What is a Theory of Everything: Livestream

welcome everyone so this is a very special and rather unusual event space time has always been about digging towards the deepest layers of reality for nearly 100 years it's felt like we've been hovering just above the bottom layer and so my friend and colleague brian keating and i decided that the fun thing to do would be to bring together today's frontline researchers uh in physics experimental and theoretical for a real conversation so brian is a distinguished professor at the university of california san diego director of the simon's observatory and host of the into impossible podcast where you will find the craziest line of the most incredible guest so please check that out he's also the author of the book losing the nobel prize so if you want to know more about brian and his amazing work trying to understand the origins of the universe that's where to look so brian thanks for joining us yeah thanks matt and thanks to the whole pbs space time studios family out there in cyberspace uh this has been a dream for me to talk not only with uh with matt and his team but also with my good buddies uh today we have stefan alexander who i've known for i'm embarrassed to say what fraction of the universe we've known each other for uh max tag mark i've known him uh almost as long and james beechum i'm a huge fan of fellow experimentalists looking to solve some of the world's greatest problems in the world of physics and today is uh quite fitting it's two occasions are marked today well one specifically uh today is karl popper's uh would have been karl popper's 118th birthday and uh some say he doesn't look a day over 70. but but carl of course is cast a large shadow over all of what we try to do as scientists and the question is is it still relevant this conjecture to pursue these fanciful ideas about theories of everything and whether they exist so part of the motivation is to address that very question and the other part is that to rekindle the series of great debates that took place in the 1920s actually in april 1920 the first so-called great debate the kurdish shapley debate which is concern which concern what is the nature of the universe on its largest scales and so today we now know that the universe's largest scale properties are determined in part by how it functions at the micro level namely the laws of physics and so these uh these physicists who are so distinguished joining us today are gonna hopefully shed some light into the nature and the inner workings of the universe and be a really good uh starting point perhaps to kick off many more great discussions uh this year in the centennial year of the great debates awesome thank you brian um so i'm gonna bring up our guests because they have the real content here uh quick introductions so we have james beacham who's a particle physicist with the atlas experiment at the large hadron collider at cern and he's also at duke university and james is really the experimentalist in the room and so he's going to be the one who keeps us in check we have stefan alexander a cosmologist and theoretical physicist with really a hugely broad range of interests including string theory and loop quantum gravity in principle we could do this entire conversation just with stefan he's worked in everything he's also a brilliant saxophonist and author of the book the jazz of physics and of course we have max tegmark a theoretical physicist with an extremely broad background also so he's worked in fields from cosmology to the foundations of quantum mechanics and now actually working deep in the field of deep learning and he's the author of multiple books including our mathematical universe and the recent book life 3.0 so uh hi everyone thanks for joining us hello it's a pleasure to be here thanks for having me good to see you all in your far-flung isolations across the globe um so we have a lot that we need to talk about today you know uh we're not going to necessarily solve the theory of everything or even fully solve what the problem is in our search for a theory of everything um but i feel like we might be able to make a little scratch today uh before we actually get deep into that i thought it might be a great idea for us to set the stage uh really talk about what we mean by a theory of everything and the related terms um and i felt that the most unbiased person to do that is probably you james as an experimentalist i'm happy to to do so um and in fact just let me just say that i think you know ryan and matt for putting this fantastic discussion together because it couldn't be more timely and the reason you know if you ask the question what is the theory of everything why are we here to even talk about this um it's it's a really good question because down deep inside the answer to that question is related to the fact that physicists for all of us you know we seem sometimes kind of stuffy and nerdy and very kind of analytical deep down inside we're very very very very frustrated for the following reason um we have two completely fantastic wonderful theories uh models of the way that the universe works in in very fundamental ways so as you know physics is the study of uh the fundamental laws of the universe the way everything works at its most elementary possible scale and we have this one theory that is called quantum field theory based upon quantum mechanics and special relativity that so accurately describes everything that goes on at the smallest possible scales the particle the level of individual uncuttable particles it's so fantastically good that it just like it's wonderful it makes sure it makes your kind of brain explode how good it is at modeling and predicting things that go on at the smallest possible scales and it's so it's it's basically passed all of our tests this particular thing that we call the standard model of particle physics it's past all of our experimental tests so far and it's the best description that we have of reality at its smallest possible scales again in terms of particles simultaneously we have a completely wonderful theory of something called uh this is called general relativity which is the fantastic description of the way things interact at the largest possible scales the scales of galaxies and super clusters of galaxies and all and the largest things in the universe and that's a fantastic theory of course developed by einstein and you know the mathematical properties developed by some other people at the same time you know over 100 years ago and that's by itself a wonderful fantastic again it's just like chef's kiss wonderful in how good it is at making predictions for example as you know one of the predictions of this theory from a hundred years ago was this notion of gravitational waves and these were only uh verified experimentally just a few years ago so it keeps winning over and over again in terms of these how good it is as a theory so you take these two things this realm of the largest possible stuff in the gen governed by general relativity and you take the realm of the smallest possible stuff the quarks and gluons and electrons and things that make up you and everything around you and you think ah there must be some way that these talk to each other there must be some way that they fit together to make a sort of theory of everything and when you do that naively remember these are two fantastically wonderful pillars that by themselves are just phenomenally good when you try to marry them together naively everything breaks you get crazy answers that indicate that something has gone horribly wrong you know things like infinite energies or probabilities greater than one these kinds of things indicate that there's something wrong with your theories so that leads us to a state that the field has more or less been in for you know i guess 80 years or something where we have these two pillars which are wonderful and we and you know physicists are again are humans and so we start thinking to ourselves there must be some way that they fit together to give a broader description and a more general a more you know a more fundamental description of everything by putting these two things together and so far we have not found uh the answer to that and so i mean you know that's sort of just broad strokes about what we talk about what we mean when we talk about a theory of everything i can go into you know we can go into some more details about what that means you know the nation the notion of the forces of nature uh kind of unifying together and then you know the the three forces of the standard model going together and unifying with gravity um but that's more or less what's uh you know that's that's more or less to set the stage as to what it is when we talk about a theory of everything fantastic james uh that i think covers it okay so we're done here well not quite so you know we have a lot to get into but what i would really love is for perhaps the three of you to to talk about what you think is the state of the field just in a few minutes like your you know your first impulse when we talk about you know where are we in this great search um and and possibly you know your your instinct for a future direction um i should also add here uh that we we're expecting lisa randall to be joining us uh today but she has professorial duties um she has some teaching duties that uh have got in the way uh and this is really the the most uh truest insight that any of you will get into our lives uh our teaching tends to take us away uh at a moment's notice but she will be joining us next week and we'll have more details of that soon okay um so maybe stefan would you like to take it from here yeah thanks matt um it's a real um honor and pleasure to be joining i'm actually a big fan of maths actually you know you happen to think and um and get to see that you and brian are doing this um i like to say brian's will you know they're going to be the next carl sagan you know of our days i've got the skills going on there um so yeah i mean where i can come in is that i work in you know at the interface of particle physics theory and cosmology theory um so going back to what james wonderful presentation and overview of kind of particle physics b in the realm where we are probing the smallest distance scale in nature at the smallest distance scale and cosmology is the science where we're looking at things also at the largest difference and the oldest times the um time scales um quantum gravity is a realm where we're trying to answer both of those questions you know um mysteries um observational mysteries actually observational anomalies in the realm where particle physics overlap with cosmology so that's some of us refer to ourselves as particle cosmologists and i being a theorist i obviously has i have to engage with quantum gravity and my take on this is that i've always come come to that with um from the perspective of um i would say inspired by my my big inspiration is richard feynman which is you have your pro your puzzles in physics and then you you you go to whatever tool kit you have available and you you're kind of agnostic about that toolkit so i'm not married to any approach to quantum gravity or any approach i mean um when it comes to theories uh have yet been tested experimentally so as a result you know i've worked on both uh published both in loop quantum gravity applied to problems in cosmology and particle physics as well as string theory applied to cosmology so let me just kind of lay out kind of you know my perspective on both approaches from a more general tape and it actually starts back with albert einstein i think the big contribution einstein made was um in terms of modern physics and of course this was applied to general relativity and special relativity is a principle of invariance the idea that there are underlying symmetries in this case symmetries that leave the speed of light um the same value for all different observers in that case for special relativity or symmetries under any change of coordinate systems the principle of general covariance which is not nothing more than an invariant principle um and this principle um kind of lived with us under the name the guise of symmetry um so that has really dictated a lot of of um you know fundamental physics leading to um string theory itself so string theory really is driven by this the idea that as we go to the shortest shortest distance scale we are to expect to see more and more symmetries unveiling itself and so that's one that's kind of one philosophy or take hypothesis that has driven research in string theory or things you may hear about super symmetry for example um which is a kind of part of string theory as well and it's but there's another thing in string theory that i think we should um i think that's interesting which is that in string theory you don't start off with a theory of gravity right string theory is an approach to try to combine ideas of gravity with with quantum mechanics together as um as james pointed out and the idea in string theory in a nutshell is that you start with a instead of a point particle you start with a string and the string has certain symmetries associated how it moves about and then you quantize that theory and when you do that and you try to keep quantum mechanics consistent the assumptions you made about quantum mechanics pops out of the equations out of that equation gravity quote unquote albeit and 10 dimensions and supersymmetric pops out general relativity in that guys pops out now what's the wrong theory of gravity i must add right but in that sense string theory you know starts with quantum mechanics and an assumption about certain symmetries and gravity emerges and i'm going to use that word um as us you know from max to maybe true on a little bit but loop quantum gravity is another approach to quantum gravity that tries to again similarly combine quantum mechanics with relativity but it does it in a different way like what luke quantum gravity does it says let's take general relativity as it is let's take einstein's theory of general relativity you know good ol as that works it works it explains gravitate it predicts gravitational waves and black holes all these zany things that have been observed experimentally it takes general relativity and it says let's quantize that let's apply the laws of quantum mechanics to general relativity and there is a caveat i'm going to say if you do this you're going to run into a problem but anyway they can succeed in kind of doing this and then you get this thing we call loop quantum gravity um and that's both theories they're both incomplete they're both limited they're both they both have their own strengths and weaknesses string theory is a lot more developed there are many more people that have worked on string theory you can do a lot of cool model building with with string theory i've certainly done that um lukewarm gravity there's some interesting questions connected to particle physics that i've worked on but i'm gonna now say the following thing i am left puzzled because it seems that when you do both string theory and loop quantum gravity and you try to apply quantization there are some unquestioned things that we assume about quantum mechanics that i think that are foundational that i think physicists no matter how bright we think we are and how it's too hard and elegant and all that stuff i think went unquestioned and some of the problems that we see lurking in both string theory why they're all these ten dimensions and why we only live in four uh what happened to supersymmetry all these things marginalized stable all these fancy things and new quantum gravity time disappears um that uh very unsettling to me personally and as a result i've taken a step back and just tried doing other things while i wait for max tag mark to solve the problem so i'm just gonna that's a beautiful segway and improv master stefan alexander has always been and now we turn to uh one of my favorite most mercurial personalities in the world uh who when i met him as a second or third year grad student helped take me under his wing even though he's a theorist and uh and i was an experimentalist still am and i said that must be why you're called max million and he said no i'm just max for now someday i'll be a millionaire and max with all your great contributions to humanity uh in your writings in your personal humanity you're you're an mit mensch as we say uh like you first introduce yourself uh for those uh 10 people who may be watching out of the tens of thousands who may not know you and then can you give us your take on where things stand what guides you and why why you think this is such a critical juncture for physicists such as us to be discussing such esoteric topics yeah so uh i'm feeling a lot of pressure piled on me already here especially by you stephanie counting on me answering all the questions uh but i'm i'm i'm honored to be with you guys here my favorite thing to do in a pandemic in a very polarized world is to talk with people like you who remind me about the really important stuff you know here we are almost 80 billion of us on this little spinning ball in space who actually amazingly after 13.8 billion years of cosmic history managed to start figuring a bunch of stuff out and i think this is a great reminder for us all to not lose sight of the really big important picture so uh let me give you my take on on theories of everything with a brief history of what i think we've accomplished and where i think we've failed and let me also um take those opportunity to uh attack physicist arrogance a little bit so when we say theories of everything we have often tend to be very circumscribed and said well physics is just supposed to do this and that's what we mean by everything and all the other things that maybe by biologists and others do that doesn't count this everything which i find a little bit arrogant uh but so and what happened was of course in already in ancient greek times in antiquity people were able to figure out some aspects of how stuff worked they realized that when you throw something or a catapult hurls a rock you can figure out the motions archimedes did a lot of stuff on that but other things they just sort of gave up on like why doesn't the moon fall down well you know presumably that's just off limits for physics heavenly objects obey different rules they're perfect heaven stuff just shut up don't ask those questions almost a sort of censorship attitude you know shut up you're asking too much uh gradually physicists have challenged this and started asking those questions anyway isaac newton came along and said hey wait a minute it's a perfectly legit question to ask why the moon doesn't fall down what if in fact the laws of gravity that work on earth also apply up in the sky and boom they did work but even at that time it was still incredibly limited what we meant by the scope of physics and everything that they were after it was basic if you took newton and he and you had him throw a hazelnut then a grape right and he could predict very accurately the shape in which they would fly a parabola y equals x squared and how long it would take for him to land but he had no clue why the grape was green and the hazelnut was brown or why the grape was soft and squishy and the hazelnut was hard right that was beyond physics then came maxwell's equations and gave us all sorts of math for colors and light and then came quantum mechanics that we just heard about here from james and stefan that explained actually why the hazelnut is hard and the grape is soft and we've now gone from after the standard model of particle physics and so much else from the situation where physics could apply be applied to almost none of the aspects of the world around us except motion to one where it can actually apply to most of the aspects of the world around us and it's a perfect time in our conversation to ask well when we talk about theories of everything what are we leaving out this time from everything and i actually think we should be even more ambitious than just talking about quantum gravity and i didn't mean to use the word just there to in any way imply the quantum gravity is easy but that's not all i think we should aspire to do i was very inspired like you stephon by by richard feynman also very much by his advisor john archibald wheeler who who once told me that he went through three phases in life first it's all particles so that's not your quantum mechanics then it's all fields and not to general relativity and this third phase it's all information and i would argue that the important aspects of the world around us that we understand the most poorly now are actually related to information more specifically they are intelligence and consciousness which i happen to think are also things that we should look at as scientists and confess that we have failed to uh to really understand well i i'm i happen some people think well we're screwed just like some people thought you could never understand why the moon doesn't fall down and they think maybe we'll never understand intelligence or consciousness because somehow it involves a soul or some life essence that's just sort of beyond physics i have um i'm more optimistic my guess is that the information that is all just information and that both intelligence and consciousness are simply in certain kinds of information processing that we as physicists have so far failed to find the equations that describe we know that some information can be processed very intelligently without there seemingly being any consciousness there because most of the information processing in our brain we're not aware of how we're not conscious of and maybe you can also have some conscious experiences that are without there being very much intelligence there i promise to not say anything about politics so i won't and but so to summarize i i think when we to me when we talk about theories of everything we should aspire to also understand more about what intelligence and consciousness is and and not just because it's important and interesting but because actually i would argue that many of the biggest failures we have in the finding a theory of everything in the traditional sense of quantum gravity have to do with us trying to sweep under the carpet the question of what is an observer really no here we have quantum mechanics and general relativity they have basically exact opposite notions of an observer in general relativity right an observer is this infinitesimally light infinitesimally small particle that has no effect on anything else and in quantum mechanics the observer actually affects that which is observed so if you're not going to define what an observer is or talk about that or try to make a physical model of it you know no wonder we're stuck unifying these these theories have officially given us permission to pursue any question at all as physicists future episodes of space time are going to get very weird so you know so james we may be able to ask any question as physicist but that doesn't mean we can answer any question um uh i feel like you might have a a more measured uh approach to uh thinking about the state of the field um uh constrained as you are as an experimentalist uh what are your thoughts well first i wanted to just kind of jump upon one thing that uh max said there which you know and also to answer your question because when i when i you know as any especially experimentalist i'm i sort of two people at the same time i have to be the uh extremely excitable curious you know kid who likes to think about these things from a very basic philosophical perspective you know it's like what's outside the universe you know how small can i cut anything you know these kind of are there more than one universe these kinds of things but i also the same time i have to at the end of the day say is this something that i can possibly ever test and i don't necessarily mean within my lifetime because i don't like to think about just you know science as being valid only when discoveries are made within my lifetime i think about in in general is there some idea you know if someone comes up with an idea and it's not possible for me to even formulate you know a a coherent description of how i would ever possibly test this idea then i am rightfully skeptical of this idea you know if you know what i mean and so you know one of the things that i always think about when you know for example max set the stage really nicely for discussions like this because i completely agree from one perspective that the notion of consciousness and intelligence are very interesting things and in fact they have to be addressed scientifically but i also think that those two concepts honestly to me they don't have i've never seen a complete you know uh coherent consistent description uh definition of what those are that i could ever really actually test and like in a in a scientific way in a physics experiment in a way and so otherwise i mean what i see is something like you know and i think the concept of emergence is fascinating and i think it definitely needs to be looked into more closely but the for me if i want to just be totally materialistic and everything i'd say look consciousness is really just some complex pattern of neuronal impulses which is based upon electromagnetism in my brain and so i in principle i could be able to model this right and if i have sufficiently advanced computers i could be able to model this at some point and then i you know at some point i should be able to you know create uh some kind of comp program that could replicate this etc etc so this is the you know this is the way that i have to think about these kinds of ideas and so when i come to ideas that are theories of everything um i also have to be simultaneously excited and uh you know looking for the next you know the the next uh big idea the next crazy idea the you know the wild idea that might unify quantum mechanics and gravity or the next wild eye that that might actually take a step back and supplant those two pillars with a more coherent framework which is what a lot of the things that max and lisa and stefan have worked on in the past but at the end of the day i you know i i'm not from missouri but i'm the missouri man show me right show me i want to know you know what the what the you know i want to be able to test this thing in a way and so to my mind the the from as an experimentalist especially working at cern right is that we are currently at a really interesting juncture in experimental physics especially experimental particle physics is that we have this fantastic machine the largest experiment ever ever built a 27 kilometer circular tunnel on the border of france and switzerland 100 meters underground the large hadron collider and we accelerate protons to 13 trillion electron volts and we smash them together you know 40 million times a second recreate the conditions of the universe after the big bang etc and we have and this is this huge jump into the unknown and you know this gigantic energy reach you know as you know from uh e equals m c squared if nature has a particle with the mass m that's all the way up here and we as a species have only ever built a collider to with it goes up to e here we'll never be able to produce it and measure its properties so the large hadron colliders with this huge jump into the unknown with all of these things that stefan was talking about sort of behind the scenes things we were looking for you know things like uh super symmetry particles um you know speaking of uh lisa you know randall some sunderm gravitons large extra dimensions any of these would be fantastic answers to some of the biggest questions that we've been facing in physics for a very long time and now flash forward to 2020 and we have found precisely one new particle and that's really really interesting because it's a very very wild and fascinating and wonderful particle of the higgs boson which is completely unlike any other thing we've ever discovered in physics ever so but it's also weird because it's the only thing we've found so far again we're going to probably take we're going to take something like 50 to you know 50 times the data that we have right now with the with the with the large hadron collider in the future but as it stands now it's strange that we have this very lonely higgs boson sitting right here so that makes us start to think very critically about sort of the the the sort of uh um the the you know these the kind of motivations for the experiments and it also leads us to this very very interesting juncture because with the higgs boson discovery we kind of were complete that's like more or less we're now out we are out of concrete you know sort of no lose predictions as to what to find in particle physics experiments and that's bizarre in a way it's a very weird place to be and you know intellectually because the entire history of the 20th century for particle physics was you know there was some kind of weird observation somebody makes a theoretical prediction and it's like that can't possibly be true pow it was true and then somebody else made an amazing thing and this this kept happening over and over and over and the last thing to be predicted definitively was a higgs boson and now it's there but we also have all these gigantic open questions including how do quantum mechanics and gravity work together but we don't have any big kind of like magic bullet directions as to how we should answer this so that to me is the kind of the crux of why this is such a such a you know a unique weird place to be but also exciting because it gives us a chance to you know get back to our roots as kind of just experimentalists and let's just explore let's explore because exploration has always paid off in the past and so this is why people talk about you know next generation of colliders and the next the next generation of colliders going through the high as high energies as we possibly can the you know we can talk about this if you want but of course the the ultimate possible energy you know if you just give me a couple of seconds to finish the the way to you know to my mind as an experimentalist the way to really answer this question i mean i'm totally okay i completely want all predictions from string theory you know so i want string theorists and you know to come up with some kind of oblique way we might be able to see like a hot spot or you know uh some poles in the cmb or i want them to say you know we can actually see this you know string theory evidence of string theory showing up an xyz experiment to lower energies i want these things to happen but at the same time we know that there's one energy that we have to achieve that would basically tell us lots and lots about the way quantum mechanics and gravity work together and this is the plunk energy and as all of you guys know if you take the basic you know if you take the basic uh constants of nature uh you know planck's constant gravitational constant speed of light things like this these numbers that just sort of they're they're there these these uh constants have these values and there's no particular reason for why these values are the way they are but if you arrange them in certain ways they're very fundamental and so if you arrange them in certain ways to get dimensions and of energy and length and time they give you these things called plunk scales and that suggests that that's the place where quantum mechanics and gravity they have to have something to do with each other there has to be some connection there and maybe it happens much much before this energy but that's the place where it has to happen and so this is the so-called planck energy the problem with that of course is that with current uh with current technology with current collider you know experimental technology it's not clear that our civilization will ever be able to build a large enough collider to reach the planck energy and even if you did you might just create a gigantic black hole so it's not entirely clear how we get there and how we would do that within a reasonable amount of time but that's the part that sort of to me is the kind of if you want to get down to it experimentally it's like if we were able to reach the planck scale in a collider that would tell us a lot and that would be a fantastic way to you know really dive into what are the experimental you know evidence that we'd have for any kind of theory of everything yeah we didn't set up the uh the super chat but uh had we done so we could take uh take donations uh just kidding we're not gonna take donations for that giant collider uh but that does bring us to this question as i mentioned earlier at the beginning today would have been karl popper's 118th birthday uh he looks pretty good for his age and i want to know you know kind of are we being kind of overwhelmed by the influence of popper in that we seek this notion of falsifiability as the apiosis of um of what a theory should be testable and how it should be uh proven or disproven if you will uh when we lack sort of the comprehensive ability in physics to really prove things and the question is is that the best we can do can we only live up to poppers demarcation hypothesis and falsifiability in terms of validating in an era when we might not ever be able to build that that you know solar system-sized accelerator or even an accelerator bigger than the you know than the current future circular collider so maybe we'll start with james uh go back to you are aren't we not a approaching the limits of experimental particle physics and b are we missing things that could be hiding in plain sight i mean there's a huge number of questions that remain such as you know why are there 16 or so 17 fundamental particles where does that number come from why are there three generations what's the cosmological constant telling us should those not be used as the as the occam's razor you know to to discriminate uh theories uh from you know pure wild speculation right and i saw that max had his hand up so i think he really wanted to say something what i was going to say max do you want to say i'm happy to answer the question why don't you go first max and then and then just a relatively quick uh comment to the interesting stuff you said there james about consciousness and show me show me i'm a big popper fan so happy birthday carl first of all and and second i think well the reason that artificial intelligence has gone from science fiction to being actual science with real conferences and real money and real companies and so on is exactly because this field has succeeded in showing you stuff fine men who stefan brought up right used to say you only understand things once you can build them so if someone thinks they understand how to make a machine that's intelligent enough to kick your butt in chess or go you should ask them to build it and now people have done that so that that's progress and i also just wanted to add that i think even though it's it's i think we need to think about that even for addressing some of the quantum gravity questions because uh you you stated and i completely agree with you james it is depressing how hard it is to even envision a collider that could detect detect an individual graviton or give the kind of experimental hints you might want for quantum gravity but i think in the meantime we can actually make a lot of progress you doing theoretical work uh for example if you have a theory of quantum gravity right then not only should you be able to have a thing an object in two places at once like in superposition like in ordinary quantum mechanics but you should have be able to have the shape of space being in two different ways at once what does that even mean the superposition of two distances or or two different time intervals and uh and i think to answer this if you want to be really preparing and be like show me what you need to do is say well okay here is stefan's theory here's james's theory here's so-and-so's theory let's work out what observers will actually observe if it were stefan's way if it were james's way etc and to do that you have to say okay here's a bunch of particles moving around processing information how do they experience this does it feel this way or that way you're facing this question of mental processes right and i i think honestly in physics this has been just as hard often as finding the math right like look at einstein for instance his real genius wasn't figuring out the math of special relativity which is relatively simple right and minkowski had written down a lot of it in lorentz before him but rather it was exactly this stuff of figuring out how an observer would actually experience things realizing that hey wait a minute what this complicated equation here means is that it's gonna that the observe that the moving this observer here is gonna feel that time has slowed down people are like whoa that's so weird right and i think uh to predict what it is actually going to what what observers will observe and experience in various quantum gravity theory is going to be even harder and i don't think we can do it if we just try to sweep the whole question of what an observer is under the carpet just to jump off of that and also go back to your question brian um i you know i didn't want to just to be clear i didn't want to at all you know try to denigrate any kind of theoretical work it absolutely has to be done i hope that i made it clear that i want all of these theories i want all the new ideas i want all the craziest ideas and i think that that's really really important because that's why for example i you know i do take seriously when somebody like you know uh just for example eric ferlindy comes up with an idea that maybe dark matter and gravity are in fact emergent properties of sort of the quantum qubit structure informational structure of space-time right i mean even as an experimentalist you know with six years of grads grad school and quantified i hear that i'm like what does that even mean right and so i want to go deep into it and understand what that means because it in fact could lead to a much more fundamental understanding of what we understand or what we what we know about the universe from a very different perspective which is i think a little bit what you're alluding to max right it's like when when when you know when you try to recenter what it means to be an observer and try to reframe that and recognize that there's a totally different description of that that's not just a slight tweak it's not an improvement it's a complete shift you know to forget about popper let's talk about cune right it's an actual paradigm shift with respect to the way you you you view the entirety of this field those are the things that i think are really fascinating to think about but at the same time i completely agree brian that experimentally you know and to on to answer your question experimentally what we have to do at all of these things and i i am very much you know i i can't underscore enough how what a what a fantastic time it is to be a physicist right now an experimentalist because we have all these amazing open questions and there's no guarantees anymore and so we really you know we're required to think in big ways both theoretically and also experimentally and so and experimentally thinking big does not just mean the sort of obvious things like a future circular collider at cern of course you have to have bigger colliders there's no question there because otherwise you'll never be able to know what's there at the same time you absolutely can you need to do these other experiments too like really nailing down the cosmological constant really doing precision measurements in all different types of lower energy machines right because the standard model is this wonderful sort of like brick that has all these wonderful you know predictions that have come out of it and it makes all these really precise predictions and basically all of them have have been you know have been verified except there's a lot that are that we never even bothered to yet because you know it's like we just assume they're right because it's been right about everything else but that's really where the new portal to some brand new discovery could be we have to really hammer at the edges of this thing too so i think all these things can happen simultaneously i don't think we should limit ourselves as as a species to only doing it's like well i'm going to build a 100 kilometer uh you know 100 kilometer 100 tv collider and that's the only thing i do absolutely not you got to do everything you got to do everything why stop there so i want to turn this to my friend stefan uh stefan you know as i said it's always held up that you know this this falsifiability is sort of as sacrosanct as girdle's incompleteness theorem is in mathematics and i've had this discussion with with you with janna levin uh even with eric weinstein and others you know do are we holding up popper to this unrealistic you know standard golden standard i know you know max has a has a little doll like i have of carl sagan here he has a little thumb doll of carl popper that he puts on and still plays a heck of a violin uh but i want to know stefan are we really you know kind of worshiping at the altar of of popper and yes to give the dead man is due today's his birthday but let's let's let's as uh address this question is there too much emphasis placed on falsifiability and maybe as some say in the comments and elsewhere we should be looking beyond popper to a postpoparian uh assessment of what constitutes science can it only be falsifiable science that quote-unquote counts that's a very tough question so i'll just give my spin on it no pun intended um i think i do think that that criterion um for the nature of the issues that we deal with them we can even um see some of this immediately just by looking at some of the problems faced by quantum mechanics itself that that standard is um too much and i definitely resonate i i never used to actually i used to think max was a madman not mad max but uh um we we go a little way back too and um but yeah i've grown i'm i'm not sure max has his own opinions about me but um i would say that i've i've grown um sympathetic to max's point of view um and the real challenge will be actually to james and his colleagues of how how then do you if you if you relax the constraints of prop you know of of popper that you know science should be falsified what you define as science the scientific evidence should be falsifiable um so let me give an example of this actually and i want to throw this out first maybe to to um to my colleagues here to discuss a little bit um the measurement problem in quantum mechanics and the young's double experiment to me was a quintessential example of this and let me just say a few things about that very quickly the experiment right you can do it you don't need to go to high energies uh i did it in my intro physics class um with the help of our lab assistant our lab tech last semester at brown and um the basic experiment is you um well there's a modern version of the experiment you shoot you have like you know um a wall right with two little holes um so that particles can go through the holes and then you have a screen that collects the particles at the end and you shoot one electron at a time you know um and the electro you can do this with light as well with photons and then what you see is that the electrons deposit themselves as particles on the wall and so you're like oh that's good because the electrons you know will go through one hole go through another hole and it will be blocked by you know the rest of the wall you know the um and then you'd see all these electrons build up and what you end up seeing is a wave like patterns all the electrons will deposit themselves and have this wave-like pattern so then you'll say well that's weird because that's what waves do not particles and the electrons come out as particles so this is uh well you said okay let's go to look to see where the electron goes and when the observer goes to look to see where the electron goes the wave-like pattern just disappears completely so this is weird and then you say okay you go back to quantum theory and you say quantum theory tell me um to explain and predict um the role of the observer in doing this and up to today we don't have a post-paperion explanation to this now i do know that max's with my friend anthony agreer has written some papers about having certain interpretations of this where you get multiple you have to in you know expand quantum mechanics are having multiple copies of the same of of max tag marks right um the so-called max i think your advisor was john ultra ball wheel as well right and back when i was a postdoc in princeton and right and i think that so anyway let me just throw this out to say that for me i'm already convinced that even like you know the double suit experiment other other things that quantum mechanics in ordinary quantum mechanics presents itself um let me also say that those things are also magical features of quantum mechanics that we use to try to build quantum computers today but they're very weird and it seems that like to really try to understand those things you kind of have to relax the rules about in this case the role of the observers or what the sets of assumptions that we're making i don't claim that i have anything more to say about as a theorist about how to address that but i kind of want to throw it out there and say that i think we've already entered into that realm um so let me just stop right there with that sure i am a great fan of popper but hey you know um we can always build up this upgrade things a little bit you know if you just take the simple-minded point of view that every theory is either true or false and and uh the whole purpose so the definition of a theory is so that can be falsified like popper said then in that case the theory that newton of newtonian physics is really just as bad as the theory that earth is flat they're both false they've been falsified by data right but that doesn't seem quite fair to say so what in what sense is is newton's gravity better i so i told you i mentioned before john wheeler right in his his final uh phase of life that it's all information i think actually information information theory is another alternative way gives you an alternative way to define what you mean by science very loosely speaking i would say a theory is something is good science if you get more out of it than what you put into it for example i found this book once in the university of pennsylvania library is about this thick and it had over a hundred thousand numbers in it they were measured wavelengths of light coming out of all sorts of different atoms all right and it just hit me that all those numbers can now be calculated super accurately from just three numbers by stefan or james using the schrodinger equation that's data compression if you're a computer scientist it's even better than g zip minus nine it's amazing you got so much more out of quantum mechanic of quantum mechanics than you put in right put in three numbers get out a hundred thousand um in contrast if you try to predict the 32 fundamental constants of the standard model using some new model that itself has a thousand parameters that's pretty un unimpressive and it's what people in ai research would just call call over fitting so you can you can make this into a definition of of of scientific theories if you want and say that the it's having the theory let you compress the data set so you can describe the data set plus the theory itself with much less information much fewer bits than you than earlier hey that's progress so and in that sense newton's gravity was enormous progress sure it didn't describe things perfectly it was ultimately wrong because it didn't include relativistic effects but you know we become sufficiently humble in physics now anyway to acknowledge that probably every single single theory we teach in our university courses anyway is just the approximation for something else right quantum gravity or whatever something else we don't have yet so i actually think this information theory way of looking at it is more true to the spirit of what we actually do as scientists and it also gives a kind of a way of thinking about children as scientists and as in general brains as scientists because we have the brain exactly in order to be able to make predictions about the future right where to find food where to not get eaten by tigers and stuff like this and one can it's it's not hard to prove that the key to making data compression if you have too little space free on your hard drive and you're running one of these programs what it always tries to do is predict what the next stuff in your file is going to be from what it's already read and and then it can store that with much much less space so if you take the if you take the just general definition of of science as being able to make better predictions of the of the future than you could before then i think you james are happy because it's you're making predictions and but it's not as rigid as as popper that you would reject things just because you're not perfect turn to james uh to address some really uh fast and furious things coming in the comments um so we physicists are very fond of swag and if you go to and enter the the uh pbs spacetime website events you'll be registered to win swag for next time and even books by our guest next week but you know here's an example of swag so this is my official simon's observatory cap and we put on it its coordinates so we put on cerro toco chile 5150 meters and this is this is 2020 edition so it's fresh off the printing presses uh i've often heard it said what we really want is an equation that uh fits on a t-shirt or perhaps next next year 2021s uh is that a legitimate goal or is that just a cute trope that allows physicists to get away with saying funny things staphon yeah sorry wear my cern t-shirt that has the standard model lagrangian on it yeah please sorry go ahead yeah take it away so i don't think i i yeah this is like i have a very very strong uh opinion about this um i don't think that math will is gonna completely um capture of the fundamental if there is a fundamental theory it's just going to be um just math math of player has played a role but math um is a tool it's a language has been very convenient um but um but i think we're going to need more than just math like the same way we rely on intuition and then mat you know to come up with a theory sometimes um [Music] i i can tell you about an interesting feynman story i learned from my friend john lanier one of the pioneers of virtual reality of how feynman was doing physics near the end of his life he's not using math okay um but the point is i think math will be part of the will be a good useful tool but this idea of shut up and calculate and that fun finally the final fear of everything will be a set of equation or one equation i have strong feelings about it i think that'll be part of it but there there's going to be other tools that we're gonna have to draw from and i don't know what that is it might look a little bit like what max is pointing to we probably need some observers floating out there what have you um but but so i so in in a nutshell i don't think math is going to be the only thing so we find ourselves with the experimental floor dropped from beneath our feet and we're trying to navigate in this realm of pure mathematical and theoretical you know landscape um but we have this guide uh you know certainly string theory has followed this guide of you know following the beauty following the symmetry and the elegance and we've been doing it for such a long time even paul durak said that it's better to have beauty in one's equations than to have them fit experiment which i by that i think he meant that experiments can be wrong but if your equation is ugly it's definitely not right but but but surely that's telling us something why is it that this mathematical elegance leads us so truly even if it does sometimes lead us astray i'm happy for anyone to address this because i would love to know um oh you know a lot of the things we've been discussing here and i think that at the end of the day i in fact have a slightly different perspective on this um than you might expect from some you know experimentalists i'm not strictly uh you know a popparian or a popularity if you will but i'm also not you know because i don't think the falsifiability is the only you know the main criterion that we need to rely upon for any kind of theory um and you know for you know for example one of the one of the most interesting things that i see in physics right now is this concept of a multiverse whether it comes from string theory whether it comes from just inflationary big bang theory you know this idea is fascinating as it stands now there's basically no way that i can coherently you know define how to test that as an idea right now there's some kind of vague ideas there's some vague sort of possible hand-waving things but it doesn't mean that it's non-scientific it doesn't mean that it's uh you know it's not science because we followed that we started with things that are known science we followed the chain of logic to arrive at this very strange conclusion that there could be you know a multiverse amongst which we are only one it doesn't mean that you know just because we can't falsify it now it doesn't mean we can't you know it doesn't mean we can't test it now doesn't mean we can't in the future right and so that's related to what you were saying matt because you know i also think that you know in this notion of that you know stefan you're talking about you know elegance of like a mathematic you know like a an equation that should be beautiful and dirac saying these things i in fact i'm much more along the lines of you know uh my colleague stephen weinberg who said simplicity is not a scientific principle and whether or not you have a beautiful equation whether or not you have a simple theory it doesn't mean anything because the universe doesn't care whether we think that its laws are simple or elegant or beautiful at all and you know and and we have in fact we might say that you know say the the standard model of particle physics maybe from one perspective it's kind of beautiful but from another perspective it's very baroque it's like why should our universe have as its gauge theory su 3 cross su 2 cross u1 there's there's no reason for that it's very complex there could be a million other choices why is it that our universe happened to choose this one instantiation of a mathematical set of objects to make real and then a bunch of other possibilities i can write down are not there so that to me is not so simple it's you know it's not beautiful it's just it is and so i would not even i would not go to the i i try not to rush to the notion of something needs to be beautiful for it to be you know uh true because you know we're just humans it may have something to say on that yeah you raised getting to the really good stuff here are all the questions that we don't know the answer to so there is i i want to say something brief about what you mentioned about the multiverse and whether it's testable or not and i also want to say something brief about uh the business of math and it's whether it's fundamental or not so it's starting with the multiverse here how can the multiverse get along with popper you say you kind of like the multiverse but also like popper it seems very untestable right talking about places that are so far away that we could never go there even if we traveled at the speed of light forever surely that's not testable so i the way i feel we should honor popper on his birthday is to just give him some credit for being very clear on what it was that was supposed to be testable he said it's a theory that's supposed to be testable not necessarily every single prediction of the theory yeah so let me give a metaphor before we go multiversal taken theory of general relativity right it predicts stuff that we can never observe namely exactly what happens inside of a black hole right yes you could jump into sagittarius a star the four million solar mass black hole at the middle of our galaxy and make some observations before you get crushed but you can never publish your results in science or nature or tell your friends right so does that mean we should no because general relativity also made other predictions that we can test like the perihelion shift the mercury the bending of starlight around the sun all sorts of general relativity stuff with ligo and gravitational waves etc so what we've done is we've tested the theory many times we agreed that the theory is science and if we choose to take it seriously we have to take seriously all the predictions of general daily not just the ones we can observe i think it's exactly the same way with the theory of inflation if you take seriously alan guth and andre linde and and the others the theory of inflation and you also take seriously the idea that that quantum gravity has more than one solution corresponding to some sort of uniform space with stuff in it then inflation tends to generically predict that you're going to make lots of space typically much more space than we can observe and kind of uniformly full of stuff starting out in all sorts of different ways uh can we fly away and see the nearest parallel universe when our max mega mark is talking with james meacham and schmeffon schmalexander no of course we cannot right are those they're super partners are those fortunately hundreds of predicted a whole bunch of other stuff that many of us including you brian have worked on measuring like the curvature space that's supposed to be omega's total is supposed to be one and it's 1.00 etc to test it to better than a percent so it's it's stuff so this is how i think we can reconcile the multiverse with popper the ultimate the ultimate reality out there may be much bigger than we can observe fine there's no law of nature saying we should be able to observe everything that exists it'd be kind of arrogant to presume that like an ostrich saying you know if i can't see it it can't exist but as long as as long as the theories that predict that stuff also predict other things that we can test then those theories are scientific so that's that's my birthday present to popper maintain his relevance in the era of the multiverse and and speaking of his birthday you know his his original kind of target of his ire was astrology so i i guess what is he what would he have been a libra i forget i'm not good with my astrology he's probably rolling in his grave right do you want me to say something about math also or should we yeah please max go ahead so this is a wonderful question of course why is it that math has been so useful in describing our world because ultimate math is one of the most successful kinds of data compression we've come across right you can write down an equation on a blackboard that can dramatically simplify your description of things why is that did it have to be that way already galileo was really impressed by this right when he when he said 400 years ago that our universe is like a grand book written in the language of math and vig eugene wigner wrote this essay in the 60s about the unreasonable effectiveness of math and since then you guys have as physicists have just been piling it on now there's a standard model of particle physics and now einstein's theory also predicts gravitational waves and black hole in spirals and math just seems to be more and more useful and even all the successes of artificial intelligence so far suggests that the mathematical descriptions of this in computation can actually at least kick our butt in the chests and translation soon and maybe driving cars and so so why is that uh i think the truth is we just don't know and we should be humble and acknowledge that but i i don't think it's a fluke james you you mentioned that our standard model is actually more complicated than it could be but to put this in perspective it's also a lot simpler than it could have been right true imagine if every single electron were just different you've discovered in your work that every single electron you've ever looked at has exactly the same quantum numbers they're entirely equivalent particles like why is that i would i just i don't know but i think i would posit that if there is a somewhere in the multiverse maybe in the level 4 multiverse or whatever some other place where things are incredibly complicated and every single particle has its own separate properties and everything is just completely messy there would probably be no versions of this program happening right there because there would be no point in even having your brain there right there would be if everything just looked completely random you couldn't make any predictions anyway so why have a brain uh so maybe there are other regions where for some unfortunate where things are messier and that's not where we are or maybe there is some other deep reason why things are so him simple here uh i i try to be just very humble and and at least admit i take very seriously the fact that our universe was just way simpler than it could have been and i i think it's telling us something so sir max you um your book a mathematical universe which i believe i have right here uh for sale at all good bookstores uh you know you you posit that that in in some sense the the fundamental layer of reality is mathematical that our universe is fundamentally mathematical and you know what we perceive as physical emerges from that uh i guess i have a couple of questions firstly do you still subscribe to this notion i i totally do i i should clarify what i subscribe to also because um there's a broad spectrum of views as to what to make of this apparent usefulness of math and science right on one end of the spectrum you have these people who say it means nothing it's just the fluke mouth is just something we invented whatever get over it and uh then there are a lot of people who who feel that math is uh for some reason very very youthful but it's still just an approximation an approximate description of of something which is fundamentally non-mathematical i i'm in that book sticking my neck out and taking the extreme opposite point of view as far as you can go in the other direction and i i belong to a very small minority of scientists to think that but i think it's interesting regardless of whether you believe it or not explore the range of possibilities and now what do i mean by that by saying that our universe is entirely mathematical i mean i mean the hypothesis that our physical world has no properties at all except mathematical properties and that sounds just so dumb when you first hear it like it just must obviously be wrong just look behind me here at those trees there you know like what what properties do they have green it's kind of leafy the leaves are a bit squishy and soft that if you're if you're a caterpillar maybe they're yummy they don't sound like mathematical properties right but if we look at them with your eyes as physicists here what we actually see is a big there's a bunch of quarks and electrons back there and what are the properties of an electron well a minus one one half one and so on and we have nerdy names for them in physics of course james you would call those the lepton number the spin and the char electric charge and so on but that's just the words that we humans made up right the electron doesn't care what we call them the properties are numbers and as james and stefan will tell you the only difference is that we know so far between an up quark and an electron and a photon are exactly those numbers that the properties are different numbers and what about the space you see behind me here like what property is this that all that stuff is in what prop what properties of space have well for starters the property three again we have a math human name we made up for it the dimensionality of space the largest number of perpendicular fingers you can have in it right but space doesn't care we call it it's a number and more we stefan talk spoke about general relativity where we've also discovered that space has the property of curvature which is just described by the riemann tensor which is a hypercube of four times four times four times four numbers that's the mathematical thing and also topology which is a mathematical thing so if you take seriously the idea that so far the only properties we know for sure that the stuff that makes everything up are mathematical and the only properties of the space that it's in are also mathematical then it starts to sound a little bit less insane i think that the idea that maybe it's actually all mathematical and we're just part of this mathematical object said god made the integers the rest is mentioned and so maybe sabine will say that next week and she might even critique some of the things that we heard today uh so that's just a teaser to tune in she's a well-known opponent of such things ranging from the pursuit of beauty leading physicist astray in pursuing mathematical beauty and elegance i don't think i've heard matt correct me if i'm wrong but i don't think i've heard any of these gentlemen these physicists using beauty for anything so i and i often say and i said to sabine in my interview with her on my podcast and she'll be on next week so it's not saying you know behind her back really for more than seven days uh but you know all experiments are beautiful and they may not look beautiful but i mean james maybe maybe we can we can say a little bit more about this uh this question before we start you know turning to uh to some other topics but uh stefan you want you're raising your finger so yeah i'll call it i'll play something very quick in response to what max said and what you and also to address this issue of beauty because i was exactly thinking about sabine when when max was describing this um because it is kind of the program if you look at all the approaches so far the quantum gravity that i've played in they all have some level of mathematical elegance complexity and they touch on different um branches of mathematics some more in the realm of algebraic topology some in the level of symmetries lee algebras and things like that right so so i resonate with what max is saying um but i also want to talk about kind of what james also mentioned which was the notion that beauty kind of in this is in the eyes of the beholder almost like you know what's beautiful to you you know there's a saying every every i think brian you've you he's have the same every parent every ostrich things there their offspring is you know the best it's the most beautiful thing out there right um so this idea of beauties also seems to have a relativity to it so your math is more beautiful than somebody else's math my theory is more beautiful than your theory my colleagues at brown the kind of theories that they work on if you don't work they'll be pissed off at me okay to say this but they love conformal field theory for example right um the math of zooming in and zooming out and everything remaining the same um so let me just say something about that um so it's more of a question which is um so if it is the case that you know there is some element of that the universe really is is mathematical how do we bring into the how do we account for the fact that it's us humans that's discovering this math and also you know i don't want to say are we inventing the math or are we then discovering a math like and where is that where is the sort of like perspective of you know this is more beautiful than the other thing right because what's complicated mathematics to me is simple mathematics of somebody else you know vice versa so that's what i just thought beauty as another you know rubric uh but but i wonder um uh if we can turn more towards you know concrete examples there are people in the chat that are asking these um can we comment i mean do we want to dip into this it's always dangerous to criticize other people's ideas um but but and it takes a lot of bravery and courage uh to be a theorist to put ideas out there uh and uh you know some of the more kind of controversial ones seem to be in the zeitgeist of the times right now with people such as eric weinstein as i already mentioned stephen wolfram uh max and uh and folks like garrett lisi lisey putting out new theories what is it about this time and what is it about these theories that will allow us to really make progress how do we get to the bottom of it given that a future collider is decades off if it ever happens uh and so by what standards will we be judged in the future maybe james you want to take that yeah james might you start yeah sure i mean you know just a quick a couple of words there so i mean in terms of you know where we go from now i mean and why this is such an interesting time for uh really potentially game changing and very you know to use a kind of provocative word wild theories of everything that are coming out which i say with the highest possible compliment i mean again it kind of goes down goes back to this thing that i was talking about the 20th century uh you know history of particle physics and just physics in general in in the 20th century is that it was this really kind of like clockwork uh uh you know progression of sort of like strange observation uh cool theoretical prediction uh confirmation you know side prediction confirmation and then this you know it was this wonderful like almost like a clockwork you know you have these discoveries coming one after another because they have these kind of like big you know theoretical uh hints these flashlights it's like you should look over there because this is a big theoretical hint and it's always just you know been right where we're waiting for it um and we're out of those again and so as and and it's almost as though the 20th century was so successful in such a quick you know quick 100 years way that it got us to a realm of theoretical understanding that far outpaced our technological capabilities as a civilization under the assumption of the state you know the the standard uh you know theoretical and also experimental and technological uh language with which we can't create experiments that can test these ideas and then that goes back to this idea of the plunk scale right it's like once you have quantum mechanics and gravity and then we put these things you know uh put these things together in the in the in the you know dimensions of length and time and energy you suddenly get oh yeah there should be something amazing happening this gigantic energy that you probably can't reach in our civilization you know if at all you know we it takes some other civilization to be able to come up with this uh energy and so that leads to this sort of like again it's very strange in the human brain when we get this it's like ah but wait a minute i want to be able to test this i want something you know where's the next discovery coming from and there's no guarantees anymore so you know for me like i was saying as an experimentalist i have to be very sort of you know like sober and also just like straightforward it's like what do we know quantum field theory seems real uh and we should go to as high possible energies as we can otherwise we'll never know what's there just to be explore right the other part of me says we need new ideas and we need to you know we need to foment more of these and so in terms of the concrete ones that might be you know it's impossible to say which one is is the best one and which one's going to be going to play out to be the you know the the true nature of reality but you know to me it kind of goes back to the you know somebody mentioned wheeler earlier and i you know there's this diagram that i think a lot of people have been haunted by you know ever since they saw it and i've been hunted by this diagram that wheeler came up with um in one of his i forget which book but it's the one where it's basically the letter u and on one side it's a very very thin uh it's a very very thin part of the u and the u turns around and then it gets wider on the other side and there's an eyeball on that part and it's looking back at the the initial part of the u so this is the universe that has at some point evolved someone to then observe it itself so you know we as humans are the the method by which the universe is asking questions and observing itself and that to me is again a sort of like very you know profound statement about compelling us to not just look at the underpinnings of the con the the current understanding of nature you know quantum mechanics and general relativity but also think very critically about what it means to be a a sentient uh you know being in this universe and asking questions about the universe itself and that to me is you know i think it'd be we could have an entire show about you know the thing you mentioned stefan in fact i think it's a fascinating question did humans did we invent mathematics or did we actually discover it i think we could have an entire discu just you know discussion about that question but i think at the end of the day you know these these how we're going to make further progress with you know is it going to be like a wolfram style thing which again wolfram's approach to such a theory of everything as i think you know if you want my personal personal opinion i think it's fascinating it's really really interesting it's also really really really difficult to vet as a scientific community because it's just sort of like if it's done in secret then it's dropped upon the world it's like i mean what do we do with this you can't expect us just to suddenly go oh yes we've changed everything and now yours is the right one it's just that you know it needs to it needs some kind of sort of embedding within the physics community to really understand what's going on you know and and in terms of things like garrett lisey's ideas and these sort of these sort of you know more speculative ideas again you know i think i think we need as many of these as possible and we need to do the you know we need to we need to never really get stuck in this notion of beauty um and you know because just you know one one last uh point on this is that in a sense this and you know there's maybe there's some things with you know for example you mentioned sabina maybe sabine and i won't agree on everything but there's certain things that i think we definitely would be would agree on is that you know this notion of beauty uh should not always just guide our our our physics and especially theoretical physics because really at the end of the day what is science you can argue where it came from you can argue what you know how consciousness arose you can argue you know we can argue about what intelligence is but science is really if you think about it science is the best method that we as humans have that we invented to more or less reduce to negligible the fact that we as humans we love to ascent to things because they're beautiful when there's not actually a pattern there when there's not actually something real we're very very good at ascending to things just because it feels good or it's emotionally interesting or you know and that that is not the way that you know but science is like okay hold on science recognizes that humans are susceptible to this type of idea and instead says okay we need a coherent and like a very robust set of rules by which we can determine truth from falsehood that reduces to negligible this human ability or this human tendency to ascend to things due to beauty so again you know this is not again like max i completely agree that the the the leaves behind you are beautiful but i also don't think that that that that that doesn't that doesn't indicate that we can't you know again reduce this this tendency to negligible with science as a pursuit so we need to uh ask some uh audience questions max do you have something quick to follow up well it was important answer to the audience question about the path forward and then if i can also take 30 seconds i can answer what i think is the deal with whether math is invented or or discovered so if you look if you think of jupiter we did not invent jupiter we discovered jupiter it's actually out there regardless of whether we exist or not but we invented the name jupiter we could have called it shmupiter instead or in swedish we actually call it jupiter you know and it's exactly the same way if you take for example plato's five platonic solids he discovered that there are five of them the cube the tetrahedron the octahedron and the dodecahedron icosahedron then he invented he invented the names for them he could have called them the shmodekahedron and the shmoop right but he could never have invented a six platonic solid it just doesn't exist right the way another planet in our solar system doesn't so that's that uh the in terms of what you commented on there the audience question about the path forward uh a method piece of advice i would give is look at each area of physics and ask who's ahead in that area experiment or theory if you're taking an area where there's the theory there's a ton of theories theory is far ahead of data dark energy for example we don't need another theory what we really need there is more measurements uh dark matter is the same there's almost as many dark matter theories as there are theorists we would really like to have more measurements to try to rule out theories and nail things down then there are other areas where it's exactly the other way around uh take uh for example the the particle data book and the many things we can measure to 10 decimal places now that we can only calculate the two decimal places we'll loop with lattice qcd right great area for theorists to go into uh and look at the those 32 numbers that you mentioned earlier so max we should we should take some audience questions now because we're nearly out of time so and and you guys have been asking like the really pragmatic stuff uh that that you should be curious about so this one this one's a great one what all right we can't build a collider the size of a galaxy um so what maybe i've seen star wars uh what may be what is the speculated accessible experimental data that could reveal new frontiers in both quantum physics and gravity you know something like something involving perhaps neutron stars or or something like that how can we get creative anyone who has a thought on that i i have my thoughts i think looking at very high energy gamma-ray bursts that for example might give you the ability to tell the difference between different quantum gravity theories because even though the effect is very small when light flies a short distance if it's been flying for 10 billion years the effects can add up and in fact i think some quantum gravity theories have been falsified uh by exactly this sort of method yes they have uh different different wavelengths of light seem to travel at the same speed as each other uh high energy ones are not slowed down by the the little loop quantum gravity uh facets that you might expect at those scales so you know things are testable to the creator i think um dark matter substructure experiments are made like me probe maybe by future gravitational lensing events um there might be interesting predictions um you know there are some crazy ideas on the table that people with with models of dark matter again that i i don't i don't claim to subscribe to them or not but you know the idea is like theories of dark matter that have some quantum gravity ideas in it that may predict substructure maybe think in future about substructure i think also the simon's telescope looking at um certain um effects of birefringence might be another thing quantum theories of gravity seem to go there as well if i can just take two quick things sort of my very you know very brief opinion on what the you know where we need to go next is that again like i was saying before we need to do all types of experiments simultaneously because who knows where the the deviation from expectation is going to show up but i really think that multi-messenger astronomy so this is you know looking for uh you know looking for like cosmic ray cosmic rays gamma gamma ray bursts you know uh uh but also gravitational wave astronomy these kinds of things this of course will be pursued in in earnest and it has to be but simultaneously the next generation of colliders either higher energy ones or the kind of more ones where will produce a very very large number of higgs boson particles those are going to be just more or less game changers i mean there's really no question whether we should have large experiments that can create a large number of higgs bosons because the higgs boson is sort of like we you know we have this gigantic standard model which is awesome and we understand everything really really well like pinpoints but our understanding of the higgs boson is like gigantic and it could be this fantastic portal into possibly answers to some of these questions so you know is it the only fundamental scalar field that exists in the universe or are there other ones that are related to it is it in fact composite is there structure inside there is it in fact does it actually talk to dark matter and also does it have what's the shape of its potential and that if you measure the shape of the potential of the higgs boson very very precisely which is what's planned for future experiments that'll give you a window into how the universe in fact came about exactly the way it did right around the moment of the big bang you know was it a first order phase transition for like electro weak symmetry breaking or was it something else and also the what the fate of the universe is so these kind of things together they sort of have to be done otherwise we'll just be ignorant for you know for decades we need a shout out to inflation also it's brian's wheelhouse here because obviously to learn about quantum gravity we would like to look at physics where it's both very small and very massive so either end states a black hole evaporation or our big bang and uh it's a real bummer that you lost in the nobel prize brian how could you because if you had discovered gravitational waves and you had kept them around right or maybe in the future if you do it with a just at a lower amplitude then uh that might very well give us fantastic clues about quantum gravity oh that might be my next book winning the nobel prize maybe just segueing to that maybe stephanie can pick up this last question yeah i want to actually resonate with what name said i think like my my post soccer advisor michael peskin convinced me of this that we simply don't know what electro weak symmetry breaking is that's what james is referring to the current standard model that's a placeholder and it could be actually the higgs is also the higgs and discovering its true nature which will tell us about electric weak symmetry breaking might actually have clues to quantum gravity we just don't know so i think i want to resonate what james said about particle collide or physics as well yeah so last question i had maybe it ties in to a little bit of what max was saying maybe not uh we hear a lot about the anthropic principle and maybe tie-ins between inflation the multiverse the landscape swampland all these things are those potential guiding uh you know fruitful guiding avenues to understand the theory of everything or are those likely to be a wild goose chase i thought that was funny i think the the one thing i hate about the anthropic principle is that the word principle is in there as if it's somehow optional when it's in fact just the correct use of use of statistics that shouldn't be optional you know if you if you have a write a paper saying you you studied the size distribution of fishes in a pond then your net is this wide and you didn't find any fish or smaller than that that paper just should get rejected that's not a principle uh i i think fundamentally physics is about making predictions for what observers should observe and making experiments to see if those predictions are borne out or not then you just have to do the calculations correctly and if it happens that in that you make a big space and some properties are different in different parts and some don't have observers you just have to fold that into your math otherwise your whole predict your whole analysis is rubbish so we only have a few minutes left and and i wanted to you know maybe end by where we should have started you know physics is great at really defining its problems and we're quite precise um you know because we have math uh but you know i do wonder sometimes if we're even asking the right question or if we know what question we're asking so when we try to search for a theory of everything what are we doing are we asking what is the primal cause why is there something rather than nothing or are we being more pragmatic are we trying to find the equation that fits on the hat so that we can do all the calculations with one equation uh i would love to just each of you to maybe say what what do you think the final answer will feel like um maybe you step on if you'd like well i'm gonna speculate i think that um the final answer should bring into account um the human being um and the diversity of the of the human being the different perspectives i mean i have friends who um who i'm also musician so you know i was just i'm a big fan of classical indian music i have friends who you know their approach to playing like music is has a mathematical linguistic take um as a jazz musician for example the role of improvisation as a scientific way into creating music that ends up like john coltrane looking very mathematical and what's that about right what's the informational content of that so i think like the various ways of bringing in the very observers max i resonate with max big time and this how to do that i mean general relativity gave us hints about how to do that i want to give a plug to my friend eric weinstein he has this idea of the observable verse and his theory i so i think we should have a marketplace of ideas but i definitely the end game i think will will start with us as humans the ones doing the creation and not throwing a baby out with the bathwater we have theories that work and they predict things but you know and i think moving forward how do we bring all these different perspectives into that new what that new science looks like how to how to engage each other as human beings and doing that beautiful max uh yeah at the risk of uh sounding like stefan and i have a mutual admiration society going here i i will agree entirely with the idea that we need to talk seriously about what an observer is i would suggest we don't just talk about human observers there was a very cute chipmunk that just walked under the table here a minute ago i'm quite sure it's observing too i think in the future we might see uh digital minds that we've built ourselves that can also observe i suspect that we'll be able to find an end game where you have some mathematical equations or some computation that describes what we call our universe and by studying it you can not only realize that it's going to have these observers in it but you can calculate what they're going to observe and if it agrees with what james and other experimentalists actually find then start to think hey maybe this is it maybe this is what we should put on on brian keating's future baseball cap merch speaking of merch uh matt uh maybe you have a few final words and we'll wrap up with a little teaser for i i would like to hear james oh yeah sorry yeah james please just ten ten seconds with my opinion on that i think that the final answer you know if you're answering asking that question i'm not convinced there is going to be a final answer and i'm not saying that from sort of like a hippie-ish perspective i'm saying that the history of science has been such that it's a human pursuit of constructing knowledge and constructing our understanding of the the universe in a better way and a little bit more advanced as we go along even if we were to you know to discover that at its basis univer you know the nature of the fundamental nature of reality is somehow mathematical and informational which are kind of the same thing um then we would you know and if we were able to figure out a way to communicate with a part of the observable universe or the universe that we're not within or some other universe even if we were come up with that that would open up new realms that we would then need to explain and i think this is why i'm not convinced there's a final theory other than humans as one version of a conscious being a sentient being in the universe that have come up with this way to ask questions about the place in which we happen to be and i think that i totally agree i'd love to see what the squirrel's version of science is i would love to see what a different you know civilizations version of science is i'm not convinced there's a final answer but i absolutely loving the fact that we as humans get to ask these questions that's life 4.0 and max's lexicon one for each level of the multiverse matt you want to take it away yeah speaking of books so um before we wrap up there are some winners of uh some of these amazing books i'm gonna read those out now so the winner of max tigmax our mathematical universe is chris lydiard congrats chris um the winner of brian's losing the nobel prize marion edwards the winner of stephen alexander's jazz of physics is omar subbasi and the there are space-time t-shirts for we have aiden beckley um my i can't quite read that uh is this tino uh patricia katrina petrina um my apologies um and arbonne nuriana uh so congratulations those well you'll need to um email us at pbsspacetime gmail.com uh and we'll get those out to you um so brian any time thanks for not having my book done otherwise somebody could win my book but it's not done yet sorry but you have finished it it's just not in this particular universe well i want to uh thank everybody and just remind everybody out there why we're doing this because as james and max and stefan have highlighted so spectacularly it's really amazing it's almost a miracle if you think about it how how uh what a time we live in and how exciting it is that we human brains can actually access some of the deeper regions of the universe and perhaps unravel future mysteries for our you know great great great grandchildren advisees to uh to take on in their phd theses it's a very vibrant field and i want to advertise next week's show we're going to have lisa randall again she was supposed to be on today she'll be on next week uh the effervescent sabine hassenfelder eric weinstein and all of us have a soft spot in our heart for lee smallin he will be on next week as well and uh we invite the guests to join in next week uh you the three of you gentlemen and please join in in the chat in case we bring something up maybe we'll read that out and uh sign up for the to get notifications about that next week and you'll receive an entry into winning the books by uh sabine lisa and uh eric and lee so these are not eric eric doesn't have a book either we're gonna work on that uh but uh for now matt any anything else you want to say i just had uh such a blast with you guys despite you know two of the three of you being theorists uh it was great now i'm just kidding love you guys all thank you so much for taking us up on this and and the audience out there phenomenal questions stay engaged we'll try to answer as many questions as we can in the next 13.8 billion years and brian thank you for uh helping pull this together um you guys have to check out uh brian's podcast into the impossible um it there's some incredible incredible conversations um stefan i watched through all of your conversations with uh with brian i learned an awful lot uh so really just thank you all i you know did we figure out the answer well i think what we figured out is that the brightest minds of our time are um really struggling with at this point the most fundamental philosophical as well as uh scientific questions uh and if you like can't figure it out well then i guess we'll never understand space talks no no no that's why we need all the young listeners or watching this to come study physics yeah and help us answer it and watch uh watch the great resources on pbs space time studio physics is not some sort of stale old field like calculus which is all done you just go learn this is work in progress that's true we should mention that matt's the videos that matt has on pbs space time those are a really good intro to anybody that's out there it's like maybe i should actually think about majoring in physics yeah you should do that for next week actually there's loop quantum gravity there's theories of everything and many other resources thanks to matt and his awesome team i just look up to you guys so much thanks everybody i can't wait to see what we come up with next yes thank you guys

Channel: PBS Space Time

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Length: 94min 44sec (5684 seconds)

Published: Tue Jul 28 2020