Murray Gell-Mann, born in 1929, United States physicist, noted for his classification of subatomic particles and his proposal of the existence of quarks. Born in New York City, Gell-Mann attended Yale University and received a Ph.D. degree from the Massachusetts Institute of Technology in 1951. He taught at the University of Chicago from 1952 to 1955, when he joined the faculty of the California Institute of Technology. Gell-Mann was awarded the 1969 Nobel Prize in physics for work begun in Chicago in 1953. His research in particle physics concerned the interactions between protons and neutrons. On the basis of a proposed property called “strangeness,” conserved by particles involved in strong and electromagnetic interactions (see Conservation Laws), Gell-Mann grouped related particles into multiplets, or families. In 1963 he and, independently, his colleague George Zweig advanced the quark theory; they hypothesized that quarks—particles carrying fractional electric charges—are the smallest particles of matter. Research in particle physics has made use of and thus far supported these theories. See Atom; Elementary Particles; Quark.