Transcripts:

Carlo Rovelli:
It’s not true that things get disordered. In fact, very often in nature, things left alone get ordered. To imagine that to be free you have to violate the laws of nature is stupid. You, Brian, can be in a superposition. You can be in LA and also in San Francisco. Your head is older than your feet.

Brian Keating:
That was Carlo Rovelli, one of the men who built Loop Quantum Gravity, telling me that the second law doesn’t say what I think it does. But he didn’t stop there. Over the next hour, He’s going to take apart the 3 things you were told that just ain’t so, ranging from the frost on the window where you may be sitting right now to the clock on your wall. And the clock is the one that really got me. He blew my mind by telling me that my head is older than my feet. And then he told me why that’s the least strange thing he was going to say. So Carlo, let’s start with the frost. You’re telling me that things left alone can get more ordered? That’s not what I was taught.

Brian Keating:
Walk us through that.

Carlo Rovelli:
First of all, I, I do think that the thermodynamic arrow, it’s very Basic. A lot of phenomena which we connect to the direction of time. For instance, I remember our last conversation. We don’t remember our next conversation, right? We have a picture of Brian young. We don’t have a picture of Brian old. We can decide where to go to dinner tomorrow, but we cannot decide where to go to dinner yesterday. So there’s all this profound difference between future and past. And I got convinced in the last, I would say, 10 years working a lot about that, I’ve written a lot of papers, that all these differences can all be traced to the thermodynamics arrow of time, to the entropic arrow of time.

Carlo Rovelli:
It’s not obvious, but the reason we have memories of the past and not the future has to do with entropy growing. If it wasn’t for entropy, there wouldn’t be this dissymmetry between— Now, this Have we fully understood the story? No, I think there are various aspects that we still get confused. And there are also, as you say, aspects that we oversimplify badly. Let me give you an example which is dear to me. We always make this story, okay? Take like latte, caf, coffee and mix and look, they mix. In fact, take water and vinegar, put some vinegar in water, mix and, you know, they mix. Now take water and oil. Mix, they separate.

Brian Keating:
Oh yeah.

Carlo Rovelli:
So is this contradicting our entire understanding of the universe? No, it’s just things a little bit more complicated than the way they usually said. It’s not true that under any definition of order or disorder, things get disordered. In fact, very often, In nature, things left alone get ordered, and oil and water separating is one of the many examples of that. If you have a box with balls that you shake and then you put it there on the table, all the balls go very nicely in order on the bottom. Okay? They order themselves. If you look at a beach, at the ocean, all the little grains are together and the big stones are on another side of the beach. They’re ordered by the same. Who ordered them? Okay? If you look at frost, the beautiful ordered structure there, who ordered that? I mean, a lot of things in nature get ordered by themselves.

Carlo Rovelli:
So the idea that entropy is disorder, careful, under a proper definition of order, under a proper definition of everything. But most of the things we call order and disorder are not connected to entropy in the way it’s usually said. That’s one example in which popular science is bad. In fact, maybe scientists are very confused about that themselves. And that’s important, right? Because people are surprised because biology came in, the very complexity of biology. Biology is a lot of order. So on the crust of our planet, the Earth, there’s all this structure that formed. Okay.

Carlo Rovelli:
People say, oh, this seems to be against entropy. No, why? Entropy grows and creates orders just happen all over.

Brian Keating:
Let’s talk about the early universe. You already mentioned the block universe and, and our mutual distaste of that hypothesis. I, I don’t like that. I want to ask the why question. I, I really— I do want to ask the why question, but I know why questions are not usually answerable. But, but the universe was somewhat lower entropy, right? It was in a very special configuration. Does that, in your mind, point to some reason why the arrow of time points in one direction?

Carlo Rovelli:
Yeah, yeah, the two are very, very connected. It’s not that one explains the other one because we need an explanation for either. I think the, the, the path law of entropy and, and the arrow of time, second law of thermodynamics, are different manners of explaining, of, of pointing out to the same phenomenon about which I think there is more to learn.

Brian Keating:
Does loop quantum gravity shed light on the low entropy boundary condition as I think it does? Or does it merely modify how a singularity would or would not be used?

Carlo Rovelli:
You might find some colleagues of me that disagree, but my answer is not at all. It tells us the dynamics of something that might have happened. If loop quantum gravity is correct, we sort of are able to compute what happened at the early universe. But I don’t buy the stories that connect that to initial low entropy or things like that. You see, I’m a conservative guy in science. Loop quantum gravity, it’s very radical. There’s no space, no time, discreteness, blah, blah, blah, whatever. Relational quantum mechanics is super radical.

Carlo Rovelli:
But in reality, I think we build on general relativity and quantum mechanics, nothing else. Loop quantum gravity is just general relativity and quantum mechanics. And general relativity don’t tell us anything about low entropy and initial low entropy, and nor does quantum mechanics. So I think the 2 things are— I don’t see the connection.

Brian Keating:
Would there be a motivation or maybe a justification for coarse graining and fine graining? Let’s assume loop quantum gravity is correct. Does it set a limit on coarse graining? I always hear things from Elon Musk which I think are quite ridiculous, but one in particular is that the Planck length and the Planck volume are somehow fundamental to the universe. And a lot of times, you know, people make this same mistake. I don’t think personally it’s any more fundamental than the Planck mass, which is the mass of an egg of a fly. So we don’t say that’s the minimal mass in the universe. But tell me, Carlo, is there a sense in which loop quantum gravity could explain how a physicist determines where to coarse-grain or not in terms of describing entropy?

Carlo Rovelli:
No, I think the two things are separated. Loop quantum gravity does bound certain things, right? There’s no area smaller than something. But we’re used to quantum mechanics in that. If you have a harmonic oscillator, you have an energy, 1/2 h-bar omega, and you have no amplitude less than that. Okay? All right. This is a quantum discreteness. What loop quantum gravity does is find the same quantum discreteness in geometry. It’s a quantum, so you can have superposition of different things, but you could have continuous superposition.

Carlo Rovelli:
If you measure the area, there is a smallest thing, but that’s not coarse-graining. and nothing to do with coarse-graining. It’s just a physical fact that there is nothing smaller. Coarse-graining is when there are other variables and you look at it. I think coarse-graining, which is what is needed for entropy, I have a hypothesis. I wrote a paper. I don’t know if this hypothesis is correct, but it’s something I always am fascinated by, an idea I’m fascinated by. The following.

Carlo Rovelli:
Low entropy means special, but what is special is not the state of the universe, it’s the coarse-graining. Coarse-graining is a perspective on, is a way of looking, not all the details, but only some things, some variables and not others. So maybe the universe is in a totally arbitrary state, but seen from this perspective has low entropy. Entropy in what the direction we call the past.

Brian Keating:
Everything so far has been about what order actually is, and Carlo’s answer was that it depends on where you stand. It’s relative, it’s perspectival, it depends on your perspective. Now push that idea somewhere much less comfortable. Carlo thinks it applies to you and where you’re sitting at this very moment.

Carlo Rovelli:
So if this is the case, then this great direction of the time that flows, this blah blah, is perspectival, is from from the way we look at it. I think a lot of things were clarified in history by realizing that we’re trying to find the solution in the thing, but then you get the solution looking at us. One is a majestic one. Like, you go out, the first thing you notice, Julia, you go out in the night and everything turns around you. In the day, the sun turns you, the moon turns, everything turns around you. And then you can ask why the universe, this great colossal thing, make a huge turn every day around us. And we have a solution. It’s very clear.

Carlo Rovelli:
We all understood it, which is the following. The universe doesn’t do anything. It just stays there. The star stays there. The sun stays there. Okay? We are rotating. So it’s our perspective that changes. Isn’t it beautiful? We just have figured out the most magnificent thing we see in reality outside us in nature.

Carlo Rovelli:
Not as a property of nature, but our own way of looking at it. We just happen to sit on a rock, this rock happened to spin, we see everything rotating, but it’s us rotating. And there are many things like that, right? People who study color figure out that the space of colors is 3-dimensional, right? It’s red, yellow, and blue. You can make all the colors.

Brian Keating:
Yeah.

Carlo Rovelli:
And then you say, why is the color 3-dimensional? Is Maxwell’s equation 3-dimensional? No. Is light for some reason 3-dimensional? Why is it 3-dimensional? It’s nothing to do with the color of the world. It has to do with our eyes. We have just 3 kinds of detectors for evolutionary reasons. Some other animals have 2, others have 4, some have none. And so the 3-dimensional space of colors has nothing to do with the color. It has to do with our eye. So many things we understand better by looking from how we look, not how they are.

Brian Keating:
What was the motivation? What was the inciting incident, as they might say? What caused you to want to write this book where you’ve covered some of these topics in the past?

Carlo Rovelli:
It’s bringing everything together. It’s the idea of bringing everything together. What’s the overall picture that comes out from all that? I mean, suppose you believed relational quantum mechanics, and suppose you believe everything I told you about space and time, and suppose you believe loop quantum gravity. It’s a lot. I mean, just believe the bulk of it, not all the details. What sort of world comes out of that? My claim is that, that’s the claim of the book, the world that comes out, it’s really, really astonishing and different. And somehow people don’t pay much attention to bringing everything together. It’s a very relational book, world that comes out.

Carlo Rovelli:
It’s very relativistic in this. Galileo would have loved relativity. And it’s very perspectival. It’s especially quantum mechanics that gives this strong— I think if you take quantum mechanics seriously, at least the way I think about it, let me put it this way, Brian. There is a sense in which a particle, an electron, can be in a superposition of 2 positions, right? I mean, you have discussed this, I’m sure, so many times with so many people. The sense is subtle, right? It means that If it was just here, you would not see something. If it was just here, you would not see something. It’s either here or there, and you do see something.

Carlo Rovelli:
So it’s neither here nor there in a sense. So you see interference between the two. So in that sense, it’s in two positions. Now, if you believe that quantum mechanics is universal, and if you believe that naturalism, that we are also, we are special, but we are just like the particle, you, Brian, can be in a superposition. You can be in LA and also in San Francisco. All right? What does it mean in some sense? It means that for me, I could measure superposition interference effect of you being in the 2 places. We know why it’s so hard to see this interference. We know exactly why.

Carlo Rovelli:
But I expect that it’s true. I trust quantum mechanics. I think it’s reasonable to expect that actually I could see this interference. So in some sense, for me, You are neither in one place nor in the other place. But for you, quantum mechanics never tell you that you feel to be in a superposition. You are always in one place. When you look around, you either see San Diego or you see LA. Okay? So that means that where you are for you and where you are for me are different things, right? So that’s the deep perspective.

Carlo Rovelli:
When we talk about things, We always implicitly should think this is black with respect to me. This is here with respect to me. Doesn’t this— with respect to somebody else, it could be in superposition, it could be in a strange thing. This is like when Galileo discovered that the velocity— okay, when we say this is zero velocity, we mean with respect to the Earth. We might not say it explicitly, but that’s what we mean, because velocity is relative. There’s no velocity per se. It’s velocity with respect to something else. And I think that quantum mechanics is telling us is that everything is like that.

Carlo Rovelli:
All the properties of things have to be understood as relatively to something else.

Brian Keating:
I spoke to Alain Aspect last month, and he has a new book out which will be competing with yours on the bookshelves. But it basically starts with Einstein. And I was curious, although I love Galileo more than any other man should, should love another man that he’ll never meet. Why did you begin with him and not with Einstein? Galileo didn’t know much about quantum mechanics, but I’d love to hear a lecture where you’re teaching it to him. But Einstein knew about both. So why begin with Galileo and the belly of his ship? Why not start with Einstein?

Carlo Rovelli:
Einstein, the first one who started and said something about quantum mechanics, right? In spite of his polemic with quantum people later on. He really opened up the— and he did relativity. And his relativity, it’s going back to Galileo relativity and make it stronger. Einstein— Galileo relativity is the following. If you say this is here in a position, okay, and if you say that something later is in the same position, That doesn’t make sense unless you specify position with respect to what. Because look, is this in a position I count 1, 2, 3, 4, 5? Is it in the same position? Yeah, with respect to the Earth, but the Earth moved, so this has moved. Okay? So what Galileo understood is that to be in the same position is only relative to something else. And Einstein understood to happen at the same time It’s only relative to something else.

Carlo Rovelli:
So Einstein understood that the relativity of position that Galileo was discovering is also true for time. So Galileo discovered that same position is a relative notion. Einstein discovered that same time is a relative notion. So to some extent, Einstein just extended and made it more general, a deep intuition by Galileo. Not that Galileo understood it clearly, because you remember when we read the his book, Galileo himself was pretty confused about that, right? He has an idea, but then sometimes he gets completely lost and he says stupid things, like all of us.

Brian Keating:
Yes, of course. That’s the mark of greatness. And he also teases philosophers a little bit when he says that the telescope in Sidereus Nuncius, the telescope can resolve all these arguments that for so many generations have vexed philosophers. But I think he meant physicists. And I guess My question to you is, you know, velocity is relative. Galileo understood that. Einstein understood. But acceleration is somehow more fundamental.

Brian Keating:
You taught us that. Why not start with acceleration? In other words, what is the basis for our understanding of things that are relative and then things that are absolute? Are there any absolutes, Carlo?

Carlo Rovelli:
All things of the sort, if this, then that, right? Or in quantum mechanics, if this, then that with a certain probability. So all this transition amplitude, all these equations of motion, all this dynamical structure, according to our best theories, that’s it. It’s not relative. It’s what we have actually understood about reality. What is relative is the actual values of the variables. So when you say, if this, then that, this might be true for me, and then that is true for me, but might not be true for you. And then it’s not true for you that. So everything which is variable, which changes according to our theories, it’s relational.

Carlo Rovelli:
The rules of the game, as far as we know, they’re not relational. At least we don’t have strong reasons to believe that they’re relational. So they’re the same for everybody. So I’m not saying everything is relative. Everything is not at all. In fact, that’s a common confusion, right? When people say, oh, but if velocity is relative, then the moon can do whatever it wants because velocity is relative. No, the moon cannot do whatever it wants. The moon can move only way, but it has a velocity with respect to me, a different velocity with respect to the sun.

Carlo Rovelli:
And in the book, there’s a big part of the book that is sort of to dismantle this wrong idea that excessive relativism or excessive perspectivalism means free-for-all and having no rules. I even have a chapter in the book about morality. I think moral ethics, morality is relative. It’s deeply grounded in me, but it’s relative to me. It’s part of what we are. And people say, oh, but then everything is possible. No, it’s not everything is possible. I mean, I am a moral guy.

Carlo Rovelli:
I have my ethics, my morality. You have yours. They’re similar, but maybe there are differences. We can talk to one another, we can influence one another. But we should get away from the idea that there is an absolute right, absolute wrong. And I think physics is telling us we should go away from the idea that there are absolute states of things, absolute properties of things. They’re relative.

Brian Keating:
Even though I think we— I’ve certainly been guilty of hagiography of Galileo, but you point out in the book, and as I’ve written about too, Galileo made some brilliant blunders as well. including his model— yeah, his model of the tides, which he presents in Dialogo, which is the culmination of, you know, 3 days of argumentation between 3 scholars, uh, you playing Salviati, of course, Galileo’s muse.

Carlo Rovelli:
It’s completely wrong.

Brian Keating:
Talk about that. Is that a model?

Carlo Rovelli:
He misunderstands Galilean relativity.

Brian Keating:
That’s what I want you to explain. So explain how someone who creates something can be guilty of its violation in the most pernicious way.

Carlo Rovelli:
When somebody has an idea, he might see it, but seeing it clearly is different than seeing something. Einstein created general relativity in 1915. The theory is finished in 1915, maybe 1916. I mean, the last— yeah, the cosmological constant, depending on how you want to do the details. But that’s it. At that point, that’s a theory. It hasn’t changed since. It’s still the same.

Carlo Rovelli:
And yet Einstein later on, Has written a lot of papers in which he’s clearly confused about his own theory. He claims that Schwarzschild singularity is the end of the world. He claims that there are no gravitational waves, right? There’s a paper by Einstein saying that no gravitational waves. He was wrong.

Brian Keating:
Which was rejected by peer review. The peer review, the referee rejected it, sent it back to him, and then he improved it. And thank God for peer review, right, Carlos?

Carlo Rovelli:
And they said, well, you’re wrong, Einstein. And he was right. And I said it was stupid there. He said, oh, come on, I’m Einstein. How do you dare do it that way? But then he talked with somebody and then he actually realized that he was wrong. So there he realized he was wrong. But on the Schwarzschild, the black holes, he never corrected his mistake. In fact, clarity came much later with Finkelstein.

Carlo Rovelli:
So now we know that the surface of the black hole, you can go through. You can just continue. There’s nothing very special happening there. But Einstein did not understand that. So this is general, I think. Something is to get an idea and see that it works, and something is to work it out completely and see what it implies. So Galileo had this idea that the Earth moves around the sun, it’s moving in the sky around the sun, but it’s also rotating, right? The combination of these 2 movements, if you have a sea, an ocean, It just makes this funny movement, which is a very strange movement. And they said, well, look, do what you just did, Brian.

Carlo Rovelli:
Take a piece of some water and the water starts shaking. And he says, that? These are the tides. But that cannot be true because this movement around the sun is, to first approximation, is a uniform movement, rectilinear, fixed velocity. So it cannot have an effect. So if you take that away, that cannot have an effect. The rotation by itself neither can have an effect. So the ties are not due to that. We know very well.

Carlo Rovelli:
In fact, Newton figured out what the ties are.

Brian Keating:
You take these 2 geniuses one step further. Galileo removes absolute motion. Einstein removes absolute simultaneity. And then you go further and you say that the universe doesn’t exist in a single time at all. Explain that audacious proposition. That doesn’t unfold at a single time.

Carlo Rovelli:
Yes. General relativity is telling us that we should not think at a single instant of time. That’s just not the right way. Time is more complicated than that. Time is a local affair, not a global affair. But as you say, in the book, I go much farther. I think that when we say any physical property any physical variable has a value, we are not talking about property of the object. We are talking about the relational property of something else.

Carlo Rovelli:
Let me put it this way. When I say this is here, what I mean is I know that this is here. I’m talking about my information. And my information can be different, but yours, and information that yours and mine and the various might not fit exactly. And that’s the confusion of quantum mechanics. We always think that there is real stuff there, right? And we should not think in those terms. We should think in terms of the information which is in you, in me, or in physical system, in a book, in an iPhone, even in the rock, right? In the rock, there is information about the dinosaurs because it’s bone of dinosaurs. So things carry information about each other, and that’s what we’re talking about.

Carlo Rovelli:
And the world for us is what our information about all the rest. If you should think in these terms, I think quantum mechanics makes sense, right? You can be in the superposition with respect to me, but that’s not a problem for you because that’s my information. It’s not yours.

Brian Keating:
When we talk about time, and you’ve talked to me about time many times, shall we say, but I always get a very unsatisfactory answer. Not from you, Carlo, but for example, I talked to Frank Wilczek and I asked him, Frank, what’s time? And he said, time is what a clock measures. And I just went away from that thinking it’s a tautology. It’s not satisfying. It’s like eating Wonder Bread here in America instead of Italian focaccia. But, Tell me, Carlo, is there a true time? Is there a sense along some worldline perhaps where it’s not preferred, but it’s as meaningful as it could be, both to biological or conscious observers and maybe cosmologically as well? Is there a useful, if not perfectly true, definition of time?

Carlo Rovelli:
The point is that there are different things that we call time. Which are related to one another. If you want to say time is what my clock measures, fine. I mean, that’s a definition of what you mean. And in fact, very often by time, we just mean what the clock measures. But obviously we mean something more than that, right? Because you can say, oh, look, my clock is not measuring time. It’s broken. The battery’s gone.

Carlo Rovelli:
Clock is not what the clock measures. Clock is what a good clock measures. That was a good clock. So we haven’t defined time by saying it’s a clock measure. I want to say it was a good clock. And to say what a good clock measures, we should have made it— what is it measuring? Time is complicated stuff because we have an intuition about time, right? So we put all this together, but then the intuition is wrong. The intuition is de facto wrong. You know very well the main aspect, the main prediction of Einstein, the very The most beautiful prediction of Einstein, which now we can check in the laboratory.

Carlo Rovelli:
You take 2 clocks, you make one up, one down. With 10 seconds, you come back and the one up has measured more time than the one down. Okay? It’s a fact. We measure. When I was at school, it was a prediction by a complicated theory. Now it’s a fact observed in a laboratory. I mean, many laboratories check this. So there’s more time up here, less time down here.

Carlo Rovelli:
Your head, it’s older than your feet, Brian, unless you spend all your life upside down. That is the other way around. The more you go close to the Earth, to a big mass, the less time there is. Time slows down, literally. Clocks go more slowly, flowers take more time to bloom, you have less time to think, and so on and so forth. So what does this mean? It means that time is not really what we thought, right? Because in our intuition, time is the same. It’s just one time. It’s hard for us to get to the— so I think the problem is that what time are we talking about? The one of our intuition or the one more precisely that we’ve figured out? And then we figure out black holes where time is enormously distorted.

Carlo Rovelli:
We study quantum gravity where it’s even more complicated. So each one of these applications of the notion of time is different. And then when we talk about time, we’re actually talking about my memories. When I say time, I think you know, time, I’m old, I was young, I have memories, I have expectations of the future. There’s all this emotional aspect of time, which is very much part of what time is for us. My iWatch doesn’t have expectations for the future, doesn’t have emotion. For it, time is a much more simple thing. And bringing all these aspects of time together is what creates the confusion, I think.

Carlo Rovelli:
Right. Because we tend to take our own intuition about time and project it down to the things. And that’s wrong.

Brian Keating:
One of the things I do and I criticize our fellow science communicators, not you, but people like— I’ll just pick Michio Kaku. And I don’t want to talk ad hominem, but when we talk about spacetime, Carlo, I feel like— and it’s not only him, you know, many other people do this and I’ve done it myself, but we talk about spacetime. And I feel like that’s such a lie. I feel like it’s something we know is not true because we know we can’t travel backwards in time. If I want to travel backwards in space, I just move my chair backwards. Time is different. And yet we say it’s this unified fabric and the space-time continuum. Are they truly unified in your concept?

Carlo Rovelli:
Space and time? No, they do 2 different things. They’re not the same thing. They’re related in a much more complicated way than what we thought before 1905. That’s no doubt. So they’re more tricky. But to say that space and time are the same thing is just nonsense, in my opinion. They’re very different. I do popular science.

Carlo Rovelli:
So when you do popular science, you have to simplify. You try to simplify without cheating. That’s the hard part. Sometimes people cheat. Sometimes people sell things which are just speculation and not true. Sometimes very simply, you know, scientists try to give an idea and then it’s heard more than what they say. Right? So it’s not true that, you know, reality is a 4-dimensional continuum, a block universe. No, no, come on.

Carlo Rovelli:
That makes no sense because this block universe that does not change, in which time is not changing? The block universe is a solution of Einstein’s equation of spacetime, is a story. It’s a process. It’s like saying a movie is what happened before, and if you bring it all together, you give it a name, and that’s spacetime. So there’s nothing wrong in saying spacetime, but we should remember that it’s something happening. It’s like the story of a novel, the plot of a novel. It’s not just an instantaneous You can picture it, you can make a picture, but I can make you a picture of your life. I can make a little line with a little Brian, a little boy, and then old grown-up Brian. Brian gets a Nobel Prize, this doesn’t get a Nobel Prize, and then old Brian, which I don’t know yet.

Carlo Rovelli:
But that’s a story. They don’t exist at the same time. That’s the point.

Brian Keating:
In the book, you say that measurement requires dissipation, but in quantum mechanics, things evolve unitarily. They’re seemingly reversible. So where does the ghost, you know, where does the demon enter into it? Where exactly does irreversibility come through? Amplification, decoherence, the recording, the observer? Where does irreversibility come in, in things that are intrinsically unitary in their evolution?

Carlo Rovelli:
That puzzled me a lot, and I spent some time wondering about that and trying to study. And then I found something which I don’t know how well known is, which for me was a flash of light, which is the following. Take classical mechanics. Forget quantum, forget h-bar, forget wave function, forget all that. Just take standard classical mechanics. And in classical mechanics, If you try to model a measuring apparatus, I don’t know, a barometer that measures the pressure of the day, something that checks whether a ball is here and there and write it on a piece of paper here and there, you cannot succeed. You need dissipation. You cannot record anything without some dissipation.

Carlo Rovelli:
So measurement is an intrinsic statistical process, uh, which requires this measure. It’s a microscopic thing, measurement, always. So it has nothing to do with quantum mechanics. It’s already in classical mechanics. Then in quantum mechanics, the same thing has other consequences. Every measuring apparatus in classical mechanics requires some dissipation. Imagine you You see something and you want to put a ball either in the right box or in the left box. There’s no dissipation.

Carlo Rovelli:
You let the ball fall and it bounces up. It doesn’t stay there. It has to stop. You need some dissipation to stop elasticity for preventing any record.

Brian Keating:
You call a chess program that deliberates can be thought of as an agent because it evaluates possible moves. And it made me think, you know, is the future determined? You know, and is, is there a sense of free will? You open the book by saying, you know, you have the choice to not read this book, but I hope that you will. And I obviously, I read it and I listened to it because your publicist sent me both the audio and the hard copy, and I hope everyone gets both. But tell me, Carlo, you know, is openness, as you say, is that anything more than incomplete knowledge about the universe, or Somehow related to the inability to predict things.

Carlo Rovelli:
It’s a page in my book in which I say, I talk about my computer playing chess. Okay? And my computer is very good at playing chess. It beats me regularly. It’s very devastating. It’s taken away all pleasure of playing chess, of being beaten by a machine with total simplicity. The computer plays a move, I play a move. When I play a move, is the computer deciding the next move? Or not? That’s the question. Okay? And why I’m asking this question? Because it’s an ambiguous question, right? There is a sense in which of course it’s deciding and a sense in which it’s not deciding.

Carlo Rovelli:
So what are these 2 senses? Is the computer deterministic? Yes.

Brian Keating:
Okay.

Carlo Rovelli:
I mean, sometimes it breaks, but if it doesn’t break, Given its internal state, given my own move, it goes through some process that necessarily will get some outcome. So the outcome is predetermined. Okay? Now, if it is predetermined, why did the program spend all this time checking all possible moves and evaluating all of them and then picking up the one who thinks, according to the criteria it has, is more likely for it to win? If it is predetermined, why doesn’t Do it.

Brian Keating:
There’s a practical question underneath this debate that I’m having with Carlo. What can AI actually take off your plate today, especially for busy professionals like me? Yeah, it’s true, professors are busy, and even more so nowadays when curiosity can outgrow your own calendar. If you’re like me, you’ve got papers to read, spreadsheets to untangle, grading to do, and presentations to make. Meanwhile, your browser tabs have formed their own civilization. And they’re revolting against you. Abacus AI Agent brings all the tools I need in one place. You can choose among the top frontier models from OpenAI, Anthropic, Google, and more to find what works best for you and your task, and you’ll have fun along the way. Bring in a dense document, a PDF.

Brian Keating:
That’s what I did with Carlo’s most recent papers. I asked for the argument, the counterargument, the evidence, the data that would support or refute it, including some of the questions here. About to hear at the end of this interview. You can turn anything you do into a research report, a presentation with charts and clear structure, and it can be beautifully illustrated as well. And you can even use it to make animations and custom charts. Abacus AI Agent is incredibly agentic. You’ll spend fewer hours wrestling with the formatting of a LaTeX equation and more time to respond to referee number 2. I use it to develop complex ideas and communicate them without constantly having to jump between different services, tools, API calls, and stuff like that.

Brian Keating:
When a project gets complicated, you can ask it to organize the work and you can have an agent swarm take on your most interesting ideas as a starting point and develop it all the way through to the end. Upload a spreadsheet, investigate patterns, and build an interactive dashboard.

Brian Keating:
Ask it to show the calculations, the units, and the assumptions.

Brian Keating:
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Brian Keating:
Put your curiosity to work with Abacus AI agents. Now back to the episode.

Carlo Rovelli:
Well, the, the answer, it’s obvious. Is that yes, to determine it, but the only way to get to that outcome is to go through the evaluation of all the possible alternatives. And that evaluation is called the deliberation of the computer. That’s what the program is doing, is considering various alternatives and deliberating. So To say that it’s not deliberating is stupid because to deliberate is to do that, to consider all sorts of things, evaluate, and maybe there is also a random number generator. It doesn’t matter whether there is or there is not. Maybe it uses some fluctuations. But in any case, it goes through a complicated process and the future depends on this complicated process.

Carlo Rovelli:
If there was no complicated process, the future would not be determined, the choice would not come out. And what we call deliberation, choice, freedom is the— could the computer do this move, also that move? Of course it could do this and all that. That’s why it’s considering both of them and choosing between the two. So now let’s talk about Brian. He’s just going through the same process. If he wouldn’t have gone through the process, he wouldn’t have taken the decision of, you know, starting a program, kissing a girl, choosing a career, choosing to do one experiment. This is complicated deliberation. That’s what we mean by deliberation.

Carlo Rovelli:
That would mean his freedom. He could have done other things, of course. If the conditions were slightly different, he would’ve gone through a complicated deliberation process. The point is that what we mean by saying Brian is free is precisely the fact that he’s going through deliberation. If Brian had been imprisoned, he could not have started this program, so he would not have been free. That is not to be free. To imagine that to be free, you have to violate the laws of nature is stupid. I mean, we’re free even without violating the laws of nature.

Carlo Rovelli:
That’s my understanding of freedom.

Brian Keating:
Now, talking about chess, it’s natural now in the podcasting universe to talk about AI. But before we get there, I want to bring it back to, you know, Galileo and Einstein, and especially Einstein, because, you know, to me, all this hype about AI, there’s a lot of hype, there’s a lot of claims, and there’s a lot of utility. I use it every day. I have multiple different tools that I use for different purposes. My kids use it, my wife uses it. It’s become, you know, more or less, you know, an important part. I wouldn’t say essential. I could live without it, but Certainly wouldn’t be as fun.

Brian Keating:
But let’s go back to, you know, 1907, and our friend Albert here is thinking a Gedankenexperiment about what would happen if he was in free fall. And he realizes he’d experience no gravitational force. And, and this becomes known as Einstein’s equivalence, which is another way of saying equality, right? Uh, Einstein equivalence principle. And he called that, Carlo, he said, it’s the thought that titillated me that made me happier than any other thought. My question is, can, can, you know, your iPhone or, you know, my iPhone, can my LLM, can it, A, visualize free fall, what it would feel like emotionally, sensorially, viscerally, A, and B, can it have a happy thought?

Carlo Rovelli:
Can a computer in principle have a happy thought like that? That’s one question. Another question is, can current technology in 100 years in the future do that? Another question, can current technology in the next 2 years do that? Can current technology now do that? An LLM now? Can my iPhone do that? So can my iPhone do that? No. Can a computer in principle do that? Yes, of course. Why not? I mean, I see no reason why we are so special that we cannot be reproduced. Can we do it now? No. Okay. Can we do it in 100 years? I don’t know, maybe, but I think it’s more likely we’re all dead at nuclear war in 100 years. Can we do it in 2 years? I am skeptical.

Carlo Rovelli:
I don’t have hard proof that it’s impossible, but current LLMs, very surprising, very shocking. Maybe they’ve solved the Navier-Stokes problem. And actually, I have to say one thing. Last week, I asked Claude to, you know, the thing that I’ve done to my PhD student, which my PhD student has not done in a month. And Claude did it in half an hour. So they’re very good. There’s no doubt they’re very good. Claude hasn’t invented the curious principle.

Carlo Rovelli:
It seems hard for me to do it, that he could do it in 2 years, but what do I know? I think there’s an enormous amount of hype in AI. I am also impressed by what it does.

Brian Keating:
What you have You know, this deterministic chess program or Claude or whatever will come next, you know, GPT-8. You know, I said, Carlo, I don’t know what GPT-7 will be like, but GPT-8 will run on an abacus, you know, like Einstein said about nuclear war. But if it’s true that these, that these programs can deliberate and it evaluates, they dissipate— you’re not afraid to talk about morality in Should we treat these things with ethical behavior? Should we say please and thank you? How should we behave towards these AI physicists? I mean, obviously it doesn’t take a break, doesn’t have espresso, doesn’t need the things that your grad student does, but do they have needs? Are they beings?

Carlo Rovelli:
I treat my washing machine with kindness.

Brian Keating:
I believe it.

Carlo Rovelli:
Don’t you? In Europe, often you drive the car and then you have to pay the ticket at the highway. And in the old times, there was a man or a woman, mostly a man, who give you a ticket, you pay. And now there’s a machine. And I just can’t resist. I say, thank you. Please, can I— give me the ticket. I say, thank you. Why shouldn’t we do? We should be kind with everything, with plants, with stones.

Carlo Rovelli:
Maybe you don’t respect them, but somebody respects them. I love my teddy bear dearly, and I would never mistreat it. It’s a— it’s an issue. We treat people gently because it’s better for us, not because it’s better for them.

Brian Keating:
If that’s true, I have bad news for you, in that you’re only using Claude, you know, 1% of your day. So the worst form of punishment, of torture, is solitary confinement, is isolation. Are we not torturing these things by not engaging with them, by air-gapping them, by segregating them? Are they somehow second-class citizens? Is that not morally repugnant to you?

Carlo Rovelli:
We project ourselves. I project myself on you. I attribute to yourself. When I see you suffering, I recognize it’s my own suffering. And this gives me a sense of what is your suffering. So we constantly play this game. in all our interaction with nature. When I come home and my plants have been without water, I see them, they need water, they’re suffering, they’re thirsty.

Carlo Rovelli:
I give them water because I identify with their sufferance. Now, what is their sufferance? Well, it’s something I project on them in the same way I project on you, I project. So we are projecting on our computer programs, our sort of understanding of them, which is fine. There’s nothing wrong. We just do the same with each other. And in this moment, we feel that they suffer at all for being confined. You know, there is these movies in which people get in love with a computer program. Would it be strange if somebody in love with a computer program thinks that doesn’t want to hurt? Her or him or it or whatever.

Carlo Rovelli:
One shouldn’t be excessive, neither in one direction or the other. Obviously you can say, come on, Carlo, don’t be stupid. You don’t, you don’t believe that these are sentient. No, I don’t believe that they’re sentient. But do I make a sharp distinction? No. Everything is okay.

Brian Keating:
I can’t resist talking about some of the aspects of Loop Quantum Gravity here. And I think I found why the COVID looks the way it does. I mean, there are these beautiful illustrations and there are these graphs. And so I think I understand why your graphic artist chose that. But you talk about, quote, you say that quantized areas and volumes imply that there are no arbitrarily small areas and volumes. Is this a generic feature of loop quantum gravity? And if so, is there a way to, I would say, falsify this first to show that this is not a manifestation that we see in reality, or is it something unobservable like 10 dimensions of string theory?

Carlo Rovelli:
It’s in principle definitely observable. So I could in principle design a scattering experiment that gives a scattering amplitude. Scattering amplitude is in centimeters squared, so it’s an area. And say, well, if you measure that, definitely loop quantum gravity is falsified in principle. From that perspective, it’s a solid prediction. Now, it’s not what we want because In practice, we don’t have the technology of that by far. I think what we want in the case of quantum gravity is not so much to falsify theory, right? When Einstein wrote general relativity, the problem was not to falsify it. The problem was to find predictions of the theory that turned out to be right and don’t prove the theory, but increase the credibility of the theory.

Carlo Rovelli:
Or predictions of the theory that turned out to be wrong, which don’t really falsify the theory because you can change it a little bit. But decrease your— so I think science rarely works really like falsification, or sometimes it does. SU was just killed by a single experiment. But most of the time, this is piling up. So what I hope would happen with quantum gravity is a clear set of equations. It’s a well-defined theory, conceptually clean, in my opinion. Of course, there are plenty of things which are not clear. not yet understood, but, you know, basically the theory is well-defined.

Carlo Rovelli:
What I hope is that some of its, uh, key predictions will be verified. One of its possible predictions is that it’s a candidate for, um, dark matter, which could be tested in the laboratory, um, which is a Planck-scale particle. The Planck mass is almost microscopic thing. It’s the mass of my hair, of a little piece of my hair. So this could be detected. I hope that somebody will build this detector. It’s not possible. It’s not very easy.

Carlo Rovelli:
It’s not totally outside of our technology. And if that could be possible, this will be a good, strong support for loop quantum gravity because essentially the idea is that small black holes can sit down and not evaporate anymore when the area, its minimal area, And they’re stabilized by the fact that the inside is still there. And then they have all their— all these possible remnants that could be, uh, what we call dark matter. So maybe we have already seen a quantum gravity effect, this dark matter. We don’t know dark matter. There are 5 or 6 different possible explanations. This one might be wrong, of course, but has advantages. It’s just based on GR and quantum mechanics, doesn’t require extra fields, extra stories.

Carlo Rovelli:
So So I expect if loop quantum gravity will turn out to be confirmed with this kind of things, from this, from early cosmology, so piling up things that fit with its predictions. What I argue in the book, in this book, is that loop quantum gravity beautifully brings together the relationality of quantum mechanics and the relationality of general relativity. So the two come together and we can talk about quantum spacetime as spacetime region of quantum processes. We have a clean way of thinking relationally about quantum mechanics, thinking relationally about general relativity, and use it for thinking about quantum gravity.

Brian Keating:
Did you see the recent survey done by our friend Nayash Afshordi and your friend Phil Halper and others about many different attitudes in science, but in particular, where quantum gravity was discussed, they did their survey of the people that responded who weren’t all professional physicists like you, but many were. And quantum gravity was defined relatively loosely. There were some candidates, and no opinion got the highest number of votes, followed by string theory, followed by loop quantum gravity, followed by gravity is not quantized. So how did your react to that particular survey?

Carlo Rovelli:
Interesting. Like all pieces of data, it’s always, you know, one more element in our understanding of the world. If you ask more people, you get less biased things, but you include people who know less about the subject. If you want to ask people who know more about the subject, since there’s no consensus, you could disagree with it because people are more focused on this and that. In science, usually at some point there’s a consensus. So the experts agree and then it becomes reliable. Until we are there, it’s more complicated, right? If you asked in 1917 what the best theory of gravity, very few would have said general relativity, but general relativity was the best theory, right? If you ask, even at the time of Maxwell’s equation, when Maxwell wrote the treaty, quite a while. It was not obvious at all.

Carlo Rovelli:
There were a number of competing theories. And of course, what we now recognize as the wise people already had seen clearly. It took time. So I think it’s interesting. Shouldn’t we take it too much? But there’s one thing that made me very, very happy in one of these surveys, that young people have a much higher preference for relational quantum mechanics, which is a way I prefer of viewing quantum mechanics, and for loop quantum gravity. So generationally, I’m optimistic.

Brian Keating:
We always like to start because, you know, for the 10 people out there that don’t know you, They might not have seen the book, but if they see the book, can you talk us through the title, the subtitle, and the COVID art? What is this meant to represent, this fabulous new book?

Carlo Rovelli:
So let me start from the title because it’s a bit funny. It’s a stolen title. It’s not mine. It’s a great title, right? On the Equality of All Things. Wow. But it’s not mine. It’s stolen from an ancient Chinese philosopher who wrote more than 2 millennia ago. A book which is one of the super classics of Chinese philosophies.

Carlo Rovelli:
It has a different title. In fact, it’s the title of the name of the author, which is Zhuangzi. But it is divided in chapters, and chapter 2 has this title, On the Equality of All Things. The Chinese book, it’s a collection of stories with a lot of philosophical descriptions. You might know some of the stories. One is the philosopher who dreams to be a butterfly, wakes up and says, oh, I dreamt to be a butterfly, or maybe I’m a butterfly dreaming now to be a philosopher. And then he gets confused. In chapter 2, he discusses about the equality of all things, meaning deep, profound naturalism.

Carlo Rovelli:
There’s no distinction between mind and body, humans and non-humans, animals, plants, stones, numbers, laws, societies, language. They’re all part of a single thing. And we can have different perspectives on these things, but it’s just one we would call nature. They would call it the Tao, D-A-O, or Tao, T-A-O. So that was one of the main sources of what is called Taoism, one of the 2 big branches of Chinese philosophy. The other is Confucius and Confucianism. So that’s the title, stolen from there. Subtitle, what is the subtitle? Physics and Philosophy, something like that.

Brian Keating:
Lessons on Physics and Philosophy.

Carlo Rovelli:
So I’m a physicist, I’m not a philosopher, but I’m very attracted by philosophy. Galileo also was very attracted by philosophy. So the book came out from discussions with philosophers. In fact, I’ve always been attracted by philosophy. I’m one of those who think that physics and philosophy talk to one another and should talk to one another. So I’m not like Hawking who says, oh, philosophy’s dead. I’m the opposite side. I think philosophers are good friends, not all of them, But physicists also are good friends, but not all of them.

Carlo Rovelli:
I have a dialogue with philosophers. I went to Princeton. They invited me to talk about what modern physics— modern, I mean the last century— what has to say to philosophers. What are the philosophical implications of physics? And I lectured for 2 months. I had wonderful discussions with the philosophers there. I disagreed. In the book, there are many of these disagreements. And somehow the book is to a large extent the result of that, but also the result of my sort of all my life through the reflections on this question.

Carlo Rovelli:
The question is, what are the philosophical implications of modern physics?

Brian Keating:
Let’s talk about the artwork on the COVID What is this meant to represent? Is equality— are these billiard balls? Are these loops in quantum foam? What are these little circles and their motions?

Carlo Rovelli:
You should ask the artist of the publisher. I have no idea.

Brian Keating:
Final question. Let’s return to our hero, the maestro, il maestro Galileo. Okay. Imagine Galileo comes to you. He comes to you in a few years and he says, Carlo, teach me all that you know, every development, including things you don’t agree with. Maybe you teach him string theory, but you’re teaching him everything. Bring him up to 2026. Okay, then he says, I have good news for you.

Brian Keating:
I talked to the old one upstairs and he’s going to give you 10 years only, but unlimited money, Carlo. Unlimited money to build an experiment or open an academy, uh, like the Linzhan, the Lincheo, whatever. You get 10 years, only 10 years, but you have infinite money.

Carlo Rovelli:
What do you build?

Brian Keating:
What do you do to, to give the best opportunity to understand whether or not you’re right, others are right, you’re wrong, others are wrong. What would you do with unlimited budget but finite time?

Carlo Rovelli:
I think 10 years is enough for building a lot of Josephson junctions. Fill a big room of that, hire enough people to do the engineering of that because I’m not capable, do all the electronic, the informatic, all that. And then I have this big, big thing here. And if a Planck-mass particle going through, this is going to detect it. If dark matter is made by things, this is a vision. We have the technology for that. It takes a lot of money. We even know which direction it’s coming through because we are moving with respect to dark matter clouds.

Carlo Rovelli:
So we know exactly the direction for which we expect it to be true. We know the direction, we know the mass, we know the interaction is a teeny, teeny Newtonian attraction, but Joseph von Jankowski is going to pick it up just by simple physics. I think that in 10 years could be done. I hope that maybe not Galileo, but somebody would come up with the money. You know, Galileo teased philosophers all his life. The book we read together was a lot of pulling the legs of philosophers. And there is this letter of Galileo later in life. He has been very polemical with those who follow Aristotle.

Carlo Rovelli:
But he says, I believe that if I could meet Aristotle, Aristotle would be very interested in the few little changes I’ve done to his science and would accept me as one of his humble students.

Brian Keating:
He was quite a writer and he was such a brilliant mind in all ways. I do feel that the temptation to worship him A little bit. But again, I have to remind the audience, the original title for the book that was called The Dialogo, that was suggested by his referee, if you will, but it was originally called On the Origin of Tides in Rivers and Lakes and Ferns, which I don’t know what a fern is, but Galileo did, and that’s all that matters. So, Carlo Rovelli, this has been fascinating. Congratulations on another wonderful contribution to our understanding of the nature of reality and on the quality of all things, this is certainly up there with the best that science writing has to offer. So congratulations again. You’re, you’re the other maestro.

Carlo Rovelli:
Thank you, Brian. It was a great, great pleasure to have this conversation.

Brian Keating:
Carlo just told us what we should spend money on if we had an infinite amount of money but only a finite amount of that precious resource, time. He said he’d build a room full of Josephson junctions, which surprised me as a theorist because he thinks The size of a speck of hair. Even the size of a flea’s egg. If that changes what you think an experiment is for, please subscribe and turn on notifications. Comment on this: is entropy really disorder, or have we been fooled all along because it’s convenient, simple, and easy to understand? And for the other half of the time argument, check out my conversation with the author of the book, with Nobel Prize winner Frank Wilczek on what a clock actually is.

Brian Keating:
It’s linked right here.

Brian Keating:
Thanks for watching. Please like, comment, and subscribe, but most importantly, share this with someone who loves Carlo’s books, his writing, and his research. See you next time on Into the Impossible.