AMA | May 2026

Welcome to the May 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 full transcript: https://www.preposterousuniverse.com/podcast/2026/05/04/ama-may-2026/ Henson Shaving is offering 100 blades free with the purchase of a razor — just head to hensonshaving.com/MINDSCAPE https://hensonshaving.com/MINDSCAPE and or use code MINDSCAPE at checkout. #sponsored Take your personal data back with Incogni! Use code MINDSCAPE at this link and get 60% off an annual plan: https://incogni.com/mindscape #sponsored

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

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• 0:56Sean Carroll?

  Hello, everyone, and welcome to the May 2026 Ask Me Anything edition of the Mindscape Podcast. I'm your host, Sean Carroll. I am recording this intro after I recorded the rest of the AMA on Saturday, May 2 of 2026. And I mention that because tonight is game seven in the first round series of the NBA playoffs between my beloved Philadelphia 76ers and the hated Boston Celtics. And I mention this because there's really nothing else on my mind right now. I'm actually working on my book while I'm not doing this, the AMA, but really, in the back of my mind, it's basketball that is taking up most of

• 1:41Sean Carroll?

  my mental space. And this is the intro to the AMA, so I can talk about whatever I want. I know that a lot of people are not especially fascinated by this topic, so you can skip ahead to the AMA itself because I might as well explain where my mental space is at. And I've talked about before how I admit that sports fandom is largely irrational, or at least irrational. It's not irrational in the sense that you're making a mistake to root for one team over another, but it's non-rational in the sense that there's no real moral calculus or ethical considerations that go into choosing which team to root for. It depends on where you were born, right? I think this is very harmless and, in fact,

• 2:25Sean Carroll?

  fine, right? I'd much rather have people...

• 2:29Sean Carroll?

  Self identify as fans of a certain team and put a lot of their emotional energy into rooting for that team than other much more harmful ways to make irrational choices about how to live your lives. So I'm all in favor of this. And I grew up outside Philadelphia. All of my sports fandom is still Philadelphia based and basketball was always my sport of choice, going back to 1976, when the Philadelphia 76ers purchased Julius Irving, because the upstart American Basketball Association was folding and some of their teams were being brought into the NBA, the more long lasting National Basketball Association. And some

• 3:13Sean Carroll?

  of those teams couldn't afford the fee to go in. So the New Jersey, no, they were at the time, the New York Nets, then they were the New Jersey Nets, now they're the Brooklyn Nets. At the time, the New York Nets couldn't afford to keep their best player, Julius Irving, and the Philadelphia 76ers, my hometown team, purchased him and immediately became NBA championship contenders. Not long after, just a few years earlier, they set the record for the worst record in a season in the history of the NBA. So it was an impressive turnaround. That year, 1976-77, they did not win. They came close. They made it to the NBA Finals. They played against Bill Walton and the Portland Trail Blazers. And that set up several years

• 3:57Sean Carroll?

  of frustration because Julius Irving, Dr. J, my childhood hero, was good enough to drag them to the NBA Finals several times. They went in that year, they went again in 1980, 80, I forget, I forget how many years, at least four or five times, they went to the NBA Finals with Dr. J. But they didn't win until in 1983, actually 1982, they were able to acquire Moses Malone, the center from Houston, who was the league MVP at the time, and he led them to a, one of the best teams' seasons in history, the 82-83 Philadelphia 76ers. They easily

• 4:38Sean Carroll?

  Cruise to the NBA championship and that was, you know, it felt good after all those years of frustration. And so I, but I grew up with, you know, the Sixers being super duper competitive and the Celtics, the Boston Celtics were their hated rivals. And I use hate and things like that in a, in a very casual sports like way. I don't hate the Boston Celtics. In fact, I have enormous respect for them as a franchise. I really, really didn't like Larry Bird personally when we were rooting against him, but now with the passage of time, I have again, enormous respect for his game and his achievements and, and the organization as a whole. But that year that the Sixers won the NBA title,

• 5:22Sean Carroll?

  they didn't actually meet the Celtics in the playoffs. They, they usually meet the Celtics. The Sixers versus the Celtics is the single most frequent NBA playoff matchup. The Sixers have played the Celtics more often than any other two teams have played each other in the history of the NBA. And it's a, it's a storied rivalry going back to Wilt Chamberlain and Bill Russell and the whole thing. And to be super honest, the Celtics usually come out on top. Dr. J's Sixers beat the Celtics a couple of times. The Celtics beat them a couple of times. The last time that the Philadelphia 76ers beat the Boston Celtics in the NBA playoffs was 1982, when I was still in junior high school, I guess, or

• 6:06Sean Carroll?

  for the beginning of high school. Yeah, high school, I suppose. So that's a long time. Since then, the Sixers have made it back to the playoffs and either done well or met the Celtics and done badly. The Celtics have just beaten them over and over again in the playoffs and especially the last few years, you know, since, I'm gonna, I'm gonna take pity on you all because I know you don't care about this. I could literally talk about this for hours and you don't want to hear it. But there's extra drama because several years ago, the Sixers fired their general manager and coach and hired Sam Hinkie, who was a analytics based way of thinking about.

• 6:48Sean Carroll?

  Basketball that he brought and he basically got rid of all their good players. And you think, oh, that's not very good to get rid of your good players. But he did it intentionally so that they could be bad and get good draft picks. And they did, it worked. This was later dubbed the process, as in trust the process by, I think it was a player on the team, Tony Roten, who first said, trust the process. But it was taken up by Sixers fans, including the Right St. Ricky Sanchez podcasters, and spread very widely. And the crown jewel of their drafting success was Joel Embiid, their center, who took as his nickname, the process.

• 7:30Sean Carroll?

  So trusting the process became also putting trust in Joel Embiid. And I swear that I've never seen a basketball player have worse luck with injuries than Joel Embiid. I've seen players just get so injured they couldn't play anymore, that that happens. Various players just never panned out because they had too many injury problems. But with Embiid, he keeps coming back and playing and then getting injured in weird ways. He's had teammates fracture his cheekbone in his face. He's had Bell's palsy. This year, just to rub it in, he had an emergency appendectomy during the last week of the regular season. He had his appendix out.

• 8:13Sean Carroll?

  Again, you can't blame him for things like this, but it has absolutely prevented them from going far in the playoffs because he's their best player. But this year, they are meeting the Celtics in the first round. And Embiid had an appendectomy and he came back 17 days after having surgery to get his appendix removed, far ahead of schedule. He played pretty mediocrely in the first game that he returned. And by then, once they lost that game, they were down 3-1 in a best of seven series. And the odds are not good for you in the NBA when you're down 3-1 and they're trying to win a four game, try to get to four games, four wins before the other team. But the last

• 8:58Sean Carroll?

  Two games, Embiid has been playing great and the Sixers have pretty easily handled the Celtics. And now it's 3-3 and this is game seven and Titanic repercussions for the happiness or sadness of all of Philadelphia sports fandom is going to happen tonight. So I say this again because it's what is on my mind. Again, I could talk for hours. There's a lot of human interest stories going on here, but the point is that it's fun, that it's quite enjoyable, that I'm glad that sports are out there. I teased people on Blue Sky the other day, I said I should do a solo podcast episode on why basketball is the best sport. And of course, people are like, no, it's not. You know, let me, let me tell you why it's really cricket or whatever. And it's all in good fun.

• 9:42Sean Carroll?

  I don't actually think that there's any objective sense in which basketball is the best sport. I do think I could come up with arguments that it is or that it isn't, blah, blah, blah. Let's all just have fun and enjoy the games and also we need to crush the Celtics tonight. I hope that happens. If it didn't happen by the time you're listening to this, don't talk to me about it. I will not be in any mood. But meanwhile, we're going to do the AMA. Thanks as always to the Patreon supporters of Mindscape for making this possible. You could become a Patreon supporter of Mindscape. Just go to patreon.com/shawnmcarroll. Let me actually check. I never remember if my middle initial is there in the Patreon listing. Where is it? Yeah, I don't know whether my, whether it's there.

• 10:27Sean Carroll?

  Yes, patreon.com/shawnmcarroll. The middle initial is there and you can sign up. Right now it's a dollar per podcast episode. We're going to change it to $5 a month at some point. We haven't quite done that yet, but still for, you know, typically what? Six hours per month at least of podcast goodness. $5 per six hours is not so bad, I think. And if you don't want to, you don't want to, that's fine. But if you do, sign up for the Patreon, then you get to ask the AMA questions, you get to ask a priority question, once in your life, that I will definitely try to answer because I can't answer all the questions that are asked, there are too many of them. And you get reflection episodes.

• 11:09Sean Carroll?

  For me, talking for five minutes after every regular podcast where I talk about how I thought the podcast went, what we learned, things like that, as well as the joy of being a member of something, being part of something, much like being the fan of a favorite sports franchise, even if it always breaks your heart. So with that, let's go.

• 11:44Sean Carroll?

  Alex says, "If there were an isolated region in space that consisted only of antimatter, would we be able to detect the fact that it is antimatter?" So there's a, I'm going to answer the question. No, we would not be able to, but there's a like, it's really close to a slightly more subtle question that is very interesting, and I think I know the answer to it, but I'm going to have to be a little bit less confident in that. Just so everyone knows, there are no isolated regions in space that might be antimatter. Space is pretty empty, but it's not completely empty. Even in between the galaxies, there is an intergalactic and intercluster medium. There's a tiny density of particles which

• 12:26Sean Carroll?

  would keep bumping into any macroscopically large amount of antimatter and annihilate and give off gamma rays and X-rays, and we would know about it very clearly. So not to mention the fact that 14 billion years ago, near the Big Bang, everything was touching everything else. So there was no way for anything to keep isolated. So this is not a realistic question, but it's a good thought experiment question. If, like you say, if Alex says, there were an isolated region of space and we could just look at it, so we're seeing photons come from it, realistically, no, we could not tell whether it's matter or antimatter. It's just a relabeling, roughly speaking. If you just, you know, they would,

• 13:09Sean Carroll?

  the people who were living in the galaxies that were made of antimatter would call what we call antimatter, they would call antimatter and vice versa. And the reason why, and furthermore,

• 13:23Sean Carroll?

  If there were only, if there was a universe that was only made of antimatter, and it had, what can I say? Yeah, so if it was completely made of antimatter, even if they knew all the laws of physics, they wouldn't be able to say like, they're made of antimatter rather than matter. So the tiny little footnote here, which makes it a little bit interesting, is there is in the standard model of particle physics, something called CP violation. CP are two symmetries, or at least two transformations you can do on the underlying particles and fields of the standard model. C says, "Switch all particles with antiparticles."

• 14:05Sean Carroll?

  And P says, "Change the parity." That is, the orientation of the axis. So you change right-handed things with left-handed things. So instead of a right-hand rule, if you did a parity transformation, you'd be talking about a left-hand rule. And that's important, because parity is violated in various weak interaction processes. And indeed, CP together is sort of the closest you could come to really trying to replace all matter with antimatter. Because I know that that's just C, but C is not a very good symmetry, but CP is. So it's sort of better to relabel, if you like. CP is the honest exchange of matter with antimatter.

• 14:49Sean Carroll?

  But CP is also violated, just a little bit. And so, there's a loophole, which I think is true. I've never really thought this through. That's why I'm answering it first, because it's an intriguing question. If there were a semi-isolated region of space, isolated in the sense that there was no matter being exchanged back and forth, and we were able to not only look at it, but like, send them a signal, and ask them questions, which we can do with photons, because photons are the same for matter or antimatter. So photons don't annihilate or anything like that, just because there's no anti-photons other than photons themselves. Let's put it that way. So if we were able to talk with them by sending signals back and forth,

• 15:30Sean Carroll?

  could we decide without touching each other or sending matter back and forth that we were made of the opposite of whatever? Like, we would call it matter and they would call it matter, but maybe what we call matter is what they call antimatter. And I think there the answer is yes, because of CP violation. So basically, what we could say is, there are particle physics processes that happen at a certain rate that is different than the rate at which their CP conjugate processes happen. So, for example, there is a kind of meson called the neutral kaon, which you can make in a certain way.

• 16:11Sean Carroll?

  And so, we would not be able to use with our potentially antimatter friends words like protons and neutrons, right? Because we don't know whether they're what we call antiprotons and antineutrons. But what we could say is, you know, your atoms have nuclei that are made of charged particles and uncharged particles. So, we call the charged particles protons, etc. And we could say, "Look, when we make a certain kind of kaon with a certain kind of collision of protons and neutrons, it makes certain kinds of other particles." Okay? And the CP violation says that there is a long-lived version of the neutral kaon and a short-lived version.

• 16:53Sean Carroll?

  And in the long-lived version, it can decay, it's neutral. So it needs to decay into a total number of particles with zero charge. And the kaon decays into a pion, an electron, and a neutrino with appropriate antiness where it needs to be. So in particular, for the ka long, it can decay into a negatively charged pion, a positively charged electron, which is what we call the positron, and then an electron neutrino. Or it can decay into a positively charged pion, the negatively charged electron, the real electron, and an antineutrino. And because of CP violation, those seem very, very similar. Those seem almost symmetric, right?

• 17:38Sean Carroll?

  Pi minus e plus nu, or pi plus e minus nu bar, in particle physics lingo. But because of CP violation, the decays into the positron version happen slightly more often than decays into the electron version. So what we could tell our friends in the other galaxy far away is that in our universe, the low-mass charged particles that make chemistry happen and so forth, that we call electrons, are the ones that appear in the less frequent decay of the long-lived version of the neutral kaon.

• 18:19Sean Carroll?

  And that is sort of an experimentally believable thing. You don't need to touch anything. You don't need to say, like, "Here's my electron. Does it annihilate with yours or not?" You can just send that information, and then you can say, "Is the same thing true with your version of the electron?" And they would be able to tell whether they are made of what we call antimatter or not. Like I said, I think all that's true. I've never... I'm only like a hack particle physicist. I'm not an expert particle physicist, so if anyone wants to check me on that, that would be perfectly allowed. David Kudaverdian says, "If I'm not mistaken, you take the fact that we are not Boltzmann brains as a good anthropic reason to think that our universe doesn't allow many Boltzmann

• 19:01Sean Carroll?

  brains, even in the future. Could you please give an example of bad anthropic reasoning and highlight the key differences compared to good anthropic reasoning, using the example above as an instance of good anthropic reasoning?" So that's not exactly what I would say, just to be super-duper careful, because the beginning of your statement is the fact that we are not Boltzmann brains. We could be Boltzmann brains. That is to say, whatever you want to say you are absolutely sure of and convinced about us, like, maybe you think you exist, and the room you're in exists, and so forth, and all of your memories are what your memories appear to be, in an eternal universe with

• 19:42Sean Carroll?

  random fluctuations, things like that, configurations like you, even if it's not just a brain, like, your whole body is there, the whole room you're in, whatever you're looking at right now, say that that's all real. Maybe the whole solar system is real, maybe the whole Milky Way galaxy is real, it doesn't matter. In an eternally randomly fluctuating universe, it is overwhelmingly likely that that configuration randomly fluctuated into existence. And the impression that you have that there was a big bang 14 billion years ago randomly fluctuated into existence in your brain. So you can't say on the basis of data that you're not a Boltzmann brain. Unless you do bad anthropic reasoning.

• 20:25Sean Carroll?

  So the reason why I, the way that I get out of the Boltzmann brain problem is I say, if Boltzmann brains do dominate, or Boltzmann fluctuations more broadly, even bigger fluctuations than just brains, if those dominate the set of conditions in the universe that are given by any macroscopic specification, then we are cognitively unstable, then we have no reason to trust any conclusions we have about the universe. And it's not that that scenario is therefore false, but it's that we should put almost zero credence on it. Because the options are, we put a high credence on it and we are not allowed to do anything,

• 21:07Sean Carroll?

  to say anything about the universe, to trust anything we believe, it's just no way to go through life. Or we can say, no, I'm going to reason as if I am not a Boltzmann fluctuation, but I am the thermodynamically sensible observer that I think that I am. And how can I justify that? By having large credence on cosmological models in which that would be true, right? In other words, it's a long-winded and philosophically careful way of getting to the conclusion that we should build cosmologies which are not dominated by Boltzmann brains, okay? That's the way that I would say it. So it's not quite an anthropic thing. It's a you need cognitive stability kind of thing, which is not quite the same thing. Now, most astronomers, you want to know, what's an example of bad anthropic reasoning?

• 21:52Sean Carroll?

  Here's an example of bad anthropic reasoning. In a Boltzmann fluctuation-dominated universe, most observers would be brains, or would be minimal observers.

• 22:03Sean Carroll?

  Whatever that is, the people take the brain thing too seriously. Who cares about the brain thing? If you want to say, "Well, I need more than just a brain. I need this or that." Fine. I give you whatever you need. The point is you would be minimal. And the world that we see around us is in no sense minimal, where minimal means a minimum deviation from thermal equilibrium. Okay? So, in that universe, this is an example of bad anthropic reasoning, remember? So, most observers would be minimal fluctuated observers. Therefore, if I lived in that universe, I would probably be a minimally fluctuated observer. I look around and see that I am not. Therefore, I have ruled out that scenario by taking data. Okay?

• 22:48Sean Carroll?

  The reason why that's bad anthropic reasoning is it does not follow that just because most observers in that universe would be this kind of fluctuation, that you would be this kind of fluctuation, because you know things about yourself. In order to get to that conclusion, you have to forget everything you know and pretend you're a typical observer in the universe and then draw conclusions on that basis. I don't think that's allowed. I think that that's almost always what cosmologists do, and philosophers for that matter. They imagine that the way to do anthropic reasoning is to pretend that they are typical observers by closing their eyes and forgetting that they're not typical observers and then opening their eyes and acting surprised when they see the reality of the world around them.

• 23:33Sean Carroll?

  I just think that's a mistake. So, Isaac Wilkins and I are, as I've mentioned, writing a paper, and it's going to be called Anthropics with Open Eyes, where you can actually take into account everything that you know, following ideas that Radford Neal came up with a long time ago. And the point is that the original argument I gave you does not rely, I never used in any way the sense that you're a typical observer in the universe. Okay? You're typical within the set of observers that have exactly everything you know about the universe. So, that's why I said, "You tell me what you take as real." And within the set of... People like that you're typical because you have no experimental evidence that you're not.

• 24:18Sean Carroll?

  And so that's good anthropic reasoning. If you treat yourself as typical within the set of observers just like you, that's fine. And there's plenty of other examples. The doomsday argument that says that humanity won't last much longer because it would be very, very unlikely for us to be in the early stages of humanity if we were typical human beings. We're not typical human beings. We're who we are. That's just bad anthropic reasoning.

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• 26:17Sean Carroll?

  Nicholas Sharowski says...

• 26:20Sean Carroll?

  I've noticed for quite some time that certain ideological groups, particularly some anti-feminist or reactionary communities, tend to weaponize rationality to give the appearance of logical rigor to what is essentially motivated reasoning. In doing so, they treat being rational as synonymous with being cold and unemotional and dismiss opposing views and justified public outcry as mere feelings. This is often captured by the now infamous line, "Are you offended?" Yet these same groups frequently commit basic is-hot fallacies, for example, jumping from statistical averages to rigid prescriptions about social roles. Personally, I think the word rationality has taken on a somewhat negative connotation for me because of this kind of misuse. As someone committed to genuine scientific thinking, what is your view on this current trend of invoking supposed rationality?

• 27:05Sean Carroll?

  And do you believe that the scientific community has a responsibility to push back against it? So I wouldn't phrase things at all in quite this way. I think that it's tempting to, in heated debates over political or cultural or theological, for that matter, issues, to attribute all of the good features to our side and all of the bad features to the other side. Now, sometimes the other side really does have more bad features than our side does, but you have to be aware of the temptation to say that all of their facets are the bad ones and all of ours are the good ones. It's just really comforting to think that, but it's usually not as true as we take it to be.

• 27:48Sean Carroll?

  So I would be much, much more careful about complaining that they're completely irrational and have used all these words because they're just motivated, whereas we are perfectly reasonable. But having said that, I think that you do point to a very real thing that is happening. I mean, let's just forget about this or that ideological group. I think that an increasingly common...

• 28:13Sean Carroll?

  Tactic these days is to take something that most people think is a virtue, like being rational, or having free speech, or something like that, and weaponizing it. Weaponizing it by taking the act and, you know, perverting it in some way by not buying into some of the preconditions for that act to actually be the virtue that it is supposed to be. There's no better example of this than the infamous Harper's Letter. I don't know if you saw the Harper's Letter. You remember this from a few years ago? This was an open letter, um, published in Harper's Magazine,

• 28:55Sean Carroll?

  with a various set of distinguished signatories, complaining about the leftist suppression of open inquiry, especially in universities and places like that. And it's that's, there are absolutely, really, examples of suppression of open inquiry by leftists on campus and elsewhere. There are also absolutely examples of suppression of open inquiry by conservatives on campus and elsewhere. And by any, I would argue that by any reasonable, fair accounting, the conservatives are much more dramatic at it. And we're seeing that right now. We're seeing it now the conservatives are in power.

• 29:40Sean Carroll?

  There are universities that are undoing tenure protections, that are forbidding faculty members from discussing certain topics in their courses, that are firing faculty members for political speech, and a whole bunch of really, really dramatic things, much worse than anything that was being complained about in places like the Harper Letter. And so there's this ability to sort of weaponize the claim like, "Well, you don't believe in free speech," or something like that, when the other side really isn't interested in free speech. They're just using your sympathy for it against you. So I do think that something like rationality could be very much used in that way.

• 30:23Sean Carroll?

  The response is just to be rational. Response is to be really rational, truly rational. Not to give up on it, not to reject the terminology. You know, I remember one saying years and years ago, in response to something online or something like that, I said, you know, what matters is not equality of outcome. I think it was about men and women in science. And what I said was, what matters is not the equality of outcome, but the equality of opportunity, right? You don't, I don't care whether there is 50/50 representation of men and women in physics departments. What I care is that a young person who has certain talents in doing science and doing

• 31:06Sean Carroll?

  physics has the same opportunities to become a physicist as, depending on whether they're a boy or a girl, or whatever, okay? And, but what I was, I was given crap for saying this because that phrase, you know, equality of opportunity, not equality of outcome, is weaponized by people who actually don't even want equality of outcome, right? They, they claim that when you're trying to argue that sexism is bad and is all over the place in academia, that secretly or explicitly you want equality of outcome and that's not what you should want. Fine, that's not what I want, but the point is, we don't have equality of opportunity.

• 31:49Sean Carroll?

  I, I really just think that when the bad guys try to weaponize good ideas, we stick by the good ideas. We talk to each other as reasonably and honestly as possible, and we exemplify doing things in the right way. We don't give up on doing things the right way, or start doing things the wrong way, or even give up on good ideas or vocabulary words just because they are being misused. We need to be open to the fact that some people might use good ideas or good concepts or whatever for bad reasons. That's fine, and we shouldn't allow people to take advantage of us. We shouldn't, you know, let them run over us by.

• 32:33Sean Carroll?

  Uh, lying and cheating and stealing and whatever, but we shouldn't give up on the good ideas. We should, we should absolutely always be in favor of rationality, of fairness, of free speech, of open inquiry, of all of those good things that a good, uh, modern, post-enlightenment liberal should care about. Alexandra Kojumtsis, sorry Alexandra, I butchered your last name, Kojumtsis, says, "Has grappling with the complexities of the universe and its laws made you more anxious or more peaceful as a human being? How has a deep understanding of physics changed your daily contentment? I personally struggle with the idea of being on deterministic rails

• 33:16Sean Carroll?

  and just a small blip of the universe experiencing itself." Well, I have, uh, it's a perfectly legitimate question and it's a tricky one and people will answer it differently. The facts of determinism, again, I truly don't care about determinism. Determinism is just not what matters. If the laws of physics were, had a truly stochastic element, like they do in objective collapse models of quantum mechanics, so what? That doesn't make me feel any better. Just that, that just means that, you know, the most compact description of physics involves some random numbers as well as some deterministic things. Like, that has zero effect on how I think about the world. I think that when

• 33:58Sean Carroll?

  people worry about determinism, really what they're worried about is the laws of physics, whether or not those laws are deterministic or stochastic. They're worried about the fact that there is a level of description on which we are impersonal mechanistic pieces of the universe obeying some laws. Okay? And that doesn't bother me even a little bit. Like, I know that, that that's true. Um, whether it's deterministic or not, I don't know the microstate of the universe. I'm not Laplace's demon, as you might recall, so it just doesn't affect my life at all. We have a really good podcast episode coming up soon where I, I talk with someone who is really good at explaining the, the difference here. Um, the real big, uh, issue is of course, life after death or mortality, right?

• 34:43Sean Carroll?

  As I've argued before, a straightforward reading of what we understand about the laws of physics makes it very, very unlikely that there is anything like life after death. Death is truly the end of our conscious experience. And I think that's super profound. And I think that, you know, if anything, scientists and philosophers undersell the importance of that. We sort of let it seep into the public discourse, but we don't make a big deal out of it. And I kind of think we should make a big deal out of it. It's a big deal. And I struggle with it a little bit. Like, I don't like the idea that at some point I won't exist anymore, right? Like, I'm not in favor of that. I mean, maybe there's a point at which I would choose to finish my existence.

• 35:28Sean Carroll?

  That's perfectly okay. But I'm nowhere near there now, and I doubt I'll be near there when the time actually comes. So that is something to truly struggle with. In my experience, the people who think that there is life after death, or heaven, or reincarnation, or whatever, struggle just as much. I don't see any systematic openness to the ending of our physical life here on Earth just because people think that there's a continuation afterward. So I think that, you know, I control what I can control, and the laws of physics and the existence of the soul after death are not things that I can control. So I'm going to deal with what's happening in the here and now.

• 36:09Sean Carroll?

  Zach McKinney says, "What is your view on the appropriate contribution of contemplative practices and psychonautic explorations, including but not limited to psychedelic variety, to understanding the nature and metaphysics of consciousness? I agree that rigorous contemporary science is needed to elucidate the neurophysiological and informatic basis of consciousness. Nonetheless, given that any complete theory of consciousness must account for a wide variety of non-normative experience, to what extent do you believe ancient practices that reliably produce and interrogate altered states of consciousness can contribute to our understanding of the nature and origins of consciousness, respectively?" So tiny correction, I don't think that "non-normative" is the word you're looking for there. Non-normative means not judgmental.

• 36:53Sean Carroll?

  Right, normative talk is, rather than, is prescriptive talk, rather than descriptive talk. Norms are, do we judge things to be right or wrong? I don't think that's quite what you mean in this particular context. But anyway, I think that there is some mild usefulness of psychedelics or various other practices that would lead to altered states of consciousness in the very straightforward sense that you could see what people do when they're in these states and you could collect data about how conscious they are, how their consciousness changes, et cetera. That's fine, I'm not quite sure how useful it is, but it's worth doing.

• 37:32Sean Carroll?

  I think there's huge potential applications of psychedelics and other practices to therapy. You know, not just psychological therapy, but physical, you know, medicinal therapy, like fixing diseases and things like that. So I'm all in for that, I'm all for that. I'm not sure that it helps us a lot with understanding the nature of consciousness. Probably what you mean is something more like, do I imagine that if I could access one of these states through drugs or other means, that I would have some insight into the nature of consciousness because of that? And that, I think, no, absolutely not at all.

• 38:14Sean Carroll?

  I know what's going on, I mean, I have certain things going on in my brain. I am changing those things going on in my brain, either through drugs or stimulation, or even some internal practice, whatever. But I'm changing the physical things going on in my brain and as a result of that, I change what I think I'm perceiving, or something like that. I don't see why that gives me any insight into the nature of consciousness at all. I'm not quite sure what I would expect to discover by doing that. I don't think that we have, in particular, discovered anything super duper important about the nature of consciousness by people doing that. Again, that's not to say it might not help you live your life, but at a scientific level, I don't think it's telling us anything data-wise about what consciousness is.

• 38:59Sean Carroll?

  Schlierer says: "Does all the complexity and awareness on Earth mean that the universe is a complex and self-aware system? Or does one living planet amongst septillions of dead ones in empty space amount to a statistically insignificant blip with universal complexity rounded down to zero?" Unsurprisingly, the answer is that depends on how you choose to quantify complexity. If I have a big system that is mostly simple, but there's a little tiny part of it that is super-duper complex, do I judge complexity by the average amount of complexity or by the maximum amount of complexity of any subsystem? I think it's entirely okay, entirely legitimate, to judge the complexity overall of a system

• 39:42Sean Carroll?

  by the maximum amount of complexity of any subsystem in it, right? But you can choose to do it whatever way you want. I mean, I think that the purpose for which you probably would be quantifying complexity is to talk about the appearance of new abilities, or modalities, or whatever you want to say, strategies for this physical system to exist in the universe. And I think that the relevant fact there is the peak complexity of any subsystem, not the average amount overall. Mark Wall says: "Having a consequentialist/utilitarian/hedonist stance, like Peter Singer, seems

• 40:26Sean Carroll?

  to require an immense amount of information to make the best ethical decisions within that framework. Do you think that it is a reasonable conclusion to say, from that position, that that makes science the most ethical pursuit, as it is a framework of gaining more information about the world? E.g., we found through scientific studies that cephalopods are sentient, so now we can make the world better by trying to not have them suffer?" I wouldn't put it that way, no. I mean, I think that science is an important part of ethical pursuit more generally, but you know me, I am a pluralist. I think that there is no one thing that is the most ethical thing to do, because if you pick any one thing you think is super ethical...

• 41:08Sean Carroll?

  And everyone did that thing and didn't do anything else. I think that would be a super unethical result, right? I think the most ethical thing is that a lot of different people are pursuing lots of different things. We need not only science, we need education, we need government, we need healthcare, we need maintenance, as Stuart Brand would say, of the world around us in all sorts of ways. We need distraction and entertainment and sports and things like that. So these are all ethical in different ways. I don't think that there's a need or a sensibility to saying that one of them is the most ethical. But certainly, you know, again, the spirit of saying that doing science is important

• 41:52Sean Carroll?

  for a good ethical understanding of the world, in that sense, yes, that much I would totally agree with. Ken Wolf says, "Since you are a fan of Jane Austen's Pride and Prejudice, are you familiar with the sequel, Death Comes to Pemberley, written by P. D. James? If so, what did you think or how do you feel in general about what is essentially fanfiction based on one of your favorite books?" Well, I will tell you, I actually did read Death Comes to Pemberley, and I remember essentially nothing of it. That should tell you what I thought about it. It's like, it's fine. I'm very much in favor of fanfiction, okay? In fact, I would love it if fanfiction were much more popular. As a general rule, I think that we have professionalized

• 42:36Sean Carroll?

  artistic and creative pursuits too much, right? There is such a thing as spare time and leisure time and the part of your life that does not just go into your occupation. And a lot of that time in the modern world, we spend relaxing or spectating in some sense, watching sports and things like that. We don't spend enough of it creating, painting, making music, writing fiction, whatever it is. So I wish everyone would write fanfiction if that's what got them very excited. I don't think that that particular example, I think, you know, I don't know P. D. James's other work. It might be very, very good, a mystery writer. Death Comes to Pemberley.

• 43:18Sean Carroll?

  Sort of a mystery novel take on a sequel to Pride and Prejudice. I do remember that Elizabeth Bennet, who was the star, of course, of Pride and Prejudice, didn't have a very big role in Death Comes to Pemberley. It was much more about Mr. Darcy, her now husband, and his friends. But, you know, something about the sensibility is just different. You know, I mean, this is not an exact analogy, but let me suggest an analogy. When there is a song and you want to imagine a cover version of the song, a cover version is not quite like a fanfiction sequel, but it's similar in some ways, right? What kind of song lends itself to a good cover version?

• 43:59Sean Carroll?

  You know, the classic cover version success is Jimi Hendrix doing All Along the Watchtower, which was written by Bob Dylan. And so what's going on there? You have a wonderful song by an amazingly brilliant songwriter, Bob Dylan, who, to many people's ears, is not the best performer, not the best guitarist, or singer, or arranger, or whatever. That's not where his strong suit is. He's good at it, but you know, it's the songwriting and the wordsmithing that is really good at it. Whereas Jimi Hendrix can perform as well as anybody, right? Playing the guitar, and he's also a super good singer and definitely a wonderful sort of blues-inflected arranger of music.

• 44:43Sean Carroll?

  And so he takes this under-performed song by Bob Dylan and turns it into a classic, All Along the Watchtower. You wouldn't want to, I mean, there's no world-class cover version of, I don't know, Bohemian Rhapsody. Like, they already did it perfectly. Queen did the perfect version. I almost was gonna say Stairway to Heaven. Stairway to Heaven was also done perfectly the first time by Led Zeppelin. But if any of you saw Hart do a cover version of Stairway to Heaven at the National, what, the United States gave some award to Led Zeppelin, right? The National Medal of Arts or something like that. I forget exactly what it was, but and Nancy Wilson.

• 45:28Sean Carroll?

  From Heart did a cover version of Stairway to Heaven that honestly was better than Led Zeppelin's version. And I say that because Led Zeppelin was in the audience and they were crying because it was so good, this version. So it's not, like I said, it's not a perfect example, but Jane Austen, you know, the equivalent here is there are people who are good at plots, right? Like coming up with some complicated set of events happening in the book. And there are people whose best thing is, you know, the details of individual characters and their reactions and their thoughts and the words into which those things are put. Okay. And Jane Austen is good at the latter, not the former. No one reads Jane Austen for the plots. You know, it's gonna end up with a happy ending,

• 46:13Sean Carroll?

  right? And if you're the kind of reader who is only interested in the plot, you're not gonna like Jane Austen. It's how you get there. It's the journey. It's the delicious sentences and one character commenting on the other and the characters just thinking to themselves, you know, what are we gonna do? And it's just so wonderfully insightful about how real people think, like real people struggle with themselves and go back and forth and say all sorts of crazy things to themselves. And that's what's enjoyable about Jane Austen. Not the list of characters or their physical situation or whatever. And, you know, P D James, from my very, very meager evidence of having just read that one book, is no Jane Austen when it comes to what Jane Austen

• 46:58Sean Carroll?

  is good at. It would be like Bob Dylan covering a Jimi Hendrix song, right? Like, who wants that? So, you know, it's not that either artist is not living up to what they're good at, but it's not, it's not that either artist is not really good at something. It's that we want to maximize what it is they're good at. And I'm not sure if this particular kind of sequel really does that.

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• 49:05Speaker 07

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• 49:11Sean Carroll?

  TK says, hypothetically, if an alien civilization were able to harness massive amounts of negative energy and open a wormhole nearby, would that cause a gravitational ripple that could be detected by LIGO? Well, you know, this is far, this is vastly unspecified, underspecified question. You know, how far away are they? How big is the wormhole? Things like that. There's two things that sort of push in opposite directions here. One is, I think, maybe this is your intuition, to make a wormhole, like a macroscopic wormhole, okay? We can't do it, by the way. That's the simple thing to guess, is that making wormholes is not

• 49:55Sean Carroll?

  possible, but we don't know that for sure. So it's not, but we don't have a recipe for doing it, I guess, is the point. And maybe you could make a microscopic wormhole that is very, very tiny, and that would definitely not cause a gravitational ripple that could be detected by LIGO. But a macroscopic wormhole, the kind that a human being could safely pass through, I think your intuition that that would require an astronomically large amount of gravitational energies being pushed around. Yes, that is true. However, so anyway, I'm getting to the two things that push in different directions. One, that's the thing that pushes you in the direction that says, you know, maybe, maybe it would require so much energy and so much

• 50:39Sean Carroll?

  manipulation of the gravitational field to make this astrophysically big wormhole, that it would require an astrophysically large amount of gravitational waves to be created. Of course, that doesn't tell you whether it's detectable or not, because if it's far enough away, it's too faint, right? I'm presuming that we're imagining a relatively nearby alien civilization doing this. But the other consideration is that giving off a lot of gravitational waves is a waste of energy, right? Those gravitational waves are not useful to the alien civilization that is making the wormhole. So if they're clever, and presumably they are, because they're an alien civilization making a wormhole, they would try to minimize the loss of energy into gravitational waves. And actually, that's not, that is something

• 51:23Sean Carroll?

  we know how to do. Anything that you do that is perfectly spherically symmetric gives off zero gravitational waves. If a star collapses in a perfectly spherically symmetric

• 51:36Sean Carroll?

  Zero gravitational waves are given off. This is a theorem. This is an implication of Burkov's theorem of general relativity. Changing matter distribution, but keeping it spherically symmetric, does not give off gravitational waves. The technical term is it's only the quadrupole moment that gives off gravitational waves. So if your alien civilization wants to save energy or wants to go under the radar and not be detected, as it were, they could probably arrange their wormhole creation in such a way that it would not cause a lot of gravitational radiation. By the way, footnote there. In the original idea for Interstellar, remember the the movie Interstellar came from an idea from Kip Thorne and Linda Opst.

• 52:21Sean Carroll?

  Kip being a former Mindscape guest and famous physicist and Linda being a Hollywood producer. And Kip was a big name. He was one of the people who made LIGO happen. He won the Nobel Prize for that. And in the original story, he wanted the detection of the wormhole to be from LIGO. So it wasn't the creation of the wormhole, but he had this idea that gravitational waves would pass through the wormhole and be detected by LIGO and that would alert scientists here on Earth that something was going on. That didn't, that didn't survive into the final movie sadly. Bill McDonald says, here comes my single, short, timely, once in a lifetime, at least in this branch, priority question.

• 53:05Sean Carroll?

  Remember, every Patreon supporter gets to ask one priority question in their lifetimes. And you're on the honor system here. By the way, they're like very, very rarely, but sometimes someone who is not a Patreon supporter tries to like join Patreon, just ask a priority question and then quit before they've paid any money. I'm not like really trying hard to enforce that, but we hope that people don't do that and mostly they don't. I'm not, certainly not accusing Bill of doing that. I'm just, it came to mind because someone tried to do it anyway. So Bill's question is on Jeffrey Epstein. When does the failure to shun a wrongdoer become blameworthy?

• 53:49Sean Carroll?

  Well, unsurprisingly, I'm gonna say that there are gradations here, right? Like, failure to shun a wrongdoer means different things in different contexts. Like, if someone is a wrongdoer, and you're not shunning them but trying to help them sincerely improve their lives and become better, then that's praiseworthy. That's not blame worthy at all. I presume that's not what is going on in the Epstein question. When Jeffrey Epstein was convicted, for the first time circa 2008, it wasn't a big deal. People forget this, because you know, you remember things in retrospect differently than they happened at the time. It was, there were, there were some news stories about it, because he was a rich guy who went to jail, but it didn't really penetrate the public consciousness.

• 54:33Sean Carroll?

  If you go onto Google and do the n-gram search, which tells you how often different terms appear in the corpus of words being written, Jeffrey Epstein doesn't take off until around 2018, really. He got like a bump in around 2016, when Donald Trump ran for president, but then a big bump, because Miami Herald did a big story on him in 2018, and that's when he super duper became infamous. And then he committed suicide, not long after that. But in 2008, the first thing was, you know, if you were into following the shenanigans of, of rich financiers, you knew about it, but I think that the person on the street didn't know his name at that time.

• 55:16Sean Carroll?

  So, there certainly were people, both before and after 2008, who accepted money. Many scientific, many good scientists, many friends of mine, took money from Jeffrey Epstein. The Santa Fe Institute took money from Jeffrey Epstein. Most of it, again, before 2008, so before he was known to be a sex offender, or whatever. And they did sort of, like, almost by mistake, take a small donation after that, and they gave it back right away. Is that blame worthy? I don't think so. I mean, I think you try to do your due diligence, sometimes you slip a little bit, and you know, you give the money back, and okay, that's what it is.

• 55:59Sean Carroll?

  Think that after 2008, once he had done that, if people knew that he was that kind of wrongdoer and just said to themselves, you know, he's a wrongdoer, but I'd rather his tainted money go to good causes than bad causes and therefore convince themselves was okay to take the money, I think that's a little blame worthy. I think that that's that was a little self dealing, a self-serving in your rationality there, but it's not like the world's biggest problem. And if you just said, yeah, that was a mistake, I made a mistake, sorry, and you were legitimate about it, I would completely forgive a person

• 56:41Sean Carroll?

  who did something like that. Now, it's clear from the files that there were people who not only knew that he was a bad person, but kind of thought it was cool, the way that he was a bad person. People like Larry Summers, you know, who we talked about, or Henry Rosowski, who many of you don't know, but he was the provost of Harvard University when I was there, or Alan Dershowitz, or whatever, Lawrence Krauss, people who, you know, were in on it. And I don't mean in on it in the sense of literally abusing children or whatever, but, you know, Lawrence Krauss asked Jeffrey Epstein for advice on how to fight against

• 57:24Sean Carroll?

  the charges against him of sexual harassment. And we know why he would do that. Larry Summers asked him for advice on trying to seduce a younger colleague, you know, who was a junior faculty member, you know, it's just like all this terrible, terrible stuff. And, and that's, you know, to me, past a certain level where, and none of these people have, by the way, said they're sorry. That's the thing, like the worst offenders are the ones who try to make excuses for it, the ones who like took money and really shouldn't have, but like it was just sort of some, you know, they did some psychology on themselves, they convinced themselves it wasn't that bad, and then realized later, like, oh no, actually that was

• 58:09Sean Carroll?

  Pretty horrible and have sincerely apologized. I let them apologize. And I think that yeah, let's move on. I'm not going to treat those people as pariahs in any sense, but it's the people who like thought that what was happening was actually what was happening in the general sense of the misogyny and the sexism and all that stuff, not necessarily the literal raping of children, but the whole skeeziness of the enterprise was there. And some people thought that that was a feature rather than a bug. And those people, I am, I'm very happy to blame them, to find them blame worthy. Sandro Stuckey says, everyone seems to agree that generative AI is having a big impact on education, at least on the way students can and should be assessed,

• 58:53Sean Carroll?

  possibly how they learn. As someone who teaches university classes, is this something you notice yourself? If so, have you changed your teaching in any way? Well, I've 100% changed my evaluating. My teaching has changed in no way whatsoever. I don't know what the impact is on learning of AI. And so in other words, it could be good or it could be bad. It's absolutely possible to take the work of struggling with difficult ideas and kind of farming that out to the AI to struggle with the difficult ideas for you rather than doing the thinking yourself. And I would absolutely

• 59:32Sean Carroll?

  expect that kind of thing to have a harmful impact on people's ability to learn. It's also absolutely possible that a good student could in all good faith, just be struggling with some ideas, use an AI to help them understand the difficult ideas in a better way. And that helps them learn things. I'm 100% on board with that also. And I, as the teacher, as the professor, I don't know which it is that they're doing, right? And I sort of can't, it's up to them. I'm very much of the opinion that once you're in a university or a college, the student is mostly responsible for how they choose to

• 1:00:17Sean Carroll?

  Approach the experience of being in college. They're responsible adults by that point. I think that the job of the professors is to give them all the advice and all the opportunities and all the insight and facts and knowledge that they can. But at the end of the day, it's only going to be as good as the student wanting to learn things, right? So anyway, I can't help it if the students want to farm out their learning to AI. I haven't noticed it that they do. I'm just saying that I don't really keep track of that. But it's very different when it comes to grading because, you know, many college students care very deeply about grades. You might have noticed, I don't know.

• 1:01:01Sean Carroll?

  As a professor, that always breaks your heart. You're like, please care about learning, not about grades. But they're not very sympathetic to that point of view. And so I've switched from mostly take-home assessments to mostly in-class assessments. You know, we do our exams in quantum mechanics in class now, whereas earlier they would have been take-home assignments. In the philosophy classes, you still have to write papers. In the seminar, it's mostly the paper that's going to give you your grade. But in a small seminar, I'm talking with the student and I know what they're doing. And there's no possible way they can be handing over to AI most of the work to write the paper. And I've seen zero evidence that any of them try to do that.

• 1:01:44Sean Carroll?

  In a large lecture class, then I'm also going to give in-class exams, short answers, where they talk about the concepts, and that's going to play a big role in addition to the paper. So that's all new. That's, you know, I've never given in-class exams before I came to Johns Hopkins. Not because Hopkins, but because of AI, precisely because of that. And, you know, it's not the biggest deal in the world. It's slightly annoying, but that's the world in which we live. You have to adapt in different ways.

• 1:02:12Sean Carroll?

  Scott says, "Can the matter/anti-matter asymmetry be explained by simply postulating that the initial conditions of the universe were such that matter was dominant? Why assume a symmetric initial condition and work so hard to find a dynamical mechanism?" Well, in a sense, yes, you can assume, there absolutely will be an initial condition that gives rise to our current condition without any shenanigans in between. You know that's true, because you can just start with our current condition, use the laws of physics, and wind it backwards, right, to something. It's going to start somewhere. Now, there's a couple reasons why that's a little bit less popular than you might think.

• 1:02:53Sean Carroll?

  One is that in the standard model of particle physics, so forget about weird things having to do with, I don't know, grand unification, or leptogenesis, which is a thing that can happen, because neutrons, heavy neutrons, not the ones we know, but heavy neutrons can decay in ways that violate baryon and lepton number. There's different schemes that could cause a baryon asymmetry, and the question is, is that more work than just positing it? So, the two things, number one, even in the standard model, so we have two things, baryon number, which is the number of baryons, baryons are protons, neutrons, things like that, and

• 1:03:38Sean Carroll?

  then we have lepton number, so neutrinos and electrons and things like that, okay? They're both separately conserved, both baryon number and lepton number, at low energies, zero temperature in the standard model. But we've known since the 70s that at high temperatures, there's an increasing probability for B plus L to be violated. So that is to say, baryon number plus lepton number is violated, although B minus L is conserved. So the difference between the baryon and lepton number of the universe stays the same in the standard model, even at high temperatures, but the total number of both baryons and leptons can change.

• 1:04:22Sean Carroll?

  So there are processes that make you one new baryon and also one new lepton, on average, okay? So... If you started with an excess that was equal in both baryons and leptons, the standard model would get rid of that excess. And therefore, you would not be left with an asymmetry today. It's easy enough to say, well, okay, I just want to start with an asymmetry in baryon number, not in lepton number, and then that would preserve some asymmetry at the end of the day. But the real reason this isn't popular is because it doesn't help you. Like, for a lot of these puzzles, like the cosmological constant problem, or the horizon

• 1:05:04Sean Carroll?

  problem of inflationary cosmology, or whatever, you're totally allowed to just say, well, it just was like that. There's no explanation at all. I'm just going to say it's like that. Okay? The hierarchy problem, it just is. And you might be right. I can't promise you that you're not right. The reason why we spend time thinking about mechanisms is that you might be wrong. And we know that we're not done when it comes to understanding the laws of physics or the origin of the universe. We know that we need to go beyond where we are now. And maybe these features, like the matter/anti-matter asymmetry, are clues to how to go beyond what we know now. If you found a theory of grand unification that helped inflation happen and helped explain

• 1:05:49Sean Carroll?

  the baryon asymmetry and all those good things, that might be evidence that that theory is correct. You know, you can't, still need to go check it, because you can't just explain things we already know to be true. You have to explain some new things as well. But that's the kind of guidepost that we use when developing better theories. You never know for sure whether that guidepost will be useful, but we have to take what we can get.

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• 1:07:58Speaker 07

  That's the number three, D-A-Y blinds dot com slash save 50.

• 1:08:04Sean Carroll?

  Mikkel Bennettson says, "Thank you for the interesting discussion with Peter Singer. I learned a lot from your exchange, especially the parts on the foundations of utilitarianism. For example, the idea that utilitarianism does not seem to require an ontological commitment to something called utility, and Singer's meta-ethical distinction between moral realism and moral objectivism." Okay, I'm gonna group a couple questions together. They have to do with the interview I did with Peter Singer recently. Mikkel Bennettson says, "Thank you for the interesting discussion with Peter Singer. I learned a lot from your exchange, especially the parts on the foundations of utilitarianism. For example, the idea that utilitarianism does not seem to require an ontological commitment

• 1:08:45Sean Carroll?

  to something called utility, and Peter Singer's meta-ethical distinction between moral realism and moral objectivism. You've often been critical of utilitarianism. Did your conversation with Singer change your mind on any aspect of it?" And then Terrence says, "Regarding the most recent episode with Peter Singer..." Whenever utilitarian comes up, you raise the rebuttal, if I can paraphrase it, as "Doesn't utilitarianism apply? We should sacrifice the happiness of one person if we can increase the happiness of five other people to a greater degree." In episode 207, Will MacAskill gave what I thought was a pretty convincing rebuttal to this, which I'm again paraphrasing as "Society at large or net utility would be worse off if we lived in a world where we could make those kinds of sacrifices." I recall from that episode that you sounded pretty swayed by Will's argument too. Have you since changed your mind about it?

• 1:09:30Sean Carroll?

  Or what did you think of Will's argument now in light of intervening discussions of utilitarianism? So let me give you the overall answer to both questions at once, which is basically like, "Why haven't you become convinced by utilitarianism?" The conversations with MacAskill and Singer, I thought were both very useful and interesting and informative. And there were parts that did impress me in one way or another, but they did not impress me in the sense of moving me closer to utilitarianism. They impressed me in the sense of realizing that utilitarians are pretty willing to give up on some of the obvious conclusions of utilitarianism.

• 1:10:07Sean Carroll?

  I think that both Singer and MacAskill, you know, look, if utilitarianism means anything, it means that if you have a choice between two options, and one raises the utility of the world and the other one raises it by less, you do the one that raises the utility more, right? I think that's what utilitarianism needs to mean. You have different notions of utility, for sure, and you have different notions of how to measure it and how to add it together. That's where all the interesting philosophical discussion comes from. But the whole point of utilitarianism is that we need to be able to sacrifice some

• 1:10:52Sean Carroll?

  bad things in order for even better good things to happen. If you don't buy some version of that, then you're not really a utilitarian. And both MacAskill and Singer, I thought, were actually...

• 1:11:06Sean Carroll?

  More reasonable as real human beings than they would be if they were honest utilitarians. That's what I was impressed by. You know, they both seemed, and I'm trying to be fair. I think this is a positive feature of them as people, although not necessarily of utilitarianism as a philosophy. I think that they were both very realistic about, you know, how real people wouldn't be able to do this, you know, and wouldn't be able to act like good utilitarians and how society shouldn't necessarily do the thing that utilitarianism might predict that it would do because it would actually secretly make things worse.

• 1:11:48Sean Carroll?

  And what you end up in either version of that is with a stance that isn't all that utilitarian to me. It's closer to like, you know, there are things we just shouldn't do, right? And when you say there are things we just shouldn't do, that's not utilitarianism anymore. That's something closer to deontology or something. So I think that, you know, it's not that any of this made me think, oh, there is a number out there called utility that I can just add up.

• 1:12:20Sean Carroll?

  That's my objection, right? And if McCaskill says, you know, society at large, net utility would be worst off if we lived in a world where we could make those kinds of sacrifices, then he's just saying that utilitarianism doesn't work, I think. That's what it means to me, that there is not a number that we can just add up and then try to maximize that number, that we have to take into account all sorts of things that are not necessarily quantifiable and trying to actually nudge people towards doing better things. I mean, maybe utilitarianism is a good kind of model to have in mind when we're individually wondering how to be good people, because, you know, it's nice to be honest about whether

• 1:13:03Sean Carroll?

  or not a certain action would actually make the world better off in some version of that quantification, but not think that that's an absolute moral commitment and to be more nuanced. And rich in the ways that we set down the guidelines for good actions and bad actions. Again, I do try to emphasize I don't have a fully fleshed out defensible moral theory. You know, I think in certain cases, I know what it means to be doing good things and bad things by my own lights, but I'm not done. I'm not finished. I don't have an alternative to offer that I could 100% stand by. So I'm just sniping from the sidelines, which

• 1:13:45Sean Carroll?

  is easy for me to do. The hard work of moral philosophy is being left to others here. Nikola Ivanov says, "In your discussion with Daniel Harlow, the one-dimensional Hilbert space seems to come from treating the universe as a truly closed gravitational system. If that assumption is right, would your own view that reality is fundamentally a quantum state in Hilbert space have to be revised too? Or do you think your framework can still survive in a closed universe?" So, you know, I think I said it in the interview. I'm not sure if it came through completely. I don't believe Daniel's argument. It's not that I think I can find a flaw in the argument. So for those of you who didn't listen to

• 1:14:26Sean Carroll?

  the episode, quantum mechanics tells a story about states of quantum systems being vectors in this space called Hilbert space. Usually I say this really big space called Hilbert space, but the whole point of what Daniel and others are saying is that there's certain reasonable calculations in quantum gravity that lead us to the conclusion that in a closed universe, the effective Hilbert space or the fundamental Hilbert space is one-dimensional. There's really nothing that goes on. A one-dimensional vector space doesn't have anything happening at all. And so what Daniel wants to do is take that seriously. He believes the arguments that gets him there. And he wants to say, okay, how can we live with that? And he has

• 1:15:09Sean Carroll?

  to invent an effective Hilbert space that is not the fundamental one, and then talk about the relationship between them and a whole bunch of other things. And then, you know, so good for him for this is what you're supposed to try to do. You're supposed to try to take your ideas seriously. Sometimes they will lead you to good places that you just declare victory. Other times they lead you to apparent puzzles and you see whether or not you can deal with them. And he's trying to deal with it. For me, I think it's, if I came to the conclusion that I was, I had some arguments that led to a one-dimensional Hilbert space, I would just say, "Well, those arguments must be wrong. We don't live in a one-dimensional Hilbert space. That's not, that's not good enough for the way that I think quantum mechanics works. So I'm going to try to find a flaw

• 1:15:51Sean Carroll?

  in the argument, not try to build extra structure on top of that one-dimensional Hilbert space." So, no, I don't think that my framework can survive in a one-dimensional Hilbert space, but my way of reconciling that is to say, "I suspect there's a mistake in the argument that says that quantum gravity in a closed universe is in a one-dimensional Hilbert space." Murray Kantor says, "I believe I heard you mention Wojciech Zurek's proposed solution to the measurement problem. What is your opinion of the approach?" So I'm not sure that I would put it in those words. I mean, Zurek has, he's a wonderful physicist who has been an absolute leader in understanding decoherence and the emergence

• 1:16:31Sean Carroll?

  of classicality from quantum mechanics. And his work there is absolutely central. I think he deserves the Nobel Prize. It's something that I cite and use all the time. Now, I don't think it's a "solution to the measurement problem." After all, what would count as a solution to the measurement problem? I think that there's two things that you need to solve the measurement problem. The measurement problem in quantum mechanics is this slightly vaguely defined thing, but it's basically, in the textbook version of quantum mechanics, there appears the word "measurement" or "observation" or something like that. You hear things like, "When you perform a measurement, the wave function collapses, and the probability is given by the Born rule," and things like that. So, the measurement problem is just,

• 1:17:12Sean Carroll?

  what do you mean by all that, and how does it happen? And the two things you need to solve the measurement problem are, first, you need a theory... That is to say, you need a well-defined physical theory of what is happening in quantum mechanics when a measurement occurs. This is exactly what the Copenhagen interpretation doesn't give you, and therefore Copenhagen is not a theory that should be judged against other theories. It's a half-theory that should be improved to a real theory. But once you have that theory, like many worlds, but also like pilot wave theories, objective collapse models, whatever, then you need to say, "Okay, in this theory, this is what happens when you and I think something like a quantum measurement is occurring.

• 1:17:56Sean Carroll?

  This is what that means in the context of that theory." Okay? So Zurich isn't proposing a theory. He's just working in conventional quantum mechanics. And I think this is one of the places where the, and I don't mean this about Zurich himself, because he's thought more deeply about quantum mechanics than most people around, but there's a lot of physicists who just don't take seriously thinking about the foundations of quantum mechanics, or even thinking about thinking carefully and rigorously and philosophically carefully about what happens in quantum mechanics. So there is a thing that you will hear, which is absolutely wrong. Let me tell you what it is. It's the claim that decoherence solves the measurement problem.

• 1:18:40Sean Carroll?

  So I don't think that Zurich has ever quite said that. Maybe he says it somewhere, maybe he believes it. I know that he's not really a many-worlds person, but I think that he's like a many-worlds person in disguise, to be perfectly honest. He doesn't want to talk about many worlds or things like that, but his stuff is completely compatible with many worlds. So the point is that if I have something like Schrodinger's cat, so I have a quantum system that is in a superposition. The cat is awake in part of the wave function. The cat is asleep in the other part. And then decoherence happens. And this is what Zurich describes very, very carefully and rigorously. There is an environment, so there's a whole bunch of photons and so forth. They interact with the cat, and they interact with the cat differently, depending on whether the cat is awake or asleep.

• 1:19:25Sean Carroll?

  And this branches the wave function of the universe, because you get the

• 1:19:31Sean Carroll?

  Cat is entangled differently with the photons in the environment depending on whether it's awake or asleep. And so the environment part of the wave function becomes perpendicular orthogonal in the branch of the wave function where the cat's awake and the branch of the wave function where the cat's asleep. So they become non-interacting, those two parts. For those of you who know a little quantum mechanics, this is a fancy way of saying there are pointer states. Cat being awake is a pointer state, cat being asleep is a pointer state. And the density matrix of the cat subsystem diagonalizes in the pointer basis. And so the density, when I say the jargon words, density matrix of the cat subsystem, what I mean is there are ways to talk about the state of the cat,

• 1:20:16Sean Carroll?

  even admitting that we're not keeping track of the state of the environment, even though they are entangled. So the full state of the universe needs complete information about both the cat and the environment. But maybe you don't have that, maybe you don't have all the photons and all their states. So you say, what can I say just about the cat? And this idea of a density matrix is what you can say just about the cat. And what happens in decoherence, and this is brilliant and important and suggestive, is that the decohere, the, the density matrix, which is a little matrix, when I say little, for the cat thought experiment, it's a two by two matrix, right?

• 1:20:57Sean Carroll?

  And the two, the rows and the columns represent cat being awake or cat being asleep. So that density matrix becomes diagonal. So there's only two entries, there's the awake, awake entry and the asleep, asleep entry. And it's a feature of density matrices that the diagonal elements are non-negative numbers that add up to one, non-negative real numbers that add up to one, okay? So that should be, that should set off bells in your head because when you hear the phrase, a set of non-negative real numbers that add up to one, you, you should think probability. That is a probability distribution, right? It adds up to one because something happens, they're non-negative.

• 1:21:41Sean Carroll?

  Because the probability of anything happening is not a negative number. And if it's exclusive, so everything that possibly can happen is included in your set, then you're going to add up to one because the probability of something happening is one. So therefore, so the unimpeachably true statement is the dynamics of quantum mechanics and decoherence make it the case that the diagonal elements of the density matrix act like a probability distribution. They have the mathematical properties of a probability distribution. All that's true. Now, the crazy false thing comes when people then say, "That solves the measurement problem." You're done. These numbers in the density matrix are just the probabilities of the cat being awake or the cat being asleep. That's just the fact.

• 1:22:27Sean Carroll?

  Where did that come from? Just because these numbers have the mathematical properties of a probability doesn't mean that you can sort of magically say, "Therefore, one of them happens and the other one doesn't." You could say that as an extra assumption, you could put that in. You could invent a new theory that says that that's true. But that theory isn't just ordinary unitary quantum mechanics. You're doing something different to it. And if you tried to invent such a theory, when the density matrix diagonalizes, the rest of the, of the, one of those probabilities becomes real and the other one doesn't, what happened to the other one? When did it disappear? How diagonal does it have to be?

• 1:23:12Sean Carroll?

  It's never exactly diagonal. It's only really, really, really close, right? You haven't solved the measurement problem at all because you don't have a theory. You've just made it clear why, in a theory like, say, the many-worlds interpretation of quantum mechanics, it is okay to interpret those numbers as probabilities. Once you have a theory, you can do that. If you don't have a theory, you can't do that.

• 1:23:36Sean Carroll?

  Russell Wolf says, "Recently, you liked a post I made on Blue Sky. It was a cross between 'Mary Had a Little Lamb' and the 'Monochrome Mary Thought Experiment', which had been reposted by Zach Wiener Smith, former Mindscape guest. This got me wondering a bit about your experience on social media as a public figure. Do you notice when a post you come across online is from someone who follows you? Does that impact how you interact with it?"

• 1:24:01Sean Carroll?

  So, on the one hand, I'm not like a super-public figure, right? Like, I don't need to worry about things that people sometimes worry about, you know, about their privacy being violated or whatever, just because I'm online. I don't have any stalkers that I know of. I have people who email me all the time, who are slightly crackpody, but I just delete those. It's not a social media problem, right? So, I don't need to worry about those issues that much. I'm not going to be doxed, or whatever, or someone appearing at my front door. Do I notice when a post I come across online is from someone who follows me? Not really.

• 1:24:42Sean Carroll?

  Look, I'll be honest, my social media strategy is not very well thought out. It's, you know, I don't, I don't put a lot of effort into being on social media these days. You know, there was a time when I was blogging every day, that I put a lot of effort into that. But since I started doing the podcast, and you know, some combination of Twitter, or Blue Sky, and the podcast constitutes my entire social media strategy. The podcast, I'm very thoughtful about, but the Twitter or Blue Sky stuff, I just am not. I'm just doing what I want. I'm just having fun, okay? So, I'm glad that I liked your post, but I'm sure I didn't notice that you were a follower.

• 1:25:27Sean Carroll?

  I'm pretty sure I didn't know. I forget what Blue Sky tells you about those things. I'm just not very cognizant, or trying too hard, about social media strategy.

• 1:25:38Sean Carroll?

  I will say that occasionally, I just said that I'm not a public figure, which is true, but like rarely, but it does sometimes happen when usually when I comment on a Philadelphia 76ers social media post on Blue Sky. So, you know, I follow, actually, I don't follow. I have a list on Blue Sky of accounts that are devoted to talking about the Sixers. And I can sort of check in on the list if I want to see what's going on in the Sixers. And sometimes I will leave a comment or like something or whatever. And very, very occasionally, someone will say, "Wait, are you that Sean Carroll talking about the Sixers here?" And so that is the closest I come to being recognized out of context on social media. And that's

• 1:26:21Sean Carroll?

  fine. It's fun. And I say, "Yes, I'm that Sean Carroll. We all care. There's many of us, and we all care about things other than what it is we do for a day job." Edward Crump asks a priority question. "Alex Velankin uses a universe-from-nothing analogy with a Coke machine where the can spontaneously appears outside, bypassing the vendor chute. It would seem that while the possibility of the event is non-zero, it is still very unlikely. I'm asking you to tunnel a number into existence. What is an order of magnitude number of likelihood when comparing both events? And yes, please describe the numerator and denominator." So I'm going to do something here that I don't think I've ever done before with a priority

• 1:27:06Sean Carroll?

  question. I'm going to give you back your priority question opportunity to Edward. You can ask another priority question, not because this is not a good one, because I don't understand what you're asking. You say, "What is an order of magnitude number of likelihood when comparing both events?" But I don't know what the two events are. You described one event, when a Coke can appears outside a vending machine.

• 1:27:31Sean Carroll?

  What am I supposed to compare that to? What's the other event? Is it the universe from nothing? I don't know. So the universe from nothing, that's a phrase I never use. I don't think it makes sense. Maybe what you are referring to is baby universe creation from a pre-existing universe, which is not from nothing, it's from a pre-existing universe. And I can't give you the numbers in either case there. That would be a calculation that I would have to do. Wouldn't be very, very enlightening. I think that the answer would be that making a universe is much more likely than making a Coke can, simply because the wonder of inflation is that I can make a very, very,

• 1:28:15Sean Carroll?

  very tiny universe to start, and it can expand arbitrarily large to arbitrarily large sizes. So a Coke can is already macroscopic, and therefore, quantum tunneling into it is actually harder than just making a little tiny bit of Planck scale-sized universe that could then grow into ours. Josh Charles says, "I've had trouble finding a way to word this question. I'm trying to understand the tension between the determinism of the Schrodinger equation and the possibility space that it constrains. I'm imagining a quantum system composed of several parts with a well-defined starting state. If it was possible to run that system forward in time and then reset it back to the starting state and run it forward again, would you make the same observations?

• 1:29:00Sean Carroll?

  That is, overall, the same deterministic outcome would be observed across all branches, but within your observational space, could you see something radically different, like a particle decaying at a different point in time?" If I understand the question correctly, yes, the latter thing is correct. At least, the many worlds story is that the evolution of the overall quantum state of the universe is 100% deterministic. So if I knew exactly, which I don't, but if I knew exactly the quantum state of the universe now, I could run it backwards using the Schrodinger equation to any earlier point, and that answer is deterministic. It is not going to change from doing it once to doing it another time. But if I...

• 1:29:44Sean Carroll?

  I can, I can basically do a mini version of this, right? I can take a spin, for example, and I can put it in a plus X state. So it's pointed along the X axis and I can measure its spin along the Z axis. And it's a 50/50 chance. And in many worlds, that means that there's a branch in which it went up and a branch in which it went down and I'm on one or the other. And I can do that again. I can arrange that spin. I can do it again. And what I would find is no relationship between when I did it the first time and the second time. There's a 50/50 chance of spin up or spin down the first time and the second time and the third time or whatever. Of course, it's a different me, right? Like, the one who does the second experiment is clearly different than the one who does

• 1:30:27Sean Carroll?

  the first experiment because the one who does the second experiment remembers the outcome of the first experiment and the other one doesn't. So, the first one doesn't. So, you know, it's not really resetting the universe, but if, if that's what you're getting at, many worlds says that the overall state evolves deterministically. The experiences of any one observer in the universe do not evolve deterministically. Okay. Arkilocus says, "What do you think is the biggest or most common philosophical blind spot in physics today?" I don't think that there's one. I wouldn't, I don't, you know, I don't, I don't rank things like that very easily.

• 1:31:10Sean Carroll?

  I think there's a handful of ways in which physicists fall down on the job when it comes to philosophically interesting questions. I mean, the measurement problem of quantum mechanics is just an obvious example. I think the anthropic principle is another obvious example. I think the arrow of time is another obvious example. There's plenty of physicists, I was just talking to a good friend the other day, who's convinced that you can derive rigorously the fact that the second law of thermodynamics is true and entropy has to increase with time without making any time asymmetric assumptions. And that's just not true because people haven't thought about it. You know, these are physics mistakes just as much as they are philosophical mistakes. I mean, more philosophical.

• 1:31:53Sean Carroll?

  Philosophical blind spot is a love of falsifiability as a solution to the demarcation problem between science and non-science. I think that philosophers know why that doesn't work and physicists don't. Physicists don't have clear understanding of what to do about things that their theories predict that are not directly observable, right? And they could clearly, they could clean that up relatively easily if they thought about the philosophical version of it. But I don't think it's like one big philosophical blind spot. I think it's just a general unease with the idea that we have to sit down and think carefully, like philosophers like to do, rather than just shutting up and calculating, which is the mode in which physicists are most comfortable.

• 1:32:39Sean Carroll?

  Nanu says, "If the universe is so old and so big, what's the simplest reason no one has shown up yet? And are we overlooking it because it's too obvious?" Presumably, this is the "no one showing up yet" refers to something like the Fermi paradox and the absence of intelligent aliens. Simplest reason is that life doesn't appear that often. That's it. You know, we have a selection effect. We know that we exist in the aftermath of life appearing. That's old evidence. So that tells us almost nothing except that it is possible for life to exist. It tells us nothing about the probability or the frequency with which life exists. So either it's very, very, very, very, very, very rare that life starts

• 1:33:23Sean Carroll?

  at all, or one of the other steps along the way, right? And maybe it's very rare that there's multicellular life, or eukaryotic life, or something like that. People don't want to admit that. They don't, they don't like to take that conclusion seriously, but it's certainly the, by far and away, the simplest solution to why we haven't been visited or noticed other civilizations.

• 1:33:47Sean Carroll?

  David Maxwell says, "Bill Bailey once called himself a 'relaxed empiricist.' If someone he trusts knows more than him and says something is so, it's so. This has obvious dangers, yet you are that person for me, not because you know everything, but because you are self-reflective, rigorous, and honest, and you're clear about how much you know. In a world where we can't keep up with everything, it seems wise, but is it? Should people approach life this way? And are you special? Or could any intellectually honest, learned person applying Bayesian principles serve this purpose?" Well, I certainly don't think anyone should put too much trust or credence in my views in areas outside those that I'm an expert in, right?

• 1:34:31Sean Carroll?

  I mean, my view is that some people know things and have thought about things very, very carefully, and some people haven't. And there's just far too many questions in the world for everyone to be an expert on everything. So we should attune our strength of belief or credences to what most experts think in those areas that we ourselves are not experts in. If you have things like the foundations of quantum mechanics, where the experts don't agree, then by all means, you know, pick your favorite expert and/or develop your opinions for yourselves. If you have areas like climate change, where all the experts do agree, then you shouldn't let your personal opinions get in the way.

• 1:35:15Sean Carroll?

  You should probably say, if you're not an expert, that they're probably right. Never 100%, right? It's never just blind trust, but you should recognize when you are not an expert, and you should listen to the experts when they are there. Now, there's a trickier question when you have something where there's not a lot of consensus, and there's not even a lot of expertise. Like, you know, there are questions of judgment, or how you should behave in the world, where no one is really an expert more than others in the sense of knowing a lot more, because there's just a lot less established knowledge. And there, I think it's okay to look to people who you

• 1:35:56Sean Carroll?

  Trust in some ways, but there exactly because everything is fuzzier. I think that the expertise matters less and you can use your judgment more. Certainly, I'm not special. I think any intellectually honest person should be someone who you should listen to about these questions. And but it's exactly those questions which are not, you know, strict reproducible knowledge based where you're more encouraged to use your judgments, to think things through. It's the more factual based questions where expertise really should have a very big impact on your credences. Mark Kumari says, "In the context of the holographic principle,

• 1:36:41Sean Carroll?

  is it correct to think of the dual descriptions like bulk versus boundary as fully equivalent in physical reality? Or is one side more fundamental and perhaps the other is a convenient mathematical trick? In short, when two theories are dual, like AdS CFT, are they equally real or is one a truer description of reality?" Well, there's a subtlety here. A true duality is one where both sides of the duality are equally valid. In fact, one way of thinking about duality is you know that you can, or maybe you don't know, but there's a thing where we can start with a classical theory and we can quantize it to make a quantum theory.

• 1:37:20Sean Carroll?

  You can think of a duality as a place where two different classical theories upon quantization become the same quantum theory. That sounds remarkable, and it is remarkable when it's true, but there are cases where we do understand that it definitely does happen and that's a real duality. The subtlety is that AdS CFT is conjectured to be a duality, but the problem is that only one side of it is really well-defined, perfectly well-defined, and that's the conformal field theory side. The AdS CFT boundary duality posits a duality between gravity in an anti-de Sitter space in d plus one dimensions and the conformal field theory without gravity in d dimensions.

• 1:38:03Sean Carroll?

  We know how to define conformal field theories. Those are the most well-defined quantum field theories we have. Conformal just means there's no energy scale or length scale in the theory. The theories look the same at all scales. But the ADS gravity side is not well-defined. We think it could be defined with string theory. The idea is supposed to be that strings propagating in that anti-decider background should give you a well-posed theory of quantum gravity. But the point is that that's understood in perturbation theory, which is start with a theory that we know or a solution that we know and look at small deviations around it. But it's not well-understood non-perturbatively when you go well beyond the solutions that

• 1:38:48Sean Carroll?

  we know. So, on the one hand, you can't really say it's duality, right? We think maybe it's duality. There's evidence that it's a duality, but you can't say for sure. So sometimes people say, "Well, the real definition of the ADS side of the duality is just the conformal field theory side dualized." But that kind of defeats the purpose of it being a duality. Perry Romanowski says, "What do you think a science communicator gives up when they accept sponsorship money from a company to discuss that company's own research? Industry research isn't a neutral search for truth. It's an attempt to gather supporting evidence for something the company already wants to believe. Even with a disclosure, the selection bias is still there. They wouldn't be talking about that study if the results had gone the other way.

• 1:39:32Sean Carroll?

  It seems like this moves beyond science communication to company salesperson or booster." I think probably this depends on details that I'm not aware of. I'm sympathetic to the general idea that, yeah, if you're doing something that purports to be science communication, paid for by a company, then you're being a spokesperson for that company. And that's fine. It's okay to be a spokesperson for that company. You know, spokespeople are okay. I have ads here on the podcast. The Patreon supporters don't know that because they get ad-free versions, but the rest of you know that. And I think that's okay if you believe in... Yeah, if you believe in the thing that you are pushing.

• 1:40:12Sean Carroll?

  I, nobody knows this, because you don't have to go through this, but I turned down an enormous number of requests for ads on Mindscape, either because I think that the company is legitimately bad, or more often, it might be very good, but it makes sort of scientific claims, especially health claims, that I have no way of adjudicating. So I don't want, as a scientist, to be saying things that I can't check for myself that have some sort of health or medicine or scientific aspect to them. And that's a huge fraction of the total number of ads that people want to place on podcasts. So, you know, when it comes to other things, like clothing companies that I've been having

• 1:40:55Sean Carroll?

  recently, you know, I will only say good things about them if I believe them, but it's easier to believe them, you know, I'll try on the clothes and like, okay, yeah, I like those, so that's easy to say. Again, but there's nothing wrong with it, if you're, if you're being paid by a company that you do believe in, then by all means, you know, be that scientific salesperson, but it's not ordinary science communication. I think that if you're a journalist, or you're a news outlet, then it is crucially important to separate, as they call it, the editorial side from the marketing side. And responsible journalists or responsible outlets will absolutely do that. Kyle Stevens says, "New research by Anthropic shows that state-of-the-art LLMs have internal

• 1:41:40Sean Carroll?

  representations of emotions. According to Anthropic, these representations correspond to specific patterns of artificial neurons, which activate in situations and promote behaviors that the model has learned to associate with the concept of a particular emotion, like happy or afraid. The patterns themselves are organized in a fashion that echoes human psychology, with more similar emotions corresponding to more similar representations. Is this a challenge for the computational functionalist regime to reconcile with the belief that LLMs do not have subjective experiences?" Uh, no, it is not a challenge to that. In fact, it's, it's an intriguing result, but it is completely expected. I mean, I wouldn't imagine it any other way.

• 1:42:23Sean Carroll?

  Remember, LLMs are, the whole point of them is to say things that sound human, okay? So, of course, if you, you know, prompt them, or train them, or nudge them, or whatever, to say things with a certain emotional valence, that'll be associated with things that we associate with that emotional valence, because we are the ones who trained it in all sorts of different ways. So this idea that there are sort of vectors that you can look at inside the state of the LLM that correspond to happiness, or sadness, or whatever, completely unsurprising. It's just, it just means that the current state of the LLM has been prompted, or programmed,

• 1:43:04Sean Carroll?

  or trained, or whatever you want to call it, to give answers that we associate with happiness, or what have you. So it's a predictive true fact, it's not that it's false, but it's a different thing than what is going on in human subjective experience. And the easiest way to check that is just to know that if your LLM is acting happy, you just gotta prompt it and say, "Okay, now start acting sad." And it will start acting sad, right? Real human beings don't actually behave that way. Life would be much easier if they would. Michael Chorost says, "There's a question I've always wondered about. I've read that many cosmologists think the universe is spatially infinite, but how can a spatially infinite cosmos come from an event that occurred a finite amount of time

• 1:43:49Sean Carroll?

  ago, e.g. 14, or 13.8 billion years? I've learned a few partial answers, but unsatisfying ones. If the cosmos is flat, that implies it must be infinite, and if the universe is flat at the Big Bang, then it was always infinite, even at that moment. I find that an unsatisfying answer, because I keep reading that during the inflation era, the universe expanded from a subatomic size to the size of a grapefruit, following 10 to the 26 expansion, sure, but the size of a grapefruit is still pretty finite." Okay, so there's a lot of things going on here. One thing that is going on that is very important is, at the level of scientific communication, people are sometimes sloppy when communicating, and the audience is sometimes sloppy when listening, okay?

• 1:44:34Sean Carroll?

  So when people say the universe expanded to the size, from subatomic size to the size of a grapefruit, sometimes people will really say that. Sometimes what they say is, "The observable universe," meaning the part of the universe we can observe today, "expanded from subatomic size to the size of a grapefruit." So it's the latter that is accurate, right? That is actually what it's supposed to be. Like, the universe could be infinite, but we're talking about a little subset of the universe that we can observe today, what we call a co-moving volume, where we trace a certain region of space as it expands or contracts toward the past. And sometimes, the careful communicator will say that word, and the audience will just

• 1:45:17Sean Carroll?

  sort of skip over it, because it doesn't seem very important, observable universe, rather than just universe. Other times, the communicator will be sloppy and not even use that word, and that's kind of a mistake. Other times, the communicator will, in their minds, be thinking, "Well, if the universe were closed and finite in size, then it would be the size of a grapefruit." And they don't tell you all those extra words they're thinking about. So all of these are possible. Like, you have to, at some point, if you care about these details, you have to learn more, so that you can figure out which is going on in any one particular case. The other set of things to worry about is, you know, what satisfies you is not the criterion for scientific success.

• 1:46:00Sean Carroll?

  So it is simply a fact that in classical general relativity, the beginning of the universe could be represented as infinitely big in space. Whether or not that makes you satisfied is kind of irrelevant. That's what is allowed to happen, according to the rules of classical general relativity. I think, and I've said this before, a lot of the problem is that the arrow of time... nudges people to think of things happening from the past toward the future. And the beginning of the universe is a place where that intuition breaks down. Okay, this is why I said just a little while ago, I never say universe from nothing. That makes it sound like there was nothing, and then there was the universe.

• 1:46:45Sean Carroll?

  And this is some process unfolding in time. But it's not true that there ever was nothing. What you mean by that is that the universe had a first moment of time. Okay. And if you say it that way, the universe had a first moment of time, and at that moment, it was infinitely big, it doesn't sound so bad. It's actually, you know, completely plausible. The third thing is that classical general relativity isn't right, right? And quantum mechanics is right. And we don't know what there is to say about the early universe in quantum gravity, because we haven't figured that out yet. So all of these statements always have to be footnoted with, we're talking about classical relativity, and we might not know what exactly we should be talking about.

• 1:47:27Sean Carroll?

  Jennifer Stoneman says, I saw that earthquake waves are used to measure the Earth's interior. That is true. Does this wave use the same math as the quantum wave of the universe? I'm taking precalculus and will take calculus, not sure after that what math class covers waves. Some of the math is the same, sure. So to be careful, the quantum wave of the universe, I'm not exactly sure what you're talking about. You might be talking about the wave function of the universe, or the quantum state of the universe expressed as a wave function. And it's a little bit trickier, because a wave that goes through the Earth, or a light wave that travels through space, these are waves in three-dimensional space.

• 1:48:10Sean Carroll?

  And sometimes, when people talk about waves, they really mean waves in three-dimensional space evolving over time. The wave function of the universe is not like that. It doesn't live in three-dimensional space. It lives in this gigantic Hilbert space that is much, much bigger. However, that aside, if we put that aside for a little bit, the equations that are obeyed by simple-to-understand subsets of the universe, like

• 1:48:35Sean Carroll?

  The wave function of an electron obey an equation that is very similar to the equations that govern the propagation of waves in the earth's interior, or govern the propagation of waves through empty space, if they are electromagnetic waves, and so forth. Basically, it has to do with the derivative of the wave with respect to time being related to the derivatives with respect to space. That is to say, how fast the wave oscillates up and down in time is related to how fast it oscillates in space, i.e. its wavelength. The specific way that these things are related will be different for quantum wave functions, earthquake waves, electromagnetic waves, and so forth, but that's part of the fun.

• 1:49:18Sean Carroll?

  There's slightly different equations in every case. Typically, the math class in which you will cover this has to do with differential equations. Differential equations are specifically equations about derivatives relating derivatives to each other. So a calculus class will be about taking the derivative of a function, or taking the integral of a function. So taking the slope of a function, that's what the derivative is, or taking the area under a curve, that's what an integral is. Differential equations, which is after calculus, is not just taking the derivative of a pre-existing function, but giving an equation that relates different derivatives in different directions and figuring out how to solve those equations for finding what the function is. That actually turns out to be very hard.

• 1:50:03Sean Carroll?

  It's great. It's what a lot of mathematicians pay attention to, and crucially important part of being a physicist, for sure. Very often, in fact, physicists don't take a class in differential equations. There's so much differential equation solving in their physics classes, their E and M classes, quantum mechanics classes, classical mechanics classes, et cetera, that they learn the differential equation solving techniques there, rather than in a specific math class.

• 1:50:32Sean Carroll?

  Alexander Knuckel says, "Does the fact that individual particles of the same type are indistinguishable in quantum mechanics have any philosophical consequences for you? In particular, if you were to step into a Star Trek-style transporter," say that three times fast, "and be destroyed locally but reassembled into the same quantum state using different electrons and nuclei elsewhere, I think that the existence of a collective antisymmetrized wave function for all the electrons should make me feel indifferent about this kind of process, but my stomach says otherwise." I'm not going to give a great answer to this because I already feel indifferent about that kind of process. I'm not bothered by the idea of a perfect Star Trek-style transporter machine.

• 1:51:16Sean Carroll?

  Of course, I'm very bothered by an imperfect one, that would be a different question, but in principle, being disassembled and reassembled, I think, leaves you the same person as you were before, just as it is like in Star Trek, contrary to what Seth MacFarlane said he believed when we had him on the podcast before. That's why on the Orville, they don't have transporter machines. He thinks that they kill you and then you get reassembled, and that's bad, but I don't think that, I think it's fine. It is an interesting point, though, that you're making. In some very real, down-to-earth sense, I mean, maybe "down-to-earth" is not the right phrase, in some super fundamental, "let's take everything literally" sense, if you

• 1:51:57Sean Carroll?

  are reassembled using exactly the same, I'm trying to say this correctly, exactly the same relative locations of different atoms, electrons, and protons, and neutrons, and everything, in exactly the same relative locations that they were when you were originally transported, in some sense, you're not even made of different particles, that's what the point you're making is. Every electron is part of one gigantic antisymmetrized electron wave function precisely because electrons are identical particles. This is not something people usually talk about, so it's a good point to bring up. There's kind of no such thing as saying, "this electron or that electron," right?

• 1:52:41Sean Carroll?

  You can say the electron that is located here, but its wave function is very, very closely connected with the wave function of every other electron in the universe in a very real sense, so much so that you can't just say... it's very hard to say this, our language isn't quite up to it, but if you have two electrons, if you know you have two electrons, then they're in a certain state, it's very hard to say, you know, electron Alice versus electron Bob, okay, because the wave function of them both is antisymmetrized, which means it's a combination of A B minus B A, and the identity of which electron is which is kind of lost in that process.

• 1:53:26Sean Carroll?

  Grace Elliott asks a priority question. You have said that strong emergence is a cogent idea even if you don't agree with it. However, it seems to me that any apparent strong emergent behavior would still be expressed in terms... could still be expressed in terms of weak emergence from a non-local fundamental theory. What am I missing? For example, say a particle in a brain behaves differently than ones in the air, rather than saying the brain exerts top-down influence on the particle, you could just say the collection of particles making up the brain exert non-local forces on it. Uh, sure, you can, absolutely, that's fine. I mean, my way, you know, in the paper I wrote with the truth parola, our way of making sense of strong emergence presumed that there was no magic involved, there's nothing ineffable,

• 1:54:11Sean Carroll?

  right? Everything is ultimately physics, one way or the other. What we were trying to do was come up with a way where you could have something like strong emergence without magic. And the closest we could come was to say, well, maybe you think you have a really good theory of how particles or other small constituents behave, and the reason you think that is you've done experiments with small numbers of particles in small regions of spacetime, and you have a theory that predicts everything perfectly, as far as you know. And unbeknownst to you, there are new effects that kick in only when you don't have small numbers of particles, when you have large numbers of particles.

• 1:54:51Sean Carroll?

  Maybe even only when you have large numbers of particles arranged in a certain way. So that particles arranged in the form of a brain affect their constituents in ways different than particles arranged in the form of a rock. Now, of course, you're welcome to say, "Well, there's just a non-local theory. You just didn't know it. You've discovered it now." I have no problem with that whatsoever. All I'm trying to do is to make room for the very conceivable process. I don't think it happens, but there's a conceivable process by which you would think that something that we know of as strong emergence happens, starting from a theory that you thought you understood perfectly well.

• 1:55:36Sean Carroll?

  If you knew the theory that was non-local from the start, then maybe you wouldn't have been tempted to call it strong emergence. Preston Justice asks a priority question. "I recently lost my brother to suicide. He was 34 years old." Very sorry to hear that, and it must be tough to write about, so let's think about what the question says here. "Although I'm careful not to over-intellectualize the grieving process, I've been able to achieve some resolve through careful thinking about the events that led to my brother's choice. My question that derives from those reflections is presented here for the purpose of rational speculation. If I acknowledge that there's a precise probability that an alternative past action

• 1:56:17Sean Carroll?

  could have resulted in a better outcome, is it rational to assign some accountability to myself? In my experience, therapists will frequently guide one to not take accountability for events that are beyond our absolute control, but if we think of control of outcomes as coming in degrees, can we not instead focus our efforts on how well we respond to accepting that partial accountability rather than denying it?" I'm going to say two things that are sort of pointing in opposite directions here, and I congratulate you on doing your best to think rationally through these things, because that's not always easy to do, and we should strive to try to do it. On the one hand, I'm completely on board with the idea that there are degrees of accountability.

• 1:57:02Sean Carroll?

  It's not that, you know, this is your fault or this is not your fault. It's that there's many, many causal influences that go into something happening. Whether it's as dramatic as somebody committing suicide or as, you know, or something non-dramatic, whatever your example might be. So it would be wrong to just pick out one thing in the universe and say that's the reason why. Usually, you know, there's many reasons that go into things. So it's completely plausible that something happened that was part of the total cause of an event coming to place. That's, that's completely conceivable. On the other hand, I don't, I think it's, it would be wrong to sort of assign blame or accountability to yourself, simply on the basis of the judgment that there was something

• 1:57:47Sean Carroll?

  you did, that had you done it differently, things might have come out differently. I think you need, the, the criteria for accountability are stronger than that. It's not just that you did something. I think that you needed, it would only be accountable if, at the time when you did the thing, it was reasonable to think that doing that thing might have led to this effect. Right? So it's not just you did something. If you do something by accident that leads to a bad effect, you shouldn't be held accountable for it. If you do something knowingly that leads to an increased probability of something happening, then you get some partial accountability for it. But I do think that in the actual case of someone committing suicide, there is a temptation

• 1:58:31Sean Carroll?

  for other people to blame themselves more than they should. Because, you know, we want to tell a story that gives us some handle over why these things happen. And especially, we like to tell stories that we have some control over why things happen and why they don't. And sometimes, most often, as far as I can tell, in cases like this, very few of us other people have that level of control over this happening. We can nudge things in one direction or another, but there's so many other things happening, so many things going on in the person's mind that we don't know about, that maybe even they don't know about.

• 1:59:11Sean Carroll?

  That we have no way of really taking that into account and saying that it, you know, this thing or that thing that we did do or didn't do would have made a difference. It's overwhelmingly tempting to do that, but I think you should resist that temptation. I think that mostly you should be thinking about, you know, just how to take that fact that it happened, that your brother committed suicide and, you know, acknowledge it and deal with it. You don't move past it. You make it part of yourself. It is part of who you are going forward, the fact that that happened. But that doesn't mean you blame yourself for it. You do your best to incorporate it into who you are going forward and accept it. You can't change it.

• 1:59:55Sean Carroll?

  And learn lessons from it if it's possible, but don't use it as a reason to learn the wrong lessons or, you know, beat yourself up unnecessarily. I think that usually these things are just not in our causal control. David Sotolongo says, "In the Nature Survey on Physicists' Attitudes Towards the Foundations of Quantum Mechanics, which you discussed in the August 2025 AMA, it looked like only about 8% of respondents said they were confident or fairly confident that many worlds was the correct explanation of quantum theory. I'm curious if you have any thoughts about what it will take to get that percentage past the 50% mark." Uh, yeah, I mean, I have thoughts. I don't know if my thoughts are very accurate. That's not something...

• 2:00:39Sean Carroll?

  I just want to get it right, you know, making sure other people agree with me is less of a priority. But I do think that there's two things that we'll have to go on. One is better explanation of what many worlds actually says. I mean, there's still a lot of people who just say, "Well, that's too many worlds. I think that's not very parsimonious. Doesn't Occam's razor say that's not right?" You know, which is completely off-base, but that's our fault for not explaining what many worlds actually says. And the other thing is, we need to get results, you know? We need to show that thinking in this way leads to better answers to interesting questions that physicists think are good questions. I said it many times, physicists are a "show me the money" kind of field, right? Like, if they-

• 2:01:21Sean Carroll?

  They can ignore the foundations of quantum mechanics and get on fine with their lives. They will do so. Maybe they're missing the chance to make some progress on important questions because they do that. But if so, the way to prove that is to make important progress, make progress on these important questions, not just the demand that maybe they're missing the chance. We actually have to make it. I'm optimistic that we're gonna make it and then people will go, huh, yeah, I guess thinking about the things in this way actually is useful. I will start doing so. Dylan Samuel says, I'm currently a PhD student in applied mathematics. And I did my bachelor's in physics and now I work on problems in fluid dynamics. It's been a pretty cool gig so far and I've also been surprised at how many concepts from fundamental physics carry over to this topic.

• 2:02:06Sean Carroll?

  However, it makes me a little sad that fluid dynamics is not really considered part of the core physics curriculum or really considered a research topic in physics. Usually, fluid dynamicists are found in mechanical engineering or applied mathematics departments. As an authority figure in physics, I'm really not an authority figure in physics, but it's it's sweet that you might think that. What do you think it would take to get fluid dynamics to be considered under the umbrella of fluid dynamics once more? Oh yeah, that's right. When I read this question, I realized I think there's probably a typo here. You wrote, what would it take to get fluid dynamics to be considered under the umbrella of fluid dynamics once more? I presume you mean under the umbrella of physics or the physics curriculum or physics departments or something like that. Or did I guess more generally, how can the space of legitimate research topics in physics change?

• 2:02:51Sean Carroll?

  Well, I gotta say, I'm not that worried about this particular question. I agree that fluid mechanics is super interesting and a lot of interesting stuff goes on. Some of it happens in physics departments, but I think you're right. It's not the majority. It's more likely to be in engineering or applied math. But the point is, it is there in engineering and applied math. I think that's fine. If if those people really are interested in the topic more than physicists are, I don't see any real harm in that. A lot of these. Decisions about what topics happen under what departments? I find her a little arbitrary and I think that, I mean especially at boundary interdisciplinary

• 2:03:34Sean Carroll?

  things like biophysics questions. It's completely okay as long as the research gets done somewhere. You know, research in quantum computing sometimes happens in computer science departments, sometimes in physics departments. Sometimes computer science departments are in the school of arts and sciences or next to the math department, other times they're in the engineering school, right? It kind of doesn't matter to me. I do realize that in different universities, it might matter for cultural reasons, right? Or reasons, you know, how much respect you get or whatever, but I don't think that that's the most important thing. So I, unless, I mean, you're asking, how can the space of legitimate research topics in physics change?

• 2:04:15Sean Carroll?

  Probably that comes down to how research in fluid mechanics, fluid dynamics impacts other areas of physics. Like, I mean, there are, you know, there is plasma physics, it's again, not a big area, it's often engineering, once again, but there's astrophysics, there's condensed matter physics. You know, does it matter for the people who are employed in physics departments, what's going on in fluid dynamics? I think that's the question. And when the answer turns out to be yes, then physicists are going to say, hmm, maybe we should start hiring people who do fluid dynamics. J. Henry Jacobs, oh yeah, J. Henry Jacobs says, "In regards to hedonistic utilitarianism, you recently had a conversation with Peter Singer.

• 2:04:58Sean Carroll?

  We raised concerns about utilitarianism, assuming an objective function where addition makes sense. Could we drop the addition assumption by using medians instead of means? I.e. do it raises the median welfare. With medians, you just need the objective function to take values in an ordered set. Moreover, medians are robust utilitarian monsters." Is this a line of inquiry that sounds familiar? I don't think it sounds familiar, but I also don't think it's a very good, workable idea. You know, the idea of taking the mean utility over a group of people is equivalent to taking The total utility over all of them, right? Because you just multiply by the number of people and the mean equals the total. The median doesn't have that property.

• 2:05:43Sean Carroll?

  And so, yes, the median utility might be insensitive to utility monsters. This is the idea of some imaginary creature that is just so good at feeling pleasure and being happy that it is completely unimportant to making other people happy. All that matters is to make the utility monster happy, right? And that's supposed to be an argument that utilitarianism isn't really on the right track. So, yes, taking the median would get rid of that problem, but it gives you the other problem. It means that the worst off people can be tortured and made as unhappy as you want, and the median wouldn't care, right? And I think this is, again, kind of why I'm not a utilitarian.

• 2:06:24Sean Carroll?

  I think that the difference between utilitarians and other approaches to ethics is this idea that rather than giving individuals some floor of dignity and happiness, it's the mean, or the average, or the median, or whatever you want to do, that matters. And therefore, there's always, for any legitimately utilitarian perspective, there will always be times when we make some people unhappy and other people even happier. Of course, the world is full of times when we make some people unhappy and other people happier, but there's no bottom to it in utilitarianism, right?

• 2:07:07Sean Carroll?

  If you start saying, "Well, I have a bottom in my version of utilitarianism", then I think you're just not being utilitarian anymore, and good for you. I don't think you really should be. So, I think that there needs to be something that says we can't treat individuals arbitrarily badly just to raise some overall standard. And I think that that belief makes one not a utilitarian. Jonathan Sorocco. I'm sorry Jonathan, in my notes here, there's no J in front of your name, so either I miscopied them, or you're actually Anathan Sorocco, I'm not sure. Anyway, the question is, given your diehard fandom of the 76ers, how do you feel about other Philadelphia sports teams?

• 2:07:48Sean Carroll?

  The Flyers won championships in your youth, do you follow them much, or was basketball the only sport for you? Basketball was always my favorite, but of course, as a kid, I followed all of the Philadelphia teams. All of them won championships in my youth. Actually, the Eagles didn't. The Eagles were good, they got to the Super Bowl with Dick Vermeil, coaching them. Ron Jaworski, Bill Bergy, etc. William Montgomery. William Montgomery? Was that his name? The running back. I'm getting old, what can I tell you? I don't think it was William Montgomery, I think that I'm misremembering the name. But anyway, it was a good team, they got to the Super Bowl, they were a bit outclassed, they lost to the, at that time, LA Raider, Oakland Raiders. I think John Madden was the coach at the time.

• 2:08:32Sean Carroll?

  Anyway, the Eagles were the only ones that didn't win the championship. Sixers won the championship, Phillies won the World Series, Flyers won Stanley Cups in the 70s, when I was younger. And so I was spoiled, all of my teams did very well. I wasn't, I was also a fan of Penn State football, they were also winning championships in the early 80s. I started following Villanova basketball, when I went to basketball, when I went to Villanova, rather. They won the championship the first time I was there, so totally spoiled, overall. But I just enjoy basketball as a sport, more. Baseball, I like going to the games, you know, it's fun experience to be outdoors, have the hot dog and whatever, but the game itself, I find incredibly tedious.

• 2:09:15Sean Carroll?

  I recognize, and before the baseball fans come on me, there are moments of drama in baseball. That are very, very hard to beat in other sports. And precisely because of the very, very clever idea that there's not a clock, right? In basketball, football, hockey, there's a clock and you're gonna run out of time at some point and it becomes impossible to make up some deficit. In baseball, even though in practice you can be so far behind it's futile, in principle, until there's the last out of the last inning, you could score an arbitrary number of runs in the future. I think that's a wonderful feature of baseball.

• 2:09:59Sean Carroll?

  But most of the time, there's a lot of standing around. I mean, the number of, someone calculated the number of seconds that the baseball is actually in play, the literal baseball, as opposed to just like standing around in a baseball game. It's very short, right? It's less than a minute or something. I forget exactly what the number is. Whereas constant activity in a basketball game. Hockey is similar to basketball in many ways, but of course, you're scoring a very, very small number of goals, just like in soccer. And that's fine, I think it's fine, but it's, you know, people, for some people, the fact

• 2:10:40Sean Carroll?

  that basketball, there's so much scoring, you're scoring at 50% of the time, right? Is a bug, not a feature, is a bad sign. For me, it's absolutely a benefit because it means that there is, that what matters is the flow and the consistency and it's much less down to, you know, random events, unpredictability, right? Of course, in hockey or soccer, the good teams usually win and the bad teams usually lose, but it's like one event in the whole course of the game that matters. Whereas in basketball, it's just constant, right? It's just like every play matters, there can be momentum shifts.

• 2:11:24Sean Carroll?

  Literally last night, as I am recording this, we had one of the historically weirdest basketball games of all time. Between the Detroit Pistons and the Orlando Magic. Detroit was the top seed in the Eastern Conference this year. Orlando was not very good. The Sixers demolished them in the playoff game just before the playoffs. But Orlando has a 3-2 lead in the playoffs in a best of seven series. So this was very strange and Orlando came out and was really crushing Detroit in the first half of the game. And so Detroit was, you know, ready to go home as far as many people were concerned. And people were making jokes about them not even trying, et cetera.

• 2:12:07Sean Carroll?

  And then in the second half of the game, it was a complete turnaround. Orlando scored 60 points in the first half, 19 points in the second half. And they ended up losing by a huge amount. Detroit had the, it had to be one of the numerically largest comebacks ever in the history of basketball or in the history of sports or whatever. And I kind of love that. I mean, this whole playoff year has been just full of amazing storylines and comebacks and upsets. And it's been a lot of fun. So football I like for different reasons. Like it's just because it's like slow and thoughtful and there are plays that are very intricate. There's this intellectual aspect to it that is pleasing.

• 2:12:50Sean Carroll?

  But and it is very violent. I don't care about the violence in terms of watching the sport, but it wreaks havoc on people's bodies. And that bothers me, so I get less pleasure out of that. But of course, when the Eagles win the Super Bowl, I'm going to root for them.

• 2:13:07Sean Carroll?

  DMI says, "AIs now seem to be getting good enough to actually be useful for some things. So I thought I could, I'd see if it could answer one of the questions you may be tired of hearing from me." Here was its answer. "Given energy conservation, any action, the integral of T plus alpha V over time, with alpha not equal to 1, has the same stationary paths, making the minus 1 and T minus V seem arbitrary. But in Feynman's path integral, different alphas give genuinely different quantum theories. So the choice is non-arbitrary there." Classical mechanics inherited the right Value without being able to explain it the way Maxwell's equations encode to Lorentz Symmetry before relativity. My question now is, was it on the right track?

• 2:13:52Sean Carroll?

  Okay, so for people who don't know what's going on, this is a question about the principle of least action. The idea being that instead of starting a system, think of a ball rolling down a hill, okay? Usually, the way that we calculate the trajectory of the ball rolling down the hill is you tell me the position and the velocity of the ball to start, and I use some version of the laws of physics, F equals ma, to predict how the ball will move subsequently. The principle of least action says, don't tell me the velocity, just tell me the initial position and time of the ball, and tell me the final position and time of the ball, okay? And then I will search through all of the possible trajectories in between,

• 2:14:36Sean Carroll?

  starting from that position at that time and ending at this different position in different time, and I will calculate a quantity called the action. And it turns out that the actual trajectories that solve Newton's equations of physics have the property that they are the minimal action over the actual path that the particle takes. So rather than positing F equals ma, or Newton's laws, you can posit what is called the principle of least action, that this quantity called the action is minimized on the real paths that real objects take. So what is the action? It's the integral over time, so the total amount summed up over time of something called the Lagrangian. And the Lagrangian

• 2:15:19Sean Carroll?

  is the kinetic energy minus the potential energy. Kinetic energy, one-half mv squared for a particle, potential energy, whatever the shape of the hill that the ball is rolling around in. So kinetic minus potential is the Lagrangian. The integral of that is the action. Minimizing the action is what gives you the real path. And so the question is... Can you change kinetic minus potential to kinetic plus potential? Or kinetic plus a half potential? Or kinetic plus whatever? You know, some different linear combination of kinetic energy and potential energy? And get the same answers? And the question is fray... DMI did not actually put the question here, only the answer. So I'm gonna infer the question.

• 2:16:04Sean Carroll?

  But it says, "Given energy conservation and any action t plus alpha v, kinetic plus alpha times potential, with any alpha not equal to 1, has the same stationary paths, making the minus 1 in the usual version seem arbitrary." So I don't think that's right. And I think that the problem is, you're saying, "Given energy conservation, any action has the same stationary paths." But that's not... You don't... You can't give energy conservation. That's not allowed. In ordinary ways of doing it, in the ordinary principle of least action, you posit that the action is kinetic minus potential, and you derive the fact that energy is conserved. If you have some other linear combination,

• 2:16:47Sean Carroll?

  then energy is not necessarily going to be conserved, right? You could have alpha equals 0. You could just have integral of kinetic energy, and the potential energy wouldn't matter. There's no way that you're going to derive from that that energy is conserved. Indeed, in general, an action with Lagrangian kinetic plus alpha potential will give you some equations of motion, not the normal equations of motion, but some equations. And energy will just not be conserved, according to those equations of motion. At least not the energy under, as we usually define it, kinetic energy plus potential energy. So, there's no solutions to the combined demands that you minimize this modified action, plus you have energy conservation.

• 2:17:30Sean Carroll?

  And the LLM should have noticed that, and it didn't. So I don't think that the LLM was on the right track.

• 2:17:38Sean Carroll?

  Larry Latson Jr. says, "I have a question about the many-worlds interpretation of quantum mechanics. I want to be a believer, but if I understand the concept, the many worlds split when the system decoheres. My question is, is this then happening everywhere, all over the entire universe? Every time a couple photons or electrons decohere in the heart of a star that is 5 billion light-years away, are we ending up with two more universes? Or does that system need to be observed by an observer? Does us looking up in the sky and seeing the starlight from 5 billion light-years away count as an observation?" So, the simple part of this question is, no, it does not need to be observed by an observer. One of the beauties of the many-worlds interpretation of quantum mechanics is observers,

• 2:18:19Sean Carroll?

  or measurements, or whatever, have no special status whatsoever. It's just equations, it's just systems obeying the laws of physics. That's all that ever happens. As far as the system decohering and branching the wave function, again, the simple answer, the most naive, straightforward answer is, "Yeah, that happens all the time, all the time, everywhere in the universe. You don't notice it. Why would you notice it? You don't care, and it doesn't bother you, and there's no problem with that whatsoever." The slightly more sophisticated thing to say is, "Look, remember, the many-worlds interpretation of quantum mechanics is not about worlds. That's not the point of the interpretation. The point is, that there

• 2:19:01Sean Carroll?

  is a quantum state, and that quantum state always obeys the Schrodinger equation, forever and ever. It never does anything else. And that's it. That's the whole thing. Any talk of worlds and decoherence and blah blah blah is our human way of coarse-graining and simplifying and get a handle on what is happening, just like we coarse-grain and simplify to talk about temperature and density and pressure in a fluid, okay? So, there is no one right way to divide the wave function of the universe up into worlds. There are better ways and worse ways, depending on one's purposes in the moment, but different people can do it differently, and it's okay. So, if you personally wanted to say, "I'm

• 2:19:46Sean Carroll?

  going to define..." Find the worlds that are relevant to my observations as only branching when I notice something, you're allowed to do that. It's okay. No one stops you as long as you do it in such a way that you obey the rules, that you have a principled, objective way of defining what a branch is with respect to whatever the quantum state of the universe is doing, that's okay. So people argue, people say like, does the branching happen simultaneously in some reference frame, or does it happen locally, only in the future light cone of the event? My answer is, who cares? It doesn't matter. It's just commentary on what is actually happening, which is the quantum state of the universe is obeying the Schrödinger equation.

• 2:20:32Sean Carroll?

  Roland Weber says, more an observation than a question. I just noticed that for the first time that the podcasts are sorted into categories on your webpage, but the latest in the solo category is about the crisis in physics. I'm pretty sure you recorded more solo episodes since then, one about immortality, one about AI, another about emergence. Have you given up on categorizing the podcasts, or is there a technical glitch? Yeah, glad you're pointing out this, Roland. It's not a technical glitch. This is probable user error, when the user is not you but me, rather. So for those of you who don't know, at preposterousuniverse.com/podcast, you can find all the podcasts. It's actually the easiest

• 2:21:14Sean Carroll?

  way to listen to them in many cases. And there are categories, or rather, there are tags put on each of the episodes, physics, economics, whatever. And the fact is, one of the tags is solo for the solo podcasts. And I just forgot that there was such a tag. So for my last several solo podcasts, I have not tagged them under the solo category. I have now gone back and tagged them. So if you check now, they're all there. Thank you for letting me know that I've been forgetting to do that. Mark W. says, "I often hear that we need a bigger particle collider to probe into deeper and smaller realms. Why is this? Don't we already whip particles around the circular colliders many times until it reaches the necessary speed?

• 2:21:57Sean Carroll?

  Why can't we keep going around and around the collider many more times until we get to even higher speeds, until the particles are fast enough to probe string theory or whatever in our current circular colliders?" So I am not an expert on the experimental or instrumental engineering side of particle accelerators, but I can give you the basic answer here. It's interesting, you know, you might think that in that big ring that you have at the Large Hadron Collider or whatever, the particles are just constantly being accelerated faster and faster speeds. That is not what is going on. There's a couple of points, I mean, some number, a handful, not just a couple, but there are specific points where the particles are accelerated.

• 2:22:38Sean Carroll?

  Most of the ring does not accelerate the particles, it just turns them around in the circle. You know, the real, this is, this is the kind of interesting thing and why something like the Large Hadron Collider is an absolute technological marvel. It's just keeping a bunch of particles together and collimated into a very thin beam. That is the real challenge here, okay? If you think about it, at the LHC, Large Hadron Collider, there are protons moving around the ring in two different directions, but that's, that's not a problem. Protons, if you have nothing but protons, you have a bunch of particles that are all positively charged. That is to say, they're all trying to repel each other and spread apart.

• 2:23:22Sean Carroll?

  So we need these super high-intensity magnetic fields to keep them together, but that's not really enough. We need to actively nudge them and collimate them into a very tight, thin beam because you want to maximize the probability that when the two beams intersect at the detectors, they will actually collide and make an event. So you want a very, very dense collection of protons. So all the real challenge is keeping the protons together in a very, very thin beam, and they get bunched up because of the way the acceleration works. So that's fine, the bunching is, is fine. So you need, so there's a sort of maximum amount of energy that you can have in the

• 2:24:07Sean Carroll?

  protons moving around the ring and keep them all in a tight beam. And...

• 2:24:14Sean Carroll?

  And that gives you a limit on how much energy you can have in the accelerator. The other thing, of course, is that everything needs to be timed very carefully. This is another aspect of the technological challenge. These particles are moving very fast, right? 99.999999% of the speed of light, or some number of dimes. It doesn't really matter. So when they pass by and you are accelerating them, you better accelerate them at exactly the right moment. But if you tried to do that at arbitrarily higher energies in a very small ring, basically everything would just splinter apart very quickly. It's not that you don't have the energy to accelerate them. The energy in a single proton moving at these speeds is not very much.

• 2:24:59Sean Carroll?

  Like, the Planck mass is not very much by macroscopic energies. The Planck mass is about 10 to the minus 5 grams, okay? It's not hard to make that much energy. The point is to put it into a single particle, to put it into individual particles with many such particles, and then keep them tightly collimated as they zoom around the beam. Now, it might be, by the way, that future technology is able to do this without building a giant circular particle accelerator. That's absolutely possible. These estimates of solar system-sized accelerators, etc., are thought experiments just to convince you that with current technology, that would be very hard. But who knows about future technologies?

• 2:25:41Sean Carroll?

  Richard Knijnenborg says, "Is the NAND gate, the N-A-N-D gate, being functionally complete relevant in John Wheeler's it-from-bit concept?" So I'm answering this question. I'm not going to give you an answer that will satisfy you, I think, but just to elaborate a little bit on John Wheeler's it-from-bit concept, because people are getting it wrong, not just Richard, but professional physicists. So John Wheeler, famous physicist, he was famous for doing physics and coining terms like "black hole" and "wormhole" and things like that. I think that the single thing that John Wheeler was best at was advising graduate students. Richard Feynman was one of his students. Hugh Everett was one of his students.

• 2:26:25Sean Carroll?

  Kip Thorne was one of his students. Jacob Beckenstein was one of his students. Robert Geroch was one of his students. He really did pretty well with the graduate students. And he wrote a paper. He was a brilliant guy. I've seen him give talks. He's passed away now, but... He was wonderful with words, you know, you might, as you might expect from the fact that he's the one who coined terms like black hole and wormhole. Spacetime foam was another idea that he had. And he wrote a paper and he coined the phrase it from bit. And it's one of those phrases that as soon as you hear it, you like it, like, ah, that's cute. And, you know, maybe a little bit of gloss on what it means. It represents, you know, matter, reality, whatever.

• 2:27:10Sean Carroll?

  Bit represents information. So you don't have to read the paper, right? You just have to go, oh, John Wheeler is saying that the world is really made of information in some sense. However, if you actually do read the paper, what you find out is that he wasn't saying that at all. And I've, I've only recently, like in the last couple of years, um, uh, realized this by reading the paper. And so I've been saying this, so if you've heard me say this before, I've been saying this a lot. He was not saying that the world is made of information. The point is that despite the fact that he was Hugh Everett's thesis advisor, Wheeler was never really a believer in the many worlds interpretation of quantum mechanics. John Wheeler was an acolyte of Niels Bohr and he'll, he said that very clearly, like,

• 2:27:54Sean Carroll?

  Niels Bohr was his favorite human being of all time and he was a follower of Bohr's way of thinking about physics. Wheeler tried very hard to convince himself and Hugh Everett and other people that many worlds was compatible with the Copenhagen interpretation of quantum mechanics. But of course, that failed because it's really not, it's really a repudiation of that. And so Wheeler himself eventually said that he didn't like many worlds. What he liked was the Copenhagen interpretation of quantum mechanics. And he was smart enough and he knew Bohr personally and he knew all these people, um, to really understand the, the depth and the radicalness of the claim being made by the Copenhagen interpretation, which most people are not.

• 2:28:38Sean Carroll?

  Most people use the Copenhagen interpretation as a stand-in for not thinking that hard about quantum mechanics, just assuming there are measurements and you get results. But people at the beginning, like Bohr and Heisenberg and Wheeler, who really thought through what it meant, had to face up to the radicalness of it. Because Heisenberg especially emphasized the fact that the Copenhagen interpretation was saying that nothing exists until you measure it. Okay? It's not that there's a wave function, or a matrix, or whatever, that exists, and then when you measure it, you get some aspect of that, which is a more conventional way of thinking. The real Copenhagen claim is that nothing exists until you measure it.

• 2:29:21Sean Carroll?

  All that exists is the outcome of a measurement, or the collective outcomes of all the measurements. Okay? That's what John Wheeler was getting at with it from bit. He was saying that the fundamental kind of measurement in quantum mechanics is the measurement of a single spin. He was arguing that other measurements could be built up from that single spin, single qubit kind of measurement, and that measurement gives you one bit. It gives you either up or down, right? One bit's worth of information. And Wheeler was not saying reality is made of information. He's saying reality is made of measurement outcomes, which is a very different claim. He wasn't thinking of reality like a computer.

• 2:30:05Sean Carroll?

  He wasn't thinking about gates, or information processing, or anything like that. He was making a statement about the foundations of quantum mechanics. So, no, is the simple answer. None gates have nothing to do with Wheeler's it-from-bit concept. Of course, because people didn't read the paper, but just like the motto, we now have it-from-qubit, which is supposed to be an upgraded version of what Wheeler was saying. It's a completely different thing than what Wheeler was saying. It-from-qubit really is saying that reality is made of quantum information, quantum bits in some sense. So that's a very different way of thinking. And there, different kinds of quantum gates are super-duper relevant.

• 2:30:48Sean Carroll?

  Someone like Daniel Harlow works with quantum information processing gates and things like that all the time. Sid Huff says, "You've commented a few times on the fact that you and Jennifer bought your first house around three years ago. You also mentioned your experience learning to chop firewood. What other things about homeownership have you found interesting, enjoyable, challenging? All things considered, are you happy to be a homeowner?" So, it's not quite that I learned to chop firewood. I grew up chopping firewood. You know, I lived in a house in the suburbs, a tiny little house. And, you know, from, ugh, I don't know, approximately 8th grade, 12th grade, anyway, we lived in a suburban house and we had a wood stove and a fireplace and I chopped a lot of wood and burned a lot

• 2:31:32Sean Carroll?

  of wood in the fireplace. But then I haven't done it since then, so I've taken it up once again. And there is a certain pleasure one gets out of the, out of the manual labor that leads to something important and enjoyable around the fireplace. But to answer the question, super happy to be a homeowner, mostly because, I mean, I've owned, we owned our condo before, right? But that's a different thing. You're in a condo association, you have to share, you get people to do a lot of the work. When you're a homeowner, you're responsible for it, an individual homeowner. And of course, our house is 100 years old, so it has, you know, it has issues. And we were smart enough, I guess we were

• 2:32:17Sean Carroll?

  smart enough, to not overextend ourselves with the cost of the home. We bought a home we could afford in the sense that we knew we would have to do work on it. So, before we moved in, a lot of renovation was done. The floors were fixed, the wiring was replaced and things like that. After we moved in, we had to replace the whole roof. It's a 100-year-old slate roof and we had to replace it. And that was a non-trivial undertaking, let's put it that way. So, we still have a list of things we want to do over the next few years. We have to save up money to do them. So, thank you, podcast supporters, for helping me to fix my house and keep it from falling apart.

• 2:32:54Sean Carroll?

  I do like it. I'll confess Jennifer is better at it than I am. She's more into it than I am. She's more knowledgeable and trustworthy about these things, you know. Her family was into it. Her brother and her father both spent time renovating or even constructing, in the case of her brother, houses. So she's familiar with a lot of what goes on and you know, she knows the difference between wainscoting and other things that I just don't know the what the words mean. I just nod along and say, yes, that sounds good. So a lot of the actual work is being done by her. I have my little parts that I take care of, like every light bulb that needs to be changed is mine. But when it comes to big things like, you

• 2:33:39Sean Carroll?

  know, the landscaping or whatever, I defer to her judgment and she enjoys it. So it's good. She's taken up, you know, feeding the squirrels, as we've said, around the house and everything. But overall, yes, you know, the huge benefit of living in Baltimore is that it's more affordable than many of the other big cities that I might like to live in. So we can have a nice house near to campus. I walk to work every day and more than enough space to like have a room that's mostly the room that I'm talking in right now is mostly used for recording the podcast and nothing else. We have so much room that I can have a podcast room, right? Which is just really nice. And sometimes we feel guilty that we

• 2:34:20Sean Carroll?

  have so much house, you know, because we grew up in not nice houses like this. So this feels good. And it's nice to shape the house. Jennifer likes to say that the house changes you because things like we didn't care about having a fireplace when we moved in. We didn't care about having a dining room. We never had a separate dining room before, right? All the modern houses, like the one we lived in LA, we were the first people to live there in that house, in that condo, in that townhouse. And so. Very modern, open concept, et cetera, et cetera. That was fine. We never used the dining room space that much. And now we have a formal dining room, right? Because it's a 100-year-old house. And we even thought about like, could we like,

• 2:35:03Sean Carroll?

  bang down part of the wall, separating the kitchen from the dining room, et cetera. But now that we're here, we love it. Like, we use that dining room a lot. We have people over. I have group meetings with my students and things like that at the house. And we sit in the dining room, and it's nice to have that space to do that. We don't need to have a TV in the living room, because there's enough other places to put TVs. And, you know, we don't, we don't like have people over to watch TV, or whatever. So the usability of the house in ways that I didn't anticipate is really, really nice. I don't spend a lot of my time tinkering around the house. I will, I will say that. That's not something that I have time for. But maybe, you know, I'm young, I can still, you know, grow and change in different ways. That might be something that I become more interested in as time goes on.

• 2:35:48Sean Carroll?

  Domino says, "I come across, I came across Veritasium's YouTube video on the Dirac equation, which showed how he was able to quantize GR, and as a side effect, theorize the existence of antimatter. Between your work and the rest of my healthy diet of popular science physics content, I know that quantum gravity continues to elude the standard model, leaving QM and GR at odds regarding singularities and relegated to their respective corners of their domains of applicability. My question is basically, how far did Dirac take us toward grand unification? Is it really only quantum gravity standing in the way, or was his quantization of GR only the first step embarking on that journey?" So, there's a lot going on here that I have to unpack. What Dirac did with the Dirac

• 2:36:30Sean Carroll?

  equation didn't have anything whatsoever to do with GR. GR means general relativity. General relativity is Einstein's theory of gravity, where spacetime is curved and responds to energy and momentum. What Dirac did was come up with an equation for the electron, the behavior of the electron that was compatible with special relativity. Special relativity, you know, doesn't have curved spacetime, doesn't have gravity. Happened around 1905, whereas general relativity happened around 1915. So gravity has nothing to do with the Dirac equation. He wasn't doing that. And he wasn't even the first to reconcile, if you want,

• 2:37:15Sean Carroll?

  special relativity with quantum mechanics or quantum field theory, because we already had Maxwell's equations, which were a classical theory of electromagnetism. And people looked at the quantum theory of electromagnetism before they had Dirac's theory of the electron. So, but what he did was make the electron have an equation that was compatible with the rules of special relativity. The electron is special because it's a fermion, it has spin, etc. That was the real breakthrough. Now, there is a subtlety that is a historic fact, historical fact, that trips people up. The Schrodinger equation, as written down by Erwin Schrodinger in 1926, or 25, he wrote it down, published in 26.

• 2:37:59Sean Carroll?

  There's sort of two versions of that equation. There's the literal version that Schrodinger wrote down, which is non-relativistic. So it applies to electrons and atoms as long as they are outside the regime of relativity. It works very, very well. But it's very, very simple to generalize the Schrodinger equation to a much more general, powerful form, which is completely compatible with relativity if the Hamiltonian, the thing that drives the Schrodinger equation, is relativistically invariant. That's just what you would do in modern quantum field theory, for example. You have a Hamiltonian, you have a state, it obeys the Schrodinger equation with that relativistic Hamiltonian. But they weren't clear about that back in the 1920s, right? They were still working things out, so...

• 2:38:44Sean Carroll?

  It was thought that maybe, rather than just coming up with a relativistic Hamiltonian, you should change the Schrodinger equation to something that would be the equivalent of the Schrodinger equation for, that was relativistically invariant and would reduce to the Schrodinger equation in the non-relativistic regime. If you know a little bit about the Schrodinger equation, you know that there's the wave function is in there and there's a first derivative with respect to time and a second derivative with respect to space. And instantly you know, it's not relativistic because relativity treats time and space on the same footing. So Dirac was looking for an equation that would treat time and space on the same footing. Now, this is too much history, but that's okay.

• 2:39:28Sean Carroll?

  I'm just going to get it right this once and then you'll know. Schrodinger, as my quantum field theory professor Sidney Coleman liked to say, Schrodinger was no dummy. He knew about relativity. He wasn't just like guessing things because he wasn't that smart. He tried first to make a relativistic equation. And he did. And he invented what was called the Klein-Gordon equation, which is still the equation that we use to describe classical scalar fields in classical field theory. So he discarded it because it didn't work for what he wanted, which was describing the behavior of electrons in atoms, because the electrons are not scalar fields, they're fermions and that matters, okay?

• 2:40:11Sean Carroll?

  So Schrodinger proposed his non-relativistic equation just because he had an idea for a relativistic one, but he knew that it didn't fit the data, okay? Dirac proposes, you know, tries to come up with a generalization of the Schrodinger equation that would be relativistic and would still describe the electron. And that's what he thought he did when he invented the Dirac equation. But he didn't. And this is where people get confused, because what the scientists do when they first invent things is not necessarily how we correctly interpret them later. The correct way to think about the Dirac equation is it's not a replacement of the Schrodinger equation. The Dirac equation is the equivalent of Maxwell's equation for the electromagnetic

• 2:40:54Sean Carroll?

  field, or the Klein-Gordon equation for a scalar field. That is to say, the Dirac equation is a classical equation for a spin 1/2 particle. In fact, a spin 1/2 particle with electric charge, so it's actually both a particle and the antiparticle. That's another complication that Dirac had to deal with, but was sorted out later. You take that classical equation of motion, and then you quantize it, and what you eventually will invent is quantum field theory, and that's what we have today. We don't use the Dirac equation today as a generalization of the Schrodinger equation. We just do quantum field theory. So anyway, the Schrodinger equation works even for special relativity.

• 2:41:37Sean Carroll?

  The Dirac equation is a wonderful classical equation of motion, which can then be quantized to give you the quantum behavior of the electron, and none of it has anything to do with gravity, as far as we know. Robo, or Rabo, says, "The Self and How to Know It with J. Eric Oliver was a great episode. Considering the self as a group of processes, somehow for me this makes some of the challenges to and techniques for optimizing life's experience a bit more tractable. You made a comment in the reflections post about the inadequate amount of time to explore the topics that were touched on. I'm wondering whether this factor should not overrule your policy of not having repeat guests." I should emphasize that differently.

• 2:42:19Sean Carroll?

  "Should not overrule your policy of not having repeat guests. I'd encourage you to loosen that restriction a bit when a conversation reveals content that could be interesting for another one or two podcasts. If that's a bridge too far, then as an alternative suggestion, you might invite an acolyte of the first guest to dive into more details." So, you know, I get it, I hear it. People have said things like this before. I'm glad you liked that podcast. There are many podcast guests, probably most, who have more than one hour's worth of stuff to say, and would be a useful person to talk to again, or in a longer conversation, or with a related person, or whatever. Here's the thing. It's much more work for me to never have repeat guests, right?

• 2:43:01Sean Carroll?

  It's much easier to have guests who I have had before. I know the basic picture of what they're talking about. We can, you know, have more conversation about it. It's just easier for me. But what it means is that the number of guests, the number of separate distinct guests I would have would be much smaller, right? Many, many podcasts, if you go out there, if they have the same sort of cadence that we do, one a week, and they fall back on regularly appearing guests, that's great. You get a certain familiarity, you know it's comfortable, you know what's coming, but it's not as novel. You're hearing the same guests over and over again. Part of my, a big part of my motivation for doing Mindscape is I want to talk to people

• 2:43:44Sean Carroll?

  and learn things from them that I don't know. And so by imposing on myself the constraint that no guest appears multiple times, I am forced out of my comfort zone. The thing is that Eric Oliver, who I thought was great on the podcast, but I never would have chosen him. If, you know, I didn't need podcast guests I thought would be good. If I could just rely on the old regulars and go back to them again and again, the variety and diversity of guests would be smaller. And I mean, maybe I would have had Eric on or not, but that kind of person, I knew nothing about him before I had him on the podcast. I didn't know about his work or whatever, so, you know, I had to think about, would he make a good podcast?

• 2:44:28Sean Carroll?

  A lot of people invite themselves on the podcast, a lot of PR people invite their clients on my podcast, and I usually say no, right? Because there's more invitations than there are slots. So I'm not like, in any sense, short of podcast guests, but the diversity would be much reduced if I had repeat guests, because I'm not going to increase the pace at which I do the podcasts, for sure. So that's the trade-off. And I choose to make it, I choose to, you know, play tennis with the net, as Robert Frost once said. You know, he was asked why he doesn't write free verse, and he liked the structure and he, of the poetry that he wrote, and he compared it to, writing free verse would be playing tennis without a net. The point is, you know, you can play tennis without a net, but you're choosing to challenge yourself by putting the net there.

• 2:45:13Sean Carroll?

  And that actually makes the activity more enjoyable. In some sense, that's what it's like for me, having to do a different guest every single week. And so I like that. Some people are gonna like it or not. I mean, it's also completely possible that years in the future, I'll just get lazy and just have my favorite people on again and again. Colin Johnson says, what is the most advanced possible sci fi tech you can imagine becoming a reality the next 20 years? I'm the worst person to ask this question to. Like, I don't, I don't either have a very great grasp on what the technologies are that are coming. Nor am I any good, or do I ever deceive myself into thinking I'm any good at making predictions about time scales for things happening?

• 2:45:55Sean Carroll?

  That's just not, I don't think anyone is any good at it, but I know that I'm no good at it. So that gives me a little bit of a, of a benefit. You know, I think that the obvious thing, there's lots of obvious things. AI is already here in some sense. We can argue whether AI is really AI or not, whether LLMs are really AI. But certainly it is a transformative technology that is going to have a big impact. I think embodying AI in robot like things will be a big deal. I think it's bizarre to me that there's so much effort placed in humanoid shaped robots. Like, there's just no reason to think that's the best possible shape for a robot. But okay, people like it, you know, all right, go nuts. It's, I don't, it's your money.

• 2:46:38Sean Carroll?

  I still think that a lot of medical advances and neurological neuroscience advances are going to be super important. So I can absolutely imagine that in the next 20 years, we'll have workable neural implants. Where we can talk to the computers directly from our brains, one way or the other. And again, like I said, I'm not any good at this, so I could be completely wrong about that, and that would, is absolutely allowed. Gene editing, synthetic biology, things like that, the ability to design new organisms. Or to change the design of ourselves as organisms. I don't think people have dealt with that very much, or really come To terms with that. I think that's going to be super duper important.

• 2:47:20Sean Carroll?

  I think that, you know, space travel is not going to be that different 20 years from now than it is now. I don't think we'll be parking on Mars or anything like that, as we talked about with Kelly and Zach Weider Smith before. But I hope that there is more space travel out there. I don't think computers are going to be, I don't think quantum computers are going to change things. They might have certain killer apps, like Scott Aronson, former Mindscape guest, has been pointing out. They could be cracking classical encryption by then.

• 2:47:52Sean Carroll?

  That has an effect, right? But I don't think it truly changes most of the world. It changes a little tiny part of the world by a lot.

• 2:48:01Sean Carroll?

  But I think that the real benefit of quantum computers is going to be materials research, like basically solving quantum mechanics problems for chemistry and materials and things like that. I don't know what the solutions will teach us, but that could lead to some dramatic new technology. I'm just not an expert, once again. Joshua Hillary says, "Do you think that morality is rational in the decision theory perspective, as in preferences are transitive, etc.?" I think it's up to you. I think that morality is not objectively out there in the world. I think that people develop their own moral systems. And I think that it is a good goal for people to have to develop moral systems that are rational in the decision theory sense.

• 2:48:43Sean Carroll?

  But many people don't. Many people have moral systems that are not rational. You know, what does it mean to not be rational? The transitivity that Joshua refers to is if you prefer A to B and you prefer B to C, you should prefer A to C.

• 2:49:00Sean Carroll?

  Probably usually people do things like that. But there's also like more subtle things, like independence of irrelevant alternatives. If you prefer A plus B to C plus B, then you should prefer A to C. That's not, I'm not sure that everyone has that embedded in their moral calculus all the time. But again, because I don't think it's more, it's objectively out there in the world, it's up to you and the moral framework that you develop and the moral framework that society develops along with you to try to make sure that it's as rational as possible. Jesse Rimmler says, "In a previous AMA, you described a preference for regulated capitalism with redistribution and a strong welfare state.

• 2:49:44Sean Carroll?

  An extension of that vision, already practiced at scale in the Nordic countries, is the socialization of profit through public capital ownership. The state acquires equity states and companies, capturing returns for citizens without directly managing firms. Norway's sovereign wealth fund is the most dramatic example. The Alaska Permanent Fund is a homegrown one. In Norway, publicly owned assets exceed 50% of GDP, Finland is at 30%. My question is, does this kind of public ownership factor into your vision of a well-functioning economy? And if the answer is not for the US, is that because of genuine structural constraints or just political will?" Again, this is something that I'm not a super expert on, so I'm open to be educated about

• 2:50:28Sean Carroll?

  this. I think my vague impression would be that this kind of socialization of profit through public capital ownership is perfectly okay in certain, specific circumstances. I mean, basically, those circumstances where the company that is being owned almost runs itself. I mean, I understand that the theory is the state acquires equity stakes while the companies are still managed privately, but that's a bit of a dance there to make sure that that happens correctly. I mean, in ordinary private corporations, the stakeholders have a lot of say in how the managing gets done.

• 2:51:11Sean Carroll?

  I have very low confidence in the ability of governments to correctly manage companies. Okay? So, this is why I think that there is a role for capitalism. I believe that incentivizing owners of companies to do the things that would lead to success for their companies is a good thing. It's good in certain ways. It's good in doing exactly what it's meant to do, making profit for those companies. Now, whether making profit for those companies is good for society is a separate question. I would like the question of how companies should behave in order to make profit to be left up to the companies.

• 2:51:55Sean Carroll?

  I think that the role of government is to shape the landscape so that the things that the companies do in their self-interest align with the interest of the broader society. So make things illegal to do that literally hurt society. Make things less lucrative to do if there's some reason to do them, but they have deleterious effects and so forth. You know, it's much like, um, there really is an analogy between economics and physics here. The flow of money in a society in some ways can be thought of as an equilibration procedure.

• 2:52:38Sean Carroll?

  You know, if you had to say, if you had two flasks full of liquid and you put a little pipe between them so liquid could flow back and forth. We all know that if you just let it go, the liquid will equilibrate, right? It'll be the same level in both containers. And if you had to ask, what would the liquid do based only on knowing the position and velocity of every molecule of liquid? That would be this enormously complicated question to actually figure out, to do the computation of what would happen to the liquid. And the wonderful thing is you don't need to. You can just say, from the macroscopic point of view,

• 2:53:20Sean Carroll?

  oh yes, it will find the equilibrium where both liquids are at the same height. Markets, when they work, are like that. The calculation that you would need to do to distribute things in the way that is best suited to successful trade and allocation of resources and things like that is just beyond the capacity of most people to do, or maybe any people to do. But the collective behavior does it by the market mechanism, again, when the market is working. So I think that it's best to let the markets solve problems like that. What should be the price of your goods?

• 2:54:04Sean Carroll?

  How much should you put into R and D? How much should you invest in new technologies or whatever? And let the government set the rules for what the constraints are. You know, you need to be able to allow your employees to unionize. You need to pay a certain number of taxes or whatever. So use the markets to solve these difficult coordination problems. Use the government to set the landscape in which these coordination problems are solved so that the solution benefits as many people as possible. I suspect that that would involve a minimal, if any, amount of socialization of profit,

• 2:54:46Sean Carroll?

  but I'm willing to be shown otherwise if there are counterexamples. Okay, I'm going to group three questions together. One is from David Wright, saying, "How should a reasonable educated person respond to the growing consensus that we've been visited by extraterrestrial beings and that they walk among us? Given the distances and time scales involved, isn't this so unlikely that it's not worth considering?" Ed Sedstuff says, "If the classic popular conception of a UFO landed on the White House lawn, how would you speculate that it functioned? Would building on any existing physics theories explain it, or would we need something completely new? What features would that new physics theory necessarily require?" And Paul Soldera says, "In the movie and book Hail Mary, the alien civilization has

• 2:55:31Sean Carroll?

  advanced to space travel but hasn't discovered relativity. What are the chances we would have advanced in space travel and science in general without understanding or discovering relativity?" So they're all about extraterrestrials flying around in their spaceships in different ways. David's question goes first because the answer is very straightforward. Yes, it is so unlikely that it is not worth considering. I don't think there is actually a growing consensus that we've been visited by extraterrestrial There's a lot of noise about that in certain circles. And it's kind of sensational enough that people listen to it and pass it around. But there's very little to zero evidence that it happens. As I said before, this pops up all the time.

• 2:56:14Sean Carroll?

  Like, we're always told, "Oh, yes, in the next six months, we're gonna get the final answers." And we never, ever are, because it's not true. The answers aren't there. Or the answer is, "No, this did not happen." So it's not even a matter of distances and time scales. It's just thinking about what you're saying. Like, why in the world would aliens do all the effort to visit us? And by the way, they have to time the visit correctly, right? Like, for most of the history of the Earth, there was not an advanced technological civilization here on Earth to talk to. So either the aliens somehow knew that we were gonna arise at exactly this time, or they've been lurking here for a very long time, just waiting for us to get technologically

• 2:56:59Sean Carroll?

  advanced. Both of those are just absurdly unlikely. And then, you know, there's no possible chance that the aliens are in these tiny spaceships, you know, big enough to land on a lawn. There's no propulsion that would work that way, et cetera, et cetera. And finally, there's no possible scenario under which they are technologically advanced enough to visit us, but clumsy and incompetent enough to crash or let their picture be taken, or whatever. It's not that hard to hide from human-level technology if you have technology that is likely to be a billion years more advanced, okay? So, no, it's just very easy to explain all this away by human beings being silly. That's the explanation.

• 2:57:42Sean Carroll?

  If it did happen, as Ed says, you know, how could that technology work? You know, it wouldn't land on the lawn. That's just not gonna happen, okay?

• 2:57:54Sean Carroll?

  Newton's laws are still true. If you want to travel through space, if you want to propel your spaceship, you need to push something else in the other direction. Now, you could use something like light sails or something like that, that wouldn't leave a lot of fuel behind, that could use, well, interstellar ramjets, use the ambient material in the interstellar medium. So who knows what the technology would be for actually traveling from one star system to another. That's perfectly plausible in the laws of physics, but probably there's technologies we haven't invented yet. One way or the other, you need a lot of propulsion. You need, you know, if you want to travel at any reasonable speed, you need to really push yourself very hard. So it's not going to fit into something 10

• 2:58:38Sean Carroll?

  meters across, or anything like that. Of course, there could be a giant mothership that sends down little baby ships. That's plausible. So that could land on the White House lawn. I shouldn't have been so definitive about that. In terms of could existing physics theories explain it, or we need something completely new, I think the chances that new physics will play a, like beyond the standard model physics, new fundamental physics, would play any important role in interstellar propulsion, etc., are very, very low, for exactly the usual reasons that the laws of physics underlying everyday life are completely understood. There aren't, there isn't any room for new physics that has a dramatic

• 2:59:21Sean Carroll?

  impact on everyday level things. And everyday level things includes, you know, spaceships, honestly, even though we don't bump into spaceships. Now, there's a couple of footnotes there. Of course, there's an enormous amount of room for technology that is novel but based on known physics, right? All of the technologies that are novel that we were just talking about, whether it's AI, or, you know, biohacking, or whatever, this is still based on the standard model of particle physics. So new materials, new propulsion systems, new fuel sources, still within the standard model of particle physics, 100% possible, and in fact, very, very likely, and something that literally travels across interstellar distances. The one loophole there is gravity.

• 3:00:06Sean Carroll?

  You know Einstein's General Theory of Relativity works very well, but there's aspects of general relativity that remain at the edge of our understanding, whether it's warp drives, or wormholes, or things like that. I'm skeptical of all of them as practical future technologies, so I don't think that they will be involved, but it's possible. The possibility is there. Finally, for Paul's question, could you imagine an alien civilization that hadn't discovered relativity? I think that's extremely unlikely. You know, it's certainly possible to imagine alternative trajectories for the history of science and the history of physics in terms of which discoveries come first. But look, why did we discover relativity? Well, because we discovered electromagnetism.

• 3:00:51Sean Carroll?

  Maxwell and Faraday and all those people figured out electromagnetism in the mid-19th century. And, you know, within 50 years, we knew about relativity, because relativity is based on the symmetry group of electromagnetism. That's really what you needed to figure out, and the fact that there's no ether that you could detect. I can't imagine any super-advanced civilization not understanding electromagnetism. And honestly, if you understand electromagnetism, and you're not, you know, I don't know, held back for some reason, if you're relatively intelligent and you understand E and M, you're going to discover relativity pretty quickly. So I think that even though the details might be very different, by the time you're building spaceships, you have discovered relativity.

• 3:01:35Sean Carroll?

  Okay, Jackson Bernatzez says, "Do you think consciousness was a trait that natural selection optimized for, or something that arose by chance along with intelligence? If it was selected for, what advantages might it provide versus an unconscious but intelligent system?" So, of course, natural selection technically doesn't optimize for things. It takes advantage of things that stumble across. I mean, the difference is, the whole point of natural selection is that it's not forward-looking. Okay, and natural selection does not go, "Oh, this new problem is going to pop up. I had better evolve something to be prepared for it." So that's what optimized. Is all about.

• 3:02:17Sean Carroll?

  Natural selection does provide a mechanism for adaptation to existing circumstances. Okay, so that's probably what you mean. I think it's probably just a slight wording issue there. So I think that the question is, is consciousness adaptive? Or is it more like a spandrel? Does it just come along for other reasons? I think it's kind of, again, not an expert on this one. But it seems not even adaptive, but almost inevitable to me. Right? Going back to the conversation we had with Malcolm MacIver years ago here on the podcast. And as well as other people who've talked about the origin of different aspects of intelligence.

• 3:03:01Sean Carroll?

  We talked to Patricia Churchland.

• 3:03:05Sean Carroll?

  Other people about the fact that when you think about the evolution of thinking broadly construed. So including puzzle solving aspects, but also self-awareness, consciousness, experience aspects. They do kind of go hand in hand. You can absolutely have some thought processes without consciousness. But at some point, you're approaching more and more complicated problems in the world, looking for more and more sophisticated ways to adapt to them. MacIver's point is that when fish climb onto land, they now have more time to think about what is happening.

• 3:03:43Sean Carroll?

  And this leads to the ability to imagine different hypothetical scenarios in the future. We talked to Adam Bulley about mental time travel and the role that that played in the evolution of consciousness. So I think that it's not that consciousness itself is adapted, adaptive, but rather that the various capacities that lead directly into consciousness are individually adaptive. And therefore consciousness, I predict, would just go along for the ride most of the time under the right circumstances. Right? I mean, again, some, you know, bacteria do fine. They thrive quite well without any consciousness at all. But in the right circumstances, when the opportunity is there,

• 3:04:29Sean Carroll?

  consciousness will come along for the ride when aspects of it are being selected for, for adaptive reasons.

• 3:04:36Sean Carroll?

  Ari Moody says, "Not having been alive during the Apollo program, I found myself deeply moved by Artemis II and seeing the moon in such a different way. I grant that 90% of the purpose for it was geopolitical, but a bit was also curiosity, exploration, achieving something purposeful. What are your takeaways from the mission and what is the bigger impact you hope it carries?" You know, there's always a debate among scientists, or at least an ongoing discourse about scientists, among scientists with respect to crude spaceflight. Crude, C-R-E-W-E-D, not C-R-U-D. That is to say, putting people in space. Because it is super duper expensive and pretty darn dangerous as well, you know?

• 3:05:21Sean Carroll?

  I mean, it's a dangerous occupation, being an astronaut. And it's very expensive, and there is some scientific return for it, but it is minimal per dollar. You get a lot more scientific return from sending robots and satellites into space than you do sending human beings into space. But, so, but that's okay. There's more to life than getting the biggest scientific bang per buck, right? There is something inspirational and human-centered and explorative about sending people into space and seeing how we can adapt to these new environments and how we can behave and what we can learn about them. It's very, very tiny. Like, what we've done so far is just very tiny, right?

• 3:06:05Sean Carroll?

  We've sent people to the moon for brief periods of time. We've just sent people flying around the moon, not even landing on it, with Artemis II. We've sent people to the International Space Station for extended periods. And what we found is that it really messes you up, being in zero gravity for that long. And there's real, real questions about whether human beings could even survive for extended periods in the gravitational field of places like the moon or Mars, which is a sixth and a third of the Earth, respectively. Even if you could get there and solve all the problems of living and breathing and surviving... Even the lack of gravity might get you in trouble.

• 3:06:48Sean Carroll?

  Of course, you could build a fake gravitational field by spinning things around. But at some point, you're asking like, why am I bothering? And then what are the dangers of this mechanism failing, et cetera? So, but, but still, and yet, I believe that it's worth seeing what we can do, right? Trying, being curious, achieving something purposeful, like you say. I'm a believer in that too. So really, I think that all of these kinds of things are worth doing. There's very real decisions to be made about how much money should be spent doing different things. We are currently in a position where we do not make those decisions on rational bases. But maybe we can get back to that kind of decision-making process.

• 3:07:32Sean Carroll?

  And then hopefully we move things forward in that direction. It is very much inspirational, very much something that human beings should be trying to do. Peter Bamber says, "I've heard that if a spaceship could be pushed up to close to the speed of light, then the crew would be able to make journeys of hundreds of light years well within a human lifetime, even though generations of human lives would have passed back home. This appears to mean that generation starships, as depicted in science fiction novels, are unnecessary to reach the stars, though they can make for good stories. Is this correct?" Well, we don't know what the right technology is going to be, you know? We need to build a big spaceship where many people can live for some period of time.

• 3:08:14Sean Carroll?

  We need to accelerate it to some speed, I don't know what that speed is, in order to get to these stars that are light years away. So the question is, what will come first? The ability to build a big spaceship that can have people live for hundreds of years, but moves relatively slowly? Or the ability to build a spaceship where maybe it's not big enough for people to live hundreds of years, but it doesn't need to be because it moves very fast and the human lifetime is enough? Who knows? I don't know. Honestly, I think that suspended animation or putting people to sleep is also a very viable possibility. And for that matter, extending human lifespans is a very viable possibility.

• 3:08:56Sean Carroll?

  So I see no, I mean, I see, yeah, no obstacles that are insuperable to doing interstellar travel. I don't know which way it will actually happen. That depends on details that none of us know the answers to.

• 3:09:11Sean Carroll?

  Stephen Reed says, "I recently watched your debate with Philip Goff from a few years back and wanted to know your thoughts on the following from the physicalist perspective. Do you believe it will ever be possible to know with a high degree of certainty if a non-human mind or entity is actually conscious and be able to have insight into the nature of that experience? How would it ever be possible to design an experiment, even in theory, to determine the answer to this? If our minds are unable to generate these experiences, won't our knowledge about these experiences and whether or not they really exist be necessarily limited no matter how clever an experiment we design?" I don't think any of the words "necessarily" are right in this question. I think it's a legitimately difficult question, and I have prodded my philosopher friends

• 3:09:56Sean Carroll?

  to be better at understanding what consciousness is so that we will be better able to judge whether an artificial being is conscious or not by the correct standards. I suspect very strongly that consciousness is a lot like life in the sense that it's not one thing, it's many different aspects that come together in a certain way in human beings and might very well come together in different ways in other kinds of creatures. Remember, we had Stuart Bartlett on the podcast years ago, and we talked about what he and Michael Wong called "lyfe," L-Y-F-E. I don't like the name, but I like the idea. The idea is that there's a bunch of things.

• 3:10:40Sean Carroll?

  I think they had seven different aspects that come together in life as we know it, but you could easily imagine life as we don't know it involving some of those aspects but not others. I suspect that consciousness is the same way. I suspect that we're going to be talking about multiple different ingredients that go into consciousness, and an artificial being might have some of them but not others. And we're going to have to decide, how do we know what are the implications of these aspects being there or not? Of course, the "how we know" question is always a very good one because there is, I mean, like you say, we can't introspect, right? We can't actually know what...

• 3:11:20Sean Carroll?

  What the AI is thinking, we can only know what the AI, well, we can know, the nice thing about the AI is that we can know what it's thinking in the sense that we can know what's going on inside the neural network that it's based on, right? In principle, we can tear it apart and look at the electrons flowing from one gate to another in whatever detail we want. In practice, that's super hard. And of course, we also can't necessarily interpret it in any easy way. But in principle, we can do it and it's a little bit more ethical to do that than to do that to a human being. But that doesn't tell us what it's feeling. Just like when we were talking to Bing Brunton recently, knowing the connectome doesn't tell you the thoughts that are going on inside a regular old biological organism.

• 3:12:06Sean Carroll?

  So we will have to be more clever, but I'm not at all worried that we can't be more clever about deciding, you know, having some decision procedure when the external behavior of the AI or some artificial agent does act in certain ways, then we will, for all intents and purposes, declare it to be conscious and/or possessing certain aspects of consciousness that would lead us to want to give it some rights and responsibilities in certain ways. Again, I think that's possible. I don't think we're anywhere close to doing it. I also think that the sort of diagnostic question is possible, but I really don't have great ideas about how to do it.

• 3:12:51Sean Carroll?

  I think that maybe I'm being way too optimistic about our ability to eventually do it. Richard Cashdan says, "You often talk about the many worlds interpretation of quantum mechanics. From a purely personal, non-scientific perspective, do you find the idea of branching selves provides you with any sense of optimistic nihilism regarding your own life choices? Or do you view the existence of other branches as mathematically true, but practically irrelevant to the human experience?" So I do know, you know, just for talking to some of the old time listeners to Mindscape, I intentionally pick some questions from people who have not gone through every single episode, right? I want to be welcoming to the newer people. So we'll sometimes get

• 3:13:33Sean Carroll?

  questions that I have answered before, or questions that, you know, are pretty like, "Oh, this, have you heard of this thing that I talked about a lot before?" Richards is not quite that, but I think it is getting at a relatively forefront issue in thinking about many worlds. Yes, I do talk about the many worlds interpretation all the time. I don't think it affects my view of big existential questions at all. I mean, you have to give an alternative. You have to say like, "As compared to what?" Right? Many Worlds says that there is a quantum state that evolves deterministically, and it describes

• 3:14:14Sean Carroll?

  multiple parallel realities, including things that are sharing a past with me. Human beings, people, agents, that are not me, but share a past with me, much as I said, like identical twins, okay? The alternative is maybe, well, one alternative is there's a single world that evolves in a truly stochastic way. So there's only one person that I can, that I will ever be. There's a sort of unified trajectory from my past to my future. It's just that we can't deterministically predict what the physics underlying that person will actually do. I don't see why one of those is any different than the other in terms

• 3:14:56Sean Carroll?

  of either how I think about purpose and meaningfulness in the world in some philosophical sense, nor how I should practically act in the world because of this. And, you know, as I've said many times,

• 3:15:12Sean Carroll?

  The existence, the reality of living in the many worlds view of the world is that you as an agent see the world as behaving according to the rules of textbook quantum mechanics. That is to say, when you measure something, you can't predict what the outcome will be other than predicting the probability using the Born rule, etc. So it doesn't affect my feeling of specialness or lack of feeling of specialness or anything like that. My life choices are exactly the same as they would be, one way or the other.

• 3:15:48Sean Carroll?

  Jamie says, "I'm interested in the idea of free parameters. I remember reading Lee Smolin say as a critique that AdS, CFT and string theory both posit extra symmetries because that gives more free parameters and more room to play. You often say how hard it is to make new theories or models because of constraints imposed by known facts and maths or by lack of free parameters. If there are no free parameters, there's no room for anything new to fit. Are free parameters epistemic or ontological? Are there no free parameters in the universe as a whole? Is this the same as the question of brute facts?" I mean, of course, we don't know the answer once and for all to any of these questions. These are questions that are at a very fundamental level of treating reality. So I'll interpret the question as, you know,

• 3:16:32Sean Carroll?

  does string theory or some other plausible alternative to string theory make free parameters or posit that free parameters exist as brute facts? Or do they invent them? Or is there some other ontological status for them? I'm not sure what Lee Smolin actually said. If he said that string theorists posit extra symmetries because that gives them more free parameters and more room to play, he's just 100% wrong. That is absolutely not what string theorists do, and he's doing it for rhetorical reasons, not for honest scientific reasons. String theory is in a weird situation where the theory, string theory as a theory, has no free parameters. You will often read that, string theorists boast about that, right?

• 3:17:16Sean Carroll?

  And there was an original hope that this lack of any free parameters meant that they could uniquely predict the physics of our observed world. What turns out to be the case is that even though there are no free parameters in the theory, the set of, the theory is a set of differential equations or something like that, right? As we were talking about before. Just like Newton's laws are a set of differential equations. And just like Newton's laws, let's take Newton's laws for planets orbiting the sun, okay? The laws are very definitive, and there's one free parameter in them, Newton's constant of gravitation. But there are many, many solutions. There's circular orbits at every radius, there are elliptical orbits of all sorts,

• 3:17:59Sean Carroll?

  elliptical orbits of all different eccentricities and different orientations, and there's an infinite number, literally, of solutions to the equations. String theory has zero free parameters, but an infinite number of solutions to the equations. This is completely unsurprising, in some sense. The surprising and depressing thing is that the solutions in string theory can take the form of entirely different-looking, low-energy laws of physics. By low energy, I mean, you know, at high energies, if you have a Planck-scale particle accelerator, maybe you're seeing the intrinsic stringiness of the world. But at low energies, you're seeing the effects of some particular solution to the equations,

• 3:18:42Sean Carroll?

  which unlike planets moving around the sun, the solutions to the equation define what spacetime is, and the fields and particles moving within it. That's a new thing in string theory, you didn't have in Newtonian mechanics. So, there's one solution of string theory that might look like three-dimensional spacetime, three-dimensional space, one-dimensional time, so four-dimensional spacetime, with the particles and fields of the standard model of particle physics. There are other solutions that look almost exactly the same, but with different values for the parameters of the standard model: the mass of the electron, the coupling constant of electromagnetism, and so forth. The mass of the Higgs boson, the electroweak hierarchy, all those numbers might be different from solution to solution.

• 3:19:27Sean Carroll?

  Also different from solution to solution are what particles there are, what forces there are, what symmetries there are, the number of dimensions of space can be different from solution to solution. And when it comes to predicting low-energy physics, it turns out that what matters is what solution to the equations you have, not just the equations themselves. So for all intents and purposes, string theory acts as if there are a lot of free parameters. There are a lot of parameters that tell you what solution you're in, okay? Now, string theorists don't put them in. They don't want them to be there. But you don't have a choice, that's the thing. When you have a set of equations and you're trying to solve them,

• 3:20:10Sean Carroll?

  you can't just ad hocly say, "Well, I want this solution, even though it doesn't actually fit into the equations. I just like it better. It gives me more freedom." You're not allowed to do that, and string theorists don't do that. They have found that their equations allow for all these solutions, and they're trying to deal with them. That's the string theory landscape problem. And other theories of fundamental physics might have the same problem or not. A lot of them, you know, it's certainly worth trying to get away from this problem by just starting with three dimensions of space, one dimension of time, gravity as we know it, et cetera, and trying to work from there rather than trying to get some theory that fits everything and then map it down to the world in which we know.

• 3:20:54Sean Carroll?

  That, the start in the real world is much closer to the philosophy of loop quantum gravity. As I've described elsewhere, string theorists have good technical, mathematical reasons to think that loop quantum gravity doesn't work, that no theory of quantum gravity that treats gravity as separate from the other forces of nature can ever work, which is why they're so invested in string theory. But we'll have to see who's right and who's wrong about that. So the answer is, we don't know. What are the free parameters? What are the brute facts? That's something, as is often the case in physics or in science, it's not a direct line from here is the way the world works, let's make predictions. It's a back-and-forth between, "Well, I think that the world works this way a little bit.

• 3:21:39Sean Carroll?

  What would that predict? Oh, okay, that would predict this wrong thing, but I can go back and tweak my way in." And it's a give-and-take between the theories and the facts. And our answer to the question of what are the brute facts and what are inevitable features of the theory, we'll have to wait until we understand things better.

• 3:21:58Sean Carroll?

  Jesse Fox says, "I know our intuitive pictures can be misleading at the fundamental level of physics, so I'm curious what your own thinking is like in practice. When you're reasoning about the quantum world, fields, branching universes, etc., does your mind generate any kind of imagery at all, even as a rough intuition, or is it entirely abstract?" Yeah, there's absolutely imagery there. You know, physicists, and also even more noticeably, mathematicians, come in different varieties. Some physicists like equations, they don't like pictures. Some physicists like pictures, they don't like equations. Some physicists even like words, believe it or not. And I'm on the pictures side of things. I see things

• 3:22:39Sean Carroll?

  through pictures more than anything else. So, look, when I talk about quantum fields, I will confess, there is in my mind, a little picture of a two-dimensional surface with a vibrating field on top of it. But the thing is, the crucially, crucially important thing is, I know that that doesn't matter. It's not important. It's not what is actually happening. At the end of the day, the physics of quantum mechanics, or quantum field theory, or string theory, whatever, is not visualizable in any accurate sense. Maybe it helps you to sort of make a proposal that you can then test by thinking about the equations underlying

• 3:23:20Sean Carroll?

  what's happening. But it's the equations that matter, at the end of the day. So if you find yourself faced with a situation where you don't have any visualization or any imagery, that's okay. It is the equations that matter. Other times, the imagery can be very, very helpful. One of the very first papers I ever wrote was on the difficulty in making time machines close time-like curves in two plus one-dimensional gravity. And I was able to come up with an argument why it wasn't possible, based on drawing pictures, drawing spacetime diagrams of anti-de Sitter space, of all things. And it was an

• 3:24:00Sean Carroll?

  argument that could only have been made by drawing the pictures. Like, there's no way you would have come up with that argument just by thinking about the equations. In principle, the equations are what you use to check whether your argument is right or wrong, but the equations are very, the pictures are very helpful in getting there. And so, I'm a believer in the pictures, but I don't reify them to what's really going on. David P. Reichert says, "Asking as someone who has only recently started listening to your podcasts, would you be up for summarizing what your views on AGI are, in particular regarding its near-future capabilities and impact, or lack thereof, and how you came to those views?" Yeah, you know, I mentioned before about quantum computing, which is a different thing,

• 3:24:45Sean Carroll?

  but there's an analogy here. Quantum computers, in some sense, have an enormously larger power than classical computers do, but they also have limitations. You just can't make as many qubits as you can make bits, especially keeping them talking to each other without decohering. So, we can, in principle, imagine all sorts of things that quantum computers are good at, but when it comes to practice, when it comes to what they will actually be good at, there might be like a small, very well-defined subset of problems where quantum computers are absolutely dominant, and other problems that we would like them to be helpful for, but they're really not. So I think that we're in that stage with AI right now, where people are just doing

• 3:25:29Sean Carroll?

  a bad job, in my personal opinion, about matching the capacities of the technology to the needs that human beings actually have. You've seen these surveys out there, where young people especially, who you might think are the easiest to adapt to new technologies, etc., are incredibly turned off by the ubiquity of AI technologies in their lives, when they didn't ask for it, okay? And it's all very, very, very distorted by money. People want to make money off of these things, which is, I just confessed above, I'm in favor of market forces in the right circumstances, but market forces aren't a very good way of finding truth.

• 3:26:13Sean Carroll?

  They're a very good way of finding prices. Those are two very different things. So, there are aspects of the financial markets, in particular, where truth is not the way to make money. And so, hyping your technology, forcing it into everything, and even sometimes, like innocently, some companies might think, they're not trying to force things on people, but they honestly think that in the future, AI will be ubiquitous, so trying to figure out how to get it into their products sooner rather than later might be the right thing to do. And also, and I think that's distorting the whole discourse about AI.

• 3:26:52Sean Carroll?

  The other thing, of course, as I mentioned before, is that large language models, which are the currently dominant technology in much of what we think of as AI, are purpose-built to sound human. And this, people like to anthropomorphize things. This is not a new discovery from AI. People love anthropomorphizing things. So when you give them a technology that, whose entire purpose is to be anthropomorphized, they're gonna do it. So I think it's just very important to realize that what LLMs are good at is different than what human beings are good at. And some of the people who are very, very smart and very, very advanced in knowing about

• 3:27:34Sean Carroll?

  how the computer programs work, make this mistake, in my view, of treating them as, you know, "Well, they're more intelligent than human beings now." And they haven't figured out what the word "intelligence" means in that sentence. You know, as we, as we saw in the, in the discourse, in the question above from DMI about the principle of least action, where you ask an LLM, and what is the LLM gonna do? It's gonna look at what people have talked about before, okay? And it's gonna try to figure out what would fit into this discourse. And it, it says something that is not the most important thing to say, because it wasn't, that wasn't the thing that people generally talk about. You know, when you go online these days, especially on X, which used to be Twitter,

• 3:28:19Sean Carroll?

  a lot of the accounts that are replying to things are bots run by AI. And I recently saw a post, because I follow the Philadelphia 76ers, was a post about Paul George and how well he was playing. And there were all these responses, saying, "Yes, Tyrese Maxey is playing great." And you're like, "Why would they say that? That was not what the post was about." Of course, it's a bot, and in recent months, there have been a lot more discourse on how well Tyrese Maxey is playing than Paul George. So the bots are just used to that, and they don't even pay attention, because attention is not a capacity that they have in this predic- I mean, they're not very advanced bots, you can always fix that. So anyway, I think that the near future capabilities and impact are

• 3:29:02Sean Carroll?

  Are very, very big. If we use LLMs appropriately in the right circumstances, they can be hugely transformative, and I suspect that they will be. I worry that they're not being used in the right ways or conceptualized in the right ways, and that could lead to dangers in all sorts of ways, as we already have seen and as we will continue to see.

• 3:29:26Sean Carroll?

  Bob Ritchie says, "In the last century, many prominent physicists suffered from depression, paranoia, substance abuse, and mental breakdown. More than a few committed suicide. What is your take on this tendency, and does it continue with today's scientific geniuses?" I don't know whether that's even a true thing. There are selection effects here, right? There's a small number of statistics here, and a few famous examples might very well bias our reasoning about it. So I would need to see a careful analysis of the relative rate of things like depression and paranoia among prominent physicists versus the general public, to be honest. But it's possible that there is a correlation there. I mean, not because being a prominent physicist leads you to depression or paranoia, but there could

• 3:30:11Sean Carroll?

  be common causes of both genius in physics and some other kind of disability or instability that could lead you to mental breakdowns, etc. So I'm by no means convinced that it's a real tendency, but I'm open to the possibility that it is. I would have to see a careful analysis to be convinced one way or the other. Tucker Hyatt says, "In Project Hail Mary, author Andy Weir compares star-eating astrophage to a nuclear reactor for its ability to store and release enormous amounts of energy. Do you see any way that nuclear energy and the use of the strong nuclear force might evolve in a biological entity?"

• 3:30:53Sean Carroll?

  I'm gonna get myself in trouble here and say, "No, I do not see such a way." I say I'm gonna get myself in trouble here because what do I know? And this is absolutely a case where there might be some clever path to doing something like that that I just don't see. But- Natural selection that drives evolution works in a very specific way. It's not just imagine the best possible thing and make it work, right? As you all know, birds fly, airplanes fly, but they fly in very different ways. And you know, trying to do what birds do, but in an airplane turns out not to work very well. Because when you have the ability to design something and you have the ability to use

• 3:31:37Sean Carroll?

  technology and bend metal to your will and so forth. The optimal way to fly has to do with jet fuel or propellers or things like that, not with flapping your wings. Evolution can find the solution where you do flap your wings because you can imagine building that up by small incremental improvements. In my book, The Big Picture, I talk about, there was a famous argument against evolution, which said, if you think about a mousetrap. The claim was a mousetrap is irreducibly complex. That is to say, it's complex, but it's complex in such a way that if you removed any one aspect of it, it would just fail. So it's either existing or not existing.

• 3:32:22Sean Carroll?

  You can't build it up piece by piece. And the argument was that biological entities are similar. Therefore, evolution can't be right. That was the argument. So that's not right. And in fact, multiple people pointed out ways that you could build up a mousetrap of the kind that we normally build today in a series of successively improved versions of catching the mouse. So you could biologically evolve a mousetrap. But maybe you can't biologically evolve a jet engine. That's completely plausible to me. Very few, if any, I don't think any organisms here on land use wheels, right? Cars and motorcycles and bikes and so forth use wheels. They're very, very effective, but it's hard to evolve them.

• 3:33:07Sean Carroll?

  So I think that nuclear power is like that, like the kinds of things that are necessary to even imagine using nuclear energy. I can't foresee a path of gradually improving technologies that would end up with a biological organism powered by nuclear energy. I could be wrong. This could just be a failure of my imagination.

• 3:33:33Sean Carroll?

  Robert Kitsey asks a priority question. "How variously coherent do you find a unified reading in which the quantum and classical are not separate ontological domains, but coarse-grained organizational regimes of one emergent temporally manifested reality, such that classical matter is the semi-classical conserved structurally bound pointer-selected manifestation of a constrained, superposed deck of degrees of freedom, and gravitation is understood as the intrinsic coupling of that organized energy structure to the materially analogous, energetically responsive, intrinsic structure of co-emergent spacetime itself, so that reality is one world temporarily manifested from admissible possibilities rather than many worlds equally realized?"

• 3:34:18Sean Carroll?

  Well, I think there's two things. One is the unified reading in which the quantum and classical are not separate ontological domains, etc., I think is more or less what we have in ordinary quantum mechanics, except that rather than saying quantum and classical exist simultaneously and there's some common thing behind them, we just say the quantum description is the common thing, is the fundamental thing, and there's a limit. There is a certain regime in which things look classical. Otherwise, all of the words make perfect sense and seem to fit together. Except, at the very end, you say "so that reality is one world temporarily manifested, blah blah blah," rather than "many worlds equally realized."

• 3:35:03Sean Carroll?

  I don't see how that follows at all. I mean, as I pointed out, the many worlds of quantum mechanics follow from the Schrodinger equation. And you can't just throw around words and say "I don't believe in the many worlds." If you don't believe in the many worlds, then you don't believe in the Schrodinger equation. Either you don't believe that the thing the Schrodinger equation describes...

• 3:35:27Sean Carroll?

  Is reality, which is fine, some people don't believe that. Or you believe that reality obeys the Schrodinger equation sometimes and not others. And people also believe that. But you have to be specific about that, right? And as many, many physicists have found through the years, being specific about that is harder than it looks. In order to fit all of the data that we already know the quantum mechanics describes, and yet alter it in some way to get rid of the other worlds, turns out to be really, really difficult. Which is why there's only a couple of active possibilities that people take seriously. Anonymous says, coarse-graining to the level of sociology.

• 3:36:08Sean Carroll?

  How much of someone like sophomore Sean Carroll's chances of becoming a physics professor are fixed versus random fortune? Like, if you hadn't randomly chosen to write papers about a positive cosmological constant, would you have been screwed? I think that there's a lot of contingency in human lives. You know, my own career as an academic has bounced back and forth to highs and lows in various ways. And one could certainly imagine small changes here and there, either making it much more successful or much less successful, right? It is true, I wrote papers on the cosmological constant and dark energy before it was discovered. That was not random. I actually, you know, cared about those issues and thought they were interesting, right?

• 3:36:50Sean Carroll?

  So it's not quite just a roll of the dice there. There's some purposefulness to it. There were also cases where I had an idea and I didn't follow up on it. And other people did and became famous and very successful because of it. And if I had just been slightly smarter about following up on that idea, or had more time, or was nudged by some random remark, who knows that I could have actually had more success as a theoretical physicist? That's life, you know, that's how things go. Is there some way of calculating the relative probability of different things? I truly don't know. If I hadn't written my general relativity textbook,

• 3:37:33Sean Carroll?

  it's much more probable that I would have gotten tenure at Chicago and I might still be at Chicago. Or I might have been stolen away by some other place. Or I might have gotten tired of physics and quit. Like, all of these are possible. So I think that all, and I tell people this when they're young students or post-docs or whatever.

• 3:37:53Sean Carroll?

  There's no strategy that is guaranteed in a scientific career, probably much like other careers, although I'm less familiar with them, to lead to success or failure, okay? All you do are change the probabilities. You can increase your chances of getting a job by behaving in certain ways, decrease them in other ways. Maybe some of the ways that you could behave differently that would increase your chances of success are dislikeable to you for other reasons, and therefore you don't want to do them. Or maybe things that would lower your chances of getting a job are so important to you, you're gonna do them anyway. That's fine. I just want everyone to know, to be cognizant of when they are increasing their chances or decreasing their chances.

• 3:38:38Sean Carroll?

  That's all any of us can do in this wacky, unpredictable world in which we live.

• 3:38:43Sean Carroll?

  Paulina Vino says, "Are you a non-cognitivist? Would you agree with the statement that X is morally wrong within your constructed moral framework is essentially a dressed-up version of 'I don't like X', which you may have convinced yourself of by reasoning according to your moral framework?" So I don't like to be too definitive about these labels, because when people start talking about the labels on different moral theories, sometimes they have implications of those labels in the back of their minds that I don't necessarily have, so it's not the clearest method of communication.

• 3:39:17Sean Carroll?

  So to me, non-cognitivism comes from the idea that moral statements are not propositions. That's usually how it's phrased. So a proposition is like 2 plus 2 equals 4, or F equals MA, or for that matter, 2 plus 2 equals 5, right? You know, propositions could be true and false. And so, it's always seemed weird to me that non-cognitivism is presented as the statement that moral claims are not propositions. I would say that moral claims don't map onto anything objectively true about the world. I'm not a moral realist or a moral objectivist like that. I guess that statement was closer to moral realism. The fact that moral, the idea, the claim that moral statements are true.

• 3:40:02Sean Carroll?

  Sort of out there in the world to be tested. You can be objective about morality, but not realist by saying that, yes, we all make up morality, but there's a uniquely correct way to do it. And we make, we should all make up the same morality. That would be morally objectivist. So I think I'm effectively a non-cognitivist in that I don't think that statements of the form X is morally wrong are true or false in the same way that objective facts about the physical world or the logical mathematical world are true or false. Okay. They're more judgment calls and different people can feel differently about them. They're more like,

• 3:40:42Sean Carroll?

  what is your prior on the Philadelphia 76ers winning the NBA championship, right? Different people are allowed to have different priors, just like they're allowed to have different moral judgments. I still would call it a proposition, but maybe the people have ideas about what counts as a proposition that I don't necessarily have in the back of my own mind. Kristof Randomski says, how much are scientists open to popularizing their science? How far?

• 3:41:11Sean Carroll?

  How far should they go with simplifying it for the sake of reaching a wider audience? This question occurred to me, Kristoff continues. During your talk with Daniel Harlow, I just couldn't shake off an impression that he is suffering when forced to talk in popular science language. He got his vitals back when you both spoke like scientists normally do during that last 15 minutes of the show. I remember Richard Dawkins in one of his books saying that we shouldn't run infantile scientific fair shows. Cheap spectacles underlying the coolness of science because science is hard and implying otherwise is misleading and cheap. Shallow shows eventually get most people disappointed with science after they realize that it's much more difficult. You're undoubtedly in the top league of scientists with skills at explaining science, but I'm not sure if all researchers are that positive about it.

• 3:41:57Sean Carroll?

  So I don't think it's quite correct to say that Daniel was suffering when he was forced to talk in popular science language. I think there's a much more innocent explanation, namely that he was trying to do a good job at it, and he doesn't do it that often, right? Which I think is completely fine. I mean, he understands the importance of doing it, but he's a young guy who has been doing amazing, high-level research in theoretical physics, and he's been concentrating on that. So he doesn't just spend a lot of time taking his high-level physics research and translating it into terms that are understandable to people who don't have the background in jargon or concepts or whatever. And he was trying to be careful about like, alright, what am I allowed to say? What am I not allowed

• 3:42:40Sean Carroll?

  to say? What makes sense? How can I translate things, right? Because it's hard. It's a skill to take these very difficult conceptions in science and turn them into something understandable. It's not just automatic. Even though everyone who is a high-level research scientist was at one point in their youth not a high-level research scientist, and therefore, in principle, you might think they should know what it's like, right? In fact, you forget. You have embedded certain ideas and certain ways of thinking and talking so deeply in how you go through the world that it's really hard to put yourself back in that state of mind where you don't have all of this background. And even if you could

• 3:43:24Sean Carroll?

  put yourself in that state of mind, there's a question of translation. How do you speak ordinary language in a way that both is fair and honest and respectful of the underlying science, but gets some truth across to the general public? I mean, I'm always very happy to admit that there are levels of understanding, right? You can always understand something about what is going on in physics without any math or physics background whatsoever. But you're not going to understand it as well as if you have the math and physics background and really dig into the details. This is just like, true for every different field that has, you know, expertise involved in it.

• 3:44:09Sean Carroll?

  To answer the, sorry, that was all background. To answer the actual question, some scientists like doing science communication and popularizing and are good at it. Some, interestingly, like it and are not good at it, that's also true. Some don't like doing it themselves, but appreciate the importance that it be done. And some give lip service to liking it, but don't really like it. They kind of disdain it and they look down upon people who do it. And some just don't like it. Some people think it's a waste of time and they shouldn't be bothered. Okay, so you get the whole spectrum of possibilities.

• 3:44:47Sean Carroll?

  I think that the median scientist does appreciate the importance of doing some outreach to a broad public. They don't spend much time doing it themselves. And also, they don't always put their money where their mouth is in terms of actually supporting the people who do it, because they're devoted to doing the science and the research. And that's what they've been trained to do their whole lives, so that's not completely surprising. Jan M. says, "The origin of COVID-19 is fiercely debated between proponents of a zoonotic versus a lab-leak origin of the SARS-CoV-2 virus. Do you have an opinion in this issue and any thoughts why the US government backs the lab-leak theory?"

• 3:45:29Sean Carroll?

  So, no, I don't have any opinion on this issue. My feeling, from not being an expert, is that most of the experts that I take seriously are on the natural side of the origin issue, rather than a artificial lab-leak origin. But there is debate, and that's good. There should be debate. My one strong feeling is that the debate should be a scientific one, carried out by experts, not a political one. And I think that a huge amount of the discourse about this issue is taken on by politicians and pundits and podcasters, rather than expert scientists. And then it becomes very emotionally charged and symbolic and tribal, right?

• 3:46:11Sean Carroll?

  And so, the easiest part of your question is why the US government backs the lab-leak theory? It's tribal. People have decided that if you're Conservative and Republican, then COVID was not a big deal. It was a plot. There was malfeasance by the CDC and Tony Fauci and all that stuff. And that goes hand in hand with a lab leak theory. It has nothing to do with the merits of the case. So I'm open to whatever the merits of the case are. I'm not especially interested. I don't think it matters that much. People care a lot for reasons that escape me a little bit. But I want the actual discourse to be done by scientists who are trying to find the truth, not political, cultural figures who are trying to make a cultural or political point.

• 3:46:58Sean Carroll?

  Jake Turin says, "After extensive debate, the American Ornithological Society has decided that it is inappropriate to name bird species after people. Many of the honorees were dead white European males. Accordingly, all such common names are being changed. It occurs to me that many physics terms, units, laws, equations, similarly honor dead white European males." Two questions. What do you think about the AOS policy, American Ornithological Society? And has there been any similar debate in the physics community? So I think it's a tough question. Honestly, I think this is a legitimate one where there are good points on both sides. I mean, I have sort of provisionally taken the attitude that

• 3:47:42Sean Carroll?

  names are labels. Names are not history lessons, right? So names don't actually tell you what happened. I mean, there's a, there's a cutesy maxim that says that things are named after not the first person to discover them, but the last person to discover them, right? Like if there are people who discovered them before others were willing to listen, those people were ignored. And finally, when the time was right and someone rediscovered it, that person gets their name on it. So there's always historical inaccuracies in the naming of things. And I think it's a little quixotic and impossible to correct the namings so that they accurately reflect the historical reality. Because historical reality is a mess and it's also hard to change the names of things.

• 3:48:28Sean Carroll?

  Having said that, History exists, and it is true that due to sexism and racism and all sorts of isms that have existed over the centuries, if all you do is name things after figures that were prominent at the time when the discoveries were being made, you will end up with a lot of things named after dead white European males. And maybe you want your nomenclature to be more inclusive, or at least less pointed toward a particular part of history, and therefore you want to change the names. I am, you know, as a pragmatist, I'm in favor of letting the individual subfields make up their minds. If the American Ornithological Society has made this decision, I haven't looked at the

• 3:49:13Sean Carroll?

  details of their process for deciding, and I'm perfectly willing to go along with it. Physics has not had nearly that much effort into changing the names of things, like the Schrödinger equation or the Dirac equation or whatever. It would be very, very difficult to do so, just because those names are so ingrained in how we talk and how every textbook is written and things like that. Sometimes there have been efforts. Astronomy has been a little bit more along those lines than physics has. So Henrietta Leavitt, for example, was the astronomer who discovered the Cepheid luminosity period relation.

• 3:49:56Sean Carroll?

  And so some people, fairly recently, not in her lifetime, have said we should call this, you know, Leavitt's Law, or something like that, right? And, you know, I think that's fine. I don't attach huge importance to it, right? I mean, it's kind of symbolic. I get that symbols matter, they are not irrelevant, so symbolic things should be taken seriously, but I don't think they're the most important things. I would rather... It's not true that there's a finite amount of attention to be put to things, but given that there's some attention to be put to things, I think that lowering the amount of misogyny and sexism in the existing community is more important than relabeling things historically to be a little bit more fair, more inclusive.

• 3:50:41Sean Carroll?

  Grace Monk says, "Why aren't there more college classes on the philosophy of physics? I took a philosophy of quantum mechanics course with Nina Emery in college, and it completely changed the way I thought about the world, even as a humanities major. My understanding is that classes like hers are quite rare. I know that many departments don't have philosophers of physics, but should that really account for a lack of classes on the kinds of physics and philosophy problems central to the podcast and to your teaching?" Well, I'm trying to be fair here, you know. I think there should be lots more classes on philosophy of physics and lots more people doing philosophy of physics. I don't think it's that rare, though. I mean, maybe I'm completely wrong here. I can usually think

• 3:51:23Sean Carroll?

  of, in philosophy departments that I know about that are of a certain size, there's usually people doing philosophy of physics. And I guess that they usually teach undergraduate courses, maybe some of them don't. Nina Emery, by the way, was my host when I visited Mount Holyoke just a few weeks ago to give a talk. I'm sure her class was great. I do think, you know, within philosophy, philosophy of physics is an extremely respected sub-discipline. Maybe extremely is too strong there. It's a respected sub-discipline. Let's put it this way. I think that the typical philosopher on the street thinks that philosophy of physics is very good philosophy. They don't quite respect it as much as what they think is

• 3:52:05Sean Carroll?

  the centrally important areas of metaphysics and value and political philosophy and things like that. Okay, that's fine, epistemology. But they get that philosophy of physics is important and respectable. In physics departments, it's not respected at all, of course. I think that what's missing is, I think there should be more recognition of the continuity between philosophy of physics and other areas of philosophy.

• 3:52:35Sean Carroll?

  You know, thinking about space and time is kind of central to metaphysics in general, maybe even to epistemology, probably not to value or politics, but it's a smooth continuum, not a discrete set of differences. I do therefore think that more philosophy departments should have a little bit more emphasis on, if not people specializing in philosophy of physics, then at least people who know a lot of philosophy of physics and physics for that matter, because it is of a continuum. That's why natural philosophy is important. I think all of physics and all of philosophy are part of a continuum for that matter. I love the point that taking philosophy of physics completely changed the way you thought about the world.

• 3:53:20Sean Carroll?

  I think that's the ideal that we're all shooting for. And it certainly is true for me, thinking about how time works, or how spacetime works, how forces and matter and energy work, changes the way I think about the world. And I think that it also provides a set of analytical tools that are very useful in a variety of circumstances. So I think it would be good if we were a little bit broader at that. Yeah, so I would think that, though. So there you go. Take it for what it's worth. Norton Uart says, "On April 7th, Martin Johnson posted a full-page ad in The New York Times with the headline 'The Universe May Be Older Than 13.8 Billion Years.' After the headline, he supplies five hypothetical equations, some abstract and presentational

• 3:54:05Sean Carroll?

  links, and the statement that the author alone is responsible for the last three equations above displayed. What is the strategy behind an ad like this? I accept that the universe may be older or younger, but I understand, and I understand why scientists would publish on this topic, but why would you place an ad in The New York Times? Who is he trying to convince?" Yeah, I'm not at all surprised by this. Look, you would be surprised probably at the volume of not just email that I get, like email is cheap, right? I've had people who have sent me emails once a day for years in a row, and I have a filter in my Gmail that just deletes them right away. Certain mailing lists that I'm on and I just delete them right away.

• 3:54:48Sean Carroll?

  I get regular appearances of new theories of everything, especially in the LLM era that we're now in that makes it too easy to do. LLMs are notoriously synchophantic and they will tell you how brilliant you are, et cetera, and I just delete them right away. But I also get physical mail, right? I get manuscripts, I get letters, I get books that people have self-published. So it's clear that not only do people think that they have the capacity to come up with important new ideas in physics, even though they lack the traditional background and academic superstructure that publishing physicists have, but they also think that other people will pay attention to them and they have the resources to try to mail them books.

• 3:55:33Sean Carroll?

  And I kind of feel bad because I just throw them all away. I don't look at them. I'm happy to tell them I don't look at them. I don't ever ask to be sent these things, but they nevertheless do it. So if you had slightly more resources, why would you take an ad out in the New York Times? Why not? You know, like clearly these people are not very good at judging the importance of their physics ideas. Therefore, maybe it shouldn't be surprising that they're not very good at judging how to get those ideas out to a broader community. And again, as I've said before, the real problem with these people is not that they are outside academia or they have different training or whatever, is that they don't listen, that they are truly uninterested in improving their understanding. That's what makes them crackpots, right?

• 3:56:17Sean Carroll?

  That they think that their idea is right and everyone should listen to them, but they have no special obligation to listen to what anyone else says. So they're kind of not worth talking to or responding to. David Carr says, "Do you have any thoughts on the reports of nuclear and space technology scientists who have died recently? I only see it being reported by conservative sites. So my first instinct is that they're sensationalizing it somehow, but I can't find any reliable sources on it." Yeah, this is actually a brand-new thing that I just noticed. In fact, so, no, it's complete BS. There's zero credibility here. There is literally a Wikipedia page on the recent conspiracy theory that scientists are dying, okay? Scientists are being killed,

• 3:57:01Sean Carroll?

  nuclear and space technology scientists. You dig into it and you're like, someone who was a secretary at the Jet Propulsion Lab is included in the list of scientists who have purportedly been killed. A lot of them are like in their 70s. And you know, people die sometimes. Look, if you, if it were at all real, if you cared about it, not you personally, David, but if someone cared about it, you would calculate the base rate, right? Are these people in these particular subfields dying at a higher rate than expected compared to the public, given their demographics, etc.? Is there a selection effect? Can you predict ahead of time, blah, blah, blah? None of this is done. It's all just the usual

• 3:57:44Sean Carroll?

  conspiracy theorizing, like, ooh, all these people have died. How could that be a coincidence? There's no connection between these people, other than they are scientists, and now people are looking for scientists dying, saying, see, another scientist died, it must be a conspiracy that is killing them. No, it does not need to be a conspiracy that is killing them. There are easier explanations than that. Maxwell Grody says, "Do you see a connection between self-locating uncertainty and Rawls' veil of ignorance thought experiment? If the thought experiment were reframed, such that when you were designing your preferred society behind the veil, you also knew that everybody else who will exist also gets to design their preferred society, and the

• 3:58:28Sean Carroll?

  society that actually gets implemented is an aggregation across everyone's preferred options, then does the veil of ignorance become a self-locating uncertainty problem? And does that framing support Rawls's argument for his lexical priority?"

• 3:58:42Sean Carroll?

  I'm worried that I'm gonna get this wrong, so I think my answer is there is a self-locating uncertainty aspect to Rawls's veil of ignorance thought experiment. So for those of you who don't know, John Rawls, as a political philosopher, said that we should design the ideal society by forgetting what we know about our position in society. You know, basically, he's saying there's just too much motivated reasoning going on in being a certain kind of person, whether it's a certain race, or a certain income class, or education level, or whatever. You're gonna, given the actuality of our contingent existence, we're gonna be happy

• 3:59:23Sean Carroll?

  with a society that privileges people like us. So he says if you want to try to be careful and design a better society, you would say, what if I didn't know who I was? What if I might end up being anybody? What if I might end up being the worst-off person in society? And he argues that what you would do is to try to design a society where even the worst-off people were not that badly off, and it ends up being very egalitarian for that reason. But he, you know, he's nuanced about it. It's easy to caricature his view, but that's the basic thrust of it. And so, in some sense, there's some self-locating uncertainty going on there. You know you're a person, but you don't know which person you are. It's attempting to be a legitimate version of the typicality anthropic move, right, that we were talking

• 4:00:08Sean Carroll?

  about before. Rawls is not saying you are a typical observer, which is the bad anthropic move. He's saying you can design the good society by imagining that you were a typical observer and didn't know anything beyond that, what kind of society would you design? So in that sense, yes, there's some self-locating uncertainty involved. What I don't see or I'm not sure of is how that helps, or, you know, what relevance that fact has to thinking about it. I don't think that thinking about it in that way leads you to any slightly different conclusions than Rawls himself was led to, but maybe I'm missing something about that. I'm open to the possibility.

• 4:00:48Sean Carroll?

  Eric Connolly says: "In your interview with Peter Singer, you pushed back a bit against the idea of utility being quantifiable and additive. To me, it seems a natural step is to treat utility more like a vector than a scalar having different components, like, say, pleasure and freedom. My utility vector might be 1 comma 2, someone else's might be 2 comma 1. These vectors are harder to compare than scalars having the same magnitude. Maybe this is nonsense, but is it something philosophers think about?" So I don't know if philosophers have ever thought about that, but I think that there is, you know, an obvious problem with it, which is that vectors don't have an ordering, right? The nice thing about scalars, simple numbers, is that you can say that a certain number is bigger or smaller than another one.

• 4:01:33Sean Carroll?

  You can't say if you have a vector 1 comma 2 and another one 2 comma 1, which is bigger, unless secretly you want to say, I mean, the length of the vector, and then you're back to a scalar again, or you want to sort of privilege the first component over the second component, or something like that. So on the one hand, I think that in fact it's absolutely true that different people have different weights that they give to pleasure or freedom, whatever, when calculating utility, but I think that the idea utilitarianism kind of only has a grip if you reduce all of those different components of the vector to a single scalar number that you can then put in an order.

• 4:02:13Sean Carroll?

  Kevin O'Toole says: "Recently hiking with friends wearing polarized sunglasses. I showed them the 45-degree lens trick." I don't know, maybe some of you folks out there have seen this before, but if not, it's very worth looking up on the internet. Anyway, Kevin says, "In the trick, two perpendicular lenses allow no light through." So you imagine polarizing lenses, and they polarize light in a certain direction, so you put them at 90 degrees to each other. It blocks out all of the light, because you're blocking both polarizations. And anyway, Kevin continues, I shall let Kevin talk. "But adding a filter between them at 45 degrees allows some light through the whole chain." I then added this, I added that, this also-

• 4:02:57Sean Carroll?

  ...happens when letting through photons one at a time, and that no classical theory could explain this behavior. So it is visible evidence that the world is quantum. They all accepted this, but the more I think about it, the wronger it feels. A classical theory of light as either waves or particles seems like it easily could just include a polarization parameter that changes as it is filtered. Is there something more accurate I could have said where my little sunglasses experiment actually defies classical explanation? So this is exactly the kind of real world thing that I personally am bad at, but your feelings are exactly the same as my feelings. I was never convinced that this particular 45-degree thing is somehow strong evidence

• 4:03:41Sean Carroll?

  of quantum behavior. But of course, it depends on what you mean by quantum behavior. You know, in the real world, the real world is quantum. So all behavior that we actually see is quantum. So if you're saying that a certain phenomenon is evidence of quantum mechanics, what you're really saying is that there is no classical theory that could explain this. And like you, I'm not at all sure that that's true, because it's a super-strong claim that there's no possible classical theory that could explain this. Is the claim somehow that just classical electromagnetism doesn't explain it? Or that I can't come up with some modified version that couldn't explain it? I am not that confident that there is no classical theory that could explain it, which is why I never bring up experiments like that.

• 4:04:26Sean Carroll?

  I think something like the Stern-Gerlach experiment, which is harder to do, you can't just do it outside with your sunglasses, but that's much stronger evidence of quantum theory. For that matter, by the way, the stability of matter is a much stronger piece of evidence for quantum theory. Electrons do not spiral into the middle of a nucleus. That tells you that electrons are wave-like in some sense, but when you look at them on a screen, they look particle-like. Classical physics doesn't explain that very well. Ophir Averbuch says: "I am a grad student in a field other than philosophy. I am considering applying for the philosophy job market. Having a philosophy appointment, do you find that not having formal philosophy training

• 4:05:07Sean Carroll?

  creates frictions, both academic and social, with your philosopher colleagues? Do you think that you have colleagues that are dogmatically unwilling to take your comments in seminars seriously, or who say snarkily behind your back, 'Those scientists should stick to their science and leave it to us philosophers to do the philosophy'?" Well, I think, you know, unsurprisingly, people are different. Different people have different attitudes towards this. In my particular philosophy department at Johns Hopkins, I've seen none of that whatsoever. My philosophy colleagues seem to respect me as a philosopher very, very well, and also the other people I know, not at Johns Hopkins, but within my subfield of Foundations of Physics,

• 4:05:50Sean Carroll?

  also seem to respect me philosophically as well as scientifically. At the same time, I know that, you know, I tried to apply for jobs either in philosophy departments or jointly in physics and philosophy departments at other places at other times, and sometimes, not always, sometimes the reason why it didn't happen is because people in the philosophy department thought that I could not teach philosophy classes, right? And I don't think that's true. I am teaching them, so it can't be true. Maybe they don't think I teach them well. But, look, that's actually reasonable. Like, I don't think it's true, in the case of me, but I certainly don't think that just because someone is an expert in some other field and sort of cares a little bit about

• 4:06:33Sean Carroll?

  philosophy, that entitles them to say they would be good philosophy professors. I think that what matters is, would you be a good philosophy professor? Some people would, some people wouldn't. I don't think you necessarily need a strong background in Kant and Hegel, or Plato and Aristotle, or Zhuangzhe, or whoever, to be a good philosophy professor, but you do need to be able to literally do philosophy, right? So the fact that I had written philosophy papers, that I had them published, that's what matters to the people in the philosophy department, as far as I have traditionally known. Of course, who knows that they're not talking behind my back? I don't think they are. I have pretty good colleagues at Johns Hopkins, but, you know, maybe they're just super-duper

• 4:07:18Sean Carroll?

  clever at hiding that.

• 4:07:21Sean Carroll?

  Final question for this month's AMA comes from Karolyi Kántor, who says, "Greetings from Hungary. Do you have any thoughts or reflections on our election results where Viktor Orban's longstanding rule was finally voted out, especially given his close political alignment with and strong support from both Donald Trump and Vladimir Putin?" Well, I mean, the joke here is, of course, Donald Trump and Vladimir Putin are both deeply unpopular people, so strong support from them might not be very helpful in this. Look, the serious thing to say is, on the one hand, you know, super congratulations to the people of Hungary, who were able to get themselves out from rule by an authoritarian figure. That's not always guaranteed.

• 4:08:05Sean Carroll?

  It can be very difficult, and they did it peacefully, and he conceded. In some sense, the election was just so overwhelming that even a would-be authoritarian could not pretend that it was not a repudiation of his rule. I think it's a very important historical result, honestly, this result from Hungary, because when you do have authoritarians in power, it can be easy to lose hope, to think, "Well, you know, they're authoritarians. There's no democratic process which will remove them from office once they get the levers of power in their hands." But that's not true. Power doesn't really work like that. It's not concentrated in the hands of one person.

• 4:08:47Sean Carroll?

  People can be authoritarians as long as the right set of other people go along with them. And when the other people stop going along, they're going to stop succeeding at their authoritarian rule. So there's always reason to keep fighting, to keep pressing, not to despair. Maybe it works, maybe it doesn't, but it might work, and that's enough to keep us motivated to try to do it. And examples where it happens, there have been recent examples in South America. Hungary is another example, where literally a very, very close compatriot of right-wing populist figures elsewhere in the world has been kicked out of office.

• 4:09:28Sean Carroll?

  Due to the work of the people. The other reason why, so not only did it work, but it's a reminder that at the end of the day, the reality of right-wing populism is itself deeply unpopular. Okay, there are moments when it seems popular, because usually not just because it's the actual right-wing populism that is popular, but because the alternatives have been bad, for whatever reason, and they've become unpopular. That's a very important factor in politics. But once you see the right-wing populism at work and you realize, "Oh, I didn't vote for that", you get all of these, you know, right now, I don't know if you know, right now in the United States, there's all these newspaper stories about interviews with Trump supporters

• 4:10:12Sean Carroll?

  who are like, "I don't like what he's doing. I never thought he would do that." And it's a very strong temptation for people on the other side to just roll their eyes and say like, "Come on, how could you not know? He told you he was gonna do this." But nevertheless, our way of getting information to voters is very bad right now, so people don't know. And then when, once these people get into office and start doing terrible things, people who previously supported them are like, "No, I didn't want that." And I'm optimistic enough to think that, you know, respect for other human beings and democratic values and liberal tolerance and even love and compassion and empathy for your fellow human beings

• 4:10:55Sean Carroll?

  is more prevalent than a sort of narrow, nationalistic, hatred-based view of the world. They both exist. In fact, most people have aspects of both of them to them inside themselves, to some extent or the other. But more people in the modern world want to be good and want to be open and want to welcome their fellow human beings into the community. And that's something that we just got great evidence from, for, from the election in Hungary. So, thank you very much, people from Hungary, for doing the right thing and sticking with it and succeeding rather than giving up. It's something that we should all keep in mind.

• 4:11:38Sean Carroll?

  As an example. And with that note, look, I don't pick the last question in every AMA randomly. I try to try to end on a happy note. And on that note, thanks very much for supporting the Mindscape Podcast. It really means a lot to me. Hope you enjoy the AMA. I'll talk to you next time.

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