We are setting off on a journey fraught with dangerous notions eternity the creation of all things from nothing and dare I utter a word not to be thrown around with reckless abandon among those of reason infinity a case in point of the library of Babel it is a library that holds every book that has ever been written and every book that ever will be written now here lies The madness each book is filled with random strings of letters 26 letters commas periods Spaces and each book is different But every volume in every one of these galleries has four hundred and ten pages Each page has 40 lines each line has 80 letters X alias that is to nothing but chance so for every sensible line of straightforward statement, there are leagues and leagues and leagues of senseless Jumbles, and incoherences. For example one volume is made up in its entirety if the letters M See these perversely repeated from the very first lines to the last another is mostly filled with gibberish until you reach the next to last page when you see o Time die It is Unbearable knowledge that in some gallery on some shelf a precious cogent book exists that remains inaccessible And no one cannot know my belief is the library stretches - dare I say it the infinitely Many say I'm mistaken that the possible number of books does have a limit and while that number is beyond my understanding I am gladdened by its distant hope That however improbable I may one day uncover Something about the library Babel which is an interesting image for the for the universe But tonight you're going to hear for some people who will give you a much more expansive Idea of what reality is? We're going to be talking a lot about the multiverse tonight and the notion of infinity and we're also going to address the question What is what are the fundamental constituents of nature? So how did we get to this this point in scientific inquiry into reality? Let's go back about 117 years to the year 1900 what did reality consist of what was physical reality? Well, everyone thought it was the Milky Way Sitting in this otherwise infinite space it was eternal And didn't wasn't created would last forever How naive that proved to be Because in 20 years and 20 years to them about 1920 it was discovered that The universe couldn't be static. It had to be expanding and we did you know, this could be empirically Verified you could see the galaxies pulling away from us. So if you extrapolate back in time You get this or origin to everything the Big Bang. So now we have a completely different view of the universe instead of it being Eternal and Static it had a finite Origin in the past and it might end in a finite future and a Big Crunch kind of like human life. You're born It's the Big Bang you die. It's the Big Crunch. That's so completely different view of the universe And this was actually exciting to some people a religious sensibility Pope Pius the 12th When decided when the Big Bang was discovered, you know this is a scientific proof of creation that the Big Bang Theory was confirmed in the 1960s when the echo of the Big Bang the Cosmic Microwave Background was detected by Almost by accident at first the scientists thought that it was bird guano on the antenna that was causing this Interference, but it turns out it's the echo of the Big Bang So now the question is what is this Big Bang event? and in it by the 1970s some guys that came along two of them are here fortunately. It's really thrilling to have them here Then they came up with the theory of the Big Bang Let's see. Do we have images of the two in there in their 70s hair? There they are not bad for somebody's hair. So they they, you know set out to answer the question You know, what? Is it that bangs? Why did it bang and what was going on before it banged and they came up with a theory which is called a theory of cosmic inflation and So now once again there's a radical shift in our idea of reality First it was a static finite universe the Milky Way Then it was the BIGBANG universe it blows up out of nothing in the seeming creation event And then goes on its merry history According to the new theory of inflation. Our universe is just you know one Member of this vast perhaps infinite ensemble of universe is called the multiverse So this is where we are right now. So let me tell you who these people are First of all, where did our universe come from? Nobody knows but our first guests will tell you His name was Andrei Linde a he is Professor of physics at Stanford our next guest is the professor of philosophy at Columbia He's the Woodbridge professor of philosophy at Columbia. Yeah. Also, he has a PhD in theoretical physics from Rockefeller University Daivari David Albert Our next Guest is a theoretical physicist and a string theorist She's one of the founding members of the Center for quantum mathematics and physics at the University of California Davis Veronica Our next participant is a professor of emeritus of applied mathematics at the University of Capetown investigates cosmology the nature of time the emergence of complexity George Ellis Our next guest is is a philosopher of science He's the only non physicists on stage But I think if he really had to we could probably calculate the eigenvalues of a harmonic oscillator very lower I'm finally the This is the father of inflation the man who really first created in 1979 professor of physics at MIT Professor Guth is famous for saying the universe is the ultimate free lunch but on investigation it turns out tax and tip are not included and you'll hear out that so anyway, these are guests and let's Let's get this thing going we saw this thing about infinity and We have somebody on stage the conservative the more conservative with the more conservative view of reality Which is Professor Ellis and he believes that nothing real can have an infinite number of components. So first of all I'm gonna ask you how do you know that and second of all are any of you people who are committed to You a reality that's infinite in some respect like the multiverse going to take issue with that. So, how do you defend that? How do you know that? I'll take a double stand on this first it for me. It's a philosophical principle and philosophical principles underlying Science and I'm going with David Hilbert who said the infinity never occurs in physical reality and that's because infinity is beyond what we can ever attain Doesn't matter how many things you've done how much stuff you've counted how far you've gone? You haven't taken the first step on the road to infinity and I think people forget that when they talk about Infinity in loose ways but more specifically if you claim there's an infinite number of anything in the universe galaxies people so it's an Scientifically unprovable because firstly you can't see them but secondly If you could see them you could never prove they were infinite because no matter how many hundred thousand Million million million million, you have proved you haven't taken the first step on the way to proving. There's infinite But I believe a scientific statement should be provable So I think any statement about science that involves the word infinity is not provable therefore. It's not science What if space were infinite and it were uniform than they were galaxies uniformly distributed throughout space? Do you think that's metaphysically impossible surely that someone's going to object to that that was a what if statement so what if statement? Yeah, well that might be true, but we can see up to 42 million light years away. We can't see anything further So you might say it's infinite time. I say to you No it isn't it closes up in itself and a finite radius or I can say that it's bounded by a Singularity of the finite distance. You can't prove you're right. I can't prove. I'm right You can say anything you like I can say anything. I'll ah By the way, that's a very controversial statement because there are many cosmologists now who believe that Our part of the universe is infinite. It's flat and it's uniformly filled with with matter including a Brian green I think who's the father of this whole thing but you know, we have to we have to proponents of the multiverse here Surely you're going to take issue with this, you know, rather metaphysical claim that he's making or maybe not I'd like to make an important distinction between what we view is space and what we view is time space I think we have no way of knowing directly whether it's inferred or not As you say we can only see a certain distance and only speculate beyond that Same thing is true about time except for time evolution. We kind of have a theory the Schrodinger equation of quantum mechanics and Quantum mechanics does not seem to have any natural way of ending time Therefore I think the reasonable assumption to pursue is that time is infinite Time is The correct statement is not the time is infinite the correct step into the time will be infinite in the far future Which we will never reach because no matter how far time has gone. You haven't reached the far future where it is infinite So it's always in the future. So it isn't true that it isn't Well IIIi don't think distinction has any real importance - I mean space-time exists we talk about space-time and and if we know it will exist. That's as good as I don't know What the tenths now means in the context of a space-time we need to floss reality. We need to It's very one of the first just a one remark from theosophy Is that Aristotle that guy a long time ago made a distinction between the actual infinite and the potential infinite I think? George's view is that There's a may be a potential infinity unless there's no boundary Allan's view might be there's an actual infinite as far as I can See, there's nothing contradictory about space or time actually being infinite. We know there are models in Mathematics and which are consistent in which they're actually in infinitely many abstract entities at any rate numbers Whether any scientific theory needs to posit the existence Of an actual infinite is a open question, I think Get to which is that given what we call them physics coma DeLucie tunneling Technical word. If you have an infinity of time you automatically get an infinity of space Coming along with it space and time were more or less interchangeable in the context of general relativity Pick up on that. I mean science is full of claims You know current science is committed to all kinds of claims about what sorts of laws things are obeying in the Centers of distant stars That we're never going to be able to witness, but we take it to be a natural extrapolation of things that we take ourselves to have good reason for believing So the observation which is surely true that there's never going to be a direct empirical proof That the world is infinite or that the world is finite It doesn't seem to me to be equivalent to a claim like we couldn't imagine ourselves Having what? we take to be good scientific reasons for Supposing that the world is infinite or finite in this or that respect. I'm Barry just mentioned one the the you know, we have the Schrodinger equation It's you know We we have all sorts of good empirical reasons For having faith in the Schrodinger equation and the Schrodinger equation doesn't present this with a natural opportunity for the time Parameter to come to an end. So it seems like a plausible thing to say that it's infinite You're absolutely right in pointing out that that's going to be one among you know uncountable numbers of claims about the world that our science is committed to which we're never going to be able to directly Empirically confirm or refute you seem to be equated that with a claim that we couldn't have anything that counts as a good scientific reason to believe one way or another About such claims and I guess I don't see how that follows You are the father of the theory of eternal inflation and eternity has a kind of intimate relationship to infinity Give us your take on this and make it funny Be stopped and that actually is similar to what actually happens in our universe Most probably now right now. Our universe tends to be well at least started up about 5 billion years ago Exponentially expanding. And if this continues then our part of the universe eventually will become empty and We will found ourselves in Something which is called de sitter space and the sitter space has largest distance From which we can ever get any information and this is called de sitter horizon So the whole universe the whole digital universe may be infinite But only part of it will be accessible to us. So in a sense, you'll say ok So what is then the unit multiverse if you have just a finite patch of everything to explore? on the other hand if we study it a little bit deeper and Study what happens in string theory? for example in string theory a lot of different working states in our working state may decay in the future and when it decays our Horizon may expand and expand and become infinite or we may all collapse and die instantly, so there are some possibilities Which right now we cannot even fully first see all of this picture of the universe didn't exist in the sense, which we Perceive it right now. It didn't exist about 35 years ago. So To come and stay I would forbid this picture being discussed because it well Against my general principle. This would probably be well III would warn us against following the lead of those who want to forbid us something but I don't think that George want to forbid He want to put a question mark here be careful because there is something we should be taken into account Seriously, and I absolutely agree with this position. I Particularly want to put a question mark against statements coming out in the popular journals saying how far away is your next self? And I just think to talk about yourself having infinite replications is kind of really stretching beyond This notion of the universe. There are exact replicas 10 to the 10 to the 100, you know angstroms or light-years It doesn't matter that scale away careful with words because multiverse is used like a slogan by many and if you try to Google the multiverse who studies it how the tendency then she grows up all the time and then you will do more careful search who actually Will dialing on Google the multiverse. It appears that most of the people who do it are from Peru and Then next Position is from France And then you will fine-tune The search and it appears that people in Peru. They playing the game dragon multiverse So What kind of game do we play and this is actually very very simple Just think about our own earth. There are many many countries on earth Each country has its own laws. Okay, China Russia us and then imagine that the size of the universe blows up to incredible ball size and that the main idea of inflation so we have China so large that anybody living in China would have no idea about United States in the United States would not have any trade war with China because it will be not infinitely but practically infinite distance and there will be no internet connection or whatever so then the this is a very simple very practical idea and then somebody comes and say oh I live in the place where these set of laws and this set of laws is unique and other laws are impossible and if I water than its liquid water and the captain of the ship just Take the ship and then suddenly in night He crashes into solid water and Titanic goes down So the fact that we have seen something experienced something it does not necessarily prove that something else is not possible and broad a set of possibilities as a Larger set of rules is more natural from my perspective than forbidding something beforehand I'm trying to bring Veronica into this but I do want to bring you in prematurely Would you as a string theorist and of course the string theory? Feeds into the idea of the inflationary multiverse because it produces something called a landscape multiverse But you have a slightly coy and cagey relationship to string theory because you see it more as a tool rather than as a fun a real description of reality But I'm I'll let you talk. I mean, I view it as a framework which allows all these possibilities Depending on what you put in so it doesn't really bother me that the framework allows all these possibilities and Whether or not there's infinitely many of them You know doesn't threaten our our notion of reality and and and so forth But let me put in a word for infinity in a context of dust can infinity be useful in physics So so far we have been talking about You know is our universe infinite or something like that and I I sympathize with all that have been sort of said on stage here that You know if you count Physical objects, let's say then, of course, you can never get infinitely many of them But you know If you it might still be mathematically useful notion in the sense that if you allow me that that can be say Zero number of a certain types of objects then I can just say well, let me talk about one over that okay, that's that's a bit silly example, but it It goes to sort of it's meant to illustrate That there could be different descriptions of the same physical Reality and those different descriptions could be useful for various different things and it could be that in one of these descriptions The thing that's most natural is the one over the what end that ends up being zero I think this is a very important point I think just as Infinity doesn't exist in physics zero doesn't exist in physics either and that's what the quantum vacuum tells us. So I don't believe that I don't believe that between my fingers. There's an infinite number Uncountably infinite number of physically different points and that's equivalent to saying that those points have zero size in fact in in in the real universe I believe that space time must be quantized will have a little finite size and then there won't be an infinite number of points between my fingers two things I wanted to add to this conversation one was about what Veronica just said in this discussion with George and that is if You can count to infinity if it took half as long to count The next thing is it did the previous thing then of course, that would be a series that converges to infinity Sure, though George thinks that that's an impossibility the other thing that I Count to infinity you say it takes you one second to say 1 1/2 a second Say to a quarter of a second say 3 and so you've run through all the numbers in 2 seconds that way Other thing I noticed was the different attitudes that Andrei and George have to what exists Andrei's idea if it said if it's not forbidden It's there George is you got to show me. It's there that it's it's there only if it's and demonstrated to be their Position minds of physics Given what I know about Andres background in physics is shorthand for waste of time Two years from Russia and one of my friends there well expressed his attitude of the difference between How things work in different countries and he say in Russia everything that it is not explicitly Allowed is forbidden In the United States everything that it is not explicitly forbidden is allowed And I much prefer this was possibility So, I think that's really very good in politics maybe not so good in epistemology So we've done infinity and eternity now, so let's move on to something I mean, how about creation now Andre and Allan but had both Years ago had a kind of really clever Creation ex nihilo scheme and I understood it and I thought I don't know whether it's true or not But it's a an alternative to you know The God bringing the world into existence and all of that and the idea was that out of sheer nothing a little nugget of false vacuum could quantum tunnel into existence that White sure nothing. They need something very particular. It's a closed space time of zero radius So it's like taking a balloon and shrinking down to a point and that's the closest you can get mathematically speaking to defining nothingness So out of this beginning of nothing a little nugget of false vacuum quantum tunnels into existence and then by the magic of inflation this blows up into the multiverse, but now everyone has Stopped believing in it and you believe that the universe the multiverse didn't have a an origin in a finite time in the past It's eternal Looking back into the past and eternal looking into the future and you know, I frankly don't understand this Why were you wrong about saying it had a finite past in the first place? Allan you had a proof of mathematical proof that the universe had a finite beginning in the in the past And now yet what was wrong with proof? Listen why should we bleed you on global warming if you okay kidding? Nothing was wrong with the proof with what's wrong is your summary of the argument The statement was never that the universe Necessarily had a beginning the statement is that we followed the era of inflation backwards The era of inflation had to have a beginning that we still think is true And it's certainly also but I think you exaggerated tremendously when you said that now all of you people Don't believe that the universe had a beginning as far as I know. I'm really just speaking here for myself and Sean Carroll we've been working together on a model of the universe that would be eternal and In this model that Sean and I are working on it will was originally proposed by Sean to give credit where credit is due We'd be living in an era where time is going forward and entropy that is disorder Which we think of as almost a proxy for what the finds the arrow of time? Disorder is growing towards the future and getting smaller towards the past And then these models with a definite beginning the universe would have begun at some finite time in the past with essentially zero entropy Zero disorder and that's still a possibility. I don't mean to say that that's not possible What appeals to Sean me about this alternative approach? has to do with the symmetry in physics symmetry of time reversal invariance all the laws of physics that we know of our time reversal invariant that is we here can be sitting on the stage and talking and time has gone forward if There's also a quantum state wherever all that is reversed then everything is happening exactly the same but in the opposite order the laws of physics don't care about distinctions between future and past and One puts in a beginning of this sort you're putting in a distinction between the future in the past We have a beginning in the past The goal is to produce a picture of the universe or multiverse Where know where those when put in anything that violates this symmetry between future and past so the way the model works There's an intermediate period which you might think of is the logical starting point Where the arrow of time is not well-defined Disorder might be growing might be shrinking doing one thing one place One thing a different place just chaos basically, but then if you follow that forward in time there are laws that we think we understand which say that Disorder will start to grow Entropy will grow an hour of time will develop Going that way and we also have in mind that all this is going to be undergoing in inflation and in fact eternal inflation If you follow the same thing backwards in time the same thing happens but in the opposite order of this the laws of physics as I mentioned don't care about T vs minus T. So if you follow up backwards in time entropy disorder starts to go in that direction inflation happens backwards in that direction So you have this two-headed arrow of time picture and the beauty of that is the full system is is completely time reversal invariant zoom same thing back So you have a nice picture of the multiverse which automatically contains an arrow of time which was not put in by hand But arises naturally just from the evolution of laws of physics that we think we already understand David you're the natural person to Critique this because you you this is the man who coined the term the past hypothesis Which a very simple coinage but is really caught on the past hypothesis explain with the past although I don't think it's in such dramatic conflict with this the Usually before we were considering Theories of the kind that we're just described we used to we used to think that we needed to make a special posit to the effect that that there was a Initial state of the universe where the entropy was very low What's going on in in Sean's proposal is is that the idea is being floated that maybe The cosmos doesn't have anything like an equilibrium condition. That is the cosmos there isn't any upper bound to the entropy that that the cosmos can have so So wherever you start out Entropy is going to go up from both sides of that. It doesn't matter what kind of state that is. That's still going to be That's still going to be a situation in which on either side of this minimum You have the equivalent of a past hypothesis. You're just not You're not claiming that that things can't be and you know that things can't be traced back even Behind that so this seems to me not something Not something that contradicts the past hypothesis It's an it's an attempt to put something like a past hypothesis in a larger framework Well, you know at the moment there's this huge controversy over the over inflationary theories in the multiverse, you know, we have the - - of the creators of The theory of cosmic inflation here on stage when the third Arguably the third father of the theory inflation is Paul Steinhardt. Who's the Albert Einstein professor of physics at Princeton and he's now become an adversary of the of the theory of inflation And there in the Scientific American I believe there was an article published by Steinhardt and some collaborator Hydrators arguing that the theory of inflation was a bit of a failed research paradigm Tell us why there's so much suspicion about the theory of inflation among You know pertinent perfectly reputable physicists Barry you you good Barry's a good friend of Steinhart so he can give the I know Steinhardt now the others about but I'm not a party to that because I'm not a cosmologists But it does remind me of a famous remark that Lev Landau famous physicist Russian physicists made about Cosmologists, I think the rim barkos something like this cosmologists often an error never in doubt That's good, oh I think all cosmologists you must be taught this in the very beginning That wasn't even your to explain to us why Why they're unhappy I mean it's there are two reasons as far as I understand it There are our intrinsic problems with the theory of inflation. It's in a way. It's too elastic there are too many versions of their hundreds of proposals for a theory of inflation and they all hypothesize a field that does just what you want the field to do and there's no empirical evidence that this field exists and the other problem is That it implies the existence a multiverse in which anything that can happen will happen. So how do you test them thing? So that's a very cool three Reasons, I don't think that I think there's reasons to think that the kinds of fields responsible for inflation could exist and so I don't think that that's their objection so much, but I do think that their objections that are interesting to Philosophers that you mentioned one. Is that as I think you mentioned earlier inflation was introduced in order to explain certain things about the initial Initial conditions in the early universe like that. The universe has a very flat geometry that the universe is very homogeneous and These need to be put in by hand in the Big Bang account without inflation inflation looked as though it was giving an explanation of This would look like fine-tuning, but their worry is and also Roger Penrose is worried Is that more fine-tuning is really needed to get inflation going in the first place. That's one worry Another is that inflation is really a whole model a big framework of theories with a lot of free parameters in them and by changing the values that parameters the the the Potential energy of the field and the curve of the field and so on You can get it to adjust various empirical consequences And that that objections seems that somewhat at odds with their other main and very interesting to a philosopher objection and that is if inflation is generically leads to internal inflation the production of all of these pocket universes and if in these pocket universes can be very different maybe even fill up the whole landscape of string theory as I think some people think Then it looks like the theory itself is predicting that Anything that can happen will happen as Allen has been quoted is as saying and it looks as though a theory like that Just can't have empirical evidence for it. And that's a really interesting issue to hash through Maybe a little bit too in a house for here I don't know but it's so I want to give you an idea of the the different proposals of poor periods of inflation Yours verse you used the term inflation first to refer to this cosmological theory then you came up with chaotic inflation which became internally eternal inflation Steinhardt was extended inflation and then we have we have also Extended I should double inflation triple inflation hybrid inflation mutated hybrid inflation tilted hybrid inflation hyper extended placeand and invariably super natural inflation And that's just that there are hundreds of others not all of which have names. I'm sorry. I'm not First because there are much more okay But what is important about them that all of them are just versions of one general principle and this principle is that in the very beginning of the universe for whatever reasons and we can Speculate whether it was tunneling from nothing as Alex Vilenkin suggested or some features of wave function of the universe or whatever the region of space tiny tiny region of space filled with some special kind of matter Which is not very specific and then the space if you follow equations of motion Which anybody can solve it's really really simple start expanding Exponentially and then after that it produces big chunk of space which is much bigger than people Expected before and after that decaying field produce all matter in the universe And it looks like science fiction you solve equation. You see that's how it is. So that's a basic principle after that, you start Fine-tuning what if I need to adjust some parameters? of the theory to describe whatever they the experimenters are going to bring us and what if I Try to implement it in string theory supergravity grant. In fact theory That's why many people's is just that many different versions. They based on the same principle now, let's compare with the history of standard model of elementary particle physics Describing weak strong and electromagnetic interactions just in describing weak and electromagnetic interactions required 20 Parameters to adjust the theory to describe experimental data marzo, the Higgs boson very large Nobody could predicted mass of the top quark very large, but people knew that top quark is necessary So what is necessary to achieve is some framework and then feed the data at the moment? there are some inflationary models which Require just a single parameter to describe all Inflation related data which Planck satellite and other experiments given one parameter is enough. Is it complicated? I don't think so. Look Here's something that people may be puzzled about one. Here's two claims about inflation as it's practiced now one That there is spectacular enormous, ly impressive agreement between its predictions and what we see Second that it's a theory that predicts that everything that can happen will okay and will for certain and there's prima facie an obvious puzzle about how to put these two remarks together with one another if you know go back to your analogy of the earth Expanding. There are all these different countries. They have different laws there an infinite number of them In fact, they have very very different laws. Things are very different going from one country to another Somebody's about to open his eyes and would like information from science about what he should expect to see Okay it seems like if you have if you have a situation that the picture of the world is there's this enormous earth on which there an infinite number of places and everything Describable is happening in one or another of those places. This is going to give the person exactly zero information About what he should expect to see and in this case, it seems puzzling Good, so this is but presumably you understand puzzlement. Yeah and good Okay You want answer this but Since I'm the one who keeps getting quoted saying that in the multiverse anything that can happen will happen an infinite number of times even Let me just clarify that sentence If something has a probability of ten to the minus six it means if you do something five times It's very unlikely to happen if you do it ten to the six times It's likely to happen. Once if you do it an infinite number of times, it's likely to happen has to happen In fact an infinite number of times, but the probability is still ten to the minus one-sixth If you do only make a finite number of observations the probability of you seeing that is very small as I like to say Even if there is a multiverse Unfortunately, the probability of my winning the lottery tomorrow is not high It remains not but let me just jump in there. Okay, go ahead What you're saying implies that the picture comes along? with some set of probabilities of this being the world that's realized or that being the word that's realized and my Understanding of the current status of the theory in which people are looking for a so-called measure over these worlds Which would provide us with the with the probability you're talking about is is an element of the theory which is so far Not in place. Okay, which we're hoping is going to be in place and is going to give us the right Probabilities is going to identify what we see as a high probability kind of an event Would somebody be wrong to say oh I see so The hard part hasn't even begun yet. Okay, all of the physics of this is going to rest in the choice of a measure That part that's a notion of uncertainty onto which we haven't even dipped or Into which we haven't even dipped our toes yet. Would that be a fair thing to say? I think I'll be a slight exaggeration I mean I Said no a lot of what Dave Dave just said is true There is a measure problem and I was just gonna get there honestly Whenever physicists talk about the measure problem they're talking about a fiendishly difficult problem having to do with defining probabilities when you have you know, in an infinite number of you know possible events and it's all physicists say You know tend to skirt it they tend to because it does seem to be all insoluble in every context in which it arises But so the measure of problem means a problem with defining probabilities. That's that's all yeah vacation so People work on inflationary cosmology are aware of this major problem When we say it's an unsolved problem, I don't know It's either an unsolved problem or a problem for which we have multiple solutions. Those are kind of equivalent statements more or less We don't yet know what the right solution is We certainly do have proposals which define probabilities and ways which seem to be perfectly consistent with everything that we know of so We think of this decision of how to define a measure as an empirical decision We do have ways which work empirically I should also emphasize that there's no doubt that it's possible to define Probabilities on infinite spaces mathematicians will be doing that for ages for a century anyway So the only quit is their many choices usually and that's the issue here So we do have to find the right choice, but there doesn't seem to be any problem in finding choices that are very sensible What we still need and hope to find is a way of definitively determining what the right measure, okay Look, let's get away from the measure problem. It's just too hard and let's get on something simple like anti-de sitter space conformal field theory Duality and the holographic principle, which you have to talk about because we haven't heard enough from you You have two interesting takes on the fundamental nature reality So in in string theory we have seen these remarkable statements which we refer to as dualities Which is the interesting situation that the same physics is? described by different theories different mathematical languages if you will and so there isn't a sensible Way to ask the question. Which one is correct? They are they're both correct in this particular example of duality, which is referred to as a DSC Ft duality or gauge gravity duality the two sides that describe the same physics are A theory of gravity in particular string theory. Okay living in higher dimensions Which is precisely equivalent to a theory without gravity a so called gauge the conformal field theory living in lower dimensions in fact, you can think of it as living on the boundary of the space-time that the gravity lives in and Well, it is believed more generally more generally so studying black holes that any theory of gravity has this Holographic nature to it that you can encode all the information that's happening in such a theory with a lower dimensional To it if you could only see the shadows on the wall You couldn't reconstruct everything that was going on at the cocktail party in the room right with shadows indeed You couldn't tell enough neither Can we tell with movies which seemed a little bit better than shadows and yet they are supposed to be you know Two-dimensional representations of our three-dimensional world because you don't see what's behind that, you know foreground things or stuff like that So here in this holographic duality, we would have, you know, clever shadows Er things that actually know the entire sea, okay, so indeed that's very counterintuitive You fit all this information on a lower dimensional theory But maybe the point to make is that a theory of gravity Already does not have as much room in it as you might have thought And that is the reason for that is is gravity in once you have gravity You can collapse black holes, for example Which is a very generic type of behavior and If you try to say pack in as much information as you can in a given region Say in this room Okay, now we can think you bring your book and we can read it in that some amount of information. I bring another book and the great brings one more book and so forth and we can pack this room with books and that's still There's no problem with that But once we sort of tried to packing so many books that we would sort of Push at the limit of how much information can be packed in Gravity takes over and the whole thing will collapse into a black hole and now we'll see that in fact the amount of information Scales only with sort of the surface area of this room rather than with a volume Okay, so gravity has somehow built in the structure of having being describable by a lower dimensional sea Okay, so that's called the holographic principle. Now this duality is a concrete realization of that This so-called EDS CFT duality. The ATS side is Stands for anti-de sitter. It's a particular space-time that has a negative cosmological constant So very different from the expanding universe that we're living in But nevertheless because it's a theory of gravity it contains black holes And in fact, we believe that black holes are behave just like the black holes that you know, we see out in our in our universe and Now the miracle is that yes, there is this other description this lower dimensional description That now does not have gravity. It does not have black holes but everything that sort of is happening around us all these black holes and stuff like that are described in this completely different language It's very square But it's a same same physics is happening in this in the bulk theory in the higher dimensional theory You've got a black hole in the boundary theory, which is a complete description as well The what looks like a black hole is actually a bath of gluons and quarks so David being a philosopher is concerned with reality as it is in itself. He wants to know which is real They're black holes, or maybe that's a naive question I'm being forced to say something that I don't That I'm not sure I believe I mean I guess there is maybe here's a way to put the question look Physics has tons of mathematical equivalences So we can talk about Say the the condition of a classical system of particles Portrayed in three-dimensional space or we can talk about it in configuration space or we can talk about it in phase space All of these are in a very straightforward sense mathematically equivalent mapable into each other isomorphic to each other There is a temptation to say in the classical case Yes, but notwithstanding these isomorphisms the three-dimensional space is the real one the Three-dimensional space is the physical one Is there an analogous question? In the kinds of equivalence is that you're talking well there may be several things one could say about this Maybe you think even in the classical case the question doesn't make sense Well, although most people would think it does. I think there's a, you know hidden assumption in this which is Who is asking okay, so you are asking and you are sort of local? object and to use Talking in sort of the position space. It's most natural So then that somehow singles out a preferred description because in some sense you're sort of providing the Basis on which to ask this question, but what is it? I don't understand how I'm I'm part of this description - There's an old question attributed to Vidkun Stein people said to him people said to him, you know, he said I can't understand why I the the Copernican theory was counterintuitive And people said well because it looks like the earth goes it looks like the Sun goes around the earth and Vic and Stein No, but Vic and Stein reportedly said what would it look like if it looked like the earth goes around the Sun? And So I take it the same question applies here. So is the claim? Sure if I prefer to describe things in 3-dimensional space, of course I'll be describing them in 3-dimensional space if there's some psychological Feature of me which prefers three-dimensional space, of course, I'll describe them in three dimensions most people would say and it sounds like you think the You think the right thing to say about this is just that it's a mistake. Most people would say in classical mechanics No, there's some metaphysically significant sense in which the physical space is Three-dimensional and in which the others and in which the others are just sort of abstract mathematical representations you think in the classical Is that if your brain is flashed on the wall right thing good exactly, right But your brain is a blast on the wall according to But that is the same brain is the one that's in the three dimensional space I Think those are two things Aren't they the same thing good if they're the same thing then? It's a linguistic question. Right? We have different descriptions of the same thing and that thing is You know, there is one thing but we're describing them in different Languages and now you're sort of trying to force me to say well isn't one preferred To the other because we somehow have this gut feeling that yes. We are living again I'm not trying to force you to say anything that the But it's just a question in the simple classical case. Most people would say indeed This is how people are taught physics. Oh, I see what's going on The real deal is three-dimensional space and there are particles moving around in three-dimensional space There are various other abstract mathematical representations which are useful in certain contexts Configuration space phase space so on and so forth These are useful. There are all kinds of problems where I'm going to turn to those But there's some sense in which I'm going to think What's really going on is the three-dimensional space with the particles moving around in it? And and it's not that I'm claiming. That's obviously right? It's Interesting that that's what most people even people with a physics education Would tend to say it's convenient and it's convenient psychologically, but why is it crucial? Because somebody wants to know what's the dimensionality of space and And it sounds to them David. What's your answer to that by the way? Yeah, very counterintuitive Answer. Yeah, that's another story. Okay, just tell me how many dimensions space n times the number of well The number of elementary degrees of freedom. Yeah. So what's the order of magnitude is it about it's it's really big. Yeah So we have 12 minutes left and the two topics I thought were interesting were you're getting onto the soft ones beauty is a guide to truth in physics that maybe - but but but George is interested in the limits of physics and the limits of science and if we knew the universal wavefunction Could we predict that the we were gonna get together and have this particular conversation and say these particular things? Does it leave any room for free will this and you have a notion of top-down causation? Which I'm very skeptical of but I want to hear about it. I want to be Free will is a difficult one, but let me make the following statement According to the standard big bank till it's heaven period of inflation. I'm happy with that We've got the last scattering surface. We matter and radiation decouple we've got particles on the last scattering so it was a question of the following if we knew everything about the last scattering service to the Finest detail could we predict what is happening in this room at this moment? Could we predict physically what you have just said, my claim is absolutely not there isn't the faintest chance That would be true. The reason is because for many many reasons I'll just take two when this quantum uncertainty between here and there and I could amplify on it the second one Is that what what coin of what because knowledge do is they? Characterize something called the transfer function which goes from here to here. We have difficulty even explaining a black hole Dark halos, and so on we have difficulty characterizing the distribution of galaxies in practical terms is not the faintest chance, but Supposing there was a chance of doing that then you would be telling me that somehow the words You've just said we're written into the last scattering surface by some Demiurge and I don't happen to believe that that could possibly have happen So the real statement is the last scattering surface set up the conditions, whereby Higher level beings like you and me could come into being where we have psychological powers in which we can argue at a psychological level and that Psychological level has real causal powers, which are allowed by the physics, but they are not Predicated by the physics the physics cannot tell you what you are going to say in Psychological terms because you're doing a logical argument and the physics has no Concept what that logical argument is and which you said is a highly heterodox point of view. And does anyone here agree with that Does anyone here because it seems to violate the unitarity of quantum mechanics and I Believe quantum mechanics is unitary because I happen to believe that mission take place every time my measurement takes place is not unity. Sorry I don't know. I don't understand what any quantum physicist says quantum mechanics is unitary So do you think this is important because it does leave A note London opening to a robust notion of free will yep. Okay and Surely this must have raised some hackles here These are excessively polite people, but they're raging inside I would like to get one clarification from suckage about what what a measurement is in your view so weather measurements before there were people and Quantum measurement problem we're getting into which is really Measurement is coming because people first discovered this in laboratories But a measurement takes place where in a superposition goes to an eigenfunction That's a non unitary process because you lose the information About the superposition and you end up with one specific that happens all the time everywhere it happened in the early universe where nuclear synthesis took place long before there was a when does it what are the well It's the law that determines when that happens. We do not know that's one of the big things We don't know how it happens and we have no specific Characterization or when it happens is one of the biggest Kuna the foundations of quantum mechanics Yeah, those pictures of the screen with the particles coming on to the screen and you cannot predict where the next particle come on Those wonderful pictures the particles. Come on one by one. Nobody can predict where the next one come but eventually you put up Those it builds up to those interaction patterns in which you can predict with great fidelity What the final? Statistical thing will be but you cannot predict what the next one will be and that is the evidence for what I've just been says That consistent with the average interpretation or many other interpretations of our mechanics that do not invoke this mysterious Giveaway function give me some way of Experimentally showing the Everitt interpretation is true just weak So look As Jim said we're getting here into altogether different territory of the measurement problem in quantum mechanics, but We now have lots of ways of thinking about the measurement It's too early to know just as with choosing between inflationary theories It's too early to know which if any of the ones we have now is going to turn out to be correct But but we have lots of ways of thinking about them which contradict crucial assumptions that you were making on our us supporting the Everest interpretation, which is putting no I'm not I'm not actually I'm a I'm a very I'm a very trenchant critic of the Everett Interpretations, no one uses the term ever ideas in any world They're three of three or four interpretations. They're all good. So there is this puzzle If we come back to my question I think Ellen and says there's ilion's of other worlds out there in which we each said different things Rather than what we actually sit here I think it is simpler makes more sense to say the Grail emergence takes place in which we do have real psychological powers And in which we can make logical arguments came to logical conclusions lead to what we say And I think that is what has happens Not that there's a zillions of other possible things happening out there which we cannot prove how happening okay, I would say nobody on stage agrees with that but Actually the whole discussion brings us a little bit back to Discussed and that is about the measure problem because right now we're returning to the measurement problem Which is a different problem Which is however very much related because in both cases were talking about whether there was something in the early universe, which was definitely Defined before anybody have seen it because the measure problem is What is the problem over the first event? Which now? Nobody have seen it. Then the wave function was not reduced and stuff like that So what is interesting about that is the measurement problem is? discussed by everyone for almost a hundred years and you can really Find people who are complete in all details agree about the solution of this measurement problem and nevertheless Quantum mechanics works pretty well everywhere agree about that So I think that this is very similar to what happens with inflationary cosmology which we do there are not so many people who absolutely agree about which probability measure in in world many world while many universe interpretation of Inflationary theory is better. But what more or less everybody agrees among? Experimentalists with whom we're discussing it who are providing us with data? so more or less everybody agrees that if you have a given Inflationary theory it gives them predictions which they check and the checking so far was pretty successful Let me take a simpler example. We've come into existence through Darwinian evolution now My claim is the following Darwinian evolution is consistent with physics, but it is not implied by physics There is no physics textbook in which you will read the chapter on Darwinian even because it isn't a physics result. It's a biology result Couple of things. I mean one thing that's striking is that people could come away from here Learning that there are two big issues in the philosophical foundations of physics that are on the table The measurement problem is Andrews saying the measurement problem old one in the foundations of quantum mechanics and the measure problem a Newer one was important difference in the two cases in the case of the measurement problem there's quantum mechanics everyone learns or takes physics learns how to use it to make predictions in the experiments that they do what they Disagree with is what's really going on when measurements are being made what the reality Iying reality is George has one view David may have another view and I have another view in the case of the measure problem It's a problem that arises for a particular theory in cosmology the theory of inflation And it's really a question of whether or not the theory itself makes any predictions at all Until the measure problem is actually solved. So these are two rather different both very important and interesting issues We have three minutes left on the notion of beauty beauty very fuzzy notion, but people great physicists like Stephen Weinberg the father of the standard model says that you know We're now in an era where we don't have a lot of experimental data and observational data that we've reached the limits of the you know, there won't be a Bigger particle accelerator than the Large Hadron Collider built in the foreseeable future. We're sort of up against an empirical wall and when that happens Physicists rely on their sense of beauty and beauty has been a very reliable guide to truth Weinberg said when he was a graduate student at Harvard Paul Dirac Came and said to the graduate students don't pay attention to what your equations mean. Just pay attention to how beautiful they are and And this is a kind of a weirdly mystical Lotus eating notion, but beauty has proved to be a reliable guide to truth in the past and now we were in a situation where theories like String theory which were thought to be beautiful initially are now looking rather ugly and people would make the same claim about inflation but I I will name them because I Did Sheldon Glashow he said it's like metal he said it's like medieval Sheldon Glashow in 71 suggested he is alternative to the standard model of electromagnetic Interactions standard model was based on the theory. Sorry for math Su 2 cross you want two different groups two different coupling constants many particles Anomalies doesn't work and he suggested his own beautiful mostly symmetric model vector model. No anomalies Everything is great and everybody sir. Oh, yeah electroweak theory one Uppsala model No It's that Because it is not beautiful and Shelley glacial model is so beautiful And then they discovered neutral currents and they're very shaded glacial model. Okay He got his Nobel Prize, but the one vessel our model survived So that's how it was Eddie got a character named after about the Big Bang theory the TV show right? Do you have one? No, there's no Andre. There's a shelter Anyone else have anything to say on any epigrammatic observations to make on beauty is a guide to truth and It's just two facts Yeah Well, first of all, I would dispute that string theory is not beautiful, but that's that's me But but I think okay, the the word beauty has all these other meanings. I would I would think simplicity and internal consistency are much more descriptive and certain types of logical rigidity and the Example of that was general relativity you alter it a little bit it crashes whereas string theory is very elastic No, no. Well, you might be I mean it has that the internal consistency is very powerful tool in fact, it's very restrictive and of I mean it's clear to all of us that whatever we propose as a theory can't be neutrally, you know self inconsistent and But you might think that that's a useless thing because you know just about anything you propose you can fiddle around with To make it self consistent, but that doesn't happen And so this takes us much further along than than one might have thought and it turns out I mean the physics packages itself in some nice way and yeah, it's This here predicts multiverse, so it was really beautiful but yeah Okay, so we've heard we've come to the end We've heard the we've heard a scientific account of the universe and we've heard the philosophers commenting on it So I think we should just give the last word to religion So the religious story is in the beginning there was nothing and God said Let there be light and there was still nothing, but now you could see it And then I have to say, thank you again everyone You
