#79 – Lee Smolin: Quantum Gravity and Einstein’s Unfinished Revolution

Lee Smolin is 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 is 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, Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum. EPISODE LINKS: Books mentioned: – Einstein’s Unfinished Revolution by Lee Smolin: https://amzn.to/2TsF5c3 – The Trouble With Physics by Lee Smolin: https://amzn.to/2v1FMzy – Against Method by Paul Feyerabend: https://amzn.to/2VOPXCD This conversation is part of the Artificial Intelligence podcast. If you would like to get more information about this podcast go to https://lexfridman.com/ai or connect with @lexfridman on Twitter https://twitter.com/lexfridman, LinkedIn https://www.linkedin.com/in/lexfridman/, Facebook https://www.facebook.com/lexfridman, Medium https://medium.com/@lexfridman, or YouTube https://www.youtube.com/lexfridman where you can watch the video versions of these conversations. If you enjoy the podcast, please rate it 5 stars on Apple Podcasts https://podcasts.apple.com/us/podcast/artificial-intelligence/id1434243584, follow on Spotify https://open.spotify.com/show/2MAi0BvDc6GTFvKFPXnkCL, or support it on Patreon https://www.patreon.com/lexfridman. This episode is presented by Cash App. Download it (App Store https://apps.apple.com/us/app/cash-app/id711923939, Google Play https://play.google.com/store/apps/details?id=com.squareup.cash&hl=en_US), use code “LexPodcast”. Here’s the outline of the episode. On some podcast players you should be able to click the timestamp to jump to that time. OUTLINE: 00:00 – Introduction 03:03 – What is real? 05:03 – Scientific method and scientific progress 24:57 – Eric Weinstein and radical ideas in science 29:32 – Quantum mechanics and general relativity 47:24 – Sean Carroll and many-worlds interpretation of quantum mechanics 55:33 – Principles in science 57:24 – String theory

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Lex Fridman?

  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, Einstein's 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, its naked emperors, its outcasts, and its revolutionaries,

• 0:44Lex Fridman?

  its madmen, and its dreamers. This is why it's an exciting world to explore through 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 physicists 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.

• 1:28Lex Fridman?

  This is the Artificial Intelligence Podcast. If you enjoy it, subscribe on YouTube, give it five stars on Apple Podcasts, support it on Patreon, or simply connect with me on Twitter at @LexFriedman, spelled F-R-I-D-M-A-N. 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, use code LEXBODCAST. 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 cryptocurrency in the context of the history of money

• 2:13Lex Fridman?

  is fascinating. I recommend A Scent of Money as a great book on this history. Debits and credits on ledgers started around 30,000 years ago. The US dollar, of course, created over 200 years ago. And Bitcoin, the first decentralized cryptocurrency, was released just over 10 years ago. So, given that history, cryptocurrency is 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 LEXBODCAST, you'll get $10 and Cash App will also donate $10 to FIRST, one of my favorite organizations that is helping to advance robotics and STEM education for young people around the world.

• 2:58Lex Fridman?

  And now, here's my conversation with Lee Smolin.

• 3:20Lex Fridman?

  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?

• 3:31Lee Smolin?

  We don't know. We don't know. This is science. I presume we're talking about science. And we believe, or I believe, that there is a world that is independent of my existence and my experience about it and my knowledge of it. And this I call the real world.

• 3:53Lex Fridman?

  So you said science, but even bigger than science.

• 3:56Lee Smolin?

  Sure, sure. I need not have said this is science. I just was warming up.

• 4:02Lex Fridman?

  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 a 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 cognitive constructs that's being formed there is the reality. And then anything outside is something that we can never really grasp. Is that a crazy idea to you?

• 4:41Lee Smolin?

  There's a version of that that is not crazy at all. What we experience 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 or veil or whatever you want to call it, there is a real world, and I'm curious about it.

• 5:19Lex Fridman?

  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 some intuitive way that's more connected to our ape ancestors? Or is it still fundamentally the tools of math and physics that really allows us to grasp?

• 5:43Lee Smolin?

  Well, 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 there are not fires, what animals and plants are good to eat and all that stuff. 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. And we're very curious about that. And I think we're just naturally curious.

• 6:28Lee Smolin?

  So we make up... This is my version of how we work. We make up stories and explanations. And we're... 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. Is that a tiger or is that not a tiger? And we go.

• 6:54Lex Fridman?

  Act.

• 6:55Lee Smolin?

  We have to act fast on incomplete information. So we judge quickly and we're often wrong. Or at least sometimes wrong, which is all I need for this. We're often wrong. 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.

• 7:24Lex Fridman?

  So you said, "We're often wrong." But what does it mean to be right?

• 7:29Lee Smolin?

  Right. 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 realist. A realist is somebody who believes in 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, there's a relative scale. There's not right and wrong. There's right or more right and 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? No.

• 8:13Lex Fridman?

  And the scientific method is ultimately what allows us to get a sense of how close we're getting to that real world?

• 8:20Lee Smolin?

  No, on two counts. First of all, I don't believe there's a scientific method. I was very influenced when I was in graduate school by the writings of Paul Feinabend, who was an important philosopher of science, who argued that there isn't a scientific method.

• 8:35Lex Fridman?

  There is or there is not?

• 8:36Lee Smolin?

  There is not.

• 8:37Lex Fridman?

  There's not. Can you elaborate? I'm 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?

• 8:51Lee Smolin?

  Sure. Paul Feinabend, he was a student of Popper, who taught-

• 8:58Lex Fridman?

  Karl Popper, yeah.

• 8:59Lee Smolin?

  Karl Popper. And Feinabend argued, both by logic and by historical example, that you name 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 been, that'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, I think of science as a community-

• 9:41Lex Fridman?

  Of people.

• 9:43Lee Smolin?

  Of people. And of a community of people bound by certain ethical precepts, percepts, whatever that is.

• 9:52Lex Fridman?

  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.

• 10:02Lee Smolin?

  Don't lie, report all your results, whether they agree or don't agree with your hypothesis.

• 10:10Lee Smolin?

  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 side 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

• 10:50Lee Smolin?

  for something that your colleagues will not be able to shout down? Because they'll ask, 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 going to have to waste less time fixing your mistakes.

• 11:33Lex Fridman?

  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? The scientific method is you should be able to repeat and experiment. There's a lot of elements to what constitutes 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.

• 12:10Lee Smolin?

  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 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 it has an inertia in a direction where the earth isn't moving, and the tower and the ball and the earth all move together. And the principle of inertia tells you it hits the bottom. It does look, therefore, my principle of inertia is right. And Aristotelian says, no, Aristotle's science is right.

• 12:54Lee Smolin?

  The earth is stationary. And so you've got to get an interconnected bunch of cases and work hard to line up. It took centuries to make the transition from Aristotelian physics to the new physics. It wasn't done till Newton in 1680 something, 1687.

• 13:19Lex Fridman?

  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?

• 13:43Lee Smolin?

  I don't know, a better job than what?

• 13:47Lex Fridman?

  Than 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 so on.

• 13:58Lee Smolin?

  Which is not the way I think of string theory. We'll straighten, we'll get our strings straight.

• 14:03Lex Fridman?

  But there is, nevertheless, in science, very often, at least temporary dead ends. But if you, if you look

• 14:11Lee Smolin?

  Sure.

• 14:11Lex Fridman?

  At the, through centuries, you know, the century before Newton and 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.

• 14:36Lee Smolin?

  Let me, can I say that more precisely?

• 14:38Lex Fridman?

  Yes. It's a low bar.

• 14:41Lee Smolin?

  Because I think it's important to get the time, place is right.

• 14:45Lex Fridman?

  Yes.

• 14:47Lee Smolin?

  There was a scientific revolution that partly succeeded between about 1900 or late 1890s and into the 1930s, 1940s and so, and maybe some if you stretch it into the 1970s. And the technology, this was the discovery of relativity and that included a lot of developments of electromagnetism. The confirmation, 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, and this is early 20th century.

• 15:29Lee Smolin?

  And then quantum mechanics was from 1905, it took a long time to develop till the late 1920s. And then it was basically in final form. And the basis of this partial revolution, and 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 the development of electricity and the electrification of cities in the United States and Europe and so forth.

• 16:13Lee Smolin?

  And the development of this science.

• 16:18Lee Smolin?

  The fundamental physics since the early 1970s doesn't have a story like that so far. There's not a series of triumphs and progresses, and there's not any practical application.

• 16:38Lex Fridman?

  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?

• 17:00Lee Smolin?

  It's absolutely necessary. And the key things were all validated, the key predictions of quantum mechanics and of the theory of electricity and magnetism.

• 17:11Lex Fridman?

  So before we talk about Einstein, your new book, before string theory, quantum mechanics, and so 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?

• 17:34Lee Smolin?

  Realism is the belief 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 describes and explains exactly what happens and why it happens.

• 18:10Lex Fridman?

  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.

• 18:24Lee Smolin?

  Some people would say that. I'm not that interested in deterministic, but I could live with the fundamental world, which had some chance in it.

• 18:35Lex Fridman?

  So you said you could live with it, but do you think God plays dice in our universe?

• 18:43Lee Smolin?

  I think it's probably much worse than that.

• 18:47Lex Fridman?

  In which direction?

• 18:49Lee Smolin?

  I think that theories can change and theories can change without warning. I think the future is open.

• 18:55Lex Fridman?

  You mean the fundamental laws of physics can change?

• 18:58Lee Smolin?

  Yeah.

• 18:59Lex Fridman?

  Okay, we'll get there. I thought, I thought we would be able to find some solid ground, but apparently

• 19:07Lee Smolin?

  Well, the ground is pretty solid.

• 19:09Lex Fridman?

  The entirety of it, temporarily so, probably. Okay, let's, 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 a, are we just another set of molecules connected together in a clever way? Or the observer, does, does the observer, our human mind consciousness have a role in this realism view of the physical universe?

• 19:44Lee Smolin?

  There's two ways, there's two questions you could be asking. Does our conscious mind, do our perceptions play a role in making things become, in making things real or 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 and mind? And that's question two. Question two, I do think a lot about, and my answer, which is not an answer, is I hope

• 20:27Lee Smolin?

  so, but it certainly doesn't yet.

• 20:31Lex Fridman?

  So what?

• 20:31Lee Smolin?

  Question one, I don't think so. But of course, the answer to question one depends on question two.

• 20:37Lex Fridman?

  Right.

• 20:39Lee Smolin?

  So I'm not up to question one.

• 20:41Lex Fridman?

  So question two is the thing that you can kind of struggle with at this time.

• 20:45Lee Smolin?

  Yes.

• 20:46Lex Fridman?

  What about the anti-realists? So what flavor? What are the different camps of anti-realists that you've talked about? I think it would be nice if you can articulate for the people for whom there is not a very concrete real world, that there's divisions, or it's messier than the realist view of the universe. What are the different camps? What are the different views?

• 21:11Lee Smolin?

  I'm not sure. I'm a good scholar and can talk about the different camps and analyze it. But many of the inventors of quantum physics were not realists, were anti-realists. They're scholars, 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,

• 21:41Lee Smolin?

  "The purpose of science is not to give an objective, realist description of nature as it would be in our absence." This 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 causality, or time, or space.

• 22:07Lee Smolin?

  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."

• 22:22Lex Fridman?

  Do you find any aspect of that? Because you kind of said that we, human beings, tell stories. Do you find aspects of that kind of anti-realist view of Niels Bohr compelling? That we fundamentally are storytellers, and then we create tools of space and time and causality and whatever this fun quantum mechanics stuff is to help us tell the story of our world?

• 22:50Lee Smolin?

  Sure. I just would like to believe that there's an aspiration for the other thing.

• 22:57Lex Fridman?

  The other thing being what?

• 22:58Lee Smolin?

  The realist point of view.

• 23:01Lex Fridman?

  Do you hope that the stories will eventually lead us to discovering?

• 23:09Lex Fridman?

  Discovering the real world as it is?

• 23:13Lee Smolin?

  Yeah.

• 23:14Lex Fridman?

  Is perfection possible, by the way?

• 23:16Lee Smolin?

  No. Well, that's... You mean, will we ever get there and know that we're there?

• 23:22Lex Fridman?

  Yeah, exactly.

• 23:23Lee Smolin?

  That's not my... That's for people 5,000 years in the future. We're certainly nowhere near there, yeah.

• 23:31Lex Fridman?

  Do you think reality that exists outside of our mind? Do you think there's a limit to our cognitive abilities? Again, descendants of apes who are just biological systems? Is there a limit to our mind's capability to actually understand reality?

• 23:53Lex Fridman?

  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 reality.

• 24:04Lee Smolin?

  Again, I think that's a question for 5,000 years in the future.

• 24:07Lex Fridman?

  We're not even close to that limit.

• 24:08Lee Smolin?

  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 or the universality of mathematics or of computing and so forth. And he believed that that universality, which is something real, which is somehow comes out of the fact that a symbolic system or a mathematical system can refer to itself and can... I forget what that's called, can reference back to itself.

• 24:50Lee Smolin?

  And build, in which he argued for a universality of possibility for our understanding, whatever is out there. But I admire that argument. But I... It seems to me we're doing okay so far, but we'll have to see.

• 25:11Lex Fridman?

  Whether there is a limit or not. For now, we've got plenty to play with.

• 25:14Lee Smolin?

  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, etc. Edison carried his luggage. All these geniuses carried their luggage. And not once before relatively recently did it occur to anybody to put a wheel on luggage and pull it.

• 25:47Lee Smolin?

  And it was right there waiting to be invented for centuries.

• 25:53Lex Fridman?

  So this is Eric Weinstein. 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?

• 26:07Lee Smolin?

  Yes, 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?

• 26:18Lex Fridman?

  What do you think it takes to be that guy?

• 26:21Lex Fridman?

  Because, like you said, a lot of really smart people carried their luggage. What, just psychologically speaking, so Eric Weinstein is a good example of a person who thinks outside the box.

• 26:33Lee Smolin?

  Yes.

• 26:33Lex Fridman?

  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.

• 26:49Lee Smolin?

  Thank you, that's a compliment.

• 26:50Lex Fridman?

  That's a compliment? Good. So what do you think it takes to do that? Is that something you were just born with?

• 26:58Lee Smolin?

  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 started 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 it. So I did wonder about that. And so I read the biographies. And in fact, I started with the autobiography of Einstein and Newton and 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 at the right time.

• 27:43Lee Smolin?

  Some of it is stubbornness and arrogance, which can easily go wrong.

• 27:47Lex Fridman?

  Yes.

• 27:49Lee Smolin?

  And I know, I know all of these are doorways. If you go through them slightly at the wrong speed or in the wrong angle, they're, they're ways to fail. But if you somehow have the right luck, the right confidence and arrogance, caring, I think Einstein cared to understand nature with ferocity and a commitment that exceeded other people of his time. So he asked more stubborn questions. He asked deeper questions.

• 28:27Lee Smolin?

  I think, and there's a level of ability and whether ability is born in or can be developed to the extent to which it can be developed, like any of these things, like musical talent.

• 28:42Lex Fridman?

  You mentioned ego. What's the role of ego in that process?

• 28:46Lee Smolin?

  Confidence.

• 28:47Lex Fridman?

  Confidence, but do you, in your own life, have 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?

• 29:08Lee Smolin?

  I don't know if I, I mean, I've contributed where I've contributed, whether if I had had more confidence in something, I would have gotten further. I don't know. Well, certainly I, I'm sitting here at this moment with very much my own approach to everything. And I'm calm, I'm happy about that.

• 29:36Lee Smolin?

  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.

• 29:50Lex Fridman?

  Your most recent book titled Einstein's Unfinished Revolution. So I have to ask, what is Einstein's unfinished revolution? And also, how do we finish it?

• 30:02Lee Smolin?

  Well, that's something I've been trying to do my whole life. But Einstein's 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 that there would have to be a radically different theory which somehow realized or resolved the paradox of the duality of particle and wave for photons.

• 30:32Lex Fridman?

  And he was, I mean, people, I think, don't always associate Einstein 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.

• 30:47Lee Smolin?

  Well, he didn't believe that the quantum mechanics, as it was developed in the late 19, 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, the stage where it gives a complete description of each phenomenon. And as I was saying, realism demands.

• 31:24Lex Fridman?

  So what aspect of quantum mechanics bothers you and Einstein the most? Is it some aspect of the wave function collapse discussions, the measurement problem? Is it the, the?

• 31:40Lee Smolin?

  The measurement problem, I'm not going to speak for Einstein. The measurement problem, basically, and the fact that-

• 31:49Lex Fridman?

  What is the measurement problem, sorry?

• 31:51Lee Smolin?

  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 an observation is taking place. And they basically contradict each other. But there's another reason why the revolution wasn't complete, 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.

• 32:28Lex Fridman?

  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 we have two totally separate things and we need to figure out how to connect them so it can describe everything.

• 32:49Lee Smolin?

  Right, and we either do that, if we believe quantum mechanics as understood now is correct, by bringing general relativity or some extension of 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 spacetime and gravity.

• 33:29Lex Fridman?

  So, where do we begin? So first- Let me ask, perhaps you give me a chance if I could ask you some just really basic questions. Well, they're not at all. The basic questions are the hardest, but you mentioned spacetime. What is spacetime?

• 33:46Lee Smolin?

  Spacetime, you talked about a construction. So I believe that spacetime is an 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 there is a four dimensional, smooth geometry which has a metric and a 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.

• 34:25Lex Fridman?

  So, okay, let's, we're gonna allow me to linger on that. So the universe has events. Events cause other events. This is the idea of causality. Okay, so that's hap- that's real.

• 34:39Lee Smolin?

  That's in my-

• 34:40Lex Fridman?

  In your view, is real.

• 34:42Lee Smolin?

  Or hypothesis, or the theories that I have been working to develop make that assumption.

• 34:49Lex Fridman?

  So spacetime, 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 spacetime is, both space and time are emergent and not fundamental?

• 35:08Lee Smolin?

  No.

• 35:09Lex Fridman?

  First, sorry, before you correct me, what does it mean to be fundamental or emergent?

• 35:16Lee Smolin?

  Fundamental means it's part of the description as far down as you go. We have this notion.

• 35:21Lex Fridman?

  It's real.

• 35:21Lee Smolin?

  Yes.

• 35:22Lex Fridman?

  As real as real it could be.

• 35:24Lee Smolin?

  Yeah. So I think that 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 spacetime also does not.

• 35:38Lex Fridman?

  But what is time?

• 35:40Lee Smolin?

  I think that time, the activity of time, is a continual creation of events from existing events.

• 35:51Lex Fridman?

  So if there's no events, there's no time?

• 35:54Lee Smolin?

  Then there's not only, no time, there's no nothing.

• 35:58Lex Fridman?

  So?

• 35:59Lee Smolin?

  So I believe the universe has a history, which goes to the past. I believe the 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.

• 36:20Lex Fridman?

  So you said the future doesn't exist?

• 36:22Lee Smolin?

  Yes.

• 36:25Lex Fridman?

  Could you say that again? Can you try to give me a chance to understand that one more time? So what, the events cause other events. What is this universe? Because we'll talk about locality and non-locality.

• 36:40Lee Smolin?

  Good.

• 36:42Lex Fridman?

  Because it's a crazy, I mean, it's not crazy. It's a beautiful set of ideas that you propose. But, and if causality is fundamental, I'd just like to understand it better. What is the past? What is the future? What is the flow of time? Even the arrow of time in our universe, in your view?

• 37:05Lex Fridman?

  And maybe what's an event, right?

• 37:07Lee Smolin?

  Oh, an event is where something changes. Or where two, it's hard to say because it's a primitive concept. An event is a moment of time within space. This is the view in general relativity, where two particles intersect in their paths or something changes in the path of a particle. Now, we are postulating that there is, at the 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.

• 37:52Lex Fridman?

  And it's, it doesn't have a connection to energy or matter or exchange of any...

• 37:55Lee Smolin?

  It does have a connection to energy and matter.

• 37:57Lex Fridman?

  It's at that level.

• 37:58Lee Smolin?

  Yes, it involves, and that's why the version of a theory of events that I've developed with Marina Cortez. And it's, by the way, I wanted to mention my collaborators because they've been at least as important in this work as I have. Marina Cortez in all the work since about 2013, 2012, 2013, about causality, causal sets. And in the period before that, Roberta Manguara Angar, who is a philosopher and a professor of law.

• 38:32Lex Fridman?

  And that's in your efforts together with your collaborators to finish the unfinished revolution.

• 38:37Lee Smolin?

  Yes.

• 38:37Lex Fridman?

  And focus on causality.

• 38:39Lee Smolin?

  And focus on...

• 38:39Lex Fridman?

  As fundamental.

• 38:40Lee Smolin?

  Yes.

• 38:41Lex Fridman?

  As fundamental to physics. So...

• 38:45Lee Smolin?

  And there's certainly other people we've worked with, but those two people's thinking had a huge influence on my own thinking.

• 38:52Lex Fridman?

  So in the way you describe causality, that's what you mean of time being fundamental? That causality is fundamental?

• 38:58Lee Smolin?

  Yes.

• 39:00Lex Fridman?

  And what does it mean for space to not be fundamental? To be emergent?

• 39:05Lee Smolin?

  That's very good. There's a level of description in which there are 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. But, but there is an emergent approximate description. And you asked me to define emergent, 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,

• 39:48Lee Smolin?

  which requires some property to describe it, which is not directly...

• 39:57Lee Smolin?

  Explicable or derivable is the word I want from the properties of the fundamental things.

• 40:05Lex Fridman?

  And space is one of those things in a sufficiently complex universe, space, three dimensional position of things emerged?

• 40:15Lee Smolin?

  Yes, and we have this, we saw how this happens in detail in some models, both computationally and analytically.

• 40:24Lex Fridman?

  Okay, so connected to space is the idea of locality.

• 40:28Lee Smolin?

  Yes.

• 40:29Lex Fridman?

  That, so we talked about realism, so I, I live in this world that 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. It's the thing that bothers me about gravity in general, or action at a distance. Same thing that probably bothered Newton, or at least he said a little bit about it. How, okay, so what do you think about locality? Is it 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?

• 41:14Lex Fridman?

  I mean, it seems crazy for it not to be a fundamental aspect of our reality.

• 41:19Lee Smolin?

  It does.

• 41:20Lex Fridman?

  Can you comfort me on a, sort of as a therapist, like, how do I?

• 41:25Lee Smolin?

  I'm not a good therapist, I'll do my best. 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. Field operators corresponding to events in spacetime, which are spacelike separated community with each other, is operators.

• 41:58Lex Fridman?

  So in quantum mechanics, you think about the nature of reality as fields, and things that are close in a field have an impact on each other more than farther away.

• 42:10Lee Smolin?

  That's, yes.

• 42:11Lex Fridman?

  That's very comforting. That makes sense.

• 42:13Lee Smolin?

  So that's a property of quantum field theory, and it's well-tested. Unfortunately, there's another definition of local, which was expressed by Einstein and expressed more precisely by John Bell, which has been tested experimentally and found to 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,

• 42:55Lee Smolin?

  and then you make a measurement on particle A, which is over here on my right side, and particle B, which is over here, somebody else makes a measurement on particle B, you can ask that whatever is the real reality of particle B should 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 the notion of locality, because it assumes that these things are very far spacelike separated, and it's going to take a while for any information about the choice made by the people here at A

• 43:39Lee Smolin?

  to affect the reality at B. But you make that assumption. That's called Bell locality. And you derive a certain inequality that some correlations, 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.

• 44:04Lex Fridman?

  In experiment, it doesn't match. So what does that mean?

• 44:09Lee Smolin?

  That means that that definition of locality I stated is false.

• 44:13Lex Fridman?

  The one that Einstein was playing with?

• 44:16Lee Smolin?

  Yeah, and 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 at almost the speed of light or the speed of light away from each other.

• 44:35Lex Fridman?

  No matter, so like the distance between them?

• 44:39Lee Smolin?

  Well, it's been tested, of course, if you want to have hope for quantum mechanics being incomplete or 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.

• 44:59Lex Fridman?

  So

• 45:01Lex Fridman?

  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?

• 45:14Lee Smolin?

  Absolutely.

• 45:15Lex Fridman?

  A crucial step. So 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. So I guess my question is, how do we solve? How do we finish the unfinished revolution?

• 45:36Lee Smolin?

  Well, that's, I can only tell you what I'm trying to do and what I have abandoned.

• 45:42Lex Fridman?

  Yes.

• 45:42Lee Smolin?

  As not working.

• 45:45Lex Fridman?

  As one ant, smart ant in an ant colony. Yep.

• 45:50Lee Smolin?

  Maybe dumb, that's why, who knows? But anyway, my view of the, we've had some nice theories invented.

• 46:01Lee Smolin?

  There's a bunch of different ones, both relate to quantum mechanics, relate 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 a student 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 it would work out this way, which work partly, and

• 46:42Lee Smolin?

  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 people, 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 at each other. And as Eric says, we need two things. We need people to get off their hills and come down into the valleys and party and

• 47:25Lee Smolin?

  talk and become friendly and learn to say not no, but, but yes, and, yes, your idea goes this far, but maybe if we put it together with my idea, we can go further.

• 47:40Lex Fridman?

  Yes. So in that spirit, I've talked several times with Sean Carroll, who's also written an excellent book recently, and he kind of, he plays around as a big fan of the many worlds interpretation of quantum mechanics. So I'm a troublemaker, so let me ask, what's your sense of Sean and the idea of many worlds interpretation? I've read many of the commentary back and forth. You guys, you guys are friendly, respect each other, but have a lot of fun debating.

• 48:14Lee Smolin?

  I love Sean. And he, no, I really, he's...

• 48:21Lee Smolin?

  He's articulate and he's a great representative or ambassador of science to the public and for different fields of science to each other. He also, like I do, takes philosophy seriously. And unlike what I do in all cases, he's really done the homework. He's read a lot, he knows the people, he talks to them, he exposes his arguments to them. And I, there's this mysterious thing that we so often end up on the opposite sides of these issues.

• 48:59Lex Fridman?

  It's fun, though.

• 49:00Lee Smolin?

  It's fun and I'd love to have a conversation about that, but I would want to include him.

• 49:07Lex Fridman?

  I see, about many worlds.

• 49:09Lee Smolin?

  No, I can tell you what I think about many worlds.

• 49:11Lex Fridman?

  I'd love to, but actually on that, let me pause. Sean has a podcast, you should definitely figure out how to talk to Sean. 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 Sean.

• 49:25Lee Smolin?

  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.

• 49:36Lex Fridman?

  Yes, and that, that'll be great to tell him on his podcast.

• 49:40Lee Smolin?

  I can invite myself to his podcast.

• 49:43Lex Fridman?

  Yeah, okay, we'll make it happen. So, many worlds.

• 49:47Lee Smolin?

  Anyway.

• 49:48Lex Fridman?

  What's your view? Many worlds, we talked about non-locality. 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.

• 50:09Lee Smolin?

  Yeah.

• 50:10Lex Fridman?

  It's just a beautiful line, but at the same time, it's very difficult for our limited human minds to comprehend. So what are your thoughts about it?

• 50:22Lee Smolin?

  Let me start with the easy and obvious and then go to the scientific.

• 50:28Lex Fridman?

  Okay.

• 50:29Lee Smolin?

  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, Mangiber, Anga and I began looking for principles, and I want to come back and talk about the use of principles in science, because that's the other thing I was going to 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, and it happens once. But, so, it's not helpful to my personal approach, to my personal agenda. But of course, I'm part of a community.

• 51:09Lee Smolin?

  And my sense of the many-worlds interpretation, I have thought a lot about it and struggled a lot with it, is the following.

• 51:22Lee Smolin?

  First of all, there's Everett himself, there's what's in Everett. And there are several issues there, 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 the smooth evolution of the quantum state. But the notion of probability is only in the second rule, which we've thrown away.

• 52:08Lee Smolin?

  So where does probability come from? You have to answer the question, because experimentalists 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, this talk about branches is not quite precise, but I'll use it.

• 52:33Lee Smolin?

  There's a branch in which everything that might happen does happen, with probability 1 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 possibilities, 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 failed, did not work.

• 53:17Lee Smolin?

  There are then... But 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, and chapter 11.

• 53:58Lee Smolin?

  There's a very good group of philosophers of physics in Oxford. Simon Saunders, David Wallace, Harvey Brown, and a number of others. And of course, there's 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 the Everett story was true and you were living in that multiverse. How would you make bets? And so, they use decision theory

• 54:41Lee Smolin?

  from the theory of probability and gambling and so forth to shape a story of how you would bet if you were inside an Everettian 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 what I put in my book. Now, to add to that, Sean has his own approach to that problem

• 55:26Lee Smolin?

  in what's called self-referencing or self-locating observers. And it doesn't... I 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 it in the book. I don't know whether it's right or not.

• 55:51Lex Fridman?

  Let's talk a little bit about science. You mentioned the use of principles in science.

• 55:58Lex Fridman?

  What does it mean to have a principle? And why is that important?

• 56:02Lee Smolin?

  When I feel very frustrated about quantum gravity, I like to go back and read history.

• 56:09Lee Smolin?

  And of course Einstein, his achievements are a huge lesson and hopefully something like a role model. And it's very clear that Einstein thought that the first job when you want to enter 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 and time. Minkowski invented this idea of spacetime. For Einstein, it was a model of his principles or his postulates.

• 56:53Lee Smolin?

  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.

• 57:19Lee Smolin?

  Which might describe indeed some quantum gravity physics in some domain, in some aspect. But ultimately 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.

• 57:38Lex Fridman?

  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?

• 58:01Lee Smolin?

  Can I say how I read that book?

• 58:04Lex Fridman?

  Sure.

• 58:05Lee Smolin?

  Because I, and I'm not, this of course has to be my fault because you can't, as an author, claim, after all the work you put in, that you were misread. But I will, I will say that many of the reviewers, who were not personally involved, and even many who were working on string theory or some other approach to quantum gravity, told me, communicated with me, and told me they thought that I was fair. And balanced was the word that was usually used. So let me tell you what my purpose was in writing that book, which clearly got diverted

• 58:44Lee Smolin?

  by, because there was already a rather hot argument going on.

• 58:52Lex Fridman?

  On which topic? On string theory specifically? Or in general, in physics?

• 58:57Lee Smolin?

  No, more specifically than string theory. So, since we're in Cambridge, can I say that? We're doing this in Cambridge?

• 59:05Lex Fridman?

  Yeah, of course. Cambridge, just to be clear, Massachusetts, and on Harvard campus.

• 59:12Lee Smolin?

  Right. So Andy Stromminger 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, the symmetries of one of those string theories, and discover the standard model, and predict all the properties of the standard model particles, like their masses and charges and so forth, coupling constants.

• 59:48Lee Smolin?

  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 Kalabi-Yau manifolds, named after Yao, who is also here. 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, String Theory with Torsion, in which he discovered there was

• 1:00:35Lee Smolin?

  not formally uncountable, but he was unable to invent any way to count the number of solutions or classify the diverse solutions. And he wrote that this is worrying because doing phenomenology the old-fashioned way by solving a theory is not going to work because there's going to be loads of solutions for everything proposed phenomenology for anything the experiments discovered. Now, it hasn't quite worked out that way. But nonetheless, he took that worry to me.

• 1:01:09Lee Smolin?

  We spoke at least once, maybe two or three times about that. And I got seriously worried about that. And is this a little...

• 1:01:19Lex Fridman?

  It sounds like an anecdote that inspired your worry about string theory in general?

• 1:01:24Lee Smolin?

  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 Linmar Goulas and Steve Gould and so forth.

• 1:01:43Lee Smolin?

  I could take your time to go through the things, but it occurred to me, maybe physics was like evolutionary biology, and maybe the laws evolved. And there was, the biologists talk about a landscape, a fitness landscape, of DNA sequences, or protein sequences, or species, or something like that. And 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, let's call it cosmological natural selection.

• 1:02:24Lex Fridman?

  Cosmological natural selection. Wow. So the parameters of the standard model, so the laws of physics are changing, 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?

• 1:02:45Lee Smolin?

  Yes. And I published that, I wrote the paper in 88 or 89, the paper was published in 92. My 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, or at least close to maximal.

• 1:03:28Lee Smolin?

  And I could deduce predictions that could be tested from that. 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 80s and early 90s.

• 1:03:45Lex Fridman?

  That's a really compelling notion, but how does that help you arrive?

• 1:03:49Lee Smolin?

  I'm coming to where the book came from.

• 1:03:53Lex Fridman?

  Yes.

• 1:03:54Lee Smolin?

  So, what got me, I worked on string theory, I also...

• 1:04:02Lee Smolin?

  Worked on loop quantum gravity, and I was one of the inventors of loop 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 background independent and ended up developing a bunch of tools, which then could apply directly to general relativity, and that became loop quantum gravity. So the things were very closely related and have always been very closely related in my mind. The idea that there were two communities, one devoted to strings and one devoted to loops, is nuts and has always been nuts.

• 1:04:46Lex Fridman?

  Okay, so...

• 1:04:47Lee Smolin?

  So anyway...

• 1:04:48Lex Fridman?

  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 such a problem?

• 1:04:57Lee Smolin?

  So I was interested in developing that notion of how science works based on a community and ethics that I told you about.

• 1:05:08Lee Smolin?

  And I wrote a draft of a book about that, which had several chapters on methodology of science. And it was a rather academically oriented book. And those chapters were the first part of the book, the first third of it. You can find their remnants in what's now the 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 in string theory and so forth. And I wasn't able to get that book published. So somebody made the suggestion of flipping it around

• 1:05:51Lee Smolin?

  and starting with the 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 won't find me criticizing individuals. You'll find me criticizing certain writing. But in any case...

• 1:06:19Lee Smolin?

  Here's what I regret. Let me make your program worthwhile.

• 1:06:23Lex Fridman?

  Yes.

• 1:06:24Lee Smolin?

  As far as I know, with the exception of not understanding how large the applications to condensed matter, say, of ADMCF, ADS-CFT 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 awe, including, and this is what I regret, my own community, that is, a community of people working on quantum gravity outside string theory.

• 1:07:09Lee Smolin?

  But, and I considered saying that explicitly, but to 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.

• 1:07:29Lex Fridman?

  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 own work on, not 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?

• 1:07:53Lee Smolin?

  Well, do we solve the problem?

• 1:07:56Lex Fridman?

  That we solve the unfinished problem of Einstein's.

• 1:08:01Lee Smolin?

  That's certainly the thing that I care about most, and hope for most. Let me say one thing. Among the young people that I work with, I hear very often and sense a total disinterest in these arguments that we older 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, they 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

• 1:08:44Lee Smolin?

  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.

• 1:08:58Lex Fridman?

  Yes.

• 1:08:59Lee Smolin?

  And this, to me, is very helpful.

• 1:09:02Lex Fridman?

  That the different ideas are coming together.

• 1:09:06Lee Smolin?

  At least people are expressing an interest in that.

• 1:09:11Lex Fridman?

  It's a huge honor talking to you, Lee. Thanks so much for your time today.

• 1:09:14Lee Smolin?

  Thank you.

• 1:09:16Lex Fridman?

  Thanks for listening to this conversation, and thank you to our presenting sponsor, Cash App. Download it, use code LEXPODCAST, you'll get $10, and $10 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 on Apple Podcast, follow on Spotify, support it on Patreon, or simply connect with me on Twitter at @LexFriedman. 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. Thanks for listening and hope to see you next time.