Full transcript
0:00I have to tell this story slightly
0:01backwards. Because I learned later that
0:04Feynman You see, this was in Caltech I
0:07was giving this lecture and there was a
0:08poster of my talk coming up and Feynman
0:11had seen this poster and he talked with
0:13colleague to a colleague of his he says,
0:14"I'm going to go and heckle this guy."
0:17You see. Okay. I start talking in the
0:20lecture and I give it in Caltech and
0:22Feynman is sitting there. And I get to a
0:25certain point and somebody else sitting
0:26behind Feynman starts to heckle me.
0:29Feynman turns around and points at him
0:31and says, "You shut up. Listen to what
0:33the man is saying."
0:35So, I was really proud of that one.
0:37>> [laughter]
0:43>> So, 65 is your paper that essentially
0:48won the Nobel Prize in 2020 which is the
0:51the singularity
0:52>> Yeah.
0:52>> theorem particularly for collapsing
0:55matters. So, there is a there are
0:57certain certain general circumstances
0:59where you will get a space-time
1:00singularity.
1:01>> Yes, well you see this was at a time
1:04when the quasars were being discovered.
1:06They were very strange these enormously
1:08energetic things and these waves coming
1:10in
1:11from these things which seemed to be
1:13very distant. The people were arguing is
1:14that really maybe it's a gravitational
1:16redshift it's not that so distant. There
1:18were lots of arguments. And the real
1:21puzzle was
1:22You see, there had been this paper there
1:24was this
1:25had been there still is this paper by
1:27Oppenheimer the great
1:29physicist Oppenheimer and the student of
1:32his Snyder and they'd written this paper
1:35which discussed what you might call a
1:37gravitational collapse. With a dust
1:39cloud and the dust cloud collapses
1:42and it gets smaller and smaller and
1:44smaller and then becomes the singular
1:46state.
1:47But the trouble with this thing is first
1:49that it's dust. And dust is a very
1:51idealized material it doesn't have any
1:53pressure and all that. So, it's it's
1:55really not real matter at all. But the
1:57main thing is exactly spherically
2:01symmetrical. So as things fall in, where
2:04have they got to go? They've got to hit
2:05central point. So the fact that
2:07everything hits the central point and
2:09the density becomes infinite at the
2:10central point is very artificial. Now
2:13people say, "Well, we don't believe
2:14that. No, no, it won't meet a central
2:16point because it's swirling around and
2:18swishing out again."
2:20So that was the general picture people
2:22had.
2:23And so this was what my theorem showed
2:26was wrong.
2:27But it doesn't come swishing out again.
2:30But if the material gets to pass a
2:33certain point
2:34then it can't escape. And this was this
2:37uh black hole picture which um
2:42Well, [snorts] I I just
2:43>> [clears throat]
2:43>> invented this I remember.
2:46Yes, it was
2:47Well, all of these things are little
2:48stories which one tells about this. One
2:50of them was I was talking to Ivor
2:53Robinson. This is when I had a an
2:54appointment. I used to I worked at
2:56Birkbeck College in London. And um Ivor
2:59Robinson was a wonderful man. He had a
3:00wonderful way of talking and he
3:02the Americans loved him because he had
3:04such a flow ideas and language was
3:07wonderful. He never wrote anything down.
3:09He was a good physicist, but he never
3:10wrote a paper. He had to have a
3:11colleague to do the writing down. It was
3:13all through talk, you see. And he was
3:15talking to me like this like one of
3:17them. I was listening to me wonderfully.
3:19Then we came to this road. We crossed
3:21the road and when we crossed the road,
3:24he stopped talking. When we got to the
3:25other side, he got talking again like
3:27this. And finally left. And I had this
3:29strange feeling of elation. I think,
3:32"Why do I feel elated in this way?" And
3:35I thought, "I can't figure what it was.
3:37I must have some thought." I thought, "I
3:39know earlier what it was." So I thought
3:41about what happened for breakfast? No.
3:43What happened when I walked through the
3:44woods? No. What happened bus when I came
3:47down on the train and all those things?
3:49No. No, it wasn't that. What happened
3:51later on? No.
3:53And then it thought, no, it was an idea
3:55which happened to me as I crossed the
3:57road. This idea come come to me.
4:00And it was the idea of a trapped
4:02surface. So, you had to characterize
4:05in a non-symmetrical way when a collapse
4:08had reached a point of no return.
4:11And this was an idea which I
4:13subsequently called a trapped surface.
4:15When you get the surface can be very
4:17irregular, it doesn't have to be a
4:18symmetrical core at all. When it reaches
4:20this level, you can tell you're in
4:23trouble.
4:24And then I developed this way of
4:26arguing how to develop these techniques
4:29for doing
4:31general things in general. There was I
4:33think it was the techniques that people
4:34hadn't worked on. You know, you work on
4:36exact solutions and all this, but these
4:38were techniques which looked at general
4:40solutions and the properties that these
4:43general solutions had to have.
4:45And you could apply these techniques in
4:47this particular case and you could see
4:49that there was no escape. You would have
4:51to have the singular
4:53thing that goes wrong. It won't can't
4:55continue the collapse in a nice way so
4:58that it comes swishing out again and
4:59that's it.
5:00>> Were we we familiar with general
5:02relativity at the time? Had you been
5:04studying it or did you begin to think
5:06about it in the '60s when you started to
5:09think about physics?
5:10>> Well, that was
5:12Again, it's it was sort of chance event.
5:14A lot of these things were chance. I
5:15kept thinking,
5:17how many things go back?
5:20And I say I say people ask me, they say,
5:21how do you what do you attribute your
5:23success to? And I'll say, well, I don't
5:24know, it's really the main point is to
5:26be lucky.
5:27And I said, it doesn't help much if
5:29you're not lucky. And I had to think,
5:31well, it was this thing which I happened
5:32to share an office with Engelbert
5:34Schucking. That was luck, you see. And I
5:36learned a lot of things from Engelbert
5:38Schucking. And he was a greater font of
5:40knowledge than this strange thing for
5:42him. And there were these things which
5:44were
5:44basically luck.
5:47And [snorts] so this was a bit of luck,
5:48too.
5:50She Dennis had told me
5:52he was that there was a talk being given
5:54by David Finkelstein in London. This was
5:56when I was in Cambridge. I had a
5:58fellowship at St. John's.
6:00And Dennis was in
6:01Dennis Sciama was in Cambridge as well.
6:04And he said he'd drive me down to London
6:06to hear this talk by David Finkelstein.
6:08And this was about
6:10the collapse of a spherical body.
6:14And how you could get rid of the what
6:16seemed to was was used to be called the
6:17Schwarzschild singularity. It's not a
6:19singularity. It's place you could
6:21actually fall through. It's what we now
6:23call a horizon. So it's the it's the
6:26horizon of what we call a black hole
6:27now.
6:28And this was a very special case, but
6:32I'd learned I I was stunned by it. I was
6:34I was amazing. You could actually get
6:36through this thing which people thought
6:37was a singularity. It's just a horizon.
6:40And you can get through. But then you
6:41still get the singularity in the middle.
6:43So it doesn't help you there.
6:45So I then began to think after this,
6:48well, how do you What about the middle?
6:50Well, maybe you can't get rid of that
6:51one even if it's irregular. And so I
6:54began worrying about that.
6:56And I thought, "What How do I treat this
6:57problem? I don't know anything about
6:58general relativity. How do I solve
7:00this?"
7:00So I thought, "Well, what do I do know
7:02about?" Well, I know about two-component
7:05spinners. I won't try and describe what
7:06they are.
7:07But I knew about them from Dirac's
7:09lectures.
7:11There's even a little bit of a funny
7:13story there.
7:15Yeah, I don't know. You see, they're all
7:16funny stories. Cuz this was a story
7:18because Dirac apparently deviated from
7:22his normal course of lectures. And
7:25people said, "Dirac would never do
7:27that." He did He thinks so much he would
7:29going to say every time exactly what
7:32we'd say every lecture in the course. He
7:34would never deviate from that. But
7:36apparently he did on this occasion.
7:39I'm not even quite sure whether that
7:40story is true or not. But but that I
7:43like to think it was true.
7:45Because he talked he gave a little
7:47week's lecture on two component
7:49spinners.
7:51And you see I'd said to Dennis, I'm
7:52going to learn about these two component
7:53spinners. What are they? So Dennis said,
7:55"Well, read this book." This completely
7:57unreadable book. So I tried to read the
7:59book. I can't remember who it was by
8:00now.
8:01Utterly unreadable. I couldn't make head
8:03or tail of it.
8:05And so that wasn't any good.
8:06But then Dirac gave a week's lecture on
8:09two component spinners.
8:12Everything has become beautifully clear.
8:15But the funny story about that is
8:17apparently this was a deviation from his
8:19normal course of lectures which he would
8:21never do.
8:23And so the story here, and I'm not sure
8:25about this, is that Dennis, you see, at
8:28this time it was Dirac's only graduate
8:30student.
8:32And so Dirac, although he didn't talk
8:33much, he did talk to his graduate
8:35student.
8:37And there was an occasion that Dennis
8:39would say, he would talk to Dennis about
8:41about what his latest idea was.
8:44And Dennis would get lost at a certain
8:45point. He said, "Well, I've got to say
8:47something."
8:48At certain point he said,
8:50"Um
8:52is that the only way of doing it?" You
8:54see, he just said
8:55he had no idea what Dirac was talking
8:57about.
8:58Is that the only way of doing it? And
8:59then he heard later Dirac gave a little
9:01talk and said, "At this point Mr. Sharma
9:03came up with a brilliant idea. He said
9:06this was not the only way of doing it
9:08and there was another way of solving
9:09this problem."
9:10So that was a wonderful story.
9:12But anyway,
9:14Dirac apparently, since it was Dennis
9:16was his only student, had said that if
9:18he talked about two component spinners,
9:20what this one person person in his class
9:22would be interested.
9:24And I like to think that was the reason
9:26he talked about two component spinners
9:28because I was in his class. You see, I
9:29have no idea if that's true or not.
9:32But that's my little fantasy.
9:36>> So so following that paper, so your 1965
9:40paper
9:40>> Yes.
9:40>> then Stephen Hawking essentially
9:43reverses it
9:45well or shows that
9:47there's also a singularity in our past
9:49according to general
9:50>> that was a conversation. Yes.
9:53You see, that was the first time I met
9:54Stephen.
9:56And he was he that time he could walk
9:58and it was he the condition that he had
10:01didn't develop very far. So, I didn't
10:03even know that there was anything wrong
10:05with him.
10:06But uh
10:07I think it was
10:09um
10:11Who was the who was the people who
10:12organized it? Well, Brandon Carter was
10:14there.
10:15But the person who organized the meeting
10:17was uh he's gone out of my South African
10:21physicist.
10:22Well known chap. Gone out of my head
10:24right now. But anyway, he there was a
10:26meeting that I had with with
10:29with um
10:30Stephen. And I would describe the
10:32details of these singularity theorems
10:35that I had. So, I'd talk to Dennis
10:38to Stephen and and
10:41and these other people.
10:43And Stephen
10:45picked up the ideas very quickly and
10:48developed them to try to apply them to
10:50cosmology. If you had a very idea which
10:53he immediately had using my particular
10:55theorem but turning it around and using
10:57it in a different context, which I
10:58thought was pretty impressive.
11:00But um
11:02that was how how we sort of got in
11:03contact originally. And then his thesis
11:07which is
11:08Stephen Stephen Hawking's thesis
11:12was
11:13one of he was on four I think four or
11:14five different sections. They were all
11:16on different topics.
11:17And the last topic was on these
11:19singularity ideas which he had.
11:22And it was a pretty impressive thesis.
11:25I think there was on four different
11:26topics and I remember saying that any
11:27two of them would have been worth a PhD.
11:30>> Right. [laughter]
11:31And And these so this the the let's call
11:34it the black hole singularity, the
11:35gravitational collapse singularity.
11:37>> Yeah.
11:38>> And the singularity that let's call it
11:40the Big Bang singularity.
11:41>> Well, that is what Stephen you see
11:42Stephen
11:44sort of turned my theorem around the
11:45other way to apply it the other way in
11:47time. So, instead of you have something
11:49collapsing inwards as you have for a
11:52black hole.
11:53You think about the bang, Big Bang,
11:55which is things coming out. And the
11:57question is maybe it could have about
11:58for some previous collapse which swirled
12:01round in some way and came shooting out
12:03again. So, the argument was to show no,
12:05it could that wouldn't work
12:08with ordinary physical stuff.
12:10>> Yeah. But, these are singularities of a
12:12very different character, aren't they,
12:14which has informed a lot of your work
12:16since? The special nature, apparently,
12:19of the Big Bang singularity.
12:22>> Well, you see my theorem wouldn't quite
12:23work in that case cuz it my theorem
12:25depended on it being asymptotically
12:27flat, you see, whereas these things were
12:28not like that. So, you couldn't apply my
12:31particular theorem
12:33to the Big Bang. You you'd have to
12:35generate a different theorem.
12:38So, a big part of what Stephen's
12:41research work was when he was a graduate
12:43student, was on
12:46using my generalizing my techniques to
12:49apply more generally so that they didn't
12:52apply to the
12:53didn't need to apply to these particular
12:56particular techniques that I used for my
12:59particular theorem.
13:00And then after a while, we wrote a paper
13:02together, which was more syncopated on
13:05the ideas that we'd had after that.
13:07>> Well, you you've been you then became
13:09interested, certainly in Emperor's New
13:11Mind and other books, in the idea that
13:14So, the the the origin of the universe
13:15is a very special state, let's say a low
13:18entropy state, a highly ordered state,
13:21which
13:22I think Well,
13:24I wouldn't put words into your mouth.
13:25You you think it's one of the greatest
13:26puzzles in all of physics.
13:28>> [laughter]
13:28>> Why?
13:29>> Well, you see, I can't remember when I
13:31wrote The Emperor's New Mind. I wrote a
13:32bit of cosmos but what was in that book?
13:35It was so long ago.
13:38>> [laughter]
13:38>> Did you still think that the the the low
13:41entropy
13:42state, the apparent orderliness of the
13:46origin of the universe is one of the
13:48biggest problems in physics?
13:50>> Well, that came about
13:53really later. You see, I can't remember
13:56the dates of these things.
13:58Early in the
14:0021st century. I can't quite remember
14:02where it was. I was visiting Princeton
14:06for a few days
14:07and there was a meeting in
14:10the the there's a a university right
14:12across the river from New York. Well,
14:15what is it? Stevens Institute. That's
14:17right.
14:18And they used to have meetings in the
14:20autumn and in the spring, I think. A lot
14:21of people came from New York state and
14:23from different parts of New York state
14:26and got together. And you had to drive
14:28there in cars from Princeton. I was in
14:29Princeton and I didn't have a car.
14:31But I happened to see there was a car
14:33over there and I thought I see Jim
14:35Peebles in the car and I thought, "Oh,
14:38there's Jim. I'm going to
14:40see if I can get a gap in his car
14:41because I want to ask him a question."
14:43And I looked in the car and there was no
14:44room in the car but I thought anyway
14:45I'll ask him a question.
14:47And the question I asked him was, "Why
14:49don't you cosmologists
14:52only think of this particularly very
14:54simple special kind of singularity?
14:57Whereas we mathematicians consider all
14:59these different complicated kinds of
15:01singularities and there are all these
15:02different things and you don't think
15:04about it. You don't even consider all
15:05these other cases. You just look at this
15:07one simple special case."
15:09And he looked at me and I said, "Why
15:11don't you look at the these other
15:12cases?" And he said he looked at me
15:14"because the universe is not like that."
15:18And I thought, "My god, he's right. It's
15:19not."
15:20>> [laughter]
15:23>> It's like this very special case. Not
15:26like these all other cases like that.
15:28And so that set me on this particular
15:30route. What Why is it on that that
15:33particular simple case?
15:36And that sort of set me thinking about
15:38this which
15:39set me thinking still on this
15:41fundamental problem. Why is the Big Bang
15:44that very very special simple kind of
15:48singularity? Not like the complicated
15:52gravitational collapse or have a great
15:53mess of stuff which is nothing like what
15:56you see at the Big Bang.
15:58So it's a huge problem.
15:59>> Yeah.
16:00>> Which people didn't seem to recognize as
16:02a huge problem.
16:04I have my own answer to that problem
16:06which I didn't come to until much later.
16:08>> Yeah. Well, I was going to ask you about
16:09that about the sorry essentially
16:11conformal
16:13cyclical cyclic cosmology. So this the
16:16idea essentially that the universe
16:19uh well, is I suppose is eternal. Uh
16:21would that be That's the picture which
16:23is what Einstein by the way preferred,
16:26right?
16:26>> Yes, I think Well, he's never He kept
16:28changing his mind. That was the trouble.
16:30For good reasons. He usually had a good
16:32reason each time for the mind change.
16:34But [snorts] you see he also had this
16:36problem with the cosmological constant.
16:39You see his equations
16:41had a little term in it, you see, which
16:43would be really nice to put that to
16:45zero. It's just this number. You could
16:46make it zero.
16:48It's called the cosmological constant.
16:50So he couldn't make up his mind whether
16:51it should be there or not, I think. And
16:53he put it there for a reason cuz he
16:56liked to have a static universe cuz he
16:58was rather keen on that idea. And that
17:00turned out not to work cuz the universe
17:02is expanding.
17:04I can't remember the history of it, but
17:06but he said he got confused about
17:07whether it should be there or not.
17:10And I think it should be there.
17:12But he introduced Well, now the trouble
17:14is now you see it's now called the
17:16mysterious dark energy.
17:20I thought mysterious dark energy is just
17:22the cosmological constant. We learned
17:23about that ever since Einstein.
17:26But it's become the mysterious dark
17:28energy. Hmm.
17:30Well, I can't help it. That's what
17:31people want to call it.
17:33>> [laughter]
17:36>> So, do you think Do you think that
17:39So, may maybe you could describe very
17:41very briefly your model. Which is the
17:44conformal cyclic cosmology.
17:46>> Well, it's a It's a resolution of that
17:49problem. Yes.
17:52Well, it's another little story, too.
17:54So, we've got these little stories, you
17:55see.
17:56I have to tell this story slightly
17:57backwards.
17:59Because I learned later that Feynman
18:02You see, this was in Caltech. I was
18:03giving this lecture. And there was a
18:05poster of my talk coming up. And Feynman
18:07had seen this poster, and he talked with
18:09colleague to a colleague and he says,
18:11"I'm going to go and heckle this guy."
18:13You see. Okay.
18:15I start talking in the lecture and I
18:17give it in Caltech. And Feynman is
18:19sitting there.
18:20And I get to a certain point and
18:22somebody else sitting behind Feynman
18:24starts to heckle me.
18:25Feynman turns around and points at him
18:27and says, "You shut up. You're listening
18:29to what the man is saying."
18:31So, I was really proud of that one.
18:33>> [laughter]
18:35>> No, Feynman was absolutely right. I was
18:37trying to explain it was this problem
18:40about the uniformity.
18:42And if the uniformity is in a very
18:43special way, it's in gravity.
18:46Everything else seems to be in a maximum
18:49entropy, or random as it can get.
18:51Except for gravity. Gravity is not. It's
18:55very very special.
18:57And this was the point I was trying to
18:58make.
19:00And Feynman picked it up very quickly.
19:03I I enjoyed Feynman. He was a He was a
19:06interesting guy to talk to. Had a
19:09So,
19:10So, in terms of
19:12the the the resolutions to these
19:14problems, so we you mentioned we
19:16mentioned string theory before and
19:18everybody laughed at that. But in in
19:20terms of trying to look for a deeper
19:24theory, so let's say quantum gravity,
19:27then
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