Gell-Mann, Murray (1929- )

Gell-Mann, Murray (1929- )

American physicist

Prior to the 1940s and 1950s, only a handful of fundamental particles—among them the proton, neutron, electron, and positron—had been discovered in particle physics research. The study of cosmic rays and particle accelerator reactions revealed that the composition of matter was much more complex than previously thought. Dozens, and then hundreds of new particles were discovered. Most appeared to meet the criterion of being a basic form of matter, but they often had unexpected properties. For example, some had lifetimes much longer (10⁻⁹ second) than was predicted for them, based on their mass. Because of these properties, they were collectively referred to as "strange" particles. Before long, physicists aggressively began searching for a way to organize and make sense out of the particle zoo they had discovered. A leading figure in this search was Murray Gell-Mann.

Gell-Mann was born in New York City in 1929. He earned his bachelor of science degree at Yale University at the age of nineteen and his Ph.D. from the Massachusetts Institute of Technology three years later. He worked briefly at the Institute for Advanced Studies and then taught at the University of Chicago from 1952 to 1954. Gell-Mann then moved to the California Institute of Technology, where he became R.A. Millikan professor of theoretical physics in 1966.

Gell-Mann has made a number of contributions to the effort to organize the "particle zoo." In 1953, he suggested that basic particles contain an intrinsic property known as "strangeness," not unlike charge or spin. He showed how the conservation of strangeness in a particle reaction could explain a number of observations made of these new particles. A similar concept was developed independently by the Japanese physicist, Kazuhiko Nishijima.

Gell-Mann next applied himself to the development of a system for placing the known elementary particles into a small number of groups. He observed that particles could be classified into a relatively small number of families of multiplets that have similar properties. Gell-Mann referred to his classification system as the eight-fold way, after the eight ways of right living taught by the Buddha.

Gell-Mann's scheme accomplished for elementary particles what Dmitri Mendeleev's periodic table had achieved for the elements. Furthermore, like the periodic table, the eight-fold way predicted the existence of new elementary particles. The discovery in 1964 of one such particle, the omega minus (Ω–) provided dramatic confirmation of Gell-Mann's ideas. The Israeli physicist, Yuval Ne'emann, independently proposed a similar system of classification at about the same time.

Finally, Gell-Mann suggested that the hundreds of elementary particles might, in fact, be composed of a very small number of even more basic particles. He called these particles quarks, from James Joyce's Finnegan's Wake, "Three quarks for Master Mark!" The first three quarks to be discovered were given the somewhat whimsical names of "up," "down," and "strange." Gell-Mann has also made important contributions to the theory of quantum chromodynamics, which attempts to explain interactions among quarks.

See also Atomic structure; Quantum theory and mechanics