Harvard Physicist Debunks (Literal) Particle Superposition | Jacob Barandes Λ Manolis Kellis

Every time one of the physicists tells you, quantum physics has proven that a particle can be in two places at once, he is lying to you. Biology and consciousness and causality and quantum physics. What is the connection? My name is Kurt Jaimungal, and this was part of my three-day tour of Harvard University, T.H. Hooft’s, and MIT, where I recorded five podcasts, including a fun salon discussion hosted by Manolis Kellis of MIT, one of the world’s top computational biologists.

A few weeks ago, Manolis very kindly offered to host myself and the theoretical physicist and philosopher from Harvard, Jacob Barandes, in a salon on the nature of quantum theory. This event is unlike any podcast I’ve seen or heard, due to the improvisational dynamic of over 70 people who attended in just a few days. Other podcasts from this tour feature Mike Levin and Anna Chunikha, as well as a separate, over 7-hour discussion, with technical and concrete information regarding Jacob’s approach to irreducible random processes. Subscribe to be notified. For now, enjoy this jazz-like conversation regarding fundamental questions such as do quantum fields really exist, what is the many-worlds problem, do parallel universes solve anything, and what makes observers like yourself special.

So Jacob, can you give us a simple introduction to what you do? Tell us, maybe two or three minutes, about your journey. How did you get to where you are? What are you excited about? What is the thing that you are most excited about? And as you know, what do you think we should really, you know, if there’s one thing that we should know, what should that be?

When I was a young child, I was really interested in the philosophy of mind. I didn’t know it was called the philosophy of mind, but I later realized that’s what it’s called. I was really puzzled about why we exist and the nature of consciousness and all these kinds of questions. I had a knack for mathematics and I went to college and I thought, well, if you love math and you love deep questions, you should study physics. And so I studied physics and I had a great time. And then I went to graduate school and I worked in high-energy theoretical physics. I got my PhD in theoretical physics. And, you know, I had some difficulty connecting with the research that was going on in high-energy theoretical physics. It didn’t connect with me on a deep level. And, you know, at the PhD level, halfway towards the end, I started to reconnect with my earlier interests in philosophy, and in particular, the philosophy of science. I became very interested in a whole range of different areas in the philosophy of science in the field that we now call the philosophy of physics and in areas closer to the sciences like the foundations of quantum. So, when I finished my PhD, I started doing research in that area, writing papers. My partner in crime here, David Kagan. We were close friends and collaborators. And I started to interact more and more with the community of people who work in the philosophy of science. And I realized that this was my calling. And so I stayed on-

What is the philosophy of science? Ah, good, good question. What is the philosophy of science? Generally, and this is the philosophy of science. Not exactly, well, I’ll say what I’ll do in a moment, but the philosophy of science, generally, has several parts. One part is the study of what scientists do, right? So it’s the study of the sociology of science, the ornithology of science. Scientists are like birds, and we observe their habits. And there’s the old line, right? That this form of philosophy of science is to scientists what ornithology is to birds. It’s actually a fair point, it’s a fair point, I must say. However, I will say – it might be useful for bird watchers. That’s true, but when the birds are suffering, you have to call an ornithologist. So, you know, and I’m not saying that scientists do that – birds don’t try to do ornithology. That’s very good, yes. But the other main aspect of the philosophy of science is to delve into our best and most successful scientific theories, and to understand how they work. And, you know, either try to understand a new way of thinking about traditional questions in philosophy certain areas of philosophy like metaphysics, of the best of-

And what is metaphysics? Well, yes, good, good question. So – that was a great question to ask. These are all great questions. Have you guys heard of the program called ELIZA? Yes. It’s on that level. I learned a lot from ELIZA. Tell me more about that. Tell me more about the thing that you just said. Well, good, yes, right. ELIZA is a very old computer program. It was a computer therapist. And whatever you told it, it would just say, tell me more about it, and it would just repeat what you said. And people would spend countless hours. Exactly. And people would spend countless hours on that, as if they were pouring their hearts out. So metaphysics is a very broad area in philosophy. It’s concerned with some of the fundamental questions about the nature of existence, questions about modality, and questions about the nature of time, and its nature, you know. So, there are areas of metaphysics that we in the philosophy of science tend to spend a lot of time thinking about. So these are questions like, what is a law of nature, right? What are the laws of nature? How do we know the laws of nature? And are the laws of nature things that exist to some extent, or are they things that we invent to understand the world around us? What is probability? When you say that something in the world is associated with a probability of 0.72, what information does that convey? Now, you can pick up a book on statistics. And when I pick up a book on statistics, sometimes I’m interested in understanding how to calculate things. But I often pick it up and look for where they say what probability is supposed to be. I feel like we should have some biology. Because metaphysics is very powerful in understanding the nature of the universe. But there’s something about biology too that’s very fundamental and that is why do we think? Why, you know, is there a soul? What is the neural basis of consciousness? Come here, look, you know. Yes, yes, yes. Wolfram has an metabolic framework. And so does Gregory Chaitin. Say that again? Wolfram, Stephen Wolfram has a biology. And Gregory Chaitin does too. That’s very interesting. Good, good, good, good. Yes, yes, yes. So, but I must say that metaphysics has the word physics in it. But it’s not physics. It’s, you know, the things that are not called physicists, and therefore metaphysicians. They are called metaphysicians. Just to clarify, they are not physicists. That’s very confusing. It’s very confusing. It’s very confusing. Yes, the name goes back to the fact that there’s a chapter in Aristotle, that comes after it, and meta just means after. It’s just, it’s the next chapter. If anyone should know, it should be the Greek man. Physics simply means natural. Physiki is just natural. So natural science is actually physics. I mean, for the Greeks, I’m sorry. Physicists were called natural philosophers, right? I mean, that’s what they were called. So metaphysics is concerned with questions that are broader than any particular science, and that are relevant, you know, to the questions that metaphysicians often ask, so here’s an intensive talk on metaphysics. Is there a precise way to distinguish the difference between assumptions and counterfactuals? That’s the kind of thing you’ll literally see. They’re completely different things, and we know they’re different things, but, you know, spending a lot of time carefully thinking about it, that’s the thing that some metaphysicians do, right? Can I hear what Manolis thinks the difference is? Yes. So I’ll get back to that in a moment, because I have some things that I need to ask, which might fall into metaphysics, and I hope we get to those questions. You don’t have to answer them all right away, and I also want to get to Kurt in a second, but one of the questions that I have is, does our existence matter? In other words, if you look at the entire biomass of the universe, you’ll find that Earth is insignificant, and the humans on it, you know, even more so, but if you look at the amount of consciousness or the amount of theories or the amount of, I don’t know, setbacks in the universe, then we play a very large role, at least from my perspective, and what’s really interesting is that at the heart of quantum physics lies an observer. Some might say, some might say, some might say. So what I want to ask you about is, does the universe care that we’re here? Does it matter that we’re here? So. Counter, counter-anthropics. Go, go, go, go, tell us more and introduce yourself. By the way, this has already begun. I don’t think this is the first question. We’re in it. You can just ask a question. This is intellectual exchange. This is a salon. People should just ask questions. I want everyone to feel that they should answer as much as they ask. I can pick up the thread, right? So this is a reference to the anthropic principle. The anthropic principle was formulated by Brandon Carter, a theoretical physicist who works on deep questions in gravity. You know, a colleague of Stephen Hawking. And the anthropic principle is that it comes in different flavors. One version of it is, you know, when you look around at the world and you see that it has certain features, some of these features might be the way they are because they are the laws of nature. Some of them might be the way they are just because they are contingent random facts, but some of them might be the way they are because of selection bias. You know, for example, we look around and we say, oh, the ambient temperature is very nice, this nice temperature between freezing and boiling. Is this because of some deep reason? And the answer is anthropomorphic. I mean, you know, we, you know, carbon-based water-dependent beings, we wouldn’t be in an environment that’s significantly different temperature than that. So the fact that we see that is a consequence of us being humans observing it. And that’s called the anthropic effect. I want to build on that a little. I volunteer at my kids’ schools. And one of the things that I volunteer to do is to answer all of their questions about the universe. Very small tasks. A small task, yes. So, for three weeks, they collect questions, and, you know, I prepare for this talk more than I have to admit for any talk I’ve given in at least the last fifteen years. And one of the questions was: Why is the sun so bright? And I used exactly the anthropic principle to say basically that if we lived on Jupiter or even Neptune, the sun would be just as bright. In other words, there’s a range of brightness that our vision has evolved towards. And at the end of that distribution lies the sun. And there’s really no option to be able to see the sun clearly. And I, you know, I think a lot of other things seem perfectly natural because we evolved here. But there’s another aspect, I thought you were going to touch on, which is that you didn’t interrupt me. Let’s be clear. You probably got there. We have only one hour, you know, for at least three hours of material. That’s okay. So what I want to ask you about is, what I thought you were going to get to is not just that, yes, biology is very compatible with the physics that we love and enjoy. But of course, there’s a weirdness to the fact that water, for example, when it freezes, it floats to the top. And that’s fundamental to why life exists at all. And I think that’s a more fundamental principle than the fact that the temperature is just right for our evolutionary adaptation. But what I thought you were going to get to is that as we observe the universe, we are observing perhaps a small fraction of the dimensions that are out there. And the laws of physics that we’ve arrived at are a small subset of the things that are observable by our biology, if you will. Am I completely off on this? No, no, not at all. So one way to conceptualize how cognitively limited we are as beings is: Another Greek word. Yes. Here you go. Philosophers love epistemology. Sorry, I must say that knowledge was one of the four virtues at the library of Celsus in what is now Asia Minor, in ancient Greek – what are the other virtues? So the other was arete, which literally means virtues, to be virtuous. And the other was sophia, wisdom. So it’s really good that we have some sort of knowledge, which literally means science. But basically the study of things. Anyway. Yes. So one way to conceptualize that is to borrow from a geometric tool that was provided by Hermann Minkowski. So Hermann Minkowski built on the emerging special theory of relativity that Einstein was developing in the early 20th century. And he provided this geometric picture that he called spacetime. And so, spacetime, as you imagine, think of graph paper, right? Graph paper, the horizontal direction on graph paper is all of space, and the vertical direction is time. And you can conceptualize everything that happens as existing somewhere in this diagram. So each one of you is a worm in the spacetime diagram, a worm that starts somewhere down here, and extends for some length here, and then no more. And then a lot of little worms come out. Oh, maybe little worms come out. Exactly. Where events that happen very quickly and then disappear, are more like points in this kind of spacetime picture. I think of it a little differently as cones of past and future potential for each point. Exactly. So the fastest thing that can transmit a signal through space is the speed of light. So, if you take any point and look at the light rays that can emanate from that point, or the light rays that reach that point, they form these things called light cones, right? The light cone gives you a way to conceptualize what can causally affect you, and what you can causally affect. And also what information can reach you. And also when. And also when, yes, exactly. Basically, when the cones intersect. That’s right, yes. So think of it this way. Can I interrupt, Nick Patterson? Ah, Nick Patterson, one last thing. There’s a question about what you mean by causality, because as I suspect you’ll get to, we have non-local mechanisms, and what causes what? It’s not very clear. The metaphysics of causality is near and dear to my heart and it’s something I’d like to talk about. Very appropriate. Well, why don’t you do that now? Yes. Let’s just, let’s just finish this other thing quickly first. We’re already at the 17th interruption. I see how this works now. This all makes sense to me. Okay. So, Kurt, Kurt, I think I know our mission. What we’re going to do offline is we’re going to go off and finish all these conversations. How about that? Good, excellent. Okay, it’s fine to keep changing topics. So if you look at the entire history of humanity. I have a question. Can we get you back to quantum physics? We are in quantum physics. We’ve taken a very nice preliminary exit off the highway. For the uninitiated only. We’ve taken a few highways since then. We’ve taken a few highways. Okay, I have a question about quantum physics. Sure, okay. So what is – it’s good to see you, Kurt. Hello, it’s good to see you. Kurt, Kurt, Kurt, can I ask you a question first? Can I ask you a question? So, so, so, so, so, Jacob, yes, Jacob came here to talk about quantum physics and we’ve been talking a lot about a bunch of different tangents, but I asked him some very simple introductory things. And you’re a podcast host called Theories of Everything, or is it Theory of Everything? Theories. Theories. And I’d like you to introduce yourself very briefly to know how you got to where you are now? Why the hell did you start this podcast? And also what have you learned that has shaken your worldview? Because one of the goals of your podcast is to spread knowledge to the rest of us. But there’s something else that I hope you also discover, you know, I don’t know. And there are very few people who actively ask a lot of exceptional people this one question that unifies everything. Tell us then, what do Theories of Everything mean to you? And are there some surprising things that you didn’t know that were like, an epiphany on your podcast? Weekly, almost. As for how I got into this, first, any story I concoct will be a fabrication because of course, after the fact, you can make it up, you can find the path in between. I like that the root of both myth and marvel is the same. But since I was a child, I was interested in puzzles, abstract mathematical puzzles. And I was always interested in mathematics and physics. I was once thinking about the nature of the universe and how anything came into being? And I asked my brother who was studying math and physics at the University of Toronto, I think, no, UBC at the time. He’s your brother. I was eight years old and we were walking to Blockbuster, if you remember Blockbuster. And I asked him how anything could come into being, how does something come from nothing? And then he explained to me what quantum fluctuations were. And then I remember going home and looking at the ceiling and then thinking, well, then there is no God. And then I became an atheist from that moment on. Or if there is, he rolls the dice. Sorry? Or if there is, he rolls the dice. Well, well, then there’s no need for a God. Good answer, good answer. In my eight-year-old mind. And then I remember telling some of my schoolmates about it, and they said, quantum fluctuations? And then I remember being very embarrassed because they were saying, what are you talking about? And then I never said the word "fluctuation" until I was 18 years old after that. Then I was great at math and physics in school. So I was encouraged and went into it in university and dropped it because I was doing improv comedy and filmmaking. Yes, oh, and that’s another story. After I was in filmmaking, the pandemic happened and I thought, well, I was watching some podcasts online. There was a guy named Donald Hoffman who had this theory of consciousness, at least it’s supposed to be a theory of consciousness that reproduces quantum mechanics, and maybe even gravity. I don’t know if he’s made that claim. But many people were interviewing him and they were in awe of Donald and they didn’t ask any, what I consider to be rudimentary questions that push you a little, not even adversarial questions. And Donald keeps referring to his papers. He says, I can prove it in my research. I was thinking, well, is there anyone here who reads his research and then talks to him about it? And I didn’t find any. So I thought, let me reach out to him and read his research and then ask him about it. And it was a very technical interview. So I treated the podcast as work hours and I was going to call it work hours instead of Theories of Everything at first. And that’s how I still treat it. When I was talking to Jacob yesterday, we talked for seven hours as if you had classes, well, potential classes where they could be seven hours long. They didn’t last that long, but we talked for seven hours. I’ll just go until the students give up. It’s an endurance contest. A class can go on for a long time, but the students won’t. And I’m very interested in the nature of reality. What is it? You mentioned metaphysics, you mentioned cognitive limitations. So one of the problems that I have with the anthropic principles is that we talk about life as we know it. Now, I know you have some claims about life that we don’t know that it has to be similar to life as we know it. I find that questionable. It should have similar properties. I hope DNA, like DNA, isn’t boring if we find it elsewhere. Well, anyway, it’s not clear to me that this is the typical case. So, red dwarfs, no, red giants last for trillions of years. Red dwarfs. Red dwarfs last for trillions of years. We don’t know if there’s some form of life in the sun, and the most common form of life would be a conscious agent in the sun, or if we invent AI and AI takes over and AI has many, many trillions and billions, well, trillions, another direction. Conscious experiences billions or trillions of times more than us, and therefore the most common conscious experience is us being an AI or a gray goo. I don’t know if that’s the most typical. I don’t buy these anthropic arguments. Furthermore, you can’t look at quantum fields and derive biology, let alone the difficulty of deriving chemistry. It’s fairly easy to derive chemistry when you know where you’re going, but it’s not that clear to me that if you change the laws you won’t be able to get life that we don’t know. As we can, well, anyway. That’s what the podcast is about. So you actually care about life on your podcast. It’s not just about physics. Well, you asked what matters and I gave this, my usual eight-year-old atheist answer, which would be, oh, well, we don’t matter because we’re a speck of dust among many stars, among many planets, and then you look at the world spatially and you say, well, because we’re spatially insignificant, therefore we’re insignificant. Well, why do we prefer what happens spatially? Can we say that what happened at Auschwitz, it doesn’t matter because you were just a small moment in history. I think what happened there matters and I think when we start to say we’re insignificant, you have to question your definition of things or question why you think what matters is important? Things matter. Well, feel free to join in anyone. Burning questions. More improv comedy. Ha ha ha ha ha. So when I was 12 years old, I asked my mom, hey mom, was God completely bored for the first 13 billion years until life started to evolve on the planet and then for another 3.8 billion years until we finally evolved so we could honor him? And my mom answered in an amazing way. She basically said, Manolis, and I was 12 years old. Manolis, do you think that the creator of space and time experiences space and time the way we do? And that blew my mind. And one of the problems that I have with prayer and miracles is that if I pray for something to happen, for my friend to show up, then that prayer had better go back in time, you know, it’s going to affect my friend who’s then going to decide to start taking a trip and eventually show up and my vision. And instead, whatever supreme being experiences time and space differently, they can respond to my prayer by affecting things in a non-causal way, you know, by going back to the future. And that’s something that I think about too. I don’t know if there’s a creator, but the thing that I think about is that we often, even if you’re an atheist, at least sometimes you think, oh, I wish this and that wouldn’t happen or maybe you get a diagnosis and you wish it wasn’t serious. And then you have no idea how many of these wishes have actually come true that you prayed for or prayed for in an alternate timeline and they’ve come true. And if someone heard your prayer and acted on it so that your prayer came true, you can’t wish for something now. You have to, you know, wish for something to happen. There’s an episode of The Simpsons where- oh, wait, it’s an episode. Gotham, where Bart finds this hand basically and he can wish for things. And, you know, every time he wishes for something, something terrible happens until that thing comes true. And I think the physical implication of that is that you had to go back in time, you know, to create an alternate universe where that wish comes true. And in your words, it messes up the entire universe. But the way I imagine it is in some sort of spacetime continuum that doesn’t mess up the entire universe, where you can still wish for something and then somehow, you know. So I’d love to hear your thoughts on that. We’ve basically talked about these intersection cones and how do you conceptualize miracles? Or is there a possibility for another type of model? Not necessarily the creator of the universe, but is it possible that there’s another occupant of the universe that doesn’t actually obey causality and constraints. And maybe, you know, quantum could be one of those things that you have these far-reaching effects. I’m going to perform the most annoying philosophical trick of all time, and I’m going to throw the question back with a question, what do you mean by a miracle? I think it’s pretty clear from the context. And he’s also a philosopher. You know, what people thought were miracles a hundred years ago is happening all the time now. Right. 500 years ago, right? I have a technical question. Sure. Is there any counter-argument to quantum gravity that you think, I mean, do you think string theory is a good theory? Well, string theory is not a belief system. Tell us about quantum gravity and string theory. Quantum gravity and string theory, well. But also to clarify the question, when you say counter-argument to quantum gravity, do you mean counter-argument to existing theories of quantum gravity, like string theory, or counter-argument to the idea that gravity should be quantum? Because those are different. To the theory that gravity should be quantum. Gravity should be quantum. Well, that comes down to the question of what you mean by quantum. And that’s sort of what I’ve been thinking about for a while. Yes, yes. So the standard way that we think about quantum theory is that there’s a very important role played by the observer. There’s a complex mathematical apparatus. And that apparatus, it engages in a form of reticence about what actually exists. But what it does is it gives us a precise utilitarian recipe for telling us what will happen when you do things. When observers do what’s called a measurement of a quantum system, the theory provides a probability for getting a certain kind of outcome, right? That’s what it does. But it doesn’t tell us what happens in between. So when you read a book about it. You know, modern physics, you know, about quantum mechanics, the book says, well, you know, the reason this particular thing happens is because this electron moves this way and a photon comes out and does this. With respect to the standard way that we know and formulate quantum mechanics today, the form of quantum mechanics that you find in all the standard textbooks, that’s all just for color. And that’s all just mythology. The theory just says that when you have an observer and the observer does this particular thing called measurements, there will be these outcomes with these probabilities. And that’s it. It doesn’t provide anything else with respect to a physical picture. Now, that’s the standard way that we know. You know, it’s in the books. But of course, people have been unhappy with this picture for a very long time. And one of the things that Einstein was unhappy about with quantum theory, it wasn’t the probabilistic aspect of quantum theory. It wasn’t that God plays dice with the universe. He could live with that. After all, Brownian motion was one of Einstein’s greatest achievements, right, which played a fundamental role in our understanding of the nature of atoms. It was, you know, one of the papers that was part of his miraculous year as an annus mirabilis in 1905. So, it wasn’t probability that was the problem for him. It was that there was no metaphysical picture of what was going on between measurements. And, you know, one of the concerns that you might have is that perhaps quantum theory is such a strange mathematical theory that any time you try to propose some kind of physical reality, or so-called ontology, which is a Greek word again, right, of what’s going on behind the scenes, that that kind of ontology would be incompatible with the mathematical apparatus. So the concern was that the mathematical apparatus of quantum theory was overdetermined. It was too constrained and that no picture that you could write down could be a picture that was compatible with quantum theory, right? That was the concern that I think a lot of people might have had. And so the attitude was that we shouldn’t talk about what’s going on. And this became known as the Copenhagen interpretation. The Copenhagen interpretation says that our brains cannot comprehend what’s going on between measurements. All we can talk about is measurements. Measurements are made by large classical things like us that are subject to the rules of classical physics. And what happens between measurements, we can’t comprehend. We have a mathematical apparatus for it, but we can’t actually visualize it or write a picture of it. And that’s what we’re trying to fill in that picture. We’re trying to fill in that picture. Let me dissect that one word, which I think might mean two things. The word is between measurements. There are two kinds of between. There’s between in quantum time, if you will. There’s, of course, between observations, but there’s also between in quantum space. And real numbers are a beautiful thing, but they might be completely imaginary because the physics of the universe is not governed by real numbers. Then there’s another. I’m not at all fond of the whole simulation hypothesis. A terrible, terrible hypothesis. I’ve known a lot of computer programmers, so I’m skeptical. However, one interpretation of quantum physics is that there’s a lot to compute. And therefore, you can’t compute something. You have a lazy computer. This physics is basically running lazy computations. And that’s why all these uncertainty principles are there. They don’t involve computing everything. Right, yes. And just when you try to look for a variable that it actually computes. Can you refute this idea? Sorry? Can I introduce you? Of course, of course. I had a good point here. What’s your name? Shrish. Introduce yourself. I’m a new student at Northeastern University. I’ve recently started working at the Media Lab as a researcher and I’ve started to delve into all of this. But what I’ve been working on for the past few days was actually inspired by your tweet about partial Lagrangian manifolds. That’s so cool. You know, this moment should feel good, right? Inspiring the younger generation is so great. What the student is referring to is my post about partial Lagrangian manifolds, which went viral on Twitter, LinkedIn, and Substack. Feel free to follow me on Twitter at ToeWithKurt on LinkedIn. You can add me by searching for Curt Jaimungal. And for Substack, you can visit CURTJAIMUNGAL.org. The links are in the description. That’s so cool. You know, this moment should feel good, right? Inspiring the younger generation is so great. I have a GitHub repository where I had a bunch of Python notebooks that I was working on. I used an artificial programming approach to try to prove some natural laws using partial Lagrangian manifolds. It was actually working. I was proving energy conservation, both from the classical mechanics side and the quantum mechanics side. Honestly, it was interesting because I don’t think the intermediate factor is actually computed, as you were saying. Because if you’re able to compute the functions of natural laws through this probabilistic approach, it’s very strange that you end up with both approaches at the macroscopic and quantum scale. So I think it’s not completely resolved, the gaps between everything. In space or in time or in computation? In terms of computation. Great. Introduce yourself first. I’m an experimentalist. Can you clarify what you mean by not computing in between? Quantum mechanics does intermediate things, right? It tells you, well, in the middle, you have a wave, and it propagates according to the Schrodinger equation, and then it interacts with a multiparty system, I don’t know degrees of freedom, whatever, the classical system. We are honored. That’s a very good question. Thank you. There are some seats in the back. Do you mind coming and sitting on the white chair there? The white cube? Yes. I’ll repeat the question. Yes, yes. The question was… Note that there are a few extra chairs. Let me repeat the question. The question was… The question was, what the hell could I possibly mean by saying that quantum theory doesn’t say what happens between measurements? I mean, there’s the Schrodinger equation, and there are wave functions, and there’s all this apparatus, right? So, what Heisenberg meant when he talked about the Copenhagen interpretation, he wrote about Copenhagen, and he coined the term, the Copenhagen interpretation, which is a chapter in his book Physics and Philosophy in 1958. The way he described it is that he said well, classical things, those have a physical reality, we understand what they are, they’ve been formulated in the context of things that live in three-dimensional space. But we don’t have the mental apparatus to comprehend the reality of what’s going on with quantum mechanics particles, the small particles, so we use this mathematical formalism, but the formalism is not real. It’s not physical. The wave function is just a mental construct, it’s part of mathematics. There’s no actual wave function anywhere. But let me throw the question back to you. Classical. Classical motion. Are you suggesting that you believe that the wave function is a physical entity in the same way that a chair, for example, is a physical entity? I can throw the question back to you. Okay. In the field of gravity, for example, or any other field, is that a real thing or not, right? I learned, I don’t know, in ninth grade that there’s a field, and what it tells you is that if you place a particle in this electric field, there’s a force that can be measured. Yes, yes. It’s a field, a real thing. I’ll take a stance, and I’ll say it now, I believe fields are metaphysically real. Fields are localized intensities that are physically and metaphysically distributed. They are real in the same way that I believe chairs are real, or that you are real. Now, I mean, yes, now it’s easy to take that stance. I agree with you. Yes. And then, we’re not in ninth grade now, we’re already. Yes. And we know that. But there’s a reason for that. But there’s a reason for that. The reason I believe fields are physically real like chairs is because fields have intensity in physical space, and you can, you know, propagate energy and signals through physical space, and so I have good reason to believe that they are physical things. Now, why don’t I believe that wave functions, or Schrodinger wave functions are physical things? Where do Schrodinger wave functions live? In the complex mathematical world. Not just the complex world. No, no. They live in us. They live in our minds. They perhaps live in our minds, but if they are supposed to live in some sort of reality outside of our minds, where would that be? What about potentials? What about potentials? I’ve got a lot. What about you? I’m old. Yes. No, no, I’m talking about unenhanced. Oh, right. This question about potential measurement. Does potential measurement have a reality? Can you guys let us in? Complete the sentence please. So the idea of existence. Please go ahead and explain potential measurement. It would be like the real thing, the thing that you can measure because you have a force, and it will derive from some abstract mathematical things that we call potentials that will be able to change based on how you define it, so it’s less real, but then you have a physical effect like iron or bone that exists for. They have a physical effect, but then the field is zero. And the question of which one is the real potential field, in fact, we don’t know. In fact, that’s not a very meaningful question. And now that the question is complete, can you now give us a little introduction for the rest of us? Well, let me see how to do that. I see Karen doing that. Okay, got it. So there are things called electric fields. We know about electric fields, right?

We know about magnetic fields. You've all been inside an MRI machine. Not everyone has been to an MRI, but you know about MRI machines. You go into an MRI machine, and it turns into a very strong magnetic field. Okay, right, good. I won't talk about why it turns into a very strong magnetic field because I don't have time to do that. We have compasses, right? You know, the Earth's magnetism. So we have these electric fields, and the magnetic field, and these fields that we represent, you know, as little arrows everywhere in space, and they tell charged particles where to go. We have this usual picture. And we have a set of equations, and equations, and laws that describe how these fields change over time. The laws are called Maxwell's equations. They go back to James Clerk Maxwell, okay, in the 19th century. Now, there's a whole bunch of these equations. Maxwell's equations are complicated. There's a whole bunch of them. And it turns out that there's a way to write them in a simpler way by introducing these mathematical things called gauge potentials. These things called gauge potentials are a little bit weird, but they're simpler. They have fewer moving parts. And you can summarize Maxwell's equations into a smaller set of equations for these potentials. And you might say, well, that's great. Let's just take these potentials to be the fundamental things. I mean, they're sort of like fields. You can associate them with places in space. What's the problem? The problem is that they're not uniquely specified. There are infinitely many different, distinct configurations of the gauge potential that all correspond to the same electric and magnetic field. So you ask yourself, well, does nature have just one of them? But if it did, there would be a tremendous amount of experimental ambiguity. We would never be able to know what the true gauge potential is. And so what most physicists would say is that the gauge potential is not physical. The electric field is physical. The magnetic field is physical. And the gauge potential is just a useful piece of mathematics, no different from the way we might think about wave functions, just a mathematical tool to simplify the mathematical procedure. And that's what we probably thought. And then these really annoying people, so David Bohm and Yakir Aharonov decided to make our lives difficult and show that under certain circumstances, when you have charged quantum mechanical particles moving through certain kinds of devices, where the electric and magnetic fields seem to be turned off, but the gauge potentials are turned on, it's possible to have experimentally observable effects on the landing sites of particles at the end of these experiments. And that raises the question, well, but if the fields are nowhere near where the particles are going, and the only thing that's around is these gauge potentials, but I didn't think the gauge potentials had any physical meaning, how can they produce an experimental effect on the behavior of the particles? I think that was a very good time. Yes, Shauli. Jack, you said something I think is, so there's a logical problem, right? But you said the reason you don't think gauge potentials exist is that they're not unique. There are infinitely many of them. And by that argument, no human exists. And if I ask you what is a human? There are a lot of us potentially. There are infinitely many of us. And what is a human? A featherless biped. To pick up some arguments more than just the fact that they're not unique, right? Because you can mess around with fun as a criminal layer. You can always get a very unique way. But there's no equivalent classroom for you, Shauli. There's only a unique Sha. Now you're first class. Let me rephrase. Let me rephrase. There must be uniqueness. Okay, let me stop for just a second and answer your question. I think what Jacob is basically saying is that if there are many different ways to interpret reality by having very powerful equations that can explain it, but... they're completely underdetermined. For example, if I take, I mean, this is one of my problems with string theory, for example, or one of the criticisms of string theory, is that there are so many different possible ways to create today's world and it doesn't constrain it. And therefore, the predictive power of things that are unobservable is very small because you have so many parameters for the problem at hand. Didn't I give up on string theory? No. Okay, what are we, what are we, is this? So, so, underdetermined and there's not a lot, is that what you meant? Do you mean underdetermined? It's radically underdetermined. So, Shelly, for example, I can do experiments on you and determine which human you are, and ultimately... I'm not sure about that. You're not, you're not underdetermined. In other words, is, is, like... Can't you, though, say that the gauge potentials encode aspects of reality as long as, you know, those aspects don't change when you change the gauge? You know what I mean? Like, it's redundant, it's not that they don't exist, it's that they exist, it's a redundant description. Yes, one way, one way to think about gauge potentials is, you know, let's say you want to describe the surface of the Earth, okay? And maybe you, I think, the surface of the Earth is physically existing, but you want to describe it quantitatively. So you decide, I'm going to work with latitudes and longitudes. And you say, I'm going to describe where things are by latitude and longitude. And then, you know, you start building theories out of latitudes and longitudes, and you start believing, I think latitudes and longitudes are real things. They physically exist, those lines, they mean something really. Then somebody comes along and says, well, actually, I think where I live should be the origin of your coordinate system. So I'm going to use a different coordinate system that's slightly different. And you go, you can't do that, because we all know that the prime meridian is definitely something, right? Big Ben. Right. And so, you know, but when you realize, wait a second, there are infinitely many coordinate systems you can use to describe the Earth, and not just things like latitude and longitude, but you have Mercator projections, you have all the different coordinate systems you can write down. You start to wonder, because there's no real coordinate system for the Earth. The coordinate system is really just, you know, a mathematical, you know, descriptive toolkit. And the fundamental thing is the surface of the Earth, right? And so the situation here is that the electromagnetic magnetic fields are like the surface of the Earth in this analogy, they're the physical thing, and the gauge potentials are like the different coordinate systems that we can use for those things. The gauge potentials are equivalent to the wave function in this sort of. So John Bell, whose name comes up a lot in the foundations of quantum, John Bell was a theoretical particle physicist and he also did pioneering work in the foundations of quantum mechanics from the 1960s through the end of the 20th century. He coined a beautiful word to distinguish between things that we think, at least we have good reason to believe are physically real and things that are perhaps like wave functions or perhaps like gauge potentials that we think are real. He distinguished between, so there's a technical term in quantum mechanics called an observable. An observable is the attributes of a physical system that observers go and measure, like the position of a particle, the momentum of a particle, the energy, anything else. And those are called observables. He wanted a word that was somewhat analogous to observable but words for things that describe how things could really be, existentially, like what was really there. And so he called those things "beables," not "observables," but "beables." And you know you meet somebody who knows the foundations of quantum just from books because they come up to you and say, tell me about the beables. What are the beables? Beables. Has nobody called them that at some point? You're going through an evolutionary process. It's like going through a chrysalis stage, right? It's a stage of endurance, and then you say, no wait, I haven't seen the light of their endurance. So what John Bell would say is that there are some things that can be considered beables. And he was very explicit about this. He clearly put gauge potentials in the category of non-beables as things that are mathematical accessories, artifacts of our description. And there are many other examples. There are many other examples. So this is an interesting story, okay? But right after that, get ready for the next question. Raise your hands. Who's ready for the next question? Oh, let me do the next question. I'll jump into the story. Okay, go for it. No, go to the story. The story? We'll continue the story, okay. So one of the most important pivotal moments in the evolution of quantum mechanics was in the early 1920s. The 1920s was the period when physicists decided that they were not going to be able to come up with good laws that would be experimentally adequate based on the pictures they were describing. So maybe, you know, if you studied chemistry in high school, you learned about the Rutherford atom where electrons orbit a nucleus, in these kinds of orbits. And people still draw these pictures. Well, up until the early 1920s, physicists were trying to make this work. They were trying to come up with a set of equations and laws that would build on that physical picture and be experimentally adequate, meaning they would agree, they would make predictions that would agree with the things they were seeing in experiments, and they couldn't find the right set of laws. They were using all sorts of different laws that they knew, that they inherited from centuries of work in physics. Then in the early 1920s, people like Wolfgang Pauli and Niels Bohr started to doubt that this was possible. And Bohr had a pivotal conversation, a set of conversations with Werner Heisenberg, who was very young at the time. He was in his early twenties. And Bohr had already won the Nobel Prize, in which Bohr revealed his great secret. He no longer believed in orbits, and electrons orbiting them. And Heisenberg took this up, and he was thinking about it, and then in the spring of 1925, Heisenberg was a PhD student in Munich, but he was visiting Göttingen, which was a center for theoretical physics and mathematics. He was working with Max Born and Pascual Jordan, and he was looking at all these formulas, and everything Bohr had told him was just sort of soaking into his brain. And he was having a tremendous hay fever attack, the worst and most important hay fever attack in history. Okay, right? So think about it this way, right? You think you have hay fever or something, and it's a terrible affliction, and you wish you didn't have it. Well, the entire history of science might have been different but for this hay fever attack, because Heisenberg was miserable, and people said his face was so swollen, he looked like he'd gotten into a fight. And so he went to this island called Heligoland, where the tree pollen levels are very low, and he went with two goals. One was to memorize a large amount of Goethe's work, and the other was to solve the quantum theory. He achieved one of these goals, one of them, okay? But this is the thing. He created a paradigm shift. In cosmic language, he created a paradigm shift in science. He said: I'm going to get rid of the physical pictures. We should not be formulating physical theories through pictures, but we should be formulating them only in terms of quantities that can be experimentally measured in principle. He says this in the opening lines of this, it's philosophy of science, like 101, a major paradigm shift statement. He says, we'll kick them out, and we'll build a theory from mathematics. And this theory that he builds eventually becomes what we call matrix mechanics. And it's a theory without pictures. It's a theory of raw mathematics. And this was the beginning of the end of the world of pictures. Everybody was astonished. Einstein said, Heisenberg has laid a great quantum egg, that's how he described it, right? The idea that if you eliminate the pictures, you suddenly get equations and laws that seem to work and give the right predictions. This was unbelievable, right? But then Schrödinger comes along immediately and brings back the pictures. He brings back the pictures, and he does it by introducing the wave function. And how does he get the wave function? It doesn't just come out of nowhere. It doesn't just come out of mathematics. It comes out of classical physics. It comes out of classical physics. So there's a way to study classical physics. You don't know that force equals mass times acceleration, or force equals mass times acceleration. Well, it turns out that you can calculate the force that equals mass times acceleration, and you can write it in very complicated mathematical ways. And there's a very abstract way to write classical mechanics. It's called the Hamilton-Jacobi formulation. And we almost never teach this to students anymore. Almost no students studying physics have ever heard of it. But Schrödinger knew about it. And the Hamilton-Jacobi formulation, it reformulates classical physics in a way that's clearly wave-like, with a clearly wave-like quantity called the fundamental Hamiltonian function, or the Hamilton-Jacobi function, which obeys this strange partial differential equation. And Schrödinger looked at this wave-like thing in classical physics. Now, let's be clear, this wave-like thing doesn't seem to have any physical reality. It's just an alternative way of describing everything that Newtonian particles do. But he took this wave-like thing and the differential equation, and he was satisfied. He looked at it and realized, my God, that looks like the iconic approximation of the wave equation. I'm going to call the wave function, I'm going to call it Schrödinger, the wave function. And he didn't call it the Schrödinger equation because it was him. That would have been too much, yes. But he uses this Greek letter psi to denote it, right? Maybe because that's the symbol for Poseidon and his waves. I mean, I've always wondered what that was. But he introduced this. But the wave function was a consequence. The wave function was a consequence of a clear mathematical appendage to classical physics. Nobody would have imbued the fundamental Hamiltonian function, this strange abstract wave-like quantity that satisfies this strange partial differential equation. Nobody would have imbued that with any ontological meaning. And the wave function was a direct descendant of that structure. Now, physicists loved wave mechanics. In fact, he originally called it wave mechanics, which is just a better name. Wave mechanics is more evocative. Anyway, he called it wave. And physicists loved it because it was now back to differential equations. They had this picture of this wave function. And Schrödinger, for at least two years, took the wave function seriously as a physical entity. He said, these wave functions, they don't live in physical space. They don't live in three-dimensional space, the space that we live in. They live in probability space. And there are statisticians around. And of course, parameter spaces. Wave functions live in parameter spaces, not in physical space. And so Schrödinger found himself arguing that perhaps the higher-dimensional space where the wave functions live, perhaps that is the seat of physical reality. And perhaps in this reality, all the possible things that could happen to a system, all appear in an embryonic version of the many-worlds interpretation. And he held this view for a few years. Now, many of you have heard of Einstein saying this famous quote, I don't believe God plays dice with the universe. That was in a letter to Max Born on December 4th, 1926. He says, you know, quantum theory is very hypothetical, but I don't think it's the real thing yet. I personally don't believe God plays dice. People don't know the next sentence in that letter. The next sentence of that letter. And they don't know the exact wording of the next sentence because it's been mistranslated. In the primary translation of the Einstein-Born letters that Irene Born did, the next sentence has been mistranslated. And I know this because I thought the English was a little bit strange. I went back and looked at the German and the German was clearly different. And I put the German through Google Translate and it was clearly a different translation. And here's the difference. In the English translation that I've read, Irene Born's translation, the next sentence is Einstein saying, waves in three-dimensional space as if by rubber bands. And he actually puts a little ellipse, dot, dot, dot, as he does. And you, my God, Einstein didn't like three-dimensional waves? That's a strange thing to say. I mean, Einstein certainly liked light a lot. Light is a three-dimensional wave. But in the original letter, it's not waves in three-dimensional space. It's waves in N-dimensional space. He dropped the N and that's crucial because when you have N particles, the parameter space is 3N-dimensional. And what Einstein didn't like was that Schrödinger was emphasizing that the seed of reality is an abstract parameter space. And that Schrödinger was emphasizing that the physical mechanical wave in this abstract parameter space is the actual existence of nature. Can you explain to us what N is? What is the number of molecules? What is N? So when you have one particle, quantum mechanics is associated with this particle, and this thing called the wave function. And the wave function in its simplest form is that at every point in space, if you want to measure where the particle is, the probability of finding it at one point in space is given by a certain mathematical operation performed on the wave function. So you can think of the wave function as sort of assigning a number to every point in space. It's sort of like a field, if you want to think of it that way. And if I measure where the particle is, I'll get one of the answers and what the field tells me is where I'm going to find the particle. And this picture is how quantum theory is usually introduced to new students because new students will typically learn about quantum mechanics, quantum mechanics for one particle. It seems as though the first two-thirds of the first book is quantum mechanics for one particle. And they get really used to thinking, oh, the quantum wave function is like a field in three-dimensional space. Right, but here's the problem. The moment you have two particles, two particles require six parameters now, you see, because you have to specify, if I measure, I'm asking where am I going to find the system, right? Where am I going to find the two particles? There's the x coordinate, the y coordinate, and the z coordinate of the first particle. And then there's also the x coordinate, the y coordinate, and the z coordinate of the second particle. And these six variables define a six-dimensional space, three times two, two particles. N now equals two particles, three times two particles. And that's where the wave function lives. The wave function is a function that lives in this six-dimensional configuration space. And for n particles, it's a 3n-dimensional space. So Schrödinger took it seriously. He says, I think this is perhaps the real situation. Then in 1928, in his fourth lecture on wave mechanics, he retracted this view. He said, you know, Max Born came along and said the wave function is not a mechanical entity. It's really about the probabilities of measurement. And I no longer hold that view. But I think by then it was too late. And many physicists continued to believe that wave functions were physical, just like anything else. Can we talk about superposition now? Because we were talking about action at a distance earlier and this whole concept, we now have these multiple particles. They can be in some kind of superposition. Explain to us a little bit about this whole action at a distance. Yes, yes. So what distinguishes quantum mechanics is that wave functions are actually reflections. So what Heisenberg was doing and what Schrödinger was doing were actually just aspects of a deeper mathematical structure, the structure of Hilbert spaces. And this formulation of quantum theory in Hilbert spaces was done by Paul Dirac in 1930 and John von Neumann in his 1932 book. And in this picture, the state of a quantum system, if you want, you can think of it like this: it's basically a wave function. The state of a quantum system is something that if one thing is possible and another thing is possible, you can superpose them and that's also possible. So, if there's a wave function that assigns certain probabilities for a particle and a different wave function that would assign different probabilities for the particle, you can superpose the two wave functions together. And that's called superposition. That's very strange, isn't it? And that's completely different from classical physics. Yes, it's different from classical physics. For example, if one of the wave functions, and if one of the wave functions assigns a very, very high probability of a measurement showing the particle is here and the other wave function assigns a very, very high probability of the particle being here and you superpose the two wave functions, what have you done? Are you saying the particle is in both places? Well, the Dirac-von Neumann axioms, the standard textbook axioms don't say that because they don't draw the picture at all. All they say is that if you have a superposed wave function, then if you measure where the particle is, there's some probability of finding it here and some probability of finding it there and anything else you want to say about it, like the particle actually being in two places, is strictly speaking outside the axiomatic scope of the axioms. That's just for color. So every time a physicist tells you, I'm going to tell you this is a secret. Every time a physicist tells you, quantum physics has proven that a particle can be in two places at once, he's lying to you. Now, I don't mean they're lying to you in the sense that this is definitely wrong. It might be right, and it might be right, but it's not right based on any interpretation of quantum theory that we have except for the many-worlds interpretation. None of the other interpretations, including the Copenhagen interpretation, including -- And now in simple English, tell us what those three or four interpretations are? Three or four? Yes. Oh, there are quite a few. Well, tell us the three dominant ones and then the fourth will be yours. So the Dirac-von Neumann textbook formulation says nothing more than that you do measurements and we predict what we're going to get, that's all. There's very little interpretational work. The Copenhagen interpretation, which we've already talked about, is the idea that there are classical things and classical things follow classical laws and quantum things that we've just used the mathematics to describe and between experiments, we can't actually say what's going on. That's the Copenhagen interpretation. In the 1920s, Louis de Broglie introduced the first pilot-wave interpretation of quantum theory. And the pilot-wave interpretation says that there are wave functions, but there are also particles, actual particles, classical-like particles that exist in specific places. And what the wave function does is it guides the particles and directs them. And that's why it's called the pilot-wave interpretation. And the reason why the particle is likely to be found in certain places where the wave function is stronger is because where the wave function is stronger is where the wave function is directing the particle. My interpretation was that particles appear where the wave function collapses. Not according to the pilot-wave interpretation. So they are actually physically manifested. The particles are physical particles, physical particles, yes. And this was a primitive picture that de Broglie put together and his colleagues at the time tore to shreds. And then 25 years later, David Bohm, the same David Bohm from the Aharonov-Bohm effect, was at Princeton. He wrote a book called Quantum Theory, in 1951. And he tried to explain the measurement process as best he could using the standard approach to quantum mechanics. And he submitted his book to Einstein. And Einstein was very dissatisfied. He said, try harder. And the next year, Bohm published research in which he, independently, presented the pilot-wave interpretation. Much more sophisticated, much more complicated. And along the way, he invents a tremendous amount of important physics, okay? And most importantly, he introduces the concept of decoherence, which is one of the central ideas in the practical implementation, I mean people talk about decoherence timescales all the time. That comes from David Bohm's work, who was trying to make his pilot-wave interpretation work. And this idea of decoherence, which I can talk about, but I'll talk about it for a moment, is what makes the problems that de Broglie was having and solves and makes the pilot-wave approach work, at least for systems of a fixed number of infinitely many non-relativistic particles, which is a very narrow kind of -- What does decoherence mean? Ah, what is decoherence? Good, what is decoherence? Okay. So, when you want to calculate something using ordinary, familiar, classical probability theory, we think about all the possible ways that can happen. We assign them probabilities. We add the probabilities together. It works fine, right? If you want to average something, what you'll do is, you know, you'll consider all the different possible values that something can have. You weight them by the probabilities, and then you add them up, and it'll work fine. When you try to do the same thing with certain quantum systems, you get the wrong answer. For some quantum systems, when you have superpositions in particular, you have superposed wave functions, what you find is that, in general, in addition to the quantities assigned to different probabilities, there are these extra terms, these extra factors, these extra things that come in and mess up the calculation. And these things are called interference effects. They make the probabilities that you calculate from quantum systems behave differently than you would classically expect, and they destroy the kind of pilot-wave picture that de Broglie was trying to develop. But Bohm realized that if you take a system, or a particle, and you actually have some kind of measuring apparatus that interacts with the particle, and you put the measuring apparatus there, and you formulate it and describe it physically, as if you've actually put it in and tried to deal with it with quantum mechanics, what you find is that the interaction with this large, complex measuring apparatus that has a lot and a lot of degrees of freedom, a lot of moving parts, it greatly dampens the interference effects, it suppresses them so much that your probabilities now look like they would according to classical statistics. And that's called decoherence. It's the elimination. He gave it a name, and he first introduced it in chapter 22 of his 1951 book. He called it the destruction of interference in the measurement process. That's exactly what he called it, but we now call it decoherence. Now, let's get back to consciousness and our role in the universe. I'm not done. There are many worlds. No, no, no, no. We've talked about many worlds. Many worlds. No, no. Just let me stop for a second. Yes. The observer doesn't need to be conscious. No, not in the Bohmian sense. The observer can be any particle that interacts with it, and therefore there's no need for consciousness in quantum mechanics. It's not enough to just have one particle, because for the decoherence process to work, you actually need large degrees of freedom. For example, one electron cannot measure another electron. Sorry. But a macroscopic body made up of a lot of atoms can cause decoherence in the system. So when do you become an observer? How many atoms do you need to become an observer? How many hairs do you have to lose from your head before you become bald? Can I ask you a question? Can you please? No, no, no, no. Explain. Explain. Just tell us. There is no definition of observer in these pictures. There is no fundamental definition of observer. The decoherence device. Yes, please. Yes. I've been thinking about some related questions as I've been reading, and the fact is that every measurement has an observer. Because if some conscious people are not looking at the result, we don't know that it was there. The measurement problem, that it's an undefined concept. Yes. That's correct. It doesn't need to be a decoherence device. It doesn't need to be a measurement. It doesn't need to be an observer. Exactly. The language of observers was required for the original axiomatic formulation of quantum mechanics because the axioms say that observers make measurements. What Bohm was trying to do, and what people trying to provide this kind of physical interpretation of quantum theory, Bohm was an example, and Hugh Everett, the many-worlds interpretation proponent, was an example, is to eliminate the observer and the measurements. And you just have systems. Some systems are small, and some are large. The larger systems cause more decoherence. That's exactly right. And this coherence means that you get more and more classical-looking results, but it's graded. There's no sharp dividing line between what is observed and what is not observed. Can you tell us what the scale of this grading is? In other words, at the top, I don't know, to this extent, it's decohering, and at the bottom, it's not, and in the middle, we don't know, it's a fuzzy gradient. And because I work in the foundations of physics and philosophy of science and high-energy theoretical physics, I didn't know the answer to this question, so I went and talked to a friend, who's a chemist. Because chemists worry about these questions exactly. They worry about when you can start to pretend that things are somewhat classical and not classical. And it's okay if there's something in between where we don't know, it's okay. It's a fuzzy line, but it's on the order of large molecules. Okay, like for example? I think he said something like sugar molecules, or polymers, I forget exactly what he said. Okay, like 10 atoms or something? No, not 10 atoms. You need more than 1000 atoms, something like that. Stop, okay. 100, now I'm just, it's bigger than 10, and it's smaller than a mole, and I don't remember exactly what the number is. What about macroscopic phenomena like superfluidity and superconductivity which are macroscopic? Well, well, I should say under normal circumstances, okay, under normal temperature conditions, right? Because it's possible to have many particles still behave in a quantum mechanical way very clearly if you keep them very cold. For example, squid, superconducting quantum interference devices, right? Or Josephson junctions. They are systems that can, under very carefully controlled, isolated, low-temperature conditions, exhibit distinct quantum phenomena on large scales. Moment, I have a question for everyone. Who's having a good time? Is this amazing? Who wants another seven hours of this, right? This is amazing. Thank you. Jacob, exactly like this is extraordinary. Okay. Yes. Let's open it up for some questions. Please, please. We'll do a flash tour. I'm not talking anymore. Go ahead. This is great. I'm not deep... And then, at some point, you'll tell us about your own interpretation, but for now, let's open it up for questions. Yes. So we'd like to move from history to the future. What are the big developments that have used the states that we can all test out in the next 10 or 20 years that could cause progress in that corner? Theoretically, he has a billion dollars to invest. What should he put it on? Excellent. I'm glad you asked that question. I'm very glad you asked that question. If someone has some money to spend, where should they spend their money? What's the good thing to invest in over the next 10 or 20 years? Okay. So I don't want to just throw it away. I want to see it grow. You want to see it grow. The number of serendipitous outcomes that have resulted from the philosophy of physics, the foundations of physics, the foundations of quantum, compared to the number of people who have worked in this field, is astonishing. So, if you were to make a list of important things that have played a central role in modern quantum technologies, right? Quantum communications, quantum cryptography, quantum computing, like all of that. GPS system. Okay, atomic clocks, I think. Yes, that's right. Yes. So, if I wanted to make a list, right, and I've mentioned decoherence, which came out of David Bohm's philosophical work on quantum theory, right? But there's entanglement itself. There's the famous EPR paper, which introduced, you know, the idea of EPR states, right? GHZ states and quantum Turing machines and quantum teleportation and important theorems, no-cloning theorem, no-signaling theorem. So a very small number of people are responsible for these fundamental results. And if our field of foundations of physics and philosophy of physics, and quantum foundations, and if our field got royalties, and if a paper in atomic physics mentioned a GHZ state, we'd get a nickel, there would be no funding problems in my field at all, okay? So the question, if you want to think about where to invest, would another million dollars in quantum computing make a marginal difference? I would say no. And that doesn't mean that quantum computing is a bad idea. Quantum computing can be really great. But the cost-benefit, right, for quantum computing, you're going to have to spend a huge amount of money to make a big impact in that field. So you want to look for fields that are severely underfunded, like real funding opportunities, and artificial fields, where the expectations are artificially low, but where you know that these fields actually generate a tremendous amount of insight and a tremendous amount of things that end up playing a big role in modern science. And I would humbly argue that the philosophy of physics, the foundations of physics, and the more philosophical side of quantum foundations, is severely underfunded compared to the contributions that it routinely makes through science. Great. Does that answer your question? So, if anyone wants to endow any professorship, that would be huge, and it would have a huge impact on this field. Let's re-ask the question. I'm a boring use-case engineer looking for what I can use for quantum progress in the next 10 to 20 years, maybe some real things I can hold onto. Practical applications of quantum theory. You can go back to it if you like. Do we have anyone who knows anything about practical applications? I don't know, but I can give you an answer. Atomic clocks, certainly, exactly, yes. I'll give you one example. Okay, I'll give you one example. By the way, every physicist in the room is allowed to answer that. No, wait, I have an example ready. I have an example here, okay? So a project that I'm working on, it's a new formulation of quantum theory, not just an interpretation, but it also comes with a precise mathematical relationship between the theory of stochastic processes, which is an old, non-quantum way of talking about systems that behave probabilistically, and quantum mechanical systems. It's this mathematical bridge between the two. And its meme coin. And its, what? We can do a meme coin. We can make a meme coin, yes, that would be great. Quantum. Well, it's absolute, but not quantum, okay. It's quantum and not quantum at the same time. So, but here's the point, right? On the one hand, what this does is it provides a different way of thinking about quantum systems because if every quantum system is mathematically dual or representable or equivalent to just a boring random system that evolves probabilistically without all the weird appendages of Hilbert space and complex numbers and all that, okay, then perhaps this sheds some light on what's actually going on under the hood of quantum theory. And that's interesting from a metaphysical point of view. But now we can flip it around and say, well, what if I have a really complicated random process that I'm trying to design? It's a complex process, and it's a process that perhaps is beyond the usual approximations that we'd like to make. There's this famous approximation called the Markovian approximation, which says that we can ignore past effects, right? We do this all the time, but what if we can't? What if we have a clearly non-Markovian system? Well, it's not clear how to simulate that efficiently. But with the bridge between these kinds of systems, and these non-Markovian systems, and quantum systems, there's

It is possible that some of these systems, which might be very difficult to simulate on a computer, could have real-world applications and be efficiently simulable on a computer. Quantum computers. All you have to do is perform this process, which is a very complex, non-Markovian process, and figure out what type of quantum system it corresponds to, and then figure out if you can build that type of quantum system on quantum hardware and a quantum computer. And so there is hope that you will be able to simulate some very difficult stochastic processes that could have practical applications across science, economics, finance, and anything else, right? Some of them might be efficiently simulable on quantum hardware. Unfortunately, we don't have any quantum computers, but one day if we do, this is likely to be a new use for quantum computers. One of the big mysteries, say what? How far do you want them to be? I don't know yet. But I'll just say, one of the big mysteries about quantum computers is - how many qubits, like? I don't know yet. Okay. But one of the mysteries related to quantum computers is what is their utility? You might think, well, quantum computers, right? They take all the classical computations, and they do them all at once, right? And that's why they're powerful, but it turns out that's not how they work. They don't work that way. There are a lot of things that you might think they would give you a speedup for, but they don't give you a speedup for. There's actually a very limited set of problems that quantum computers, at least as far as we know, give you a noticeable speedup with. One of these programs is known to be breaking RSA. So a quantum computer will make it very efficient at breaking RSA, prime factorization, that sort of thing. There are a couple of other problems that we know quantum computers can be very useful at solving. One of them is just efficiently simulating quantum systems. That could open up a whole other avenue, right? Simulating very complex real-world worlds, non-quantum stochastic systems using quantum hardware. And anytime you find some potential new uses for quantum computers, that's something that it might be useful for. Can I ask a question there? When you said Markovian systems, I was wondering about the idea of having concepts, especially in finance, where past information doesn't tell you anything about the next step in something. Is that a very limited view? If you have enough quantum computation, could a Markov process be different? Is there information in the past? Well, I said there is. Yes, yes. And now, to be clear, I am not an expert in finance or in algorithmic trading or anything related to that. So you can frame anything I'm about to say here with the huge, huge, great - you've convinced me now that anything you say will be accepted - there's a very narrow set of topics that I have absolutely no business whatsoever. Anyone who knows me will know that, but okay. But I'll just say, one always takes a risk when designing anything that's doing some sort of strong approximation, right? But of course we have to do approximations all the time. I mean there's an old saying that every model is wrong. Yes, because it's an abstraction. Absolutely. Every model is an abstraction. Every model entails some sort of simplification, so that if we tried to do the whole thing, it would be the original thing, right? A model, by definition, is some sort of simplification that we can work with. And we always have to make some sort of approximations. And the question is: are all these approximations legitimate? Are they all justified? Now, if there are good, strong reasons to justify a Markov approximation, the idea that all we care about is the present when predicting the future, if that's justified, we'll do it. But if the only justification is, well, this is where the light is, and the lamppost is shining there, so I'll look there, I don't know how to do anything else, that's not a good justification. And I would say that having a formalism for being able to deal in an elegant and efficient way, with processes that take the past into account would be useful, useful at least in modeling and seeing if it's useful for finance. We're on the flash round. Raise your hands, go ahead. So - introduce yourself. Matt Sampson, I'm a pediatrician and I also do a competition in the genomics lab, and it was great. I'm taking a little bit of it. The modeling and measurements that you're talking about, you know, health and disease are doing measurements all the time. And historically, we've come to understand human health and disease through classical physics, the heart is a pump, there's diffusion, and there's chemistry. Do any of the things you're talking about, space and time, waves, will help us understand how molecules work in cells, or how cells work together, or how a doctor measuring blood pressure affects the way we interpret that pressure and what we do about it? My answer to that question is probably no, at least not directly. However, there might be indirect consequences for how we practice medicine. And the reason is that one way we practice medicine is by using causal modeling. And that leads us, now, to see how smart it is to separate it again into the kind of question of what is causality, right? So, you know, if you think of the heart as a pump, I mean the heart, whatever quantum theory model you have, we'll probably ask it to be able to replicate you know, the observed behavior of macroscopic classical systems. The heart seems to be a large macroscopic classical system. Some of us have bigger hearts than others, but everything seems to be our hearts are large enough that we can deal with them classically. But if you're trying to discover drugs, right? If you're trying to understand how certain medical interventions will have a causal effect on disease outcomes, you're interested in a topic called causal modeling. Now, causal modeling has become a very, very advanced field of statistics, a very complex field, I mean, you know, doing double-blind studies, you know, observational randomized, randomized, you know, double-blind studies, that sort of thing, right? We do causal modeling. We have a set of variables, a set of things that we're trying to study, and we're trying to understand how they relate to each other, right? We're trying to understand how, you know, some quantitative attributes of some physical states are related to other states, or related to medical interventions, or drugs, or... That's right, isn't it? You want to have a causal model to understand why that happens, and a predictive model to illustrate what that intervention will affect in the future. That's right. So, how much increased explanation or causal explanation will come from incorporating some of those theories that you want? Not directly, but the causal modeling framework gives an interesting way to think about causality itself, okay? So, you know, for example, if you want to understand why we think a certain drug has a certain effect on a population, right? Of course, we'll give the drug to some population, and we won't give it to the population, we're basically controlling a variable, and we're looking to see if there are, you know, correlations, statistical correlations that show up. And we're not just looking for correlation, we're looking for causal relationships, right? Causal correlations. And in order to discover causal relationships, and not just statistical correlations between things, we have to keep in mind that we can do interventions. We have to imagine that some agents, the agent is the person running the study, can choose to activate a variable or not activate a variable, and then find out, you know, what kinds of consequences we'll get from that. That's the operator. But in an observationally independent way, that's the whole point of double-blinding. It's in an observationally independent way, but it depends on the idea of an agent doing an intervention, okay? And this idea that we're doing causal modeling using this interventional concept of causality is becoming pervasive, and I know people are talking about causal modeling, for good reason. Because in everyday life, when you're doing medical checkups, or we're trying to understand interventions of a more general type, it's not even a drug, right? We have people, and people are agents, and agents can choose to intervene or not intervene in certain ways, and we can study the health correlations from them. That's how we can discover causal relationships. An agent can intervene. So I want to open this question up to everyone and rephrase it slightly. How much evidence is there that biology deals with quantum effects? And in which biological processes have quantum effects been observed? There are some theories that consciousness arises from quantum. Let's turn it off, please. That's absolutely right. And this is a question for everyone here. For example, it has been hypothesized that microtubules in neurons have quantum properties. I have absolutely no concerns about many different aspects of biology at a very early stage. It's not necessary for us to be humans and the pinnacle of evolution as we like to think, which is ironic. I mean, anyway, but it could be bacteria, it could be like bats, it could be anything that does some sort of sensing or some sort of feedback. My guess is within one of the oldest oxphos processes, oxidative phosphorylation in a type of mitochondrial energy production. I'm sure there are quantum effects being exploited, but I'm not an expert. So I'd like to open it up somewhat. Who will give the harsh response to this response? The harsh answer is the only thing we take. So I understand this. I might say that this is inversely proportional to the amount we know about the system. Because I think we use this probability in biology to substitute for a lack of measurement in French or a lack of detailed signal, you know. Yes, because you incidentally mentioned two or maybe three things that we don't know much about, any neural function and I've measured a few microtubules and early life. I see where you're coming from. I'm not saying there isn't a lot of probability there. And I don't know how it manifests. But the one thing I'm saying is that we shouldn't forcefully impose it in the less explored areas. Yes, yes. So I work in a lot of areas where people use this field to explain things they don't understand, for example, genomics. They say, oh, it must be a genetic effect. I'm like, that's nonsense. So I'm not saying that just because we don't know much about them. On the contrary, I'm saying it for very specific reasons. But, you know, we have a neuroscientist there, you know, in psychiatry too. I'm curious to see if anyone wants to engage with this, yes, there's quantum here, because that's what I think you're getting at, right? So John, John, go ahead. Yes, yes, exactly. Yes. So that's within the realm of physics. And let me do a very quick trivia here. It's a parenthesis, but I think you guys will like it. Just make sure to close the parenthesis, otherwise you'll get an error. So in a sequoia tree, in a sequoia tree, where does all the biomass come from? The very simple explanation is that it must be the soil. It's just absorbing nutrients. It's carbon. It's carbon, de-carbonizing the atmosphere. All the wood actually comes from that process that John just mentioned. And thus fixing carbon atoms from the air. And when you lose weight, where does the weight go? Why is it quantum? Go ahead, John. Why is it quantum? Well, for that, why do you do it? Why do we talk about it? It has very specific chemical interactions that it can reproduce and rearrange and interfere in a measurable way. So if I understand anything from the lectures about... Quantum doesn't mean uncertainty. It's here. Quantum receives something, then it has a quantum effect, then it interacts. Okay, so everything is quantum, which is good. We'll do static exploration. Yes. Yes, yes. Olfaction. There's a known phenomenon in olfaction that is better explained and predicted. It's that measurements are computed by quantum representation. So, this is where, unlike consciousness, where you can't measure anything. Okay, let me just... But this is the flash round, so I'm happy to move to the next question. Oh, okay. I just want to ask what you mean by consciousness arising from quantum mechanics, because... We'll get back to that. This might be the end. Certainly. Flash round, go ahead. Go ahead. Uh oh. Uh oh. If he has to look at his phone, that's a problem. Naive questions are always the best questions. What was that? What kind of question? A naive question. It's a naive question. An advanced naive question. I love it. You're not trying to influence. It's... Yes. It's not trying to influence. Does quantum field theory explain non-locality unnaturally, since there is only one electron field everywhere? Does quantum field theory naturally explain non-locality? So the problem with the word "non-local" is that it needs precision. Okay. What do you mean by non-local? No, this isn't me being a pedantic philosopher. There are different definitions of non-locality. I need something more precise. But tell us, give us some options. We have two electrons in a tangent. Yes. They were here once, and then they were separated. One on the moon and the other on Earth. But nobody noticed... A measurement, whatever it is on one of them, you determine the spin of the other. It seems like something weirdly non-local is happening. So does quantum field theory solve this problem? No. No, quantum field theory does not solve this problem. Quantum field theory does not answer any of those fundamental problems by quantum mechanics. But since you have only one electron field everywhere, well, I guess. The electron field, is it de-localized and spread out in space? You can link a photon and an electron too, and then you have two different fields, right? So, yes. Quantum field theory does not solve the problem, the fundamental problems of quantum mechanics, the measurement problem or the non-locality problem, yes. Very naive question. This assumes that nobody noticed either of the two throughout their separation, right? But notice something really important about this question. Notice that in all these discussions about non-locality in quantum mechanics, going back to Einstein, Podolsky, and Rosen, and the EPR paper, and the example, there's a particle here, there's a particle, they interacted, they got entangled, and they went far, far away, and then somebody measured one of them. And somebody measured the other. Notice that you have agents and interventions again. You have observers playing a central role in this picture. Oh, they hit something, right? If they hit something. Hit, yes, the observer. If they hit something and it's not counted as an observer, you don't do like, you don't axiom. If one of those particles hit the moon, and the other drifted off into space, it would look like it was in the other direction. Yes. If that person, you know, had their spin determined at that moment. I said their spin was determined. What do you mean by determined spin? In the sense that now, at that moment in time, say, where are you to measure it? I mean, okay. Then you can say, well, there's nothing real. We're not here. But no, no, no. But you see, that's exactly the point, isn't it? If you get rid of the idea that there's a fundamental axiomatic role played by the observer, then exclude the observer and go back to... So look, before quantum mechanics came along, physics moved to a completely impersonal picture, right? The Laplacian model of physics is that there's a set of things everywhere. Particles are moving in different positions, different velocities, and a giant differential equation describes how this state of the universe updates moment by moment. There's no role for observers. And there's not even a role for causal effects between things. Observers, causal effects, these are all just colorful language, descriptive language, ways of summarizing things that you see, ways of painting a picture. But ultimately, it's all irrelevant, right? Then quantum theory comes along, and suddenly the observer is back again. The observer plays a central role. A lot of interpretive approaches to quantum theory, not just mine, but Bohmian mechanics, all these other approaches demote the observer to being a normal system. There's no fundamental role played by the observer. When systems become entangled and some system, like the moon, not an observer or anything else, comes along, and interacts in some way with the particle, there's no collapse. And so the causal effect that's supposed to propagate superluminally, it becomes actually more obscure to say that this is what's happening in this picture. So Jacob, can I chime in for a second? So let's talk about the moon for a second. So basically you have this entanglement, and let's assume there was no human observer, but this touches the moon, and now you've just kicked the can down the road. You've basically transferred the uncertainty to the next stage, so every time it bounces somewhere, this secret is spread and carried. And sort of my problem with all of that is the concept that there was no intervention on either of these two particles is something that it basically collapses into. This kind of non-locality assumes that nobody has touched it for a while. And then there must be, of course, some communication and coordination so that nobody touches it, so that I can eventually pass that information over there. And then, yes, this thing is observed. And I know something about here, but even passing that information back is just-- When Schrödinger introduced the term entanglement, Schrödinger wrote, he also wrote in German, and he also wrote in English. He introduced the word entanglement. He introduced this word in 1935. And the paper in which he introduced the idea, he talked about exactly what you're talking about. He described it as the regression problem, right? Yes, trace it back. Trace it back. Systems interact with entangled systems. More and more systems start to participate in the entanglement. And he called entanglement - he said entanglement was not one, but the feature that made in his mind quantum theory different from pre-quantum physics. He was very clear about that on the opening page of that paper. So this infinite regression question is a very interesting question, but here's the thing. When you take a physical theory, a weird, counterintuitive physical theory, we have a lot of counterintuitive physical theories. Special relativity is a great example of a counterintuitive theory. Counterintuitive theories often lead to situations that seem contradictory at first glance, right? In special relativity, there's this famous paradox, which is not a real paradox, and it's called the twin paradox. The twin paradox is the statement that if I'm moving relative to you, you'll see my clock running slow, but I'll see your clock running slow. How can I see your clock running slow and you see my clock running slow? It seems like a paradox, right? It seems obvious that there's some sort of contradiction that I see your clock running slow, but you, because I'm moving relative to you, see my clock running slow. Both can't be true, but when you try to determine if this paradox actually happens, and if you describe the situation very carefully, and you describe how you can actually verify whether the paradox happens or not, you'll find that it doesn't happen. The paradox doesn't actually happen. And the paradox was just an illusion. Non-locality in quantum mechanics, at least if non-locality is given a causal equivalence, you might think that this non-locality is not just some sort of non-locality where two things are correlated, but there's some sort of effect that actually propagates faster than light. It seems that way, and when you model quantum systems in the traditional way with observers doing interventions, it seems like causal things are happening, and that goes back to causal modeling. When you think about causality, and causal modeling, in terms of interveners, intervening agents, and that's how you define causal relationships, it certainly seems like there's a causal effect that propagates, but if you remove the observer as a fundamental primitive from the axioms of the theory, if you say no, I don't want to, don't talk in terms of Alice and Bob as observers, tell me in terms of atoms. What do atoms do? Tell me the story of this causal effect propagating at the atomic level, the microphysical level. It disappears because there are no more interveners, there are no more agents, and so what you need now is to find another way to talk about causal relationship. You need to put another definition of causality, and there was one person who did that, and that's John Bell. In John Bell's second version of the famous Bell's theorem, a paper in 1975, local Bell's theorem, it's what he called it, the term Bell's, he tried to find a version, a way to formulate this non-locality in quantum theory that showed that it was causally non-local, and that there were instantaneously propagating causal effects, but without relying on agents and interveners. He tried very hard to do that, and arguably he didn't succeed. So it appears superficially that some non-local causal factors are happening, but if you try to formulate it in terms of atoms without a good, strong theory of causal effect, it's very hard to say that this is happening. Bell tried to do that, but he didn't succeed. Well, last chance for questions, for people who haven't spoken before. "So, perhaps many of us heard about these things when we were 22 or 20 years old, and we were inspired to learn something a little more than high school physics, and I'm amazed when I look back, you know, 30 years later, 35 years ago, how you're still the same, I mean, at that time, you're quoting from a 1975 book, right? Can you give us a glimpse of what has happened in the last 50 years? And I wonder if you're not saying much, because we're not smart enough, I don't know. Or we're not ready. We're not worthy. That might be a theory, but if you can, are we really so frozen that we're still talking about these 150-year-old theories as if they were the art stick?" Yes. "That's all I need to know." Oh, Jacob, you wrote your paper. You wrote more than- Yes, yes, you're continuing. I'll expand on it a little and just say this. This thing that we're doing here, this thing that- No, this thing that you've brought into existence, this intellectual exchange, this discourse that we're now engaged in, this intellectual connection that we're now witnessing, there's very little of that in. Physics now you might think, well, I'm in the physics department we should all sit around and talk like this and talk about what's going on, right? All the amateurs Is this, like, philosophical going on now? No, this is not happening in physics departments. It's not happening in physics departments, okay? Why is it happening in physics departments? In a way, it's complex historical reasons. Now, in the first half of the 20th century, okay, you're looking at the great physicists of the early 20th century. That was happening. Right, that was happening all the time. Yes. Right, they were deeply engaged with philosophers. They were deeply engaged with the Vienna Circle and the positivists, and they were reading Karl Popper, and they were arguing about Schopenhauer, and they were arguing about- they were all claiming, in all aspects of the discussions about quantum theory, that they were the true deputies of Kantian philosophy and Kantian philosophy. They were all doing that, right? Then something changed in the intellectual environment of physics. And the best I can say is that it was the war, and it was the migration of physics to America, and it was also money, okay? When there's a lot of money at stake, people suddenly feel like they're in a hurry to get concrete, practical results. There's no time to sit around and talk about philosophy. It would be good to study finance. Well, more questions, more questions. We need more of this. I'll just say, we need more of this. Here and there, there. Can you give us an idea of what's possible? I mean, what's real, right? I told him that waves are not, perhaps fields are. I can sort of feel what "observable" means, but what is, at least in - you sir, are capable. It's a bee, it's already represented. You, no, so, not only are you capable, but your bee is too. No, so, what I mean by this, what I mean by this. So, I don't know what the fundamental capacities of nature are. We don't know the fundamental capacities of nature yet. Now, if you- What's your gut feeling about what- Well, I mean, we don't know. I mean, we know about atoms. Atoms are made of smaller things, maybe electrons. We don't know what the fundamental constituents of nature are. Electrons and photons seem to be manifestations of perhaps quantum fields. Perhaps quantum fields are not fundamental. We don't know what the fundamental capacities are. However, just because something is not fundamental doesn't mean it doesn't exist. Imagine you came from a rainstorm and walked in and said, oh my God, I'm really wet. And your friend says, no, you're not. Of course, I'm looking, I'm wet, I'm clearly wet. The person says, no, you're not. You say, well, in what sense are you saying I'm not wet, sir? And your friend says, well, at the level of individual water molecules, wetness doesn't exist. Water molecules are fundamental. Wetness is not a fundamental thing, and therefore it doesn't exist. And you go, oh, come on. Things can't exist without being fundamental. You exist, even though you're not fundamental. Jacob, I have an answer to your previous question. You asked me what is a miracle? I have an answer. Do you want to hear it? Yes, please. Well, so, so. What is a miracle? I was talking earlier about wishing for something and then that wish needs something non-causal and outside the cone of the present and future to happen and I have the distinction between a miracle and its inverse. If I want to do something, I don't just wish for it. I make a phone call and cause a series of causal events to happen and I just expect it to show up somewhere in the future probability cone. A miracle is a wish that does not causally result from that external cone. In other words, a miracle is something that I should have done earlier if I wanted it to happen. And I'm sorry to say this frankly, but I think it will be a lesson for all the young people in the room. If you want to do something. You should have already done it. You should have already done it. Start working on that forward cone. Don't worry about that causal relationship. Anyway, so, but on capacity. I don't know what the fundamental capacities are, but I know that at some level, there are non-fundamental capacities like you. So, Jacob, tell us now about your perspective. We've talked about the Copenhagen perspective, and some other people's, and your perspective. Good. So my perspective is that physical systems have actual physical configurations, just as we imagined in the pre-quantum world, but the laws that we didn't have and couldn't come up with in the early 1920s, right? They couldn't come up with the right laws in the 1920s because they were stuck in some old models. They thought the laws had to be Markovian. All known physics up to that point was Markovian. You know what's happening now, and you can predict the future. They were working on this in the 1920s. This was before the modern theory of stochastic processes. This is certainly before people talked about non-Markovian stochastic processes. Yes, there was Brownian motion, and there were Wiener processes, but like the comprehensive complex theory of stochastic processes, it was certainly not available outside of the Markov approximation. And the best I can say from my deep dive into this literature, is that no one, no one has imagined that you can take classical constituents, physical ontology, physical configurations, and give them non-Markovian laws and see if you can get quantum mechanics out of it. And no one has ever done that. So what you're saying is that it's just non-Markovian. Non-Markovianity alone is not enough. You need a particularly strong form of non-Markovianity called indivisibility. It's called indivisible stochastic processes. The term was introduced in a 2021 review article. Explain what indivisible is. Explain what indivisible is. Indivisible is what cannot be, okay, so. So what makes a process indivisible? So a standard Markov process is one where you determine what's happening now, in the present, and then you have a law that tells you what's going to happen next. If you know what a Markov chain or a Markov process is, these are processes by which you can sort of sequence, and you can do the evolution of the system in steps. You have, at every moment, a law that tells you what's going to happen next. You have another one happening next to it. And notice that you can divide it. Exactly. And an indivisible process simply fails to possess that property. It fails to possess the property that you can take any duration and divide it into sub-intervals that have legal descriptions. Beautiful, thank you. And once you've done that, you'll have a more general class of processes, processes that naturally exhibit phenomena that look like interference. And if you want to know why quantum computers are so useful, I mean there's another explanation, quantum computer, the many-worlds interpretation. And one of the reasons why David Deutsch, one of the founders of quantum computing, wanted to develop quantum computers was to prove that many-worlds was correct because he said quantum computers could do more than classical computers could do. And the only way to explain that is that they're doing computations in all these parallel universes. But he was very disappointed. We were all very disappointed when we discovered that many computations could not be done faster on quantum computers. Then people started to wonder, well, if there are indeed all these many worlds and computations are actually happening in all these worlds, then why can't many computations be done more efficiently on quantum computers? This strongly suggests to me that those other worlds don't actually exist and that you're getting the advantage of quantum computers from a different source. And the different sources, if you try to design a computer using Markov processes, and all computers are essentially Markov chains. They are deterministic Markov chains, Markov chains. Once you allow yourself not just probabilistic computation, but indivisible probabilistic computation, you have a more general set of systems. And with more general sets of systems, you can do more things. And - but it's less predictable because of the clock - it's less predictable. It allows you to sort of know - and the things that you can do that give you an advantage over the classical state are not obvious. Amazing, thank you. Okay, next question. Hi, Chris Flynn from Fidelity Investments. Thank you very much, this is fascinating. You've answered my first question somewhat, but is there a way to observe or measure a quantum system without actually interfering with it? Unfortunately, no. However, there is a very interesting protocol known as weak measurements. It was introduced by some people in the foundations of quantum, which is interesting enough. Aharonov is one of them. Yes, yes. So Aharonov was involved, two people involved. David Albert participated. He actually, he moved from physics to actual philosophy. A lot of people who work in philosophy, they started physics as physicists, which he did, and they ended up doing philosophy of physics. Weak measurements work as follows. You don't study just one system. Take 10,000 identically prepared copies of your system. And don't do what we call a projective measurement. Do a very, very gentle measurement. Interact with it in the gentlest way. Now, if you do it this very gentle way, you won't get an answer from each system. The interaction will be so weak that when you send in a measuring device, you let it interact very weakly. Then you take out the measuring device and you look at the measuring device. And you'll get very little information about the system you measured. Very little. But the benefit is that you don't cause this projective collapse of the system. And you might go, well, but if I don't get any information from it, what's the point? It's a partial collapse. You have to get rid of it. That's right. You do it very gently. But you do it with 10,000 systems. With 10,000 of them. And they are similarly prepared. And for each one, you graze it very slightly. Just get a little, just scoop a little off the top. Just a very small piece off the top, right? And you collect all the data. You can actually get some information from all the data. Now, here's where the interpretation problem comes in. So this is an experimental protocol that you can actually do. You can do this experimental protocol. You can actually do it. And lo and behold, you'll get results, you know, you'll take all the data, you'll put it into the computer, and you'll get a number. And the fact that you can get a number out of measurements has made everyone very excited. There's a kind of philosophy, not a small philosophy, a kind of stance, right? Towards science. That if you can measure it, it's science and that makes it cool. Regardless of whether you have any good interpretation of what you're doing. There's no doubt that we can do these measurements. These are so-called weak measurement protocols. People have been doing them. The question is when this number comes out, what does it mean, right? And there's been a lot of dispute over the years. It's like you got a number, okay, but what does this number tell me? It's not like, I haven't done a standard measurement of my quantum system, so I can't say that I'm measuring some property of my quantum system. I got some number, what does this number mean? And people have tried to interpret what this number means and they've said some strange things about what this number means. And the question of what this number means is now an almost philosophical question. So, yes, there are ways to do measurements. Where you barely interact with the system, and you can get a number. And I must say that the number has mathematical significance. The number calculates what's called a matrix element of a self-adjoint operator. So there's like, but the question is, what is it, does it tell you anything physical about the system you were measuring? And that's very ambiguous. So I would say that at least according to the standard picture of quantum mechanics and all the interpretational frameworks that we know, to get an actual, reliable, robust result from a measurement process, you're going to have to have a non-coherent outcome of the process in question. And that will inevitably result in some deviation or change in the system. And one way to see that is that quantum mechanical measurements are inherently non-commutative. If you measure A, non-commutative. If you measure property A, and you measure another observable property or B, and B must have a certain feature, it must be incompatible with A, and it must satisfy what's called the integration relation or the uncertainty principle. But if you measure A, then B, then A again, you might get a different answer for A. And no matter how gentle your measurement of B is, as long as you measure it strongly enough to get some reliable, robust information, there will certainly be some consequences of measuring A. Last quick question, it's a very small question. Yes. What is the relationship between consciousness and quantum? Okay. Small question. We

Let's take the easier one. Take the easier and the last one. There is absolutely no way to answer this question without me telling a little story. Can I tell a story? We will take the story. How many of you know, and have heard of Mary's room? How many of you have heard of Mary's room? So the philosopher and the philosopher Frank Jackson introduced a thought experiment called Mary's room. Mary's room works like this. Mary is a very brilliant scientist. She lives in a black and white room, and in this black and white room everything is black and white and shades of gray. Even her skin, somehow, they've changed her skin. She has never seen color. You have never seen color. But she is very smart. She has access to a black and white version of the internet. She has access to all the information there. She has advanced scientific equipment. She has an electron microscope. She has everything, she can even talk to people. Of course, their color has to be changed before they enter, and she can cut open their brains and be able to look into their brains. She can use electricity, she can do absolutely everything, and she has unlimited intellectual capacity. Can she cross the so-called explanatory gap? Well, I have to see what the explanatory gap is. There are two problems in the philosophy of consciousness, the easy problem and the hard problem. The easy problem is not an easy problem. The easy problem is: Will science one day reach the point where we can have a sufficiently advanced model of the brain that we can describe and explain the behavior of conscious beings? And most people would say that this is a difficult problem, but you can imagine science reaching the stage where perhaps there is enough technology, and we can simulate it, we can design minds and simulate them on sufficiently powerful computers, we can say, well, when the brain is conscious, it does these things, we can predict what it will do, at least probabilistically, but it cannot do it in others. So this is still a distant dream at this stage, but perhaps it is one day we can imagine doing it. The hard problem of consciousness, which was formulated by the philosopher David Chalmers, is okay, well, once you have this model, why does it feel like anything? What about subjective experience? Like the fact that, yes, the brain does these things, there are these kinds of neural correlates, these brain states, neural correlates of conscious experience, neural correlates of consciousness, NCCs, but why does it come with redness, like the distinct feeling of redness? And there are people who doubt that there is a hard problem, so they say, oh, it's an illusion or something like that. When the thought experiment of Mary's room was, part of what it is supposed to do is, technically, what was originally introduced in Mary's room is the argument against physicalism, but I have read it differently. Mary can do all the science, all the science you can imagine, she is immortal, she can do science for centuries, she can develop all the science you can imagine, she can do every experiment that has ever been done, but she will do it, and perhaps even be able to reach the stage where she can discover what to do to her brain, like what electrodes to push so that she gets the experience of the color red, okay? Perhaps she can do that, but can she explain how you go from the physical thing in the brain to the actual experience of color suddenly? How do you get the physical things, where does that come from? This is the explanatory gap between the easy problem and the hard problem, and there are many people who doubt that the hard problem is solvable precisely because of the Mary's room argument, because even if you imagine unlimited scientific experience, even if you can describe it, okay, this brain state corresponds to the feeling of red, and this brain state corresponds to the feeling of green to blue, you have the brain states written out, but you still don't know why it comes with these specific feelings, and this is the hard problem of consciousness. Now, some people doubt that it exists, I feel sorry for you if you do, but now let's go back to the quantum state, okay? Let's assume we were able to say, okay, some brain processes inherently use quantum mechanics phenomena, so what, will that get us across the gap from the easy problem to the hard problem? Just because quantum mechanics happens in the brain perhaps and plays a fundamental role in certain processes, even if you know that, even if you can model it, okay, okay, how can you go from that to, then when this happens, this is how I will do it, redness, this is red, I will actually get the experience of the color red, and when you have the experience of the color red for the first time, when Mary has the experience of the color red for the first time, she has learned something. When she leaves the room for the first time and suddenly sees color, she has learned something new to her, and she doesn't know why, and none of her scientific experience at that point can explain why she is suddenly having these experiences. So I think the hard problem is unsolvable, and I think that's a good thing. I think there are deep problems in nature that we may never be able to reach, and I don't think understanding whether quantum mechanics works in the brain or not will allow us to cross the explanatory gap from the easy problem to the hard problem. This is just my opinion, and I could be wrong. Do you think it is unsolvable in principle or is it unsolvable with our current models? From my point of view, it is unsolvable in principle, the hard problem, unsolvable in principle. This is my point of view. In Mary's room, it's not sort of an argument, but the possibility of artificial general intelligence. Well, that's an interesting question, isn't it? So is Mary's room an argument against AGI? I don't think so necessarily. AGI might just be an easy problem. In the sense, if we can figure out how to model a system that behaves consciously, can we simulate it, and isn't simulation AGI? Artificial General Intelligence, like a computer that behaves indistinguishably from a human. However, if you then ask, does this computer have an internal subjective experience? That we cannot know. And I don't think any scientific research will tell us the answer to that. There is a term that was introduced before David Chalmers in the 1970s, called the P-zombie, which haunts the nightmares of metaphysicians everywhere. As you know, a P-zombie is not a zombie. P-zombies work and behave remarkably exactly like conscious beings. They are like your AGI computer, and they have been carefully designed so that they mimic the exact same processes that go on in a normal human brain. And it's hooked up to a robot, and the robot looks like a person and walks around and talks and says, oh, this is painful, oh, it's a bad feeling, or I see red, or whatever they say, right? But does this computer have? Is there something like being that computer? Does it have an internal subjective experience like the kind we think we have? If it doesn't, it's called a P-zombie. Now, there is a view among some metaphysicians and some philosophers in their minds that P-zombies, philosophical zombies, which is short for P-zombies, are conceptually impossible, and they are inconceivable, and that anything that behaves sufficiently like a conscious being, ostensibly, meets the requirements, okay, we've solved the easy problem for it, it behaves like a conscious being, then it is conscious, it has full consciousness, it has internal experience, and it is not logical, it is not reasonable, to even be able to talk about it lacking that internal conscious experience. As someone who studies neuroscience and biology and all that, and by the way, our next salon will be about consciousness, what if we are pretending? In other words, if you look at the neural basis of subjective experiences, there are many experiences, for example, if you cut the corpus callosum, it is possible that you actually have a part of the brain that is unaware of the commands that were given to the other half of it that then led to taking an action. Yes. And that part of the brain that never saw this command will rationalize the action as something that it really wanted, and then the question is, is the brain a very, very good employee and never wants to be caught not knowing, and will always make up a story, including when asked, why do you think? In other words, do we know that we ourselves have any consciousness beyond what we claim to do, and yes, absolutely, your answer was very provocative by saying maybe you don't, but I do. There is no experience that can prove to me that any of you have consciousness. True, yes. However, if I separate myself from my mind, perhaps my mind will say, oh yes, of course, you are very conscious, and here are all the great things you have that prove to you that you are conscious. Like, why would I believe that? Consider a world where all humans are P-zombies and lack internal conscious experience, and a world where they do, in fact, have internal conscious experience, and obviously they would look identical by construction. And that tells us that we might never be able to answer this question. But if you transfer yourself from the self to the other person looking at the self, is there anything you can do to prove that you are actually conscious? As I said, anything you can do in a world without internal conscious experiences, except for the zombies, can be done in a world with internal conscious experiences, and so I don't think any of that- that's true, but is there something in that? The opposite direction? Before we continue, I want to tell a joke. Of course, of course. This is a joke. I told this joke to David Chalmers, and he really liked it. Okay, okay, this is a joke. And those who have some background in high energy theory will enjoy this joke, okay? Okay, okay? This is a really good joke. What do string theory zombies eat? M-brains? P-brains. P-brains. Ha ha ha ha ha ha! Send me, do you know what he sent me back? I sent him that, and he sent me back a zombie emoji. I have a zombie emoji from David Chalmers on my phone. I've saved it all these years. Okay, I remember the part where we were supposed to finish at 7:45? I looked at my watch, and I said, oh, is it maybe 7:55? It's 8:55. Who had a great time tonight? Great! So, Kurt, Jacob, I can't thank you guys enough. Thank you for gracing us with your exceptional thoughts, and also for bringing so many new guests to our salons. And one of them commented, "The audience looks a little different." There's like more energy and all that. That's it, you guys. So, thank you to all the first-timers. I hope you continue to come. Thank you to all the old-timers who are repeat visitors. And again, thank you so much to both of you. It has been extraordinary. Thank you for the invitation. I mean, it's beautiful, and thank you, Kurt, for helping me build this. And thank you all for contributing. It has been amazing. Amazing. Amazing. New update. I've started a subreddit. The writings that are there currently are on language and undefined concepts, as well as some other mathematical details. A lot is being written there. This is content that is nowhere else. It's not on Theories of Everything. It's not on Patreon. Also, the full transcripts will be put there at some point in the future. Many people ask me, Kurt, I've spoken to so many people in theoretical physics, philosophy, and consciousness. What are your thoughts? And while I remain neutral in interviews, this subreddit is a way to look into my current deliberations on these topics. 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