AMA | June 2026

Welcome to the June 2026 Ask Me Anything episode of Mindscape! These monthly excursions are funded by Patreon supporters https://www.patreon.com/seanmcarroll (who are also the ones asking the questions). We take questions asked by Patreons, whittle them down to a more manageable number -- based primarily on whether I have anything interesting to say about them, not whether the questions themselves are good -- and sometimes group them together if they are about a similar topic. Enjoy! Blog post with AMA questions and transcript: https://www.preposterousuniverse.com/podcast/2026/06/01/ama-june-2026/ New paper I talk about in the beginning of the episode: S. M. Carroll, N. Diachenko, and S. Dulani, "Toward a Phenomenologically Acceptable Quantum Cyclic Universe." https://arxiv.org/abs/2605.30405

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

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• 0:58Sean Carroll?

  Hello, everyone. Welcome to the June 2026 Ask Me Anything edition of the Mindscape Podcast. I'm your host, Sean Carroll. So I don't know whether this is percolating into other parts of the world. Probably it is. But here in the United States, one of the many, many news stories going on. It's a news-rich environment these days. You have to at least say that. One of the many stories is that senior officials, senior elite members of our governing classes, both literally in government and in industry, have been picking fights with the Pope, with our new Pope, Pope Leo XIV. He's an American Pope from Chicago, first-ever American Pope.

• 1:42Sean Carroll?

  But he's liberal in various of his inclinations. Not 100% so. Like, you know, there's always going to be the case that the Pope is Catholic, right? The Pope is going to agree with a lot of... Parts of doctrine that the Catholic Church likes to promulgate, and some of those will not quite count as liberal, some will, it's all very confusing, and it's all constructed by human beings, not actually given by God, but so be it. The Pope has been pushing back on various aspects of modern technology and governance. You know, he has noticed that you should be nice to immigrants is part of what Jesus preaches in the New Testament, in the Gospels. And yet, there are people who claim to be following Jesus' teachings, who are not really very kind to immigrants.

• 2:27Sean Carroll?

  So, he says those things, and that riles people up. Most recently, he put out an encyclical that questions some aspects of artificial intelligence and the possible worries about dehumanization and not taking the soul seriously enough. And I haven't read the encyclical, I have to say, but it seems that there's a lot of good stuff in there, a lot of thoughtful things. You know, the Pope and I are not going to agree on everything, but I can still respect, I have people on the podcast who I don't agree with, but I still respect as thinkers. And as far as I can tell, the Pope seems like someone who is a respectable thinker, who actually is not just going through the motions, but really taking things seriously and trying to do some good in various ways.

• 3:11Sean Carroll?

  So that gave me the idea, why don't we have the Pope on the Mindscape podcast? I think that Pope Leo would make a good podcast guest. After all, we are both alumni at Villanova University. You know, he's an Augustinian. Augustinians are the order that is in charge of Villanova, and he was a math and statistics major, back when he was an undergraduate, as well as being from the US. And I think that there would be a wonderful conversation to be had about science, and religion, and AI, and the human spirit, and things like that. Sadly, and I never do this, so I'm leaving this for a, you know, a very offhanded intro to the AMA, I have no way of getting in touch with the Pope. I was talking with a fellow Villanovan just earlier today, which is what gave me the

• 3:56Sean Carroll?

  idea, but they don't have any connection to the Pope either. So, if anyone out there in podcast land knows how I can Get in touch with the Pope to invite him on the podcast. I would love to do that. As long as he's willing to talk for an hour over the internet, then, or in person for that matter. I think we would have a wonderful conversation about philosophy and religion and science and a whole bunch of interesting things. As always, you know, I do like to have people on the podcast, I very often do, that I don't completely agree with. But I want people who I respect. I want people who have something interesting to say that we can learn from. That's the criterion. You know, so people are always suggesting podcast guests to me, and I do think that I'm always open to that.

• 4:39Sean Carroll?

  Many, I've had many guests on the podcast who were first suggested by random people emailing me or leaving comments on the podcast page, etc., or on Patreon, saying, "Oh, you should invite this person." So that can work. I get many, too many of them, to be honest, so I can't even accept a good fraction of them. But I welcome them because I want to be nudged out of the usual circles that I would tend to move in and so forth. But just to reiterate, because it's been a while since I have, you know, what I'm looking for is intellectually respectable people who have something interesting to say. And I think that the two failure modes that I get most often from people making suggestions are either

• 5:20Sean Carroll?

  they pick someone who is just very diametrically opposed to me, who I wouldn't respect, and you want to have a debate. And we're just not about having debates here on Mindscape. I want to, I want to have someone on the podcast who I want to let you listen to. I don't want to debate them. I don't think that each individual podcast episode, well, for my podcast, everyone should have their own podcast. But on my podcast, each individual episode is not a clash of views. It's an articulation of one view. I'll ask questions and I'll register my skepticism from, from point to point. But mostly I want to hear the argument so that I can understand them better. And it's the sum of all podcasts and also of all other things that you're listening to in life that should give you a balanced view, not each individual episode.

• 6:05Sean Carroll?

  So I don't want to have debates with people and smack them down or anything like that. The other and even more common failure mode is that people suggest Guests who are not actually, I don't know how to say this exactly right, because it's a broad world out there and there are many different ways to be useful and productive in society, but I want people who are really developing ideas, okay, in a really useful, rigorous way in some sense. That doesn't necessarily mean you're a professor. We've had artists and writers of various sorts, but these are people who are like really doing the creative work in a way that is making an impact on other people who are really doing the creative work. And the failure mode that I have in mind is, a lot

• 6:48Sean Carroll?

  of people suggest guests who are basically other podcasters, or pundits of various sorts, right? Voices that are out there on the internet, or on the airwaves, or what have you, who are, you know, saying lots of things about lots of different things, and saying it in a way that you might be fooled into thinking that it's really intelligent, but is just not actually engaging with the best intellectual discussion on these issues. That's why it tends to be professors that I have, because it's their job to be serious about these things. That's absolutely not a requirement, but I also don't want someone who is just very, very articulate, and very, very smart even, but not really a subject matter expert

• 7:33Sean Carroll?

  at the highest level. That's really what I'm looking for. So the Pope, Pope Leo, absolutely a subject matter expert at a certain subject. I would love to have him on the podcast. If anyone literally knows how to get in touch with him, or the relevant people, let me know. I mean, don't just email me saying, "I think you should Google it," or whatever. You know, I can do that. But if you have some special in, then let me know. It probably won't happen. I know this is a long shot. So if you're listening, Pope Leo, I do appreciate your work, even though we don't always agree about everything. And I appreciate all of the input that I do get from listeners, and the support. As you know, these AMAs are funded by Patreon supporters of Mindscape, and you could be a Patreon supporter if you

• 8:15Sean Carroll?

  so chose. All you have to do is go to patreon.com/shawnmcarroll, and for a nominal fee, you could be getting ad-free versions of the Podcast, you could be asking these AMA questions. Once in your life, you could get a priority question that I would do my best to answer. We also get little reflection audios after the every interview podcast. I don't do it after a solo or an AMA because I've just been talking for a long time anyway. But there's a lot of benefits spiritually as well as intellectually to being a Patreon supporter. So think about that if you're not already. Thanks to everyone who already is. And with that, let's go.

• 9:10Sean Carroll?

  I'm going to start by grouping three questions together. When I ask the Patreon supporters for the AMA questions, I put up a post saying, you know, give me your questions. And at the beginning, the opening of this month's version, I mentioned that I was working on a paper with a new theory of the universe. And so hopefully, it's out by now, or at least hopefully by the time you're listening to this, it's on the archive. And if it is, then I will put a link to it in the show notes. But the questions all have to do with that, since I made a provocative little statement. Sandro Stuckey says, please tell us about that paper you're working on, the one that suggests a new scenario for the possible

• 9:50Sean Carroll?

  history of, you know, the entire universe. Ben Lloyd says, is cosmic expansion existing enough to, sorry, this should be like commas here or something, is cosmic expansion existing enough to invalidate the Ponqueri recurrence being applied to our universe? Or can recurrence still happen in eternally inflating de Sitter-like cosmologies because of finite de Sitter entropy? I'm asking because I recently saw a physicist argue the Ponqueri recurrence likely does not apply to our universe, since the theorem assumes something like a bounded system with finite accessible phase space conserve dynamics and our universe has expanding spacetime, rather than particles confined in a fixed finite volume.

• 10:30Sean Carroll?

  And then Sean Sullivan says, "With the recent DESI and DES data suggesting a preference for dynamical dark energy that weakens over time, the possibility of a big crunch could be back. Given that our universe is highly anti-satropic, how would you imagine the big crunch to physically occur? Would the collapse happen synchronously, or would high-density areas hit localized singularities where voids are still collapsing? What would the mechanics of those localized crunches look like to an observer?" So, to the rest of you, these three questions don't sound like they're pointing in the same direction, but they all have to do with this paper that we just came out with. This is myself, Nadia Diachenko, who is a grad student here at Hopkins, and Sakshi Dulani,

• 11:15Sean Carroll?

  who is a postdoc here at Hopkins. And the title of the paper, I'm going to try to remember the title of my own paper. It's something like "Toward a phenomenologically acceptable quantum cyclic universe." So, what does that mean? Let me first mention that there's this idea out there called cyclic universes, right? What if, the universe is currently expanding, but what if it stops expanding, starts recontracting, and goes toward a big crunch? And what if, besides that, the big crunch is not the end of the universe, but it just goes into a bounce? So, after the big crunch, you could bounce back into a big bang, you could expand, have

• 11:58Sean Carroll?

  an ordinary expanding universe, and then you could, again, re-collapse and contract to a crunch and then bounce, and you could do this an infinite number of times. That's the idea of a cyclic universe. And so there's sort of two pieces of magic that are going on there. One is turning the big bang into a big bounce, so saying that there is a prehistory to the big bang. And of course, I've said similar things, and other people have said similar things. This is an old idea, but it's still not exactly clear the best way to make it work.

• 12:31Sean Carroll?

  So you don't just have an end of spacetime at a bang or crunch. You have a bounce in from one phase to the other. And then the other piece of magic is you need the current expansion of the universe to stop and turn around and go toward collapse. And there's various philosophical questions here about a universe that repeats. Is it an exact repeat? Is it only approximate, et cetera, et cetera? Okay, I've never been especially fond of these ideas, of the cyclic universe idea, mostly because I care about the arrow of time. So you know, the arrow of time problem has to do with the fact that our observed universe has a very low entropy initial condition near the big bang. So the options are either number one, that is the beginning of the universe,

• 13:15Sean Carroll?

  and you have to explain why it had low entropy. Or number two, it's not the beginning of the universe, and you put it into some bigger context and try to explain why it seemed to have low entropy. So the problem, as I see it with most cyclic cosmologies, is that they are cyclic but not periodic. So they are cycles. The universe expands, contracts, bounces, expands, contracts, bounces, and does that a very long number of times. But the cycles are not exact copies of each other. And this is just a feature of most models, okay? We're not talking about what is necessarily true. We're talking about ideas that scientists have actually explored.

• 13:59Sean Carroll?

  And so in particular, this goes back to Tolman, I think. Richard Tolman is his name, like many years ago, thinking about the possibility of cyclic cosmologies and pointing out that entropy will increase from cycle to cycle. Again, not just as a matter of necessity, but as a matter of what is overwhelmingly likely. And so Tolman said that the cycles will take longer and longer each time. And from the point of view of the arrow of time, many, many of the modern versions of cyclic universes have a similar feature, that entropy, it may or may not go up and down a little bit, but it's increasing from cycle to cycle.

• 14:41Sean Carroll?

  And what that means is that if you think about going backward in time, the entropy is increasingly finely tuned, right? And the same thing for every other fine tuning feature of the universe. Like if you think that it's weird or demands explanation that our universe is smooth and homogeneous at early times, or if you think it's weird that our universe is spatially very close to flat, and you have some dynamical mechanism that makes that happen, the universe gets either smoother or flatter over time. Then if you go backwards, the opposite happens. So if you just have a spatial curvature, for example, if you, you know, in inflationary cosmology where you don't try to make it cyclic, you just say, well, there was some curvature, but I inflated away. And that actually makes sense.

• 15:25Sean Carroll?

  But if you inflate curvature away again and again, okay, over the course of many, many cycles, then as you go backwards, the curvature gets bigger and bigger. And eventually the curvature gets to be infinity, and you have a singularity, and you have to explain what is, why things are like that. You're not really benefiting from the cyclic nature of the universe. So because this fine tuning into the distant past seems to be worse in a traditional cyclic model than in a, just a model with a regular Big Bang, they've never been my favorites. Now, I have been interested in models where the universe lasts forever, but is not cyclic. Models where the far, far past and the far, far future

• 16:10Sean Carroll?

  expand forever in their respective directions, so opposite directions in time from each other. But locally, from their point of view, it looks like the universe is always expanding, and it never repeats. There is sort of a minimum entropy, minimum size stage, but that size doesn't need to be small, that entropy doesn't need to be low. As long as there is some point of the universe existing and having an entropy, generically in the models that I have thought about, with Jennifer Chen and other people, the universe expands in either direction of time and gets bigger and bigger once and for all. There's no repetition or anything like that. Okay, all of that is sort of traditional cosmological talk, by which I mean, it's sort of semi-classical.

• 16:56Sean Carroll?

  That is to say, we imagine that we can describe spacetime using the classical equations that Einstein gave us in general relativity, and there might be some quantum fields living on that classical spacetime, but it's basically a mishmash of quantum mechanics and classical general relativity. So you also know, in fact, if you listen to last week's podcast, you know that I'm interested in taking quantum mechanics seriously for its own sake. And what that means is not starting with spacetime, fields, all that stuff, but just starting with the quantum state, thought of as a vector in Hilbert space obeying something like the Schrodinger equation. And you can ask similar questions about the arrow of time in that context.

• 17:41Sean Carroll?

  So the framework in which we're working is the following. We imagine that the theory of everything is a vector evolving in Hilbert space, you know, some quantum state evolving in Hilbert space, maybe a mixed state for those of you who are experts out there, not a pure state, but it doesn't really matter. And it obeys some version of the Schrodinger equation, okay? And that's it. That's the fundamental theory, you know, for some choice of the Hamiltonian of the universe. And then there will be, hopefully, some map or some procedure where you can say, okay, given that the quantum state looks like this, that corresponds to a certain view of what spacetime looks like. And you might gesture toward what that looks like without knowing exactly all the details.

• 18:25Sean Carroll?

  That's sort of the stage we're at right now. The interesting thing is that just saying that simple picture, just saying the universe is actually a vector in Hilbert space, a quantum state evolving according to the Schrodinger equation, and not worrying about the details about spacetime and bounces and dark energy and all that stuff, still lets you say quite a bit. First off, there's a very important distinction. The very first question you ask is, is Hilbert space, the space of all possible quantum states, is it finite dimensional or is it infinite dimensional? And both cases are very plausible and worth thinking about. Traditionally, most people think of Hilbert space as infinite dimensional. There's some reasons to think that maybe it's not, from quantum gravity and things like

• 19:09Sean Carroll?

  that, but you always start by thinking about infinite dimensional Hilbert spaces. The simple harmonic oscillator has an infinite dimensional Hilbert space. The standard model of particle physics has an infinite dimensional Hilbert space, okay? But it's one of the questions we don't know the answer to. Is that really true for the universe as a whole? So if the Hilbert space is infinite dimensional, that's kind of equivalent classically to an unbounded phase space. So think about, you know, planets orbiting the sun. If the planets orbit in closed orbits, like circles or ellipses, there is what is called the Poincaré recurrence theorem. They will always eventually come back to where they started, or at least arbitrarily close to where they started.

• 19:50Sean Carroll?

  There's a time scale over which, for all intents and purposes, the system just repeats itself over and over again. And that makes sense, because in a bounded phase space, the system only has a finite number of things it can do and an infinite amount of time in which to do them, so it's going to end up doing the same thing over and over again. The alternative is an unbounded phase space, and then you don't need to have recurrences or repetitions. The system can just change in a different direction forever. And that's basically what you get with an infinite dimensional Hilbert space. The universe can simply change, or the quantum state can simply change forever, there's no need to recur or anything like that.

• 20:31Sean Carroll?

  So that kind of description would work, in principle, with that kind of spacetime interpretation of a universe that expands in both directions, in the past and the future, okay? A universe that sort of has a U-shaped curve for entropy and a double-headed arrow of time, where entropy increases both toward the far, far past and the far, far future. So that's the picture that you The quantum version of the picture where you explain the arrow of time dynamically. Whereas if you have the finite dimensional Hilbert space, then that's like the planets moving in the sun in circular or elliptical orbits.

• 21:11Sean Carroll?

  There's going to be a certain time after which the universe just returns to its pre-existing quantum state. So this fact is unsurprisingly known as the quantum recurrence theorem, and people have written papers about it. It's a well-known thing. In finite dimensional Hilbert spaces, you start the quantum state wherever you want, you will eventually come back to where you began. Now, the time it takes to come back to where you began, the recurrence time, is generally hilariously long. It's like very, very, very, very long. The details depend on what you count as really recurring, okay?

• 21:48Sean Carroll?

  But to give you a very vague idea, the area of our cosmological horizon in de Sitter space, so just to make sense of those words, we live in a universe with dark energy, which is accelerating. That means there is a horizon around us, and once we get rid of all the matter and galaxies and things like that, and we're just in empty space, there's a well-known calculable size to the horizon that is around us. The horizon just means there are points that are so far away that space is expanding too fast. If you're at one of those points, you can never return to where we are, okay? That's the horizon that is around us. It would take, you'd have to move faster than the speed of light.

• 22:29Sean Carroll?

  Stephen Hawking and his friends have shown that the horizon in de Sitter space, a universe with a positive cosmological constant, has an entropy and a temperature, just like the horizon of a black hole does. And the entropy of our de Sitter horizon in the real world is something like 10 to the 122, okay? A very, a pretty big number, 10 to the 122. The number of particles in the observable universe is only like 10 to the 88th by comparison. So 10 to the 122 is a big number. If you have a quantum system in thermodynamic equilibrium with a certain entropy,

• 23:08Sean Carroll?

  then there's a well-known fact that the dimensionality of Hilbert space is roughly speaking e to the entropy. Okay, so that's e to the 10 to the 122, which is a preposterously big number. And I'm building up to the fact that the recurrence time is roughly, again, very roughly speaking, because who cares, these numbers are too big to be precise about it. The recurrence time is something like e to the dimensionality of Hilbert space. So e to the e to the 10 to the 122. And by the way, when the numbers are big enough, it doesn't matter whether you use e or 10 or 2 as your base.

• 23:47Sean Carroll?

  Uh, e to the e to the 10 to the 122 is approximately equal to 10 to the 10 to the 10 to the 122. That's just how these uh, exponentials really work out. So all of which is to say, if the universe as a whole were described by a finite dimensional Hilbert space, it would, there would be a very, very, very long time between recurrences, but they would eventually happen. Okay, and the reason why I've never been excited by that possibility is the Boltzmann brain problem. If you have, you imagine that, okay, I'm gonna imagine a universe with a finite dimensional Hilbert space.

• 24:28Sean Carroll?

  Uh, its quantum state will just cycle through Hilbert space until it eventually comes back to where it left. And I'm gonna invent an interpretation for that quantum state in terms of spacetime. And I'm gonna say, okay, at some moment, there was kind of a big bounce, sort of a big bang slash crunch phase. And from there, my quantum state does things which I interpret as, the universe expands and cools and structure forms and all those things. And then it is just sitting there in thermal equilibrium for a recurrence time, for a very, very, very long time. But it's not in exact thermal equilibrium, there are fluctuations, and those fluctuations can make Boltzmann brains. Or...

• 25:10Sean Carroll?

  Boltzmann observers, Boltzmann fluctuations of whatever kind you like. And the universe lasts for so long, between the recurrences, that most people like you and me are going to be random fluctuations out of thermal equilibrium, not people who really grow up in a thermodynamically sensible environment in the aftermath of the Big Bang. So because of this Boltzmann brain problem, I never thought that finite dimensional Hilbert spaces gave you a good description of the universe as a whole, at least not in conventional quantum mechanics as we understand it. Now, of course, maybe that doesn't bother you because you say, "Well, I hear all these questions,

• 25:54Sean Carroll?

  and this has to do with Ben Lloyd's question. Isn't the universe expanding? Isn't it supposed to expand forever? Shouldn't Hilbert space be infinite dimensional? Maybe, you know, but we have to be careful. And these are some of the things that we don't currently understand. In particular, two well-known, successful physicists, Tom Banks and Willie Fischler, have for a long time, for 20 years now, been pushing the idea that the fundamental dimensionality of Hilbert space, not just of our observable patch. So there's one argument that is very, very believable, that says the dimensionality of the part of Hilbert space describing our observable universe is finite dimensional.

• 26:34Sean Carroll?

  But Tom and Willie want to say, "No, the whole universe has a Hilbert space that is infinite dimensional." That, sorry, that is also finite dimensional and about this size. And really, the dramatic thing they're trying to say is, "There isn't independent universe beyond our horizon." Basically, everything in the universe is just sort of the same thing as we see within our visible horizon, but maybe remixed from the point of view of some other observer somewhere else. So nobody sees a boundary to spacetime or anything like that, but there, everyone has a horizon around them and can only observe a finite amount of universe, and that's all of the universe. And so it's a finite dimensional Hilbert space.

• 27:20Sean Carroll?

  Really have a complicated version of why that does not give you a Boltzmann brain problem. Basically, they're not Everettians. They're more Copenhagen-esque and they have strict rules for what counts as an observer and things like that. And none of it really makes a lot of sense to me, even though I have tried. Because I'm just so Everettian, deep down, that I have trouble wrapping my brain around what they're saying. But as an Everettian, it's very straightforward. There's a quantum state, it's evolving, that's all you have to work with. And so if most of the time, people like me, and if I conditionalized on the existence of an observer like myself, then I found that, oh, it's just a random fluctuation in empty space, I would count that as bad. And that's why I was not that excited about these ideas.

• 28:04Sean Carroll?

  But what we realized, Sakshi and Nadia and myself, is that there's a loophole to this argument. And it's kind of like a fussy, technical loophole, to be perfectly honest. But just the existence of a loophole, I think, is very interesting. There's not, in other words, a knock-down argument that the universe can't be cyclic and described quantum mechanically in a finite-dimensional Hilbert space. And so the loophole is the following. The way that you get the ordinary Poncaré recurrence theorem from Henri Poncaré at the end of the last century is to say, you know, there's some space of possibilities,

• 28:47Sean Carroll?

  some space of states through which the system evolves over time. And if you don't really, really finely tune it, it will fill that space. I mean, you have to define what you mean by the space that you're allowed to be in. So you can't change the energy of the system or other conserved quantities. But otherwise, the system will wander around through this space of possibilities. So if you look at the solar system and the relative arrangements of the planets, it's not just that they will come back to the arrangement they're in right now. If you wait long enough, they will go into every possible arrangement, given what the constraints are on the positions of the planets. And so, there was a footnote there, you know, unless you really fine tune things, right? If, let's say, you only had two planets,

• 29:31Sean Carroll?

  and the period of one planet was exactly twice the period of the other planet, then you wouldn't wait this very, very long time for everything to approximately line up. They would actually, since their frequencies are what we call commensurate, the frequency of one is twice the frequency of the other, since the frequencies are related by rational numbers, or by integers, in fact, in this case, then they repeat exactly, and they repeat exactly much, much more frequently than you would have figured out from this Poincaré recurrence inevitability argument. It turns out that exactly the same game can be played in quantum mechanics. If the energies, if the energy eigenvalues, to be technical about it,

• 30:15Sean Carroll?

  if the allowed exact energies of your quantum system are related by integers, so if they're commensurable with each other, then all of the wave function will return exactly to where it started, and the period, the time for it to do that, is much, much shorter than the typical Poincaré recurrence time. And so, therefore, if you can imagine a finite dimensional quantum mechanical system that has a spacetime interpretation as universe expands, recontracts, crunches, bounces, and then expands, and the cycle returns again and again, you can, number one, avoid the Boltzmann brain problem,

• 30:59Sean Carroll?

  because the period is much, much less than what you had in the typical case, the generic case, and because the period is much, much less, there's just not enough time to make that many Boltzmann brains. And number two, you're not explaining the arrow of time, but you're accommodating the arrow of time, because your cycles, unlike the traditional semi-classical cosmological cyclic universes, in this model, the cycles are exactly repeating each other, okay? So in this model, which is the model we proposed in our paper, What is happening to you right now, just like Friedrich Nietzsche warned you about, has already happened to someone like you an infinite number of times in the past and

• 31:44Sean Carroll?

  will happen to someone like you an infinite number of times in the future. In our model, the universe expands from a big bang, it branches, because it's already in quantum mechanics, so there's different branches where different things are going on. It then sort of approaches thermal equilibrium, which looks like empty space, just de sitter space with a positive cosmological constant. It lingers there for what to you and I would count as a very long time, but still a very short time compared to the naive recurrence time. And then it starts to, you know, matter starts to appear and it looks like the universe is re-collapsing. But of course, it's just the expansion played backward in time, statistically speaking. It doesn't need to be an exact copy, just to be super duper clear about this, we're

• 32:29Sean Carroll?

  clear in the paper, I'm not being clear right now. The contracting phase is not exactly the time reverse of the expanding phase, it's statistically very, very similar. What is exactly the same is the cycle as a whole. So one expanding phase is exactly the same as the next expanding phase and so on down the line. So you're not explaining the arrow of time by making the initial condition natural, it's exactly the opposite of that, you're just super duper fine tuning it. But what we're arguing is that there is a way to super duper fine tune so you get a phenomenologically acceptable universe, okay? So you're not ruined by the Boltzmann brain problem, you have exact cycles forever and ever, and it's, at the end of the day, it's all just quantum mechanics that is suggesting

• 33:14Sean Carroll?

  this. You know, we, in the paper, we wave our hands about how to map this quantum system onto a classical system, but, you know, spacetime with a metric and things like that, but that's the part, of course, that we have the least confidence in, in the paper. When we're just solving the Schrodinger equation, we get it exactly right, when we're trying to interpret that as an emergent spacetime, it's much harder. So again, just to be super clear, in this model, unlike most other cyclic cosmologies,

• 33:47Sean Carroll?

  The arrow of time reverses during the crunch. So the entropy increases in both directions away from the big bounce. And so what you and I would call the crunch has a reversed arrow of time to what you and I call the big bang. Of course, the people living on the other side of the bounce would call the phase they're in the big bang and the phase we're in the big crunch. So I hope that I covered all the bases there for these three questions. Sorry to go on about it. I think I thought that the paper didn't quite deserve its own solo episode, but it did deserve some explication here in the AMA. All right, let's change gears a little bit.

• 34:25Speaker 03

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• 34:52Speaker 01

  ChatGPT for Teens is designed to help teens learn, think critically, and grow their skills. ChatGPT for Teens supports active learning by breaking concepts down. Rather than giving teens the answer, study mode helps teens work through problems, and interactive quizzes test their knowledge and provide immediate feedback. Safety protections are on by default, and parental controls offer families additional options like setting study hours and quiet hours. Visit chatgpt.comPARENTS to learn more.

• 35:20Sean Carroll?

  C. Jolando, or Jolando, I'm not sure how to pronounce it, says, "You suggested that one reason current AI systems probably aren't conscious is that they don't get bored or tired. Giacomo Leopardi, the 19th century Italian poet philosopher, has a striking theory of boredom. Because desire is inseparable from human existence, consciousness suffers when it has no object, occupation, fear, pain, or illusion to absorb it. On this account, boredom is not just a lack of stimulation, but consciousness experiencing the burden of its own empty duration. Do you think boredom or tiredness are merely useful behavioral markers of consciousness, or do they point to something deeper? That consciousness requires an ongoing self-relation across time

• 36:03Sean Carroll?

  with needs or desires that can fail to be satisfied?" Bueno, por un lado, voy a repetir mi usual disclaimer. No soy un experto en la consciencia y no tengo ninguna teoría profunda sobre la consciencia. Tengo sentimientos vagos y tengo firmes convicciones de que la consciencia no requiere que cambien las leyes de la física, ¿de acuerdo? Ese es mi único falso creimiento sobre la consciencia. Pero todo lo que dices, no estoy familiarizado con el trabajo de Leopardi, pero me suena bien. Quiero decir, todas estas palabras suenan más o menos como lo que estoy familiarizado con pensando en la entropía y la cognición y cosas así, ¿sabes? La razón por la que sentimos que el tiempo está pasando, esta es otra pregunta que vamos a llegar a más tarde en el AMA, pero sentimos que el tiempo está pasando porque la entropía

• 36:48Sean Carroll?

  está aumentando, porque estamos constantemente cambiando, ¿verdad? No somos cosas estáticas, no somos programas de computadora que puedes apagar y luego encender de nuevo. Tenemos procesos que están sucediendo debajo de la superficie. ¿Recuerdas la conversación que tuvimos con Antonio Damasio hace muchos años aquí en Mindscape? Habla de sentimientos y su regulación homeostática. Esa es una forma de decir que el cuerpo y la mente, que se genera por el cuerpo, tienen una forma en que quieren estar, tienen estados en los que quieren estar y gradualmente nos alejamos de esos estados y el cuerpo y la mente tratan de nos sacar de esos estados,

• 37:31Sean Carroll?

  como un termostato hace la regulación homeostática. Y creo que muy razonablemente este tipo de alejamiento produce estos sentimientos de fatiga o cansancio o lo que sea, y que la consciencia surge muy naturalmente a través de la evolución como parte del mecanismo por el que trabajamos esto. Saber en qué estado estamos nos ayuda a sentir como si deberíamos trabajar para arreglarlo, para volver a nuestro lugar feliz, nuestro equilibrio, o lo que sea que quieras llamarlo. Así que creo que hay probablemente, o al menos plausiblemente debería decir, ni debería decir probablemente, ¿qué sé? Pero hay una conexión plausible entre todas esas cosas, ¿sabes? No sé, los poetas filósofos son grandes personas, pero no son conocidos mucho por

• 38:16Sean Carroll?

  sugerir teorías falsificables, así que no sé qué es la versión moderna de esto, pero puede que esté en el camino correcto. No veo razón por qué no. Dennis Michael Briggs, aka Mike, says, "How do you feel about being deep faked 40 years after your death, à la Richard Feynman?" Well, you know, mostly I don't care. Like, I'll be dead, right? It doesn't really bother me. I think it's silly. I don't like deep fakes of Richard Feynman either. Like, it's not the same thing. What do you think you're doing, enjoying and watching these deep fakes? It's just remixing things Feynman said, but in a way that is necessarily degraded. It's practically a theorem, right? The information, when you run it through some processing,

• 39:02Sean Carroll?

  it only gets worse, right, over time? So you're not really listening to the actual Feynman. If you want to listen to the actual Feynman, read his books, or, you know, watch the videos, or whatever. So I think I feel sorry for the people who think it's cool to do it. I mean, it might be different if you're just

• 39:19Sean Carroll?

  doing it for purely entertainment purposes, but it's not a good way to learn, and it's not honoring the person you're doing it for. Sean Bentley says, "My 14-year-old son had a well-timed quantum physics question, right when you called for AMA questions." Here it is: "If a particle is in a superposition, do the different positions move through space at identical speeds? And if not, could the different spatial positions of the particle experience different passages of time?" So this is actually an excellent question, because there's sort of two ways of answering it. One way says no, and one way says yes, and they're, you know, sort of depends on how you interpret exactly what is going on in the question.

• 40:02Sean Carroll?

  So the way that would say yes, different parts of the wave function experience different passages of time is, you know, wave functions spread out, unless they're already infinitely spread. To be a little bit precise about it, just to be, we'll be precisely correct, and then we'll be more hand-wavy about it. A quantum state of definite speed is a quantum state of definite momentum, right? Those are the same thing. And in quantum mechanics, just good old ordinary quantum mechanics of a single particle, the only kinds of states that you can get, the only kind of wave function you can get with a definite velocity or momentum, is spread out all over space. It is a plane wave that is not localized to any position whatsoever. This is a reflection of the uncertainty principle.

• 40:47Sean Carroll?

  If you know the momentum exactly, you know the position not at all, right? So, any localized quantum wave function necessarily involves parts of it moving at different velocities. And there is a rigorous version of that statement, which is to say, I can take the quantum wave function as a function of position. I can transform it into a quantum wave function as a function of momentum, that is to say, as a superposition of different states with definite momentum. And then what I would find is that it's not perfectly localized in momentum. There's different momenta, and they move at different speeds, and that's the answer to the question.

• 41:29Sean Carroll?

  So, in a very real sense, wave function spread out because different parts of the wave function are moving at different velocities. Okay. The version of the answer that says, "No, it is not true," is you shouldn't really reify, that is to say, take too literally the idea that the wave function is literally a combination of particles at different positions. Okay? It is spread out over position. It's literally a superposition of different possible measurement outcomes for the particle. But if you're an Everettian, like I am, or if you're any other person who is realist

• 42:09Sean Carroll?

  about the wave function, then when the particle is not being observed, it doesn't have a position. Okay? It's not that it has many positions. It's not even that there are many particles with slightly different positions, and it's a combination of all of them. What the particle has is a wave function. And the wave function represents different places you could see the particle where you to measure it. But when you're not measuring it, it's not that there are particles with different positions or different speeds. Okay? So, when you ask the question, literally phrased, "Do the different positions move through space at identical speeds?" No, because there are not "different positions" for the particle. Right?

• 42:54Sean Carroll?

  If you visualize it in your head, I have something that looks like, you know, a bell curve. Okay? A distribution with a peak that tails off to right and left, and that's my wave function. And what I said earlier is that the wave function spreads out over time. But that spreading out, certainly you could casually attach words to it like different parts moving at different velocities. But it's not that I can point to a specific position x and saying, what is the velocity of this position? There is no direct assignment of velocities to positions in that wave function. There's only the wave function as a whole. So in order not to get confused further down the road in thinking about quantum mechanics,

• 43:35Sean Carroll?

  I think it's worth trying to just be persnickety and get it exactly right, which is the way that you'll get some real insight on what the wave function is actually doing. Marie Roskew says, in episode 268 with Matt Strassler, you were talking about terms in physics that are not accurate, like, we say particle, but we mean wave, et cetera, as we just saw. And Matt said at one point that he found the word matter being problematic and unclear. And then later I heard Jacob Brandis, another Mindscape guest, in one of his talks, saying pretty much the same, and he put it like this. Anything that is not the gravitational field, that can force gravitational fields or respond to gravitational fields, we can refer to as matter. Where do you stand on that matter?

• 44:18Sean Carroll?

  Um, yeah, you know, this is something where I'm pretty forgiving, actually, like in this sort of use of nomenclature, and maybe I shouldn't be. I don't necessarily defend my, my easygoing nature on this particular issue. But the point is, it's absolutely true that physicists use the word matter and mean different things. Physicists use almost every word in multiple meanings and expect that as long as they're talking to other people who know what they're doing, they will understand the context that you're talking about, you know? Astronomers refer to any atom bigger than helium as a metal. So oxygen is a metal and so forth, right?

• 45:00Sean Carroll?

  But they know that, you know, they talk about the metallicity of a stellar atmosphere or something like that, because they assume that you know what they mean. Likewise, if a cosmologist talks about matter in the context of the accelerating or the expanding universe, they're distinguishing matter from radiation. They mean any kind of... Source of energy density with the property that its energy density decreases as the scale factor to the minus three. That is to say, the energy density goes down exactly as the volume goes up, because that's what slow-moving particles do, like dark matter particles, or stars, or galaxies,

• 45:45Sean Carroll?

  okay, or black holes for that matter. But you know, if you ask, well, are neutrinos matter by this definition? You know, neutrinos have mass, but their mass is very low, so they move relatively fast, right? Do they move slow enough to count as matter? And the answer is, in the current universe, neutrinos are matter to cosmologists, because they're moving substantially slower than the speed of light. But in the early universe, neutrinos were not matter. They were radiation, because they were moving close to the speed of light. And that's just one definition of the word matter. But the point is, you know, we invent words in natural language long before we start

• 46:27Sean Carroll?

  putting them to work in scientific rigorous contexts, and therefore we overload the individual words. So as long as the subset of people to whom you're talking knows what you're talking about, it's fine. The place you can go wrong is when experts start using words in their localized expert way of talking, when they're talking to broader audiences who are not experts, even if they're experts in something else, rather than, you know, the general public. Then it can get very, very confusing. And I think that it's just a tiny aspect of the broader issue that it's sometimes hard to talk to non-expert audiences.

• 47:08Sean Carroll?

  And the reason why is because when we're trained to be experts, we start thinking in a certain way, start talking in a certain way, and it becomes almost impossible to remember what it was like to not think and talk that way. And so it's a real skill to be able to talk to audiences who don't know the jargon, even if the jargon is sort of non-threatening, like the word matter. Matter is a great example of a thing, you know, unlike, let's say, Hilbert space. When you say Hilbert space, everyone knows you're talking jargon, right? So they're like, what does that mean? The problem with words like matter is you can say it and people think they know what you mean. And maybe they don't really know what you mean. And then it's on, it's the burden of the speaker to try to be as clear as possible.

• 47:55Sean Carroll?

  Josh says, "Christian List made a compelling case that your own compatibilist intuitions are philosophically defensible. But I think former Mindscape guest Robert Sapolsky, who you helped with his quantum mechanics chapter, sits in more the hard incompatibilist camp alongside philosopher Derek Perrinboon. Given that List argues the whole levels of description framework dissolves the incompatibilist threat, do you think you've swayed Sapolsky's mind? Or is it time to get him and/or Perrinboon back on the show to defend their stances?" So it is not time to get anyone back on the show to defend their stances. The point of Mindscape is not to have debates back and forth. I'm glad to have people with different perspectives, but we don't have episodes that respond to other episodes.

• 48:39Sean Carroll?

  That's just not how we work. And, but I don't think anyone's mind is being changed or anything like that. You know, and I, I hate to say it because I do like to be fair to people I disagree with. But generally, when I talk to people who are so-called hard determinists, people who, which is a bad thing to be and a certainly bad label for what they are. Again and again, quantum mechanics says the world's not deterministic. So if you're a hard determinist, you're wrong. Sorry about that. But the point is that they don't want to believe in free will. That's, they're really the anti-free will camp. That's actually what they are, and that's a respectable position to have. Determinism is not, but that is.

• 49:21Sean Carroll?

  So the problem is that they absolutely refuse to understand what compatibilism says. I had this experience with Sam Harris. I had this experience with Robert Sapolsky. They try to argue against compatibilism by making a case for determinism.

• 49:44Sean Carroll?

  And I'm just like, do you know what the word compatibilism means? It means that free will is compatible with determinism. So you can't argue against the claim that free will is compatible with determinism by saying the world is deterministic. We've already admitted that that's allowed as a possibility. I think, by the way, it's not true, but it's allowed. If it were, I would still believe in free will. And I've told them that. I told Sam Harris that. I told Robert Sapolsky that. It just has no impact. I really don't get it. You know, there are better arguments, and some people do have better arguments. But I mean, at the, you know, neither Sam nor Sapolsky are professional philosophers.

• 50:25Sean Carroll?

  They just think that they're finished with this question when they say that things are deterministic. And I think that the real experts, I don't know Paragum, but I'm sure that he's a little bit more subtle about it and recognizes that just shouting about determinism is not actually a counterargument to compatibilism.

• 50:45Speaker 00

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• 51:15Speaker 01

  ChatGPT for Teens is designed to help teens learn, think critically, and grow their skills. ChatGPT for Teens supports active learning by breaking concepts down. Rather than giving teens the answer, study mode helps teens work through problems, and interactive quizzes test their knowledge and provide immediate feedback. Safety protections are on by default, and parental controls offer families additional options like setting study hours and quiet hours. Visit chatgpt.com/parents to learn more.

• 51:44Sean Carroll?

  Adam Mills says: "I have a crackpot question about UFOs. Consider the claim of gravitational propulsion put forth in recent years by the UFO community, essentially a non-reactive system that instead manipulates the medium of spacetime for propulsion, fine. What has me thinking is this: Considering that the Earth is subjected to a myriad of gravitational influences, including the Sun, the galaxy, the Great Attractor, etc., wouldn't this give it a sort of complex trajectory through spacetime? And if so, in order for an object that is existing outside of the influence of gravity, like a UFO, to follow an object that is being influenced by gravity, like the Earth, wouldn't it also need to know that very specific trajectory through spacetime in some way?

• 52:27Sean Carroll?

  If that all tracks, my real question is this: How would you speculate that this could be accomplished? What mechanism or concept do we know of that can bridge between two objects that are theoretically separated by gravity like this?" Look, the only honest answer here is that all of this is just nonsense. As I said before, you know, my reason for not giving a lot of credence to claims of UFOs being alien intelligences and so forth is just that the scenario as a whole makes no sense. You know, why would these aliens be doing this? Why would they be so bad at avoiding detection? Why would they be so good at avoiding clean, crisp images being made of them, but they were only allowed to make fuzzy little images, etc., etc., etc.?

• 53:11Sean Carroll?

  There's lots of reasons to just give this essentially zero credence. These particular efforts, and I'm not super familiar with them, I just don't have the patience, but I, you know, by mistake have been exposed to some of them, to try to imagine how UFO propulsion, or rather UFO motion without propulsion in some of the cases, could just sort of get rid of gravity, right? Like, these people clearly don't know what gravity is, they don't know how general relativity works, they're just making things up. And if you're trying to sort of attach sensibility to them, it's taking a list of random numbers and trying to think about what it means, right? It doesn't really mean that that much. There are things within general relativity...

• 53:53Sean Carroll?

  About moving through spacetime, quote unquote, faster than you might expect, right? That's what the Alcubierre warp drive is all about. But I think that even in that case, there's not a well posed, what we would call in physics, an initial value problem. That is to say, given the state of the universe, including your warp drive spaceship at one moment in time, how does it move around in the future? It's more like a plausibility argument that you could in principle imagine something like this, even if we don't know how to actually make it happen. But we don't know how to make it happen. And the kind of technology involved in making it happen, even if not in what the UFO people are saying, but the sort of closest you could do in respectable science is still so hilariously far away

• 54:38Sean Carroll?

  from what we're actually doing in technological reality, that this is not something that I think is a high priority thing for us to think about. Let's put it that way. David JS asks a priority question. Remember that all Patreon supporters get once in their life to ask a priority question that I will do my best to try to answer. And so David says, can you please take a few minutes to explain what philosophers mean when they talk about ontology and reality in relation to physics? Are these terms rigorously defined? I ask because some claims that our underlying reality is a wave function, because I hear some claims that our underlying reality is a wave function in Hilbert space. Yet I've never heard anyone claim that a high dimensional classical phase space is real

• 55:22Sean Carroll?

  in anything like the same sense. To my mind, both mathematical objects are just convenient constructions which allow us to calculate and allocate probabilities to outcomes in a rational way. A common sense view of what is real might be that the world on a small scale is actually made up of particles or fields or whatever, whose behavior is what we would like to model. Have I misunderstood what philosophers of science are saying when they use terms like ontology or reality? So I'm not going to say a lot about reality because that's a contested field. What counts as something real? I mean, it's contested in many different ways. Are mathematical objects real? Are emergent higher level structures real? Is free will real, right?

• 56:04Sean Carroll?

  It really just is both an issue of what is your view of how reality works? And your view of what counts as real? And I have a particular point of view that I put forward in The Big Picture and elsewhere, but people don't agree. So I think that good philosophers are very careful when they use words like that to explain what sense they're saying that something is real or not. Ontology is more clearly defined and more sort of uniformly used. It's the set of ingredients in your most fundamental description of reality. It's what exists according to that more or less physical version of reality.

• 56:49Sean Carroll?

  Of course, if you're not a physicalist, then your ontology might include supernatural beings and things like that. But I don't think that most people include numbers in their ontology, even if they're mathematically realists. That I'm not sure. When you hear people say things like "reality is a vector in Hilbert space," those people are more likely to be physicists like myself than real card-carrying philosophers, although, of course, I dabble back and forth. And what that means is that reality, whatever it is, is exactly modeled, is exactly represented by a vector in Hilbert space evolving according to the Schrodinger equation.

• 57:30Sean Carroll?

  Sometimes that sentence is shortened to just saying "reality is a vector in Hilbert space." And then I think there's some tedious discussion that happens about, "Well, are you saying that the mathematical structure is real or whatever?" Like, no, that's not actually what is being said. We're just trying to get through our day without having every single caveat attached to every single sentence that we say. What we're trying to say is, there's reality. Physical world, okay, and it is what it is. It's not sort of expressible in terms of anything else. It is reality. It's sort of unique in that way. But it is represented mathematically as a vector in Hilbert space.

• 58:14Sean Carroll?

  So any question you could ask about reality can be turned into a question about that vector in Hilbert space and how it evolves with time. Now, that's an especially simple version of ontology. More complicated versions of ontology are also entertained by plenty of people. And the question about high-dimensional classical phase space is very well put. People argue about that, okay? If I say, if I didn't know about quantum mechanics and I was a Newtonian physicist and I thought that the world is made of these particles moving in three-dimensional space, there are N particles, capital N particles. What is the ontology of that theory? And someone might say, "Well, it's N-point particles moving in three-dimensional space."

• 58:59Sean Carroll?

  Someone else might say, "Actually, it's a single point in a 6N-dimensional space." That 6N-dimensional space is the phase space for the whole system, the positions and velocities of every single particle. And I know that people actually do argue over which of those is a better description or more real or whatever. To me, those are the same. They're mathematically completely equivalent. It's like saying, "Is Hamiltonian mechanics or Lagrangian mechanics real, right? Or is our numbers real when they're in base 10 or base 2?" Like, it's just a translation from one point of view to another. So I think that, you know, you have a fair point if you're worried that people who talk

• 59:44Sean Carroll?

  about these things, including myself, sometimes do it sloppily. They say things without all the caveats attached to every single sentence or every single word in every single sentence. But I think the meaning is clear. People are arguing about, you know, what are the ingredients in your most fundamental description of the world? And those ingredients are your ontology. It would be very different in quantum mechanics than it would be in classical mechanics, that's for sure.

• 1:00:13Sean Carroll?

  Marson Chady says, "Does cold fusion belong in the same category of impossible things as perpetuum mobile, or perpetual motion machine?" Um, no, certainly not. Um, like, I don't even think that perpetual motion machines are impossible as a matter of logic, right? They're impossible as a matter of the laws of physics as we currently understand them. That's true enough, but the laws of physics as we currently understand them might not be right, so I wouldn't even call that impossible. I would, I would say it violates the laws of physics. Cold fusion, as far as we know, doesn't even necessarily violate the laws of physics. When it first came out, that was like when I'd first arrived at graduate school, roughly speaking. Um, so I was at Harvard, and there were people in the physics department, applied

• 1:00:57Sean Carroll?

  physics, astronomy, who were thinking very hard about, you know, could this work? Could we understand this? Could we do the math, understand quantum tunneling and nuclei and things like that? And they basically all came around and said, "No, it doesn't seem to actually work." But that's different than impossible, right? Like, you know, you might, I don't think there's a theorem that says that something like cold fusion cannot possibly work. Uh, I think what there is, is the real-world scientific progress that says, you know, we've done the experiments, we've seen experimentally that a lot of these claims are not true. Uh, we've done the theory, we see that the particular setup that people have been looking

• 1:01:39Sean Carroll?

  at can't really work this way, according to the laws of physics as we understand them, and we move on. But we don't claim that things are impossible in science. That's just not how, uh, things are just not as clear-cut as that. We learn by going back and forth between theory and experiment and so forth. Ed Sedstuff says, "If there were, if there were practically infinite universes, would math necessarily be useful in all of them?"

• 1:02:07Sean Carroll?

  Well, it depends on what you mean by useful. I'm tempted to just say yes, that math would be useful in all of them, but of course, many of them, well, sorry, I need to back up, because you didn't say all conceivable universes, you just said a practically infinite number of universes. So you could absolutely imagine a practically infinite number of universes and still nowhere near all conceivable universes, right? But if you were thinking about all conceivable universes, many of them would be anthropically disallowed. That is to say, there's no way for intelligent conscious creatures to exist in these universes. And if you're skeptical about that, if you think, well, maybe life is really much more

• 1:02:46Sean Carroll?

  robust than you think it is, most possible universes don't have laws of physics, or at least they don't have predictability and reliability in any way that we can imagine. I mean, given any universe, I can take the universe and I can sort of stop it at one moment of time, and then it just have complete random nonsense after that moment, right? There's no reliability of what's going to happen from one moment to another if you don't have these laws of physics that are always obeyed. That to me is sort of an interesting tension for people who are human about the laws of physics, like myself, people who think that there's no separate ontological existence for laws of physics, there's just the world that falls into the patterns that it falls

• 1:03:31Sean Carroll?

  into, and then you can ask why? Why are the patterns so rigidly enforced? What is the enforcement mechanism, et cetera? But anyway, I do think that there wouldn't be observers in most of the possible universes that we can think about. Now, if you mean, would it still be useful for external observers, not in that universe, to use math to describe what goes on in the universe, then yes. I mean, even if there's just random numbers, we use math to describe random numbers, right? We have probability distributions, we calculate means, all sorts of things. So I think that math is just very flexible. It's something that would exist, would be useful in just about any circumstance. It might be more or less useful, depending on the circumstances, but it would definitely

• 1:04:16Sean Carroll?

  be there. Chris Rogers says, "Occasionally I think about how complexity can arise as entropy increases. As I was swirling milk into my coffee, it got me thinking." What are your caffeine habits? Are you a coffee or tea man and how many cups a day? Also, if I may ask a follow-up question, I heard a rumor that electric kettles are not a thing in the US. As a Brit, this is hard to comprehend. How do you make tea? Uh, good. I'm mostly a coffee kinda guy. Uh, I like tea too. I'm not actually that doctrinaire about these things. I have my, after many years of experimentation, I have my coffee-making routine down to, um, a routine, I guess. Uh, I went through lots of different

• 1:05:00Sean Carroll?

  possibilities and I actually settled on like the lowest tech, simplest one, which is I do grind my beans. Um, I think there, I am convinced that grinding your beans right before you brew the coffee, uh, makes it a little fresher than if you bought the pre-ground beans. And then I just do a pour-over. I just have a big old mug and a plastic cone that I put a filter into and I put the beans in there. Sometimes I'll put some Turkish spices in with the ground beans and I'll pour hot water right over it. Um, how many cups a day? Um, always at least one, as many as three, not a huge number, really. Like usually two, two or three maybe. Um, as far as the kettle situation is concerned,

• 1:05:43Sean Carroll?

  you're completely right. Um, Americans generally don't use kettles and our household is an exception to that. We love the electric kettles. It's just super duper useful. So, we have a kettle and when I pour my hot water over the cone to make the pour-over coffee, it is from an electric kettle. They're super convenient. But look, I, I don't think that they're so convenient that it's some kind of disastrous mistake, that they're not that common in the United States. You can microwave water and heat it up. You can put a tea kettle over the stove and heat it up that way. You know, I've done it both ways. It's just not that bad. So, uh, I do think the kettles are, um, useful and I use one myself, but I, I don't comprehend the lack of comprehension about alternatives. I think alternatives are

• 1:06:28Sean Carroll?

  not that hard to find. Perry Yuan says, "What are the boundary conditions for something to be a Boltzmann brain? Does it require a full conscious observer with memories and subjective experience? Or could something much simpler, a particle, atom, measurement event, or wave function collapse, count in any meaningful sense? And if a small observer-like fluctuation formed, could it persist and interact with its environment, potentially becoming part of a larger emergent system? Or is a Boltzmann brain by definition, an isolated and short-lived fluctuation with no real developmental continuity?" Well, I think that the important thing to keep in mind here is that it doesn't matter.

• 1:07:10Sean Carroll?

  It doesn't matter what your personal criteria are for making a Boltzmann brain, or a Boltzmann observer, or other kinds of Boltzmann fluctuations. The important point is that we have, by hypothesis, we're imagining a situation where there are randomly fluctuating things happening. And in that set of randomly fluctuating things, they fluctuate forever, so the fluctuations don't damp out and quiet down, right? They will just keep going, fluctuations forever and ever and ever. And the fluctuations are random and more or less ergotic is the word that we use. So in other words, any configuration that you can imagine that is compatible with conservation of energy and things like that will eventually come to pass in these random fluctuations.

• 1:07:55Sean Carroll?

  And then you can do statistical mechanics on this, and you can show that usually the system will be in very, very high entropy states, basically thermal equilibrium. There will be fluctuations, and you can tell me the relative likelihood of those fluctuations. Namely, if the fluctuation decreases the entropy of its surroundings by a factor delta s, change in entropy, s is for entropy, then the probability, the relative probabilities of such a fluctuation goes e to the minus delta s. Which is to say, you will get non-zero probabilities for every single fluctuation you can imagine, but the larger the fluctuation you care about, the less frequently it will happen, the less likely.

• 1:08:40Sean Carroll?

  It will be. So the reason why it doesn't matter what counts for Boltzmann brain is that if you tell me what you think should count, okay, so maybe what you think should count is just a brain out there in empty space with nothing else going on. Maybe you think, no, no, no, it wouldn't count unless there was a period of time over which the brain gathered information, maybe has a body with some sensory organisms, organs rather. Maybe you just insist that there be like a whole planet with an atmosphere and a star or whatever you want. Okay, you tell me what you want. Fine. With overwhelming probability in this

• 1:09:21Sean Carroll?

  scenario, that thing that you want will exist much, much more often as a random fluctuation from the surrounding thermal equilibrium than it will as something that developed in a thermodynamically sensible way from a very low entropy Big Bang boundary condition. So people have put work into thinking about like how much of a fluctuation do you need for Boltzmann brains and things like that, but it really basically doesn't matter quantitatively. As long as you have an eternal universe with random fluctuations in it, most observers are going to be minimal such fluctuations. Even if you literally said, I insist that

• 1:10:06Sean Carroll?

  the fluctuation include me and my environment and literally everything I can see inside my past light cone for the last 14 billion years. I think that'd be entirely unjustified for you to say that, but even if you did, the fluctuation would be just that big and nothing else. And tomorrow, when you look outside and look at the microwave background, it'll be gone. Because you didn't need that, right? You just fluctuated into existence. So. Um, I think that's the important lesson of the Boltzmann fluctuation thing. You're not going to get out of it by thinking hard about what is required for a Boltzmann brain. The other thing to emphasize is that the fluctuations are not that quick, right? Like, short-lived.

• 1:10:50Sean Carroll?

  I mean, it depends what you mean by short-lived. But remember, the whole point of the Boltzmann brain is that we're looking for trajectories through phase space that are the most likely ones, given some boundary conditions on whatever macroscopic features you want your brain to have. So there's no, like, sneaky internal correlations that you might have in the real world, because, like, in the real world, we all come from a lower entropy past. So what that means is that, very roughly, the future evolution of the Boltzmann brain, so, like, you fluctuate into existence, and then what happens? If it's just out there, maybe it would freeze, maybe it would, like, freeze into a rock

• 1:11:32Sean Carroll?

  and only very, very slowly decay, like, whatever it actually you think would happen. The assembly process of the Boltzmann brain is exactly like that but played backward in time. There's an absolute symmetry between the future of the Boltzmann brain. At whatever moment you have installed your conditions that I want the brain to look like this, the future and past will look statistically the same. So that might take a very long time for the Boltzmann brain to fluctuate into existence. At least it might take, you know, years or millions of years or whatever. But it's, that's very, very short compared to the lifetime of an eternal universe.

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• 1:13:06Sean Carroll?

  Alex DeBrow says, in your recent interview with Christian List, the intentional stance was discussed mainly in terms of interpretation from the perspective of an observer. But Daniel Dennett's framework also included the design stance, which wasn't discussed by List, and that seems crucial because it grounds intentional explanation in objective functional organization rather than mere observer projection. Do you think Dennett is sometimes unfairly characterized as a pure instrumentalist about agency and intentionality when his actual position was closer to the idea that higher level patterns are real insofar as they provide stable predictive and explanatory power, much like your own poetic naturalism?

• 1:13:46Sean Carroll?

  Yeah, in some sense, I'm not the perfect person to ask this about because when you're asking questions like is someone sometimes unfairly characterized? Sometimes, right? You know, I certainly don't have the data on how often that happens or how many people think that way. But there's a very general tendency in many intellectual circles where you're dealing with difficult questions that when someone has a nuanced view on a difficult intellectual question that is a little bit related to a simplistic view, but is much more nuanced than it, people will inevitably attribute to them the simplistic view that is closest to their nuanced view because people don't carry around in their brains a very accurate representation of other people's nuanced views.

• 1:14:31Sean Carroll?

  Okay, it's just too much work, you know, you gotta get every, keep everything straight. Even if you like really work to understand somebody and then you think, okay, I've done it like this person actually has a quite an intricate view and I'm going to try to get it right. Like a few days later, it's gone. You're back to thinking of the sort of cartoon straw man version. So Dennett is, you know, has always tried to be very straightforward about physical stuff, making up the world, being the fundamental things that exist and higher level things emerge from them, although he didn't use the word emergence a lot, but that was definitely the word I would use to describe what he was talking about.

• 1:15:11Sean Carroll?

  And people absolutely do point at positions like that and claim, "Oh, you don't think that uh, tables and chairs exist, okay?" And he didn't think that. I mean, sorry, he didn't think the tables and chairs don't exist. As you say, he thought that they do exist. They're real patterns in the world. Now, I also, and I've had, I had this disagreement with Dan. I, I tried to talk him out of it, but he was kind of too willing to feed that misimpression by calling, by referring to himself, and Keith Frankish and others also have this label for themselves, illusionists about consciousness, okay? There's a bunch

• 1:15:54Sean Carroll?

  of people out there, and Dennis was one, and Frankish is another one, who say, "I am an illusionist about consciousness." And if you say, "Oh, so you mean you think consciousness is an illusion?" And they will go, "Oh, no, no, I don't mean that." Dan will specifically say, "Consciousness is real, but it's not what you think it is." Or "Qualia is real, but they're not what you think they are," or something like that. So the illusion is not the existence of consciousness, it's the way that consciousness comes about and where it comes from that is the illusion, okay? That's way too nuanced for people to really wrap their brains around, and so they're gonna get accused of saying that consciousness is an illusion, and that's a little bit their fault. I think that that's just, uh, bad marketing on their part.

• 1:16:40Sean Carroll?

  Anthony Rubo says, "The Knicks, the New York Knicks successfully moved on to our chagrin. Are you rooting against them due to their status as Sixers villain, or rooting for them due to their current Villanova connections? And if both, which wins out?" So, for those of you who don't know, uh, my beloved Philadelphia 76ers had a heroic comeback in the first round of the playoffs against the hated Boston Celtics, uh, only to be entirely humiliated in the second round by the New York Knicks. And, uh, the Knicks, you know, I gotta say, like... There's a little bit of resentment in certain circles, and I'm in some of those circles, that the Knicks get too much attention. Because historically, the New York Knicks have not been a great franchise.

• 1:17:24Sean Carroll?

  They won a couple of NBA titles, but the last time they did that was in the 1970s. Their overall historic winning percentage is less than 50%. They don't have a lot of people... They had some good eras. The Patrick Ewing era was very good, but overall, they're a pretty mediocre franchise, all things considered. But because they're in New York City, they get a tremendous amount of publicity and people root for them and things like that. Nevertheless, I can root for the New York Knicks in their current incarnation, in part because literally three out of their five starting players came from Villanova. And the interesting thing there is that Jay Wright, who used to be the coach at Villanova,

• 1:18:07Sean Carroll?

  he only found success, as a coach, in his own words, once he stopped recruiting the highest-ranking basketball players and started recruiting people who fit into the system. People who would buy in and really play the right way and all those other cliches, rather than just those who could shoot the highest percentage and jump the highest and things like that. So you might think that that kind of strategy is exactly what would play well in college basketball, but ultimately, those players wouldn't be huge successes in the NBA. Turns out, they're also huge successes in the NBA. So I can root for New York. I do think that they not only humiliated the Sixers, they went on to then humiliate

• 1:18:51Sean Carroll?

  the Cleveland Cavaliers in the conference finals. And so now they're headed to the NBA Finals, where they will face either the San Antonio Spurs or Oklahoma City Thunder. I think whoever comes out of the West, either Oklahoma City or San Antonio, will be pretty strongly favored in that series. But having watched the Knicks clean the floor with the 76ers, they're legit. They're good. And I think that they're going to surprise some people by doing better than expected in the NBA Finals. Really, like all of my... 98% of my emotional attachment to basketball is rooting for the Sixers and against the Celtics. As long as it's anyone else playing, I can just enjoy the game.

• 1:19:37Sean Carroll?

  Baldur says: "The scenario of the philosophical zombie, in all honesty, felt to me not even worth thinking about because it seemed so obviously constructed." But then again, could AI be a real-world example for the described zombie? Acting human on requests, delivering motion pictures and sounds so real that it seems human, but having nothing going on inside? Uh, no, it could not. There might be a family resemblance, and there might be very, very interesting questions about the extent to which AI can mimic human behaviors without undergoing the conscious inner life that we attribute to ourselves. But the true zombie thought experiment says that you're imagining a physical system that

• 1:20:21Sean Carroll?

  behaves literally in every way, the same way as a human being. And that includes the behavior of the atoms and neurons in their bodies, right? That's part of behavior. The whole point of the zombie thought experiment was not simply to say, can you mimic speech and output from a conscious agent without consciousness going on inside? It's to say, can you have exactly the same physical behavior at all scales and still not have conscious behavior? And so, as a physicalist, as someone who thinks that consciousness is emergent, my answer to that is clearly no. You simply can't. It is inconceivable that that could happen because consciousness is a label that we

• 1:21:02Sean Carroll?

  put on certain physical behaviors, and that's all part of the emergence story. So, strictly speaking, an AI that is not thinking in the same way as a human being would not count as a philosophical zombie. But again, I do think that there's very interesting questions to be asked about, um, what are the requirements for the inner life of the AI before we start treating it as conscious? And again, as I've said, I don't think that we're close to that, but we might be close sooner than we think, so it's something that's very important to, uh, have strong ideas about and really think them through carefully. OneArmedWolf says Mindscape has become an important part of my life.

• 1:21:46Sean Carroll?

  My question is, what are your long-term plans for the podcast? Do you have a number of episodes you'd like to hit? Or is it more free-form? Do you ever think about the end of Mindscape? And if you plan to go on forever, that's fine, too.

• 1:21:59Sean Carroll?

  Thank you. I'm glad that it's an important part of your life. And before anything else happens, let me say I have no plans to stop doing it anytime soon. We're at, what, episode 350-something right now? Of course, there's been many more episodes than that because the AMAs, the holiday messages, the special episodes and things like that don't get numbers. So we're probably over 400 episodes total. But I think in terms of numbered episodes, once we hit 500, I would contemplate, you know, do I want to keep doing this? Probably the answer will be yes, but I'm just letting you know that I might contemplate it. Look, it is exhausting. I mean, doing the podcast by itself wouldn't be exhausting, but my life is exhausting with being a professor and having students

• 1:22:42Sean Carroll?

  and writing papers and writing books and traveling and just trying to live my life. It's, it sometimes is like a bit much, to be perfectly honest. Every individual part of it is good. I'm, I'm super blessed and fortunate in those, in those ways. And the podcast in particular continues to be great fun for me to do. I love talking to these people and having these conversations and sharing them with the world. So I have no, I'm certainly not thinking of ending it or even tempted to end it because I'm bored or run out of things to talk about. If, if and when it does end, it's not going to go forever. It will end some point. And when that happens, it will be just because I, there's only a finite number of things you can do in life.

• 1:23:25Sean Carroll?

  You have 3 billion heartbeats and you have to spend them wisely. And I gotta figure out, you know, for how many years do I want to crank out one podcast every week without fail? It's been, it's been a number of years and I've, I've done 51 weeks a year, every year. Okay, Michael Keely says, "It strikes me that the late 19th century, early 20th century was a particularly fertile period for adoption of more philosophical ideas in areas such as science, economics, politics, and other fields, with a lot of paradigm-shifting ideas in this timeframe. Do you think this period was particularly rich time for deep philosophical thinking and adoption of radical ideas? And if so, what do you think it was about society at this time that made us more open to new ideas?"

• 1:24:10Sean Carroll?

  Well, I don't know. I'm not gonna put forward an opinion on that particular time period being better than other periods in history. I mean, I do think that other periods in history, if we're just asking about, "Does philosophy have an impact on these other areas?" I think that earlier eras often had large philosophical impacts. I mean, there's certainly very big philosophical impacts on the founders of the United States, thinking of the Constitution and the Declaration of Independence and their plan for the government and things like that. The discourse over the founding of modern science with people

• 1:24:50Sean Carroll?

  like Descartes and Galileo and Newton and Bacon absolutely was infused with philosophy at that time. Going back to Aristotle and Plato, I mean, those people wrote philosophy, but they also wrote about politics and wrote about literature and wrote about all sorts of things. So maybe one could make an argument that it's the 20th century, or the mid 20th century, or, I don't know, the world-going electronic or post-World War II, I don't know, the world being completely connected, but maybe, I don't know how to objectively judge this, but maybe philosophy has dropped out of the conversation relative to where it used to be. And I can think of two obvious reasons why that might be true, if it is

• 1:25:35Sean Carroll?

  true. One is just that the rate of change is faster. Philosophy is a slow field, like philosophy is for people who are willing to take their time to sit and think deeply about things without any obvious short-term payoff, right? And that mode of thought has become less and less... Common, let's just put it that way, in the late 20, early 21st century. And the other reason is just that knowledge has become very specialized, right? Knowledge has become bigger. There's more things that we know now than we knew 100 or 1,000 years ago. It is harder for any one person to be a master of all these different areas. And therefore, specialization occurs.

• 1:26:18Sean Carroll?

  And specialization means that people in any one area are not paying that much attention to other areas. So it's not just philosophy. I think that physicists don't pay a lot of attention to economics, or biology, or politics, or art, or whatever. And likewise, chemists don't either, nor do historians, et cetera. You know, people don't pay as much attention as maybe they used to, to all these other things, simply because there's too much of it out there. Again, I don't know if that's actually true, but I think it's plausible. And I think the solution is, you know, I don't think that we can demand that every person be an expert in everything. That's not plausible, that's not feasible.

• 1:27:00Sean Carroll?

  What we can do is try to encourage people to talk to each other, right? To actually engage with people who are experts in different areas, to get feelings for what the relevant thoughts might be, and to take the opinions of experts outside their field seriously. Like, as someone who has been a university professor for many, many years, I'm well aware that people in Department X don't always have very high opinions of people in Department Y for just about any choices of X and Y. And I think that's a tragedy. I think that's just terrible. Like, people are not humble enough about the fields they're not expert in. And that's not only true for, you know, people on the streets who get their ideas from podcasts.

• 1:27:42Sean Carroll?

  It's true for the best intellectuals we have in the world also. So that is a feature of the modern world that I think we could certainly do a lot better at. Okay, I'm going to group a couple of questions together. Rob Gebala says, "Has your credence that advanced AI could become an existential risk to humanity increased in recent years? I'm especially curious whether developments in autonomous AI agents, including systems that can coordinate complex tasks and even higher humans online, have updated your view meaningfully." John Plasterer says, "You've developed some well-formed opinions on the limitations of language models and articulated them on your show. With the recent result from OpenAI disproving a well-known central conjecture in discrete geometry, does this change your view on language models directly contributing to new physics?

• 1:28:27Sean Carroll?

  If not, what would change your opinion?" So both about, you know, the capabilities of LLMs and other AI models and things like that. So for John's question first, the recent discovery, or proof, I guess, of a conjecture by an LLM, I don't even know which one this is referring to, because there's been several of them. There's been impressive work with using LLMs to be able to either disprove or prove mathematical conjectures. Actually, to me, this is not very surprising at all. And I like to emphasize, I have been surprised, I'm overall very surprised, at the improvement in LLMs from 10 years ago to today, by a lot.

• 1:29:11Sean Carroll?

  They're much more capable in many ways than I thought they would be. But given where they are now, the fact that they can prove or disprove well-formed mathematical conjectures, isn't that surprising to me? Just like I was not surprised when AI became good at chess, or Go, or protein folding. Those are, to me, exactly what computers should be good at, right? It's very, very well-formed, clearly articulated problem spaces that are too big for humans compared to computers. So it's just a matter of time before human beings became outclassed at that by the computers becoming more clever. So I don't know how far that will go.

• 1:29:53Sean Carroll?

  But I think that it's, you know, this feeds back into Rob's question also. I think it's important to recognize that we, one of the huge mistakes that people make, and people make it at different levels, so I'm sure that you, the person listening right now, doesn't make this mistake. But many people still today insist on thinking of intelligence as a single, one-dimensional thing. I was having this conversation with Alison Gopnik, former Mindscape guest, a little while ago, when we were both in Santa Fe. We were talking about how frustrating it can be to get through to people who have an overly simplistic view of intelligence that leads them to think that, you know, any day now, AI is going to be just as good as PhDs or whatever.

• 1:30:37Sean Carroll?

  The reality is that they're going to be just as good as PhDs at some things and not others. And that's just not that sophisticated a thing to understand. I think it should be very understandable. What we kind of hit on was, you know, what we should emphasize is the fact that intelligence is not one-dimensional. It is a nonlinear, high-dimensional, spiky, weird kind of space. If you think about the space of, number one, problems you can solve, and number two, methodologies that you can use to solve those problems. And LLMs do very, very impressive things, not in the same way as human beings. And therefore, it is completely unsurprising to me that they're going to be really, really good at some things, totally less good at other things.

• 1:31:22Sean Carroll?

  You know, I actually, like, I'm pro-AI in the sense that I think that this can be a wonderful tool to use. And you can very clearly tell when you're talking to the AI about research-level questions, that as long as you're asking it questions that have already been answered and talked about in certain ways, they're quite good. I use it like as a hypercharged version of Wikipedia, right? If the answer is out there, or is closely related to an answer that's out there, they're super good at that. As soon as you start talking in a way that is not common, that is trying to change the way that we think about a certain problem, which is something that's very common in my kind of research, then it stumbles, then it has trouble, because it doesn't really

• 1:32:07Sean Carroll?

  know how to put things together in the right way. So I'm not surprised about the math results. To Rob's question about existential risk to humanity, I mean, I think I still haven't heard what the risk is. What is the scenario by which AIs are going to be an existential risk? I think that there's sort of two kinds of scenarios. One is completely vague, and just based on the idea that the AIs will be so intelligent that they will outwit us somehow. And I think that's a very shallow analysis that doesn't really get into what it means for an AI to have motivation, or goals, or values, or planning, or anything like that.

• 1:32:51Sean Carroll?

  And not to say that it's impossible, I just haven't heard any reason to think that those sorts of scenarios where the AI is so smart, we can't cope with it, make any sense at all. The other kind of scenario is that we are really stupid, and we put AI in everything, and give it control and responsibility over things that it shouldn't have, and we can't really control what it's going to do. That, I see, is perfectly plausible. That's clearly happening right now, right? Plenty of people are turning tasks over to AI, and then realizing, oh, actually it doesn't do such a good job. And if those tasks are super, super important, then we're gonna be in trouble.

• 1:33:33Sean Carroll?

  Again, I see no possible way in which that's existential. Like existential risk means literally eliminating human beings from the planet. I can imagine planes crashing, I can imagine people losing their bank accounts, I can imagine all sorts of things like that. I can imagine companies going under because they fire a bunch of employees, thinking that they can effectively replace them with AI, and realizing that that doesn't work quite that way. But none of those is an existential threat. We have plenty of existential threats that are just much bigger than that one, from nuclear weapons to even worse biological worries, so I would worry about those first.

• 1:34:12Sean Carroll?

  Robert Ruxendrescu says, "When talking about the top five players in NBA history, how do you personally classify them? What matters? Does team performance matter? Do the number of championships matter? Stats? Should we look at offense and defense equally? What would be your top five and why?" So, again, I'm going to give an unsatisfying answer. I think that the project of talking about the top five players in NBA history is completely ridiculous, completely ill-formed. It's just not a good question for all sorts of reasons. I mean, mostly because the game changes, right? Someone who might have been the most effective player in the 1950s is not going to be the most effective player in the 1980s, and that player's not going to be the most effective player now.

• 1:34:56Sean Carroll?

  Not just because the training regimen and the skillsets have changed. They have. People have become more athletic and so forth. But it's completely false. By the 1960s, the athletic level in the NBA was very, very high. You see those old films of Bill Russell and Wilt Chamberlain. Those people would dominate today very, very effectively. But the useful skills have changed, right? Your three-point shooting did not matter in the 1960s. The NBA literally didn't have a three-point line. But most importantly, it's a team sport. And most importantly, even more importantly than most importantly, it's a results-oriented sport. So, here's how I think about it.

• 1:35:40Sean Carroll?

  When I was a first-year college student at Villanova, that's the first time Villanova won the NCAA basketball championship. And for those of you of a certain age and a certain inclination, you remember that game because Villanova beat Georgetown in the final game in one of the biggest upsets in NCAA history, and also one of the most thrilling games. Villanova played out of their minds. It was a statistical fluctuation. They barely missed any shots, and still, they only won by like two points, right? It was still very, very close. Because Georgetown with Patrick Ewing was just an incredibly talented team. Everyone thought that they would win quite easily. And Ed Pickney was the center.

• 1:36:22Sean Carroll?

  For Villanova, the guy who got matched up against Patrick Ewing, he was not as good as Patrick Ewing by any stretch of the imagination. And I remember the two of them became friends, Patrick Ewing and Ed Pigney, and they were being interviewed years later on some TV program. And Patrick Ewing said, yeah, you know, I've finally gotten Ed to admit that our team was actually better, even though we didn't win that game. And I think that that's just a wrong way of thinking about it. What matters is who wins the game. That's the point. Like, the fact that you, like, maybe should have been better in some metaphysical sense in other possible worlds, you won the game, who cares? It matters who wins the game. That's what the game is about.

• 1:37:07Sean Carroll?

  That's why we play the games. That's why it's fun to watch them, because you don't know ahead of time who's going to win. And so when you say the top five players, and I don't mean for Robert to, you know, bash you, like, everyone in the world talks about the top five players. We have our favorite players to watch and things like that. But I just think that, you know, if, once you start taking the project seriously, it falls apart. Like, what do you mean? As you, as you say, how do you classify them? Does it, is it the team performance that matters? Because it is a team sport. Is it individual stats? Is it championships? And the answer is none of that. Who cares? What matters is who wins the game, and, you know, you need to watch the game to see what happens.

• 1:37:48Sean Carroll?

  I do remember, you know, the fact, for the fact that it's a team sport, it is very important. Apparently, there was a story, I don't even know if this story is true, but it's one of those stories that is a pretty good story, so you tell it anyway. Michael Jordan on the Chicago Bulls, in the early days, you know, we forget now, but he really struggled for the team, for the Bulls, to win. You know, Michael Jordan was incredibly effective right out of the gate. As soon as he landed in the NBA, he was very, very dominant, but his team didn't go very far. And it was mostly because the team wasn't very good in different ways, you know, and it was just hard for them to get over, past really good teams that were around, like the Boston Celtics, the Detroit

• 1:38:32Sean Carroll?

  Pistons, et cetera. And Phil Jackson at some point had just become the new coach of the Bulls and he was trying to convince Michael Jordan that it was a team game and that he should sort of not just try to do everything himself. And the the story, which again, I don't know if it's true, goes, uh, so at one point Phil Jackson says, all right, Michael, if you think that you're so good and you're better than anybody else, you're going to play one on five. Okay, we're going to play by the real rules of the NBA, but there's going to be five people on the other team and you're just going to be the one person. That's going to be your entire team. And Michael Jordan is like, sure, all right, I'll do it. I'll beat these chumps. And all right, he says, okay. And then they

• 1:39:13Sean Carroll?

  go to like, start playing and and Phil Jackson says, well, no, you got to inbound the ball. You got to throw the ball from outside the out of bounds line to a player inside. And Jordan is like, but there's only me. And Phil Jackson is like, yeah, that's right. It's just one of you. Doesn't matter. You can't even inbound the ball unless you have a team playing together. Uh, I like the fact that it's a team game. That's one of the joys of the NBA. You can't even compare different teams on, uh, from different eras. So I like the reality of the game. I like the actuality. I like the games being played and seeing which team is going to win and all that stuff. Now, having said that, having

• 1:39:55Sean Carroll?

  been grumply philosophical about it and, and, you know, trying to be metaphysically accurate, there is a question, which is very down to earth. If you're a general manager of an NBA team, would you, would you trade one player for another, right? Or who would you draft first? Or who do you want to sign as a free agent? Those are very operational questions because that's not who is the best. That is which person at which contract level will help the rest of the team I already have win more games, right? And that's a very down to earth question. And again, there, I don't think that you can just look at stats or, uh, skills. You have to fit in with the rest of the team. That's because it's a team sport and I think that really matters.

• 1:40:39Sean Carroll?

  Leo Behe says, "In your interview with Alex O'Connor, you said that you don't find necessity to be a compelling explanation for the constants of nature, and that they could have easily been different. I believe you also consider possibility to be an epistemic concept rather than an ontological one. If so, when you say that the constants could have been different, are you basically saying our knowledge underdetermines the values of the constants? Or are you saying that you think we will not find deeper laws that the constants are derived from? Or have I misunderstood you completely?" What I'm saying is, you know, I think about possibility and necessity in the language of possible worlds, right? Following David Lewis and other people, if you think that we can imagine the space

• 1:41:23Sean Carroll?

  of all possible worlds, and the problem is, we can't, right? That's too big, a space, all possible worlds. And, you know, the space of possible worlds is much, much bigger than the space of branches of a wave function in Everettian quantum mechanics. In the branches of the wave function, you still have the same laws of physics pushing you around in each branch of the wave function. In all the possible worlds, you literally have every possible world with all the different kinds of laws of physics. Some worlds don't have laws of physics, different dimensionalities of spacetime. Some worlds don't have spacetime. Some worlds are just a point, you know, like literally every possible world. So necessity, in that context, is defined as something that is true in every possible world.

• 1:42:06Sean Carroll?

  And there's very, very little that you could even think of, very few properties that count as necessary under that definition. People have tried to argue for the necessity of God, but I think that their arguments are pretty weak, pretty feeble. Possibility is when at least some worlds have a certain feature, okay? And there, a lot of things are possible, as we learn on Mindscape, but they might not be actual in a large number of worlds, or very many worlds at all. So when I say the constants could have been different, I'm saying that I see no obstacle to imagining possible worlds that are more or less like ours, but the constants Have different values.

• 1:42:50Sean Carroll?

  Now, I might be wrong about that because, of course, it might be that the phrase "a world like ours" implies some levels of physics that we don't know about. Okay, so if you were having this conversation in the 1850s and you didn't know about quantum mechanics, you might have thought that worlds like yours had certain properties. And then you realize, oh, my own world doesn't even have these properties that I thought it did, because I didn't know about quantum mechanics. And so that might be true for our universe as well. It might be true, in other words, that the deep-down laws of physics that give rise to our universe are incompatible with other values of the constants of nature.

• 1:43:32Sean Carroll?

  I just think that's very unlikely, given what we actually do know right now. I don't even think that most possible worlds have something you would call constants of nature. So things could be very, very different. I also think it's kind of a misguided attitude. As a scientist, I think that we're not about looking for necessity in what happens. We're about looking for actuality. We're trying to figure out how the actual world works. And so I think that I'm happy to imagine all sorts of other worlds. And the job of science is to figure out which one of those imaginations matches the world around us that we actually see.

• 1:44:12Sean Carroll?

  Paulina Vino says, "Can you explain what the classical limit is and how it's calculated?" Sure. So in quantum mechanics, as you know, we have this idea that the world is described by a state. That's a very vague way of saying things. And it is a very vague way of saying things. And it's intentional, because it's very hard to talk about what the quantum state is without either being very mathematical sounding or prejudicing your physical view of what the quantum state is. So here are two different ways of saying what the quantum state is. One way is to say it's a vector in Hilbert space. Okay, that's what we were talking about earlier in the AMA.

• 1:44:55Sean Carroll?

  So what that is simply saying is that we have this View of the fundamental ontology of reality that we can represent mathematically in a certain way. And there's a big old vector space, you know, either infinite dimensions or a very, very large number of dimensions. Unless you're Daniel Harlow and you think it's one dimension. But most of us think it's a very large number of dimensions, 10 to the power 10 to the 122 at least, or much bigger than that. And it's a vector, it's a little, you know, thing with a direction and a arrow with a length and a direction is moving around in that space. According to some law of physics, that's accurate in quantum mechanics as we know it.

• 1:45:37Sean Carroll?

  But it's not very helpful if you're not already up on what all those words mean. The other way of explaining what the quantum state is, is to say it's a superposition of possible measurement outcomes. So if you have the down to earth idea that there is a wave function that depends on X, the position of a particle. Then that wave function squared gives you the probability of seeing the particle at that point, if you were to measure it. Okay? So the quantum state either way that you want to talk about it, that second way is a little bit more physically transparent. But also a little bit tricking you into thinking that there's some implicit notion of space in the quantum state. That may or may not be there, depending on what kind of model you're actually looking at.

• 1:46:21Sean Carroll?

  So the classical limit is a matter of emergence. So emergence happens when you have one theory, the lower level or the microscopic theory, in this case, quantum mechanics. And there is a map to another theory that in general is many to one. So many different states in the microscopic theory get mapped under the emergence map to the same state in the macroscopic theory. In this case, the macroscopic theory is just classical mechanics, either Newtonian or relativistic or whatever you want to have. So what we're saying is for a wave function. There can be wave functions that are more or less localized around some location in space.

• 1:47:02Sean Carroll?

  And when that happens, you can map them to an idealized point particle at that location in space. And then there's a theorem due to Paul Aaron Fest that says, under the right conditions, and we're not going to go into what the right conditions are, but they are there. Under the right conditions, the average value of the wave function, the expectation value, roughly speaking, where it is peaked, right? Around, if it's localized in space, then you put a dot at sort of the middle of the wave function. And the Aaron Fest theorem says that dot will obey the classical equations of motion. So you can derive Newton's laws of motion from quantum mechanical laws underlying it.

• 1:47:47Sean Carroll?

  So there's actually two, and that's the classical limit. So secretly, there were two big steps there, and they're both important, and sort of we tend to ignore one and pay attention to the other one. The first one is, you have to start with a wave function that is more or less localized around some classical point. Like when I say I have a wave function, it's really concentrated near some point. Some wave functions are like that, some are not, right? Some could be spread out, or some could be like, oh, there's a bunch of it here, but there's also a bunch of it over there, very, very far away. Those are not classical-looking wave functions. Most wave functions don't look classical. That's just a feature of it. And then the other one is, if you obey these conditions, and under Aaron Fest theorem,

• 1:48:30Sean Carroll?

  that basically say, you know, the thing is heavy, macroscopic, it's not being pushed around by microscopically tiny forces, all the forces pushing it around are big and macroscopic themselves, then you will obey the classical equations of motion. So that first part, localizing the wave function, we think we understand how it happens, is through decoherence. If you start with a wave function that is not localized, but then it bumps into other things in the world, interacts with them, becomes entangled, then either, depending on your favorite way of talking, it will either collapse to a localized point, or the world will branch into different branches, on each of which, the wave function is relatively localized.

• 1:49:12Sean Carroll?

  And then you follow Aaron Fest theorem and say that the thing that is localized around that point, that point obeys Newton's laws of physics, and you get the classical limit.

• 1:49:22Sean Carroll?

  Redlinks says, "I plan to begin studying physics at university after this summer. Do you have any advice for someone aspiring to become a physicist?" Um, I've been asked this question before, but you know, not everyone listens to every episode and, and new generations come to life, uh, so I'm always happy to tackle this one again. You know, I'm not great at giving advice. I, yeah, I'm literally an advisor as a, as a professor, you know, one has students and one advises them, so I have to do it. But I'm always very tentative about it because everyone's situation is different and you have to respect that. And the advice that you need is not, are, not always going to be the advice everyone else needs, right? And you have to take that seriously.

• 1:50:05Sean Carroll?

  So you really, you know, you shouldn't look for the right thing to do. You should look for the right thing for you to do. And so depending on who you are and what your abilities and inclinations are, um, some version of studying all the physics you can is very important. And I say that very specifically because some people who get interested in physics, again, depending on what they want to do. Do you want to be an experimentalist or a theorist, et cetera? But a lot of people say, "Oh, you know what's really important for physics is mathematics. So I'm going to study all the mathematics that I can." And mathematics is absolutely important for physics and I studied a lot of it and I won't discourage you from doing it, but don't do it instead of studying physics.

• 1:50:47Sean Carroll?

  Like, a lot of times, the mathematics you need is taught to you in the physics courses, right? There might be extra mathematics that's even better. And again, I'm not going to dissuade you from studying it, but it's not quite as important if what you want to do is studying, is become a physicist as it is studying physics. And when I say study, I mean, you know, go to class and do the work and things like that, but also very importantly, don't wait for the classes to teach you things, right? Like, you're a free agent, you're a person with inclinations and free will. You can choose to learn things. You, you live in an environment, you kids now, don't know how good you have it compared to when I was your age.

• 1:51:29Sean Carroll?

  I spent a lot of time just lurking in bookstores, gazing longingly at all these books on physics that I couldn't afford to buy. Nowadays, you go online, you can get MOOCs, online courses, you can get lectures, you can get lecture notes, you can get YouTube videos, etc. You can learn things that you want to learn, and you need to learn it seriously, right? Not just superficially. Like, if you actually want to be a physicist, you really do have to get that information into your brain. I know that this is a new problem that people are facing now, they didn't face in my age, that AI, LLMs are super helpful in some ways, but they can be a crutch that can stunt your development if you use them incorrectly.

• 1:52:14Sean Carroll?

  If you're constantly going to the LLM to ask for help in answering questions, you're not training your brain to answer those questions, right? You can't build a machine to lift weights for you and expect to get stronger. So you need to actually use your brain to tackle the problems. So whatever is the thing you don't know yet, is it statistical mechanics, E and M, whatever, learn it. Super symmetry, quantum field theory, who knows? Tackle all these things, read about them, learn it, do the problems, and think. And then the other thing, of course, is at a more sort of big-picture career level, take that same philosophy, but apply it not just to learning, but to doing. Physics.

• 1:52:58Sean Carroll?

  So go to seminars, go to talks, think about open problems in physics. Notice what other people are doing. Read their papers, look at the archive. You know, at first, you will, especially if you're just starting at university, it will be all nonsensical babble. You will not understand it. But it takes time, and it will leak in, you know? I remember like at one point in my first year in grad school, we were going to these seminars, my friend Ted Pine and I, and I said, "You know what? I'm gonna start asking questions in these seminars." And he looked at me like I was crazy. He's like, "What are you talking about? You have no idea what they're talking about in most of these seminars." And I said, "Yeah, I'm gonna try anyway."

• 1:53:41Sean Carroll?

  And, you know, I don't know whether my resolution was successful or not.

• 1:53:47Sean Carroll?

  But you have to, you know, engage in the discourse a little bit. And it's a tricky thing to do because you have to sort of be bold enough to ask good questions and have suggestions and think thoughts that are not already out there. But you also have to be humble enough to realize, you know, I don't really understand this stuff yet. And other people maybe understand it better than I do, and I have a lot to learn. So you're literally asking questions, learning more, thinking about open problems, thinking about what are the kinds of physics that you are most interested in, all that stuff. Take it actively, take it seriously, take the initiative, and good luck with it.

• 1:54:25Sean Carroll?

  Rue Phillips says, I want to learn more on moral philosophy. Who are your favorite moral philosophers? And he suggested books. I'm particularly interested in learning more about moral constructivism. Yeah, I think that my favorite books, I don't even know if they're books, but you know, you can also read papers. Papers are often just as interesting as books in this field. They're both, you know, people write different things. Like, I love all of the, what is the, is it the Oxford series on like the very short introductions, right? You get these tiny little books and they introduce you to some topic. And so like moral realism might be a topic. For that matter, entropy or whatever, there's like little very short introductions on all sorts of things. Those are fun books to read and they give you an overview of the field.

• 1:55:09Sean Carroll?

  And they're really meant to be sort of punchy and fun to read and give you a feeling for what is going on. Sharon Street at NYU is probably the philosopher from whom I've read and heard the most about moral constructivism in particular. More, again, from papers than from books, but she might have some books out there, I'm not sure. I certainly recommend checking out the Stanford Encyclopedia of Philosophy, the SEP. The Stanford Encyclopedia is this amazing source. I wish we had something equivalent in physics, but they get, you know, high-level researchers to write these survey articles

• 1:55:51Sean Carroll?

  in encyclopedia form on all sorts of philosophical topics. And they have references to all of the Literature that you can just click on, etc. So, well, when it's available, sometimes you have to actually go and get a book and read it. But yeah, I wouldn't say I have favorite moral philosophers other than that. I have a grab bag, you know, I think that I admitted before that I don't really have a once and for all well articulated moral philosophy. I have feelings, I have impressions, I have convictions about this and that different thing. But I wouldn't say I have a systematic approach, so I don't really have like a list of top five moral philosophers that I really appeal to.

• 1:56:37Sean Carroll?

  Nikola Ivanov says, if quasi classical reality emerges through decoherence, stable records and the thermodynamic arrow of time. Could observers with very different bodies, environments, or evolutionary histories coarse grain the same underlying quantum state in genuinely different but equally valid ways? Or would any observer capable of forming records and making successful predictions converge on the same emergent patterns? This is a great question. You know, if you listened to my solo podcast last week, you know that I'm fascinated by this question of how you start with this bare bones, very, very austere picture of quantum mechanics as describing a vector in Hilbert space and from that finding all the richness of the world around us.

• 1:57:22Sean Carroll?

  So Nikola's question is, could you find two different worlds around us in the same quantum state doing one kind of thing? I think the answer is no, I don't really have a theorem about that, but I'm would be very suspicious of it. Because you kind of need two things and you already put your finger on the two things you need. One is you sort of in the dynamics, you need some sense of space and locality. So I'm thinking, I'm going to grant us the idea that to get observers capable of forming records and making successful predictions, we're going to need something like a traditional spacetime description. That is to say, you have time, so things are changing over time.

• 1:58:07Sean Carroll?

  And you also have space, so things have locations. And what space really means is it gives you a way of saying some things are next to you and bumping into you and interacting, and some things are far away and not interacting with you. That's really all you need in the most general sense. But I think you do need those two things. And my suspicion is that if you have that kind of local description emerging from the quantum state, it will be more or less unique. I think that there's one very famous counter example to that, which is ADSCFT. There's a duality where you have a very different notion of what is local and what is not local.

• 1:58:47Sean Carroll?

  So I think that that is a good warning out there, that you shouldn't be too quick to say there's only one way of finding local physics in the quantum state. But the other thing you need is that thermodynamic arrow of time, right? You need this progression from low entropy to high entropy so that you can have records and predictions and things like that. And I think, but I've never actually done this, this is something I've thought about doing, but never quite done it. I think that if you have two different descriptions of the sort of emergent classical picture from the quantum state, and the arrow of time is going one way in one of them, or there is an arrow of time in one of those descriptions, then there won't be an arrow of time in the

• 1:59:31Sean Carroll?

  other one. It will just look like thermal equilibrium or something like that. Or either, or something like that. I'm not exactly sure what it is. The reason why I haven't successfully investigated this is because I'm not really sure about the general ways in which you could get two different local descriptions. I think that ADSCFT is the most obvious example. There's some other examples, like the Ising model and things like that, has a duality which looks non-local but isn't really in the same sense. So ADSCFT is so special and weird that maybe it's the only good example. If I had another good example, then I could sort of investigate this question more clearly. But that's my feeling, that's the best I can give you right now.

• 2:00:14Sean Carroll?

  I suspect that the requirements of both having this sort of local spacetime description and having a notable thermodynamic arrow of time together make things more or less unique in the way that spacetime and observers would emerge.

• 2:00:29Sean Carroll?

  MSFV says, "What if alien life is relatively common, but as there are millions or millions of billions of years more technically advanced than the human race currently, we cannot tell them from what we perceive to be nature." Sorry, when I'm recording this, it's early in the morning here, and I'm not in my most articulate reading these questions here, but MSFV is asking whether or not the aliens might be out there and we just haven't noticed them yet, okay, just because they're so technologically advanced. You know, anything's possible, it's possible, but I don't think that's very likely.

• 2:01:08Sean Carroll?

  I think it's more likely that they're technologically advanced and just are uninterested in spreading the news throughout the cosmos, but you know, I kind of think, and this is something we should be open-minded about, but you know, the laws of physics underlying everyday life are pretty well-understood, right? I've made that point, like the laws of physics that are relevant to what's going on in you and me, we have a good handle on those fundamental laws of physics. So what that means is that if there are new laws of physics, if there are new ways of doing technology, there's a huge obstacle to them, which is that they're made of things that are either too heavy to make, unless you have a particle accelerator, or they're

• 2:01:53Sean Carroll?

  too short-lived, or both usually, right? Like the Higgs boson you can make, and then it decays in a zeptosecond. That's why you're never gonna get like Higgs boson-based technologies, they decay in 10 to the minus 21 seconds. So, I tend to think, of course, and this is, you know, it's always possible that physics outside the everyday life regime will be discovered that might be put to good use, but it's plausible that it won't be either, right? Like, it's been, I don't know, 50 or 75 years now, where all the technological advances we've seen around us have been based on the same laws of physics. It's not, it's not new laws of physics. Leading to new technological advances anymore like it was 100 or 200 years ago.

• 2:02:35Sean Carroll?

  So if that's true, then the aliens are more or less limited to E and M and gravity and the nuclear forces, just like the rest of us are. And I imagine it would be very hard for them to hide from us. Even as I'm saying this out loud, I'm realizing that there are loopholes here that we can pretty easily climb through. Of course, the aliens, it depends on what kind of alien civilization we're talking about is the problem. That's why it's hard to make very general statements. Imagine that there was some set of aliens that, I don't know, had spread through the stars and, you know, they had 100 different star systems with planets on them where they lived, okay? And they were communicating with each other through ordinary down-to-earth technologies like lasers or whatever.

• 2:03:18Sean Carroll?

  There's no reason for them to waste their energy in spreading radio waves in all directions, right? They should be able to point their signals at each other fairly effectively. That is something you can do with existing laws of physics. So we might just not be in the line of fire or the line of communication. That's completely possible. So that's not the aliens trying to hide, it's just that they're not trying to draw attention to themselves. And I think if the aliens were out there but just not trying to draw attention to themselves, then it would be completely possible that we haven't detected them yet. Ken Wolf says, "In Canada, our constitution has a notwithstanding clause that allows

• 2:04:01Sean Carroll?

  either the national or provincial governments to pass laws notwithstanding the fact that they violate certain provisions of the Charter of Rights, with specified guardrails like the need to be renewed by a majority vote every five years. Many people here are dead set against the clause, but I see it as a compromise between democratic rights and individual rights, which are inevitably in conflict and both of which always need to give way to accommodate the other. Do you agree that that is the right way to think of it?" I shouldn't comment specifically on the Canadian Constitution. I don't really know anything about that. And I think that the crucial question here, as for many constitutions, is how the rules get interpreted by the actual, living, breathing human beings who are in the court system or the legislature or whatever.

• 2:04:46Sean Carroll?

  As we've seen here in the United States with our Supreme Court, very, very clear words in the text of a constitution can somehow be mangled in the minds of people sitting on the judiciary to mean very different things. So that is an issue that you have to worry about. Maybe it would sound good to violate certain rights in a certain piece of legislation and everything because it serves the greater good, but there's a slippery slope there, just violating all sorts of rights. On the other hand, maybe it is a good way of doing it. I'm not exactly sure what the provisions of the Charter of Rights that might be violated are. That's why it's very, very hard for me to judge.

• 2:05:30Sean Carroll?

  But let me just say, the bigger picture is a fascinating and important one, namely, how do you set up a constitutional system, or a legal system for that matter, that balances the idea that we're going to be democratic and give people the right to decide what happens in their country and the laws by which they live, versus the fact that people make bad decisions sometimes. People do bad things and want to do bad things, do bad things intentionally to other groups or whatever. Those are not the only considerations to balance. Obviously, in the modern world, there's this consideration that is maybe more important than ever, that power gets effectively concentrated in the hands of a small number of people

• 2:06:13Sean Carroll?

  just because of their enormous wealth. And that is something that was not as obvious as something to worry about back in the days where these constitutions were being written. Anyway, the bigger question, I think, is a difficult one because democracy is never going to be perfectly stable, right? If ever... Everyone, or almost everyone, in a country doesn't want the country to be a democracy anymore. It won't be. There's no safeguards that you can put into a constitutional system that says, even if everyone agrees to overturn the Constitution, we won't let them do it. Right? You just can't do that. You can't legislate or constitutionalize your way

• 2:06:57Sean Carroll?

  out of some of these dilemmas. So I kind of think that you do have to take these balancing considerations very carefully, but you have to do so in a way, I think, well, I think the best you can do is to try to disperse the power and the ability to change things dramatically. You know, the people who wrote the US Constitution, which I do know something about, tried to do this. They had the separation of powers between the executive, the legislative, and the judicial branches. They had even in the legislative branch, they had two different houses, right? The House and the Senate. And then there's all sorts of checks and balances. It was established pretty early on that the Supreme Court could decide that legislation

• 2:07:42Sean Carroll?

  was unconstitutional, things like that. But that doesn't really work if people are not devoted to maintaining that. It's always ultimately going to be in the hands of human beings, who are the legislatures, or the judges, or whatever. So therefore, you need a good, robust constitutional system, but you also need a value system in the human beings, both the voters and the people in government, the government officials, where they respect the idea that power should be dispersed, and you need to build consensus, and you need to have checks and balances and compromises and all of those things.

• 2:08:23Sean Carroll?

  This is an ethos which is degraded in the modern world, where you have people who just think that they're the smart ones, and they know better than anyone else, and therefore the power should be in their hands. And I think that ethos needs to be combated. And you know, more and more, I think that civic education is as important in the modern world as constitutional design.

• 2:08:47Sean Carroll?

  Bill McDonald says, "What is the likeliest cause of human extinction? Artificial intelligence, natural stupidity, or something else?" Well, as I said before, I don't think AI is a likely cause of human extinction. I think that, you know, AI can cause huge problems, but I think we do need to actually be careful about understanding what the likely problems are. And extinction is always bad, and it would be a problem, but there are much more real world problems that AI is going to cause, as well as benefits that it's going to cause. Natural stupidity, on the other hand, absolutely could be a bigger threat to human extinction.

• 2:09:26Sean Carroll?

  Again, human extinction is just not very realistic, I think, in any kind of scenario. I think that we shouldn't go right there. Like, if millions of people die, or billions of people die, or billions of people are thrust into subsistence-level poverty, those are really bad things that could happen, right? And in a much more realistic scenario than extinction of the whole human race. So we should kind of be paying more attention to those disastrous-level events that aren't quite extinction-level events. But I think that there's a very standard list of bad things that could happen, that you could, in some sense, classify as natural stupidity.

• 2:10:10Sean Carroll?

  I mean, an example of natural stupidity is, one of the big ways that you can get massive death on a terrible scale in the modern world is by setting off a nuclear bomb in some place, some densely populated place. This is clearly something that is a real threat, because it has been done. We set off nuclear bombs in Japan during World War II, and those were tiny bombs compared to what we can build now. So, of course, the human race, if it were rational and sensible, would be really working hard to make sure that the chances of nuclear weapons going off are as small as possible.

• 2:10:51Sean Carroll?

  And part of that is the big countries that have nuclear arsenals trying to safeguard what they do. In a sensible way, the other part is making sure that it doesn't proliferate. Right? Like I said, I'm not being very original here in this analysis. Nuclear proliferation is a really bad thing. And we had a treaty in place that was doing a good job of preventing Iran from developing nuclear weapons technology. And it was canceled unilaterally by our government because the President of the United States was upset that the treaty had been negotiated by his predecessor, not by himself. That's the kind of human stupidity, natural human stupidity, that I am very, very worried about.

• 2:11:35Sean Carroll?

  I think the biological problems in the sense of new pandemics, bioengineered pandemics and things like that are another super big problem. Climate change is going to be a problem that, again, won't cause extinction, but will cause enormous human suffering. These are all, in some sense, preventable problems, or at least problems that we could do a much better job than we currently do in lowering the probability of them happening. So natural stupidity is perfectly sensible as an explanation for why these remain worrisome problems. Kevin's disobedience says, "I don't think I've ever heard your opinion on nuclear energy. Do you think we should be using more of it to power the world? And if not, why not?" So I kind of don't have an opinion about this, in the sense that I kind of don't care.

• 2:12:20Sean Carroll?

  Like, when I was younger, I was very pro-nuclear power because I thought it was more sustainable than fossil fuels and it was just easier to implement than some of the longer-term renewable options. These days, it's a weird thing where, you know, much like one's opinion about whether or not the COVID-19 pandemic came about because of a lab leak or sort of natural evolution of the viruses, has become less of a science question and more of a signaling what tribe you belong to kind of question. And I feel like nuclear energy has also become that. I think that nuclear energy is fine if it works and is safe. That's about it, right?

• 2:13:02Sean Carroll?

  And if that's true, if it's cost-effective and you can make sure that... You protect against disasters and you can store the waste, etc. If all that's true, then it's good. And those are all engineering problems that should be faced by engineers, not by politicians and pundits and things like that. And of course, there are political issues in do you have the willpower to make sure that if you have nuclear power, you do it safely. So it's not as if politics is erased from the question, but it's part of it. And I'm not an expert in any of the engineering problems that are really the questions that need to be answered there. So if the people who know what's going on think that it's a good thing, then I'm in favor of that.

• 2:13:45Sean Carroll?

  I do think that ultimately, it's not the long-term benefit, the right way to put a lot of eggs in that basket. I think that renewables, solar and wind, etc., plus hopefully new fusion technologies would be even better, long-term solutions. But again, I'm not the expert, and if the engineers, the technical people who actually study this stuff, think differently, I'm willing to defer to them. Eric says, "Even after your conversation with Christian List, I'm still missing something important about compatibilism. Speaking about higher levels of description like goals and motivations is useful and real, but I have trouble pinning down where choice affects the physical world. It seems like the suggestion is not that my free will causes a butterfly effect that

• 2:14:28Sean Carroll?

  changes the micro-world and ultimately changes the macro-world, but instead, the micro-world does its thing and, on our higher level of description of agents, a higher level of description, agency is real and can exist independently and with autonomy. But where does the rubber hit the road? Where and how do my choices affect the physical world?" So that's the kind of question I think you can only even think about asking if you're not really grasping the whole idea of levels of description deep in your soul, okay? How do my choices affect the physical world? I don't know. If I choose to order a burrito to be delivered for lunch versus ordering a hot chicken sandwich, that choice affects the physical world.

• 2:15:13Sean Carroll?

  It affects who comes to deliver my food and what the food is when it Gets delivered, right? Like, obviously, it affects the physical world. That's not even a question. I think the reason why it sounds like a question is because you're trying to have it both ways, which is always the problem with emergence and multiple levels. You're thinking about the microscopic things going on underneath the surface in addition to the higher level description where there are people making choices. And you're saying, well, like, what is happening there underneath at the atomic level that is bubbling up to be these choices? And that's a perfectly legitimate question, but it's not a necessary question.

• 2:15:56Sean Carroll?

  The whole point of the levels of description picture and taking those levels seriously is, I can ask these questions at any level I want and stick with just that level. So when you say, how do my choices affect the physical world? That's a question that is being asked at the level of agents making choices. If I choose to answer your AMA question or not, I'm affecting the physical world. If someone chooses to start a war or not, they're affecting the physical world in a very large-scale way, right? So you can't worry about what's going on at the lower level once you have decided that the upper level really is an effective autonomous description.

• 2:16:38Sean Carroll?

  If you think it's not, if you think that, you know, I should just always use the lower level, then do that and don't ever talk about choices affecting the physical world. But you better be prepared to understand the position and velocity of every single atom in the person you're talking about. Renee DiPaola Jr. says, "What if the way our cognition works is limiting how we approach the laws of nature? What kind of science would an octopus or a dolphin create?" So I think I've opined about this before also, but I do think that there is some universality in science as it gets ultimately created. There's a lot of contingency, by universality, I mean,

• 2:17:21Sean Carroll?

  more or less, anyone would have done it the same way: aliens, other species, AIs, whatever. The process would be different. The historical trajectory could absolutely be different. I could absolutely imagine different parts of science being put together in different orders than others. But I think ultimately, science is trying to describe a pre-existing thing, namely, the physical world, nature, right? And I don't think that an octopus, or a dolphin, or an ET, or an AI, could ultimately come up with a description of the same physical world, which was equally successful as our description, but somehow radically different from it. You know, there's only so many things you can say about a physical system,

• 2:18:05Sean Carroll?

  and we're trying to say them as well as we can. And there's not even enormous flexibility in the order in which we discover things, just because the things that we see around us at the fundamental level seem to be quantum fields. And quantum fields get organized by distance scales, right? You experience and describe macroscopic things first, and then, as you get better and better at science, you dig more and more microscopic. And I think that's going to be true for octopuses, or dolphins, or whoever, just as well as for human beings. Michael Beddison says, "You recently posted on Blue Sky that people should use AI to educate themselves or find inspiration,

• 2:18:49Sean Carroll?

  but should, quote, 'just don't ever,' unquote, 'cut and paste from it into things they claim to have written.' I'm sympathetic to the concern, especially when AI is used to bypass thinking or cut corners, but I'm curious where you draw the line. Suppose someone uses an LLM to draft or improve prose, then carefully checks, revises, and stands behind every sentence. Is that still bad practice, or is the problem specifically uncritical copying and misrepresentation?" I think it's pretty bad practice, but also, you sneak something in here into the question. It's a perfectly good question, by the way. I like the question. It's important and difficult.

• 2:19:27Sean Carroll?

  Set of issues that we're gonna have to deal with. But the little sneaky part is where you say, suppose someone uses an LLM to draft or improve prose. Those two verbs, draft and improve, are very, very different in my mind. I absolutely am sympathetic to people who, you know, have a paragraph that they've written and they would like the AI to propose, you know, either improving the grammar or the punchiness of it or whatever. I don't do that, it's not my thing, but I get it if you want to do that, especially if you're not a native speaker of the language that you're writing in or anything like that. That's very different than having the LLM draft your prose and then you revise it.

• 2:20:10Sean Carroll?

  You know, the important thing here is that there's two things going on. One is the text that is being produced. The other is the attribution of credit or responsibility of that text to some agent. And if you want to sign your name to the text that is being produced, then it better be produced by you. I don't think that's an unreasonable standard, even in the LLM era. There are things called editors and editors get credit too, but they get less credit, right? Like when I write a book or when I publish an article in a magazine or whatever, there's an editor and those editors get credit usually like in the acknowledgements of the book

• 2:20:53Sean Carroll?

  or maybe in the, you know, the front matter of the magazine, et cetera. So it's a different kind of credit, but they get acknowledged. But the person whose name is on the text as the author is me. And even though it's a little bit collaboration, at the end of the day, the creation event was in my hands and I helped shape even the editing process, right? And so if all you do is prompt an LLM to produce something and then you revise it, you're the editor, not the author. And you shouldn't get authorial credit, even if you prompted it very, very carefully. So I think that that attribution aspect is very important. I mean, we had, and again, I have opinions about this,

• 2:21:37Sean Carroll?

  but I recognize that the issues are real and difficult. I am on the various editorial boards of various journals and we've had these discussions, you know, and I've had colleagues who said, look, if someone comes up with a really good article.

• 2:21:55Sean Carroll?

  That is a true contribution to human knowledge that we would ordinarily publish in our journal. Why should we care if that person did all the writing themselves or did it via an LLM, one form or another? And my argument is, you know, in part of the job of a scientific journal, or a philosophy journal for that matter, is to put out scholarship into the world that improves human knowledge. But there is another part, there is another job that the journal does, which it attributes credit to the authors. You know, people can get jobs on the basis of their list of publications, they can win

• 2:22:37Sean Carroll?

  awards, they can be asked to give talks, et cetera. And if you ask someone to give a talk on some brilliant paper that they are the author on and they show up and it's clear that they have no idea what's in their own paper, that would look bad, right? That is, you're not doing your job as the journal if you're giving credit to someone who wasn't actually the author of the paper. So I think that this is going to be a negotiation that we're going to have to have. And I tell my students the same thing, my students in the classes that I teach, you know, I say, "You should treat the LLM as a person in the sense that you can talk to them about what you're writing, but if they write things for you, that's called plagiarism, and you can get in trouble."

• 2:23:21Sean Carroll?

  And I think that in the LLM era, we're going to have to be much, much more careful and clear about what those distinctions really are. Louise Bulu says, "In a previous episodes, you said about your path to becoming a scientist that, quote, 'I didn't have the environment.' How much work do you think about, how much do you think about, 'I deserve to be here, this is the result of my work' versus seeing it as luck versus not thinking about it at all?" Well, again, okay, this is another set of very complicated questions having to do with responsibility and free will and things like that. There's a fascinating ongoing discourse in philosophy about moral luck.

• 2:24:01Sean Carroll?

  Like, I don't even know the good examples, but sort of a related example is if you drive drunk and you hit and kill somebody, you are in for an enormous amount of punishment, right? But if you drive just as drunk and you happen not to kill anyone, then the punishment is very different. You might not get caught at all, or you do get caught, but you don't get nearly as much punishment as if you actually killed somebody by accident. And that's not, you know, something you necessarily control. You just got lucky or not. I think there's an enormous amount of luck in the world. I think that, um, I think it was Branch Rickey who said luck is the residue of design.

• 2:24:42Sean Carroll?

  And he was exaggerating a little bit, but there's a point to what he's trying to say. The point he was trying to make, Branch Rickey, by the way, was an old baseball general manager. So he's not a scientist or a philosopher, but he did have a way with words. Luck is the residue of design means there are all sorts of random events happening all around you, right? Some things you can control, some things you can't. You have to understand you live in a world where not all events are under your control. What you can do is be ready for them. What you can do is be able and prepared to take advantage of when the luck works in your favor or to bounce back from when it doesn't.

• 2:25:25Sean Carroll?

  And I think that, again, if you want to dig very deep into it, so, okay, why do you have the ability to do that? Well, because of your genetics or your upbringing or your teaching or whatever. I don't know about all those ways that the credit or the responsibility can diffuse through history and so forth. But I do think that, you know, there's a mixture of luck and response to the luck that comes into anyone's career. Some, like, the single thing when it comes to I deserve to be here, that the single biggest sense In which I think I don't deserve to be here. I think I deserve the job I have. I think I deserve, you know, the ability to write papers and write books and do podcasts.

• 2:26:10Sean Carroll?

  But my house here in Baltimore is really nice. It's much nicer than any place that I grew up in or anything like that. And part of that is Baltimore is just much cheaper real estate than other places. But yeah, the house we have is like hilariously big and there's only two of us and two cats living here. And so there are times when I go like, I don't deserve this. Like, this is too much, but I'm not giving it back. That's just not going to happen. Kamaria says, why have Dr. Leonard Susskind and others stopped talking about the holographic principle in the last few years? Has the holographic principle been disproved, disproven? No, not at all. I'm not sure that it's true that they have stopped talking about the holographic principle. I think that plenty of people still talk about it. Of course, like many things, when

• 2:26:55Sean Carroll?

  an idea is new and being developed, people are very excited and thinking about it and developing it. And then it gets developed and you sort of absorb it into how you think about physics. I remember some time ago, someone said, I forget who it was, saying, when you use conservation of momentum in your physics papers, you don't cite Galileo, right? So I don't think that holography is, has gone away in any sense. It's still very much part of the ADSC of T correspondence. It's still very much part of how we think about black hole physics. It's still very much part of that paper that I wrote that I just talked about at the beginning of the AMA, because we motivate the idea that the Hilbert space of the universe is finite

• 2:27:38Sean Carroll?

  dimensional using holography. I mean, we motivated it by quoting other people who motivated it, like Banks and Fischler. But holography is absolutely at the heart of that. So just because you don't hear about it necessarily, doesn't mean it's been disproven in any sense. You would have heard about it if it had been disproven. Julian Bertram says, "What do you think about the concept of 'sortition', that is to say, electing representatives by a completely randomized lottery, not just for jury duty, but citizen assemblies and possibly even parliament or congress? I first heard about it in a subway take from Riz Ahmed and thought it was a joke, but I learned about it and am now a true believer." You know, I was skeptical when I first heard about it. I think I first heard about it here on Mindscape from Astra Taylor years ago when we were

• 2:28:20Sean Carroll?

  talking about democracy and she had a documentary film and book out on democracy. Actually, did she have a film out? Maybe. She definitely had a book out, but she's also a filmmaker. And she introduced me to this concept of sortition, the idea that rather than vote for representatives, you just pick them randomly from the population. And apparently, like, that sounds like maybe not a good idea. You'll get some good people, some not-so-good people. But empirically, it kind of works. You know, there are examples of when this has been done and it's been successful. And you can see why. Like, on the one hand, yes, you have no way of picking only the best people, not the not-good people. But on the other hand, you're freeing yourself from all sorts of biases and institutional

• 2:29:04Sean Carroll?

  influences that can lead you to not-good outcomes, right? That can lead the interests of the legislature to be something other than the interests of the people. And sortition, if it's done correctly, should at least align the average interests of the people with the average interests of the people in the legislature. Then, of course, you have to ask, how do you turn those interests into legislation? And one worry about sortition is that legislation in a big country like the United States is so complicated, and you have these people who are not experts in it, that you would basically be handing over a lot of the responsibility for legislating to permanent staff, who are not elected at all.

• 2:29:46Sean Carroll?

  That's kind of already true, even right now, so I'm not sure that that's a big worry, but, you know, it's something to think about. What I think would be a better idea, if we were just hypothesizing fantasy constitutions, would be a two-legislature, a two-house system.

• 2:30:03Sean Carroll?

  Body system for the legislature where you had like the professional legislators and then you had the randomly selected citizens in the other house. And they could both, you know, have to just, just like the House of Representatives in the Senate works, like the Senate is more or less useless. But you could have the House of Representatives elected in the usual way. And then you could also have a, a sortition house that could also pass legislation and would need to be consulted, et cetera, et cetera. Um, I think you can do much better than that. Like one of the things that is coming, becoming clear to me, writing the physics of democracy is everyone has always said it, but it's sinking into me how very, very bad our system of representation is.

• 2:30:44Sean Carroll?

  For one thing, the obvious thing that people always do complain about is that it is winner take all elections for various important elections, like who's going to represent you in the House or Senate. But also it's just geography is no longer sensible way to divide up who should be representing who like at best. Even if everything worked perfectly, if you have a system like the US where you have geography, like states and congressional districts, um, picking out who gets to represent a, a set of people in Congress. You're always going to get forty, forty-five, even fifty percent of the population unrepresented. Cause they lost the election, right? And they, their candidate didn't win and therefore they have no

• 2:31:29Sean Carroll?

  representation in Congress. You know, there are a lot of Democrats living in red states, a lot of Republicans living in blue states. And in the current system, they basically are shut out from representation. And there's various different ways you could do it better than that. I mean, one simple old school way is just to give political parties more power and more influence and have people vote for parties and then the parties choose representatives. But there's something in the US that makes people a little bit allergic to letting political parties have too much power. But there's other ways to do it as well. So I think that sortition is one of the interesting ways of thinking about, um, different ways that you could do legislators differently, better, more representatively

• 2:32:10Sean Carroll?

  than we currently have. But I don't think it's the only way or necessarily a way that you should use exclusively.

• 2:32:17Sean Carroll?

  Murray Dunn says, "I have a question about the physics behind the measurements made by LIGO, the Laser Interferometer Gravitational Wave Observatory. If the gravitational wave is making space expand, why doesn't the light used for making the measurement expand with it?" Uh, it does. It will, light will get red-shifted or blue-shifted by passing gravitational waves, that's fine. But it doesn't really change the fact that it takes a different amount of time in the rest frame of the gravitational wave detector for the light to travel from one point to another. And that's one of the reasons why it's crucially important that something like LIGO is an interferometer.

• 2:32:57Sean Carroll?

  They're pushing gravitational waves, sorry, they're pushing lasers, laser beams down two perpendicular directions. And as the gravitational wave pulls and pushes in different directions, what you're detecting is the difference. So you don't need to do the impossibly hard measurement of actually measuring how long it takes light to travel, you're measuring the difference in how long it takes light to travel down those two tubes. And even if the light gets blue-shifted or red-shifted, it's still traveling at the speed of light, right? Its velocity is the same in the rest frame of the gravitational wave observatory. So therefore, in that rest frame, the time that it takes is different, and that's all that you really need to measure the gravitational waves.

• 2:33:41Sean Carroll?

  Evan Dorn says, "Do you have any advice for someone who's interested in publishing but who isn't currently affiliated with a university or other research organization? Particularly if they have a relevant background, but they haven't worked or published in science in a while, and so don't have many connections." I don't think connections matter at all. I think that's really just not the point. I'm not quite sure why people think that connections are relevant to publishing. Credentials are relevant in the sense that they act as a simple first filter for the editor or the, you know, whoever is accepting your submission to a journal to say like, "Is this person legit or not?" But there are absolutely plenty of examples of people who don't have academic affiliations who do publish refereed articles in the literature. I would say just if you actually

• 2:34:26Sean Carroll?

  Have something good, just submit it to a journal, see what they say, right? Like, don't decide ahead of time that you don't have the right connections or whatever. It might be hard to get on Archive if you have both no publication record and no academic affiliation. But getting something published in a journal would help you get into Archive, right? That's just the way that it works. And also, I mean, let me point out that the existence of such filtering mechanisms is not bad. It's not a mistake. I'm sure that your article is worth taking very seriously. But if you look at the total set of articles submitted to journals and to Archive, etc. From people who have no publication record and no academic affiliation.

• 2:35:12Sean Carroll?

  The track record would not look good. The set of publications is not very impressive. So there's, there are always just everyday efficiency interests involved in how much attention is paid to these things. But if you're really in sort of immersed in the literature, you know what is going on, you know how papers are written. You know who to cite, you know what the counter arguments to your thesis are that you can mention in your own paper and explain why they're not good counter arguments. And you write it carefully and sensibly, then a good journal will absolutely take it seriously. And then you just have to see whether the referees agree. Scott Collins says, "Listening to the excellent Christian List episode, I noticed that List often greets questions with an eager 'good'.

• 2:35:57Sean Carroll?

  You do this too, as do many of your guests. It often seems to indicate the question is one that experts have already debated and come to some kind of consensus on. Is this a rhetorical technique common in academia? Is it sometimes used to attempt to deflect questioners from probing further, assuming the ground is already well trod?" I think it is, something that is used very often in academia, that's that rhetorical tic, if you want to call it that. But I don't think it's for that somewhat nefarious purpose that you're suggesting here. I think it's almost the opposite, in fact. I think like saying good is, you know, David Albert, who was a former Mindscape guest, is one of the Primary, um, uh, people who do this kind of thing over and over again.

• 2:36:41Sean Carroll?

  Perpetrators, that's the word I'm looking for. So you can use in two ways. One is when you're just talking yourself and you sort of have reached the end of some point. And you say like, okay, good. We've established that point. Let's move on to the next one. When you're giving a lecture, when you're answering AMA questions, I'm, I don't know, but I'm sure that I've already used it in this AMA because it's, that's what it signals to hopefully the listener. The other thing is, like you say, when we're having a conversation and someone asks a question and you say, good, generally what that means is yes, you are putting your finger on the good question.

• 2:37:17Sean Carroll?

  In other words, to any point that someone could make, there's always silly questions that you can ask, like questions that miss the point or are changing the subject or whatever. When you say that a question is good, you're indicating that aha, you've put your finger on the interesting place to go next. And, uh, and academics love that. That's what we're all about. So that's why we tell each other that we're doing a good job. Pete Faulkner says, Australian painter Angela Brennan has a new work in the Art Gallery of New South Wales collection entitled, How An Apple Falls And How The Universe Expands. It's a work from her exhibition on being an atom and is a two meter by two meter oil in which forms that I read as gravitational masses drift through a field of deep blue that feels very much like curved spacetime.

• 2:38:02Sean Carroll?

  What do you think in that? What do you see in that image as a physicist? And does it speak to you how you think about gravity as an approximation at successive scales, Newtonian, Einsteinian, and whatever quantum gravity eventually reveals? So I actually did look up the painting. I was not familiar with it. I know, I always tell people, don't tell me to like read papers or watch videos or whatever, because I'm not going to do that. And you'll notice almost never are there AMA questions where someone is asking me to read a paper or watch a video. The fact is there are plenty of AMA questions where someone is asking me to read a paper or watch a video. I just don't choose to answer them. So keep that in mind when you're asking the questions. But looking at a single piece of art that I can do, okay? And I did look at this one. It's a great painting. It doesn't look especially sciency to me.

• 2:38:46Sean Carroll?

  Doesn't really invoke any of that in my mind. I think that's fine. I think that what it invokes or what it's inspired by, by the artist, or what it invokes in other people appreciating the painting, need not always be exactly the same. Different paintings, different works of art will speak to different people in different ways, and that's great. We don't want all the same things on our walls, et cetera. And so I think that when it comes to the relationship between physics and art like this, I absolutely think of it as one of inspiration. And I think the same thing is true for science fiction novels, or Marvel movies, or whatever. That one thing that science can really, really do is push us out of the ruts we are in, right?

• 2:39:28Sean Carroll?

  One of the things about science is, we have all sorts of ideas about how the world works, but science is just relentless in telling you that your ideas are usually wrong, and forcing you to come up with better ideas, right? Ideas like conservation of momentum, or quantum mechanics, or relativity, or the Big Bang, are not obvious. They're not intuitive. They were not suggested 10,000 years ago. We had to be forced to think about the universe in different ways than we're used to. And that kind of being forced to think in new ways is super helpful in the artistic world, because we're always in ruts. Even as a fiction writer, or a fine artist, we always have the same thing we do over and over again. And being inspired in a new way is crucially important.

• 2:40:12Sean Carroll?

  So whatever the resonance might be for some, for me, or for someone else, I'm very much in favor of artists thinking about science in ways that might inspire them to make better art. Kyle Stevens says, "In general, if we observe two phenomena that both appear to be extremely improbable, should that increase our credence that they are causally related rather than independent? For example, if intelligent life is extraordinarily rare in the universe, and Earth's unusually large moon is also a relatively rare outcome of planetary formation, is the coexistence of those two rare features itself a meaningful Bayesian evidence that the moon played a causal role in the emergence of intelligent life? More broadly, when two apparently low-probability phenomena coexist,

• 2:40:56Sean Carroll?

  is it rational to update toward correlation even before a concrete mechanism is established? Or are humans too prone to over-infering relationships from anthropic selection effects, and effectively having a sample size of one?" You know, I think it's fine to take unusual-looking coincidences and say, "Maybe they're related." In other words, it's a completely legitimate Bayesian move to say, "I have a set of theories, a set of propositions about how the world works. In some of them, these two phenomena are correlated in some way. In some of them, these two phenomena are not correlated in any way." And then noticing that they both have unusual aspects and are coincidentally,

• 2:41:40Sean Carroll?

  you know, both have unusual aspects at the same time in the same world, increases our credence in the set of theories where there is actually some causal connection between them. I think you have to be very careful, though. I mean, Bayes' theorem says that you have a prior, and then you update it with a likelihood. And in this case, the prior that you might have started with might be really, really, really small, depending on how crazy the theory is. And the updating by the likelihood might also be pretty darned small. Maybe you increase your credence, but not by that much, if it's pretty easy to have these two low-probability events even without any causal connection between them. So, right now, like, the Earth, for many reasons,

• 2:42:20Sean Carroll?

  is just the very obvious, hospitable home of life in the solar system, even if the moon weren't here, right? So, I don't necessarily think that it's a very strong amount of evidence pushing you in that direction, but it might be a little bit of evidence, and that's okay. And people have to sort of train themselves, if they're trying to be good Bayesians, that there are probabilities that are other than 0 or 1. Even that there are probabilities other than 0, 1, or .5, right? Everyone, there's this thing where either you have no idea, and then it's .5 probability, or you think you know it, and it's either 0 or 1. The good Bayesian knows better than that. There's a lot of probabilities other than those three special numbers.

• 2:43:07Sean Carroll?

  Steve H. says, "Does dark matter have to be independent degrees of freedom? If we can reproduce the observed metric using an intrinsic spacetime response, is there a principled reason like EFT consistency or locality that rules out a purely geometric sector in favor of a particle-based one?" I don't think that there's any in-principle theoretical reason that rules it out. I think there's data that rules it out. Like, we've done the experiment, and it is ruled out. There are multiple ways in which we have tested the presence of a gravitational field versus the presence of matter in the universe, and they're appearing in different places, sometimes, ordinary matter, the matter that we can actually see. We see that in things

• 2:43:50Sean Carroll?

  like the Bullet Cluster. We see it really indirectly but even more reliably in the cosmic microwave background. There's overwhelming evidence that gravity is not doing what ordinary matter does, and that's very, very hard to explain with what you would agree is an alternative theory of gravity rather than something like dark matter. There's this big wishy-washy gray zone where people call certain theories theories of alternative gravity, but really, these theories contain independent degrees of freedom that are propagating and have energy and are causing a gravitational field. So you could just call them dark matter, right? If you're going to fit the data in modern cosmology, you're going to need dark matter.

• 2:44:33Sean Carroll?

  Michael Wall says, "In your 2018 firewall paper with Bao, Chatwin-Davis, Pollock, and Remen, unitary evolution is manifest only in the global wave function, not on any single semi-classical branch. For an observer confined to one branch collecting Hawking radiation, what does recovering the black hole's information actually amount to? And how does that picture relate to the page curve, which seems to describe purification within a single observer's branch?"

• 2:45:01Sean Carroll?

  Yeah, how does it relate to the page curve? Let me put that aside and let me think of whether I can actually answer that one. But let me get to the heart of the question, which I think is a very good one. And it sort of was an implicit message of that paper, which is that often physicists talk in a very, very slipshod way about information conservation in quantum mechanics and in quantum gravity, right? We insist that information be conserved in the evaporation of a black hole, but we put aside the fact that, in fact, information is not conserved whenever we measure a qubit, whenever we measure a spin, right? Measurement processes in quantum mechanics, as we teach them in our undergraduate courses, destroy information. They are not unitary.

• 2:45:45Sean Carroll?

  Now, an Everettian like myself can say, "Well, that's because the overall evolution of the wave function is perfectly unitary." But within a branch, or if you like, as experienced by any one observer, things do not look unitary. Information is lost. So you can't actually recover the information in a black hole, okay? You can't do that as a practical matter by going out there with a detector and collecting all of the radiation. If you knew something about the radiation, if you knew that it was sort of in some certain kind of state, then you might be able to figure out which state, which specific example state it was within that class of states. But as a theorem in quantum mechanics,

• 2:46:30Sean Carroll?

  you can't just do a measurement and, without knowing anything about the state, detect what it is. That's just quantum mechanics for you. The page curve, for those of you who don't know, is a curve that represents the amount of entropy in the radiation given off by a black hole. And the point is, if you think that information is conserved when you're first giving off radiation, you haven't given off that much. You're giving off more and more radiation, and you're calculating entropy as the entanglement entropy, okay? The real quantum mechanical entanglement between the radiation and the rest of the world. And what happens is, the radiation if, overall, the... Information is conserved in the usual way.

• 2:47:12Sean Carroll?

  That information in the radiation is entangled with information in the black hole. So the entropy of the radiation goes up. But at some point, the black hole is too small to be entangled with all the radiation. And the radiation starts being entangled with itself. And so the entropy of the radiation goes down. Okay, so I'm not exactly sure how to phrase how that. It's completely consistent with everything we said in our paper. I'm not quite sure how to phrase it. But I think that what's happening is the page curve applies to the wave function of the universe. Right, the page curve is not about what happens on one branch. And so when the entropy of the radiation goes back down to zero, when the black hole has disappeared, that's presuming that you're talking about the

• 2:47:57Sean Carroll?

  the factor of Hilbert space representing the radiation degrees of freedom in the wave function of the entire universe. That's the entropy that is supposed to be zero. Jeffrey Segal says in the last AMA, when talking about tunneling of a Coke can, I think you mentioned that a new universe is more likely to form than a Coke can to suddenly appear. If I got that right, does that mean that a new universe is more likely to form than a Boltzmann brain, which I would assume is much less likely to appear than a Coke can? That would seem to me to be fairly reassuring that I am unlikely to be a Boltzmann brain. Well, I think you got it right, except I have to emphasize very strongly, maybe. Like, all of those statements are not true. They're not known to be true, not settled.

• 2:48:42Sean Carroll?

  They are aspirations that we hope are true in certain versions of quantum gravity. Okay, so in other words, if certain things work out to be how we think quantum gravity works, then there will be processes that make new universes. And if that can happen, then that can happen more frequently than making brains. So certainly, you are tempted in that perspective to say that explains why I'm not a Boltzmann brain. Because every time I make a certain universe, that will eventually lead to bajillions of observers. Maybe not as many as in the ultimate Boltzmann brain scenario, but. But at least for a while, there'll be more observers than a single one. So if it's easier to make just that one universe than a single brain,

• 2:49:27Sean Carroll?

  most observers are going to find themselves in the ordinary thermodynamic phase of the universe's evolution. The problem with that is, well, number one, we don't know if quantum gravity works that way. If baby universes get created at all, that's fine. But number two, there's what's called the measure problem in quantum cosmology. Not the measurement problem. The measurement problem is about what happens when you measure a quantum mechanical system. The measure problem, or the cosmological measure problem, is how to compare different sizes of infinity in a universe that might be infinitely big and infinitely old. So how do you compare the number of ordinary observers to the number of Boltzmann brains? Certainly, when Jennifer Chen and I proposed our theory,

• 2:50:09Sean Carroll?

  one of our hopes was this was a reason why there might be more ordinary observers than Boltzmann brains. But I wouldn't trust any of that, given our current state of cosmological knowledge. Steve Bonner says, "Some neutrino detectors are built in deep mines to keep out particles other than neutrinos, but they're surrounded by ores that may be undergoing radioactive beta decay. Is this a problem? Is it possible to distinguish those neutrinos from others of celestial origin that may be of greater interest?" Yeah, it's a problem. This is absolutely a known thing. There are backgrounds, is the simple word that is attached to this, beta decay, but other backgrounds as well. In fact, back when I was at the University of Chicago, a friend of mine, Juan Coyar, is a professor there who looks for dark matter.

• 2:50:54Sean Carroll?

  He builds dark matter detectors in his labs, and he was able to get his hands on this incredibly valuable stuff, namely some bricks of lead that had been transported across the Atlantic Ocean in a ship that sank some decades ago. So because all this lead was just sitting at the bottom of the ocean for decades, I don't know, maybe centuries, I forget exactly how long, it had been shielded from cosmic rays, and it had given off much of its native radioactivity. So it was much more radioquiet than a brick of lead that would just be sitting up here in Your basement or something like that. So that's kind of stuff serves as very effective shielding for dark matter detection experiments.

• 2:51:38Sean Carroll?

  Now, nothing is perfect, so you will always get some backgrounds. The good news is that you have ways in principle of distinguishing signals from noises. For one thing, the energies should be different. You're not, depending on the kind of detector you have, you might not just be detecting the existence of a neutrino. You can also detect the energy deposited by that neutrino event. Sometimes, depending on what you're doing, if you have like a big water tank that can detect Shirenko radiation or something like that, you might be able to get the direction in the sky that the neutrinos are coming from. And in fact, people have made little photographs of the sun in neutrinos because you can do exactly that.

• 2:52:19Sean Carroll?

  So there's all sorts of ways of statistically distinguishing the neutrinos that are signaled from those that are background. You might not be able to do it on a neutrino by neutrino event basis, an event by event basis, but that's very common in particle physics. In particle physics, it happens all the time that you see events that could be really interesting signals or just background noise, and you can never tell just by only looking at one of them, which it is. You have to construct and collect a huge amount of data. That's why it's very important that the Large Hadron Collider is not just high energy, but also very high luminosity, a tremendous number of events per second. It gives you the statistics to do things like find the Higgs boson.

• 2:53:02Sean Carroll?

  James Brown says on moral philosophy, "Why is it that it seems like a battle for the one true moral theory of everything? Is it not more useful to apply the framework that is most appropriate to the situation as in physics? Domain of applicability, I think, is the phrase you use. I share your concerns about utilitarianism, but I think specific instances where it could prove useful, and I think that the same might be true of deontology, virtue ethics, and so forth." Well, I would say yes and no. Like, I get the implication here. In fact, Will MacAskill, who was a former Mindscape guest, his PhD thesis, as I think he mentioned on the episode, was on taking that approach seriously.

• 2:53:42Sean Carroll?

  Like, basically saying, "Let's imagine that we're not sure what the right moral framework is. Maybe it could be deontology, maybe it could be virtue ethics, whatever. Well, what we should do is assign credences to the different possibilities and then get expectation values for different actions. If one action is, like, really good under one theory but really bad under another theory, then you should take the average under whatever credences you have." So, I don't know whether that's a sensible thing to do or not. I thought it was a cute little idea. But, on the other hand, I don't think that that's going to be the best possible way of doing things. So, the thing about domains of applicability in physics is, it's absolutely true that

• 2:54:25Sean Carroll?

  if you just want to get a rocket to the moon, you can use Newtonian gravity. You don't need to use general relativity, even though general relativity has a wider domain of applicability. But general relativity is more fundamental, right? General relativity applies when you want to get a rocket to the moon, but it also applies in black holes, whereas Newtonian gravity applies only to one but not the other. So, I think that the same thing should be true about morality. I think there should be a once and for all true theory for the simple reason that if you think that every moral question in every possible context has a right answer, then the union of all such right answers is a single theory, okay? It might not be a simple theory, and the same thing is true in physics.

• 2:55:07Sean Carroll?

  The philosopher Nancy Cartwright has often argued for a patchwork approach to the laws of nature, that you should literally think of just different laws of nature operating in different domains, and you should not talk about deriving one from the other, or even making sure that one and the other are compatible with each other. They're just different. I think that doesn't quite make sense, because they have to be compatible. I can't get a different answer if I take two theories that have overlapping domains of applicability and ask the same question within them, right? I should get the same answer. That's what it means to be compatible. So I think that what is being pushed against is the idea that there is a simple, austere, beautiful, and rigorous theory of everything in either physics or morality.

• 2:55:52Sean Carroll?

  And that, you know, I can hope for, and I do hope for, but I can't give you any strong argument that it must be there. The real theory might just be a mess. You know, I've had this conversation with many physicists, and they say like, "How are you sure that there is a theory of everything?" My answer is, because the universe does it, right? Whatever the sum total of things the universe does is, that's the theory of everything. The question is, can you compress all of those doings into an incredibly tiny, compact formalism? That I don't know. I think that there's plenty of reasons to be impressed with how well we've done at that project, but we can't guarantee it's going to keep working. Lishan Aklog says, "Modern theoretical physics has long explored extra-spatial dimensions, as in string theory,

• 2:56:36Sean Carroll?

  or emergent lower-dimensional formulations of spacetime, as in holography. Yet additional time dimensions remain highly exotic and largely absent from mainstream theories. Is there a deep structural reason for this?" Uh, yes, there is. Roughly speaking, as soon as you have extra time dimensions, they have been explored. They don't work, roughly speaking. I mean, some people are pluckily, you know, chipping away, trying to make them work better and better, but they have not convinced anyone else that they're good. So there is neither any motivation for doing that, from experiment or from theory, other than, "We should try all the possibilities," which is fine. We should try all the possibilities, I'm all in favor of that. But there's no

• 2:57:20Sean Carroll?

  piece of information we have about the universe that says, "Oh, if only there was more than one dimension of time, we'd be able to explain this piece of information." And the other thing is, once you say like, "Okay, let's just play with it, right? Let's like, let's add more dimensions of time and see what happens." All hell breaks loose. You know, one of the bedrock principles of physics in the world as we know it is the idea of an initial value problem, right? You tell me the state of the universe at one moment of time, and I can pretend to be Laplace's demon, and I can tell you what's going to happen next. The initial value problem. If you have two dimensions of time, there's no such thing as the word next, right? Just like in one dimension of space, there's only one direction to go in. You can go forward or backward in that direction, but there's still only one direction to go in.

• 2:58:05Sean Carroll?

  Whereas in two dimensions of space, now you can go in circles or straight lines. There's an infinite number of things you can do. Same thing is true with time. So as soon as you have multiple dimensions of time, you can't predict the future from the present. You can't even prevent yourself from coming back to visit yourself because you can go in a circle in time. Right? So anyway, it's worth trying. People have tried it. It's Akbar's at USC is probably the biggest name among the people trying it. But there's been no breakthrough that says, oh, yes, if you just try to this particular tweak, it makes other questions in physics get better rather than worse. Brandon Wheeler says, what is your view on the changes the New York City mayor is doing?

• 2:58:48Sean Carroll?

  Yeah, so Zoran Mamdani is the new mayor of New York City. Look, I don't live in New York. I don't really follow all the actual politics. So if your actual question is specific policy changes that the mayor has tried to implement? And are they good policy changes? I have no idea like cities are very complicated. Certainly, I think his heart is in the right place. You know, he's trying to make the city more livable for the majority of its citizens, not just the wealthiest and most influential. He has all the right enemies. Let's put it that way. And I also think that his approach is good. You know, he is a positive person, right?

• 2:59:30Sean Carroll?

  Like he's not, he's always smiling and doing fun things and joking and things like that. But he's making things happen. He's fighting. And I think that fighting for what you believe in is the single most important thing that people on the sort of Democratic Republican divide on the Democratic side don't take seriously enough. You know, they think that if they can just make eggs get cheaper, everyone will vote for them. But I think that the idea that you're fighting for people's interests is absolutely underappreciated by our professional political.

• 3:00:01Sean Carroll?

  And finally, you know, I've seen some of the videos that Mumdani has done and I'm super impressed with his willingness to go deep. You know, he did this video wishing everyone a happy St. Patrick's Day. And it's just a, it's almost what you would do if you were trying to show how clueless and feckless typical politicians are. Because if you say, okay, make a happy St. Patrick's Day video, you've seen videos like that all the time. You kind of know what to expect, blah, blah, blah. I almost didn't want to click on it, but people who I respected were saying, you got to watch this. And he gives this wonderful history lesson of how the Irish came to New York and all the problems

• 3:00:44Sean Carroll?

  that were happening and problems were happening back in Ireland. And he just explains it in a very compelling way. And I love the fact that he's just not insulting the audience's intelligence. He's assuming that they're as interested in this cool, detailed, nerdy stuff as he is. So all that can also can always be used in the service of bad policy decisions. Okay. And that's why I'm saying, I don't know what the policy decisions are. I mean, I like the idea that wealthy people should pay more taxes. I've said that plenty of times. Other than that, I don't know any of the policy details. But on style points, I think he's doing very well. Paul Torex says, last AMA, you answered the question of whether morality is rational in the decision theory sense. You pointed out that decision

• 3:01:29Sean Carroll?

  theory includes subtle things like independence of irrelevant alternatives. And you noted, because I don't think it's objectively out there in the world, it's up to you and the moral framework that you develop. Is rationality, not just rationality in some particular theory, just rationality, also up to you and the rational framework you develop? And why is it different or similar? So I think that you have to be careful about what exactly is being asked here. Because the way the question is asked, is rationality up to you and the rational framework you develop? You know, I think that there's something called rationality. And if you have something that is not within that framework, you wouldn't call it rationality. You wouldn't call it a rational framework. You'd be a framework.

• 3:02:11Sean Carroll?

  And in fact, I don't then, I don't mean to dismiss that possibility. I think that nearly every living human being has a framework for making decisions that is not 100% rational, right? On the independence of irrelevant alternatives, I forget how many times I've told the joke, probably several times, but there's a joke due to Sidney Morgan Messer, the famous Columbia University philosopher, who apparently Morgan Messer was, I'm sure I've told this joke before, but he was at a diner and the waitress says, "What kind of pie would you like?" Or, "Would you like any pie for dessert?" And he says, "What kinds do you have?" And she says, "Oh, we have apple or blueberry." And he goes, "Oh, okay, I will have the apple pie." And she comes back and says, "Oh, no, wait, I forgot, we have apple, blueberry, and cherry."

• 3:02:56Sean Carroll?

  And he says, "Oh, in that case, I'll have the blueberry." So, the existence of cherry pie was an irrelevant alternative, and he was sort of sacrificing his pie choices just to make a joke, namely that he was acting irrational, by now suddenly preferring the pre-existing choice of blueberry, just because he was alerted to the choice of cherry. But the point is, it's a joke because people do that kind of thing all the time in the real world. So, when you say rationality, it's something that has been developed by human beings, as is often true in philosophy, it's an attempt to make systematic and logical some rough guidelines, impressions, intuitions that we have, right?

• 3:03:38Sean Carroll?

  And are independent alternatives really supposed to be, sorry, yeah, irrelevant? Yeah, are, I suppose I should say, are irrelevant alternatives really supposed to be independent? Or not? You can choose that, right? Or you can just choose to be whimsical, or you can choose to be self-contradictory, or you can choose to, I mean, again, in some sense, just like for the laws of physics that we were talking about, and the laws of morality, you can always be 100% consistent and logical and rational, just by saying that my moral theory is that everything I have ever done and will ever do is morally good. There you go. You're rational, right? So I just think you'd be super duper careful.

• 3:04:23Sean Carroll?

  I mean, if what you're asking is, is rationality unique? Is that, does what everyone agree on it? I think like the basics are pretty agreeable, but then there's always fussy things at the boundaries that people could choose to disagree about. So I don't think it's the most important thing in the world to care about whether rationality is unique or objective or out there in the world. It's what you agree on. It's what, it's what people mutually will say like, okay, we're going to agree that this kind of reasoning should follow these kinds of rules. And if we all agree, then we should be happy.

• 3:04:57Sean Carroll?

  Robert Kitsey says, because too many of your stories seem familiar. Did your Bucks County High School football team beat mine, Council Rock, in the 1984 homecoming game? If so, I remember our schools being major rivals. I was a soccer player, but football was a big part of our high school culture back then. It's a small world. It's very possible that sounds vaguely familiar. I went to Pensbury High School, and you're 100% correct that Pensbury and Council Rock were two big rivals in that neck of the Bucks County woods. But what counts as a rival depends very delicately on what activity you're talking about. So in football, yes, Council Rock and Pensbury were the big rivals. I was never that much into high school football

• 3:05:41Sean Carroll?

  as, when I was in high school. I was on the debate team, the speech and debate team, the forensics team. And Council Rock, for whatever reason, didn't have a forensics team. So they were not my big rivals. It was actually Harry S. Truman High School. They were our local rivals and schools like LaSalle College High School in Philadelphia and places like that. Henry Jacobs says, on downward causation. In the case of macro states versus micro states in the context of statistical mechanics, it seems easy to dismiss the idea of downward causation. However, when aggregating people and their actions into a nation and its actions, the actions of the nation, the high level, will affect the citizens, the low level, through enacting laws or going to war. Does this count as downward causation?

• 3:06:25Sean Carroll?

  Maybe. I mean, that's literally what we suggested in the paper I wrote with a truth parola on what emergence can possibly mean. We said that the space for downward causation is at these levels where even the lower level is already pretty high. And the reason, there's a very specific reason why. The reason why is that when your lower levels are fundamental physics, you have very strong constraints from things like locality and the small number of degrees of freedom per particle, et cetera. The individual constituents of your theory are themselves simple and their interactions are local. So there's really no room for higher levels to directly affect them. Whereas if your lower level is individual humans and your higher level is some collective set of people

• 3:07:10Sean Carroll?

  like an economy or a government or whatever, then the boundary lines are a little bit less clear, right? And so I can imagine, so I'm honestly saying that I'm not sure. I can imagine a principled understanding of downward causation that was relevant to a human level and a collective national level or something like that. You know, there are plenty of examples you can point out. You know, the Constitution of the United States affects the lives of individuals, right? I don't think you can deny that. But what you can deny is that, well, you cannot deny that that statement is true understood in its own right.

• 3:07:55Sean Carroll?

  You can deny that it's the right kind of statement to make because you can try to take a hardcore point of view that says the Constitution is a piece of paper. It has no effect whatsoever on people's lives unless they're literally reading the Constitution. What happens in the world is that people have ideas in their head because of what we attribute to the Constitution. And it's those people that have effects on our lives, right? So in other words, you can always reframe the discussion in terms of the Constitution or laws or whatever in terms of individual people and their beliefs and their actions. The question is, is that the most efficient way to do it? Are you losing something important when you do that?

• 3:08:39Sean Carroll?

  So I'm very open to a rigorous discussion of why downward causation is the best possible way of understanding the relationship between levels at that level. I have not seen such a discussion and we didn't do it ourselves. Peter42 says, "If it turns out there's no singularity at the center of a black hole, and none at the start of the Big Bang, do we still need a theory of quantum gravity?" Uh, yeah, sure. Because singularities are not a major motivation for quantum gravity. Uh, sometimes they're presented that way, but I think that a more honest presentation would be to say that one of the nice things about quantum gravity is it should get rid

• 3:09:23Sean Carroll?

  of singularities, because you can't have singularities in quantum mechanics, because the Schrodinger equation is linear. That's just how it works. Um, singularities are inherently nonlinear kind of phenomenon. But you can certainly imagine getting rid of the singularities in a classical theory. People have tried to do that. The reason you need quantum gravity is because gravity exists and quantum mechanics exists. That's it. That's the, that's the total sum of the argument. People have also tried, um, in respectable ways to see whether you could make a theory where gravity is itself classical, and matter fields and energy fields are quantum mechanical. I think that the chances of something that, like that

• 3:10:04Sean Carroll?

  working are essentially zero, pretty, pretty close to zero. Um, so I think that, which is good, because it gives us room to invent quantum gravity. We're not done doing that yet, and it's fun to think about it. Gary says, "Fermions are things that take up space, and bosons are things that don't. Therefore, helium is a fermion, right? Yes, please?" Uh, no, helium is not a fermion, but it's a composite particle with fermions inside. So, the truth is, and this is a very tricky thing, and I'm not, I'm not an expert in it, so I'm not going to get exactly all the details right, but therefore, because helium is itself a bosonic thing that has constituents that are fermionic, the truth is that in some circumstances, it acts like

• 3:10:48Sean Carroll?

  a boson, and in some circumstances, if you push it too far, if you get out of the domain of applicability, where you can treat the helium atom as a single degree of freedom, then the fermionic nature of its constituents becomes important, and you have to think about those. And that's why helium does in fact take up space. Laura says, "There were multiple moments in your conversation with Alan Roth on morally contested markets when I was disappointed by the rigor and thoroughness of his answers to your questions, and I wondered if you experienced something similar as the interviewer." Small examples of this were his vague definition of market and failure to maintain the significant distinction between market and marketplace that he made early in the discussion, pointing out that what he actually designs is marketplaces.

• 3:11:33Sean Carroll?

  The most important issue he did not adequately address was poverty. It came up in almost every example of a morally contested market, but even after you asked several questions about it, I wasn't satisfied and got the sense that you weren't either. So I wouldn't say that I wasn't satisfied. I think that, you know, we had to be careful when we're talking to somebody, especially someone in a different area, or even someone in the same area but at a different level of expertise, higher expertise or lower expertise, or even someone with the same exact expertise at the same level but who's interested in different things. We had to be careful to admit that people are interested in different things, okay?

• 3:12:13Sean Carroll?

  So he was just not really into, you know, worrying about addressing poverty as an issue. He was interested in these sort of economic, sort of moral slash economic questions about the nature of contested markets in their own rights, right? For their own sake. I think he would be very quick to admit that there would be cases where, in reality, in society, maybe you have a situation where in an ideal marketplace, a certain set of transactions is perfectly allowed, but because the marketplace is not ideal for all sorts of reasons, asymmetric information or asymmetric resources of other kinds, maybe it's sensible to have a law banning them. I think that's fine.

• 3:12:58Sean Carroll?

  So I read, I picked up on his reluctance in the same way that you're picking up on it, but I just read it as he was not focusing on that. That's just not what he was caring about for this discussion. It's perfectly legit for us to care about it, to be interested in it, but that's why we talk to lots of different people here on the podcast. Lots of different areas because I'm not trying to present. I do want every podcast to have the property that the guest gets a chance to put forward their best arguments and their point of view, but I don't ask that the listeners accept the point of view as the truth. You should figure out what the truth is from the overall impression over many, many

• 3:13:42Sean Carroll?

  podcast episodes and hopefully many, many things that are not episodes of Mindscape at all. Marek Borick says, I'm curious how you handle the personal finance, your personal finances and if you invest. Do you have someone who does it for you? Are you handpicking a handful of stocks, bonds, ETFs yourself? I don't even know what an ETF is. Are you maxing your 401k and Roth IRA and have any guests you've had on the podcast change your attitude towards your personal finance? So I'm pretty minimalist about personal finance, honestly. Like I'm a big believer in being responsible and Jennifer, who my wife, who as a longtime freelancer had to be super responsible, right? Because you don't know from month to month what your income

• 3:14:27Sean Carroll?

  is going to be. We tend to be pretty cautious. So I'm a big believer that people should put as much as they reasonably can into retirement funds or savings or something like that.

• 3:14:41Sean Carroll?

  And I also, but I don't put any effort into sort of guiding my retirement funds like they're in some index funds, I presume, or, you know, Merrill Lynch, I think my bank account is Bank of America, which is, which owns Merrill Lynch. So I think that some Merrill Lynch thing is going on there. And I do, I do put as much as I can from my salary from Johns Hopkins into the retirement fund. But look, and then I just let it go and I hope it's okay. Figures crossed. We've been, Jennifer and I have been beginning to pay more attention to this stuff. It's that time of our lives. Like, you know, what happens if we both die? Where does the house go? Things like that. So we are beginning.

• 3:15:27Sean Carroll?

  To do that, it's a little bit late, but okay. The reason I want to answer the question, I know that none of what I'm saying here is especially enlightening. I just wanted to use this as an excuse to lament how badly, as a society, we treat both our young people and our old people. Younger than me and older than me. Like, the people in my age bracket right now are fine. We're not all fine, obviously. You know, one of the difficulties in answering questions like this is I want to make the answers interesting and useful to as wide a fraction of the listening audience as they can be. And I know that some people have way less wealth and money than I do, and some listeners have much more wealth and money than I do. So it's very different circumstances.

• 3:16:08Sean Carroll?

  But, you know, if you're able to save money when you're very, very young, it is hugely helpful to you when you get old because of the miracle of compound interest. And if you were like me when you were very, very young, there was really no possibility of saving a lot of money. I mean, not only is your income very low, but you're instantly saddled with debt when you go to college or whatever. And the amount of debt that a lot of modern college students are saddled with is enormously greater than I had to deal with. And I also got to sort of postpone paying it because I went to grad school. And in grad school, you get paid, but you don't need to pay off your debts yet. But as soon as I was a postdoc, a lot of my free income was just going to, like, those would have been good years to put into retirement accounts,

• 3:16:53Sean Carroll?

  but a lot of it is just going to paying off my student loans. And that's bad. And it's just sort of a terrible system. We tell people to be responsible, and we make it very hard for them to do it. And then it's even worse when you're older. Like, I know, young people, you think you have it bad. But for many, many people here in the United States, when I say society, I mean the United States because that's the one I'm familiar with. Being old is terrible. We do have social security. Certain forces in our government are trying to get rid of it. It's a minimal amount. It's not a huge amount of money that you get, but it can make the difference between poverty and, you know, a relatively reasonable lifestyle. But we just pile on all these extra expenses, right? Healthcare is just the most obvious one. But there's all sorts of other things that get more expensive

• 3:17:37Sean Carroll?

  and things that you need to do when you get older. Housing, I mean, if you become less able to get around by yourself or if you start losing your cognitive capacities, you can deal with that, and the way you deal with it is by spending money. And so we have this thing where, you know, we teach people to save money over the course of their careers and then as soon as they get old, we siphon it away as soon as we can, trying to make it sure that the system gets all the money out of people before they die, right? And, you know, that's a slight exaggeration, but only a slight one. And I'm shocked that we let that happen. I mean, this is a place where democracy isn't working very well because clearly, a lot of the interests of a lot of people are not actually being served by

• 3:18:21Sean Carroll?

  the social organization that we've set up. I don't know how to fix that, you know, but it's something that I think is worth saying out loud over and over again, because I think that we often hear, the voices we often hear, including from people like me on this podcast, are not the ones going through those particular problems. So we have to draw attention to those problems existing. So to any of you out there, if you have the wherewithal to put money into retirement, do it. It will pay off for your future self. And if you're older and thinking about, you know, like, how can I afford housing and healthcare? Good luck to you. I don't know what to tell you. We don't live in a universe that makes that one easy.

• 3:19:04Sean Carroll?

  Brandon Lewis says, "I've long known that cats express emotions through their tails, but I've often assumed that their emotions just kind of leaked out this way. Recently, I heard it described as a tail language, which got me wondering, how intentional do you think cat tail movement is? Are cats consciously in control of their tail movement? How much tail expression do you get from Ariel and Caliban?" Uh, I would be very skeptical about tail language as a concept. You know, you have to be clear. There's all sorts of ways in which animals, and human beings for that matter, communicate without language as such, right? I think that language should not be thought of as synonymous with communication, okay? You can get your point across without

• 3:19:47Sean Carroll?

  using language sometimes. I think that's what animals generally do. I think we should maintain the idea of language for something symbolic, right? Something that is also modular, can be put together in different ways, inform complex thoughts, which I don't think many animals actually do. Maybe some of them do, and that's, you know, a thing that we can study. We've talked about it here on the podcast, and it's an intricate, difficult thing. But I don't think that Ariel and Caliban are putting together complex thoughts with their little walnut-sized brains and expressing them through their tails. It is true that cats' tails are very expressive. That's true. But I do think that it's essentially entirely unconscious.

• 3:20:26Sean Carroll?

  When we had Puck, our little stray cat, who we eventually found a home for with our Mindscape listener who took in Puck. Puck was very expressive with his tail, and in particular, you know, we had him, he had a room here in the house when we were taking care of him. And we, a couple of times, we tried to let him out of the room and put Ariel and Caliban away so that Puck could explore a little bit. And if he, if he went outside his room, his tail became like five times the size. It puffed up hugely. He was very, very expressive. And you could actually, over the course of time, over the course of about 15 minutes, you could see the tail gradually shrinking as the puffiness of the tail. As he calmed down, and you could, you could totally judge exactly his level of nervousness from the tail.

• 3:21:10Sean Carroll?

  But I don't think that that was intentional. I don't think he was trying to send us a signal. I think it's just his immediate bodily response. Anders Marchsteiner says, is it just animals and people that have free will, or can plants and mushrooms be said to have it to any degree too? Or is it what they, what, or is it what they do always a reflex to the environment? I think, you know, you can, you can listen to the episode that I did with Christian List, and he spelled out what in his mind are criteria for having free will. And no, plants and mushrooms do not have them. Or he wrote a book. You can buy the book if you're very interested in these questions. The point is that free will has something to do with rational control over decision-making, right?

• 3:21:53Sean Carroll?

  You do things for reasons that you can articulate and exist in your brain. You cannot ask a mushroom why it is growing in a certain way, and it cannot give you an explanation for that. That is part of what his definition of free will is. And I think that part makes perfect sense to me. David Maxwell says, "Moral philosophy debates always surprise me by seeming to present a meta-ethical dichotomy between consequentialism and deontology. My intuition is that any sensible framework should be a hybrid. Certain things like rape have no conceivable place, whereas lying surely must depend on balancing the consequences. In my mind, some ethics are absolute, while others are just good policy. Why aren't hybrid approaches discussed more?"

• 3:22:35Sean Carroll?

  I maybe should have grouped this with the previous question about morality, but I think that there are hybrid approaches. But I also think, from talking to people like Peter Singer, that there's more overlap with the practice of these moral philosophies than you might think, right? Like, you might say about if you want to make a cartoon version of utilitarianism, you say, "Well, alright, we're trying to increase the overall utility of the world, the overall happiness, or whatever. Therefore, an action I take should increase everyone's happiness as much as it can, so I should give away all my money up until the point where I'm as happy as the least happy person," or something like that. But as Singer points

• 3:23:18Sean Carroll?

  out, like, if everyone tried to do that, everyone would be unhappy. You have not actually increased the happiness of the world. So, the way that you would actually end up acting, I think, in some versions of utilitarianism, is not that different from how you would act if you thought deontology was a better approach. You can absolutely fit the idea that rape has no conceivable place into utilitarian framework by saying that rape causes a huge amount of negative utility. That's it. So, I do think that these approaches are more common in practice than they might be in principle. I think that's an interesting kind of thing to think about. I don't know if the principles are blended together very

• 3:24:00Sean Carroll?

  much, but I do think that that is a sensible thing to try to do. But it's not like, I don't think it's a patchwork in the way that we talked about before. I think there's a right answer, but the right answer might not be the form of pure utilitarianism, or pure deontology, or pure virtue ethics, or anything else, as we currently understand them. Dennis Banks says, "It seems like Dan Dennett influenced your thinking on a range of philosophical issues. I've been reading some of his books and articles recently, and I'm starting to understand why. What a sharp-minded and talented writer. But I was wondering, are there any philosophical positions that you think Dennett got wrong?"

• 3:24:39Sean Carroll?

  Look, I'm not, again, the world's expert on the writings of Dan Dennett. I do think that he's written about a lot of things. He's much more interested in consciousness and free will than I am. Those are things that I keep talking about because I think that there's, they relate to things that I do care about, like physics and emergence and things like that. But I don't have detailed opinions about the actual workings of consciousness or free will, like Dan Dennett or Christian List might. So I think that generally I'm in agreement with the positions that I know about from Dennett. I do think, as I mentioned earlier in the podcast, that I disagree with some of his labelings, or some of the ways that he would express his opinions.

• 3:25:21Sean Carroll?

  And I also think that, you know, I, this is not going to surprise anybody, but I think there's, he could have gone even further, and in even more interesting directions in this sort of same way that he was going, if there had been more physics in what he talked about. I think that there's a very, I mean, Dan was very clear that he was not an expert on physics, right? That he didn't have that in his toolkit, as it were. And that was fine in his mind, for, you know, you have to pick and choose what you're an expert in, and he was more interested in things like consciousness and free will, metaphysics, ontology, epistemology. But I do think that the overlap between the things he was interested in and physics was more than he suspected.

• 3:26:02Sean Carroll?

  And I think that physics is something which, if you understand it, can help clarify your view on things like emergence and real patterns and things like that. So I encouraged him to move in that direction. Mewash Viachor says, "In the spirit of Physics of Democracy, do you think that we should strive to become fractal or scaleless societies? That is, is there value in having layers of self-governance, identity, legislation, values, personal connections, et cetera, apply with approximately equal weight at scales from families and local communities, through neighborhoods, cities, regions, countries, all the way to continents and the earth?

• 3:26:43Sean Carroll?

  Or should certain scales be privileged, as, say, nationalists insist that nations should be? Not necessarily meant as a political project, but I'm very curious to hear your take on the pros and cons." Well, I want to emphasize that the idea of the physics of democracy is a descriptive one, not a normative one. That is to say, I'm trying to see whether or not we can learn about how things work by applying a physics-oriented lens to some of these problems in politics and society, rather than saying physics teaches us that we should do things one way or the other. So I would interpret your question as saying, is it possible to have better

• 3:27:24Sean Carroll?

  by the standards we already have, by the norms that we already hold to, would we be more effective if there were more autonomy between the different layers of government than there are now? Like, in the present world, I think it's true that sort of the nation-state is the primary locus of governance. And, you know, I think that, I'm not sure, is the answer. I don't think that there's any principle that says that if an organization is completely scale-free or power-law or fractal or whatever, that that's better. I think that there are reasons why dynamically, in different circumstances, those kinds of distributions arise naturally, and maybe politics is not one of them. I mean, you

• 3:28:08Sean Carroll?

  can see in the United States, which, again, I always apologize for always using American examples, but those are the ones I know, having grown up here, there was a very strong tradition of federalism at early moments in the history of the country. And even at a more fine-grained level, there was a tradition of local control of things like schools and roads and things like that. So there was a distribution of responsibilities at different levels. And I think over time, it's become the power, the responsibility, has become more and more concentrated in the national level, in the larger level. And I don't know if there's an inevitability to that. That's a good physics of democracy kind of question. Is there a reason why? Is there an instability to an arrangement that starts off by giving

• 3:28:53Sean Carroll?

  equal amounts of responsibility to different levels? Is there a sort of natural concentration of power? After all, there's plenty of systems in the world that don't naturally take on scale-free or fractal Geometries, so maybe governance is like that. And maybe that makes it less effective. I can imagine an argument that says it would be more effective if if things were more spread out. But you know, you can see kind of why it happens. Like, there are, you know, you have this idea, this utopian idea in the United States that states are the laboratories of democracy. Okay, so different states can try different things, and if they're successful, then other states can catch on. And that's something that gives us more flexibility than if we just did everything at the national level.

• 3:29:38Sean Carroll?

  But, of course, if you do that, and every state is trying different things, and then people do decide that something is better, they will often turn to the national level to say, okay, implement this and make sure everyone does it, whether they like it or not. And sort of there's a natural tendency to sort of appeal to the highest level of authority and make it impose what you want to be imposed as widely as possible. Again, that's not saying that's what it should be, but I think that you can see why that would happen. Stan Manilov says, "You sometimes say that in black holes, the singularity is not a place but a moment of time in the future, or that space and time switch roles inside a black hole. Is there actual physics behind these statements, or are they just different ways of describing

• 3:30:22Sean Carroll?

  the fact that classical general relativity breaks down at the singularity?" So, there's absolutely physics behind these facts, these statements. They are not made up. You can find explanations in, for example, my first volume of the Biggest Ideas in the Universe book, Space, Time and Motion. I do not say that space and time switch roles inside a black hole. That's not something that I say. People say that, I disagree with them. Time is time, space is space. What switches roles are the coordinates that we use to describe space and time, but who cares about that? You don't have to choose coordinates that switch roles. So I wouldn't ever say that. But I would say that the Big Bang is a singularity which is a moment in time in the past.

• 3:31:07Sean Carroll?

  And in black holes, in short shielded black holes, in non-spinning black holes, when they spin and they have electric charge, things get more complicated. But in the simplest short shielded black hole, it's just a mathematical fact that the singularity is indeed in the future. Schlier says, "Do branches of the Everettian multiverse contain the full possibility space of evolution?" So I'm not sure by evolution whether you mean the evolution of the dynamical system called the universe, or something like natural selection and Darwinian evolution. But in either answer, in either case, the answer is no, they don't. The branches of the Everettian multiverse contain what is predicted by the Schrodinger equation, whatever that turns out to be. There might be examples that just don't happen, right?

• 3:31:52Sean Carroll?

  If I take an electron with a spin, and I measure its spin, and I measure it to be spin up, and then I measure it again, there's no chance, if I've done my experiment correctly, that it's not going to be spin up again. That's what quantum mechanics predicts. It's not like everything happens. Certain things happen and certain things don't. A much more rigorous example is conservation of electric charge. Conservation of electric charge insists that things that, possible evolutions for which the electric charge of the universe changes its value, do not happen. Those are possible worlds, conceivable worlds, they just don't happen, according to the evolution governed by the Schrodinger equation.

• 3:32:33Sean Carroll?

  So it's the Schrodinger equation that is in charge, not just some vague idea that everything out there that possibly happen, will happen. Christian Dobos says, "Does your one-guest-one-appearance approach prohibit you from inviting people on the podcast who, from inviting people on whose podcast you already made an appearance? Did this happen before, and if so, were the topics overlapping?" No, there's no, I don't care about how many times I appear on other people's podcasts, or that they appear on mine. I don't think it happens very often. It happens sometimes, you can go back. When was the last time it happened? Maybe Daniel Whiteson, maybe? I don't really remember.

• 3:33:15Sean Carroll?

  But the point being that I don't usually invite podcasters on my podcast. I might invite people who are academics, who have some interesting thing to say, in an intellectual way, who might happen to have a podcast. But simply having a podcast is not a good enough reason to have someone on the show. Look, I had Peter Singer on the show. He has a podcast, but I'm not inviting him on my podcast because he has one. It's for other reasons, right? So these days, more and more people do have podcasts, so the overlap happens. And other people don't have this policy that I have. So I don't, you know, I might appear on someone else's podcast many times. Um, and, and that's perfectly okay.

• 3:33:58Sean Carroll?

  Ryan Cobine or Cobine says, even though Ukraine seems to have the initiative and is inflicting tremendous losses on Russia, it is nevertheless true that Russia is now probably the world's second most experienced and proficient country in drone warfare. Given the cost differential between what was conventional warfare, as the US has demonstrated in Iran, and contemporary drone warfare, the US's withered arms production capacity and the People's Republic of China's dominance in all areas of manufacturing. What is your outlook on the future of war and international power? Does the drone era make nuclear conflict more likely or warfare in general less likely or what?

• 3:34:37Sean Carroll?

  I mean, you know what I'm going to say, which is that I'm not a super duper expert on the future of warfare and international power. I do think that technology is going to keep changing the nature of war, which it always does, right? Like every generation, war is a little bit different than it was before. And that's why we have this old axiom about people or old saying about people always fighting the last war, because the next war is going to be different in various ways. Drones are clearly much more important now than they used to be. They might be even more important. Drones used as delivery for bioweapons, which doesn't happen now, but could very easily happen, are an obvious place to think of. More and more cyber attacks could be part of war.

• 3:35:22Sean Carroll?

  That's where, that's a place where AI could level the playing field and allow other countries to sort of attack more advanced countries and damage their cyber infrastructure in dramatic ways, you know? Like if you wiped out all the electricity and all the internet in a country, that in the modern Era would do an enormous amount of damage to it right away, uh, cause enormous suffering. Um, so I, I, my only very vague, um, thought is that whatever war is today, it's not going to be like that 20 or 50 years from now. So it's most important. Look, this is, this is a different version of the same reason why you shouldn't go to university

• 3:36:06Sean Carroll?

  with the idea of becoming an expert in some technical field that will then get you a job that will last your lifetime. Because what is an interesting technical field will be different in 20 years than it is today. It's much more important to go to your university and get an education in being a well-rounded human being. And then you pick up the parts of specialization that will be useful in your future career later on. Likewise, I think that what will lead to dominance in war is not just the ability to be really good at building drones, but a broad-based technological capacity, a flexibility, a flexibility, uh, at the level of strategy and tactics in the policymaking arm of the country,

• 3:36:49Sean Carroll?

  in addition to, um, the actual ability to build the technology. Does drone era make nuclear conflict more likely? I don't think so. Like, I really don't think that once you have a nuclear bomb, it's that difficult to deliver it. You know, they're blunt instruments, right? You don't need really pinpoint control. The great thing about the drone era is you can pinpoint your small-scale attacks. It kind of isn't necessary for nuclear war. I think the nuclear proliferation is definitely making nuclear conflict more likely. I certainly don't think that drones make warfare in general less likely. I think that there's this sort of longstanding hope that if war becomes more terrible,

• 3:37:30Sean Carroll?

  people will stop doing it, but I see no empirical evidence that that is actually real. Josh Powers says: "In light of the relativity of simultaneity and the resulting implication of a block universe that includes all past and future time, I have trouble understanding how subjective experience of time passing could be possible. It's tempting to use an analogy with motion through space, but I can only conceive of experiencing motion through space if I also experience time passing. I don't know what I could experience the passage of time relative to if all time already exists. Can you suggest any reasonable ways to think about subjective experience in a block universe?" Well, I think that the whole problem of subjective experience is a tricky one, as

• 3:38:13Sean Carroll?

  you know, if you've listened to this podcast or any other one. But again, I'm perfectly physicalist about it, so I don't think that there's any obstacles to this in principle. I think that where it comes to the block universe versus the flow of time, there's two things I would say. First, I don't really think that the alternative, you know, that you're a presentist and you really think that time actually flows in some sense, I don't think that's really coherent. I'm not quite sure what it means to say that. So I think that the problem of reconciling subjective experience of time's passage with the block universe is just with us, like it or not. But it also just doesn't seem that hard to me. I think that, I mean, it seems hard because problems of experience and thinking and cognition

• 3:38:56Sean Carroll?

  are hard, but not something specifically about presentism or time is hard. There's a possible confusion because people keep wanting to bounce back and forth between the vocabulary of presentism, which is sort of our folk physics way of thinking about the world, and the vocabulary of eternalism. You can't help say things like, "I experience time passing," right? Those are words that sort of came out of a presentist tradition, and those words should be replaced by better words, if you're really trying to say what a block universe person would say. Namely, you should say, "This particular instantiation

• 3:39:37Sean Carroll?

  of myself at this particular location in space in this particular moment of time is thinking in this particular way." Okay, why would a person, why would the, the example, the version of a person at some particular place in time be thinking in a particular way? Why is it that me at some particular moment of time has the impression in the folk physics way of thinking about things that time is passing? And I think that's, we sort of understand the basic reasons that need to be articulated into a more complete understanding, but people like Janan Ismail and others have, have worked on this. The fact is that you, at every moment of time, the version of you at 12 o'clock and the

• 3:40:20Sean Carroll?

  version of you at 1pm and the version of you at 2pm, have in your mind both a, a picture of your present configuration. You think you know who you are, where you are, how you are ranged. You might not be 100% accurate in that, but you have it. You also have an impression of what you were like in the recent past, okay? Where you were, what you were doing. And you also have a projection into the future of where you might go, where you hope you're gonna go, where you expect to go, where you want to go, et cetera. And you are constantly updating all of these different pictures, and they're different pictures, right? Your projection into the future is different than your memory of the immediate past, and it's that difference, that imbalance, which is ultimately traceable to the thermodynamic

• 3:41:04Sean Carroll?

  arrow of time, that we conceptualize as an experience of the passage of time. It's not that quote unquote "time is really passing, time just is a label on the four-dimensional block universe," but at every moment of time, every instantiation of you contains an unbalanced set of impressions about the past and the future. And it's that unbalanced sense, uh, set of impressions that we attribute to, or that we, um, interpret as a sense of time passing, is what I would say.

• 3:41:38Sean Carroll?

  David Sotolongo says, "If one believes that in the vast majority of worlds, artificial superintelligence kills off mankind, and also believes it's practically impossible to stop ASI from coming into being, do you think it makes sense to ignore the worlds where ASI kills off mankind and instead just focus on making sure that whatever ASI gets created ends up being beneficial to mankind rather than creating a dystopia?" So I'm gonna have to deny the premises of the question here. I don't believe the vast majority of worlds ASI kills off mankind, and I also don't believe that it's practically impossible to stop ASI from coming into being. I don't even think that there is a coherent idea called ASI. As I was saying before, there's many different levels of intelligence,

• 3:42:22Sean Carroll?

  directions of intelligence, and we're not helping ourselves where we blur all those important distinctions and lump them together in one thing. We should take seriously what we actually have and might create, not just project some vague ideas about superness onto the concept of intelligence. But okay, having said all that, I think the questions like this are in the genre of questions that become very difficult because you're saying, "Okay, I have this thing that I think is very, very unlikely, but if it happens, it would have a huge, huge, huge impact," right? And I mean, very unlikely and very huge impact. So I need to multiply the percent chance that it happens by the impact, and I have

• 3:43:03Sean Carroll?

  to sort of weigh that against things that are quite likely and have much smaller impact. I think that in general, questions like those are really, really hard. It's not hard in principle to do the math. What's hard to do is to know whether or not doing the math is the right thing to do, and it's really hard to understand the error bars on your math. Is something that is unlikely a 1% chance, or a 10 to the minus 100 chance? Those are very, very different numbers. Is the impact really extinguishing life on Earth, or is it costing us a few billion dollars in revenue? Very, very different outcomes. So I think that my general strategy...

• 3:43:47Sean Carroll?

  For these questions is to be somewhat incrementalist about them. That is to say, not to really base my actions on these best case or worst case scenarios in the relatively far future, but to be prudent about the direction we're moving in, step to step. I think that we have much more control and understanding of what short-term possibilities are than we do long-term possibilities. That doesn't mean that long-term possibilities aren't important. It means that the way to handle long-term possibilities is to handle the short-term possibilities. Okay? Now, obviously, that's not true in cases where we do have a good handle on the long-term possibilities.

• 3:44:27Sean Carroll?

  Like, if we keep dumping fossil fuels into the atmosphere, the Earth's going to heat up. That's very predictable. That's not a small percentage chance of happening. But these really weird speculative science fiction scenarios are not very much of that character. And so for them, I think that, you know, moving carefully step by step is the right strategy to take.

• 3:44:52Sean Carroll?

  Okay, I'm going to group, let's see, three questions together. They're all long questions, so I'm going to have to read them all, and you'll have to decide whether or not you can remember them as I read them. So Dan R. says, "I really enjoyed your Christian List episode. As I consider myself a good Bayesian, I was hoping you could briefly discuss how much credence we should assign to deterministic arguments, such as those put forward by neurobiologist Robert Sapolsky, who was, by the way, was a Mindscape guest. We did talk to him here, if you want to listen to the conversation. For the listeners, he argues that human behavior is nothing more than an unbroken chain of biological and environmental luck. He specifically rejects immersion complexity as a loophole for free will on the basis that a complex system is still entirely constrained by the deterministic laws of its basic parts.

• 3:45:37Sean Carroll?

  What I find to be his strongest philosophical argument is when Sapolsky asks, "Even if we operate with intent at the macro level, where did that intent come from if not an unchosen lottery of genes, hormones, and prior environment?" Then Ian Carey says, "I enjoy your talk with Christian List, since I am one of those people who stubbornly find the issue of free will and determinism confounding. One point I had a hard time wrapping my brain around was when List talked about the possibility of having different levels of description for a system where some levels are deterministic and others aren't. If my mental states, including my choices, are the result of the underlying state of atoms, etc., that make up my brain, and those atoms and particles follow the fundamental laws of physics deterministically..." Footnote, by the way, they do not,

• 3:46:20Sean Carroll?

  because there is quantum mechanics. People want to forget that, but okay, I'm gonna put it there. That's me, Sean, talking. Now we go back to Ian. "How can it logically follow that my choices are not solely determined by the underlying physics? In other words, if fundamental physics equals deterministic and my brain equals fundamental physics, how can we get my brain is not deterministic?" And then Mike Cohen says, "Enjoyed the Christian List conversation very much. I can't totally internalize his and your view of the possibility of determinism there but not here, because it feels to me as though different levels of reality blend continuously into each other with no clear dividing line between a level whose past and future is determined by laws and a juxtaposed level of thought that is agenerative. Therefore, the concept

• 3:47:02Sean Carroll?

  of different but supportive levels that do not share determinacy seems off. However, this is my lived experience of free will. I have it, and since levels of determinism probably cannot be resolved, I'm happy to truck along with my, along my agenerative road. In physics and philosophy, there are many mansions. I will trouble myself no more about free will." That's probably a good attitude that you have there, Mike. Okay. So the general principle of all these, the general query underlying all these questions is, I hear what you're saying about levels and so forth, and I kinda wanna get on the train that says that at higher levels, there might be free will, even if at lower levels, we're just obeying the laws of physics. But I am reluctant to see how you can have such

• 3:47:44Sean Carroll?

  an ontological difference between the lower level and the higher level. You know, at the most basic level, let's just simplify the question. If the lower level is deterministic, how can the higher level not be if the higher level is just made of the lower level, right? What else is there? I put it in those simple terms because the answer in those terms is super duper simple. The emergence involves coarse graining, right? Coarse graining means you're throwing away information. So when I flip a coin, I cannot predict if I do a good job of flipping the coin. I cannot predict whether it's going to have heads or tails, right? And even though, even if I thought incorrectly, that the fundamental laws of physics were

• 3:48:25Sean Carroll?

  deterministic and really there was an answer embedded in the microstate of me and the air molecules and the coin and all that stuff, I don't know that microstate. As you may have heard, I am not Laplace's demon. I'm going to have to get the T-shirts made saying that I am not Laplace's demon. That's definitely something I'm going to have to do. What that means is, in the same macrostate that I use to describe the world at the level of people and coins being flipped and things like that, there are included both microstates that will end up with the coin landing heads and microstates that will end up with the coin landing tails.

• 3:49:05Sean Carroll?

  And from my macroscopic level of observation, I am not able to distinguish those microstates. So the macro theory, even at its best, even doing as much as it can possibly do, can make at best probabilistic predictions. It is not a deterministic theory. You can know everything you want to know about the standard model of particle physics, but if you want to predict when a volcano is going to erupt, good luck with that. That's not what geologists try to do. I mean, you can do better and better by collecting more and more data, but typically, what you actually do is have theories of frequencies, predictions, probabilities for things in natural selection or biology. It's exactly the same thing.

• 3:49:47Sean Carroll?

  You can see the animal, but you can't, by looking at the animal, read all of its DNA sequence, and therefore you can only make probabilistic statements about will the baby be a boy or a girl, right? So it's very, very easy for there to be fundamentally different kinds of behavior at a macroscopic level than at a microscopic level. Okay. So I think that that answers all the general questions. Let me go through very, very quickly here. You know, Dan R. says, "A complex system is still entirely constrained by the deterministic laws of its basic part." Sure, it is, but you don't know the state of the basic parts. And it's not just you happen not to know. They are literally unavailable to you at that macroscopic level.

• 3:50:31Sean Carroll?

  In some sense, at the microscopic level, it is entirely valid to say that that intent that you had at the macro level came from an unchosen lottery of genes, hormones, and prior environment. So what? You don't know. It's not part of that macro theory. The macro theory is one in which people are not predictable and make choices. And that's just how the macro theory goes. To Ian's question, I think that was very close to the way that I answered already. But he says, "If fundamental physics equals deterministic and my brain equals fundamental physics, how can we say my brain is not deterministic?" The answer is, your brain is not fundamental physics. Your brain is a very coarse-grained description of certain fundamental physics, and that changes everything.

• 3:51:15Sean Carroll?

  That changes the space of possibilities and implications very strongly. So for Mike, I don't even think Mike's asking a question here. I think that Mike is just talking through his process of becoming, accepting of the picture of many levels. I think that's a good process to talk yourself through. Okay. Thomas S. says, "I'm reading the particle at the end of the universe, and it got me wondering, do you feel that the SSC, the Superconducting Superglider, would still be a worthy undertaking today, assuming funding was secured? Or was its merit predominantly predicated on goals that were since made redundant by the LHC?" I don't think it would be a good idea now. It was a better machine.

• 3:51:57Sean Carroll?

  So, the Superconducting Superglider that was planned during the Clinton administration before they canceled it, to be built in Waukesha, Texas, would have reached higher energies than the Large Hadron Collider would have. It sort of would have leapfrogged what the LHC is able to do. But not by a lot, okay? By a noticeable amount, but not by a huge amount. So, you always have to do a cost-benefit analysis in these things. You know, by the way, why did the LHC even get built? There were absolutely... Absolutely, discussions at CERN and in Europe, should we even bother building Large Hadron Collider? Because it's on a similar timescale to the SSC and it's not as good.

• 3:52:41Sean Carroll?

  And some very smart people in the European physics community said, "Don't worry, the Americans won't do it. They're gonna falter and not do it and we have to be ready to leap on the opportunities." And they did, and they've won Nobel Prizes, etc. I still think, by the way, that a Nobel Prize should be given out somehow to people who either built the LHC or did the experiments. And I know, I know it's very difficult because they have a self-imposed rule, only three people can do it. But somehow you gotta figure out a way to do that, I think, because that was a tremendous accomplishment. But anyway, given that they did build the LHC, it would not be a big enough improvement versus the cost it would require to build the SSC today.

• 3:53:26Sean Carroll?

  Which is why, well, that's one of the reasons why that's not really an ongoing concern, building a new SSC. If you want to build a new particle accelerator, which I highly recommend doing, you might as well build an even bigger one than the SSC was supposed to be. It's been a long time and it's gonna take decades to build it, so you might as well think big. And I think that's what people are trying to do. Of course, the other reason that the SSC is not a major component of our thinking is that no one thinks that the United States is gonna do it. The United States has more or less abandoned the idea of being a leader in particle physics. The choices now are between China and Europe.

• 3:54:06Sean Carroll?

  And maybe some other places might surprise us and step in, but those are the leading candidates right now. Okay, the last question of this AMA is a relatively long question, but I think it's worth it. Let's see if you agree. Chris Kaltvasser says, "I'm sorry that the Sixers fell to the Knicks. I was also disappointed by my Detroit Pistons. I appreciated you mentioning the amazing comeback that Detroit had against Orlando in Game 6, where they went into the half down by 22 points, but somehow managed to come back in the second half and completely shut Orlando down." It's that game that I have a question about for you. In that game, Detroit didn't just chip away at the lead. They completely obliterated Orlando in one of the most lopsided halves in NBA playoff history.

• 3:54:51Sean Carroll?

  Here's the thing, I didn't even see the second half. I was so disappointed that I didn't have the stomach to watch what I thought was going to be the end of their season. I was quite elated to discover they had won, though I'm not sure I learned my lesson. Because I repeated the very same move in the next series against Cleveland in game seven, which by the way, they they didn't win. After a completely lackluster first half, I turned the game off again. And this time, however, I later learned that they had no ability to turn things around. I was at least gratified that I didn't spend the second half watching a group of millionaires thinking more about their summer vacations than repeating their historic performance. So my question is, would you have turned off a Sixers game if they were down 22 points going into halftime in game six?

• 3:55:34Sean Carroll?

  So the Sixers were down to the Celtics, I think it was game five, either game five or six. They won games five, six, and seven in their first round series against the Celtics. And in one of those, they were down by a lot. And if they had lost the game, they would have lost the series. They're not down by, it was not nearly as dramatic as Detroit's turnaround against Orlando, though. And I do think it's a very legitimate question. And this is why I'm answering it, not because people care about Sixers and Pistons, but because there's a question of sports fandom and how to be a good sports fan if you're rooting for your team, right? I am very much on the side, I said this before, but I think that modern sports fandom has been contaminated in part.

• 3:56:17Sean Carroll?

  I don't know whether it's because of betting or fantasy sports or just the internet or whatever. But too many fans think of themselves as fake general managers rather than as actual fans. So rather than rooting for the team as it is actually constructed, they spend a huge amount of time complaining that the team is not how they would have constructed it. They want to fire the coach, they want to fire the players, or etc. I'm just not like that. If the players are on my team, I'm going to root for them. I'm going to root for them to play well. That's what I want to see happen. But of course, the reason why you want to see That happen is because you like it when they win and you're sad when they lose and it is not missed my attention entirely that you get sad when your team loses and why are you doing this to yourself?

• 3:57:03Sean Carroll?

  Why are you inflicting this pain on yourself? And you know, the NBA and most sports have the feature that the last game of the season that your team plays, they will probably lose, right? Because half the teams that don't make it to the playoffs on average, or probably more than half, will lose their last game of the season. Once you get into the playoffs, the only team that ends its season on a victory is the team that wins the championship. Right? So, most people will go into the offseason unhappy in some sense. And so, at what point do you give up? At what point do you stop watching or whatever? I will certainly say, you know, for the Sixers in particular, which I'm most familiar with,

• 3:57:45Sean Carroll?

  it was more fun to watch them in some sense. Well, it was fun to watch them in different ways when they were completely struggling intentionally because they tore down the team in order to rebuild, okay? When they, when they did very, very well in the draft lottery and got Joel Embiid and other players. But before then, they were just terrible and it was still kind of fun to watch them because there were no expectations. Right? Like they were terrible, but you kind of knew the players and I didn't watch all the games because that would be, you know, I still don't watch all the games, but never have watched all the games. But you would still watch occasionally, you would know what was happening, even though they were probably gonna lose. And that was okay. And then they became good for the last several years, the Sixers were good.

• 3:58:30Sean Carroll?

  And when Embiid was in his MVP prime, then I watched a lot of games and I was very sad whenever they lost. And now, they're like, they've declined a little bit from what they were three years ago. Like, we all know like the literal exact moment when they declined because three years ago, Joel Embiid had just won the MVP the season before and he was playing even better. The next year than he, than he was playing in his MVP season and the Sixers were regular. Embiid was only playing three quarters because they were so good that they would have an unbeatable margin of a lead going into the fourth quarter. But then he got injured and since then it's not been the same.

• 3:59:13Sean Carroll?

  And now it's less fun to watch because you're again always comparing expectations and reality and we know how good they could be if it weren't for all these stupid injuries and things like that. And they're not that good and that breaks your heart. So I don't ever think I give up after one half of basketball because by definition, if your team is losing by N points after only a half, in principle, you could be winning by N plus one points in the next half. Like giving up after three quarters is a lot more defensible, I think, than giving up after a half. I will however, sort of half give up. Like I will sit in front of the TV but really be working on writing my book with the volume turned off, right?

• 3:59:57Sean Carroll?

  And just in case they happen to do a miraculous turnaround. And so I guess all I'm saying here is it's a weird relationship between the fan of a sports team and the players. There's a lot of emotional investment, all flowing in more or less one direction and it's very unpredictable and out of your hands. And how you should manage the emotional roller coaster that is being a sports fan of almost every team is an individual choice. There's no moral mistake you're making by giving up because you know, you don't owe them anything, that's for sure. But there's a lot of benefit to being around when they make the miraculous comeback. So maybe you want to give them the chance to do that. Maybe there's a broader lesson here and we should all give each other the chance to

• 4:00:41Sean Carroll?

  make a miraculous comeback in our lives. So that's a good place to wrap up this month's AMA. Thanks as always for everyone for listening and supporting the Mindscape Podcast. I'll talk to you next time.

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