Category: Science & Technology

It is no accident that the quark—the building block of protons and neutrons and, by extension, of you and everything around you—has such a strange and charming name. The physicist who discovered it, Murray Gell-Mann, loves words as much as he loves physics. He is known to correct a stranger’s pronunciation of his or her own last name (which doesn’t always go over well) and is more than happy to give names to objects or ideas that do not have one yet. Thus came the word quark for his most famous discovery. It sounds like “kwork” and got its spelling from a whimsical poem in James Joyce’s Finnegans Wake. This highly scientific term is clever and jokey and gruff all at once, much like the man who coined it.

Gell-Mann’s obsession with words dates to his youth, when his fascination with linguistics, natural history, and archaeology helped him understand the diversity of the world. The native New Yorker skipped three grades in elementary school and entered college early. After zipping through Yale and MIT, Gell-Mann was just 21 when he began his postdoc work at the Institute for Advanced Study in Princeton, New Jersey, back when Albert Einstein was still strolling the campus. Gell-Mann later worked with Enrico Fermi at the University of Chicago, and he debated passionately with renowned physicist Richard Feynman during his many years at Caltech.

It was at Caltech that Gell-Mann helped to lay the foundations for our understanding of the components that make up matter. He drafted a blueprint of subatomic physics that he called the Eightfold Way. At the time, physicists understood that atoms are constructed from protons and neutrons, but they had also found many other mysterious particles. The Eightfold Way made sense of this baffling menagerie, finding within it places for particles never even imagined. The work was so important that it netted Gell-Mann a Nobel Prize in 1969.

In 1984 Gell-Mann pursued his dream of working in other fields by cofounding the Santa Fe Institute, a think tank where scientists are encouraged to cross disciplines.

Located high on a hill in the New Mexico desert, surrounded by cottonwood trees and outcroppings of rose quartz, the institute is a place where an ornithologist can trade data over lunch with a political scientist while excitedly scrawling statistical equations on a window with a Sharpie for lack of paper and pen. With its geometric design, brightly colored walls, abundant hiking trails in the vicinity, and generous supply of candy in the kitchen, the Santa Fe Institute seems a bit like a playground for scientists.

DISCOVER contributing editor Susan Kruglinski recently sat with Gell-Mann among the oversize leather couches in the institute’s cozy library to talk about what it is like to have lived the history of modern physics:

(Graphic from http://particleadventure.org/quarks.html website)

DISC: You are best known as the person who discovered the quark, one of the fundamental particles that make up the universe, yet for years many of your colleagues weren’t convinced that quarks really existed. Why not?

GELL: You can’t see them directly. They have some unusual properties, and that’s why it was difficult for people to believe in them at the beginning. And lots of people didn’t. Lots of people thought I was crazy. Quarks are permanently trapped inside other particles like neutrons and protons. You can’t bring them out individually to study them. So they’re a little peculiar in that respect.

DISC: How should a non-physicist visualize quarks? As tiny spheres trapped inside atoms?

GELL: Well, in classical physics you could think of a quark as a point. In quantum mechanics a quark is not exactly a point; it’s quite a flexible object. Sometimes it behaves like a point, but it can be smeared out a little. Sometimes it behaves like a wave.

DISC: When people picture particles smashing together in a particle collider, what should they be imagining? It’s not like billiard balls colliding, is it?

GELL: It depends on the circumstances. At very high energies, two particles that smash together do not bounce off each other but create a vast number of particles. You would have all sorts of little chips flying off in all directions—that would be a little more like it.

DISC: So it would be like smashing an apple and an orange together and getting bananas?

GELL: No, no, no. Little bits of all kinds of things. Getting a whole bunch of little chips of apple and orange, but also chips of banana and antibanana, grapes...

DISC: How many types of elementary particles are there?

GELL: We have a thing called the standard model, which is based on about 60 particles, but there may be many more. These are just the ones that have a low energy, so we can detect them.

DISC: The 1960s and 1970s could be considered a heyday of particle physics, when many subatomic particles—and not just elementary ones, it turns out—were being discovered. Could you talk a little bit about the events leading up to your discovery of the quark?

GELL: That was very dramatic for me. I had been working for years on the properties of particles that participated in the strong interaction. This is the interaction responsible for holding the nucleus of the atom together. The family of strongly interacting particles includes the neutrons and protons; those are the most familiar ones. But now tens, dozens, hundreds of other particles were being discovered in experiments in which protons collided with each other in particle accelerators. There were lots and lots of energy states in which we saw relatives—cousins—of the neutrons and protons.

DISC: These particles are similar to protons and neutrons but don’t normally exist in nature?

GELL: They are produced in a particle collision in an accelerator, and they decay after a short time. After a tiny fraction of a second, they fall apart into other things. One particle that I predicted, the omega-minus, can decay into a neutral pion and xi-minus, and then the pion decays into photons, and the xi-minus decays into a negative pion and a lambda. And then the lambda decays into a negative pion and a proton. The interior of the sun has a very high temperature, but even that very high temperature is not enough to make all of these things.

DISC: Do all these exotic particles exist anywhere outside of physics experiments?

GELL: They existed right after the Big Bang, when temperatures were incredibly high. And they occur in cosmic-ray events. [Cosmic rays themselves are mostly protons, but when they strike atomic nuclei in the earth’s atmosphere, these rare particles can be produced.]

CONTINUED.....

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