Making Sense with Sam Harris - #318 — Physics & Philosophy

Episode Date: May 1, 2023

Sam Harris speaks with Tim Maudlin about the foundations of physics and metaphysics. They talk about the nature of scientific reductionism, emergence, functionalism, the nature of time, presentism vs ...eternalism, causation, the nature of possibility, the laws of nature, David Lewis’s possible worlds, rival interpretations of quantum mechanics, free will, and other topics. If the Making Sense podcast logo in your player is BLACK, you can SUBSCRIBE to gain access to all full-length episodes at samharris.org/subscribe. Learning how to train your mind is the single greatest investment you can make in life. That’s why Sam Harris created the Waking Up app. From rational mindfulness practice to lessons on some of life’s most important topics, join Sam as he demystifies the practice of meditation and explores the theory behind it.

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Starting point is 00:00:00 Thank you. of the Making Sense podcast, you'll need to subscribe at samharris.org. There you'll find our private RSS feed to add to your favorite podcatcher, along with other subscriber-only content. We don't run ads on the podcast, and therefore it's made possible entirely through the support of our subscribers. So if you enjoy what we're doing here, please consider becoming one.
Starting point is 00:00:52 Well, the big story of this week was the firing of Tucker Carlson from Fox News. I normally wouldn't have much to say about this, but this has been such an enormous story, at least for those of us who follow media, and everyone has commented on it, it seems. But no one has made what I consider to be the most important point about all this. So I feel like I have something to add to this conversation, which is otherwise an extraordinarily boring one. I don't know Tucker. I believe we've met twice. I think he interviewed me twice. He was one of my first TV interviews. I don't know Tucker. I believe we've met twice. I think he interviewed me twice. He was one of my first TV interviews. I don't even know what show that was back in the day. I feel like it was a PBS show. Is that possible? So I think he's interviewed me twice, but not for a very long time. In any case, almost no one has done more to stoke the fires of Trumpism and populist outrage than Tucker Carlson in recent years.
Starting point is 00:01:49 He's done hour after hour of broadcasts on how the establishment is against you. They are against you. The you being the millions of people in Trump's base who have completely lost trust in institutions. He has been the journalistic foil to Trump's demagoguery for years. And for that reason alone, it should be obvious I would not be a fan of his. But as a result of the Dominion lawsuit against Fox, we now have several text messages that Carlson sent privately to his colleagues at Fox. These were entered into evidence for the upcoming trial, which was only prevented by Fox agreeing to pay three quarters of a billion dollars in settlement to Dominion for defamation. In any case,
Starting point is 00:02:40 we now have a window onto what Carlson actually felt and presumably feels about Donald Trump. In one text, he says, I hate him passionately. This was sent January 4th, just two days prior to the attack on the Capitol. He went on to say, we're all pretending we've got a lot to show for it because admitting what a disaster it's been is too tough to digest. But come on, there really isn't an upside to Trump. On the topic of Trump skipping Biden's inauguration, he texted, hard to believe, so destructive, it's disgusting, I'm trying to look away. Just before the Capitol riot, Carlson wrote, we are very, very close to being able to ignore Trump most nights. I truly
Starting point is 00:03:26 can't wait. And right after the Capitol was stormed, he texted, Trump has two weeks left. Once he's out, he becomes incalculably less powerful, even in the minds of his supporters. He's a demonic force, a destroyer, but he's not going to destroy us. I've been thinking about this every day for four years. Let me read that final line again. He's a demonic force, a destroyer. I've been thinking about this every day for four years. Okay, so here you have someone who has done hundreds of broadcasts supporting Trumpism, pandering to Trumpism, and distorting reality in all the ways you have to distort it to disregard the danger that Trump posed. And here we see that all the while, Carlson believed that Trump was a demonic force, a destroyer. Now, here's the only point I want to make. This should matter. It should be impossible
Starting point is 00:04:28 for Carlson to have an audience after it has been revealed that he's capable of this level of dishonesty. Think about it in every other context. Think about the pharmaceutical executive who knows that the drug he's marketing doesn't work or is dangerous, but in public touts it as both safe and effective. Revealing that about a pharmaceutical executive should be the end of that executive's career. It's the very essence of fraud. Now, I highly doubt that these texts were the reason why Carlson got fired from Fox. I guess that remains to be seen. But if I had to bet, I would bet that Carlson pays no price at all for his fraudulence. In fact, I expect him to build an enormous media business once he finds his feet. And that says
Starting point is 00:05:20 something quite scary and depressing about our culture, or at least a large part of our culture. But happily, this tawdry business has absolutely nothing to do with today's podcast. Today I'm speaking with Tim Maudlin. Tim is a professor of philosophy at NYU and the founder and director of the John Bell Institute for the Foundations of Physics. and the founder and director of the John Bell Institute for the Foundations of Physics. His interests primarily focus on the foundations of physics, as well as metaphysics and logic, and his books include Quantum Non-Locality and Relativity, Truth and Paradox, The Metaphysics Within Physics, and two volumes on the philosophy of physics. Tim has also been a Guggenheim Fellow, philosophy of physics. Tim has also been a Guggenheim fellow, and he's taught at Rutgers and Harvard, in addition to NYU. And I reached out to Tim almost as an act of continuing education
Starting point is 00:06:12 for myself in philosophy. His area of focus in the philosophy of physics and metaphysics has really not been my wheelhouse philosophically, and I had some questions I just wanted to put to him. We talk about the nature of scientific reductionism, emergence, the nature of time, causation, the nature of possibility, natural law, David Lewis's possible worlds, rival interpretations of quantum mechanics. We have a long wrestling match over the topic of free will, and touch a few other things here. Anyway, Tim performed a kind of philosophical therapy for me on a few points, and also I think we demonstrated that certain rival intuitions on the topic of free will can't quite be resolved through argument. I think I have come to that conclusion after this conversation. Perhaps
Starting point is 00:07:05 there's more to say on that topic, but it just seems to me that if you experience yourself in a certain way, certain points just can't land. Whereas if you have a different experience, moment to moment, certain points are not only obvious, you can't see how experience can be seen any other way. Anyway, you can make of our exchange what you will. It was a lot of fun. And now I bring you Tim Maudlin. I am here with Tim Maudlin.
Starting point is 00:07:40 Tim, thanks for joining me. Thanks for having me. So, thank you for doing this. I am very eager to talk to you about the interesting philosophical questions thrown up by our understanding of physics, but in particular, I have something that I'm curious about that I will drop on you at some point as we take the tour here, you being a philosopher who knows much more about the current implication of physics than I do. But before we jump in, how would you describe your intellectual background and the kinds of questions you focused on as a philosopher? Well, when I was an undergraduate, I kept bouncing around between different things,
Starting point is 00:08:22 and I ended up getting a degree that was a joint degree in philosophy and physics. And then my PhD was in history and philosophy of science. And in general, philosophy and physics tend to go together pretty naturally. Probably most philosophers of science who have expertise in a science have it in physics. And I think that's because the basic philosophical impulse is always to get to the bottom of things somehow. And there's a certain sense, it's not the only sense, but there's a certain sense in which physics lies at the bottom of the empirical sciences. I don't want to say that, sometimes physicists say that in a very denigrating way, I don't
Starting point is 00:09:00 want to do that at all. But there is a sense in which as you push down, you kind of push down from biology to chemistry to physics. So I think that basic search after foundations explains both of those interests. Maybe we can press into that question you just referenced, which is this kind of the concept of reductionism and the occasionally overweening claims that physicists are apt to make about how everything reduces to physics. And this connects to the concept of emergence, emergent phenomenon, emergent properties. The mind is generally thought of in science as an emergent phenomenon
Starting point is 00:09:49 born of information processing in biological brains such as our own as to whether or not that's going to happen in the computers we're building and their software remains to be seen. But certainly we know intelligence is an emergent phenomenon of information processing. I guess the jury's still out on consciousness and there being a qualitative character to mind. But how do you think about reductionism and emergence, in particular with respect to causal powers? For instance, if we say that something is a higher level phenomenon, an emergent phenomenon, if it has causal powers, so for instance,
Starting point is 00:10:35 we're using our minds, we're using language, we're perceiving the world at this moment, this is all considered to be emergent to super know, on the basis of, to supervene on the basis of, you know, neurophysiology and its micro events. But if it has causal powers, if, you know, my understanding of English grammar, say, or my intention to use a certain word in this sentence has causal powers, doesn't it only have causal powers at the level of its micro constituents, which is to say at the level, you know, at bottom, at the level of physics? Doesn't the reduction actually run through, even if we can't conceive of, much less explain, higher level phenomenon in terms of their micro-constituents, which is to say we're never going to actually be able to think about things like conversations or stock markets or
Starting point is 00:11:33 cocktail parties or anything else in terms of subatomic particles and fields of electromagnetism. But aren't the causal powers of those higher-level phenomenon nevertheless reducible to their micro-constituents? Okay, so there are a lot of words you use that are multiply ambiguous, and so it's very easy to get lost in this thicket. Among those are emergence, supervenience, explanation is going to be a big one here, and causation. And part of the problem is even in the philosophical literature and in the physical literature, people can mean literally diametrically opposed things by emergence.
Starting point is 00:12:19 So there was a time when some of the so-called British emergentists, the hallmark of emergence was a phenomenon that could not be explained on the basis of microphysics, couldn't be accounted for, and was fundamentally novel and only emerged at some time or in some systems or something like that. emerged at some time or in some systems or something like that. But my view is that the supervenience claim, as far as we know, is true for what we call the ontology. That is, there's a certain sense in which my computer, just to take the example I'm about to give you, my computer is nothing but a collection of atoms put together in a certain configuration. And everything it does, we think in principle,
Starting point is 00:13:10 could be accounted for by just studying how atoms interact and how electrons interact and then how this whole very complicated gadget is put together. But let me just give you an example I use a lot. So suppose I've got my computer, it's on the table, and there's a little display of spinning rainbow colors going on, coming off the screen, photons coming off the screen. And I call in a physicist, kind of a super physicist, and I say, can you make a prediction about this display, what's going to happen? And you imagine the physicist could kind of scan the thing all the way down to its microstructure and do some calculations
Starting point is 00:13:54 and say, well, that little spinny thing is going to go on for the next four years and five hours and 47 seconds, and then the screen is going to go blank. And I say, okay, thank you very much. And then I call in a computer scientist and I say, you know, what's the deal with the screen? And the computer scientist doesn't even look at the computer, looks at a bunch of papers that are sitting next to the computer that is the program, I've just programmed the machine, and says, look, you've got a loop here, right? Step 10 says go to step 12, and step 12 says go to step 10. That little thing's going to spin forever because you're in a computational loop. Now, in terms of the actual prediction,
Starting point is 00:14:39 I take it the physicist will be right because in 10 years and so on, the computer screen is just going to burn out. And that's not the business of the computer scientist to predict. I mean, the computer scientist is dealing with the system using a different set of analytical categories. But I would claim that the computer scientist has actually given me much better information or understanding than the physicist does, right? If the physicist has just ground out a very long calculation on the basis of its physical structure, it may give me good predictions, but it sort of gives me no real insight of the kind I wanted. So to that extent, these other categories that we use to understand the world, including
Starting point is 00:15:26 biological categories, computational categories, economic ones, as you mentioned, I mean, the basics of economics presumably would not change if you change fundamental physics, as long as there were people or creatures that wanted to exchange goods and that had more or less the same psychology that humans have, that they're greedy and they're trying to make money, then all sorts of economic explanations for why things happen would be unchanged by even radical changes of physics at the lower level. So the idea that all explanation or all scientific understanding reduces to physics, I think that's just plainly wrong. And in fact, disciplines other than physics are much broader because they would continue to have explanatory power,
Starting point is 00:16:19 even if the physics were quite different. But nonetheless, my computer really is nothing more than a bunch of atoms put together obeying the laws of physics, right? In terms of what it is made of or what it really is, that's what it is. And there's a sense in which the physical structure accounts for everything else that it does. I think what I hear you alluding to is what often goes by the name of functionalism in the philosophy of mind. And I guess we could take it more generally than that, which is, and another way to come at this is to distinguish the software and hardware layer of your computer or many other things like minds. And we could acknowledge that any physical instantiation of a certain function, let's say a mind or a stock market or anything else, that physical instantiation does, in fact, reduce to physics, but it has a logical structure that can be implemented in multiple instantiations,
Starting point is 00:17:26 even, as you say, in conditions where the laws of physics are different in important ways. And certainly, even within our world where the laws of physics are the same, we know we can implement, let's say, a calculator on highly non-analogous physical substrates. And we can do arithmetic with the wetware in our heads, and we can do arithmetic in silico on a computer. And the same logic can be implemented very differently. But in each instantiation, what happens next, differentiation what happens next and the causal properties of each sequence of events is a matter of what the physics is doing, but it can't be understood at that level. You can't look at a collection of atoms in a computer and a collection of atoms in our heads and extract the rules of arithmetic from those two different systems, even if each is implementing the rules of arithmetic. Does that get at what you're saying?
Starting point is 00:18:32 Yeah, something like that. Or again, to go back to your own example of the stock market, you've got a broker sitting there and he's either going to press the sell button or not. And again, theoretically, a complete physical specification of his brain should allow you to predict where his finger is going to go. But for all that, you might say, that gives me no insight of the kind I wanted, right? I wanted to know what motivated him, right? What was he thinking? What was he trying to achieve? Oh, he's greedy, right? He thought that the price was going to go down. He thought he should buy it now or he'll lose money. All of that can be perfectly true, right?
Starting point is 00:19:11 He can only do that because he has a brain and he can only, you know, he only has a brain. His brain is made of atoms and it has a physical structure. But there's just all sorts of different levels of conceptual structure that one can bring to a given situation. And those different levels provide different sorts of insight into what's going on. And in many cases, the physical level, even though it's not there, even though it's there, isn't the right one to give you the kind of understanding that you want to get. I mean, let's take another simple example, pianos. There are no microscopic pianos. There kind of can't be atomic level pianos because pianos are just complicated instruments that need lots of parts put together in certain ways. In that sense, pianos only, quote,
Starting point is 00:20:01 emerge at a higher level. But are they predictable? Well, yeah, in a sense. I mean, if you tell me how all the microstructure is put together, I can predict that when you hit the key, the hammer will hit the string and it'll vibrate. None of that is a mystery physically. And that's because nothing new has emerged really ontologically. I mean, there's a certain sense in which a piano is just a bunch of atoms that have been connected together in a very particular sort of way. So what would you put, what would you class as an emergent phenomenon that is perplexing and, you know, otherwise unforeseeable and not understandable at the level of its micro constituents. Yeah, I think the only example I know of, which is the hardest problem in the world,
Starting point is 00:20:50 is consciousness, right? Is subjective feelings pain, you know, to take an obvious example. There's nothing in physics, there's nothing in the conceptual repertoire of physics, which would allow you to predict not just from small to large, but no matter how big it is, that any physical behavior would have associated with it a feel or a subjective state. That's why it's come to be called the hard problem of consciousness. On the other hand, contrast that. You could predict all kinds of behavior. I mean, just as I can predict the behavior of my computer, we think if I knew enough about the brain, I might be able to predict the words that are going to come out of my mouth and your mouth and the vibrations of the air and so on. But any of that should be associated with a subjective feel.
Starting point is 00:21:42 That I think we have no grip on whatsoever. And it's not just that we don't have a grip. I don't even know what a grip on it would look like. Yeah. Well, you and I are in agreement there. And the hard problem of consciousness is something that's quite central to my interest, but I'm going to leave it to the side because I have so much else I want to talk to you about. But just to revisit this issue of emergence for a second. So come back to a property or a function like arithmetic, right? The fact that it's substrate independent, the fact that a certain concatenation of events can constitute arithmetic in our brains, but it can also do that in a computer made of atoms that don't at all resemble what's in our brains, but it can also do that in a computer made of atoms that don't at all resemble what's in our brains. And presumably, we could do this in all kinds of
Starting point is 00:22:34 systems that one currently wouldn't imagine could be a proper computer, could be made a proper computer in some sense, and implement arithmetic. So therefore, arithmetic itself can't really be reducible to any one of those things or any string of those things. Or is there something about that that I'm confusing ontologically? Okay, so now you've brought up, opened yet another independent can of worms, which is the status of mathematics, mathematical entities. So this is not like stock trading and pianos. We all agree that there can't be stock markets without some physics or pianos without some physics. They're fundamentally physical things in that sense. Although I guess I would hesitate with the stock market in that if stock markets are also substrate independent
Starting point is 00:23:26 and open to a functionalist definition, then doesn't that play the same kind of havoc with reduction? No, not really, because if you give a functionalist definition of the sort you're thinking of that's in a way substrate independent. I mean, take the definition of a Turing machine. It's given a kind of very abstract. It's got a certain number of internal states and their inputs and their memories and then their rules for how things evolve. Nonetheless, in order to have such a thing, you need something physical. You need something. It may be
Starting point is 00:24:05 that many different substrates can realize it, but you need a physical substrate. The question of the relation of mathematics or arithmetic to physics seems to be quite different. What the normal thought is that arithmetic is just completely independent of any physics, that even if there were nothing physical, it would still be the case that 1 plus 1 equals 2. It would still be the case that there are an infinite number of integers. Even if the physical world is finite and there aren't an infinite number of anything physical, still there are an infinite number of integers. Why? Because, well, you can't stop, right? Every time you get to an integer, there's a different
Starting point is 00:24:45 one that's one bigger. So, I mean, my view about that is what's called Platonism. That is that the mathematical realm is independent of the physical realm entirely in a way that stock markets aren't. Well, perhaps we'll touch on that again because central to my concern today is to talk about the existence of things that don't exist concretely. And obviously, mathematical objects like numbers are part of that picture, although different from what I want to focus on. But before we get there, let's talk about time and why that is such a difficult notion scientifically. We have this common sense experience of time, which includes things like duration and change and sequence. It's bound up with our capacity to remember what's happening.
Starting point is 00:25:44 capacity to remember what's happening. And it's also bound up with our sense of, that we understand something about causation, because causes precede their effects. If my thumb hurts now, it's because I hit it with a hammer yesterday. It's not because I'm going to hit it with a hammer tomorrow. And so that implies a certain structure, which we take into account in virtually in every moment of our living, how has physics put pressure on our common sense notion of time? All right. So now, again, I should just warn you that what I'm going to say, you'll hear a lot of people object to, but nonetheless, I'm going to say it because I think it's obviously true. I don't think physics has put any pressure on the idea that time is fundamentally directed, that some things come before other things, that causes come before their effects.
Starting point is 00:26:33 There's a very specific account of the structure of time, or we might call the temporal structure of the world, that was given by Newton, that's kind of a very commonsensical one, which involves the notion of simultaneity, of thinking that if I snap my fingers here, okay, at that very moment that's marked by that finger snap, that moment, as Newton says, exists throughout the heavens, right? The very same moment exists in London and on the moon and at the farthest stars. Newton said something like that. And then you can think of time as the succession of these global instants, which is going forward,
Starting point is 00:27:18 right? It has a direction in a way that space doesn't have a direction, and there's duration. You can measure. There's a fact about how much time has passed, and there's certainly a fact about what happens before what. When we get to the theory of relativity, the special and general theories of relativity, they deny that there's this global simultaneity. They deny that if I snap my fingers here, there's any fact at all about exactly what was going on on Alpha Centauri at that moment, because there's nothing that counts as being at that very same moment on Alpha Centauri. So it's a shock in a way to the everyday conception. On the other hand, the everyday conception not only believes that there's this kind of global instant, but that we're immediately aware of it.
Starting point is 00:28:05 I mean, all of us are shocked the first time we're told when you look up at the sky, if you were to see a supernova, your normal thought is, gosh, that star just exploded. And then someone says, no, no, no, no, no. It exploded millions and millions of years ago. And the light has been traveling to us ever since, what you're seeing isn't what's going on right now. And that's true even for Newton, right? For anybody. So you have this tendency to very naively think that you're being presented right now with the world around you as it is right now. But any kind of just a little bit of thought about how the information got to you and you realize, no, there must have been a time delay. It took
Starting point is 00:28:52 some time, just as it would take time for a letter to get to you, right? When you read a letter, you don't think, gosh, this is going on right now. You think, this happened a few days ago, what's being reported. Yeah, I would just add that the same, you can say as much neurologically, what's happening when you touch something with the tip of your finger and you see your finger do that with your eye, the transit time through the visual system and through the sensory motor system is different and there's got to be some time of integration at the level of cortex that's creating this unity of effect or the so-called solving the binding problem. So the present moment is a confection somewhat born of working memory and some period
Starting point is 00:29:35 of integration that is not just truly punctate in the now consciousness. Absolutely. I mean, there's no question that time perception, again, the subjective feel of time is a very complicated neurological construct. And there could be people, you know, there are sort of temporal illusions you can make and trick people about events that are pretty close to each other in time and get them to think that the time order is different than it was. And we kind of understand how that works. That kind of complicated neural investigation is not where I spend my time. And I don't know, I know a bit about it, but not a lot. On the other hand, one does want to, you know, I think, say the perception of time is a bit
Starting point is 00:30:19 different thing than time itself. I mean, we all think that after the Big Bang, there was nobody around perceiving anything, but stuff happened and it happened in a certain order, and it took a certain amount of time for stars to form and for galaxies to form and so on. So time itself, physical time itself, is independent of our perception of it, and our perception may be very, very complicated in a way that time itself isn't. Okay, so I just want to revisit this claim that the notion of a present moment, the notion of now is specious at the widest scale, right? So to say that you snap your fingers now, that now doesn't hold for anything outside your reference frame. So when you're talking about
Starting point is 00:31:07 now in another galaxy, you really can't utter that sentence coherently, right? And I guess just to spell this out a little more, the reason why is because based on relativity, if you snap your fingers and then I snap my fingers a second later, you know, so your snap preceded mine by a second in our reference frame. Well, you can, based on relativity, you can imagine someone far enough away moving fast enough, say, in relation to us, where the sequence is truly reversed. It's perceived that I snapped before you snapped. where the sequence is truly reversed. It's perceived that I snapped before you snapped. Well, yeah, I mean, no, no. I mean, for you and me, let me try and I'll try and get people to fire up their imaginations a bit, which would help me try to explain this. Newton's picture, which is kind of the everyday picture, is again that time comes in these global instants. You can imagine a snapshot of the entire
Starting point is 00:32:07 universe now, another snapshot a second later, another snapshot a second later, and you sort of stack up all those snapshots the way you would frames on a film, and that gives you the entire history of the universe. And that idea, the technical name for it is that there's a foliation of space-time. So you imagine space-time as being four-dimensional, as having kind of three spatial dimensions and one time dimension. And then you imagine slicing it like a bologna into all of these layers that just one lies on top of the other, right? So that was Newton's picture.
Starting point is 00:32:42 Nothing to do with anybody's reference frame or anything. This is just objectively the structure of time. What happens when you go to relativity and you just have to keep stuff about reference frames out of it. It has nothing to do with reference frames or anything like that. It just doesn't have that foliated structure. It has a very different one called a light cone structure. So for every event, there's a past and future light cone, and that's perfectly objective. That's just as objective as anything Newton had. It's just not a slicing. And I'm sure people interested in this have at least seen pictures of light cones somewhere. But you kind of imagine a double cone with the snapping of your fingers right at the apex with a cone
Starting point is 00:33:23 going downward and a cone going upward that are called the past and future light cones. Now those, according to relativity, are as objective as anything. They have nothing to do with anybody's reference frame or anything. And all of the things in my future light cone are objectively later than that finger snap. Everything in its past light cone is objectively earlier than it. And everything outside of those two, the whole region that's outside the cone, these are events that are called space-like separation. Those have no definite temporal order with respect to the finger snap. Now, if you and I tried to snap our fingers at space-like separation, we couldn't do
Starting point is 00:34:05 it because we're too close and we would have to snap with such precision that we could never, ever do it. So if you kind of imagine, and again, I'm sorry to have people do this in their heads, but if you have this picture of this double cone and then you keep making the cone flatter and flatter, kind of flatten it out, you'll see that it more and more carefully approximates a kind of plane. And those thin regions outside the cone, those at space-like separation, you sort of never run across them in everyday life. But the further away you get, the bigger that region gets. And so if you're light years away, then that region can get quite large. Okay, so there's this, I mean, you seem to be endorsing more of a common sense notion
Starting point is 00:34:53 of time than certain physicists might. You alluded to that in offering a footnote before you began. I'm offering a footnote before you began. I guess the two views here can be loosely described as presentism versus eternalism in some sense, because the eternalism piece I've often thought of by reference to the phrase, a block universe, which I don't know the... Do you know the origin of that phrase? I don't know who first started using it. I do know that that is, again, a phrase that objectively does us a disservice. And I'll just say a word that I can say with certainty about it, which is that Hugh Price, who wrote a book trying to argue against a fundamental direction of time, and this is something I believe, that time has a direction.
Starting point is 00:35:46 Time goes forward, we're all getting older, right? I mean, physics didn't tell us that isn't true. You know, it would be a really amazing discovery for physics to say we're not actually getting older, right? I'm still waiting for the discovery that tells us that isn't true. Right. So I think there's nothing to that. Now what Hugh does in his book is he gives us
Starting point is 00:36:05 explicitly, there's a paragraph where he defines what he means by a block universe. And the problem is it has two pieces to it. One piece is to say that the past, present, and future are all equally real. And I believe that. I think they're just facts about what happened in the past, facts about what's going on now, facts about what are going to happen in the future. I think the past people are just as real as past pains and sufferings were just as real as the ones we endure, and the ones in the future will be just as real. Were just as real or are just as real? Because are just as real gives us a block. They will be just in the sense that they're to our future, right?
Starting point is 00:36:40 I mean, they haven't happened yet, but they will happen in some case or a sera. Things will happen in some very particular way. And then he adds a second clause, which is that, and furthermore, there's no fundamental direction of time. And I kind of endorse the first one and completely reject the second one. So then you say, do I believe in a block universe? Well, I'm not a presentist. I mean, some presentists hold, to me, the very peculiar view
Starting point is 00:37:05 that all of reality is confined to what presently exists. And then if you say the sort of natural thing to say, which is that, well, presently there are no living dinosaurs, you say, yeah, but still, dinosaurs are not fictional, right? They're not fictional in the way that Sherlock Holmes is fictional. Dinosaurs are real in a certain sense of real. Of course, they existed earlier than we do. They're in our past light cone. But they're not actual. This actually brings me directly to the topic I do want to raise with you. So maybe I'll just start the slide into that. But let me just prop up the two views we have begun to talk about here, this presentism versus eternalism. I mean, I think that presentism does, to some
Starting point is 00:37:54 degree, I don't know all of its implications in science at the moment, but my understanding of it does capture what I consider a common sense notion of time, which is that the past no longer exists. You know, whatever happened, happened. And its effects may be evident in the present. You know, so we can see the ruins of the Colosseum in Rome, or you can see the dirty dishes you left from lunch. But eternalism suggests, and that's what's also going by the name of the block universe, suggests that in some very real sense, the past time in which the Colosseum was full of living Romans who were shrieking for the blood of gladiators is still real, right? And as is your past self still devouring lunch, right?
Starting point is 00:38:42 Like it's not, those moments have been experientially left behind by you in some sense. I mean, you never were there in ancient Rome and you are no longer having lunch, but, or the you with which you're currently identified as this sort of keyhole view of the cosmos through your conscious mind in this moment. But on this view of a block universe where you've fully spatialized time and given it no real preferential direction, the past is still, in some sense, actual, even though you can't actualize it. And worse still, for common sense, the future is also out there. And, I mean, although there is a version of the block universe, I think, that's called the growing block universe, where the future isn't yet real.
Starting point is 00:39:33 But let's leave that aside for a second. I mean, it's almost like, you know, reality is a novel, and you're on page 63 now, and yet page 1 and page 180 exist just as much as the page you're on. And that's the intuition confounding sense in which time gets fully spatialized in a block. And so it sounds like you're not signing up for that picture. Well, no. And again, I mean, I just have to kind of signpost some words you used. You used the word still, and still was doing a lot of work there. Is the gladiatorial battle, battles in the Roman Colosseum? I mean, you imagine a kid going to a museum and they see a picture of these gladiators and they say, is that real? And there's obviously a sense in which you would correctly, if you've
Starting point is 00:40:25 just been seeing pictures of unicorns and the Loch Ness Monster, you say, oh no, that's real. It really happened. Now, of course it happened in the past. If he says, is it still real? Then you might say, oh, by still you mean, is it going on right now? No, no, no, it's not going on right now. It went on in the past, really did go on in the past. And so if you have this picture with these, you know, if you can have this picture of this four-dimensional structure with these light cones kind of in your mind, and you say, right now, I'm at the cone point of one of these cones, all of that is real. The whole thing is real. The stuff in my past light cone, I correctly say, happened a while ago and isn't going on real. The whole thing is real. The stuff in my past light cone, I correctly say, happened a while ago and isn't going on now. The stuff in the future will happen
Starting point is 00:41:09 and isn't going on now. The idea of what's going on now gets kind of a bit messed up in relativity because unlike there being just a single thing, you have this whole outside region that's actually quite large and doesn't correspond to your naive sense of the present. What really gets lost is the naive sense of the present, quite honestly, as stretching out. But I think the other thing you said was, well, if I do all this and I completely spatialize time and get rid of a direction, but that's what I don't want to do. I don't think time is... That's what many people believe happens when you, quote, spatialize time. You get rid of a directionality to it.
Starting point is 00:41:52 And I think there's nothing in physics and never has been anything in physics that suggests that time doesn't have a direction. And certainly physicists always treat it as having a direction, always. Often it's so obvious because we know the way time normally goes. When I put in a time coordinate, the direction toward the future is supposed to be where the numbers get bigger, except when I'm sending off rockets. Then I count down. Then in the direction toward the future, I go 10, 9, 8. But at all other times, if you just give me a time coordinate and don't tell me anything else, the convention is that as the time coordinate gets larger, that's the forward direction of time. So it's so obvious and so easy and there's so little to debate about it that you can kind of fly under the radar, but it's there. If someone tells me there's no direction of time, I literally have no idea how to understand the world I'm living in. But what about all the talk in physics around the math actually having no implication of directionality, that the equations are reversible, and therefore entropy sort of comes to the rescue of intuition here. Again, two things just happen. The first thing is people say, look,
Starting point is 00:43:07 there's no directionality in equations. Then you say, well, actually, it turns out there is because the CPT theorem and C and P are violated. There's a technical sense in which in quantum field theory, which is the best theory we have, there is a directionality of time. Nobody disputes that Nobel Prizes were given for the discovery of parity violation. And so there's no physical dispute that there's a symmetry that's called CPT, where the T is time symmetry. And there's a general argument that any good theory should respect that symmetry, but the CP part violates it. And so the only way to get the whole thing to work is to have TB violated too. There can't be a time symmetry. So they say,
Starting point is 00:43:50 look, in the equations of physics, you don't see this. And you say, well, actually in the equations of physics as we have it, you do see it. And then they say, oh, well, let's forget about that. I mean, it's a very strange situation. And then they bring in stuff about entropy. Now, the thing about entropy is in everyday life, of course, there are many, many time asymmetries. Typically, although not always, if I show you two photographs taken a few years apart of somebody, you can put them in time order and figure which is a picture of them younger and which is a picture of them older.
Starting point is 00:44:21 You might get it wrong. If they had a lot of cosmetic surgery, you might get it wrong. If they had a lot of cosmetic surgery, you could mess that up. But there are all kinds of pretty reliable temporal regularities, and they demand an explanation. And the explanation for them often goes through entropy. That's true. But what are you trying to explain? You're trying to explain why typically this happens before that. And so you're already assuming a time order and even stating what it is you're trying to explain. You're trying to explain why things typically happen in a certain time order and not in the reverse order. And entropy considerations are often important for understanding that. They do help comprehend that.
Starting point is 00:45:06 But that doesn't at all suggest that time doesn't exist or time order doesn't exist. You assume it exists just to state the problem. Yeah, well, I will be the first to admit that they should hand a Nobel Prize out to whoever can explain what's happening to my face in the mirror, because that shrieks for explanation. But you alluded to the fact that many physicists or certain physicists wouldn't agree with you here. I'm thinking of, though I'm not super familiar with their work, I'm thinking of people like Julian Barbour or Carlo Rovelli. I mean, who are you thinking of when you're imagining having to debate someone on this topic? Well, the people you just... I mean, Julian has an extremely idiosyncratic view.
Starting point is 00:45:52 I don't think... He got interested in trying to get rid of space and time, spatio-temporal structure at a fundamental level altogether in favor of something called relationalism or relationism. And he pushed that program as hard as anybody has pushed it, but that's not mainstream physics. Carlo's views are a little bit hard for me to understand, but the idea that there's a deep problem that connects entropy to time itself as if, I mean, one might put it this way. Some people seem to think that if entropy isn't going up or down, then the direction of time will have disappeared, that you couldn't say that anything happened before or after anything else. That's a pretty widespread view,
Starting point is 00:46:39 and one I think that just doesn't, I don't think there's any reason to believe that. think that just doesn't, I don't think there's any reason to believe that. I don't think that there's a problem there. There is a problem about explaining the manifest time asymmetries we see, and that's a good problem. A lot of this has to do with what gets defined in terms of what, and it's a very delicate situation to decide what you think should be the defined object and what should be the defining object. So I personally think, for example, to give the example I think you would agree, if we're worried about causation, and causation can be a very puzzling subject, I think it's part of the definition of a cause is that when you have a cause and effect pair, the cause precedes the effect,
Starting point is 00:47:29 right? So I'm going to assume I have a good notion of time precedence, of time order, of earlier and later, and use that in defining causes. There are people who want to flip that around and say, no, no, no, no, I don't understand what before and after mean, but I have some independent grip of causation, and I'm going to somehow wheel in causation to define time order. And it seems to me this is just putting the cart before the horse. I mean, this is putting the thing to be defined in the wrong spot, trying to define the later thing in terms of the earlier thing in terms of the later thing. It just doesn't make any sense to me. Well, I think we do have at least, we think we have an independent grasp of the concept of causation because we can talk about the possibility and, in general, the non- them as opposed to pushing from behind. So the fact that we can have a conversation about that suggests that causation is separable from the temporal order you just sketched. Right. But I guess my feeling is that part of the great triumph
Starting point is 00:48:37 of the scientific revolution was to eliminate that kind of teleology. That, oh, I understand why things are doing what they're doing now in terms of them being pulled by something in the future. Now, of course, often you understand why things are going on the way they are now in the sense that someone is aiming at something in the future, right? I mean, you look at the builder building the house and you understand what he's doing in terms of having plans in his head and wanting to accomplish something and taking steps to accomplish it. That's a kind of teleology and teleological explanation. But the theory of evolution successfully eliminated the kind of teleology you're mentioning from biology, and I think did a good job of it and said, you know, evolution and evolutionary
Starting point is 00:49:26 pressures and selection pressures all explain why there's this appearance of design in nature, even though there isn't a designer, even though it's not aiming at anything. And I take that to be a great triumph of science. If someone says, gosh, the reason that such and such is going on today is that something that's going to happen in 100 years is pulling it forward, I think that's contrary to physics, it's contrary to biology, it's contrary to chemistry, it's kind of contrary to everything. So I think we've gotten rid of that. I hope we have. Okay, so let's land on my topic of, you know, where I'm genuinely uncertain, which really is the genesis of my interest in this conversation,
Starting point is 00:50:11 and it relates to the concept of possibility as it exists in physics, but also as it exists in, I guess, metaphysics and in philosophy. And I guess my question is, what if there is only the actual? Is there some scientific reason or logical reason to rule out the possibility, I realize that's circular, that possibility itself is just an illusion, right? And that, because, so the current sense of possibility, I think we all have is that it itself is kind of mysterious because in some sense it is the assertion that reality includes things that don't exist. You know, that there's more than the actual, right? There's the actual, there are the things that actually happen. But then there are the things that haven't happened yet but might happen.
Starting point is 00:51:04 They're the things that haven't happened yet but might happen. They're the things that could have happened had we done something differently, but they didn't happen because we didn't do something differently. And all of that space seems to exert an influence on what is actual in a way that is kind of inscrutable. is kind of inscrutable. So I guess the, I mean, because so it seems that if something comes into being at time T1, say, right, and becomes actual at T1, it does seem somehow necessary to say that its possibility was real at time T0. And so the question is, in what does that possibility consist? And perhaps now I'm realizing that we could start talking about David Lewis's modal realism here, which it might be worth addressing, however briefly. identical sets and that anything that is possible really is in fact actual. And all we're adding to this picture is an idea. We live with this persistent idea that other things might have happened or might yet happen. You could have married a different person, you could have worn a different outfit, but in reality, there is always only the person you married and the outfit you wore, and the
Starting point is 00:52:26 rest is something you're thinking. Yeah, I understand what you're saying. Let me go back. There's a kind of wonderful discussion of these basic questions by Nelson Goodman in his book, in his set of lectures, Fact, Fiction, and Forecast. And he talks about everyone has a philosophical conscience, and that conscience is his set of lectures, Fact, Fiction, and Forecast. He talks about everyone has a philosophical conscience. That conscience is a set of things you think are pretty much okay to believe in. Then there are things that are not obviously okay to believe in. It doesn't mean you
Starting point is 00:52:57 immediately rule them out, but you would require some work to explain them, right? And he says people of different consciences, for him, among the things that he can't accept without further explanation are unrealized possibles, which is exactly the thing you've been talking about. Angels, he says. Neutrinos, he says. It's not that he won't accept neutrinos, but he needs some explanation. He doesn't quite understand what they're supposed to be. Two out of three ain't bad. You know, he has a whole list. And he just says, look, this is my conscience. If you have a different conscience, you're going to think, you know, you might think I'm allowing too much, you might think I'm allowing too little. And part of what you were saying was, look,
Starting point is 00:53:38 what about unactualized possibles, right? We all agree that everything actually is possible. If you'd like to continue listening to this conversation, you'll need to subscribe at SamHarris.org. Once you do, you'll get access to all full-length episodes
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