Brian Greene and Sir Roger Penrose: World Science U Q+A Session

so [Music] [Music] hey everyone good morning at least uh to those of you on the east coast of america it is quite unusual for us to gather at this early hour um i'm used to speaking publicly at this early hour so i'll do my best of course we're doing it at this time because of the guests that we're going to be speaking to in just a little while sir roger penrose who is in oxford i think is in oxford certainly is in the uk and to accommodate the time there we are starting on our end a little bit early relative to what we normally do but i guess for some of you out there this is a really good time those who join us from the other side of the world in fact if you don't mind those of you who are willing just in the discussion if you can just say where you are watching from i always like to see the variety of different places that were able to reach with these conversations so i saw a few earlier from various parts in the world india argentina germany spain miami that's an exotic one wow that's scrolling by too fast for me to read but uh chicago rhode island yeah a bunch of india switzerland amsterdam pakistan melbourne i guess i didn't really pronounce that correctly melbourne melbourne they always get on my case in australia when i pronounce that incorrectly but anyway thanks for joining us and we're going to be speaking to roger penrose i don't know in about um 20 25 minutes or so what i'll start with first is little discussion of maybe a little preamble to what roger and i will talk about and maybe take a few of your questions before we get into the conversation as you no doubt know roger penrose is one of the great minds in mathematical physics or physics or mathematics he has made impact in both of those arenas as well as a crossover between the two i don't even think he remembers the fact there's no reason why he should remember the fact that you know i went to oxford as a graduate student and i went there because i wanted to study with roger penrose and on the first day there i showed up in his office and we had a little chit chat kind of thing and he told me what he was working on and at that time it was so to my ears so mathematical that it felt to me that it was too far away from physics for it to be something that i wanted to work on and i was pretty upfront about that and he suggested that i move over to talk about or work on i should say physics in the physics department is right across the street from the mathematical sciences institute at oxford so i was only his student for about two weeks then i moved over to be a student of particle physicist graeme ross i also spent a little time initially working with the astrophysicist james binney so it all worked out well for me but the irony is the irony of it is when i went over to work on physics ostensibly i got into string theories many of you no doubt no and in that work on string theory i had to make use of and learn and master and apply some of the very mathematical techniques that roger penrose was describing to me in our first meeting so although i left working with him to do things that were less mathematical i wound up doing things that were equally mathematical just a couple hundred yards across the street as as things turn out but again i don't even think he remembers that that brief meetings that's all it really amounted to but what we'll talk about with roger of course is the work that resulted in his being anointed if that's the right word here he is a knight that's really where the word anointed should be used but his in the announcement from the nobel prize committee that roger won the 2020 nobel prize in physics he shared it and you may recall that we had a conversation with andre guess one of the two individuals that he shared the prize with which is fantastic that work of course is in the arena of black holes it's the mathematical side of black hole so we'll get into that conversation but the other thing to really bear in mind is roger is a thinker whose ideas span a whole range of different subjects he's not one of those scientists who just drills down further and further further in one particular area as some of you i'm sure know he has ideas about cosmology we'll get into those a little bit he has ideas about the arrow of time he has ideas about mind and the relationship between mind and computers can the mind really be thought of as a biological computer many people use that analogy some people take that analogy really quite seriously roger has arguments based on girdles incompleteness ideas incompleteness theorem where he tries to argue and to many people he has successfully argued i'm on the fence on this maybe he'll convince me today if we get into it that the mind really cannot be likened to a standard computer because he believes that the mind is able to access certain kinds of understanding that stands outside of the algorithmic step-by-step methodology that's intrinsic to computation as we usually talk about it so for him the mind is something that certainly transcends that metaphor it really cannot be likened to a computer and he has ideas about where consciousness arises and it has to do with some issues in quantum mechanics that we will also hopefully have a little bit of time to talk about issues in quantum mechanics we have discussed in these sessions from time to time the gap in our understanding of quantum mechanics not everybody believes that there is a gap i am one of those physicists who certainly does believe that there is a significant gap this quantum measurement problem this if you will second step that has to be employed when using the framework of quantum physics in quantum physics we use the basic equation that er that schrodinger gave us some time ago but you take that equation and that's not enough you then have to take that equation i don't know if you're seeing that equation but i see the equation right now but uh you take that equation and then you have to augment it with the second step the second step in which you go from the fuzzy nebulous probabilistic description that this schrodinger equation provides you and you have to extract a single definite reality from that haze of possibilities for which you have probabilities how do you do that and this is a question that many people have worked on there are solutions that people have proposed i would say it's fair to describe the situation as still unsettled and roger penrose has taken that unsettled quality of quantum mechanics and within there he argues we may find the answers that we've been searching for for consciousness i'm skeptical i have to say i'm highly skeptical many others are too but it just gives you the sense of the boldness of thinking that pemrose has brought to bear on things that sparked his imagination which is a a rare and wonderful quality and so we'll get into that as we as we head onward let me just spend a couple minutes just giving a little bit of background on some of the ideas of black holes so that this conversation just has a a little bit of a framing because we may not start from the beginning i'm not sure where we're going to go in the conversation but many of you know back in november of 1915 albert einstein was putting the finishing touches on his general theory of relativity and he wrote down the final equations of the general theory in a paper that got published in 1916 but was at the prussian academy in november of 1915 that he wrote down the equations and this was a monumental moment in the history of scientific ideas gravity the most pervasive and obvious force in the cosmos was brought within a strong mathematical description one that went beyond newton's description which had various puzzles and problems having to do with the speed with which gravity would be communicated from place to place and so einstein writes up this paper and just about a year later a german mathematician physicist named carl schwarzschild it turned out he was at the russian front during world war one it's kind of an amazing story he somehow gets a hold of this paper and starts to calculate with it and he comes up with a solution the first exact solution to einstein's equations again i'm not exactly sure what you guys see but i i see that equation in front of me right now popped up on the screen which is a wonderful that's the so-called schwarzschild metric and that equation describes the gravitational field around a spherical object and in that equation it becomes clear if you just squint at it that something unusual happens when the size of the object the spherical object gets sufficiently small in fact you can see it in the equation when r equals 2g m newton's constant the mass of the object multiplied by 2 when its size becomes equal to that number which is known as a schwarzschild radius something strange happens you get a zero in one term on the second term you get something that looks infinite so something strange is happening and indeed the interpretation of that is that you're getting what's known as an event horizon you're getting a point of no return if you cross that distance if the object is sufficiently small if it's within its own schwarzschild radius which is just a number take its mass multiply by two multiplied by g if the radius of the spherical object is small enough if you crush it down small enough then the warp in space is so significant that you can't get away and by you i mean anything and as we love to emphasize that also includes light and if light can't escape from an object then that object is black and ultimately this is what's known as a black hole so you know it's also interesting to note i don't think we get into it with roger but you should sort of bear in mind as well this possibility of black holes not using that language but dark or frozen stars it actually emerged long before einstein's general theory of relativity just to give you the full intellectual landscape here the history of these ideas way back in the 1700s there was an english physicist i think his first name is last name is mitchell i think it's john mitchell i hope i'm not saying that you can correct me if i'm wrong someone can look it up and wikipedia right now i think it was john mitchell he asked a very simple question which is okay on the surface of the earth there's a certain escape velocity i don't know what it is 11 kilometers per second or something but whatever there's an escape velocity where if you throw an object up faster than that speed it will escape the gravitational pull of the earth but then he noted hey even in newton's theory if you made the mass of the earth bigger then the escape velocity would be up be higher not be up it would be larger number the bigger the earth the bigger the source of gravity the faster the object has to leave the surface to be able to escape the gravitational pull and just go off into space and he said what if you keep on doing that make the mass of the object bigger and bigger and bigger make the escape velocity larger and larger larger at some point the escape velocity will exceed the speed of light if the escape velocity exceeds the speed of light then light can't escape the object goes dark so this idea of a dark object because gravity is so powerful the light can't escape really does not originate with this short child solution does not originate in einstein's theory but it's einstein's theory that supplants newton's description of gravity so the fact that there are these dark objects at least in principle according to the mathematics in einstein's theory means that you got to kind of take them seriously you got to really think about them and einstein when he encountered this result i don't know if it had anything to do with the fact that schwarzschild had beaten him to the punch schwarzschild gets the first solution of einstein's equation einstein took his own equations and he can only solve them approximately so schwarzschild gets his exact solution when einstein sees it he is completely skeptical not of the situation where the object is larger than its own schwarzschild radius you know a star of the earth whatever but he's very skeptical that there would ever be an object that would be small enough that its physical radius would be within its own short styled radius short child number and so he's basically saying that these dark objects do not exist they're in the mathematics but they don't exist and to make the rest of the beautiful long story short we now of course believe that they do exist in the nobel prize this year is for the theoretical ideas that roger penrose developed to substantially bolster the mathematical case for the existence of these objects as well as the observational case that came from the observational teams that studied the black hole that we now call a black hole at the center of the milky way galaxy it's interesting as i said that i pause for a moment because i suspect that roger penrose might not describe his own work as establishing theoretically the existence of black holes per se we'll get into it a little bit but you know what what he really showed as we'll talk about in a few minutes is that singularities places where the mathematics in some sense of general relativity breaks down places where you can't extend the trajectory of a light beam any further in some sense places where space unexpectedly comes to an end it's really time coming to an end to be a little more precise that's what his mathematics and his singularity theorems establish now of course black holes are an example of that we have a an event horizon this edge surrounding this singularity but his insights really have to do with the singularity not so much with the existence of the horizon so i wonder how there's a little subtlety there and we'll talk about how the community responded to the theorems that he proved in the 1960s which showed that this kind of singular structure deep inside for example a black hole was an inevitable consequence of certain conditions within the general theory of relativity so it's a beautiful story again goes all the way back to the 1700s and i'd like to think that that story in some sense can be thought of as i mean it's a dominant specific collection of ideas that we'll talk about but it's also the case that in a sense what roger has spent a lot of his life's work on is thinking about things that are impossible or thought to be impossible from one way or another what i mean by that well we'll talk about how roger studied and no need to show any of these things uh to the audience that we'll talk about when roger joins him but he he constructed various shapes that are impossible to build in the real world but on paper you can draw them in a way that is both convincing and perplexing shapes as it turned out that inspired escher in some of his drawings roger has been focusing upon the problems within quantum mechanics again issues that some people think or solve some people think can't be solved he's been talking about issues in cosmology what happened at the big bang was it really the beginning of it all so these are the most perplexing questions the kinds of questions that some people say are insoluble impossible to solve but raj is all about trying to find the unexpected solution the creative solution to things that otherwise people would suspect would remain puzzling forever all right let me take a question or two before we bring um roger into the conversation just so that we keep this a little bit interactive uh escape velocity someone confirms 11.19 kilometers per second so i was pretty close and i don't know if anyone confirmed the first name of mitchell i think it's john as i said but who knows um sam banner one question i'll get to before we bring roger m when a particle of a particle anti-particle per that's entangled when it falls into a black hole what happens there that's a good question uh i wish we had three hours with roger i don't know how much time he's willing to give us i think we probably have to wrap it up in about an hour or so but that's a deep question sam and it's really at the forefront of research today last few years people have been deeply perplexed and and coming up with all sorts of creative ideas for what entanglement between particles means when one has fallen over the edge of a black hole does the edge of a black hole in some sense snap the entangled quality of those particles according to einstein's ideas that would not happen because as we'll talk about with roger the edge of a black hole is not some special location in space from the standpoint of physically measurable qualities at that location there's no sign post there's no obvious marker that lets you know that you're at the horizon of a black hole so classical ideas would suggest that that's not the case the entanglement should persist right across the horizon however when you think about that deeply together with what's known as the information paradox with black holes as we'll talk about stephen hawking shows 1974 that black holes can radiate if things can get out of a black hole the question is do they show an imprint of the things that fell into a black hole and in order for information not to be lost they had better show an imprint but that imprint through a circuitous chain of reasoning that i won't try to recount right now suggests strongly that the entanglement across the horizon of a black hole needs to be rethought there's tension between the information being imprinted on the outgoing radiation from the hawking process with the persistence of entanglement across the horizon those ideas are in tension due to something called the monogamy of entanglement yeah physicists do come up with uh strange names of things but it turns out you can't have entangled particles that are in mutually entangled pairs at least if it's maximally entangled this can't be maximally entangled with this and that particle be maximally entangled with something else further out but that ladder entanglement had better be there if information is to be imprinted on the outgoing radiation okay there there's the argument i said i wouldn't recount it but i just did so something's got to give because everything can't be entangled in that manner and some have suggested that maybe the entanglement across the horizon of a black hole gets snapped and if it snaps that can yield energy and if you then look at the entire event horizon of a black hole if you have these snapping processes all over that surface that surface will have a lot of energy now it's a real thing in fact people have given it the name firewall a hot surface that would incinerate anything that approaches it so the whole idea of falling into a black hole is a subtle one when these quantum ideas come into the story so yeah sam that's a great question one that as yet does not have a full answer but i should say maybe we'll talk about this in a subsequent discussion there's been a lot of progress of late i'm talking even in the last few weeks few months in making mathematical sense of these ideas and i would say that there's growing consensus that the puzzles that people encountered in the one that i just described uh are nearing their conclusion that people are getting more and more comfortable that there are ways of thinking about these things which don't have any internal inconsistencies and allow for information to not be lost as it falls across a black hole i don't believe roger agrees with that statement maybe we'll have a moment or two to talk about that as well in one of the approaches that he has been developing he makes use of the possibility that information is lost inside of a black hole many of us from the string theory community and uh the gravitational community that is informed by some of the ideas of string theory do not think that's the case that we believe that information is preserved but uh again not not a done deal and it's it will be interesting to hear roger's views now the other thing i should say roger's not a great fan of string theory as many of you know in fact he wrote a book and i don't remember the exact title of the book but i i do know that one of the words in the title was fantasy and i think fantasy was uh his description of string theory so maybe we'll get into that a little bit again i don't i'm not defensive about these kinds of things as you all know i just find it deeply interesting to uh hear a variety of different perspectives all right so i think roger's going to join us in just a few minutes assuming that uh time in the uk is still in sync with our time here and if you have questions feel free to jot them in the chat i'll try to look sometimes it's hard during a live conversation for me to switch my attention over to grab questions i do have someone who's going to try to pull out some questions on a separate sheet so i just see a few of you have already uh asked some relevant questions but um yeah like darshan doesn't penrose often criticize string theory darshana um bulkar yeah and um uh we'll see we'll see what uh what roger's feeling on those ideas is today and um i doubt his perspective has changed on it but it's it's interesting to hear in more detail what it is about string theory that strikes him as wrong-headed or going in the wrong direction or perhaps even the word fantasy so we'll see how that looks going forward uh terence lau do you think there's matter that exists inside of a black hole that's a good question too terence the inside of a black hole is a curious place as i was mentioning you know there are some who suggest that there might not even be an interior to a black hole that's one idea that people have floated but in the more traditional approach matter crosses over the edge of the horizon of a black hole the matter doesn't disappear it just is in a different location and so as that matter is pulled closer and closer toward the center the singularity of the black hole it still exists of course it's within the event horizon of the black hole the deep question is what happens when it hits the singularity does it still exist is it somehow flushed out of our universe is it thrust into a different universe we can't really answer these questions because of this singularity the singularity that roger penrose proved is there and and the curious thing the curious thing we'll talk about with roger as well is that you know singularities it's hard to uh it's hard to really understand what they mean because they are in essence a diagnostic tool that shows us that our mathematics breaks down if our mathematics is breaking down it's breaking down so it's not as though the singularity is a thing it's not like a marble it's not like a diamond or a jewel it is a diagnostic which basically is nature or the mathematical description of nature telling us that things are not working all right so let me now with that preamble give a brief introduction to sir roger penrose roger penrose is the emeritus rusball professor of mathematics at the university of oxford emeritus fellow of wadham college at oxford as you know and as we discussed he was recently announced to be a recipient of the 2020 nobel prize in physics he's previously won a great many awards so many that it would take half our session to describe them many of you know roger from his wonderful books for a general audiences emperor's new mind was the first book wonderful book that i remember reading in the 1980s very impactful book for me uh the road to reality this deep and uh expansive tome on the mathematical approach to describe in the world back in 2004 and uh his work on black holes black hole singularities in the 1960s is uh what we'll talk about here today is that's what he has been awarded the nobel prize for so with that let me bring roger penrose into the conversation hi roger how are you hello i'm i'm fine thanks it's very good to see you i was just trying to think the last time that we crossed path i think it was at a at a discussion of cosmology at princeton do you remember that it was uh you remember that occasion yes yes right i think it's maybe 2015 2016. i mentioned to the audience you probably do not i would be shocked if you did remember do you know that i was your student at oxford for about two days do you remember that i knew i knew you were yes i i don't know whether i remember you specifically then but yeah we only met once yeah we met once and you described to me some of the work you were doing yes yes yeah and it was um on the sort of more mathematical i was describing to the audience how it's somewhat ironic that i switched over to physics because i wanted to do less mathematical things and then i wound up doing string theory and algebraic geometry and compactification just a couple hundred yards across the road over at the physics building so go figure that's how the world works in any event deep congratulations on winning the nobel prize um well thank you very much yeah it's a must be have been a thrilling moment uh to be recognized in that way and i'd like to talk about some of the work on singularities black holes perhaps we can even get into some of your other ideas in cosmology maybe a little bit on quantum mechanics and consciousness if time permits but can we start it's always nice for our audience to just hear a little bit about your own background if you don't mind i was i was reading an interview and it was it was interesting to me to hear you note and again perhaps the interview got it wrong so correct me if i'm wrong that when you were young you were really good at mathematics but you weren't the fastest kid you needed to be given extra time to actually do as well as you could is that is that accurate i was always very slow yes yes i could do it but i was slow no i had this was actually in canada during the war years and i think i was in i forget exactly which grade it was but we i i hadn't done particularly well in maths and i had a teacher who i regarded as very insightful he was mr net and he realized i got you know fairly low marks but i think he realized also that uh i i got low marks because i only got about halfway through the paper so he decided that he would let me have um the end of the period which i after that there was a play period i think and he said well look you can keep on going right the way through the next period and occasionally i needed even a bit of the next period after that but then i used to do pretty well i used to get in the 90s and you know he he recognized i was just slow not stupid although i did i did get moved down to class um yes in my first year when i was in canada i was in a combination of high grade two and low grade three i was in low grade three and my teacher there decided i was too stupid being in low grade three and she moved me down into high grade two um but then uh she couldn't quite fit me in the crack between those two so eventually she moved me up into high grade three which was better it's better because i couldn't start sure she couldn't stand me i think was the main thing i don't know what it was i was just too slow that's so interesting you know it's funny because when i give final exams in my classes at columbia i don't make them time i tell the kids you come in and we set it up in such a way that they can sit and some have stayed as long as 12 or 14 hours we will start we'll start at three o'clock in the afternoon and i i have a ta and sometimes someone leaves at five or six in the morning because my view is very similar i don't care how long it takes i just want to see whether you can get it done um no i think that that was certainly right i mean i did speed up a bit afterwards and i managed to finish finished papers but uh and so when you were when you were young were you were you doing mathematical problems were you uh tinkering with puzzles and was that the kind of yeah my father was well he was a scientist but he worked in human genetics but he he was really interested in mathematics also i had an older brother who was very he was different from me he was very precocious and which way ahead but he also was interested in mathematics and physics i learned a lot of physics from him but for my father a lot of mathematics and we used to make polyhedra and various things like that and we had a great interest in that i think it was i remember one occasion when i noticed there was a pattern on one of the uh floor i think whether it's a floor or a sink surface i can't remember but it was a tessellation of regular hexagons all over you see yeah i looked at this pattern and i asked my father well look suppose this thing extended way way over around and could it go all the way around the earth and make a sphere you see so he said no you couldn't do that but you could do it with pentagons so he taught me about a dodecahedron you see so there's a of course that came back again with the non-periodic yeah so that it was at the origin if you're thinking about the what's now known as penrose tiles um i think more the origin was something else that i got from my father which was actually he had a book uh due to the famous uh physicist mathematician kepler johannes kepler and in this book there was a picture with all sorts of non-crystallographic designs i mean they were see how far you can get with with octagons and things like that and mixed up with hexagons and things like that little patterns with combinations of these and the biggest one had a lot of pentagons and i had seen that before although i wasn't thinking about it when i was finding out about these non-periodic pentagonal patterns but then later on well there were two two amazing things about that picture one of them was that i was i think it was shortly after quasi crystals and people were seeing the five-fold tenfold and the eightfolds and i went to switzerland and visited there and i was talking to a chap called nissan and he had claimed that there were 12-fold ones nobody believed him at the time and then he showed me the diffraction patterns and i looked at the diffraction patterns with a um 12-fold a little dodecagon and then little squares and pentagons and things all the way around and i thought i i sort of arranged the dots you see these you get bright spots on the bragg peaks and in the diffraction pattern and i noticed they made little shapes like pentagons and squares and things i joined hexagons and squares and things i joined them up and i made this pattern around the unsightly going inwards from the dodec again and i looked at this thing and i said i'm sure i've seen that picture before where have i seen that and i realized it was in the kepler picture and it was one of the one called ff i think it is just right over at the side and it was exactly the same person but the other thing was the biggest one with the pentagons later on i think i was giving a talk again bringing in the kepler and i wondered whether this pattern of pentagons would fit into my my own patterns and i found a place where exactly the same lines including some little lines he put in inside one of the dodeca he had decagons decagons and pentagons things like that you couldn't quite tell where it was all going but i took this and i managed to match it with one of them exactly in the middle of one of my pentagon patterns so he more or less had it before wow much closer than the islamic people and people often said maybe in exa islamic tilings you might see these things but they have interesting peasants with pentagons and things but never never one of these things but the captain did remarkable very remarkable yeah now there's also i i was reading that you were inspired by a impromptu trip to the van gogh museum what was that about that that was an escher exhibit is that right that was at the um there was an international congress of mathematicians they had those every four years i think i was in my second year as a graduate student in cambridge and uh somebody told me i guess i learned about the international congress which was in amsterdam in the netherlands and so i went to it with a friend and then i remember seeing one of my lecturers there this was sean wiley who taught me about algebraic topology and he had his hand a catalog and it had this escher picture with the the night and day with the birds in the night on one way and the white birds in the dark and the dark birds and the white and then sort of meshed together in the middle and i thought that was extraordinary and he said well you go to the in the vanguard museum there is an exhibition by this artist m.c escher i'd never heard of it before or him before so i went there and i was absolutely stunned by the amazing things there particularly the one called relativity with people going upstairs and do you know the picture with a i i think i do know that one and now didn't you and your dad start to draw well we see i i came away from that exhibition i think it was in the vacation period afterwards and i thought i would like to draw something that i hadn't quite seen in the exhibition and i put pictures with roads and bridges and rivers going off in possible ways and i whittled it down simplified it to this thing people now call the tri bar this is the impossible triangle thing is that right and i showed my father you know and he showed it to all his friends it made more made them feel a little ill my father decided to uh draw a building yeah that's it yes he drew buildings um impossible buildings and then he came up with the staircase and so we decided we'd write that's it we'd write a paper about this which we did but we couldn't decide which journal to send it to because we didn't know what the subject was we had no idea what the subject was so my father said well i happen to know the editor of the british journal of psychology so perhaps we'll set psychology and send it to them right so this is a staircase in which you continue to walk upstairs and yet you still find yourself at your starting point as you go around yes so so anyway we published this and then we we credited escher in in the in the uh acknowledgements and sent a copy to usher i mean for asha's uh the museum yeah i think we're the catalog in the museum and in the meantime ash had produced belvedere which was a picture with a similar kind of impossibility is that the one with the waterfall uh no he did the belvedere is a sort of building with with uh it's got pillars which are joined up in the impossible way got it got it okay and uh and then he my father sent a copy of this paper to to asher and he got a copy and he then had a correspondence from my father quite a bit and um uh the the staircase was the first one he did based on the this is called ascending and descending right the waterfall he did a little bit later got it amazing so let's turn into um to the uh initial work that you began to do thinking about relativity and ultimately what turns into black holes so you know between 1915 when einstein wrote down the equations and say you know mid 1950s and so forth general relativity was no longer the exciting arena of physics most people were focusing on quantum mechanics and nuclear physics atomic physics things of that sort so when you started to think about einstein's ideas were you kind of off in a quiet area of research at that point i wouldn't say quite that there was quite a bit of activity but in britain it was almost entirely in mathematics departments i think or entirely as far as i know people were you know playing around solving the equations in clever ways and that's what they were doing um i got interested i guess let's see i should it was in 1958 when i was back in cambridge as a research fellow i was doing pure mathematics when i was a graduate student algebraic geometry and things like that but but i learned a lot about tenses and how you'd how useful it was to draw little pictures with arms and legs which joined up together rather than indices and uh i've never seen those pictures you haven't seen them i don't know if i have uh i'm not sure i can illustrate i guess i could it looks like you have a whiteboard behind you there i don't know if it'll show up on the camera yes i could use that but um but i guess i can imagine you're basically tying together the indices from different tensors as opposed to just having repeated uh letters and they just join them with lines that's right yeah yeah there is a picture in carlo rovelli's book i just if you can find that i'd have to find the right page yeah okay good enough but anyway um yeah you just instead of seeing an index here in an index here just draw a line draw a line yeah sure then i develop various notations for symmetrizations and then you can do symmetrizations on top of anti-symmetrizations and this is very useful in many areas of physics and mathematics and um but i had a good friend denis sharma who who i got to know primarily because he was a friend of my brothers oliver oliver was at cambridge doing physics and i was doing an undergraduate degree in london university college london in mathematics which included applied maths which which is a lot of physics in that but i remember being inspired by a radio talks by fred hoyle and fred hoyle was i think there are about five of them he started with the earth and then he moved out and moved out and moved on cosmology and eventually talked about the steady state model which he and bondi and gold had developed because there was a paradox in those days about cosmology because people had worked out the age of the universe and they'd also worked out the age of certain clusters of stars called globular clusters and the globular clusters were older than the universe which was seemed like a paradox and so the steady-state model emerged out of that so well the big bang was not really the beginning at all and you had a steady state model it was actually due to mistake because they the astronomers had mixed up two types of uh variable stars cepheid variables and and they've got the wrong ones and therefore they got the universe too young but but that wasn't known at the time right and uh hoyle was describing this in his radio talks he was said when the the galaxies recede from us and they receive you so you need them to recede and then in the gaps between the galaxy you get new material hydrogen produced popping up i guess in that approach right yeah that's right it was a clever idea and it was wrong but it was a clever idea and uh i quite liked it and i heard fred talking about the remote galaxies as they uh well you see when they got faster than light they would disappear so he said they would just appear when they got faster than night i thought this is a little strange and i started drawing little pictures with like cones and and what i really saw what happened is that they didn't disappear they just faded away gradually they got dimmer and dimmer and dimmer and so i was visiting cambridge and i'm visiting my brother in the kingswood restaurant and i was sitting down having having lunch with him and i explained my puzzle to him about the galaxies disappearing and he said well i don't know about cosmology but sitting on the table over there is a good friend of mine dennis sharma and he knows about cosmology and he'll he'll tell you the answer you see so i went and talked to dennis and i drew my little pictures with the light cones and and he hadn't seen this before and he said well i don't know about that but i'll talk to fred and ask him but apparently this made an impression on him but when i did go to cambridge as a graduate student dennis was absolutely he sort of got hold of me and said look you've got to learn about physics and awful lot of physics and cosmology and he used to drive me uh to visit uh stratford for the play the shape shakespeare plays and things like that so we used to go quite commonly and he would drive at great speed around these windy roads to test relativity no doubt exactly because it was this mark's principal he was a great fan of principles who said that you were the rotating bucket well it was but this was he was the i mean he was going to go around the wrong great the side of the car i said no that's that's the action of the fixed stars [Laughter] that was his so without the stars you wouldn't have felt that centrifugal force just now as you whipped around that's right so we thought look supposedly remove the stars one by one one more then what would it be like what would happen to the election would you be determined by the car then you'd take the car to pieces what's left you see now that was quite an important uh influence on me indeed yeah just i don't want to go a diversion too much but do you do you agree with that perspective do you think that without the distance stars if you were to rotate you wouldn't feel uh i'm not sure about that well it doesn't einstein never i mean it was a big influence in his origin of the theory but it never really worked right within with his model no i'm i'm not really proponent of that scheme but it did it did lead to this scheme of spin networks yeah which was you just whittle it down to a few few spinning particles and how do they know how they're spinning and so on yeah so it influenced me in that direction so what then pushed you in the direction of of thinking about what we now they weren't called black holes well it was 1958 i'm getting better this was when i was back as a research fellow and dennis said i i'd already got interested in relativity at that time um because dennis was i think and then he said well look come with me to a lecture given by this fellow david finkerstein at king's college london and so i went and and david was explaining how with the famous solution called the schwarzschild solution which describes a spherical body in einstein's theory and we usually just think about the vacuum outside the body because chartreuse also had a way of describing the matter inside but that wasn't so important it's really the outside but then you imagine squashing this body down and down and down until it reaches this scale which is called the schwarzschild radius and at this short short radius if you look at the formula the the equations you see it just goes crazy at that point and it looks as though you've got a singularity that is to say looks as though things go to infinity and zero and just doesn't make any sense i think we have that equation we can probably bring it up as you're talking yeah at this r equals 2m in inappropriate units when the radius reaches what's called 2m in in in appropriate units and for the sun i forget it's just a few kilometers yeah three kilometers for the sun two kilometers or something yes um for the earth i don't know about that big or something a couple centimeters yeah yes and uh but but people thought in those days well you never would squash anything down that far so so what's the problem but fingerstyle's talk was was a more theoretical one and he was describing how if you change the coordinates the sort of infalling ones and then the like cones are tipping over like this then you get rid of that singularity and i was very impressed by this at the end of it he talked to me and i told him that's been spin networks and he told me about relativity and he sort of swapped subjects he considered because he was working i was working on combinatorial physics and then i changed it in relativity and he changed from generativity to combinatorial physics what an impact you both had on me but anyway i thought when i came back from the lecture i thought well gosh he's got rid of that singularity r equals two f but that's still the one in the middle maybe there's a theorem of some sort which shows you can't get rid of this you push them this way in that way but you just got rid of it i thought what do i know about general relativity i mean i've never seen anything like that what do i know about general relativity that other people don't know and maybe might miss you know just sort of some way of looking at it what do i know well i know about two components spinners and why did i know about them because i was playing without general sort of tensor systems and usually in an algebraic way and with these diagrams and all that stuff and i couldn't see how the spinners fit into this and so dennis gave me an incomprehensible book by course and really a good book much of information in it but it was very incomprehensible but then curiously enough very strangely i went i think at that stage when i was in first year as a as a fellow i went to the second core second part of the course of quantum mechanics given by paul dirac i leaned to the first part of the course when i think it was an undergraduate then i went to the second part of the course and curiously in the middle of this course he deviated from his standard uh exposition and talked about two component spinners now i i just thought this is great for fortune but i learned afterwards talking to people who went into direct in i think there was a biographer or something who was i was talking to a woman who was working on his early papers and uh she said it was most unusual for direct i think it was she or maybe it was graham farmer who told me it's most unusual for for direct to deviate from his course so i don't know but it happens that dennis sharma was his only graduate student around about that time and i think he possibly mentioned that if he talked about two spinners there's somebody who might be interested in him but he did he gave a very very clear two or three lectures on it made absolutely clear to me and so that was the thing i knew and i knew that you could you basically you split your tensor index into two and one's a spinner and that's the complex conjugate of it that's a very beautiful idea um but then i thought well let's try and apply this idea to general relativity i haven't seen anybody do this before and it works amazingly well i'm quite surprised how well it worked and you could the main point was you've got a very good understanding of the viral tensor you see the curvature tensors they're called the riemann tensor and it splits into two pieces and one of these pieces is called val w-e-y-l bile tensor and this the richie tenses the other part and that part describes directly the matter so it's likely charge in electromagnetism in electromagnetism maxwell's equations you have the charge current vector which is the source then you have the maxwell field which is the field so the maxwell field is the photons if you like now with quantized things it's the electromagnetic field that's how we can see each other without maxwell we wouldn't be here we wouldn't be seeing each other so or we wouldn't understand why we're seeing each other well you wouldn't people wouldn't know how to do it i guess that's true too i mean i think it's it's important to huge huge revolution in physics up quite unrecognized to the degree it is by the general public i think yep huge revolution but anyway that's not the thing i'm mentioning here but in the einstein theory you could do a similar thing you have the richie tensor which is the source and then you have the vial tensor which is likely maxwell field and when you write it in spinners it looks the equations look just about the same it's got two more indices but it's just four instead of two and it's a very similar equation so i really understood about how the curvature acted on light rays because of the spinners and that was very useful to me right all this is sort of background and this is much earlier this is 58 right um i can ask you one question on on that before we get into the details of what it is that you use this technology to to prove you said that you're at figelstein's talk and he shows that the singularity at the horizon at r equals 2g m over c squared that that is just a coordinate singularity that's not a real singularity by changing your description you can show that the math doesn't blow up no problems there and then you said that you said but there's still this other singularity at r equal to zero at the center of the solution that schwarzschild gave us and you said that your motivation was to figure out some way of proving that that singularity could not be gotten rid of but most of us most of us sort of approach things the other way right was like we want to get rid of singularities right well it's not the question what you want it's a question of what's true but what was motivating you to think that you couldn't get rid of that singularity i don't know i mean it's the same the thing is the curvature there is an infinite that's true yeah it goes like one over r to the sixth i guess as r goes to zero right for example like crazy yes you get to the middle but of course that doesn't tell you that if you had an irregular case uh that was what i was thinking about you know suppose you perturb it does that singularity remain so physically that would be rather than just spherical stuff falling in perfectly spherical all the way it might have an un a shape that's not symmetric and then maybe it wouldn't all collapse right at the center so you wouldn't have a singularity that's right well you see as i learned later but this is you see i i didn't do much after the finkelstein talk except familiarize myself um about spinners and how light rays behaved in accordance with the violin and richie tensor you could see clearly the difference between the two which he just focuses it's like a positive lens and the vial is like a an asthmatic lenses squashes and fletches like that and so i you know i appreciated all that stuff but it wasn't till much later i guess in the 60s now when i was at princeton well i've been at princeton and i got to work on gravitational waves john wheeler who was uh very interested in gr and i think quantizing was one of the things they were trying to do there i didn't much care for the way they were doing it um then i went for i was a two-year nato fellowship and for the half well it was about a third of the second year i went to syracuse university in new york state where there are an awful lot of relativists there including well peter bergman who had been einstein's last absolutely right and then there were people like arthur comar and well engelbert shooking was there um and various other uh anger troutman visited just after i went there and ted newman was the big ivor robinson ted newman race sax i think was in the army at that point but but he did visit i remember talking to him um but ted newman i got to know very well um and we developed spinner sort of techniques for looking at gr but the the main thing was more um later on when i started thinking i'm i guess i was back in princeton again later on just trying to think how what the ordering of this it was in london when i was back in london when when the um you see the point was the quasars had become puzzling to people these were these very bright radio sources which seemed to be not only 100 times brighter than an entire galaxy or whatever it was and uh very small too i guess it's more so smaller than the polar solar system because they had variations which indicated you know that the speed of light to get across from one side to the other you they'd have to be smaller than solar system and this was indicating to people that you you are looking as though you were down to the scale of the schwarzschild radius the aric equals 2m or you get it with a um constants in um but just at that scale um you can see uh you're playing around with that scale let's just say these act we've got physical phenomena which are probing that kind of scale so various people including fred hoyle and and uh and his collaborators um we're looking at the possibility of of maybe gravitational collapse i don't think they were thinking about black holes in the sense we do know but they certainly thought that something funny was happening down at this schwarzschild radius scale which happened to be the case but but they didn't know what was going on but the whole question you see um i guess this was in in the 60s in 1960 uh 64 that's right and since 1964. i guess i'd been to some conferences or something about it and john wheeler had worried me i thought well i can't drive whether it was yes i must have been at a conference then and uh john wheeler was worrying about whether the singularities were real or not yeah and the what there had been this paper in 1939 uh by oppenheimer and snyder where they studied a dust cloud so this means it's matter with with no no pressure and it's falling immediate completely symmetrically in towards the center spherically symmetrical to the center and there you've got this singularity in the middle which is infinite density and this is a picture of a black hole it's the one people use often a black hole but people were suspicious of this for two reasons one was it was dust and therefore no pressure that actually as it turns out was not a good reason because pressure works the other way but that that wasn't the point i mean probably stronger actually yes that's just that's but then nevertheless the fact that there's no pressure and somehow there's nothing to stop the particles coming together and the main point is it's just focusing right into the middle so of course you get a singularity there's nowhere else to go i mean it just aims at the central point and this would seem to be an artifact give it a little bit of irregularity it's swished around and called squarely on again and this was given a lot of credence particularly because there was a paper by liscious and kalanikov two russians where they appeared who to have proved that in the general situations you did not get singularities yeah these were only artifacts of special case secular singularities and and this paper was out in the in the journals and i had a look at the paper i certainly looked at it but i didn't i didn't there was a mistake in it which was discovered i think by belinsky later on and he then joined with the other two and they corrected it but this is part of a result of the work that we've done to show that singularities are actually quite generic einstein himself also wrote some papers oh yes yes no he i don't think einstein you see let me finish the story here because of course um yes yes yes yeah let me finish this story and i'll come back to what else i would have thought because i think you're absolutely right um as some other people he probably would have had a similar let me come to that um the the so i was trying to think what happens in the general situation and i believe liscious and kolachnikov i looked at the paper i did not knowing the mistake in it but i did i just had the view that i didn't quite see that you could properly prove anything using that method i mean maybe you could but it wasn't it wasn't sufficiently persuasive to me that they were right and i thought quite likely it wasn't true that you did get singularities in a general situation i remember walking in a park i used to live next to a park and walking in that and trying to imagine myself in this collapsing material and i came to the view that it had to be that that if it was a local problem if it getting things get curvatures getting big they just would go out again but if it was something non-local some non-local condition all the way around in some sense that it would have to be a condition of that sort now i i know what to do but i had for another reason it's very there's a lot of coincidence in these things i had been writing in 1964 another paper on something quite different this had to do with the asymptotic properties of fields including gravitational fields as you go out to infinity and what happens at infinity and i had this trick for conformally transforming infinity squashing it down into a finite region n-rows diagrams that we now call there's a much easier way of thinking about what happens at infinity as you don't think of it as infinity because i was no good at doing all these things with limits and everybody was doing limits and orders of magnitude and so on i didn't like that kind of stuff so i've got geometry squash it down and you can see where infinity is and and it was i could see it was a very useful way of thinking about it but the main thing was um this is now not about infinity but i was writing no sorry i was writing this paper which was about the papers infinity and i was i got stuck at one point because in order to prove that the gravitational field behave in the right way it's the sort of peeling properties that ray sax had let's not go into that here there was a very beautiful way in which the curvature peeled off as you as you came in from infinity really and uh i had a nice way of looking at that and she had to show that your vile curvature your conformal curvature had to be finite at infinity and i couldn't quite prove that unless infinity had to be spherical that is to say you've got you look out of the sky and you see a sphere out there if you think of that's infinity well there's that sphere and then there's time so the infinity is a three-dimensional space which consists of that celestial sphere in time but it's really the one in the other way you're looking out your lighter is going out rather than coming in from but it's the same picture so it's the sky right out there but i couldn't quite prove that it worked if the sky had a funny topology it might be a taurus you know i think like a shape of a surface of a doughnut um or but then the proof didn't work so i thought well that's this is a nuisance i thought any any sensible purpose person would say well just assume it's a sphere of course it is i thought well look maybe it's not it would be maybe you can prove it's not it's actually a sphere so i've developed an argument using looking at boundaries of futures you take a a point and you look at its future cone so it spreads out so this is currently in space time the point makes this cone but then it's going to cross itself do all sorts of complicated things but it still makes us fear if you understand what these the way these crossings and how they behave and what the boundaries of futures look like so i got a good feeling i i sketched out a proof in the appendix i it was a bit sketchy but i think it's essentially okay but um the point was i got familiarity with what boundaries of futures looked like right and so then i the next part of the story was when i was back in england and i was working at birkbeck college and a friend of mine this is ivor robinson who was who's an englishman but and he was working in he headed a department relativity in dallas texas which was at the wasn't part of the university of texas at that time but it was an institute and he was i don't know what he was talking to me about but he had a wonderful way of speaking and the americans all loved him because he had this what he did have a wonderful way with words there's no question about it and he was talking to me like this and just all of a sudden he waved his arms around like this i was walking down the street going towards where my office was yeah walking down the pavement the sidewalk and then we got to a crossroad and as we crossed the road we had to look out for traffic so the conversation stopped and then we got to the other side and he started talking again again like just like this then when he left i started thinking i got this strange feeling of elation that something something that clicked just as i crossed the street i didn't think it was crossing i had to go through all the things in the day what was it was it something i had for breakfast was it walk i'd done later or what was it this or that no no then it came back oh it's crossing the street i know what it was so i had this idea of what happens when you're just inside what you now call the horizon the light rays you imagine a two two dimensional surface so it's just like a balloon and then this balloon there's a flash of light on the surface of the balloon and that flash of light if you normally think if it's like an ordinary spherical spherical-like balloon with the ones concave and the other convex but on the concave side the light would converge on the convex side it would diverge but if this balloon were inside just inside surrounding the material and just inside what we call the horizon the light rays on the outside would be coming in as well and so they both be converging and if they were both converging you don't need it to be actually spherical it can be an irregular balloon but if you light rays are converging on both sides then from what i knew about the futures of boundaries that you'd have a compact boundary and i can knew that you could prove something from that that you'd have to have a singularity so that was a trap the trap surface that you were able to it was the trap surface which was the key to characterization of a collapse which has gone too far right and it's not a local characterization because you can have trapped surfaces locally you can you take two pass light cones and they intersect in which is locally trapped so there's nothing wrong with it being but it's trapped locally but all the way around and that's the problem and when you get that you have a singularity so the proof as long as the energy density that is to say the light rays there's a general tendency for them to focus inwards if the richie tensor is has a positive focusing property that means positive energy so if it's n or non-negative right well not to be zero is still all right if it was negative that would wreck the theorem so your nobel prize winning result you actually came to by following this sense of elation yes reconstructing during the day when it happened yes and extract have you had other moments of elation that i haven't had one that i'd forgotten that's i think the only time i'd forgotten i'd have to no i have had i have had ideas which i've forgotten and resurrected that's true right yeah yeah that's an amazing story that's an amazing story quite like so so you write this paper where you write up what you just described to us so so beautifully what was the reaction well that's what i was come back thinking my other question which is again singularities are usually the kinds of things that we teach our students throw away the solutions that are singular those are the non-physical ones here you see of course there were people who didn't believe me i had a remember a a letter from um jim badi's son well you know what his name is jim bardeen yes no not not the one who got two nobel prizes yes no he he wrote me and told me that my proof was all wrong so i had to tell him that you misunderstood there were people who thought he was wrong technically there's an error or they're just saying we don't believe it i mean like a technical error they were claiming i don't think they just didn't follow it okay um there was one very good reaction which was from charlie misner who actually gave me a better proof there was one part of my proof which was messy and he said why didn't you do it this way i knew i knew that argument i just hadn't thought of using it so i said nice thank you i hadn't thought of that so that so my laser description it's not the one given in the paper in my later descriptions you use charlie's improvement right that was just a technical point which made it better didn't change the argument particularly it's it made a much neater way of do doing it so that was that reaction but let me give you another reaction i remember i was in princeton this must have been following that uh and i remember going into the lecture room and find hold of wherever it was there and uh and bob dickey came in and slapped me on the back and said he was very pleased with result oh you've really done it now you you've shown you've shown general relativity is wrong yeah so a lot of people that was their reaction because you get these singularities general relativity is wrong and bob dickey was very keen on this because he had his objective theory trouble the theorem works in his theory too so it wasn't much of a a a resolution of his problem but um let's go back to einstein so einstein was highly skeptical of short style solution and so forth because he died by then he died of them but of course but he was highly skeptical what do you think einstein's reaction i think he would have thought general relativity is wrong really inspect i mean there's quite a lot yeah i think i remember also um um philip morrison phil morrison yeah i remember talking to him about it and he said oh yes i mean he he didn't believe in black holes and all that and you thought it was wrong in general but he was wrong i didn't realize he thought it was gr was wrong but it wasn't such a well established theory at that time i think i mean of course there was the nobel prize won by by taylor um yeah yes that's right yeah for the spin down rate that's right spin down i mean that that was impressive because that really showed that they it agreed with gr and gravitational radiation yeah so so had einstein thought of your argument back say in 1915 or so he might have discarded the general theory of relativity that's an interesting point it took a long time before people were you see there was a long time for people really thought you got right down to that level it took the quasars you see really well you have to go back to chandrasekhar too yeah because there were studies of uh that was the work chandra sega did on the boat when he was 19 or something going to cambridge or something from india or something we're going to cambridge yes and he did this calculation to show that that that white dwarfs were unstable if they were more than about one and a half times the mass of the sun right they would collapse yes yeah so he'd already showed that and and he realized there was a problem and he i think in his paper he was very modest about it he just said this leaves us pondering on other possibilities or something like that right so now obviously you you you didn't think that this proved that the general theory of relativity was wrong you know this is just revealing equality that's not a theory yes um uh now black holes were not yet um call black holes at that point but how did john wheeler the man who coined the term black hole or popularized it what was his reaction to your proof oh he he was very pleased with it yes i think he he thought it was a no i think people who were really into relativity and weren't prepared to give i mean they obviously were prepared to give it up in the sense of arguing that when you reached a level when quantum mechanics right impact on gr and that you might expect not to happen until you had radii of curvature of 10 to the minus 33 centimeters so you're looking at 10 orders of magnitude smaller than the an ordinary particle right uh 10 to the minus 13 10 to the minus 33 what are we talking about 20 yeah well it depends if you call 10 to the minus 18 or so maybe the radius of a proton then you're looking at 10 to the you know 15 orders of magnitude smaller but yeah yeah sure that's right 10 to 15. you know if you're looking at sort of nuclear forces that's right so you're looking at tiny tiny things way beyond the sorts of physics we're worrying about normally right if you have a gravitational collapse then you're faced with this sort of problem you will is that what goes wrong and in my paper i just say oh well something goes wrong and we don't know what it is right i think i did i can't remember what i said about quantum yeah yeah you did mention that quantum mechanics might be the resolution to it but but your paper wasn't black holes per se it doesn't talk about event horizons it's really talking about inevitability of these singularities so so were you thinking black holes as the place where your theorem would really be realized in nature well that was the natural thing you see i remember giving a talk yes well that's another part of the story of course when i thought about the theorem in the paper i gave a talk at uh king's college london in in late 1964 and uh despite what the movie says stephen hawking was not there oh the uh the the theory of everything movie that's right who the person was there was jl singh who was a distinguished uh relativist who had this very geometrical way of looking at i liked his book very much because it had this geometrical way of thinking which which was my way of thinking too um and he was there at the talk he just happened to be visiting london i think i was pleased he was there um but what the thing that worried me a bit is that it proved you had singularities but you couldn't necessarily see them because they seemed to be hidden by this horizon didn't mean that they were necessarily and you might imagine more extreme situations such as a cursed solution which which rotates see the normal rotating generalization of the schwarzschild solution for with rotation is the cursed solution and this nice exact solution but you can have an angle an angular momentum parameter and a mass parameter and if the angular momentum gets too big then you lose the horizon and you get what you call a naked singularity which you could actually see the singular point and the question arose might you have those situations sure you'd be likely to get the black holes but there might be more extreme cases where you could get naked singularities and the theorem i proved didn't distinguish between the two it didn't say you necessarily got i mean you you actually looking at the perturbing this virtual solution so you expect that the in those cases you would retain the uh the horizon but there might be other cases where you where you didn't necessarily which was worse it'd be worse than black holes but i think i thought postulated this thing that i call cosmic censorship which was that that black holes were you know forbidden to be seen they were censored by the horizon right now that has not been proven right i mean disprove no i think it's still a generic situation i remember i went to a talk 20 years ago by salt tukulski where he was doing work on these light ellipsoid mass sources for gravity and he claimed that you could have the singularity popping out beyond the horizon but then i guess there's been more recent work which has shown that that's actually not true in that case so yes well i think you see you can get specific particular solutions well i think the the horizon the node from the charge right the charged version of the short shift solution the rise in the noise from solution if it's like the curve with too much rotation here you have too much challenge yeah then again you get a naked singularity right questions can these ever be realized yeah you get solutions but the question is are they generic would they survive general perturbations right and that's what's not proved right and i thought that to costly thing certainly doesn't violate that as far as i as you say i don't think it's yet established right so so as observational work progressed and you know andre guez you know uh who has won the prize with you as the observations began to establish the existence of black holes did you feel vindicated like this is yeah i think so i was really glad to see i think whether the earliest what was the earliest one i forget there was the double star wasn't it which looked as though it was a black hole oh i'm not even sure i know what that one is um the double star system which was the first persuasive indication yes it's sort of sucking there one there was a a big red charge or something yeah and it was accreting onto a smaller mass and you could see the effects of the accretion i see pretty cool you see i used to go to these uh texas conferences yeah i went to them one of those ones i i went to the first one where that's where roy kerr talked about his solution right but then i think this is yes that was it was stimulated it was really the angle about shocking um rival robinson alfred shield got together and said we need to bring the relativists and the astrophysicists together because they're really evidence for for the general relativity playing a big role in gr it was still a lot of people were skeptical of it for a long long time but i could see they used to invite me often several times at least to give torture talks on black holes which i did a few times and uh like it was nice to see how gradually and the beginning people were very skeptical i think it was a very small minority who really thought these things were really there and then gradually they built up and you could see until it was about fifty percent of them zoomed off the other side the majority of people were accepting them after that point right it took quite a long time for them to take pick up on them yes and when the uh when the event horizon telescope actually showed what we like to call a photograph presumably that's a pretty uh pretty stunning stunning moment you spoke about elation as your experience of this idea that you were able to thankfully reconstruct when you got the call about the nobel prize with that also a moment of elation or is that a different uh glorious combination of things which which kind of spoiled the event by the time i heard about it oh really well yes because when people ask me what were you doing you said what were you wearing or something but actually was probably the first indication was in my i was in my birthday suit because because i was having a shower and the phone rang and this was patrona my who's my pa and she told me she just had this strange phone call from somebody who wanted to know my phone number and she said i don't give out your phone number to strangers and said what's it about and they wouldn't say what it was about and it was somebody from sweden you see so she slightly smelled the rat i think and said well isn't it about a prize and she's i'm i can't tell you anything about it i'm afraid yeah but she wanted my phone number so then i called patrona back and she said um i said well you might as well give her the phone number because if you give it to me an iphone it's not not any different so sure so then a little while i waited for a bit and then i got the phone call and that was from for one month she said well the the president of the um swedish academy of sciences wants to have a word with you and so would you hang uh hang on for a bit then she said well i'm afraid he's not available at the moment i think he's trying to get hold of the people in america and germany um but um she she she sort of hung up and then then the phone rang again and this time it was the the president of the academy of sciences and he started talking to you a bit and then in the middle of the conversation he hadn't mentioned the nobel prize in the middle of the conversation he said oh excuse me i think i i have to can you hang on so i hung on the phone i just waited and waited and waited and waited wait i didn't know what this is about but if it's important you'll call me back so i hung up but then he did call me back eventually told me it was a nobel prize but by then i was beginning to get pretty suspicious about all these things i wonder if you're the first laureate to ever hang up on me i don't know it was quite a long time i mean if it had been only a minute i was being on still like several minutes yeah that's fantastic the ceremony has not yet happened or or they're doing it by zoom or andrea i don't know how they do it for most of them in my case since i'm the only one in who's actually resident in uk there are three other british british is it two in chemistry and one in in no one in chemistry i've gone between numbers yeah sorry two uh there's biology isn't it this yeah there's biology two two two biology which would be uh jennifer doudna and chippendi but they're they're all elsewhere i think they're in the us so so i would have been the only one yeah so what they've i mean they are giving me a car to take me down next week and to to the to the embassy or the residence of the of the ambassador i see okay with my wife and my son very nice and that's that's that'll be the audience i guess yeah it's an unusual time unfortunately but uh it doesn't take away from the the honor in any way and congratulations on that can we shift gears to talk a little bit about cosmology is that uh sure yeah well it's it's a natural progression yeah it is of course i guess so i guess to connect the dots because stephen hawking who wasn't actually at that lecture but certainly uh at a subject yeah well i should continue that because dennis heard about the lecture yeah and he got hold of me and said would you like to give a repeat in cambridge right she did so you know this was in early 65 right then then steven was at that talk and more importantly i had a private session with stephen and and george ellis maybe brandon carter i can't remember certainly george was there and so we had a long session together and i just talked about the details of the methods i was using and stephen picked up on it very quickly and the first thing he did was to use my exact theorem but in the reverse time direction and using not for local but for very far off right and it was it was a clever idea i hadn't thought of using it i was thinking it was a local it's not doesn't have the power when you use it at the distance because you have to assume you have a coaching surface which is space-like which is um non-compact right and of course that's less uh i mean for a local thing you can assume it goes off to infinity so that's fine right that's for for a cosmological model it doesn't have quite the force so so steven then developed the techniques and made many many uh advances um on these techniques and he had a lot of help from brandon carter i think because there was a occasionally there were um mistakes in the argument there were what i call mistakes with the first kind the second kind i just say you just find a new way around them and it's fine it still works right so there were never any any mistakes with the second error so to speak yes and there were some even in the thesis which which was dennis and i were examiners of him and um you you were examiners for for stevens it's not like in the film where cape thorne was there kip thorne was not there no it was just the two of us but i'd say there were a few mistakes but i was going to point them out to stephen in the in the oral but he'd see he he found them all already no you know he'd done it was an amazing piece of work he'd done four different topics and i said in the account well any two of them would be good enough for a phd right but the the last one was that was on the sink only the last one was on the singularity cosmological singularities and then we got together he did three papers in the royal society and there were certainly significant advances particularly on the uh getting rid of the koshi surface condition which i think was perhaps the most significant thing he did was looking at kosher horizons and their properties and um no i think we did a lot of good work on that that's clearly true so the general conclusion was that under fairly generic conditions cosmology would have to have a big bang like singularity much as a black hole has a central singularity that's right right yes well the next part of the story is was i was in princeton you see yeah i was in princeton and we were about to go off to a meeting in stevens institute in hoboken just across the river from new york sure and lots of people from new york state were that was a thing that was going they were going on for many years they had important meetings and uh people from princeton would go up going up there and they you had to drive out in various cars and i noticed in the back of one of the cars was in the middle i think was jim peebles and of course last years and of course this was a long time before that and i asked him i said since i took the opportunity of making him an asking impression there was no room in the car like i didn't go up with him but i said why don't you there's all these different solutions you come up with much more complicated than ones you consider in cosmology why don't you look at all these other complicated kinds of models and he looked at me and he said because the universe is not like that and i thought my god it's not like that is it i think he was talking he was thinking about the cosmic microwave background and the evidence of how uniform it is and so it's a singularity of great uniformity it's not like any of those messes and this was a great a moment of revelation to me because i thought gosh now you've got to explain why up to that point it was as you say the arguments for singularities work just as well in the future as in the past future singularities past ones futures black hole singularities past ones but it's very different and if the idea would be it's quantum gravity if it solves the problem but then that doesn't make any sense but if it's quantum gravity why does quantum gravity tell you you've got this extraordinarily uniform initial state and this great massive and it's all tied up with second law of thermodynamics and there's a clear point that the uniformity means that the gravitational degrees of freedom we're not activated and the second that's what drives the second law of thermodynamics is really fundamental to physics so highly ordered gravitational degrees of freedom that then can become disorder yes what is the the vile curvature so this is again the biochemistry if you think of vial curvatures describing gravity which was not really the way many people thought of it but that was the way i thought of it vile curvature is the gravitational field and that is zero at the beginning i mean we don't know if it's exactly zero but it's it's suppressed right and the fact that you get this uniform vowel curvature zero initial state and then allows you to have the potential to clump into clouds of gas stars galaxies sun and we get our energy from the sun in a low entropy form i mean that's the whole point that schrodinger pointed out very crucially we don't get energy from the sun because it all goes back again apart from global warming but that's a small effect as we get as much energy from the sun as we as we shoot back out again but the difference is we get it in a low entropy form and it goes out in a high entropy form so it's small number of photons coming in spread out over many many photons going out yeah i think 20 times as many photons out has come in typically yeah something like that and that's really what we live on it's it's the entrance in there and that's because the sun is a hot spot in the dark sky and it's a hot spot in the dark sky because it clumps from gravity and that's where all life and everything where it all comes from this fact that we have this low entropy in gravity even though it's high in everything else so i had no idea why this is and i thought gosh it must be some very peculiar theory of quantum gravity because it's some very peculiar thing which is so grossly asymmetrical in time that was the view i held for a long time and it must mean that um the theory is crazy but probably crazy anyway but very crazy because it's so different in the past in the future right and then i formulated this thing called the vile curvature hypothesis just a hypothesis just says in singularities in the past type pretend there aren't any space like ones that would be cosmic censorship violated then you've got two kinds past kinds future kinds and just different future kinds are a great mess vile curvature running wild maybe there's where kaletnikov and polinski and this shits are right right possibly i don't know if they're right or not it's quite possible but absolutely wild kind of behave in the future absolutely crazy and ms misner did the same sort of analysis and that's uh very possibly the sort of thing you get why is it so different is it just quantum gravity crazy quantum gravity or is it something else right now while this is going on we're developing more conventional cosmological ideas i'd love to hear about your more maverick recent thoughts on how to incorporate this cosmos can i first have your thoughts on on the like inflationary cosmology you and i have actually had conversations about this in the past and i know that you know i knew it was anything i heard about it and i it just made me feel ill whenever i saw it because well i mean i i knew it you have this problem i mean my my outlook on it was different from other people's you see i think many people were worried about the scale and variance of the of the background which is a big feature and i couldn't see how to explain it and that's sure and inflation was an attempt to that wasn't the main reason it was put forward initially but never mind it was certainly uh something and it's in favor but it was to my mind a very ugly theory if i may be hard to say that because you had to invent this field the infotainment field which had this very specific it only was invented for this one purpose so it had to have this peculiar kind of shape of its potential curve and it just just to make it do this what you're supposed to do and it didn't solve my problem and which you could see quite easily because you just think of collapsing universes and you can put an infotainment field in just as well reverse time so many people in inflation view the implaton field as more of an existence argument or a toy model for a cosmology in which you'd have repulsive gravity early on because of the pressure being sufficiently large as we were talking about before and and so the real quality of inflationary cosmology i think most people hang their hat on is a period of accelerated expansion in the early universe regardless of how it comes about the infotom field just being one toy model if you will that doesn't resonate with you at all though it doesn't help you you know i mean you could put that in whatever it is and then you you see you had this mess at the end and nothing i mean it doesn't work i mean unless you put asymmetrical physics in i mean time is asymmetric right no okay then my my claim my argument would fail but i didn't see that in any of the schemes that people put forward they'll just say when you know when curvatures get big or blur something right not telling you anything which i think most people would say we put in you know the so-called past hypothesis that for reasons that we can't really explain you had low entropy initial conditions and of course that's the puzzle that one wants to explain and then if you imagine that there's accelerated expansion forever into the far future then you get the time asymmetry not from the fundamental laws but from the solution where you'd have this but you're choosing a this is my picture of the deity a little pinprick in the 120 possible 10 to the power 10 that's true yeah 124 whatever it is yes sure yeah well that's that's i mean that's just you need a theory you don't need to no it just seemed to me that's that's the wrong picture right but i just i thought you had have a crazy quantum gravity i didn't like the idea but it i couldn't see i i thought it probably you need it for just make the reduction of the state vector too which you probably do but that's not with a crazy theory like that right but what about the idea and it comes what about the idea that people like andre linde and others have developed in various guises where you imagine that early on you had some chaotic state where the infoton field might be wildly undulating and then just it just so happens that in a tiny region maybe 27 centimeters across the infoton field just happens to get a uniform value allowing for the negative pressure that can drive the repulsive gravity what about that idea well i've described this in my book fashion fashion fantasy yeah i got this initial state which are all like that occasionally gets this little tiny smooth bit right okay what's the likelihood of that whether you've got 10 to the 10 to the 10 to the minus 24. okay well how about making universe which is only about as big as our galaxy right that's even more probable right it's much much much much much more probable than the other one right so we're going to do it by that argument why do we see our universe keeping on going going it's not just done for our galaxy our life yeah ongoing and going and going right and it doesn't even help to make you could say okay well you made me need lots of them to get human beings or whatever it totally makes sense but but again some would say that maybe one's being too quick and conflating small measure with small probability i mean because certainly in the space of all possibilities we're talking about a very small measure to give rise to the universe in that formulation but how do you know that small measure means small probability there could be some other fundamental principle that wouldn't have the something guiding the creator's pin into it into this right the region for some other reason sure you might have but it's not it's not the right theory well you need a theory for that yeah so tell us what you've been thinking about yeah you see this was the the other ingredient to this discussion again i was thinking you see i had this picture of infinity squashing it down in the future to make nice description of and i was just thinking about how boring the universe is in our picture okay it's exciting now all sorts of interesting things going on some of them nice some of them horrible but it's think of the remote future well these supermassive black holes will swallow up in entire galactic clusters and then they'll drift away from each other and you just get these black holes black holes they sit there and they sit there and they sit there eventually they evaporate away by hawking i mean it's all really pretty boring when you've just i mean some people say black holes are exciting but you get bored with them if there's that's all there is in the universe and uh and they just drift away from each other and then they evaporate by hooking them that's really boring so then i thought well who's going to be bored by this universe it's only mainly photons running around that's most of what's running around and these photons don't get bored easily not just because they don't have experiences in the ordinary sense of word but because the time progression is zero for a photon it gets from here by that to infinity to it in zero time right so it's at this boundary which is infinity it reaches it and that's i think well maybe there's something on the other side of that boundary well in the asymptotically fact it's now but if you've got a cosmological constant so being convinced of the cosmological constant which took a little while for me because i had wrong reasons for just believing in and i think it was jerry ostriker who persuaded me i remember we were going into dinner somewhere some college and i said to him well all this stuff about the cosmological council maybe maybe it's just dust or something like that and he looked at me and he said that's not the point putting positive lambda in there solves an awful lot of problems in cosmology it makes lots of things come together so okay accelerate expansion cmb the critical density it all works together so much better okay you win cosmological constant so that means space like infinity is space-like so now i knew it was space-like now a lot of photons come and they hit this space-like surface what's on the other side now i should explain just going a little back i had this vial curvature hypothesis for the initial big bang but my student paul todd who had been working on these things and he thought much white nicer way of phrasing this was not to say that but to say because it's it's unmanageable really because you could say that the vile curvature at a singularity is zero is a mess because if it's singular everything's going wild anyway to say it's infinite zero at the same time doesn't make much sense but if you stretch it out by this uh informal stretching to make the bang into a nice finite boundary infinity makes by a theorem of helmet friedrich you can see that future infinity isn't going to be nice and smooth space like by the past okay let's postulate that it's nice and smooth it doesn't quite give you the volcano which hypothetically it makes the bar character finite but that's not bad but then i thought okay let's take adopt that picture and now when you match them it makes the dark averages zero because by helmet friedrich well by various arguments it's got to be zero on future infinity and so if you match this to the big bang then it's there on the other side now you can see this completely crazy completely crazy because on the one side you've got very very rarefied low density cold colder and colder and colder and colder yeah on the other side you've got enormously hot density enormously hot completely the opposite what right do i have to match the two right now the argument is and there's a bit of hand waving in this but okay in the future here's where most of the hand waving is actually in the future it's mainly photons and photons have no mass photons respect the conformal structure equations maxwell's equations don't notice if it's squashed or not the equations are conformally invariant so that the maxwell field becomes perfectly finite infinity photons are fine what about the big bang well now it's the opposite you have a very very hot situation and now you're stretching it out the squashing of the future infinity makes it warmer again if you like more dense and warmer this stretching of the big bang makes it uh much much colder and less dense why are you allowed to do this because you've got massive particles no you haven't because the particles when they move around they move around faster and faster and faster then by einstein z equals m c squared this tells you that the energy in the radiation the mass if you like in the radiation completely dominates the mass is now completely irrelevant so the particles in the big bang are effectively massless which you get right at the beginning so there again they respect the conformal geometry so the future and the past if you take this view and this is where it's crazy but all crazy things have been right in there i mean if you look out at the sun you see where it moves around the sky to say that the earth is moving not the sun i mean that's crazy and it's right but what if you have some uh massive particles hanging around in the far future yes i mean as people have said to me i remember gary gibbons saying that was the weakest part of my theory i said well yes it is it's part of my theory but if that's the weakest part i'm quite happy that what i say is that and there is an argument for this and it needs more working on but the sort of argument is what's the first thing people do in particle physics when they classify particles what they do is they look for what are called the casimir operators of the poincare group now there's a little bit of jargon here poincare group is the group of symmetries of special relativity now what are casimir operators well these are things which are completely conserved and one of these in the ordinary theory of particle physics of special relativity you see particle physics particle physicists usually consider the physic they don't talk about gravity you've got special relativity and uh you've got the part of the these um casimir operators which are absolutely conserved are mass and spin now when you've got a cosmological constant you might argue that this isn't the right group the right group you put the cosmological constant in it doesn't really play much of a role until you've got this exponential expansion starting to come in and then the group maybe you could say it's not really the poincare group it's the decisive group and you look for the casimir operators in the distinctive group and you see that mass is not a cosmetic operator now this argument is not terribly strong one it's just for me it was where i say okay i don't have to take current particle physics that seriously to say that mass has to be an absolute constant over huge cosmological time scales and i would argue for various reasons that the lifetime of the dark matter particles you see this this is going a little ahead of myself here but you have dark matter as the main constituent of material in the universe that the dark matter particles would gradually decay and their decay would have a lifetime of about 10 times uh 10 to the 11 years so that's that's uh another ten times the times the age of the universe of the universe so that's about the lifetime and these things would then decay but you also have to have a a mass this is just particles okay i'm not arguing that the massive the electrons would have to lose their mass they can't decay because it's got charge right and they're so electron positron annihilation but you need to get rid of everything that's right but they're not gonna they they can't meet each other they get separated yeah and and you get you get hydrogen but no the idea is that the mass itself would have to fade out very very gradually right that doesn't have a proper theory as it stands so i would say gary givens is completely right that's the weakest part of the theory but if that's the weakest part i'm quite happy we need we need to work on that and we need to see how the proper theory of particle physics in this cosmological context really works so in this approach you really do imagine then that it's a cyclical process where the far future attaches to the far past it's a different person's father right different person far past um so um in terms of predictions for things that might see if this theory is correct i know you've written a few papers over the years what what's the state of things now i know things have been a as it settled do you have a sense of what one would look for i could think of three observational features the first one was the first one the first one that i thought about was circles in the cmb that's right this is the collisions with supermassive black holes so if you have a galactic cluster then the galaxies in the cluster assuming that each one has a supermassive black hole in it they will gradually collide with each other we will collide with andromeda in a little while a few thousand million years i guess and uh probably they were galaxies black holes will spiral into each other and they will be one walloping explosion in mostly energy will go out in the form of gravitational radiation this gravitational radiation will make its mark on the crossover between one eon and the next and this mark on eon is a cycle is that is that what you call that yeah yeah like i call it eon aeon i looked up in the dictionary to see how long an eon was because it didn't want if it was a certain number of years that was no good it wasn't a certain number of years so i thought okay i'll call it a neon and i like to spell it with ae because that looks fancier and that's a choice that's allowed in the dictionary i guess i uh yes yes that's just a lot of spelling so the a a the eon starts from the big bang and ends with this remote future squashed right you i've i've now made it into this compactified version big bang stretched to remote futures squashed that's one enon then there's a next eon somebody after us and the next one and the next one and there's one before us and a black hole explosion this is a collision between two black holes form this basically an impulse because it's in the sort of time scales we're talking about the spiraling in is almost impressive yeah right with this great impulse coming out hitting the crossover this will cause a in this crossover surface what you've got to wait for 380 000 years before you actually see the effect of it yeah and that's jim peeble's work basically with his colleagues in various places uh nobel prize last time what you do from big bang to 380 000 years and a point the big banks stretching out to about eight times the diameter of the moon here now the rings would encounter this with they'd be coming out and they would start to i will they will dis burst a little but they pretty well remain a delta function i think yeah and so you look back at us and you see this heating heating or cooling it depends on whether it's and it's it's counter counter intuitive in a certain sense but the most distant ones would be blue shifted that is the signal is coming towards us and the closer ones will be redshifted the signals going away from us that's the way the geometry works so that um it's hotter and colder circles in the in this that's right now so people have looked people have looked for those right so my understanding is that they haven't found we've looked and found them some people looks and haven't found them it's easier not to find them to find them i'll tell you that well you see i i the first people to look where were were um david spurgle and in princeton yeah i remember at the 2000. he had a look and he got uh uh and to to do the analysis they looked at it in a way which i learned later was not terribly appropriate but they started to see signals at first and then realized this was not right then they got rid of them and then they they didn't see any evidence of signals i think that's quite fair um i suggested twisting the sky at that point which was a way of seeing whether whether the signals check i thought there was a slight change in signaling but it wasn't quite what i expected so i didn't make any noise about that it i agree that they didn't see any signals right then a little later on who's an armenian who i knew from other things he'd done and he'd showed me that he'd looked for low variance rings but the difference in the way he'd looked at it you see the the way that spurgle and and hadjian had looked was to look for the over the whole sky consider a radius ring and then look at the temperatures and see where there's non-garcianity in there right something one random about the over the sky and when they corrected for the things that were wrong they found that there was no evidence for this that's that's true i'm not disputing that right but when what showed me he was doing it differently he was fixing the center and then looking not for a high or low temperatures but for lower variation in the temperatures and he considered to have found a signal i think and then since he was looking at fixed centers with different rings i said well look if you're doing it that way maybe you will see diff several rings with the same center because if they would look see if it's the same galactic cluster that galactic cluster will compress into one point from our perspective and if these collisions come several times maybe one supermassive black hole swallowing lots of others or several explosions in the same galactic cluster whichever it is they would be centered at one point so you've got concentric rings got it right so he then looked for concentric low variance rings and oh there was a lot of fuss about this i his analysis was done initially in a way which was not considered appropriate and i think it was right probably not to consider it appropriate because he's not appropriately taken into account the usual procedure that people use which is to uh put in the the um the curve the uh what's called the power spectrum you see what you do how do you know that an effect is real or not is it random or is it real well you make a comparison with a lot of fake skies so you make a thousand fake skies or something now how do you know whether the fake sky is a a proper fake sky what do you say you say it's a fake sky which fits the same power spectrum that's the dogma i mean it's okay it's a pretty good dogma it's at least you can you can use it and you can bear it that's that's you see for each harmonic you see you've got these different you imagine the sky is like a drum and it and it vibrates and has different there's an overall way of vibration which is called the l value and with each within each l value you've got the m values which are the details of it and the power spectrum is looking at the l values okay now you can use this l value and then vary within the m values and why he hadn't really done this initially so they were right to criticize him on this but then he did do it this way eventually and uh i can't quite see why uh the criticisms are there and he then tested this well twisted in the sky that was i thought quite a good way of doing it you could see that when you when you twist the sky that the effect starts to go away and the more you twist the more it goes away so it's a favor it's favorite circles i see but then the poles i'm going to take polls i mean christoph meisner pavel nyrovsky and uh i've got the chain another poll who did the analysis on the computer analysis they looked at the w see we only looked at w map data they looked at the w map data that's the first of the satellites which you really could look at the variations in temperatures you uh looked at planck now or then we looked at planck well i should say that that the polls look at w map and they found an effect and they gave a probability of the effect which was 99.4 percent ah this isn't the planck data i think in the wmap data was 99.6 or seven i think confidence level so it looked as though there was something there everybody ignored his paper their paper um i'd never seen any complaint of the analysis they did uh then they did it for the planck data and they found a 99.4 percent confidence level um and then and i did it a different way by looking there we had a lot of trouble with referees and so on and your your your claim at the moment is that this theory's alive and well and perhaps there is even i should go to the next fact you said yeah please because this is this was already colliding black holes one point i was talking to christoph of this and we talked to what where do we go from here and we decided we'd look for i'd never dared to look for the hawking points before you see what happens to supermassive black holes they are well it may take 10 of the goodness knows how many years before 10 10 to 103 years i think is what don perry billion mouth solar mass black hole 10 to 100 years or so yes google years or something 100 years that's a pretty long time and in that length of time the radiation will these biggest black holes will evaporate entirely away in terms of black or mainly photons yeah now what does that do in the crossover well you just see what happens it's squashed into a little point it's useful to imagine these escher pictures with angels and devils so that's a nice conformal map and you can see what infinity looks everything gets squashed at the edge right so all the radiation gets squashed in this little teeny weeny point so all the energy of that black hole all the mass in that black hole is squashed into that little point now i never faced up to this because this you talk about singularities that's the singularity in the crossover everywhere else you've got nice smooth equations and you could tell what happens as you go across but here you've got one singular point so you might throw up your hands but you don't throw up your hands because you can tell that there's a mass there by doing an integral around it so even when you cross over to the other side you can't get rid of there being a mass there so it's it doesn't depend on what theory you have of what happens to this radiation in the crossover so it'll be that's where quantum gravity really makes its mark but what it does it doesn't make much difference it's just a burst of a huge amount of energy in that tiny little point now that spreads out to eight times the diameter of the moon this is the standard suffering jim peebles and his colleagues worked out for the um 380 000 years so eight times the damage of the moon you should see slightly warm spots okay well we have this paper out i don't know about six months ago or so in the monthly notices of the royal astronomical society where we claim at 99.98 confidence level this is using kristoff's analysis these points are there also this is in the planck data also if you take the five strongest points and you look at where they are you look at the wmap data and you see points there in exactly the same places you find another one in the wmap data and look back in the planck data and it's there in the same place so you have six points which i think are genuine i'm not sure whether the weaker ones are genuine because the analysis which gives you this high degree of probability is only overall it doesn't tell you that for any particular point right have you heard from the microwave background experts around the world on on this one it's a strange kind of conspiracy of silence i remember talking this is before this paper i talked to christoph about this and i said i think he said to me how much how much response do you have on your paper in the european physical people i said zero how about you and he says zero so it's a conspiracy of silence but then we it's not quite zero in the sense that there's the papers by um by douglas scott and collaborators and they uh they looked at the rings i think and claimed they saw that i was glad for them to look at the rings because they found the pictures looked almost the same as vaj's people exactly the same so they found the same distribution of the rings and then they waved their hands and said oh it's not not it's only random right but it's not random even if you just look at it particularly if you look at the centers you look at the centers of the points in the plant data that's what's most distinctive and what's more this is i found very striking is what's more not only are they clumps in certain regions but they're clumped in temperature now the temperature gives you another parameter in various analysis because you look for them for low variance not because they're warm or cool you look for them because the the temperature variance around the ring sure and you look up for triples of rings of low variance temperature and then you plot the centers and they're clumped and they're clumped in temperature as well as in variance so if you look to the um lower right hand part of the picture you see a great region of red spots red means warm which means blue shifted which means distance i hope i've got it the right way around so that's a very distant region technically in standard cosmology would be outside what we call our horizon so you shouldn't even see them at all but in this you can because you're looking into the previous eon you're looking further out than you can see into our eon right the at the top right you can see a blue region which is presumably within our uh i don't know there should be some signal seeing in the micro background in our own i don't know i haven't tried it's a curious it's a curious state of affairs because you know thinking science and sociology blending them for half a second so the inflationary theory has been the dominant view for a long time full disclosure i have to say that i am certainly in that camp that is the way that i've long thought about things but but even paul steinhardt one of the inventors of the inflationary theory has now moved on to create his own version of cyclic cosmologies and he now claims that inflation is not as secure as people claim it is and now you've got another cyclic approach which is again heading off and again i just i can't respond to any of the details of what you're referring to in the data i'm not a cnb expert haven't looked at the analysis but it certainly is um if nothing else is an exciting time that there are competing approaches to thinking about the deep question of how the universe got to be and what the true nature of the world is uh so it is i mean yeah i mean i had these arguments against inflation before that was pretty good but this model i think really is hard for inflation to model because not just the hawking points i mean you've got these really energetic points at the crossover yeah in this conformally stretched big bang and you've got to explain them you've also got the clumping both in temperature and and in re in this region in the sky which is surely goes against inflation because that says yeah of course and i think one of them you say why haven't people seen the hawking points before because they're pretty obvious probably yeah what do you think the reason they haven't seen is just haven't looked people haven't thought well they're not there because inflation says it must be very uniform so why look for spots like that right i don't know but the cmb folks are so fastidious and so careful yeah analysis but uh but then it'd be interesting to see where this where this all will go certainly exciting can we segue to a little bit of quantum mechanics which is of course relevant to everything we've been talking about oh sure um you know so quantum mechanics among you know one of the two great descriptions of the world emerging in the 20th century fantastically accurate predictions um you're of the perspective and i have to say on this i fully agree with you and it's my perspective as well that quantum mechanics is not a done deal quantum mechanics not a full description because what we usually call the quantum measurement problem um do you want to describe that for a moment because i have a few questions on your perspective on on the measurement problem what it's telling us well my perspective i know you shouldn't bring in names here but einstein schrodinger and iraq all believed something had to be done about quantum mechanics to deal with this issue the issue is i mean people say quantum mechanics is the most wonderful theory in physics we've ever had or something well it's a wonderful theory i don't like to call it that wonderful because it's mutu it's self-inconsistent now what do i mean by that well the schrodinger equation tells you how the quantum state evolves the quantum state is the way we describe things in physics there's a small caveat to that because i might say what about the density matrix matrix yeah i mean that that's a little bit of a uh we can put that to the side for now yep put it aside it doesn't it doesn't solve the problem right but the problem is that you've got this evolution of the quantum state by the schrodinger equation beautiful equation works wonderfully when you can test it it works actually perfectly then what do you do with it well as schrodinger himself pointed out i mean he was very clear on this although people take it the wrong way in my view he described this cat in the box he was really saying look you could have a cat in the box according to my equation that's shorting and talking if you like when he was writing his equation you could have an evolution of the cat in the box in which it evolved to a dead and a live cat at the same time this is ridiculous there must be something wrong with the theory that was his viewpoint but people pick it up and say oh no you could make it if we had more and more best better boxes better cats better experiments or something you could make a cat in the box which has been all at the same time but schrodinger was really pointing out the absurdity of this situation which i agree with einstein agreed and even dirac although it's hard to find he was a man on a few words so he can't he was and he usually was very careful of these words that he didn't say anything that uh that he didn't totally have a mathematical backup right this was the case he didn't but he did certainly if you find the right place you can find a good quote from direct sure but he did say there has to be something wrong because the evolution as used in quantum mechanics where you say evolve according to the schrodinger equation and then you don't say that the schrodinger equation describes reality you say make a measurement and it tells you the problem is well what's making a measurement when you wheel in on the cupboard this machine which makes a measurement that machine is made out of the same things as everything else so why doesn't it evolve according to the throning equation it doesn't make a measurement it would say doesn't say i see this or this or this i see a particle here or particle here or a particle here i see this super position if possible here positive here is particle here and it might have a dial on it which says particle here superposed with seeing down by that particular supervisory seeing particle here right but you don't see that you see any one of them so that isn't the way the world works the world does not evolve according to the schrodinger equation it evolves according to this curious mixture of schrodinger evolution collapsible wave function schrodinger evolution collapse of the wave function i mean that's what quantum mechanics when anybody uses quantum mechanics that's what they do they use this of course and they say well i'm not clever enough to understand how quantum mechanics explains this i'm just working here well none of us are quite quantum clever and basically just say we just use it as an algorithm for making predictions and we're not actually describing the world but but you use the language inconsistent and that was the point i wanted to pick up on yes because other people use more polite languages say perhaps it's incomplete and and and so why do you say inconsistent as opposed to we still need to go further i think because people who say incomplete nobody listens to them so i'm trying to be a little ruder no i don't know i it is inconsistent because i mean i think they're just polite you see incomplete i guess probably well another way to say anything do you say newton's theory is wrong or incomplete i say it's you know it's it's it's the right theory in a limited domain of reality and then you go outside that domain and it fails and you have to extend your theory and and so forth but what i mean a little bit differently is here so let's go back to quantum mechanics yeah there are approaches for instance the boom de bruy approach to quantum mechanics that gives an answer to the quantum measurement problem it's a self-contained theory it's non-relativistic although some people say you can relativize let's put that to the side wouldn't that be a consistent version of quantum mechanics or would you perhaps not call that quantum mechanics any longer well um i i had long talks with bob when i was at back up back college because we were he and the bezel highly yes i we we and the various other people we used to have weekly meetings we had lots of long discussions so so i didn't know about his point of view but it was hard to pin him down i always thought he was very much like a like a wave function himself he he was talk about something and he sort of spread out over the universe like a wave and you pick your question you ask him a question you see and it would collapse on this and give you a very precise answer to your question and then it would start to spread out and spread out over the universe again like this so i thought he was very much in his arguments very much like a wave function which would collapse from time to time but but yes i know there are there are all sorts of models like that and the drw theory which has spontaneous collapse sure and i i'm a great respect of all these i i have great respect for all these theories i think they're i i certainly would say go with it do it but i think you see the thing i've been i've taken advantage of of of the lockdown to do something which i never really worked on which is to develop the few ideas that had on collapse of the wave function to see what more you can say about it yeah and the thing is i certainly think it's a gravitational effect i think that's yeah right strong argument for that which has depend i mean it's a very limited argument but it's fairly string and it's strong in its limited context it says you see the fundamental principle behind einstein's general theory of relativity is the principle equivalent it says the gravitational field at least instead of locally yeah is equivalent to a free-fall i mean galileo you imagine him dropping a big rock and a small rock even if he didn't actually do it he certainly thought about it and there's an insect on one looking at the other would not experience any now this means there are two ways you could look an experiment say you're doing a tabletop experiment quantum experiment and you want to take into consideration the earth's gravitational field one way is to put into the hamiltonian quantum jargon but whatever you do it's a procedure you put in the potential for the gravitational field just as though it was any other quantum field and go ahead fine the other way of doing it is say no no that's wrong you should imagine your coordinate system's dropping freely and there's no gravitational field you do it that way you get almost the same answer why almost well there's this the expression is exactly the same except for what's called a phase factor this is just a multiple wave function you multiply by this thing which is called the phase factor now that phase factor you say when you make a measurement you could use squares and it doesn't make a difference but you look at it carefully and you see it's got in it the term involving the cube of the time an exponential of the cube of the time which means that you're you have what's called a different quantum vacuum see in quantum field theory you have different kinds of vacuum and you have to settle on which vacuum you're using to make sense of your theory but you should be consistent with your vacuum in order to have a system quantum field here now here you have a different vacuum depending on which viewpoint you're taking well that could be fine stick to your vacuum and you're okay that's okay unless you have say a big say uh baseball sitting on the table and you're trying to put that into a superposition of being here and here that's now making it a quantum object now you have to consider the gravitational field of the baseball and you where now you're in trouble because if you use the old you say look let's say the newtonian view which means putting a term in the hamiltonian that's fine you've got no problem but if you say that's not the right outlook you should use the einstein in perspective then you have this vacuum which is changing all the time and you've got superpositions of different ones then you're in trouble how do you estimate the trouble well you can make a measure of what's wrong and it's a it's a kind of uncertainty in the in the system and you take an integral of that over the whole system and you see that uncertainty is a is an uncertainty in the energy of the system and then you use the heisender heisenberg time energy and certainly relationships i guess which says it gives you a lifetime so that's a lifetime of the system and that is a prediction it says that if you have a system with a superposed baseball it can only remain in that superposition for a certain length of time for a baseball it would be ridiculously tiny fraction of a second right so you have to have smaller things to get it bigger and bigger so that you could preserve this quantum state for long enough to see the collapse so you're saying that the linearity of quantum mechanics gets spoiled by gravitational influences that's the perspective what i'm saying is it's you want to be more even-handed lots of people talk about quantizing gravity and that's what you're supposed to do the singularities but you see that's very far from what we can have to look at physics at 10 to the minus 33 centimeters or something that's very hugely far from any measurement but what about the other way around not the effect of quantum mechanics on gravity but the effects of gravity on quantum mechanics now that is much more within the scale of things we might be able to measure right and there is an experiment which has been going on for goodness knows i don't know a couple of decades by now i think by dirk barmister and colleagues of his which he's getting pretty close to the stage of actually performing it he i think maybe by in within the next year or two he might well see something there are other experiments i have a colleague yvette fuentes who who has a plan for doing doing experiments with those einstein condensates and there are other things people have in mind i think that's a big important area to try and do experiments to test to see whether you can actually without you know bringing in an observer or something like that in a con self-contained physical system see a collapse of the wave function yeah via gravitational influence gravitational effect yes right is this is this why for instance you're not a fan of string theory's attempt to give a quantum theory of gravity or is that a broader set of i think the the trouble i have with that is more than the dimensionality the extra dimensionality you see i think that why does that bother you you're this maverick thinker who has all these wild ideas yeah the possibility of more dimensions goes all the way back to klutz and klein you know in the early part of the 20th century well look you see i i have my public and my private reason to object okay and i'm now i'm i'm public i'm not slightly public yeah yeah really just us and a few friends really listening oh yeah just a few friends well the public reason was always to do with the arguments i've just been giving you that there is a trouble with gravity that that i mean you can't the theories don't don't really coexist properly and that no i have a public reason which is that's one of the public reasons the other one was more to do with the the problems of the extra dimensions as you were saying yeah um i mean this tiny i mean you're trying to get rid of them by making them very very small but the trouble is when you're making them very small you you you um um have problems with stability the quantums i mean i don't and i did argue i i think don't want to go into this i haven't really thought about these arguments for a long time i don't i haven't seen anybody contradict them i have written a couple of papers on that why you why you would expect and in books too why we would expect these um tiny little knots or whatever they are of extra dimensions tied up into the knots why they would be unstable and and you would you they would decay and stuff like that i mean there are arguments a lot of them invoke issues of supersymmetry which again you can question and then imagine breaking and the effects of but um yeah i mean i i certainly appreciate the concern i guess my view is that um there are issues worth thinking about but by no means would it be enough to i think i never could i think the trouble i had the strength let me put it in a different way the trouble have a string theory is that it's really pretty in a blunt way it's being done by mathematicians now you see i might be calling a mathematician i hope i am but it's i mean what this great strength of string theory and and what's done is amazing things it has done in mathematics and i agree it has done amazing things in mathematics let me take edward whitten and and followers of him and sure there have been they've made big inroads revolutions in different areas of mathematics that's completely true but when it comes to physics i think you have to apply different criteria and i think the exciting theory is to develop for that reason and i have nothing against that at all but to make them into physics is a huge stretch for a squash i've put a lot of stretches the other way around you've got to squash all this and you've got you don't see any evidence for the super symmetry you've got problems with that you've got problems with the making the higher dimensions stable um [Music] i could never quite see even with the uh with the super symmetry you you have them stable but still right i really don't want to go into that too much that's okay i guess i would just and then i do want to move on to one final thing if you uh grant us a few more minutes i would say that for for for me just from my perspective the fact that you could extract general relativity from string theory a quantum mechanical description of vibrating filaments and you can pull einstein's ideas out of it if the history of science had gone in a different order we would have had string theory before the general theory of relativity and then with these extra dimensions the ability when appropriately thinking about them to embrace all of the successes of the past symmetry breaking family structure of particles discrete symmetries may be tied up with the geometrical form of the extra dimensions it just strikes me that there's a lot of successes of the past that so naturally fit within string theory which puts gravity and quantum mechanics together at least on paper in a consistent way but i get your point i mean it is not yet connected to observable physics that we can test and who knows when that will happen so that's that's definitely um i think an aesthetic quality which is somewhat different you see i think there is an aesthetic which is important in mathematics which is not quite the same as the aesthetic in physics i think in a way it's been the mathematical one which has been driving the strings now you see i'm a great admirer of mathematical aesthetics and and what you can do with it and i think it's tremendous yeah i don't think it's spilled over into the physics i think that the physics it's a different thing and i i think i think we could go on all night yeah no i agree but i can certainly see that that's a that's a valid point but i wanted to um to turn to now a final topic if you would are some of the ideas you've been developed to helping unconsciousness on on what it is that's happening inside of our heads you know there's this deep hard problem of consciousness how is it that we have qualia sensations of colors emotions thoughts understandings and my my take on your position is that you are you are straight down the line physicalist you are not imagining a duelist picture of the world is that correct yeah that's certainly the way i view myself i mean differently but and and so so then the challenge is to understand what's happening up here in the language of physics or the language of physics that we've yet to fully articulate so one question along those lines is many people use the metaphor of a computer as the model of of thought processes inside the head and you have come out with an argument that you feel that that is a completely misguided metaphor that what we do inside of our heads is not likened to the algorithmic approach say of a conventional computer i think we have to be a little careful because there are different parts of our heads yes for sure for sure i think understanding you know the quality of human understanding i mean if we talk about cerebellum i'm quite prepared to believe that that may be a computer analogy it might work very well well as we know it's completely unconscious and of course we don't understand how that works either but um the arguments as you say understanding no this goes back again to my graduate student days when i was in cambridge and i went to cambridge uh let's do pure mathematics algebraic geometry i sort of even that i was doing all slightly off-beat kind of theory but i decided i would like to go to other lectures on other topics and i went to a wonderful course by herman bondi on general relativity which was a great course i worked to a course by a mathematician called steen a logician where i learned about computing machines i learned about uh touring machines i knew what they were i learned about girdle's theorem now i'd previously been worrying with a colleague of mine when i was an undergraduate ian percival we had lots of discussions about these things and i was really troubled by the idea that girdle's theorem seemed to prove that there were things in mathematics that were true and you couldn't prove okay now i learn about girdle's theorem in steen's lecture and the way i learned it he made the it made it very clear what it was that you have a set of procedures of proof now if you accept these procedures of proof and that if they come up with feed in the theorem chug chug chug chug if it comes up and says yes it's true then by examining the methods of proof in the procedures you look at the the axioms and the uh well you defined it up into maxims and metal never mind all that stuff as long as you believe you look at the first one and say okay yeah that's okay anything you get from that must be tracked that's true that's all right that's all right not sure about that ah it's okay i see why that works you go through all that anything that if it comes up with yes it's true then you believe it's true girdle produces a statement which your belief in its truth is actually outside your understanding that it's true i mean it's amazing i i just thought that's absolutely stunning you show this thing is true but cannot be proved by means of those proof methods you prove it by means of your belief in the trustability of those truths but your trust your understanding of those proof procedures that goes beyond the following of the truth procedures now what does it mean by understanding it well something about your conscious goings-on and i thought that i had the view that it's got to be something non-computational in and it's not a turing machine of course it might be a turing machine which is so complicated that we could never understand it but then the argument you've got went through all complicated things mainly in my book shadows of the mind which followed the emperors of mind but really the argument is much simpler than that you say well it's it's nice to pick on a nice on a a theorem which i didn't know at the time which is typical good stein's theorem it's a really lovely theorem it's proved in 1945 where you take any integer and you write it in the binary form which means sums of distinct powers of two and then you look at the exponents and you see those are numbers which are not written that way so you write those as extended powers of two and then you look at the index and you go on and this chain comes to a limit and then you have two procedures you take you look at that number and you replace all the no you you place replace all the twos by threes the numbers got hugely larger then you subtract one so please hold the threes by fours subtract one fours by fives subtract one good stein's theorem says that this procedure always ends with zero now some of them lectures with that you say okay try it with three you just comes down try with four i would not recommend using your laptop programming it into that i would not recommend using your mainframe i would not recommend using any computer known on the planet take out a piece of pad of paper and a pencil and work it out yourself you can see why it comes it's it's tricky if it was four you can see what comes down it's a little trickier to see why for any number it comes down it depends on something called transfinite induction what about this is not that the point about this is how do we know it's true how did evolution produce in this algorithm in our heads by natural selection something which is so complicated from the experiences of our ancestors you know killing sabretooth tigers or whatever they were doing domesticating animals growing crops um that's nothing to do with this kind of stuff what we've developed is this general concept procedure whatever it is of conscious understanding so my argument was that it cannot be the production of some very complicated algorithm because natural selection could never have come across something that we can see it's true by um simple reasoning let me try it before i don't have to go to the transfiner thing so um okay so then i thought i'm i didn't know about good signs at that time but i knew about the girls theorem then i thought to myself well there's something going in our heads which must be non-computable what kind of physics can it be well there's a continuum problem and do you put thing on a computer well i didn't think that was probably it you could get good approximations that that's a point which you have to worry about is but let's i didn't settle on that i just thought it's not that's not the problem well what about newtonian dynamics well you could put that in the computer what about general relativity yeah well now we even know because with calculations and ligo and all that stuff sure you can put that on a computer hard to do but still computational calculations what about quantum mechanics then i thought about dirac's first lecture what did he do he took out a piece of chalk he was talking about first of all particles and he said well an electron could be here and it could be here and in quantum mechanics it can be here and in here at the same time you're going to the superposition of this state and that state and that's a quantum state can involve civil positions what about a piece of chalk and he took out a piece of chalk put it here and here and i think he then broke it in two now the trouble is when i say i think my mind wandered and i think i was looking out of the window and think about something else i have no idea what when my concentration came back to the lecture he'd gone on to the next thing i vaguely remembered in mentioning something about energy but i had no idea what it was that resolved this problem so i was left with this puzzle of the red collapse of the wave function and so i thought well that must be it that must be where there is something non-computational going in so i eventually well i thought i eventually would write a book about it and i had this idea that i would write the became the emperor's new mind around about the same time stephen hawking was writing his brief history of time i remember yes he he got um um really got to write the forward see that actually that time not many people knew about him and i kept wondering you know he is this this great physicist a great thinker and nobody seems to have known anyone i i remember wheeling around in his wheelchair and thinking that yeah and uh at that time he wasn't very well known but then after the briefing yes it was you just told him his name yes um what's his name the one who wrote before never mind uh i'm not sure actually uh yep he was a well-known expositor of science in the us um are you saying he brought the forward to hawkins a brief history of time well yes so i thought well i've got that i don't even know who that was all the time someone in the chat will no doubt uh tell us i thought well i need somebody to write it so i thought of martin gardner yeah all right so i sent my book to martin gardner i'm not sure i'd finished it at that point i wrote to him and i would not be nervous about what he thought he said no i agree with you right he was very happy to write her so i thought then okay well at least the book probably won't disappear without trace right but uh it probably is more than that absolutely did more than that of course but but but but if you're hanging your hat on incomputability being in the measurement problem does it disturb you that there are proposed solutions to the measurement problem that are computable like we were talking about before you know the boom correct you see that's all yeah you just think they're wrong um no no i think they were wrong right that's right no it's a great challenge how do you make a measurable how do you make a a theory that's included which is non-computing and you see there are there are are there here's a little direct again you see this is interesting i don't know whether this is it's a nice example and i think it could be a representative the iraq didn't just discover the equation of the electron but he had a period of his life where he studied classical electrodynamics now why on earth was he doing that i don't really know but he was looking at classical particles and how do they and he ran into this equation because he was looking at the self the self acceleration problems you you have to look at sure and then he got to these uh self-accelerating particles or exponential behavior and so you have to ha you now have a third order equation it's got too many parameters because you've got all these runaway solutions yes but how do you get rid of the runaway solutions well you've got to look to see eventually is it going to run away it's like a tiering machine you've got to know is that turing machine ever going to stop or not i think it's probably a non-computable problem see you think it's non-computable to determine whether you'll have a runaway i see you're saying that it may be a long time in the future that the electron just takes off or or something of that i mean i don't know i don't have a problem but it's at least it's a candidate right because it's it's looking to the ultimate future you're saying is this this solution is to be richard this solution is to be discarded if at any point it runs away and the runaway is is that it goes on computing and and the space goes out to infinity gotcha something like that i mean i don't know whether it's not but i think it's it's an interesting candidate so one final question that's related to this do you think that girdle's incompleteness theorem tells us something specific about the ultimate physical laws yeah what do you what do you think it tells us well i do i wouldn't have said that necessarily you say only because because it contains the physical world contains conscious beings you see and so i argue that conscious beings fair enough when i wrote the book i tried to reign to learn up about neurophysiology and i did learn a sign of that about the hodgkin uh nerve propagation and all that stuff and then i thought that's not going to have a hope you see how can you preserve quantum coherence in nerve propagation when it you know you've got these electric fields propagating right into the brain it seemed to be hopeless and so at the end of the book i just did a follow the fuddled argument which i didn't really believe and that was it a bit of a denumber you know i didn't know but then read my book and he wrote to me i get lots of letters from people who for a little bit you know crazy theories from time to time and i thought here's another one you see and he talks about these microtubules what are they you see but then he's got pictures of them somewhere they must be real so i look them up and i think gosh they are real now they're much more promising not just because they're smaller they're tubes and and well i didn't even know the difference between a and b lattices but the a-lattice microtubules are extremely symmetrical and i think i was aware of the fact there's a thing called the yantella effect that if you have symmetrical molecules and things like that then you can have a ground level in the quantum system which is shielded which is degenerate so you can have information in the ground level which is shielded from excited levels so there's a much better chance in these little little tiny tubes which are uh whether in the wall pretty well all cells not quite also but in most cells but most of them are b lattice where the symmetry is not so big so you've got to look for highly symmetrical cells i don't mean cells highly symmetrical structures ins within the cells which might preserve some kind of quantum here well it's very speculative i don't i'm not saying it's anything less than speculative but all these discussions of consciousness but even if it's even if you were right or or it's a stepping stone to be right do you agree that this approach would still leave open the mystery of why we have inner sensations at all i mean that hard problem of consciousness is still it seems to stand beyond any of the ideas we're talking about do you agree with that um i think things are mysteries when you don't you see people used to worry about load stones didn't they and there were some mystical fields right and they're still mysterious you don't see them but you understand them because you've got a beautiful theory of them and you can make them do things for you like radio waves and you can write you've got maxwell's equations to do it and then you've got quantum electrodynamics which make you do things which transistors and goodness knows what which sure and do we i mean is there does it remove the mystery just because you have a theory which describes them i don't think it does someone say that's an unfair analogy to draw though because all of those examples are third-party available phenomenon objective qualities of the world and let me get to conscious experience it's the one thing that's only available subjectively so it stands outside all those analogies i don't think it is only available subjectively and here we go back to stuart hammeroff i mean what does he do what's his day job on that job i'm not sure whether it's day or night he puts people to sleep on certain quotes because he says it's different from sleep he puts people under general anaesthetics and he's extremely interested in what this actually doing what kind of substances do it it's not a chemical effect because the different materials which put you to sleep are not chemically related right it's some physical process or something okay i mean uh i that it means you can probe consciousness well you see not just you can't probe it uh so i mean you know even you know psychedelics right we can probe it in many many different ways that's true i can't get inside your head and you can't get inside my head by getting inside it you see i don't know i mean or you don't have wires attached to one person's head and so you can just yeah what else is thinking you might have someday right yeah at that point maybe one would think of it as an objective uh quality and the analogy might i mean i could see the the trouble you have of thinking of things as internal in some sense right well i'm i'm not stopping it stopping making trying to make theories about it so i mean i can see why people think it's some you could see it's an excuse for not worrying about the problem and i think that's in quantum mechanics if you look back at uh what the old people when they were young in those days you used to think about quantum mechanics we'll call them yes absolutely and a lot of them thought that it was the conscious perception yeah which reduces the con the quantum state yeah vigner yeah yeah i know i talked to vigner about these things yeah for norman did you think that it was nutty when you heard about when he would say things like that no i didn't think it was nutty i didn't um no he actually he was fairly broad-minded about these things he thought this was one point of view so i think i never thought i don't think i like all these things you i think you've got to have a stage in your life where you believe some of these things um so there was a stage in my life where i thought you know i thought many worlds made sense things like that yeah i i went through that period too yes i had stayed in my life when i thought string theory was a wonderful idea actually i'm still in that idea yeah no i still do it i i like the strings i never have anything against the strings it's just good when the dimensions went up too high that's what worried me right so i mentioned that that was the final question but if you don't mind i do have one final point that i'd like to just end there's been a lot of interesting work lately the information paradox in in black holes where everything is heading toward i think a communal belief at least among the string theorists and many quantum gravity people that information is not lost in black hole evaporation stuff falls in it evaporates and you could in principle recover the information that fell in you're not of that perspective right absolutely not yes there's a question about how much of it is in the radiation yes i mean i guess i used to think most of it was destroyed in the singularity but i think uh don page was arguing that it's about 50 50. 50 50 right i could it doesn't make much matter when it comes to the hawking points there's all those squizzles through those points anyway so don't make much difference no but there has to be a non-unitary behavior there in the uh no well 50 well 50 50 is is is pretty bad isn't it but now but now the page curve the arguments right that are inspired by string theory but right within the structure of gravity general relativity that you can understand the page curve you can understand the entanglement it all seems to be holding together in a way that's unitary yes but look you've got a single think of the conformal diagram you've got a singularity here you've got ports out here you've got information which you've got particles which get destroyed on the singularity you've got its partner said an epr partner which goes out the other side right now one of the victims of quantum mechanics is you you can't copy information sure sure no cloning here we're saying no cloning here now if you're saying this information is retrieved in the exterior well it's copying what's what's going on in the singularity yeah i mean the arguments that some are putting forward you know susquehanna mel de santa others that in some sense the outside and the inside really shouldn't be thought of as distinct and they're really describing in some sense the same state as opposed to a copy of a state but uh maybe that will take us too far afield to uh to film the depths of those arguments you're quite right i don't believe it right that that's certainly uh the point i wanted to get to in some sense i've slightly shifted my view on that so because my view usually was okay quantum gravity whatever it is you're applying quantitative describes theory it's it's not the right theory it's got to involve the collapse of the wave function so any argument which which and i still believe this argument any arguments which depends on unitarity at this level where you've got a hugely early it's it's missing a part of the story you know he was sitting on the monstrous part of the story not just the tiddly powers maybe most gravity phenomena you see i'm missing a little tiny about but no this is the main picture i totally understand so so that you've got to find a very gravitational gravitized quantum mechanics you can't use arguments from unitarity that's just yeah that would be my normal argument against this i mean certainly you don't want any firewall or anything i don't know what what's the current view on star wars well that's an interesting question so i think the current view on firewalls is that um from a certain perspective it would be as if there's a firewall because in some sense the gathering up of the external information changes the system in such a way that generates the firewall so it's not abstractly that it's there but it's the act of acquiring the information that causes the firewall to exist at least i asked this very question last week to juan mauldin who gave a colloquium at columbia on the latest thing and that was the answer at least that i understood that he gave i've not investigated it fully enough on my own and and drove to if you took a spaceship towards the galactic center yeah would you encounter a firewall i don't i don't know the i don't know how these new ideas impact the uh you might see it too in event horizon telescope there's no yeah right exactly exactly so these uh these things are not just abstract anymore but anyway it's been a it's been a great conversation uh roger penders thank you so much for spending the time covered we covered quite a lot of ground you know from the the early aha moments through ideas of black holes in the 60s through cosmological ideas through quantum mechanics measurement consciousness you've sort of covered it all which is great so thank you so much without mentioning twisted theory except yeah we haven't done twister theory yeah so that'll be our next conversation uh so we'll launch that at some point enjoy enjoy the ceremony next week uh which which is uh you know well deserved honor winning the 2020 nobel prize in physics and uh you know much success with all these wonderful ideas going forward you know i'm just excited to see where where it all lands out so again thank you for joining us and uh and congratulations again thank you very much indeed thank you all right everyone so we've uh we've been at it for two and a half hours now i think unfortunately i'm not gonna do much more because um i uh i desperately need to use the facilities i can't um sit this long as i used to but uh i hope you enjoyed the conversation with uh roger penrose a lot of wild ideas uh uh really and the amazing thing is that it's not just ideas in a vacuum these are ideas now that have at least some of them been tested through the observation of black holes so in any event we will continue to have these sessions on a semi-regular basis as i mentioned before happy to hear your suggestions many of you do suggest that we have a conversation with roger penrose which i'm glad that we have done and uh i'm looking forward to our getting together sometime soon again sign up for the world science festival newsletter follow world science festival on youtube if you want to follow me on twitter i always announce these events there too that we're having i'm at be green on twitter i don't even know what my handle is on facebook i don't use it that much anymore i probably should and my son tells me i should start using instagram so for those of you in the younger side of things instagram at some point soon i will start using that as well again thanks for joining us looking forward to our next session look out for the announcement of when that will be okay brian greene signing off you

Channel: World Science Festival

Views: 318,140

Rating: 4.8451843 out of 5

Keywords: Nobel Prize, Nobel Prize in Physics 2020, Darkness Visible: Shedding New Light on Black Holes, gravitational waves, black holes, quantum mechanics, singularity, Event Horizon, radio telescopes, astronomy, general relativity, gravity, Brian Greene, Shep Doeleman, Vicky Kalogera, New York City, NYC, world science festival, World, Science, Festival, Big Ideas Series, Breakthrough Prize, Sir Roger Penrose

Id: 7oCQuvhQY6o

Length: 173min 17sec (10397 seconds)

Published: Thu Dec 03 2020

Reddit Comments

[u/mailtest34]

I remember how back when I was an undergrad student, I printed and made into a hardcover Brian Green book, cause it was too expensive to buy and only available in translation