Quantum to the Cosmos: A Brief Tour of Everything

welcome everyone thanks for joining us today for one of our first live sessions in quite some time but I'm excited to do it and those of you who've come to our other live sessions probably have noticed that this background is different from the one that I had for all those dark days of the virus where outside my window was the uh the lonely outskirts of Upstate New York here I am back in my office at Columbia University and it's kind of an interesting thing I don't know how many of you have seen Oppenheimer by now but a little known fact well a well-known fact to physicist but to those walking in the streets of Upper Manhattan a little known fact is that this building where I'm sitting right now pene physics Hall Columbia University was actually where some of the work on the atomic bomb took place the early work Leo salard and en Rico firery and the the these were the early days of trying to determine the details about radioactive decay and of course the key question that people were interested in was whether or not you could get a chain reaction that would require the radioactive decay to give off more neutrons than were required to stimulate that decay because after all if one Neutron gets you two well we all know what happens from there two gets you four gets you eight and so forth but if one gets you one one times one doesn't take you very far toward the kind of exponential growth required for the possibility of a chain reaction and indeed it was Leo salard as some of you may know the history who recognized that this idea of radioactive decay and the Chain Reaction could indeed give rise to a powerful weapon and he drove out from here in Upper Manhattan to see Albert Einstein in Long Island 1939 I think it was to convince Einstein to write Roosevelt that letter that convinced Roosevelt the need to try to make use of these ideas before anybody else in the world got there first so a lot of history in this building right here and happy to talk a little bit about that if that's where the conversation I'm about to have with Sean Carol should take us but you all should feel free to send in any questions that you have I don't have a whole lot planned because Shan and I have such common interest that there's kind of almost no subject in science at least where Sean and I don't have a similar resonant passion perhaps that's the way of saying it whether it's quantum mechanics or the arrow of time or cosmology or the measurement problem we uh always seem to find ourselves in a place whenever we get together of shared interest so anything that you ask that resonates with one of us will likely resonate with both of us so feel free to send your questions in and we have someone monitoring the chat right now to try to pull out those that seem the most relevant to the conversation we're going to have before I bring shown in let me just quickly note what you just saw in that little introductory sequence we are having our first Live Events world Science Festival that is in New York City since before the pandemic right I mean 2020 we were and root to having the 2020 World Science Festival when of course everything shut down and we've not gone live in New York City since then we have gone live other parts of the world those of you who are in Australia know that we do World Science Festival of Brisbane and we've done that a few times now since the dark days of the pandemic but we're not doing doing a full Festival but we are doing what we call science in September we're doing seven events seven kind of intense events that are spanning artificial intelligence cosmology quantum mechanics issues of new ideas of cosmology that perhaps are competitors at least in the minds of some to the inflationary Theory Sean and I know that will talk a little bit about that in just a moment Sean and I are doing a program with Carlo Rell and Elise crw on issues in quantum mechanics at September 23rd at I think it's 4M so if you find yourself in New York City September 21 to 24 please join us for those live events in New York City but otherwise at some point you'll be able to see most of them as we will put them out into the world at some point through uh the usual digital means that we've been doing for the last few years all right with that let me now bring in my friend and colleague Sean C professor of physics and philosophy at John's Hopkins University author of many books that I'm sure many of you have read something deeply hidden his book on quantum mechanics the big picture his book on kind of everything and then his book on the hour of time and nature of time let me not get the title wrong I'm doing this all from memory but from eternity to hear and I believe there's one other that he will remind me of when he comes in so please join me in welcoming Shan Carol to the discussion hey how you doing good Brian although after your intro I'm worried I'm gonna get a lot of questions about mirror symmetry that I'm not gonna be able to uh help anybody with hopefully you can chime in well I'll jump in on those but um um did I get all your books or did I leave no not even close oh let me then help me out here please got every title right that you got got but I mean my most recent book is called the biggest ideas in the universe volume one space time and motion so what I'm doing in a three-part series of books is explaining all the ideas of modern physics with the equations to people who don't know any equations so I teach you calculus and in book one we go all the way up to Einstein's equation and book two is all of quantum mechanics and Quantum field Theory effective field Theory gauge Theory the higs mechanism it's a lot of fun so let me ask you by the end of book two can someone calculate like a fan diagram or the uh magnetic moment of uh the electron or something like that they cannot but to do that they should go to graduate school but they will look at a findan diagram and know what it means that's the goal yeah yeah you know and I have to ask you a question on on on books it's an interesting thing because I think you and I are both very similar we take the language that we use very seriously and we view the book itself as more than just trying to convey information it's meant to try to grab you in a way that holds your attention and Sparks your imagination but here's the thing that that that's interesting when you talk to people who've read your books what fraction of them do you think have really gotten what you were trying to say and what fraction sort of come in with a preconceived notion of how things are and take away more or less what they were looking for well I think it's a great question but over the years uh you know you and I have known each other for long time so we've grown in wisdom since we knew each other for the first time I I perceive the purpose of a book or a talk or a class or whatever as a little bit different like I don't see people's knowledge and opinions changing in little spurts when you read a book when you take a class I think that reading a book might have a huge effect on someone but they don't even know it because they don't even recognize until five years later you know or taking a class or whatever so I I absolutely see people read my books and then say things that I'm like really you got that because I didn't say that but I think that there's a sort of larger vager yeah but nevertheless overly o over mostly positive impact that they had yeah no hugely so and I think we view that you know I mentioned you know these World science postal events that we're doing and we sort of see it obviously in the same light namely you want to bring people into these ideas and keep the excitement going as at least to counteract all the other nonsense that's happening in the world and and if someone takes away that level of enthusiasm and excitement is actually enough you know uh and if they take away more you know it's really icing on the cake there um and so so what's volume three of this three volume set you mentioned one and two volume three will be complexity and emerg so it's between you and me don't tell anybody but everything that didn't fit into volume one and volume two uh but the theme will be you know more than two particles colliding in a findan diagram right it'll be many particles in the collective behavior from cosmology to thermodynamics up through complexity and life so let why don't we jump off from there you know with complexity and life because that speaks to a question that you and I have both spent some time thinking about which is the arrow of time you know this strange phenomenon that the laws of physics which people can now learn about at the level of mathematical detail in the two books that you've already mentioned those laws of physics have this curious property that seems counter to experience that any process that happens in One Direction with small caveats that we don't need to get into right now the reverse process can also happen and so we have this beautiful symmetry in the laws of physics between One Direction in time and processes unfolding in the reverse direction of time but yet in everyday life it's anything but a symmetry between between those things I mean it's why we all laugh when people run a reverse Run film of anything you know people diving into a pool and unding it's like it looks weird it's funny cracking an egg unracking an egg it looks odd so where do you think we stand in trying to explain that tension between experience which doesn't show the Symmetry in the way time unfolds but the laws of physics that seem to have this built-in symmetry well good I'm glad that we have these eight hours to fill up so I can explain this fully I mean it's a it's a rich thing I'm teaching a whole first year seminar course here at Johns Hopkins on the AR philosophy uh this counts as a Physics course um but I think maybe it's also cross-listed in philosophy I'm not sure but it's mostly physics we're doing statistical mechanics Etc but we're also watching some time travel movies just because it's fun Y and I think that it's a there's a lot for the perspective historian of science to think about here because the laws of physics being symmetric with respect to time kind of crept up on people right no one wanted that no one ordered it no one even remarked on it when it happened you know once Newton had written down his equations Newton was smart enough to say like these work equally well forward or backward but he didn't as far as I know no uh it wasn't until LL over hundred years later who first said you know if I know exactly the state of the universe at any one moment I know both the future and the past perfectly well and there was this gradual shift that wasn't really completed until relativity came on the scene According to which physicists anyway started thinking of all moments of time as real you know I think that people who are have not been poisoned by taking physics courses tend to think of the world as the current moment of time right that's reality and then there will be a world doing something different and I still feel that way I still feel that way intuitively of course you do right right but suddenly the laws of physics are implying a slightly separate story right and so a new puzzle arose because of this beautiful structure that we called Newtonian mechanics and this this puzzle has persisted with quantum mechanics and relative and the whole bit why is the past different from the future you know the short answer to your question is I think that we there's like one thing we understand very very well and two things we don't the thing we understand is entropy is increasing entropy is a way of measuring the disorderliness the randomness the disorganization of something yeah so we have a law the second law of Thermodynamics that says in a system left all to its own self if you start it in a low entropy organized State and it just wanders off it will increase in entropy like you say you can break the egg very easily Unbreaking the egg doesn't happen very much and that's simply that there are many ways to be disordered compared to ordered so left to its own devices it's going to find one of the disordered States uh except for the word simply yeah I agree with everything you just said like this is very contentious right you know people really can find things to to worry themselves but I think basically yes I think that's basically it but then this this leaves us two very very important things still to be resolved by science and philosophy for that matter one is why was the entropy ever so low and the the joke that I I'm sure my listeners have these listeners have heard me say before some a fraction of them the reason why the entropy of the universe was lower yesterday than it is today is because it was even lower the day before yesterday yeah and that's that is the entire reason and then the reason why that's true is because it was even lower the day before that and you can play this game for 14 billion years until you hit the Big Bang so there's a puzzle for cosmology that you and I have both thought of very carefully which is why was the conditions near the Big Bang so low entropy and we I I would at least say let's see what you say but we don't know the answer to that uh that's that's still on the table but then the other thing looming in the background is I would claim that this fact that entropy is increasing with time is the really the only reason why the past is different from the future fundamentally so we have many manifestations of the arrow of time the breaking of the egg but also our memories only work in wonder I have photographs on my phone of things in the past I have no photographs of things in the future causes precede effects we age in the same d a million different ways so we have to try to fill in that story by explaining why all those phenomena reduce to entropy increasing and that's I'm very very interested in right now yeah I mean the remarkable thing about that too which I'm not sure everybody appreciates but it obviously is implicit in everything that you said when we see some degree of order today it actually is a remnant of the extraordinary order that for whatever reason was in place at the time of the Big Bang so the very fact that you have the egg that can then crack is because we had that orderly State back then because without that orderly State back then there would be no order today and therefore no opportunity for the entropy to do what it ordinarily does yeah 100% I mean the low entropy of the Big Bang is the most valuable resource in the universe and we're using it up we have a long way to go there's not like an entropy crisis like there is an energy crisis but you're absolutely right the way I put it is if you find a cracked egg you think that there must have been an uncracked egg sometime in the past but the only only reason you have any right to think that is because the early Universe started with low entropy whenever you're in the kitchen thinking about how the mess occurred you're implicitly relying on your knowledge of what happened at the Big Bang now some of the the audience no doubt because a lot of the people listening here have some familiarity or perhaps a deep familiarity with cosmological Theory such as inflationary cosmology which is kind of the dominant Paradigm and no doubt what may come to mind for those listeners is well if the early Universe underwent this rapid swelling that kind of smoothed everything out and took you know perhaps the curvature that had might there flattened it all out and so on is that a mechanism by which we can assure ourselves of that low entropy and of course I'm tossing you the softball question because we know that doesn't really work because I mean why don't you take us through why that doesn't that reason is natural but it doesn't really work the reasoning is natural and it might end up being a little part of the solution as a whole but it's certainly not itself the solution as a whole and I think you and I can agree like that if you pulled all physicists we might being the minority there right I think a lot of working cosmologists haven't really coton on to this idea we have this idea of the inflationary Universe which I love I think it's great and Alan Guth who helped invent the idea he and I and Saki dulani are actually writing a paper on the Arrow of time and its relationship to inflation so hey wait a second so you weren't you Allen's student uh I was his postto postto okay and sakshi was kind of my student so this is incestuous little circle here but yes keep going physics and philosophy are both incestuous little circle so I don't know if you know sakshi is joining Johns Hopkins as a post yes I did know that yeah you're reminding me I'd forgotten but yes I do remember now so she for those who don't know out there she is a philosopher very interested in physics and who knows a lot about the arrow of time so we're going to try to tackle some tricky philosophical questions about infinity and how to measure what is likely and not and so forth but anyway that that's that really is why it's such a tricky question because there is a a way of talking that is the following if you have any little region of space that is ready to inflate okay and by this we mean a little region of space that has a tremendously high density of energy in a very specific form false vacuum energy is what we call it but it's basically a smooth patch of SpaceTime very very tiny if it's in exactly the right conditions it can literally grow and expand forever right parts of it can grow and become universes like ours other parts can keep growing and become very different and you make a whole Multiverse out of this little tiny patch and that's one of the Miracles of inflation and so there's one point of view that says how hard can it be to get one little patch of universe ready to do that and there's very good reasons to think it could be very very hard and you have to work harder there so I think that the question of why inflation which is this little tiny patch of space that expands to make a big universe just like ours why it ever would have started in the right way is something that a lot of working cosmologists will say oh come on you know but I think it's crucially important and just to say one more sort of sociological thing when was in grad school late 80s early 90s I was in an astronomy department and there was a big sociological divide at that time between astronomers and physicists none of the astronomers believed inflation this had been proposed 10 years before right in 1980 but they said to themselves look you've made one prediction namely the universe is flat we've gone out and measure the density of the universe it's not enough to make the universe flat I'm going to move on with my life but the physicist love inflation because it was kind of natural and elegant and whatever and then 20 years pass and the tables have completely turned the astronomers love inflation because it makes extra predictions about the density perturbations in the early universe and the microwave background it's highly quantitative and you can match onto things and so forth but many of the physicists are saying to themselves well are we sure that the story we told isn't really cheating so that's what makes it fun I think it's a great research area right for two questions in in one a quick one what fraction of the physics Community do you think is really convinced that inflation is the right Paradigm for cosmology and what fraction are willing to question that dominant perspective right now well I think that there's no close second competitor so to me I would say that in my own personal view I give inflation a 50% chance of being right which is a giant percentage chance for an incredibly speculative theory of the very early universe but my second best criteria my second best Contender with like 48% is something we haven't thought of yet right I don't have any good Alternatives so inflation is good enough and it has so weak competition I would say right now that for most physicists who care about these issues at all they they tend to be pro- inflation uh you say inflation yeah just to be clear presumably you're talking about the framework inflation that there was some Source regardless of the details that gave that energy density that gave rise to this repulsive gravitational push that led to all of the things that you just described but you're not committed to a particular incarnation of the theory are you no not at all and in fact this is one of the uh arrows in the quiver of someone who would be anti-inflation you know I I might have given the impression saying that it makes predictions and we're testing the prediction but really what I should say is it's flexible enough to fit the data that we have you know the data that we have is from the observational point of view highly precise and very very quantitative but the input you need to reproduce that data is actually just a small number of parameters yeah uh it's not like you're you're predicting a hundred different numbers and then going and measuring them all independently you're predicting three numbers and then you're measuring them and you can fit so one of the things about is maybe it's it's like you say a framework a family of theories and it can fit the data but it's not exactly as if maybe something else couldn't either and what would it take on the observational front for you to come to the conclusion that inflation is not the right Theory well there are okay let's let's back up uh in the 1990s before we discovered the dark energy in the acceleration of the universe that was a thing thing we did in 1998 we found that 70% of the energy density of our universe today is in this thing we call dark energy and that that was a huge Boon for inflation for various reasons one of which is it filled in the missing stuff that the astronomers 10 years earlier were unable to identify it's also a slow version of inflation you know in terms of me that's the other reason why it's so good the universe can accelerate right which inflation needs to have yeah so um be but before then people were really worried about the fact that the one prediction inflation had made because we didn't have precise measurements of the microwave background or large scale structure either so the one strong prediction of inflation was the universe should be flat and it didn't seem to be flat that is to say the density of stuff in the universe wasn't the amount predicted by inflation because we didn't know about the dark energy yet and so some very with the theory and mess with it yeah so that I can make it compatible with a nonfat universe and there and I get why they did that because they said I don't have any second best theory if if my one prediction comes wrong I'm gonna tweak my theory to get that prediction right I'm not going to give up on the theory to me honestly that's still true you know until we have a second best theory it's hard for me to imagine one specific observation that would make me say inflation is wrong versus say some weird version of inflation some unexpected version is the right one so it's super important for us as a field to develop Alternatives yeah so what do you think of and I I don't want to put you on the spot at all but of course you know you and I are both aware that Paul steinhardt one of The Originators yeah of the inflationary idea you mentioned Alan Guth before there's Andre Lind there's Paul steinhardt with Andreas albrech usually described you know stra bins also is put into the collection of people who developed the key ideas in recent years Paul rather vocally and energetically has said he no longer believes in inflation even though he was one of the people who thought of it and has put forward this other approach indeed we're going to have a little session at our events in September where he's going to describe cyclical ideas to cosmology where do you come down on on the position that Paul has now staked out I think there's two aspects of his position well let's let's just back up Paul is great he's super duper smart I'm going to listen to anything he says whether or not I believe him he's worth paying attention to um this position that you just outlined I I would separate into two separate positions one is he thinks he has alternatives to inflation and the other is whether or not he has Alternatives he thinks that inflation is uh untenable just as a theory all by itself so on the Alternatives I am very happy that he's developing them I am completely unimpressed with the ability of the alternatives to actually do their jobs largely for reasons related to The Arrow of time actually I think that unlike inflation which does not solve the arrow of Time problem but might play a role in an ultimate solution I think the cyclic and bouncing cosmologies are are pretty hopeless when it comes to the arrow of time I might be wrong about that this is my personal point of view but that's why I'm not personally dropping things and and spending time on on studying that the other argument I think is very interesting and it's a it's a legitimate challenge Paul says the following you know as I just mentioned once inflation starts it's not hard and maybe it's even more likely than not that it keeps going forever what we call Eternal inflation and then again we don't know but more likely than not you can get regions of the universe with all sorts of wild different conditions right that's what gives rise to the cosmological Multiverse so Paul's point is pretty simple the whole idea of inflation was to say no matter where you started you ended up in a universe that looks like ours and now it says if you start in this specific place you end up in all possible universes so predicts nothing it can get a region the universe where it looks like anything then what are you predicting and I I absolutely abely feel the force of that worry but to me it's not a showstopper it's a challenge we need to better understand how to make probabilistic predictions in this kind of scenario and and guess what we need philosophy as well as physics to help us with that yeah know it's interesting so a couple years ago Paul and I had a energetic Email exchange H about these issues um a friendly Email exchange I mean like you I have the same opinion that Paul's one of the great physicist of our age and uh it's always a joy to argue with him because it always is enlightening even if you don't fully agree with the position but yes I would say that a big part of the issue is indeed as you just mentioned if a theory can give rise to many different universes or subuniverses within a large universe or universes within a Multiverse whatever language you like to use then what kind of predictions does it make and of course the natural answer that many in the inflationary cosmology Community will offer is well we just need to work out a so-called measure on the space of universe as much as you're noting something that gives us a measure of the probability the likelihood of this universe versus that universe and hopefully our universe would be relatively High measure a likely outcome of this process and that perhaps would give us some confidence that these ideas are right but Paul's response to that is hey Brian and rest of you inflationary cosmology proponents this measure that you talk about that's doing all the work of your theory and so to just think of it as well we just need this extra little piece is perhaps a little bit disingenuous and and and that may be the Crux of where he's coming from yeah and I think that's fair of course since the the other thing that I would say on his side is we don't have the measure so uh to say that it's yeah doing all the work I don't know whether it's doing all the work because we don't have it yet but let me uh raise another thing I'm sure the listeners will enjoy which is the many worlds interpretation of quantum mechanics which I'm a fan of in many worlds when I do a measurement of a Quantum system right here in the office right I don't need to look at the cosmology or anything like that I measure a spin in a undergraduate laboratory and the rules of quantum mechanics as far as observers notice is that there's a probability that you get spin up or spin down and many world says there's a world where you get spin up with 100% probability in some world and there's going to be some world with 100% probability where you got spined down so there's a huge challenge as you know hanging out at Columbia with David Albert and other people there's a huge challenge to many world's Advocates how do you recover this measure this probability and I think you can do it in that case I think the data have guided us uh because we do quantum mechanics experiments we know in the case of many worlds precisely what measure we need to get and we get it you know it's it's the one that is sort of most natural but that again this is very fertile ground for a collaboration between physics and philosophy because I think that careful thinking about what it means to be a probability what it means to be Infinity how you deal with these uh tricky problems has a very good chance of answer answering these questions in the inflationary context just like it does in the many worlds context so in fact there are some who have made an argument that the many worlds of many worlds interpretation of quantum mechanics and the many universes of internal inflation May in fact be one and the same thing so answering one through some complex chain of translations may take you from one articulation of the answer to one problem to an articulation of the answer to the other now I am tempted to go down this rout of quantum mechanics that you have opened up here however I am reluctant to do so because as I mentioned at the outset you and I are going to do a live conversation we got time for that in in New York in in September 23rd Saturday again anyone who's around September 23rd I should say this is 2023 in case you're watching this in the years's 2037 and you're going to clear your calendar for September 23rd so for all those who are not fans of closed Tim like curves just ignore what I just said and we'll just carry on with other things that we can talk about but I want to go back to this issue of how perhaps inflationary expansion might have gotten started because one other answer that has historical antecedence really comes from boltzman who was thinking about these ideas of entropy as disorder and how sure the second law of Thermodynamics says that entropy increases but it's not a law in the traditional sense of a law something that can't be violated rather it's an overwhelming tendency that entropy will increase but as we all know there can be unusual fluctuations in which there is order produced as opposed to disorder and boltzman himself imagined that perhaps the order that we see right now now could have been preceded by a whole long history of disorder and who cares how long that era of disorder lasted so long if sooner or later the rarest fluctuation well not the rarest but a really rare fluctuation happened dropping us down to the low entropy configuration from which the world as we know it could then slowly emerge as the world went back up the entropy Hill of course you can imagine a similar kind of set of words for inflation cosmology early Universe I don't even know what I mean by that but way back when there's this wild undulation of everything every field curvature and so forth and this energy field we usually call the inflaton field but it's that energy that little packet of energy that we needed to start inflation that you made reference to it may have just threw sheer chance after eons and eons even though that word isn't even Define back then somehow it coalesces into this nice smooth patch of energy and then everything goes forward from there is that a convincing scenario in your mind or is that somehow cheating convincing would be a slight exaggeration I think uh you know I I do think that something like that is very plausibly on the right track I mean as you know I wrote a paper with Jennifer Chen years ago where we suggested that the way to ask this question rather than to say here is the most natural initial condition to start with because it's pretty and simple and so forth we can ask ourselves the question what does the highest entropy state of the universe look like and actually years later I wrote another paper with another student Aiden Chatwin Davis where we where we finally to my satisfaction showed that in a universe like ours the highest entropy state is empty space we're moving toward that in our universe now right our universe is not only expanding but acceler ating we think that we have some vacuum energy that is pushing us apart it's never going to go away so if we wait long enough 10 to the 100 years from now will be empty space with no stars no planets no galaxies no black holes anything like that that is the highest entropy State the universe could be in so the real question for cosmology in my mind is why don't we live in the highest entropy immediately from the GetGo yeah why don't we always live there yeah answer is anthropic and this isort the modern version of boltzman's thing because he boltzman didn't know about general relativity or the cosmical constant so he would have said if we think of the universe like a box of gas that gas should be in equilibrium right it should be the same temperature everywhere the same density everywhere that would be the highest entropy State why don't we live there now that's not that's not exactly correct because there's something called gravity but that's okay it's it's a whole story but boltzman's answer was if you wait long enough you will fluctuate downward in entropy just like you said it was one of Bol B's answers I I very much encourage people to directly go back and read boltzman's papers from the 1890s they're readable and they're kind of funny and he's wildly inconsistent he says well clearly the answer to this problem is very simple it could be this or it could be this or it could be this and he gives completely incompatible stories so maybe it's not so simple but anyway the modern version would be can you start in that high y empty space yeah and somehow fluctuate upward in entropy to something that would look like inflation from which you would then settle back down to a universe like ours and this is It's wildly hubristic even to talk about this kind of thing that's why they pay us the big bucks to talk about it because we don't know what we're doing we don't know whether the system is infinite or finite we don't know how quantum gravity works we don't know a million things so I would like something like that to be true I can't promise you that anything like that has been completely sold out right now one one one aspect of it that I think does fall out quite naturally is that time doesn't have a single Arrow but two different arrows it has one arrow in our universe and in the whole Multiverse around us but if we go to the far far far far far past the arrow of time points in the Direction and there's toward the super far past and the super far future entropy is increasing both directions and I think you recover the Symmetry that we started with yeah exactly exactly and that and I to me that's much more satisfying and it fits together more so than the cyclic Universe for example or just starting the universe in some weird boundary condition so you know if if one thinks about high entropy in the early Universe versus the low entropy be condition that we know had to Prevail in order to be compatible with our own observations usually we imagine that high enty configuration differing from what we put into our equations when we want that low entry starting point by virtue of the gravitational degrees of freedom being highly excited in the early stages versus them not being highly excited right lots of black holes filling space you know things things of that sort and you know a paper that I wrote a while ago that you were not a great fan of which is which is fine but the basic idea I'm a fan of anyone writing papers about the early Universe in the arrow of time you know the idea that that occurred to me uh and a couple of other folks at Columbia at the time was look if by some means the gravitational strength was extraordinarily lower maybe turned off in the early universe and that could explain why the gravitational degrees in Freedom were not excited now of course the mechanism of turning off the gravitational degrees of freedom that becomes the devil in the details because you don't want to turn it off in a way that somehow is slipping low entropy in the back door now I don't know enough about it but I probably should but I've read that the loop quantum gravity people believe there's a natural means by which the gravitational strength would indeed be turned off analogous to what we were writing about in that paper are you familiar with what those guys are saying and and and uh whether or not that's a viable means of not exciting the gravitational degrees of freedom in the early Universe I have not heard of that no I haven't um I would say you know just one for me guiding principle which was emphasized by Hugh price who is another philosopher of physics is that if you want to explain the asymmetry of time in our universe by appealing to fundamentally time time symmetric dynamical laws like we think we have you'd better have the far future and the far past look the same and I'm not sure that that kind of model does that right right yeah it's a good it's a good point I don't know the answer either in that particular again I think that not nearly enough people are thinking about this even if Brian's model or my model are not the right ones maybe some young person listening to this will go figure out the right one and mention us in their Nobel Prize Acceptance Speech but it is a very interesting sociological question you know when I think of the great physicists of you know the the early 1900s mid 1900s I do think of them and maybe it's just a romantic notion as both physicists and philosophers people really bound up with with the big ideas and yet it seems like in a number of Arenas quantum mechanics being one of them and again I'm reluctant to go too far into the details but we can talk at a more General level why weren't they more worried about some of the philosophical issues of quantum mechanics which can actually even be thought of as physics issues really but there seemed to be a significant focus on on you know getting the calculations matching them to experiment but then not pushing that one step further to really say okay what the heck does this mean for reality and is this giving us a sensible picture of the world I mean Einstein did a little bit but you know even in eppr it was P&R that wrote the epr paper and Ein gonna get stuck on it but any was concerned with the issues so and there was certainly an era I mean I'm a little bit older than you but not hugely so you know I was doing my post-doctoral work in the in the 80s and there was definitely a sense of stay away from the philosophers we just put them to the side so so where did this kind of cyclical behavior in terms of our respect for philosophy come from and where do you think we are now in that cycle yeah and and just to be super clear it's not even a question of respect philosophy but a a question of the respect for these kinds of foundational questions yeah yeah to you and I it's natural to associate that with philosophy because the philosophers get it they're very much interested in these foundational questions right uh whereas physicists exactly like you said I mean historically during our lifetimes uh have not wanted to do that and I think it I don't I I try to be super fair right like it's easy to paint the people you disagree with as kind of Dopey um if if I try to give the strongest possible argument for the strategy that was taken over the last 50 years of ignoring the foundations of quantum mechanics I would say it was hard to know how to make progress yeah even if you thought the question was important when you when you as you know you had grad students you like train them not only solve the equations but also pick the right problems to work on and I think that uh for a long time you know we didn't know about decoherence entanglement like most people who even today take an undergraduate quantum mechanics course don't learn about entanglement I certainly didn't yeah exactly so I think that a lot of people there was such a richness of really good questions to be addressed in Quantum field Theory and in condensed matter physics and in astrophysics and in general relativity why would you spend your time banging your head against the quantum measurement problem I think that's that would be the attitude I don't agree with it yeah yeah I think that there's productive um progress to be made bangging your head against that problem but I'm guessing that was the reason they just didn't see how to make that progress yeah and again they could do just for those of the again I'm sure everybody knows the language but just to fill in you know Quantum measurement problems the idea is how do you go from the fuzzy Haze of possibilities Allowed by the quantum probabilities to the single definite reality of experience upon measurement or observation or some kind of interaction how does that actually happen and you mentioned David Albert before you know he's a philosopher here at Colombia you know when I first came to Colombia as a young man back in whatever that was 1995 or six or something like that this philosopher David Albert gets in touch with me and he says I want to have lunch with you I didn't know who he was at the time but I was game to meet new people at Colombia and we had an an incredibly enlightening lunch for me because my attitude toward quantum mechanics at that point was quantum mechanic done deal that's what I've been taught graduate school I'd used it nobody had Ever Raised any issues about it at all sure i' heard the measurement issue a little bit but my attitude was if you're pushed to the wall it's the many worlds interpretation then you just gota you just gotta kind of make it work and and so obviously you know David as well as I do he wasn't having any of that nonsense no and you know so we sat there for hours and I had walked into that as you know Mr physicist and I kind of walked out a little bit with my tail between my legs because he had raised issues that I couldn't fully address and I was surprised that I couldn't address some foundational issues in quantum mechanics it was something that I wasn't I wasn't fully aware of them so I know there are some in our community who still are very much you know put the philosophers to the side they've never done anything for physics I've certainly heard some of our colleagues say things like that I can say firsthand they've certainly done stuff for me and and I think they've definitely done important work for the field as a whole because um while you and I may be in the minority I'm pretty convinced that they foundational open issues and quantum mechanics that still need attention before we can really say that this is a done deal and we fully understand it well enough to say that uh uh reality according to Quantum Mechanics is something that we understand I mean I assume you're in a similar frame of mind oh 100% you feel that you've solved it by now which could be a you know I wrote an article when something deeply hidden came out I I put an OP ad in the New York Times complaining about the fact that physicists don't understand quantum mechanics and I was sure I was going to get deluged with uh emails from physicist saying well I understand quantum mechanics I only got one I will not reveal who it was from but you know most of the physicists are were like yeah actually I'm glad you're pointing this out so I do think that maybe people are softening up a little bit I I think that if anything it's not you know I would like to think that it's because of philosophers and people like me who are philosophy the adjacent you know telling them they should I think it's technology that changes how people view these things we're building quantum computers now we're doing we're using the resources of quantum mechanics in a way that are much less is much less simple-minded than we had to use it like people can talk about the the absolute genius contributions of fan and Weinberg and and Salam Etc gmon but and it was all based in quantum mechanics and Quantum field Theory but to a really large ENT it was a very simple application of quantum mechanics right like the field Theory and the calculation is very very subtle and complicated but all they were doing was calculating a wave function and squaring it to get a probability at the end of the day and so the the facts about measurement and entanglement and what it all means and like they didn't need to worry about those things but when you're building a quantum computer suddenly there's this thing called decoherence you know interacting with the environment and sharing entanglement around suddenly entangle lement is a resource suddenly you have to understand this stuff and you know whether you've ever listened to a philosopher in your life or not suddenly the foundations of quantum mechanics seems like a little bit more respectable to you yeah yeah and again um just to go there a little bit so again for those in the audience entanglement no doubt you've heard is this idea that you can have two particles in quantum mechanics that can be far apart from one another but in a mathematically precise way act as though they one or right next to each other you measure one of these particles and it seems to have an instantaneous influence on the other this of course is what Einstein called spooky action at a distance he said that as a pejorative not a wow reaction at a distance it was not like wow cool how can you Quantum mechanicians or quantum mechanics people believe in a theory that has that sort of quality which leads to a rich and wonderful history of ideas that no doubt you and I will have some time to talk about next Saturday at our live event in New York City if if Carlo and at least let us have a word in edgewise I mean people have a lot to say so yeah no that that's that that will be arranged so I think I think we'll be all all good on that front but it's interesting you mentioned the New York Times and the OPB that you wrote and the only you know one response that was of the sort that you were concerned about I wrote an oped back in 2005 which was on you know the anniversary of special relativity and sort of explaining some of the ideas and equals mc squared was one of those things and in that article I tried to undo a misunderstanding that E equals MC s is only relevant for nuclear processes I think there's a yeah and so I got all these angry responses mostly from chemists and I'm not trying to diss any chemists perhaps who are listening to us who said how could you have gotten that wrong how could you possibly mislead the public equals MC squ is only relative to nuclear only relevant to nuclear processes and it was so interesting to me how a whole community of scientists had somehow missed the boat I mean obviously many chemists do know correctly but but you don't need to know it yeah yeah that's right you don't need to know it and and there's the there's this kind of lore that can settle in and and infect a whole generation of thinkers if they don't encounter it in some way that makes them grapple with it more fully you know and I think the same same thing with quantum mechanics and entanglement the way that I say it is that physicists uh to their credit they care a lot about getting the right answer they don't care about getting the right answer for the right reason they're very happy to give false understandings of why they got the right answer whether it's Quantum field Theory or the measurement problem also special relativity but but uh the arrow of time is a huge example of this I I taught a course last year at Johns Hopkins on the philosophy you know topics in the philosophy of physics and I had a couple of physicists take the class and I had one woman who was a student who you know when we were talking about the arrow of time and I said look unless you make some time asymmetric assumption somewhere you're not going to derive that the past is different from the future and she said oh no I just had my stat Mech course and you know my professor told us how to do it I said and I said no no they did not discussion about it as usual you could find exactly the place where they smuggled in right in assumption but it's all over the place which is which is why you know the the foundations maybe the there's still it's it's not just that it's important to get things right and tidy things up I think that we're in a we're in a moment of time in the history of fundamental physics where there's some looming questions we don't know precisely how to make progress on them whether it's particle physics or cosmology or gravity or whatever it's kind of a natural thing to step back and say okay without strict experimental guidance let's reexamine all the details about how we got here and ask how we might do something different yeah in terms of experimental guidance you know there's some wonderful astronomical things that are happening right you got the Simon Observatory you got uid you got the Nancy G Roman's telescope I mean there's all sorts of wonderful data what do you think on the particle physics front so you know Large Hadron Collider was developed to find the higs particle July 4th 2012 fantastic you know that was there and that oh you were at CERN oh that's beautiful you know it must have been quite emotional I would imagine you know for that to happen I mean just for people to know this is an idea that began as a mathematical idea in the 1960s Peter higs and glair others as well who didn't share in the prize but a number of individuals gave a mechanism by which the ordinary particles that inhabit the world around us could have acquired the masses that they have but it was a completely theoretical idea and I'm I'm slightly embarrassed to say but I will say it anyway because I've said it before when I was a graduate student and we learned about the higs mechanism by which particles would acquire their Mass I did not realize that this was a hypothetical idea it was taught with such certainty I'm sure the the professor yeah so I for a long time I was like of course it's the higs idea I didn't know that it was still a waiting confirmation but you know I was disabused of that notion you know in the ensuing years and then so this mathematical idea goes from equations in the 60s to experiments searching for the predictions of those equations to confirmation in 2012 that's the journey that's the journey that is like the Prototype of of of excitement and it's spectacular that it happened but the machine was also built for another reason you know obviously one reason is find something unexpected of course that's most ex of all but there's this thing called super symmetry that you know the super and super symmetry is the same super as and super String Theory an idea that's certainly close to to my heart and things that I've spent time on we had hoped that a whole class of particles the super symmetric partners of The Gnome particles will be found and they've not been found as yet at the large hron collider so where do you think that leaves particle physics and and where do you see things going honestly I think you're underselling the weirdness of it because it's absolutely true that we were hoping to see super symmetry but even if you are a partisan of some alternative to Super symmetry there were tremendously good reasons to think we would find something at the large adron collider not only be for for two reasons which I think are worth laying out one is there's dark matter in the universe and a popular model for dark matter is weekly interacting massive particles maybe from Super symmetry maybe from something else but the word weak there means the weak interactions of particle physics and this energy scale that the large hydron collider looks at for the first time in human history is around the weak energy scale so just the fact that there's Dark Matter fits very naturally with the idea that there's more particles to be found at that scale and then there's what we call the hierarchy problem uh the H mechanism for understanding symmetry breaking in and particle masses works very well but if you just naively write down the equations and make a theoretical guess as to the energy scale of that uh which gives the energy and mass to all these other particles it should be much higher than it actually is so there's a big hierarchy between the higs mass or equivalently the weak scale the high energy scales of particle physics Grand unification plank scale what have you and again super Symmetry and other models that purported to be solutions to the hierarchy problem predicted a bunch of new particles at the LHC so I was very surprised I was not surprised to see the higs uh I was not a super partis in for super symmetry in particular like I I tend to be you know uh pretty ecumenical in my models so I don't know what it was going to be but I really would have bet a lot of money at even money that we would find something yeah Archy problem so I have made lemonade out of out of these lemons um my current sort of hopeful guess is that the reason why we haven't seen anything at the Large Hadron cider and the reason why we nevertheless have a hierarchy problem is because of a deep issue with Quantum field Theory and quantum gravity that we don't understand and and again I'm going to keep saying it but ripe for philosophy physics um uh collaborations here because the large hadon we spent n billion dollars building the Large Hadron Collider and in some very real sense the motivation was naturalness right the naturalness of the value of the higs go on yeah that's a problematic term to spend a lot of money chasing down when you haven't completely defined it or you know Etc so uh you know I'm kind of hopeful I I both want to have a better understanding of what we mean mean by naturalness which also feeds right back into the measure problem and internal inflation and things like that and it also and also I I think that we're sort of being cheap and easy about extending our ideas of quantum field Theory up to high energy scales that lead us to the hierarchy problem Etc because we know there is quantum gravity in the universe we know there is something you know we can go into it at Great length things like the holography uh principle the black hole information puzzle I think that it's perfectly clear that Quantum field theory is not the final answer to what the universe is it's some relative and it certainly like Quantum field Theory at low energies but I would love for the absence of particles at the Large Hadron CER to be the first good clue that we really have to make a bold leap Beyond Quantum field Theory yeah I mean it's a very uh optimistic interpretation which is which is a good one and I can't help but also emphasizing you made a mention of dark matter and the natural way that super symmetric particles could have could have been the dark matter just to underscore that when you consider a potential Dark Matter candidate what we as physicists as you know need to do is you need to follow the number of those dark matter particles that would persist until today based upon how many would have been the natural number in the Eur Universe based on thermodynamic equilibrium and so on and the remarkable unbelievable fact that without fine-tuning any parameters super symmetric particles the most basic ones would persist in just the right abundance to be the dark matter how could it have not been the case that super symmetric particles are the dark matter it was such a convincing argument and yet so far it's seems that it's it's not the case so we can really be misled by these ideas of of naturalness these ideas of fine-tuning you know you really do need to take these ideas and shake them really hard because you can absorb them as yes of course it has to be that but then the universe sometimes will Accord that kind of reason but sometimes it doesn't sometimes it doesn't I will never forget um there's another famous coincidence that is very similar to this the M coincidence yeah uh if you look at a Galaxy you look at lots of different galaxies they all need Dark Matter to explain their rotation and their structure Etc but uh morai mgrm noticed this absolutely fascinating and potentially important fact inside a certain radius in each Galaxy you don't need Dark Matter the visible matter is perfectly good to explain the Dynamics is always a radius that is sort of the crossover point from where inside you don't need it outside you do and he said I bet I could just change the theory of gravity or inertia is what he actually did and the very remarkable thing is that this crossover radius it's different for different galaxies but the what it numerically works out to be is the radius when the acceleration due to gravity is a certain number and that number is the speed of light times the Hubble constant today and the Hubble constant is not a constant right it changes as the universe expands and it should have nothing to do with each other those two numbers this radius at which you need dark matter and the expansion rate of the universe they should be unrelated yeah and I remember vividly sitting at a cosmology conference in Princeton and Milgram gave his talk and he explains this and I was sitting next to Juan Mala who we know is you know a friend and one of the great string theorists and and thinkers of the world and he leans over to me and says is that true that there's this coincidence and I said yeah and he goes it must be right then he was ready to give up on dark matter and replace it with modified gravity and I said well yes but sometimes there are just coincidences and I think that's right you know gravity could be modified but dark matter I think is real so nature is not being quite kind to us yet yeah although even that's a little bit still up in the air what exactly the resolution's going to be I mean there's a lot of circumstantial evidence for dark matter but the failure to find it where does that does it not shake you up at all or you just say hey look there's so many possible candidates for what it might be and there's so many parts of parameter space that we've not yet explored so yeah we haven't found it yet we will so I I I am not shook not shook yet about Dark Matter uh to me for two two reasons number one if you go back and look at especially the cosmic microwave background radiation which is by far our best evidence for dark matter but also things like the bullet cluster and other other things I to me and I'm kind of an extremist on this not everyone agrees but they should I think we know that dark matter exists we might also modify gravity that I'm a big fan of I've written papers I love modifying gravity but I think that we've crossed a threshold where we have enough evidence empirically to say that dark matter of some sort has to exist and the other thing is you know the like you say there's lots of candidates for what the dark matter is I I I gave just a few years ago a talk where I was asked to you know in our old uh phase now we're asked to give talks like what is the state of the field you know so uh I but I knew that a lot of the audience members were super symmetry fans and you know weekly interacting massive particle fans so I did something almost no one ever does which is you always see these plots for dark matter experiments of here's the theoretical you know differ models that could predict different cross-sections here are the limits and here our limits yeah and then as we get new limits we erase all the predictions that are incompatible with the limits right so I actually went back and found a plot from before we had done any of the LHC or any of the weekly interacting massive particle detectors and I I looked at their predicted range of parameters and this was a couple years ago but roughly speaking we had ruled out about 50% of the ameter space as we'd understood it Circ the year 2000 so I can't be that surprised by that failure but also something called the ax on and there's other Dark Matter candidates so we're not basis point yet the fact that we haven't found the dark matter so I said we take questions I do see one question from our audience which uh a basic one but an important one which is a questioner notes that they always mix up dark matter and dark energy and can we just give a little explanation so feel free to jump in on that one if you would show that that's pretty easy I mean honestly I wish they had been named something a little bit more dramatically different from each other you know we we have these three components that that at least are important to the universe ordinary matter the kinds of matter that we find here on Earth in in the lab about 5% of the matter of the total energy budget of the universe dark matter is matter it's kind of like it's a particle probably maybe tiny black holes but it's something like that comes in discreet chunks and can evolve like we know a lot about dark matter we know how much of it there is we know where it is we know kind of how it evolves and it's 25% of the mass of the universe probably it's some particle we haven't detected yet and then the dark energy we don't even need that name in in in my view because the dark energy is some kind of energy that is smoothly spread throughout space and doesn't dilute away as the universe expands so the the first guess is that it is perfectly smooth and perfectly constant and that is exactly what Albert Einstein gave us in 1917 what he called the cosmological constant what modern physicists call the vacuum energy and it's a perfectly good fit as far as I have have seen the plots to all of the data we have about Dark Energy but you know we fooled ourselves before we discovered the Dark Energy like you would have won money off of me if you had said in 1995 70% of the energy of the universe is the cosmological constant I would have said no that's unnatural etc etc and we were wrong so once we did discover the acceleration of the universe we say okay let's let's be more cautious now sure there's a very natural candidate that was given to us by Einstein and it fits all the data but it might not be right so we allow for the possibility that the dark matter is something Dark Energy rather is something dynamical it's not just a fixed constant it changes slightly not yet observably and we go look for it and that's a very worthwhile thing to do we build telescopes we do the observations if we find that the dark energy is not quite constant then that would be hugely hugely important and again my interest is that we do that I've written papers on exactly that possibility I would love it if that were true there's different ways to do it but my bet at even money once again is that Einstein was you know got right yet again and it's just a vacuum energy but it's interesting the Einstein right Einstein wrong in that because one of the famous quotes it was a secondary quote I think Gau was the one who said that Einstein claimed that the cosmological constant was his biggest blunder as the saying goes when it was realized that the universe is expanding because Einstein introduced it to try to make the universe static but the fact of the matter is there is a verifiable quote of Einstein's where he says that it would be future observations that would determine whether the cosmological member the cosmological constant is actually part of reality so he recognized actually that it was an interesting possibility it naturally fit into the equations and that we didn't have the data back in his era to really determine whether or not it was part of reality and so I don't think he would even be that surprised necessarily I mean it's usually framed as Einstein threw it away when the universe of and smacked himself in the head and now even Einstein's wrong ideas are right which would make you think that he would be oh my God this is insane that bad idea that I threw away is actually true but I think he'd be like yeah I suspected that observations in the future would determine whether it was right or wrong let me ask one final question because I know that you need to go make dinner and uh I don't want do it yeah I don't I don't want to exhaust everything that uh we can talk about uh we should do this again sometime and as well as we'll do it live in in New York on the 23rd but I've read some papers I consider them a little bit on the um fringy side but wonder if you've encountered these that if you look at certain data that makes us potentially question homogenate and isotropy which of course is underlying all the mathematical analysis by which we come to the conclusion that we need to have dark energy there are some models which suggest suggest that you don't need Dark Energy if you if you give things up in the in the right way and that there may be some evidence for that have you looked at any of those and what do you think I am uh yeah highly non-conveniens that it's just like some person in their basement with a theory like you and I get those in the email all the time this is not that these are cons cosmologists um I don't think it works for two three reasons I have some reasons but you know if it was one good reason that's all I would need right um one is I think the right way to think about this is using what is known as effective field Theory um there's this set of techniques that that we use in theoretical physics to sort of bundle up uh things that we don't completely understand right in particle physics you can say I can totally well predict the probability of to electron scattering without knowing whether super string theory is right you know there are ways that I can make low energy predictions without knowing everything about what happens at arbitrarily High energies and I think that if you use that technique in cosmology which has become uh increasingly popular in recent years you can include a term which is essentially the nominal Dark Energy contribution from large scale structure and it's very very negligibly small and the the the other reason I would give the other respectable reason is um intuitively it makes no sense at all so what people are saying is you know we we model the universe by having matter and energy be completely homogeneous we solve our equations and and for certain purposes that's supposed to be okay but the real world is is clumpy right there's galaxies and so forth so let's add in a correction from including the clumpiness right and there's a way to do that formally which much like Quantum field Theory gives you an answer that is infinity and then and you say well it's Infinity in this calculation clearly the calculation is wrong but because it's Infinity maybe it's big maybe it's noticeable and I don't I don't think that's the right logic to use there because intuitively what you're saying is we know the effect of stars and galaxies and dark matter and it's to decelerate the universe we're asking what is the effect of the gravitational field of the stars and galaxies on the expansion of the universe but everything we know about general relativity is that that's a small effect squared right I mean that's a small effect times a small effect so your intuition is this should not matter and I think it doesn't matter I think that the the third reason is there are people who have spent much more time than me looking at it who said no it doesn't work yeah right which is a a pretty good indication as well but yes all three well look it's it's been a a great pleasure spending this time with you Sean I'm looking forward again if you're watching this in the year 2037 ignore what I'm about to say but uh 2023 September 23rd of 2023 Sean and I together with Carlo relli and leis Crow are gonna talk about quantum mechanics in New York City live and iners 4 pm so if you're interested in around New York City at that time please join us so looking forward to seeing you then in person Sean it's been a while I'm looking forward to convincing Carlo and Elise that many worlds is right this is my chance there we go so we can duke it out on stage so thanks a lot for joining us and we will see you then all right everybody else let me just uh say a couple words before wrapping it up there's one point that Sean made that someone else asked about in the question so I might just quickly address it which is can we make a prediction for the amount of dark energy that we believe to be suffusing space responsible for the accelerated expansion that was observed in 1998 and here's the crazy thing and this is really kind of nuts right we can measure the amount of dark energy necessary to explain our observations as Sean mentioned is about 70% of the entire mass energy budget of the universe when we try to actually do the calculation though we get a number that is huge compared to that if you look at the quantum fluctuations in the vacuum every single mode every single wavelength contributes the amount of Zero Point Energy or dark energy that would be out there and when you add up over an infinite number of modes unsurprisingly you get the infinite answer that we heard reference to and so this is perhaps the greatest mismatch in the history of physics between something that's been observed and measured the amount of dark energy and our attempts to calculate that number they differ even if you put in natural cut offs Beyond which we can't really trust our theoretical calculation still the answer that you get is about 10 to the 120 times larger than the amount that we observe right a mismatch of a factor of 10 to the 120 and so this is a beautiful example of some indication of deep lack of complete understanding and and I say that not with my head held low in shame but rather with my head held high in the excitement of all it is that we still need to learn all that we still need to figure out so that's really the state of our understanding there are some deep problems that we have solved there's some deep problems yet to be resolved and I hope that some of you in the audience will be inspired to think about these questions get an undergraduate degree in physics a graduate degree and really join in the ranks in the in the Relentless March of humanity and trying to understand the universe at its deepest level again if you're in New York September 21 to 24 of the Year 2023 we're going to do our first Live Events World Science Festival events something called science in September six interesting conversations artificial intelligence cosmology quantum mechanics with Sean Carlo relli Elise croll and others we got a handful of Nobel laurates we've got breakthrough Prize winners touring Prize winners so it's going to be an exciting handful of days and so please join us if you are in New York City then but until next time we're going to try to get into the habit of doing these live sessions again so until next time please stay curious and stay connected to the Deep questions of reality so looking forward to joining you either in New York soon or online in the not too distant future until then signing off from New York Brian [Music] Green [Music] oh

Channel: World Science Festival

Views: 328,599

Keywords: Black Holes, Brian Greene, Breakthrough Prize, Event Horizon Telescope, black hole, Einstein, general theory of relativity, supermassive black holes, Astronomy, Infrared telescope, What is a Black Hole, physics, World Science Festival, World, Science, New York City, Sean Carroll, Inflation, What is time?, The Big Bang, Inflation (cosmology), Andrei Linde, Alexei Starobinsky, Alan Guth, 2014 Kavli Prize, Quantum fluctuations, radiation

Id: WGN4Jv5sWQI

Length: 77min 16sec (4636 seconds)

Published: Fri Sep 15 2023