Lee, Tsung-Dao (physicist)


(1926- ) Chinese/American Theoretical Physicist, Particle Physicist

Tsung-Dao Lee is a world-renowned theoretician who, together with chen ning yang, predicted that conservation of parity is violated in the weak interactions of the atomic nucleus. Their discovery led to significant developments in particle theory and won them the 1957 Nobel Prize in physics. Only 31 years of age at the time, Lee became the second youngest physicist to be awarded the Nobel Prize.

Lee was born on November 24, 1926, in Shanghai, China, the third of six children born to Tsing Kong Lee, a businessman, and Ming Chang Chang. He attended the Kiangsi Middle School in Kanchow, Kiangsi, graduated in 1943, and entered the National Chekiang University in Kweichow province. When the Japanese invasion forced him to flee to Kunming, Yunan, he enrolled at the National Southwest University, where he met his future collaborator, Yang.

Lee entered the United States, in 1946, on a scholarship from the Chinese government. Although he had never formally earned an undergraduate degree, he enrolled in graduate studies in physics at the University of Chicago, where his friend Yang was also enrolled. He earned a Ph.D. in 1950, working under the eminent Indian-born astrophysicist subramanyan chandrasekhar, for his dissertation “Hydrogen Content of White Dwarf Stars.” That year he married (Jeanette) Hui Chung Chin, a former university student, with whom he would have two sons, James and Stephen. After spending a few months as a research associate at Yerkes Astronomical Observatory, in Lake Geneva, Wisconsin, from 1950 to 1951, he was a research associate and lecturer at the University of California in Berkeley. He then accepted a fellowship to the Institute of Advanced Study in Princeton and became a member of the staff. He was appointed assistant professor of physics at Columbia University in 1953, promoted to associate professor in 1955 and to professor in 1956 (at age 29, he was then the youngest professor on the faculty). By this time Lee had a substantial reputation, for his work in statistical mechanics and in nuclear and atomic physics.

In June 1956, Yang collaborated with Lee on a paper that raised the question of whether parity, the assumption that nature makes no distinction between left and right, is conserved in weak interactions. At the time physicists universally believed that physical reactions would be the same (i.e., have parity, or equality) whether the particles involved in them had a right-handed or a left-handed spin (i.e., the quantized rotation property). If the physical process proceeds in exactly the same way when referred to an inverted coordinate system, then parity is said to be conserved. If, on the contrary, the process has definite left- or right-handedness, then parity is not conserved in that physical process. This law of conservation of parity was explicitly formulated in the early 1930s by the Hungarian-born physicist eugene paul wigner and became a component of quantum mechanics.

The strong forces that hold atoms together and the electromagnetic forces that are responsible for chemical reactions obey the law of parity conservation. Since these are the dominant forces in most physical processes, physicists assumed that parity conservation was an inviolable natural law. In the early 1950s, applying the principle of conservation of parity to individual subatomic particles and their interactions had proved highly successful in accounting for the behavior of those particles. By the end of 1955, however, a puzzling contradiction between the parity principle and the other principles employed to order the evergrowing number of subatomic particles had emerged. In particular, questions were raised by results beginning to pour forth from the many high-energy accelerators built in the United

Tsung-Dao Lee together with Chen Ning Yang predicted that conservation of parity is violated in the weak interactions of the atomic nucleus. Only 31 years of age at the time, Lee became the second youngest physicist to be awarded the Nobel Prize.

Tsung-Dao Lee together with Chen Ning Yang predicted that conservation of parity is violated in the weak interactions of the atomic nucleus. Only 31 years of age at the time, Lee became the second youngest physicist to be awarded the Nobel Prize.

States after World War II, indicating that one form of radioactive decay appeared to violate the conservation of parity law. One of the newly discovered mesons—the so-called K meson—seemed to exhibit decay modes into configurations with differing parity. Exploring this paradox from every conceivable perspective, Lee and Yang discovered that contrary to what had been assumed, there was no experimental evidence against parity noncon-servation in the weak interactions. The experiments that had been done, it turned out, were not relevant to the question. In their landmark 1956 Physical Review paper, “Question of Parity Conservation in Weak Interactions,” Lee and Yang made the startling proposal that the universally accepted conservation of parity law might not hold true in weak nuclear interactions, which include radioactive decay.

Their suggestions for experiments capable of deciding the issue were immediately taken up by chien-shiung wu at the cryogenic laboratory of the National Bureau of Standards in Washington, D.C. Testing radioactive cobalt atoms at temperatures approaching absolute zero, Wu found the evidence Lee and Yang were looking for: the law of parity did not apply to weak interactions. Shortly after her announcement in January 1957, other experimentalists confirmed her results. In the wake of this paradigm revolution generated by the three Chinese American physicists, Lee and Yang were awarded the Nobel Prize in physics that very year.

In 1960, Lee became professor of physics at the Institute of Advanced Study, Princeton; he returned to Columbia in 1963 to assume the first Enrico Fermi Professorship in physics. Since 1964 he has also made significant contributions to the explanation of the violations of time-reversal invariance that occur during certain weak interactions.

As did Yang, Lee became deeply involved in the development of Chinese science, and specifically its integration into world science. Working together with the Chinese Academy of Sciences, he founded the China Center of Advanced Science and Technology World Laboratory in 1989. Since then he has traveled to China every year to participate in international academic exchanges.

Through his brilliant insights, Lee has made invaluable contributions to the modern formulation of symmetry principles in particle physics. The renowned American physicist j. robert oppenheimer described Lee’s work as characterized by “a remarkable freshness, versatility, and style.” As a 77-year-old professor at Columbia University, Lee summarized his relationship to his work in a statement of moving simplicity:

To me, scientific research is as important as breathing, and it equals my life.

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