quantum mechanics

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multiverses
Did well, I guess.

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Alastair Wilson
that

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multiverses
um Hi, Al Wilson. Thanks for joining me on on multiverses.

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Alastair Wilson
Thanks for having me on.

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multiverses
um I’d like to start 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 modality?

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Alastair Wilson
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.

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multiverses
you

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Alastair Wilson
So there are various kinds of alternative possibilities. There are like 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. 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.

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multiverses
Okay, very good.

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Alastair Wilson
So when we say that the world’s modally rich, we say it’s not just made up of what actually happens, it’s kind of full of possibilities as well, um unrealized ones.

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multiverses
Yeah.

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multiverses
Yeah. And and um 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.

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Alastair Wilson
and

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multiverses
Things could have gone otherwise. um So yeah, we’ve got a fancy label for it. um And what to what do philosophers want to say about these things? like yeah know What are the kind of approaches that one can take to modality? um

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Alastair Wilson
but it’s like I’d say, philosophically, it’s always been a puzzle. um but Time has 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.

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multiverses
you

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Alastair Wilson
um But we only ever see one possibility for the way things could turn out, the one that we ah ourselves and inhabit. And we don’t ever see, we can’t ever see directly the other alternative possibilities. So we can kind of reason about them, think about them, but we never kind of bump into them. um And so that what 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.

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Alastair Wilson
Or are they just things we make up? Are they just some kind of 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. um 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 s skeptical view that says alternative possibilities aren’t aren’t real at all.

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Alastair Wilson
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.

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multiverses
Yeah.

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Alastair Wilson
The alternative possibilities are imaginary.

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multiverses
Yeah. 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 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 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 realised.

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Alastair Wilson
Thank

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multiverses
Yet we do have this strong feeling that

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Alastair Wilson
you.

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multiverses
that that needn’t be the case. um And so I guess the philosophy here is trying to maybe connect with and explain um that, I don’t know, folk vision of of possibility.

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Alastair Wilson
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,

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Alastair Wilson
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.

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Alastair Wilson
um along with that kind of 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 kind of

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Alastair Wilson
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?

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Alastair Wilson
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.

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multiverses
Uh-huh. Uh-huh.

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Alastair Wilson
But we do i take that to be kind of data for philosophers to explain.

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multiverses
Mm hmm. 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 throw 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 and the and the sort of the clue is in the name.

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multiverses
He was trying to ground or make yes make these modal claims claims about real things. and But perhaps you can give a description of of of how his project was worked.

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Alastair Wilson
Yeah.

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Alastair Wilson
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 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

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Alastair Wilson
there’s alternative possibilities ah right there in the the basic structure of the world and are thinking about the world that need a proper theory to account for them. And proper theories should be, I think, things Lewis realists. 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,

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Alastair Wilson
kind of went huge, kind of kind of expanded out 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 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.

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Alastair Wilson
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.

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multiverses
Uh huh.

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Alastair Wilson
In some sense, these other universes are just more of the same.

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multiverses
Uh huh.

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Alastair Wilson
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 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 theming kinds of things um of a wholly different kind.

00:10:51.69
Alastair Wilson
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.

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Alastair Wilson
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. ah Some people think even Lewis couldn’t really have believed it. And I don’t believe it, but I think that it ah is right, it stands a chance at least of being right about in some important respects. oh

00:12:12.11
Alastair Wilson
So I like the kind of different version of modal realism, which I guess we’ll come to too shortly.

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multiverses
Yeah.

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Alastair Wilson
um But I think kind of Lewis was kind of looking in the right, um in the wrong sort of place for the right kind of theory.

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multiverses
Yeah.

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Alastair Wilson
yeah

00:12:28.96
multiverses
Yeah. And as you say, I mean, 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, okay, well, I don’t know.

00:12:41.94
Alastair Wilson
i

00:12:49.21
multiverses
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 or um you know there are some there is just some hidden chance to other things.

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Alastair Wilson
It’s not a thing. It’s not a thing.

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multiverses
um

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Alastair Wilson
Yeah, I mean, I think what um yeah yeah the kind of the idea of essences goes along, which will fix the bill if youre 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.

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multiverses
Right.

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Alastair Wilson
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.

00:14:02.03
multiverses
Yeah.

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Alastair Wilson
ah And Lewis’s is kind of a very transparent view compared to a lot of the other ones and in the table.

00:14:10.62
multiverses
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. um Or at least my chances would have been boosted by 50% or something.

00:14:34.29
Alastair Wilson
Yeah.

00:14:35.20
multiverses
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. But you can If you assume the godside view, then you could say, OK, 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 um 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 ground our ideas of probability.

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Alastair Wilson
Yeah.

00:15:14.68
multiverses
whoops

00:15:15.92
Alastair Wilson
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 oh 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.

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multiverses
Right.

00:15:47.21
Alastair Wilson
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 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 a 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 of those kinds. um So Lewis actually

00:16:30.53
Alastair Wilson
um is keen to defend that part of the view, that there’s kind of no preferred ah measure 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.

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multiverses
Mm-hmm. Mm.

00:16:49.48
Alastair Wilson
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 um

00:17:03.18
Alastair Wilson
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 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.

00:17:36.21
Alastair Wilson
ah

00:17:38.70
Alastair Wilson
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 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.

00:18:09.15
multiverses
Right, good, yeah. So, and I think, I mean, let’s 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

00:18:33.76
Alastair Wilson
Yeah.

00:18:35.67
multiverses
suddenly expands the set of things that I believe in to encompass all these ah you know counterparts of me and 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 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?

00:19:06.71
Alastair Wilson
Yeah.

00:19:10.87
multiverses
um

00:19:11.19
Alastair Wilson
Yeah, it’s true. This is a tough um ah tough kind of line to to try to hold. I think it… I’m 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 this, about automated possibility, so much as wanting to understand ah what we do when we think with them.

00:19:43.28
Alastair Wilson
ah because the argument might go, it’s no coincidence that we’ve evolved to 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. ah and And so that’s a really deep part of our lives, our engagement with the world.

00:20:12.14
multiverses
Mm.

00:20:15.09
Alastair Wilson
Something has to explain why we think that way.

00:20:17.38
multiverses
Mm.

00:20:18.02
Alastair Wilson
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 food 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 kind of 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.

00:20:51.03
Alastair Wilson
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.

00:20:51.90
multiverses
Mm hmm.

00:21:02.47
Alastair Wilson
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 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.

00:21:45.74
multiverses
Perfect. I mean, and I think that brings us, you know, straight to Everatian quantum mechanics, um which is, you know, as you described, 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 at at ah um as well. Yeah, maybe give us a reminder of of of the kind of core claims of um Everett and and and and his formulation or interpretation of of quantum mechanics.

00:22:16.18
Alastair Wilson
Yeah.

00:22:24.25
Alastair Wilson
Right. So the the phrase Everettian is kind of what a lot of philosophers and physicists, philosophers of 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. um 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 ah 1950s when he developed this interpretation was more that there should not be any collapse of the wave function.

00:23:02.00
multiverses
Right.

00:23:03.06
Alastair Wilson
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 of 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 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.

00:23:36.09
Alastair Wilson
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 everything.

00:23:43.67
multiverses
Mm.

00:23:50.29
Alastair Wilson
um And so there’s a whole kind of tangle of different theories, different ways of understanding quantum mechanics there. 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.

00:24:09.65
multiverses
Mm hmm.

00:24:10.59
Alastair Wilson
But we can kind of infer their existence from the results that we get of quantum experiments done in our world.

00:24:21.42
Alastair Wilson
There’s 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. ae 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.

00:24:47.54
multiverses
Right. Yeah, and I think just to um i mean’ 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 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,

00:25:31.61
multiverses
um this this mathematical thing, the wave function, ah doesn’t evolve smoothly and nicely as it normally does, 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. um And it it wasn’t, you know, firstly, it’s not clear what a measurement is, what defines that. um And, you know,

00:26:05.17
multiverses
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.

00:26:40.47
multiverses
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.

00:26:50.08
Alastair Wilson
Yes.

00:26:51.82
multiverses
Or maybe you always had two worlds, one where it was going to go through one slit and another it was going to go through another split ah slit. um So yeah I think I just want to remind people that

00:27:04.77
multiverses
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. um

00:27:29.13
Alastair Wilson
Yeah.

00:27:31.68
Alastair Wilson
so

00:27:34.31
Alastair Wilson
um ah um

00:27:46.49
multiverses
Well, perhaps I can say here, I do really like your way of thinking about, um in your book, um 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.

00:27:48.69
Alastair Wilson
but

00:28:10.44
multiverses
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.

00:28:20.40
Alastair Wilson
Yeah.

00:28:23.98
multiverses
And from that we can infer that it’s sort of created a whole jigsaw. um pat I don’t know if you can kind of cash that out um further because I thought that was a beautiful analogy.

00:28:31.93
Alastair Wilson
Yeah. Well, 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 can make sense of um why someone would make a whole ah puzzle.

00:29:10.10
Alastair Wilson
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.

00:29:18.91
multiverses
Mm hmm.

00:29:20.60
Alastair Wilson
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.

00:29:53.46
Alastair Wilson
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 things 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.

00:30:10.54
multiverses
Hm.

00:30:10.87
Alastair Wilson
This world isn’t mysterious. 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,

00:30:44.72
Alastair Wilson
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 with 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.

00:31:08.86
multiverses
Uh

00:31:10.28
Alastair Wilson
They found out ours is not the only galaxy. um Ours is not the only concrete universe is really not very big a step beyond that.

00:31:14.18
multiverses
-huh.

00:31:19.09
Alastair Wilson
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 universes kind of by the the traces they leave um 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.

00:31:35.02
multiverses
Mm hmm.

00:31:37.87
Alastair Wilson
um And it’s evidence for a kind of thing we’re already used to believing in.

00:31:42.82
multiverses
Mm hmm.

00:31:42.94
Alastair Wilson
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

00:32:15.13
Alastair Wilson
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.

00:32:25.67
multiverses
Yeah, yeah. I mean, I’m 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. um You know, where does that, how does this connect to, and it seems like it’s a very simple kind of relationship between um Lewis’s view and this new one, except we now have motivation to believe in these worlds.

00:33:05.11
multiverses
We have strengths on these worlds.

00:33:05.19
Alastair Wilson
Yeah, so 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. um And the place he was looking for them was somewhere kind of completely causally cut off from ours with no kind of common ah mechanism, generating all the different worlds, ah no mechanism for him generating them at all. um And, in thinking of them that way, it does make it really hard.

00:33:36.42
multiverses
Uh huh.

00:33:36.95
Alastair Wilson
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 by by thinking thinking them through.

00:33:39.78
multiverses
Uh huh.

00:33:52.85
Alastair Wilson
And one one reason why kind of 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.

00:34:14.89
multiverses
Right.

00:34:15.77
Alastair Wilson
So if um like

00:34:19.91
Alastair Wilson
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.

00:34:24.79
multiverses
Uh huh.

00:34:30.31
Alastair Wilson
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.

00:34:37.33
multiverses
Uh

00:34:40.67
Alastair Wilson
It’s not even true about them.

00:34:42.59
multiverses
huh.

00:34:43.48
Alastair Wilson
And so it was actually that conviction that physics is contingent, that alternative fundamental physics is are 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 option 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.

00:35:07.67
multiverses
right

00:35:08.33
Alastair Wilson
But the question is, why why think that?

00:35:08.33
multiverses
so what

00:35:11.28
Alastair Wilson
ah And I think we can just give up on the idea that quantum mechanics could have been false. 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.

00:35:27.47
multiverses
Right. 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, OK, so Lewis, he 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, ah you know,

00:35:50.21
Alastair Wilson
Thank

00:35:58.73
multiverses
If this world, you know, if our physics were different, then, you know, this world would would be quite different.

00:35:58.83
Alastair Wilson
you.

00:36:05.92
multiverses
There’s this whole sci-fi, you know, franchises that could be ah based on this. um

00:36:14.64
multiverses
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, okay, I don’t know if the Planck constant were different then, and if it was, I don’t know, 10% 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, okay, all of the, all that is,

00:37:14.80
multiverses
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 correctly.

00:37:32.81
Alastair Wilson
Yeah, nothing is possible that’s not physically possible. So um the it 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.

00:37:36.31
multiverses
Yeah.

00:37:46.77
Alastair Wilson
Imagine something like accelerating past the speed of light. It’s just not possible. There’s no quantum universe where something does that. um

00:37:58.38
Alastair Wilson
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 kind of 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.

00:38:24.61
multiverses
Mmhmm.

00:38:31.92
Alastair Wilson
like Bad luck for that bird. um like any That could happen at any time to any any bird. It would take a kind of pretty unlikely quantum events to do that, but it 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 the Lord of Nature, just some really, really unlikely events.

00:39:02.51
multiverses
Mm hmm.

00:39:04.34
Alastair Wilson
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.

00:39:17.38
multiverses
Right.

00:39:17.47
Alastair Wilson
At the start, I started off 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.

00:39:32.67
multiverses
Uh

00:39:32.81
Alastair Wilson
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.

00:39:38.09
multiverses
-huh.

00:39:46.57
Alastair Wilson
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, in 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. 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.

00:40:11.99
multiverses
Yeah.

00:40:14.33
Alastair Wilson
um And so Even Lewis, with all his possibilities, you 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 in somebody that hasn’t come across the proof, but has encountered the constant their prime number, it’s probably going to regard that as they cannot open possibility.

00:40:49.53
multiverses
Mm hmm.

00:40:50.17
Alastair Wilson
And so they might reason, well, if there is a largest prime number, it’s got to be pretty big.

00:40:52.89
multiverses
Mm hmm.

00:40:54.37
Alastair Wilson
um And Lewis can’t make sense of that sort of possibility, because for him, every Lewis world has a largest, has no largest prime number.

00:41:00.19
multiverses
Mm hmm.

00:41:04.56
Alastair Wilson
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 ah 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.

00:41:36.88
Alastair Wilson
um 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.

00:42:00.35
multiverses
Mm hmm. Mm hmm.

00:42:01.75
Alastair Wilson
We can be wrong about it. 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.

00:42:13.42
multiverses
Mm hmm.

00:42:13.88
Alastair Wilson
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.

00:42:22.56
multiverses
Mm hmm.

00:42:29.66
Alastair Wilson
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.

00:42:49.30
multiverses
And as you said, it leaves open, and 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 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

00:43:14.99
Alastair Wilson
Yeah, I mean, a water spout 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 kind of a fortunate conspiracy of the motions of all the particles of water.

00:43:27.38
multiverses
Yeah.

00:43:31.39
Alastair Wilson
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 events.

00:43:42.48
multiverses
Yeah.

00:43:45.27
Alastair Wilson
giving us.

00:43:45.46
multiverses
Yeah.

00:43:45.67
Alastair Wilson
But the feature of quantum mechanics, um the feature the twin feature of linearity and unitarity,

00:43:53.03
multiverses
yeah

00:43:53.20
Alastair Wilson
oh just kind of pretty much guarantee that you’ll be able to find possibilities like that. Because it’s it basically says kind of for only two possibilities that are possible, there’s kind of one in between them that’s also possible.

00:44:05.84
multiverses
Yeah, right.

00:44:05.98
Alastair Wilson
um And so you get a kind of fullness of the space of possible of quantum possibilities

00:44:11.78
multiverses
So, for example, I could um very, I mean, just as a ah thermodynamic miracle would be me sort of floating up into the air pushed by lots of air molecules. A quantum one would be

00:44:23.23
Alastair Wilson
Yeah, some sudden unlikely gusts of wind.

00:44:25.51
multiverses
Yes, yes, exactly.

00:44:27.29
Alastair Wilson
Yeah.

00:44:27.34
multiverses
um And a quantum one would be 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. um

00:44:47.59
Alastair Wilson
Yeah.

00:44:49.28
multiverses
And both of those are are um 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

00:45:08.35
Alastair Wilson
Yeah.

00:45:12.21
multiverses
carefully picks the Planck constant as one of them. There are other things which, at the moment at least, are up for grabs and, you know, certain, yeah, certain features of the space which 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.

00:45:42.34
Alastair Wilson
yeah

00:45:43.12
multiverses
But in our current state, at least, we can um we can

00:45:49.69
multiverses
It may be the case. It may be the case that there is a there are modal truths about um worlds with slightly different physics, is even though quantum mechanics is overarching in E, correct?

00:46:03.12
Alastair Wilson
Yeah, so i i i was I was controlling on this point, I think it’s important that on any kind of mode of 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?

00:46:20.16
multiverses
Mmhmm.

00:46:21.89
Alastair Wilson
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. So is it compatible with fundamental physics? If so, there’s guaranteed to be a possibility out there with it in. Is it incompatible with fundamental physics? Guaranteed not to be a possibility out there. We don’t 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 biological language are going to be compatible with um fundamental physics or not.

00:47:13.57
Alastair Wilson
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 modality of 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. um and kind of how we can be wrong about it and correct ourselves on it.

00:47:44.98
Alastair Wilson
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.

00:47:58.46
multiverses
Uh

00:47:59.35
Alastair Wilson
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.

00:48:04.22
multiverses
-huh.

00:48:11.57
Alastair Wilson
um So we know that kind of whatever the initial quantum state of the universe was, it could have produced a world like ours. like Ours is one of the quantum possibilities that derived from whatever the initial quantum state of the universe was.

00:48:24.51
multiverses
Mm hmm.

00:48:28.43
Alastair Wilson
um And we know there are others as well, um probably ones without any life in.

00:48:37.36
Alastair Wilson
The kind of question is, though, kind of just how weird 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 in 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.

00:49:09.90
Alastair Wilson
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,

00:49:41.83
Alastair Wilson
then the number of effective dimensions of space and time ah does vary across the different quantum worlds.

00:49:50.30
multiverses
Mm hmm.

00:49:51.65
Alastair Wilson
The number of effective dimensions of space in space-time. But there are other accounts of quantum gravity rivals to string theory, 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.

00:50:24.89
multiverses
Mm hmm.

00:50:25.18
Alastair Wilson
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 of them. 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 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.

00:51:09.58
Alastair Wilson
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 directly engaged with real real tangible progress in fundamental physics that we kind of don’t know if we’re going to get.

00:51:20.48
multiverses
All

00:51:33.17
Alastair Wilson
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.

00:51:38.76
multiverses
right.

00:51:46.00
Alastair Wilson
ah No, we’re we’re in a really enviable position on this sort of picture. too you know 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. um 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 problem, working at what possibilities there are.

00:52:16.56
multiverses
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 there that there 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?

00:52:46.95
Alastair Wilson
Right. Right.

00:52:49.22
multiverses
um um and But it might turn out that physics is rolling and therefore it was never possible all along.

00:52:53.42
Alastair Wilson
Absolutely. Absolutely. That’s that’s the that last way is the way I would put it. And there’s really two kinds of possibility that we kind of 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 needat they definitely need to be philosophically distinguished and 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.

00:53:32.57
Alastair Wilson
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.

00:53:43.47
multiverses
Mm hmm.

00:53:47.05
Alastair Wilson
um 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 we can theorize both about what’s gonna happen in our world, 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.

00:54:33.88
Alastair Wilson
um So I think of it as something like our degrees of belief and the chances.

00:54:40.83
multiverses
Uh-huh.

00:54:40.92
Alastair Wilson
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.

00:54:48.31
multiverses
Uh-huh.

00:54:55.25
Alastair Wilson
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 it 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.

00:55:13.48
multiverses
Yeah.

00:55:13.84
Alastair Wilson
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 a fair die.

00:55:29.85
multiverses
Uh-huh.

00:55:33.42
Alastair Wilson
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.

00:56:12.19
multiverses
Mm hmm.

00:56:13.17
Alastair Wilson
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 that and so what we kind of 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.

00:56:55.17
multiverses
Yeah. Yeah. Yeah. I think that.

00:56:57.54
Alastair Wilson
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 real chance of a given outcome. Those are two separate sources of uncertainty, kind of two separate kinds of uncertainty. 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 there’s no uncertainty in the other.

00:57:39.60
multiverses
Yeah, very good. I realise one thing we, and perhaps something that’s been suggested but but not been made explicit is, why do we

00:57:52.85
multiverses
Again, why do but how does these actual Everett worlds around us, um how do they relate to what we should care about in our world?

00:57:54.83
Alastair Wilson
out

00:58:04.09
multiverses
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.

00:58:20.04
Alastair Wilson
Thank you.

00:58:37.89
Alastair Wilson
Yeah, um so this is ah this is tough. It’s not easy to explain why we should care about these entities’ possibilities in the same way that it’s not easy to explain why we should care about the physical chances associated with with it with a dice, it with dice that we’re playing with.

00:58:53.78
multiverses
man

00:58:55.71
Alastair Wilson
i mean um

00:58:58.81
Alastair Wilson
Why is it that if this particular die is weighted towards the sixth side, ah that we should expect that it will land sixth more than we should expect it will land one?

00:59:11.66
Alastair Wilson
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.

00:59:17.00
multiverses
Mm hmm.

00:59:20.62
Alastair Wilson
and Some people have said it’s actually impossible to solve philosophical problems. It would be like solving a human problem of induction and saying why the future should resemble the past.

00:59:28.14
multiverses
Right.

00:59:28.20
Alastair Wilson
ah You kind of 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. ah Nonetheless, it is obviously the right thing to do. To be like more confident, oh like on a far 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

01:00:00.12
Alastair Wilson
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.

01:00:32.55
Alastair Wilson
ah

01:00:35.76
Alastair Wilson
If the many words view is correct, then there’s going to be an awful lot of people just like us, which have different outcomes from what they’re in fact 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.

01:00:56.77
multiverses
Yeah.

01:00:59.04
Alastair Wilson
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 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,

01:01:34.13
Alastair Wilson
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, right that 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.

01:01:51.76
multiverses
No.

01:01:55.98
Alastair Wilson
So the only thing available to set your confidence by is 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.

01:02:29.04
Alastair Wilson
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 going to say you’re irrational if you don’t set your beliefs a certain way. Which is partly the the lesson of skeptical arguments in general, but in particular of humans, skeptical argument against induction. There’s going to be no way of persuading a skeptic that they have to set their beliefs in a given way. 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.

01:03:13.71
Alastair Wilson
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.

01:03:25.18
multiverses
Mm.

01:03:26.26
Alastair Wilson
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. 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.

01:04:11.51
multiverses
Yeah, I think 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 silver bullet argument which links behavior or rationality and um the way that we act with respect to chance.

01:04:29.09
Alastair Wilson
So.

01:04:40.99
multiverses
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, 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 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

01:05:42.20
multiverses
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 person? it would Is that the kind of gloss that of of the argument that works?

01:06:02.72
Alastair Wilson
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. um So, you know, you you toss a quantum coin, it lands heads. Why did it land heads and not tails? There’s no like good answer to that question. There simply is a kind of explanatory gap in reality. It lands heads in one branch, it details in another.

01:06:35.48
Alastair Wilson
You ask the person in one branch, what did it land heads? ah The equivalent to asking them, why are you in this branch and not in that branch?

01:06:40.36
multiverses
Hmm. Hmm.

01:06:45.24
Alastair Wilson
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 chance of even? well, 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

01:07:16.17
Alastair Wilson
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.

01:07:24.22
multiverses
Hmm. Hmm.

01:07:26.40
Alastair Wilson
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. But sometimes unlikely things happen. And you know there’s ultimately no explanation for why one person gets lucky and another person gets unlucky. That’s just luck. That’s the nature of luck. um And so there’s still luck in this world. There’s kind of no luck in in this picture.

01:07:52.85
multiverses
Right.

01:07:53.00
Alastair Wilson
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.

01:08:04.30
multiverses
Right.

01:08:06.10
Alastair Wilson
Let’s say that’s the nature of luck. Some people will be in better spots than others if there’s a lot of people distributed over spots.

01:08:16.41
multiverses
Yeah. Yeah, if anything, I guess it really sharpens the our understanding of of luck in that, you know, there are 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. And then at some future point, I could look back and say, well, 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.

01:08:45.68
Alastair Wilson
Yeah. 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.

01:09:27.75
multiverses
Mm.

01:09:28.53
Alastair Wilson
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

01:09:57.66
Alastair Wilson
you’ll think the chance of finding yourself on a heads branch is higher than finding yourself on a tails branch.

01:10:01.52
multiverses
Thanks.

01:10:04.76
Alastair Wilson
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 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.

01:10:44.95
multiverses
Yeah, yeah.

01:10:45.63
Alastair Wilson
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.

01:10:58.65
multiverses
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 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 existence we have?

01:11:30.96
Alastair Wilson
Yeah, it’s tricky, it’s tricky. um Some people very much say that it does, that like you should, um I mean, some people will use this as an objection to the the many worlds 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 in so far as it affects the totality of everything.

01:12:07.53
multiverses
Yeah.

01:12:07.74
Alastair Wilson
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. 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 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.

01:12:32.87
multiverses
Right.

01:12:36.04
Alastair Wilson
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 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.

01:13:14.73
Alastair Wilson
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 vi 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.

01:14:00.89
multiverses
Mm.

01:14:01.40
Alastair Wilson
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,

01:14:39.69
Alastair Wilson
you know that’s ah that’s a no-loss thing, nobody suffers at all, you might be more more open to risk-taking.

01:14:42.07
multiverses
Ah.

01:14:47.25
Alastair Wilson
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.

01:14:56.01
multiverses
but

01:14:57.93
Alastair Wilson
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

01:15:33.60
Alastair Wilson
in terms of whether it would be rational to change your behaviour, I think my official view is no.

01:15:41.57
multiverses
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 which dice I roll, I suppose.

01:16:00.02
Alastair Wilson
Yeah.

01:16:02.46
Alastair Wilson
I mean, it i it makes it harder for me to kind of quite ever understand Everett himself, the originator of the many worlds view, um who ah kind of believed in the reality of all these many worlds. um And yet simultaneously yeah ah had a career in military research doing projects, including one on how to maximize civilian death rates in nuclear weapons campaigns.

01:16:34.35
Alastair Wilson
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 bothered by that. Maybe he was just more rational than we are.

01:16:55.06
multiverses
Right.

01:16:55.27
Alastair Wilson
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.

01:17:12.71
Alastair Wilson
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 the things that really matter, but it’s gonna tell you kind of what it is to care about something, at least. um So yeah, I i guess the thing the thing that ties, I’ve noticed it ties together different kind of adherents of the Many Worlds approach is like intellectual-mindedness.

01:17:28.85
multiverses
Yeah.

01:17:51.27
Alastair Wilson
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.

01:18:08.09
multiverses
yeah

01:18:08.11
Alastair Wilson
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 ah 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.

01:18:32.84
multiverses
Yeah. Indeed. Yeah, out this has been a really wonderful discussion. And I know your 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 oh, yes, are there any places?

01:18:55.04
Alastair Wilson
This is

01:18:56.81
multiverses
I mean, I should mention, I’ll mention your book at the beginning. So on contingency, I’ve forgotten the full title. um

01:19:05.60
Alastair Wilson
called The Nature of Contingency, Quantum Physics as Modal Realism.

01:19:10.45
multiverses
Yes, yeah. um Anywhere else that people should confine to you.

01:19:12.06
Alastair Wilson
yep So there’s ah there’s a book coming out soon called Modal Naturalism. 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

01:19:38.58
Alastair Wilson
And ah I’ve also got a and as his volume coming out later this year called Levels of Explanation, 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 i’ been working on um most recently. ah

01:20:11.94
multiverses
Yeah, I think that would be… um

01:20:13.20
Alastair Wilson
Yeah, I think those are the ones to mention.

01:20:15.00
multiverses
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 and engage. 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, brilliant.

01:20:36.63
Alastair Wilson
yeah my My view is a pretty pretty straightforward. but you know These things overlap intensely and the idea to look for like a kind of sharp dividing line between physics and metaphysics is pointless.