Tsung-Dao Lee

Tsung-Dao Lee

Tsung-Dao Lee (born 1962) disproved the principle of parity.

Tsung-Dao Lee and his colleague physicist Chen Ning Yang developed the revolutionary theory that the unusual behavior of the K-meson (a subatomic particle) is a result of its violating a supposedly inviolable law of nature, conservation of parity, which defines the basic symmetry of nature. A few months after their theory had been announced, fellow physicist Chien-Shiung Wu obtained experimental confirmation of their remarkable discovery. For their work, Lee and Yang were awarded the 1957 Nobel Prize in physics.

Lee was born in Shanghai, China, on November 24, 1926. He was the third of six children born to Tsing-Kong Lee, a businessman, and Ming-Chang Chang. Lee attended the Kiangsi Middle School in Kanchow and, after graduation, entered the National Chekian University in Kweichow. After the invasion of Japanese troops in 1945, Lee fled to the south, where he continued his studies at the National Southwest Associated University in Kunming.

In 1946, Lee was presented with an unusual opportunity. One of his teachers at Kunming was the theoretical physicist Ta-You Wu. When Wu decided to return to the United States (where he had worked toward his Ph.D. degree), he invited Lee to accompany him. Lee accepted the offer, but found himself in a somewhat peculiar position. He had not yet received his bachelor's degree and found that only one American university would accept him for graduate study without a degree. He therefore decided to enroll in that institution, the University of Chicago.

At Chicago, Lee selected a topic in astrophysics for his doctoral research. Working under physicist Enrico Fermi, he completed that research and was awarded his Ph.D. in 1950 for his dissertation, on the hydrogen content of white dwarf stars. While at Chicago, Lee also renewed his friendship with physicist Chen Ning Yang. Lee and Yang had been acquaintances at Kunming, but they became very close friends after both reached the United States. They were separated in 1950 when Lee went to the Yerkes Astronomical Observatory at Lake Geneva, Wisconsin, and Yang went to the Institute for Advanced Studies at Princeton University. Lee then spent the next year (1950-51) as a research associate at the University of California at Berkeley. The two friends were reunited in 1951, however, when Lee accepted an appointment at the Institute for Advanced Studies.

Lee's departure from Princeton in 1953 for a post as assistant professor of physics at Columbia University seems to have had little effect on his collaboration with Yang. The two worked out a schedule that allowed them to continue meeting once a week, either in New York City or in Princeton. By the spring of 1956, these regular meetings had begun to focus on a particularly interesting subject, a subatomic particle known as the K-meson. Discovered only a few years earlier, the K-meson puzzled physicists because it appeared to be a single particle that decayed in two different ways. The decay schemes were so different that physicists had become convinced that two distinct forms of the K-meson existed, forms they called the tau meson and theta meson.

The single difference between these two mesons was that one form had even parity and the other form had odd parity. The term parity refers to the theory that the laws of nature are not biased in any particular direction. That is, if one has two sets of interactions that are mirror images of each other, the physical laws describing those interactions are identical. This concept is known as the conservation of parity, a concept long held by physicists.

The problem that Lee and Yang attacked was that vast amounts of experimental evidence suggested that the theta and tau mesons were one and the same particle. The only contrary evidence was that the two mesons had opposite parity and, therefore, supposedly could not be identical. During an intense three-week period of work in the spring of 1956, Lee and Yang solved this puzzle. Their solution was to suggest, simply enough, that in some types of reactions, parity is not conserved. The beta decay of the (one and only) K-meson was such a reaction. They then devised a series of experiments by which their theory could be tested. The fundamental elements in the Lee-Yang theory were announced in a paper sent to the Physical Review on June 22, 1956 and later given the title, "Question of Parity Conservation in Weak Interactions."

About six months later, the experiments suggested by Lee and Yang were carried out by one of their colleagues, Chien-Shiung Wu, first at Columbia and then at the National Bureau of Standards. The experiments confirmed the Lee-Yang prediction in every respect. Less than a year later, the two theorists were awarded the 1957 Nobel Prize in physics for their work.

After promotions to associate professor (1955) and professor (1956) at Columbia, Lee returned to the Institute for Advanced Studies in 1960 for three years. He then was appointed Enrico Fermi Professor of Physics at Columbia in 1963. In 1984, he was made University Professor at Columbia. Beginning in 1981, Lee held appointments as honorary professor at a number of Chinese universities, including the University of Science and Technology (1981), Jinan University (1982), Fudan University (1982), Quinghua University (1984), Peking University (1985), Nanjing University (1985), and Zhejiang University (1988). He married Hui-Chung Chin (also known as Jeanette) on June 3, 1950, while they were both students at Chicago. The Lees have two sons, James and Stephen.

Further Reading

Crease, Robert P., and Charles C. Mann, The Second Creation, Macmillan, 1986, pp. 205-7.

McGraw-Hill Modern Scientists and Engineers, Volume 2, McGraw-Hill, 1980, pp. 215-16.

Nobel Prize Winners, H. W. Wilson, 1987, pp. 615-17.

Weber, Robert L., Pioneers of Science: Nobel Prize Winners in Physics, American Institute of Physics, 1980, pp. 167-68.

Bernstein, Jeremy, "A Question of Parity," in New Yorker, May 12, 1962, pp. 49ff. □