Daniel and Jorge Explain the UniverseDaniel talks to Carlo Rovelli about a fascinating alternative way of thinking about the nature of reality. And aliens.
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Hey, it's Horehand Daniel here and we want to tell you about our new book.
It's called Frequently Asked Questions about the Universe.
Because you have questions about the universe, and so we decided to write a book all about them.
We talk about your questions, we give some answers, we make a bunch of silly.
Jokes as usual, and we tackle all kinds of questions, including what happens if I fall into a black hole?
Or is there another version of you out there that's right? Like usual, we tackle the deepest, darkest, biggest, craziest questions about this incredible cosmos.
So if you want to support the podcast, please get the book and get a copy of not just for yourself, but you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters, and.
For the aliens. So get your copy of Frequently Asked Questions about the Universe is available for pre order now, coming out November two. You can find more details at the book's website, universe faq dot com. 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 counterintuitive, probabilistic aspects of it that have 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 one hundred years, and that may take another hundred years to solve. But some recent ideas may be showing us a path forward, even if it's a stranger path than we imagined. Hi, I'm Daniel. I'm a particle of physicists and a professor at UC Irvine, and I'm still confused by quantum mechanics. Confused but not frustrated, you might say, I'm deliciously confused. What can be more delightful than grappling with the deep mysteries of the nature of reality, seeing the truth written down in cold, black and white 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 Jorge Explain the Universe, a production of iHeartRadio in which we tackle 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, ones that might elude humanity for centuries or forever. We don't shy 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 of quantum gravity, mostly loop quantum gravity, if I understand correctly. He also became a household name as the author of the book Seven Brief Lessons on Physics, which sold more than a million copies into was translated into forty one languages. I've read it and enjoyed it immensely and heartily recommended to you. Today, Professor Ravelli 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 very much, Dadiel. It's a pleasure in 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 a 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 reditional quantm mechanics is trying to do One of.
The difficulties of the problem of quantum mechanics is to say exactly what the problem is. So quantum mechanics, on the one hand, it's extraordinarily successful. It is used in a lot of our technology, is used a lot of our understanding of the world. We explained with quantum mechanics, the basic of chemistry, basic of astrophysics, 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 not formulated differently than previous basic physical theories, and these difference puzzles everybody and This is where the problems can in because the scientists disagree about how to think about 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 let drop the question at the banquet say oh, by the way, what do you think quantum mechanics? And ten minutes later everybody is screaming against everybody.
But is this a conference of philosophers or physicists in your mind?
No, no physicist huicism, including the ones to say there is no problem at all, what are you talking about? And that they say, of course there is a problem. You know, this is where is the problem? I mean, how how can we characterize the problem? Well, sort of all physical theories from say Newton, or maybe even before from the card or even from Aristotle all the way to Maxwell and to Einstein, special activity, general activity, lectodynamics. The series describes some systems and the systems some variables. I don't know pendulum, it's a physical object and the variable is the angle with the vertical And to tell you how this variable is and evolves given something that you know at the beginning, and you know where it is. You know the velocity, and then you have any questions that tell you how the variable changes continuously in time. So, of course this allows us to make predictions because we can measure the position the velocity, then close our eyes, wait two seconds, open again, and the new position ner velocity can be predicted by the theory because the cery tell us exactly how it moves in time. So that's how Newton physics works, or Maxwell theory works. Of Ilin theory works well Quartamacaly, 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 this is in between, So the data that you know, the addiction that you make, all devils go loose. Namely, every strange 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 you think about quantum mechanics in this way. I mean, you make a measurement that's a language which is used. The observer makes a measurement and you make a prediction of what's going to happen at the next measurement sometime later, and the prediction is bingal. It works, I mean, it tells us exactly what we see, but if you ask what happened in between, it's confusing, and the reason is 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 ball for that, or an atom or a molecule, and you throw it in some way, then quantum mechanics tell you where it's going to be, or at least pability distlution of what's going to be. Because if the prediction ofquant the mechanics are probabilistics are not not exactly. That's one of the characters is still quantum mechanics, but it's telling me the sort of probility is going to be here, that the probably going to be here, to probably going to be here. Then in between, what happens to the mathematics is this particle opens up in a wave. It's everywhere, and with this wave you compute to different probabilities. So the particles at the same time many positions in the mathematics. So some people say, okay, so the particle is in many it's a wave, it's all over. But then when you look at the particle, it's not a wave. It's in a simile position. So other people say, oh, come on, I mean, we look at the particle. It's always a particle. When we look where it is, it is always in one point. But when you compute how it goes 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 you can compare to measurements, but to make those predictions you need this intermediate step, which seem sort of nonsensical and conflicts with our sense of like what is real in the universe around us.
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 happen, 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 you read in 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 observer? What about the observer itself isn't to observe itself a quantum system, so it should be described by quantum mechanics as well, so it should also open up at like a wave. But that's it, and that's where people start disagree. And some physicists think, yes, we do our waves to multiple copies of Daniel and me and and some versions of us, some answers are given, is some other versions of different answers 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 starts. So the disagreement is realized in a number of so called interpretations of quantum mechanics. Ways to make sense about this funny story about the observer and the measurement and on the market, there are many, but maybe three or four four or five which are dominant, and many variants of these which 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 a technical thing about using it. Everybody agrees on using the theory, but everybody disagrees on if you want on what happens between the measurements, that's what we'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 it very important to predict what happens when we look, because it's very practical. We need to know how transistors work and whether our airplanes will fly. But when we're not making measurements, where we're not looking, where 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? Is that philosophy or do you think they're forever intertwined.
I think they're for every intertwined, and I think they should be for ever intertwined, because it's precisely by asking those kind of questions that in the past the physics has made the big jumps. Let we make an example of maybe two. One 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 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 Newton mechanics and allowed Galileo to understand Galileo relativity, and its debate on on on which Kepler built. Kepler was a strenuous defender of the idea that the Earth is not the central the universe. The universe is not the center going around the set. But if you think for a moment, is this Earth is a central unise? 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 can make that can distinguish if the Earth is a central unise. So it's not, because you know, I mean it can stay somewhere and see it moving but what does it mean if I am moving, I see I see the center moving. So it's really a non empirical question, and yet it's a profoundly scientific question. Why because it gives a different way depending if you answer one way or the other. If you start by thinking the Earth is the center, everything goes around, or if you start by allowing the Earth to be one of the things move, so you go to a completely different way of conceptualizing reality, and one which worked very well, the other was bad was or the good one. So I think this is one of the aspects of science which I think is often misunderstood. I would say science is not just about you know Closi r Eide, 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 of thinking reality. How do you put things in cases. One way of putting things in cases is in one case is the Earth and in the other the celestial bodies, the Sun, the moon, the planets, the stars, and then you throw that away. That's not the right characterization. The right way is there are stars, the planets, and then there is satellites to do something different and that 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 into petitional quantum mechanics should turn out something like that. Namely, one way of thinking about this story will turn out to be useful on the long run.
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Yeah, very good, and I think this is a nice way of putting the question. Let's take a let's take a concrete case, were simplest the quantum mechanical experiment and measurement that we can make. We can take an atom, a radioactive atom, right, so just a piece of a block of radius uranium. It waited there and you put around it's some detectors of radiation. You know, the guy the detector that click when when a radiation arrives. The wait for a while, and after a while one of these clicks cling. Okay, and then you say, okay, the atom has emitted a radiation and it has been detected by these detectors. These are the fact. Now, how do we describe these in the equations? What do we do? When we do quantum mechanics, we pretend that this radiation is some particles that are inside trapped inside the atoms, and they have a wave that describes them. There's a wave that the wave function describes them, and no other mathematics. 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. Imagine that this this wave continuously leaking out. So this is 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 them happen, as you say, something happens. We go from this quantum wave to a classical factor, which is one single detector that happens, and this is the measurement. Now, different interpretations try to fill up the story in different ways. Let me just compare to one or two interpretations. Why is the many world interpretation that you mentioned, and the other is the Kopanagen interpretation of dimension. The many world, in a sense, is the most radical idea of taking away very seriously. The Kopanagen interpretation is the one we study at school, the one the teacher tell you and tell you how to use. So the minimal interpretation says that there's this wave that come out and you see only one detector clicking. But why do you see one detective clicking? Because in reality, you yourself are a wave. Okay, so you, yourself are a superposition of different you, like the particle in 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, is split up in one you that sees this detective clicking, one you that sees that detective clicking, one you that's is that the techno clippi, 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 other it 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 implausible. The problem is everything you do with quant 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 interpretations.
Can ask you a question actually about that many world interpretations, there's 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 of well, many words place exactly on the fact that there is a contingency in who you are, which is hard to make in either informal or in words, and it is left a little bit vague into that. So it is a concern that some philosophers have a race about many wolves.
All right, Well, as long as philosophers agree with me, then I'm assolid for that.
Okay. Yeah, but you know, you can always find a philosopher that's.
Okay as a low bar apparently. All right, So that's the many world's interpretation.
Let's go to the kopanagen, which is what you study at school. Okay, community says, well, there are special things which are observers, okay, which are classical, namely a big, a big compared 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. Have to isolate things. You go to small things, so they are classical objects. There are many, all the ones around us, and this is a classical So forget quantum mechanics. About this. When a quantum system interacts with a 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? And 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. Copenhagen. It's works with an approximation to say, well, imagine that your theory is wrong for big things. Forget about it, and still use it for small things. And you know as why. It appeals to everybody who does not want to ask questions, and you can. But if you don't ask questions, you don't get answers. I mean those science scientists is about asking questions. A lot of scientists who says, 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 that large majority of people agree that there's something to say better here. So let's come to relational quantum mechanics. What does 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 people we have about the world. So up to this confirm all systems aplentum.
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. There's nothing that separates an observer in the sense of quantum mechanics from a piece of stone. Of course, you know, there are the people who have eyes, their machines, they're the things that store information, But that's irrelevant here. The point is in relational quantum mechanics. That's a suggestion of relig Quantum mechanics as a measurement happens in some sense every time two systems interact. But the actual element of reality which is realized in the interaction. So when the detector clicks or the particle is here, is here because I see here, the particle hits another particle, and therefore it has a specific position that has to be thought not as a property of the particle by itself, but as a relational property of the particle and the system it is interacting.
With in relation to the thing during the measurement.
Exactly in relation to the same during measure which it can be anything. We can be another party in a sense. So therefore, the central idea of religion wanted 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 do not describe how the system is it interacts, how the system interacts with something else.
Okay, So, for example, we have a particle and it's flying along and it has a certain wave function for things it might do, and Copenhagen interpretation says it stays probabilistic until something classical interacts with it. Relational 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, it 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 a relative to the system against which the particle is interacting, which doesn't need to be a macroscopical object, doesn't need to be anything special, it's anything. But the subtlety is the following I suppose the particle interact with my machine in my detector, Okay, and I'm I'm not a distance and the tooth is 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 wave function of the particle and the wave function of the machine, because the machine is quite mechanical.
I see. So for example, I'm here talking to you, so I'm measuring you. I'm collapsing your wave 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 interpetition it does require it has a cost. There's a conceptal cost, because, as you said, a reality is a little bit more subjective, no subjective relative. I'll come back to the difference in subjective and relative. So it weakens realism in a sense, but it's still a realistic interpretation. 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, more than not asking the question. Then you come to this subtle them. In your example, you talked about you and me and the listeners all people. Okay, that's fine, but the key intuition of relationship quite the mechanics is this has nothing to do with people. That's the key point. And that's a big difference with respect also with Copenhagt, and in a sense, right, this is nothing to do with subjectivity. That to do the subject the fact if you and I are subject of perceptions as you do.
You would also work if you and I were dogs or bananas or particles, right, exactly the same mathematics.
World, exactly as I'm the safe story would work. And to make an example of this, because I think that you know relatives 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 continuitive if you think at the beginning, which is velocity. When we study Glean theory or Newton theory, we learn that velocity is not absolute, velocity is relative. So what is the velocity of the moon. Well, there is a the loss of the moon we respect to this Earth. The velocity of the moon we respect to the Sun. The velocity the moon we respect to the center of the galaxy. The loss of the moon we respect to the cosmic micro wave background average. Which one is the true one? Well, none, It's a velocity. It's a notion that pertains the two objects. The moon is something else. It's always the loss of the moon with respect something else. We sort of know that, right because when we say don't move, we know that don't move is relatively 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 your little daughters would jump out of the train and don't move with respect to the earth, right, you mean, don't move expect to the train. And she understands correctly, right that she should move respect the train. And she's just still moving very fast because the train is running. So we understand that velocity. 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 Sun, I'm not saying that the Sun is a subject that sees the Moon and perceives something. It has nothing to do with that, nothing to do with mind, the subjectivity, Just physics, pure physics. There is a quantity 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 how they move. We respect one of them.
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. You 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 mental game I like to play is 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. 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 traditional quantum mechanics in a sense the following suggestion, we understand better quantum mechanics if we just interpret all properties, all variable in this way, not just velocity. Okay, any variable that you can think about a system only makes sense 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. That variable was realized in this interaction, namely, describe the way when system affected the other one.
And can use even the same language. Because now we talk about a 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 when you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite, But the people in the dairy industry are US. Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times. The same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is us dairy Tackling greenhouse gases, Many farms use anaerobic diges yess that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient deentse dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I'm a neuroscientists at Stanford, and I've spent my career exploring the three pound universe.
In our heads.
We're looking at a whole new series of episodes this season to understand why and how our lives look the way they do. Why does your memory drift so much? Why is it so hard to keep a secret, When should you not trust your intuition? Why do brains so easily fall for magic tricks? And why do they love conspiracy theories? I'm hitting these questions and hundreds more, because the more we know about what's running under the hood, better we can steer our lives. Join me weekly to explore the relationship between your brain and your life by digging into unexpected questions. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
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Now, you went strongly in saying, does this mean that reality itself it's relative to I hesitate. Namely, this same reaction could have been raised against the Galileo 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 silent things, in spite of what you have understood about relativity to velocity, is still very solid. 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 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, as 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 in an empty universe can't have a velocity. Now you said that everything is relational the way velocity is. Does that mean that a single particle in an empty universe does not exist or cannot have any property because it would need something else in order to measure it. Can a single particle universe exist?
No, if quantum mechan next is the correct description of the unis, and in fact that can be said in a besides way. There's a philosopher which is Malodorato, who is an elaborated match on that, saying, if we take a relation of quantum mechanis 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 descriptional unis needs to be If you use this way of thinking about quantum mechanics, so scripture relatively to something else. So in the moment in which you're saying the description uniits, so you're assuming there is something outside that is looking at the universe. I mean 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 wave functional unis what is it is a mathematical object that allows you to predict what you would measure if you are outside the universe interact with it. But then it's not the universe anymore because there is something else outside the universe interacting with it. So the way functual units is meaningless. It's always a wave function of something.
I was hoping to use that example to lead you down the garden path to admit that that means the universe can't exist, but you just went straight there and said, if this is true and 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 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 within, not from outside, in completely different parts of our culture. First, this was famously an immense issue anthropology, Right, you want to describe a society. When the Europeans went around the world to try to describe society is objectively non European societies maybe I don't know some people in their Amazon. And then they realized that they were not doing nothing objectively. They were just comparing their own culture with the culture of these people. I mean they were interacting with these people and not being outside a cultural scheme, but doing something enormously 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 encountered this, I know what I can expect, and I know what I can expect what kind of things have around me. But the idea that physics give a list of all or everything existing with the state, it's first of all, totally implausible 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 of 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 like that. It's model, as the philosopher says. So it's always a story about giving some initial condition, 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, 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 the toll state of the universe. Why it's total, 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 that units from that outside 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 make 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 needs to think about philosophy. And I know that you talk about quantom mechanics a lot, and you're quite an expert on this. So I want to try to ask you a question that maybe nobody's asked you before, put you on the spot, 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 meet extraterrestrial physicists, right, and we go and we say it to them, Oh, wow, you must know the secrets of the universe because you figured out how to travel here from distant stars. 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 it'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 true in universal I mean, I don't think this can be denied, and people who denied it, I think have a tought way of denying it. Intern of physics, in some sense, it's true, it works described realities. 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 sweet friends are in the cafe. That's the fact. It's true. And I believe that science is a higher level of understanding. Fact is a 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 it, or even that we're close to the end of it, that seems to me unbelievably full of self pretention. And I see no sign that we're close to that. And we have a sort of experiment of that because we know what past centeries 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, really going in a different direction, which doesn't mean that they are better than us. We are better than them because we know what they in some objective sense, and the objective sense that if both men came alive, and if I could have enough time Bom and 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 aliens 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 too different. It might be different because they have a different way of perceiving reality. Right, we view reality on the basis of what's useful to our there being an evolution, not on the basis of you know, some countin rationalism, or simply even if they had the same senses, because culture then was going in other directions. But I believe there is communication, right, Cultures communicate, So maybe with these aliens we could learn to communicate and we will be very surprised of learning completely different perspectives. If they are more advanced than us in some sense, or maybe they would be surprised to learn something from my or maybe both so was I don't think there is a path two tools, and they would know everything we know and more. Maybe they would never figure out quantu mechanics, and we teach them quantum mechanics. Look, it was fantastic. You're right, it's a relationship.
Will send you to meet the aliens and how they don't need you.
There is a great novel, The Dark Cloud, The Black Cloud, in which there is this it's a huge cloud that come towards the Sun, and somebody realizes that it's actually an intelligent something down there, and it's uh. Somebody realized that it is going to be a disaster for the Earth is going to sack the energy of the Sun. And so the scientists arrived to communicate and just gently convince this cloud to leave us alone. But then there is one scientist so too, and I don't remember that, said wait a minute, I want to learn everything you know. So the cloud answer, well, it's tandreous. I mean, your little brain is. But they really want it. So the cloud 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, they don't understand, but then they start understanding, and then finally they start learning. And then they're lost because they're considered full and they're putting the psychiatic hospital and the body knows.
What I see. That's the danger of talking physics with aliens is you can see reality so clearly that 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 radical 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 that could tell us, Look, Copenhagen fails here, and we need relational quantum mechanics, or we can dispense with the many worlds. 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 is 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 interesting, and so far many of these tests have been done and quant mechanics always going to be right, and all alternative through the moment have been all eliminated. But the various interpretations like many world or debudy bomb, the pilot wave interpretation, hidden variables, or relational quantum mechanics, which I think are the main ones. So cubans maybe in one sense they are not distinguishable in an empirical way. As far as I know, nobody has come out with the experiment to distinguish 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 in which we finally agreed that the Earth is not the center of the universe, even if there's no experiment that tell us that the Earth is or is not the central of the unions, because there's no way to measure just what the center center unions, namely the progress of science, will work better with one conceptual scheme than the other. I do want to gravity my main The reason I've got into the issue of interpreational quantum mechanics and nan the mechanics goes back to the nineties. In fact, my first papers on that in the late nineties, and then other people came in and have developed it and in recent years have been a much stronger increase in interest in it. And it's not isolated because there are other people who have very similar ideas. So VISI 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 Zilinger, by Chancellor of Grupner, 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 quantum say 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 out this works very well well with general relativity, where location is relation. Nothing has a position to be somewhere. It's only meaningful if you're some well respect to something else. And now things start staying together well, because to be next to something is a 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 in exchanging something, rather than having you know, a big canvas there and placing things and saying that's that's what reality is. So I hope that the discussion about individual puantmya is going ahead. It's not locked, 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 is 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 a sense of reality nature 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 quantm mechanics and physics and relativity and of course aliens and philosophy. I want to thank you very much to point our listeners to your book helgi Land, which has just come out recently, and it's a 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 very mention. That was great.
Thank you, thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last sustainability to learn more.
Hi, everybody, it's Katie Couric. Have you heard about my newsletter called Body and Soul. It has everything you need to know about health and wellness, from skincare and serums to meditation and brain health. We've got you covered and most importantly, it's information you can trust. Everything is vetted by experts at the top of their field. Just sign up at katycurrek dot com slash Body and Soul. That's k A T I E c O u ric dot com slash Body and Soul. I promise you'll be happier and healthier if you do.
Hi.
I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcasts in America. I mean neuroscientists at Stanford and I've spent my career exploring the three pound universe in our heads. Join me weekly to explore the relationship between your brain and your life. Because the more we know about what's running under the hood, better we can steer our lives. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
