Transcription
I have to tell this story slightly backwards because I learned later that Fineman, you say this was in Caltech. I was giving this lecture and there was a poster of my talk coming up, and Fineman had seen this poster and he talked with a colleague to a colleague and he says, "I'm going to go he'll heckle this guy." You see, okay. I start talking in the lecture and I give it at Caltech and Fineman is sitting there and I get to a certain point and somebody else sitting behind Fineman starts to heckle me. Fineman turns around and points at him and says, "You shut up listening to what the man's saying." So I was really proud of that one.
So '65 is your paper that essentially won the Nobel Prize in 2020, which is the the singularity >> yes theorem, particularly for collapsing matter. So there is a there are certain general circumstances where you will get a space-time singularity. >> Yes. Well, you see, this was at a time when the quasars were being discovered. It was very strange, these enormously energetic things and these waves coming in from these things which seem to be very distant. People were arguing, is that really, maybe it's a gravitational redshift that's not this so distant? There were lots of arguments. And the real puzzle was, you see, there had been this paper, there was this, had been, there still is this paper by Oppenheimer, the great physicist Oppenheimer and a student of his, Snyder, and they'd written this paper which discussed what you might call a gravitational collapse. It was a dust cloud and the dust cloud collapses and it gets smaller and smaller and smaller and then becomes this singular state. But the trouble with this thing is, first, that it's dust. Now, dust is a very idealized material. It doesn't have any pressure and all that. So it's, it's really not real matter at all. But the main thing is, it's exactly spherically symmetrical. So as things fall in, where have they got to go? They've got to hit the central point. So the fact that everything hits the central point and the density becomes infinite at the central point is very artificial. And people say, "Well, we don't believe that." No, no, it won't meet a central point because it's swirling around and swishing out again. So that was the general picture people had. And so this was what my theorem showed was wrong. But it doesn't come swishing it out again. But if the material gets past a certain point that it can't escape, and this was this black hole picture which, um, well, I, I just invented this. I remember. Yes, it was. Well, all these things, there are little stories which one tells about this. One of them was I was talking to Ivor Robinson. This was when I had an appointment. I used to work at Birkbeck College in London and Ivor Robinson was a wonderful man. He had a wonderful way of talking and he, the Americans loved him because he had such flow of ideas and language was wonderful. He never wrote anything down. He was a good physicist but he never wrote a paper. He had to have a colleague to do the writing down. It was all through talk, you see, and he was talking to me like this, like wonderful, was listening to me moderately. Then we came to this road, we crossed the road, and when we crossed the road, he stopped talking. And we got to the other side and he kept talking like this. And finally he left and I had this strange feeling of elation. I think, why do I feel elated in this way? And I thought, can't pay what it was. I must have some thought I know earlier what it was. So I thought about what happened for breakfast. No. What happened when I walked through the woods? No. What happened to the bus when I came down and trained and all those things? No. No, it wasn't that. What happened later on? No. And then I thought, no, it was an idea, what happened to me as I crossed the road. This idea came to me. And it was the idea of a trapped surface. So you had to characterize in a non-symmetrical way when a collapse had reached a point of no return. And this was an idea which I subsequently called a trapped surface. When you get this surface, it can be very irregular. It doesn't have to be symmetrical at all at all. But when it reaches this level, you can tell you're in trouble. And then I developed this way of arguing how to develop these techniques for doing general things in general. There was, I think it was the techniques that people hadn't worked on. You know, you worked on exact solutions and all this, but these were techniques which looked at general solutions and the properties that these general solutions had to have. And you could apply these techniques in this particular case and you could see that there was no escape. You would have to have the singular thing that goes wrong. It will can't continue the collapse in a nice way. So, it comes swishing out again and that's it.
>> Were you familiar with general relativity at the time? Had you been studying it or did you begin to think about it in the 60s when you started to think about physics?
Well, that was again, it was sort of chance events. A lot of these things were chance. I keep thinking how many things go back and I see people ask me, how do, what do you attribute your success to? And I said, well, I don't know, it's really the main point is to be lucky. And I said, it doesn't help much if you're not lucky. And I have to think, well, it was this thing which I happened to share an office with Angel Ching. That was luck, you see. And I learned a lot of things from Angelbert Ching and he was a great font of knowledge from this tremendous thing for him. And there were these things which were, were basically luck. And so this was also a bit of luck too. She Dennis had told me he was that there was a talk being given by David Finkelstein in London. This was when I was in Cambridge. I had a fellowship at St. John's and Dennis was in, Dennis Sharma was in Cambridge as well. And he said he'd drive me down to London to hear this talk by David Finkelstein. And this was about the collapse of a spherical body and how you could get rid of the, what seemed was used to be called the Schwartz singularity. It's not a singularity. It's a place you could actually fall through. It's what we now call a horizon. So it's, it's the horizon of what we call a black hole now. And this was a very special case, but I'd learned, I, I was stunned by it. I thought, this is amazing. You can actually get through this thing which people thought was a singularity. It's just a horizon and you can get through. But then you still get the singularity in the middle. So it doesn't help you there. So I began to think after this, well, how do you, what about the middle one? Maybe you can't get rid of that one, even if it's irregular. And so I began worrying about that. And I thought, how do I treat this problem? I don't know anything about general relativity. How do I send? So I thought, well, what do I know about? Well, I know about two-component spinners. I won't try and describe what they are, but I knew about them from Dirac's lectures. It's even a little bit of a funny story there. Yeah. I don't know. And you see, they're all funny stories because this was a story because Dirac apparently deviated from his normal course of lectures. And people said, "Dirac would never do that. He, he fixed on what he was going to say every time, exactly what we'd say every lecture in the course. He would never deviate from that." And apparently he did on this occasion. I'm not even quite sure whether that story is true or not. But, but I like to think it was true because he talked, he gave a week's lecture on two-component spinners. And you see, I'd said to Dennis, I've got to learn about these two-component spinners. What are they? So Dennis said, well, read this book, this completely unreadable book. So I tried to read the book. I can't remember who it was by now. Utterly unreadable and I couldn't make head or tail of it. And so that wasn't any good. But then Dirac gave a week's lecture on two components. Everything has become beautifully clear. But the funny story about that is apparently this was a deviation from his normal course of lectures which he would never do. And so the story here, and I'm not sure about this, is that Dennis, you see, at this time was Dirac's only graduate student. And so Dirac, although he didn't talk much, he did talk to his graduate student. And there was an occasion that Dennis would say, he would talk to Dennis about about what his latest idea was. And Dennis would get lost at a certain point. He said, "Well, I've got to say something." And at a certain point he said, "Um, is that the only way of doing it?" You see, he just said, he had no idea what Dirac was talking about. Was that the only way of doing it? And then he heard later Dirac gave a little talk and said, at this point, Mr. Sharma came up with a brilliant idea. He said, this was not the only way of doing it, and there was another way of solving this problem. So that was a wonderful story. But anyway, Dirac apparently, so it was Dennis was his only student, had said that if he talked about two-component spinners, what at least one person in his class would be interested. And I like to think that was the reason he talked about two-component spinners because I was in his class. You see, I have no idea if that's true or not, but that's my little fantasy.
So, so following that paper, so your 1965 paper. Yes. Then Stephen Hawking essentially reverses it, well, or shows that there's also a singularity in our past according to general.
>> You see, that was a conversation. Yes. You see, that was the first time I met Stephen and he was, he at that time could walk and it was, he, the condition that he had didn't develop very far. So I didn't even know that there was anything wrong with him. But, uh, I think it was, um, who was the, who were the people who organized them? Well, Brandon Carter was there, but the person who organized the meeting was, oh, he's gone out of my, South Africanist, well-known chap. But anyway, he, there was a meeting that I had with with with, um, Stephen and I would describe the details of the singularity theorem that I had. So I talked to Dennis, to, uh, Stephen and and and these other people and, uh, Stephen picked up the ideas very quickly and developed them to try to apply them to cosmology. He had a very idea which he immediately had using my particular theorem but turning it around and using it in a different context, which I thought was pretty impressive. But, um, that was how, how we sort of got in contact originally. And then his thesis, this is, um, Stephen, Stephen Hawking's thesis was one, he was on four, I think four or five different sections, they were all on different topics. And the last topic was on these singularity ideas which he had. And, uh, it was a pretty impressive thesis. I think there were in four different topics and I remember saying that any two of them would have been worth a PhD. Right. And these singularities, so this, the, let's call it the black hole singularity, the gravitational collapse singularity, >> and the singularity, the, let's call it the Big Bang singularity. That's what Stephen, you see, Stephen >> sort of turned my theorem around the other way to apply it the other way in time. So instead of you have something collapsing inwards as you have for a black hole, you think about the bang, a big bang, which is things coming out. And the question is, maybe it could have been from some previous collapse which swirled round in some way and came shooting out again. So the argument was to show, no, it could, that wouldn't work with ordinary physical stuff. Yeah. But these are singularities of a very different character, aren't they? Which has informed a lot of your work since, the special nature apparently of the Big Bang singularity.
Well, you see, my theorem wouldn't quite work in that case because it, my theorem depended on it being asymptotically flat. You see, whereas these things were not like that. So you couldn't apply my particular theorem to the Big Bang. You, you'd have to generate a different theorem. So a big part of what Stephen's research work was when he was a graduate student was, um, using my generalizing my techniques to apply more generally so that they didn't apply to the, didn't need to apply to this particular, particular techniques which I used for my particular theorem. And then after a while, we wrote a paper together which was more encapsulated all the ideas that we'd had after that.
But you, you've been, you then became interested, certainly in "The Emperor's New Mind" and other books, in the idea that, so the, the, the origin of the universe, it's a very special state, let's say a low entropy state, a highly ordered state, which I, I think, well, I wouldn't put words into your mouth, you, you think is one of the greatest puzzles in all of physics. Why?
>> Which I can't remember when I wrote "The Emperor's New Mind". There was a bit of what was in that book, it was so long ago.
>> Do, do you still think that the, the, the low entropy state, the apparent orderliness of the origin of the universe is one of the biggest problems in physics?
Well, that came about really later. You see, I can't remember the dates of these things. Early in the 21st century, I can't quite remember where it was. I was visiting Princeton for a few days and there was a meeting in the, the, there's a university right across the river from New York. What is it? Stevens Institute. That's right. And they used to have meetings in the autumn and in the spring, I think. And a lot of people came from New York State and from different parts of New York State and got together. And you had to drive there in cars from Princeton. I was in Princeton. I didn't have a car, but I happened to see there was a car over there and I thought I said, "Could Jim Peebles be in the car?" And I thought, "Oh, there's Jim. I'll go and see if there's a gap in his car because I want to ask him a question." And I looked in the car. There was no room in the car. But I thought, anyway, I'll ask him a question. And the question I asked him was, "Why don't you cosmologists only think of this particularly very simple, special kind of singularity, whereas we mathematicians consider all these different kinds of complicated kinds of singularities? There are all these different things and you don't think of, you don't even consider all these other cases, you just look at this one simple, special case." And he looked at me and I said, "Why don't you look at these other cases?" And he said, he looked at me, "Because the universe is not like that." And I thought, my God, he's right. It's not. It's like this very special case, and not like these all other cases like that. And so that set me on this particular route. What, why is it on that, that particular simple case? And that sort of set me thinking about this, which set me thinking still on this fundamental problem, why is the Big Bang that very, very special, simple kind of singularity, not like the complicated gravitational collapse? You have a great mess of stuff which is nothing like what you see at the Big Bang.
>> So it's a huge problem.
>> Yeah, which people didn't seem to recognize as a huge problem. I have my own answer to that problem, which I didn't come to until much later.
>> Yeah, well, I was going to ask you about that, about the, so essentially conformal >> cyclic cosmology. So this, the idea essentially that the universe, uh, well, has, I suppose, is eternal. Would that be? That's the picture. Which is what Einstein, by the way, preferred, right? Initially, I think.
Well, it's never, he kept changing his mind. That was trouble for good reasons. He usually had a good reason each time for the mind change. But you see, he also had this problem of the cosmological constant. You see, his equations had a little term in it. You see, which would be very nice to put that to zero. It's just this number. You can make it zero. It's called the cosmolog. So he couldn't make up his mind whether it should be there or not. I think. And he put it there for a reason because he liked to have a static universe because he's rather keen on that idea. And that turned out not to work because the universe was expanding. I can't remember the history of it. But, but he suddenly got confused about whether it should be there or not. And I think it should be there. But he introduced, well, now the trouble is now, you see, it's now called the mysterious dark energy. I thought mysterious dark. And it's just the cosmological constant. We've known about that ever since, but it's become the mysterious dark energy. Well, I can't help it, that's what people want to call it.
So do you, do you think that, so maybe you could describe very, very briefly your model, which is the conformal cyclic cosmology?
>> Well, is there, it's a resolution of that problem. Yes.
>> Well, there's another little story too. So we've got the little stories. You see, I have to tell this story slightly backwards because I learned later that Fineman, you say this was in Teltech. I was giving this lecture and there was a poster of my talk coming up and Fineman had seen this poster and he talked a colleague to a colleague of he says I'm going to go he heckle this guy you see okay I start talking in the lecture and I give it Caltech and Fineman is sitting there and I get to a certain point and somebody else sitting behind Fineman starts to heckle me. Fineman turns around and points out and says you shut up listening to what the man's saying. So I was really proud of that one.
No, Fineman was absolutely right. I was trying to explain it was this problem about the uniformity and it's the uniformity is in a very special way. It's in gravity. Everything else seems to be in a maximum entropy random as it can get except for gravity. Gravity is not. It's very, very special. And this was the point I was trying to make and Fineman picked it up very quickly. I, I enjoyed Fineman. He was, he was an interesting guy to talk to, you know.
So, so in terms of the, the, the, the resolution to these problems. So you mentioned we mentioned string theory before and everybody laughed. But then in terms of trying to look for a deeper theory, so let's say quantum gravity.
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