Lex Fridman PodcastLee Smolin: Quantum Gravity and Einstein's Unfinished Revolution | Lex Fridman Podcast #79
EVERY SPOKEN WORD
105 min read · 20,649 words- 0:00 – 3:03
Introduction
- LFLex 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, 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. 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 @lexfridman, 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 LEXPODCAST. 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, is fascinating. I recommend A Cent 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 LEXPODCAST, 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. And now, here's my conversation with Lee Smolin.
- 3:03 – 5:03
What is real?
- LFLex 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?
- LSLee 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.
- LFLex Fridman
So, you said science, but even bigger than science, what-
- LSLee Smolin
Sure, sure.
- LFLex Fridman
... I think-
- LSLee Smolin
I need not have said this is science. I just was, you know, warming up.
- LFLex Fridman
(laughs) Warming up? Okay, now that we're warmed up, let's take-
- LSLee Smolin
Mm-hmm.
- LFLex Fridman
... 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, is fundamentally what's in our human perception, the visual cortex and so on, the, the cognitive constructs that's b- being formed there, is the reality, and then anything outside is something that we can never really grasp. Is that-
- LSLee Smolin
You see-
- LFLex Fridman
... a crazy idea to you?
- LSLee 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. Um, so we don't see the raw world. We see a very processed world. We feel something that's very processed through our brains and our brains are incredible. Um, but I still believe that behind that experience, that mirror or veil or whatever you wanna call it, there is a real world, and I'm curious about it.
- LFLex Fridman
Can we truly
- 5:03 – 24:57
Scientific method and scientific progress
- LFLex Fridman
f... H- 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 grasp it?
- LSLee Smolin
Well, let's talk about what tools they are, what, 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. Uh, 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, we're very curious about that, and I think we're just naturally...... curious. So we make a... This is my version of what ha- w- how we work. 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. Where... To survive, we... "Is that a tiger or is that not a tiger?"
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
(claps) And we go.
- LFLex Fridman
Act.
- LSLee Smolin
We have to act fast on incomplete information. So we, 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 and...
- LFLex Fridman
So you said we're often wrong, but what does it mean to be right? So-
- LSLee Smolin
Right. That's, that's the, uh, that's a, that's an excellent question. To be right... Well, since I'm, uh... 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 the, 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? Now-
- LFLex Fridman
And the scientific method is ultimately what allows us to get a sense of how close we're getting to that real world?
- LSLee Smolin
F-... No on two counts. First of all, I don't believe in a scientific method.
- LFLex Fridman
All right.
- LSLee Smolin
I'm a... I was very influenced when I was in graduate school by the writings of Paul Feyerabend, who was an, a, an important philosopher of science who argued that there isn't a scientific method.
- LFLex Fridman
There is or there isn't?
- LSLee Smolin
There is not.
- LFLex Fridman
There's not. Can you elaborate if, if... 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.
- LSLee Smolin
Sure. P- Paul Feyerabend, uh, he was a student of Popper who taught-
- LFLex Fridman
Karl Popper, yeah.
- LSLee Smolin
Karl Popper. And Feyerabend 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 ta- 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, and that-
- LFLex Fridman
Of people.
- LSLee Smolin
Of people. And as a community of people bound by certain ethical precepts, percepts, whatever that is.
- LFLex Fridman
(laughs)
- LSLee Smolin
(laughs) Um.
- LFLex Fridman
So in that community, a set of ideas they operate under, I'm... Uh, meaning e- ethically of kind of the rules of the game they operate under. So-
- LSLee Smolin
Don't lie. Report all your results, whether they agree or don't agree with your hypothesis. Um, 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 mathematic 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 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 this 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 gonna be questioned and you still may propose or publish mistakes, but the community is gonna have to waste less time fixing your mistakes.
- LFLex Fridman
(laughs) Yes. But, uh, if, if you can maybe linger on it a little longer-
- LSLee Smolin
Sure.
- LFLex Fridman
... what's the gap between the thing that that community does and the idea of the scientific method? What's... The scientific method is you should be able to repeat an experiment, uh, th- there's a lot of elements to what constitutes a... 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, um, close to the truth.
- LSLee Smolin
Right. But the... 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 it has an inertia in the direction which the earth isn't moving, and the tower and the ball and the earth all move together. When the principle of inertia tells you it hits the bottom, it does. Look at... Therefore, my principle of inertia is right." And the Aristotelian says, "No, Aristotle's science is right. The earth is stationary." And so you've got to get an interconnected bunch of cases and work hard to line up and explai-... It took centuries to make the transition from Aristotelian physics to the new physics. It wasn't done till Newton in 1680-something, 1687.
- LFLex 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, uh, 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.
- LSLee Smolin
I don't know. A better job than what?
- 24:57 – 29:32
Eric Weinstein and radical ideas in science
- LFLex Fridman
- LSLee Smolin
Yeah. There are things which are right there in front of us which we miss. And I'll quote my friend Eric Weinstein-
- LFLex Fridman
Hmm.
- LSLee Smolin
... in saying, "Look, Einstein carried his luggage, Freud carried his luggage, Marx carried his luggage, Martha Graham carried her luggage," et cetera. "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."
- LFLex Fridman
(laughs)
- LSLee Smolin
And it was right there waiting to be invented for c- centuries.
- LFLex Fridman
(laughs) So this is Eric Weinstein?
- LSLee Smolin
Mm-hmm.
- LFLex Fridman
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 on the luggage, a lot of things will fall into place?
- LSLee Smolin
Yes.
- LFLex Fridman
That-
- LSLee Smolin
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-"
- LFLex Fridman
Yeah.
- LSLee Smolin
"... (sighs)
- LFLex Fridman
What do you think it takes to be that guy? Because-
- LSLee Smolin
O-
- LFLex Fridman
... like you said, a lot of really smart people carried their luggage.
- LSLee Smolin
Mm-hmm.
- LFLex Fridman
What, just psychologically speaking ... So Eric Weinstein is a good example of a person who thinks outside the box-
- LSLee Smolin
Yes, he is.
- LFLex Fridman
... who, uh, resists almost conventional thinking. Uh, 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.
- LSLee Smolin
Thank you. That's a compliment.
- LFLex Fridman
That's a compliment? Good. So what do you think it takes to do that? Is that y- something you were just born with?
- LSLee Smolin
I doubt it. Fo- I ... From my studying some cases, 'cause I'm curious about that, obviously, and just in a more concrete way, w- when I started out in physics, 'cause I started a long way from physics, so it took me a long, uh, 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. L- some of it is luck, being in the right place at the right time. Some of it is stubbornness and arrogance which can easily go wrong.
- LFLex Fridman
Yes.
- LSLee Smolin
And I know, I know all of these are doorways if you go through them s- slightly at the wrong speed or in the wrong angle, they're, um, they're ways to fail. But if you somehow have the right luck, the right confidence or arrogance, caring. I think Einstein cared to understand nature with a ferocity and a commitment that exceeded other people of his time. So he asked more stubborn questions, he asked deeper questions. Um, 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, um. But-
- LFLex Fridman
So you mentioned ego. What's the role of ego in that process?
- LSLee Smolin
Confidence.
- LFLex Fridman
Confidence. But d- do you f- in your own life, have you found yourself walking that nice edge of too much or too little, so being t- over-confident and therefore leading yourself astray or not sufficiently confident to throw away the conventional thinking of whatever the theory of the day of, of theoretical physics?
- LSLee Smolin
I don't know if I ... I mean, I've contributed what I've contributed, whether if I had had more confidence in something, uh, I would've gotten further, I don't know.
- 29:32 – 47:24
Quantum mechanics and general relativity
- LSLee Smolin
- LFLex 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?
- LSLee 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.
- LFLex Fridman
And, and he was ... I mean, people, I think, don't always associate Einstein with quantum mechanics 'cause I think his connection with it, uh, founding, as, as, uh, one of the founders, I would say, of quantum mechanics, he kind of put it in the closet. Is it-
- LSLee Smolin
Well, he didn't believe that the quantum mechanics as it was developed in the late 19- mid or late 1920s, uh-... 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 as I was saying realism demands.
- LFLex 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-
- LSLee Smolin
The measurement problem. I'm not gonna speak for Einstein. But-
- LFLex Fridman
(laughs)
- LSLee Smolin
... (laughs) the measurement problem w- basically, and the fact that there-
- LFLex Fridman
What is the measurement problem? Sorry.
- LSLee 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 and no measurement is taking place, and the other is when a measurement or an observation is taking place and they contra- they basically contradict each other. But there's another reason why the revolution was incomplete 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.
- LFLex Fridman
So for the most part, general relativity describes big things, quantum theory describes little things, and that's the-
- LSLee Smolin
That's right.
- LFLex Fridman
... revolution that we found really powerful tools to describe big things and little things, and it's unfinished because w- we have two totally separate things, and we need to figure out how to connect them so it can describe everything.
- LSLee 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 quantized-
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
... 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.
- LFLex Fridman
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, they're not at all... the basic questions are the hardest. But you've mentioned spacetime. What is spacetime?
- LSLee Smolin
Spacetime... You talked about a construction. So I believe that spacetime 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 there's 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.
- LFLex Fridman
So okay. Let's... we're gonna... Allow me to linger on that. So the universe has events.
- LSLee Smolin
Yeah.
- LFLex Fridman
Events cause other events.
- LSLee Smolin
Yeah.
- LFLex Fridman
There's this idea of causality.
- LSLee Smolin
Yeah.
- LFLex Fridman
Okay. So that's, that's hap- that's real. Okay.
- LSLee Smolin
That's in my-
- LFLex Fridman
In your view, is real.
- LSLee Smolin
... or hypothesis, or the, the theories that I have been working to develop make that assumption.
- LFLex Fridman
Yes. So spacetime, you said four-dimensional space is kind of th- the location of things and time is whatever the heck time is. And, uh, y- y- you're saying that spacetime is, uh, both space and time are emergent and not fundamental?
- 47:24 – 55:33
Sean Carroll and many-worlds interpretation of quantum mechanics
- LFLex Fridman
So in that spirit, I've, uh, talked several times with Sean Carroll, who's a- 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, uh, I'm a troublemaker, so let me ask, uh, what's your sense of, uh, 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.
- LSLee Smolin
I love Sean, and he... No, I really... He's not... 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 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... There's this mysterious thing that we so often end up on the opposite sides of one of these issues.
- LFLex Fridman
It's fun though. (laughs)
- LSLee Smolin
It's fun and-I'd love to have a conversation about that, but I would want to include him.
- LFLex Fridman
I see, uh, about Many-Worlds. Well-
- LSLee Smolin
No, I, I can tell you what I think about Many-Worlds.
- LFLex 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 would, I, I actually told Sean I would love to hear you guys just going back and forth, uh, so, um, I hope you can make that happen eventually, you and Sean.
- LSLee Smolin
I won't t- I won't tell you what it is, but there's something that Sean said to me-
- LFLex Fridman
Okay.
- LSLee Smolin
... in June of 2016 that changed my whole approach to a problem. But I'll, I have to tell him first.
- LFLex Fridman
Yes. And that's, that's, that'll be great to tell him on his podcast. So... (laughs)
- LSLee Smolin
I can't invite myself to his podcast, but, um-
- LFLex Fridman
I, I told him, yeah, okay. We'll make it happen. So, uh-
- LSLee Smolin
So-
- LFLex Fridman
... Many-Worlds.
- LSLee Smolin
... anyway, um-
- LFLex Fridman
What's your view? Many-Worlds, we talked about non-locality, Many-Worlds is a- also a very uncomfortable idea, or beautiful depending on your perspective. Uh, it's, um, it's very nice in terms of, um, I mean, there's a realist aspect to it, I think you called it magical realist. (laughs)
- LSLee Smolin
Yes.
- LFLex Fridman
Which is, it's just a beautiful line. But, uh, at the same time, it's very difficult to, for our limited human minds to comprehend. So, what are, what are your thoughts about it?
- LSLee Smolin
Let me start with the easy and obvious and then go to the scientific.
- LFLex Fridman
Okay.
- LSLee Smolin
Um, 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 Mangabetta and Unger and I began looking for principles, and I wanna come back and talk about these, the principles in science, 'cause that's the other thing I was gonna say and I don't want to lose that. Um, when we started looking for principles, we made our first principle there is just one world and it 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 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.
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
And just has the other one, the Schrodinger evolution, which is just smooth evolution of the quantum state. But the notion of probability is only in the second rule, which we've thrown away. 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 'cause 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's 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-
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
... and get numbers that you can define as something like frequentist probabilities.
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
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. 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. 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.
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
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 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.
- 55:33 – 57:24
Principles in science
- LSLee Smolin
- LFLex Fridman
Let's talk a little bit about science. You mentioned, uh, these principles in science. What does it mean to have a principle, and why is that important?
- LSLee Smolin
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 that Einstein thought that the first job when you went e- entered 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 y- principles or his postulates. 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, in some aspect, but ultimately could, would be important because they model the principles, and the first job is to tighten down those principles. So, that's the approach that I'm taking.
- LFLex Fridman
So, so speaking of principles,
- 57:24 – 1:09:50
String theory
- LFLex Fridman
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, um, what's the trouble with physics today and how do we fix it?
- LSLee Smolin
Can I say, uh, how I read that book?
- LFLex Fridman
Sure.
- LSLee Smolin
Because I... and I'm not... this of course has to be my fault because mis- you can't as an author claim after all the work you put in that you were misread.
- LFLex Fridman
(laughs)
- LSLee Smolin
But (laughs) I will s- I will say that many of the reviewers who are not personally involved in it, even many who were working on string theory or some other approach to quantum gravity-
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
... told me, communicated with me, and told me they thought that I was fair and balanced was the, was the word that was usually used. So, let me tell you what my purpose was in writing that book which clearly got diverted by... because there was already a rather hot argument going on. And this is-
- LFLex Fridman
On which topic? On string theory specifically or in general in physics?
- LSLee Smolin
No. More specifically than string theory. So, since we're in Cambridge... Can I say that? We're doing this in Cambridge?
- LFLex Fridman
Yeah, yeah. Of course. (laughs) Cambridge, just to be clear, Massachusetts and, uh, on, uh, Harvard campus.
- LSLee Smolin
Right. So, Andy Strominger is a good friend of mine and has been for many, many years.
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
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 standard model particles, like their masses and charges and so forth, coupling constant. 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 Calabi-Yau manifolds named after Ya- Yau, who 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.
- LFLex Fridman
Mm-hmm.
- LSLee Smolin
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 Tortion, in which he discovered there was z- an... 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 the theory is not gonna work because there's gonna be loads of solutions for every proposed phenomenology for anything the experiments discover. Now it hasn't quite worked out that way, but nonetheless he, he took that worry to me. He, he... we spoke, uh, at least once, maybe two or three times about that, and I got seriously worried about that.And this is a little.
- LFLex Fridman
It sounds like an anecdote that inspired your worry about string theory in general?
- LSLee 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 Lynn Margulis and Steve Gould and so forth. And I could, I could take your time to go through the things that occurred to me, maybe physics was like evolutionary biology.
- LFLex Fridman
(laughs)
- LSLee Smolin
And maybe if the laws evolved and there was... So biologists talk about a landscape, a fitness landscape, of DNA sequences or proto- protein sequ- 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 pa- parameters of the standard model. And I'm happy to discu- it's called cosmological natural selection.
- LFLex Fridman
Cosmological natural selection?
- LSLee Smolin
Yeah, and I pub-
- LFLex Fridman
So, so the parameters of the standard model, so it's the, 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?
- LSLee Smolin
Yes. And I published that, uh, I wrote the paper in '88 or '89 and 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. 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 '80s and early '90s.
- LFLex Fridman
That's a really compelling notion, but how does that help you arrive-
- LSLee Smolin
I'm coming to where, where the book came from.
- LFLex Fridman
Yes.
- LSLee Smolin
So what got, what got me... I worked on string theory. I also 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, one, in 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 are two communities, one devoted to strings and one devoted to loops, is nuts and has always been nuts.
- LFLex Fridman
(laughs) Okay, so...
- LSLee Smolin
So anyway-
Episode duration: 1:09:51
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