Does beauty deceive physics? | Michio Kaku, Sabine Hossenfelder, Max Tegmark, Juan Maldacena

foreign [Music] faith and physics I'm your host Mary Jane Rubinstein this evening's debate is brought to you by The Institute for arts and ideas in partnership with closer to truth please find their interviews with some of the most foremost thinkers of our time at closer to truth.com and now for some fantasy faith and physics we think that we pursue the Sciences solely for knowledge and Truth but is this a mistake untestable ideals like Beauty have been baked into theories throughout the history of science Paul Dirac one of the greatest scientists of the 20th century proclaimed it is more important to have Beauty in one's equations than to have them fit experiment and recently Roger Penrose described String Theory as a fashion quantum physics as a faith and Cosmic inflation as a fantasy arguing that scientists suffer from the very same prejudices that affect the rest of us do we pursue science out of a pure desire for truth or should we accept that some ex some assumptions especially at the foundations of physics are akin to religious beliefs dressed in mathematical language should we see science as simply another theology or would that undermine the field of physics and the progress it has made over the past few centuries we have I'm excited to tell you invited four magnificent speakers to address these questions today first Juan malasena is world renowned for his field-defining contributions to the foundations of string theory and quantum gravity he works at the institute for advanced study in Princeton New Jersey is a theoretical physicist who specializes in quantum gravity she's the author among other things of existential physics a scientist's guide to Life's biggest questions and then we have Max tegmark who is a pioneering physicist cosmologist and computer scientist based at the Massachusetts Institute of Technology he is the author of our mathematical Universe which argues that reality is fundamentally a mathematical structure and finally Michio Kaku is a famed futurist and co-founder of string field theory he has spent his career inspired by the search for a Theory of Everything his latest book is called Quantum Supremacy how the quantum computer Revolution will change everything okay a quick word on format we will open the conversation with two-minute responses to an opening question and then we'll move on to discuss three major themes pertaining to this opening question all right heading in here we go opening question we are going to start with Michio Kaku here we go two minutes on the question Professor Kaku is mathematical Beauty a guide to truth please well mathematical beauty is a guide to truth but not the soul guy because ultimately we have to rely on experiment however when you look at the fundamental theories without exception every single fundamental theory has a description in terms of beautiful gorgeous mathematics so what do we mean by Beauty to a physicist beauty is symmetry so when you scramble objects you get the same thing again after you do the manipulation and so if you take a look at Einstein's theory of gravity reparametrizations in space-time generates general relativity if you take a look at the standard model uh s-u-n special unitary groups and N Dimensions is the Symmetry group of quarks for example now hypothetically if you want to win a Nobel Prize in physics or at least be a contender your theory has to at least explain three things things first your theory would have to incorporate Einstein's theory of gravity which as I said before has a beautiful Cemetery behind it second the standard model your theory would have to explain quarks and neutrinos and electrons and all the zoo of subatomic particles that we see in our atom Smashers that's the second thing that your theory has to has to explain third anomalies and divergences if you simply get a sheet of paper write Einstein's theory try to quantize it what happens it blows up in your face because of the fact that there's something missing a cancellation mechanism to cancel the divergences now so far the only Theory which can do all three is string theory now that doesn't mean it's correct who knows maybe there's a higher Theory someplace but the only theory that can give a reasonable explanation of all three characteristics of a theory of everything is string theory now of course there are competing theories but they all fall down at some point they have anomalies they diverge they don't have electrons they don't have matter as we know it there's always something wrong with one of these theories and so far the only Theory which can pass these is string theory now of course people of course can have their own opinions about this thing some people are critical but when I was a child we used to play a game and the game was put up or shut up that is if you say something try to top it try to say something even better or keep your mouth shut so my attitude is very simple you don't have to believe in a certain Theory at all you can believe in another theory but that other theory has to satisfy these three criteria that I just laid out that to me is the acid test of whether you're embarking upon the true road to understanding the universe if you can't do it then well maybe you should shut up okay thank you so much Michelle Kaku has thrown down um let's move if we can to Sabina hasenfelder can you answer the question please address the question is mathematical Beauty a guide to truth I think I'm going to go with Definitely Maybe So I think we develop our sense of mathematical Beauty through experience in physics we get this experience from the theories that we work with and this shapes our sense of beauty I think it's often a sense that can't be formulated in concrete mathematical requirement requirements it's rather it's rather a gut feeling a sense for what works and what doesn't work and that's valuable exactly because we can't strictly formulate it and I also think this is why some people are drawn to physics instead of mathematics because you can bring in this intuition this gut feeling but this sense of beauty only helps us as long as we stay in that corner of mathematics which we have experience with if we're looking for a completely new theory that might use entirely different mathematics it won't be of any use we have to get there by other means but once we get there we develop a newfound sense of beauty and this has happened several times in the history of physics for example Kepler's elliptical orbits were once thought of as ugly so was the idea that the Universe expands or quantum mechanics but we don't say that today anymore we have developed a new sense of beauty so I think mathematical Beauty can be helpful in cases when the new Theory resembles the previous ones but if that isn't the case it can stand in the way string theory is a cautious example businesses think it's beautiful because it conforms to their sense of beauty that they have developed from the existing theories that doesn't mean it's right though and then there are alternatives like Loop quantum gravity that many physicists think are ugly because it uses very different mathematics but that doesn't mean it's wrong fantastic thank you so much Max tegmark is mathematical Beauty a guide to truth I'm gonna go with yes and I want to take a little historical perspective here of course already in ancient times thinkers like Plato and others felt that there was something truly beautiful about physics about nature and even saw mathematics in music and in the world around us since then I think we've learned two main things one from studying physics and one more recently from studying artificial intelligence from studying physics we've discovered Evermore beautiful patterns and not just rotational symmetry translational symmetry time translation Symmetry and so on which were known for a very long time but also new ones like what michoaco referred to so-called gauge symmetries that involve properties of Elementary particles Etc and eminenter showed us this beautiful relationship between symmetries and things that are more permanent in nature stay conserved so absolutely there there's something there and we kept finding more but artificial intelligence has very recently also shed light on what we even as until what intelligent beings even get drawn to it and and find interesting in the world around them which says I think very deeply related and AI if you have some data set with a lot of numbers and you can explain that data set with much fewer numbers you're like ah this is great that is actually often used even as a measure of intelligence how much you can compress the data and that's only possible if there are patterns in the data that that you've uncovered and uh I think to me something now feels very beautiful even if it isn't in the traditional sense of being symmetric but if you just find patterns and structure there for example there I once pulled out a book in an old library Shelf with about a hundred thousand numbers that measured the wavelength of spectral lines coming out of atoms we can now compute all of those hundred thousand numbers from three numbers in the Schrodinger equation that's also Beauty in this AI sense where you get way more out of the theory that than you put into it right thank you so much and finally Juan malacena can you please let us know whether in your world mathematical beauty is a guide to truth well I think beauty is a bit in the idol either of the beholder so I think that mathematical and physical consistency is a guide to truth and by by mathematical consistency I mean the internal consistency of equations and by physical consistency I mean that it reduces to the known physics in the appropriate regimes so here we are talking about fundamental Theory So Physical consistency includes reducing to semi-classical general relativity and also to the standard model of particle physics I guess more generally we could demand that it reduces to general relativity plus some quantum theorem not necessarily that of the standard model now in the past it as as we discovered deeper theories we found that they are in some sense simpler in the case of the standard model and gravity they are also based on something called the gauge principle which involves a certain let's say so-called symmetry it's not quite a symmetry in the standard sense but um to the extent that symmetry is associated psychologically to Beauty then you could call them beautiful and for some reasons sometimes people say theories which have a larger gauge group are more beautiful but this is a bit subjective we also have Concepts like Simplicity as let's say in Occam's razor so sometimes simpler theories are called Beautiful I mean I think the bottom line is that the theory is beautiful when it works and uh and by works I mean it's mathematical and physically consistent now of course whether theory is true or not is decided on next by experiment so if you agree but if if in order for a theory to agree with experiment it probably has to be as a necessary condition physically or mathematically consistent so I think those two conditions are a guide um and I will also end up here we're talking about beauty of theories but I would also say that sometimes experiments are beautiful so they're beautiful when they manage to do something seemingly impossible for example you could say that the Detectors of gravity waves are beautiful in this sense thank you this is amazing because you have provided a brilliant transition into our first theme question which kind of intensifies the opening one um Juan when you say a theory is beautiful when it works which is to say mathematically and physically what do we do if these two are at odds with one another um our opening description cited Paul Dirac is saying it is more important to have Beauty in one's equations than to have them fit experiment was he right about that Max I'm going to send it over to you first it's more important to have Beauty in one's equations than to have them fit experiment what do you think on this well it's sometimes better to be uh wrong in an interesting way than right in a boring way in in the sense that the former can sometimes point the way forward I think that's why he what Iraq was getting at and I want to I want to add what you Juan said there about Occam's razor because I think when we say that a physics theory needs to work right what we really mean by that is not just that it should be able to explain all the measurements so far like all those spectral lines in the book but that it should also be able to predict new things that we haven't seen yet and that's where the beauty actually of Simplicity really shines you know this is well known in machine learning that if you don't insist on having a simple description you can find the so-called overfitting description which just memorizes all the data and it is useless for predicting but the the more beautiful your theory is in the sense of being being a minimalistic being short having little information in it the more it will generalize to the Future in a sense there's this free lunch theorem as well known in complexity theory that says that if someone gives you just a string of random numbers right there is no algorithm there's no computer program with fewer bits of information that can just output that and so when we find uh an a way a physics theory that can describe a lot of data beautifully in one sense in the sense in the Occam's razor sense doing it with much less information we know that this is just not random data that we've actually discovered some pattern and that's where the power of generalization comes from the power to make new predictions in physics for things we haven't seen yet and when you check you know wow the prediction worked missio does that sound right to you that you get us as simple you get as simple as possible a theory and you maximize the possibility that it might fit in new experimental data yes I think so and it goes back to when I was in high school when I was in high school I was struggling to learn the Schrodinger wave equation which was horrible it was ugly and I said to myself how can God be so malicious to create this short Angel wave equation and then one day I picked up a book and there was the Dirac equation simple elegant gorgeous beautiful all the the difficulties summarized into an equation half an inch long the theory of the electron and I began to cry okay I've never done that before crying over an equation and then I realized there's something hidden there power that beauty is not just for beauty's sake it's power power to compute things power to understand the universe and then when I got into quantum gravity we have to calculate the scattering of gravitons and when you do that the loop diagrams you get diverge they blow up in your face and it seemed hopeless absolutely hopeless to create a quantum theory of gravity because every time you calculate the finding diagrams they blow up on your face and then one day one day I read a paper where they showed that there are actually two sets of finding diagrams one set of family diagram has let's say an electron going around and the other one has a super electron going around and they cancel exactly this to me was a shock because it meant that again beauty is this not for beauty's sake it's just not there to be admired and people say oh wow that's pretty no it has power power to eliminate the divergences in fact to our knowledge the only way known to eliminate the divergences of quantum gravity is through supersymmetry so that super particles cancel against each other such a simple idea such a simple idea that has the power to do something that the greatest Minds could not do many people had given up trying to quantize gravity because every time you quantize gravity it blew up in your face and there was a solution symmetry super symmetry the symmetry of particles canceling against their super partners and of course we don't have any experimental data concerning this yet that's an embarrassment but in my heart of hearts I think one day we'll find it so theory is going to lead experiment that nature is telling us something that all the divergences of quantum gravity are there for a reason pointing to the direction of super symmetry which to our knowledge is the only way to cancel the horrible Infinities in quantum gravity Sabrina hussenfelder how are we doing so far you you and your opening statement talked about the importance of contextualizing our ideas of beauty that different people find different Generations particularly of people find things beautiful at different times um do Simplicity and symmetry are they always beautiful are they beautiful from a limited perspective are attachments to Simplicity and symmetry perhaps leading Us in the wrong way or do you think that this is correct that if we stick with the principles of Simplicity and symmetry we will eventually find that our Theory does in fact play out experimentally well it just didn't work with supersymmetry right so I'm not sure there's even that much of a question uh like people have been looking for Grant unified theories and supersymmetric particles since the 1980s and they haven't found them so clearly it doesn't work but maybe let me uh let me come back to the question you asked about Dirac and his statement about beauty because I think there are kind of he became a victim of his own success so he derived this beautiful equation and he didn't really know why it worked so he tried to come up with an explanation and I think he stumbled on this idea of beauty so he started thinking that his sense of beauty was what led to this success and he later tried to use it again and it didn't work for example with his um what did he call it the large number hypothesis um so so it I found it interesting what who owns said about consistencies or inconsistencies because what Iraq was actually doing with his equation was that he was trying to remove an inconsistency between special relativity um and the then known version of the Schrodinger equation so he he misidentified the origin of his success and to some extent was still suffering from this today so string theory was actually an approach to to try and resolve an inconsistency as a machine correctly said um to my best knowledge it was never actually proved that it did indeed resolve the inconsistency one do you want to come back here and and weigh in um yeah well the regarding the question of course if you take the question out of context he's of course incorrect what the ACT probably meant was that an interest in mathematical structure might lead to apparent contradiction with experiment but usually there's a long chain of reasoning in interpreting experiments so he meant that perhaps it's more likely that there is some error in the chain of Reason in the theory now it's also true that their accent later in his said this later in his life the ark was trained as an engineer and for him it was important that the questions work in the sense that we mentioned before um and he was interested in symmetries and general principles and of course he had a tremendous success with the direct equation and his prediction of the positron he also suggested the existence of monopods which have not yet been seen but it's quite likely that they exist um and Sabina mentioned the fact that the variation of the Newton constant with them that's some the case where it didn't work now an interesting example I think for this is yam Mill's Theory so when young and males propose the theory it was supposed to apply for the description of pions and and it did not work but later it was useful for the development of the standard model so it applied to the weak interactions and to the strong interactions another example is the following in 1939 in a thought Iraq said in a talk about the power of mathematics and physics that the group of analytic Transformations on the plane on the two-dimensional plane was an interesting mathematical subject that might be interesting for physics he didn't know how but actually in the 1980s this was indeed brought to the study of phase transitions in two Dimensions by 11 polarconological and we use it to explain experiments and so on so that's a case where you know some beautiful mathematics then had some implications for um let's find another example of a famous mistake that turned out to be useful was when Einstein felt was mathematically elegant to include the so-called cosmological constant in his equations of gravity and then he later called that his greatest blunder and now of course in hindsight we know he was right there is actually Dark Energy in our universe and a lot more of it than of the kind of atoms that make up us are there to move into the second theme though um May there be some assumptions that can't be demonstrated experimentally or that won't be demonstrated experimentally should we accept the idea that some of the assumptions of the foundation of physics for example the idea just that there is a grand unified theory out there could be akin to religious convictions are these sorts of assumptions Faith dressed up as mathematics um Sabina I will start with you well I guess it depends on what you mean by accept so should we accept them as established by evidence no of course not because they aren't sure we accept them as an inspiration that physicists use to develop new hypothesis uh it's fine with me because I'm very pragmatic person you know for what I'm concerned anything goes if something comes out in the end but there's there's a risk you know that people run down uh dead ends and then send in front of a wall and look at the beautiful wall and we're not getting anywhere so I think one has to be a little bit mindful of um you know what what is Faith and and what is actually um science what about you Michio do you think that these assumptions say that the notion that there's a grand unified theory has the structure of Faith or is it different from faith well personally I think that eventually all things are testable it just means that our instruments have to be souped up to the point where they can reveal the true nature of things for example dark matter we don't know what dark matter is it makes up most of the matter of the universe some people think it is a presence of supersymmetry which is of course a symmetry of the string in particular the fotino when you look at the fortino you find that its properties are what you want that it is massive it has it's not massless and it is invisible and that's exactly what dark matter is if I held dark matter in my hand it would be invisible and yet it would sift right through my fingers we'd never seen anything like that before on a stable on a stable canvas of physics but there it is in outer space now that won't clinch String Theory but I think it would go a long ways towards showing the super symmetry is a legitimate physical symmetry of the universe also there are other ways of testing these theories when we look at the fact that string theory exists in other dimensions some people laugh and say this is science fiction but already scientists are trying to look at deviations of the inverse Square law this goes back to Isaac Newton Newton would say that in your living room gravity diminishes as the universe Square across your living room that has never been duplicated experimentally but on now our instruments are at the point where they can and so we can look with deviations of the inverse Square law which would indicate the presence of higher Dimensions also satellites in outer space we're talking about Lisa laser interferometry space antenna which will give us the best look at creation itself now of course it's very difficult to look at the incident of creation so much radiation existed back then but we hope to get a snapshot of the instant of creation and String Theory actually takes you before the Big Bang String Theory does not stop at the big bang it gets even before the Big Bang and therefore this gives you a testable parameter by which you can rule out certain string theories if they don't fit the characteristics of the universe as it was being created now of course we cannot measure the universe before creation but the universe at the instant of creation itself I think will eventually be measured by satellites and that will give us a third way to test these theories so in summary I think that yes all gray theories can be tested does anybody want to hop in here there are two things that I'm hearing from Michio that I think are you go go for it Max yeah first I I like to say that um to me the def the core principle of science is what is humility in in the sense that I would rather have questions I can't answer that answers I can't question that's what I mean when I say I'm I'm a scientist and that humility includes always being open to the idea that my pet theories are all wrong but as Mitchell said always testing them testing them testing them I wanted to comment also on on what Michio said about how more and more things become testable and make clear that even if there are some things you cannot test at all that doesn't mean that the the theory that that came from itself isn't scientific because when we test in science are theories not things so for example Einstein's theory of gravity is absolutely scientific because it makes a lot of predictions we can test and have tested like Mitch you mentioned but it also predicts what happens inside of black holes which we cannot test and then come back and publish it in the physics journal does that mean relativity is unscientific of course not it doesn't mean we shouldn't trust what generativity predicts what happens inside the black holes well as meet you said if you want to replace if you don't like what happens inside black holes you got to come up with a new Theory that that says something different about what happens for the untestable but that still Express explains everything else that we can test and that's proven to be super hard so many of today's biggest controversies in physics where some people are quick to dismiss them as science fiction are exactly in this category for example inflation are the most popular theory for what put the bang into our big bang we don't currently have the technology to go directly measure some certain aspects of this but this theory has already made a lot of other predictions that have been very successful and that's why we take it seriously but with the humble understanding that it might still be wrong same thing there's been a lot of talk about parallel universes there's a number of you here have worked on that are predicted by inflation some variants there over or predicted of some variants of quantum mechanics again you can't necessarily go observe that directly but if you can predict a lot of other things if you can if you can test a lot of other things predicted by unitary quantum mechanics with no wave function collapse right then you're logically forced to take those things seriously too so to summarize I don't think the fact that some predictions of a theory can't be tested at the moment or ever in any way make the theory itself non-scientific as long as it predicts other things that we can test because that means the theory is still falsifiable um we then have to have the humble stands that it might be wrong and just keep testing it well and I hear you're making a distinction perhaps between unadulterated faith and uh something like a scientific humility here um as an answer to this question um the litmus test is unadulterated faith is if someone says that I believe proposition X to be true and there's no data you could possibly give me that's going to change my mind right whereas the humility that defines science is if you have a if you have something that can be tested you should be able to explain to people with which test and which data you know will will change your mind and always be open to the idea that that you might be wrong it's important to not get too emotionally attached to our theories Juan how are you doing in here yeah so I think in order to propose a theory we need to make some suppositions so as a theorist you don't have to believe them you just need to assume them until you figure out the consequences so you'll never invent a new theory if you don't start with some assumptions so for example you can assume the universal Newtonian law gravitation and then you can calculate how planets will move now you could assume a different theory of gravity so for example you can assume the north from theory of gravity or the Einstein theory of gravity and then figure out how planets move and then in that way you can figure out which of these theories is correct um You probably never heard about the nostrum theory because that's one that is incorrect but it was suddenly one that was proposed at the time um so um now you you only need to believe them while you are doing the calculation or not even believe them but you just need logically deduce from some assumptions now our current theories are mathematically very complex and it is very difficult to do calculations even with the even with the Ethereal standard model for example so this has led to the kind of new breed of theorists uh I think I'm among them uh who have specialized in the structure of fundamental theories and the um some have been successfully tested like the standard model and some have not so for example strength there is one that has not been tested against nature yet um and we are happy to assume various things at various points so we are happy to assume granular Grand unification for one Richard project and not to the next in one paper we might assume string theory in the net next we might only assumes in my classical gravity or only assume inflation and you know inflation doesn't need String Theory so you can only assume inflation nothing else um and in particular you don't need to be consistent in your assumptions in the sense that from one paper you assume one thing and for the next paper you assume another so it's not the type of consistency that is required from a politician or moral leader or whatever so consistency is only required of theories not theorists [Laughter] that's fascinating this sort of like that sort of perspectival approach to it that you work with in a particular theory for a particular experimental setup is this what you're saying yes yes we're experimental set them and you just to deduce the consequences of those assumptions you might not uh know exactly what they are because there is a long chain of calculations and you need to compare various theories and so on um now we all have some beliefs like I think we believe that there is at least one true theory um we also believe or perhaps hope that there are not too many consistent theories so that consistency alone might help us guide us towards the correct theory if there are so many theories then consistency alone will not be able to guide us to the correct Theory by correct I mean the one that is described in nature um and also we hope that the gap between Theory and experiment will become smaller now you also mentioned the belief in Grand unified theories there are various things we could mean with this first I first I indeed believe that gravity should be put together with other forces I think it's not mathematically consistent to have gravity and feel Theory completely separate there matter creates deforms the structure of space-time and structure of space-time makes matter move in a different way so they have to be fit in a consistent mathematical structure and this is certainly an assumption that we well with a strong belief that we have um now sometimes people so it's gravity and quantity mechanics should be unified in this way now sometimes people talk about ground unification in the context of cage theories this is a bit more narrow in this case it means that there is a very simple single big so-called gauge group that somehow breaks into smaller ones we have in the standard model now I think there is a one interesting piece of evidence for this which is the unification of the couplings but this is just one numerical Queen coincidence maybe it's just a coincidence but it's an interesting hint now as Grand unification necessary or always true in our more fundamental theories such as String Theory now it's not it depends on the particular geometry of the internal Dimensions but there's a more abstract sense in which gravity and the other interaction ceremony manifestation of the same thing so in that that sense I think there is some kind of identification do you think that's right Sabina what is what is the status of this of this belief this belief that um gravity and the quantum should be reconcilable there should be one Theory to to hold everything together um what's the status of that conviction is that is that a is that a Justified belief is it an unjustified belief but it's partly justified in the sense that we do have an inconsistency between general relativity and the quantum theories of the type that the standard model uses and this inconsistency has to be removed resolved somehow by something that doesn't necessarily mean that you go and quantize gravity maybe it's something else entirely but we need to find some kind of resolution and yeah we still haven't found it uh you know if we heard you'd have heard of it so you're not quite as um optimistic as Michio is of about string theories being the one that's going to do it uh I guess not I mean it hasn't been going on at Workforce to actually String Theory right um I mean for what it's uh resolution of the problem of quantum gravity is concerned strings theory has had some other applications it was something that Max alluded to earlier you know often we find some piece of mathematics and it doesn't work for one thing but then a couple of decades later it comes in handy for something entirely different so um that's that certainly very interesting but for for what strings Theory also Theory of Everything is concerned it hasn't been going very well you know the the adsc correspondence of course which Juan invented shows this beautiful Duality between on one hand string theory and on the other hand more traditional particle physics even though I suspect Juana you were motivated by doing it very much because if you're interested in string string theory and using particle physics techniques to study during Theory it's as uh Sabina said very much been used in the opposite direction now where people of course use your Duality to study heavy ion collisions and so on so basically using string theory as a tool for solving other problems this to me is one of the there's also very beautiful well I think I think this shows that string theory is not disconnected with the rest of physics in fact in some sense strings have already been discovered so strings were discovered before String Theory wearing was invented so what they were discovering hadron collisions and now usually they are not called evidence for string theory and so on but it was the reason why string theory was invented and um we now think those strings are made out of gluons out of the particles of strong interactions um but what the reality says is that these two types of strength there is a fundamental string theories and the string theories that are made out of gluons are not fundamentally different they're they're similar and in some theories we can in some theories with supersymmetries or supersymmetry is useful for doing calculations sometimes and so it's like a toy model and uh for supersymmetric theories one can show this in in great detail one can do the mathematical computations and show how you know chains of blue ones turn into Strings moving some higher Dimension and so on um so I I think so String Theory had uh had successes I think had success in understanding how uh you could have a perturbation Theory so how you can calculate graviton Corrections at higher orders um and how it could describe certain space times negatively clear space times but it's not a complete Theory yet so there are situations we cannot describe so for example the beginning of the universe is something we cannot describe yet so we don't understand how to describe it so I would I would call String Theory not so much as a theory but as a theory under construction so the they're all let's say string theory of the 80s is just an approximation to some theory that we think it exists but we don't know exactly what it is and one do you think it'll it'll get there yeah I very much hope so but I think people are making progress and we're understanding more aspects now how much more progress will I think the most important problem to understand in strength there is the beginning of the Big Bang this is the most interesting reason uh most interesting rationale for studying quantum gravity and this is something we don't yet know how to describe and so max hop in and then I'd like to hear from Michio after you Max go for it I did that one more quick uh reaction about the question of whether there is a unified theory yeah I think we humility tells us two things here one of course we shouldn't be too confident though with three Theory the unified theory is going to be this Theory String Theory or Luke quantum gravity or any other particular Theory but I think there's a very good argument that there is a theory that it's mathematical and unifies everything in that you know we are confused right now as physicists about how to put everything together right but our universe is not confused whatsoever it's it keeps doing its thing every day it obviously works in in some particular way and as long as that way is also described by by mathematics well that means that there is a mathematical Theory out there for us to discover oh wait hang on a second though does it mean that there's a mathematical Theory out there for us to discuss I know I'm like playing right into your into your that there's a mathematical Theory out there for us to discover or that we have invented a particularly useful form of mathematics well we mustn't conflate the language of mathematics which is the the words and symbols we use to describe things with with the structure that is being studied so if a universe is in fact some mathematical structure you know Einstein thought or it was uh three plus one dimensional pseudo reminding and manifold with some tensor Fields quantum mechanics says it's a Hilbert space Etc if it is something that can be described with math and that's how it operates right then that's very good news for us physicists because it suggests that if we work hard enough maybe we can actually discover equations which which fully captured and that is a unified theory in the sense that you know maybe one day someone can print a t-shirt or something which which from which you can actually derive both quantum mechanics and gravity and so on I'm just saying we shouldn't be we should be humble and not assume that we know which Theory it's going to be but there's no the inconsistences we have are all in our heads uh that's what I'm saying they're not in our universe our universe doesn't show any sign of being inconsistent Michio you I I do I detect certainly humility from you but you do seem to know to think to think that you have a good sense of which Theory it's going to be um do you think of string theory as a theory under construction or do you think it's it's pretty close I think it's pretty close um however the progress and string theory has been explosive because of the work of of one and adsc ft we're talking about taking String Theory into a new domain that we never couldn't penetrate before a non-perturbative domain a domain where we think on the other side of the fence there's ordinary Quantum field Theory which is amazing who would have thought that string theory would have a double identity one identity is a theory of gravity and the other counterpart as a theory of ordinary matter this is incredible so string theory has had an explosive absolutely explosive interest in the last few years because of that work however there are some flies in the ointment and I think this hasn't been mentioned yet but I think one of the problems of string theory and even though I promote the theory is the landscape problem the theory gives you're not just something that very closely approximates our universe but it gives you perhaps an Infinity of other universes a Multiverse of universes now of course Marvel Comics and Hollywood has discovered uh the Multiverse uh winner of the Oscars and so on and so forth but we physicists take this Multiverse idea very seriously and the way we deal with this is usually with computers for example when we calculate the mass of quarks interacting with other quarks to create subatomic particles the human mind is not strong enough or smart enough to do the calculation we do it by computers with something called lattice gauge Theory and so we've given up trying to have the human mind master the Dynamics of the the Quark we rely on computers so I think and this is a long shot that quantum computers may eventually give us some insight into the true vacuum of string theory and by that I mean use the quantum to tease apart the mysteries of the quantum digital computers are not powerful enough to probe the different vacuum of string theory so I think that maybe one day a quantum computer will be powerful enough to probe the quantum universes that go into a a string theory and just remember that even ordinary quantum mechanics has this problem quantum mechanics that's where the whole problem of the Multiverse originated from so we think that something that bedeviled ordinary quantum mechanics well also bedel string theory and the ultimate solution may be to use quantum to defeat the quantum that use quantum computers to gain insight into the true vacua of string theory that's fascinating um so to take that to transition to our our final theme and question um we keep it seems at its limits at the limits of uh theoretical physics in particular um coming up against assumptions on the one hand and conclusions on the other hand that may in fact remain untestable things like the very existence of a grand unified theory whether there might be one out there or not the notion of one kind of Multiverse or another kind of Multiverse a Quantum Multiverse string theoretical Multiverse the inflationary Multiverse are these the same multiverses what happens inside black holes um what happens what what exactly does inflation look like there may be some persistent untestabilities here does this untestability to your mind undermine the pro the the project of physics or does it strengthen it and Juan we will start here with you well I I think when we talk about physics in general I mean most of physics is based on tested theories and contact with experiment and so on I mean here we're talking about the search for the next layer so the unknown fundamental laws of physics and I think for this the most important thing we could do is to continue the experimental exploration so that the construction of more powerful accelerators rich in higher energy is better telescope the telescopes that see further into the universe including gravity wave detectors and so on and they're also interested in small scale experiments searching for new particles from axions to dark matter and so on foreign now so what we are talking about here is just a very an aspect of fundamental Theory and in particular the aspect that has to do with quantum gravity which is very hard to test experimentally with our current and in future near future experiments however it's a clear inconsistency in our present understanding so we could hope that by only the consistency Criterion we could make some progress um it's something that had worked in the past with uh let's say Maxwell's equation so the development of general relativity but that's uh that's what we are talking about here going to very high energy is much higher than the ones we could reach in the near future perhaps perhaps if we understood the theory well enough then we would be able to make a prediction that we could test perhaps through some cosmological observation but as we said our theories are not understood well enough to to make these predictions um so I I think in general we are we are making uh progress towards the development of this Theory based on just consistency um and there are various ideas people bring in um I mean sometimes uh the ideas sometimes come out of come are not directly related to string theory so for example there was a recent development about holography using the so-called yeah Guitar model so it's a model that was inspired by condensed matter physicists and we were talking before about symmetries and one interesting aspect about this model is that it's based on disorder random interaction so the complete lack of symmetry so it's completely the opposite philosophy but the the model itself develops a kind of over there or symmetry out of the interactions so it's it's a new idea that people are exploring and we're exploring we're somehow connected with other ideas in string theory but it's not directly related but this is an example of how looking how we're looking an example of the methods we are using to looking for the theories finding general principles and taking ideas from other areas of physics also what do you think Sabina are we getting are we getting closer here are we are improved Technologies going to help uh root out some of the you know the limits that we have come across I'm going to improve testability things like that uh yes but probably not in the way that uh huan envisions it um so but first I want to say something else so Mishu he said we physicists take the Multiverse very seriously I would like to object I don't take it seriously and I'm pretty sure if you took a representative sample of our physicists and you asked them about it you'd find that most of them don't take it seriously I wanted to say this because uh because the the sample of physicists you see in events like this or that you hear talking uh on the media or something does not give you a good impression of what most businesses actually work on um so um when it comes to new technology I think where we're going to see the most progress come from is probably Quantum technology because there's such a lot going on there like with Quantum Computing Quantum Optics Quantum information Quantum Metro biology Quantum sensing there's so much going on I think sooner or later they're just stumble over something that they don't understand and then then they'll come and ask the theorists uh how do you explain that uh and and then I think from there on uh we will develop a new Theory it it goes together with my belief that it's a mistake to try to put the blame on gravity when it comes to the unification of uh Einstein's theory and quantum theory people have tried to doctor around with a gravity try to quantize it I think our problem is that we don't really understand the quantum part of the question so this is why I think this new technology is is going to help us make progress happen again the foundations of physics fantastic um well it sounds like even if you uh disagree perhaps on the status of the Multiverse um you're both uh hopeful that Quantum Computing is going to help get us past some of these some of these impasses well thank you all so much this has been a really wonderful conversation um please join me in thanking our speakers for 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Keywords: learning, education, debate, lecture, IAItv, institute of art and ideas, IAI, philosophy, michio kaku, michio kaku string theory, sabine hossenfelder, sabine hossenfelder particle physics, max tegmark mathematical universe, max tegmark multiverse, juan maldacena theory of everything, maldacena, hossenfelder, kaku, tegmark, physics, physics debate, string theory, string theory debate, theory of everything, theory of everything physics, theory of everything debate, why is string theory wrong

Id: Zzj7GpKHZjE

Length: 53min 14sec (3194 seconds)

Published: Thu Sep 14 2023