Within Reason - #140 Sean Carroll - The Limits of Scientific Explanation

Episode Date: January 26, 2026

Get all sides of every story and be better informed at https://ground.news/AlexOC - subscribe for 40% off unlimited access.Come to my UK tour: https://www.livenation.co.uk/alex-o-connor-tickets-adp1641612.For early, ad-free access to videos, and to support the channel, subscribe to my Substack: https://www.alexoconnor.com.Sean Michael Carroll is an American theoretical physicist who specializes in quantum mechanics, cosmology, and the philosophy of science.TIMESTAMPS:0:00 – Tour0:32 – Can Science Alone Explain the Universe?6:08 – The Principle of Sufficient Reason10:07 – What Are the Laws of Physics?18:22 – The Fine-Tuning Argument32:39 – Does the Multiverse Undermine Morality?36:29 – Free Will and the Multiverse42:24 – What Is Emergence?56:21 – What “Stuff” Do Materialists Believe In?1:02:41 – How Does Consciousness Work on Materialism?1:17:31 – What Could Move Sean Away from Materialism?

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Visit medcan.com slash moments to get started. Hey, I'm going on a tour of the United Kingdom. If you've ever been interested in that big question of God's existence, or try to make sense of religion in the 21st century, or consciousness, or anything philosophical, then join me on stage as I try to work out some of these topics with you. I'll be in conversation with a good friend, but also bring questions because there will be an extensive Q&A, and maybe even an opportunity to hear and rate some of your philosophical hot takes. The tour dates are on screen. The link to buy tickets. is in the description, and I hope to see you there. Sean Carroll, welcome to the show. Thanks very much for having me. Is science, on its own, enough to understand the universe? The universe, maybe. I do think that there are plenty of questions out there

that science is not up to the task of uniquely answering. Maybe those questions include things like mathematics, which is sort of purely formal and logical and would be true either independently or whatever the scientific facts about the universe were. I would also say that things like morality and aesthetics are not out there in the universe, except for the fact that they're invented by we human beings who are part of the universe. But I do think that science is up to the task of explaining what the universe is and what happens in it, and that's basically science's job.

You're one of those people that's difficult to know where to even begin, given everything that you cover in your work. But I think that perhaps one sort of overview picture here is on this question of what science does. You just said that science explains. I often speak to physicists who say that really the job of physics and science is to kind of make predictions about the future. And really all it does is like observe things that happen

and sort of describe the things that happen and use that to make predictions. Other people think it's got explanatory power. Some think it's purely functional. What do you think is the actual role of science? What can it do for us? It's interesting that scientists are so bad at this themselves. But that's why we have people like philosophers of science, historians of science, sociologists of science, et cetera.

I mean, if you were talking to an archaeologist and you tried to make the claim that the purpose of science was to predict the future, they would be like, what are you even talking about? You know, I think that different kinds of science have different capacities. I'd just like to say that science describes the universe. the past, present, and future of the universe. In physics contexts, physics contexts are very special because physics has this remarkable ability to simplify complicated things down to the essence of just a few moving parts,

and that gives us the ability to make predictions with wonderful precision in the future. So we tend to valorize that or almost fetishize it. Like, that's what we want to be able to do. But there's a lot more to science than that. Certainly people who study the cosmic microwave background, in cosmology, the leftover radiation from the Big Bang, they're doing science, I'm pretty sure,

even though they're not trying to predict the future. So I think of science as doing its best to find a model of the universe, of how reality works. Whether you count that as an explanation or not is more a philosophical question or even a linguistic question. But if we have a mathematical or at least a super well-defined formal structure that maps on to the universe in a definite way, then that's the goal of science to achieve such a thing.

Well, does that satisfy you in terms of the word explanation? I mean, you know, maybe it's something that you're agnostic about, I'm not sure, and you say it's a question for the philosophers. Then again, you are a professor of natural philosophy. I do count myself, yes, I can put on that. What do you think? Do you think that science does explain or does it just describe things? I think sometimes it explains, sometimes it doesn't.

You know, if you want to say, why is energy, conserved. Well, we can give you an explanation because we can give you a deeper principle that applies more broadly and it explains why energy is conserved. It's because the laws of physics are the same from moment to moment in time. And there's a theorem by M. E. Nerther, the famous mathematician, that says, when laws of physics are the same over time, there'll be a conserved quantity called energy. So that's kind of an explanation. It makes you feel good. But I also think those explanations bottom out. I think that there are many possible worlds that we can imagine. imagine worlds with different laws of physics in them. And why do we live in this world rather than some other world?

Well, ultimately, there might be some part of the explanation that says we couldn't live in those other worlds, but there's going to be some brute facts. There's just going to be some fact that says, well, it's this way rather than some other way because that's what we discover when we look at the world. Do you believe in the existence of brute facts then, as defined, I think, by most philosophers, as kind of a fact that is, true, I guess it's not necessarily true. It didn't have to be true. Exactly. But it is true and somehow just doesn't require any kind of justification. It's just true and it doesn't go any deeper than that. Well, I would go so far as to say that nothing requires a justification or an explanation. I mean, my attitude is it's nice when you're able to explain things, when you find a deeper principle that explains why things are one way and another. But we don't have the right to demand that of the universe. And so I do believe that.

that there are brute facts. Arguably, the fact that the universe exists at all is a brute fact. It's not the kind of thing for which we would ever expect to find a reason why that is true. We find reasons why for things that happen within the universe. Why was I late to work? Well, because there was an accident on the freeway and it slowed down traffic. Okay? Like that makes sense to us, but that's because there's a context and we can ask counterfactual questions. We can say, okay, if there hadn't been that accident, would I have been on time? And if the answer is yes, then it made sense to say that there was a reason why. Why does the universe exist?

It's just hard to imagine the universe not existing. So I'm not really even sure what would count as an answer to that question. Yes. Well, there's this principle in philosophy called the principle of sufficient reason, which we're kind of driving at here. You said a second ago that we have no right to demand an explanation for anything. And I think that's true in the sense that we might not be able to apprehend the explanation. There might not be like an explanation that we can uncover.

It might be too complicated or outside of our grasp. But a lot of philosophers think that if something is true, there must be an explanation or a reason why that thing occurred, even if we won't actually know what that thing is. And some reasons for thinking that are like, well, trivially, if you think it's possible that things can occur for no reason with no exonerate. explanation, then some people ask like, well, why doesn't that happen all the time? You know, you're not worried as one of our sort of fellow colleagues, I suppose we could consider him. William Lane Craig likes to point out, you're not worried that a car or like an entire village has just popped into

existence, you know, while you're here doing this. But if you believe that things can happen without an explanation or without a reason, just as a brute fact, you know, why not? Why aren't you worried about such things. And so that might give us reason to think that at least in most cases, actually we kind of do need to demand that there is an explanation. Yeah, I think that many philosophers do accept the principle of sufficient reason going back to Leibniz. And I think that they're wrong. I think that is a very wrongheaded thing to ask for. And the examples you gave illustrate perfectly why they're wrong. Because a lot of people have in mind that either there is a reason why literally every fact is true. Every fact that.

that exists, I mean, that the formulation of the principle-sufficient reason is, for everything that is true, there is a reason why it is true. Or there's no reasons, right? Or like anything can happen, cars and chairs can pop into existence, like chaos is loosed upon the world. I think it's pretty clear that there's an intermediate position where some things happen for some reasons and other things are just brute facts. And, you know, maybe that's true. Maybe it's not. I think it is true. But surely you can't argue against it just. by saying that without imagining that everything has a definite reason why it's true, then nothing can possibly have reasons at all. I think the question that would jump out would be like, okay, if there are some things which don't require an explanation, and there are some things that do require an explanation, do we have an explanation why there are some set of things that need an explanation and some set that don't? Or is it this kind of arbitrary distribution? Because it feels weird to say that there's like a reason why this particular thing doesn't need a reason. You know what I mean?

I do, but by my hypothesis, you don't need a reason why there is no reason for that. That's the joy of it. I think that this idea that there are reasons for things, which again, very often is true, but sometimes it's not, goes back to Aristotle and other classical thinkers. And it made perfect sense in that world. But the world is different now because we understand it better. And in particular, it's not just that we have gotten rid of the principles fission reason. We've replaced it with something called the laws of physics. You know, Aristotle had no idea of what Newton would invent with classical mechanics or would later come on with relativity or quantum mechanics or whatever.

There are laws of nature. And those laws, as far as we know, the correct laws, are never disobeyed. but why those laws rather than some others, maybe there's no explanation for that. So it's very, very far away from saying, oh, things just happen. You can't explain it. You know, one thing after another. It's, no, things happen because the laws of physics say so and they're extremely restrictive. Why these laws rather than some others might not be an answerable question. Now, okay, I hope you don't mind me sort of pressing a little bit on this because, gosh, I've been speaking to so. many philosophers and scientists with all kinds of different views on the nature of science that

I'm sort of left in a spin. And when I hear someone say the laws of physics, it's this sort of philosophical buzzword because this terminology of law is kind of borrowed from like legal history, right? We've got this sort of set of rules that you have to follow, right? Whereas I'm kind of tempted to say that it's not that things don't fall to. the ground because of the law of gravity, but rather we have a law of gravity because things fall to the ground. In other words, the laws are descriptive rather than prescriptive. But it sounds like if the laws of physics are to like replace this principle of sufficient reason, it sounds like you give the laws of physics this ontological status of being these like things which exist

prior to the observations that they sort of, you know, have this, have this grip on. Like, do you think that the laws of physics, like what do you think is like their nature? Do they sort of exist somewhere out there? Are they like written into the rule book? Like, how do you think about what a law is? This is exactly a well debated point in the philosophy of science about humanism versus anti-humaneism concerning the laws of nature. I think that going back to Aristotle or maybe even to Newton, there was this default assumption that if there were laws of physics, they governed the behavior. It's a governing conception of laws where the laws of physics really bring into existence what happens next from what's happening now. Whereas Hume comes along and says

something exactly like what you just said. What really exists are a bunch of things, doing things at different moments of time. There's an apple, it's falling, it's fallen to the ground. Okay. And we invent these ways of describing what happened. And so I don't say, and I'm entirely in favor of that perspective. I think that's the right way to think about the laws of physics. They are descriptive of what happens in what is called the Humian mosaic, the set of everything that happens in the world. And they're very, very compact descriptions. You don't need to say force equals mass times acceleration separately for every object in the universe. You just say it once. And it's going to be of universal applicability. So I wouldn't say that the laws govern what happens or even the laws explain what

happens. I would say the laws describe what happens. The fact that there are laws that are apparently never violated means that things are not going to pop randomly into existence. What's going to happen next is whatever the laws of physics say. But the laws of physics are patterns in the universe. They are not forces that bring things into existence. And as far as we know, once we discover the fundamental laws of physics, which maybe we're close to, maybe we're far away from, we have no idea, those will be brute facts. They may have been some other way, but here's how they turn out to be. And I think one of the, I mean, we're sort of talking here or skirting around the edges of this idea of where these laws came from and maybe where they came from or the

reason that they are as they are is a kind of brute fact. But that question will seemingly be tied up to like the origin of the universe, right? Because people kind of think that for there to be laws of physics, there need to be things for them to describe, and the stuff that is described by the laws of physics would have began if and when the universe began. And yet some physicists talk as though the laws of physics will one day explain or describe the origin of the universe. Some people sort of have this optimism that science will get there, will be able to describe the origin of the universe. And yet, if all science really is in terms of the laws that it concocts, is just a description of things within the universe. Is that a, is that a sort of mistaken folly?

Well, it depends on exactly what you're looking for. If you're looking for a description of the first moment of time in the history of the universe, there's no reason why science couldn't in principle provide that. That's what science does. It provides a description of what happened in the universe. We don't know whether there was a first moment of time or not. Maybe there was. Maybe there wasn't. But either way, there's absolutely zero obstacle to a complete scientific description of it. If what you want, because you have some internalized need for an explanation why the universe came into existence at all, science is not going to be able to give you that. Science describes what actually happened. And do you think that's then just the role of philosophy? Or do you think it's like just an unanswerable question?

I don't think it's a well-formed question. When you ask why is it true, you're presuming that there is a reason why it is true, but you have to be open to the possibility that some questions, some things that happen do not have reasons why. And again, maybe the set of things for which there are no reasons why is very, very tiny, and we should keep looking. I'm all in favor of looking for explanations for everything we can hope to explain. What we don't get to do is demand ahead of time that a certain phenomenon has a particular explanation

rather than just being the way things are. Yeah, I think maybe one of the reasons why most physicists that I've spoken to at least don't agree with that is because it seems like the whole philosophy undergirding science in the first place is the expectation that there will be explanations for things, that there will be reasons why things had happened. Like if we just thought that there were, even like sometimes, you know, that there were some things that just happened with no reason, it sort of seems to cut against the philosophy of, that the motivation. science in the first place, which is the discovery of the reasons behind the universe, right? But I suppose you don't need to abandon that entirely just for a small set of things. Well, I think we're mixing up to very different things here. I think that it's very plausible. The laws of nature or the laws of physics are inviolate, that they're never violated. The things never happened randomly in apparent contradiction to what the laws of physics would have predicted. That's very different than saying

that the laws of physics themselves are not explained by something deeper. I think that the set of things that happen obeying the laws of physics is a perfectly respectable expectation. Maybe it's not true. Maybe we'll have to update someday, but I see no reason to think that anything that ever happened in the universe violated the laws of physics, which would mean, which would be what you need to have happened if you want to say something just happened with no explanation in the sense of the prior state and the laws of physics. But that can't be the explanation for the laws of physics themselves. It's a different kind of question. And we have to be open to those different kinds of questions, maybe not having the same old kind of answers. We'll get back to the show in just a moment.

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by going to ground.com slash AlexoC or by scanning the QR code that's on your screen. Use my link to get 40% off their unlimited access vantage plan. That said, back to the show. Hmm. So, you know, well, I know you know about the, fine-tuning argument for the existence of God. And I don't want to just do the boring thing of just asking you exactly what you think about that. But specifically, when people talk about this,

the problem that we're confronted with is that the universe abides by a certain number of constants, which seem very, very finely balanced, to the degree that if you were to increase gravity or its strength by like the most unfathomably tiny amount, the universe would all collapse in on itself and the reverse is true as well. And so we're kind of typically given three options here to explain why it is that the universe is finely balanced to allow atoms to form and planets and stars and stuff. One is it's just by chance, which seems incredibly unlikely. One is that God did it, you know, which seems maybe a bit too easy. And the third is necessity, that there's some kind of reason why it had to be that way, or maybe not a reason why it had to be that way, but it just had to be that way.

is the version of the sort of description of the laws of physics that you're describing here a version of this necessity route of saying without sort of any reason why they kind of just had to be the way they are or is it more like a chance direction where you say it's kind of just by chance but the fact that it did happen this way despite the odds requires no no explanation like which of those sort of categories do you sort of fit into. I know it's not the God one. Well, I think that two things. One is you left off a very promising explanation, which is the multiverse, where different parts of the universe have apparently different values for the constants, and therefore we're going tautologically to find ourselves in a part of the universe, which has conditions accessible to life, right? I mean, there was never

any chance that we would be having this conversation in a part of the universe which did not allow for the existence of life. So really the only question, question is, is the universe big and diverse enough to allow for life anywhere? Or did we just get lucky, like you said? I don't think that there's much sensible to be said about the option that you painted as some necessity for things to be one way versus another. I don't think that makes any sense. Like I said, I think that things could very easily have been otherwise. I think that the most likely explanation for the apparent fine tuning of constants of nature is some kind of diversity within the environments that exist within our universe.

It might be literally the cosmological multiverse, where you have regions very far away where conditions are different. It might be something more subtle in the space of quantum worlds, in a many-worlds version of quantum mechanics or something like that. But that seems to be a very simple way out of the apparent fine-tuning questions. And it wouldn't be at all associated with some necessity for it to have been that way. It's literally the opposite. It's saying elsewhere, it's not that way at all.

Well, the reason I leave that out of the three options is because I see any kind of multiverse explanation as a version of the chance thing. Like, yes, it is exceedingly unlikely that the constants would be as they are. But there are exceedingly many incarnations of this universe. And so, of course, one of them is going to be finally tuned. And that's the one that we're going to find ourselves. And so I kind of see it as a version of the chance argument. But theists will hear you say that. And in the way that we might look to a theist and say, well, you're just kind of trying to explain away a difficult scientific problem by saying God did it.

Are we here just trying to sort of explain away a difficult problem by saying that there's a multiverse or are there other independent reasons to already suppose that there might be such a thing? So I think a couple things. One is I would vastly prefer to separate the two possibilities, one of which is there's a multiverse and the different constants of nature. appear different locally in different regions, and therefore, by a selection effect, we find ourselves in a region that is hospitable to life, versus a thing that says, there's just one universe and we just got lucky

that the parameters of that universe allow for the existence of life. Those are two very different scenarios, and I wouldn't want to conflate them together. I certainly don't think, and then the question, are we just sort of doing just the same thing that the theists do by invoked

some mechanism to explain these apparent fine tunings. I think that there's two things going wrong with that. One is there's nothing wrong with invoking mechanisms to explain things you see about the universe. That's what science does. That's how you invent scientific theories. You try to fit the data by proposing a hypothesis or a model that accounts for that data. And if the data include the fact that the energy density of empty space or something like that could have been very different, but is just right, allowing for the existence of complex structures that physically transmit and process information in a way that we recognize as being characteristic of intelligent life,

those are data that we should use in constructing our theories. And the other is that, as you hinted at the end there, indeed, we have reasons that have nothing to do with explaining fine-tuning for expecting that there is some kind of multiverse out there. The reasons are not airtight. We really don't know for sure, but both from cosmology, inflation, string theory, all these speculative cutting-edge ideas, and from quantum mechanics, like we said, the many worlds formulation of quantum theory, we get a multiverse out of theories that were invented for completely different reasons. They were not invented to get you a multiverse,

but you try to follow and take seriously their implications and you find that there is one out there. very, very different than the story with Theism. Let's just put it that way. Yeah, I think that's probably true. But then how much stock do you place in the theistic explanation for fine-tuning here? In other words, is it sort of like, that's nonsense because we have this other explanation? Or is it like, no, this fine-tuning problem does increase my credence in the existence of God. It is a sort of viable option for me. It's just like it doesn't compare to the scientific explanation? Like, where do you sort of place it on that level of convincingness? My usual line is that I think that the fine-tuning argument for the existence of God is the best

argument that people have for the existence of God. But it's a terrible argument. It's really, it's really not very good at all. And for various reasons, I'll just mention two of them very quickly. One is that the fact that the physical constants of nature are fine-tuned really means, the following thing. It means that they take on values that allow for the existence of physical configurations of matter that behave like living creatures, right? We metabolize, we reproduce, we process information, like we said, all of while obeying the laws of physics in a way that wouldn't have been possible if the various constants of nature were very different than they are right now. That is exactly what you would expect if God didn't exist. That's what you expect under naturalism, that if you want to have life in a naturalistic cosmology, you better have some complex information processing systems and the constants of nature better allow for those. If God exists, you don't need that. God can make anything alive because God is God. I think a lot of theists really undersell God's ability to do things.

I mean, generally they believe that many of them believe that there is life after death that doesn't involve physical stuff or find too. at all. So, if anything, the observation that the constants of nature are fine-tuned to allow for the existence of physical configurations of complex adaptive matter is evidence that should increase your credence in naturalism, not theism. And the other objection is that exactly because the fine-tuning argument is the best possible argument, why is that? It's because it plays by the rules of scientific investigation. It says, here's a data point. I'm going to try to invent a theory. that explains this data point, I am going to judge my theories using Bayesian reasoning. I'm going to calculate a likelihood. I'm going to say, what would the likelihood of the universe looking like this be under this particular theory, and then we'll compare it to the data. And you can do that for, I'm certainly happy to agree that the likelihood that the parameters of nature would allow for life would be large under theism. I think that's okay. But there's a whole bunch of other things you can ask. Should we expect the

universe to look this way if theism were true. There's a whole bunch of other features of the universe that we would not expect, like just the fact that it's big, the fact that there's a hundred billion or a trillion galaxies in our observable universe. That's not what you would expect under theism, and especially the idea that human beings are somehow special in God's eyes. Now, you can say, well, maybe the whole universe is special in God's eyes, and maybe we can accommodate and expect that exactly this kind of universe is what God would have made. But too late, because you had the chance for a very, very long time, cosmologically, we had no knowledge of the fact that there were extra galaxies out there, that the universe was big, that there was a big bang, or any of those

things, you could easily have used your theory of theism to predict that that would probably be what the universe is like, and nobody did. So you can't claim now that's exactly what you have expected under theism. That's a great point is that it does seem a bit sort of, shall we say, post hoc. It's not strictly speaking, you know, like irrational. If you're a seist and you're confronted with this problem of a big universe, you know, it's not enough to make you into an atheist, but to say, no, no, no, this is, you know, this is how God would have done it. It's like easy to say now. My friend Phil Halper likes to point out that the early Christian Gnostics who believed in like the evil demi-a-oh.

urge creator of the material universe, that the fine-tuning argument kind of fits better with that because you've got these like meta-conditions which make it really, really difficult to bring about a material world. And yet it comes about, implying that sort of the true creator of everything, the source of all being, really doesn't want the material world to exist. But this sort of evil, you know, trickster comes in and just sets things up just right, that the fine-tching argument kind of points a lot more strongly to something like that than it does to the god of traditional traditional theism. Yeah, and I think the way, I'm sorry, go ahead.

No, please. I was just going to say the theists in the modern world are pushed to invent a version of God who wants to be completely invisible, right? Who wants the world just to act according to the laws of physics. And then you have to invent a reason why, oh, no, God would have wanted to do it that way so that we would have no idea that God actually existed. it would be very, very trivially easy for God to let us know that God existed. Again, he's God, he can do anything he wants.

There's many different versions of the universe that would fit really well into a theistic explanation and not so much into a naturalistic explanation to be forced into the corner where, yeah, it looks like our universe always obeys the laws of physics and is governed by purely materialistic rules, but God would have wanted that way is a little bit of a post-talk copy. about. Okay, so I've got two philosophical questions for you since this is a philosophy show, although you struggle to believe it, the number of scientists I've been speaking to recently. The first is that you said earlier that you don't believe in the principle of sufficient reason. That is, you think that there are things that can occur without any explanation or

justification, and that satisfies you to think maybe the universe's existence and the nature of the laws are just a brute fact. If somebody's listening and they do believe in the a sufficient reason. And they do think that everything requires an explanation or some justification. Again, not to say that we would need to know what it is, but just that there is some reason why everything that happens happens. For someone who does believe in the PSR, do you think they have good reason to believe in some kind of theistic picture that there must be a sort of unmoved mover holding everything in place? Or would you still, if you woke up tomorrow like Bertrand Russell, by Jove, the principle of sufficient reason is sound, would you still be satisfied in your atheism?

Well, I think that the principle of sufficient reason relates to theism in a very well-known traditional way that is pretty obviously a cop-out like we were just talking about. The whole argument for the existence of God based on PSR types of reasoning says, you know, for everything, everything is a true fact about the universe, There must be a reason, but there's this large number of things that is true about the universe. Therefore, we don't want to get into an infinity of explanations. The reason for X is Y and the reason for Y is Z and just go down in an infinite regress. Somehow that bothers us. Maybe you could just accept that. I don't know, but somehow that bothers us. Therefore, there must be a single thing, an entity that is necessary, that is the grounding the explanation for all these other things. But of course, course, what you just did is contradict the very first assumption you made. You just said that for everything that has to exist, there has to be a reason why it exists, except for this special thing that I know about. And it's only reason for existing is it had to necessarily exist.

And that's a very hard argument to counter, not because it's good, but because the only counter is, no, it didn't. I can imagine universes where God doesn't exist. There's no necessary thing there. You invented a reason to make him exist. I don't need to accept your reason. Okay. So second philosophical question, which is slightly different, and a little bit tangential in the fact that, in the sense that it's kind of an ethical question, which is you probably sometimes asked whether your scientific and philosophical views affect the way that you live your life. But specifically here, take the multiverse, right? If I'm to believe that there are a sort of near infinite number of universes, and it depends on what kind of

multiverse you're talking about. But suppose there's a version of the multiverse which says that if in one universe, you know, I turn left, there's another universe in which I turned right. And every single possible outcome occurs. Every time there's a quantum decision to be made, two realities spring off. Then over the entire picture of reality and the entire multiverse, it seems as though all behaviors and actions kind of balance out. Like anything I do in this universe is balanced out by something in a different universe. I suppose my ethical view is broadly speaking that we should minimize suffering as much as we can. Maybe I'm like a utilitarian. Doesn't this lead us to a pretty radical conclusion, which is that if I want to minimize suffering, there's no reason why I should only

want to minimize suffering in my universe. And like I want suffering to be minimized overall, but I've realized that if I'm really good and I give to charity in this universe, there's another universe in which I'm really evil and cause lots of suffering. And overall, because it all balances out, the amount of pleasure and suffering will be constant. So why not in this universe just cause as much suffering as I can and just be evil and selfish and terrible? Because I know that it will be balanced out by a universe somewhere else, if that makes sense. It does. I think that it'll be a perfectly valid way of reasoning if your physical theory was that everything, every possible universe happens, and it happens with sort of equal probability somewhere.

But nobody has a physical theory like that. In the real physical theories of the origin of the multiverse, number one, it's not that everything happens. Some things happen, some things don't. Many things happen, but some things just don't happen. The most obvious blatant example is electrical charge is always conserved. And the negative electric charge never turns into a positive electric charge anywhere in the multiverse as far as we can currently tell.

And likewise, there's plenty of other. things that just have zero probability of happening, despite the fact that many things do happen. The other is that, and much more importantly, when there are different things that happen in different universes, there are different probabilities you attach to them. They're not all created equal. So people ask me about being a utilitarianism, being utilitarian in the many worlds formulation of quantum mechanics, I say it's the same as being a utilitarian in any theory where there are some probabilities for things happening or not. If you say there's a one in a hundred chance something happens,

and you use that probability to maximize your expected utility, given that there be certain utility in the one-universe in the 1% and a certain other utility in the 99%, that's the same as saying there's one universe in which the bad thing happens and 99 in which the good thing happens, at least as far as the math is concerned. So I think that morality is more or less completely, unchanged. I think there's one mistake you could make by thinking that I just add up the utility

of all the universes without taking probability into account. And then if you thought that the universe existing was overall a good thing, your moral righteousness would be maximized by splitting the wave function of the universe as quickly as you could into many, many different copies of the universe. But nobody in their right mind really believes that. You take the average in all these universes, and that means that you just act the same way you thought you should. I'm a little bit confused about how the probabilistic distribution of different universes concords with the existence of human free will. I don't think that free will exists.

You do? I'm a compatibilist like most philosophers. Yeah, okay. And so I suppose maybe I guess under compatibilism, you would just think that this probabilistic distribution does apply to our actions. And our actions are kind of determined, but you have like a conception of freedom that works with that. Like you're not a libertarian, like, free will proponent, in other words. So the existence of quantum probabilities has absolutely nothing to do with free will for or against.

The whole idea of compatibilism vis-a-vis free will, the word compatibleism means compatibleism between our ordinary conceptions of ability to choose and deterministic underlying laws. Those are the two things that are supposed to be compatible. So adding a little stochastic element to the underlying laws and either increases or decreases our compatibilist free will. Just the fact that the laws of physics have probabilities in them doesn't mean that you are overriding the laws of physics to exert your will upon the universe. If what you mean by free will is some kind of libertarian ability to override the laws of physics, I don't believe in that. then very few people do believe in that. Very few professional scientists or philosophers do. If what you mean by free will is the ability to make choices at the emergent level of human beings,

where I am not Laplace's demon, I don't know the microstate of every particle in my body or anything like that, that's perfectly compatible with the microscopic laws whether or not they are fully deterministic. And can we just help to clear up what I think might be a common misconception, at least about your view, when it comes to probability? Because, Because on the macro level, at least, when I talk about probability, I'm usually talking about epistemic probability. Like if I flip a coin and I've got it under my hand and I say, what's the probability that it's heads? You want to say about 50%. But really, like, it's either heads or tails.

And if it's heads, it's 100% heads. The fact that I look at it, it's like, oh, it's 50% chance of being heads. And then I look at it. And suddenly it's 100% chance of being heads just by me looking at it. No, clearly I'm talking about the probability in terms of what I can know, like my epistemic probability. But the actual probability that it's head or tails is like 100% one way or the other. And so a lot of the time when we talk about probability, we're really just talking about the fact that we don't know which way something's going to go, but there is like a hundred percent chance it will go one way or the other. But your view is that probability that isn't just epistemic, like actual probability is built into the foundations of the universe, right?

Not really. I think my view is that you shouldn't use phrases like actual probability. I think that the only probability that exists are subjective probabilities. Probability is always a measure of our ignorance of the universe. There is a universe. The universe is what it is. In my favorite view of fundamental physics, it is purely deterministic in its evolution. There's nothing that we couldn't in principle predict if we knew everything about the current state. But we don't know the current state. We don't know the laws of physics. We don't know lots of microscopic information about what's happening inside this room. So there's lots of things we don't know about the past, present, future, the situation, a whole bunch of things. We deal with that by assigning probabilities to them. If you were an omnipotent and omniscient being, you would not use the concept of probability. You would just say what happens in the universe.

And the same thing is true for quantum probabilities, in particular in the many worlds approach to quantum mechanics, the future evolution of the quantum state of the universe is 100% deterministic. But what will happen is you will get different measurement outcomes in different branches of the wave function of the universe, which we interpret as different worlds. And when you get them, when you say, oh, I measured a particle to be spinning clockwise versus counterclockwise, there's a moment when you don't know which branch you're on. You know, if you know the wave function of the universe, that there is one branch where it's clockwise, another branch where it's counterclockwise, but you don't know which one you're on. So guess what? You assign a probability. You have a credence for being on one

branch or the other. And that's the nature of all probability as far as I can tell. And it's a very sensible, unified picture. Again, it rubs some people the wrong way because they don't want to be like that. Never promised you a Rose Garden. Sorry. Now, I'm glad to hear that because I'm in complete agreement. I don't know why I thought we might disagree there. But yeah, I mean, it's like if you're, I guess one way of thinking of it is like if you get on an aeroplane and it's either going to Los Angeles or it's going to Chicago and you sort of wake up on the plane and you don't and you don't. You might say, gosh, I've got a 50% chance of being on a plane to Los Angeles. It's like, no, you don't. Like, you're definitely 100% going one way or the other.

What you're describing is just that you don't know. And when someone tells you, all you're doing, you're not collapsing a probability distribution that's built into the universe. You're just finding out which of the airplanes you're on. And similarly, when you find out what happened in some quantum event, you're not actually collapsing some real probabilistic cloud of maths. You're just finding out which sort of branch of reality you're on. I have a whole podcast with David Deutsch on the sort of quantum many worlds, multiverse type stuff if people are interested. But I think that's, you're just That's a really helpful picture. Use a term a moment ago, which I want to ask you about, you said if we're talking about something like human beings as emergent, or like the emergent level of human beings, what does that mean? Well, what it means is that we think that there's a way of describing the world, which is the level of fundamental physics, quantum field theory, particles, atoms,

electric fields, quarks, all that stuff. That's a language to describe the world, which is very, very effective, very, comprehensive. And I could describe the room I'm sitting in right now, in principle, at that level. I could tell you exactly what quantum fields were involved, what their configurations, their quantum states were, all that stuff. But I don't know that. I don't know all that information. There's like a huge number of quantum particles here in the room. And I don't know the locations or the momenta of all of them or how they fit together, any of that stuff. Am I therefore totally lost?

No, there is a way to describe very effectively, very usefully, what is happening in the world based on dramatically incomplete information by bundling up a bunch of these microscopic degrees of freedom into macroscopic objects. I can talk about a table and a computer and a microphone and books behind me and all these things. None of those words exist in the fundamental description of nature, and yet they're incredibly informative. I understand the causal powers and the relationships between all these objects that are emergent objects at the macro level. You could have multiple nested macro levels if you want, but we're skipping right from particles and atoms all the way up to people and tables and chairs and things like that. It's a remarkable feature of the world that we can describe it very accurately, very informatively, based on a tiny, tiny fraction of the microscopic information that's actually there. But we all use that. And maybe what we think of now is fundamental is not fundamental. And there's something even deeper than that. So the fact that the world appears to us as multiple lested emergent levels of description is incredibly useful for getting through the day and dealing with what happens in the world. Now, I agree with that, and I want to talk about this concept of emergence. And I suppose the question to ask is, do you think that emergence, that is, you know, like stuff that kind of comes out at a higher level when you put smaller, more foundational stuff together and you get kind of new stuff emerging?

Is that a feature of the universe and the things within it? Or is it a feature of our descriptions, right? Because if I've got, you know, a bunch of people, if I've got like 22 people stood on a field, and I just sort of mentally group them into two teams, and I start talking about like football teams. And you've got this sort of emergent concept of a football team, which emerges from the individual players on the pitch. It doesn't feel like the universe is actually doing anything there. It feels like I'm just kind of applying a description that's useful for me to sort of navigate the world. But then sometimes people talk about emergence as not just a descriptive thing.

I mean, a popular example is something like the wetness of water or temperature emerging from vibrating atoms because the temperature, you know, an individual atom isn't hot, you know, that kind of thing. When you talk about emergence, do you think that like real emergence exists? There's a sort of better philosophical terminology here, strong and weak or whatnot, but you get what I'm driving at. Or do you think it is just a descriptive thing that humans are doing? I think it's 100% real. I think it's 100% objective fact about the universe. And indeed, Daniel Dennett, who was a great philosopher who thought about these things, coined the phrase real patterns in a famous paper he wrote, to describe exactly this phenomenon.

Like we said, like I emphasized in talking about emergence, the feature of emergence that is relevant is that the higher level emergent things are described on the basis of wildly incomplete information. Take the air in this room. We can describe it using its temperature, its density, its velocity, quantities like that. And there's a very, very specific procedure for forgetting the microscopic information. That is to say, to go from the microscopic description in terms of literal atoms and molecules moving around in different positions and different velocities and averaging over them to define things like temperature and pressure and velocity of the air. If you did something else, if you did a different way of throwing away the microscopic information, you wouldn't get an emergent theory. Because the thing about the description of the air is that if you tell me the temperature and the pressure, et cetera, I can predict what's going to happen next, right? That's what weather forecasters and climatologists actually do. They do literally that. They don't care about atoms. They care about fluids and the atmosphere. But if you did your map from the microscopic theory to the macroscopic theory incorrectly,

you would not get a theory that you could make any sense of at all. It would not give you the right information to predict what was going to happen next. So there's an objective fact about the world that I can ignore some pieces of information and still be able to make reliable predictions or accurate descriptions, which is very, very precious and not some of it. something that human beings just made up. But I talked about a football team a moment ago. And I don't know your ontology of sports teams, but I kind of get the impression that a sports team isn't like a real thing.

It's something that we've kind of mapped on to individual players. But I can also talk about a football team in the same kind of way that, you know, a scientist might talk about weather or wind or air pressure or in that I could say, you know, well, the team is playing very defensively, or maybe you're the manager and you say, I need the team to be defensive in order to win the game. You don't actually even need to really understand what that would involve for individual players, all you need to know is what the team is doing. And so, yeah, there's sort of a truth of the matter. We can speak objectively, and make predictions about who's going to win the game based on the behavior of the team without knowing the individual players' decisions. And yet, I still want to say that this emergent sort of

thing, the sports team, isn't real. It's like it's a, it's a concept. Why? Why not just accept it? Why not just deal with the fact that you talk about tables and chairs and sports teams as real all the time? Because I suppose I don't have the same kind of issue with recognizing, I suppose, that really when I talk about a table, I'm talking about a bunch of atoms that are arranged in the shape of a table that I've put a label on. And of course, in my day to day sort of common experience. I don't speak like that, but I also don't, you know, act as though it's made mostly of empty space. I know that that's true when I'm doing science, but it doesn't really inform the way that I sort of work on my sort of day-to-day life. Similarly, yeah, like, I mean, I talk about sports teams. I talk about nations. You know, I think that England exists. But if you ask me to precisely define, you know, what counts as England and why there's a particular barrier and whether it really exists and is it made out of the land mass, is it made out of the... I would say, to be honest, I don't know.

And really, it kind of doesn't exist. It's more of a concept that I'm applying to a mix of geography and people and stuff like that. But I just... Maybe it's like a point of intuition that I just don't think that the thing has this like ontological existence in the universe, alongside things like... So you don't think that tables exist? I do not. I'm what's known as a myriological nihilist. Did they exist before we knew about atoms?

Okay, so this is where things get a bit complicated because when in this conversation... Not for me. They get complicated for you because I think tables exist. Well, I think, to be clear, right, I think tables exist in the sense that the thing that you are referring to when you say the word table exists. But in the same way, my favorite example to describe what I mean here is if I asked like, do you think the left-hand side of this microphone exists? The answer is yes, the left-hand side of this microphone exists. But clearly it's like designation as a thing, the left-hand as opposed to the right-hand, is just a mental distinction, right? But if I said, you know, before we looked at the microphone, before we were here, did the left-hand side of the microphone exist?

The answer is yes, because the thing I'm referring to now in our conversation did exist. But its distinction as like an ontological object that really exists in the world is still like mind-dependence. Does that make sense? Like I sort of see the sports team in the same way. Like, yeah, the sports team exists, but its designation as like a distinguishable object from other sports teams and that does stuff is still dependent on the mind. But the thing that I'm referring to is that concept, that collection of things, that set of players. Does that make sense? I mean, I understand the point of view.

I just don't see the attraction in it. I would just like to say that the left-hand side of the microphone and the table and the sports team, these are, are all real. And the reason why they're real is because talking about them provides us with useful causal information about how the world operate. If I said, oh, I spilled paint on the left hand side of my microphone. I'm not sitting here thinking like, I have no idea what that means. What are these strange terms that he's using? Like, you've conveyed information to me. So that's my criterion for when something is a useful, really truly existing concept at the higher emergent level. So, and, you know, and this is all in the service of trying to,

to understand emergence, but we're slightly sideline here, and I think it's really interesting. There is a problem with this view, in my view, which is that, I mean, you've said that the reason why you want to be able to say that, you know, the left-hand side of the microphone exists or a sports team exist is because it's useful. I think it's true. It is useful to have those concepts. But I want to say that there are things that exist, even if it's not useful to know that they exist. And there are things that don't exist, even if it would be really useful that they did. And the problem to me with saying that, well, as long as in my head, I put a box around those 11 players and call it a sports team, yeah, there's this real thing called a sports team. If I'm watching the game and I'm the only person in the arena who, for some reason, takes those 11 players on one side and then also takes the goalkeeper from the other team and I just decide to like call it a new thing.

I just say, oh, that's, you know, that's a, that's a sports team plus. Sports Team Plus 1, that's a new object that exists in the universe. And I told my friend about it. I said, hey, I just created this new thing in the universe. It's called a Sports Team Plus. He would say, you're clearly just making stuff up. And maybe you want to say, well, that wouldn't be a very useful category. Maybe it would be in some circumstances. But even if it's not useful, I can still do that. I can just arbitrarily. I said I'm a myriological nihilism. The radical opposite of this is myriological universalism. The view that every combination of objects does actually produce a new object. In other words, it seems to lead to my ability to say something like, okay, I'm just going to take this bust of Michelangelo's David that's behind me and my left pinky and the minute hand on the eastern face of Big Ben. And I'm going to say that that is a new object and I'm going to call it a glorb. And that's a real thing that exists in the universe, that is emergent of those two things considered as a whole. But that would be insane, not just because it's not useful, but also because it just doesn't seem like that's a real thing.

You know what I mean? So how do you avoid that objection, that you sort of exploded the number of things that could possibly exist in the universe? Yeah, because I don't think that anything that you can possibly group together counts as a really existing object. There are things that play causal roles in the world that, like I said, provoking. informative knowledge of what the world is doing. And I think that the example of the air in the room is really good. I get things like temperature and density and pressure by taking a small region of space, literal location in space, like here's a cubic millimeter and I'm going to average, like how many particles are there, what's their density, things like that. It turns out as a true

fact that is not in any way a necessary fact, but a contingent fact about reality, that doing those little averages gives me a thing that exists in the sense that I can make predictions on the basis of its current state. If I had done the same thing averaging over squares or cubes in momentum space rather than physical space, I would get the same number of variables and I'd be able to predict nothing. It's useless. It's just like the glorb that you define. And all of this is discussed by Dennett in his paper on real patterns. There are some patterns that form sensible combinations of things at the emergent level and some that don't. And we kind of all know this because we refer to the world and have objects in it long before we know that they're

made of lower level things. The emergent level has an autonomy of its own. This is Philip Anderson's point, the famous physicist, when he wrote the famous article, More is Different. You can study the higher level for its own sake. Like, you have freedom to define whatever you want. But that doesn't make it a good scientific description of the world. I see. Okay, now I'll admit to you as well that in speaking about emergence and human beings is emergent, I have a slight vested interest. And there's a topic which you know I have to ask about, which is consciousness.

And I suppose I want to begin by asking, do you consider yourself to be a materialist? I mean, I know that you're a physicalist about consciousness, but just like broadly speaking as a prior, metaphysics. Are you a materialist? I prefer physicalist to materialist because I think that we've moved past the point in the history of our knowledge of the world where we say the world is made of materials. What the world is made out of is a little bit more abstract than that, but it is physical stuff doing physical things. And I want to ask what is a deceptively difficult question because people say to me sometimes, you know, yeah, I'm a materialist. I believe the universe is just made out of material or it's just made out of physical stuff. I'm like, okay,

cool, what is that? What is physical stuff? What's the sort of operative definition that makes physicalism a definable worldview? Well, there is absolutely a problem in physicalism, namely that we keep changing our best theories of physics, right? Like you would have said, you would have given a different answer in 1850 about what is the physical stuff that makes up the world as you would have been 1950, because we had revolutions and relativity and quantum mechanics and things like that. That's why I have sympathy for structural realism that admits there is something out there that is real, but we don't know what it is for the final answer. What we know is that there are certain structural relations embedded in there, even as our ontology continues to improve along the way. Having said all that, I think that our best current answer to the question is that the world is a vector in Hilbert space, which is a fancy way of saying the world is described by a quantum state, within the space of all possible quantum states. And we know a lot about what the mathematics of that involves.

And I was cheeky enough to write a paper called that everyone can look up online called Reality as a Vector in Hilbert space. It's not necessarily the final answer, but it's our best current answer. And that answer is very far away from the world of tables and chairs moving in three-dimensional space. And that's just a juicy scientific philosophical problem for us. to connect the two to reconcile the manifest image of the world with the scientific image of the world. And to what degree do you think that not just this view, but any scientific view,

and I'm sort of throwing the Philip Gough line at you here, can really inform us about what stuff is rather than just what it does? I mean, we talked about science as being descriptive as sort of coming up with laws that describe things that we observe. But if you're looking for what this stuff actually is, which when you're, you say you've got a metaphysical position, I'm a physicalist, I believe the universe is made out of a particular kind of stuff, if the stuff that you describe is mostly described in terms of something that occurs or a mathematical sort of formula or something, you're still left with this ontological gap of what the stuff is. Do you think that science can tell us what stuff is, or can it only ever really tell us what it does to the extent that we'll never quite be able to

like grasp the isness of whatever's down there at the foundation. I don't think there's anything to be grasped. I don't think there's any answer to the question. What is it aside from how does it behave and how does it interact with other things? I think the world, the universe, reality is sui generis. We have to occasionally throw in some Latin in a philosophical conversation. It's what it is. Like there's no answer to the question, but what is the universe? It's the universe. It's reality. We can describe it. We can talk about it. We can subdivide it. We can talk about how one part of it interacts with the other part. At the end of the day, the universe is the universe. It's the thing that isn't explained in terms of anything else. Yeah. I just, and I know that this is a well-trodden path and we'll move on presently. But you can understand to me and to our listeners as well, perhaps, when you say something like, you know, there's nothing more than like what it does. But you've used the word it. You know, it's like, it's like, It's sort of embedded into our language that if you say all there is is what it does, there is no what it is, then when you say what it does, if there is no thing that it is, what does that word it like mean there, you know?

I think this is all just a relic of the fact that in our everyday experience, we deal with subsystems of the world, you know? What is this computer really? Like, what do you mean? You mean what it's made of, right? like, okay, there's little pieces you can use to assemble it in a certain way. But when you apply those conceptions to the universe to reality as a whole, there's, again, no reason to expect that we get the same kind of explanations. What is the universe?

It's the universe. That's the answer. It is uniquely the universe. It's impossible to imagine an answer to what the universe is other than it's the universe. have you seen the clip of Richard Feynman being asked about magnets? I've mentioned this before on the show. A long time ago. I don't remember it very well, but yeah.

Well, it's just, it's quite, it's quite entertaining because it's somebody, some interviewer sort of saying, like, so, you know, magnets, like, what, what's going on there? Like, why do they do that? And Feynman's like, oh, you know, something about a magnetic field and whatnot? And the guy's like, but like, but why does that happen? Why is there that field? Why does it do that? And Feynman's like.

that's it, man. Like, that's all there is. And it's really funny because I kind of associate myself with both sides. I totally understand the physicist saying, like, look, man, you've reached rock bottom. Like, that's it. That's the ground floor. But I'm also kind of still like, there's got to be something that it is. So it's a, I do feel a little bit in limbo in these conversations, but I think that's

quite an interesting example of the same kind of phenomenon. Of course, that self-same Philip Goff that I've just mentioned uses this as a root to say that, well, the isness of the universe is consciousness, because there's only one thing that we sort of know for what it is in itself. There's one thing that we experience, like, directly, and that is experience itself. We know what experience is, and we've got this big gap in the bottom of physics that we don't know what it is, we only know what it does, so maybe we can just plug up that gap with consciousness. I know you're not a panpsychist, but presumably you believe in consciousness. I know some people don't. I've heard you talk about consciousness in a way that I'd be surprised if you took the sort of illusion route or something that says that it literally doesn't exist. And yet, you're a physicalist. You think that there is this sort of field of stuff, the physical matter,

even if we don't quite know what that is, that somehow bumps together in the right kind of way, and then gives rise to something that isn't just like, you know, a rock crumbling off a cliff or something, but is experience famously, the redness of red, the taste of Coca-Cola, the sound of children's laughter, whatever it is. What is going on there, in your view? What is giving rise to this sui generis, to use the same term that you did, a thing in the universe called experience? I don't think it's any different than tables and chairs. I think that experiences and conscious awareness of things is a set of vocabulary words that we use to describe collective behavior of particles and forces in the universe under the right circumstances.

I can say that the table has a certain height, that it has a certain tensile strength, things like that. In the same way, I can say that this particular person is having an experience of seeing the redness of red. I literally see no gap there at all. This is just one of the sets of vocabulary words to describe what happens in the world at a higher level. Yeah. I mean, you'll be familiar, of course, with the reasons why people are suspicious at this, but perhaps we can try to be specific and make it interesting. I mean, for a start, it seems as though I could give a complete description of the activities of a brain. I could describe the sort of electrochemical processes and the way that neurons fire and connect with each other and the brain regions and all that kind of stuff. And were it not that we already knew, there was this thing called experience that sort of came along with that, I wouldn't expect or predict that there would be this thing that the philosopher's called qualia, you know, the redness of red. I would just predict that there would be some atoms and neurons moving around and bumping into each other in various ways.

It seems in other words that like a physicalist description of the brain would not predict, at least on its own, that there is this thing called experience that goes along with the neurons moving around in physical space. What do you think of that? I don't see why not. I think that's just because you're not very good of predicting things. But neither am I because it's very, very complicated. I mean, we're literally trying to compare two things. One is a physicalist understanding of nature at its most fundamental, which, as we said, currently takes the form of some quantum mechanical theory of fields and particles and stuff like that, which is literally the best understood feature of all of science, because we can absolutely make precision measurements, we can set things up, we can simplify things, we can get rid of all the complications, we can test things to 12 decimal places, and we have, we can push our experiments, well beyond our everyday realm of experience,

and we still get the right answer. And it's all beautiful, pristine, and it makes perfect sense. On the other hand, we have consciousness and the brain, which is literally the least well-understood thing in all of science. It's incredibly complex. We don't know exactly what's going on, even at the physical level in the brain, much less the emergent level of psychology and experiences and things like that.

And you're saying, well, I am a little bit unsure how to connect one to the other. And I'm going to say, that is the completely unsurprising result of this. Why in the world would you expect to, with our current state of the art, to be able to make explicit that connection? And the fact that you don't is certainly not any reason to change our fundamental notion of how reality works. It's obviously to admit that we don't understand how the brain works very well. I use the analogy, it's like saying, I can't find my car keys, I should buy a new car. That's not the right strategy to use in this situation. You have to be a little bit more patient than that.

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Enjoy your own with Corona Serro, 0% alcohol and a source of vitamin D. Corona Serro, the official non-alcoholic beer of Milano Cortina 2026. Yeah, I suppose for the person who thinks that consciousness is inexplicable on physicalism, it's more like, I don't understand how a car could even possibly exist in the universe, as I understand it. and people sort of view consciousness that way. And I think commonly people will say, and there are more and less sophisticated versions of this, but they'll say, look, you know, consciousness is just something science will explain. Like it's no surprise.

It's super complicated. And we haven't gotten there yet. Yeah. But there are philosophers of mind who don't just want to say science hasn't explained consciousness yet, but that in principle cannot do so. It seems to occupy a different kind of space. Thomas Nagel is the sort of famous name here that I think, most succinctly puts this case in what does it like to be a bat. And one useful way of getting at this

is with the famous thought experiment that I've heard you speak about before, but I had a question about your interpretation or response to this. Famously, Mary's Room, I talk about this all the time on the show. And most people are familiar. You know, Mary is in a room. It's totally black and white. She experiences no colour for all of her life. But she has given every single piece of information that could possibly be written down onto a piece of paper and understood and like comprehended by her. She's given that and she becomes an expert. She learns about the wavelengths of light. She learns about the biology of the eye and the brain chemistry and all of that kind of stuff.

But she's never seen blue. And then at the end of her life she steps outside. She looks up. She sees the blue sky. And the question is, does she learn something new? And the implicit answer is, yes, she learns something new. She learns what it's like to see blue. And whatever that extra thing is that she's learned is what consciousness is.

I've heard you talk about this before. And I just want to give you space to respond to that. And then I've got a follow-up question if your answer remains the same as it did when I last heard you speak about that. So what do you think about that? I'm a little bit thrown off my game because it's always red that she's never seen. And you're making it blue. And I'm not quite sure how to change gears so quickly, Alex. So let me give it a try.

And I think there's different, I have one opinion, but there's different ways of stadiums. Let me state it this way. Mary's room, even though Frank Jackson, who popularized a thought experiment, has repudiated the conclusion that it is used to draw. Many other people still stick with it. I get that. I did not know that. Yeah. Oh, no.

He's totally a physicalist now. Wow. Really? Do you know why? Like, was there like a... Because it's a bad argument. I can explain why I think it's a bad argument. I cannot promise I can explain why he.

changed his mind about it. But look, it's supposed to be a refutation or repudiation. I was mixing up those two words together of physicalism. It's supposed to be, you're supposed to reach the conclusion that physicalism can't be true. Okay. Well, what is the physicalist saying about what's happening to marry the color scientist in her room? He's saying that when she's in her room and everything is black and white and she's reading all the books on color theory and getting all of these pieces of information, she's learning. She's learning. things, and what that means to the physical list is there are certain connections between certain neurons in her brain that are firing and strengthening so that when you ask her questions, she can answer them, et cetera, et cetera. A usual physicalist, reductionist account of what it means to be learning those things. Then she steps outside, blue light wavelength photons impinge on her retina for the first time, and she sees the color blue. What happens to the physicalist? Different neurons. fire in her brain and different synapses are strengthened. No one disagrees with that. And now she says, oh, now I know what it's like to see and experience the color blue. Where in the world is there any problem with that? Like, where is the refutation of physicalism? The physicalist explains this with 100% fidelity. There's nothing missing. I think the issue is quite specific. At least the the issue that I think is interesting, which is that we're indebted to Galileo for telling us that maths is the language of the universe. And the scientist wants to, it sort of wants to say that everything which it's possible to scientifically explain is something that you could in principle formulate in the language of mathematics.

I don't know if you agree with that, but that's sort of the tradition that we inherit from Galileo, right? is this idea that anything which is scientifically true can be mathematicized. And if something can be mathematicized and explained or described in a mathematical formula with letters and numbers, then in principle, everything that there is to know could be written down onto a piece of paper. Now, I understand that when Mary exits the room and there are different neurons that fire in her brain

and that gives rise to the experience, that's fine. But if there is any kind of knowledge that she gains, anything that you could class as knowledge. And if the scientific, the scientist, to use the sort of religious buzzword, believes that anything which can be known can be described in the language of mathematics, it would imply that the very knowledge that she has of that experience of blue could in principle have been written down onto a piece of paper, such that when she read and understood that thing on that piece of paper,

she got that knowledge that she gets when she walks out. she could get that just from reading something that's written down. So, like, the problem for me is specifically the fact that it's, it's not so much about physicalism, but more about scientific description. The idea that one day science will be able to explain or describe consciousness implies to me, and maybe I'm wrong about this, that science will one day be able to take that knowledge that Mary gains when she steps outside of the room and write it down onto a piece of paper such that just by reading that thing on the piece of paper, you would get the same knowledge. I don't think that's possible. And so my question to you is, do you think that's possible? And if it's

not, then what is like a scientific description that cannot be written down in that way? I think this is just very clearly a problem with getting mixed up linguistically, not scientifically or philosophically. As I said, when Mary reads about the science of color or the artistic descriptions of color, certain neurons do certain things in her brain. When she sees the color blue, different things do different neurons. Different neurons do different things in her brain. I could write down what the neurons are doing with no problem at all. But me writing down what the neurons are doing doesn't make the neurons do that. What makes the neurons do that, what makes the neurons do that is seeing the color blue. And again, I don't think the physicalist has

any problem capturing any of this. But so, but, okay, so, so in agreement with that, you could write down what the neurons do, but that's not going to make the neurons fire. Yeah, exactly. When, like, when, when, when those neurons fire, and I can, I could, I could, I could describe to Mary what neurons will fire in which way when she does step outside, such that she has a complete understanding of the neurons that are firing. Yet, when the neurons actually do fire, she will discover that it's not just that, oh, well, neurons are firing in my brain. It's like, oh, and I'm having this experience. In other words, yeah, like, those neurons don't fire until she steps outside, but you could, you could describe what those neurons are doing. And it seems

like she would still not expect or know what it's like to see that blue, even if she had a full understanding of those neurons, implying that the whole totality of what you could scientifically write down on a piece of paper would still not include that experiential aspect of blue. I know it's going to seem like we're kind of going around in circles here, but I want to make sure I'm being very specific here, because I understand what you're saying. Those neurons won't fire until she steps outside. But the point of a scientific explanation is that you should be able to take that new thing that happens when those neurons fire, that experience that comes with it, and sort of reduce it onto the piece of paper, which I just don't think is possible.

But it doesn't give you the experience. Telling Mary about what neurons fire when she sees the color blue doesn't make those neurons fire. That's a purely, my only point, my point is not to disagree that there's something new. My point is to disagree that physicalism has any difficulty describing it whatsoever. Mm-hmm. Because the neurons have to fire to get the experience. Okay, let me put it this way then.

Do you think that if you did explain to Mary in her room exactly which neurons were going to fire in what way when she stepped outside and she understood the totality of everything that could be known about the brain that she would predict that she would have this thing called

like qualia and blueness would arise? She might be able to, but again, the ability to go from a reductionist lower level description to the higher level emergent description is very difficult and it's not like necessarily an easy step. The important point for the philosophical point of the thought experiment is that all of that knowledge that she gains doesn't make those neurons fire. So you're using a linguistic construction to say she learned something new even though she knew all the facts. but that's an incorrect linguistic construction to the physicalist. The physicalist wants to know which neurons are firing. It's a different set. So it's a different thing happening.

No problems. And given that Mary's room is unconvincing to you and apparently to Frank Jackson as well, which is interesting to hear, when it comes to consciousness, just in closing here, what do you think, are you totally just nonplussed by it? Are there any of these kind of thought experiments or problems? the stuff that, you know, someone like Philip Goff writes about in Galileo's era or whatever, I know you've debated him a few times or Thomas Nagel or these guys. Is there, like, is there anything in that? It's sort of like the question I asked you about God earlier. You don't agree with it, but is there something about it that makes you go, gosh, this is a bit weird and needs explaining, or are you just like, it's just brain chemistry? Like, you know, what's

everyone going so crazy about? Like, you can understand why so many philosophers are completely perplexed by this experience thing. And what do you think is the strongest consideration that would maybe move you out of physicalism if it were like powerful enough? I think it would be easy to move me out of physicalism if there was just evidence that something was happening that physicalism couldn't explain. I think that consciousness is the worst place to look for that

precisely because the human brain is incredibly complicated and it's the last thing we should expect to understand. So I have zero, you know, epsilon maybe, but effectively no worries about that. Of course, there's a huge number of super interesting questions to ask about consciousness, how it works in the brain, precisely because it is very complicated and we have very little current level understanding of it. It's a wealth of interesting questions. But in terms of a currently available challenge to physicalism, I really don't see anything in consciousness that arises that standard. Well, that's great to hear because I've had a lot of non-physical, on the show. I've had idealists and panpsychists and the like. And I think my audience were,

I've seen some comments sort of being like, you know, why, we, we need to get a bit of materialist representation here or physicalist representation. So I'm glad to say that you have expertly provided it. Sean Carroll, thank you so much for your time. It's been great fun. Thanks very much for having me. It's been a lot of fun.