1969 Nobel Prize in Physics

A picture of a caucasian man in his 80's with curley hair and glasses, wearing a dark suit.
BEVERLY HILLS, CA - SEPTEMBER 19: Honoree Murray Gell-Mann, Ph.D., Nodel Laureate attends USC Center for Applied Molecular Medicine's 'Rebels With A Cause' Gala at Four Seasons Hotel Los Angeles at Beverly Hills on September 19, 2012 in Beverly Hills, California. Photo by Brian To/WireImage/Getty Images

The 1969 Nobel Prize in Physics was awarded to American theoretical physicist Murray Gell-Mann "for his contributions and discoveries concerning the classification of elementary particles and their interactions."

Quantum Chromodynamics

Understanding of the physical structure of matter grew throughout the twentieth century, largely because of advances in the technology of particle accelerators that were able to explore the atomic and subatomic realms.

Cyclotrons were developed in the 1930s and design improvements led to the synchrotrons in the 1950s, with growing efficiency and increased collision power.

As their power grew, the scale at which they could explore became smaller and smaller. At these smaller scales, and with the new mathematical modeling techniques of quantum physics, it became more and more clear that the existing models that guided particle physics were incomplete or mistaken. The common understanding that the components of the atomic nucleus, the proton and the neutron, were fundamental particles came into question as these particle collisions began to show hints that they were made up of even smaller pieces. These smaller pieces, in turn, demonstrated the ability to recombine together in unexpected ways, resulting in hundreds of new particles that do not normally occur in nature.

The search to explain this physical structure was one of the key questions that occupied theoretical particle physicists of the third quarter of the twentieth century.

The outcome of the collisions were an array of unknown particles that were like puzzle pieces that had to be interpreted to determine the physical structure, without the actual ability to re-assemble them together back into the original particles,  

The theory that ultimately had the most success at explaining these particles and the forces that bind them is called quantum chromodynamics.

Murray Gell-Mann called it the "Eightfold way" initially, because the mesons and baryons within the structure were organized into an octet. (A similar model was independently developed at the same time by Israeli physicist Yuval Ne'eman to explain the data.)

Within this explanations, the various hadrons (including the proton and neutron, plus a variety of the new particles observed coming out of particle accelerators) were described as composite particles made up of quarks and bound together by the strong nuclear force. The quark model was also independently proposed by George Zweig in 1964, which gives the suggestion that Gell-Mann was on to something ... and subsequent experimental confirmation of the predictions of his model came before the end of the decade, setting the stage for the 1969 Nobel Prize in Physics.

The full formulation of quantum chromodynamics within the Standard Model also includes gluons, which are the gauge boson that mediate the strong nuclear force. In fact, it is the energy of the gluons, the binding energy of the strong nuclear force, which provide most of the mass within the hadrons. A proton's mass is far more than just the sum of the individual quark masses.

Famously, Gell-Mann got the name "quark" from James Joyce's Finnegan's Wake, which contains the lines:

Three quarks for Muster Mark!

Sure he has not got much of a bark

And sure any he has it's all beside the mark.

Since the proton and neutron consisted of three particles apiece in his model, he dubbed these components with the curious name "quark."

Murray Gell-Mann

Murray Gell-Mann was born in New York City on September 15, 1929. He earned his undergraduate degree in 1948 from Harvard University and his Ph.D. from the Massachusetts Institute of Technology in 1951. He worked at Princeton University Institute for Advanced Study in 1952 before going to work at the University of Chicago in 1953.

In 1955, Gell-Mann joined the faculty at the California Institute of Technology, where he remained until his retirement in 1993.

Read more in the more complete biography of Murray Gell-Mann.