Remembering Tsung-Dao Lee 李政道 (1926–2024)
Tsung-Dao Lee (李政道), Member (1951–53, 1957–58) and Faculty (1960–62) in the Institute for Advanced Study’s School of Mathematics/Natural Sciences, died on August 4 at his home in San Francisco. He was 97.
Throughout his distinguished career, Lee made significant advancements in theoretical physics, authoring more than 300 research papers and several influential books. Most notably, in 1957, during his time at IAS, he was awarded the Nobel Prize in Physics alongside his Institute colleague Chen-Ning Yang (楊振寧), Member (1949–54) and Faculty (1955–66) in the School of Mathematics/Natural Sciences. The pair were awarded the Prize for their revolutionary work on parity violation in weak interactions, which fundamentally changed our understanding of the laws of physics.
Prior to Lee and Yang's work, most physicists believed that the laws of physics were symmetric, meaning that the mirror image of any physical process should behave in the same way as the original process. This principle was known as “parity conservation.” However, Lee and Yang realized that this assumption had never been tested for weak nuclear interactions, which are responsible for certain types of radioactive decay. They proposed experiments to test whether parity was conserved in this type of interaction.
The experiments were carried out by Lee and Yang’s colleague Chien-Shiung Wu (吳健雄).1 Her work showed that parity was indeed violated in weak interactions, indicating that some physical processes do have a preferred “handedness,” where their mirror images behave differently than the original process. This discovery was revolutionary because it showed that one of the fundamental symmetries that physicists had often taken for granted was not true in all circumstances. These insights led to major refinements in particle physics theory and enhanced scholars’ understanding of the fundamental laws governing the universe.
Although best known for his contributions to the field of particle physics, Lee’s early work focused on stellar astrophysics. In 1950, he completed his doctoral studies with a thesis on the hydrogen composition of white dwarf stars. His research demonstrated that these stellar remnants contain minimal hydrogen, specifically less than 1% of their mass. This provided strong evidence that white dwarfs represent the final evolutionary stage for most stars.
Lee's research in this field was praised by prominent theoretical physicist Subrahmanyan Chandrasekhar2 in a letter recommending Lee’s appointment to the Institute as a Member. Chandrasekhar’s letter reads: “My association with Mr. Lee has convinced me of his ability and originality. He has an exceptional aptitude and curiosity for theoretical physics.” Lee’s initial area of interest, white dwarf stars, continues to captivate scholars within the astrophysics group at the Institute. Recent research by Martin A. and Helen Chooljian Member Sihao Cheng, published in Nature, proposes a new theory to explain why a population of such stars stopped cooling for ten billion years.
Lee's time at the Institute was crucial in shaping his academic career. In a letter dated November 15, 1962, addressed to Director (1947–66) J. Robert Oppenheimer, he wrote: “I came to the Institute in 1951 as a young member in physics. Since then, I have been at the Institute for about five years. […] As a result, almost all my scientific works have connected in one way or another with the Institute. I am thankful to my colleagues at the Institute for the advices [sic] and stimulations that I received from them throughout these years; and I wish to express my gratitude to you as the director of the Institute for the influence that [you] exerted on me especially during my early formative years.”
As a Chinese-American scientist who achieved great success in the United States, Lee also served as an important bridge between the scientific communities of China and the West. Lee directed considerable efforts to nurturing Chinese scientists through the establishment of programs such as CUSPEA.3 In an interview with Adam Smith, Editor-in-Chief of NobelPrize.org, conducted in 2007, Lee described how, in the late 1970s and into the 1980s, “there was no way for a Chinese college graduate to go to [the] United States or Canada or any place to study” because the cost was prohibitive. His program, organized primarily to support students working in physics, was extended through his friends and colleagues to also assist biology students, as well as those in other fields. Lee’s efforts have been described as having placed Chinese physics on a “more and more robust footing.”
Lee’s commitment to academic freedom was also emphasized in a letter addressed to Stanley Deser, Member (1953–55, 1993–94) in the School of Natural Sciences. The letter was sent in the wake of the Tiananmen Square protests and government crackdown which took place in 1989. Lee wrote: “I am happy that, in spite of the turmoil, this year's 74 new CUSPEA students were all allowed to come to this country [the United States]. In addition, many Chinese scientists like Professor Ye Duzheng (a former Vice President of the Chinese Academy of Sciences and current President of the Meteorological Society, who personally led several marches of scientists and made speeches at Tiananmen Square supporting the movement) have been free to travel and attend meetings abroad. The universality of science and the free exchange between sciences of all nations has been a powerful force in helping to preserve civilization in difficult times. As a scientist, this is something that I believe in deeply.”
Lee's life and career exemplified the power of challenging established scientific principles in pursuit of pushing the boundaries of knowledge. His intellectual curiosity, innovative thinking, and dedication to science and the scientific community will continue to inspire scholars at the Institute and beyond for generations to come.
[1] Wu visited the Institute and Princeton University on January 17, 1957 to deliver a lecture on “Parity and Charge Conjugation Nonconservation in β-decay.”
[2] Chandrasekhar himself would go on to win a Nobel Prize in Physics in 1983. He served as a Member in the School of Mathematics/Natural Sciences in 1941 and a Member in the School of Natural Sciences in 1976.
[3] The China-U.S. Physics Examination and Application (李政道奖学金), known as CUSPEA, was founded by Lee in 1979 and was active until 1988.
