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33| Taking Chance Seriously — Alastair Wilson on Quantum Modal Realism
209 Plays4 months ago
Things happen. Or they don’t. How then should we make sense of claims that something might happen?
If all these claims do is express doubt, then the puzzle can be easily resolved. But if the claims capture some objective feature of the world, what is it?
Our guest is Alastair Wilson, a professor of philosophy at the University of Leeds. He takes chance seriously, in particular, he is a realist about our modal claims (claims like “either candidate could win” or “if Szilard hadn’t got Spanish flu, the atom bomb would not have been invented”) may be true or false, not just opinions or expressions of ignorance.
Alastair does this by connecting our modal talk to Everettian quantum mechanics. He argues that modal claims are assertions about the many worlds within the universal wavefunction. If in all worlds where Szilard did not succumb to Spanish flu, the atom bomb was never invented, then this claim would be true.
It is a bold and fascinating way of bringing physics and metaphysics together. What can happen, what is possible, what could have been? These become questions for natural science.
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Transcript
Introduction to Multiverses Podcast
00:00:00
Speaker
I'm James Robinson, this is Multiverses. History seems to be littered with small events which have had an outsized effect. The stalling of Archduke Franz Ferdinand's car as he went into the centre of Sarajevo led to his assassination on that fateful day in 1914. If his car hadn't stalled, perhaps the First World War would not have broken out. And we make the same sort of claims about the future. We often say, well, this might happen or that might happen. And it often doesn't just feel like we're talking about our ignorance. We're not saying I don't know what's going to happen. We're talking about what feels to us like real possibilities, real alternatives. And yet we know that there's only one set of events that we'll experience. So what are we talking about when we talk about these alternatives?
Guest Introduction: Alistair Wilson
00:00:51
Speaker
I guess this week is Alistair Wilson, a professor at the University of Leeds. And like myself, he studied physics and philosophy many years ago at the University of Oxford. And like many who did that undergraduate degree, he came out convinced that the Everett interpretation or or the many world's interpretation of of quantum mechanics is our best way of understanding our most fundamental theory of nature.
Are possibilities real and physical?
00:01:15
Speaker
And unlike many, Alistair went on to try to understand what that means in terms of how we should think about these questions of of chance, of possibility and impossibility. And he kind of boldly conjectured that actually we can solve this riddle of what we're talking about by thinking in terms of every world's. So for example, if one was to make the claim if the car hadn't stalled, the First World War ah would not would would still have broken out, let's say. Well, Anastasia's saying, well, that's a claim which is a candidate for truth or falsity, and it's truth or falsity is based on what happens in forever-at-worlds, worlds which are just as real, just as physical as our own, but ones which we don't happen to inhabit. But there's an ever-at-world, just like our own, know many ever-at-worlds, just like our own, where there was someone that was called the
00:02:10
Speaker
and dukeke franz ferdinand and everything was identical to our own world up to a point in time um where the car didn't stall. And in all those worlds where it didn't stall, if the First World War still broke out, well then the claim that, you know, even if it hadn't stalled, the first world would ah war would have broken out is true. So that's the kind of the theory in a nutshell, I guess. um And it's very bold because many people would say, well, you know, even before we had an inkling of what quantum mechanics was, we were making these kind of modal claims, right? And so somehow, you know, how can they be connected to our understanding of of of contingency? And furthermore, one might say, well, we also make claims about things which
00:02:53
Speaker
um aren't possible within
Updating understanding of chance through physics
00:02:56
Speaker
every world. We might want to say, well, what if the fundamental, you know, what if quantum mechanics were false, right? What if um the the laws of nature had been slightly otherwise? But I think it's, you know, completely fair game, actually, to say, well, we should learn from our best theory of physics and update our talk of, you know, our folk conceptions, right? We've done this for space. We've done this for time. We've um updated our understanding of what those concepts are.
What is modal realism?
00:03:23
Speaker
in light of the looks, so could the same be true about how we think about chance and contingency and luck? So this is a fascinating conversation, a really good introduction, I think, to modal realism and all these sort of issues. I hope you enjoy it as much as I did.
00:03:56
Speaker
Hi, Al Wilson, thanks for joining me on on multiverses. Thanks for having me on. I'd like to ah start by talking about modality. um Perhaps you can take us through this this term of art. What are we talking about and when we talk about madeity yeah modality? is The term modality is a good example of philosophers taking something fairly familiar and making it sound unfamiliar with a fancy name. um really modality, as I think about it, is to do with alternative possibilities. So there are various kinds of alternative possibilities. There are alternative ways things could be as far as we know, or there might be more objective sorts of possibilities, possibilities for the way the world really could turn out.
Exploration of different world outcomes
00:04:43
Speaker
And my work's been on the relation between those two kinds of possibilities, but with a special focus on that second question, ways the world really could turn out. And the contrast between ways the world really could turn out as opposed to ways it really couldn't. um And the idea that we can we can discover facts about that sort of thing, as well as discovering just facts about the way things in fact do turn out. Okay, very good. Well, it's modally rich, we say it's not just made up with what actually happens, it's kind of full of possibilities as well. um Unrealized ones.
00:05:17
Speaker
Yeah. and and And that is a familiar feeling to everyone. We all feel there are many things that could happen today. And there are things that could have happened um you know earlier today. Things could have gone otherwise. um So yeah, we've got a fancy label for it. um And what do what do philosophers want to say about these things? like you know What are the kind of approaches that one can take to modality? um Well, I'd say philosophically, it's always been a puzzle.
Experiencing time and possibilities
00:05:51
Speaker
um Time is always presented a puzzle because you only ever see kind of one time at once, but the same person sees different ah times as they live their lives. um But we only ever see one possibility for the way things could turn out, the one that we ah ourselves in inhabit.
00:06:10
Speaker
And we don't ever see, we can't ever see directly the other alternatives possibilities. So we can kind of reason about them, think about them, but we never kind of bump into them. um And so that when when you've got something in that sort of more ephemeral category, you can have all sorts of philosophical disagreements about it. ah one of One of the core ones, I guess, what I think of as the core one is the question of reality, which is a question that philosophers love to ask, especially people doing metaphysics love to ask. So kind of our alternative possibility is real.
00:06:45
Speaker
Or are they just things we make up? Are they just human-generated imaginary things? And I don't think the answer to that is at all obvious. My own view is that alternative possibilities are real. In fact, they're real and physical, part of the physical world. That's an unusual view. ah But a lot of philosophers agree that alternative possibilities are real. They just disagree with me about what kinds of things they are. But then there's the whole more skeptical view that says alternative possibilities aren't um't real at all. There's no such things. We kind of just imagine them or pretend that there are such things. Really, there's just this world that we live in. There are possibilities are imagined. Yeah. mean I mean, I think there is a case to be made that um alternative possibilities aren't real. um But maybe if we focus on, you know, if if we take the assumption
00:07:39
Speaker
that they are, um which I think is something we we do intuitively feel when we when we regret things. We generally think that things could have gone um another way. And even though, as you say, we only ever see things going one way, in a sense, in that when there are apparent alternative possibilities, only one thing is realized. Yet we do have this strong feeling that that That needn't be the case. um And so I guess the philosophy here is trying to maybe connect with and explain um
Philosophical vs. scientific approaches to possibilities
00:08:16
Speaker
that, I don't know, folk vision of of possibility.
00:08:21
Speaker
Yeah, I think really the kind of the crux of disagreement is whether the distinction between possibility and impossibility is one that kind of cuts deep, one that kind of is to be found in nature, as opposed to something that we kind of project on to nature. I mean, we definitely have different attitudes of the kind you're describing to sit to things that are possible and things that are impossible. um For a start, we aren't going to try to bring about something that we think is impossible. There's kind of no point. Whereas if something we regard as possible, we might try and bring it about. But even if it's kind of in the past,
00:08:59
Speaker
we might kind of regret something more if we think we could have done it differently. Whereas if we think it's completely outside our control, there was no possibility of kind of us having done anything in it differently or things having worked out any differently. We don't regret it in the same sort of way. There's some sense there's no kind of no alternative possibility there to mourn if what we kind of thought we wanted would actually turn out to be impossible. um So I think possibility and impossibility definitely feed into our kind of cognitive lives, both in the kind of future-directed what can we do, what can we affect, what's the point in like trying to achieve things,
00:09:34
Speaker
um along with that past-directed sense of ah what could we have done differently, what would have happened if we had. um And yeah kind of for better or worse, yeah We care about those questions. We don't just care about what actually happens. We care about how it how the relations are standing to all the alternative possibilities. And I say it's it's a very puzzling thing how these kind of ephemeral thing, alternative possibilities could end up being so important to us. And I think it's ah that's actually a puzzle that most philosophical philosophical theories of ah vol alternative possibilities of modality don't do a very good job of explaining. ah There are various theories of of possibilities of something like
00:10:25
Speaker
kind of property the world could have or complete sets of sentences that somebody could say ah consistently. um And those accounts can have certain philosophical virtues, ah but they don't do a very good job good job of explaining why we care about these alternative possibilities so much. um if they're only these properties out there not instantiated by anything, or if they're only the sets of sentences that nobody ever does um kind of say completely or maybe even could say completely, why should we care about those sets of sentences? um So like most of the most plausible philosophical theories of possibility seem to run into real trouble in explaining why we should care about them.
00:11:15
Speaker
But we do i take that to be kind of data for philosophers to explain. Right. So and maybe we can start talking about concretely one of the perhaps one of the most famous examples of an attempt at least to make sense of our talk of of possibilities and and modal talk. We should have thrown necessities there as well. um And so so I guess David Lewis um might be familiar to manning listeners here. And he had a project of modal realism in the and the sort of the clue is in the name. He was trying to ground or or make yes make these modal claims claims about real things. and But perhaps you can give a description of of how his project worked.
David Lewis and grounding modal claims
00:12:10
Speaker
so i mean i i I love Lewis's project. I think it was kind of ultimately misguided, but kind of gloriously misguided and shows a kind of ah kind of philosophical courage that is kind of rare to kind of follow your kind of intellectual convictions where they lead. um Because I think Lewis's instincts were all good ones, or mostly good ones to kind of think there really is something there in modality to explain these alternative possibilities. It's something really deep. It's not this kind of shallow um part of reality that alternative possibilities
00:12:46
Speaker
ah right there in the the basic structure of the world and are thinking about the world that need a kind of a proper theory to account for them. And proper theories should be, I think, things Lewis realists, you should if you want to explain something, you've got to kind of admit the reality of whatever resources you need to give that explanation. You've got to kind of be honest. If you want, you kind of can't conjure real relevant stuff out of nowhere, you have to kind of um pay the suitable theoretical costs for the explanatory benefits you want to you want to secure. So Lewis, in wanting to kind of give a real, proper, thorough underwriting for ah modal thought and talk, kind of
00:13:36
Speaker
went huge, kind of kind of expanded out what our conception of reality from one world like the one we live in to countless um in infinity of worlds, kind of just like the one we live in. Real solid s things, most of them at least, the ones that aren't just made of ghosts. um Real solid things just like ours, just somewhere else as opposed to anywhere that we can get to. And this is a kind of incredibly bold theoretical inference. um But Lewis thought that in at least one sense, it wasn't too bold, because it wasn't inferring to the existence of a whole different kind of thing that we'd never encountered before. In some senses of the universe, they're just more of the same. They're more things like the one we live in. So you know you his his his idea was that you could just kind of expand the quantity of
00:14:31
Speaker
things of the kind that you already believed in and account for modality that way without having to bring in any new mysterious kind of magical-seeming kinds of things
Quantum mechanics and understanding possibilities
00:14:41
Speaker
um of a wholly different kind.
00:14:45
Speaker
in order to account for modality. So in some sense it's quite a kind of cautious conservative view, you're not expanding your sense of what sorts of things there are in the world, but in other sense it's a kind of rat radically expansionary view, you're expanding which things you think, how many of those things there are, you think there are in ah in a really big way. So he saw that there were countless possible worlds, um that, crucially, that those things were the same sorts of things that our world, and they only differed from our world in virtue of us being in ours and not in any of theirs, that they were inhabitants of all those worlds that are just as real as we are, thinking that they're the actual ones, and we are mere possibilities. But kind of seen from the the God's eye view, um we're all kind of just as real as any others. There's no sense in which one of them is really the actual world and the others are really just possibilities.
00:15:38
Speaker
they're all kind of co-possibilities from that sort of point of view. And I think it's ah it's a beautiful, incredibly bold theory. Almost nobody believes it. Some people think even Lewis couldn't really have believed it. um and And I don't believe it, but I think that it has done the chance, at least, of being right about in some important respects. ah
00:16:06
Speaker
So I like the kind of different version of modal realism, which I guess we'll come to too shortly. um But I think kind of Lewis was looking in the right, um in the wrong sort of place for the right kind of theory. Yeah. Yeah. And as you say, I mean, there's there's many nice properties of this theory. One is that While it massively expands the amount of stuff there is, it's not appealing to some kind of hidden nature of things to explain modality, which is another approach to say, OK, well, I don't know.
00:16:43
Speaker
The reason you can't build uranium spheres of a certain size is to do with causation, and causation is just something we can't see, but it just necessitates things.
Essences in explaining possibilities
00:16:55
Speaker
Or, um you know, there are are some, there is just some hidden chance in us to other things. I think what um yeah yeah the kind of the idea of essences going along fits the bill if you you're describing there. There are a lot of people that want to say, well, I don't know, ah charges of the same kind necessarily repel each other. Why? Well, it's just in their nature. There's nothing kind of more that can be said.
00:17:25
Speaker
um And so you're you're you're positing kind of natures or essences of things which can't be seen directly, which are kind of responsible. um And if the world is full of those sorts of kind of rich natures or essences, then maybe we just need one of them um because kind of all of the claims about all the other possibilities can somehow be grounded in the essences in our world. But yeah, there are reasons for not liking that. It's quite opaque. How will we ever find out anything about these essences, for example? And Lewis's is kind of a very transparent view compared to a lot of the other ones and in the table.
00:18:04
Speaker
And it makes it quite easy to at least ah a certain level to understand claims about chance and probability, when you can take some kind of measure over these different worlds and say, well, you know, If I had got up a little bit earlier, then I would have made that bus. Or at least my chances would have been boosted by 50% or something. And then you know you can look across those worlds. um Of course, you can't actually look across them. And this is one of the problems we'll we'll maybe get to.
00:18:37
Speaker
but you can If you assume the godside view, then you could say, okay, well, if I look at these worlds where there is someone a lot like me and had started the day with almost the same circumstances, but they just got up a little bit earlier, let's peer into those there's different places which are completely disconnected from this world, but let's just imagine we can do that um and and see what happens and do some kind of count or or measure over them um to figure out, to to ground our ideas of probability.
00:19:08
Speaker
so so yeah i mean there's definitely in in lewis something of that so So Lewis famously has the um account of counterfactuals given in terms of his real possible worlds. He says the truth about the counterfactuals would have happened under which circumstances. ah up but ah are to be explained in terms of facts about the distribution of possible worlds. But interestingly, he doesn't do that tempting thing you described, which is to say there's a probability measure over all the worlds. The probability measure for him over the world is quite context-specific, quite high level, sort of projected on by us. He's a humane about laws, which is to say that he doesn't think that the laws of nature are kind of inherent to the world, but they are a matter of like,
00:19:53
Speaker
the the patterns that happen to turn out and the best way to sum up those patterns. ah So all that has to say is goes to say that Lewis um explicitly kind of denies that there's kind of in reality any kind of significant ah probability measure over his worlds. There's no sense in which there's more worlds of this kind than worlds of that kind because there's like typically going to be infinitely many or both kinds. um So Lewis actually um Is keen to defend that part of the view that there's kind of no preferred ah measure of of probability or of um kind of proportions of worlds ah In his picture because he thinks that if you had such a measure you could make trouble for the view He thinks you could maybe run try and run him into paradox or try to create skeptical arguments out of modal realism using such a probability measure and
00:20:51
Speaker
um
00:20:55
Speaker
But the the idea that there is a probability measure over the possible world is a very attractive one. um John Bigelow developed these ideas in the 1970s as part of kind of a theory a little like modal realism. And um Robert Pargeter talks about it as well. ah And It's also a feature of the version of modal realism which 30 years after Lewis I find myself defending.
Why believe in Everett worlds?
00:21:28
Speaker
ah
00:21:31
Speaker
That sort of version says there really is a probability measure over all the worlds. And it finds it in quantum theory. to so So it's a bit of a left turn for this um kind of ah debate to have taken. And it's not where Lewis would wanted would have wanted to look for his metaphysics. um But I'm interested in the idea that we can find contributions to this debate about modality from physics rather than kind of from pure metaphysics only. Right, good, yeah. So, and I think, I mean, let' let's start talking about that, because I think, you know, one thing that will just be very much at the center of people's minds is, well, why should I believe in all these Louisian worlds, right? You know, okay, maybe there's some convenience for being able to talk about modal truths, but that doesn't seem enough motivation um to
00:22:28
Speaker
suddenly expand ah the set of things that I believe in to encompass all these, ah you know, counterparts of me and so worlds where nothing like me exists, but okay, they're, they're similar, they're physical worlds. But I have no access to them. I can't see them. I can't um sort of discover them or have no evidence for them other than the fact that we talk with modal language. um And furthermore, like why you know to your points earlier, like why do I even care about what's going on in these worlds, um given that I have kind of no causal connection to them? um Yeah, it's true. This is a tough um ah tough kind of line to try to hold.
00:23:10
Speaker
i think that that
00:23:14
Speaker
And kind of sympathetic to the idea that there is a kind of purely philosophical case to be made um for something like modal realism, it wouldn't go from the idea of kind of wanting to capture kind of what we say about these, about alternative possibilities, so much as wanting to understand ah what we do when we think with them. ah because the argument might go, it's no coincidence that we've evolved to ah carefully weigh alternative possibilities when considering course of action. It's no coincidence that we have these patterns of regret of things that we think we could have done differently, but we don't have the same sort of regret for things. and We don't regret that one plus one is not equal to three because we know that it couldn't have been.
00:24:00
Speaker
ah and And so that's a really deep part of our lives, our engagement with the world. Something has to explain why we think that way. For every other feature of the way we think, it seems there's an explanation of of of why we think that way. um like our perception is there to kind of tell us facts about the physical world we live in, like tell us where the fruit is. kind of That's a clear account of why we have perception. We need it to find food and escape predators. But why do we have this deep rooted pattern of thinking about alternative possibilities? It's not at all obvious. and i think some you know We need a substantial explanation there.
00:24:43
Speaker
And so it's not crazy to bring in something like real possible worlds to to give that explanation if they really did give the explanation.
00:24:55
Speaker
But then the question comes, can these alternative possible worlds, these other things just like ours, really explain why we have these patterns of reasoning. And the causal isolation point that you just made, I think is a really important one. If they make no difference to us, then it's really hard to see how they could help. Like maybe there's something, some really kind of substantial explanation needed here, but you might think alternative possible worlds just couldn't help because they are kind of separated off completely from our own. um and
00:25:27
Speaker
And I think that does support looking for a view where the possible worlds are real, and maybe are not so completely separated off from our own as all that. It's perfect. I mean, and I think that brings us yeah straight to Eparatian quantum mechanics, um which is, you know as you describe, as you hint, I guess, um offers us a set of worlds but worlds which are united somehow within um and and touching on one another and at ah um as well. Yeah, maybe give us a reminder of of off the kind of core claims of um Everett and and and and his formulation or interpretation of of quantum mechanics.
Many Worlds interpretation of quantum mechanics
00:26:17
Speaker
Right. So the the phrase Everettian is kind of what a lot of kind of philosophers and physicists, the physics will use. But this approach is more is more commonly known as the Many Worlds interpretation. That's the kind of the widespread label. And that label is controversial because not everybody that believes the Many Worlds interpretation thinks there are, in fact, many worlds. ah Everett ah Everett's original argument in the 1950s, when he developed this interpretation, was more that there should not be any collapse of the wave function.
00:26:55
Speaker
ah that we don't need to have a collapse of the wave function as basic, and we don't need to have indeterministic random probabilities as basic in the theory either. um And exactly what he thought we should have instead is disputed. The most common way of reading or developing the kind of the idea that ever came up with is in terms of many worlds. um But there are versions of it that say that just kind of one world, but many different kind of groups of minds within that one world, so-called many minds of use. And there are ones that say we kind of don't have any world or what or mind. It's all about the kind of the relations of different states stand into other states, so-called relative states or relational versions of everyone. And so there's a whole kind of tangle of different theories, different ways of understanding quantum mechanics there.
00:27:50
Speaker
ah And I'm most interested in in the many world strand, the kind that says there really are multiple quantum universes, and we live in just one of them. But we can of infer their existence from the results that we get of quantum experiments done in our world.
00:28:14
Speaker
a sense in which what we see when we do a quantum experiment is is something like a kind of shadow of the other world or an echo of it. a So we don't kind of we don't see things in other worlds directly, we can never travel to them, but their existence makes a difference to what we see because if they weren't there we would have no explanation for why the quantum experiments that we do do turn out the way they do. Right, yeah and I think just to um i mean it refer people to the episode with David Wallace, where we go into a lot of detail on the motivations for the for many worlds. But as you as you mentioned, it's all the Everett interpretation in in general, and David Wallace is sort of
00:29:00
Speaker
formulation of that is very much in the many worlds or multiverse way of things. ah But as you as you mentioned, it was a solution to this this kind of measurement problem where um people are puzzling over ah the apparent fact that when measurements took place, according to quantum mechanics, at least in the early days, people would say, okay, well, When you do take a measurement, um this this mathematical thing, the wave function, ah doesn't evolve smoothly and nicely as it normally does.
Wave function collapse problem
00:29:33
Speaker
But at the point at which someone decides to ah inspect ah you know how it looks, what it's doing, it suddenly kind of collapses and changes shape very, very abruptly.
00:29:46
Speaker
um and it it wasn't, you know, firstly, it's not clear what a measurement is, what defines that. um And you know,
00:29:58
Speaker
it wasn't clear at least to Everett that you needed that at all. Maybe you could just stick with the nice smoothly evolving wave function, this thing which is describing the the physical state of the world, um and at points where it sort of seems to do things that you don't see, like maybe electron going through two slits at once. um Well, actually, perhaps it is, right? Perhaps it is going through two suits at once, and but as at the points at which you try to expand that very microscopic event out into something on the visible scale.
00:30:33
Speaker
um Then it, you know, it appears as if it just went through one slit. um But what you actually end up with is it did go through both slits, but you have kind of two worlds. Or maybe you always had two worlds, one where it was going to go through one slit and another is going to go through another split ah slit. um So I think I just want to remind people that
00:30:57
Speaker
While again, it seems like we might be introducing a whole lot more stuff into the world, the kind of spirit of um Everett was was one of pass money and and and not trying to add anything extra to the physics or or to the philosophy, um to kind of use David Wallace's phrase, but to you know just take quantum mechanics at its word, I guess.
Jigsaw puzzle analogy for the multiverse
00:31:21
Speaker
um yeah
00:31:24
Speaker
so
00:31:27
Speaker
um ah
00:31:39
Speaker
Well, perhaps I can say here, I do really like your way of thinking about, um in your book, I think you can use the analogy of a kind of jigsaw, a piece of a jigsaw puzzle, to to to to try to tease out this way of understanding that Even in the Everett multiverse, we really don't have access to these other worlds. um But what we do sort of have access to is evidence of the edges of them, I guess, or evidence of the machine that has created our jigsaw piece. And from that, we can infer that it's sort of created a whole jigsaw.
00:32:22
Speaker
um pat I don't know if you can kind of cash that out um further because I thought that was a beautiful analogy. If you found the jigsaw piece lying around um outside, what would be the most reasonable conclusion that it had been made ah just on its own? and then dropped outside, or that a jigsaw puzzle containing it had been made, it had been somehow separated from the rest of its pieces and then dropped outside. The latter is much more common because we couldn't make sense of um why someone would make a whole ah puzzle. We would make sense of why any given piece might have dropped out of that puzzle. It's hard to make sense of why a piece might have just kind of existed on its own without any puzzle to go in. It would have been an odd thing to make.
00:33:13
Speaker
um And broadly speaking, you can make the same kind of inference for words. If you see ah the results of quantum experiments and can't explain those without bringing in something peculiar and mysterious, the collapse of the wave function, but you can explain it by inferring that there are more worlds just the same as ours.
00:33:46
Speaker
ah then you're doing again what David Lewis did and you're kind of use it you're you're kind of saying, well, we'll just have more of things the kind of thing we've already got and use those to give an explanation. And those things can't be themselves mysterious because we you know we we we know what they're like. We live in one of them. This world isn't mysterious.
Conservative nature of Many Worlds theory
00:34:06
Speaker
So more things like this can't be any more mysterious either. Whereas the collapse of the wave function, especially if it connects up, if it's supposed to connect up to things like consciousness or um kind of human observation ah in some distinctive way, that is mysterious. I mean physics never otherwise connects up with consciousness. It would be kind of peculiar if we had to bring consciousness in just when quantum mechanics ah came along. Whereas if our quantum world was one of many,
00:34:38
Speaker
um then all we've got is more of the same sorts of things we already live in. And so that's the sense in which it's sort of of a conservative view. um And I mean, expanding our horizons isn't a isn't a new thing for science to do. I mean, people used to think the world was a few hundred miles wide. They found out it was a lot bigger than that. Then they found out ours is not the only planet. And they found out ours is not the only so star system. They found out ours is not the only galaxy.
How science expands our universe understanding
00:35:06
Speaker
um Ours is not the only concrete universe is really not very big a step beyond that. it's The fact is these things are getting harder to see each time um to the extent that we can only see the other universe is kind of by the the traces they leave um ah in quantum experiments, so to speak, the shape of the edge of our own jigsaw piece. But you know that's evidence nonetheless, I think. um And it's evidence for a kind of thing we're already used to believing in.
00:35:36
Speaker
a world like ours. So putting all of these things together, I think you can make a case that the Many Worlds interpretation is certainly kind of no less bizarre than the other alternative interpretations. The bizarreness just amounts to how much stuff there is. But already our universe with all the stuff we think there is in it would have seemed bizarre to somebody living 2,000, 5,000 years ago. Like how could the world be that big? um ah
00:36:08
Speaker
Isn't that bizarre? Yeah, we don't think it's bizarre now. And so maybe in 500 years' time, the idea that there's many quantum worlds just like our own won't seem bizarre at all. Yeah, yeah. I mean, I'm um suddenly very sympathetic to this view, as as as you'll know. And ah yeah I'm hopeful that more people will be won over. But let's just take it as, you know, canonical, right? like Let's just, let's buy into the, you know, these ever-ashian worlds. Where does that, how does this connect to, it seems like there's a very simple kind of relationship between um Lewis's view and this new one, except
00:36:54
Speaker
We now have motivation to believe in these worlds. We have constraints on these worlds. I said that. I think Lewis had kind of got a lot of stuff right, but was kind of looking for the worlds in the wrong place. And the place he was looking for them was somewhere kind of completely causally cut off from ours with no kind of common mechanism generating all the different worlds. No mechanism for him generating them at all. um And in thinking of them that way, it does make it really hard. You seem to cut off any possible explanation for how those things could be relevant to us, why we should care about them, why it is that we think about automated possibilities so much and we make our plans ah by by thinking thinking them through. And one one reason why
00:37:52
Speaker
Lewis didn't want to kind of look to physics for what those worlds might be like, was because he thought physics itself had to be contingent. if He thought physics itself had to be the kind of thing that varied across those worlds. so if um like
00:38:13
Speaker
you know The actual physics gives us some worlds. For Lewis, those worlds would all be inside one of his worlds because they would all be generated by the physics of one of his worlds. And then he also thought there was going to be other worlds with different physics where quantum mechanics was false. And so quantum mechanics couldn't be an account of those possible worlds. It's not even true about them. And so it was actually that conviction that physics is contingent, that alternative fundamental physics is possible. and that quantum mechanics, even if it's true, could have been false. It's those sorts of convictions that led Lewis to kind of write the kind of options I've described off the table altogether. he didn't He just didn't think that quantum mechanics could possibly account for all the possibilities, because he was convinced that there was a possibility where quantum mechanics was false. right So the question is, why why think that? ah And I think we can just give up on the idea that quantum mechanics could have been false.
00:39:10
Speaker
as easily, really, as we can give up on the idea that mathematics could have could have been false. um We don't think two and two could have been five. um Ultimately, I think we can come to a conclusion where we don't think quantum mechanics could have been false either. Yeah, I think that's one of the most kind of bold claims that but you make, because like I feel like many people will want to say, well, Yeah. Okay. So Louisi had some difficulties in sort of connecting why we care about these alternative worlds, but they really encompassed all of the sort of things that we we do with our modal language because we do say things like, well,
00:39:51
Speaker
ah you know If this world, you know if our physics were different, then you know the this world would would be quite different. There's this whole sci-fi franchises that could be ah based on this. um
00:40:08
Speaker
and And therefore, if we want to claim, I mean, here's the key thing. There's nothing stop us stopping us from saying those things. But if we want to claim that there's some truth to those things, then we'll need to say, you know one of the approaches at least is to is to say, well, actually those alternative um worlds which don't have the physics, which we we do in fact have, do represent something real. And that's how we... make sense of but of that. And that's how we can say, OK, I don't know if the Planck constant were different then. And if it was, I don't know, 10 percent larger, then all these things would follow through. um And that claim becomes is something that's ah a candidate for truth or falsity. On the other hand, you're saying, well, no, OK, all of the all that is
00:41:08
Speaker
there is what is real and what is physically real are kind of co-extensive. They map onto the same set of things. There is nothing that is um real that is not physically real, if I understand great. Yeah, nothing that's possible that's not physically possible. So um yeah the it's it's true that we can imagine a lot of things that are going to turn out not to be possible on this sort of view. Imagine something like accelerating past the speed of light. It's just not possible. There's no quantum universe where something does that.
00:41:48
Speaker
um
00:41:52
Speaker
But actually, I think the possibilities out there in the the quantum multiverse in the space of all the different quantum possibilities are really very various um and very varied. including things that would be kind of apparent violation of laws. um So there's definitely alternative possibilities where a large amount of water kind of spontaneously shoots out of the ocean in a unpredictable water spout with no calm warning and knocks any given bird out of the sky. like Bad luck for that bird. and like any That could happen at any time to any any bird. It would take a kind of
00:42:33
Speaker
pretty unlikely quantum events to do that, but there's there's no impossibility there. And so kind of a lot of the things that we kind of imagine that I don't know you might see in even in sci-fi are going to turn out to be actually possible because they just don't involve violations of Lord of Nature, just some really, really unlikely events. Of course, there are going to be other narratives that do violate the Lord of Nature. um But it's not, I think, automatic that every story we can tell has to correspond to a genuine possibility. At the start, it does not by distinguishing between things that really could happen and things that really can't happen. And that distinction, I think, nobody can really make a good case that that distinction is completely transparent. I mean, some things seem to be possible but aren't.
00:43:26
Speaker
And then some things seem to be impossible, and it turns out that they are actually after all possible. So Kant famously declared that space-time was necessarily Euclidean in its structure, that it it necessarily didn't have any curvature to it. These days, the but the contemporary view of space is that it is curved, um according to our best series of gravity and general relativity. quantum to gravity, there's such a thing as space-time curvature. um So science going by can kind of teach us that things we thought were possible are actually impossible.
Science's impact on possible vs. impossible
00:43:59
Speaker
It can teach us things that we thought were impossible are actually possible. So the boundary between the possible and the impossible shifts over time as we learn more. um And so
00:44:11
Speaker
Even Lewis, with all his possibilities, still can't allow for every hypothesis we might take seriously. like Think about maths. Think about the hypothesis that there's a largest prime number. It turns out to be impossible. um It's actually quite easy to prove that it's impossible. But it's somebody that hasn't come across the proof, but has encountered the constant prime number, is probably going to regard that as they cannot open possibility. and so They might reason, well, if there is a largest prime number, it's got to be pretty big. Lewis can't make sense of that sort of possibility because for him, every Lewis world has the largest has no largest prime number.
00:44:58
Speaker
um And so already certain things that we might want to kind of think about, theorize about, try to imagine, try to reason about aren't going to be found anywhere in Lewis's plurality of worlds. um And so you have to kind of give a different account of what it is to find out that there couldn't be a largest prime number. um that There is no largest prime number. It's not a matter of kind of ruling out the possibilities with the largest prime number because there aren't any. So in the same way, for everything we think we can imagine that um we can't find the possibility for in the quantum multiverse, there are things we might think we can imagine that we can't find the possibility for in Lewis's picture either. For a modal realist, possibility isn't something that we can just directly read off. We can be wrong about.
00:45:57
Speaker
because it is responsive to reality. It's like if there really is a world like that, then it's really possible. And if there isn't, then it's really impossible. And sometimes it might not be obvious which. um So I think this is actually a kind of in the end, an advantage of a view like modal realism, it makes room for understanding how we can be wrong about in our judgments of possibility, and how we can correct them over time in response to evidence. um we might think there's a world of a certain kind and conclude there isn't. But once we get ourselves used to doing that, we should be open to kind of more perhaps surprising hypotheses about what all the possibilities are like, for example, that they are all quantum possibilities.
00:46:43
Speaker
And as you said, it leaves open, um I mean, quantum physics leaves open a lot of possibilities. You mentioned these kind of random water spouts just popping up. um And you nicely characterize or um the difference between those kind of quantum miracles and also thermodynamic miracles and the latter a bit more um common, I guess, but still pretty uncommon. So one could- What if that actually would be that sort of thing? ah Maybe something I don't make was not the best term for them, but something that could happen um just by a fortunate conspiracy of the motions of all the particles of water. And you could you could have a water spout like that launched by some very likely quantum tinkerings, or it could be just um more of a coincidence without any particularly quantum unlikely event giving us. But the feature of quantum mechanics um
00:47:43
Speaker
the feature the twin feature of linearity and unitarity ah just kind of pretty much guarantee that you'll be able to find possibilities like that because it it's basically says kind of for only two possibilities that are possible, there's kind of one in between them that's also possible. um And so you get a kind of fullness of the space of possible of of quantum possibilities. So I like it um very, I mean, just as a A thermodynamic miracle would be me sort of floating up into the air, pushed by lots of air molecules. A quantum one would be... Yes, yes, exactly. that And a quantum one would maybe be just teleporting all of my, all of the tails of the wave function of my atoms, suddenly sort of appearing or like concentrating in a, manifesting in ah and another location of of space.
00:48:41
Speaker
um yeah And both of those are are possible. I've just never encountered them yet. And even beyond this, there might be possibilities to do with, I guess this is an open question, to do with the structure of space time itself that are afforded for within um quantum mechanics. So, well, there's certain things that are kind of unchangeable and I carefully picks the prank constant as one of them. There are other things which, at the moment at least, are up for grabs and, is you know, certain, yeah, certain features of the space which
00:49:24
Speaker
might vary across worlds. It might turn out that, you know, when we have a more advanced theory of, you know, when we have a kind of final theory of physics, if we ever get there, it could rule out those things being otherwise. But in our current state, at least, we can um we can
00:49:43
Speaker
It may be the case. It may be the case that there is a ah there are modal truths about um worlds with slightly different physics is even though quantum mechanics is overarching, correct? Yeah, so I, I and was I was controlling on this point, I think it's important that on any kind of modal realism, we can kind of be wrong about what the possibilities are. It's kind of not up to us what the possibilities are, it's up to reality. It's like which possibilities are really out there? Which possibilities ah does reality kind of really afford us? And ah one of the things I really like about the the view I've been describing as this sort of quantum modal realism um is that it makes those questions about what possibilities there are just be straightforward scientific questions.
00:50:36
Speaker
So kind of, is it compatible with fundamental physics? If so, there's guaranteed to be a possibility out there, was it? Is it incompatible with fundamental physics guaranteed not to be a possibility out there? We don't kind of know all the truths about fundamental physics. And even if we did know the truth fundamental physics, it's not obvious to work out whether um certain things described in like biological language are going to be compatible with um fundamental physics ah or not. So it doesn't give us all the answers, but at least it kind of gives us traction on it. It like it lets science get a grip on the facts about what's possible and what isn't. And I think that's ah kind of crucial because one of the biggest kind of embarrassments for philosophy of ah modality, but possibility and necessity is that nobody can give a halfway plausible account of how we know ah what is what really is and what isn't possible.
00:51:33
Speaker
um and kind of how we can be wrong about it and correct ourselves on it. Philosophers have really struggled to give any kind of plausible account of that. Whereas um the quantum motorist picture just kind of makes it a matter of what quantum possibilities there are. So I've mentioned kind of fundamental physics, like kind of what the particles and so on can do, but it also involves cosmology in a pretty basic way.
00:52:05
Speaker
um So we know that kind of whatever the initial quantum state of the universe was could have produced a world like ours. Like ours is one of the quantum possibilities that derives from whatever the initial quantum state of the universe was. um And we know there are others as well, um probably ones without any life in. The kind of question is, though, kind of just how We are the quantum worlds that are out there. There are ones that kind of differ um from hours in of whether the sun's shining today. There's ones that differ ah from hours in terms of whether the sun was shining 10 million years ago. There's ones that differ from hours in terms of whether there was even the sun at all, whether the sun formed. There are ones that differ from hours in terms of whether any stars formed. I think we're in a position to know that.
00:53:04
Speaker
um Are there ones that differ from ours in terms of whether there was any ever any stable atomic matter? I think probably yes, cosmology does put us in a position to know that. um Are there alternative possibilities with like different numbers of spatial dimensions from ours? Here we start to run into the limits of knowledge in cosmology. um So in some versions of like fundamental physics and cosmology, ah particularly versions of string theory that get called M theory, then the number of effective dimensions of space and time ah does vary across the different quantum worlds. The number of effective dimensions of space in space-time. But there are other accounts of quantum gravity rivals to string theory.
00:53:55
Speaker
where it doesn't, where all of the quantum possibilities have like three spatial dimensions plus one temporal dimension. So there's a big question that we just currently in our current state of knowledge of physics don't know the answer to. Could there have been more than three spatial dimensions? and But it's exactly the kind of question that progress in physics could on the quantum motorist view eventually reveal to us. Because if it turns out that string theory gets vindicated, then we'll know what there could have been more. Maybe we could only have ever survived in a world with three spatial dimensions, but there could have been six often.
00:54:31
Speaker
um Whereas if some other non-string theory approach is vindicated, then we'll find that actually there couldn't have been um six spatial dimensions. All of the different quantum possibilities ah actually have the same number of spatial dimensions. And that sort of progress is kind of within, I mean, maybe we're not going to find out for sure to tomorrow, which is the truth. But, you know, within 50 years, we've got a good chance of like, like coming to a reasonably confident view as to whether string theory is correct or not, I think. And suppose we do, we'll be well we know we'll have a way of settling these deep questions about what what's possible for our universe. um And I love that feature of the view that it makes these philosophical questions about what really could happen
00:55:20
Speaker
directly engaged with real real tangible progress in fundamental physics that we kind of don't
Science and philosophy's interaction
00:55:27
Speaker
know if we're going to get. We just don't know how things are going to turn out. and it it kind of It shifts us away from this picture of metaphysics as this kind of timeless thing that like people 4,000 years ago were in just as good a position to do as we are today. ah No, we're in a really enviable position. on this sort of picture that our ancestors could never have dreamed of having such good evidence about what the real possibilities for the universe are like, as we now do. ah And we're getting it from from fundamental physics and cosmology, um rather than from kind of sitting in an armchair thinking about what we can imagine, which is kind of how philosophers have often approached the problems, working at what possibilities there are.
00:56:11
Speaker
Yeah, yeah, it's it's an exciting time. And how should we I mean, I'm just curious, how how do you think we should talk about, you know, this idea? Some contenders for our best physics claim that, you know, say that they could be alternative, um you know, other other other worlds may have different spatial dimensions. do we say Should we say that's possible? Or should we say that seems possible? Or should we say that's possible according to this physics? But um um and but it might turn out that physics is rolling and therefore it was never possible all along. Absolutely. that's that's the That last way is the way I would put it. um There's really two kinds of possibility that we kind of
00:56:59
Speaker
We know how to distinguish an ordinary talk. We do it we kind of without even noticing that we're doing it most of the time. But that neat they definitely need to be philosophically distinguished and and disentangled. These are epistemic possibilities. What's compatible with what we know or what is kind of an open ah open question for us at any given time. And that can change. So like as we get more evidence, that can rule out certain epistemic possibilities. um Whereas what's really possible in the kind of timeless sense, like what the ways the universe could have turned out like, that doesn't change over time. Though as time goes by, some options may no longer be there, like live options either. And it's not a matter of kind of what evidence we've got, it's a matter of kind of how the world is in itself, what what possibilities it it affords. um but because we can But we can theorize both about what's going to happen in our world,
00:57:57
Speaker
and about what the whole space of possibilities is like. ah And when we theorise about what the whole space of possibilities is like, um those different alternatives that we're kind of weighing up, taking seriously, they can only be alternative epistemic possibilities. They can't be alternative genuine possibilities because what we're thinking about is which alternative genuine possibilities there are. and It's not like a genuine possibility that there'd be more genuine possibilities than there in fact are.
00:58:28
Speaker
um So I think of it as something like our degrees of belief and the chances. So there's real probabilities out there in the world. Like if you've got a, you you hand me a die and say, you roll this die. And I think, well, it's either fair or it's biased.
00:58:50
Speaker
And I'm not sure which. And I roll it 10,000 times and it lands six, exactly one sixth of the time. And I conclude it's actually fair. ah So what kind of it it was fair all along, but maybe if you were a very suspicious character, I might have started off believing it was biased. So my degree of belief about the way it would turn out differed from the way like the real chance of it landing a certain way. But over time, my degree of belief about the way it will turn out kind of comes into alignment with it the real chance that I see over a long period of time that it is in fact ah a fair die.
00:59:28
Speaker
um And I think of the objective possibilities of and the subjective possibilities as kind of like that, that the epidemic possibilities are kind of how things could be for us. And the more, as far as we know, and the more we know, the more we'll be able to bring what we regard as a serious possibility in line with what really is a serious possibility. And in some kind of ideal limit, if we knew everything, then we would be certain that impossible things wouldn't happen. And we would like have our confidence in various things happening, exactly matching the physical probability of all those things happening. But we're never going to reach that sort of knowledge. So we're always going to have those sorts of two possibilities kind of relevant to our thinking. There's the stuff which is possible because we can't rule it out. There's the stuff which is possible because it really can happen. And so what we kind of
01:00:26
Speaker
doing when we learn about what really can happen is ruling out various epistemically possible hypotheses that aren't genuinely possible about what is genuinely possible. So we're improving our knowledge of the genuine possibilities by discounting the scenarios which seemed possible but turned out not to be. yeah Yeah, yeah, I think that and it is i mean you do it is kind of tricky to keep track of those things. But I think we do it a lot of the time, especially and it's kind of we do it most easily when like playing games or when when gambling or whatever, ah we're not inclined to kind of unless we're kind of very bad at the game, we're not inclined to mix up our own expectation with the like real chance of a given outcome.
01:01:17
Speaker
but the two separate sources of uncertainty, kind of two separate kinds of uncertainty. um I may not know who's going to win this hand of poker, but who's going to win is already fixed by the cards. There's uncertainty in one sense, but no uncertain but there's no uncertainty in the other. Yeah, very good. I realised one thing we, and perhaps something that's been suggested but but not been made explicit is, why do we
01:01:47
Speaker
Again, why do but how do these actual Everett worlds around us, um how do they relate to what we should care about in our world? And you know do they solve this problem of regrets, for instance, or, um you know again, within the actual world that we're in, there's just going to be one foot way that things are. so how do we make sense of, again, this idea that it seems that things, you know, we want to talk about things having alternate possibilities, and there are these other worlds there, but in the kind of strand we're in, it seems there's only going to be one way that things are going to be. Yeah. um So this is ah this is tough. It's not easy to explain why we should care about existed possibilities.
01:02:42
Speaker
in the same way that it's not easy to explain why we should care about the physical chances associated with a dice, with a dice that we're playing with. I mean, why is it that if this particular die is weighted towards the sixth side, that we should expect that it will land sixth more than we should expect it will land one? It's really hard to give a clear philosophical answer to that question, why it is that the chances kind of compel our beliefs to follow them. Some people have said it's actually an impossible to solve philosophical problems. It would be like solving a human problem of induction and saying why the future should resemble the past. We would have to do that if you're really going to give a good explanation of why we should um defer to the the chances of the known the known chances of a a gambling setup. Nonetheless, it is obviously the right thing to do.
01:03:38
Speaker
to be more confident on a fair die, of course we should be more confident that it's going to be one to five than that it is going to be six. It's like five times more likely to be one to five than it is to be six if you roll it once. um ah How do we know that? Good question. Do we know it? Definitely we do. ah so Somehow or other those chances are relevant. And for the quantum modal release, those chances just are like the measure of the alternative possibilities. So the alternative possibilities are relevant, kind of whether we like it or not. And we're going to have, you know, we may not be in a very good position to explain how that could be so, but nonetheless, we should kind of live with it. I mean, I think the the the kind of start of an explanation is if along the following lines.
01:04:27
Speaker
ah
01:04:30
Speaker
If the many worlds view is correct, then there's going to be an awful lot of people just like us.
Predicting outcomes in the multiverse
01:04:35
Speaker
which have different outcomes from one that in fact is going to have. And if we want to kind of predict the future um and work out what result we're in fact going to see, we need to take into account there's a whole lot of people that we can't rule out the hypothesis we might be there that are seeing these different results. So how should we react to a situation where we know that there's a lot of people who currently can't rule out us being any of them and those all see different results? How should we
01:05:04
Speaker
react. If we knew exactly which person we were going to be, we'd know exactly what result we're going to see. We wouldn't need any uncertainty. But we can't know that because they're like all indistinguishable up to the present time. So we have to kind of divide our confidence somehow over us being this person that's going to see one thing or this person that's going to see the other. um you know If it was a quantum dice roll with like six different outcomes, we'd want to consider all the people that are going to see one, all the people that are going to see two, all the people that are going to see three, all the people that are going to see four, all the people that are going to see five, all the people that are going to see six. And all of those people, as of now, are completely indistinguishable from each other. So nothing you can look at in the world right now is going to tell you which one of those you're going to be. So the only thing available to set your confidence by is
01:05:56
Speaker
what is like physical facts about those worlds. And the only available option are the quantum mechanical weights of the branches or the probabilities associated with each outcome. And there are various kind of philosophical arguments to give that kind of if you're going to set your degrees of belief at all, you should set them following the quantum weights because they're kind of the only good candidates for something to set your beliefs by. Some people think that settles it. I don't really think that settles it because maybe there is always like, there's no rational way to set our beliefs or we should just like shrug. I don't think there's any kind of um argument that's gonna say you're irrational if you don't set your beliefs a certain way. Which is partly the the lesson of the of s skeptical arguments in general, but in particular of Hume's skeptical argument against induction. There's gonna be no way of persuading a skeptic that they have to set their beliefs in a given way.
01:06:54
Speaker
But I think in a quantum universe, what we can show is like, if you're going to make us a plan about how to set your beliefs, it had better be the plan that goes with the quantum way that takes account of the distribution of um all the alternative possibilities that there are. So you take the alternative possibilities into account that way by taking into account the probability distribution over them when you're doing your planning. And the reason for that is ultimately that as far as you know, you could be any of them. You don't know which one you're in. So it's that lack of knowledge. You don't know which world you're in. combined with the inability to just like check which world you're in directly that kind of leads us into this situation where we have to to, if we're going to like have any kind of coherent belief setting recipe for the future, we have to set it the way we do. so So the world's kind of getting indirectly in that sort of way. don't get they They don't become the things we care about because we can see them.
How other world facts shape actions
01:07:51
Speaker
But they become the kind of things we can share about because it's facts about them which shape how it is that we go about seeking stuff we do want in our world. Yeah, I think that that gives a clear idea of um of why one might be motivated. um You know, like you said, there may no may not be a um
01:08:23
Speaker
silver bullet argument which links behavior or rationality and um the way that we act ah with respect to chance. How does this argument work with respect to, do we can we use the same sort of argument to think about counterfactuals, things that we we could have done, or does it become a little bit harder because there you say, well, um No, it it seemed like, you know, although it seemed like I could have got up earlier, ah actually, I am the one in this branch and, you know, that was always a different or it is just a different world where someone like me got up earlier. um And therefore, you know, why should I care about what happened there? Because now it's not
01:09:19
Speaker
a question of me um not knowing you know about the the kind of future development of things. And and like I know that I didn't get up earlier. um So it seems ah a little bit harder to kind of understand where the regret comes in. um But on the other hand, one might say, well, actually, that person was just like me and I can regret that I am not that person, right? Like, why did it turn out that I wasn't that
Luck in quantum possibilities
01:09:51
Speaker
person? it would Is that the kind of gloss that of of the argument that works? Yeah, I mean, ultimately, I think there's kind of been no explanation for why things go one chancey way as opposed to another chancey way.
01:10:09
Speaker
um So you toss a quantum coin, it lands heads. Why did it land heads and not tails? There's no good answer to that question. There simply is a kind of explanatory gap in reality. It lands heads in one branch, it lands heads and not tails in another. You ask the person in one branch, why did it land heads? um the equivalent to asking them, why are you in this branch and not in that branch? And there is just no answer to that. There's no kind of guarantee that there has to be ah ah like ah an answer to every why question and certain kinds of why questions on this view just don't have answers for perfectly good reasons. Of course, there's a lot of why questions you can answer. Why were the chances even?
01:10:58
Speaker
were because of symmetries of the the physical set situation involving the quantum coin, most likely. um Why did the coin land at all? Well, because it was set up and tossed. ah ah Why did it land heads as opposed to know not landing? Well, there was a chance of it landing heads, but there was no chance of it not landing. um a And you can even kind of say, well, kind of if it was a bias call, it was more likely to lend heads than tails. Sometimes unlikely things happen. And you know there's ultimately no explanation for why one person gets lucky and another person gets unlucky. just That's just luck. That's the nature of luck.
01:11:44
Speaker
um And so there's still luck in this world. There's kind of no luck in in this picture. There's no luck in how the entire set of quantum possibilities develops over time. But there there is unavoidable luck in like where you find yourself in that. um that's a say that's That's the nature of luck. um Some people will be in better spots than others if there's a lot of people distributed over spots. yeah um yeah If anything, I guess it really sharpens the our understanding of of luck in that you know terre many there are many um duplicates of me, or however you want to call them, who are having exactly the same experience right now, but will have very, very different diverging experiences in the future. At some future point, I could look back and say, well right like That could have been me, right? um And really feel it because, you know, we were so um indistinguishable um prior to a certain, I don't know, chance quantum event, which completely changed the parts of our world.
01:12:57
Speaker
It's always hard thinking about kind of kind of agency in physics because i mean there's a notorious like kind of free will and determinism sorts of questions. There's also the question of whether like adding indeterminism seems to help at all. ah But I think the the way to understand kind of ah what one's doing when one makes a choice in the a quantum multiverse is this kind of deciding how one wants to set the chances. um So it's it's a bit like deciding, you know, seeing that a coin is going to be tossed and deciding kind of which side to align yourself with. um So if you think that the chance of it coming up heads is um higher than the chance of it coming up tails, then
01:13:53
Speaker
you'll think the chance of finding yourself on a heads branch is higher than finding yourself on a tails branch and so um you'll want to take action such as betting on heads if you have to bet which will kind of give you the payoff in the higher proportion of the branch because you think you're more likely to be find yourself on that side so you're more likely to find yourself with the payoff. um So ultimately, kind of decisions are all about the the chances. You want to kind of maximize the chance of finding yourself in a world with a good outcome. And to do that, you need to know what the chances are, and and ideally to be able to kind of control them to some extent um as well.
Influence of multiverse on risk-taking
01:14:40
Speaker
Yeah.
01:14:41
Speaker
but you want to You want not just to be yourself on the world with a good outcome, but ideally you want um to minimize the bad outcomes completely. Yeah. I guess my final question and maybe relates to this train of thought is, is there a way in which this conception of of of the world, and such a a rich world so full of possibility, does it affect how you kind of think about yourself, not just you know the the papers you write as a philosopher, but the way that you, I don't know, think about this incredible it existence we have. It's tricky. um Some people very much say that it does, that like we you should um
01:15:34
Speaker
I mean, some people will use this as an objection to the the many-world view or the quantum motorist view. They say, well, if the totality of everything is going to be the same, whatever I do, then there's no point doing anything. So if I accepted this view, I would become apathetic or nihilistic or something like that. I wouldn't be bothered to do anything because I think I couldn't change the totality of everything. But to me, it seems somewhat, I don't know, almost narcissistic to think that you what you do only matters insofar as it affects the totality of everything. um Maybe none of us can affect the totality of everything, but we can still kind of situate ourselves with respect to things that we value.
01:16:10
Speaker
um And so I think it makes perfect sense to kind of continue to act. And in some sense, Like if this mini world view is to be ah like a serious contender, if it's to be taken seriously, of course it kind of can't change our world view too much because we know how to live in a world like this. We know the basic parameters of our of our external world. We know what corresponds to like successful life engagement with them. We know like what makes sense to do if you want, if you're hungry is to go and get something to eat. We just have so much like straightforward
01:16:49
Speaker
secure knowledge of how to interact with our world. but Any theory that said that knowledge was all nonsense just couldn't be right. There's a sense in which like if the many worldviews are right, it's been right all along. So all along, what we've been doing is living in one of many quantum worlds, interacting with other creatures inside our quantum world.
Everyday life and Many Worlds view
01:17:10
Speaker
So it kind of has to make sense that in a quantum world, you should continue to live pretty much the way we do. So I think it would be wrong to expect this sort of view to to revolutionize too much. I think it can maybe give you certain reflective, make available certain sorts of reflection. So for me, one thing it has, I think led to is a reduction in my levels of risk taking over time, because it's very vivid to me
01:17:40
Speaker
vi ah the thought that, you know, even if I take a risk and get lucky, there are people um in worlds that really exist that were just like me up to that moment that took that same risk, did not get lucky, and they suffered and maybe their loved ones suffered too. And though I kind of got lucky and turned out not to be one of the unlucky people with unlucky loved ones, nonetheless, those people are ah real, physical and unhappy. And to the extent that you can control the risks, you can control whether there even are such unlucky people. So to the extent that you can choose to reduce your risk, you can you can choose to reduce um the amount of misery. And if you feel like if you take a risk and get away with it, then that's like,
01:18:35
Speaker
you know that's ah that's a no-loss thing, nobody suffers at all, you might be more more open to risk taking. But I think that that sort of thing is very much a kind of a personal judgment thing. I think it might even be, according to my official view, irrational, to be moved by that sort of reasoning. and People are very irrational, and like i I'm not ashamed of of that. But I think kind of Perhaps the right thing to say is that a purely rational person wouldn't change their actions at all on coming to be convinced that the Many World View is correct. But because we're not purely rational creatures, we're emotional humans, probably some of us will change a bit here and there. People do have strong emotional reactions to it, which suggests that you know people do do care about whether the Many World View is true or not. But I think
01:19:29
Speaker
in terms of whether it would be rational to change your behavior, I think my official view is no. That's fine. I think it's it's good to... This is the forum where you can give your unofficial view and say, well, actually, you know knowing knowing that these things are real, it not only changes the bets that I'm going to place, but whether I roll the dice in the in the first place or and know which dice I roll, I suppose.
Everett's military work vs. his theory
01:19:58
Speaker
i mean ah i it It makes it harder for me to kind of quite ever understand Everett himself, the originator of the many worlds view, um who ah of believed in the reality of all these many worlds.
01:20:17
Speaker
um And yet simultaneously ah had a career in military research doing projects, including one on how to maximize civilian death rates in nuclear weapons campaigns. um He must have known that if his theory was right, kind of doing this was effectively ah killing an awful lot of civilians in an awful lot of possible worlds. He didn't seem to be bothered by that. Maybe he was just more rational than we are. But is a little bit his his his choices were certainly somewhat his life choices were certainly somewhat off-putting, but I don't think they were necessarily kind of irrational by his own lives. It really just depends on on what you care about.
01:21:06
Speaker
um And believing in the many world view isn't going to turn you into a nice person. It's not going to make you care about things that Maybe kind of you ought to care about things that really matter, but it's going to tell you kind of what it is to care about something, at least. um So yeah, I guess the thing the thing that ties i've I notice that ties together different kind of adherents of the Many Worlds approach is like kind of intellectual-mindedness.
Open-mindedness and Many Worlds understanding
01:21:47
Speaker
it is just a very different looking theory. Even though it says, you know, how things have always looked is just how things in fact look in a quantum multiverse. The way in which things get to look that way is not the way we would have expected. We didn't expect to have encountered the world we see around us in virtue of living as part of a quantum multiverse. So there's definitely a lot of surprises in there. So you have to be kind of quite open minded to surprising theories to take it seriously. um But you know if there's a if there's a lot if there's a if there's something big and hard to explain, then you might need something quite surprising to explain it with. Indeed.
01:22:33
Speaker
Yeah, out this has been a really wonderful discussion. And I know you're you're you're off to do more um theorizing and thinking this afternoon. um So yeah, I just want to say thank you again. um And yes, are there any places I mean, I should mention, I'll mention your book at the beginning. So um on contingency. I've forgotten the full title. It's called The Nature of Contingency, Quantum Physics as Modal Realism. Yes, yeah. um Anywhere else that people should um can find you? So there's ah there's a book coming out soon called Modal Naturalism.
01:23:19
Speaker
science and the modal facts that I've co-written with Amanda Bryant. That's about how science can reveal alternative possibilities. It's not so much about what it is to be a possibility, so much of which possibilities there are and how science gets a grip on that. um
01:23:34
Speaker
And a I've also got a, this volume coming out later this year called Levels of Explanation. ah which is about all the different kinds of explanatory structures all over sciences, philosophy, maths, how we can explain the world at all different levels. Those are the kind of two main projects I've been ive been working on um most recently. ah
01:24:08
Speaker
but Yeah, I think that would be um good to the ones to mention. I look forward to that book coming out and I think that could be another good discussion as I realize yes. We haven't touched upon all this work that you've done on just general how metaphysics and and and physics in engaged. But I think this has been a great example of one place where, in a sense, metaphysics and physics completely merge. And what is metaphysical possibility is just physical possibility. So yeah, but yeah my my view is a pretty, pretty straightforward. There's, you know, these things overlap intensely. And the idea to look for like a kind of sharp dividing line between physics and metaphysics is
01:24:44
Speaker
is is kind of a pointless endeavor. My computer has beeped to tell me it's low battery, so the timing is a little rare.
01:25:00
Speaker
Thank you for listening. You can find our Wilson at AlistairWilson.org. unlike team, there is an I, an Alistair, or just such for Alistair Wilson philosophy. His book that we've been talking about is The Nature of Contingency, Quantum Physics as Mobile Realism. If you enjoyed this podcast, or even if you didn't, please share your approbation or disapproval with your friends, enemies and acquaintances. Until next time, thanks for listening.