Frank Wilczek, 2004 Nobel Prize in Physics Press Conference
BROWN: It's a pleasure to welcome everyone to MIT on this bright and glorious morning. I'm Bob Brown, the provost of MIT, and I'm standing in for President Charles Vest, who happens to be traveling. He, Chuck, would very much love to be here. During his time as president, this will be the only Nobel laureate that we've received that he does not introduce personally.
It's a glorious day for American science, for MIT, and for the Department of Physics with the awarding of the Nobel Prize in physics to Professor Frank Wilczek. I'm going to let Marc Kastner, the department head in physics, make the formal introduction. Mark?
KASTNER: Thanks, Bob. Before I begin, I'd like to introduce two other physics Nobel laureates who are here-- Jerry Friedman and Wolfgang Ketterle.
Jerry shared the prize with the late Henry Kendall, another faculty member in our department, in 1990. And when I introduced Wolfgang to the department colloquium after his Nobel Prize was announced in 2000, I pointed out that we had had five Nobel Prize winners in the physics department in 25 years. And I thought that once every five years was pretty good, but the faculty should really work a little harder.
And here you see they come through.
Frank Wilczek is, as Bob Jaffe says, a luminary. He is one of the great minds of modern physics.
In 1972, when Frank began his research on quantum chromodynamics, the theory of the strong interactions, we knew there were quarks. And we knew it because of the experiments of Jerry Friedman and Henry Kendall. And a lot was known, but the pieces of what held these quarks together, the strong interaction, were fragmented. There was no way of putting it together.
The work that Frank did with David Gross and Politzer put things together in a way which allowed physics to move forward. And it is one of the great cornerstones of our understanding of modern physics.
Frank came here from Princeton about the time of the millennium. And it really began a new century for MIT physics. It gives me great pleasure to introduce him to you.
WILCZEK: Thank you.
All right. That's enough, that's enough. OK.
An occasion like this I think is, first of all, an occasion to give thanks. And I have a lot of people I want to thank.
I want to thank my parents who were first-generation Americans. My grandparents emigrated under difficult circumstances around the time of World War I. And my parents grew up in very difficult circumstances in the Depression, but worked very hard to get themselves educated and then to support my education. And I was very pleased to be able to call them this morning with this news.
I also want to thank the United States for--
--supplying the system of education which did so well by me. I'm a public school guy all the way and a beneficiary of the excellent public schools of New York City in the 1950s. And I think it's very important that the country continue-- or recover-- the excellence in its education that it's had. I also got excellent instruction at Chicago before coming to Princeton, where after that it gets famous.
I also want to thank my wife, Betsy. It was the time I was meeting and courting Betsy that I did this work, and I don't think that's entirely a coincidence.
We're still together, and she's here, and I thank her very much.
Although they didn't have much to do with this work, I'd also like to thank my daughter for making life a lot of fun and enabling me to keep happy and productive, I think, at a reasonable level ever since.
More seriously, I'd like to thank the community of physicists, I guess represented by Jerry Friedman here especially, the community of physicists who really laid the foundation of insight and facts that we were able to leverage into a fundamental theory of the strong interaction. And our input definitely was important-- I don't want to be too modest about this.
--but it absolutely was not from out of thin air. It was rooted in hard experimental work and theoretical insights from a large number of communities. We stood on the shoulders of giants, but also on the shoulders of a lot of only reasonably tall people, a very large number of average height people, and even a few dwarfs were important.
Finally, I'd like to thank nature for being so kind as to really become simple and understandable at short distances. Our work is really a vindication of the whole idea that it is possible to understand nature precisely and mathematically by studying the fundamentals that go on at short distances and high energies and building up from there. So I'd like to thank mother nature for her good taste--
--in choice of principles, and symmetries, and rationality.
So I don't know what I'm supposed to do now.
So maybe I'll just say a few words about what's up on the board, which is representative, and then take questions.
So starting over here--
BROWN: Can you grab the microphone right up front, the wireless? [INAUDIBLE].
WILCZEK: This one?
BROWN: No, no.
WILCZEK: Oh, in here. Oh, that. OK.
BROWN: It's on.
WILCZEK: --this this was the result of the calculation that came from calculating processes in space and time where gluons interact with other gluons and modify the distribution of colored charge. Or they can also go through intermediate quarks. And there are a number of different kinds of processes.
I won't go through the details, nor--
--give you a quiz on this. But the result of this calculation was a formula for how the coupling of the strong interaction changes as a function of energy.
And what we found is that as a result of quantum fluctuations and rearrangements of color fields in the vacuum, in empty space-- what you call the vacuum, in empty space-- the effect of a charge at higher and higher energies-- or equivalently, at shorter and shorter distances-- gets weaker and weaker. This is what's called asymptotic freedom.
And because the its effect gets weaker and weaker, the particles behave more and more as if they were free of any interactions, as the energies get larger and larger or the distances get smaller and smaller. That's why it's called freedom. It's also simplicity, because it means that the complications due to the interactions become less and less severe or less and less necessary to take into account as you go into higher energies or shorter distances.
So that was the formula from pen and paper calculations. And the original calculations-- because they had many cross-checks and they involved techniques that were pioneering at the time-- really filled notebooks. Nowadays, that calculation is often assigned as an exercise in quantum field theory classes. It's still difficult to do in less than a page or two, but that was the core calculation.
From that calculation it was a relatively straightforward-- but not trivial-- exercise to derive experimental consequences. In a variety of different experiments, which I'll be happy to explain if someone asks, one can check whether this predicted behavior of the effective charge getting weaker and weaker at high energies and short distances in fact occurs.
And most gratifyingly-- well, this is, of course, entirely manufactured data, but gives the spirit of the actual curve, which I didn't bring in-- our prediction for how the strength of the coupling should vary as a function of energy has been vindicated now by many thousands of measurements and literally hundreds of different kinds of experiments.
And so I still find it a miracle to think that the calculations and concepts that on the one hand you scribble on paper match the results that are measured in accelerators with these gigantic magnets and detection apparatus' that seem to come from an entirely different universe of discourse and concepts. And yet, one maps onto the other with this amazing accuracy.
And then I'll display one more thing. So this all has to do with the behavior of the so-called strong interaction, which is responsible for building up protons and neutrons out of quarks and for the interactions of protons and neutrons that are responsible for building up atomic nuclei and holding them together and responsible for our mass. So if you think you're overweight, you have me to blame--
This one is one of the theoretical uses of this insight. We would like to construct, as much as possible, a unified description of the different forces of nature. But when we go out and measure, we find that several of the different forces don't seem to want to be unified in that they appear to have very different strengths.
So here, alpha-3 is the inverse strong coupling constant-- alpha-S is the same as alpha-3-- this coupling constant that describes the strength of the strong interaction. Here its inverse, so it increases as the energy increases. And instead of getting a curve, because I plotted it with a logarithm, it gives more or less a straight line. But the details don't matter. The point is that the coupling constant changes as a function of the energy.
And likewise, the coupling constant for the weak interactions and for the electromagnetic interactions change depending on the energy or distance at which you measure them. And likewise, even the gravitational interaction.
And so you can see if the dream of unification at short distances can really be achieved by extending and extrapolating this kind of calculation to other interactions and to higher energies. And miracle of miracles, it works-- well, more or less.
It works quantitatively in detail, doing justice to the accuracy of the experiments.
I should say, before getting carried away, but what's actually measured is what's in this oval here. And the rest is extrapolation. And those of you who know about logarithms will know that to get a logarithm to change by a factor of 10 is a very enormous extrapolation. So that's the sort of thing we're talking about here. We're going from a 100 GeV in energy to 10 to the 18th GeV in energy to make this extrapolation-- so, far beyond what we've measured. But because of the success of the theory, we have some confidence that it makes sense to do.
And when you do it in full detail, you find that it more or less works with the particles we know. However, if you really wanted to get it to work accurately, you'd have to up the ante and include something that is called low-energy supersymmetry.
Now, low-energy supersymmetry is something that has consequences. It's something that has to show up at the next great accelerator, the Large Hadron Collider at CERN. So we're actually making predictions for the near future. We can be shot down or not. I'm not going to give back my Nobel Prize--
--if it doesn't work. On the other hand, I'll be in the market for a second one--
But this is an example of how we build on insights from the past to makes predictions for the future. And it's a very exciting future indeed for this kind of work. So with that, I'll take questions.
KASTNER: Before questions, let me take this opportunity to introduce one more of our department's Nobel Prize winners, Sam Ting.
Sam was actually our first physics Nobel Prize at MIT in 1976. And all the ones before this year were in experimental physics, so this is a breakthrough year for us. This is our first prize in theoretical physics.
BROWN: Be glad to take questions.
MODERATOR: [INAUDIBLE] phone [? mob. ?] Ask the phone if they have any questions.
BROWN: People on the phone, do you have any questions?
REPORTER: Hi, yes. My name is [INAUDIBLE]. I'm from the Washington Post.
REPORTER: I wonder if you could describe your collaboration with your two colleagues, where it took place and the circumstances.
WILCZEK: Yeah. Well my collaboration was with David Gross only. David Gross was an assistant professor when we began the work. He got promoted to associate professor somewhere in there. And he was my thesis advisor. And we worked very intensely together.
David Politzer was a graduate student at Harvard. And we learned of his work really only after both groups had found their main results. We learned of his work through Sidney Coleman, who was a brilliant physicist, David Politzer's thesis advisor. David Politzer was at Harvard and Sidney was on leave from Harvard to Princeton.
And Sidney realized that we were working on related things. So we knew of each other's existence at an early stage and remained in friendly competition by having occasional communications.
AUDIENCE: What does it mean for you to have won this prize?
WILCZEK: Makes me very happy.
It also makes me relieved. I'd be lying if I said it came as a shock. The theory I've thought for a long time was very, very important. The data in favor of it has been clear for at least 20 years. And so every year at this time for the past 20 years or so, I've had an unpleasant week and a sleepless night.
I'm very pleased that that's all over with.
But more seriously, I think it's very welcome recognition for an endeavor-- understanding the fundamental interactions of nature and understanding them in a precise mathematical way-- that is one of the crowning glories of our culture. It's one of the things that people will think about 1,000 years from now, if there are still people, or their robotic descendants, or whatever. But it's one of the real gems of our culture that you can understand nature in this way, and then when you do you find very beautiful things.
And I hope to pay back in the sense of using this recognition to feed some of it back into the field as a whole and make sure that it keeps supported and keeps vigorous.
BROWN: Yes, in the back.
AUDIENCE: I was wondering if you could in layman's terms describe this theory of the strong interaction, because you kept referencing back to that.
AUDIENCE: And I need to have that building block for me to--
WILCZEK: OK, so what is the strong interaction. When people in the 1930s started to get a reasonably mature understanding of what atomic nuclei were, they realized that atomic nuclei can be thought of as built up out of protons and neutrons, but that the interaction that held them together between protons and neutrons had to be a fundamentally new interaction. The interactions that were known at the time-- electromagnetism and gravity-- were not sufficient to hold atomic nuclei together. So this became the problem of the strong interaction-- what is it that holds atomic nuclei together.
That's not an easy thing to investigate, because nuclei are very, very small. And so the experiments were at first relatively crude. They consisted in throwing different particles together at high energies and seeing what came out. And people hoped, I suppose, that what came out would be simple building blocks and that you would understand the protons and neutrons-- or maybe the protons and neutrons themselves would be deflected by a ways, then that would tell you what their interactions were.
But what happened instead was that when the particles were smacked together you found whole new worlds of phenomena, that there were many, many unstable particles besides protons and neutrons. They have funny names like pi mesons, rho mesons, lambda, [? sigma. ?] A lot of them are just Greek letters.
But anyway, though in a way similar properties to protons and neutrons, they had very powerful interactions. You could turn protons into lambda particles, but then you could also turn lambda particles into protons. So they seem to be more or less on the same footing. And understanding that whole complex of phenomena became what's called the problem of the strong interaction.
And it got completely out of hand by the 1960s. There were hundreds of particles, no real rhyme or reason to why there were so many or the patterns. Then primarily Murray Gell-Mann-- but with a lot of help from others-- started to see patterns in this and found that he could understand the observed kinds of particles by postulating that they were made out of other things, quarks, that had somewhat simpler properties. So some things were made out of three quarks and other things were made out of a quark and an antiquark-- those are baryons and mesons. And those were the strongly-interacting particles.
There was no real understanding of what a quark was other than it was some kind of mysterious thing that you could build other things out of. Part of the mystery was that individual quarks were never discovered. They can't exist in isolation. And so this was clearly a provisional understanding.
Then, well, skipping a lot of very interesting complications and very deep insights, certainly one of the next great milestones was when Friedman, Kendall, and Taylor, and their collaborators did the very smart thing of using a microscope to study inside of protons and neutrons. Of course this is not the kind of microscope you buy at a hardware store. It's a microscope that involves very, very high energy electrons and a lot of interpretation of what you see.
But using that, they were able to probe inside the proton and show that-- with some clever interpretation-- what you were seeing was something like quarks, and furthermore that the quarks inside the proton at very short distances were interacting with each other surprisingly weakly when they got close together. So that posed the problem for us-- how can you get a consistent description of entities, that is consistent with the basic principles of quantum mechanics and special relativity, that interact very weakly at short distances but powerfully at long distances, because we know quarks can't separate from each other.
And that at first seemed to be a contradiction, because in most consistent realizations of quantum mechanics and special relativity charge tends to build up a long distances-- I'm sorry, charge tends to get shielded at long distances, so the effect of coupling gets smaller at long distances, which is the opposite of what we wanted. That's the ordinary behavior of matter in dielectrics or things you learn about in ordinary undergraduate physics.
But what we found, somewhat to our amazement-- I think more to David's amazement than to mine, because I didn't know as much--
--we found a unique kind of theory, the so-called non-abelian gauge theory, a theory with very remarkable mathematical properties and high amounts of symmetry, that had the opposite property, that instead of charges canceling themselves and shielding at large distances they anti-screened. So the charge would grow at long distances, get smaller at small distances. So a very small seed charge and weak interaction could build up to a strong interaction.
And those theories were so rare, theories that had that kind of behavior were so rare, that with only a few broad hints from experiment and implementing that requirement we were led to a unique theory of what the strong interaction had to be. And that's what's now called QCD, or Quantum Chromodynamics.
So part of that was introducing in addition to the quarks what are called gluons, colored gluons with specific properties. So along the way we discovered gluons and showed that the interactions really simplified at short distances.