366 | Jim Al-Khalili on Time, Quantum, Biology, and Cosmology

The Nature of Time

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1:00Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, John 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.

1:34So 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?

2:07I 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 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.

2:38But 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,

3:12and 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 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.

3:57Jim 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? Aha, okay. It's a tough question because it's one that we've been thinking, we, humanity, has been thinking about for millennia. You know, going all the way back to the ancient Greeks, there were big philosophical debates about whether time was real,

4:30whether it's an illusion, whether it flows.

4:34And 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, and certainly I would like to think more about the nature of time than the ancient Greeks, but we may not be that much closer to answering the ultimate question.

5:07All 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 is 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. Okay. It's a real thing. It exists, and I also go further and say it exists and it has a direction.

5:40That'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 universe 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.

6:13You're going to say that it's not simply a matter of the present state of the universe and its evolution. There's something oomphy about it. There's something built into it? Yeah. 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. 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,

6:47I would say that time has a direction. This is a longstanding debate, which you know very well. You've written a lot about how does time's directionality, its irreversibility emerge from something deeper, maybe something that's time symmetric that doesn't pick out a direction.

7:07And my view, maybe with something we'll get into later on, is that it's the other way around, that time's direction, directionality, irreversibility is more fundamental. Okay, good. And symmetric equations and symmetric laws of physics, I think, are just idealizations that aren't giving us the whole picture. Yeah, no, that's very important. And I just want to get it on the table. Well, 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.

7:41You know, we said that we're going to do the podcast at 10 a.m. 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. Yeah, I mean, in my book, I sort of start off by making this distinction that many philosophers of time, and that is a field of research, philosophy of time, would argue, which is a distinction between physical time, the time that enters into our laws and equations of physics, and manifest time, psychological time,

8:14which 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 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? So why does it seem like, you know, time passes? They are so obvious. People wonder why scientists and philosophers are spending effort trying to study this.

8:49But that is different from time, the physical time that enters into our 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 mechanics.

9:22Well, 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. Yeah. Yeah. I mean, in a sense, I'm sort of deliberately, I am naive about some of the philosophical issues because, you know, 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,

9:55start to worry about some of these foundational problems in physics because time is finite, right? Time is running out and I don't have to publish or perish anymore. You know, I don't have to work on the sort of mitty 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 the 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.

10:26As 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,

10:56it's not just the philosophers come up with the questions and physicists come up with the answers. It's more complicated than that. But I don't have a training in philosophy. So what I've, the background research I've done for the book has mostly been from very much from a physicist's perspective. It'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.

11:31I 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 actually talk to each other.

12:02And there should be more formal structures to allow that to happen. Yeah. 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, there'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 that are coming back from the big astronomical surveys, for example.

12:34So 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 out from lots of directions, no single person has to approach it in more directions themselves.

13:06Other people can use their skills, you use yours. We should mention, Jim is on the side of the angels here. You've actually collaborated with philosophers about these philosophy of time questions. Yeah, 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 unafraid to sort of fund some of these more speculative areas of research, which the usual sort of public funding bodies are reluctant to do.

13:39And 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, it was an opportunity to do something really interdisciplinary. And the nature of time and the error of time was a big feature of that. So I reached out to one philosopher of physics I knew, and I asked him if he'd like to join.

14:12He said he didn't have time, but he pointed me in the direction of several others. So Simon Saunders at Oxford, who's I'm sure someone you know very well. Yeah. A fellow Everettian, as we say in the quantum world. So Eddie Chen in UC San Diego, I published a paper with a couple of years ago, and Karim Thibault 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. 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 do flappy.

14:51Do you therefore have a stance on things like presentism versus eternalism? Not a strong one, no. I mean, because I can see the arguments for each case. For me, I guess, because 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. You know, that in 4D space times, all times exist in the same way that all points in space exist.

15:27And 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 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 naturally feel is the right way of thinking about things. Before you jump back in, you know that feeling when feedback, notes, and data are coming in from every direction?

16:02ChatGPT work can make sense of it all, turning scattered inputs into ready-to-review work. With your permission, ChatGPT work can gather context from apps and files, summarize incoming messages, rebuild decks, and help finalize high-quality documents for your team or clients. Stay in control as you move from a goal to polished work faster with ChatGPT work. Download the ChatGPT desktop app today and take on your most ambitious work. Healthcare can feel complicated. That's why Optum uses technology to connect the people and processes that make healthcare easier, more affordable, and more effective.

16:40We're making it clearer for you to know exactly what your benefits cover. And to help you better manage your health, we're coordinating care between your doctors and your technology. We believe better, simpler healthcare is always possible. That's healthy optimism. That's Optum. Visit Optum.com to learn more. Well, this is going to get us into some deep waters.

The Arrow of Time

17:03We might as well get there. Let's talk about the arrow of time. We've already mentioned it a little bit. 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 want to tell that conventional one first? Yeah. Yeah. So, I mean, so this is something that goes back to the mid-19th century and people like Boltzmann and Maxwell 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 change over time, whether it's Newton's laws of motion, whether it's Schrodinger's equation of quantum mechanics and so on, all seem to work perfectly well if you switch time over.

17:47You may have to do mathematically a few other technical things, but they are what we say, time reversely invariant. They don't break any laws of physics if you run them backwards. And since these are fundamental dynamical equations that we believe describe nature correctly, then there's no directionality in time baked in there. That directionality, that arrow of time somehow must emerge from them. And the big debate in the 19th century, which often is referred to as Lohschmidt's paradox, Joseph Lohschmidt was the person who first highlighted this dilemma, is that there is an area of physics where the directionality of time is apparent.

18:31And that is in thermodynamics and the second law of thermodynamics, which I always say is so famous, but it couldn't even make it to the number one spot in thermodynamics, says that this quantity entropy, which we may or may not want to talk about a bit more, increases in an isolated system or increases or stays the same, but it doesn't decrease. That gives a directionality to time. So how do you reconcile that with these time symmetric laws and equations of physics?

19:05And 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 we need to be concerned about. You know, 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.

19:37But I think for most physicists, it's the dynamical time symmetric equations that are the more fundamental. And the directionality to time emerges, you know, for example, with what we say, zooming out, coarse graining, you know, looking at larger and larger systems, and suddenly you see something emerging.

19:56That's the traditional 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 all physicists, maybe not even the majority of physicists would agree with, which is that irreversibility is more fundamental, then how do I justify that?

20:28Well, 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 doesn't look wrong. Both those apply only to isolated systems. Sure. And so, for me, certainly, time symmetric dynamical equations, because they only apply to isolated systems, they are an idealization.

21:03They're not true in general, because 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. Okay. Whether it's losing, whether it's the hot cup of coffee in the fridge that's cooling down, or whether it's a quantum system decohering because it's interacting with its environment, those are irreversible processes that give a directionality to time.

21:49And so, for me, because nothing is truly isolated in our universe, 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 error of time within that system.

22:23But outside, there's still a direction to time. So I'm willing to entertain this point of 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?

22:59Yeah. 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.

23:13If, right. Well, if by open, an open system, do you mean just the system itself? You're not including its surrounding environment? Well, if the surrounding environment is a thermal reservoir at 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? Right. Well, there's no arrow of time that we can perceive if we're looking at that system and its environment.

23:45Unless 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 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.

24:24The past hypothesis, we have to acknowledge that there must be a special moment that the universe is off in a special state. Well, 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.

24:58You're not proposing, you're not proposing changing any of those equations whatsoever, you're just proposing looking at a different context. Absolutely. I mean, if we take Schrodinger's equation, for example, it is correct and perfectly precise, provided it's dealing with an isolated system, which is 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 plus some add-ons.

25:31Yeah. 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. Okay. Of that larger, what's called the master equation, because an isolated system is 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 because I don't know what the rest of the world is going to do.

26:02Like, 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. Yeah, 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.

26:39You 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 systems environment is itself still constrained. There's still a lot more 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?

27:17I 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.

27:50Why the heck aren't we teaching students about entanglements and decoherence, you know? And entanglements 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.

28:28Things are decohering 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 as well. We will. But that'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. Yeah. 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.

29:01But, you know, why don't you tell the audience what 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, 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.

29:48And if it's time-symmetric, then if you run the clock backwards, that means yesterday should have higher entropy than today. Right. 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?

30:18Well, if you push the special moment to last week, then sure, yesterday would have lower entropy than today, today has lower entropy than today, 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, 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.

30:57From that very moment onwards, entropy is increasing. So we've satisfied time symmetry and the second ortho-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, you know, 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 of an isolated system, namely the entire universe, that can both be time symmetry invariant, but also satisfy the second law of thermodynamics.

31:39It seems we can't get away from requiring a past hypothesis when we're dealing with the whole universe. And 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. Yes, yes, that's right. I mean, for me, the past hypothesis is, it says the universe starts off with very low entropy or in a very special state.

32:20But 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 be a certain, have certain values for the universe to have evolved in the way that it has. And I would argue that the past hypothesis is simply part of that.

32:52It'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 fundamentals and in this very special state. Healthcare can feel complicated. That's why Optum uses technology to connect the people and processes that make healthcare easier, more affordable and more effective. We're making it clearer for you to know exactly what your benefits cover.

33:22And to help you better manage your health, we're coordinating care between your doctors and your technology. We believe better, simpler healthcare is always possible. That's healthy optimism. That's Optum. Visit Optum.com to learn more. Before you jump back in, you know that feeling when feedback, notes, and data are coming in from every direction? ChatGPT Work can make sense of it all, turning scattered inputs into ready-to-review work. With your permission, ChatGPT Work can gather context from apps and files, summarize incoming messages, rebuild decks, and help finalize high-quality documents for your team or clients.

34:01Stay in control as you move from a goal to polished work faster with ChatGPT Work. Download the ChatGPT desktop app today and take on your most ambitious work. So 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?

34:32Like, 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?

34:47Yeah, so having the entropy of the universe very small and allowing the second law to do its thing or whatever mechanism that gives us an hour of time, that's all part of, you know, 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.

35:21And, you know, that's something 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.

35:52An 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. Good. No, 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 OK. But we did start with, like, the hardest part of the question.

36:24There'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? Well, very often cosmologists have a simplified view of entropy as being two things.

36:56There's thermodynamic entropy. You know, the universe started off in a hot, dense state, but it was in thermal equilibrium. And there's unusual, 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 expanding and gravitational entropy was very, very low. My background is nuclear physics. And so for me, nuclear fusion entropy plays a very important role.

37:29You 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 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.

38:07It'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. It's 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.

38:39If there was no fusion entropy, the sun would have clumped down to, you know, matter would have clumped together or 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 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.

39:13We haven't run out of steam yet. 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 against entropy or the second law of thermodynamics. And my personal reaction is, no, that's exactly backwards. Life is taking advantage of the second law of thermodynamics. It's using that free energy from the sun to maintain its equilibrium, not its equilibrium, its structure, its organization, its metabolism and so forth.

39:45So do you have a dog in that fight? No, 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.

40:17But 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, not the neutrons, 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.

40:48How, 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. One 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.

41:18A 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've got to think harder about what life is doing. And, 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 where it could harbor life, even if it's just microbial life. You know, maybe multicellular life is the really the sticking point.

41:50And 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, outer, you know, suburbs of some galaxy to help it increase its entropy. It seems a bit wacky. 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.

42:24But it does occur to me that first we should talk about quantum mechanics.

What is Quantum Mechanics

42:28Yeah.

What is Quantum Mechanics

42:29So, what is your favorite way? We started with what is time. So, now what is quantum mechanics, Jim?

42:35When I was a grad student, I had two PhD supervisors, both staunch Copenhagenists, right? So, this is the traditional view of quantum mechanics that's espoused broadly by Bohr and Pauli and Heisenberg and others. And I know it's unfair and people who, you know, who support that viewpoint hate it when you say that's the shut up and calculate interpretation. But I did have that attitude when I was a student.

43:07You know, 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. Okay. 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.

43:40Oh, yeah, that was sketchy. 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, you know, 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.

44:11But it also means that I don't think we can adopt whatever interpretation we're 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 parallel worlds or there aren't. Either there's a sort of invisible guiding potential or there isn't.

44:41Either the wavefront 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 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.

45:14But 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. Yeah, 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.

45:55You 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 do 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.

46:27And quantum biology covers a bit of a span of different topics. It's become a hot topic in recent years. What is your particular interest in quantum biology? Well, I started off over two decades ago, a molecular biologist, a colleague of mine, John Joe McFadden, with whom I went on to write a book on quantum biology called Life on the Edge. So he, the story is that he, this was the late 90s, in fact, so right, more than a quarter of a week ago. Time passes. And it's not just because COVID and we lose sight of the last few years.

47:01It's longer than that. He gave a talk in the physics department. He was trying to explain some aspect in genetics, which he felt needed quantum mechanics to explain it. It's 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.

47:33And 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 whether quantum mechanics plays a role in living systems in cells.

48:07So it's quantum biology is not, well, life is made of atoms and atoms behave quantum mechanically. Therefore, life is 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.

Quantum Biology

48:26That's not quantum biology. Quantum biology is the non-trivial quantum mechanics, you know, long-lived quantum coherence and quantum entanglement. And 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 learned that quantum mechanics would be deleterious to life and therefore has evolved the ability to stop quantum mechanics from doing something.

48:59And 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.

49:31I 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, Pert Lovdeen, who published a paper in the early 60s, in fact, saying that it could be that the proton in the hydrogen bond between the strands of DNA can transfer from being close to one strand across to the other. Essentially, there's a potential barrier, an energy barrier in the middle between the strands.

50:07And 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, Lovdeen said in this paper, that maybe the proton can get across via a quantum process, via quantum tunneling.

50:37So 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 far behind because I've got computational chemists running these huge monster codes and simulations, adding in more ingredients all the time.

51:11And 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? Healthcare can feel complicated. That's why Optum uses technology to connect the people and processes that make healthcare easier, more affordable, and more effective. We're making it clearer for you to know exactly what your benefits cover. And to help you better manage your health, we're coordinating care between your doctors and your technology. We believe better, simpler healthcare is always possible.

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52:20Download the ChatGPT desktop app today and take on your most ambitious work. And 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? Like you mentioned, the Schrodinger equation, perfectly time-reversible. Measurement is not. And so how do you think about that? For me, measurement, you know, I don't think there's a problem with measurement.

52:52Well, 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, you know, what Schrodinger's cat is doing, how healthy it is.

53:11The measurement process, first of all, involves, you know, you're talking about this is what's called the choice of basis. You know, 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, you know, that we're not the only, 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.

53:44And 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. You know, I still use the dead or alive rather than awake or asleep. You're old school. That's okay. But, you know. But dead or alive, you know, we always remind listeners it's a thought experiment. No cats were harmed.

54:09Decoherence doesn't cause the cat to be either dead or alive. What it does is get rid of the mixture. It gets rid of the interference between them. So the cat dead and alive at the same time no longer exists after decoherence. But you still have a live 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. And it's then that third stage, which is why is it when you open the box, do you see just one outcome?

54:44And here's where interpretations come into there. I mean, certainly, you probably know from past chats we've had, I'm not the biggest supporter of Everettian, many worlds, quantum mechanics. But I do have to admit it is the simplest, cleanest way of describing the measurement problem because it says decoherence in and of itself has caused reality to separate. And so there is a universe in which I open the box and the cat's dead.

55:16There's another universe in which I open the box and the cat is alive. So I think the many worlds interpretation is the cleanest at explaining away the measurement problem. I think Bohmian pilot wave theory also reasonably well explains the measurement problem. But don't push me on it because I've forgotten exactly what the argument is. You might know off the top of your head. Yeah, it's I'm not even I don't want to shed more light on Bohmian mechanics than it needs. So, yeah, so the measurement problem I don't think is a problem.

55:52I think I think if you subscribe to a particular interpretation, then that interpretation solves that final step in the measurement process. But the idea of, you know, consciousness causing the state and things like that, I think we've sort of grown beyond that now. But you did sneak in an arrow of time because you entangle in one direction 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.

56:28There's no measurement taking place. It's evolving symmetrically in time. It's unitary evolution. The measurement process that the founding fathers, the Copenhagenists, would have talked about was this what they call 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. In modern parlance, we talk about the environment in becoming entangled with the system and and that entanglement is a one way process.

57:11Even I'm not sure if you need to resort to saying the system decoheres, whether it is the is the decoherence that gives it the arrow or is it entanglement? A system can become entangled with its with a partner.

57:31Is 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 admit. Yeah, that is what counts as decoherence for me. Macroscopically distinguishable or 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 just want to entangle with one qubit, you can easily reverse that.

58:01Reverse that. Exactly. So I think it's a it's exactly thermodynamics or stat mech at work. Once you entangle with enough things, you effectively in practice lose the ability to reverse it. In the same way of zooming out on molecules of gas in a box. If you zoom out and you see it, they're not just bouncing around symmetrically. That's right. Yeah. Yeah. Yeah. And so so the arrow of time, the quantum version, you know, the measurement going forward rather than backward. Does that play a role in quantum biology?

58:33Like it sounded like from your previous description that worrying about decoherence was going to be a big thing. One of the mottos we hear in biology is that biological organisms are warm and wet. So 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 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.

59:04You know, you do it in a vacuum. You do it in absolute zero. You try and shield it from surrounding disturbances. And yet you're saying in this, you know, 300 degree Kelvin system where there's thousands of chemicals, so much is going on and you're saying quantum 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 maintaining the system.

59:36So there's backflow 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, it's trying to avoid a directionality to time for the quantum system for as long as possible. So is it, is it fair to analogize it as saying, you know, we're people who are trying to build quantum computers or spending lots of money trying to maintain entanglement between a few qubits and they've had some success, but there's a long way to go.

1:00:18But they've only been doing it for a few years and nature has been doing it for billions of years and maybe they've come up with some clever strategies. Yeah, I don't see why not. You know, there are certainly people, people like, you know, Seth Lloyd, I'm sure another Mindscape guest of yours. Not yet, but I know Seth very well. He hasn't. Oh, right. Okay. Oh, you should have him on. So, you know, people like that would argue that, yeah, life has had a long time to, to, to find whatever tricks are out there.

1:00:48Billions 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. And so there's been enough time to explore what possible ways quantum mechanics might be of benefit to life. And if they, if life has found a way of doing it, then sure, you know, we should be looking to see, you know, there are, there are a number of examples of, of, of quantum effects that look like happen inside living cells.

1:01:23You know, the, 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 already been experimentally confirmed. They, they utilize things like quantum tunneling. Um, and then of course there's the poster child of quantum biology, which is the, uh, uh, idea of magnetoreception that certain animals, uh, uh, have evolved. The ability to, to, uh, uh, uh, uh, gain directional information, you know, birds that are migrating, um, not by studying the sky or, or landmarks on the ground or prevailing winds, but, uh, by sensing the earth's magnetic field, uh, uh, uh, and the strength of the magnet that helps them know whether to go north or south.

1:02:14Uh, and, and, and the only theory in town that we have that would explain that would be that inside a particular molecule, uh, in these creatures' eyes, there are a pair of entangled electrons, uh, that, you know, so photons come in, it's in the eyes. So photon knocks one of a pair of entangled electrons onto a neighboring atom. So they're far apart, but they're still entangled, uh, and their, uh, orientation and the way they're spinning is very sensitive to the earth's magnetic field.

1:02:47It seems crazy, but why, you know, why wouldn't, you know, life has had a long time. So, so that's, and there are, there are plenty of amazing things that, that nature has, has evolved to, to, to, to do, you know, why not, why not use quantum mechanics 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 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,

1:03:19that doesn't mean that the other electron gets to tug on it in any particular way. And I think that people get that impression when they just use the word entanglement. Yeah. Yeah. I mean, the idea here is that, uh, the, 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, the percentage of time, you know, if you were to take sort of snapshots of those two electrons at any given moment,

1:03:53how often would they be, you find them spinning the same way, how often we find them spinning the opposite direction, triplet and singlet states, we call them. Um, um, 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 electron and the other one instantaneously doing something itself. It's what that quantum state looks like in terms of populations of.

1:04:24Yeah. Triplet relative to singlet spin states. It starts sounding. It's like, I haven't done it very, 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. So, you know, no, I got, I put you on the spot there. Sorry about that.

Cosmological Initial Conditions

1:04:41Let me put you on the spot again, though. Never, 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 sort of upgrading our discussion of the cosmological initial conditions and low entropy to the world of quantum mechanics?

1:05:21Yeah. Well, I mean, I think that, you know, if there are 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. There are other arrows of time, the causal arrow of time, the, you know, and so on. The, the, the, the quantum entanglement or quantum decoherence arrow of time, which we talked about for me is the best, the most irreversible, non-negotiable one way process.

1:05:58Right. And so what I've been thinking about in, over the past few years and, and together 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. The, you know, with the idea of having, you go from a special micro state to, you know, to, to, to, to, to, to less special ones here, here we're saying, what if the universe, rather than just saying the universe started in this very ordered state, we say the universe started off in a very pure quantum state.

1:06:42Very, very pure in the sense that if there's a measure of entropy at the quantum level, that would be very low. Then, then the question is, well, how, what measure of entropy do you have at the quantum level? Right. And, you know, you know, there are various ideas here. We, we, we, we hit upon what's called entanglement entropy. We didn't hit upon it. You know, we, we, we, we decided that would be a good, a good measure, which is the idea that, you know, you can have a system that is in a, in a, what we call a pure state.

1:07:13So it has, 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, but if it's made up of two subsystems, then if they're not entangled with each other, if they're just isolated, they also have zero von Neumann 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, add it all together, you have to have zero because the overall system that contains both has zero.

1:07:52So what happens? So you, so there must be some, yes, you have to subtract something, right? They both have, you subtract something in order to get the answer to work out as zero. That thing that you subtract is the entanglement entropy. And what we have tried to argue is that the universe started off with very low entanglement entropy, that all the parts of the universe, the subsystems of the universe were in pure states.

1:08:23And 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, how much do you have to divide them up? At what point do 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 at the 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.

1:08:57But 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 been gaps. I'm super duper sympathetic to that. 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 got to get back to this myself. Things are a bit more difficult for me now because a couple of years ago, I took early, I mean, I'm only 63, but I took early retirement from my academic role at Surrey in part because along with a lot of you, I mean, I know you have your, your, your difficulties in the US at the moment with funding.

1:09:47We 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 and, and at Surrey, I don't know how many tens of million there were in deficit. It was 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. Wow. Okay. Uh, and I felt because I could see the politics getting more toxic, uh, and because I had spent 30 years teaching undergraduates and I'd done all the academic stuff and the committees and endless, you know, stuff that you're, you're fully immersed in now.

1:10:35Thanks. I, I, I, I've done that. I've been there. I've done that. I thought, do 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, uh, 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, uh, 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.

1:11:11So I, I need to find other people, academics who are still in, 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. Keep, keep Disney, you know, so, so I don't know when I'm going to get back to thinking about those things. I'm trying to find, I'm trying to like justify why I've not, I, yeah, I'm just, I just do it because I'm not a good planner and I'm lazy.

1:11:47You 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, 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 better get to work because I'm going to do what I wanted to do. The only chance I have is now. Yeah. You know, uh, my, 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.

1:12:22And she was just like, what's the point? You've retired. And I said, 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 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. That's a big step. Yeah.

1:12:52Well, 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 have to it. And we're too old for that. If you're going to do something, it's better be what you want to do at this point. Exactly. Exactly. That's right. I don't need to. I don't need to do anything other than what I'm perfectly excited about. Speaking of which, um, I think the last big question to, uh, address here is to return to exactly where we started, the reality of time.

The Reality of Time

1:13:31Uh, 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?

1:14:06Well, I make a distinction between, you know, time doesn't exist and time is emergent. Um, certainly I think if, you know, if you're sitting outside of the universe and, and you've, you've, you've some, you've combined quantum mechanics with relativity theory, you know, something that was done many years ago by, uh, Wheeler and, and, and DeWitt,

1:14:36provided you're sitting outside the universe, you know, I'm, I'm, I'm not, I'm inside the universe. It's a, it's, it's time. I have no issue with the idea that time may be emergent from something more fundamental, quantum entanglement or something like that. And in the same way that, you know, maybe space is something that is emergent or something more fundamental, but I don't think that means it's not real. I, I, I, it's not, it's not the same as, you know, 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, a real tangible thing.

1:15:19I 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, you know, 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.

1:15:54Yeah, I think so. I think, I think if you see something where, you know, there's no system in thermal equilibrium, say, well, there's no, 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. But me looking at that system, if it 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, you know, in the, if the universe, you know, 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?

1:16:38Well, you see, I would still say yes, even, yeah, even without extracting myself outside of the universe, there is still time is still passing, maybe it's still asymptotically sort of cooling down towards some sort of, you know, desert space, you know, and 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 don't, 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.

1:17:21It's almost back to Newton's absolute clock ticking by, although we now know 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. It started off from something else. Does 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?

1:17:53Yeah, 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 and making 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, maybe we would never be able to answer them. But I, you know, it's, they're too, that itch has to be scratched. And if the Greeks are scratching it, and we're still scratching it, what's wrong with that?

1:18:38Why should they be easy? Exactly. Yeah. How boring the world would be anyway, if we had all the answers, right? I'm glad to be very sure. 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. Clear it up and start again. It's in the process. And this is a process is not going to end anytime soon. So I hope not. Jim Akalili, thanks so much for being on the Mindscape podcast. My pleasure. It's been great fun. It's been great fun.