Speaker 1Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, Sean Carroll. A long time ago, 15 or more years ago now, when I was writing my first trade book, From Eternity to Here, we were talking about the title. We liked the actual title, right? From Eternity to Here. I think that either Jennifer came up with it or we brainstormed it together. I forget. But that seemed to both be fun and also fit what was actually in the book. Then, of course, you need a subtitle because you're cute with the title, right? And when you're cute with the title, you need the subtitle to actually explain what the book is actually about. So I was talking about that with my publisher, Stephen Morrow, and eventually he mentioned that the word quest was very popular in publishing circles at that moment in time. Publishing goes through all these various fads and phases, and at the moment they thought that books that were about quests were really selling well. So the subtitle ended up The Quest for the Ultimate Theory. of Time, which is a perfectly decent subtitle, and especially decent, especially appropriate because the quest is not over yet, right? I was not proposing in that book to answer all the questions that one might have about the nature of time. I discussed the questions and we talked about various possibilities, but clearly with an eye to saying there's a lot left to be done, which I bring up now because today's guest, Jim Al-Khalili, has a new book out called On Time, and his subtitle is On Time, and it's a book called On Time, which is The Physics That Makes the Universe Tick. So it's a very similar theme to what I wrote, and it was more than 15 years ago now in From Eternity to Here, but there has been progress since then. And of course, even absent any progress, two physicists thinking about the same general area, especially one as big as this, are going to have their own angles on it. So Jim is a very accomplished both physicist and communicator. His topic is something that I've talked about already on this podcast. You've heard me talk about it. I wrote books about it, et cetera. So this is an excuse or an opportunity, if you want, for me to play dumb, to pretend I don't have strong opinions about the nature of time and how it works, and get a different perspective, because I'm a huge believer that no one person is ever going to be able to state or explain things in the perfect way for every member of the audience. Hearing it in different ways is interesting. And also, I have a lot of questions that I don't know the answer to that I think are really interesting. So if you have any existing research-level problems, I'm trying to think about them, make progress on them. It's always fun and useful to talk to another physicist who's thinking about the same problems. So let's go. Jim Al-Khalili, welcome to the Mindscape Podcast. Jim Al-Khalili, welcome to the Mindscape Podcast. Hi, Sean. Pleasure to be here. We're talking about a topic dear to my heart as well as to yours. So I'm not going to be reluctant to load you with all the tough questions. So let's start with, what is time?
Speaker 2Aha, okay. It's a tough question because it's one that we've been thinking, we, humanity, has been thinking about for millennia. Going all the way back to the ancient Greeks, there was a time when time was real, whether it was an illusion, whether it flows. And the more we've understood about the workings of nature, I guess just the more complicated the answer becomes about the nature of time. Not just, is it real? Is it all an illusion? Is it just in our heads? But also within physics, what do we mean by time and how it enters different areas of physics in different ways? So in a sense, we know a lot more about time than certainly I would like to think about. To think more about the nature of time than the ancient Greeks, but we may not be that much closer
Speaker 1to answering the ultimate question. All right, that's perfectly fair. You said a lot of true things. You've not told me what time is. I need something down to earth here. Okay, for me, time
Speaker 2is a real thing. It's tangible. It's part of four-dimensional space-time, the fabric of our existence, of reality itself. It's not just that thing that clocks measure. It's a real thing. It exists. And I also go further and say it exists and it has a direction. That's not just something that emerges or that we're conscious of that maybe digging deeper doesn't exist. I think that's there baked into the
Speaker 1universe as part of time. Well, let's explain. You said a couple things that are actually sort of touching on big picture controversies. And we want to let the audience know that they're controversies because they might sound pretty unobjectionable. First, well, the thing you just said, that time has a direction. I mean, obviously time has a direction, but you're going further than that. You're going to say that it's not simply a matter of the present state of the universe and its evolution. There's something umph-y about it. There's something built into it.
Speaker 2Yeah. I mean, I think I make the distinction between time or the directionality of time if we're talking about the whole universe, viewing it from outside the God's eye view. Yeah. And it may well turn out that time doesn't have any directionality once you zoom outside, but within the universe, or certainly for us, measuring systems, seeing how they evolve, I would say that time has a direction. Now, this is a longstanding debate, which you know very well, you've written a lot about. How does time's directionality, its irreversibility, impact emerge from something deeper? Maybe something that's time-symmetric, that doesn't pick out a direction. And my view, and maybe this is something we'll get into later on, is that it's the other way around, that time's directionality, irreversibility, is more fundamental. And symmetric equations and symmetric laws of physics, I think, are just idealizations that aren't giving us the whole picture.
Speaker 1Yeah. No, that's very important. And I just want to get it on the table. We'll come back to it later and we'll talk about it in detail. That's great. And the other thing that you mentioned is you think that time exists, which again, most of us think that time exists. We said that we're going to do the podcast at 10:00 AM and things like that, and it worked. But there is a perspective that said time is just a tool we use. It's not something out there in the world.
Speaker 2Yeah. I mean, in my book, I sort of start off by making this distinction that many philosophers of time, and that is a… …a field of research, philosophy of time, would argue, which is the distinction between physical time, the time that enters into our laws and equations of physics, and manifest time, psychological time, which is the time that we perceive. And in a way, you know, you talk to a non-scientist and they say, "Well, after all, that is everything. We can't ever talk about something other than what we perceive and imagine." Certainly within our own… …our own psychological time, yeah, it's obvious. And a lot of things about time, you know, why does yesterday come before today? Why is today before tomorrow? Why does it seem like time passes? They're so obvious, people wonder why scientists and philosophers are spending effort trying to study this. But that is different from time, the physical time that enters into our laws and laws of physics. So yeah, there are certain problems of time, that are philosophical problems, you know, does it flow? What is the meaning of now? And so on. And there are other more concrete problems that physicists and philosophers worry about, which is things like the arrow of time or, you know, how to reconcile different ways of defining time when you're dealing with different areas of physics, say, relativity theory and quantum
Speaker 1mechanics. Well, in your new book, you're not afraid to at least chat about some of these deep philosophical issues. I think it's pretty clear, I don't know, maybe you feel differently, it's clear to me that while you're chatting about them, you're like, I'm a physicist, I can't wait to get back to the physics part of these things.
Speaker 2Yeah, yeah. I mean, in a sense, I'm sort of deliberately, I am naive about some of the philosophical issues, because this is not a subject I've spent my entire career thinking about. I've sort of come to it late in the day, and in part, you know, a lot of physicists, particularly theoretical physicists, start to worry about some of these foundational problems in physics, because… Yeah. …time is finite, right? Time's running out, and I don't have to publish or perish anymore, you know, I don't have to work on the sort of nitty-gritty stuff, I don't have to think about the big questions. So, I've sort of come to this rather late in my career, and I'm aware there are people who've spent their entire lives studying this stuff, who quite rightly would see some of my ideas as a bit naive and maybe half-baked. But I, you know, I try and be honest about it, as you say, you know, I say I'm a physicist, I'm… Like you, I am aware that philosophy and philosophy of physics is very important. And I have friends and colleagues who, as I'm sure you do, who poo-poo philosophy as just navel-gazing, and, you know, physicists are the ones who are really answering the big questions. I still think there's huge importance, you know, in physicists and philosophers talking together and trying to, you know, it's not just the philosophers come up with the questions of, you know, come up with the answers. It's more complicated than that. But I don't have a training in philosophy. So what the background research I've done for the book has mostly been from very much from a physicist's perspective.
Speaker 1It's interesting because this is going to be a slight deviation, but, you know, it's a podcast. We can talk about whatever we want. We both agree that philosophy of physics has some interesting things to say. And maybe we both agree that physicists don't know what the philosophers of physics are saying usually. I was just the other day reading a statistician who knows a lot of physics and talks to physicists and just bemoaning the fact that in his mind, physicists don't understand even the most basic parts of statistical analysis and how to distinguish between one curve fit and another one. And I'm sure that he's right in some sense. And what do we do about that? Like, I think that we need to not just say physicists should read philosophy, physicists should read statistics or whatever. I think we need to act. We need to actually talk to each other and there should be more formal structures to allow that to happen.
Speaker 2Yeah. I mean, certainly a lot of physics is becoming more interdisciplinary and we are talking to each other, but it's also there's a lot to learn out there. Yeah, it's too much. You know, I know astronomers and cosmologists, for example, are having to learn some really clever and complex statistical analysis. You know, just the reams of data. They're coming back from the big astronomical surveys, for example. So they're having to retrain themselves in these things. Other physicists are having to learn a lot of computer science and AI and machine learning because that's a tool they're using. And those physicists working on the boundaries, on foundational problems, need to talk to philosophers and learn more about the philosophy of physics. I don't think we can be all things to all people. But you're right. We need to talk to each other. If you're tackling. A problem that you need to come up from lots of directions, no single person has to approach it more directions themselves. Other people can use their skills.
Speaker 1You use yours. We should, we should mention Jim is on the side of the angels here. You've actually collaborated with philosophers about these philosophy of time questions.
Speaker 2Yeah. And it was quite a new thing for me. So this was a big research grant I had from the John Templeton Foundation, a charitable organization in America. That is, it's a. I'm afraid to sort of fund some of these more speculative areas of research, which the usual sort of public funding bodies are reluctant to do. And I basically got that research grant off the back of my public engagement or science communication activities, because that's how they knew me. And they wanted a big public engagement aspect to that research proposal that I put together. But at the same time. You know, it was an opportunity to do something really interdisciplinary and the nature of time and the hour of time was a big feature of that. So I, you know, I, I reached out to one philosopher of physics. I knew that I asked him if he'd like to join, he said he didn't have time, but he, he pointed me in the direction of several others. So Simon Saunders at Oxford is I'm sure someone, you know, very well as a fellow Everettian, as, as we, as we say in the quantum world, Eddie Chen in UC San Diego, published a paper. I'm sure someone you know very well, as a fellow Everettian, as, as we, as we say in the quantum world, Eddie Chen in UC San Diego, published a paper. I'm sure someone you know very well as a fellow Everettian, as, as we, as we say in the quantum world, Eddie Chen in UC San Diego, published a paper. with a couple of years ago and Kareem Thabo in Bristol. So these are three philosophers of physics. I think all three of them have basically have PhDs in theoretical physics. It often happens. Yeah. Right. Yeah. A lot of philosopher physics actually starts off in physics and they have that grounding in mathematical physics that I guess you need if you don't just want to be fluffy.
Speaker 1Do you therefore have a stance on things like presentism versus eternalism?
Speaker 2Um, not a strong one. No, I mean, because I, I can see, uh, the arguments for each case for, for, for me, I guess it's because, because I, you know, I'm, I'm a physicist and I've studied and taught relativity for many years. I guess eternalism is the thing that comes naturally to me that, you know, that in, in 4D space times, all, all times exist in the same way that all points in space exist. And, and the notion that somehow the future doesn't. But the present and past do particularly as, you know, with every five of my being, I've, I've been trained in thinking about relativity in the sense that the present moment may be special to us because you could only ever exist in the now, but zoom out outside of space time and there's nothing special about it. So eternalism, I guess, is what I'd naturally feel is the right way of thinking about things.
Speaker 1Well, this is going to get us into some deep waters. We might as well get there. Um, let's talk about the arrow of time. We've already mentioned it a little bit. Uh, there's kind of a conventional story about how the fundamental laws of physics look like they don't have an arrow, but we have one anyway. Do you, do you want to tell that conventional one first?
Speaker 2Yeah. So, I mean, so this is something that goes back to the mid 19th century and people like Boltzmann and Maxwell and, and, uh, and others were arguing about, which is that all our fundamental, all our dynamical equations of physics, the equations of physics that describe how things work. Things change over time, whether it's Newton's laws of motion, whether it's Schrodinger's equation of quantum mechanics and so on, um, all seem to work perfectly well, if you switch time over, you may have to do mathematically a few other technical things, but they're, they are what we say, uh, time reversely invariant, they don't break any laws of physics if you, if you run them backwards and since these are fundamental dynamical equations that we believe describe nature correctly, they don't break laws of physics if you, if you run them backwards. And since these are fundamental dynamical equations that we believe describe nature correctly. Um, so. Yeah. Um, then there's no directionality in time, but baked in there that that directionality, that arrow of time somehow must emerge from them. And, and the big, uh, debate in the 19th century, which often is referred to as, uh, Loschmidt's paradox, Joseph Loschmidt was the person who first highlighted this dilemma is that there is an area of physics where the directionality of time is apparent and that is in thermodynamics. The second law of thermodynamics, which I always say is so famous, but it couldn't make, couldn't even make it to the number one spot in thermodynamics, um, says that, uh, this quantity entropy, which we may or may not want to, to, to talk about a bit more, uh, uh, increases in an isolated system or, or increases or stays the same, but it doesn't decrease, uh, that gives a directionality to time. So how do you reconcile that with these time symmetric laws and equations? And certainly our perception of time pointing in one direction, not the other. It's so obvious. We surely think that second law of thermodynamics must be correct. And those time symmetric equations are the things that, you know, we need to be, be concerned about. You know, we, we grow older, balls roll down hills, cream mixes coffee and all the usual, you know, shuffling cards makes them more shuffled. All those things suggest that somehow, surely there is a directionality to time. So. Let's worry about how those symmetric equations come about. But I think for most physicists, it's the dynamical time symmetric equations that are the more fundamental, right. Uh, and, and, and the direction at a time emerges, you know, for example, with what we say, zooming out course, graining, you know, looking at, at larger and larger systems and suddenly you see something emerging. Um, that's the stats that the traditional, uh, view that, you know, how does irreversibility. Emerge from time symmetric equations. I come at it from the other direction for me, if I'm going to take this stance, which is a controversial one, I guess, in the sense that not, not all physicists, maybe not even majority of physicists would agree with, uh, which is the irreversibility is more fundamental. Then how do I justify that? Well, for me, whether we're talking about the second law of thermodynamics and entropy. Always having to increase or certainly not decrease, or whether we're talking about time, symmetric dynamics, running the movie forwards or backwards, you know, it, it doesn't look wrong. Both those apply only to isolated systems, uh, and, uh, and so for me, certainly time, symmetric dynamical equations, because they only apply to isolated systems, they are an idealization. Um, they're not true in, in general, because also no system is truly isolated apart from the entire universe itself. But if we're embedded within the universe, then I would say that time, symmetric dynamical equations are just an ideal limit that doesn't exist in reality. Everything is interacting with its surroundings.
Speaker 1Okay.
Speaker 2Whether it's losing, whether it's the hot cup of coffee and the. Fridge that's cooling down or, uh, or whether it's, uh, a, a quantum system de-cohering because it's interacting with its environment. There's a, there, those are irreversible processes that give a directionality to time. And, and so I, for me, because nothing is truly isolated, uh, in our universe, uh, there's, there's an inevitable directionality error of time and only. When. you idealize a situation and isolate a system from its surroundings, do you lose that? Well, even then you don't lose it because you still have entropy increasing. If you isolate it when it's far from equilibrium, it will move towards equilibrium. Once it reaches equilibrium, then there's no hour of time within that system. But outside, there's still a direction to time. So I'm willing to entertain this point
Speaker 1of view. So I mean, I think the usual thing people would say is, look, I can imagine if I don't have an isolated system, just considering a bigger system, and that might be isolated. And then the original thing I cared about is now a subsystem. And I can derive all of the open system equations from the isolated system equations. But okay, so you're suggesting a change of perspective where we should take the open system point of view more front and center? Yeah. Love that. That sounds great. But even in a non-isolated system, even an open system, if everything is in thermal equilibrium, there's still no arrow of time.
Speaker 2Right. Well, by an open system, do you mean just the system itself? You're not including
Speaker 1its surrounding environment? Well, if the surrounding environment is a thermal reservoir, some fixed temperature, and my system is at the same temperature in thermal equilibrium, they can be interacting, but there's no arrow of time. Yeah?
Speaker 2Right. Well, there's no arrow of time that we can perceive if we're looking at that system and its environment. Unless the environment is the entire universe, and therefore, inevitably, we are observing it and observing the absence of an arrow of time from outside of the universe, then yes, I... I concede that there is no arrow of time. But within the universe, a system and its environment will necessarily be embedded within an even larger environment, and therefore, the arrow is there. I agree that for the entire universe, there is no arrow of time, or there is time symmetry, which is why I still think we have an issue. The past hypothesis... We have to acknowledge that there must be a special moment that the universe took off in a special state.
Speaker 1Well, yeah, and I do want to get to there in the past hypothesis, etc. But just to be super-duper clear, when you say that you want to take the directionality of time as something fundamental, and you say that the traditional guesses at fundamental laws of physics, like Schrodinger's equation, or Einstein's equations, or Maxwell's equations, or Newton's equations, they don't have a direction. You're not proposing changing any of those equations whatsoever. You're just proposing looking at a different context.
Speaker 2Absolutely. I mean, if we take Schrodinger's equation, for example, it is correct and perfectly precise, provided it's dealing with an isolated system that's undergoing what we call unitary evolution. But of course, if I say no system is truly isolated, but even quantum systems are open, then it's not the Schrodinger equation we use. It's the Schrodinger equation. It's the Schrodinger equation, plus some add-ons. And those add-ons are what give us the irreversibility. So they're not add-ons to the Schrodinger equation. The Schrodinger equation is a special case of that larger, what's called the master equation, because an isolated system
Speaker 1is a special case of an open system. I guess I'm just sort of flailing around here, because I haven't really thought about things in this way. It seems to me that there would be lots of different open system equations, but I don't think there's a lot of open system equations because I don't know what the rest of the world is going to do. I can more or less predict what's happening in this room, but if a meteor hits it tomorrow, then I will not have predicted that.
Speaker 2Yeah, of course. I mean, I think even in an open system, we are having to idealize and pick some environment surrounding the system that we're interested in describing. And, you know, the simplest idea is to say that, well, you know, your quantum system is embedded in an infinite heat bath that's just, as you say, a thermal equilibrium at some constant temperature, which has no memory of what happens next. You know, the system just leaks into it, and it doesn't care, and it doesn't change. But that's a simplification. It's an idealization. Of course, in reality, a system's environment is itself still constrained. There's still a lot
Speaker 1more that's going out on beyond that. Okay. Is this a program? Is this like a project to sort of replace our... When we teach kids, undergraduates, the laws of physics, we teach them the Schrodinger equation. Do you think that there is a wholesale upending of the usual way we think about physics that starts from an open system point of view?
Speaker 2I certainly think the way we teach undergraduates quantum mechanics is something that has to change. You know, I've heard you talk about this on your podcast as well, that, you know, the traditional way of, you know, one-dimensional Schrodinger equation, square barriers and square wells and harmonic oscillators, who cares, you know? But especially given that, you know, these days, you know, we hear a lot about new quantum technologies, quantum computing, and so on. Why the heck aren't we teaching students about entanglement and decoherence, you know? And entanglement and decoherence inevitably require an appreciation of open systems. So, maybe it's, you know, too complicated to teach as a first course in quantum mechanics, but I certainly think, you know, by the time... If you're doing another course as an undergraduate level, or certainly as a graduate student, then we should be absolutely going beyond the Schrodinger equation and saying that's a special case of what is a more general, you know, everything is entangling with everything else, things are decoherent, and... And, of course, that inevitably leads on to something that's close to both our hearts, which is we can start talking about the interpretations of quantum mechanics.
Speaker 1We will. We will. But let's... Okay, good. I can't avoid talking about quantum mechanics because it's so seductive, but I do want to sort of finish up the classical kind of entropy story. You briefly mentioned the past hypothesis, a formulation from previous Mindscape guest, David Albert. And, you know, that's a slightly... That's part of the more conventional view, which you're contrasting. But, you know, why don't you tell the audience
Speaker 2what it is and how it's supposed to work? Okay. So, I mentioned that all... No system is truly isolated, but we tend to... If we're thinking about the entire universe, then there's nothing outside it for it to interact with. So, we have to treat it as a... Like an isolated system. And if we say that, okay, so today is the... The universe has a certain entropy. Tomorrow, it'll... Because of the second law of thermodynamics. Thermodynamics have higher entropy. But if we were to describe the whole universe at a fundamental level in terms of all the particle interactions, and we had some super equation that would describe everything, then that equation, fundamental equation, because we're dealing with this, what is an isolated system, should be time symmetric. And if it's time symmetric, then if you run the clock backwards, that means yesterday should have higher entropy than today. But if you go back to yesterday and someone measured the entropy and said, "No, actually, it's lower." You know, it's, "Oh, I thought it should be higher, but it seems like it was lower. It seems that universe entropy is going." There's nothing special about today. And so, how do you get rid of this problem? Well, if you push the special moment to last week, then sure, yesterday would have lower entropy than today. Today has lower entropy than so on and so on. But that moment last week also has a problem because the week before that entropy was even lower. So, the past hypothesis says you push this point, and I'm teaching grandmothers to suck eggs. You're very quietly sitting there waiting for me to explain something that you've explained a million times. The past hypothesis suggests that if we push that special moment all the way back to the beginning of time, to the big bang, then there is no before to worry about entropy increasing. From that very moment, you push this point all the way back to the beginning of time, to the big bang, then there is no before to worry about entropy increasing. From that very moment onward, entropy is increasing. So, we've satisfied time symmetry and the second law of thermodynamics. Of course, what we've done, which is a bit of a problem, is that we've broken what's called time translation invariance. We've picked a moment that's special. It's the big bang, so I guess that's already a special moment. If something has to be special, it might as well be the big bang. It might as well be that rather than today or last week. Exactly. So, the past hypothesis gets around this problem. Yeah. The past hypothesis gets around this problem of an isolated system, namely the entire universe, that can both be time-symmetry invariant, but also satisfy the second law of thermodynamics. It seems we can't get away from requiring a past hypothesis when we're dealing with the
Speaker 1whole universe. The idea is that the past hypothesis plus the definition of entropy plus time-symmetric underlying laws, that's it. That's the package. This is the usual picture. This is maybe not your picture, but that's supposed to explain all of the ways in which the past and future are different.
Speaker 2Yes, yes, that's right. I mean, for me, the past hypothesis is, it says the universe started off with very low entropy or in a very special state. But there's also what's called the fine-tuning problem that the universe had to start off in, you know, the speed of light and the other constants of nature and the strength of the forces and so on had to have certain values for the universe to have evolved in the way that it has. And I would argue that the past hypothesis simply... It's all part of that. It's not an additional sort of requirement or assumption on top of the initial conditions that the universe had found itself in. It's all part of it. It started off with all these values for the fundamental constants and in this very special state.
Speaker 1So this leaves us then, though, with sort of two kinds of questions that are ripe for investigation by physicists and fellow travelers. Why was the early universe low entropy? And we can talk about that. But then there's the more basic question, like, why does that do the work that we need it to do? Like, you started at the beginning of the podcast mentioning the passage of time, the flow of time, these experiences we have. How are you going to get that from saying that 14 billion years ago, the entropy of the universe was small?
Speaker 2Yeah, so having the entropy of the universe very small and allowing the second law to do its thing or whatever. Yeah, it's a mechanism that gives us an hour of time. That's all part of understanding physical time. Nevertheless, our perception of time passing, that now is a special moment, that time seems to flow, whether we're drifting along the time axis or time is flowing past us, whichever way you want to think about it. Those are still parts of psychological time. And, you know, I'm... That's something I... I don't have a clear idea even how to articulate, how to reconcile physical time with manifest time. You know, is our psychological time really just, you know, are we kidding ourselves? You know, we say, you know, physicists tend to say, right, there's no evidence. There's nothing in the laws of physics that says that time flows like a river. That flow doesn't exist. An arrow may exist, but the flow of time doesn't exist. And yet we perceive it to flow. So reconciling how we think of time, how we imagine time, how we perceive time, and how time pops out of the mathematics of our laws of physics are things that we are still, I think, struggling with. I don't have an answer to that.
Speaker 1No, that's extremely fair. You know, kudos to you for actually saying what we don't know the answer to. It is... People have to accept that there's some things we do know the answers to and some things we don't. That's okay. But we did start with, like, the hardest part of the question. There's many steps. There's many steps in between, between the Big Bang and the human experience of time passing. I mean, there's cosmology, but then there's also biology, the origin of life, complexity, things like that. How well do you think that we can relate those to increasing entropy in the universe?
Speaker 2Well, very often cosmologists have a simplified view of entropy as being two things. There's thermodynamic entropy. You know, the universe started off in a hot, dense state, but it was in thermal equilibrium. And there's the usual, you know, people say, "Yeah, but if it started off in thermal equilibrium, it's already at maximum entropy." And the argument is that, well, you know, you've forgotten about gravity and the things that expand, and gravitational entropy was very, very low. My background is nuclear physics. And so for me, nuclear fusion... And fusion entropy plays a very important role, you know, the universe expands, and when it's cool enough, when it's still hot, you know, cool enough quarks can combine gluons to make protons and neutrons, and then you can make atoms and so on, but expands at a certain rate, and as it cools, it slows down, it gets to a point where you can't make fuse any heavier nuclei than hydrogen and helium. You've got to wait for... You've got to wait for stars to form. And so there's still that very, very low fusion entropy locked into, I guess, the nature of the strong nuclear force. Yeah. It's there waiting to happen. So in a sense, gravity isn't just giving us an out, giving us a way of saying the universe had low entropy to start with, it also enables fusion entropy to increase. When stars, when matter clumps together to form stars... Then stars can reignite, and fusion starts again, and you can have entropy increasing. So we live in a world now where, you know, stars are still shining, the sun is a source of low entropy. If there was no fusion entropy, the sun would have clumped down to, you know, matter would have clumped together, would have died and reached maximum entropy a long time ago. The fact that it's still a source of low entropy is because of nuclear fusion. And then things like life have used... They've used that low entropy to maintain their low entropy, you know, but all the time entropy is increasing. But this fusion entropy for me is a big middle step that runs alongside gravity and is the reason why we're still, the universe is still at relatively low entropy. We haven't run out of steam yet.
Speaker 1I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle? I want to get your version of, you know, what is the response when people say life, in the sense of a biological organism, is a struggle?
Speaker 2No, not really. I think I agree with you that, you know, life is a mechanism for using low entropy photons from the sun, you know, useful energy versus useless energy. And then that low entropy is a thing that it utilizes and converts it into low entropy to maintain its structure, to maintain itself far from equilibrium. But it spits out higher entropy, it spits out thermal photons, you know, right, which are, I don't know how many, you know, a dozen, two dozen thermal neutrons for every, thermal photons for every photon from the sun, which is low entropy. So yeah, that low entropy source is there and life is feeding on it and making use of it. It's not a struggle against it. It's utilizing it. Like, how, you know, we still don't have a good definition of what life is. How does it do that? And why don't other things do that that are non-life? I don't know.
Speaker 1One thing that I actually don't have a strong opinion about, or I guess a strong feeling of how best to phrase things is sometimes people want to say, in that spirit, life is a way for the universe to increase entropy, right? Like, we take this low entropy energy from the sun. Like you say, we radiate it out, a bunch of low energy photons, increase the entropy. I don't know if that's true or not. I mean, I kind of have a feeling like the entropy is going to increase anyway. There's no law that says it increases as fast as possible. You got to think harder about what life is doing.
Speaker 2And, you know, we tend to think that there must be life elsewhere in the universe. It's so vast and there's so many places that could have, could harbor life, even if it's just microbial life. And, you know, maybe multicellular life is the really, the sticking point and here on earth is the only place. But if life only exists on earth and we can't rule that out, then that's a very tiny part of the entire universe, the whole universe is relying on this tiny planet in this, you know, the outer suburbs of some galaxy to help it increase its entropy.
Speaker 1It seems a bit wacky. So. So I do want to give you a chance to talk a little bit about biology because you've written papers on quantum biology in particular, but it does occur to me that first we should talk about quantum mechanics. Yeah. So what is your favorite way? We started with what is time. So now what is quantum mechanics, Jim?
Speaker 2When I was a grad student, I, you know, both my, I had two PhD supervisors, both staunch Copenhagenists, right? So this is the traditional view of quantum. So quantum mechanics that, uh, espoused broadly by, uh, Bohr and Pauli and Heisenberg and, uh, and others. Uh, and I, I know it's unfair and people who, you know, who, who support that viewpoint hate it when you say that's the shut up and calculate interpretation, but it, I, I did have that attitude when I was a student, you know, my, my supervisor would say, Jim, you know, An electron is an electron is an electron. Don't worry about, you know. But I did. And, you know, together with other grad students, we formed what was called, we called it the Carlsberg Group, which you may know historically is the Carlsberg Brewery that funded Niels Bohr's Institute in Copenhagen in 1920. And we would, you know, almost in secret, you know, have these discussions about interpretations of quantum mechanics. This was like the mid-late 80s when it was still. Oh, yeah, that was catchy. You weren't really, you know, allowed to say those sorts of things. You know, you're a bit of a, yeah, a maverick if you follow that. But I, so the one thing that I'm firm and feel strongly about is that I'm not a Copenhagenist, that I'm a realist. I believe, you know, objective reality exists out there. And it's not just brought into existence through measurement and all the other business. But it also means that I don't think we can adopt whatever interpretation we like just depending on a whim or whether it's a Tuesday or, you know, who you last spoke to. I always say that of the sort of plethora of different interpretations of quantum mechanics, they can't all be right. You know, either there are parallels. Well, worlds or there aren't. Either there's a sort of invisible guiding potential or there isn't. Either the way it spontaneously collapses or it doesn't. I don't have a strong view on which one is right. Some I favor over others for different reasons. But I do believe there is a correct interpretation. And we may or may not, maybe not in our lifetime, certainly actually hit upon the way now.
Speaker 1The way nature does things. And when you say you're a realist, in particular, I take it you're because some Copenhagen people get very touchy when you say that they're not realists, because but they want to say, well, I'm a realist about measurement outcomes. But the rest of us are realists about the quantum wave function, the thing that appears in Schrodinger's equation. And it sounds it seems to me, correct me if I'm wrong here, that once you start studying quantum biology, you're going to start thinking of the wave function as something real, like it's playing a role. In pushing energy around in a cell.
Speaker 2Yeah, yeah, absolutely. And, you know, while I don't need to, you know, put one interpretation ahead of any others, if I'm doing quantum biology in the same way that I didn't need to back in my past life as a nuclear reaction theorist. You know, when I was studying particle collisions and scattering of nuclei, you know, I use the equations, I use the mathematics. I think of these things as really happening. The wave function is really something that is really evolving in time. What I measure is doing something to it. But I've not needed to pick a particular interpretation in order to do my research. And the same goes with my work in quantum biology.
Speaker 1And quantum biology covers a bit of a span of different topics. It's become a hot topic in recent years. What is your particular topic? What is your particular interest in quantum biology?
Speaker 2Well, I started off over two decades ago, a molecular biologist, a colleague of mine, John John McFadden, with whom I went on to write a book on quantum biology called Life on the Edge. So he, the stories that he, this was the late 90s, in fact, so more than a quarter of a century ago. Time passes and it's not just because COVID and we lose sight of the last few years, it's longer than that. He was trying to explain some aspect in genetics, which he felt needed quantum mechanics to explain it. Something called adaptive mutations, E. coli bacteria will mutate in two possible different directions. And if the environment was going to be conducive to one particular direction of mutation, it would preferentially pick that. He was saying, well, how does it know in advance that there's something waiting for it that will give it an advantage? Maybe it's described as a quantum superposition and then, you know, the act of measurement actually preferentially pulls it in one direction. Most of my colleagues in the physics department just thought it was completely crazy. I was interested enough to chat to him about it. And so from that, from then onwards, it became just a bit of a hobby to look at. And so I think it's really interesting to see how quantum mechanics plays a role in living systems and in cells. So it's quantum biology is not, well, life is made of atoms and atoms behave quantum mechanically. Therefore, life is like everything's made of atoms. So in that sense, everything's, nor is it, you know, the chemical bonds that hold the molecules of life together. The chemistry relies on quantum rules. That's not quantum biology. Quantum biology is the non-trivial quantum mechanics, you know, long lived quantum coherence, quantum entanglement. The way I've described it is, has life evolved the means to take advantage of the tricks of the quantum world to help it, to give it an evolutionary advantage or the opposite? Maybe it's learnt that quantum mechanics would be deleterious to life and therefore has evolved the ability to stop quantum mechanics from doing something. And the last few years, most of my work with, my PhD students and colleagues at Surrey has been to look at one particular mechanism, which is the bonding between strands of DNA. So in the double helix of DNA, the two strands are held together by hydrogen bonds, which is a hydrogen atom, which provides the glue between the nucleotides in DNA. And because my background is nuclear physics, I never say it's a hydrogen atom, it's a proton. I don't care about electrons. That's chemistry. So it's a proton. And that idea goes all the way back to a Swedish physical chemist, Per Lövdin, who published a paper in the early 60s, in fact, saying that it could be that the proton in the hydrogen bond between strands of DNA can transfer from being close to one strand across to the other. Essentially, there's a potential, a potential barrier, an energy barrier in the middle between the strands. And so that proton likes to sit on one side. It's more stable to sit on one side than the other. But it could somehow, if it could get across to the other side, and then those strands split, separate, they unzip in the process of replication. If that proton's on the wrong side, that could lead to a mutation. So that was the idea that was interesting. And he said, Lövdin said in this paper, that, "Maybe the proton can get across via a quantum process, via quantum tunneling." So that's what started us thinking about how likely is the proton to jump across from one strand to the other? And if it does, how likely is it to do that via quantum tunneling rather than having the energy to sort of go all the way over the top of the barrier? The energy coming from, I guess, colliding with nearby water molecules. And gradually, we've got more and more sophisticated in our calculations. And I've been left with this idea. I've been left far behind, because I've got computational chemists running these huge monster codes and simulations, adding in more ingredients all the time, and the story keeps changing. But it's fascinating, because it's still trying to address this question. Has life evolved the ability to use quantum mechanics?
Speaker 1And this is all part of my master plan, because we're now going to bring it back to the arrow of time. Right. Because quantum mechanics and the arrow of time have an interesting relationship, right? It's a Schrodinger equation, perfectly time-reversible. Measurement is not. And so how do you think about that?
Speaker 2For me, measurement, I don't think there's a problem with measurement. Well, measurement, I guess, the way some quantum physicists have written about this is it's broken down into different stages, and it's not just you open the box to see if what should Schrodinger's cat is doing, how healthy it is. The measurement process, first of all, involves, you're talking about, this is what's called the choice of basis. What are you measuring? Position? Are you measuring momentum? What is the most obvious thing that's going to be measured? And when I say "you," I don't mean someone with a PhD or wearing a white lab coat. It's not only physicists that can do measurements, anything surrounding a quantum system can be measuring it. Then the second step is the system becoming entangled with its surrounding environment, and that is what leads to decoherence. Now, going back to the Schrodinger's cat in the box, and you'll forgive me because I know you're a cat guy, I still use the dead or alive rather than awake or asleep. You're old school. That's okay. But dead or alive, we always remind listeners it's a thought experiment. No cats were harmed. Decoherence doesn't cause the cat to... to be either dead or alive what it does is get gets rid of the the uh the mixture it gets rid of the the um interference between them so the cat dead and alive at the same time no longer exists after decoherence but you still have an alive cat and a dead cat somehow you know it's not like it's one or the other i just don't know because i haven't opened the box um and it's that then that third stage which is why is it when you open the box do you see just one outcome and here's where interpretations come into there i mean certainly i i you know i you probably know from past um um chats we've had i'm i'm not the biggest supporter of everetti in many worlds quantum mechanics but i do have to admit it is the simplest cleanest way of describing the measurement problem because because it says decoherence inalienable of itself has caused reality to to separate and so there is a universe in which i open the box and the cat is dead there's another universe in which i open the box and the cat is alive so i think the many worlds interpretation is the cleanest explaining away the the measurement problem i think bowman pilot wave theory also reasonably well explains the measurement problem but i don't push me on it because i've forgotten exactly what the argument is you might you might know off the top of your head yeah
Speaker 1it's i'm not even i don't want to shed more light on bowman mechanics
Speaker 2than it needs yeah um so yeah so the measurement problem uh i don't think is a problem i think i think if if you subscribe to a particular interpretation then that interpretation solves that final step in in the measurement process but the idea of you know consciousness causing the state and things like that i think we've sort of
Speaker 1grown beyond that now but you did sneak in an arrow of time because you uh entangle in one
Speaker 2direction and not the other yes so so the the there it's back to open systems and isolated systems all the time assist a quantum system in this case is isolated there's no measurement taking place it's evolving symmetrically in time it's unitary evolution the measurement process that's the founding fathers that's the founding fathers that's the founding fathers that's the copenhagenist would have talked about was this what they called the irreversible act of amplification you know you have a measuring device that is a classical device interacting with a quantum system and that's what pulls it out of this unitary evolution and gives irreversibility yeah uh in in modern parlance we talk about the environment uh intact in becoming entangled with the system and and that entanglement is a one-way process even i'm not sure if you need to resort to saying the system decoheres whether is this is the decoherence that gives it the arrow or is it intact see entanglement a system can become
Speaker 1entangled with its with with a partner um is that i like to just define decoherence as entanglement with an environment and once you agree on what the environment is which is a tricky thing i i admit yeah that is what counts as decoherence for me
Speaker 2distinguishable so whatever but but would you say that entanglement of a system with something else is itself an irreversible process no because entanglement you can still describe it if you
Speaker 1just want to entangle with one qubit you can easily reverse that reverse that exactly so i think it's it's a it's exactly thermodynamics or stat mech at work once you entangle with enough you effectively in practice lose the ability to reverse it in in the same way of zooming out on
Speaker 2molecules of of gas in a box if you zoom out and you see it they're not just bouncing around
Speaker 1symmetrically that's right yeah yeah yeah and so so the arrow of time the quantum version you know the the measurement going forward rather than backward does that play a role in quantum biology like it's it sounded like from your previous description that worrying about decoherence was a big thing one of the mottos we hear in biology is that biological organisms are warm and wet
Speaker 2so it's hard to maintain quantum coherence yeah that that's one of the big criticisms that you know people say you know the why quantum biology is a load of nonsense you know it's uh it's it decoheres in femtoseconds you know what's the chance you know we work hard to isolate a quantum system in the lab to maintain coherence you know you do it in a vacuum you do it near absolute zero disturbances and yet you're saying in this you know 300 degree kelvin uh system where there's thousands of chemical everything so much is going on you're saying quantum uh effects can persist well the point there is that you know has life evolved the ability to you know fine-tune the environment so the environment isn't just causing this one-way decoherence maybe the environment is a flow of information you know technically we say the environment isn't Markovian there's some non-markovianity so the environment is itself it's helping keep the quantumness going rather than causing it to sort of leak away very very quickly so in that sense it may be that there's a um it's it's trying to avoid a directionality to time for the quantum system for as long as possible
Speaker 1so is it is it fair to analogize it as saying you know we're people who are trying to build quantum computers or um lots of money trying to maintain entanglement between a few qubits and yeah they've had some success but there's a long way to go um but they've only been doing it for a few years and nature's been doing it for billions of years and maybe they've come up with some clever strategies
Speaker 2yeah I I don't see why not you know there are certainly people people like you know Seth Lloyd uh I'm sure another mindscape guest of yours um not yet but I know that very well he hasn't oh right okay oh you should have him on um um you know people like that would argue that yeah life has had a long time uh to to to find whatever tricks are out there billions of years you know life has isn't isn't there's no directionality to it in the sense of exploring this would work that everything happens by accident and the things that work work right and then they and things that don't work get left behind uh and so there's been enough time to explore what possible ways quantum mechanics might be of benefit uh to life uh and if they if life has found a way of doing it then sure you know we should be looking to see uh you know there are there are a number of examples of of quantum effects that look like uh happen inside living cells you know the way um photosynthesis take uh uh absorbs sunlight that's still an open question of whether quantum mechanics is playing a role there or not um enzymes the way they move particles around they might utilize they that's all been experimentally confirmed they utilize things like quantum tunneling um and then of course there's the poster child of quantum biology which is the uh idea of magneto reception that certain animals uh have evolved the ability to to uh gain directional information you know birds that are migrating um not by studying the sky or landmarks on the ground or prevailing winds but uh by sensing the Earth's magnetic field uh uh and the strength of magnets if it helps them know whether to go north or south uh and and the only theory in town that we have that would explain that would be that inside a particular molecule in these creatures eyes there are a pair of entangled electrons uh that so photons come in it's in the eyes a photon knocks one of a pair of entangled electrons onto a neighboring atom so they're far apart but they're still there so it's it's it's it's a neighboring atom so they're far apart but they're still entangled uh and their orientation and the way they're spinning is very sensitive to the Earth's magnetic field it seems crazy but why you know why wouldn't you know life has had a long time yeah so that's and there are there are plenty of amazing things that that nature has has evolved to to do you know why not why not use quantum
Speaker 1mechanics as well quantum mechanics isn't magic right absolutely but this is a good opportunity to ask I mean maybe this is an unfair question because it's one of those things about quantum mechanics is it very hard to explain entanglement is not a force right when we talk about these two electrons and you say like okay they're entangled and one electron moves around that doesn't mean that the other electron gets to tug on it in any particular way and I think that people get that
Speaker 2impression when they just use the word entanglement yeah yeah I mean the idea here is that uh the two electrons their quantum state is a superposition of both of them spinning in the same direction and one spinning in the opposite direction to the other and the the percentage of time you know if you were to take sort of snapshots of those two electrons at any given moment how often would they be you find them spinning the same way how often we find them spinning the opposite direction um triplet and singlet States we call them um that depends very sensitively on an external magnetic field interacting with that with that quantum state so so it's not about a force pushing one and the other one instantaneously doing something itself it's what that quantum state looks like in terms of populations of yeah relative to singlet spin states it starts sounding i haven't done it
Speaker 1very um it starts sounding very abstract to the person on the street i know and like i said i have not figured out how to explain it either so you know no i got i put you on the spot there sorry about that let me put you on the spot again though nevertheless so we have some quantum mechanics on the table we talked earlier about the past hypothesis and low entropy near the early universe but you know as well as anyone the usual ways of talking about the past hypothesis start by saying let's assume that everything is classical let's let's think that we're just in a box of gas okay and and we know that's not true so how much advancement has been made in the past? has been made in sort of upgrading our discussion of the cosmological initial conditions and low entropy to the world of quantum mechanics yeah well i mean i think uh that you know if there
Speaker 2are different arrows of time for example we have the thermodynamic arrow of time that ludwig Boltzmann gave us the second law of thermodynamics the increase in disorder um there are other arrows of time that you the causal arrow of time the you know the and so on the the the quantum uh entanglement or quantum decoherence arrow of time which we talked about for me is the best the most irreversible non-negotiable one-way process right uh and so what i've been thinking about and over the past few years and and together um with eddie chen in san diego is whether quantum entanglement and decoherence provide us with a more fundamental past hypothesis than the thermodynamic past hypothesis uh the you know with the idea of having uh um you go from a special micro state to you know to to to less special ones here here we're saying what if the universe uh rather than just saying the universe started in this very ordered state we say the universe started off in a very pure quantum state very very pure in the sense that um if there's a measure of entropy at the quantum level that would be very low then then the question is what how what measure of entropy do you have at the quantum level right uh and you know there are various ideas here we we we hit upon what's called entanglement entropy we didn't hit upon it you know we we decided that would be a good a good measure uh which is there are a number of other things that we can do to understand what it means to have a system that is in a in a what we call a pure state so it has uh uh the measure there is is what's called von neumann entropy right so so a system in a pure state has zero von neumann entropy um but if it's made up of two subsystems uh then if they're not entangled with each other if they're just isolated they also have zero von norman entropy but those subsystems can interact with each other they can become entangled with each other so their individual von neumann entropies go up but overall when you add it altogether you have to have zero because the overall system that can contains both has zero so what happens so you so there must be some yes you have to subtract something right they both have volume you subtract something in order to get the answer to work out zero that thing that you subtract is the entanglement entropy uh and what we we have a i've tried to argue is that the universe started off with very low entanglement entropy that the all the the parts of the of of the universe the subsystems of the universe were in pure states and gradually as the universe has evolved rather than thermodynamic entropy increasing everything is becoming gradually more and more entangled with everything else of course the difficulty there is how how big are those subsystems how how much do you have to divide them up at what point you say right now i've got down to the fundamental pinpoints you know so it's it's it's i don't know this is an area that you've been working on as well you know it's a at a moment it's a bit fluffy and we haven't followed up that paper with anything else partly because we've both been doing other stuff but i i tend to think that we we started off on something that we thought was very interesting and when we haven't seen it through you know there's there are still big gaps
Speaker 1i'm super duper sympathetic to that i i feel like i've written a bunch of papers where i was sort of saying something and inviting other people to extend it and work at it and they didn't and i realized that oh this is my job isn't it i got it's down to me yeah yeah i gotta get back to this myself
Speaker 2things are a bit more difficult for me now because um a couple of years ago i i took earlier i mean i'm only 63 but i took earlier retirement from my academic role at surrey in part because along with a lot of you i mean i know you you have your your your difficulties in the us at the moment with funding we do and i don't think we're we're in that position but certainly a lot of universities in the uk were going through you know tightening of belts uh and and um at surrey i don't know how many tens of million there were in deficit it was uh the responsibility or the deans of the different faculties to put their houses in order and it became apparent that physics had to lose actually lose academic positions and i felt because i could see the politics getting more toxic uh and because i had spent 30 years teaching undergraduates and i've done all the academic stuff and the committees and endless you know stuff that you're you're fully immersed in now thanks i i've done that i've been i've done that i thought you know what you know i've got my other interests i've got my writing my broadcasting i can carry on with my research theoretical physicists are relatively cheap um so i stepped back from that so it didn't it did mean that my my research uh activities you know because that the work with eddie chen on this on the past hypothesis came out of this grant with the templeton foundation well i'm not writing grant proposals anymore now you know and you know and i'm not a member of academic staff so i'm not in a position to be able to do that so i need to find other people academics who are still in in post so i'm an emeritus uh professor now it means i have a small desk still uh sorry i can go in now and again but i'm i'm happy doing you know doing the writing doing the broadcasting uh 10 month old twin grandchildren so i don't know when i'm going to get back to yeah thinking about those things i'm trying to find i'm trying to like justify why i've not
Speaker 1i yeah i'm just i just do it because i'm not a good planner and i'm lazy you know i don't even justify it at the level of sophistication that you've achieved there but there is something i mean the arrow of time uh has us all in its grip and there's a point of your life where you can sort of either say you know i've i've done pretty well i'm kind of going to like just downshift and fade away a little bit or you can say like boy i've done pretty well i'm kind of going to like i better get to work because if i'm going to do what i wanted to do the only chance i have is now
Speaker 2yeah you know my wife really keeps going on about you know so the first year after i stepped back from my academic position i was still working just as hard and she's just like what's the point you've retired no i've not retired i'm still you know i've got too much to do too much to think about so i i have slowed down a bit now but i guess most of my time has been taken up with the writing uh and so i haven't i haven't done a lot of writing i haven't done a lot of writing i haven't i haven't missed the research that much i've still got two phd students one has just submitted his thesis so i've got one more and i don't think i'll take on any more grad students well i sort of can't be a primary supervisor anymore if i don't have a permanent position i would be a secondary supervisor with a colleague and of course then the project that is chosen for the student would not be my choice so it may not be the thing that i want to devote what time i
Speaker 1have to it so and we're too old for that like we're gonna if you're gonna do something it's better be what you want to do at this point exactly exactly that's right i don't need to
Speaker 2i don't need to do do anything other than what i'm perfectly excited about speaking of which um i
Speaker 1think the last big question to uh address here is to return to exactly where we started the reality of time uh you do talk about this in your book uh but now that we've talked about the past hypothesis and schrodinger's equation we can we can sort of revisit it at a more sophisticated level um you know that there's a lot of people some very close friends of ours doing general relativity quantum mechanics quantum gravity who think that time is not doesn't exist or isn't fundamental or is emergent or something like that and i i like to say like that's something we just don't know and we should be open-minded about people get annoyed when i say we should be open like you need to have a position they don't care what the position is but what is your position on this one
Speaker 2well i make a distinction between you know time doesn't exist and time is emergent Certainly, I think if you're sitting outside of the universe and you've combined quantum mechanics with relativity theory, something that was done many years ago by Wheeler and DeWitt, the famous Wheeler-DeWitt equation where time doesn't exist, fine, that's provided you're sitting outside the universe. I'm not, I'm inside the universe. I have no issue with the idea that time may be emergent from something more fundamental, quantum entanglement or something like that. In the same way that maybe space is something that is emergent or something more fundamental, but I don't think that means it's not real. It's not the same as temperature is an emergent property from lots of molecules moving around. It's just something that we perceive on the macro scale. But we zoom in. It sort of disappears. I think if time is emergent, then nevertheless, it's a real tangible thing.
Speaker 1I do wonder, and this is a true open question, again, which I don't have a strong feeling about. We've had people like Tomas Hertog and Daniel Harlow on the podcast, and in different ways, they're both considering whether or not time doesn't exist, but if you separate out an observer from the universe, even in a timeless universe. That observer thinks the time is passing, right? It's this sort of relational thing. You're a subsystem of the universe, and maybe that's compatible with your view that we should take a more open systems view of the laws of physics in general.
Speaker 2Yeah. I think so. I think if you see something where there's no system in thermal equilibrium, you say, "Well, there's no arrow of time there. Time doesn't exist." Well, that's really talking about the arrow of time rather than time itself. So, me looking at that system, if suddenly it's no longer isolated, it's open because I'm interacting with it, then of course, there's an arrow of time and time is real. I even think if the universe, trillions and trillions of years from now, when the entire universe reaches thermal equilibrium and there's just nothing is happening, is time still passing? Hmm. Well. You see, I would still say yes, even without extracting myself outside of the universe, time is still passing. Maybe it's still asymptotically sort of cooling down towards some sort of space. We can still point to trillions of years back in time at the beginning of the arrow, there was a big bang in which the universe had no entropy. So, even if nothing is changing, time is still passing. It's just that you can't measure. There's nothing that you can use to measure the passing of time. So in that sense, time really becomes quite a real fundamental thing that exists. It's almost back to Newton's absolute clock ticking by, although we now know that that's wrong in the sense that time is relative and different reference frames, but time is like that absolute clock. Time is something that is happening. Even if it fundamentally didn't start off like that. Yeah. It started off from something else.
Speaker 1Does it strike you ever that, you know, all this time since Aristotle and Augustine and Newton and whatever, we still don't know the answers to these pretty basic questions that we can ask?
Speaker 2Yeah, it does. It's frustrating. And I think for a lot of people, they assume then, you know, obviously our taxpayers money is being wasted on you guys, if you've not made progress, we make progress by developing science and technology. We make humanity's life better. That is happening all the time. Even though there's a subgroup of people who seem to deny that science actually works. But the fundamental questions, yeah, sometimes, maybe they're too hard or maybe we'd never be able to answer them, but you know, that itch has to be scratched. And if the Greeks are scratching it and we're still scratching it, what's wrong with that? Why should they be easy? Exactly. Yeah. How boring the world would be anyway if we had all the answers, right? It's a bit like doing a jigsaw puzzle. You know, the joy is in doing the jigsaw puzzle, not in finishing it. You finish it, you think, oh, great. Okay. Right.
Speaker 1Cheer up and start again. It's in the process. And this is a process. It's not going to end anytime soon. So I hope not. Jim Al-Khalili, thanks so much for being on the Mindscape podcast. My pleasure. It's been great fun. Have a great day. Bye. Bye. Bye. Bye.
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