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At about 2:33 a.m. on August 4, local time in the United States, Nobel Prize winner in Physics, Chinese-American physicist Tsung-Dao Lee died at his home in San Francisco at the age of 97. His most dazzling label during his lifetime was "parity non-conservation", which was the theoretical discovery favored by the Nobel Prize, but his contribution to physics was far more than that.

Just a few months ago, the Beijing Electron-Positron Collider (BEPC) measured the quantum state properties of a certain particle for the first time, providing strong evidence for the standard model of particle physics. This major achievement was published as an editor's recommendation article in the top international journal Physical Review Letters on May 2. To this day, this scientific device created by Tsung-Dao Lee is still in operation, with positrons and electrons accelerated to near the speed of light, colliding, and then annihilated in a vacuum pipe. As a top physicist in the world, he particularly likes Du Fu's famous quote: To study physics carefully, you must enjoy yourself, why bother with fame and fortune?

In 1956, Chinese-American physicist Tsung-Dao Lee, winner of the Nobel Prize in Physics. Photo/Visual China

"High-energy" scientists

A Ph.D. in theoretical physics from the University of Chicago is the only formal degree that Tsung-Dao Lee has ever obtained.

Tsung-Dao Lee was born in Shanghai in 1926. In 1935, he entered the primary school of a local private middle school. In 1937, the Battle of Shanghai broke out. When he was less than 11 years old, he moved to the British Concession with his family and directly transferred to a middle school. Later, due to the Anti-Japanese War, he moved to many places with his family and did not graduate from middle school. In 1943, Tsung-Dao Lee was admitted to the Department of Physics of Zhejiang University, which moved to Guizhou. Later, he transferred to Southwest Associated University and embarked on the path of studying theoretical physics. After the end of the Anti-Japanese War, Southwest Associated University was closed, and Tsung-Dao Lee missed the university diploma again.

The lack of a degree did not stop him from making a name for himself in the theoretical physics community. In 1946, Lee, who did not have a degree, went to the United States to study at the University of Chicago on the recommendation of his mentor, and received his doctorate in 1950. In 1953, he became an assistant professor in the Department of Physics at Columbia University, and was promoted to full professor three years later. At the age of less than 30, he set a record as the youngest professor in the university's 200-year history. He taught at Columbia University for 60 years until his retirement in 2012.

In 1956, he and theoretical physicist Chen Ning Yang published a paper titled "Questions on the Conservation of Parity in Weak Interactions". Parity is a quantum mechanical quantity. Before that, the physics community generally recognized that parity is conserved in any interaction, but this assumption was broken by the two scientists. The following year, after experimental verification, Tsung-Dao Lee and Chen Ning Yang shared the Nobel Prize in Physics and the Einstein Science Award that year, and Tsung-Dao Lee became the first Chinese scientist to win the Nobel Prize. Until 2014, Tsung-Dao Lee was the youngest Nobel Prize winner since World War II.

In 1961, Chen Ning Yang (right) and Tsung-Dao Lee in Princeton, the United States. Photo/Visual China

In addition, Lee also dabbled in soliton quantum theory, anomalous nuclear states and other branches of physics, and wrote scientific monographs such as Field Theory and Particle Physics. In the view of Wang Yifang, an academician of the Chinese Academy of Sciences and director of the Institute of High Energy Physics of the Chinese Academy of Sciences, Lee's deep cultivation in the field as a high-energy physicist is unmatched, and his love and dedication to physics infects all those who work with him.

Wang Yifang recalled to China Newsweek that he had heard Tsung-Dao Lee's report as early as the early 1980s when he was an undergraduate. After the report, Wang Yifang asked Tsung-Dao Lee questions, but "he certainly didn't remember me at that time." In 2001, Wang Yifang joined the Institute of High Energy Physics as a researcher. After that, he participated in many academic talks in the field of high energy physics between China and the United States, and finally had the opportunity to formally introduce himself to Tsung-Dao Lee. He found that Tsung-Dao Lee's concern and desire for the development of science in his motherland had never changed over the years.

Tsung-Dao Lee had directly promoted the design and construction of BEPC. Particle collisions are a powerful tool for mankind to discover new particles and overturn old theories. BEPC, which broke ground in October 1984, was China's first high-energy accelerator and an important opportunity for the start of domestic high-energy physics research. In the previous few years, in order to implement BEPC, Tsung-Dao Lee traveled around the country and abroad to demonstrate the plan and seek cooperation. Wang Yifang believes that judging from the development history of high-energy physics in China, BEPC was the best choice at the time in terms of academic, technical, and funding standards. At that time, China had almost no foundation in the field of accelerators. If it wanted to build an electron-positron collider and plan its performance to surpass that of foreign countries, it had to overcome numerous difficulties. "Without Tsung-Dao Lee's full efforts, there would be no construction and success of BEPC."

In 1988, BEPC completed its first electron-positron collision, achieving another breakthrough scientific achievement in China after the atomic bomb, hydrogen bomb, and artificial satellite. Wang Yifang recalled that from 2004 to 2009, BEPC had a technical upgrade, and Tsung-Dao Lee paid great attention and support. After 2010, Tsung-Dao Lee participated less in domestic collider projects due to health reasons, and he did not come to China again after 2013. "It has been almost ten years since I last saw him in the United States," Wang Yifang lamented.

After 2010, Tsung-Dao Lee continued to produce academic works, including several papers on the Daya Bay Reactor Neutrino Experiment. This was also a research project promoted by Tsung-Dao Lee, aimed at finding new neutrino oscillation modes. In 2012, the research results of the reactor were rated as one of the top ten scientific breakthroughs of the year by Science magazine.

Wang Yifang said that the latest generation of particle colliders in China are under development, involving the most cutting-edge fields of high-energy physics. Although the exploration is of inaccessible particles, the most microscopic and the most macroscopic are one in the early days of the Big Bang, reflecting the same scientific laws. Perhaps it is precisely because of the yearning for this ultimate law that Tsung-Dao Lee would "pursue physics carefully and enjoy life, why bother with fame and fortune?" This line of his favorite poem has become his life principle.

"Elegant intellectual"

Li Zhengdao became a U.S. citizen in 1962. Zhu Bangfen, an academician of the Chinese Academy of Sciences and a professor of physics at Tsinghua University, believes that Li Zhengdao's love for talents is never based on nationality.

Since the 1970s, Tsung-Dao Lee and his wife, Qin Hui-yu, have begun to visit mainland China and have made many suggestions on the cultivation of scientific and technological talents and basic scientific research in China. In 1979, Tsung-Dao Lee designed and launched the Sino-US Joint Training Program for Physics Graduates (CUSPEA), providing scholarships to outstanding undergraduates to study for a doctorate in physics in the United States, thus realizing the "going out" of talents. After two batches of students were piloted, CUSPEA was officially implemented in 1981. Since then, a total of 76 American universities have participated in the joint training, and nearly 1,000 students have been selected from across the country to go to the United States. This program pioneered the large-scale overseas dispatch of Chinese students.

"In addition to going abroad, we also need to keep them here." Zhu Bangfen told China Newsweek that during the CUSPEA period, Tsung-Dao Lee was always worried about the lack of scientific talent in China after the unrest. In 1986, the China Center for Advanced Science and Technology (CCAST) was established, initiated by Tsung-Dao Lee. Zhu Bangfen was one of the first CCAST experts. He said that at that time, there was a serious outflow of domestic scientists. The original intention of Tsung-Dao Lee to establish this academic institution was to build an international academic platform to attract domestic scientists to stay in China to do scientific research.

The establishment of CCAST is a milestone event in the domestic physics community. Over the past 30 years, the center has held nearly 20 international academic seminars and hundreds of domestic seminars. In Zhu Bangfen's view, these seminars have injected cutting-edge knowledge in the field into the domestic scientific research community, which not only broadened the horizons of domestic researchers, but also pointed out the direction for research. The topics of the seminars were almost all selected by Tsung-Dao Lee himself.

Zhu Bangfen remembers that at that time, Tsung-Dao Lee would frequently visit the Institute of Theoretical Physics of the Chinese Academy of Sciences where CCAST is located to organize many academic activities, including the compilation of academic papers, and Zhu Bangfen also participated. Although he did not have direct academic cooperation with Tsung-Dao Lee due to professional differences, he still felt his vigorous scientific research enthusiasm and strong organizational ability during the conversation. "He is very willing to do trivial things himself and always tries his best to get things done."

In addition, Tsung-Dao Lee also facilitated the establishment of China's first junior class at universities, advocated the establishment of a postdoctoral system, and established the China Postdoctoral Science Foundation. In 1986, the National Natural Science Foundation of China was established, and Tsung-Dao Lee served as an honorary advisor. After his wife passed away in 1996, Tsung-Dao Lee donated $300,000 to establish the "Qin Hui-yu and Tsung-Dao Lee China University Student Internship and Training Fund" to support outstanding university students from six universities including Peking University and Shanghai Jiaotong University to conduct basic scientific research training. In accordance with his wife's last wishes, no less than half of the students who received funding in each class were female.

"Tsung-Dao Lee has played a great role in promoting the improvement of China's education system and the development of educational concepts," said Zhu Bangfen. What impressed him most was that at the first "Innovation China Forum" hosted by CCAST in 2010, Tsung-Dao Lee, as the chairman of the forum, mentioned the "Three Character Classic" of learning: "To innovate, you need to learn; just learning to answer is not learning; the more you ask, the more you create." Zhu Bangfen believes that asking questions means that you have a thorough understanding of knowledge, which is one of the things that China's scientific innovation lacks the most. "Tsung-Dao Lee can always express philosophy in simple language."

Wang Yifang was also deeply impressed by Li Zhengdao's conversation and called him a "very elegant intellectual." At that "Innovation China Forum," Li Zhengdao said that in the field of basic research, China missed classical mechanics in the 17th century, missed electromagnetism in the 18th and 19th centuries, missed relativity and quantum mechanics in the 20th century, and must not miss it again in the 21st century. "He is an amazing scientist, a role model who is far-sighted and leads by example," said Wang Yifang.

Author: Zhou You