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.
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? 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.
How should a nonphysicist visualize quarks? As tiny spheres trapped inside atoms? 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.
When people picture particles smashing together in a particle collider, what should they be imagining? It’s not like billiard balls colliding, is it? 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.
So it would be like smashing an apple and an orange together and getting bananas? 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...
How many types of elementary particles are there? 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.
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? 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.
These particles are similar to protons and neutrons but don’t normally exist in nature? 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.
Do all these exotic particles exist anywhere outside of physics experiments? 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.]
But when you predicted the quark in 1964, you realized it was not just another “cousin” particle, right? That’s right. Looking at the table of known particles and the experimental data, it was clear that the neutron and proton could be made up of three particles with fractional charges, which I called quarks. [Until then all known particles had charges that were a whole multiple of the charge in a proton.] Quarks were permanently confined in the neutron and proton, so you couldn’t pull them out to examine them singly. The neutron and proton were no longer to be considered elementary. It was not a difficult thing to deduce. What was difficult was believing it, because nobody had ever heard of making the neutron and proton composite. Nobody had ever heard of these fractional charges. Nobody had ever heard of particles being confined permanently inside observable things and not directly attainable.
As time goes on, physicists seem to find more and more particles. Could there be an infinite number of them? All of us theorists believe in simplicity. Simplicity has always been a reliable guide to theory in fundamental physics. But the simplicity may not lie in the number of named particles. It may be that the theory, expressed simply, gives rise to huge numbers of particle types. The particles might go on forever, but you detect only the ones that are light enough to play a role in your experiments.
Now researchers are pinning a lot of hope on finding yet another set of predicted particles in experiments at the Large Hadron Collider. Do you think this will bring some clarity? Well, there is another possibility, that they find some phenomenon that is utterly unexpected. It would upset us if they found something totally new, totally mystifying, but that’s what would be most exciting.
You were thought of as a math prodigy as a child, but math wasn’t your only passion, was it? I remember when I was around 5, I looked through my father’s books. He had had a very substantial library, a huge library. And when the bad times struck—the Depression—he had to get rid of them when we moved to a tiny apartment. He had to have the furniture taken away. He couldn’t sell it; he had to pay to have it removed. He paid somebody five dollars to take away his library. Heartbreaking. But he had a few books left, 50 books or something like that. One of them was a book that gave etymologies of English words borrowed from Greek and Latin. So I learned all these Greek and Latin roots and how they went to make up English words. It was exciting. That started me on etymology, and I have loved etymology ever since.
I was always OK in math. Actually I loved math, loved studying it, loved using it. I loved history. I was particularly in love with archaeology and linguistics. And I could discuss anything with my brother—archaeology, etymology, anything at all. He never did anything with it, but he was very, very intelligent and very knowledgeable about all sorts of things. He was passionate about birds and other living things. Not so much the scientific principles of ornithology, but just seeing the birds and identifying them and knowing where they were, and what kind of nest they had, and what songs they sang. Going with him on a bird trip was the best thing—the best thing—I did in those years. My brother taught me to read from a cracker box when I was 3.
When you were going into college, you were interested in studying archaeology, natural history, or linguistics, but your father wanted you to make money as an engineer. I said I’d rather be poor or die than be an engineer because I would be no good at it. If I designed something it would fall down. When I was admitted to Yale, I took an aptitude test, and when the counselor gave me the results of the exam, he said: “You could be lots of different things. But don’t be an engineer.”
Then how did you settle on physics? After my father gave up on engineering, he said, ‘How about we compromise and go with physics? General relativity, quantum mechanics, you will love it.’ I thought I would give my father’s advice a try. I don’t know why. I never took his advice on anything else. He told me how beautiful physics would be if I stuck with it, and that notion of beauty impressed me. My father studied those things. He was a great admirer of Einstein. He would lock himself in his room and study general relativity. He never really understood it. My opinion is that you have to despise something like that to get good at it.
Why is that? If you admire it sufficiently, you’ll be in awe of it, so you’ll never learn it. My father thought it must be very hard, and it will take years to understand it, and only a few people understand it, and so on. But I had a wonderful teacher at Yale, Henry Margenau, who took the opposite attitude. He thought relativity was for everybody. Just learn the math. He’d say, “We’ll prepare the math on Tuesday and Thursday, and we’ll cover general relativity on Saturday and next Tuesday.” And he was right. It isn’t that bad.
You’ve known some of the greatest physicists in history. Whom do you put on the highest pedestal? I don’t put people on pedestals very much, especially not physicists. Feynman [who won a 1965 Nobel for his work in particle physics] was pretty good, although not as good as he thought he was. He was too self-absorbed and spent a huge amount of energy generating anecdotes about himself. Fermi [who developed the first nuclear reactor] was good, but again with limitations—every now and then he was wrong. I didn’t know anybody without some limitations in my field of theoretical physics.
Back then, did you understand how special the people around you were? No. I grew up thinking that the previous people were the special ones. Even though I knew most of them. I didn’t know Erwin Schrödinger [a pioneer of quantum mechanics]; I passed up a chance to meet him for some reason. But I did know Werner Heisenberg fairly well. He was one of the discoverers of quantum mechanics, which is one of the greatest achievements of the human mind. But by the time I knew him, although he was not extremely old, he was more or less a crank.
How so? He was talking a lot of nonsense. He had things that he called theories that were not really theories; they were gibberish. His goal was to find a unified theory of all the particles and forces. He worked on an equation, but the equation didn’t have any practical significance. It was impossible to work with it. There were no solutions. It was just nonsense. Anyway, it was interesting that Wolfgang Pauli [discoverer of the exclusion principle], who did not go in for particularly crazy things—at least not in physics—was taken in by Heisenberg’s stuff for a little while. He agreed to join Heisenberg in his program.
But then Pauli came to the United States, where various people worked on him—including Dick Feynman, and including me. Many of us talked to Pauli and said, “Look, you shouldn’t associate yourself with this. It’s all rubbish, and you have your reputation to consider.” Pauli agreed, and he wrote a letter to Heisenberg saying something like: “I quit. This is all nonsense. There’s nothing to it. Take my name off.” In another letter, Pauli drew a rectangle on the page, and next to it he wrote: “This is to show the world that I can paint like Titian. Only technical details are missing. W. Pauli.” In other words, Heisenberg had provided only a frame, with no picture. I knew Pauli fairly well. I knew Paul Dirac [another founder of quantum mechanics]. He was a remarkably eccentric person.
Of course I knew these people when they were old, not when they were young and carrying on their most important activities. But still, I knew them. And those were the people we were supposed to admire. I didn’t think the people around me were going to be so special. I guess, looking back now, the era does look exciting.
There’s a big difference, though, that my teacher Victor Weiskopf kept pointing out. And that is that the people who were working out the consequences of quantum mechanics, shortly after quantum mechanics was discovered in 1924 and ’25, began to understand how atoms and molecules really worked, and they asked elementary questions about the world that even ordinary people might ask. For example, Victor used to say, one question is, Why can’t I push one finger through the other finger? Well, ultimately it comes down to the exclusion principle [which shows that two particles cannot occupy the same space at the same time]. And so on. Whereas now you have to be sophisticated to even ask the questions that we’re answering.
One of your best-known interactions was with Richard Feynman at Caltech. What was that like? We had offices essentially next door to each other for 33 years. I was very, very enthusiastic about Feynman when I arrived at Caltech. He was much taken with me, and I thought he was terrific. I got a huge kick out of working with him. He was funny, amusing, brilliant.
What about the stories that you two had big problems with each other? Oh, we argued all the time. When we were very friendly, we argued. And then later, when I was less enthusiastic about him, we argued also. At one point he was doing some pretty good work—not terribly deep, but it was very important—on the structure of protons and neutrons. In that work he referred to quarks, antiquarks, and gluons, of which they were made, but he didn’t call them quarks, antiquarks, and gluons. He called them “partons,” which is a half-Latin, half-Greek, stupid word. Partons. He said he didn’t care what they were, so he made up a name for them. But that’s what they were: quarks, antiquarks, and gluons, and he could have said that. And then people realized that they were quarks, and so then you had the “quark-parton” model. We finally constructed a theory—I didn’t do it by myself; it was the result of several of us put together. We constructed the right theory, called Quantum Chromodynamics [QCD], which I named. [QCD describes the interactions between quarks and gluons, which bind quarks together.] And Feynman didn’t believe it.
He didn’t believe that the theory was correct? No. He had some other cuckoo scheme based on his partons. Finally after a couple of years he gave up because he was very bright and realized after a while that we were correct. But he resisted it, and I didn’t understand why he had to be that way. Partons...
Feynman was famously eccentric. Did you guys ever do anything wacky together? We did lots of playful things. One of his friends was an elderly Armenian painter. My late wife Margaret and I were friendly with him too. He had some important birthday, and Margaret and I dreamed up this idea of giving him a peacock. So we conspired with the Feynmans to do it. They drew his attention somewhere else while Margaret and I got the peacock from the car and put it in his bedroom. A peacock in his bed! It’s a marvelous way to give somebody a present.
Did you find it strange that Feynman became such a celebrity? Feynman was a peculiar case because he was a very brilliant, terrific, successful scientist, but he was also a clown. He was more of a clown than he was a scientist sometimes.
But you and Feynman could get into really deep conversations about physics. You were well matched, weren’t you? For some years, and then I got fed up with him. He was just so turned in on himself. Everything was a test of his brilliance. So if in discussing things we came to some interesting conclusion, his interpretation of it was, “Gee, boy, I’m smart.” And it’s just annoying, so after a few years I just wouldn’t work with him.
When you think about people like Feynman or Einstein or some of the other physics legends, do you think of them as geniuses? Is there such a thing? Einstein was very special—I mean, creating that theory, general relativity [which describes gravity as a product of the geometry of space and time]. To do it today or to do it 34 years ago would be striking, remarkable, an utterly remarkable achievement. But to do it when he did, in 1915, that’s just unbelievable.
When you were at the Institute for Advanced Study, Einstein was also there, although he was near the end of his life. Were you able to absorb anything from him? I could have. I could have made an appointment with his secretary, the formidable Helen Dukas, and gone in and talked with him. I could have asked him some questions about the old days. If it were today I would do it in a moment. But all I could see then was that he was past it. He didn’t believe in quantum mechanics, didn’t know about the particles that we were studying. And he didn’t know about this and that. If I showed him what I was doing, he wouldn’t make anything of it. And if he showed me what he was doing, I wouldn’t believe it. So I didn’t do anything. I would say: “Hello. Good morning.” And he would say, “Guten morning.” That was about it.
What are you working on today? Along with several other people around the world, I’m looking to see if there might be alternate ways to mathematically characterize entropy, the measure of disorder of a system. It might be useful to employ alternate formulas for looking at different circumstances such as financial markets or social interactions. Maybe this will turn out to be an extremely flexible tool for handling all kinds of situations. That’s what people hope. Other people think it’s nuts.