Tsung-Dao Lee, 97, Physicist Who Challenged a Law of Nature, Dies

Tsung-Dao Lee, a Chinese American physicist who shared the Nobel Prize in Physics in 1957 for overturning what had been considered a fundamental law of nature — that particles are always symmetrical — died on Sunday at his home in San Francisco. He was 97.

His death was announced in a joint statement by the Tsung-Dao Lee Institute at the Jiao Tong University in Shanghai and the China Center for Advanced Science and Technology in Beijing. Dr. Lee was a longtime professor at Columbia University.

The theory that Dr. Lee overturned was called the law of conservation of parity, which said that every phenomenon and its mirror image should behave precisely the same. At the time he challenged the theory, in 1956, it had been widely accepted for 30 years.

Dr. Lee was then a young professor at Columbia, where he had been promoted to full professor at age 29 — the youngest in the university’s history at that point.

He had become intrigued by a problem involving the decay of so-called K mesons, which are subatomic particles. These particles decay all the time, forming electrons, neutrinos and photons. Experiments had shown that when K mesons decayed, some exhibited changes that suggested that each differed from the others. But they also had identical masses and life expectancies, indicating that they were the same.

This apparent contradiction created quite a conundrum for physicists. They had assumed that weak nuclear forces, like meson decay, obeyed the law of conservation of parity just like the two other fundamental forces that govern quantum physics: strong nuclear forces, which bind protons and neutrons together in the nucleus, and electromagnetic forces, which govern the attraction and repulsion of electric charges and the behavior of light. In other words, scientists had assumed that the orientation of weak nuclear forces could always be reversed.

Dr. Lee asked a research group at Columbia to perform a simple experiment to see if that was the case. The results suggested that it might not be.

He called on Chen Ning Yang, a professor at the Institute for Advanced Study in Princeton, N.J., whom Dr. Lee had worked with and had also known as a graduate student at the University of Chicago, and together they went back through all the studies and experiments involving weak forces.

Dr. Lee and Dr. Yang came to the conclusion that there was only one reasonable answer to the problem raised in K meson decay: Unlike strong nuclear forces and electromagnetic forces, weak nuclear forces did not obey the law of conservation of parity. It was a revolutionary idea because it meant that in nature, some particles are, in effect, right-handed while others are left-handed.

In the fall of 1956, Dr. Lee and Dr. Yang published their theory in the journal Physical Review.

A groundbreaking experiment by the physicist Chien-Shiung Wu involving the decay of cobalt atoms was performed later that year, confirming that Dr. Lee and Dr. Yang were right. They were awarded the Nobel Prize the following year.

Dr. Lee was just 31 when he accepted the prize; he and Dr. Yang were the first Chinese-born laureates.

Dr. Lee had an exceptionally long and productive career. He retired from regular teaching at Columbia in 2012, at age 86, but continued to contribute ideas to particle physics research into his 90s. His name is affixed to two theorems, the Lee Model and the Kinoshita-Lee-Nauenberg theorem — and he developed important theories on black holes and dark matter.

He was also a prominent physicist in the field of relativistic heavy ion colliders, and from 1997 to 2003 he was the director of the RIKEN BNL Research Center at Brookhaven National Laboratory on Long Island, which houses the laboratory’s collider.

In a 2007 interview with the Nobel Institute on the 50th anniversary of his Nobel Prize, Dr. Lee attributed part of his success, particularly his insight into parity nonconservation, to his nontraditional education.

Tsung-Dao Lee, who was often known as T.D., was born on Nov. 24, 1926, in Shanghai, the third of six children of Tsing-Kong Lee, a merchant with a background in working with chemicals, and Ming-Chang Chang. Dr. Lee said he grew up “in a family of learning.”

He was in high school when war broke out between China and Japan, forcing him to abandon his studies. It was during this time that he discovered physics. Stumbling across some science books, he was immediately intrigued, but as he was no longer receiving a formal education, he was left to teach himself. It helped him develop his own approach to solving problems.

In the 2007 interview, he recalled tackling Newton’s laws, particularly Newton’s famous equation of force equals mass times acceleration, based on what he could glean from the books.

“Newton realized the force is a function of space, and he knew the function,” Dr. Lee said. “One was elasticity. It’s linear in the distance. And the other one is gravitation. So once the left-hand side is a nonfunction of space and the right-hand side is acceleration, then you can solve it to be right. I thought, ‘That’s interesting.’ But that was not the thing that was stated in the book, so this was my approach.”

In 1943, despite not having a high school diploma, he was admitted to National Chekiang University (now Zhejiang University), which had moved to Guizhou because of the war. Though he started as a student in chemical engineering, he switched to physics when his professors discovered his talent in that field.

The continuing war with Japan forced Dr. Lee in 1945 to switch to National Southwestern Associated University in Kunming, where Dr. Yang, his future collaborator, had also studied. At the university, Ta-You Wu, an influential atomic and nuclear physicist, nominated Dr. Lee for a Chinese government fellowship to study in the United States. By 1946, Dr. Lee, who had completed only two years of college, was at the University of Chicago, having been accepted as a doctoral student.

At the time, the University of Chicago was one of the world’s premier centers for the study of physics. The department was led by Enrico Fermi, the Italian-born physicist who had overseen the first successful nuclear reaction and who had been awarded the Nobel Prize in 1938. Dr. Lee became Dr. Fermi’s sole doctoral student in theoretical physics, meeting with him every week.

It was an extraordinary learning experience, partly because of Dr. Fermi’s teaching technique, which Dr. Lee explained in the 2007 interview with the Nobel Institute.

“‘You see,’ he said, ‘there are things that I would like to know,’” Dr. Lee recalled Dr. Fermi saying. “‘Lee, why don’t you look up and give me a lecture next week.’”

“I was very happy to teach Fermi,” Dr. Lee added. “Of course, this is an excellent way of building the student’s confidence. And then he would ask me questions and I would have to answer.”

Dr. Lee received his Ph.D. in 1950. Over the next three years, he worked at Yerkes Observatory in Williams Bay, Wis., as a guest lecturer at the University of California, Berkeley, and at the Institute for Advanced Study in Princeton. He was then hired by Columbia University as an assistant professor.

Dr. Lee received many awards aside from the Nobel, including the Albert Einstein Award in Science, and he had a minor planet (3443 Leetsungdao) named for him.

In 1950, he married Jeannette Hui-Chun Chin. They had two sons, James and Stephen. Dr. Lee became a United States citizen in 1962. (Complete information on his survivors was not immediately available.)

Dr. Lee remained fairly modest about the discovery that brought him the Nobel Prize. It was the product of insight about something that, it turned out, was hiding in plain sight.

Nobody saw it before “because it was a mental block,” he said in the 2007 interview. “Nobody looked for it.”

Alex Traub contributed reporting.