AS244: Sean Carroll, Part 2

Transcript

This transcript was generated automatically and may contain errors — the audio is the record.

0:00:29 Thomas: Hello, and welcome to Atheistically Speaking. This is episode 244, and I'm your host, Thomas Smith. All right, it's what you've been waiting for. It's part two with Dr. Sean Carroll, and in it, we get to finally find out what on earth William Lane Craig is talking about with his Borde-Guth-Vilenkin theorem. So if you've ever wondered why on earth he talks about that so much, you're about to find out. Well, let's get to it.

0:01:09 Thomas: Hey, I wonder if I could ask you, one of my... one of the best contributions to the internet at all is your debate with William Lane Craig. I love it. I've watched it probably three times. Do you mind if I ask you some questions about that? Well, okay. Let me just say, what is William Lane Craig's obsession with bored Guth Vilenkin? He says it more, 20 times a debate. Bored Guth Valenkin theorem. What, what does he, can you go into that? Does he have a misapprehension of what that is? Maybe you could explain it a little bit and how he's misapplying it, or or if maybe he's not, I don't know.

0:01:22 Sean: Sure.

0:01:47 Sean: Well, it's a little bit unclear because he doesn't always say precisely the same words when he brings it up. You know, he certainly wants to leave you with the impression that there is a theorem that says the universe had a beginning. And he is smart enough to know that the Borde-Guth-Vilenkin theorem does not say that. So he's usually careful enough not to say exactly those words, but he certainly says words that would lead you to believe that that is what is going on.

0:01:52 Thomas: Right. Right.

0:02:16 Sean: The Borde-Guth-Vilenkin makes some assumptions, and those assumptions might not be true in the real world. In fact, strictly speaking, there's almost no chance that they are true in the real world because it's a statement about classical space-time and the real world obeys the rules of quantum mechanics. So someone like Alex Vilenkin, one of the authors of the theorem, thinks that this theorem is a strong clue that even if we did understand the full rules of quantum mechanics and cosmology, there would still be a beginning to the universe. Someone like Alan Guth, who is one of his co-authors and another author of the theory, thinks once we understand quantum mechanics in cosmology, we will realize that there is not a singularity and there is no beginning. And that's just because the theorem doesn't say anything one way or the other because it doesn't apply to the real world.

0:03:06 Sean: And he will sometimes say that it sort of makes it more probable that there was a beginning or something like that, but he never spells that out. So I really think that it's mostly a rhetorical device.

0:03:21 Thomas: It sounds as though, now I, it seems to me, as someone who doesn't know much about it, that William, William Lane Craig is, I mean, he's some kind of a genius, it seems like, he's able, able to maybe cherry pick the physics that go his way and present it in a really coherent, or something that sounds coherent, something that sounds convincing that, oh, he's read all the papers. He knows all the theories. He knows it all. And this is what he presents. But it's interesting to hear, like, how obscure is that? I mean, among physicists.

0:03:46 Sean: Right.

0:03:54 Thomas: Synthesis.

0:03:53 Sean: Well, it's hilarious because if you Google Borde-Guth-Vilenkin theorem, 98% of the references are to theology debates, right? You know, either William Lane Craig or somebody else. I mean, it's a fine theorem, but like I said, because the universe is not classical, it's quantum mechanical, the actual implications of the theorem for physical reality are kind of meager. So it's not a central point of discussion among physicists. I mean it was a wonderful proof, a very clever demonstration that those guys did. They're incredibly intelligent people, but it's like something that is a major player and how we think about the early universe.

0:04:31 Thomas: Right, right. So you talked a lot, and you have in multiple places, but in this debate as well, about we make models. Not me, but you. People make models of the universe, and that's the way we try to understand it. It's not really as a result of thinking real hard and saying, well, there must be a cause, and therefore, you know, blah, blah. That kind of thing. Could you talk a bit about, because I think you referenced and William Lane Craig references, like your own model of the universe. Could you talk a little bit about for people who don't know what goes into it? I mean, why is it that you have a model of the universe? I assume you worked with someone on it and, but it's not, you said several times, like it's not true or you don't think it's true. Like, can you explain to a lay person what that means and kind of how that works?

0:04:41 Sean: Yeah.

0:05:22 Sean: Sure. I had this model that I wrote down with a graduate student of mine at the time, Jennifer Chen, who subsequently got her PhD. In 2004, we proposed sort of a version of the multiverse that could be eternal and could have an arrow of time that points in opposite directions in the far, far past and the far far future. And this is becoming actually sort of more popular framework for people to think about. So that's gratifying to me. But, yeah, I think that William Lane Craig thought that I would go in there and defend this model as the right view of the universe, but that's not how science works. It's a different game than theology.

0:06:01 Sean: We propose hypotheses, and then we explore them, and we test them. You know, John Horgan just the other day wrote a Scientific American column where he accuses me of – where he describes me as being a multiverse true believer. But in the real world, I would place at most a 50% chance that the multiverse exists. So if that's a true believer, then I wish all true believers were as cautious and tentative as I was. We propose lots of different ideas. We don't know that any one of them is right when we propose it, and hopefully a good scientist does not fall so much in love with their own idea that they insist that it's right before the evidence is in. So, and these big questions like what happened at the Big Bang, where we obviously don't have the theoretical knowledge to say anything definitively, everyone's model is at best extremely tentative, and you should explore them, see what, what works, see what fits into other things we understand, and hopefully someday some decades from now we'll know which answer is right. Yeah.

0:07:07 Thomas: So it's a question of someday there will be experimental evidence that we'll have access to or something like that where we'll figure, ah, this narrows it down a bit or, you know, this model.

0:07:19 Sean: Some combination of experimental evidence and and theoretical improvement, you know, our ideas are not that good right now. So you can't say whether they're right or wrong.

0:07:25 Thomas: How many, it sounds like such a stupid question, but like how many models are there that go with all the experimental data that are at least like yours somewhat, you know, somewhat, what's the word I'm looking for? Viable? Is that, yeah, like, is that, are we talking like hundreds, thousands, or just a couple, a handful?

0:07:48 Sean: Yeah, I mean, it might even be difficult to draw a sharp line between where one model ends and another one begins, right? Like some models are just elaborations on other models. I did for the debate with Craig, you take half an hour and Google a bunch of theories of the early universe that had a universe where it was eternal rather than the beginning. And I found like 17 or 18 in half an hour. So that gives you sort of a ballpark figure. That's just ones that are eternal. Plenty of models just have a beginning or don't talk about the beginning at all. So yeah, I think it's something we just admit that we don't know if we're being honest right now.

0:07:54 Thomas: Oh, okay.

0:08:22 Thomas: Interesting. Okay. Well, I'm sorry. It's a weird question, but just for, you know, for someone who's not a scientist, it's a little, it's a little odd. I feel like it should be, there's one theory that everybody's working on, you Know, and it's like, this is our best theory, but it's not really how it works.

0:08:36 Sean: We don't have the answer to this one. This is tough. Well,

0:08:39 Thomas: So it seems like a fundamental misapprehension that people like William Lane Craig have. And I wonder what your view on this is, that in their mind, there definitely had to be some time when there just wasn't anything. There was zero anything, no quantum laws, no anything.There's no laws of physics, nothing. And then there were things. And it's like they can't get their mind around that. Could you explain how that, I mean, I get the impression from reading you and from, you know, listening to your talks and stuff that that just really isn't how physics works. But how do you bridge that gap?

0:09:16 Sean: Even worse than the many worlds interpretation, this is a case where our ordinary language and way of thinking breaks down. Because the way that you just described it is pretty close, but we can't help but using words like there was nothing and then there was something. And that's not right because there was not a moment of time when there was nothing. Time itself is part of the universe coming into existence. So the only strictly correct thing to say is that these are models where there is a first moment of time in the history of the universe. There is a moment before which – there's no such thing as before. There's no such thing is an earlier moment than this moment. There are moments after, and for every moment after, there's some before and some after, but this was the first moment. And that may or may not be true. That's just how it is. It's certainly absolutely plausible given what we currently know about the laws of physics.

0:09:32 Thomas: Well, Just to make sure I have it right, because I have had this argument with theists before. Is it correct to say, would I be correct to say that we don't have any reason necessarily to believe that there ever was a nothing in that strict religious sense? Would that be correct? I mean, hmm,

0:10:29 Sean: I mean if there were – if you have a – it's really just way better if you start talking about the universe having a first moment, because then you don't start talking about nothing because there was no nothing. There was no time. There's no moment. There was no state of the universe, which was nothing. There was just the universe and it has – and time goes from t equals zero to some number. That's all it is. There's no transition from nothing to something.

0:10:39 Thomas: Right, right. Right. Okay. I think that is what I was trying to say. I probably just didn't say it right. Okay, thanks for that. So, there's really, I get you. So once time started, that's when you can start using ordinary language, but we can't really use our language before that. So, okay, could you talk a little bit about the arrow of time? This is something I've, you know, I've heard you talk about so much. It's so fascinating that entropy is what determines, you know, if you could give a little bit of a condensed version of that that's what determines our arrow of time or

0:11:12 Sean: Right. Yeah. I mean it's important here to distinguish between time and the arrow of time. The arrow of time is a particular feature that time has in our universe, which is just a catch-all phrase for all the different ways in which the past and future are different from each other. Like the most obvious one I always refer to is you remember the past. You do not remember the future. We have records, photographs, or history books that refer to events of the past with high specificity in a way that we don't have photographs of the future, but there's really many ways that this arrow manifests. Itself, right? We were all younger once. We're getting older. The most important one is really that entropy is increasing. The entropy of a system is its disorderliness, its disorganization, randomness. And the universe as a whole started out very, very low entropy, started out very organized in a very special state compared to all the different states we could imagine it starting in.

0:11:38 Thomas: Hmm.

0:12:34 Sean: And ever since, ever since the Big Bang, we're very, very close to the Big Bang. The universe has been growing in entropy, becoming more and more randomly ordered or disordered, if you want, more disordered. And so time, ever since Einstein came along, we know that time is very, very much like space. There's no reason for it to have an arrow. If you were out there in outer space in a spacesuit, there'd be no difference between all the directions in space, right? Up, down, left, right, forward, backward. You could rotate yourself around and nothing would change because you're just floating in space. So we know there's no arrow of space.

Of course, there could be. If you're here on Earth, there's an arrow of place. There's a difference between up and down, right? We all know where down is. And that's because, of course, the Earth is underneath our feet. So the amazing realization is that time is exactly the same way. Despite all of your commonsensical experience with time where the past and future are things that are truly different, like the past already happened and the future didn't yet, the laws of physics treat them exactly the same. And the resolution is exactly the sameness for the arrow of space. The reason why we treat the past, the future differently is not because of the laws of physics, but because we're in the aftermath of the Big Bang, which is a very, very special low entropy event.

0:13:58 Thomas: Yeah. One thing I thought of when I heard you talk about this in the past, and sorry if this is a nonsensical question, but could there have been such a thing as a high entropy Big Bang or is a Big Bang by definition something that is a low entropy state?

0:14:14 Sean: Actually, that's a very good question. The Big Bang could certainly have been much higher entropy than it was.

0:14:20 Thomas: Then it was.

0:14:21 Sean: Let's put it that way. Although, at the same time, if you sort of say, given some stuff or given some universe, what is the highest entropy it could be, it probably would not look like the Big Bang at all. In fact, it looks like empty space. It's where we're going to in the future. Everything is moving apart from everything else.

0:14:21 Thomas: Okay.

0:14:37 Thomas: Right. But then, of course, that couldn't be a Big Bang, right? That couldn't have been. Okay. So maybe it's possible that that is the only way a Big Bang could happen is to have at least lower entropy than empty space.

0:14:40 Sean: Right. Exactly. That's right.

0:14:51 Sean: Well, I think it's fair to say that a Big Bang has lower entropy than the maximum that empty space has. But again, our Big Bang had a much, much, much, lower entropy than it needed to, than it had to.

0:14:56 Thomas: Right. It's an overachieving Big Bang. We should all thank it.

0:15:05 Sean: It is, yes. Right.

0:15:08 Thomas: So, okay. One thing I'm going to kick myself if I don't ask you about, because this is something that has bothered me forever, is it regards Boltzmann brains. But I think I should ask you if you could, could you explain the Boltzman brain brain problem, just so I'm not asking something that no one will have any idea what it's about.

0:15:23 Sean: Sure. If you imagined that – Boltzmann was a fantastically influential Austrian physicist from the 19th century, and he was the one who really understood entropy better than anyone else. So he was asking himself these questions. Why is the past different from the future? And what he realized is he came along before general relativity or the Big Bang or any of these things. So he imagined that the universe lasted forever because that's what Isaac Newton would have told you. And if the universe lasts forever and it's full of particles and atoms and so forth and these atoms are just bumping into each other in perpetuity, most of the time, the universe will be near its maximum possible value for the entropy. It will be as disorganized as possible. But just through rare random fluctuations, occasionally the entropy will go down.

0:16:15 Sean: So we say with the second law of thermodynamics, entropy always goes up. But Boltzmann is pointing out that, well, maybe that's just a feature of our local environment. Maybe it's not an absolute law of nature. And maybe, in fact, this is our universe, he says, and we live in one of those rare fluctuations that went very, very low in entropy and then will come up again. But that doesn't work. That's a bad idea. I mean, it was a fascinating and brilliant idea, but it is not our universe. And the reason why it's not our univers is because if you live in that kind of universe that lasts forever and you wait for random fluctuations to come along and make something orderly, it's much easier to make a small amount of order than a large amount of order. So if you wait for a person to come along, a person qualifying as an orderly thing, then you don't need to fluctuate into a whole universe with a Big Bang.

0:17:09 Sean: You don't even need to fluctiate into a full galaxy's worth of stars and planets and so forth, or even the solar system. You can just fluctuate to one person out there in the middle of nothingness. And in fact, if you just want an intelligent observer, you don't even need that person to have a body. It could just be enough atoms coming together to make a brain that lives long enough to look around and go, "Ha, thermal equilibrium all around me," and then it will die. And these are called Boltzmann brains, and these would be the most likely intelligent observers, the most populous version of living creatures in a universe that was mostly high entropy and random and just occasionally fluctuated into something more orderly. Now, this is obviously not our universe, so there is something wrong about Boltzmann's scenario.

0:17:58 Thomas: Did Boltzmann himself come up with that objection, or did someone come up with that later about his theory and it's called Boltzman brains because of that?

0:18:06 Sean: Yeah, he did not think of that, as far as I know. In fact, he was a little bit embarrassed to even have come up with the idea of the fluctuations. You know, it was a kind of speculation that was far outside what physicists of the day were allowed to do. But it was Arthur Eddington in the 1930s, a British astrophysicist, who first pointed out this objection. And he did Not phrase it in terms of brains. He phrased it in terms of mathematical physicists. He said if you want to wait until a mathematical physicist is produced, you'll just produce a mathematical physicist, you won't produce the whole earth and Cambridge University and anything like that. So it wasn't until much later in the 21st century that Andy Albrecht and Lorenzo Sorbo, two physicists thinking about the accelerating universe and dark energy and so forth, rethought this scenario and labeled it the Boltzmann brain idea.

0:18:13 Thomas: Okay, So one thing I can't wrap my mind around is that it seems to me so much harder to fluctuate a brain than it would be to fluctiate some sort of scenario that could lead to Darwinian processes that would create a brain. Just based on reading like Dawkins and things like that, with how complex that would need to be, with how specific every single molecule would have to be to form a thinking operating brain. Has anyone ever run the numbers on that? Like actually figured out?

0:19:26 Sean: Yeah, it's trivial. It's not hard. Because look, think about, you know, here we live in a universe where I exist and you exist, right? And there's another universe where only you exist and nothing else, not me or not the rest of the earth and whatever. The rest of us is much, much, higher entropy, right. So just by counting the number of states that look that way, high entropy states are much more frequent than low entropy ones. So there are many, many, very many more states where you and the room you're sitting in right now exist alone in the universe than states that looks like the universe we actually think we live in.

0:19:28 Thomas: Oh, okay.

0:20:12 Thomas: It's so weird because he wasn't even talking about, because this was before four quantum mechanics, right? So he was just talking about atoms bumping into each other and somehow making people or brains.

0:20:17 Sean: Yeah, that's right. Yes. Yes.

0:20:23 Thomas: Man, that doesn't really make sense. Okay. Well, maybe I'll just have to...

0:20:27 Sean: There's a difficulty because you have to be very, very careful about what question you are asking. If you're asking the question, I'm going to wait forever in this fluctuating group of stuff and ask, given that a person appears, what is the most likely prediction for everything else? And what Eddington was pointing out is the most likely prediction is still that everything else is very, very high entropy. There's a separate question you can ask, which is, what kind of fluctuations could I imagine such that once they happened, it would be very likely that things like people would later on appear?

0:20:27 Thomas: Hmm. Sure.

0:21:07 Sean: And then you get something probably much more orderly. But that's just not the question that is relevant.

0:21:11 Thomas: But isn't it possible that... This is all dependent on how complex brains are somewhat. I mean, right. I'm not at all. So if a brain was just two molecules, that would be far more likely to happen than if a brain was a gajillion, if it required, if a thinking mind required a gijillion molecules in just the right way, wouldn't that reduce the frequency of that happening in his hypothetical universe?

0:21:18 Sean: No, not at all. It would, but when it happened, it would still be overwhelmingly likely the rest of the universe was high entropy.

0:21:39 Thomas: Right. Okay, I'll ask one more try on it and then I'll give it up. But if we found out that it was far easier to create create a mind as a result of Darwinian processes and the fluctuation to start those Darwinian processes was easier than it would be to make an entire operating brain, wouldn't it mean that that would be more frequent in an infinite time than an actual fluctuated brain?

0:21:48 Sean: It doesn't matter how easy something is because you have infinite time to wait and everything that can happen possibly is going to happen.

0:22:17 Thomas: Well, but it's a question of frequency, right? Isn't that the whole, yeah, that's what I meant.

0:22:19 Sean: That's right. So if you say how frequently will it happen, then the states with higher entropy happen much more frequently than the states with lower entropy.

0:22:27 Thomas: All right, fair enough. I tried. I guess I either don't get it or I'll go back and listen and maybe I'll understand after I listen again. But thanks for doing your best to make sense of my ramblings. So, I have some questions from my listeners that I would like to run by you, if you don't mind. So, Michael is asking, in general, okay, this might have been something that somebody wrote recently. I'm not totally sure. Let's give it a try. He's asking about your position on falsifiability with respect to scientific theories. I think he said someone mentioned you recently or something in a talk. Do you have any idea about what he might be talking about, that you've moved away from falsifiability, possibly?

0:22:46 Sean: Sure.

0:23:12 Sean: Yeah. I mean, I didn't move at all. Actually, this is something That that I've been a little bit mischaracterized as. There have been debates in the last 10 years or 20 years or whatever about things like the multiverse and string theory and the many worlds interpretation of quantum mechanics vis-a-vis their falsifiability. What is the prediction that they're making that could falsify them? And what I and other people have tried to point out, I mean, in some cases, there's a simple answer, which is, yes, they do make falsifiable predictions, but let's just imagine – let's grant the cases where they don't. What we've been trying to point out is that falsifiability has never been the right way to demarcate what is scientific from what is not scientific. We are not moving away from it. We are nicht geben auf es. Wir sagen nur, wenn ihr die Wissenschaftsphilosophie machen wollt, dann könnt ihr es vielleicht richtig machen.

0:23:14 Thomas: Oh, okay.

0:24:04 Sean: And so we want to – I wrote a little article saying – John Brockman writes these annual edge question centers where he asks writers and scientists and so forth a single question and they write a few hundred words on this question. So the question was, what scientific idea do you think should be retired? And I said falsifiability. And my goal was not to say we used to believe in falsifiability. Now we don't anymore. It was to say we never should have been talking about this. It's a fine rule of thumb. It was invented by Karl Popper because he didn't like ideas like Marxist interpretations of history or Freudian psychoanalysis, where it was really the case that literally anything that could happen in the world, they could tell a story about how that's exactly what they would have expected.

0:24:59 Sean: So that's why he wanted to say you need to have falsifiable predictions. If Popper were alive today and you told him about the multiverse, he would have said, "Of course, that's scientific. It says there's a universe out there that is different from ours." I mean, that is very – it's true or it's false, right? What are we having this argument about? Out. But this slogan of making falsifiable predictions has been used by people who don't like the multiverse or string theory or whatever to point out that the predictions these theories make are untestably far away and therefore it doesn't count as science. If you do a more nuanced understanding of what science is and you understand that it isn't quite so cut and dried about whether whether something is falsifiable or not, it's more of a question of what is the best explanation we have for the data?

0:25:49 Sean: What can we do to improve our credence in believing this particular hypothesis about the world? Then the theories like the string theory and the multiverse and many worlds are just ordinary scientific theories. There's nothing weird about them. They might be harder to decide than other ideas because their predictions are so far away. But that's our problem. That's not the universe's problem. It's not the theory's problem, just we human beings have difficulty deciding and maybe we'll never decide and so be it.

0:26:20 Thomas: Yeah, that's actually something that I think pervades the skeptic community a little bit. I actually think, I've heard Massimo Pagliucci talk about this, about the falsifiabilty as a criterion for what's science versus not, I think is actually outdated, like you said. I think there may be skeptics listening that aren't aware of that. I think it's actually a very outdated philosophy of science concept. So, gotcha.

0:26:43 Sean: Right. And that was my plea to retire that idea, not because I'm changing what counts as science and not, but when you get to the boundaries where the question is interesting, you have to be a little bit more nuanced than that.

0:26:55 Thomas: Gotcha. Well, here, how about a fun science fiction question? Melina is wondering if humans might ever be able to create artificial gravity. What could you say about that?

0:27:07 Sean: I mean, there's some trivial sense in which you can. You know, you just spin the spaceship, right? And then, you know, exactly.

0:27:12 Thomas: Spinning something? Yeah, she probably doesn't mean that. That's too easy.

0:27:16 Sean: That's why I'm not going to really count that. I think that Einstein taught us a long time ago that in some sense, gravity is indistinguishable from acceleration. So when your spaceship is accelerating or spinning or whatever, it looks very much like gravity. What you really want, probably, is to manipulate. Yeah, you want anti-gravity or something like that. And there, the answer is essentially no. It is not going to happen. And that's because gravity is a very simple force. Every particle, every little bit of energy or mass pulls things towards it. That's all gravity ever does. It's very different than, let's say, electromagnetism. Because with electromagnetism, you have positive charges and negative charges. And in everything around you, you know, the computer in front of you, the chair you're sitting on, there's an enormous amount of gravitational or, sorry, of electromagnetic force potentially available, but it almost exactly cancels because the number of positive charges is equal to the number of negative charges. And everything we do in life with electromagnetism is based on creating slight imbalances between the positive charges and the negative charges, but there's nothing like that with gravity.

0:27:25 Thomas: Hmm. Anti-gravity. Oh, yeah. Yeah.

0:28:26 Sean: Gravity just pulls everything together. So roughly speaking, when gravity is here, it's going to stay here. You're not going to make it stronger or weaker.

0:28:33 Thomas: Well, there you have it, Dr. Sean Carroll's spoil sport.

0:28:36 Sean: Sorry.

0:28:36 Thomas: Sorry, everybody, we can't invent a spaceship in your garage that's going to fly away. So, Marcel wants to know if and how the multiverse hypothesis has more proof than the God hypothesis, or if that's even a valid question. I think this is something you hear a lot. I mean, I think we've already referenced it. People, theists will say, oh, well, if you have a lot of faith to just create the multiverse in order to get rid of the question of God, that sort of thing. What do you think about that?

0:28:37 Sean: Yep, that's my job.

0:29:03 Sean: Well, many thoughts. I mean, the first is as soon as you introduce the word proof, you've already gone wrong. I mean that's not how science works, by proving things right or wrong. Again, we accumulate evidence. And I talk about this at great length in the new book, The Big Picture, available at Amazon right now. They can hurry up and buy it.

0:29:22 Thomas: They can click in the show notes for the link on Amazon. Absolutely.

0:29:24 Sean: There you go. And there's a process called abduction, which is philosopher speak for inference to the best explanation. So the question isn't this piece of proof or that piece of disproof. The question is, given what we know, what is the best explanation for what we have seen? And given what theory, what hypothesis is doing the best? And again, like I said, for the multiverse, it's nowhere near established. I mean, it's an idea. It's a perfectly respectable idea. I give it about 50% chance of being right. Um, God, I give way less than 1% chance of being right. And why is that? Well, because the way that we do it is we say under these two hypotheses, we make predictions. What should the world be like? What do you expect the world to be like, and then we apply an idea called Bayes' theorem, which says starting with some beginning credence in the different ideas, how do our observations change those credences, and the universe looks kind of like you might expect it to look if it's part of a multiverse, and it looks nothing like you'd expect it to look if God had made it.

0:30:27 Thomas: Yeah. Actually, I should say in your book, I really appreciate your breakdown of Bayesian probability and all that because I always hear that used. I knew a little bit of something about it, but having you lay it out made a lot of sense. It makes me understand it better. How about, do you have have time for a couple more quick questions?

0:30:43 Sean: Yeah, a couple more quick questions.

0:30:44 Thomas: Excellent. So Adrian wants to know about the irreconcilability of quantum mechanics and general relativity. So solve that now, if you would. No, I'm just kidding.

0:30:54 Sean: All right, We don't know the answer to that. One of the points I make in the book is that when we say that general relativity and quantum mechanics are irreconcilable, what we really mean is that we don't have the complete or any complete version of a theory that would lead to general relativity in the classical limit. But if you just want to understand the motion of the moon around the earth or why wine glasses fall to the ground when you knock them over because of gravity, we do understand enough about quantum gravity to make those predictions. So we have sort of a working everyday understanding of quantum gravity just fine. It's the deeper ones, what happens inside a black hole or near the Big Bang that we don't know. I am sort of interested right now in ideas that are just bubbling to the surface and I'm working on myself that say that maybe we can use ideas directly from quantum mechanics and quantum information to show how gravity might come into existence.

0:31:53 Sean: In other words, what we usually do whenever we're physicists doing quantum mechanics is we start with some classical theory that Newton would have recognized like electromagnetism or gravity and we quantize it. We take this classical theory and we try to make it into a quantum theory. But nature doesn't work that way. Nature doesn't know about classical mechanics. That's just a good approximation. So what we're doing now, instead of quantizing gravity, is we're saying, can we find gravity within quantum mechanics, which I think is a very provocative idea.

0:32:25 Thomas: Wow. Yeah. So what about, I just remembered, it wasn't somewhat recently, LIGO, they actually detected gravitational waves. Is that right? They finally got...

0:32:33 Sean: Detected gravitational waves, which tells us so far nothing about quantum gravity, purely classical. So

0:32:37 Thomas: Oh, okay. So what implications does that have exactly? That didn't favor one theory or the other or something?

0:32:46 Sean: Far, it's just completely compatible with Einstein's general theory of relativity as we understood it. It will almost certainly teach us a lot about astrophysics and the universe, what is out there making gravitational waves. If we get really, really lucky, it will teach us something about gravity itself because we'll learn what black holes are like near their event horizons.

0:32:51 Thomas: Hmm.

0:33:08 Thomas: Hmm. So it didn't say like, oh, Einstein's picture was correct and this quantum gravity nonsense is incorrect. It's not really how it works.

0:33:15 Sean: Now, any good quantum theory of gravity will look like Einstein's General Relativity in the classical limit.

0:33:21 Thomas: Gotcha. Okay, last patron question here. Richard wants to know how you feel about being pulled into atheist causes. I don't know if that accurately describes what's happening, but are you comfortable with the role of being a rock star to atheists? And let me add personally for me that your rock stardom doesn't have much to do with atheism, I don'T think. For me, it's just that these cosmology questions are the most fascinating kinds, and I just love the way that you're able to explain them to idiots like me. So that's why I'm such a fan. It's not an atheism thing. But to Richard's question, what do you think about being a Rockstar for Atheists?

0:33:55 Sean: Yeah, I don't think that I am a rock star for atheists necessarily. I don't think I'm in the top five atheists that anyone would list in terms of

0:34:03 Thomas: I definitely don't any of your songs, So I haven't heard, yeah.

0:34:06 Sean: Exactly. But I kind of want to blur the boundaries there a little bit. Whether it's physics or philosophy or atheism or whatever, I think we're trying to understand how the world works and I'm not in any sense crusading or advocating against religion. I think that there are religious beliefs that are incorrect and I think the people should have correct beliefs. I'm saying almost nothing about the cultural or society – social impacts of religion. Religion. I think that many of them are negative. Some of them are positive. None of them is my area of expertise. So I'm much more about how the world works. And I think part of that is whether God exists. That's a big part of how the world works, another big part is the equations that describe quantum gravity.

0:34:57 Sean: Another big part is how complexity and life evolve over the course of cosmic time. So, you know, these bump into different labels, but it's all the same project of just understanding the universe in which we live.

0:35:10 Thomas: Excellent. All right. Well, one more time, the book is The Big Picture on the Origins of Life, Meaning in the Universe Itself. He's Dr. Sean Carroll. Thank you so much for coming on. One more big thank you, and this was the best. I really enjoyed it. Thanks.

0:35:25 Sean: Thanks so much for having me. This was a great conversation.

0:35:27 Thomas: All right, have an excellent evening.

0:35:29 Sean: All right. Take care. Bye-bye.

0:35:42 Thomas: Oh, that was so much fun, ah, I, this is seriously, I'm so glad to have this podcast, if for nothing else, than having gotten to talk to Sean Carroll and ask him about things like the Boltzmann brain problem, so speaking of, I wanted to say some words on that, and what I was trying to get at there, because I think similar to the first episode with Sean, I just, I rushed through things because I don't want to take up his time, you know, with my stupid thoughts, but, um, But I still am so, I don't know, I'm a tiny bit skeptical on parts of the Boltzmann brain problem. So once again, what I should have said is that I agree with most of it. I understand, rather, I understand most of that. I get that it makes more sense that there would be just enough low entropy to create life.

0:36:31 Thomas: So maybe there would just be, I don't know, a small habitable place where you and I could exist, or etc. Maybe it would just the sun and the earth, or whatever. And we wouldn't observe these billions and billions of galaxies that just aren't necessary. There would be other, those are other low entropy states that aren't necessary under Boltzmann's version of an eternal universe where things just fluctuate. What I, the only part I don't get, and I, again, I should have framed it this way at the time. The only part I don't get is the final jump where you go from, well, and furthermore, you could just have a physicist or even a physicist's brain.

0:37:16 Thomas: That's the part I'm just not sure is correct. The only reason I'm willing to even entertain the tiniest, minute possibility that what I might be saying is right and Sean Carroll could be wrong, which in general I completely doubt that possibility, the only reason is because it seems like this is contingent on biology, this seems like it's contingent, because for me, the question that I think I got out, but maybe I just didn't get it out quite right, is the frequency of worlds in which there is just some sort of mind, or rather the frequency of fluctuations given infinite time, in which you somehow fluctuate a brain, a functioning mind that can think, it's got to be, to my mind, vastly smaller than the frequency where you fluctuate just enough to get a replicating piece of bit of DNA or something, something that under which Darwinian processes can act.

What I meant to bring up, or what I would have had, I thought I was going to get anywhere, which I didn't. I didn't think I was gonna get anywhere. Because, again, it's 99% probability that I'm just totally wrong. But what I was gunna bring up is the infinite monkey theorem.

Now, you may have heard of it, where you think, how many monkeys would it take to get to the center of a Tootsie Roll Pop? No. How many monkeys it would take banging on keyboards to type out Hamlet, for example? And it turns out that s a super easy calculation.

0:38:49 Thomas: Assume spherical horses and assume monkeys that, that's a weird joke that I wonder if anyone, someone will get. Anyway, assume monkeys are just randomly hitting letters, not doing so in some predictable way or some, or they're just constantly hitting one button. They're actually random. It turns out that if you have an entire universe, so as many atoms as there are in our universe, if that many monkeys were randomly typing out just random letters, it would still take orders of magnitude longer than our universe has even been around to type Hamlet. And I have got to imagine that getting every single molecule just right, every single atom just right to form a functioning mind has got to be vastly harder to do than that.

0:39:39 Thomas: Now, I get it. You get infinite time. I get that you get infinite time in Boltzmann's universe. So, it will happen given an an ultimate time, or at least it's highly probable. Now, there's actually a chance, if we're dealing with purely random chance, it is actually possible that you would even just get the same letter over and over, like talking about the infinite monkey theorem. There's nothing that says you wouldn't just get the letter A from here to eternity. There is nothing that makes you not, except it's just extremely, extremely, extreme low probability. But anyway, I get that infinite at a time, you'll have a mind at some point. But what I'm thinking is, given the power of Darwinian processes and the complexity of minds, they're just so complex. It seems to me that that's a legitimate biology question.

0:40:28 Thomas: How complex are minds? If they were far less complex, we're talking about like an ant mind, then yeah, sure, maybe a fluctuation that just creates a tiny little brain that doesn't do anything. Sure, I could see that happening more frequently than than some Darwinian process, but when you talk about a mind as complex as ours, or a theoretical physicist, to use Eddington's example, that it seems to me you could try to make some probability based on what would you need fluctuation-wise to have the minimum habitable environment, minimum just habitable environment and a replicating molecule under which Darwinian processes create incredible stuff. I think a mind is more probable from that and so we would expect, and again this is me, I'm probably wrong.

0:41:19 Thomas: But to me, it seems like if that were true, then the Boltzmann brain problem, yes, it's still obviously a problem because we wouldn't have all this low entropy all across the universe. I totally get it. But we would expect, it doesn't, the last part might not be true where you could just fluctuate a brain. I think it would be more likely that you would have some sort of corporeal body that resulted from a Darwinian process that led to a mind, then it would be that you would just fluctuate a mind. And I don't know, I still can't wrap my head around that. I still, it would take an incredible calculation, I'm sure, that I can't do. Let me know if you think I'm crazy on this or if I should just take Sean Carroll's word for it. But the only reason I am even entertaining the notion that I could still be correct on this is because because I don't know that I had time to really make my case properly.

0:42:13 Thomas: And I think that Sean may have just been talking about the low entropy state in our universe would be improbable, which it obviously would be. So that's my little bit on our disagreement in part two. That anyway, who knows? I just have wondered that for so long when I've heard the Boltzmann brain problem. It's probably been a couple of years that I've just thought, no, that can't be right. Well, that was a lot of fun. Again, the most rewarding thing maybe I've ever gotten to do.

Man, I'm on a roll with really rewarding things like the James and Eli debate and getting to talk to Sean Carroll. It's so fun. Live in the dream. I'm loving this podcast, and it's made possible by listeners like you, and specifically by patrons at patreon.com/atheist, who, by the way, you may have noticed, got to ask, got to know that Sean Carroll was the guest early, and they got to pose some questions for Sean Carroll, So that's another benefit of being a patron that you might enjoy one day if you can spare a dollar per episode on patreon.com/atheist. That's it for me this week. Thanks again so much. What a week it was. I hope you enjoyed it even a tenth as much as I did, and that will be a very happy listener if you did. So thanks, and see you next week.