Princeton, New Jersey. Lee remained there until 1953, during which time he and Yang were able to accomplish much together. Lee quickly became a widely known scientist, studying statistical mechanics, nuclear physics, field theory, hydrodynamics, astrophysics, and turbulence.
But it would be his investigation of the conservation of parity with Yang that would bring Lee great fame and the Nobel Prize. The parity rule was formulated in the 1920's and seemed to be firmly supported by experimental data. Few scientists questioned its factuality, and physicists tried to make all their observations fit the parity principle.
Lee and Yang discovered the limitations of the parity principle when they observed the characteristics of k-mesons, subatomic particles produced by giant atom smashers. Lee and Yang as well as other scientists saw that the pattern into which the k-mesons disintegrated was irregular. Because this behavior did not conform to the principle of parity, Lee and Yang said that the rule of parity was clearly not valid in this instance.
They then suggested experiments to test their calculations. At the laboratories of Columbia University, radioactive cobalt was cooled to a point in which its thermal motions were lowered to a minimum. A magnetic field was applied so that the spinning cobalt nuclei fell parallel to the applied magnetic field. According to parity, as they spun, half of their electrons should have gone toward magnetic north and half toward magnetic south. What happened instead was that many more electrons came out the south end of the nuclei. This showed that one end of the nucleus is different from the other. This had not been known before, and it defied the principle of parity. Scientists began referring to particles as right-handed or left-handed. As a result of Lee and Yang's theories, the principle of the symmetry of space was destroyed.
Lee and Yang's work dramatically changed physics. After the elimination of parity, scientists began to understand confusing scientific information that had been gathered in their study of atoms.
When Lee resigned from the institute to become assistant professor of physics at Columbia University in 1953, Dr. J. Robert Oppenheimer, famous physicist and director of the institute, stated his regret and called Lee “one of the most brilliant theoretical physicists we have known.” By 1956, at age 29, Lee became a full professor at Columbia, the youngest person ever to attain that rank at the university. In 1960, he returned to the Institute for Advanced Study. He returned to Columbia in 1961 and-remained there for the rest of his career.
Lee and Yang published the results of their work in The Physical Review in 1956 and 1957 in two articles: “Question of Parity Conservation in Weak Interactions” and “Parity Nonconservation and a Two-Component Theory of the Neutrino.”
In 1957, at barely 31 years of age, Lee became the second youngest scientist ever to receive the Nobel Prize in physics. (The youngest was 25-year-old Sir William Lawrence Bragg, who shared the physics prize with his father, Sir William Henry Bragg, in 1915.) Lee and Yang also became the first Chinese receive a Nobel Prize.
In his presentation of the prize, Professor O. B. Klein, member of the Nobel Committee for Physics, said to Lee and Yang, “Through your consistent and unprejudiced thinking you have been able to break a most puzzling deadlock in the field of elementary particle physics where now experimental and theoretical work is pouring forth as the result of your brilliant achievement.”
In addition to the Nobel, Lee and Yang also jointly received the 1957 Albert Einstein Commemorative Award in science of Yeshiva University and the science award of the Newspaper Guild of New York. Lee was elected a fellow of the American Physical Society and the Academia Sinica, a research institute of Nationalist China. He was also elected a member of the National Academy of Sciences. Princeton University awarded an honorary doctor of science degree to Lee in 1958.
Since 1979, Lee has worked to promote academic exchange between physicists of China and the United States.