Transcription
I think this is too often in physics. People who think a certain area is very beautiful mathematics and therefore it's got to be true of the physical world. And there is a big branch and perhaps I shouldn't be rude enough to mention what this main branch is in that area, but there is string theory.
[laughter]
I do mean string theory. There is a lot of feeling that this must be the basis of physics because it's such beautiful mathematics. And I say that's not a good guide at all. Just because you think the mathematics is beautiful in certain respects, sure. But that's not a good guide in itself.
[applause]
Well, thank you very much and so it's it's a huge honor to be here talking to to Roger. I thought I'd begin by saying that when when I was an undergraduate, so I started doing physics at Manchester in 1992, I think it was. And one of the first books I read to prepare me for my undergraduate physics was The Emperor's New Mind. And I think we might talk about consciousness later on, but the two things that really stuck with me was that book gave me my picture, my default picture of quantum mechanics, which I've always carried with me. But also it for the first time I think made me think about mathematical beauty. And I remember so vividly reading about how you describe complex numbers and the fact that mathematics is beautiful. So, could you talk a bit about that idea that mathematics is a beautiful thing and also mathematicians have a have an aesthetic sense?
Well, I think that what drives people to do mathematics is certainly I mean, beauty. But it's a particular kind of beauty which I suppose which has a purity which you don't find in other areas. I mean, lots of things are beautiful, but they're sort of complicated and arbitrary in a way. But, what's so special about mathematics is it has this a very I don't know quite the right word to describe it, but it's pristine, I suppose word that one might use. It's uh it's a very kind of pure kind of beauty. And some people just don't feel it. I think it's true. I don't think one should be rude about people who don't see the beauty in mathematics. I find that sometimes it's rather the opposite to find people who do see the beauty in mathematics, which maybe is a little strange in a way. So, I find myself to be a little strange in that way, too. So, I'm not sure I can answer your question. I mean, there certainly is a beauty in the subject, and that is what drives mathematicians to do mathematics. Or it drives physicists often to do mathematics. And then it's certainly a subject which
You see, when I was at school, well, I should say this was when I was in Canada because during the war years, we we the family went and lived in Canada, sort of getting out of the way of the war, which good in other ways. But, anyway, no, it was a lovely time in Canada, and I remember I didn't do very well in my mathematics tests. And I just No, I didn't get very high marks at all. I got low marks. But, one of the teachers was very insightful, and he realized, looking at my papers, that it was not that I was very stupid, but that I was very slow. And I it took me a long time. I think I just didn't know my tables very well. I had to work them out each time, you see. But, I knew how to work them out, so I thought it was good enough. And so, I didn't know instantly how to do it. And I think he was a very good teacher and he realized that if I was allowed to take as long as I like and I remember sitting in the class and then there was a play period afterwards and I looked out of the window and I could see all these people having fun out of the window and here I was slugging away still working at this test. And maybe even the tip of the they the whatever came after the play period occasionally I leaked into that one. But then I would do very well. I get into the high 90s, you see. Whereas before it was I would, you know, 30% or something. Fail. So he realized I was just slow. But I think it was slow in a curious way because I I knew the ideas but I couldn't sort of even even then maybe not what 7 * 7 was or probably that one was fairly easy because it's a bit more distinctive than some of the others. But um no, I was not very good at even doing the arithmetic.
And we were talking just before we came on about Dirac. So you you knew Dirac very well and um I remember Dirac saying that um the beautiful mathematics is often used by nature. But I I remember reading The Road to Reality you disagree with that to some extent that nature doesn't necessarily select the most beautiful mathematics.
>> I think it's hard to know, you see. I mean you find it's beautiful when it works afterwards but you may not see why because sometimes the beauty doesn't come in till much later. And you actually see how these things fit together in a way that you've never seen before. So you can't sort of judge it early on to see whether that I don't what mathematics applies to physics. We don't know yet. I mean we know some of the things that I certainly what attracts me in how mathematics applies to physics is in something which is a very beautiful area of mathematics and I think that's true. But then other people work on things which you don't look particularly beautiful to me at all. Maybe this is important in other ways. It can be just complicated. I don't know. There's no straight answer to your question, I think.
So, you don't think that beauty is necessarily a guide to the laws of nature don't have to be beautiful mathematics?
I think it's a misleading guide, you see. You're attracted and think I think this is too often in physics. People who think a certain area is very beautiful mathematics and therefore it's got to be true of the physical world. And there is a big branch Perhaps I shouldn't be rude enough to mention what this main branch is in that area. But there is String theory.
[laughter]
I do mean string There is a lot of feeling that this must be the basis of physics because it's such beautiful mathematics. And I say that's not a good guide at all. Just because you think the mathematics it is beautiful in certain respects, sure. But that's not a good guide in itself.
How >> So, I think that's the trouble there. How did you get interested in physics?
Well, I got interested in physics in a rather strange kind of way, I think. You see, I was doing mathematics at university in London, at University College in London. And I remember going up to visit my brother who was doing physics research at that time in Cambridge. And I went up to visit him for some reason. I've forgotten exactly why. And I had been hearing these talks on the radio by given by Fred Hoyle. Where he was talking The first thing was about the solar system or something. Got broader and broader. And then he talked about cosmology in the last one. And he said something which I didn't quite believe, you see. And I said to my brother, I said, "Look, I didn't quite believe what Fred was saying here." And he said, "Well, I don't know either. I'm going Sitting at the table over there is the person who will give you the answer. And this was Dennis Sciama. He was sitting by himself, un unusually, by himself at this table. And I sat down and explained my little problem to me to him. And he said, "Well, I'm not sure about that. I'll go and ask Fred." Fred Hoyle, that was. And
[snorts]
so Um but the thing was, apparently, I made an impression on on Dennis. And he thought this was a really quite an interesting question that I'd raised. Why did the galaxies disappear one by one when they went faster than light? So, I thought, "No, they didn't disappear. You will always see them, but they would fade gradually, you see." And it was quite a simple argument to see why they did that. But apparently, Fred had got that little bit wrong. And he said, "No, that's wrong." Because he was He was a steady state theory at the time that Fred was talking.
>> Well, you see, Dennis was a great steady state No. You see, I had one of my great admirations of Dennis was when the microwave background was discovered. This is the radiation which is permeating the whole of the universe at a certain stage. And this microwave background was discovered. And this showed, really, that the steady state model must be wrong. And Dennis, when he You see, he used to give lectures about steady state model. He had big screens and saying how wonderful it was. And when it was turned out to be wrong, he gave these lectures. And in first slide would say, "I was wrong." I was very proud of Dennis. Since I mean, I was I followed him very much in the steady state. I was a follower of that. And then when he changed his mind, I thought that was showing a real the right attitude to science. When you see you're wrong, you admit you're wrong. Absolutely. And I thought that was really impressive.
So, we You mentioned We mentioned string theory before. And everybody laughed at that. But in in terms of trying to look for a deeper theory, so let's say quantum gravity. Then of what do you think of that attempt?
Well, you trying to lose to think that. I thought well, it might it's got to be quantum gravity. But since you got to have something extremely asymmetrical in time. So, maybe quantum gravity is a very peculiar theory which is asymmetrical in time. And I went through several years of my life thinking that. And then I changed my mind. That's not the answer.
[laughter]
But I did that was my sort of solution. The quantum gravity had to be very peculiar time asymmetrical theory. And Big Bang was a quantum gravity which had this funny I says had to be time asymmetrical because the Big Bang was so very special. And all the singularities in black holes and all that are very very general. They're completely different. The ones in black holes are very very complicated with this conformal curvature going to infinity. Get going completely wild and these Russians have worked out what they might be looked looked at applying and so on. No, I I accepted all that. Nothing like what the Big Bang was like. So, there's something very peculiar about the Big Bang. It's not like any other singularity.
Oh, that's right. Because because probably the most fashionable approaches at the moment are to So, approaches like so-called emergent space-time where you essentially picture quantum mechanics as the base framework and you attempt to see how space-time would emerge from some underlying theory. It could be a network of qubits or whatever it is.
>> Eventually, I lived out of that phase. Did you? Because because that's what most not not most maybe but many physicists would would say today. Certainly with work on black holes and the black hole information paradox and so on. So, why did you why did you what do you say? Grow out of it?
I think the thing was to realize it was not a quantum gravity problem. That's the thing, you see. Because it doesn't I mean it If it were, you wouldn't get this huge asymmetry. And it's in your right in your face. It's not a subtlety. It couldn't be there in your face. But my sort of solution is to think that quantum gravity is a very strange theory, which is time asymmetrical. Well, I eventually lived out of that phase, my God, and thinking, "No, no, that's not the answer." So, my my answer is something which people still have trouble believing in, I have to say. Even though there is some remarkable new evidence. You know about this. This is the The the new evidence is this young lady who in uh University of Yorkshire or something There was she. And she made a remarkable discovery. Very recently, the last couple of years ago. Of this huge ring in the sky. A very, very distant galaxies, which form this beautiful circular ring. And another one, which is a big arc, and that she showed me is probably really a circle, too. Not quite the same center. This ring and this arc And now she's found a third one. So, what are these huge rings doing? Where do they come from? They're so big that there's no time for anything within the standard model of cosmology. They'd have to be right in well, before the Big Bang. And that is not what people think. There shouldn't be a before the Big Bang. But then I said, "Haha, that's nice, because my theory says there was a big before the Big Bang."
[laughter]
So, I'm very keen on her ideas.
[laughter]
We've had good chats after that. No. No. So, essentially is there a way of explaining in a a couple of minutes so the idea how does So, our universe is expanding, dark energy is is driving that expansion and dominating it. So, the standard cosmological model is that goes on forever and you have a heat death at some point. So, how does that map on to a new uh eon, let's say? Absolutely amazing galaxies. The key point has to do with mass. How do I put this now?
[snorts]
You see, the space-time metric is a thing which has 10 components. At any point there is 10 numbers which define what the metric is like. Space the curved space geometry of Einstein needs this thing which is called the metric. And the metric has 10 components. Now, nine of these 10 components I should really say that the nine independent ratios of the 10 components are describing what the light cone is doing. The light cone tells you what light does. So, you see you follow a point flash of light here, as time evolves, it becomes a sphere which goes out and that's the light cone. Now, that is 9/10 9/10 of the geometry of space-time. What is the remaining 10th? The remaining 10th is one number. That number is thing that you get by combining the two most famous formulae of 20th century physics. One of them, of course, Einstein's E = mc squared, energy and mass are equivalent. The other one is Max Planck's E equals H new or HF. Energy is frequency. So, that tells you that mass and frequency are equivalent. So, that if you want a clock, that's a frequency. In other words, to have a scale of time or a scale of space, which is the same thing basically, you have to have a mass. If you don't have mass, you don't have scale. So, that's the key point. Where don't you have mass? Well, one place you probably don't have mass is in the remote future. Pretty well photons. It's more complicated than that, but that's the main story. What is there? Well, there are gravitational waves, too. They don't have mass, either. Photons. They just go out. They don't have any mass. So, in the remote future, there is no mass. So, it forgets how big it is in a certain sense. How about the Big Bang? That's the other place where you forget mass, because the energy is so enormous. The closer and you go back into the Big Bang, the less important the mass of particles become. They're effectively massless for a completely different reason. And so, they're massless at the Big Bang, they're massless in the remote future. So, the key idea is that those both ends you don't have any mass. And so, therefore, the geometry is the geometry of conformal physic conformal geometry, which is a very beautiful geometry. I used to play with it when I was before I went to university. Geometry of circles and things like this. Now, it's a really lovely kind of geometry. You don't have scale, but big and small are equivalent. Uh but angles are important and those sorts of things. So, velocities are important, I suppose, but you don't actually have the scale. And then, if you don't have a scale, where don't you have a scale? At the Big Bang, in the remote future. So, what I'm saying is the Big Bang is really somebody else's remote future. It's an eon, I call it an eon, a cosmic eon. Our cosmic eon started with the Big Bang. It ends, in a certain sense, with the remote future. And then you draw a picture which stretches out the Big Bang, squashes down the remote future, and you have a nice picture of the entire history of the universe. And then you can stick that on to another picture. It's generally the same as the previous eon. And in the previous eon, there were galaxies, galactic clusters, and all this stuff. And every now and again, in the remote future of the previous eon, there will be the galactic clusters whopping into the black There are these enormous black holes. These enormous black holes will whoop into each other. Huge burst of gravitational energy comes through. That's one of the things which get through, gravitational waves. They come through and maybe produce these wonderful rings that Alexia Lopez, that's the name of this young lady who's made this wonderful discovery, produced the rings. I never thought of it before, but when I heard about her rings, I went, "My god, that's I should have thought of that. This is something a nice effect that this theory should I should have thought that's a nice prediction." I never made the prediction, but that's sort of retrodiction, you see, coming from her, her discovery of these wonderful rings.
And so, you you don't In that picture, you don't require some kind of unification between quantum mechanics and and gravity. So, do do you picture space-time as fundamental?
>> It's not You see, it's not really quantum at all. It's a very different perspective. I'm not saying In fact, quantum mechanics is is a perturbation in this picture. It's a very classical. And I think people don't like that. They think, "Oh, it's got to be quantum mechanical." I thought that, too. But, this is a divergence from that view. It's saying the Big Bang is not quantum mechanical. It's It comes from the fact that it's conformal. Because the mass has got lost. Once you've lost the mass, you have a conformal picture. And then the Big Bang is very like the remote future. That's In fact, it's so much like it that our Big Bang is the continuation of the remote future of this previous eon. So, there there is no theory in that picture from which underlies general relativity, let's say this. General relativity is a is a a base theory, let's call it.
>> you would say it is a result of a result of a generalization of it. But, it's not saying it's quantized. No. So, it's not quantum general relativity. See, that's the difference. I think people were saying, "Oh, well, you've got to quantize GR before you can explain the Big Bang." This a very different picture. It is a generalization in the sense you're looking at space-time within the broader spectrum of conformal space-time. And you say, "Well, conformal geometry is a bit of a deeper picture." And that the mass gives you a scale, but the mass is only important later on or earlier on. Before the Big Bang when you're going back to the remote future of the previous eon or after the Big Bang like us now. But, there was this stage a crossover from one to the other where the mass was not important. It more or less disappeared. To continue watching this video, click the link in the top left or in the description below. With a free trial, you can enjoy the full talk and thousands more. Thank you for being part of the conversation.