# Yang Chen-Ning

Yang Chen-Ning or Chen-Ning Yang (simplified Chinese: 杨振宁; traditional Chinese: 楊振寧; pinyin: Yáng Zhènníng; born 1 October 1922), also known as C. N. Yang or by the English name Frank Yang, is a Chinese theoretical physicist who made significant contributions to statistical mechanics, integrable systems, gauge theory, and both particle physics and condensed matter physics. He and Tsung-Dao Lee received the 1957 Nobel Prize in Physics for their work on parity non-conservation of weak interaction. The two proposed that the conservation of parity, a physical law observed to hold in all other physical processes, is violated in the so-called weak nuclear reactions, those nuclear processes that result in the emission of beta or alpha particles. Yang is also well known for his collaboration with Robert Mills in developing non-abelian gauge theory, widely known as the Yang–Mills theory.

## Early life and education

Yang was born in Hefei, Anhui, China. His father, Ko-Chuen Yang [zh] (楊克純; 1896–1973), was a mathematician, and his mother, Meng Hwa Loh Yang (羅孟華), was a housewife.
Yang attended elementary school and high school in Beijing, and in the autumn of 1937 his family moved to Hefei after the Japanese invaded China. In 1938 they moved to Kunming, Yunnan, where National Southwestern Associated University was located. In the same year, as a second-year student, Yang passed the entrance examination and studied at National Southwestern Associated University. He received a Bachelor of Science in 1942, with his thesis on the application of group theory to molecular spectra, under the supervision of Ta-You Wu.
Yang continued to study graduate courses there for two years under the supervision of Wang Zhuxi, working on statistical mechanics. In 1944, he received a Master of Science from Tsinghua University, which had moved to Kunming during the Sino-Japanese War (1937–1945). Yang was then awarded a scholarship from the Boxer Indemnity Scholarship Program, set up by the United States government using part of the money China had been forced to pay following the Boxer Rebellion. His departure for the United States was delayed for one year, during which time he taught in a middle school as a teacher and studied field theory.
Yang entered the University of Chicago in January 1946 and studied with Edward Teller. He received a Doctor of Philosophy in 1948.

## Career

Yang remained at the University of Chicago for a year as an assistant to Enrico Fermi. In 1949 he was invited to do his research at the Institute for Advanced Study in Princeton, New Jersey, where he began a period of fruitful collaboration with Tsung-Dao Lee. He was made a permanent member of the Institute in 1952, and full professor in 1955. In 1963, Princeton University Press published his textbook, Elementary Particles. In 1965 he moved to Stony Brook University, where he was named the Albert Einstein Professor of Physics and the first director of the newly founded Institute for Theoretical Physics. Today this institute is known as the C. N. Yang Institute for Theoretical Physics.
Yang retired from Stony Brook University in 1999, assuming the title Emeritus Professor. In 2010, Stony Brook University honored Yang's contributions to the university by naming its newest dormitory building C. N. Yang Hall.
Yang has been elected a Fellow of the American Physical Society, the Chinese Academy of Sciences, the Academia Sinica, the Russian Academy of Sciences, and the Royal Society. He was an elected member of the American Academy of Arts and Sciences, the American Philosophical Society, and the United States National Academy of Sciences. He was awarded honorary doctorate degrees by Princeton University (1958), Moscow State University (1992), and the Chinese University of Hong Kong (1997).
Yang visited the Chinese mainland in 1971 for the first time after the thaw in China–US relations, and has subsequently worked to help the Chinese physics community rebuild the research atmosphere which was destroyed by the radical political movements during the Cultural Revolution. After retiring from Stony Brook, he returned as an honorary director of Tsinghua University, Beijing, where he is the Huang Jibei-Lu Kaiqun Professor at the Center for Advanced Study (CASTU). He is also one of the two Shaw Prize Founding Members and is a Distinguished Professor-at-Large at the Chinese University of Hong Kong.
Yang helped to establish the Theoretical Physics Division at the Chern Institute of Mathematics in 1986 at the request of Shiing-Shen Chern who was serving as the inaugural director of the Institute at the time.
Yang was the first president of the Association of Asia Pacific Physical Societies (AAPPS) when it was established in 1989. In 1997 the AAPPS created the C.N. Yang Award in his honor to highlight young researchers.

## Personal life

Yang married Tu Chih-li (simplified Chinese: 杜致礼; traditional Chinese: 杜致禮; pinyin: Dù Zhìlǐ), a teacher, in 1950; they had two sons and a daughter together. His father-in-law was the Kuomintang general Du Yuming. Tu died in October 2003. In January 2005, Yang married Weng Fan (Chinese: 翁帆; pinyin: Wēng Fān, a university student. They met in 1995 at a physics seminar; the couple reestablished contact in February 2004. Yang called Weng, who is 54 years his junior, his "final blessing from God". Yang formally renounced his U.S. citizenship in late 2015.
On 1 October 2022, Yang became a centenarian.

## Academic achievements

Yang has worked on statistical mechanics, condensed matter theory, particle physics and gauge theory/quantum field theory.
At the University of Chicago, Yang first spent twenty months working in an accelerator lab, but he later found he was not as good as an experimentalist and switched back to theory. His doctoral thesis was about angular distribution in nuclear reactions.
Yang is well known for his 1953 collaboration with Robert Mills in developing non-abelian gauge theory, widely known as the Yang–Mills theory. The idea was generally conceived by Yang, and the novice scientist Mills assisted him in this endeavor as Mills said:
   During the academic year 1953-1954, Yang was a visitor to Brookhaven National Laboratory...I was at Brookhaven also...and was assigned to the same office as Yang. Yang, who has demonstrated on a number of occasions his generosity to physicists beginning their careers, told me about his idea of generalizing gauge invariance and we discussed it at some length...I was able to contribute something to the discussions, especially with regard to the quantization procedures, and to a small degree in working out the formalism; however, the key ideas were Yang's.
The Yang-Mills theory was called by The Scientist:
   The foundation for current understanding of how subatomic particles interact, a contribution which has restructured modern physics and mathematics.
Subsequently, in the last three decades, many other prominent scientists have developed key breakthroughs to what is now known as gauge theory.
Later, Yang worked on particle phenomenology; a well-known work was the Fermi–Yang model treating pion meson as a bound nucleon–anti-nucleon pair. In 1956, he and Tsung Dao (T.D.) Lee proposed that in the weak interaction the parity symmetry was not conserved, Chien-shiung Wu's team at the National Bureau of Standards in Washington experimentally verified the theory. Yang and Lee received the 1957 Nobel Prize in Physics for their parity violation theory, which brought revolutionary change to the field of particle physics. Yang has also worked on neutrino theory with Tsung Dao (T.D.) Lee, 1957, 1959, CT nonconservation (with Tsung Dao (T.D.) Lee and R. Oheme, 1957), electromagnetic interaction of vector mesons (with Tsung Dao (T.D.) Lee, 1962), CP nonconservation with Tai Tsun Wu (1964).
In the 1970s Yang worked on the topological properties of gauge theory, collaborating with Wu Tai-Tsun to elucidate the Wu–Yang monopole. Unlike the Dirac monopole, it has no singular Dirac string.
Yang has had a great interest in statistical mechanics since his undergraduate time. In the 1950s and 1960s, he collaborated with Tsung Dao (T.D.) Lee and Kerson Huang, etc. and studied statistical mechanics and condensed matter theory. He studied the theory of phase transition and elucidated the Lee–Yang circle theorem, properties of quantum boson liquid, two dimensional Ising model, flux quantization in superconductors (with N. Byers, 1961), and proposed the concept of Off-Diagonal Long-Range Order (ODLRO, 1962). In 1967, he found a consistent condition for a one-dimensional factorized scattering many-body system, the equation was later named the Yang–Baxter equation, it plays an important role in integrable models and has influenced several branches of physics and mathematics.

## Awards and honors

* Nobel Prize in Physics (1957)
* Ten Outstanding Young Americans (1957)
* Rumford Prize (1980)
* National Medal of Science (1986)
* Oskar Klein Memorial Lecture and Medal (1988)
* Benjamin Franklin Medal for Distinguished Achievement in the Sciences of the American Philosophical Society (1993)
* Bower Award (1994)
* Albert Einstein Medal (1995)
* Lars Onsager Prize (1999)
* King Faisal International Prize (2001)
* C.N. Yang Hall, a residence hall and activity center at Stony Brook University, was dedicated in 2010.
* Marcel Grossmann Awards (2015), “for deepening Einstein’s geometrical approach to physics in the best tradition of Paul Dirac and Hermann Weyl”
* Asian Scientist 100, Asian Scientist (2016 and 2020)

## Selected publications

* Yang, C. N. (1983). Selected Papers, 1945–1980, with Commentary. San Francisco, CA: W. H. Freeman & Co. ISBN 978-0-7167-1406-4.
** Yang, Chen-Ning (2005) [1983]. Selected Papers, 1945–1980, with Commentary. World Scientific Series in 20th Century Physics. Vol. 36 (2005 ed.). Singapore: World Scientific. ISBN 981-256-367-9.
* Yang, Chen-Ning (2013). Selected Papers of Chen Ning Yang II: With Commentaries. Singapore: World Scientific. ISBN 978-981-4449-00-7.
* Yang, C. N.; Mills, R. L. (1954). "Conservation of Isotopic Spin and Isotopic Gauge Invariance". Physical Review. 96 (1): 191–195. Bibcode:1954PhRv...96..191Y. doi:10.1103/PhysRev.96.191.
* Mills, R. L.; Yang, C. N. (1966). "Treatment of Overlapping Divergences in the Photon Self-Energy Function". Progress of Theoretical Physics Supplement. 37: 507. Bibcode:1966PThPS..37..507M. doi:10.1143/PTPS.37.507.
* Yang, C. N. (2005). "Remembering Robert Mills". In 't Hooft, Gerardus (ed.). 50 years of Yang-Mills theory. Singapore: World Scientific. ISBN 978-981-238-934-3.
* Lee, T. D.; Yang, C. N. (1956). "Question of Parity Conservation in Weak Interactions". Physical Review. 104 (1): 254–258. Bibcode:1956PhRv..104..254L. doi:10.1103/PhysRev.104.254. S2CID 2044624.
* Lee, T. D.; Yang, C. N. (1952). "Statistical Theory of Equations of State and Phase Transitions. II. Lattice Gas and Ising Model". Physical Review. 87 (3): 410–419. Bibcode:1952PhRv...87..410L. doi:10.1103/PhysRev.87.410. ISSN 0031-9007.
* Byers, N.; Yang, C. N. (1961). "Theoretical Considerations Concerning Quantized Magnetic Flux in Superconducting Cylinders". Physical Review Letters. 7 (2): 46–49. Bibcode:1961PhRvL...7...46B. doi:10.1103/PhysRevLett.7.46.