Murray Gell-Mann’s contributions to physics
On this date, 91 years ago, was born Murray Gell-Mann, notable physicist and Nobel Laureate. Considered as one of the most important figures in the development of the Standard Model of particle physics, he revolutionized the field by proposing the theory of quarks (fundamental particles making up most of the ordinary matter) before unfortunately passing away almost two years ago, on the 24 May 2019, at the age of 89.
Life and career
Born and raised in New York City, Murray Gell-Mann pursued his higher education at Yale University, acquiring a bachelor in science in physics in 1948. Then, he spent some time at the Massachusetts Institute of Technology (MIT) writing his Doctoral thesis in the field of subatomic particles. His work would later inspire Nobel Prize laureate Eugene Wigner in his work on the fundamental symmetry principles.
After obtaining his Ph.D., Gell-Mann joined the Institute for Nuclear Studies at the University of Chicago where he climbed from instructor to acclaimed professor in the matter of a few years. In 1955, he then went on to spend most of his active life working at Caltech in Pasadena, teaching and eventually co-founding the Santa Fe Institute (a center for multidisciplinary studies specialized, amongst others, in the study of complex physical, computational, biological, or chemical systems). Additionally, he intermittently spent some time at CERN where he gave occasional lectures.
The “Eightfold way”
In the 1950s particle physics was in chaos. Hundreds of elementary particles were being discovered from the experiments. Scientists ran out of Greek alphabets to name these particles. J. Robert Oppenheimer joked that the Nobel Prize in physics should go to the physicist who did not discover a new particle that year!
In an attempt to bring order to the classification of subatomic particles, Gell-Mann introduced a model known as the Eightfold Way (inspired by Buddha’s Eightfold Path to enlightenment and bliss).
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This scheme arranged these hadrons, which regroup baryons (ie. protons and neutrons) and mesons (subatomic particles made up of one quark and one antiquark), into multiples of 1, 8, 10, and 27 respectively (in total there were eight groups) based on their fundamental properties (symmetries in their fundamental forces) and as such, members of the same ‘family’ were to be considered as declinations of the same fundamental particle. This model allowed him to describe the magnetic properties of protons and neutrons, amongst others.
The discovery of quarks
In 1964, in order to complete the requirements of his Eightfold Way scheme, Gell-Mann introduced a postulate about the theoretical existence of three new subatomic particles which he named quarks in reference to James Joyce’s novel Finnegans Wake and its famous quote “Three quarks for Muster Mark!”.
His theory was motivated by the claim that the properties of the most fundamental particles known at the time should be explained by the interaction of even smaller “building blocks” within and that the rules which arose from the Eightfold Way would occur naturally if particles such as protons and neutrons were composed of these quarks bound together by the strong force. In addition, as a tool to exploit quark models and study predictions that arose from such systems, he introduced current algebra which allowed him to describe the weak and electromagnetic forces arising in strongly interacting particles (such as quarks).
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Furthermore, Gell-Mann conceptualized the existence of gluons. Particles similar to photons but simply carrying the strong nuclear force instead of the electromagnetic force. As such, he proposed that the exchange of gluons was what allowed quarks to be held together. And soon, the newly introduced quarks, antiquarks, and gluons became accepted as the elementary particles which govern the structure of hadrons (a subatomic composite particle made of two or more quarks, often neutrons or protons).
Later on, Gell-Mann, together with Heinrich Leutwyler, introduced a quantum field theory adapted to quarks and gluons under the name of Quantum Chromodynamics (QCD). It has proved successful in accommodating all strongly interacting particles and flavors of quarks as more came to be discovered. As such, the QCD suppressed the need for the eightfold scheme in explaining the interactions and behaviors of quarks.
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Coincidently, Russo-American physicist Georg Zweig came to a similar conclusion as Gell-Mann. He independently discovered these elementary particles whose properties agreed with those suggested by Gell-Mann, simply naming them “aces” instead of “quarks” however, it was Gell-Mann naming which eventually caught-on.
The Nobel Prize
A few years later, in 1968, came the first experimental confirmations of the existence of quarks, allowing Gell-Mann to be honored with the Nobel Prize in physics the following year for his contributions and groundbreaking contributions to the classification of the properties and interactions of elementary particles.
These first pieces of evidence came from the Stanford Linear Accelerator Center as well as results from the Gargamelle bubble chamber at CERN which yielded particles with charges matching Gell-Mann and Zweig’s predictions. To this date, the properties and behavior of quarks have been widely tested with varying and increasing levels of precision, in high-energy particle colliders around the world. Scientists now claim the existence of six different types of quarks, which come in two different states (quark and antiquark) containing six flavors (up, down, charm, strange, top, and bottom).