Cheng Chin, a UChicago physics professor, with Chen Ning Yang (Ph.D. ’48) in Yang’s home in Beijing in 2007. Courtesy of Cheng Chin.

Chen Ning Yang (Ph.D. ’48), a Nobel Prize–winning physicist whose research transformed understanding of how particles behaved, died on October 18 in Beijing at 103 years old. His death was announced by Tsinghua University, where he served as a professor.

Yang and his colleague Tsung-Dao Lee (Ph.D. ’50) discovered a phenomenon that disrupted the principle of parity conservation in 1956. Prevailing thought held that for fundamental physical interactions there was always a symmetry between a subject and its mirror image, a principle to which which the pair found a counterexample. Yang and Lee were awarded the Nobel Prize in physics the next year, at just 35 and 30 years old, respectively.

Yang is also remembered for the Yang-Mills theory, developed with physicist Robert Mills, which used gauge theory—a mathematical framework—to describe the behavior of elementary particles.

The first of five children, Yang was born on September 22, 1922 in Hefei, China. He earned his undergraduate degree from Tsinghua University, where his father was a professor of mathematics, before moving to the United States.

Arriving in the U.S. from Beijing in 1945 on a Boxer Indemnity Scholarship, Yang initially enrolled at Columbia University to receive his doctorate under Enrico Fermi. However, after his arrival, he realized that Fermi had relocated to Chicago a few years prior and subsequently registered at the University of Chicago.

Yang and Lee—who met playing a board game in I-House—became devoted students of Fermi, frequently attending informal night lectures the professor would give graduate students. “We learned that physics should not be a specialist’s subject; physics is to be built from the ground up, brick by brick, layer by layer,” Yang wrote. “We also learned in these lectures of Fermi’s delight in, rather than aversion to, simple numerical computations with a desk computer.”

Yang was influenced by other influential physicists of the era as well, eventually receiving his doctorate with Edward Teller, colloquially known as “the father of the hydrogen bomb,” as his dissertation advisor. Yang and Lee also took a class with Subrahmanyan Chandrasekhar, who drove from the Yerkes Observatory in southern Wisconsin to Hyde Park every week to teach the class.

After completing his Ph.D. and teaching at the University for a year, Yang moved to the Institute for Advanced Study at Princeton, headed by Robert Oppenheimer, later joining Stony Brook University. Yang was working near Lee, who was at Columbia, and they began working on their theory together.

They were confronted by the peculiarity of the kaon, a particle which seemed to decay in a manner that didn’t maintain symmetry between the left and right sides. They theorized that the weak force—a fundamental interaction in nuclear physics that governs the decay of atoms—ignored mirror symmetry in an October 1956 paper published in the Physical Review. The theory was quickly borne out in an experiment, making Yang and Lee Nobel laureates within a year of the article’s publication.

In his Nobel banquet speech, Yang—who often went by the nickname Frank, after Benjamin Franklin—described the dual influences of China and America on his life and research.

“I am heavy with an awareness of the fact that I am in more than one sense a product of both the Chinese and Western cultures, in harmony and in conflict,” Yang continued. “I should like to say that I am as proud of my Chinese heritage and background as I am devoted to modern science, a part of human civilization of Western origin, to which I have dedicated and I shall continue to dedicate my work.”

Yang became a professor at Tsinghua University in 1999, leaving Stony Brook for good. In 2015, he renounced his U.S. citizenship to become a citizen of the People’s Republic of China.

Cheng Chin, a professor in the Department of Physics, met Yang twice in 2007 and 2013, both times in Beijing. In an interview with the Maroon, Chin said that he had been familiar with Yang since his childhood in Taiwan; Yang and Lee, the first Chinese-born Nobel laureates, were celebrated as an inspiration for children in schools.

It was the novelty and courage of Yang’s theories that left a deep impression on Chin. “He’s a kind of hero to many young scientists who are thinking outside of the box and bold enough to propose something that other great physicists would not even believe,” Chin said.