What is Relational Quantum Mechanics?

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Thanks for your support, and if you have a hamster that can read, please let us know. We'd love to have them on the podcast. We all know that quantum mechanics can't be quite right. I'm not talking about the counter intuitive, probabilistic aspects of it that it forced us to accept that the world we live in is fundamentally weirder than we have ever imagined. Probabilities and correlations and uncertainty is no. Those bits are probably right, But there's a problem at the heart of quantum mechanics, one that has baffled physicists and philosophers for nearly a hundred years, and that may take another hundred years to solve. But some recent ideas maybe showing us a path forward, even if it's a stranger path. Then we imagine, Hi, I'm Daniel. I'm a particle physicist and a professor at u C Irvine, and I'm still confused by quantum mechanics. Confused but not frustrated, You might say, I'm deliciously confused. What could be more delightful than grappling with the deep mysteries of the nature of reality, seeing the truth written down in cold black and white and mathematical equations, and struggling to gain an intuition to incorporate those alien concepts into our human brains. After all, that is the deepest goal of physics, and that's the goal of our podcast. Daniel and Jorgey explain the university production of My Heart Radio, in which we tackled the biggest and hardest and nastiest and funnest of questions of the universe, the ones that make your brains twist, the ones that slip away from you just as you thought you had figured them out, the ones that might elude humanity for centuries or forever. We don't show away from any questions on the podcast, but we seek to approach them and explain our knowledge and our ignorance to you. My friend and co host Jorge is on a break, but I have a special treat for you. We are very lucky to have as a guest one of my favorite physicists, one of my favorite writers, and one of my favorite writers about physics, truly a poet of science communication. Today we'll be talking to Carlo Rovelli about some of the problems at the heart of quantum mechanics and explaining a lesser known but absolutely fascinating alternative version of quantum mechanics. So today on the podcast, we'll be answering the question what is relational quantum mechanics? So it's my great pleasure today to introduce Professor Carlo Rovelli. He's a professor of physics in Marseille, and he cut his teeth and made his name for himself developing theories of quantum gravity, mostly loop quantum gravity. If I understand correctly, he also became a household name. Is the author of the book Seven Brief Lessons on Physics, which sold more than a million copies and was translated into forty one languages. I've read it and enjoyed it immensely and heartily recommended to you. Today, Professor Rivelli is here to talk to us about his new book, Hell Go Land and a fascinating alternative take on the measurement problem in quantum mechanics. Professor Velli, welcome to the podcast, and thank you for joining us. Thank you question that it's a pleasure in the honor of being here, wonderful. Well. I always love talking about quantum mechanics and puzzling over it with other people. I feel like every time I talk about quantum mechanics with somebody else, I think of a new question I've never thought of before, or a new angle on it, or a new mystery frankly like a new corner of my mind that I haven't ever really examined, and I get confused, and so it's always fun to figure things outside of on the fly. So today we wanted to talk about your new book and Hell Go Land, And the book essentially lays out for lay audience this idea of relational quantum mechanics, sort of a new interpretation on quantum mechanics. And the first question for you I have is if you could describe for us what is the problem that relational quantum mechanics solves, Like, why do we need another quantum mechanics interpretation? What is it? At the heart of relational quantum mechanics is trying to do One of the difficulties the problem of quantum mechanics is to say exactly what the problem is. So quass mechanics, on the one hand, it's extraordinary successful, is used in a lot of our technology, is used a lot of our understanding of the world world. We explain with quantum mechanics the basics of chemistry, basic apastrophysics, all sorts of stuff, and it works. It works fantastically. On the other hand, there is a persisting, mysterious aspect about this theory. It's a theory that it's a it's sort of formulity differently than previous basic physical theories. This difference puzzles everybody, and this is where the problems can in because the scientists disagree about how to think abou quantum mechanics. If you if you want to, if you go to a physicist conference and you want to really start a furious discussion, just like drop the question at the banquets, say oh, by the way, what do you think going to mechanics, And ten minutes later everyone's screaming against everybody. But is this a conference of philosophers or physicists in your mind? No, No physicist physicist physicism, including the one to say there's no problem at all, what are you talking about? And that they say, of course there's a problem. You know, where is the problem? I mean, how how can we characterize the problem? Well? Sort of all physical theories from saying Newton or maybe even before from the card or even from Aristotle all the way to Maxwell and Twinstein, special activity, general activity, electro dynamics. The theories describes the systems and just the sens the system with some variables. I don't know a pendulum. It's a physical object and the variable is the angle with the vertical and tell you how this variable ease and evolves. Given something that you know at the beginning and you know where it is, you know the velocity, and then you have you have any questions that tell you how the variable changes continuously in time. So of course this allows assume ex predictions because we can measure the position. The velocity doesn't close our eyes with two seconds, open again and the new position. New velocity can be predicted by the theory because they tell us exactly how it moves in time. So that's how Newton physics works, or Maxwell theory works of ice. Since theory works well probamical, it does not work this way. That's the point. It works in a completely different manner. It does not tell us what happens at the pendulum while he's moving. It only tells us the prediction without saying what is in between. And if you try to reconstruct, what is this in between? So the data that you know and the prediction that you make, all devils go loose, namely every stray. Things happen, and people disagree about what happened in between in between, you mean that moment when you close your eyes and you're trying to use physics to predict the future exactly. So typically think about quantum mechanics in this way. I mean, you make a measurement, that's the language which is used. They'll certainly makes a measurement, and you make a prediction of what's going to happen at the next measurement sometime later, and the prediction is binger. It works. I mean, it tell us exactly what we see, but if you ask what happened in between, it's confusing. And the reason it's confusing one way of presenting it, one of the many ways of presenting it is the following. If you have a particle, an electron, or a little mole for that, or an atom remocal, and you throw it in some way, then going to mechanics tell you where it's going to be, or at least probility distribution of what's going to be. Because the prediction about the mechanics and probabilistics are not not exactly that's one of the corrector is still going to mechanics, but it's telling me the sort of probility going to be here that you're probably going to be here, to be going to be here. Then in between, what happens to the mathematics is the particle opens up in a wave. It's it's everywhere, and with this way you compute the different probabilities, so the particles at the same time many positions in the mathematics. So some people say, okay, so the particle isn't many, it's a wave, it's all over. But then when you look at the particle is not a way. It's in a single position. So other people say, no, come on, I mean, we look at the particle is always a particle. When we look where it is, it is always in one point. But when you compute how it goes from from here to here, it's not in one point. And if you assume that it is in one point, you're led to make some kind of mistakes and things like that. So it's capable of making predictions, concrete predictions, or be can compared to measurements. But to make those predictions you need this intermediate step, which seems sort of nonsensical and conflicts with our sense of like what is real in the universe around exactly. So, but the real problem, it's the thing people are debating with is what does it mean that the theory describe what we measure. That's why it's called the measurement problem. In a sense, it's like when we measure something special happened, But we are not special, right, We are just you know, piece of the universe like any others. So the standard formulation of quantum mechanics, the one reading textbooks, it's only in terms of the observer and the measurement, which is fine as long as you don't ask, what about the physics of the observer? What about the observer itself isn't to observe itself a quantum system, so it should be described the quantum mechanics as well, so it should also open up on it like a wave. But that's it, and that's where people start disagree. And some physicists thinkly, yes, we do. We do our waves the multiple copies of Daniel and me and Carolo and some versions of us, some some some answers are given, is some other versions of different. It is given because we're a wave of different configurations of ourselves. Other people think, no, come on, that's not a good way of thinking about reality. And that's where the the disagreement start. So the disagreement is realized in the number of so called interpretations of quanto methadnics ways to make sense about this funny story about the observer and the measurement and on the market that there are many but maybe three or four or four or five which are dominant, and many variants of these which is pretty different from one another, and give a profoundly different picture of reality. And that's the beauty of the story. It's not just a technical thing about using the theory. In fact, it's not the technical thing about using Everybody agrees on using the theory, but everybody disagrees on if you want on what happens between the measurements, that's what way you're putting it. So I think it's really fascinating that it's so important to us to understand what happens when we're not looking. Right. Clearly, physics takes it very important to predict what happens when we look, because it's very practical. We need to know how trans star's working, whether our airplanes will fly. But when we're not making measurements, where we're not looking, when we're not watching the universe, we still want to know what is real, what is going on? We want to have like a model in our minds of how the universe works. Are we still doing physics in that case there's that philosophy or do you think they're you know, forever intertwined. I think they're forever intertwined, and I think they should be forever intertwined, because it's precisely by asking those kinds of questions that in the past physics has made the big jumps. Um, let me make an example of maybe two. What example is is the Earth the center of the universe. This was a huge debate at the time of between Copernicus and Newton. It's it's it's a center of debate, and nobody could say that this was not a scientific debate, because that's the debate that started that allowed Newton to do new to mechanics and allowed Galileo to understand the Gali little relativity, and this debate on on which Kepler BILLT. Kepler was a strenuous defender of the idea that there is not the center the universe. The universe is not the center. Going around the said, but if you think for a moment, is this Earth as the central universe? A scientific question in the sense of something we can test them, of course not. There's no way of testing. There's no there's no operational meaning, there's no measurement that I can make that can distinguish if there Earth is the central universe. So it is not because you know, I mean it can stay somewhere and see moving. But what does it mean if I am moving, I see I I see the center moving. So it's really a non empirical question. And yet it's a profound way scientific question. Why because it gives a different way depending if you answer one way or the other. If you start by thinking there Earth is the center, everything goes around that all. If you start by allowing there is to be one of the things moves, so you go to a completely different way for conceptualizing reality, and one which worked very well. The other was bad. It was not the good one. So I think this is one of the aspect of science which I think is often misunderstood. They would say, sciences is not just about you know, close your eye, make make a model, make mathematics, make a measurement, make a prediction, and that's it. Science is about understanding reality, meaning building up a conceptual structure, the way you're thinking reality, how to put things in cases. One way of putting things in cases is in one case there's the Earth and in the other the celestial bodies, the sound, the wound, the planets, the stars, and then you throw that away. That's that's that. That's not the right characterizasue. The right way is there are stars, the planets, and then there are satellites. Do something different and that's works really different, and boom, we understand the universe better. So I think there are questions which are not directly empirical but are scientific, and I think the interpetitional quantum mechanics turn out something like that, Namely, one way you're thinking about the story will turn out to be useful on the long run. So then let's dig into the details of the different interpretations, just to recap for our listeners, what exactly is the problem that we're trying to solve here. The way I think about it sometimes is that we have these particles, and our mathematical model of them is that they are probabilistic. They can have the probability to be doing one thing or another thing. But of course that's not what we measure when we measure something, it does either one thing or the other. And the question is, how do you go from being probabilistic to being sort of classical. And you know, it seems arbitrary to say I'm making a measurement now or I'm not making a measurement, And you can ask questions like, well, when it interacts with other particles, why isn't that a measurement? Or if I'm making a measurement and I'm using a stick, and you know the tip of that stick is made of quantum mechanical particles, So why doesn't it just interact with my stick the way it interacts with other quantum mechanical particles and maintain it's probabilistic nature. And you know, people think about like do you have to have a conscious observer involved? But there's all sorts of fun things that you can dig into there. And had a fun conversation with the author of What is Real, which people can also dig into if they're interested in more details on what the measurement problem is. And the classical approach to people take this Copenhagen interpretation seems sort of arbitrary. It says that you know, the wave function moves by the shorting air equation, and it's smooth and continuous, and then boom, all of a sudden, when there's a measurement, everything collapses. But it doesn't tell you what a measurement is, right, And so there's this deep question still the heart of the most common interpretation. And let's listener as the podcast can also check out our episodes on the Many World's interpretation. But today I want to talk about your idea or this concept of relational quantum mechanics. So how does relational quantum mechanics deal with the measurement problem in a way that's different from this our try obviously unworkable approach of the Copenhagen interpretation. Yea very good and I think this is a nice way of putting the question. Let's take a let's take a concrete case. Was simplest the quantum mechanical experiment and measurement that we can make. We can take an atom, radioactive atom, right, just a piece of a block of radius radius uranium. They waited there and you put around it some detectors of radiation, you know, the guide detector, the click when when a radiation arrives to wait for a while and after a while, one of these clicks flink okay, and then you say, okay, the atom has emitted a radiation and it has been detected by these detectives. This is the fact. Now, how do we describe this in the equations? What we do when we do want to mechanics, we pretend that this radiation is some particles that are inside trapped inside the atoms, and they have a wave that describe them is a wave the way functions describes them and never automatics. These waves leaks out from the atom or from the nucleus of the atom slowly and continuously, and it's all over so and slowly. The imagine that this this wave continuously leaking out. So there's this continuously wave that around spherical and go out. So each one of the detectors is touched by these waves. Goes on. Then at some point the measurement happened. As you say, something happens. We go from this quantum wave to a classical factor, which is one single detector that happened, and this is a measurement. Now, different interpretation try to fill up the story in different way. Let me just compare to one or two interpretation. What is the many world interpretation that you mentioned, and the other is the Copenagen interpretation that dimension the many world, in a sense is the most radical idea of taking away very seriously, the Copenaga interpetition is the one we study at school, the one the teacher tell you tell you how to use. So the many one interpretation says that there's this wave that come out and you see only one detector clicking. But why do you see one the technical clicking, Because in reality, you yourself are a wave. Okay, So you, yourself are a superposition of different you like the particle and different positions in a superposition different positions. So it's not true that there is one detector that clicks. All the detectors clicks, but you yourself interacting with these detectors split up in one you that sees this the technical clicking. One UITs is that the tector clicking. One U that is that the technical clipping, and so on. Okay, So now you would imagine that the wave contains copies of you, and the reason you've seen one and not the others is only because you happen to be one copy of you and not the other copies of the other. Now does this work. Yes, it works. Is it plausible, Well, it sounds very implausible, extremely implosed. Well, the problem is everything you do with pant the mechanics sounds implausible. So many people say, Okay, we have to accept this, that in reality we live in immense waves, that the copies and copies of ourselves, and that's the many world interpetation. Can I ask you a question actually about that many world interpretation? There is something about that that's never set right with me. But maybe it's very naive and and that's this you say that there are many, many copies of me, And so it breaks the problem of why is this one detector clicked by saying it's not just that one detector clicked, all of them have clicked, just in other versions of the universe. But that doesn't make all the versions of the universe equal or on the same footing. Because I'm in this one, you know, this is the one that I feel is the truth that I'm making the measurement in. And that's different from the other ones because I'm not in those other ones. And maybe there are other means in the other ones. And let's say that they're you know who I actually am. But this is the one that I'm experiencing, and so it still feels to me like it has a special place. Is that a naive concern or is that something that you think many worlds can address. It is a concern because about many words plays exactly on the fact that there is a contingency in who you are, which is hard to making, not either informals or in words, and it is left a little bit vague into that. So it is a concern that some philosophers have raised about about many worlds. All right, Well, as long as philosophers agree with me, then i'm solid. Okay, Yeah, but you know, you can always find a philosopher that has a low bar apparently. All right, so that's the many worlds interpretation. Let's go to the cobanagen which is what you said at school, okay, The communities says, well, there are special things which observers, okay, which are classical, namely a big, big compared to to the quantum phenomena. It's when you don't see quantum phenomena because they're too subtle for you. They are not visible to you there because you're too heavy to see quant phenomena. To isolate things, you go to small things, so they are classical ob genia many all the ones around us, and there is a classical So forget quantum mechanics. About this. When a quantum system interacts with the classical world, bingo, that's a measurement. And this works in practice very well. That's what we do in the laboratory. But in theory it obviously does not work because what is a classical system? But we I am many electrons and protons, and each one of them it's a quantum particle, so each one has a wave, so I have a big wave. I am a quantum system in a sense copenagen it's a works with an approximation saying, well, imagine that your theory is wrong for big things, forget about it, and still use it for small fixed And you know that's why it appeals to everybody who does not want to ask questions. And you can, but if you don't ask sans, you don't get answers. I mean, on those sides of scientists about asking questions, A lot of scientists who say, as well, I don't want to care about that. There were more in the past, in the sixties and the seventies, in the eighties, I would say the majority of physicists would have said, oh, come on, just use the theory. It works very well. Nowadays there are less and less people who do that, so I would say the large majority of people agree that there is something to say better here. So let's come to relationship quantum mechanics. What does the relational quantum mechanics says about that? It says that all systems are quantum, and that's the first assumption. Let's see that we're, as far as we know, quantum mechanics the best ecup, but we haven't about the world. So after to disconfirm all systems have led to So that's already in contradiction with Copenhagen interpretation that says like I am classical and you are classical. It says everything is made of quantum. Even classical objects are just like massive quantum objects. This is just what quantum objects look like when they're really big, exactly. So therefore there is nothing which is an observer, but by itself, nothing that separates an observer in the sense of quantum mechanics from a piece of stone. Of course, you know, there the people who have eyes, the machines, there are things that store information, but that's irrelevant here. The point is in a relational quantum mechanics. That's the suggestion of relational quantum mechanics that the measurement happens in some sense every time two systems interact. But the actual element of reality which is realized in the interaction, so that when the detector clicks or the particle is here is here because they see here, the particle hits another particle, and therefore it has a specific position that has to be soked, not as a property of the particle by itself, but as a proper relational property of the particle and the system it is interacting with in relation to the thing during the measurement, exactly innovation to the same door and literally which could be anything. We can be another party in a sense. So therefore, the central idea of religion wanto mechanics is, let's be radical in the following sense. We describe the world in terms of systems, particle, electron, et cetera. And these have the properties variables that describe them, But these variables don't describe how the system is, it interacts, how the system interact with something else. Okay, so for example, we have a particle and it's flying along and it has a certain way function for things that might do, and Copenhagen interpretation says it stays probabilistic until something classical interact with it. Relation or quantum mechanics says it can collapse when it interacts with anything, but that collapse is different for depending on who is interacting with it. So if it interacts with this particle might collapse in this way. If it interacts with somebody else, that might collapse in another way. In that sense, it's also sort of like a branching of what reality is real, because what is real now depends on who is doing the measurement. Is that right? That's exactly correct. So the so called collapse of the way function is by itself, something which is relative to the system against which the particles is interacting, which doesn't need to be a macroscopical object, doesn't need to be anything special. It's anything but this. The subtlety is the following. I suppose the particle interact with my machine, my detector, okay, and I am I am a distance and the two are not interacting with me. So with respect to me, there is no collapse happening. So the way the particle and the machine are gonna manifest themselves to me later on if they interact with me is still computed with quantum mechanics. So if I want to compute what happens with respect to me, I still use the way function of the particle and the way function of the machine, because the machine is quite mechanical, I think. So for example, I'm here talking to you, so I'm measuring you. I'm collapsing your way function. But our listeners have not yet heard this podcast, so from their point of view, you and I are still in some uncollapsed quantum state, and only when they hear this does it collapse into an actual stream of words. So for us it is collapsed, but for them it's not yet collapsed exactly. So I believe that this is coherent. This can be made clearing by going into details. It offers a possible solution of the puzzle quantum theory. This is a relation with dempetition. It does require it has a cost. There's a conceptual cost, because as you said, reality is a little bit more subjective. No subjective relative. I'll come back to the difference subject in relative. So it weakens realism in a sense, but it's still a realistic interpetation. So I think that this cost is more worthwhile paying for being fruitful for the future of physics than imagining that there are many copies of myself, or than not asking the question when you come to the subtle team. In your example, you talked about you and me and the listeners all people. Okay, that's fine, but the key intuition of relationship about the mechanics that this has nothing to do with people. That's the key point. And that's a big difference with respect also with coping again in a sense, right, this is nothing to do with subjectivity. That's it to do the subject. But factly you and I are are subject of perceptions as need to do. You would also work if you and I were dogs or bananas or particles, right, exactly, the same mathematics work, exactly as I'm the same story would work. And to make an example of this, because I think that you know, relative to observer observable are often misinterpreted as subjective while it's just relational. For instance, there's a very well known example of relational notion in physics which students struggle at the beginning when they encounter it the first time, because it's very contin intuitive if you think at the beginning, which is velocity. When we study Galian theory a Newton theory, we learn that velocity is not absolute, velocity is relative. So what is the velocity of the moon. Well, depend there's the velocity of the moon we respect to this Earth, the velocity of the moon we respect to the Sun. The velocity moon we respect to the center of the galaxy, the loscy moon respect to the cosmic microwave background average. Which one is the true one? Well, no, it's a velocity. It's a notion that pertains the two objects, the moon and something else. It's always velocity of the moon with respects something else. We sort of know that, right, because when we say don't move, we know that don't move is relativitally to something. For instance, if you're in a train and your little daughter is jumping around and you say don't move, you don't mean that you little daughters to jump out of the train and don't cove with respect to the earth. Right, you mean don't move respect to the train. And she understand correctly right that she should soon move respect the train and she's just still moving very fast because the train is running. So we understand that velocities are it's it's a relational notion. But this is nothing to do with subjectivity, right because if I say that the moon has a velocity respect to the sound, I'm not saying that the Sun is a subject that sees the moon and perceives something. Is nothing to do with that, nothing to do with mind subjectivity, Just physics, pure physics. There is a quantity to velocity which doesn't depend on one thing. It depends on two things, the Moon and the Sun. And it's velocity the relative velocity of the two, say how they move respect one of that. So that's a big philosophical step, right, You've sort of taken away from the moon the fact that it can have a property called velocity. Say, you can't have a property called velocity. Only a pair of things can have this property. A single object cannot. And the sort of the mental game i'd like to place to imagine, like a particle in an empty universe, can it have a velocity? Well, it has no meaning to have a velocity if you are the only thing in the universe, right, And so I want to also ask you about this concept of cost. You're talking about the cost of a theory, and so here is that the cost you mean that you're like now changing philosophically what it means to be real that no longer can you include in your sort of you know, category or your index of what it means to be that you have a certain velocity that you've like taken that away from objects. Yes, this is the course, and I think you said it very cleanly. It's a deep philosophical point when we realize that velocity is not a property of an object you need another object, is a property of two objects. A quantum mechanics in a sense. The phone suggestion that we in this em better quantum mechanics if we just interpreted all properties, all variable in this way, not just velocity. Okay, any variablity, even think about a system only makes sense if you if you have another system. You're saying it's this is a variable with suspect to this other system. And what you mean is that there was an interaction to these two systems and that variable was realized in this interaction. Namely, describe the way one system affected the other one. And can't you use even the same language. Because now we talked about velocity. We say velocity of the moon as measured by an observer on the Sun, or as measured by observer on the Earth. Now you can say the location of this particle or the color of this particle as measured by this observer versus as measured by that observer exactly. Now you went strongly in saying, does this mean that reality itself it's relative to um? I hesitate. Namely, the same reaction could have been raised against the Galileo and Newton when they started using velocity. In this sense, I think that the reality of the motion of the moon and velocity of the moon and the Sun and things, in spite of what we have understood about relativity velocity is still very solid. Still we still have a realistic interpretation of motion, and so I would like to think about relational quantum mechanics as a realistic picture. So reality is there, it's I mean, things are there, and then there's nothing to do with us. Of course, we are just a part of nature. Is not that nature is a part of our mind. That's my naturalism if you want. But the way reality is is subtle. According to quantum mechanics can be described. Reality can be described by systems that have a properties relative to other systems. So then can you have something which exists by itself like imagine, you know, the sort of simple example I mentioned earlier. For velocity, a single particle an empty universe can't have a velocity. Now you said that everything is relation on the way velocity is. Does that mean a single particle in an empty universe does not exist or cannot have any properties because it would need something else in order to measure it. Can a single particle universe exists? No, if quantum mechanics max is the correct description of the units. And in fact that can be said in a beside the way. There's a philosopher which is Madorato who is elaborated much on that, saying, if we take relationhp quantum mechanics correctly, we cannot talk about the quantum state of the universe. We cannot state of the quantum state of everything. We cannot even talk about the description of the universe because the scripture universe needs to be if you use this way of thinking, a point of mechanics scripture relatively to something else. So in the moment in which you're saying the description units, so you're assuming there is something outside that is looking at the universe. Well you can, but then in your reality there is something else in addition to what you just called the universe a moment ago. For instance, the famous way functional units, what is it is a mathematical object that allows you to predict what you would measure if you are outside the universe to interact with it. But then it's not the universe anymore because there is something else outside the universe interacting with it. So there's the way functional use is meaningless. It's always the way function of something. I was hoping to use that example to lead you down the garden path to admit that means the universe can't exist, but you just went straight there and said, if this is true, then we don't have a meaningful concept of what the universe is. I mean, isn't that a problem? I mean, if we want a theory of reality that tells us what is happening, doesn't it need to also allow us to think about what reality is. I think that it's a deeper point one of the things we have understood more and more in modern physics, but also another realm of modern culture is that we're always part of the story. So we see reality from we think, not from outside in completely different parts of our culture. First this this was famously an immense issue and toropology, right, you want to describe a society. When the Europeans went around the world to try to describe societies objectively, um, non European societies, maybe I don't know some people in their matson and then they re allies that they were not doing nothing objectively. They were just comparing their own culture with the culture of these people. In some of they were interacting with these people and not being outside a cultural scheme, but doing something and olmously interesting, not something that lacked value, but that was not a stepping out from what is being described. And I think physics to some extent has encountered the same set of problems. Namely, we described the universe from within. We are part of the universe. What physics tell us is if I encounter this, I know what I can expect, and I know what a what I can expect, what kind of things aide around me. But the idea that physics give a list of all or everything existing with the state, it's a first of all, totally unplausible by itself, right, I mean, how many stars there are in the universe, and how many atoms in each one of these stars? So it's just totally outside or a capacity. But even in principle, what does it mean. I mean, physics is all in the form if this, then that, right, If I found this pendulum in this way, then it's going to move that like that. It's model, as the philosopher says. So it's always a story of out given some initial conditions, this is what I expect to happen, given some data, this is what comes later, and then it tells what kind of atoms are around, the forces are around. But we shouldn't expect from physics the total novel of the universe. That's what everything is in the universe. That's at all the state of the universe. Why it's not that's far outside our capacities, And probably I would say it's meaningless because of what we said before, because that would be an issue that God might have if he or she exists seeing from the units from the outside, not of all our business. And I think this makes exactly the point that you were talking about earlier, that we want to know the answers these the philosophical questions, because they tell us which questions then makes sense to ask which questions have answers, and which questions are even relevant to think about. I think that's some of the most important reason why physicists need to think about philosophy. And I know that you talked about the mechanics a lot, and you're quite an expert on this, So I want to try to ask you a question that maybe nobody has asked you before, put you on the spot, and and that's this. Have you thought about what it might be like to talk about physics or quantum mechanics with aliens? Imagine that we have meet extraterrestrial physicists, right, and we go and we we say with to them whole you must know the secrets of the universe because you figured out how to travel here from distant stars. Do you think there's any possibility that we would be asking the same questions or that their answers to our questions would make any sense to us. Do you think that the way that we look at the universe is sort of the way Europeans, you know, looked at other cultures. Do you think that's deeply imbued with our human bias, or do you think that we are probing something universal which should be part of sort of like some galactic physics project. Great question. A bit of both, but more of the first and the second. That's my answer. There is a precise sense in which what we discover in science is it's just two in universal mean. I don't think this can be denied, and people who denied it, I think have a toak way of denying it, and don and physics in some sense, it's true. It works described reality. It's I mean, the fact that everything is made by atoms and there are ninety and so kind of different atoms. That's a fact. It's like when you you know, when you go down the street and you see that you know your three friends are in the cafe. That's a fact. It's true. And I believe that science is a higher level of understanding. Fact is the way humankind organizes an understanding of reality better and better. But from this, to have the idea that there is a unique, clearly path to the perfect description of reality and we are on need, or even that we're close to the end of it, that seems to me unbelievably full of self pretension, and I see no sign that we're close to that. And we have a sort of experiment of that because we know what asked centurists, scientists thought, and we do know that some of the things that we know would be meaningless for them, It would not answer their questions in really going in a different direction, which does not mean that they are better than us. We are better than them because we know what they are in some objective sense, and the objective sense is that if both one came alive, and if I could have enough time also want to me sitting here, I believe that I could slowly arrive to convince him that there are a lot of interesting things he doesn't know. So I think it's the same with some aliens. If some millions would come, I wouldn't be surprised if they have a completely different story. And it might be possible that we just don't understand one another because the story is two different. It might be different because they have a different way of perceiving reality. Right, we view reality on the basis of what useful to our They're being an evolution, not on the basis of, you know, some contient rationalism or simply even if they had the same senses, because culture of them was going in other directions. But I believe there is communication, right, Cultures communicate, So maybe with this aliens we could learn to communicate. And we were very surprised of learning completely different perspectives. If they are more advanced than us in some sense, or maybe they will be surprised to learn something from us, or maybe both. So in other ways, I don't think there is a path to tools, and they would know everything we know any more. Maybe they would never think about quantum mechanics and we teach them quanto mechanics. That was fantastic. You're right, it's a relationship. But will send you to meet the aliens and how they don't eat you. There is a greater novel, The Dark Clouds The Black Cloud, in which there is this it's a huge cloud that come towards the sermon and somebody realizes that it's actually intelligent something down there, and it's uh, and somebody realized that it is going to be a disaster for the Earth is going to exactly edge of the sound. And somehow so the scientists arrived to communicate and so gently convinced this cloud to leave us alone. But then there is one scientist so too. I don't remember. That's the Wait a minute, I want to learn everything you know, So the cloud answer, well, it's tandrous. I mean your little brain. But they really wanted to so they can say, okay, if you really want, so, I think it's two of them. They sit around the screen, okay, and the screens start flickering, and they just look at this at the beginning. At the beginning, they don't understand, but then they start understanding, and then finally they start learning, and then they're lost because then they're considered fool and they're putting all the psychotic hospital and the body knows what. That's the danger of talking physics with aliens is you can see reality, so clearly the humans can no longer relate to you. So let me bring it back to one last question about relational quantum mechanics. What you're proposing here is really a ratheric of departure on a way of seeing the universe, imagining that objects don't contain on their own properties, but that these things are just dependent on pairs, essentially things that are measuring other things. So my question to you is that how could we know if this is true. Is there some experiment we can do? They could tell us, look, Copenhagen fails here and we need relation or quantum mechanics, or we can dispense with the many worlds, like is this something which can only ever be a philosophical conversation among physicists motivating our questions about reality, or is this something we can actually one day put to the test. I don't see any way it could put to the test. There's some interpretation quantum mechanics that assume that quantum mechanics actually wrong, and so they can be tested because you can do an experiment to see where the quantum mechanic is wrong right, And they're very interesting. And so far many of these tests have been done and quant mechanics always going to be right, and all alternative from the moment have been all eliminated. But the various interpretation like many world or de bullyable, the pilot wave interpretation, hidden variables or relationship quantum mechanics, which I think are the main one. So cubans maybe in one sense, they are not distinguishable in an empirical way, as as far as I know, nobody has come out with experimented distinguished them, and in a sense studying them, there's no experiment making a difference, So how would we know, Well, I think exactly the same way, which we finally all agree that the Earth is not the center of the universe, even if there is no experiment that tells us that the Earth is or is not the center of the universe, because there's no way to measure just what the center the center units, namely, the progress of science will work better with one conceptual scheme than the other. I do quanta gravity my main the reason I got into the issue of integrational quantum mechanics, and the mechanic goes back to the nineties. In fact, my first papers on that in the late nineties, and then other people can and have developed it and in recent years have been a much stronger increasing interest in it. And it's not isolated because there are the people who are very similar ideas, So which why is really part of a little group of interpretation just similar in some sense, maybe with different emphasis, different tone. I'm thinking of writings by Zeilinger, by Chancellor Bruckner, by Richard Haley and another. There are a number of ways of going in the same direction, so in my own work and trying to put up a quantic see of gravity, I found that this way of thinking, it's much more helpful when you don't have space, you don't have time to locate things, you don't have the observer. This relational way works well. And one reason it works well, it works through well well with general activity, where location is relations. Nothing has a position to be somewhere. It's only meaningful if you're some well respect to something else. And now the things start staying together well, because to be next to something is possibility of interacting with something, so you can exchange information with something. That's what we're talking about in physics, this being next to one another and exchanging something, rather than having, you know, it becomevast there and placing things and saying that's that's what reality is. So I hope that the discussion about indevidual quadema is going ahead. It's not blocked, it's not the same as thirty years ago. And I think that with the new ideas, with the new things being discussed, at some point it will become more and more clear that one way of viewing things it's productive. It works. It doesn't require us to assume things which are absurd, but it does require us to assume things which are necessary to make in sense of reality. Wonderful. Well, that's a fascinating insight into how we might make steps forward. And I agree with you that it makes sense to unify quantum mechanics with relativity if quantum mechanics itself becomes sort of relativistic, not in the sense of things moving at very high speeds, but in the sense that the objects and the quantities we measure themselves are relational or relative to other objects. So that makes a lot of sense. Well, thanks very much for this fascinating conversation, really stimulating, you know, about quantum mechanics and physics and relativity and of course aliens and philosophy. I want to thank you very much, and I want to point our listeners to your book Health Go Land, which has just come out recently, and it's fascinating read on these ideas and how they were developed, and people who are interested in digging more deep into them might encourage you to check them out. So Carlo, thanks you very much for joining us on the program today. Thank you. Emaually, that's what's great. Thank you. Thanks for listening and remember that Daniel and Jorge explained. The Universe is a production of I Heart Radio or more podcast for my heart Radio, visit the I Heart a new Apple, Apple Podcasts, or wherever you listen to your favorite shows. H