He is particularly well known for his role in bringing organization into the world of subatomic particles, which before his work seemed to be verging on chaos, and for developing the concept of quarks. In the latter part of his career his focus has shifted from the most basic aspects of nature to complex adaptive systems, which he currently explores at the Santa Fe Institute.
Gell-Mann was born in New York City on September 29, 1929. His father, Arthur Gell-Mann, ran a language school, but was knowledgeable in a wide range of subjects. The younger Gell-Mann was significantly influenced by his father, not only displaying a lifelong fascination with languages, but also cultivating his own array of erudite interests. As a child prodigy, Gell-Mann taught himself calculus and considered pursuing a career in ornithology, linguistics or archaeology, though his father convinced him that to do so would most certainly mean a life of relative poverty. As a compromise between his father’s suggestion of engineering and his own inclinations, Gell-Mann settled on physics, a subject he at first found boring. At Yale, however, where Gell-Man completed his undergraduate education at 19, his view of the field changed. He came to enjoy theoretical physics so much that he decided to continue his studies in graduate school.
In 1951, Gell-Mann obtained his Ph.D. in physics from the Massachusetts Institute of Technology. He carried out his doctoral research on subatomic particles. It was a hot topic at the time, largely because many of the physicists involved in the Manhattan Project had recently returned to their labs and were attempting to use particle accelerators to unravel the mysteries of the atomic nucleus. The accelerators enabled the discovery of a large number of unstable particles, and Gell-Mann’s first major contribution to physics would be to help explain the unexpected behavior of some of the particles.
Following a short stay at the Princeton Institute for Advanced Studies, Gell-Mann accepted an academic post at the Institute for Nuclear Studies at the University of Chicago in 1952. While working at the Institute, he introduced a new quantum number he termed strangeness to account for the decay patterns of certain unstable particles. As Gell-Mann conceived it, strangeness is a quality of elementary particles conserved during strong nuclear and electromagnetic interactions, but not weak nuclear interactions. The concept enabled him to predict decay events and the existence of the Xi zero particle, which was experimentally detected in 1959.
Once Gell-Mann conceived of strangeness, he was able to use this quality of elementary particles to develop a classification scheme he referred to as the eightfold way (a reference to the Eightfold Path toward nirvana that is central to the Buddhist faith). He carried out most of his work in formalizing the subatomic particle patterns he observed during his years at the California Institute of Technology, where he received an academic appointment in 1955. Similar to Dmitry Mendeleev’s construction of the periodic table, Gell-Mann’s eightfold way charted all known hadrons (a class of subatomic particles governed by strong nuclear force) and predicted several new particles where gaps in the table were left. He further calculated the properties of the particles he believed would later be discovered through the use of more powerful particle accelerators. With the development of such accelerators, the Eta particle was found in 1962, the Phi particle was found in 1963, and the Omega-minus particle was found in 1964. The latter discovery was particularly momentous because the properties of the Omega-minus particle were revealed to be almost identical to Gell-Mann’s theoretical predictions.
Gell-Mann’s continued contemplation of subatomic particles eventually led to his development of yet another landmark theoretical breakthrough. The symmetry of Gell-Mann’s classification scheme seemed to suggest that hadrons are composed of smaller, fractionally-charged building blocks. Rather than abide by the tradition of identifying subatomic particles with letters of the Greek alphabet or Greek roots, Gell-Mann called these building blocks “quarks.” He initially described three and coined their names: up, down and strange quarks. Quarks were a purely mathematical construct theorized by Gell-Mann (notably, George Zweig independently proposed the existence of fractionally-charged particles, which he called aces, at about the same time Gell-Mann introduced quarks). But with them he was able to account for the composition of more than 200 subatomic particles then known. Moreover, experimental physicists have since succeeded in detecting quarks, although none have ever been isolated.
In the mid 1970s, the first particle was produced that could not be satisfactorily explained with Gell-Mann’s three original quarks. A fourth quark was proposed, and later a fifth and sixth. These additional quarks are known as charm, top (or truth), and bottom (or beauty). The six types of quark are known as flavors of quark, and each possesses an anti-quark counterpart. Quarks are now considered to exhibit a property called color (no resemblance to the traditional notion of color). Gell-Mann greatly contributed to the development of the concept of quark color in the 1970s.
The following decade, Gell-Mann became a vocal advocate of interdisciplinary research, especially in investigations of complex systems. He has been associated with the Santa Fe Institute since the early 1980s and published the popular book The Quark and the Jaguar: Adventures in the Simple and the Complex in 1994. In addition to the Nobel Prize in Physics, Gell-Mann has received a large number of other awards and honors, including the Franklin Institute’s Franklin Medal, the Ernest O. Lawrence Memorial Award bestowed by the Atomic Energy Commission, and the Erice Prize, decided upon by the World Federation of Scientists, a group that advocates science for peace. He is a member of several prestigious scientific societies and has at various times served the United States government as a scientific advisor.