Murray Gell-Mann, one of the founders of modern particle physics, died on 24 May, aged 89. Gell-Mann’s most influential contribution was to propose the theory of quarks — fundamental particles that make up most ordinary matter.
To bring order to a plethora of recently discovered subatomic particles, in 1961 Gell-Mann proposed a set of rules based on symmetries in the fundamental forces of nature. The rules classified subatomic particles called hadrons into eight groups, a scheme he named the eightfold way in a reference to Buddhist philosophy.
In 1964, he realized that such rules would naturally arise if the particles were composed of two, three or more fundamental particles, held together by the strong nuclear force. (US–Russian physicist George Zweig came to the same conclusion independently in the same year.) Protons and neutrons, for example, would be made up of three of these more fundamental particles, which Gell-Man named quarks, inspired by a quote — “Three quarks for Muster Mark!” — from James Joyce’s 1939 novel Finnegans Wake.
He also posited the existence of gluons: particles that carry the strong nuclear force in a similar way to how photons carry the electromagnetic force. Inside hadrons, quarks are held together through the exchange of gluons.
Researchers at the Stanford Linear Accelerator Center in California confirmed the existence of quarks in 1968, and Gell-Mann received the Nobel Prize in Physics the following year. His theory of quarks and gluons was later successfully tested in countless, increasingly precise experiments at high-energy particle colliders. Physicists now know of six different types of quark, together with their antimatter counterparts.
Gell-Mann was born in New York City in 1929, and did much of his work at the California Institute of Technology in Pasadena, where he taught from 1955 to 1993. In 1984, he co-founded the Santa Fe Institute, a multidisciplinary centre for the study of complex systems in New Mexico.