Lee Smolin: Quantum Gravity and Einstein's Unfinished Revolution | Lex Fridman Podcast #79
the following is a conversation with Lee Smolin he's a theoretical physicist co-inventor of loop quantum gravity and a contributor of many interesting ideas to cosmology quantum field theory the foundations of quantum mechanics theoretical biology and the philosophy of science he's the author of several books including one that critiques the state of physics and string theory called the trouble with physics and his latest book Einsteins unfinished revolution the search for what lies beyond the quantum he's an outspoken personality in the public debates on the nature of our universe among the top minds in the theoretical physics community this community has its respected academics it's naked Emperor's its outcasts in his revolutionaries its Mad Men and his dreamers this is why it's an exciting world to explore it's a long-form conversation I recommend you listen back to the episodes with Leonard Susskind Sean Carroll Michio Kaku max tegmark Eric Weinstein and Jim Gates you might be asking why talk to physicist if you're interested in AI to me creating artificial intelligence systems requires more than Python and deep learning it requires that we return to exploring the fundamental nature of the universe and the human mind theoretical physicists venture out into the dark mysterious psychologically challenging place of first principles more than almost any other discipline this is the artificial intelligence podcast if you enjoy it subscribe on YouTube get five stars an Apple podcast supported on patreon or simply connect with me on Twitter Alex Friedman spelled Fri D M am as usual I'll do one or two minutes of ads now and never any ads in the middle that can break the flow of the conversation I hope that works for you and doesn't hurt the listening experience this show is presented by cash app the number-one finance app in the App Store when you get it you scolex podcast cash app lets you send money to friends buy Bitcoin and invest in the stock market with as little as $1 since cash app allows you to buy Bitcoin let me mention that the currency in the context of the history of money is fascinating I recommend a cent of money as a great book on this history debits and credits on Ledger's started around 30,000 years ago the US dollar of course created over two hundred years ago and Bitcoin the first decentralized cryptocurrency was released just over ten years ago so given that history cryptocurrencies still very much in its early days of development but it still is aiming to and just might redefine the nature of money if you get cash app from the App Store or Google Play and use the code Lex podcast you'll get ten dollars in cash app will also donate ten dollars the first one of my favorite organizations that's helping to advance robotics and STEM education for young people around the world and now here's my conversation with Lee Smolin what is real let's start with an easy question put another way how do we know what is real and what is merely a creation of our human perception and imagination we don't know you don't know this is science I presume were talking about science and we believe or I believe that there is a world that is independent of my existence in my experience about it my knowledge of it and this I call the real world so he said science but even bigger than science what sure sure I need not have said this is science I just was you know warming up warming up okay now that we're warmed up let's take a brief step outside of science is it completely a crazy idea to you that everything that exists is merely creation of our mind so like there's a few not many this is outside of science now people who believe sort of perception is fundamentally what's in our human perception the visual cortex and so on the the cognitive constructs that's being formed there is the reality and then anything outside is something that we can never really grasp that's the crazy idea too there's a version of that that is not crazy at all what we experienced is constructed by our brains and by our brains in an active mode so we don't see the raw world we see a very processed world we feel something was very processed through our brains and our brains are incredible but I still believe that behind that experience that mirror fail or whatever you want to call it there is a real world and I'm curious about it can we truly how do we get a sense of that real world is it through the tools of physics from theory to the experiments or can we actually grasp it in in some intuitive way that's more connected to our ape ancestors or is it still fundamentally the tools of math and physics that really allow us to grow so let's talk about what tools they are what you say are the tools of math and physics I mean I think we're in the same position as our ancestors in the caves or before the caves or whatever we find ourselves in this world and we're curious we also it's important to be able to explain what happens when there are fires when they're not fighters what animals and plants are good to eat and all that stuff and but we're also just curious we look up in the sky and we see the Sun and the moon and the stars and we see some of those move in we're good we're very curious about that I think we're just naturally curious so we make up this is my version of what I were we make up stories and explanations and where there are two things which I think are just true of being human we make judgments fast because we have to we're to survive we is that a tiger is that not a tiger and we go act we have to act fast on incomplete information so we we judge quickly and we're off and wrong but at least sometimes wrong which is all I need for this we're off in Iran so we fool ourselves and we fool other people readily and so there's lots of stories that get told and some of them result in a concrete benefit and some of them don't and so he said we're often wrong but what does it mean to be right right that's that's the that's a that's an excellent question to be right well since I'm I believe that there is a real world I believe that to be you can challenge me on this if you're not a realistic realistic somebody who believes in these this real objective world which is independent of our perception if I'm a realist I think that to be right is to come closer I think first of all this a relative scale is not right and wrong this writer more right than less right and you're more right if you come closer to an exact true description of that real world now can we know that for sure now in the scientific method is ultimately what allows us to get a sense of how close were getting to that real world no one to counts first of all I don't believe his scientific method ha I was very influenced when I was in graduate school by the writings of Paul fire Robin who was enough an important philosopher of science who argue that there is no scientific method there is or there is not there's not can you elaborate if sorry if you were going to but can you elaborate on the what does it mean for there not to be a scientific method this notion that I think a lot of people believe in in this day and age sure Paul Farben or he was a student of popper who taught opera Karl Popper and Farben argued both by logic and by historical exam well that you named anything that should be part of the practice of science say you should always make sure that your theories agree with all the data that's always meant it's already been taken and he'll prove to you that there have to be times when science contradicts when some scientist contradicts that advice for science to progress overall so it's not a simple matter I think that of science as a community and a people of people and as a community of people bound by certain ethical precepts precepts whatever that so in that community a set of ideas they operate under I'm meaning ethically of kind of the rules of the game they operate under don't lie report all your results whether they agree or don't agree with your hypothesis check the training of a scientist mostly consists of methods of checking because again we make lots of mistakes we're very error-prone but there are tools both on the mathematics and the experimental side to check and double-check and triple-check and a scientist goes through a training and I think this is part of it you can't just walk off the street and say yo I'm a scientist you have to go through the training and the training the test that lets you be done with the training is can you form a convincing case for something that your colleagues will not be able to shout down because the last did you check this and did you check that and did you check this and what about seeming contradiction with this and you've got to have answers to all those things or you don't get taken seriously and when you get to the point where you can produce that kind of defense and argument then they give you a PhD that's and you're kind of licensed you're still going to be questioned and you still may propose or publish mistakes but the community is gonna have to waste less time fixing your mistakes yes but if you can maybe linger on it a little longer what's the gap between the thing that that community does and the ideal of the scientific method was the scientific method is you should be able to repeat an experiment there's a lot of elements to what construes the the scientific method but the final result the hope of it is that you should be able to say with some confidence that a particular thing is close to the truth right but there's not a simple relationship between experiment and hypothesis or theory for example Galileo did this experiment of dropping a ball from the top of a tower and it falls right at the base of the tower and an Aristotelian would say Wow of course it falls right to the base of the tower that shows that the earth isn't moving while the ball is falling and Galileo says no wait there's a principle of inertia and has an inertia in the direction with the earth isn't moving and the tower and the ball in the or thought moves together when the principle of inertia tells you at his at the bottom it does look like therefore my principle of inertia is right you know Stettin Ian says no peristyle science is right the earth is stationary and so you gotta get an interconnected bunch of cases and work hard to line up and isolated centuries to make the transition from Aristotelian physics to the new physics it wasn't done till Newton in 1687 in 1687 so what do you think is the nature of the process that seems to lead to progress if we at least look at the long arc of science of all the community of scientists they seem to do a better job of coming up with ideas that engineers can then take on and build rockets with or build computers with or build cool stuff with I don't know a better job than what then this previous century so century by century we can talk about we'll talk about string theory and so on and kind of possible well you might think of as dead ends and and so on not do it we will string whistles straight but there's never less than science very often at least temporary dead ends but if you if you look sure at the through centuries you know the century before Newton in the century after Newton it seems like a lot of ideas came closer to the truth that then could be usable by our civilization to build the iPhone right to build cool things that improve our quality of life that's the progress I'm kind of referring to let me can I say that more precisely yes I think it's a it's important to get the time places right yes there was a scientific revolution that partly succeeded between about 1900 or late 1890s and into the 22 1930s 1940s and so and maybe some if she stretched it into the 1970s and the technology this was the discovery of relativity and that included a lot of developments of electromagnetism the conformation which wasn't really well confirmed into the 20th century that matter was made of atoms and the whole picture of nuclei with electrons going around this is early 20th century and then quantum mechanics was from 1905 it took a long time to develop to the late 1920s and then it was basically in final form and the basis of this partial revolution we can come back to why it's only a partial revolution is the basis of the technologies you mentioned all of I mean electrical technology was being developed slowly with this and in fact there's a close relation between development of electric electricity and the electrification of cities in the United States and Europe and so forth and the development of the science the size of the fundamental physics since the early 1970s doesn't have a story like that and so far there's not a series of triumphs and progresses and there's not a there's not any practical application so just to linger briefly on the early 20th century and the revolutions in science that happened there what was the method by which the scientific community kept each other in check about when you get something right when you get something wrong is experimental validation ultimately the final test it's absolutely necessary and the key things were all validated two key predictions of quantum mechanics and of the theory of electricity and magnetism so before we talk about Einstein now your new book before string theory quantum mechanics on let's take a step back at a higher level question what is that you mentioned what is realism what is anti realism and maybe why do you find realism as you mentioned so compelling realism is you is the belief in the in an external world independent of our existence our perception our belief our knowledge a realist as a physicist is somebody who believes that there should be possible some completely objective description of each and every process at the fundamental level which which describes and explains exactly what happens and why it happened that kind of implies that that system in a realist view is deterministic meaning there's no fuzzy magic going on that you can never get to the bottom you can get to the bottom of anything and perfectly describe it some people would say that I'm not interested in determinism but I I could live with the fundamental world which which had some chance in it so deep he said you could live with it but do you think God plays dice in our universe I think it's probably much worse than that in which direction I think that theories can change and theories unchanged without warning I think the future is open you mean the fundamental laws of physics can change you okay we'll get there I thought I thought we would be able to find some solid ground but apparently for the ground is the entirety of it temporarily so probably okay let's uh so realism is the idea that while the ground is solid you can describe it what's the role of the human being our beautiful complex human mind in the in realism do we have them are we just another set of molecules connected together in a clever way or the observer this is the observer our human mind consciousness have a role in this realism view of the physical universe there's two ways there's two questions you can be asking it does our conscious mind you are perceptions play a role in making things become in making things real or if things becoming that's question one question two is does this we can call it a naturalist view of the world that is based on realism allow a place to understand the existence of and the nature of perceptions and consciousness in mind and that's question two question two I do think a lot about and my answer which is nine answers I hope so but it certainly doesn't yet so what question one I don't think so but of course the answer to question one depends on question two right so I'm not up to question one yeah the question two is the thing that you can kind of struggle with at this time as what about the anti-realists so what flavour what are the different camps of anti-realist that you've talked about I think it'd be nice if you can articulate for the people for whom there is not a very concrete real world as there's divisions or there's a it's Messier then the realist view of the universe what are the different camps for the different views I'm I'm not sure I'm a I'm a good scholar and can talk about the different camps and analyze it but some many of the inventors of quantum physics were not realness weren't I realist in their scholarship they lived in a very perilous time between the two world wars and there were a lot of trends in culture which were going that way but in any case they said things like the purpose of science is not to give an objective realist description of nature's it would be in our absence this movie might be saying Niels Bohr the purpose of science is as an extension of our conversations with each other to describe our interactions with nature and we're free to invent and use terms like particle or wave or a causality or a time or space if they're useful to us and they carry some intuitive implication but we shouldn't believe that they actually have to do with what nature would be like in our absence which we have nothing to say about do you find any aspect of that because you kind of said that we human beings tell stories defined aspects of that kind of entire realist view of Niels Bohr compelling that were fundamentally are storytellers and then we create tools of space and time and causality and whatever this fun quantum mechanic stuff is to help us tell the story of our world sure I just would like to believe that is an aspiration for the other thing driving being what the the realist point of view do you hope that the stories will eventually lead us to discovering discovering the real world as it is yeah it's perfection possible by the way though oh well that's you mean will we ever get there and know that we're there yeah exactly that's not mine that's for people 5,000 years in the future we're certainly nowhere near there yeah do you think reality that exists our sight outside of our mind do you think there's a limit to our cognitive abilities is again descendants of apes for just biological systems is there a limit to our minds capability to actually understand reality sort of there comes a point even with the help of the tools of physics that we just cannot grasp some fundamental aspects of that again I think that's a question for 5,000 years in the future element I think there is a universality here I don't agree with David Deutsch about everything but I admire the way he put things in his last book and he talked about the role of explanation and he talked about the universality of certain languages of the universality of mathematics or of computing and so forth and he believed that universality which is something real which is it somehow comes out of the fact that the symbolic system in a mathematical system can refer to itself and in every I forget what that's called in reference back to itself and build in which he argued for a universality of possibility for our understanding whatever is out there but I'm I admire that argument but I it seems to me we're doing okay so far but we'll have to see whether there is a limit or not for now we got we got plenty to play with yeah there are things which are right there in front of us which we miss and I'll quote my friend Eric Weinstein in saying look Einstein carried his luggage Freud carried his luggage Marx carried his luggage Martha Graham carried her luggage etcetera Edison carried his luggage all these geniuses carry their luggage and not once before relatively recently did it occur to anybody to put a wheel on luggage and pull it and it was right there waiting to be invented for centuries so this is Erik Y Stein yeah what do the wheels represent are you basically saying that there's stuff right in front of our eyes that once we it just clicks we put the wheels in the luggage a lot of things will fall into place yes that I do I do and every day I wake up and think why can't I be that guy who was walking through the airport what do you think it takes to be that guy because link you said a lot of really smart people carried their luggage mm-hmm what just psychologically speaking so Erik wants that is a good example of a person who thinks outside the box yes who resists almost conventional thinking you're an example of a person who by habit by psychology by upbringing I don't know but resists conventional thinking as well just by Nature that's that's a compliment good so what do you think it takes to do that is that something you were just born with I doubt it well from my studying some cases because I'm curious about that obviously and just in a more concrete way when I start out in physics because I started a long way from physics so it took me a long not a long time but a lot of work to get to study it and get into so I did wonder about that and so I read the biographies and in fact I started with the autobiography of Einstein and Newton in Galileo and all those all those people and I think there's a couple of things some of it is luck being in the right place the right time some of it is stubbornness and arrogance which can easily go wrong yes and I know I know all of these are doorways if you go through them slightly at the wrong speed or any wrong angle they're their ways to fail but if you somehow have the right look the right confidence and arrogance caring I think Einstein cared to understand nature with ferocity and commitment that exceeded other people of his time so he asked more stubborn questions he asked deeper questions I think and there's a level of ability and whether ability is born in or can be developed at a sensor which can be developed like any of these things like musical talent dimension ego what's the role of ego in that process confidence confidence but you do in your own life if you found yourself walking that nice edge of too much or too little so being overconfident and therefore leading yourself astray or not sufficiently confident to throw away the conventional thinking of whatever the theory of the day of theoretical physics I don't know if I I mean I've contributed where I've contributed whether if I had had more confidence in some things I would have gotten further I don't know whether certainly hi I'm sitting here at this moment with very much my own approach to telling everything and I'm calm I'm happy about that but on the other hand I know people whose self-confidence vastly exceeds mine and sometimes I think it's justified and sometimes I think it's not justified your most recent book titled Einstein's unfinished revolution so I have to ask what is Einsteins unfinished revolution and also how do we finish it well that's something I've been trying to do my whole life but Einsteins unfinished revolution is the twin revolutions which invented relativity theory special and especially general relativity and quantum theory which he was the first person to realize in 1905 there would have to be a radically different theory which somehow realized to resolve the paradox of the duality of particle wave for photons and he was I mean people I think don't always associate I style with quantum mechanics because I think his connection with it founding as a one of the founders I would say of quantum mechanics he kind of put it in the closet is it well he didn't believe that the quantum mechanics as it was developed in the late 19th middle late 1920s was completely correct at first he didn't believe it at all then he was convinced that it's consistent but incomplete and that also is my view it needs for various reasons I can elucidate to have additional degrees of freedom particles forces something to reach the stage where it gives a complete description of each phenomena and as I was saying realism demands so what aspect of quantum mechanics bothers you and Einstein the most is it some aspect of the wavefunction collapse discussions the measurement problem is it the the the measurement problem I'm not gonna speak for Einstein but the measurement problem basically and the fact that what is the measurement problem sorry the basic formulation of quantum mechanics gives you two ways to evolve situations in time one of them is explicitly when no observer is observing or no measurement is taking place and the other is when a measurement or observation is taking place and they can treat they basically contradict each other but there's another reason why the revolution wasn't completed which is we don't understand the relationship between these two parts general relativity which became our best theory of space and time and gravitation and cosmology and quantum theory so for the most part general relativity describes big things quantum theory describes little things and that's the revolution that we found really powerful tools to describe big things and little things and it's unfinished because you wouldn't have two totally separate things and we need to figure out how to connect them so it can describe everything right and we either do that if we believe quantum mechanics as understood now is correct by bringing general relativity or some extension or general relativity that describes gravity and so forth into the quantum domain that's called quantize the theory of gravity or if you believe with Einstein that quantum mechanics needs to be completed and this is my view then part of the job of finding the right completion or extension of quantum mechanics would be one that incorporated space-time in gravity so where do we begin so first let me ask perhaps you can give me a chance if I could ask you some just really basic questions well there at all the basic questions and the hardest but you mentioned space-time what is space-time space-time you talked about a construction so I believe the space-time is a intellectual construction that we make of the events in the universe I believe the events are real and the relationships between the events which cause which are real but the idea that here is a four-dimensional smooth geometry which has a metric in the connection and satisfies the equations that Einstein wrote it's a good description to some scale it's a good approximation it captures some of what's really going on in nature but I don't believe it for a minute is fundamental so okay let's we're gonna allow me to linger on that so the universe has events events cause other events there's this idea of causality okay so that that's happy let's in my in your view Israel or hypothesis so the theories that I have been working to develop make that assumption so space-time you said four dimensional space is kind of the location of things and time is whatever the heck time is and you're saying that space-time is both space and time are emergent and not fundamental no sorry before you correct me what is mean to be fundamental or emergent fundamental means it's part of the description as far down as you go we have real yes as real as real it could be yeah so I think the time is fundamental and quote goes all the way down and space does not and the combination of them we use in general relativity that we call space-time also it is not but what is time then I think that time the activity of time is the continual creation of events from existing event so if there's no events there's nothing then there's not only not no time there's no nothing so so I believe that history universe has a history which goes to the past I believe that a future does not exist there's a notion of a present and a notion of the past and the past consists of is a story about events that took place to our past she said the future doesn't exist yes could you say that again can you try to give me a chance to understand that one more time so what the events caused other events what is this universe because we'll talk about locality in nonlocality good because it's the crazy I mean it's not crazy it's a beautiful set of ideas that you you propose but and if because all these fundamental I just like to understand it better what is him what is the past what is the future what is the flow of time even the era of time in our universe in your view and maybe it was an event right Oh an event is where something changes or where to I it's hard to say because it's a primitive concept in the event is a moment of time within space this is the the view and general relativity where two particles intersect in their paths or something changes in the path of the particle now we are postulating the theories I have two fundamental level a notion which is an elementary notion so it doesn't have a definition in terms of other things but it is something elementary happening and it's it doesn't have a connection to energy or matter or exchange of any ties to have the connection energies at that level yeah it involves and that's why the version of a theory of that I've developed with Marina Cortez and they say by the way I want to mention my collaborators because they've been at least as important in this work as I have marina Cortes in all the works since about 2013 2012-2013 about causality Carlos set and in the period before that Roberto mangabeira Unger who is a philosopher and a professor of law and that's in your efforts together with your collaborators to finish the unfinished revolution so yeah and focus on causality and focus on mental yes as fundamental to physics so and there's certainly other people we've worked with but those two people's thinking had a huge influence on my own thinking so in the way you describe causality that's what you mean of time being fundamental that causality is from the yes and what does it mean for space to not be fundamental to be though that's very good this is a level of description in which there events there are events create other events but there's no space they don't live in space they have an order in which they caused each other and that is part of the nature of time for us so but but there is an emergent approximate description and you asked me to find a version I didn't an emergent property is a property that arises at some level of complexity larger than and more complex than the fundamental level which requires some property to describe it which is not directly explicable or drivable is the word I want from the properties of the fundamental things and space is one of those things in a sufficiently complex universe space three-dimensional position of things emerged yes and we have this we saw how this happened in detail in some models both computationally and analytically ok so connected to space is the idea of locality yes that so we talked about realism so I I live in this world at like sports you know locality is a thing that you know you can affect things close to you and don't have an effect on things that are far away mm-hmm it's the thing that bothers me about gravity in general or action in a distance the same thing that probably bothered Newton or at least he said a little bit about it okay so what do you think about localities it's just a construct is it us humans just like this idea and are connected to it because we exist in it we need it for our survival but it's not fundamental I mean it seems crazy for it not to be a fundamental aspect of our reality it does and you comfort me and a sort of as a therapist like how do i I'm not a good therapist okay there are several different definitions of locality when you come to talk about locality in physics in quantum field theory which is a mixture of special relativity and quantum mechanics there is a precise definition of locality operative field operators corresponding to events in space-time which are space like separated can meet with each other as operators so in the in quantum mechanics you think about the nature realities fields and things that are close and if you have an impact on each other more than farther away that's yes that's very comforting that makes sense so that's a property of quantum field theory and it's well tested unfortunately there is another definition of local which was expressed by Einstein and expressed more precisely by John Bell which has been tested experimentally and found fail and this setup is you take two particles so one thing that's really weird about quantum mechanics is a property called entanglement you can have two particles interact and then share a property without it being a property of either one of the two particles and if you take such a system and then you magically make a measurement on particle a which is over here on my right side and particle B which is over here and what somebody else makes a measurement in a particle B you can ask that whatever is the real reality of particle B it not be affected by the choice the observer at particle a makes about what to measure not the outcome just the choice of the different things they might measure and that's a notion of locality because it assumes that these things are very far space like separated and it's going to take a while for any information about the choice made by the people here at a to affect the reality of B but you make that assumption that's called bell locality and you derive a certain inequality that some correlation functions of correlations have to satisfy and then you can test that pretty directly in experiments which create pairs of photons or other particles and it's wrong by many sigma in experiment in is a match so what what does that mean that means that that definition of locality I stated is false the the one that Einstein was playing with and the one the one that I stated that is it's not true that whatever is real about particle B is unaffected by the choice that the observer makes as to what to measure in particle a no matter how long they've been propagating and almost the speed of light or the speed of light away from each other it's no matter so like the distance between them well it's been tested of course if you want to have hope for quantum mechanics P in completely wrong and corrected by something that changes this it's been tested over a number of kilometers I don't remember whether it's 25 kilometers or 170 kilometers but so in trying to solve the unsolved revolution in trying to come up with a theory for everything is causality fundamental and breaking away from locality absolutely fun a crucial step so the in your book essentially those are the two things we really need to think about as a community especially the physics community has to think about this okay I guess my question is how do we solve how do we finish the unfinished revolution well that's I can only tell you what I'm trying to do and what I have abandoned yes it's not working as one ant smart ant in an ant colony yep or maybe dumb that's why he knows but anyway that's become my view of the we've had some nice theories invented there's a bunch of different ones both related to quantum mechanics related to quantum gravity there's a lot to admire in many of these different approaches but to my understanding they none of them completely solve the problems that I care about and so we're in a situation which is either terrifying for students or full of opportunity for the right student in which we've got more than a dozen attempts and I never thought I don't think anybody anticipated would work out this way which work partly and then at some point they have an issue that nobody can figure out how to go around or how to solve and that's the situation we're in my reaction to that is twofold one of them is to try to bring him we evolved into this unfortunate sociological situation in which there are communities around some of these approaches and to borrow again a metaphor from Eric they sit on top of hills in the landscape of theories and throw rocks in each other and as eric says we need two things we need people to get off their hills and come down into valleys and party and talk and become friendly and it's learning to say not know but but yes and yes your idea goes this far but maybe if we put it together with my idea we could go further yes so in that spirit of talked several times with Sean Carroll who's also written an excellent book recently and he kind of he plays around is a big fan of the many-worlds interpretation of quantum mechanics so I'm a troublemaker so let me ask well what's your sense of Sean and the idea of many-worlds interpretation I've read many the commentary back and forth you guys you guys are friendly respect each other but have a lot of fun debating I love Sean and he know I really he's not he's articulate and he's a great representative or an ambassador of science to the public in four different fields of science to each other he also like I do takes philosophy seriously and unlike what I do in all cases he has really done the homework he's read a lot he knows the people he talks to them he exposes his arguments to the to them and I did this mysterious thing that we so often end up on the opposite sides of with these issues it's fun though it's fun and I'd love to have a conversation about that but I would want to include him I see about many worlds well no I can tell you what I think about many I'd love to but actually on that let me pause Sean as a podcast you should definitely figure out how to talk to Sean I would I actually told Sean I would love to hear you guys just going back and forth so I hope you can make that happen eventually you and sure I want I won't tell you what it is but there's something that Sean said to me in June of 2016 that changed my whole approach to a problem but I have to tell him first yes and that that's they'll be great to tell him on his podcast so I can't invite myself to his podcast yeah okay we'll make it happen so so many worlds anyway um what's your view many worlds we talk about nonlocality many worlds is also a very uncomfortable idea or beautiful depending on your perspective it's it's very nice in terms of I mean there's a realist aspect to it I think you called it magical realism yeah it's just a beautiful line but at the same time it's very difficult to far eliminate human minds to comprehend so what it what are your thoughts about it let me start with the easy and obvious and then go to the scientific okay it doesn't appeal to me it doesn't answer the questions that I want answered and it does so to such a strong case that when Roberto mangabeira Unger and I began looking for principles and I want to come back and talk about the use of principles in science cuz that's the other thing I was gonna say and I don't want to lose that when we started looking for principles we made our first principle there is just one world that happens once but so it's it's not helpful to my personal approach to my personal agenda but of course I'm part of a community and my sense of the many-worlds interpretation I have thought a lot about it and struggled a lot with it is the following first of all there's Everett himself there's what's in Everett and there are several issues they're connected with the derivation of the born rule which is the rule that gives probabilities to events and the reasons why there is a problem with probability is that I mentioned the two ways that physical systems can evolve the many-worlds interpretation cuts off one the one having to do with measurement and just has the other one the Schrodinger evolution which is smooth evolution of the quantum state but the notion of probability is only in the second rule which we've thrown away so where there's probably come from and you have to answer the question because experimentalist use probabilities to check the theory now at first sight you get very confused because there seems to be a real problem because in the many-worlds interpretation the this talk about branches is not quite precise but I'll use it there is a branch in which everything that might happen does happen with probability one in that branch you might think you could count the number of branches in which things do and don't happen and get numbers that you can define as something like frequentist probabilities and Everett did have an argument in that direction but the argument gets very subtle when there are an infinite number of abilities as is the case in most quantum systems and my understanding although I'm not as much of an expert as some other people is that Everett's own proposal it's failed did not work there then it doesn't stop there there is an important idea that Everett didn't know about which is decoherence and it is a phenomenon that might be very much relevant and so a number of people post Everett have tried to make versions of what you might call many worlds quantum mechanics and this is a big area and it's subtle and it's not the kind of thing that I do well so I consulted that's why there's two chapters on this in the book I wrote chapter 10 which is about Everett's version in Chapter 11 there is a very good group of philosophers of physics in Oxford Simon Saunders David Wallace Harvey Brown and a number of others and of course is David Deutsch who is there and those people have developed and put a lot of work into a very sophisticated set of ideas designed to come back and answer that question they have the flavor of there are really no probabilities we admit that but imagine if you if the Everett story was true and you were living in that multiverse how would you make bets and so they they use decision theory from the theory of probability in gambling and so forth to shape a story of how you would bet if you were inside average in the universe and you knew that and there is a debate among those experts as to whether they or somebody else has really succeeded and when I checked in as I was finishing the book with some of those people like Simon who's a good friend of mine and David Wallace they told me that they weren't sure that any of them was yet correct so that's why I put in my book now to add to that sean has his own approach to that problem in what's called self referencing or self locating observers and it doesn't I just tried to read it and it didn't make sense to me but I didn't study it hard I didn't communicate with Sean I didn't do the things that I would do so I had nothing to say about in the book and I don't I don't know whether it's right or not let's talk a little bit about science you mentioned these principles in science what does it mean to have a principle and why is that important when I feel very frustrated about quantum gravity I like to go back and read history and of course Einstein and his achievements are a huge lesson and hopefully something like a role model and it's very clear the Einstein thought that the first job when you want to enter a new domain of theoretical physics is to discover and invent principles and then make models of how those principles might be applied in some experimental situation which is where the mathematics comes in so for Einstein there was no unified space in time Minkowski invented this idea of space-time Fry's time it was a model of his principles or his past humans and I've taken the view that we don't know the principles of quantum gravity I can think about candidates and I have some papers where I discuss different candidates and I'm happy to discuss them but my belief now is that those partially successful approaches are all models which might describe indeed some quantum gravity physics in some domain and aspect but ultimately could would be important because they model the principles and the first job is to tie down those principles so that's the approach that I'm taking so the so speaking of principles in your 2006 book the trouble with physics you criticized a bit string theory for taking us away from the rigors of the scientific method or whatever you would call it but what's the trouble with physics today and how do we fix it can I say how I read that book sure because I and I'm not this of course has to be my fault because you can't as an author to claim after all the work he put in this you were misread but I will I will say that many of the reviewers who were not personally involved in even many who were working on string theory or some other approach to quantum gravity told me communicate with me and told me they thought that I was fair and balanced was though was the way that was usually is so let me tell you what my purpose was in writing that book which clearly got diverted by because there was already a rather hard argument going on and this is on which topic on string theory specifically or in general and physics know more specifically than string theory so since we're in Cambridge can I say that we're doing this yeah Cambridge just to be clear Massachusetts and on Harvard campus right so Angie's rominger is a good friend of mine and has been for many many years and Andy so originally there was this beautiful idea that there were five string theories and maybe they would be unified into one and we would discover a way to break that symmetries of one of those string theories and discover the standard model and predict all the properties of standard model particles like their masses and charges and so forth coupling constants and then there was a bunch of solutions to string theory found which led each of them to a different version of particle physics with a different phenomenology these are called the khalaby Yau manifolds named after Yahoo is also here not certainly we've been friends at some time in the past anyway and then there were nobody was sure but hundreds of thousands of different versions of string theory and then Andy found there was a way to put a certain kind of mathematical curvature called torsion into the solutions and he wrote a paper of string theory with torsion in which he discovered there was and not formally uncountable but he was unable to invent any way to count the number of solutions are classified the diverse solutions and he wrote that this is worrying because doing phenomenology the old-fashioned way by solving the theory is not going to work because there's going to be loads of solutions for everything proposed phenomenology for anything the experiments just go now it hasn't quite worked out that way but nonetheless he took that worry to me he did he we spoke at least once maybe two or three times about that and I got seriously worried about that and this is just a little it's almost like an anecdote that inspired you're worried about string theory in general well I tried to solve the problem and I tried to solve the problem I was reading at that time a lot of biology a lot of evolutionary theory like lynn margulis and Steve Gould and so forth and I all right I could take your time to go through things that occurred to me maybe physics was like evolutionary biology and maybe the laws evolved and there was the Baris talked about a landscape a fitness landscape of DNA sequences or protein synthesis sequences or a species or something like that I took their concept and the word landscape from theoretical biology and made a scenario about how the universe as a whole could evolve to discover the parameters of the standard model and I'm happy to discuss that's called cosmological natural selection cosmological natural selection yeah so so the parameters of the standard model so it says the laws of physics are changing it this this idea would say that the laws of physics are changing in some way that echoes that of natural selection or just it adjusts in some way towards some goal yes and I published that I wrote the paper in 1880 or 1890 paper was published in 92 when I first book in 1997 the life of the cosmos was explicitly about that and I was very clear that what was important is that because you would develop an ensemble of universes but they were related by descent through natural selection almost every universe would share the property that it was its fitness was maximized to some extent were these close to maximum and I could deduce predictions that could be tested from that and and I worked all of that out and I compared it to the anthropic principle where you weren't able to make tests or make falsifications all of this was in the late eighties and early nineties that's a really compelling notion but how does that help you arrive I'm coming to whatever where the book came from yes so what we've got me I worked on string theory I also Don Luhan gravity and I was one of the inventors of the quantum gravity and because of my strong belief in some other principles which led to this notion of wanting a quantum theory of gravity to be what we call relational or background independent I tried very hard to make string theory backward independent and ended up developing a bunch of tools which then could apply directly to general relativity and that became a loop quantum gravity so the things were very closely related and have always been right closely related in my mind the idea that there were two communities one devoted to strings and one devoted to loops is nuts and this always been nuts okay so so anyway there's this nuts community of loops and strings that are all beautiful and compelling and mathematically speaking and what's the trouble with all that why is that why is there such a problem so what so I was interested in developing that notion of how science works based on a community and ethics that I told you about and I wrote a draft of a book about that which had several chapters on methodology of science and it was rather academically oriented a book in those chapters were the first part of the book the first third of it and you even find their remnants in what's now the last chapter last part of the trouble with physics and then I described a number of test cases case studies and one of them which I knew was the search for quantum gravity and string theory and so forth and I was unable to get that book published so somebody made the suggestion of flipping it around and starting with a story of string theory which was already controversial this was 2004-2005 but I was very careful to be detailed to criticize papers and not people you don't you won't find me criticizing individuals you'll find me criticizing certain writing but in any case here's what I regret let me make a program with y-yes I as far as I know with the exception of not understanding how large the applications to condensed matter say of a DMCA a DSC of T would get I think largely my diagnosis of string theory as it was then has stood up since 2006 what I regret is that the same critique I was using string theory as an example and the same critique applies to many other communities in science and all including and this is where I regret my own community that is a community of people working on quantum gravity outside string theory but and I considered saying that explicitly but I say that explicitly since I'm it's a small intimate community I would be telling stories and naming names of and making a kind of history that I have no right to write so I stayed away from that but was misunderstood but if I may ask is there a hopeful message for theoretical physics that we can take from that book sort of that looks at the community not just your your own work on now with causality and non locality but just broadly in understanding the fundamental nature of our reality what's your hope for the 21st century in physics well do we solve the problem it would solve the unfinished problem of my science this is that's certainly the the thing that I care about most in hopefully let me say one thing among the young people that I work with I hear very often and since a total disinterest in these arguments that we other scientists have and an interest in what each other is doing and this is starting to appear in conferences where the young people interested in quantum gravity make a conference may invite loops and strings and causal dynamical triangulations and causal set people and we're having a conference like this next week a small workshop at perimeter and I guess I'm advertising this and then in the summer we're having a big full-on conference which is just quantum gravity it's not strings it's not loops but the organizers and the speakers will be from all the different communities yes and this to me is very helpful that the different ideas are coming together at least people are expressing an interest in that there's a huge honor talking to you Lee thanks so much for your time today thank you thanks for listening to this conversation and thank you to our presenting sponsored cash app download it used coal export cast you'll get ten dollars and ten dollars will go to first an organization that inspires and educates young minds to become science and technology innovators of tomorrow if you enjoy this podcast subscribe on YouTube give it five stars an apple podcast follow on Spotify supported on patreon or simply connect with me on Twitter and lex friedman and now let me leave you with some words from lee smolin one possibility is god is nothing but the power of the universe to organize itself listening I hope to see you next time you