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January 19, 1999

Sir Roger Penrose: A Mathematician at Play in the Fields of Space-Time


The impish man sitting in a warren in a remote corner of the mathematics building at Oxford University in England is Sir Roger Penrose, 68, mathematician, physicist, author, teacher, perhaps one of the greatest living disciples of Albert Einstein. In the 1960s, Penrose laid much of the foundation for the modern theory of black holes, objects so dense, according to Einstein's theory of general relativity, that they would collapse space around them, creating a hole from which not even light could escape. He is also the inventor of so-called Penrose tiles, which can cover an infinite plane without ever repeating their pattern.

Jonathan Player for The New York Times
At Oxford University, Sir Roger Penrose, mathematician and physicist, held forth on Einstein, the shape of the universe, quantum theory and chess masters versus I.B.M.
Americans know Penrose from his books on scientific questions, including "The Emperor's New Mind" (Oxford University Press, 1989), which criticizes the idea of artificial intelligence, and "The Nature of Space and Time" (Princeton University Press, 1986), which he wrote with his friend Stephen Hawking.

Q. In the last year, there has been an accelerating pace of discoveries in physics and cosmology? Which have impressed you most?

A. Some of the most impressive things, I think, are pictures the Hubble telescope has sent down where the gravitational lens effects have been observed. This is the bending of light through Einstein's theory of general relativity, which tells you that light is bent by a massive body such as the sun. The sun bends light and acts as a lens. You can detect distributions of mass this way. You may not be able actually to see the mass in this big galaxy, but if there are other things behind it, you can see its lensing effect.

Q. Were you surprised by some of the recent discoveries confirming the existence of black holes?

A. "Surprised" would be a little too strong. I think recent evidence is pretty potent that black holes are there. For a long time, the evidence was rather indirect. But you knew there was an object out there that was too massive to be anything else.

Q. So how are you voting on the shape of the universe?

A. Well, there are three main models. One, is positive spatial curvature -- that the universe is like a huge sphere. Two, is zero spatial curvature -- a so-called flat universe. Three is negative -- "saddle-shaped" spatial curvature. I go with saddle shaped. For a host of reasons, I think that's the most likely. And the evidence is in fact shifting toward that. The universe seems "low density" and therefore of negative spatial curvature.

In terms of new discoveries, what I wouldn't like is the cosmological constant -- the mysterious cosmic repulsion Einstein inserted into his equations to keep the universe stable -- being non-zero. I've worked in General Relativity for most of my life and there are aspects to the theory, which when you don't have the cosmological constant, are much more appealing -- at least to me.

Now, if they find that, yes, there has to be a cosmological constant, I'd have to go along with that. I'm not saying that I've closed my mind to it. I would just prefer the cosmological constant not to be there.

Q. And if the cosmological constant is there -- what does that do to your work?

A. Complicate it! (Laughs.)

Q. You seem to have a good capacity to live with being wrong.

A. Well, a scientist should have. If I'm really shamefully wrong, I have to adjust.

Q. When you're doing some way-out mathematical computations, do you sometimes feel like an explorer?

A. Oh, yes, but also like an archeologist. You are looking for clues that are sort of lying there, hidden. And you see different forms of what may be underneath there and you see some of the corners and you have a sense that there may be some structure that may have influence on various different areas. Then you dig away until you can find what the structure is.

Q. There was a debate in this newspaper last fall, "the end of science." Do you agree with those who argue that when it comes to physics and mathematics that we know just about all that can be known?

A. The argument is that accessible, important ideas will run out, that either we'll never understand certain things or we have already understood them. This is an absurd position to take. People have been saying that for centuries.

I can think of a least one major area, which I'm absolutely sure is missing from the present-day physics, which probably will come in the next 50 years or so, and it will be a tremendous revolution. It has to do with how to understand quantum mechanics. See, quantum mechanics describes small-scale phenomena -- atoms, molecules, particles. And if you have certain rules, which if you try to apply them to large objects, they give you nonsense. They will tell you that a baseball can be here and there at the same time.

There are endless ways that people try to argue around this. But to me, it says that the theory is just not right and that there is a level that things go over from the quantum to the classical. I think one can make good estimates as to what level that is. And I even have proposals for experiments, which I hope will be performed, which would tell whether this is right or not.

Q. Among many physicists today, the leading candidate for Einstein's dream of a unified "theory of everything" is the theory of superstrings, based on the notion that elementary particles are not points but strings?

A. String theory is an example of science being driven by fashion. And I have mixed feelings about it. Some of the mathematical notions which people associate with string theory are very appealing. But just because they are appealing doesn't mean that they are right. In a book I'm trying to write now, I want to talk about all these theories, including my own baby, twistor theory -- a mathematical scheme for re-expressing the structure of space-time in which individual points are not regarded as the fundamental things, but entire light rays are taken as more fundamental as individual points. Sorry. I can't explain it in a less complicated way. My point in the book will be that twistor theory certainly hasn't solved some of the problems that I thought it would, but it's very much alive.

Q. Ten years ago, in "The Emperor's New Mind," you said that computers were not likely to ever have consciousness -- that all they could do was merely "compute." With all the recent advances in computer technology, do you still feel that way?

A. Yes. A computer is a great device because it enables you to do anything which is automatic, anything that you don't need your understanding for. Understanding is outside a computer. It doesn't understand. Whereas to know what the calculations are supposed to do, what the answers mean when it's finished, requires your understanding and that's complementary to the computation.

And the understanding aspect of it, is something that requires one's awareness, consciousness. If you didn't have consciousness, you couldn't understand. The strong artificial intelligence people feel that consciousness is some kind of "emergent" phenomena; it's something that just comes about.

Q. Why do you think some of the artificial intelligence proponents seem to have such a stake in the notion that a machine can outthink a human being?

A. I think that one reason is that people really cannot think of anything else which they would call "scientific." And these computing devices are tremendous and they can do computations in a fantastic way. But the artificial intelligence proponents think that's all there is. They think that a scientific theory has to be computational. If you come from mathematics, as I do, you realize that there are many problems, even classical problems, which cannot be solved by computation alone. Another reason is people get work, they get grants, they publish papers and they want to get more money. So they don't like my coming along and saying, "No, no, there are limits to what you can achieve this way."

The third is, it's a bit like religion. The question of what the mind, what consciousness is, is related to what people want religion for. Some religious people feel happy with a certain viewpoint and they don't like to be challenged. These artificial intelligence people are somehow happy because they have a model that they are content with and they don't want somebody coming around that disturbs that.

Q. In the match a while ago between IBM's "Deep Blue" computer and Garry Kasparov, whom were you rooting for?

A. I was rooting for Kasparov, human chauvinist that I am. I'm not sure that he was the right person to play the match. Because he depends too much on being brilliant. I think Karpov, who plays more consistently, but not so brilliantly, would be a much better person.

Q. So you don't think that anyone will ever be able create computers with emotions?

A. No. I believe there is something going on in a conscious being, which includes many animals, as well as ourselves, that is not a computational activity. And to be conscious at all is not a quality that a computer as such will ever possess -- no matter how complicated, no matter how well it plays chess or any of these things. It doesn't mean, on the other hand, that somebody sometime in the future could not build some kind of a device, NOT a computer, which did whatever we do. I'm saying we won't get at it through computation alone.

Q. What are you working on now?

A. Two major research areas. The first is twistor theory, and more specifically, in developing its relation to Einstein's general relativity, which I think is key. Once that connection is made clearer, then the hope is, it will give good leads on how to combine general relativity with quantum mechanics. There's a big gap there. If twistor theory can incorporate general relativity then it will give leads on how to unite general relativity with quantum theory.

The other thing I'm working on also has to do with the measurement problem in quantum mechanics. It's the link I mentioned earlier between the small scale and the large scale -- and the possibility of experiments that will show the limitations of present-day quantum mechanics. This is an experiment that I hope will actually be performed in space. It's much more directly related to observation than twistor theory, which is mathematical. If the experiment comes out the way I hope, it will tell us we need a major revolution in quantum mechanics.

Q. You have toys here in your office. Why?

A. (Laughs) Science and fun cannot be separated.

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