“We had very little money,” Dr. Gell-Mann said.

Young Murray was already showing signs of precociousness, multiplying large numbers in his head and correcting his elders on the pronunciation of foreign words. With the encouragement of his mother and help from a piano teacher who gave lessons at a local settlement house, he won a scholarship to Columbia Grammar, a private school on West 93rd Street, where he earned the nickname “the Walking Encyclopedia.”

Graduating as valedictorian at age 14, he went to Yale, also on scholarship. But physics was not his first choice as a major area of study, he said in the oral history. He considered archaeology or a field related to natural history. His father, however, pushed him to choose engineering, saying it would lead to a well-paying job. Murray resisted, and they settled on physics as a compromise — “to please the old man,” Dr. Gell-Mann said — and he soon found that the subject fascinated him.

“My father was absolutely right,” he said.

After Dr. Gell-Mann earned his doctorate at the Massachusetts Institute of Technology, in 1951, J. Robert Oppenheimer, who had directed the Manhattan Project, brought him to the Institute for Advanced Study in Princeton, N.J. From there he went to the University of Chicago and worked under Enrico Fermi.

The two decades after World War II were a golden age in physics, with experimenters discovering one new phenomenon after another for theorists to explain. Some particles bombarding the earth as cosmic rays seemed to defy the known laws of physics: They did not disintegrate nearly as quickly as the equations predicted. Dr. Gell-Mann showed that this behavior could be explained by positing a new physical quality, which he named “strangeness.”

As with energy, there is a law of conservation of strangeness. (It is conserved in strong interactions and electromagnetic interactions but not in weak interactions.) Once this was taken into account, physicists could explain the particle’s surprisingly slow decay.