What do Black Holes & the Big Bang tell us about Quantum Mechanics?

0:00 We have to keep at least one line free in the aisle. There's space down here. So it's a great pleasure to welcome everybody to the first annual lecture in the Memorial of Denizhiana. this is a parallel lecture was given earlier this year in Trieste and we hope this by the same speaker as you'll hear today we hope this will be the first of a series an annual series in memory of Dennis Schoen and the idea is to focus on topics that were of great interest to Dennis just a few words about Dennis' connections with Oxford and also with CISO, he was a fellow senior researcher at All Souls from 1970 to 1985, and after that he spent much time here, both at All Souls, in physics, and as a member of Watson College. But from 1985 onwards, he was a professor at Trieste, at CISA, the School of International Studies, the section of which supports astrophysics, and he ran a very active group. Before then, he was a lecturer at Cambridge University, and it was in that spell that he had produced a whole school of students who are some of the most brilliant in astrophysics, cosmology, theoretical physics. and these students in turn had many collaborators and his influence has permeated vast realms in cosmology and theoretical physics just to name one or two of his students former students, Martin Rees and Stephen Hawking So it's a particular pleasure to have Sir Roger Penrose today give the first

2:30 Roger was a collaborator in the early days with Stephen Hawking and one of their contributions to cosmology which is probably one of the most fundamental results of cosmology was to prove that the universe actually went through a singular phase at the Big Bang Roger has made several contributions to the development of general relativity theory. He has written a number of popular books, as I should, of course, remind you, one of the wonderful things about Deliciano was his efforts towards popularization, towards translating cosmology and physics to a general audience. And again, many of these books were well-known. And Roger Penrose's recent interests on the interface between general relativity and quantum theory and today he's going to talk on what do black holes and the Big Bang tell us about the nature of quantum mechanics. Of course I should have forgot to say that Roger is retired now but he was a professor, a small professor at Oxford for many years. So it's a great pleasure to have Roger talk. I hope you can hear me at the back. It's really an extremely great pleasure and honor for me to be able to give this first Dennis Sharma Memorial Lecture. Dennis Schauer, more than anybody else, was somebody who not only interested me, excited me in physics, but also taught me in a normal amount. Prior to coming to Cambridge, or going to Cambridge, I was a pure mathematician, I studied pure mathematics at London University, and I went to Cambridge afterwards again to study, do pure mathematics work in algebraic geometry of a sort but I got to know Dennis I'll say something about my initial meeting with Dennis and

5:00 from then on he I think made a special effort to get me more interested in physics which he succeeded in doing and when I say he had more effect perhaps on me than any other in the direction of physics. This is saying a lot, because when I was in Cambridge, as a graduate student, I went to Dirac's wonderful lectures on quantum mechanics, two terms worth of those which I found absolutely thrilling and mind-boggling and eye-opening and everything, and also in a similar way, lectures by Herman Bondi on general relativity, completely different style, but they had as much influence on me as the Dirac lectures. But none of these had as much as Dennis did in many different ways. I first met Dennis, it was something like 50 years ago now, almost exactly 50 years ago, I would say. And I'd come up to Cambridge, I was in London at the time, I think to see my brother, I can't remember exactly what I was doing. But I met my brother Oliver, who was a research student at Cambridge at the time, at the Kingswood Restaurant. That's where they all used to go and have chats about physics and philosophy and mathematics and various things. And then sitting there was Denis Sharma, who was a good friend of all of us, and he said, I must introduce you to Denis, he's a cosmologist. Now, this to me was particularly interesting because I'd been listening to Fred Hoyle's lectures on the radio. I guess this would date, it wouldn't date, but I can't. We gave a series of wonderful talks on the radio, and I even remember rushing home every time to hear these talks, and he talked about the steady state universe at the end, and then he described how, as the galaxies receding from us, at a certain point, they went faster than light, and when they went faster than light, they disappeared from view. But I didn't think this was right. I stopped him drawing little pictures. That's what I've been doing ever since, was drawing little pictures. Apparently it wasn't quite the thing that you were supposed to do with And all I did was take out a little napkin at the restaurant and drew a few little pictures. And Dennis looked at this and he said, goodness. And then, I think he may have taken this to frame a while and so on. But I think Dennis was sufficiently impressed by that. I'll show you what the picture was I drew. It wasn't quite as full. I've taken a bit longer over this one. you can see

7:30 this is meant to be a space-time diagram time going up and space this way and these cones represent the light curves so that light goes along the cones here in the future and this is a sort of schematic picture of the steady state universe here we have the galaxies over here which you could say were travelling faster than light but of course they never are because they're always inside the light cone and suppose there's this is you in the middle And you're looking out, and suppose you happen to see some galaxy here, this is a galaxy, and you happen to see it, and then you wait a little longer, you can still see it, and you wait longer and longer and longer, and you can still see it. It fades away, it gets redshifted, and it gets dimmer and dimmer, but it never disappears from view. And that, I drew a picture of something like that. So Dennis was sufficiently impressed by that, apparently, and he thought it was worth wasting a lot of his time telling me about physics and getting me to be excited about physics, which indeed he succeeded very well. Anyway, I'll come back to this picture later on. I'm not sure whether it's best to use the setter one as a spare, or whichever way around that matter. Another thing that Dennis was very good at was not just explaining ideas and getting excited about them and relating this and that thing, and he knew everything that was going on, certainly in cosmology and in much of physics, so he was a real minefield for knowledge of all sorts of things to do with physics. but another thing he was particularly good at was if he thought that there were two people who should get together because each one maybe had something and the other one would benefit from knowing then he made some significant effort in getting these people together it was a particular occasion when he suggested I come down to London I was from Cambridge, I'm sorry come down to London and hear a lecture given by David Finkelstein on each fortune of singularity and I, well I wasn't that keen to London and Cambridge, but I agreed to do this. And I found the lecture quite fascinating. It was about the singularity in the standard solution, which we now refer to as the solution describing the black hole. But in this solution, there is a singularity. Well, there is something that used to be thought of as singularity. Now, in fact, I should put the picture up, because this picture

10:00 has a lot of similarities to the one that we've just been looking at. That's the standard collapse to a black hole. I could also say something about the... I'm going to get the boat on, can I? That would be three on once, this way. This is the problem with singularities. Einstein's general relativity, well, in 1915, more or less, was where it started, and very soon after that, Schwarzschild discovered the solution of the Einstein equations for the vacuum surrounding a spherically symmetrical body, say a star, and I refer to it as the Schwarzschild solution. and this has well I can refer to this diagram here it has a region which we now refer to as a horizon but people didn't appreciate that at the time but this looked like a singularity here and I think Schwarzschild thought it was and Einstein probably thought it was and it was really the matre in 1933 who first pointed out that this thing was not a singularity if you change your coordinates you could get through it and it was perfectly regular and then Friedman and other people Friedman found the first solutions to the cosmological solutions which have the Big Bang singularity and the Chandra State car showed that you couldn't have a white dwarf star if it was too heavy, too massive, it had to collapse into one of these configurations and so on. But let me say something more about this, I'll come back to this slide I think I'll put it back here in a moment now let's talk about the space-time diagram for the black hole or the collapse to black hole, here we have the history see time is going up the picture here, this is some spherical body, of course they have to pull away one of the dimensions, so think of that as a sphere, and it's collapsing inwards and in a certain sense it carries the light turns with it to a certain degree, and what you find is that this a certain distance out from the center, which is referred to as the, that's the R equals 2m region up there, was thought to be a singularity originally, but with this transformation of coordinates, and this is the one that David Finkelstein actually used, it's one which has a picture which looks very much like this one here,

12:30 and he showed that by this change of coordinates, you could get rid of the singularity here, but you still have this one in the middle this is where you have the curvature going to infinity and the density in the matter as it collapses in goes to infinity and so there's nothing you can do about that one that really is singular but this on the outside here is really what's called a horizon and you see it's very similar to the picture that we've just been looking at at the beginning so here you have again what's called a horizon but this is a cosmological horizon as you look out at the universe So, here are lines of sight coming out of your eye, later on, and later on still, these lines sort of converge on this, what's called the horizon. And anything which crosses the horizon, after it's crossed, then you certainly can't see it. So, you couldn't see this event here, ever, no matter how long you waited. Whereas, you still see the galaxy earlier in its history. So as you go up here, your lines of sight come down closer and closer to the horizon, they will always intersect the galaxy, so you can see it, but it sort of fades away rather than disappearing. So that was the thing that I was worrying about in my initial talk with Dennis. that you have something here, but it's the other way around, if you like, the observers on the outside looking in, and here you have this horizon, and things falling in, you can still catch sight of them, no matter how long you wait, even though they're fade away, you won't see them because they're dim out. but in Finkelstein's lecture, he was he convincingly showed how you could get rid of this horizon, how you could piece them together in a very clever way to get these other parts of the picture together but I was struck by the fact that you couldn't get rid of this thing in the middle, so at that time I started wondering, is it possible that there's a general theorem which tells you that no matter what you do, you can't get rid of these some other singularities, you think you can still there. Well, I didn't have any of the tools at the time to be able to handle this problem, but it started me thinking about these issues. And later on, as Joe mentioned in his introduction, one has the theorems that I and Steve Tolkien and Bob Gerrach and other people proved, which showed that under very general circumstances, you still have these singularities. You can't be, even by introducing perturbations into the

15:00 initial collapsing material, you can't get rid of the singularity in the middle. It's stuck with it. It's a problem for classical general relativity. I can copy this up here. The question at the bottom, then, is what are we to do about it? Well, you see, the mathematics, you can keep on working on the mathematics of general relativity, and you might be able to learn something about the nature of these singularities, what they look like, how complicated they are, and so on, but you really need to look at the physics, because the physics, this is just telling you, basically, that classical general relativity gives up, you've got to do something else, and the standard view is that what you've got to do is to bring quantum mechanics into the problem, it's a problem of quantum gravity. so that is the conventional picture on this but let me compare this picture I'm getting confused this one is in the middle I keep thinking this one is in the middle but I'll do my best these are the standard cosmological models the original Friedman models but nowadays we've had to modify them slightly because people believe there's a cosmological constant that just means you have certain acceleration it doesn't change the pictures very much but at this stage it's just a mild gloss basically these are the standard models where you have the matter uniformly spread and you don't have your regularities spatially and you have these various different overall geometries you could have a negative curvature, you could have a flat or you could have a positive curvature it's a negative, a flat, and a positive there's a lot to talk about, people thinking it's flat I'm still going to bet on this one if I'm allowed to bet if it's that one the trouble is you can't tell because you never know if it's in slightly one way or the other so it's much better if it's one of these because then you can find definitive evidence in favour of it That's not much of an argument, let's see. Anyway, you see, here we have these singular states. This is the Big Bang. And this is to be compared with the singular state that we have here. In a certain sense, this is the Big Bang in reverse. Matter is falling in.

17:30 If you happen to fall into this black hole, you would eventually run into that singularity. It's the end of time, as far as you're concerned, you see. Here's the beginning of time. All the models have a beginning of time. This one here has an end of time as well. So you can see with the black hole singularity, there's a local end of time, if you like. So how are we to treat these things? What is the right way of handling? I think I'll take that one off for a moment. Quantum gravity, that seems to be what we should be doing to look at the singularities. What is quantum gravity? Well, what people usually mean by this is that it's the appropriate application of quantum field theoretic procedures to Einstein's general relativity or else to some modification of Einstein's theory if you feel driven to some modification. One doesn't usually imagine that the rules of quantum theory must be checked. One thinks, okay, if it doesn't work then you need to fill it around with the Einstein theory one way or another. But nobody wants to touch quantum mechanics. I shouldn't say that, but not many people do. But is that the right thing to do? Or should we be looking at some more even hand in marriage between quantum field theory and general relativity with some give on both sides? I may say that this is very much my own view, that we do need some give on both sides. It's not just applying the rules of quantum mechanics to Einstein's theory or some other theory of gravity. engineer something quite new on the quantum theory side as well and what reasons do i have for saying this well first of all let's go back to the models of the universe that we had here as i said before these models describe a spatially homogeneous universe so there are no wrinkles as far as space is concerned it's absolutely uniform whereas we know that there are wrinkles in the universe it's irregular in all sorts of ways and here i've indicated something of that these are you're supposed to compare it with the other picture and the difference being is that this is irregular you have the mass distribution is lumpy to some degree and where it gets lumpy gets lumpier and you have certain places where you have collapses to black holes and so here

20:00 we here i've indicated the collapse to a black hole and that may be taking place in various places in these universe models and although in the original symmetrical one look at the re-collapsing case the case with positive spatial curvature if you have no cosmological constant and that's slightly muddy, but never mind. You have these models which expand and re-collapse, and they're not completely symmetrical in time. But that's not what we expect realistically, because what we expect realistically is something much more like this, where this final big crunch, as it's called, consists of the congealing of a great number of black holes. So it's a great mess. I've tried to draw it as a mess. You might think the singularity is a bad enough mess already, but that's not really correct. Here we have a very nice regular smooth organized singularity, at the end we do have an incredible mess. That's what we expect from just, well, if you imagine, the uniform, pretty uniform initial state and then clumping and then things collapsing to black holes and so on. That's the kind of picture that we expect to be a realistic view of the universe as a whole. Now this is all tied up with the second row of thermodynamics. Let's see that one. It's a little bit. Let's see what it means. I want to say something about the second law of thermodynamics. See, if we have an asymmetry in time, we might think it's got something to do with thermodynamics. It has. And the main thing, what's the second law it says? It says that entropy of the universe increases with time. And roughly speaking, entropy is a measure of disorder. So the disorder, if you like, is increasing in time. And it's a very sort of pessimistic view of the universe. of the universe, and gloom and despair is associated with the second law of thermodynamics. I think this is not an appropriate view, and I'll tell you why I think it's not an appropriate view. On the second law, I'm all in favour of that. I mean, I'm against that. It's just that it shouldn't be depressed. That's all I'm saying. And the usual discussion of the second law tends to take place in something like this. You imagine a box, and the gas could be all out of one corner initially, and then it gradually spreads up, and this is a comparatively low entropy state and as the entropy increases and time increases

22:30 as entropy increases you get a more and more uniform, boring if you like, state of the universe so this is a depressing view of the universe it gets more and more boring as time goes on but suppose you introduce gravity now here I'm thinking about gravitating bodies and the picture looks almost the other way around here we have a uniform distribution of gravitating bodies to clump, and then they produce black holes, and you get a picture where the pictures look the other way around. It's still entropy increasing as time increases, there's nothing against the second law, it's just that it looks different. And if you like, in a certain sense, it's getting more and more interesting as time goes on. So these things, in fact, in any physical processes, these things are going on together, so the fact that we get lots of interesting things happening in the universe is something to do with these two processes in the universe now, in fact although gravity is so weak it's the weakest of the known physical forces it is nevertheless one of the most important which is perhaps the most important and it's intimately connected not just with the second law it's intimately connected with the second law as we know it I think it's easier for me if I use the side ones to point that so let's do that Here is a picture. You see, people might say, well, one is the entropy, a lot to do with... Is that better? You can see what I've written on it, yes. Well, there's a clock, yes. I was worrying about that, but since I'd left my clock, so I could go around or not, people would wonder when is it going to stop and probably do it. in a sort of ordinary way I mean how does the second law affect us well it's very important but it's very important the sun is very important to us people often say well sun is important because we get energy from the sun but that is what Schrodinger particularly pointed out is not the whole point it's not the central point we get energy but energy is conserved so what happens is that as much energy as we get in. Actually, it's slightly more. Because there are certain processes taking place in the Earth itself. It sets the same amount, basically.

25:00 So we don't actually get energy from the Sun. The Earth does. It throws away as much energy as it gets. But the point is, it has to do with entropy. See, the entropy is a cause of the second law. It's going up all the time and you have to keep it down. You wouldn't be able to survive entropy down. The important point is to keep the entropy down. And we do this see this picture really, except I've gone off the edge there, the picture conveys what I'm trying to say here the point is that we get comparatively few high energy photons from the sun and we spew back far more low energy photons. So we get the same energy from the sun as we spew back, mainly at night, so if you like it goes back in the day too. do it, we get it, in a smaller number of degrees of freedom. And entropy, if you want to have a precise measure of entropy, you have to take into account the degrees of freedom. If the same energy is confined to a smaller number of degrees of freedom, then this is low entropy. So you have low entropy here, and high entropy there. This is much more random, if you like, than this, roughly speaking. So, that's how we keep ourselves alive, not because the sun's out there pouring out energy, but because the sun is a bright spot in a dark sky. It's an imbalance between the hot sun and the dark sky. If this whole sky were uniformly bright as the sun, we wouldn't be able to do anything with it. It would be totally useless to it. So it's this imbalance that we live off. And why is there that imbalance? Well, the imbalance is there because the sun is there, and the sun is there because it condense out of a previous uniform distribution of material to form this body which would heat up even without thermonuclear reactions, it would heat up and they keep it going for longer basically without it collapsing too far we have this the key thing is that we have a previously uniform distribution which now has concentrated into these lumps and that's where we get our that's how we live if you like that's to do with this previous picture that she's probably got lost somewhere oh no, it's got lost oh no, it's white

27:30 here we have this process, this is what produces the sun, if you like, and that is an entropy increasing effect, but there's an enormous reservoir of entropy here and that's how it is and we're living off a little bit of that that's really how it works But it's this clumping procedure which produces the sun in the first place, and that is how we manage to survive and keep our entropy low and so on. It's just a little bit of this reservoir of low entropy which is present in uniformity in the initial state. So this goes back to the pictures that I was showing before, this picture here, it ties in with this, start off with uniform distribution and it gets lumpier and lumpier and lumpier and that's an increase of entropy and it's the key thing that we live off and it's absolutely crucial that the universe started so uniform and gets lumpy as time goes on. I think it's the wrong way around. It is, isn't it? It shouldn't matter. It shouldn't matter. It's the pictures that are important and the more sophisticated. A little bit of assistance. Thank you. Let me say something about the nature. You see, we have to figure out, say they're different. In what way are they different? Geometrically, how are they different? Well, one can be a little bit more qualitative about this. let me say something a little bit about the geometry here in fact it's a little lecture on general relativity comes almost very bonded but not quite this is space time curvature what is space time curvature well let me just give you a rough idea it also splits into two pieces and the Ritchie part. Now, how do you see space-time curvature? Well, you see, one of the troubles is that you don't see gravitational force, because if you fall in the gravitational field, then you don't feel it. I should have got a transversal layer on which has all this things there. Here we are. I'll have to show you later. I'll have to show you. That's a mistake. Here we are.

30:00 This picture. If this is Galileo dropping a big and small rock off a leaning tower or something, and there's an insect on one looking at the other one and it seems to hover in front of it as though there was no gravitational field. And here we have an astronaut looking at his space station and not appearing to feel the gravitational force because it's cancelled out by his falling freely. And this is now a familiar thing that you don't feel the gravitational force directly. But what you can feel is the deviations from uniformity. imagine that's the astronaut here surrounded by a sphere of particles which are then dropping in the earth's field and here we have um that's the astronaut accelerating a certain amount this particle here being closer to the earth's center accelerates a bit more this a bit less this slightly inwards and so relative to the astronaut in the middle there is this distortion this is going a little further away from the astronaut this is going further in the upper direction, and these are coming in for science. This is what's called the tidal effect. It's something that confuses people at first, that would confuse me at first. If you imagine, say, that was the Earth, and this was the Moon down here, then you see the effect of the Moon's gravitational field on the Earth's oceans, which are to pull it in the direction of the Moon, and also there's this bulge in the opposite direction, which tends to puzzle people. But the point I'm making here is that the field in free space, the gravitational field is manifested in this distortion effect. Spherical things get distorted into ellipsoidal shapes. And that is an effect of what's called the vial part of the curvature. This happens in empty space. But if you happen to be, if that sphere is surrounded to matter, and here I've surrounded the whole Earth, just to make it more dramatic, then you see there's a net inwards effect too. So matter surrounded causes an inward acceleration. In the presence of matter outside, you get this distortion. parts of the curvature. This is the whole curvature, which is the distorting effects. It's better if I give you the space-time picture, I think. The space-time picture I put on this one here. It's the same as those pictures out there, but I've drawn them all the time. And you see, here's the distortion, which is what you feel in empty space, and here's the inwards acceleration due to the presence of matter inside. I've tried to draw that matter here.

32:30 So this is a time which is time which is progressing up like this, here time which is progressing up like this. This is called Ritchie Curvature, the effect of Ritchie Curvature, and what's left is the, wow, curvature of the Gaussian part. So that's a slightly rapid account of the curvature, but this is a good improvement. And also you can see what it's got to do with curvature on the surface. we have these lines which are things called geodesics on a curved surface and the world lines of particles, those are these brown lines here, that should be geodesics in space-time and they either go towards each other, which is the positive curve, one at the top over there with a negative curvature which is the use of absence which is the one at the bottom and you see these are fixed in mind in the curvature the curvature of space-time ok, why am I saying all this just to give you, that's a rapid lecture in general relativity okay, now the point about all this is what's going on here in this picture, well this picture what you seem to have is the type of curvature, the blue one you can see the bottom of it, the richer curvature is all that you have at the beginning that's just a lot of matter around things get pulled inwards and when you get near the black holes you get lots and lots of vile curvature. So it goes from the blue one to the red one, if you like. Richie to vile is the way, it sort of goes along with the second law. But what we've got to explain about the universe, if we are going to understand singularities, if we're ever going to understand why the singularities are the way they are, we need a theory which explains why the beginning type, the Big Bang type, seems to be with a curvature which is this kind, And when you get near the end, the singularity of collapse here, you've got lots of the other kind. In this case, it's a large probability of infinity. So that's what we appear to see, and you need a theory which explains that. Now, what about quantum gravity? What about the various theories that people play around with, of which there are many? Well first of all, I should say quantum gravity theory should be a time asymmetric theory. it has to explain this gross asymmetry that we see quantum gravity is supposed to explain the singularity as you see but yet the second law

35:00 seems to tell us we have this irregularity the uniformity of the universe that we see doesn't come just from the second law it also comes from the very close to uniform nature of the background radiation, the cosmic background which is now a very important part of cosmology tells us Singularities in the beginning seem to be vile curvature going to zero, and in the end seem to go to infinity, that's what we seem to see. It's not just a small effect, it's absolutely stupendous. And we don't really know what the universe is like as a whole, we don't know how big it is and so on, but as a sort of lower limit of the extraordinary specialness that we have in the Big Bang. See, the second law just says entropy is going up. But the big puzzle is, why did it start so low in the first place? Why did it start at the top? I mean, why did it start at a very low figure? In fact, how special was the universe? How low was the entropy? But you can get an estimate for this. This comes from the famous Bekenstein-Hawking black hole formula, I won't go into details, but you can estimate that the singularity of the Big Bang and gravitational collapse are of a completely different nature, and the specialness of the Big Bang is at least as special as one part in 10 to the power, 10 to the power, 120. three. So that's a number that even if you tried to write a zero on each particle of the observable universe, you couldn't write this down in the ordinary way. Of course, I can write it down with the observable experiment. That's what we're allowed to do, but it's an absolutely huge number. And that gives a measure of how special the Big Bang really was. So it's not a small thing to explain. It's something absolutely stupendous to explain. Okay. And here's a schematic picture showing you we get in the final singularity is in the nice uniform nature of the initial singularity. Okay, people talk about irregularities and so on, but that's absolutely chicken feet compared to the overall uniformity. And, well, going back to the question I raised before, what are the reasons for believing that the correct quantum gravity theory should involve a non-standard quantum mechanics? Well,

37:30 standard quantum mechanics It doesn't make sense. I haven't explained it yet, so I can't see why it doesn't make sense. Those of you who have done physics scores, of course, you probably think it makes sense again. First of all, if it doesn't make sense, then you do it long enough to know that it mustn't make sense. That's the way it works. Well, I've painted too bad a picture because it makes a lot of sense, but it doesn't all together make sense. So something needs to be done, and it's the measurement problem, and I'll come to that. Gravitation is the most natural place to introduce a change. So if you are going to change quantum mechanics, and what's being suggested here is simply doesn't make sense, you don't have to make a change. Gravitation is the most natural place because it has quite different principles from the rest of physics. And when you start to bring these in, that's the sort of time you might expect to see a change in quantum physics. quantum gravity is supposed to resolve the space-time singularity problems yet singularities in our universe seem to be gross in time asymmetric and we have to relate this to time asymmetry in quantum mechanics well there is one, I'll come to that in a moment information lost in Hawking Evaporation, I'll come to that too quickly conflicts between foundational principles of quantum mechanics and general relativity it's what's called a problem in time quantum mechanics. I'll say a little bit about these not to take too long but maybe just issues I know where am I well let me say something about present day approaches to quantum gravity here they are spring theory or end theory we hear a lot about these the loop variable approach of Ashton Kahn, etc the only one that really tries to come to terms with the singularity problem in a serious way but all of these use standard quantum field theory and are essentially time symmetrical so this is one of the reasons that I would say we're not going to be able to find you see what I've written on the back most such approaches to the extent that they address the singularity problem at all would seek simply to eliminate the singular state to achieve instead a bounce so that's the picture that people often suggest is okay the big bang wasn't really the beginning there was a previous collapse and then class came out again that's a view which is often expressed as a well quantum gravity is then again it's thus it seems to me that once you've done that even if such if successful and i should say they're

40:00 not successful but if they were such a program would abandon the best hope we have to resolve the mystery of the second law thermodynamics i said a real mystery and the mystery is why was special. Not just that it was so special, but it was so special in a very particular way. It could have been, you know, like that. No, it was uniform. And that uniformity is the way in which it was special. Well, sometimes people would say, well, the explanation for all that is inflationary cosmology, and the various reasons for arguing in favor of inflationary cosmology, I'll work there, I suppose, is that you see, if you look in different directions, you see temperatures in the cosmic background, which are almost equal, not quite, but almost the same. So people say, well, those two regions were never in thermal contact. They're completely separate. If you look at the universe models that I was showing, I won't go back into that now, but you see that the parts of those are never intersect, so they seem to be completely causally separate from each other. So how could those temperatures be the same if they were never in contact with each other? But the trouble is that this reason is a bad reason for believing in what's called inflation. You see, I don't think I said what I was going to address here. Some people say inflation is going to solve those problems. It's quite a common picture of cosmology that the universe expands by an exponential degree and you'd spread it went all nice and flat and nice and regular and everything and different bits were in causal contact because the picture isn't quite the ones that I showed you before but the trouble is, okay that might be true that the universe is like this but it's not an explanation for what we're trying to explain here because, well, thermalization, you see the idea is that the reason the temperature is the same is because they were in causal contact at one time and different temperatures were even up body, put them together, then they make a lukewarm body. And that's what's supposed to be going on there. But okay, suppose that was what went on there. Then, that was an entropy increasing procedure. The entropy would have been even lower before the thermalization than after. So you've made your problem worse. The universe is even more special than

42:30 the one we see. You have to think about that, because it's an argument that people often bring up. And it seems to me it's just wrong. That this is not, okay, I say there might be inflation for other reasons, but the existence of inflation is not the explanation, because we have to explain not just the temperatures being equal and all that, we've got to explain the second law, we've got to explain why the universe is so extraordinary so, and this is just making that problem worse. the other sort of explanation reason for believing inflation is that we why is the universe so nearly flat and things like that and you expand out a small smooth region exponentially and it looks pretty flat the trouble is that also doesn't work I don't think I'll go into why that doesn't work but it seems to me that the reasons for inflation don't they don't the original motivations are not not really resolved by the theory itself I'm not saying inflation wasn't that I don't believe it was, but that's another issue the reasons don't seem to me to be these particular reasons aren't very good ones that's really in sight so let me throw that away I've been talking about quantum mechanics and general relativity and how we try to put them together and so on, and I haven't said much about quantum mechanics physics when we think about quantum mechanics. Well, the thing about physics, what's so strange about quantum mechanics, is we've spent many centuries learning about classical mechanics, even right up to Einstein's general relativity, where we have certain equations which tell how the system evolves in time, they're deterministic, and they are symmetrical in time, and they are local. I'll use those words there. But then we might choose to do something about molecules and atoms and fundamental particles and so on, and we want to do quantum mechanics. And if we do that, we do something quite different. In a certain sense, we're using different equations. We use an equation of the Schrodinger equation. The Schrodinger equation is deterministic, time-symmetrical, and local. Notice that there's exactly the same words I've got up here. So what about all the probabilities? I mean, surely quantum mechanics have got all this uncertainty and probabilities and goodness knows what. True, but they're not down at the quantum level. If you describe how

45:00 particles, how molecules behave and you can, if you know what the input is, the Schrodinger equation, we've got a particle and not a computer, you can work it out. You can see what it's going to do. And what it does is this. But that's not what happens when you do what's called making a measurement. That's only half of quantum mechanics. mechanics. So if you use letter C for classical U for what's called unitary evolution, that means the Schrodinger equation, or R, which is the reduction of the state or the collapse of the wave function, something quite different. It's what you do when you make a measurement. Think of a Geiger counter, that's a good example. A quantum particle enters the Geiger counter, it's a quantum thing, it enters it, it clicks real quick, that's a classical activity. Somehow you've magnified something from this level to this level. And in that process, the way you describe it in present-day physics is something quite different from what you would do if you simply evolved the quantum state according to the Schrodinger equation. People have this sort of feeling, I think, at the backs of their minds. Well, the Schrodinger equation is more accurate than classical physics. If you really knew how to teach you complicated V systems, you applied the Schrodinger equation, then you'd see how something like this comes about. But I don't believe that. as I'll explain in a moment I think I'll put this that's how we do quantum mechanics, or whatever view you have to take about what's really going on that's what we do ok, what's quantum theory? well, it appears there we are there because one of the Particles in quantum mechanics is that they have this dual behavior, they behave like particles or they behave like waves. And here are two experiments, idealized experiments, which you might do. Here is a source of particles, could be photons, say. Here we have a, what's called a beam splitter, think of it as a half-silver mirror. So half the light goes through, half the light is reflected. And if you have detectors here and here, that's indeed what you find. each particle either is detected at B or at A not both, not neither if these were ideal detectors and so on. But if you had a slightly different set up with fully silvered mirrors here and another beams that are here, then if these segments were the same then you would find the detector placed here

47:30 would always find the photon the detector placed here never sees it. So that somehow here you've got a wave-like two different roots in a particle-like behavior where it does one thing or the other. And these seem to be in conflict with each other, and the way one understands this in quantum mechanics is to think that when the photon is between here and here, it somehow co-exists in the two states at once, it feels out both roots, the state is the superposition, as it's called, of alternative A and alternative B. That's the way you do quantum mechanics. What is a superposition? Well, then we don't ask that question. You're allowed to make these superpositions. And then you say you've got these weighting factors, I've called them W and Z. What are they? Well, you might think they're probability of one thing happening in the other. No, they're not. They're not probabilities. If they were, you'd never get cancellations. Probabilities are all positive numbers. They just add up. These are complex numbers. They involve the square root of minus one. Here comes all the monkey business of quantum mechanics. Very beautiful, I should say, too. So you have this formalism where these superpositions persist. As long as you keep down on a level, then these superpositions just keep on going alongside each other. But then when you make a measurement, you do something completely different. Let's say you preserve the superpositions that are the measurement process. Suddenly you do something quite different. And these things do, they're not actually probabilities, but they're sort of square roots of probabilities. you see where they are plotted on this complex plane, and you square the distance to the origin, now the ratio of the two, as they call squared moduli, of these two complex numbers do indeed, would be the probabilities of all tensors. So that's where the probabilities come in. The R process here is in this going from one level to the other. As long as you stick down here then you don't ever see any probabilities it just evolves in a deterministic way. the way quantum mechanics works. I should say that it works, but it's not really a fully consistent idea because you might say, well, when are we supposed to do one, when are we supposed to do the other? What is a quantum level? How small do things have to be to satisfy the U rule and how big to satisfy the C rule? And when is the R rule coming? Well, that's the sort of thing you shovel under the rug and you get on doing your quantum mechanics to go to ask questions. It's actually basically a

50:00 Copenhagen view as far as I can make how it's more or less, you're not supposed to probe but it's easier to do it. Okay, that's fine. I've got nothing against that if you want to do quantum mechanics but if you want to go further and understand what's really going on underneath then you have to think a little bit more about what might be going on. And this is just the structure of quantum mechanics. How does it relate to what I've been saying before? Well, we don't see any time asymmetry Here, the Schrodinger equation is time symmetric, you don't see it at the classical level, you don't see it at the top of that picture, where you see it is in the measurement process, the bridge between the two levels, that's where you see the time asymmetry. In fact, let me make that a bit more explicit. What I've got here, here we have a stupid little experiment here, purely hypothetical. Here we have a source of photons over here, emits them one at a time if you like. Here we have a beam splitter, half of the mirror if you like, in the middle. and a detector on the other side and mirrors which will sort of guide things from one end to the other. let's suppose you register that this emits a photon. Whenever it emits one, it's supposed to register this back. There's nothing wrong with that. And so the normal way you do calculations in quantum mechanics would you say this thing called aptitudes, those are the complex numbers which are fairly superpositions. You say there's an aptitude SMD, that's going straight through turns out to be 1 over root 2 an amplitude for SMB that's going down and being absorbed into the floor again 1 over root 2 you square them and you get the relative probabilities of a half a half, half the time it goes through to here, half the time it goes down onto the floor, that's fine it's the right answer, no problem but what happens if you try and do this in a reverse direction in time, I'm not trying to reverse the experiment that's ridiculous, you couldn't do that I'm just going to ask my questions the other way around. I'm going to say, okay, what I've just done is to say, suppose S emits a photon, what's the probability of D receiving it? Now I'm going to say, suppose D receives a photon, what's the probability of S emitting it? And you also run through the same calculation, there's

52:30 nothing time-symmetric, asymmetric in the mirror and all that, you get one over root twos. You see, the two things, if you know it's come here, where could it have come from? It could have come from the lap, it could have come bouncing out of the ceiling. Those are the two alternatives, the altitudes are 1 over root 2, take the squares, you've got the probability of a half. You see, if D receives it, then you see half the time it came from a lambda, the other half the time it came careering out of C. That's nonsense. That's just the wrong answer. Almost every time it would have come from the source. You can't use the usual probability law in the reverse direction of time. It just doesn't work. There are all sorts of ways you can try and fill it in. make it make it work, but it doesn't so let me just say, this is what I mean when I say there's time asymmetry as we see here the time asymmetry comes from the application of the standard rule forming the squared modulus and what does it mean? what it means is something completely time asymmetrical or at least you get the right answer time asymmetrical in earlier transparency I thought we lost now I said something about various reasons for this one, yeah, that's it, information loss and hawking evaporation, I'll just say something about that, although it's really for the experts, but it's, I'll actually put that up here. here we have a black hole over here, collapsing material sits around for an awful long time in fact, lots longer than the age of the universe eventually, Hawking radiation is supposed to emit radiation according to Hawking's beautiful calculations and eventually it loses energy once the ambient temperature has gone down below the black hole, takes a long time and finally disappears in a pot And the question is, what happens to the information in the collapsing material? Is it lost altogether? Is it retrieved somehow magically in the final pot? Or is there some kind of a little nugget which sits around at the end, who's got all the information in it? And there's a lot of argument. You find people argue and argue and argue about these. People who come from quantum field theory backgrounds usually try to argue for these two. Hawking originally, when he put this forward, was, I don't really believe him, it should be lost.

55:00 And they say, I agree with him, I think it is lost, and in a rather stronger sense than he originally meant. I don't want to say too much about this, except that it is another route to what I want to tell you in a minute. And here, there's a sort of argument that Hawking can look forward. I think the colours are better when I do it in a middle one, aren't they? That's the edge. Put it back there. I think I won't go into the argument because it's really been distracted a little bit but the point of the argument is that you lose information when you produce black holes and you get absorbed into the singularity and somehow you've got to get it back again or you've got to get the phase space falling back again and for this you need the reduction process to be something objective but let me give you a different reason what I want to say here. It's just one of the early reasons I had for believing that there has to be a gravitational link. If you bring gravity and quantum mechanics together, it's got to say something about the measurement process. And that was one of the reasons for believing that. A stronger reason comes from an absolutely central part of quantum mechanics, which is quantum linearity. Suppose you have a let's say a photon, I call it a photon it could be any kind of particle which comes out here, hits something or other, and spews out a lot of junk. That's the green stuff at the top. I hope it looks good. Or, it might have gone another way, this way, hit something else, and produced another lot of stuff. Now, this has come, say, from a beam splitter, where you have the superposition of the two things. And what it means is that when it's done what it's going to do, these two outputs also have to be in superposition so all this green stuff here and all this brown stuff here are in superposition if you follow the rules of U quantum mechanics, the unitary evolution the part that is described by the Schrodinger equation part of the bottom of this diagram here then you find that indeed these results must be in superposition. Well, that's alright as far as it goes.

57:30 Well, as long as we don't take it too far, that's the trouble. And that's what Schrodinger Schrodinger since he produced his own equation was allowed to say rude things about it. the rest of us who didn't were supposed to say rude things about it. But Schrodinger did, let me be a bit rude about it too. Let me consider a situation like this, where we have a source emitting a photon, and here we have a detector. Someone's going to go sailing along to the detector, and it's fine, the detector will just say, yes, I see you. Well, we might do something else. We might attach to that detector a murderous device. Here I've done a gun, you see. It kills a cat. And so that's going to be the implication of this photon going on. Well, that seems to be a little bit unfortunate, but that seems to be what happens. On the other hand, we might choose to be a little bit more humane for a cat, and insert a mirror here, so the cat is alright. But suppose this is a mean splitter. Then we have to do both at once. So, according to the linearity, that cat should be in a superposition. That's the famous Schrodinger's cat. Not quite the way he described it, but essentially the same thing. So he was saying, okay, don't take my equation too seriously. When you get up to cat level, something new is going to happen. Okay, so that's what Trenny says, and I agree with him. But let me go back to this kind of answer here. That's that saying, it's basically that this picture is an approximation. That there is something new coming in. It's got a great bit of a mess before we have to return on, so I'll put a little one out. all three levels, if you like are an approximation to some missing theory that missing theory I'm calling OR that stands for Objective Reduction it also spells OR which is rather convenient that is alive OR, dead which is what we want but it's a new theory, it's not contained in the ordinary quantum level I've talked about these levels for a while

1:00:00 the quantum level, atoms, molecules and so on. The classical other big things, cricket, balls, planets, etc. But what is the division between them? And normally people would say, well, there isn't any particular division, and there's no distance division that we can tell, certainly not cricket level. And just to say why it's not that level, there are these famous things, again, I don't want to say too much about this, but it's a very important part of quantum mechanics. It's the famous Einstein, Podolsky, Rosen objection to quantum mechanics, which more or less shows that quad mechanics is, in a fundamental sense, non-local. If you recall the words that I had here, local, local, but when you do a measurement, except I've probably mislaid that if you do a measurement, then it's non-local. And it's the process of making a measurement which exhibits the non-locality. And in the original Einstein-Podolsky-Rosen experiment, well this is the, I should say the Bohm version which is easy to understand, you have a step, something which starts in spin zero state, it goes on two-skin half states, they could be ordinary electrons or protons or spin half atoms, say. And then you have detectors here and here, and you want to explain the relative probabilities between what you see at the two sides. And there's a conflict between what quantum mechanics says and what any, what's called realistic model, would tell you, local, I should say, realistic model. So you can't... Another way of putting this is that these two entities, they go apart, are still one thing. And the measurement you make on one side will influence what happens to a measurement on the other side, no matter how far apart they are. And experiments were done first, some in Paris, but not first, but some of the best ones in Paris by an aspect. What's happening up there? An aspect. And in this experiment you had photons something like 12 meters apart. So Pong Mechanic stretches to 12 meters. Now there are Now, similar experiments over distances of 10 kilometers, like Guizan, and I'm not done with that, but that's the record still, but so I know it is. Quantum mechanics affects, stretch through enormous distances. So you can't say that cricket balls are too big for quantum mechanics to find a sense of physical dimension. If it's not physical dimension, what is it? Well, let me go back to... let me go back to Schrodinger's poor cat

1:02:30 and really the trouble is okay, Schrodinger had a cat because it was dramatic but in a sense it's slightly confusing because you have to worry about what the cat feels and things like that so let me not do that I'm going to consider here a lump of material so if the photon goes one way it pushes the lump to here if it goes the other way, the lump stays in the original position I still have this beam squitter, so it has to be superposed. As long as the linearity of quantum mechanics is maintained, right after the size of this lump, that should be in a superposition of two different locations. Now, I'm going to try and say that this is an approximation that something different will happen and I have a picture here indicating that what different thing happens has to do with that spludge at the bottom you won't see that it's just a light Here we have the lump being moved from one place to another or it's put into a superposition of the two So, if you start to worry about the gravitational field of the lump, that's what I'm saying, then you have to get new things coming in. Because each lump location will slightly distort the space-time, so we have, this is a kind of schematic picture of space-time diagram, time going up this way, and here's the lump in one location distorting the space-time, then it becomes a superposition of two different lump locations, and that superposition of two different space-times starts to come into conflict with the fundamental principles of Einstein, because gravitational fields have this principle that I referred to before, a principle of equivalence. Gravitation is not force. You have to look at it a little more carefully. But related to that, and more relevant to the discussion here, is what's called the principle of general covariance. And that is if you consider a superposition of two different space-times, is what I'm trying to do here then you have fundamental problems there because you can't say which point of which space-time is to be identified with which point of the other space-time because saying regular points is cheap according to Einstein's theory and if you look at this quite carefully you see that there are real conflicts between the principles of general relativity and those of quantum mechanics I'm not going to go into details here

1:05:00 But just to give you what I regard as a sort of minimalist view, we don't want to change things more than we need to. I'm only going to consider very special circumstances where you have two different states, each of which would on its own be stationary. I should be asking about the time. Two states, each of which would on its own be stationary, and the question is what happens to a superposition? Well, what we're supposed to do is look at these stationary states, and you saw the Schrodinger equations for each one separately, and then you work out what the distribution of mass is. I won't do it again and go into the details here. What you find is that a certain quantity EG, it's the same as the EG on the other transparency, but here I'm describing it in a more straightforward, simple-minded way. What is this EG? Well, that's an energy. And it's the energy it would cost me, if you imagine these two lumps of coincidence originally, and then I try and pull one, it is only one one, suppose I had two lumps in coincidence, and I pull one away from the other, taking into account only the gravitational attraction between the two, how much energy does that cost? Not very much but still it's a certain amount and I'll call that EG. What I say is that that EG to be a little bit more accurate, what is it? Well, let's see, you take the difference between the two mass distributions and then count one positive and the other negative and then work out the gravitational self energy of that difference. That's more for the experts. And that EG is then There's supposed to be a fundamental uncertainty, representing a conflict or a tension between the general principles of Einstein's theory and those of quantum mechanics. And that, e.g., is a fundamental uncertainty in the energy, and that, like with an unstable nucleus, you see a uranium nucleus is unstable, and associated with that time scale, the K-time, is a certain energy uncertainty. That comes from the Heisenberg uncertainty principles of time-energy uncertainty relation, tells you this energy can't be exactly at a well-defined value if it's going to decay. I'm using that the other way around here. I'm saying if there is a fundamental uncertainty in its energy, then it will decay. What does it decay to? I'm saying that this superposition of two lump locations decays to one or the other.

1:07:30 it does so at a time scale which is of the order of Planck's constant divided by and so it's something quite explicit you could work out now usually people think well when you start talking about gravitation on the campus in the same breath you're talking about things absurdly out of the range anybody could do you're perhaps talking about the Planck length that's 10 to the minus 33 cm 20 orders of magnitude smaller than a fundamental particle times 43 seconds, that's the air 20 watts of magnitude shorter than the fastest decay rates that you see in algorithmic physics. So why worry? These things are way out of range. But the key difference is that all those things come from multiplying together Planck's constant and the gravitational constant. Both are small on ordinary scales. What I'm doing is something which divides one by the other. You have Planck's constant on the top and the EG involves the gravitational constant on the bottom so you have to look to see is it going to be important or not you can't just dismiss it out of hand because it's a quotient of two small things and they might be losing the signs so we have to look at it more seriously also I should look a little more carefully at how you work out this EG energy because that's also rather important let me do this here here we have lump location and then we try to pull it apart from itself and see if you look like that now if these were uniform spheres you'd know how to do a calculation but then you know they're not because they're made of individual nuclei and when you pull them apart well what do you do first of all you might say well these nuclei are protons and neutrons and those protons and neutrons quarks, and quarks are treated as point particles, and if you have point particles and you separate them, no matter how small amount you separate them, you're going to get an infinite effect, you'd have instantaneous reduction on this scheme, you'd never see any problem at all. So that can't be right. But it's not right, it's not what I said. What I said was that you have to solve a Schrodinger equation, each state has to be stationary. So what you have to do is not to take these as points, but to take a spread which you get from solving the Schrodinger equation for that object that you're talking about. So the object, you have to solve the Schrodinger equation

1:10:00 for that in a stationary state and see what the spread actually is in the mass distribution. There's a slight correction term which I refer to here which comes from the gravitational interaction and this is what we refer to as the Schrodinger Newton which I mentioned here. They've done some work on this to see explicitly whether these equations make sense in this context and in the way I've been describing it so you have something much like the bottom where you have some distribution and you pull them apart like that and you have a calculation it does mean you have to know in detail what the mass distribution is but I want to end by describing I think I'll do it on this one an experiment a proposed experiment that my colleagues here are trying to do in developing this idea see this effect, is it really, is what I'm saying really right well, it's much more impressive if you can do an experiment, see, and this is the idea so I've mentioned my colleagues up here and some visual input from and this is the initial sort of idea here we have a source Let's say a single photon comes along, it's beam split, and this hits a little crystal, it's a little mirror if you like, it gets reflected off, and then it gets slightly displaced, if it comes this way, it gets a little kick from the photon, it gets slightly displaced, if it goes the other way, it's in its original position. such as Schrodinger's luck, as I was just describing. Then you somehow got to keep this photon. One of the initial problems of this experiment, proposed experiment, was that to give it enough kick, it seemed you had to have an X-ray photon, and how do you keep an X-ray photon for something like a 10th of a second, which is what it seemed to mean. I've got pictures here, let me pull the whole thing down, of what this thing looks like. It's some sort of a crystal, and when it gets hit, it gets, when the photon comes this way it slightly displaces it to the blue location, when the photon goes the other way it's in the red location. So you have a lot of these nuclei giving you where most of the masses and you work out this gravitational self-energy and the difference between these two mass distributions, and you get some number

1:12:30 take the reciprocal of that, times h-bar, and this gives you basically the time scale according to me, and colleagues, I should say Deyoshi and various other people This should decay to one or the other. Now let's suppose it doesn't. Then, after you keep these going for one first experiment, you send this all out into space, and you send this from one space station to another, maybe an Earth diameter away from it, and it takes a tenth of a second, but that's one plausible way of doing it, but that needs a lot of expense in persuading the right people if it's interesting to do it. Anyway, you have to keep your photon somehow, and then let's suppose it doesn't go to one or the other, it stays in superposition, Schroding's equation is right, Schroding was wrong, suppose that happens, and then when they all come back again, it all runs back. You get your timing, so it all comes back together, and everything goes back into the laser, so long as you don't get decoherence and all sorts of other problems which might happen through the experiment, not being absolutely perfect. If, however, this becomes one or the other, then the photon with it has to be in one room or the other. And when it comes to here, half the time it will go into this detector. So that's the sort of primitive version of this experiment. It's not probably very doable in that form. My colleagues have come up with very ingenious ways of handling this. and that's one of the key ideas instead of hitting it with a single x-ray energy photon you hit it many many many times with a much weaker photon so you keep hitting it fast imagine a ping pong on top of a diving board the diving board is this thing here but you have to bear in mind the length of this thing is about the width of a human hair and the width of it there. Well, that's the width this way, I should say. Okay, so this thing is the photon comes this way, it's been split into these two things, and then it goes through here, because you have a very clever kind of mirror, which switches from being 99.999% reflective to triceum in a trice, I'm not sure how quick a trice is, but pretty quick. It allows us to say the less than the time it takes the photon

1:15:00 And then, since you let it in when it's transparent, took it over to a perfect mirror, bounces away, this bounces away, you should keep it tied, this one over here bounces in this slightly complicated way and moves that little mirror here by this sort of amount here, and then after the appropriate time you run it all back again to see if this little purple thing here has remained in its position or has it done one or the other, or have you lost So you have to design a very clever experiment. My understanding, my colleagues, is that they don't see any instruction to doing an experiment of this nature, which is about, say, 10,000 times below the level I need. However, I should explain that if they're successful, there are something like 10 million times the present record for a Schrodinger's cap. The present record for a Schrodinger's cap, as I understand it, is by Anton Zeilinger and his collaborators. where they have a little physical fullerene more of his carbon 60 or carbon 70 these balls that look like softballs and two slick experiments and we find that these things do exist in two places at the same time for a brief period of time little mirror here would be something like 10 million million calories at large so if they're successful in this experiment even if they don't get up to a level this experiment seems to need that would be very impressive indeed well you might say well we're going to go 10 million, 10 thousand and all that much maybe not it'll be interesting to see what happens thank you very much Thanks, Roger. We have a reception shortly, which everyone is invited, but let's first take a question until we're at three minutes. Can you hear that? I have heard that there are already conflicts between quantum mechanics and spatial relativity.

1:17:30 Can you talk about that? Can I just give you a question that there are, you say, conflicts? Conflicts between quantum mechanics. And special elements. Yeah, and special elements. Well, there are in a sense. It depends on your point of view. I mean, you could say, well, Dirac solved the problem with this equation for the electron. But then, of course, quantum field theory has its infinities and it's not really a consistent theory. so it's not clear that there is a full resolution even renormalizable theories still have infinities I'm thinking of the measurement procedure or something ah, yes, like the EPR that's not directly a conflict it's a conflict with, if you like a too direct way of thinking about causality the kind of causality that you have to except in quantum mechanics, something which is called quantum information, if you like. I prefer to call it quimblement, because I don't like the word information in there, because information is something you like to think of as restricted by the speed of light. And the problem you're referring to is in these experiments, the non-volved experiments. Somebody does a measurement over there, how does it influence the one on the other side faster than light? But the thing is, it doesn't do it in a way where you can send a signal from one side to the other. So it doesn't conflict with Einstein's principle that you can't send a signal faster than light, or you can't send information faster than light. You can, however, send this thing called quantum information, if you like, faster than light, or backwards in time even. Which is alright, it's not actually inconsistent. It's not inconsistent with special relativity, but it's a funny one. I think it's a different talk, so I think I prefer not to go to that in any depth. And the answer is that, yes, there are puzzles, either with these EPR things, and you have to have the right attitude of mind, it's not directly a conflict, if you don't conflict with the Einstein causality of sending messages to us, that you have a conflict with certain pictures that you'd like to have. But the climate movement point of view, I think is the way around it. But then you have other problems which go through a quantum field theory where opportunities, and they're not fully resolved. About the universe being so special, what's your view on the anthropological principles? It needs to come into discussion. I know that they were keen on it because this is the kind of argument people bring up usually when they can't see any other way of fixing the parameters in their theory or something.

1:20:00 But it has to be taken seriously under certain circumstances. But it doesn't affect any of the arguments I made. I don't want to go into it, but you might say, well, I speak to some of the argue, they say, well, inflation only occurs in regions which are initially smooth enough that you can trade. So they say, well, the probability of finding that may not be very great, but since you've got to live in one of those things, that's what happened. But the trouble with those arguments is that you take a region which is only attempted to cut the dynamics, so that's good enough for us, we don't need the area as much as that. So if you use an anthropic argument, you don't get that. It's not good enough. It doesn't work. Anthropic arguments have their place, and I'm not against them as such. But for any of the things I was talking about today, I don't think they resolve any of the problems. And let me just leave you with that. We need more discussion. Okay, well, we have a reception provided by all souls, just outside, with which everyone is welcome. and let's thank Roger Penrose for giving his first British Honourable lecture a very, very, very lecture Thank you