09/23/2016

Of Fashion, Faith, and Physics

16:16 minutes

An artistic representation of a wormhole, via Shutterstock
An artistic representation of a wormhole, via Shutterstock

In his new book Fashion, Faith, and Fantasy in the New Physics of the Universe, theoretical physicist Roger Penrose argues against the widespread attention given to some prominent theories about the universe, including string theory. Some ideas in physics, he says, are merely fashionable, attracting attention without solid experimental support. He also criticizes physicists who seek to apply quantum theories too widely to the macroscopic world, and takes aim at the idea of cosmic inflation.

Segment Guests

Roger Penrose

Sir Roger Penrose is author of Fashion, Faith, and Fantasy in the New Physics of the Universe (Princeton University Press, 2016). He is the Emeritus Rouse Ball Professor of Mathematics at the University of Oxford in Oxford, United Kingdom.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. You know, there are lots of theories about the way the universe works. And while some of them complement each other, they can’t all be true. You have your classic weirdness of Einstein’s relativity, there’s the newer weirdness of string theory, and all sorts of theories of theoretical physics and cosmology that seek to answer the questions where the universe came from, how it works, where might be going.

My next guest has done a lot of thinking about all these different theories. And some– he’s not such a fan of some of them. He even admits about having his own crazy model of the universe. Sir Roger Penrose is professor of mathematics at Oxford, author of the new book, Fashion, Faith, and Fantasy in the New Physics of the Universe. Welcome back to the program, Dr. Penrose.

ROGER PENROSE: Hello. Good to hear you.

IRA FLATOW: Your book takes issue with three very prominent theories– string theory, quantum mechanics, and cosmic inflation. Tell us about the problems you have with them.

ROGER PENROSE: Well, string theory– I don’t mind the strings. In fact, I rather liked the idea when I first heard about them. The problem is more the fact that string theorists found themselves driven to have a space which had– well, initially 25 dimensions, and then 9 dimensions. And I found that rather discouraging. I didn’t believe that for various reasons.

IRA FLATOW: Mm-hmm. And cosmic inflation– you really– you come down very heavily against that. It’s the winner of a Nobel Prize, is it not?

ROGER PENROSE: No, not unless it’s from winning this year. [CHUCKLES]

IRA FLATOW: Well, didn’t Alan Guth– didn’t he win a Nobel Prize?

ROGER PENROSE: No, that hasn’t. There’s always the possibility that it might win. But it’s certainly become a significant part of current cosmology. The belief is that in the very early stages– a tiny, tiny fraction of a second, the universe indulged in what’s called an exponential expansion, and this stretched everything out to an enormous degree. And it was supposed to explain certain things originally.

And my trouble with it originally was that I didn’t think it actually did the things that was supposed to do, for various reasons. It doesn’t actually stretch the universe out. But it does do other things– which, if it’s true– there are certain puzzles. If it’s not true, you have to have something else which does it. These are puzzles to do with the cosmic microwave background, this radiation, which is coming in all directions– microwave radiation, electromagnetic, coming in from all directions.

And there are certain observations about it which are hard to explain without inflation. So the reason that inflation didn’t just die– wasn’t stillborn, in my view, is that it actually turned out to explain various things which weren’t part of the original idea behind string theory. I’m behind inflation theory.

IRA FLATOW: You have your own model called the twisters, a concept you called my own crazy-looking cosmological model.

ROGER PENROSE: Ah, but the twisters are nothing– well, we don’t know yet– nothing to do with the cosmology. That’s something– not exactly an alternative to strings, although that’s the chapter heading– it’s a direction you might go in if you don’t like strings, or, in fact, if you do like strings. Because there is a version of twister theory which involves strings as well. But the problem, as I said before, that I have with strings is not the strings, but that the string theorists found themselves needing more than three space dimensions, whereas twisters are very much bound up with having three space dimensions.

IRA FLATOW: Do twisters solve the problem of uniting Einstein with general relativity with the quantum world?

ROGER PENROSE: They don’t do anything like that yet. I mean, of course, one of the reasons behind the idea is that they might eventually do this. But it’s more that– most people, when they think about uniting quantum theory with gravity or general relativity, they think of what’s called quantum gravity.

IRA FLATOW: Right.

ROGER PENROSE: The trouble is quantum gravity, to my mind, is the wrong thing to do. Because quantum gravity implies that you’re using standard quantum theory or quantum field theory, and applying it to gravitational theory, or Einstein’s general theory of relativity. Whereas, in my view, the union between these two great schemes will be something with give on both sides, so that quantum theory has to give, as well as the idea of space-time coming into accordance with quantum principles. The quantum principles themselves will have to change.

IRA FLATOW: Mm-hmm. You talk about how difficult it is for new theories to be accepted by scientists.

ROGER PENROSE: That seems to be very true.

IRA FLATOW: Tell us about why that is so difficult.

ROGER PENROSE: Well, I think the communities get very much interconnected with each other. And if a problem arises– I mean, think of the string theory community– there are certain problems which are accepted as being problems, and then they will figure some way around it and then go a little further, and the whole thing gets a very sort of tightly knit community. And if you introduce something which goes against that view, it’s not been going to be looked upon very kindly by these people because they’ll have to change all these things that they’ve been doing.

And I think that’s one of the reasons that– that’s the fashion aspect of it. Fashion is something which keeps people going along the lines that they have been going along. And it may be that if there is some fundamental problem with it, they prefer not to look at those fundamental problems.

IRA FLATOW: Is that where the faith comes in? They still have faith in it?

ROGER PENROSE: It’s a bit like that, too. The faith, though, is not about string theory. The faith– my chapter about faith is about quantum mechanics. And I mentioned a minute ago about the give on both sides. Well, that’s basically it. And why do I say there’s got to be give on the quantum side? You see, unlike string theory, quantum theory has a huge amount of experimental support. See, some people complain about string theory and they say well OK, it’s all very well, but it doesn’t have any implications that we can measure experimentally.

That’s not really my objection to it, although that is an objection. My objection to strings is more that the higher dimensional idea doesn’t really make sense in the physical world in which we live. When it comes to quantum theory, the issue was pointed out by Schrodinger a long time ago with his cat. And the idea is that you have an equation– this is the Schrodinger equation.

Another way people refer to this as unitary evolution. And this is in quantum mechanics– see, if you have the state of the world as described by quantum mechanics, the quantum state, then that evolves in time by a very definite equation. And this is the Schrodinger equation or unitary evolution.

And the trouble is, with that equation, as Schrodinger was clear to point out, that you could easily have an experiment in which a cat was dead and alive at the same time. And that’s ridiculous. That was what he was more or less saying. So he was arguing that there needs to be something else which goes beyond the evolution that he had put forward, the Schrodinger equation. And that is a change in the rules of quantum mechanics that we presently understand.

IRA FLATOW: Do we know what that change is or it needs to be, or how to get around it?

ROGER PENROSE: Well, those of us who believe there should be a change don’t necessarily agree about what the change should be. But the change, in my opinion, has to be when gravitational effects become significant. And this can be at a very tiny scale– that you might think it was tiny. I mean, there is an experiment, for instance, which is being worked on by [INAUDIBLE] and his colleagues in Leiden and the Netherlands and in Santa Barbara in the US. And they’ve been working on an experiment, which puts a little tiny mirror– this mirror is about a tenth of the thickness of a human hair in diameter– and this mirror would be put into a superposition of two different locations.

So we know in quantum mechanics that particles can be two places at once– this strange idea. But you have to believe that sort of thing if you explain things like the two said experiments in very many fundamental experiments in quantum mechanics. We know it happens with the individual particles, that they can be two places at once, but we don’t believe that it can happen to cats. So where’s the dividing line between the two? Well, it’s not quite a dividing line like that, in my view. But it’s something about how long these two positions can last.

So in this experiment by [INAUDIBLE] and colleagues, you try to put this little mirror– as I say, a tenth of the thickness of human hair– into a superposition of two different locations. But they’re not very far apart. They’re only about the diameter of an atomic nucleus apart. But you hold it there for as long as you can. And the idea, on the scheme that I’m trying to promote, you can only do this for a matter of– depending on details, a few seconds or a few minutes. So this is within the capabilities of current experimentation. It’s not quite there yet, but I would expect that within the next decade they will have an answer to this question.

IRA FLATOW: Mm-hmm. You also take on our idea of the multiverse, the many– unlimited number of universes that we may be living in. Do you think that’s–

ROGER PENROSE: Yes, one of the reasons people go to this kind of view comes from quantum mechanics. You see, if you think about the cat again– you see, the view would be no, no. The cat has to be in the superposition position of alive and dead. In my book, it’s not alive and dead. I have the cat going into a room which has two doors, and the doors are– one of them– and the other one are open– only one is open, but it’s a superposition of one being open or the other. And it’s like a two-slit experiment but with doors and cats. And the cat goes to some food inside the room.

And you would think well, a cat either goes through one door or it goes through the other door. But quantum mechanics says it would be in a superposition of going through the two doors. And why is it that you don’t see this sort of thing? Well, the many worlds explanation is that well, if somebody is watching the cat and seeing it come through, well, whichever door, there would be one person seeing it come through door a, and the same person, I should say, seeing it come through door b. But these two instances of the same person would then be thought of as inhabiting two separate worlds.

So somehow the world is viewed as splitting. When I say the world, that’s the universe would be viewed as splitting into two versions of it, one which would have the cat going through door a, and the other, which would have the cat going through door b. And so that’s the way they understand this particular conundrum. And the thing is, that’s the faith. People believe oh, no. You mustn’t monkey with quantum mechanics. The rules that we understand have to be held too at all scales. And if you believe that, then yes, you’ve got to believe that the observer of the cat is somehow split in two and inhabits these two separate worlds simultaneously, and the experience of the observer somehow splits in two.

I’ve always found this is a reductio ad absurdum. And Schrodinger himself, as I say, pointing this out as a contradiction to experience. And not just Schrodinger, I should say– three hours of the fundamental people who founded quantum mechanics– Einstein, De Broglie, and most surprisingly, perhaps, Dirac, who was the one who formulated the rules that all quantum mechanics people use. And he himself is on record– and I have a quote of in my book where Dirac actually says this, that quantum mechanics is a provisional theory.

IRA FLATOW: Yeah.

ROGER PENROSE: And we’ve got to be prepared for a better theory to come along in which the world does not split in this way, because that’s an absurd contradiction. I mean, there are other people who believe it does split, and that’s the view you are referring to, the many worlds interpretation of quantum mechanics.

IRA FLATOW: Talking with Sir Roger Penrose, professor of math at Oxford, author of the new book Fashion, Faith, and Fantasy in the New Physics of the Universe on Science Friday from PRI, Public Radio International. Do we need a new physics? Do we need–

ROGER PENROSE: Well, I think we do. Yes. Certainly– well, you see, people– if they believe that quantum mechanics– a new physics, of course– string theory isn’t really an accepted theory of physics in the sense that it doesn’t make predictions that can be measured currently. Quantum mechanics makes many such predictions.

IRA FLATOW: And they’re very accurate predictions, right?

ROGER PENROSE: Indeed. But none of them reach this sort of level of mass displacement. There are quantum experiments, which, I think the current record is 143 kilometers. So it’s not a question of distance. You can have quantum effects which straddle at least that distance [INAUDIBLE].

IRA FLATOW: That’s the [INAUDIBLE] at a distance concept.

ROGER PENROSE: Yes, it is. That’s exactly [INAUDIBLE].

IRA FLATOW: That’s how apart we’ve observed it happening.

ROGER PENROSE: That’s the current record of– there are also experiments where you observe stars. And then the distance between one edge of the star and the other, you get interference effects, which mean that the photons that come to you from those two extremities of the star are automatically entangled with each other. This is part of the framework of quantum mechanics.

IRA FLATOW: Are you then saying that we need a way to explain the macro world and the quantum– this tiny world of quantum mechanics with one overarching theory?

ROGER PENROSE: It’s not as though you have a different theory for each. You have a theory which involves– and in my view, it will have to involve [INAUDIBLE] relativity. So it’s when the curvature of space-time starts to become significant. And I have a crazy-looking picture in my book, which is showing the– if you move a rock into a superposition of two locations, then the space-time goes with it first, and then there’s a point at which one of them has to be chosen over the other. And that happens in a calculable time scale,

IRA FLATOW: How do you get people to– if you say it so hard– and one of the things you point out in your book is that because some of these issues are so ingrained in the scientific community, it’s hard to get resources– money– to investigate these other ideas. Who’s going to get a graduate student to work on some of these new Ideas?

ROGER PENROSE: [CHUCKLES] You’re dead right. It’s very hard. I mean, I find this particular– not so much with the quantum mechanics, because I haven’t been trying to do this experiment. It’s, as I say, people in the Netherlands and in Santa Barbara, and there is money to do that experiment. Whether more would help them do it quicker, I have no idea. But things where I notice the difficulty of getting funding is for the cosmological scheme.

You see, the third topic is the fantasy one, which, as you say, I’m not so happy with inflation. And I think inflation can’t be right. Well, it’s a very artificial theory. I have a picture where you see all the different curves that people sort of draw by hand, more or less, in order this particle, referred to as the inflaton which nobody has really observed or anything, but is supposed to be what is responsible for the inflationary scheme.

IRA FLATOW: So Roger, I’ve run out of time.

ROGER PENROSE: [LAUGHS]

IRA FLATOW: Yeah, we could go. Your book is what, 600 pages? Something like that?

ROGER PENROSE: Read the book then, yes.

IRA FLATOW: Sir Roger Penrose, professor of mathematics at Oxford, author of the new book– this will get you to think very carefully– Fashion, Faith, and Fantasy in the New Physics of the Universe. Thank you for taking time to be with us today.

ROGER PENROSE: Thank you very much.

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