Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 244 | Katie Elliott on Metaphysics, Chance, and Explanation

Episode Date: July 24, 2023

Is metaphysics like physics, but cooler? Or is it a relic of an outdated, pre-empirical way of thinking about the world? Closer to the former than the latter. Rather than building specific quantitative theories about the world, metaphysics aims to get a handle on the basic logical structures that help us think about it. I talk with philosopher Katie Elliott on how metaphysics helps us think about questions like counterfactuals, possible worlds, time travel, mathematical equivalence, and whether everything happens for a reason. Blog post with transcript: https://www.preposterousuniverse.com/podcast/2023/07/24/244-katie-elliott-on-metaphysics-chance-and-time/ Support Mindscape on Patreon. Katrina (Katie) Elliott received her Ph.D. in philosophy from the University of North Carolina, Chapel Hill. After being an assistant professor of philosophy at UCLA, she is now on the faculty at Brandeis. Her research covers topics in metaphysics and the philosophy of science, including explanation, chances, and the logic of time travel. Web page Brandeis web page PhilPeople profile

Hey, everyone, it's Cal Penn. I'm inviting you to join the best-sounding book club you've ever heard with my podcast, Earsay, the Audible and I-Heart Audio Book Club. Every episode, I nerd out with amazing guests and dive into the best new audiobooks available on Audible. It's the book club for your ears. Listen to Earsay, the Audible and I-Heart Audio Book Club. On the I-Heart Radio app or wherever you get your podcasts. Exema's Unrelenting, Itch and Rash.

If you know the feeling, you should know the facts. The eczema medication you're taking may not be right for you. Visit MyRawtruth.com and talk to your dermatologist about your symptoms and treatment options. Hello, everyone. Welcome to the Mindscape podcast. I'm your host, Sean Carroll. You might know if you follow the physics news that Jim Hartle passed away recently. Jim was a wonderful theoretical physicist, a founder of quantum cosmology, frequent collaborator with Stephen Hawking, Murray Gilman, people like that.

He was also one of the collaborators with Thomas Hurtog, our recent Minescape guest on the wave function of the universe, again, with Stephen Hawking, what you could predict, how things came out and so forth. And he passed away recently. It was very sad. Jim had an important role in my life. He hired me for my second postdoc and always struck me as someone who was a very deep thinker, very careful, but with a puckish sense of humor that made him very fun to be around. So I was being interviewed by a reporter from physics today for the write-up they were going to do, the obituary, if you want to call it that, on Jim's passing. And he mentioned that he was talking to Thomas Hurtog before. And we were talking about the relationship, the reporter and I were talking about the relationship of physics and philosophy.

Jim was sort of pro-philosophy, but he wasn't into it, right? He thought it was a good thing, but he wasn't himself reading a lot of philosophers or anything like that. So apparently the reporter had also asked Tomas about it. And Tomas had related the story that he and Stephen and Jim had written a paper, which I think was called Eternal Inflation without metaphysics. Metaphysics, you know, word borrowed from philosophy. And Tomas explained to the reporter that the editor of the journal made them remove the word metaphysics from the title because he didn't think it was appropriate.

So this was my opportunity to reveal a little secret here. it was not the editor of the journal who objected to that use of the word. It was the referee, and the referee was me. I was refereeing their paper, and I thought they misused the word metaphysics. They had defined it in the paper as parts of the theory that are not observable, that make no difference to the observable predictions. I get why they would say that, but there's more to metaphysics than that. I think that people in different academic disciplines should play nicely with each other and respect each other's terminology. But I get it. I get why people have this misapprehension about what metaphysics is. If you go to a bookstore and go to

the metaphysics section, good luck to you. There's a whole bunch of things about crystals and oras and new agey stuff and things like that. I think that people out there don't really know what metaphysics is. You've come to the right place if this is, that description includes you. Katie Elliott is a philosopher, metaphysician. They call them metaphysicians, not metaphysicists. So we're going to learn. Katie was nice enough to agree to, rather than focus in on one of her particular research problems, which would have been very interesting, we basically are trying to give an overview here. We're going to work up to some questions that she does research on about time travel, about possible worlds, about what a cause is, what an explanation is, things like that.

That's what Katie does for a living. But we're going to build up there gradually by giving an overview of what metaphysics is, why the idea of the idea of, metaphysics might be useful? Is it just replaced by physics? No, it's talking about things that are supposedly even more fundamental than physics, right? The logical structure of possible physical realities in addition to our actual physical reality. And I hope that you come away with the impression that metaphysics is actually useful, that metaphysics plays a role, and it's not just talk about unobservable things that have no consequences. So let's go. Katie Elliott, welcome to the Mindscape podcast.

Thank you so much. It is really exciting slash terrifying to be here. The terrifying, we're going to have to work on that. I want to terrify more of my guests. I think that too many of them are complacent, so I'm glad you're starting terrified. Yeah, when you, at the beginning, we were chatting and you were like, you're really dumb and this is going to expose this to the world. I thought that part was. I got to do more of that, right.

There's more of that, yeah. You know, I just recently started for our Patreon listeners. I started doing like a little couple minute video afterward, just saying, hey, you know, that was fun. Here's what I learned, whatever. But I got to start spreading the rumor that what I'm really saying is, geez, what an idiot. Exactly. Here's where I roast. Just for Patreon supporters, yeah.

Anyway, so let's start, let's warm up with something easy. What is metaphysics? What is that? That's not easy. great question. I feel like that's the kind of question where you could ask a bunch of different philosophers and get a lot of different answers,

but the sort of like stock things that people will say is that metaphysics is something like the study of what there is or a study of what there is. I suppose there are many different studies of what there is, but metaphysics is one of the studies of what there is. Or maybe metaphysics is also interested in relationships of fundamentally

in a kind of proprietary sense. of fundamentality. So that's very big picture. Then you might think, well, look, you know, science is the study of what there is. And that's true. So maybe metaphysics is something like the unrestricted study of what there is, or really trying to get the full story about the whole kitten caboodle and not just pockets of it. So maybe the more specific version of the question is,

how do you conceive of the relationship between metaphysics and physics? My understanding is that the name metaphysics got stuck just because it's the book Aristotle wrote after he wrote the book, the physics. That's my understanding too. I mean, so I have how I like to think of the relationship between science, physics, and the kind of inquiry that I do. I think that, again, different philosophers will give you different stories about, like, what the relationship is.

but for me, I think of myself as a metaphysician because ultimately the kinds of questions I'm interested in are about what kinds of things exist and what they're like. But the methodology that I'm committed to is that sort of the ideas that the main way we're going to figure out interesting stuff about what the world is like is by studying the success of scientific inquiry or maybe the success of a particular instance of scientific inquiry,

say the history of physics or something. So we're going to look at this discipline, both its content, what it says the world is like, but also what it does and how it works. And that's going to tell us a lot about what the world we live in is like. And one way of seeing that is that if you take for granted that science is successful, then you might ask yourself, like, well, what are the preconditions for the success of science? What does our world have to be like in order for this kind of intellectual discipline to be as successful as it's been? And some of us, though not all of us, but some of us think the world would have to be quite particular in various ways. It would have to be law governed. There would have to be things like causes.

Maybe there would have to be things like chances. So there would have to be these certain metaphysical ingredients in the world in order for science to proceed as it does at the rate of success that it does. And so science, the success of science is going to tell us something about these metaphysical policies. Okay, so that's a little bit different than I would have guessed. I mean, trying to, of course, we can just disparage metaphysics or any other field if we want to, but I figured that maybe a friendly physics versus metaphysics distinction would be that metaphysics thinks about sort of the logically necessary aspects of how the world is and physics thinks about the more contingent aspects, like these are the actual laws versus the idea

of laws? Yeah, totally. So metaphysics is an enormously broad project, and the kinds of questions that I'm interested in might best be like subtitled metaphysics of science or something. But it is true that the sort of main methodological tools we have as metaphysicians is just what happens and then like thinking about it hard. And the thinking about it hard stuff is presumably invokes, all kinds of logical principles, all kinds of reasoning principles, maybe some stronger claims about what we get a priori know to be true about the world just by thinking about it hard. But, I mean, to be clear, there are lots of metaphysicians that are, just as you say, interested in non-contingent things. So maybe they're interested in the nature of numbers or doing metaphysics of logic or trying to understand the relationship between a table and its micro-constituent parts. I mean, you name it.

We can, what's God like? What's truth like? Yeah. We can go. Lots of questions. I'm glad we're going to answer them in the remaining, you know, 50s three minutes. We're going to start with what's God like and work up to. What are numbers?

Let's begin. And maybe again, just for the audience that is not tuned into this, spending their spare time, reading metaphysics books. How do you contrast that with similar sounding words like ontology and epistemology? Yeah, great. I think of ontology. as a thing metaphysicians are interested in. So I guess I think one, you know, ontology is sort of like the collection of things

that you believe in, the stuff you believe in. So if you're an atheist, God is not in your ontology. If you're a theist, God is in your ontology, you're a deist or something. So it's like the big bucket of stuff you believe in. And then one metaphysical project is to try to give, you know, the ontology of existence. maybe the fundamental ontology of existence.

So what, at the most fundamental level, are the things that there are, that are real? And we get very spicy about that. It's not like our dragons real or something. You know, it's like our extended symbols real. You know, it's these sort of abstract ideas. So does the world come with this kind of stuff? And then epistemology is something like

the study of how we come to know about the world. and yeah, to get it means something like theory of knowledge, but just very broadly, it's questions about how we know stuff, what we know, how we know it, how we should reason about the evidence we have. I would like you to tell me whether extended simples are real. I don't know. First tell me what an extended simple is. What for a Shiba Kleinschman at USC? You should have her on the podcast. She'll talk to you about extended simple. How about what an extended simple is supposed to be? I like so I like just that throwing out the drawing out the drawing. jargon there because it gives us a little glimpse into the way you're actually thinking about it, not when you're just dumbing it down for us.

Yeah, fair enough. So a symbol is an object that has no parts. And an extended object is just an object that's extended in space time. And so the question is, could there be something partless that's extended in space time? I think that's the question anyway. The answer is I don't know. But surely that kind of sounds like a physics. question, doesn't it? Or is the metaphysics coming in when we're deciding, you know, not just

the instrumental things that physicists like to talk about, you know, invoking things to make predictions, but the harder questions of which parts of these are real and actual? I mean, this is kind of interesting. Maybe you don't think of things in this way, but how does, tell me if this resonates with you. So, like, certainly not every metaphysician would think this, but I think a relatively common thought is something like, look, we could ask questions just about what are coherent pictures of what the world is like. What are, you know, science doesn't sort of start from an infinite set of options. Whether we start from a highly constrained conceptual framework about general, we have general background assumptions about what the world is like and what kinds of things we should even be looking for or could coherently look for. and the

businesses is going to start their project from enormous amount of background assumptions, quite substantive background assumptions, about what kinds of things they could even really be looking for. There's a lot of options that just sort of aren't on the table. And maybe the metaphysician is trying to think, okay, for real,

in the biggest sense possible, what are the options on the table? So, like, what kinds of objects even coherently make sense? what kinds of things could you even try to build, try to use in an ontology of a theory of what the world is like. So like, you know, our souls

on the table, that used to be a big question. And so the question about extended simples, I take it is not the question of like, are there any extended symbols, though that would be an interesting and important question. But just do these things make sense? And if they

make sense, how would they behave? And if we know how to think of them, could positing them do any work in some of these cases where we're trying to understand what's going on at the base level. So maybe the metaphysician is trying to pick out like conceptually coherent frameworks for some kind of scientific inquiry to even sort of take place in. How much do the best modern metaphysicians, it always makes me sad they're not called metaphysicists, but I've learned to make my piece with that. How much do they think about modern physics in terms of, of just the basics of quantum mechanics and relativity and so forth. Yeah, I think there's a huge amount of variation.

So I think the gambit runs with contemporary successful metaphisions all the way from like, not at all to like, oh, my work is highly constrained by the results. And I need to be on the cutting edge of advancements in, say, quantum mechanics to figure out like what the cutting edge story of what the world is like. So there's a huge range and the range isn't sort of random. It's, I take it, it's reflected in the kinds of questions that the particular metaphysician is interested in.

So some questions, it seems like no matter how the physics shakes out, we're going to have to figure out, I don't know, what numbers are like or what truth is. And then other questions, it seems like how the physics is going to shake out might make a big difference.

Like, is the world deterministic? Or what is space and things like that? Or what is space? Yeah, good. Good. So, yeah, let's get a little bit. Let's get a little bit more specific, because you did a great job of telling us the basic project, but there's all sorts of delicious specific questions that we'll never have time to get to all of them. But as I mentioned before we started, I was recently tricked into writing a short piece

about something called the Principle of Sufficient Reason, giving the physicist's view on this. I mean, I could have made it very short by saying most physicists have no idea what the principle of sufficient reason is, but I went a little bit further than that. So why don't you tell us what it is? Is this, and is it something that the modern metaphysician believes in, keeps in mind, thinks about? Great. So let me try to bluff my way through this part. Principle of sufficient reason. I don't know much about the history.

You might take it, it's something like this. Something like the thought that, look, you just sit back and like kind of think about how things work. And you think about them real hard. You think like, well, here's got to be the way things work. Everything that happens, there's got to be some story about why it happened. I'm not sure how to fill in this premise. I'm not sure how to tell you why you should think that for everything that happens, there's got to be some story about why things happen.

But we can think about that. But suppose I got you on board. with the thought that like look for everything that happens there's some reason why it happens maybe you come to that conclusion just by looking at the world around you and say well for many things there's a reason why it happens and I think that's the general way or maybe you've got some kind of religious background and principles that make you think this and then the thought is look for everything that happens there's not just sort of a reason why it happens but there's some reasons you give such that given those reasons the event that we were initially

trying to give a reason for had to occur. So for everything that happens, there's a certain sense of which it had to happen. There were some background reasons or background conditions that were sufficient for bringing about the thing that we began with. And I think this, I think historically the power of this principle has been as a kind of a priori principle that was supposed to sort of guide methodology. So, you know, well, when you're looking at the world and trying to organize it in a way that makes sense to you, one of the things you can have in your back pocket is that, well, whatever's happening, you're going to be able to find some other thing that was sufficient for it. And you could see how that would sort of guide your exploration of the world.

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I'm blowing, and everyone asks how. The best skincare is Farmhouse Fresh, and the award is you, your best you. Visit Farmhousefreshskincare.com and use code radio for a free starter routine with any purchase. And I think clearly Quantum Mechanics is going to mess with this a little bit, but even back in the classical world, in the Laplace's demon kind of world, the physicist would joke and say, yeah, there's a reason for every. namely the laws of physics and the initial conditions for the universe. Those are the reasons why everything happens.

But maybe that... That's a hilarious physics joke. That's the new... We amuse ourselves. Isn't that what is most important? But is that what one might have in mind? I mean, it's certainly not what we invoke in our everyday life when we say, oh, the reason why I did this is the laws of physics plus the initial conditions at the Big Bang.

Like, we try to be a little bit more local and macroscopic than we say, that. Yeah, I mean, so, I mean, maybe one of the things that's interesting about metaphysics as opposed to physics or something is that a lot of the problems or questions that we're working on, you can arrive at with a very thin understanding of what the actual details are. So if you had something like the principle of sufficient reason and you were a physicist, the real question you're going to be interested in is something like, well, what are the reasons that were sufficient to bring this thing about? And so the reason your joke is funny is because it's contentless. Like, yes, yes, yes, I know the initial conditions and the laws would ever bring things about,

but my question was more detailed than that. I wanted to know a more detailed story or maybe a more local story or something like that. But from the kind of philosophical standpoint, I really do think that just thinking about the initial conditions and the laws is enough to start generating some of the puzzles that animated people and thinking about the principle of sufficient reason. So for instance, you might be very worried about free will. You might think to yourself, oh my gosh, I just stole this candy bar. Everything happens for a reason. Let me now reason my way back to the initial conditions and the laws. Why did I steal this candy bar? Well, because the initial conditions were thus and so, and the laws were yay and blay.

And those things guaranteed. That was sufficient for me to steal this candy bar. And so why is everyone so mad at me? It wasn't my idea to set the initial conditions of the laws as they are. In what sense do I have, you know, freedom? And that little argument, I mean, I'm not saying that wasn't the most careful version of the problem of free will or something. But what's interesting about that little argument is it doesn't presuppose anything about the actual content of the laws or the content of the initial conditions, the mere fact that the world is somehow guaranteed to be such that everything that happens happens for,

reason generates this puzzle or this anxiety about free will. But I guess this is why it seems challenging to me to be a metaphysician because I don't think that there actually is the principle of fission reasons. I don't think that that's true. Yeah. But it's seductive, right? And, you know, it's seductive to say something like, well, without laws, things wouldn't make sense.

But, you know, what do we know, really? Like, how confident are we when we say things like that? How confident are we that when we're reasoning about things that are very different than our universe, that we can say things that are not overly tainted by our real world experience? Here's how I, like, when I'm trying to, like, sleep at night and tell myself that I'm doing a real thing. Here is the story that I, that I give myself. For any kind of inquiry, you have to start by taking some things for granted. And if you don't take some things for granted, you just can't get anything done. And for me, the kinds of projects that I'm into, like stuff about laws causes that kind of thing.

What you're meant to take for granted is the thought that, okay, there's this intellectual human enterprise that's been successful sort of cross historically. Let's call this thing scientific inquiry. And as the philosopher, let's try to step back and see if we can find commonalities between different episodes of successful science. And one thing that arguably, this is all debatable, of course, but one thing that arguably is a commonality between many different successful scientific theories is that they make a distinction between the claims in the theory that are meant to be true or maybe universally true and the claims that are meant to be laws. There's some kind of project that involves distinguishing some of these things, some of these true sentences as laws and some of these true sentences as merely true sentences. Same thing for causes and correlations. So across many different successful episodes of science, there's some pressure to make this distinction between mere correlations

and something above and beyond correlations, causes. Or for the stuff I'm particularly interested in, enormously common that episodes of scientific inquiry develop theories that have probabilistic content. But, you know, with the standard interpretation of quantum mechanics, we get this sense that not all probabilistic content is created equal. Some of it is really getting at something important about the world, where some of it is just a reflection of our ignorance.

So you start by sort of taking for granted that there's this successful enterprise. It's made these distinctions. And then the job of a philosopher isn't to say, oh, now I know for sure there are laws of nature. I have no idea if there are laws of nature. That sounds bananas. And if I had to bet, I would just bet, you know, whatever. I don't know, that we're a simulation or something.

I don't know what the world is really like. But the thought is, okay, well, this successful epistemic inquiry is making this distinction between these two kinds of things, laws and non-laws. Let me now go in and try to figure out what the purpose of that distinction is. And if I can say anything at all about what the world would have to be like to ground that distinction as being genuinely about the world. Like if we're saying some things are laws, what are we really saying about the world? And so to do that project, I don't need to have much confidence that I'm really getting on to what the world is really like or we as people are really getting on to what the world is like.

I'm making a bunch of conditional claims, all of which I might give up on immediately. So the first is that there's something that deserves the name scientific inquiry. The second is that it's been successful in these various ways. The third is that it makes this distinction. I'm making lots of assumptions. and then I'm just trying to figure out, okay, how could I build a theory of what reality is like on which it would make sense to distinguish between laws and non-laws

or on which it would make sense to distinguish between causes and non-causes and in which human beings could discover those things, and they would be important for inquiry. So it's something like that. And I think for that, I don't have to be very confident that I'm getting things right or something. It's like a just-so story or it's like a proof of concept or something. How could these ideas all fit together and make sense?

Well, you mentioned causes several times. I would like to get into what this means because I'm fascinated by this. I have an angle here. You can tell me whether I'm on any track that is right or wrong. Bertrand Russell famously said that once we understand physics, there's no more causes. Is that like a friend of yours? Yeah, he was a name dropping. Do you know Bertrand Russell?

That's amazing. Sir Bertrand, yes. The idea being. that once you have classical mechanics in hand, it's just a matter of patterns, right? It's just one thing after another. And in fact, as Laplace pointed out, you could run forward or backward equally well. So it's not that anything goes. There's still laws, but they're not written as a series of causes and then effects. And so my angle is that that's true at the level of fundamental physics, but then in the macroscopic world where we only have some probabilities

and things like that. We have an arrow of time and it becomes possible to talk about causes preceding effects and you have to dig into like alternative worlds, possible worlds and counterfactuals and things like that and that's fun and a good thing to do. That's it. That's my angle. I'm trying to actually do it, but I haven't done it yet. So tell us what the modern metaphysician thinks about these things. I think those are the two basic angles for the modern metaphysicians. So I mean, the way I would to introduce the topic is again to say something like look start with this very metaphysically innocent notion that there are just these patterns in which things happen we might call those correlations so there are relationships of sometimes constant

conjunction sometimes statistical correlation this thing happens and this other thing happens and there's this thought maybe it's not a thought that we get from physics so i take the i take the the moral that maybe we don't sort of get this thought until we go up more macroscopic or something. But there's this thought that not all of these correlations are created equal. And one question that I'm interested in is what it is that we're looking for when we look for something more than a correlation. Why, what in our goals of theorizing are pushing us to posit something over and above this correlation? But whatever the causal relations are, there's something over and above these correlation relations. When I see this thing over and above, does that suggest anything to you?

It's like a philosophy thing. I mean, I worry about it because it suggests spooky essences of some sort, which I'm against in principle. It definitely suggests something spooky. Yeah. So now the metaphysician starts to debate about like what that spooky thing is. And the thinnest sort of answer is that all that spooky thing is, is that, you know, you might have particular instances of like one-off correlations or small correlations. are small correlations, but the causes are like the big global correlations, the patterns that are that hold at a totally universal scale. So something like the thought that what the laws of

nature are are sort of the patterns that are held most globally in the entire picture, whatever the thing is. So that would be like a very, go ahead. Yeah, can I try to wrap my brain around this? I think this is an interesting distinction that I haven't quite heard before. So if I throw a baseball and it goes a certain number of feet. That's a little local microscopic event. But the cause, or at least run one aspect of the cause in this telling, is the fact that many, many baseballs get thrown and many other things get thrown and we abstract those into laws of physics and that's that global law that is the cause, not the specific me throwing. It's not the global law that's the cause, but what makes it the case that that particular event

was an instance of the causal relation, say, is that it's an instance of this big global pattern, say the classical laws or something. Okay. And does the notion of causes and effects involve counterfactuals necessarily? Like, I think that it does. So we were saying, we got into this by sort of saying, what are the contemporary options?

And contemporary option number one is to try to understand causation just in terms of those global patterns. So somehow go from claims about the global patterns to claims about this thing cause this thing, and the metaphosition is going to weave those all together to try to reduce the this thing cause this thing to this stuff about the global patterns. And nothing about counterfactuals. Now, the other sort of popular way to go, and I think it's fair to say, or at least it would have been definitely fair to say 15 years ago, like the way to go or the sort of most

currently popular way to go is to tell some kind of story that relates causes not to these big regularities, but to these claims about counterfactuals, these claims about what would have happened under various conditions. One

reason that you might want to pause before you move to team counterfactual is that one thing team regularity really has going for them is that the stuff they believe in is very normal. So they believe in like the distribution of events. Yeah.

And they believe in like patterns in the distribution of events. And that's not spooky. Right? That's like normal boring stuff. The real world. The actual world. Yeah. The actual world.

The kind of factual is it's less clear what's making them true. And it's less clear sort of what they're saying about the world because they don't, on the face of it, they don't say anything about what the world is like. They say things about what the world would be like if things were different. and both how we come to know those things and what about the world could make them true is much more fraught than the question how could we know the regularities

or what could make the regularities true? Very easy to say what would make them true harder, but still we could imagine saying something about how we know that they're true. But now that you've got these sort of weird claims about what the world would have been like and a very natural thought, At least I think it's a very natural thought, is that what you would have naively said is, oh, it's because, look, the reason why I know that had I not thrown the window, sorry, the window, had I not thrown the rock, the window wouldn't have broken, is really, I know that throwing rocks is a cause of windows breaking, and like normal atmospheric conditions aren't a cause of windows breaking.

So you might have put causes on the bottom of counterfactuals. You might have thought, oh, it's the causal facts in our world that make the counterfactuals. true and the picture that you were suggesting, which is a popular picture, is to try to reverse that to say no, there are some counterfactual facts that are grounding or making true the causal claims of the world. And so now you want to sort of know, well, what makes the counterfactuals true and what are they about? And now you're off, you're ready. So I think you've made a good first step, but I want to hear more about what's making your counterfactuals true and how you think we come to know them. Sure. But I am on team counterfactual. And the reason why is because I worry that team regularity will end up living

in the physicist's joke that the only cause for anything is the laws of physics and the initial conditions of the universe. Whereas I can counterfactually say if things had been different, if I hadn't thrown the rock, the window wouldn't have broken. And I know that people are really going to say, yeah, but what if someone else throws a rocks and break the window? Then the window would have broken anyway, even if you hadn't thrown your rock. And that's why it's hard. And I get that it's hard, full employment for metaphysicians. But I also very much get the worry that you're sort of peeking at that in order to think about counterfactuals, I have to go well beyond the actual world and to all these other

possible worlds. And how legit is that? I mean, so how legit is that? I mean, that's definitely thinking about that project is highly legit. and then thinking that there's going to be a successful answer to that question is certainly legit from many people's perspective. And then, you know, if I'm team regularity, I'm like, good luck, bro. Like, yeah, let me see you do that. It's my skepticism that that's ever going to be a successful project that makes me, you know, stay and toil away at team regularity.

So the question of sort of how to understand the philosophers have a term of art, modal, modal facts for facts about what could be true or what must be true or what would be true under various conditions. And it's a very hard question to see either how to reduce those claims about the modal facts to what actually happens. So go from what could happen to what actually happens or what would happen to what actually happens. Ground them all in the actual world. It seems very hard. Or posit something over and above or in a addition to the actual world that can serve as the grounders or truth makers of those things. So just, I mean, just famously, just to give you a taste of how this can go, there's a very

influential philosopher named David Lewis. David Lewis was a fan of using the kind of possible world talk that you were invoking a second ago to think about modality. Many people are fans of using the possible world talk to think about modality. But Lewis thought those possible worlds were actual concrete worlds so that when we were making a claim about what would happen under various conditions that claim was made true by by actual concrete worlds in which there were you know anything you can imagine were actual concrete worlds so that would be like a really metaphysically robust you'd believe in lots of things apart from the actual world to make those counterfactuals true so yeah tough tough question it seems a little team counterfactual is popular so

It does seem a little extravagant, but that's okay. Extravagance is something I've learned. There's other options. I don't want to suggest that that's the only option. My best skin ever at 45? Give me a theme song and a best skincare award because it feels like this. Right.

That's farmhouse fresh skin, all right? I'm blowing. And everyone asks how. The best skincare is farmhouse fresh. And the award is you. Your best you. Visit farmhousefresh skincare.com and use code radio for a free starter routine with any purchase. But so let me home in on, since I have you here, I'm going to take advantage of this,

let me home in on what I gather to be one of the issues, that Lewis would say something like, yeah, you know, something is a cause of something else if in another possible world, if A hadn't happened, then B would not have happened. But then he has to add, it's like the nearest possible world. We're going to change A, but we're not going to change anything else about the world. And then the big question there is, what is nearest supposed to mean? Like, I could imagine a possible world where I throw the rock at the window, and then just as the rock is going to hit the window, I violate the laws of physics,

so the rock just goes through the window. And that's a very close possible world, but I violated the laws of physics, so that seems like a really big difference. And so I guess how do you measure what's a big change in the world versus what's a small change seems to be a looming issue here? Yeah, so maybe one way to try to help to clarify what's going on here. So many people like this possible world talk as a way to make sense of what we mean or what the truth conditions are or what the semantics are of various counterfactual claims. So forget about our problem about causes. for just a second. Just think about ordinary counterfactuals. Consider the counterfactual.

If Katie were a kid in 2023, Katie would have TikTok. Is that counterfactual true or false? Well, there's a way of thinking about it that makes it seem true, and there's a way of thinking about it that makes it seem false. Way of thinking about it that makes it seem true, Katie would have TikTok is that like when I was a kid in the 80s, I was very influenced by trends that just wanted to fit in. And so if we sort of hold fixed that fact about me that Katie is somebody who when she was a kid was focused on trends, it seems like, well, if I were a kid now, I would still be interested in trends and like TikTok is the trend. On the other hand, another feature of me is that now at the age of 41 or whatever, I don't know anything about the technology the kids are using. If we hold fixed that fact, if we hold fix that fact about me,

Then we want to say, well, if Katie were a kid today, she wouldn't have TikTok because she, like, doesn't know anything. She's like a Luddite or whatever. She doesn't know anything about tech. So it's a general fact of counterfactuals that when we're evaluating them, we can make them seem true by fixing the background context in one way. Or we can make them seem false by fixing the background context in another way. And that closeness or that similarity relation is how a philosopher is how a philosopher is, thinking about what's going on in those different evaluations we want to give in the counterfactual. One context told you that the sort of relevant worlds to look at are worlds where Katie's a kid and she's into trends. Another context told you that the relevant worlds to look at were worlds where Katie's a

kid and she's like a Luddite. And so now when it comes to the question of like how to understand these counterfactuals that are grounding causation, there's a sort of question about like, okay, well, we need some similarity relation, just like we do with every counterfactual we're evaluating. But now it needs to be kind of like the real one or the physically important one. And trying to figure out what the sort of like physically important relation of closeness on possible worlds is something that like Lewis and other metaphysicians who are interested in kind of, some people are just using possible worlds as a model to make counterfactuals come out, right? And some people are using possible worlds to tell them about what the nature of reality is like.

And if you're doing it for that second project, you better have something to say about what the proprietary closeness relationship is. I feel like this wasn't a successful speech. Anyway, the closeness thing is a problem. And Lewis famously said, as you noticed, that the sort of closest worlds that are the, going to need to get your counterfactuals to operate in the right way are going to be worlds with slightly different laws of nature, what he called small miracles or whatever. Well, I think it was a very successful speech because it brings up what I think is something to help you fall asleep at night when you're worrying about whether any of this is useful.

I mean, there's a glib answer to the, would Katie be on TikTok question, which is, I don't know, there's no such thing as Katie who is a kid now, because Katie, wasn't a kid now, so don't ask me that question. But the response to that is, but what we care about are questions like, did this patient get better because we gave them this medicine? And that's an equally counterfactual question. So even though we're playing games with the metaphysics to make it dramatic, the underlying issues are kind of pretty down to earth. Yeah, that's right. So I really like that speech, and I really sort of want to emphasize it.

it seemed like metaphysicians are just like jerks. We're just like jerks who are out there saying nonsense for like no reason or something. But it really is true that what's driving us isn't, well, depending on the person, but like I'm not trying to be an obscurest jerk. It's just that when you start saying very normal things like this explains this, as you said, did the medicine explain the recovery or was the medicine a placebo? Just a very natural question like that, immediately, as you point out, starts to invoke counterfactual comparisons. You want to say, well, would the patient have gotten better without the medicine?

That's immediately a counterfactual. And that's not just some goofy counterfactual about whether Katie would have liked TikTok. That's a counterfactual that's going to ground actual research that we really care about. Now, I'm not saying that, like, we have to understand what that question means in order to do the actual research. But it's a desire to understand better simple claims like that that drives the metaphysician into positing things that will look pretty weird from the perspective of just on the street comet sets. So that's exactly the kind of question we're trying to ask. And all these questions are hard enough if in the possible world where Isaac Newton had been right and the laws of physics were deterministic and, you know, Laplace's demon could be. be telling us what's going to happen next, but he wasn't right. We have quantum mechanics. So we have

certain events that, let's be super precise about it. There are certain events for which our best physical theories can at most predict the probability with which they will happen. Does that throw a monkey wrench into our attempts to find cause-effect relations in the world? Yeah, great. I will tell you how I think about the answer to this question, but I don't want to say that it's like the way people think about the answer to this question. By the way, this is just a very philosopher way to talk. Like philosophers always want to give every possible answer to the question and then say, who knows, right? But I think here on the podcast, you're welcome to tell us what you think is correct. I just want you to know the menu of options and I want to mitigate the hate mail that I'm

going to get after this. Okay. So many, many different things. you could think about the switch from the success of deterministic pictures to the apparent predictive success of indeterministic pictures. Here's how I think about it. I think there used to be a pretty strong methodological principle guiding scientific inquiry across many different instances of scientific inquiry. that was something like this, to the extent that you have probabilistic content in your theory, that probabilistic content is a marker of the non-ideality of your theory. That a kind of ideal theory of the world, maybe this theory isn't achievable, maybe we could never know it, maybe we could never find it,

but the kind of ideal theory of the world will be fully deterministic. And to the extent that your theory has some probabilities, it, that's a marker of your ignorance. Maybe not in a way that we blame you for or something, but there's something that you haven't filled in yet, and you're still trying to make pretty accurate predictions using your probabilistic model, but that's a marker of incompleteness.

So statistical mechanics would have been like that. Yeah, exactly. So you've got these, exactly. And you see this pressure to exactly that the statistical mechanical project is trying to recover the determinism at the bottom, from these probabilities at the top. Exactly. For me and for people who do projects like mine, a big shift in the at least temporary popularity

of the standard interpretation of quantum mechanics, where these probabilities are not taken to be a mere expression of our ignorance, but as describing something irreducibly stochastic about the structure of the world, that shift was a really big, ideal because it represented a giving up on, or maybe it shows that this norm for determinism was never there, or maybe it shows that there was a switch. We let go of the norm and said, okay, we'll now accept that you can have a complete theory in some sense or an ideal theory

in some sense that's irreducibly probabilistic. That's from like a big picture viewpoint was a big shift in the way science is conducted. Yeah. And it, it corresponds to. to a big shift in how we have to understand certain projects that science was undergoing. So what is prediction? Our understanding of prediction now it looks like has to change. And our understanding of explanation looks like it has to change. So maybe our old understanding of prediction was something like ideal prediction is just saying what happens, like before it happens or before you check. But now we don't want to be in a position where we can say what happens before it happens.

If anything, that's going to be a marker of us having failed because we're thinking the world is really genuinely indeterministic. So now our predictive enterprises aren't to get what happens right. It's to, I don't know, match our credences to the chances or match our credences to the probabilities given by the theory. We want to make predictions at the rate at what, you know, we're doing something predictively different now. And as we were talking about at the start with the principle of sufficient reason, we're arguably doing something different in our explanatory. project or we need to rethink our explanatory project because now we're not trying to find sufficient reasons for things to happen. There are no sufficient reasons for things to happen. Instead we're trying to do something else. You offered maybe we're trying to find sufficient

reasons for the probabilities to obtain other options too. So for me, the big shift between more classical mechanics to the quantum picture isn't so much about trying to figure. out like what is the right way to interpret the probabilities of quantum mechanics? Those are people's projects. That's just not my project. What do those probabilities say about the world? To what extent are they real? To what extent do they show that there's something strange going on with observation and reality? There's all those kind of like local questions. But there's a kind of big global question which is like, oh wait, are our science changed one of its major guiding norms?

And what does that tell us about the nature of explanation and prediction? And so, like, our story about causation has to be really different in a fundamentally indeterministic world. And thinking about that is one of the things I like to think about. But maybe you would agree with me. I get my hackles are raised when people say, because of quantum mechanics, there's no such thing as cause and effect. Because you don't. Yeah, that is. That's too far.

Who said that? There are people on the internet who say things like that. Okay. All right. Yeah. No, I don't think that's true. But you could imagine, I mean, look, you could imagine taking the view that, look, causation, explanation, prediction, those were things that we thought we could do in a deterministic world.

Now that we found out that the world was indeterministic, we have to give up on all those things. I think that's obviously the wrong reaction. I think the right reaction is, oh, now we have to reconceptualize all those things so that they make sense. Well, especially because we never were Laplace's demon. We never had all that information. So it was always, at best, some probabilities getting involved there. Yeah, that's exactly right. There's a question that gets related to this, which is the presentism versus eternalism question. On a recent Ask Me Anything episode, someone said, if you are living in a truly indeterministic universe, can you still be an eternalist? Because you don't know exactly what's going to happen in the future. And my answer was, sure, why not? It's just that there is a future. But we don't know which one it is. That's our ability to predict. That's not the fundamental ontology of it. And then the comment on YouTube, which I happen to stumble across, was, well, then

what difference does it make? You know, if you can be an eternalist no matter what's happening, then it seems pretty content-free to be an eternalist versus a presentist. And I want to say, yeah, that's fine. I don't really, I'm not, you know, in love with being an eternalist. I just am. But if you don't want to be, and it still gets you all the predictions that I'm kind of happy with that. I don't know if I'm giving up too easily there. Well, so I definitely agree

with you that eternalism and indeterminism are totally compatible. There's like, I think thinking about that is pretty interesting because normally when we think about indeterminism, we tend to think about it in a heavily epistemic way. We think about it. We want to sort of describe it as, oh yeah, we can have a complete story about the world at a time. We can have a complete story about the laws of nature, so we wouldn't know what was going to happen in the future. If eternalism is true, you could know what was going to happen in the future without that in any way impeding the indeterminism of the world,

that there's a fact of the matter about what happens in the future is totally consistent with there being some probability of what was going to happen in the future. your enemy on YouTube, who has accused you of the contentlessness of eternalism, I don't think it's, I think they were thinking that the good thing about eternalism or something was that it was going to make sense of the deterministic indeterministic distinction. And I don't think that's right. So I think whatever the appeal is of eternalism or presentism,

It's not driven by a, by wanting a picture that makes sense of, say, deterministic or indeterministic relationships. I think it's much more driven by, well, it's driven by lots of things, but it's driven by even just naive things about thinking whether or not there's a fact of the matter about what will happen in the future. So today you're going to eat a sandwich for lunch. Let's just stipulate that. You haven't eaten the sandwich yet. If I say, Sean has a sandwich for lunch, is that true? And is it true now? And if it's true now, what makes it true?

And if presentism were true, what could make true these claims about the future or the past if there is no future and past? That's a much more humble way for your YouTube enemy to get motivated about the distinction between eternalism or presentism. But I'm hardcore on your side. Eternalism totally consistent with indeterminism. But then this leads right into what I'm. really one of the things I really wanted to talk about with you, which is Newcomb's paradox. Oh, yeah. And I have very strong feelings about Newcom's paradox.

I'm not going to tell you... You seem like a guy who would? I would. And I'm not going to tell you what they are. I want you to give us your take first. Well, all good people are two boxers. Do people know this puzzle? No, one boxing is absolutely correct.

One boxing is absolutely correct. Yeah, but people don't know the puzzle. So explain the puzzle. Great. Here's what Newcomb's paradox is. You're going to play a game. In the game, you can either pick an opaque box by itself, or you can pick an opaque box and a clear box. Right.

And the bean says, look, I'm terrible at remembering the rules of all these paradoxes of like sneaking beauty, who was a Tuesday or what. So I get that it's hard to get it right on the spot. So we're picking either the opaque box or both boxes. Right. You can pick the opaque box or both boxes. And what's in the boxes? And the opaque box either has $0 or $1 million in it. And the clear box, you can just see in the box, it's got $100 bucks in it.

Are we doing this right so far? I think that sounds right. I think. And the bean tells you, look, Rob, I'm going to make a prediction. If I predict that you're going to take both boxes, I'm going to put $0 in the opaque box. and if I predict that you're going to take just the opaque box by itself, I'm going to put a million dollars in there. So the bean is going to make a prediction before you pick.

The bean doesn't control you. And the bean will have either put the money in or not put the money in before your pick. So when it's time for you to pick, there's an opaque box that either has $0 or a million in it, and there's a clear box. with $100 in it. And you can pick either both boxes or just the opaque box. Now you have some background information,

which is that people have been playing this game show for time and memorial. Every time somebody has picked both boxes, the bean has correctly predicted that they were going to pick both boxes, and so they've put $0 in the opaque box. So there's an extremely high correlation between picking both boxes,

and walking out of the game with just $100. On the other hand, when people decide to pick just the opaque box, the bean has an extremely high track record of having predicted that correctly and therefore putting a million dollars in the opaque box. So there's an enormously instanced regularity, an end of as big as you like, that people who pick one box walk away with a million dollars and people who pick both boxes walk away with only $100.000.

$100. And now the bean has made their prediction. They've put the money in the box. It's time for you to pick. And you, Sean, well, I, Katie, I pick both boxes. And you're going to walk away with just $100. I'm going to pick one box and walk away with a million.

Great. Well, that's why you are an enormously successful academic and podcaster. My best skin ever at 45. Give me a theme song and a best skin Award because it feels like this, right?

Can you feel like that? That's Farmhouse Fresh Skin, all right? I'm blowing and everyone asks how. The best skincare is Farmhouse Fresh and the award is you, your best you. Visit Farmhousefreshskincare.com and use code radio for a free starter routine with any purchase. Wasn't that delicious? So good. Your bill, ladies?

I got it. No, I got it. Seriously, I insist. I insisted first. Oh, don't be silly. You don't be silly. People with the Wells Fargo Active Cash credit card prefer to pay because they earn unlimited 2% cash rewards on purchases.

Okay. Rock paper scissors for it. Rock paper scissors, shoot. No! The Wells Fargo Active Cash credit card. Visit Wells Fargo.com slash active cash. Terms apply. What is your justification?

Who do you want to go first? Do you want to give your explanation why? Yeah, sure. I'll go first. I had in front of me two boxes. I didn't know how much was in the opaque box. I knew there was $100 in the clear box. My choice can't make any causal impact on what's going to be in the opaque box.

I know that no matter what I do, I'll do better by picking both boxes because that always gets a $100 bonus from that clear box I pick up. So there I am. take both boxes. I excitedly open the opaque box and oh, there's nothing in it. And I go home a loser. But at least I have my rationality. At least I can tell my grandkids that I understood what I was doing. Right. Whereas I will have a million dollars. I think my grandkids are going to be happier with me. Because the way that I think about it is, there are two possible worlds that I could be in. There's a possible world where there's a million dollars in the opaque box,

in a possible world where there's not. And it is true that the fact that I'm in one possible world or another pre-exists me making the decision. So nothing changes on the basis of me making the decision, like you said. But the rub is that this magical being, who is the game show host, does know which possible world I'm in and is telling me. And so I'm going to believe the magical being who knows, more about the set of possible worlds and I'm going to pick living in the world where I get a million dollars. That makes perfect sense to me. It's perfectly rational. Yeah, great. Let me ask you this. So I understand everything you said. Totally see it to appeal. There you are standing in

front of the two boxes. You're fully intending to take the one box. What do you think would have happened at that moment? What you're about to pick boxes? What do you think would have happened if you would have taken both boxes? The one box would have been empty. The opaque box would have been empty. How would that have worked? Well, it is either empty... The one was there or it's not there.

Right, exactly. And I don't know. And the trick of the question, as in many metaphysics thought experiments, you can always just say, but there are no magical beings like this. Okay. But the trick is that magical being,

this comes from me being a determinist. Not a determinist. Sorry, I shouldn't say that. An eternalist, right, as thinking that there is a fact about the future, even if I don't know what it is. And you're telling me there's another person who does know what it is, and they're telling me. And the fact is that there's only two possible futures, one in which I pick both boxes and get 100, one of which I pick one box and get a million. I'm going to do the one where I get a million because I like money.

I totally get the choice. I'm a little skeptical that the eternalism plays much of a role in this review. reasoning, but it is true that the one boxer gets to brag about being rich. I have a bit of a, I have a schick about this, which I haven't published yet, but my schick about this is, the problem of this stick is I don't know any facts about any of the material involved, but there's this religion called Calvinism, right? Yes. And I don't know if this is actually true of real Calvinism, but my sort of, you know,

elementary school version of Calvinism is that Calvinists have this picture about predestination God picks whether or not you're going to heaven or hell before you sort of live your life. God writes down in God's book of heaven or hell whether or not you're going to heaven or hell. And then you might think, well, if God's already picked, what's my motivation for living in a good life?

And the answer to the Calvinist, skiv, again, supposedly, is, well, as you, like, obviously God wouldn't have picked a bad person to go to heaven. God looks at your whole life and sees what you do, and on the basis of that decides if you're going to go to heaven or hell. So when you do good acts, what you're doing is you're giving yourself evidence. You're not making it the case that you go to heaven. You're giving yourself evidence that God preordained you to go to heaven. And when you do bad acts, you're giving yourself evidence that God preordained you to going to hell. And I think the structure of this is exactly like the Nukum's problem.

So the Calvinist sort of gives you a one-box answer, which is that even though it's already written in the book, whether or not you're going to go to heaven or hell, still don't sin, not because your sinning has any causal effect on whether or not you're going to go to heaven or hell, but because it's evidence that, you know, you're sitting is evidence that you're going to go to hell and you don't want to create a situation where you have a bunch of evidence.

so you're going to hell because then you'll probably go to hell. I love that. I think you've made Calvinism make intellectual sense to me. I might become a Calvinist now. Or at least I'll be friendlier to the Calvinist so I meet on the street, which is not very many of them. But okay, okay, good. And then we're going to add another wrinkle to this whole game

of predestination and whatever by saying, well, what if I have a time machine? There's a longstanding set of questions about if I had a time machine I could go to the past, could I, and separately should I, do things to change how things turn out? And presumably this is right up the metaphysical alley of people who think about these questions.

Absolutely. No, makes no difference. It's fun to think about. Perfect. No one's going to deliver it out. Yeah, right. So is there, I mean, I can imagine different versions of time travel, one in which you do change things,

one of which you don't, one of which there's different timelines come into existence. You know, is there like a retinue or a menu of possibilities that we think about metaphysically? Yeah. So, again, name-dropping this dude, David Lewis. So there's a, I guess, there's a tradition among science fiction authors that Lewis sort of piggybacks off of trying to think about a particular kind of time travel scenario. So some time travel scenarios, and they're getting like popular in TV and media or stuff, are these kind of like multiverse time travel scenarios where when I go back to the past, say, to write some wrong,

what I actually do is I travel to a different timeline or something. And when I'm in that timeline, I prevent, you know, whatever. I wanted to stop the bully who picks on me. And I go to a different timeline where I, you know, tie the bully's shoes, together or something. Whatever interesting questions there are about that kind of model, that kind of model isn't the one that philosophers have spent the most time thinking about. And it's not the kind that science fiction authors, at least a while ago, didn't spend

that much time thinking about. And the reason is because the sort of fantasy is to, like, go back and change the past. And the thought is, well, in the multiverse story, you don't go back and change the past. you go somewhere else and do something else. Like I want, I want to get the bully who, you know, harassed me in my childhood and going to some other universe or whatever, some other bully. That's not my fantasy. So we think about the sort of single timeline time travel stories.

Let me just, let me just, I would say to quickly mention the fact, you're completely correct in your impression that in the movies and TV, this multiple timeline thing is the latest rage. But I have noticed that even though it is not intellectually respectable, the writers still like their timeline the best. So there's all these stories of like our heroes completely erasing entire timelines from existence, which makes them, you know, genocidal maniacs. I know. It's terrible. I know. I want to stand up for all the people whose timelines get erased for narrative consistency.

Yeah, just because it's not your timeline. It doesn't mean you could just click it away or snap it away or whatever. It's brutal. That's my thought. But anyway. So we like the single time line stories. But the bummer about those is that it seems as though you can't change the past. Yeah.

And, you know, that sort of ruins the fantasy. But the kind of classic philosopher's paradox is this thing called the grandfather's paradox. And basically the story is just, you hate. your grandpa as people do or whatever. No, people love their grandpa, but you hate your grandpa. You want to go back in time and murder your grandpa. You don't want him to live to the age of 30 or whatever. You're really angry at your grandpa.

And it seems like you should be able to do that. It's, you know, if you're dead set on harming someone, I don't know. Philosophers always do like the most violent, upsetting version of whatever the case is. So sorry about slipping all the violence in. But anyway, you should be able to kill your grandfather. It shouldn't be that hard. It's not like your grandfather's a superhero or something. You're going to travel back in time.

But on the other hand, of course, if you kill your grandfather before your father is born, then your father won't have you. And so you can just sort of, as you're trying to kill your grandfather, you can just look down at your own body and see, oh, I'm going to fail to kill my grandfather. And I know that because I know that, you know, things happen in the future that are inconsistent with my killing my grandfather. So it seems like there's a sense of which you can kill your grandfather and a sense of which you can't kill your grandfather,

and that sounds incoherent. So what's the solution? Well, and it seems to me very similar to Newcomb's paradox in the sense that what is new is that rather than a magical being, it's you who has some information about the future, right? So your personal future is the universe, sorry, I guess your personal past is the universe's future once you've traveled into the past, right? Like you know that your grandfather will have kids and you, like you say, you look down your body and you have evidence of it.

Yeah. And so like one way of, one way that I like of making this feel extremely weird is, you know, imagine you try to kill your grandfather a bunch of times. You're going to fail every single time. It's going to start looking like this hilarious comedy of errors. I mean, the first time you try to kill your grandfather, there you're going to like, I don't know, a bird is going to fly by as you're trying, you're going to fail. The second time you're going to slip on a banana peel. The third, you know, who knows? You know you're going to fail.

Sure is that you're going to fail every time, even though this task is apparently easy. You are well prepared for it. Somehow you're going to fail. And it's not like some cosmic, it's not like the time police is going to come and arrest you. It's just that a series of events is going to transpire such that no matter how many times you attempt to kill your grandfather. From your first personal perspective, it's going to seem like there's some kind of magical force

protecting your grandfather, because no matter what you do, you're unable to get it. Do we learn any lessons philosophically from, because I completely agree with your conclusion there. What philosophical lessons do we learn is something that I'm very touchy about because people, I've published about time travel, and people goof on me all the time, but I think it's a non-serious topic,

and I see their perspective. But here's a reason that I like to, think, well, so one of the reason I like to think about time travel is a reason you've already alluded to, which is that it, when we're thinking about this kind of eternalist picture, we want to be able to cleanly separate claims about what we know or could in principle know about the future from what is the case about the future or whether the future is determined. And it could be hard to sort of cleanly separate those conceptually. This time travel story helps you sort of cleanly separate claims.

from what you know about the future to sort of what the causal impact is that you have on the future. But so let me ask you a question about what you think about this time travel case. So take some kind of local system that you think is genuinely indeterministic. It could be like something radioactive decaying or just to have it simple. Let's just say we have a genuinely indeterministic coin. We're doing a coin toss and somehow it's really indeterministic, even though that's not physically real or whatever, just pretend. So you watch the coin get flipped and it lands on heads.

And now you travel back in time to the beginning of the coin flip. On the one hand, we've said the coin flip is genuinely indeterministic. And we haven't changed anything physical about the coin. So you going back in time doesn't change anything intrinsic to the setup of our experiment. You know that the coin is going to land head. The question is, is it consistent with what you know about the future that the coin still has a 50-50 chance of landing heads? Or is the right thing to think now that, oh, there's something about your time travel that has transformed this otherwise indeterministic system into a deterministic? Good.

My answer would be that we have converted it to a deterministic system in the sense that I am a eternalist who's going to be open. in the sense that I am a eternalist who's going to be open to the closest we can come to genuinely probabilistic, indeterministic events, which is just that something is going to happen, but we don't know what it is. It's purely epistemological.

And so what you're saying is that because I have a time machine now, I do know what's going to happen, so now it's deterministic. Now I think we know what's going to happen. Great. And does that imply something, so it seems like that implies something that might have been surprising, but maybe you won't be surprised by this, which is that

the, whether or not the sort of experimental setup was indeterministic or deterministic turns out to now be a global feature of the entire system, rather than an intrinsic or local feature to the mechanics that were underwriting the coin flip. Yeah, I think that's perfectly fair, because what I really have worries about issues with is the notion of true indeterminism, like as opposed to fake indeterminism or whatever. And the example I always have in mind is, you know, someone is reading out a list of numbers in base 10, you know, digits between zero and nine. And you strive and strive to understand what is going on, how to predict what number is going

next, and you do all the statistical tests, you find no correlations, it looks as random as it is possible for random to be. And then they reveal at the end that they're literally just giving you the digits of pie starting with the millionth digit, right? So secretly there was a deterministic rule that was telling you what's going on. You just didn't know it. I don't know what is true in determinism and what is not. I get that epistemologically, I might know what's going to happen or not, but something's going to happen. Something is definitely going to happen. Are you saying that like, I don't know what you're saying yet. Are you saying that it sounded like you were saying because take any particular

distribution of events, it's consistent with that distribution of events, both that it was the object of a secretly deterministic process or it was the product of a genuinely stochastic process. The frequency with which the event occurs sort of underdetermines whether or not. it was produced by a deterministic system or an indeterministic system. And so are you thinking because the outcomes are always going to be consistent with both options, we should default to thinking there's a secret deterministic explanation or something. Oh, no, I wouldn't say that.

I do think that in the list of all lists of numbers, most of them do not have any nice algorithmic simplification like the digits of pie. So in the list of all things that could happen, in the future, if it's not deterministic, most of them will not have any secret underlying deterministic process. I'm just saying I'm not sure there is a difference between saying I know of the simple deterministic rule underlying it versus I know of the future list of things that will actually happen, right? I mean, in both cases, it's a matter of my knowledge and the existence of a simple deterministic rule underlying it is interesting, but maybe I'll get it or maybe I won't, and that's

okay. I'm not being very clear. This is my fault here. I get that there is a question, what are the simplest, most compact form of the laws of physics that tell us what happened in the future? But I'm open to those simply being a list of things that happen in the future. It still counts as a law. I see. So, and this is, Okay, good. So this is getting us back to Newcomb's puzzle. So when I say about Newcomb's puzzle, Sean, what are you doing?

You're picking the one box that's bananas, you should pick both boxes. What I'm thinking is that, you know, there's this genuine fact of a matter at a particular time about what the causal influence will be between picking the boxes and the predictor

and the causal, there is no causal influence, so go for it. And your thought is look, there's no substantive difference between whether or not my influence over the thing is causal or evidential. All I really care is about the evidential relations. And so whether or not this thing is backed by some underlying reality isn't important to me. It's all about the epistemology. So if I know about the outcome of the system ahead of time, it's got to be a deterministic system because all there is to the notion of determinism is something about what you can know and when you can know it or something.

I think that that's roughly true, although, you know, I haven't stated it perfectly, but it does seem consistent to me with the idea that you can go into the past as a time traveler in a single world universe and the things that you know have to happen in your future now are going to happen and you can't prevent them, but there's other things you don't know where you would act exactly as if you have free will about doing this or that. do you think do you think there's a difference so suppose

God were building a world God's building two different worlds the first world that God is building you can know the initial conditions and the laws and use that information or not you but a super some super mind some Laploccian demon could from the initial conditions and the laws

deduce everything that's going to happen that's world one world two the initial conditions and the laws underdetermine what's going to happen in the future, but they do it in a probabilistic way. It's some kind of stochastic situation. God is trying to build those two worlds. Do you think there's any ingredient that God would have to put in to the deterministic world or the indeterministic world to make it indeterministic or make it deterministic? I guess what I'm trying to say is that

To the extent that eternalism makes sense, there's no such thing as an indeterministic world if I allow for super smart, pan-temporal beings who can tell me exactly what will happen in the future. But isn't there just a totally, so like, in one situation, the initial conditions and the laws fix what happens, in another situation, the initial conditions and the laws don't fix what happens. Isn't that a non-epistemic difference? Maybe there's no knowers in these worlds at all. Right. I think that I guess one way of saying what I'm trying to say is that I would count the complete future history of the universe as a candidate law of physics. Uh-huh. Not a very useful one, but if that were somehow made accessible to me, I mean, in practice,

it isn't, so that's fine. In practice, we deal with probabilities all the time. I'm a complete subjectivist about probability. I think the probability is always about what we know. And so if you tell me someone out there could in principle have a complete list of everything that happens in the future, and if I could get a whole of that, that would count to me as a deterministic law. Can I ask you one more question about this? Of course. So one of the things that's sort of encoded into the principle of sufficient reason is a kind of symmetry between explanation and a certain sort of prediction.

So, according to the principle of sufficient reason, what it is to be in a position to sort of fully explain something is to be able to give reasons that make epistemically sufficient concluding that sort of P is going to happen or whatever. Yeah. On the kind of picture that you're alluding to, where we get determinism because we get the sort of full world histories, do you think there's an explanatory? asymmetry between the, say, laws that are determined by partial world histories versus, so just to go back to our coin flip case, you've seen the coin land heads before you travel back in time. That gives you great evidence that the coin lands heads. But presumably it doesn't play any role in explaining why the coin land's heads.

And in general, these sort of eternalistic facts, these facts about the future. they're going to give us great predictive evidence about what's going to happen. What do you feel about their explanatory power? Well, I think that there absolutely is a distinction between the case where the information I need to have now in order to predict the future with 100% fidelity is pretty simple, right? Is the current state of the universe plus some dynamical laws versus the case where someone just needs to literally tell me what happens in the future. And so maybe that distinction maps on to the existence of explanations. But I think that's up to us. I don't think explanations are

spooky things out there in the world either. I think that the existence of a possible compact statement of regularity is very, very useful, whatever you want to call it. When you think of, say I have two empirical theories. that are observationally equivalent. I don't know how observational equivalent to make them. Maybe they're just observational equivalent about a particular outcome,

but let's say they're at least observational equivalent for everything that actually happens. But their contents are different. Maybe they're different formulations of Newtonian mechanics or something. Make the same predictions. Do you think there could be two theories

that make the same predictions, but one is a, better explanatory story than another, or one is genuinely explaining, whereas the other one is just making predictions, but not genuinely explained. I think that if the two theories, this is a great question, and I think I'm actually going to extend it in just a second, but to actually answer it, I think that if the two theories make literally the same predictions, like there's literally a mathematical equivalence between them, like you know, Hamiltonian versions of classical mechanics versus Lagrangian versus of classical mechanics, then I think that they literally are.

are the same theory. I think that there's no sense in which one is the right one, one provides better explanations, or anything like that. They're equivalent. They're saying the same thing. But I think the reason why we're tempted to think that one is better explanation than the other is because we don't know what the final laws are. And thinking in terms of one formulation of the laws might lead us naturally to extend to them in certain ways, right? Give us ideas about what happens next, what a better formulation of it is. And starting from a Hamiltonian versus Lagrangian might take us down very different hypothetical roads, right? So in practice, since we don't know the laws, there could be a big difference between different

mathematically equivalent but morally, mathematically equivalent ways of thinking. And so any time two theories are mathematically equivalent, whether or not one is true or the other is false, those mean the same thing. For one theory to be True implies the same thing about the world than for the other theory to be true if they're observational equivalent. That's right. If they're observationally equivalent and actually true, I mean. Yeah.

Oh, sorry. If they're observational equivalent and actually, I was wondering if there could be a case with they're observational equivalent. One was true. One was false. But I mean, I mean true in the sense that we're not going to tomorrow do an experiment that overthrows both of them. Yeah, sorry.

They really are their observations are, they're empirically adequate. but their observation equivalent. Then they're the same theory to me. And I think that I have a lot, like a lot of my project, I have a project. That's so sweet. Is to start from like the most basic formulation that I can imagine of the fundamental laws of physics and recover the manifest image from it, right? And you know, say, okay, this is why we have tables and chairs and things like that.

And what almost everyone does, physicists and philosophers, to me, me is that they cheat. They know what the manifest image looks like, so they're just going to burden their ontology with ideas about laws of physics and space and, you know, what have you. And I really want to get those as effective, emergent, higher level, approximate things and figure out why those are nevertheless useful to us. That's very interesting. Is that your way of saying that it's completely nuts? No, no, no, no, no. The thing I'm particularly interested in is this idea that something like observational equivalence implies equivalence all the way through or something,

that there couldn't be sort of two theories that give us different claims about what the unobservable world is like, but make the same claims about what the observable world is like, so that they're sort of the truth of the theories is underdetermined by, it's not just underdetermined by the evidence we actually have, but it's underdetermined by all the evidence we could possibly obtain, because they sort of agree about the observable world but disagree about the unobservable world. Well, no, I do.

I mean, that's what I was gesturing at badly when I said if both theories are true. I mean, in the case of Hamiltonian mechanics versus Lagrangian mechanics, you can literally start from the equations of one and derive the equations of the other. So I think that it is impossible to imagine a case where tomorrow we will do an experiment

that says one is right, the other ones. For sure. Yeah, for sure. So that's what I have in mind. Different theories that even in principle make all the same predictions. There couldn't be any deeper fact about the world that would make you say, ah, one of these formulations is sort of getting the structure of reality better than the other formulation

or something. Not if both, you know, not unless there was some experiment we could do, which was compatible with one, but not the other. Yeah. I do think, you know, like I said, there's different, different theories can leave. you to extend them in different ways, so I think it's very important to think about them. But if they're, if I can truly do a mathematical equivalence, let me give it, let me give one very down-to-earth example. I know that it's late in the podcast, so we're down to the

hardcore listeners now, so they're willing to go down roads further than the beginners, the, you know, the casuals who are just listening for the first 10 minutes. You know, if you have a box of gas with 10 to the 23 particles in it and you want to say, okay, the laws of physics are, you know, that four, for each particle, they obey Newton's laws, and they bump into each other. And so where the system lives, the conventional thing to say is, is in three-dimensional space or maybe, you know, six-dimensional phase space. And there's many, many points.

The system is a set of 10 to the 23 points in a six-dimensional phase space or a three-dimensional space. Okay. Alternatively, it's one point in a giant six-times 10 to the 23-dimensional phase space, right? And those are mathematically equivalent, but almost everyone says, yeah, but come on, it clearly lives in space, lives in three-dimensional space, right? Like, that's just a mathematical trick you're doing. I want to say, nope, it's equally real. It's equally good. There's no improvement of one over the other. The reason why you think there's an improvement is because you

often have incomplete information. And one of these ways of talking generalizes better to the case of incomplete information, right? And the other one doesn't. So to me, the reason why you want to privilege one equivalent theory over another one is not because of the theories themselves, but how they fit nicely into a bigger framework. Great. Let me just go, you know, philosophy, intro philosophy on you. Do you ever think about stuff like whether or not we're living in a simulation or whether or not

We're like living in a dream or the matrix or something like that. I mean, one way of thinking about those skeptical scenarios is that they're trying to describe a way things could be observationally equivalent for us. But the underpinnings of reality be radically different. So I don't know. Maybe I'm just a brain in a vat. It seems to me like there's a television. What is this called? computer monitor in front of me.

But really what's going on is that like some scientist is poking my brain and some kind of science fiction story. Now I feel like what you're going to say pretty quickly is that there's like possible experiments that could be conducted in these scenarios to

distinguish the brain and the vat case from the real world case. Is that what you're going to say? No, not necessarily. I mean, that's certainly true. I mean, at least it's plausibly true. But I'm willing to consider the thought experiment where there aren't any experiments we could do. What I would ask is, which is more explanatory? So I'm certainly open to the possibility that I am a brain in a vat or I am in a simulation or whatever.

But if my best theory of the universe is, here are the laws of physics, here are the initial conditions, and I'm a brain in a vat, versus here are the laws of physics here are the initial conditions. And both of those theories make exactly the same predictions and statements, etc. I'm not going to waste time, thinking that I'm a brain in a bat or living in a simulation or whatever. I mean, maybe there's some anthropic reason or something like that. But until, so I would say that until we do some experiment or have some insight that is better explained by this extra little bit of metaphysical baggage, I'm not going to pay too much attention to it. Good. So just flagging some things.

So we've got at least three ideas. is in the conversation. One sort of idea is, you know, if the theories are observational equivalent, do we give a damn which theory is true? Should I worry about it? Should I spend time sort of agonizing about it? Another question is, how would we know if they're observational equivalent? Could we ever get evidence for one theory over the other? And you said something really interesting. You said that you thought one theory, we might pick one theory over the other because it was more explanatory than the other. And then the third thing is that, well, if they're observationally equivalent,

they don't say anything different across the board. So what it would be for one of the theories to be true, what the world would be like if one of the theories is true, is just the same as what the world would be like if the observational equivalent theory was true. And those are sort of three different notions and the strongest kind of thing to think is, well, what the world would be like,

if the brain and the VAT scenario is true and our regular hypothesis is true, there's no important difference between what those theories are saying about the world because they make the same observational predictions. That seems like a very strong thing to think. Then there's a kind of much, the sort of weakest thing to think is like, who cares? These are stupid questions. We shouldn't worry about these very high-fluent questions.

And it's the middle ground that I'm particularly interested in. So when you say, oh, well, one of these theories would be explained, and the other theory wouldn't be, even though they are observational equivalent. Do you have any idea about how you would tell which theory was the better explanation? Or like what comes to your mind when you say things like, oh, we could look to see which was more explanatory? Yeah, I think that we have to be a little bit more clear about observational equivalence. I mean, in the case of Hamiltonian mechanics versus Lagrangian mechanics, they're not just observational the equivalent. They are mathematically equivalent to each other, right?

The brain in a vat or simulation is a little bit different because there, even if I, by stipulation, cannot notice any difference, in principle, there absolutely are observational differences. I could get a picture of the brain in a vat, you know, in the evil scientist laboratory or whatever. But, I mean, there's a much more down-to-earth example of exactly this, which is the cosmological multiverse, right? where you say, okay, we have observational access to a finite amount of space time, and what happens past that? And if you put on the table two options. One is that it's just more of the same forever and ever and ever, and the other is, no, no, in different regions very, very far away,

conditions are highly different. Observationally, to us in the real world, those are absolutely equivalent. in principle, if you imagine that we have access to regions that are further than we can possibly see, then they're not. And I think that there are explanatory differences between them, because in the single universe case, if you have a number like the cosmological constant, you have to say, well, that's it. I need to come up with an explanation for this number. Maybe the explanation is we were just lucky, but I need to figure out my best understanding why it was that. Whereas in the multiverse example, I can't come up with a single explanation for why that number is what it is because it's different numbers in different parts of the universe and I have a completely different explanatory framework involving anthropics and selection and things like that. So I do think that that's the sense in which there's different explanatory capabilities for different theories that have exactly the same observable consequences.

Yeah, that's all totally reasonable. Can I try one more on you? And then I will give up this. I don't even know what the project is. Here are two different possibilities. So when I clap, you hear that sound. You see my hands go together and then you hear that sound. Hypothesis 1, there's a correlation between clapping my hands and that sound.

But there's no causal relationship. So throughout all time, when I clap my hands, it'll make that sound. That's true for other people's hands too. It's just a huge coincidence. There's no causal relationship between those two things. That's hypothesis one. Hypothesis two, there is a causal relationship between those two things. My hands going together cause that sound.

Because the first hypothesis sort of has it built in that its observational stuff is going to be just like the second hypothesis. So you're never going to find a case where somebody claps their hands and doesn't make the sound. I'm wondering whether you think like, oh, these are like two different live possibilities or whether you think, eh, there's not much to, there's not much different between these two possibilities. Well, we haven't talked about in this podcast, but I've mentioned before the humian, anti-humian distinction. And it was Barry Lower, who was a previous guest who years ago first told me I should

really care about this distinction. And my result, my answer was, no, I don't need to care about this distinction at all. But he has changed my mind about it. Now I realize that I should, and the reason why I should is because I think it changes how we think about other possible worlds and counterfactuals, right? Whether the laws of physics have oomph and existence and spookiness all by themselves versus if they're just a convenient summary of things. But anyway, and you can give us your opinion about that distinction if you want. But for the hand clapping, I would say at the level of fundamental physics as we currently understand it, I just don't want to talk a language of causes and effects at all.

I do want to just talk the language of correlations, patterns, differential equations, what have you. I think that the language of causes and effects becomes relevant in the macroscopic world where we have incomplete information, and we have an arrow of time, and then we're saying, well, given the way of the universe evolves, macroscopically, every time you clap your hands, you hear a noise. I think that's a perfectly fair thing to attach the words cause and effect to. It's an emergent, higher level thing that when you clap your hands, you hear a noise. Yeah, see, I figured you were going to say the difference between the correlation case and the causation case is that in the causation case, if you were to clap your hands an additional time,

then it would make the noise. And in the correlation case, we don't have a strong reason to think that if you were to clap your hands an additional number of times, it would have made the noise. So I wondered if, like, this was part of your counterfactual, your love of counterfactual. Well, I think I can be a humian and still think that there are laws of physics, right? So I do think that the existence of the noise after the clap does follow from the persistence of these patterns over time. So I still would predict that every time you clap your hands, even though I don't want to talk about it at the fundamental laws of physics way as a cause-effect relation, I still think that I can make the prediction. You're not a clapping sound skeptic. I am not.

And I don't know, so are you humane or anti-humane? Where do you fall there? We didn't get a chance to talk about that. What is the right answer? The right answer is the anti-humans are right. I mean, it depends on what you're into. If you're into, there's a lot of bad things about being a humian, a lot of normal things that people think that you can't say. And I think it would be really nice to say those things.

On the other hand, the anti-humian theory is always very sort of sketchy. I mean, not always. There are people who are anti-humans and they will not like it if I say their theories are sketchy. But the basic cost of anti-humanism is you have to say what it is that you're positing, what the hell you're talking about. that's very hard to do. I think pursuing that project is sort of more interesting than pursuing the Humean project or something. I have aesthetic reasons for wanting to be an anti-Aidohy.

I think that's okay. I have aesthetic reasons for wanting to be humian. I think that these laws of physics are just spooky essences that I want to get rid of. I want to scrub all the spookiness from my ontology. I want my ultimate ontology at the end of the day to be a single point in a high-dimensional space evolving according to some equations. That's the world I want to load in. That is the saddest thing I've ever heard. And that is the perfect place to end the podcast. Thank you very much, Katie, for telling me

the sadness that I have to wake up to or not go to sleep with every time I think about it. And thank you very much for being such a good guest on the podcast. Thanks. This was really, really fun. You should do something having to do with philosophy, John. You're good at it. Someday, you never know. In the future, what would the magical being say about that? In I shop Ashtro. At Astro, I find statement dresses, powerful suits and Afrocentric styles made for my life.

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