2024-08-05
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Renowned physicist Tsung-Dao Lee passed away at the age of 98.
The news first came from the Weibo account of Fudan Physics Professor Shi Yu, and was later confirmed by @中国新闻周刊 and others.
Tsung-Dao Lee is one of the first Chinese scientists to win the Nobel Prize. In 1957, he and Chen-Ning Yang won the Nobel Prize in Physics for their discovery of the "law of parity nonconservation under weak interactions."
He is also known for his contributions to the Lee model, relativistic heavy ion collision (RHIC) physics, and non-topological soliton field theory.
In addition to his academic achievements, he also played a huge role in promoting the development of Chinese science: he proposed and assisted in the construction of the Beijing Electron-Positron Collider, proposed the establishment of the National Natural Science Foundation, and established a postdoctoral system.
Tsung-Dao Lee was born in Shanghai on November 24, 1926. His ancestral home is Suzhou, Jiangsu.
In 1956, Tsung-Dao Lee and Chen-Ning Yang, then professors at Columbia University, published their jointly proposed theoretical hypothesis of parity non-conservation in the American journal Physical Review.
The law of parity non-conservation means:
In weak interactions, the movement of mirror-image substances is asymmetric, which was verified by Wu Jianxiong using cobalt-60.
△Photo taken by Tsung-Dao Lee (left) and Chen-Ning Yang (right)
Before 1956, the scientific community believed in the "conservation of parity", that is, the mirror image of a particle has exactly the same properties as itself.
Specifically, scientists at the time discovered that the spin, mass, lifetime, charge, etc. of the θ and τ mesons were exactly the same, and most people believed that they were the same particle. However, when the θ meson decays, two π mesons are produced, and when the τ meson decays, three are produced, which shows that they are different particles.
But after in-depth research, Tsung-Dao Lee and Chen-Ning Yang boldly asserted that τ and θ are exactly the same particle (later called K mesons), but in the environment of weak interactions, their laws of motion are not necessarily exactly the same.
To put it in simple terms, if these two identical particles are reflected in a mirror, they decay differently inside the mirror and outside the mirror.
In other words, parity is not conserved for the "θ-τ" particle under weak interactions.
This view is called the "Lee-Yang hypothesis".
At first, the scientific community believed that this group of particles was a special case.
But shortly thereafter, Chinese-American experimental physicist Chien-Shiung Wu cleverly verified the "parity non-conservation" - to be precise, in early 1957, three groups of scientists in the United States confirmed this theoretical hypothesis through experimental results almost simultaneously.
From then on, parity violation was truly recognized as a basic scientific principle with universal significance.
In April 1957, Li and Yang won the Einstein Science Award for their theory of parity non-conservation in weak interactions.
In October of the same year, the two were awarded the Nobel Prize in Physics.
△The King of Sweden awarded Tsung-Dao Lee the Nobel Prize.
At this time, it was only 13 months since Li and Yang published their paper. Li Zhengdao was only 31 years old, the second youngest Nobel Prize winner in physics in history (the youngest winner was British physicist William Lawrence Bragg, who was 25 years old).
The two also became the first Chinese scholars to win the Nobel Prize.
After winning the Nobel Prize, Tsung-Dao Lee also collaborated with Chen-Ning Yang on other projects.
For example, the two established a general theoretical framework for many-body problems in statistical physics, and also worked together with physicist and MIT professor Huang Kexun to study the statistics of Bose hard-sphere systems.
Let us turn back the clock and review Tsung-Dao Lee’s student career.
Public information shows that Tsung-Dao Lee showed a unique interest in mathematics and physics from an early age. He learned to read at the age of 4 and began to learn mental arithmetic addition and subtraction.
In middle school, popular science books such as "The Expanding Universe" inspired his strong interest in physics. Affected by the war, he studied in many places. In his senior year of high school, he was hired as a substitute teacher of physics and mathematics for lower grades because of his excellent academic performance.
In 1943, Tsung-Dao Lee was admitted to the Department of Electrical Engineering of Zhejiang University through the national university entrance examination.
But one month after entering the university, under the influence and advice of Zhejiang University's Physics Department professors Shu Xingbei (theoretical physicist, father of Chinese radar) and Wang Ganchang (nuclear physicist, academician of the Chinese Academy of Sciences), Li Zhengdao changed his major to the Department of Physics.
At that time, there were few students in the Department of Physics and the courses were merged with the Department of Chemical Engineering, but Shu Xingbei often discussed physics with him, and Li Zhengdao established a holistic understanding of physics.
Later, Li Zhengdao gave up his pen and joined the army, but his plan was stranded due to injury.
In 1945, 19-year-old Tsung-Dao Lee transferred from Peking University to the Department of Physics at Southwest Associated University as a sophomore. During this period, his teachers included Wu Dayou, the father of Chinese physics, and Ye Qisun, the founder of modern Chinese physics.
For various reasons, Tsung-Dao Lee never obtained a formal diploma for elementary school, junior high school, high school, or undergraduate studies.
△Tsung-Dao Lee studying at Southwest Associated University
In 1946, under the guidance of the "Seed Plan" for developing the atomic bomb, Li Zhengdao was selected by Southwest Associated University and recommended by Professor Wu Dayou of the Department of Physics, and received a national scholarship to study in the United States.
His destination was the University of Chicago—but since he had no undergraduate degree, he could only be an informal student at first.
Later, because he chose to study the quantum mechanics course taught by Edward Teller, the father of the hydrogen bomb, and achieved outstanding results, Teller introduced him to the Nobel Prize winner in Physics Enrico Fermi and he became a formal graduate student at the University of Chicago.
In June 1950, Tsung-Dao Lee pursued a Ph.D. in theoretical physics at the University of Chicago, and his thesis was "The Hydrogen Content in White Dwarfs."
The paper states that the hydrogen content in a white dwarf is no more than 1%, and determines the Chandrasekhar limit upper mass of a white dwarf to be 1.44 times the mass of the sun, which was later recognized by the scientific community.
This conclusion was praised by Nobel Prize winner in Physics Subramanian Chandrasekhar, and the paper also won the President's Award. For a time, Li Zhengdao was hailed as the "prodigy doctor".
△Tsung-Dao Lee during his doctoral studies
After obtaining his Ph.D., Tsung-Dao Lee conducted research at the University of Chicago, UCLA (University of California, Berkeley), and Princeton Research Institute.
In 1953, 27-year-old Tsung-Dao Lee went to the Department of Physics at Columbia University as an assistant professor and was promoted to associate professor two years later.
In his second year at Columbia University, Tsung-Dao Lee established the "Lee Model".
This is one of the few solvable models in quantum field theory and has had a significant impact on subsequent field theory and renormalization research.
In 1956, Tsung-Dao Lee, then 30 years old, was hired as a professor at Columbia University, setting a record as the youngest professor in the university's 200-year history since its founding in 1754.
In 1960, Tsung-Dao Lee began serving as a professor at the Institute for Advanced Study at Princeton, while also teaching as an adjunct professor at Columbia University.
In 1964, Tsung-Dao Lee was elected a member of the National Academy of Sciences of the United States.
In 1972, Tsung-Dao Lee returned to China for the first time since he went abroad in 1946.
From then on, in addition to studying physics, his life also had a second main theme: promoting the development of the country's scientific cause.
In the 1970s and 1980s, Tsung-Dao Lee made a number of suggestions for the training of scientific talents, all of which were adopted:
Li Zhengdao also actively promoted scientific exchanges and cooperation between China and the United States.
During 1978 and 1979, Tsung-Dao Lee arranged for a Chinese high-energy physics expedition to visit the United States. The two sides signed a cooperation agreement, paving the way for China to develop high-energy physics and build high-energy accelerators.
In 1979, Tsung-Dao Lee returned to China to give lectures in person, and gave lectures for seven consecutive weeks at the Science Hall of Beijing Friendship Hotel, mainly on the two courses of "Particle Physics and Field Theory" and "Statistical Mechanics".
Not only that, he traveled back and forth between universities in China and the United States for a long time, and finally made possible the CUSPEA project.
CUSPEA, the full name of which is the China-U.S. Joint Graduate Program in Physics, was an examination used by my country to select and send students to study physics in the United States from 1979 to 1989. It was jointly founded by Tsung-Dao Lee and the Chinese physics community.
You have to know that there was no channel to send international students to North America at that time, and until the early 1980s, there were no GRE and TOEFL exams in China.
However, through CUSPEA, nearly a thousand Chinese physics students went abroad for further studies over a period of 10 years, and cultivated people such as electrorheological/magnetorheological fluid physicist Tao Rongjia and Rockefeller University professor Ren Haicang.
In 1994, Tsung-Dao Lee was elected as a foreign member of the Chinese Academy of Sciences.
In 2006, Peking University established the Center for High Energy Physics, with Tsung-Dao Lee as the first director.
In 2016, at the call of Tsung-Dao Lee, Shanghai Jiao Tong University established the Tsung-Dao Lee Institute to promote research in physics and its interdisciplinary subjects.
In his later years, Tsung-Dao Lee was still active at the forefront of academic research in physics. From 2008 to 2010, he collaborated with students to propose the concept of "timeon" and published many papers.
The violation of parity conservation was originally a study of why there is a difference between left and right. The purpose of the time quantum is to prove that time is divided into past and future.
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