At 31, he and a colleague won the 1957 Nobel Prize in Physics for discovering that subatomic particles, contrary to what scientists thought, are always symmetrical.
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.