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SPEAKER 1: Well, the title is Nature Simple, which is rather a large question. Of course, if you just look around you, nature doesn't appear very simple. There's a tremendous diversity of phenomena. And over the centuries, we've learned how to interpret them first in terms of 92 chemical elements and then how to interpret the chemical elements in terms of a certain number of elementary particles. But even at that level, even at the level of elementary particle physics, as you find it in textbooks on the subject, nature still has the appearance of a tremendous non-simplicity.

There are, oh, three or four large classes of particles that we call leptons, hadrons, photons. And there are at least four classes of interactions, gravitation and electromagnetism which are fairly familiar and others that are less familiar, the weak nuclear force and the strong nuclear force. And they're not terribly similar to each other. So you might not want to say that, on the basis of what we already know, nature has that appearance of simplicity.

But simplicity after all, is what we intuitively feel must be found at really the most fundamental level of knowledge. I don't know why we feel this so strongly, but it's certainly an ancient dream that someday we would find a few simple principles that would determine why everything is the way it is. And so the fact that it doesn't appear simple at the level we've reached tells us that we must not be at the fundamental level.

And what I'm going to talk about today are the attempts that have been made in the last decade or so to try to see below what I call the textbook level of elementary particle physics to what is a deeper level. And we have been receiving all kinds of intimations that underneath the level of elementary particle physics, which supposedly underlies all other phenomena, there is a deeper level, deeper in the same way that elementary particle physics is deeper than chemistry, say, and on that level, the world does look remarkably simple. There are powerful symmetries which relate all the forces of nature and all the particles of nature so that the description, mathematically, is much more simple, much more elegant than one might have imagined.

SPEAKER 2: It's a fascinating idea that there are a few basic principles and that there's symmetry in those principles, that everything has its complement in nature. Does that seem something that is possible for people to grasp without an advanced knowledge of physics? Is that something that can be understood in a way that's still meaningful without understanding the mathematics of it? Or would any attempt to try be just an oversimplification to the point that it wouldn't have any meaning?

SPEAKER 1: Well, I think one can try to understand it on the basis of analogy, always recognizing the imperfection of the analogies. For example, well, to take an example that played a very large role in the history of physics, we now know that there is a symmetry in nature, which technically is called translation invariance. But speaking very simply, it means that the laws of nature look the same wherever you happen to be.

The laws of nature, do not depend on how you choose what you're going to call the 0 of your system of measuring latitude and longitude and up and down. And to us, that's very natural. But it's taken a long time to realize that. If you live on the Earth, then it just doesn't seem that that's true. The Earth pulls you down and the stars are up there. And for thousands of years, people thought there was a different physics in the celestial sphere than here in our dull, sublunary world.

Well, we now know there isn't, that in fact, it's all governed by that symmetry, the symmetry of translation invariance. Now, that symmetry is in a sense a broken symmetry. It applies to every atom in the Earth. Every atom of oxygen or silicon or iron in the Earth undergoes an interaction with every other atom. And the law that governs that interaction is completely independent of where the atoms are. Two atoms of oxygen, whether they're here or on the other end of the universe, will attract each other or repel each other in exactly the same way.

And yet the Earth manifestly breaks the symmetry. The Earth is here. It's not there. So we've always, in science, been going through this process, often with tremendous difficulty, of trying to see behind appearances and see an underlying symmetry. And in the case of translation invariance, although normally people don't call it that, this is something now that has become part of everyone's way of thinking about nature.

I think most people now have firmly embedded in their minds the idea that the laws of nature are pretty much the same wherever in the universe you happen to be. Most people now don't think the Earth is at the center of the universe, but that took a long time in coming.

SPEAKER 2: I'm interested in the idea that you have to see beyond appearances to the reality. Because I know that in other fields than science, in, say, sociology or even in certain areas of philosophy, there is a theory that the only things that exist or at least of whose existence we can be sure of are the appearances, that it's somewhat idealistic in both senses to try and assume that there are laws governing everything.

I know politically also there's this sense of all, we can do is deal with one problem at a time. We can't make basic principles that a society is going to be built on or that a legal system is going to run on. The idea that everything has to be dealt with individually, that we can't have basic concepts, is this something that science contradicts?

SPEAKER 1: Well, it's a very good question because there is in fact an endless tension between, on one hand, our commitment of scientists really only to pay attention to things that have observational meaning, to only ask questions that can be answered by experiment, on the other hand, our desire and our temptation if you will, to make theories, very often theories which deal with things which can't be observed, as for example, many of us now think the quark, the fundamental particle which is the constituent of the constituents of the nuclei of atoms, not only cannot be observed with today's techniques but in principle can never be observed. Which tremendously tempted and find it very natural to make theories about these things, even though those theories cannot be direct--

Well, the theories can be confronted with observation, but the things we're talking about cannot be directly observed. It's a danger. But in fact, we always do go back and tie what we're talking about down to observation. And I think that's one great thing about physics and about natural science in general. And that is that no matter how woolly are speculations are, we do in the end have always the danger of being proved wrong by experiment. And it's only that feeling that experiment could prove you wrong that gives you the feeling that you're really saying something that isn't just woolgathering. And as to whether that's true in philosophy and sociology, I pass.

SPEAKER 2: Can I restate what you're saying as there's a sort of interaction in your observation between, on the one hand, the concrete, observable, direct reality of things and the abstraction of the law that you're trying to set up that applies to many things that's beyond the reality and that the way you figure out the interaction between those two things is through practice, through experimentation, through actual activity in the world?

SPEAKER 1: Yes, that's exactly what I would have said myself. And just to add one thing, we have to realize that we are somewhat accidental, that through a variety of circumstances human beings happen to be about 2 meters large and a tenth of a metric ton heavy. And we are used to certain perceptions. We think of things as having definite color, definite substance, definite composition. We have all kinds of intuitive ideas about the way the world works which are based on the particular size and shape and mass we happen to have.

In dealing with what's fundamental, we often have to go to levels which are either much larger or much smaller than the level-- than the scale on which we happen to live. And that means that increasingly we seem to be dealing with ideas that are counterintuitive, that are very strange, that cannot be expressed except mathematically.

And some people get the idea, I think, that we do this perversely, that we do it because we like to, because we want to get away from ordinary experience. As for instance, I think some people might have the feeling that we build accelerators to produce particles that have never existed in the universe except in our accelerators simply because we enjoy having fun and doing things that are as exotic as possible. And that just isn't true.

The laws of nature are what they are, and we're trying to get at them. And some phenomena are more relevant to them than others. And often the phenomena which are relevant to them are just not the phenomena which are relevant to us in our everyday lives.

SPEAKER 2: Tell me something about how you work as an investigating scientist, if you can. What are the steps of the process that you go through when you're working on a new idea?

SPEAKER 1: Well, I don't to what extent I am like others. I suspect I'm probably like a large minority of scientists. I think there are some scientists, perhaps Einstein, who make great magical leaps from one step to another in a way that can't be understood. What I do is worry a lot. I get something in my mind, which doesn't quite seem right but smells interesting. And I worry about it. I worry about it in the shower. I worry about it while raking leaves. I worry about it sitting at my desk.

Often I watch television at my desk just because I want to sit at my desk and not do anything else, but I don't have any calculations to do. All I'm doing is just worrying. And sometimes, I go on worrying and I never get anywhere. But usually I'm worrying about two or three different things at the same time, and one of them will gel. And then that's wonderful. Because when you begin to see the way out, then you have calculations to do and you can make theories and write papers and life gets very exciting again. And then you start worrying about something else.

SPEAKER 2: Now, when you say you're worrying about something, would this be something that didn't go right in an experiment and you're wondering how to explain it or?

SPEAKER 1: It could be. It could be. Sometimes, there are experiments that give results that are very paradoxical, and you worry about what that means. Very often the result, the answer is the experiment is wrong. And not to run down my experimental friends, but it happens often enough so that it's a possibility you always have to keep in mind. Very often, though, for me, it's an internal worry. I understand three or four different things in a certain area, but they don't quite jibe with each other. I can see a possible application where the three or four different things I think I understand would have different consequences.

So there's an inconsistency between them. I normally don't worry about that unless it smells like it might be important. There are, of course, grand problems that we all worry about. Why is the charge of the electron what it is? Why is the universe here? I mean, we all worry about those. But very often I worry about niggling little things that just don't happen to seem consistent in what I already know.

SPEAKER 2: And then those niggling little things can turn out to be the clues to grand theory.

SPEAKER 1: If you have good taste and good luck, they sometimes are. And more often, they don't.

SPEAKER 2: What is it about the process of this kind of investigation that you like? What keeps you going with all these worries and minor details that don't quite fit?

SPEAKER 1: Well, it really isn't fun. And I think some people say they do it for fun, but I wouldn't call it that. Because in fact, the period of worrying, which is the most important period, is agony. You're not doing anything. You're not sitting at your desk calculating beautiful mathematical expressions. You're really just wasting your time.

It is really just for those moments when things click that you do it all for. But it isn't that personal a satisfaction. Physics, unlike art or mathematics, I think really is a historical process. It is working toward a definite goal. And you're serving as part of that historical process, and that's very exciting. It is something outside you. You're not worrying as a painter does about where to put the next daub of paint. No one will ever be able to say whether you were right or wrong.

We really have ways of finding out whether we're right or wrong. And that wonderful interaction with the real world is one of the recompenses.

SPEAKER 2: I'm interested in this idea of your historical sense. Do you feel close to the physicists that have preceded you? Or are you very conscious that there will be physicists who come after you who will be looking back at your work?

SPEAKER 1: Yeah, I do feel that I-- for one thing, we feel part of a great tradition. I think that just as a member of, say, Reverend Jackie, who is speaking here, a member of the Benedictine order, and can look back to St. Benedict of Nursia and back to 500 AD, we also feel that we are members of an order, if you will, that has its great heroes and its great victories and its defeats. And that we feel a wonderful sense of kinship with the past and with the future.

When you really get down to it, though, it's often more frustrating. On one hand, looking back at the past, it's very hard to understand the work of the past. In fact, one of the best indications of how much scientific work shapes the way scientists think is that it's now very hard for us to read the great papers of the past because it's very difficult to put yourself in the mind of, say, a Heisenberg writing in 1925 and see what was bothering him. Why didn't he make the next step? Why did he make that step?

I find it almost impossible to read some of the great founding papers of quantum mechanics, although I think I understand the physics. Perhaps because I understand the physics, I can't read the original papers. On the other hand, looking toward the future. I suppose the only thing-- one thing you feel is resentment that the future scientists will know so much more than we do, and it's just not fair.

[LAUGHTER]

SPEAKER 2: The principle of trying to get inside someone else's mind in the past and that being difficult because you just can't see why he didn't know the right answer, because you know it, so it's difficult to understand how he didn't, do you ever apply that to yourself? Do you ever realize that you've been thinking along lines that prevent you from seeing the right answer just because you're so stuck in a certain frame of mind that you can't get beyond it to a new concept?

SPEAKER 1: Yes. Unfortunately, usually too late. There are some examples in my life, which I much regret. To take one, which I don't think I can explain the details of, there's a certain mathematical formalism called the functional formalism. Let it pass, whatever it is.

From the time I was a graduate student until about 1971, I felt that it was a waste of time, absolutely fruitless, that it was Wurtzel-Flummery. And then in 1971, it began to be apparent through the work of younger physicists, especially young men in Utrecht, that in fact, it was indispensable and that the next step, even in the very theories that I had been working on, could not be taken without it. And I had to learn it at the cost of some agony, mental and spiritual.

That has happened to me more than once, although that was perhaps the worst example. And I don't know what lesson one draws. Because in fact, one can't draw the lesson that you have to learn everything, because you can't learn everything. We're always in the position of deciding not to learn something, deciding not to read a certain paper. Not because we're narrow minded but because there's just too much to learn and too much to read to get anything done. Maybe Murray Gell-Mann can learn everything and read everything, but I can't.

And for that reason, we always have to make these decisions of closing our mind to certain things. And too often, those decisions are wrong.

SPEAKER 2: This seems to me to be the closest kind of integration between a scientist's thinking and the thinking of people who are not scientists in that that seems to have all kinds of political and social and historical applications that extend to science. OK, if you are a medieval scientist and you believe that the world works a certain way and God and religion set up certain laws, it seems to me that that's going to affect your thinking even about things that could later be tested in fact, such as how the universe really does work, as opposed to social ideas, which are later considered to be wrong but can't actually be proven.

I guess what I'm trying to get at is that it seems that science is one of the things that shapes the general picture of how we look at the world. And that's something that goes into our thinking about all kinds of systems, not just physical ones but also maybe social ones. A simple universe might suggest that we could have certain basic social principles. A complex universe that human beings can never hope to even understand might suggest that we have societies that we really can't control. Does there seem to you to be any correspondence there?

SPEAKER 1: I think it's certainly very wrong to try to draw lessons from the detailed contents of natural scientific discovery for ordinary human life or social science. There have been people who've tried it, such as Herbert Spencer, who tried to make a kind of physics out of society. And it just doesn't work. In fact, a friend of mine once said that he thought it was a good idea for the social scientists to try to pattern themselves after a physical science, but they chose the wrong physical science. They shouldn't have tried to use physics as the model but they should have used meteorology. Because the uncertainty of weather is much more like social systems than the beautiful simplicity of physics.

On the other hand, I think it's true, and in fact, I'm convinced of it, that the general bulk of scientific discovery can't help but change the way people think about the world. At the simplest level, we do not see the world as mysterious anymore. We certainly don't understand everything, but we understand an awful lot. We know the causes of things.

We don't know exactly why it'll rain tomorrow, but we in general why rain occurs. We don't know exactly how the continents will form, but we have a pretty good idea more or less. Even perhaps the most difficult problem of all, of how the brain is able to think, is yielding to this analysis. With lots of holes, we have an idea that there are no mysterious effects without causes. And that, I think, is the most profound revolution in human thinking. We don't have to look in a supernatural world for explanations of what we see around us.

Now, that doesn't necessarily imply anything about what conclusions we draw about the supernatural world, but it can't help affecting it a bit. I think even beyond that, the way the scientist operates, which has changed over the centuries-- scientists now are not what scientists were in Newton's time. Science itself has changed the scientific method. But the scientific method, as it is changing, is continually serving as a kind of model of human thinking. Not the only model, but it's one way that human beings can think about things.

SPEAKER 2: What is that model and how do you feel it's changed?

SPEAKER 1: Well, I think what the model is is a problem that philosophers endlessly debate about. To try to really define the scientific method has proven much more difficult than to do science. And in fact, remarkably enough, one can do science without having a very clear, explicit statement of what the scientific method is.

We all know roughly what it is. It's paying attention to observation and thinking things through logically and not believing in things just because they make you happy or because someone told you to believe them but because you've checked them against observation. There's a lot of theory in it. There's a lot of building hypotheses and then verifying them or refuting them by observation. And there are all kinds of ways of saying it, and I'm not sure of the right way of saying it.

But it doesn't really seem to matter how one says it. One knows what it is. I mean, I don't know how to define a giraffe, but I think I recognize a giraffe when I see one.

[LAUGHTER]

The changes have been considerable. Certainly, people thought about it in a different way. The ability of theory, for example, to deal with things that are not directly accessible to observation, like quarks for example, and yet not to depart from this ideal of always checking against observation is something I don't think that could have been imagined a century ago or earlier. And another huge difference is-- I think it's new to this century is the sense of the all-embracingness of physical science.

That is that there is not a separate law-- science of chemistry and a separate science of physics and a separate science of biology, but they're really just science. And within science, there are separate principalities which, for reasons of convenience, often overwhelming convenience, have to work under their own laws. But there really is only one science.

SPEAKER 2: Something that I think people have really gotten frightened about in the latest developments in science, at least the latest as the general public is aware of them, are two kinds of principles that are sort of related. And it seems to me that you're saying that science has in a way gotten beyond the myths that came out of this. I'm talking about relativity and about the idea that the world is so complex and so mysterious and so detailed that we're never going to really be able to say that we understand it.

And then of course, relativity says and even if we do understand it, it's going to be different somewhere else. Those are the popular misunderstandings, perhaps, of those scientific principles. It sounds like you're saying that that's not the right attitude, that a person who understands science believes that human beings can understand their world can even control it or at least work with it to some extent and don't have to feel that relativity or the principle of the mystery of science or whatever negates our own ability to control our lives and to control our world.

SPEAKER 1: Well, as to relativity, it is after all a principle of simplicity. I mean, the principle of relativity is that the laws of nature are the same no matter how you're moving, as long as you're moving in a straight line and constant velocity. That was true, incidentally, before Einstein. And what Einstein did, technically speaking, was to restore that to being true after for a while it had seemed not to be true.

The other principle that you're talking about, the principle of the complexity of nature, I don't really know what you're referring to except I suspect you may be referring to quantum mechanics. And there again, I don't see complexity but rather simplicity. It is unfortunately a simplicity which is very far removed from ordinary experience.

Quantum mechanics, much more so than relativity, challenges ordinary human intuitions about the way the world works. And it's something you just have to get used to. And it is probably the biggest bar to communication between scientists and non-scientists that exists now. Actually, the younger generation of scientists growing up find it much more easily to think in quantum mechanical terms and sometimes have trouble thinking about ordinary classical physics, which just shows that human nature is infinitely malleable.

But taken together, quantum mechanics and relativity in fact don't give a picture of a complicated world but of a simple world. And I would say simple in a wonderful, logical sense. Quantum mechanics allows you to imagine a great many possible universes, including very complicated ones. So does relativity.

But if you put them together, you find that they are nearly logically incompatible. And as a result, just as a mathematical exercise, which we haven't yet quite been able to finish, but we can see sort of see the shape of it-- as a mathematical exercise, one can deduce from quantum mechanics and special relativity taken together everything else.

Now, that's the real simplicity. The real simplicity is not how many quarks there are or how many kinds of interaction there are. The real simplicity is the logical simplicity, whether or not from a few principles you can deduce everything else. And I think that looks more hopeful now than it ever has in the past.

SPEAKER 2: This is a qualitatively different stage of science then than we've ever known before in human history.

SPEAKER 1: I think it's been moving in this direction for a long time. And in fact, the physics that we now are working with, quantum mechanics and special relativity, was more or less complete by 1930. And I think what has happened in the last decade or so has been the realization of how powerful those principles are.

It is a remarkable development, but I think it's been going in this direction for a long time. And I hope it will continue to go and that it will reach some kind of fruition during our lifetimes.

SPEAKER 2: And then human beings, for the first time in history, will be able to say that in some sense they've understood the totality of the universe or understood a part of that totality?

SPEAKER 1: It's hard to even imagine saying that. Somehow or other, I find myself just stopping short of that point. And I can't conceive of really understanding things that well. And yet, we're moving in that direction. And everything we do, we do as if we thought we were going to reach that point.

So I don't know. That's a mystery to me. What will things be like when we understand that much? Is that possible? I don't know.