AMA | September 2023

0:00:00.0 Sean Carroll: Hello everyone. Welcome to the September 2023 Ask Me Anything edition of the Mindscape Podcast. I'm your host Sean Carroll. We are approaching, it occurs to me episode 250 of the Mindscape Podcast. I just published 248 last week, and I'm not gonna do anything special for the 250th episode. Doesn't seem quite glorious enough to do it, but we have approximately 50 episodes per year. So it reminds me that we just passed our 5th anniversary at the beginning of July and I didn't do anything as far as I remember. It was a hectic time, the beginning of July, I was trying to get my book, traveling a little bit et cetera. So I wanted to at least spread some thanks, some gratitude for everyone who's been listening all the new listeners too. But everyone who has enjoyed Mindscape over the last five years. That's a lot of episodes.

0:00:51.8 SC: It's not exactly 50 per year because the AMAs don't get numbered, things like that but it's pretty impressive. I would not necessarily have bet five years ago that we'd still be doing this now, certainly not every single week, but it's a lot of fun for me to do. It's a little bit of work. I will not lie about that, but I think it's absolutely worthwhile. So far, I'm learning a lot, that's for sure. I'm hoping that other people are learning something too. It's absolutely the case that part of my motivation for doing this is to counteract some of the misinformation, some of the bad information that is out there. I know that Mindscape is not the most controversial or action-packed or even gee whizz, my podcast out there. But there's a lot of cool ideas to talk to.

0:01:45.1 SC: I mean just the fact that I don't like to have the same guests on more than once. There's a huge number of guests that I've had, that would be great to have back but there's also an even huge number of people who I've not yet had as guests. It'd be easier for me to have guests on over and over again, no doubt about that. But I never know when I'm gonna discover something new and interesting by just having someone who I've never talked to. Most of the guests by now, that I have on Mindscape are people who I've not really interacted with very seriously before having them on the podcast. So that's what learning and surprise is all about. Some episodes will resonate with some people and some won't, but that's part of the excitement. So I am very proud of what we've done here.

0:02:31.7 SC: Very proud of having the Mindscape Big Picture Scholarship, which you can donate to, that is helping people study the big ideas at university. Very very pleased that people sign up for Patreon. As you know if you're a listener, these Ask Me Anything Episodes are funded by Patreon supporters and they're the ones who are asking the questions. You can become a Patreon supporter. It's pretty easy to do at patreon.com/SeanMCarroll. And five years is a long time. Will we be we still be doing it five years from now? I bet we bar I think so. I think it's still not run out of things to do yet. At some point if I think that it's just work then I will quit. Then I will let, easily say like this is an worth it anymore.

0:03:17.8 SC: But five years. I think that there's two Mindscape guests who have, are deceased now, which is very sad to me. Herbert Gintis I think I mentioned before, passed away earlier this year. He led along in a productive life but also Mari Ruti has passed away. She's exactly my age. We knew each other back in graduate school but cancer does not care how old you are. And she fought cancer for a couple of years and that eventually as often happens, the continued very harsh treatments of the cancer, were what ended up not being able to be treated anymore. And so she passed away a couple of months ago. Very sad but life is going on, right? If you haven't listened to Mari's episode, it's a special one because it's a bit of a departure from what we did on Mindscape, otherwise but she was a uniquely good person at making a different kind of thing palatable and exciting and interesting to other audiences.

0:04:21.2 SC: In this case, Lacanian psychoanalysis, which is not our forte here but I couldn't think of a better person to talk about it than Mari. And she's very very missed by her friends. And I hope that she recognized before she died how loved she was around the world. And it's part of time passing, it's gonna happen to all of us. So it's just a reminder that we've been around for a while now, doing the podcast. Again, tremendous thanks for everyone listening. Either if it's completely passively or supporting the podcast, leaving reviews on iTunes or supporting on Patreon or leaving comments on the webpage at Preposterous Universe. I thank you all, for participating in the journey. It's a great one and we're going to continue on for a while. So with that let's go.

[music]

0:05:27.6 SC: Jason Ricciardi says, "I've heard you mention that Twitter is dying several times on Mindscape and I was wondering why you feel that way, and what do you think about it now that it's rebranding to X?" Yeah, this is obviously a big important question. I kind of simply say Twitter's dying and I go on with it. I don't wanna dwell on it, but okay this is a perfectly good question. Let me give you my thoughts as of September 2023 subject to change. Of course, if things change, yeah I do think it's dying. It won't completely die of course, that I think is an exaggeration. Twitter will exist even though it's been branded X whatever it's gonna be called it will exist I think in the years to come, at least as long as this podcast does would be my guess.

0:06:10.3 SC: But it's changing and it's absolutely changing for the worse in many noticeable ways. The most obvious ways is it's much easier to be an asshole on Twitter now than it used to be. It's easier to be racist or anti-Semitic or just basically combative. You can see in the people who were previously banned and invited back. It's not hard to see the general trend of who has been invited back after having been gotten rid of, Donald Trump. One of the most obvious examples there, and more importantly to me because the people, there are people on Twitter who are harassed, right? In various ways and I'm generally not one of them. I'm not really a target of harassment but I don't like it that other people are harassed. It sort of lowers the tone makes it less pleasant overall.

0:07:03.3 SC: And I feel bad for the people who are harassed and I'm not the only person who feels that way. And therefore a lot of the good people who I like on Twitter have left, or are leaving or are using it less. I'm still there but I use it a lot less. I basically post announcements for new podcasts and I occasionally retweet things, but I don't engage a lot like I used to. It's just a little bit less pleasant. Many of the people like I follow who, like I said have literally closed their accounts. There was recently an article I think in nature about scientists leaving something like 40% of scientists polls said that they'd either left Twitter or were using it a lot less now. So that just makes the platform less enjoyable, less fun et cetera. So looking for alternatives is the current mode that I'm in.

0:07:53.2 SC: There's another article by the way I think Washington Post maybe, that mentioned. It's there's a lot more disinformation on Twitter now than there ever was before. And these are studies, these are people collecting data. This is not vibes. This is not an anecdotal impression. We all have our own thing that we see, right? Our own timeline on social media. So your experience might be great, but you can't extrapolate from your experience to somebody else's. And many people have a much less great experience right now. And that just means that the conversations are not as good. And obviously, there is not just an idea that many people have been welcomed that you don't want to be interacting with. But the way that the algorithm arranges the conversations has been dramatically altered. And there's been a lot of ink spilled or electrons destroyed about the blue check mark system for those of you who are not on Twitter bless your hearts.

0:08:53.2 SC: There used to be this thing called being a verified user, and you would get a little blue check mark by you. And it was originally because people like Shaquille O'Neal who was a big celebrity user in the early days, well it was it's easy to start a Twitter account and claim to be Shaquille O'Neal, right? So they decided to introduce this idea of verification that would make sure that you really were who you claimed to be. And it spread, not only to just celebrities and athletes but to journalists and politicians and academics and so forth, so that if you got that little blue check mark you knew this person was at least who they said they were. You didn't have to listen to them, but at least they were somebody. And there was at least some preference given. And this is always where it gets contentious but there's an algorithm in Twitter that sorts the order of replies and shows you suggested posts even if you don't subscribe to people.

0:09:45.5 SC: And being a verified user was a little bit of a boost there. So that has gone away. Now there's still blue check marks and they're still called verified users but they have nothing to do with being competent, with being in authority, with being who you say you are. What they have to do with is, you signing up and paying $8 a month. But those people are still boosted in the conversations. And it used to be that there was at least a slight positive correlation between being a verified user and being a constructive addition to the conversation, because you could get verified by for example being in authority in some subject. When news would break, when a country would get invaded or there was a disaster somewhere and you could go to the trending topics and click on them, it was useful to do so because there was some journalist who had spent 20 years in this country and was on the ground and could tell you what was going on and you would, had not heard of them before but you could find them.

0:10:48.4 SC: Now when you do that, the people who are shown to you are people who spend $8. And those are not only not positively correlated with giving useful information, they are actively negatively correlated with giving useful information. Some people who spend the $8 to be verified are of course perfectly reasonable, but many of them are just people who wanna mouth off, people who embody the Dunning-Kruger effect. And so it's become way less useful. And it's not only less useful for people like me, trying to find news and new pieces of information, but there's been various degradations of what is called the API, which lets people use Twitter automatically to post information and things like that. So emergency services or informational services find it much harder to use Twitter. For me, one of the fun aspects of Twitter was Kelly Truelove who posted under True Sci-Fi had these lists of physicists and astronomers and writers and philosophers and so forth and would make, on Twitter, and would make graphs where who followed who, and how you could find people and things like that.

0:11:56.9 SC: Very very useful. No longer exists on Twitter, because you can't get the information. You can't download it, not allowed to anymore. The company has been steadily but absolutely un mistakenly making it harder to use Twitter. The way that I read Twitter used to be something called TweetDeck. Now that is removed, I can't use it anymore, right? So that, it's just a much worse experience overall. The statement is that, going forward they're gonna remove the ability to block people on Twitter, which is just a disaster. I mean it's a true disaster for people who are harassed but it's a disaster for people like me who have to sift through a lot of nonsense, to try to find something interesting. So for many many reasons, I think that Twitter is seriously declining. And again it's not just the vibes are bad.

0:12:47.0 SC: It's very tangible degradation of the experience. Like a vibes based argument would be, well I don't like that they renamed it X versus Twitter. I couldn't care less that they renamed it X versus Twitter. I think that it is a terrible business decision to give up a free connection to basically a word that had entered the English vocabulary on the basis of your corporation, right? The idea of tweeting and retweeting and quote tweeting are out there as words that people use and you give up those words, that just makes no sense to me. But I don't claim to be a genius business person. So maybe there is some logic behind there. I don't know. I also don't care. They can call it whatever they want. It's just much less useful to me now than it was. I don't know what's gonna happen next.

0:13:37.7 SC: I am personally spending most of my time on Bluesky, to the extent that I'm doing anything at all. But I can't really push Bluesky very hard, because it's not open yet. You need an invite to get there. It's still in Beta. Hopefully, it will roll out to open enrollment very very soon. But honestly the reason I like Bluesky the best, is it's not trying to be anything else. It's not trying to improve things. It's basically just Twitter on a different platform. It's, there's tiny marginal differences that people make a big deal out of, but it's easy to use. You sign up and you use it and it's kinda like Twitter and that's all I really want, right? I know there's other options Mastodon and Threads and so forth. Lots of people love Mastodon. I just didn't like it that much.

0:14:21.9 SC: It's something for, Mastodon is Twitter for Linux users. [laughter] I used to have a Linux box on my desk in my office. And there's a certain kind of person who loves Linux as an operating system rather than Mac OS or Windows because they can really get in there and they can fiddle with it and they can make it exactly what they want which is great. It's also just much harder to use if you're not devoted to it. And Mastodon has that feeling for me. It's not friendly to the new users. And so I don't see it being anywhere near the scale that Twitter is. Again I could be completely wrong. I have no special insight on these things, but I think it's a loss, Twitter I really do.

0:15:05.7 SC: I think that it was very important to me. I've certainly connected with many of the Mindscape guests in the first time by reading their Twitter accounts. I've met, made friends in real life from Twitter. I've learned things by talking to people on Twitter. So it's not trivial to me. I think it's a true loss, and I feel bad but like I said life goes on. Things change. We adapt and we move on. Next I'm gonna group two questions together. Amy Ferguson says, "Your work often explores profound questions about the universe. I'm curious about your personal reflections. In your downtime, do you often find yourself contemplating deeper, bigger picture ideas as a matter of personal interest? And has the nature or frequency of these reflections changed from when you were younger?" And then Mike Johnson says, "Does the idea of eternity ever cause you to break out in a cold sweat?"

0:15:56.9 SC: "The idea of eternity is one of the few things that will make me lie awake at night, staring at the ceiling trying to make it make sense. I have an overwhelming sense of dread and confusion when I think about the idea of there being no end. And even if there was an end, what does that even mean? I know when I'm dead, I won't have a brain capable of these thoughts so it doesn't really matter. But for now the idea scares the bleep out of me." So see I think you see the relationship between these two questions reflecting on giant bigger picture ideas. Mike is a little bit specific about the idea of eternity. Amy is more open-ended about different kinds of big picture questions. I've always loved thinking about big picture questions. Do I do it more now that I'm either older or more educated or it's my professional job or whatever?

0:16:47.0 SC: I don't think so. I do think that your reflections change. I hope that they do, and they certainly did. For me it's actually hard to remember, to be honest, how I thought about these things when I was 16 years old or whatever, because one does become extremely different in one's thought processes. As you learn things, as you think about your own thoughts and realize, you know that thought really wasn't that smart. [laughter] We are always, I hope thinking about our thoughts, right? Thinking about where we're coming from and hopefully, we can re interrogate some of the ways in which different thoughts fit together and then change our minds. So certainly I have a much more sophisticated, I think I would like to say more sophisticated point of view on these things. But I don't think that the fundamental nature of frequency of these reflections has changed.

0:17:39.9 SC: I wanna know what the universe is, what it's made of, how long it's gonna last, where it came from, our place in the universe. I think about all these things and I did, I've long thought about exactly those things. The idea of eternity in particular doesn't bother me. No, I mean it's interesting because some people are bothered by the idea that the universe will end, right? The idea that it's not eternal bothers some people. I think that bothering or a cold sweat is just a not quite the right way or the best way to approach it in the sense that, what it is what would be better would be an acknowledgment that our everyday intuitions trained as they are by evolution in our lives and things like that, just aren't up to the task of thinking about eternity pro or con, right?

0:18:34.4 SC: So why should we feel comfortable and happy thinking about these questions? So even though I like thinking about these big deep questions, I don't expect that my instincts or intuition are going to be very helpful or really going to tune me to think about them in the best way. You really have to try to be open-minded I think, and say like, well I thought it should be this way but it's not that way. I think that I, it would be more satisfying to me, or more rewarding if it were this way, but it just isn't, that's the kind of attitude I want to take in my reflections on these deepest questions. Ahmad Shaker says, "I just watched your video on Renormalization." This is referring to, from a couple of years ago the biggest ideas in the universe videos that are leading into the books that we're in the process of putting out.

0:19:26.2 SC: So Ahmad says, "I think I understand why we can ignore energies above a certain cutoff, but the loop diagrams still have an infinite amount of diagrams between let's say 2 EV and 3 EV. What happens to these?" Good. This is a great question actually. I never quite thought about it in that way. It's kind of an interesting version of a way that you can think about it. Like I can say all the words that I'm saying and they make perfect sense to me but someone hears them and reinterprets them in a slightly different but completely legitimate way, and reaches something else. So the idea here just to back up is, in Feynman diagrams when you're calculating some process, so Feynman diagrams remember are little pictures of elementary particles bumping into each other, but they're not just evocative little pictures. The physicists who do this for a living use Feynman diagrams to do calculations.

0:20:17.9 SC: The diagrams correspond to a certain equation which you then, typically an integral, which you then solve to figure out what exactly is the probability of this process occurring. And when you have a loop in a Feynman diagram, so that you can imagine the topology of these little pictures you're drawing, you can draw tree diagrams like an electron comes in and goes out, a positron goes in and comes out and they exchange one little photon between them. There are no loops, there's no closed curves in that diagram but if they exchanged two photons between them, now there's a loop that you can sort of draw when you go around. And the rule and Feynman diagrams land is you add up the contributions from every possible diagram. When there is a loop in the diagram, there is a free parameter because you can ask how much momentum is going down any one leg of that loop.

0:21:10.8 SC: And it turns out it is not fixed by the external conditions, by just momentum conservation et cetera. So you integrate overall possible values of the momentum going through the loop. And this integral will often be infinite if you do it in the sort of straightforward conventional follow-your-nose way. This is what led to all the discussion in the 1940s and 50s, about infinities and renormalization in quantum field theory et cetera. And the reason why it's infinite is the correct reason. Let me say it correctly first then we'll back up. The correct reason is because you, when it is infinite some loop diagrams are not infinite but many are. The reason why they are is because you're integrating the momentum going through the loop from zero to infinity. And some functions that you integrate from zero to infinity like one over x squared forget zero.

0:22:06.4 SC: How about integrating one into infinity? There are some functions you can integrate and get a finite answer, okay? But there's other functions I guess maybe e to the minus X would be a better example. You can integrate that from zero to infinity perfectly well. There's other functions which the integral gets bigger and bigger and bigger and just gets infinitely big. So the whole idea of what are called effective field theories is to put a cutoff on that momentum, to not integrate from zero to infinity, but from zero to some finite number. And then the integral becomes finite. And you can read about that in my upcoming book, "Quanta and Fields" which is the second volume in the biggest ideas in the universe series. So anyway Ahmad's question is, "But if you just look at a finite range of momenta that you're including," so forget about the infinitely big momenta, I should have said that the justification for ignoring the infinitely big momenta is we don't know what's going on.

0:23:06.2 SC: Infinitely big momenta. Momentum is inversely proportional to distance in quantum mechanics and field theory. So you're effectively talking about infinitely short distances where space-time itself might not be a valid concept. So there's a justification for doing this, but technically an integral is a sum over an infinite number of things, right? So as Ahmad correctly says, "Just between two electron volts and three electron volts, there are an infinite number of momenta that you're adding up in some sense." The answer which is sort of disappointingly mundane is, that's just what calculus is for. Calculus is exactly about adding up an infinite number of things and getting a finite answer, because really you're adding up zero times infinity, okay? And that's ill-defined as it is simply stated boldly that way. The zero that I'm talking about is the contribution from a single number between in this case two electron volts and three electron volts.

0:24:10.0 SC: It's the area under a curve of zero width, right? It's the curve that goes from a certain number to the same number without moving at all. That's gonna have zero area under it. But there's an infinite number of them that we add up to get the whole area under the curve between the starting value and an ending value. So it was Newton Liveness who taught us how to do this which is to disco discretized, to chunk up that curve into finite area rectangles, add all them up, but then take the limit as the rectangles get skinnier and skinnier. And by doing that, you get a well-defined limit a finite answer for your infinite sum. It's exactly the same thing in Feynman diagrams. There's nothing different than that. You get a finite answer for the integral over this loop momentum of all the possible momenta between 2 EV and 3 EV.

0:25:00.5 SC: That's just not a problem. That's just calculus. The only problem comes when you're considering momenta that go infinitely big. And that's a whole nother story. Cooper says, "Has your thinking on complexity changed at all? In light of your recent conversations with Sam Bowles and David Krakauer, both emphasized the teleological nature of complex systems and my impression was that you hadn't thought of that feature being a fundamental aspect of complexity." Well, yes and no. On the one hand I think that you're right, that I... Well I guess the way that I would put it is, I had not thought that anyone would use the feature of teleological behavior or tele-genomic matter as David likes to say, as a fundamental characteristic of complex systems. It is certainly a characteristic of some complex systems and I'm very very interested in understanding how that can be the case in a world where the fundamental laws of physics are not teleological at all.

0:26:03.9 SC: So this is a classic case asking about emergence, right? How do you get purposes and goals emerging out of the mindless purposeless interaction of microscopic subsystems? I think that's a perfectly legitimate question to ask. I think it's perfectly legitimate to say this is a fundamental problem that we should focus on. I don't think it's right to say that that's a necessary central feature of complex systems. I do think that the galaxy is complex, our galaxy is pretty darn complex. It is not tele-genomic in any useful sense. So I think that I mean I get why you would want to do that because as David would say, there is a such a big difference once matter becomes tele-genomic. Once a complex adaptive system has goals, and that's back in the day you would, in Santa Fe Institute circles, hear a lot more talk about complex adaptive systems than you do now.

0:27:06.8 SC: These days we more often just talk about complex systems and I think that's an important difference. If you stick the word adaptive in there, then I would absolutely get that teleology is playing a big role. The idea of a complex adaptive system is that it has information about the external world. It processes that information and it uses that information to get something that in some well-defined sense it wants, even if that thing is just to stay alive to continue existing, right? I think that there are precursors to that, that count as complex. And so my argument would be that if you skip right to tele-genomic matter and complex adaptive systems that have goals and so forth, you're skipping over a lot of interesting things, right? I mean you're talking about the evolution of the species without talking about the origin of life.

0:28:03.6 SC: And you're absolutely welcome to do that. That's a fine thing to do, but you wouldn't wanna argue that the origin of life is uninteresting. You wouldn't want to argue I think that the various kinds of systems that seem complex to me but don't yet have purpose or teleology in them, are somehow less interesting or don't count. So I'm just, I don't think there's really any incompatibility here. I'm just pumping for a more expansive notion of complexity that includes the thing that I care about, which is where these complex systems came to be in the first place. Complexogenesis, right? That's something that dovetails very nicely with my interest in entropy and thermodynamics in the era of time. So I don't want it ruled out from this whole area of inquiry. Rob Gebolar says, "I have a question about your confidence in the claim that all physical laws relevant for our everyday life are known."

0:29:03.1 SC: "What about the possibility of a new force which is so weakly coupled that we would not see it in current collider experiments but which becomes relevant when very many particles are involved at mesoscopic or macroscopic scales? After all gravity is like that and we wouldn't have found it by only looking at collider experiments." Yeah sure. A weak new force is absolutely something that we can be interested in and look for and are interested in, and do look for. If you look up the various places papers and books and so forth, where I've talked about this idea, I explicitly consider this possibility. The fact is that ordinary matter is made of only three things at the end of the day, protons, neutrons and electrons. Maybe you could add in photons and gluons if you wanted to like look at a higher-order perturbation.

0:29:54.9 SC: But roughly speaking the quantum numbers that are non-zero from the matter in you and me are the numbers of electrons, the numbers of protons, the numbers of neutrons. So that actually makes it very simple to look for new weak forces, because all you have to do is measure the force between electrons, protons and neutrons and other electrons, protons, neutrons. So the parameter space is kind of small. You can actually do everything. And so all you have to do, is look at heavy collections of matter, with different abundances of protons, neutrons and electrons, right? People have done that. There are limits. There are quantitative, numerical limits on how big such a new force can be. Of course, it's not necessarily the same as gravity, because gravity is what we think of as an infinite-range force. It stretches over astrophysical distances. You could imagine a force that is stronger than gravity but shorter range.

0:30:52.9 SC: So it's not as obvious in an astrophysical setting but we've looked for that too. And the answer is, if you go down to the scales that are like neurological scales, right? The sizes of the separation between neurons in your brain or something like that, the limits on the strength of any new force are comparable. I forget the numbers, but they're in the same ballpark as the strength of gravity. And the thing about gravity is, it's a super weak force. Like you say we do notice it, but only because all of the earth is pulling us down. So if you care about the force exerted by a neuron on another neuron or even by the earth on another neuron, there's just no room for that, those are ruled out. So yeah, that's a absolutely conceptually allowed thing to think about.

0:31:49.5 SC: But the data have spoken on that one, they're not there. They there could be other forces there, but they're too weak to make any difference to our everyday lives including our biology. Chris V says, "What are your worries and hopes for the future?" I don't wanna say too much about this, 'cause we have an upcoming podcast about worries and hopes for the future, but I think that some of the worries and hopes for the future are kind of predictable. Like there are trend lines, environmental ones especially when it comes to climate change or pollution or things like that. There are trends and they might look bad and that's a worry. And I think that's a perfectly legitimate worry, but then we can also work against them. My worries and hopes therefore are actually more concentrated. I guess I'm talking about the worries right now.

0:32:38.4 SC: Let's talk about the worries. The unpredictable things, the things that might have a rate or a probability of happening but we don't know what it is, and it's small, okay? So the question when you have something that would be a disaster but it's unlikely to happen is, how do you balance a small probability versus a giant impact if the thing does happen? AI is an example that people like to use. And I'll just repeat my usual thing that I say about AI. I think there's plenty of good reasons to worry about the impact of AI on our lives and I am absolutely in favor of worrying about it, and putting safeguards in place. I am not impressed by people who leap right to destroying all life on earth. I think that that is not a very plausible scenario.

0:33:30.5 SC: And if there's some other scenario where 100 million people die or even more likely, a scenario where billions of people are slightly worse off, that's really bad. We can worry about that. That's much more plausible than extinction-level events and is absolutely worth worrying about. And if we do worry about it, I think we will also ameliorate the probability of the extinction level events. So I don't think, so AI is not high on my list there because I think that if we just take the realistic worries about it, we at least can try to ameliorate them, whether we will or not yet, that I don't know, I'm kind of more worried to be honest about things that just seem unlikely but are not new and sexy, like new bio-weapons, pandemics, good old-fashioned nuclear war, right?

0:34:21.5 SC: I think these things are still quite possible. Again we don't need to jump right to extinction-level events to imagine millions of people being adversely affected by them. And the timescales, the frequency with which these things happen are sufficiently rare, that human beings are not good at planning for them. It hasn't happened the last five years of course the pandemic thing did, I get that. But otherwise, in a few years, we'll say, well it's been a while since the last pandemic. I'm not so concerned about that one anymore. And human beings bless their hearts they're just not good at planning for things like that. So it's those kind of not completely implausible disaster scenarios that have timescales longer than 10 years between when they generally happen, that I think are very good to worry about. Sunspots and solar flares are another one that I've talked about before.

0:35:15.9 SC: In terms of hopes, I don't know. I have mentioned recently the podcast that we did with John Danaher about our coming automated Utopia. I think we're getting very good as a society at creating wealth, creating food, creating power, creating knowledge, power in the sense of electricity and things like that. Not political power. We might even arguably be getting better at protecting the environment if we really put our minds to it, where we have the capability technologically, let's put it that way to protect the environment. I always go back to the podcast we did with Joe Walston, talking about how just moving people into cities is a tremendously beneficial thing to do for the environment and it is happening, right? So I can imagine the following idea. This is probably utopian but that's okay. You said what are the hopes?

0:36:09.8 SC: I can imagine that technology has been improving so quickly that there's a mismatch in the timescale between the rate of technological improvement and humans habits of mind that organize society and how quickly those get updated. Maybe right now we're still in a medieval mindset, where it comes to society even though we have a much more abundant physical environment in which we live. So the idea that we should just take all this wealth and make sure every person is fed and housed and has basic health care and education, I think is a feasible thing. We could do it as a certainly in the United States we could do it, if we wanted to, in the world probably we could do it without too much extra effort, but we don't even try, right? To literally like just feed and clothe everybody. That's considered, I don't know something that society isn't meant to do.

0:37:08.5 SC: I think that's an outdated conception. So the utopian in me wants to think that we at least might contemplate dramatically shifting how we organize society, so that everyone is given some basic needs, we have the physical capacity to do that. It's our choice not to be doing it right now. So my hope is, that we catch on to the fact that we can do it and the fact that everyone benefits if we do it, if we just make sure there are no homeless people, there's nobody living in poverty, there's nobody who doesn't get an education, or there's nobody who dies as a child unnecessarily et cetera. All those things we could do, those are my hopes for the future. Maybe this podcast increases the probability that it happens by 0.0001% or something like that. That's my single biggest hope for what the Mindscape podcast can possibly do.

0:38:00.5 SC: David Maxwell says, "Does tenure for university positions act as a break on society's intellectual advancement by keeping those with old ideas around, at the expense of those with fresh ideas. Is it still an appropriate way to allocate the limited resource of funded academics or research positions?" I think I've said, talked about this before so maybe I'll try to keep it brief but I think, yes, I think so because you can't just change one aspect of a system like this and expect all the other aspects to go ahead unchanged. If it weren't for tenure, why would most people even try to become professors? [laughter] Most people who become professors spend a lot of time a lot of years of their lives training for it. They're generally hard workers, pretty effective at the work that they do. They're generally smart cookies and they're talented and they could make a living other ways.

0:38:54.7 SC: Even my literal set of graduate students who I work with and who I know, they either "succeed" by becoming faculty members or they don't succeed at becoming faculty members and get much higher paid jobs doing something else. But a lot of that is a trade-off. We say okay we're not gonna give you as much money or material rewards as you might otherwise get, but we'll give you job security. And that's very attractive to people. The idea like I'm going to work and work and work and get tenure. That's the goal a lot of these people have. And it would be completely wrong to discount the more highbrow fact that tenure gives you freedom. Tenure gives you the freedom to work on new things. Like if I were hired to be a cosmologist, and I decided I wanted to work on philosophy instead, if I had tenure which I don't by the way, but I have a different position which is good for other reasons, I could do that.

0:39:48.8 SC: You can switch fields, you can let your creative juices flow. Many people have zero desire to let their creative juices flow, that's fine. But in many ways, tenure is just a simple set of compromises that keeps academia full of smart people working hard on their things. Now obviously, there's plenty of people who just kind of chill out after a while don't work very hard, or not productive, that is the price you pay. Very often those people are useful in other ways, whether it is teaching or administration or just being a voice of wisdom that you can talk to in the seminar room and things like that. So I do think that there should be more variety in how these things are organized. That is to say, I wish that different academic institutions didn't all use the same systems, so that maybe some people who kinda liked it one way could go to different universities or different research institutes.

0:40:50.4 SC: But guess what, this has been tried. [laughter] There have been universities and research institutes that have tried to not have tenure. Nobody wants to go there, or the people go there and say please let's institute the idea of tenure. Okay? So it's an incentive for smart people to do their thing. I think it's a fairly good system overall. Paul Cousin says, "Is it common to contact an author to let them know that you cited their work. Or do cited authors usually find out via Google Scholar or something similar?" It is completely uncommon to contact an author to let them know you cited their work. It's fine. You will sometimes get emails with a paper attached saying, "Hey I wrote this paper. It's on something you're interested in. Maybe you're like to read it whatever."

0:41:36.0 SC: That's completely okay. But it's not the norm. It's not common. When I write a paper and I have, I don't know 20, 30, 40, 50 citations in it I do not email all the people who are in my list of citations. In fact, it's more than that. Like I was reading, as I'm recording this, I'm preparing a week from now, I'm going to have a public debate with Philip Goff. You remember Philip he was on the podcast. He is one of the champions of Panpsychism out there in the world right now. And so we're having a debate about Panpsychism, Pro and Con. And so I was reading a couple of papers about Panpsychism and I read one and it was literally the whole paper, was a response to me, was a response to my paper on consciousness and the laws of physics.

0:42:22.2 SC: And I never knew. [laughter] So I was like "Oh this is kind of flattering". I didn't really agree with anything that was in the paper, but it's still it's kind of nice to know that people are taking it seriously. So I don't know. I mean maybe they, it should be more common to let people know but maybe you don't wanna let people know when the whole point of your paper is to say the person is wrong. Okay? So I think that it raises an interesting question of what is the future equilibrium way that academics and scholars will find out about papers that are interesting to them? 'Cause there are too many papers, right? There's just too many papers to read. If you are a successful ongoing researcher who has a research group with students and postdocs in it, then those students and postdocs are your way of knowing what is interesting in the research literature right now.

0:43:09.5 SC: They're the ones who are young and learning and energetic and are reading everything and they will tell you if something interesting comes up. If you're all by yourself, then you have to do a little bit more work. So Google Scholar, Google Scholar by the way, not only is a place where you can go and find out who cited your paper, they will send you a daily update. Here's how many people cited your paper. Here's all the new papers that cited you. So I do that, and it's not ego surfing. I'm not like oh happy that someone cited me. I wanna know if someone is building on the work that we did in various interesting ways. There's also Semantic Scholar which does something like the same thing, but it's not quite tied to citations. It's just here are papers we think you would be interested in given what papers you've written about before.

0:43:56.0 SC: So again I don't think that we're done yet. I don't think that we're in that equilibrium state where we know the best way for people to find these things out, but hopefully, we're improving the state of affairs. Okay, I'm gonna group two questions together. One is from Fabian Rose Stalin, by the way before I actually answer this, I should have said this in the intro but a couple of things. Number one, we're getting a lot of questions in that call for questions in the AMAs these days. So the fraction of them that I get to answer is smaller. Apologies for that. I make a tiny bit of effort. If I don't recognize someone's name from previous AMAs, I try to give them a little bit of preference. I'm not very good at that. It's not at all systematic. I'm sorry if you've been asking questions and have never gotten one through.

0:44:42.1 SC: My apologies for that. But I do try to spread the wealth a little bit. And the other is, I will reiterate the instructions. Number one, keep your questions short. Number two, only one question per AMA. So there's some folks in there that seem to have not noticed those instructions but those instructions help you get a question answered. Anyway, neither one of these apply to either these questions. I just I don't know why it just came up into my brain right now. But Fabian says, "I recently thought of the fact that when I do something good for a future person like future me, I'm actually doing something nice for an incredibly huge amount of future people on different branches. Somehow it's made it even more enjoyable to do something nice like cleaning the house for my future selves. Have you had any philosophical realizations or something similar from this way of trying to understand the self in the context of a branching universe?"

0:45:34.5 SC: And the other question is by Gauta Eanaval who says, "Are believers in the many world interpretation of quantum mechanics faced with different ethical considerations than believers in one world interpretations? It seems to me that my relationship to a future version of me on a different branch resembles my relationship to a person living today that I will never meet. And if so, I would think the joy of dodging a bullet that could be set up by having a lucky draw of a quantum process using the universe splitter app should be diminished by the fact that another person on a different branch was hit by the bullet. With a one-world interpretation of quantum mechanics, this would not be so." So both of these have to do with different levels of seriousness. Thinking about the ethical implications of the many world's interpretation of quantum mechanics. For Fabian's question, I think this is the more straightforward answer here.

0:46:25.5 SC: I do not as a matter of sort of rigorous scientific understanding, think of the impact of actions I take today on future generations any differently, because I believe in many worlds than I would in ordinary single-world classical or quantum physics. And I think that to be consistent if you're a, if many worlds is your favorite theory, that's how you have to behave. So we always talk about deriving the born rule, right? Deriving the probability rule in quantum mechanics the idea that the probability of seeing something is given by the amplitude squared of the wave function. And there's different arguments about the best way to do that. Chip Sebens and I had a way to do it that I kind of like, but the implications go way further than just arriving the probability rule. The implication is that, the world's count by a certain amount that is weighted by their wave function squared.

0:47:29.2 SC: So the short... To skip to the answer here, even though there are in some sense more people in the future, each one of them counts less [laughter] I don't mean to disparage them but they count as much as a person times the way function squared. And what that means is that, the total amount of counting is constant over time. It does not grow just because the universe splits or subdivides. You start with a very thick branch at the beginning and it splinters and divides but the total weight on all the branches remains fixed. I think you have to think that way if you want to accept many worlds and take it seriously and move forward with your life. Because otherwise, I could do a Stern-Gerlach experiment. I could measure a spin of a particle that was in a 50-50 chance and suddenly it's now, there's a universe where it was spin up a universe where it was spin down. And I could do that or I could, it could be done without me knowing, let's put it that way. And if it's done without me knowing then suddenly there are twice as many people in the multiverse 'cause there is a whole nother universe.

0:48:40.0 SC: Right. And in fact, most quantum measurements are of exactly this form. I don't know that they're even going on, but it shouldn't affect my going through life whether someone somewhere out there in space is doing a measurement of a quantum system. And the only possible way that it can't is if I think that the people post-measurement count only as much as them times their wave function squared. That is the consistent way to accept many worlds as a theory, and therefore, I don't think it matters that there are more people, more copies of me in the future. And likewise, for Gauta's question, this idea of how do you deal with the reinterpretation of probability in a many world interpretation versus a single stochastic world. I think that any prediction, any way that you have of dealing with the future world is...

0:49:37.0 SC: I gave examples in something deeply hidden and so forth, that you could contrive rules that would make you act differently if many worlds were true versus if it's not. But they're absolutely contrived. They're not very natural. If you think that there's a probability that something is going to happen or not in a single world, versus saying both things will really happen, but they are weighted, they're weighted by numbers that add up to one, I think that there's no difference in how you act or think in those two situations. And maybe you think that there should be, but then you shouldn't accept many worlds 'cause it's not gonna work out for you in various ways.

0:50:17.6 SC: Lothian 53 says, "In the many worlds interpretation of quantum mechanics, how do we know that the other worlds continue to exist past the point where we lose contact with them?" Well, we don't any more than we know that our world will exist tomorrow. Alright, how would we know that? We have a prediction on the basis of a model, the prediction of many worlds is that all the worlds are equally real. They just keep existing. The other world's likelihood of existing from moment to moment is the same as ours. There's nothing special about it. It may be that we live in a multiverse where there's a terrible genocidal evil demon who lets those worlds come into existence, and then wipes them out of existence. That would be weird and bizarre, and we have no empirical reason to think that, but if you wanna think that, you are welcome to do so.

0:51:07.7 SC: Stevie CPW says, "How do you feel about data science being accepted as an alternative to algebra and calculus in higher education admission requirements?" Well, I had mixed feelings about that. There's a positive side and a negative side. On the positive side, for a long time, I've thought that statistical reasoning should be given much more weight in... This is actually not higher education, typically the people are talking about this, it's usually the high school level that people most care about this question. There's only a finite number of years in high school, and there's a lot of good math to be taught, algebra, geometry, calculus. I think that statistics also deserves a place at the table, and that means that something has to go. Whatever that is, that might be different for different people, etcetera, but I think reasoning about probabilities and uncertainties is very, very important and is also mathy. It doesn't have to be just, here's a coin flip. So you can get really deep into serious math and solving equations if you study probability carefully. And I think that maybe data science more broadly, same kind of thing, how do you fit a curve to some data? How do you deal with errors and uncertainties and things like that?

0:52:25.6 SC: Central limit theorem is a whole bunch of very good things that you can absolutely talk about as part of a respectable math education. That's the good part. The bad part is that there has been a movement in certain places, California, for example, to simply water down the high school math curriculum. And I think that's a disaster. I think that's terrible. Even when it's done with the best of intentions, some people are saying, "Well, some students are less prepared than others and they struggle in math classes because they're less prepared." And guess what, unsurprisingly, that lack of preparation is often correlated with either socio-economic status, or racial categories, or things like that, and it seems like effectively they would say it seems like we're discriminating against these students by making them take the same classes as people with better preparation. And therefore, the conclusion that they would have that I think is terrible would be everyone should have less math or easier math, or something like that. It is somehow discriminatory to offer calculus in high school, or to demand that every student know algebra. I think that's terrible. I think that the way out of discrimination is not to make everything easier for people, but to give people the resources to do the hard work. If people aren't learning algebra and calculus as well as they should, dump money on the problem would be my solution.

0:53:51.5 SC: The education system is failing. Good. Make it stop failing. Don't say, "Well, it's failing, and therefore, let's fail equally." That's not the way to do it. I think that you help people who have lived through discrimination by offering them opportunities. And one of those opportunities is learn math. That includes data science, as well as algebra and calculus and geometry. But if what you're secretly or not so secretly doing is using data science as a way to just make things easier and less rigorous and less challenging and less mathy so that no one's feelings are hurt, I think that's a huge mistake that people are making. Ken Wolf says, "In the visual arts, entertainment or literature that you enjoy, is there something that you would regard as comfort food? Whether it is a specific work, body of work or genre, is there something you go back to again and again, not out of respect or admiration or to gain a new insight, but just because it puts you in your happy place? By way of full disclosure, some of mine are Star Trek, anime, romantic comedy and the 1812 Overture." I'm not sure from Ken's placement of commas whether anime and romantic comedies are two separate categories or one category of anime romantic comedy. Both are perfectly plausible answers there.

0:55:10.4 SC: Absolutely. So this is a perfectly good question, and I'm a huge believer in comfort food, by the way, both literal comfort food and figurative comfort food. When it comes to eating, I'm a huge believer in comfort food. When I've had a long day or a really long week or whatever, it's gonna be pizza and buffalo wings for me. And in past, it also would have been ice cream. I'm not as young as I used to be. I can't just wolf down the pint of ice cream without any ill effects like I could have when I was in my youth, in my salad days. But I know that the pizza and the wings are not good for me, but they make me feel better. Those endorphins come rushing in, and I think that's perfectly fine. Macaroni and cheese, whatever it is, and I say that as someone who is also very willing to eat crazy challenging food and be rewarded by that. But I think that the variety is good, and I feel the same way about arts, entertainment and literature. In fact, both Jennifer and I, we have a routine where we work really, really hard during the day, and then we kind of collapse and we don't wanna do anything challenging. We'll read, of course, but usually like once it's late at night, we're reading fun, simple things. The simplest things for me, the most fun things that are still rewarding are just reading the science fiction stories or the science fiction authors that I grew up with as a kid.

0:56:35.5 SC: So Heinlein and Zelazny and Le Guin and the Dragonriders of Pern or something like that. I can just read that stuff over and over again. Then I've discovered newer ones. Iain Banks is really difficult to read the first time, but upon re-reading, it's fun 'cause you're already in. You know what world building has already happened, so I can just reread those. They're rich enough. I can reread them again and again. And we watch TV, we watch a lot of TV 'cause it's fun, and whether it's Poirot or Columbo, Murder Mysteries, or recently, I'll tell you a story, I was recently... As part of Johns Hopkins, I should... Let me back up even more. Sorry about this, but look, it's my AMA, I can tell you whatever I want. So one of the... I was thinking about this the other day, one of the super great things about my new job here at Johns Hopkins is that I'm really finally at this advanced stage that I've reached living the dream of being an interdisciplinary academic scholar.

0:57:40.1 SC: So as you know, I am in practice, I should say, a member of the physics department at Hopkins and also the philosophy department at Hopkins. But I'm also, with Jenann Ismael, we founded a natural philosophy forum. I'm also on the faculty board for something called the Alexander Grass Humanities Institute, and I'm also a faculty affiliate of the SNF Agora Institute for Democracy. And I have friends and potential future collaborators who're in the engineering school. So I'm not just doing physics and philosophy, I'm engaging with people who are doing the humanities and literature and arts, people who're doing the social sciences and democracy, people who're doing engineering. And it's just like a kid in a candy store as it were. I'm having a enormous time. Finally, I feel like an undergraduate again. I get to think about all these things, and it's not like that narrow-minded, professionalized, hyper-specialized academia that I can do fine in, but it doesn't really make me super duper happy.

0:58:42.3 SC: Anyway, why am I telling you this? Because at the Humanities Institute, I ran into and made friends with a woman, Virginia Jewiss, who is an Italian scholar. She translates Dante and things like that, but she's also a media scholar. She works in the Italian TV industry. She helps Italian TV companies make things, so make shows and so forth. So here in the US, at Hopkins, she taught a course, first year seminar course on the Prestige TV era, like some of the best TV shows that we have now. And so we were talking about it and she said, "Yeah," she asked her students to become familiar with five different TV shows. And she said it was The Sopranos, The Wire, Mad Men, Breaking Bad, and Jane the Virgin. And I, like apparently every other person response was, "Jane the Virgin, huh? That doesn't fit into the pattern that has been established with these other shows."

0:59:49.1 SC: And she says, "Yes." And when she was telling me this, I had never seen an episode of Jane the Virgin, and she said, "Yes, it's a very different kind of show. For those of you who don't know, Jane the Virgin was, it was a fairly recently, I think it ended 2019 or something like that, it was a slight parody adaptation of a Venezuelan telenovela. The Spanish-speaking world has this tradition of telenovelas, which are like hyper-charged soap operas. These ridiculous plots, secret twins, dead people coming back to life, people being married, people being brother and sister, all these crazy tropes. And so Jane the Virgin is kind of a, not really a parody, it's like a loving parody of it. Let's put it that way in an American context. So now it's set in Miami, it's called Jane the Virgin because Jane is mistakenly artificially inseminated with someone else's sperm and has a baby, even though she's still a virgin. Okay, and it goes on. And Ginny explains to me that this show, even though it's extremely light-hearted and fun, and it's basically a comedy, dramedy maybe, whatever you wanna call it, but it hits a huge number of really deep issues.

1:01:06.6 SC: For one thing, it's a bunch of immigrants in the United States, so they're dealing with... It ran from what, like 2015-2019. Guess who got elected president of the United States in that era, and there was a serious set of issues that have not gone away for people who might be undocumented or family members who're undocumented. But also questions of religion because Jane and her family are Catholic, questions of obviously premarital sex, but then she has the baby, raising a baby, questions of abortion. And it goes on to a whole bunch of super serious issues are actually dealt with in this show, but in a kind of light-hearted and fun way when they're not tugging on your heart strings. Anyway, the point is that we have been watching Jane the Virgin and just loving it. It's great.

1:01:58.6 SC: But it illustrates what I wanted to say at the very beginning, but I'm too wordy to get there, which is that even my comfort food, I like to be high quality comfort food. It doesn't need to be challenging, but it needs to be good. I cannot watch TV shows or eat food that is just bad. I remember having a discussion with a friend of mine a little while ago where we reminisced about how much we love Kentucky Fried Chicken growing up. And I said, "Yeah, I actually... I did remember loving it so much, I recently went back and had some Kentucky Fried Chicken, and my friend said, "Oh man, was it really good?" And I said, "No, it was awful. It was really bad." It's just I don't know whether the quality of Kentucky Fried Chicken has gone down or whether I have just changed as a person, but just because something is junky and supposed to be comforting doesn't mean that it works.

1:02:48.8 SC: So even though I have pizza and wings, I care a lot about the quality of the pizza and wings. Even though I like to watch a silly telenovela TV show late at night when I'm not in the mood to be challenged, it still has to be quality writing, surprising, intelligent characters, et cetera. So lots of things like that, whether it's music or reading or TV, but I will close this. You clearly asked a good question. I rambled on for a while there. Carlos Nunes says, "As an economist, I loved your episode with Sam Bowles. Economics is famously known as the dismal science, given that its intention of offering precise explanations and making accurate forecasts often fall short of their lofty goals. Do you think that economics will ever become a true science or will economists always fail predictions, meanwhile arguing that things couldn't have been any different after the fact?" I don't wanna give economist advice. It's a tough thing. Anything when human beings are involved or other complex adaptive systems, it's way harder to make useful predictions than it is in physics where you can be spherical cow about it and ignore all those complications.

1:04:01.9 SC: I think economics is a science. I think political science and sociology are also sciences. They're just difficult sciences because they involve human beings. You can throw in psychology and urban design and things like that, other things that we've all talked about here on Mindscape many times. I think that the standards have to be adjusted to be realistic. Maybe it will never be the case that economists will predict when the next stock market crash will happen, but maybe they will be able to ameliorate the effects of that crash. Maybe they will be able to successfully say what the probability of a crash is, and they will be able to successfully do so as a function of the other measurable economic variables. So you can become better and better at being a science and understanding what's going on, and giving some insight into the future without making a precise quantitative prediction. I don't think that's quite fair. We shouldn't hold up physics or even chemistry as the model for, you have to do this, otherwise, you're not a science.

1:05:06.7 SC: I do think that when things are complex like they are in economics and maybe arguably even more in psychology, sociology, etcetera, it's easy to be led astray, it's easy to be led astray by what we want to be true, by our political commitments, by our personal experience, rather than coldly and calmly looking at the evidence and judging it fairly, which is what we're supposed to do. So there's a challenge there, and maybe progress will be slower because of that, but science to me is just looking at the world, the world that is out there and trying our best to model it and understand it. That's what we're doing. So that's just as true for economics as it is for physics or astronomy. Kevin O'Toole says, "I loved your Berkeley presentation on the arrow of time in causal networks," which by the way, AMA listeners, you can find on the internet, if you just google the arrow of time and causal networks, you can find a talk I gave on that. And then Kevin continues, "Explaining in broad strokes why the direction of perceived causality is the same as the direction of increasing entropy. However, it's always hard to tell listening to something like that, was your presentation teaching a well-established consensus or advocating one possibility in a broad ongoing discussion?"

1:06:21.9 SC: Good, this is actually a really good question because you're right, when you hear a talk on the video or when you watch a talk on YouTube, you can learn a lot from the talk. But what you don't get is what the audience is thinking. Maybe there's some Q&A afterward, but very often what the audience is thinking is left unspoken in the Q&A and only talked about in mumbles afterwards. So you don't know. So just 'cause someone says something in a talk doesn't mean the audience agreed with it certainly. In this case, well, also maybe they're not telling me, but I always do try to figure out. I try to ask people what they actually thought, et cetera, especially when I'm giving talks to audiences that are different than the ones I usually talk to. So in this case, in that context, I'm trying to bring together two different sets of ideas, one from statistical mechanics, when we talk about entropy and the arrow of time and things like that, and the other from causal network research, and which just assumes the directions in which the arrows are going from causes to effects, it cares a lot about what arrows exist, but it presumes we know what directions the arrow is pointing, especially they always point from past to future.

1:07:34.5 SC: So I'm trying to join together these two things, and that audience was extremely expert in causal network dynamics, causality, things like that. They were not expert in statistical mechanics, except some of them were. There were a couple of stray physicists in the audience. So I think that my impression is the following, that both groups were slightly annoyed at how easy it was to understand the part they already knew, but they were happy to get the part they didn't know, and they didn't have any objections to the way that things were brought together. Does that make sense? So the physicists were like, "Why are you telling me about the second law of thermodynamics? I know that." But when I explain to them Judea Pearl and casual networks, they're like, "Wow, this is really cool." And the causal network people were just the opposite, okay? , so the question about whether or not those two areas can be successfully brought together, no one seemed to be dead set against that, and they thought that was an interesting kind of thing. I think that different people will care more or less about it.

1:08:41.3 SC: Some people are like, "Oh yeah, that's really foundationally important to understand why this comes before that." And others are like, come on, I don't need to know that when I inject medicine into someone's arm, and then some physiological effect happens, which is the cause and which is the effect, right? That's kind of trivial for them. So some people may or may not care, but I did not hear anyone object to the fundamental idea or the specific way in which I was trying to make it happen. Lionel Miziara says, "In the last AMA, you told us that Boltzmann brains were not possible because quantum mechanically, temperature does not consist of atoms moving around. How can that be? Isn't the very concept of temperature based on the movement of atoms?" So by the way, it's not that Boltzmann brains are not possible, it's that it is possible that they're not possible. [laughter]

1:09:30.1 SC: In other words, we are expanding, the universe is expanding and accelerating and emptying out. There's an open question about the nature of the future quantum state of the universe, even putting aside the possibility that we'll re-collapse or crunch or anything like that. The fact that the universe will be empty and we'll have a non-zero vacuum energy, just assume all that is true, what is the nature of the quantum state in that future accelerating universe empty space state? And there are two possibilities, one is that it just quiets down. It just settles into a constant static thermal quantum state, what we call the density matrix or a mixed state. But the other is that it seems to do that, but really, there's only a finite dimensional Hilbert space that we live in, only a finite number of possible quantum states that the future universe can evolve to, and eventually it will come back to where it is today and it will recur over and over again. Or there are sort of in between versions where it will fluctuate even though not strictly recur because it's an open system, okay? . So that's an open question. We don't know the answer to that.

1:10:38.9 SC: So it is in the case where the universe just settles down once and for all, then there will be no Boltzmann brains, but there's absolutely this other open possibility where there still will be. So I wanted to footnote that. But the interesting question here is, isn't the very concept of temperature based on the movement of atoms? And the answer is no. It was in the 1880s. You would have said that and everyone would have agreed with you. What temperature was supposed to be is the thermal energy, the average thermal energy of the atoms or the molecules or whatever in your gas or your material substance. That's just not true anymore in quantum mechanics, and like physicists always do, we use the same word for a rather different concept. So in quantum mechanics, of course, you can have a circumstance where you literally have a bunch of atoms moving around with different velocities, and then you can attribute a temperature to it. You're just describing it quantum mechanically. That's fine, but it's a special case of a more general thing that can happen. The more general thing that can happen is that you have a... Well, like I said, what we call a density matrix or a mixed state.

1:11:49.6 SC: What does that mean? Ordinarily in quantum mechanics, when you hear a little bit about quantum mechanics, you talk about wave functions. The electron is not just a point particle with a location, it's a wave function all spread out. Well, you also probably have heard that in statistical mechanics, even though we know that there really are in... Well, we would have known if classical mechanics had been true, that there really were particles with definite positions and momenta. In statistical mechanics, we recognize that we don't know the exact position and momentum of everything, and therefore we have a probability distribution over all those things. So you might think that in quantum mechanics, you could have a probability distribution over wave functions. Maybe the analogy is you don't know what the wave function of the electrons is. And that's almost true, but there's a technical complication because wave functions are vectors. You can add them and subtract them. You can't add and subtract positions and momenta in classical mechanics. But in quantum mechanics, you can add and subtract.

1:12:54.6 SC: By the way, sometimes people think that you should be able to add positions. You can add momenta of two particles if they're at the same point, but when they're not at the same point, you can't add their locations together. You might think, "Well, no, I have a vector telling me the location of one particle and a vector telling me the location of another. What stops me from adding them?" The answer is, you don't have a preexisting preferred origin to your vector space, so it's not actually positions of particles are not actually vectors. We treat them that way sometimes, but they're not vectors that you can sensibly add together, 'cause that sum would depend on your origin, which is not what a good vector space is supposed to do. Anyway, so that new feature in quantum mechanics that you can add together quantum states means that you can have two quantum states that are different from each other, but only a little bit different, only like rotated as a vector by a little bit.

1:13:45.8 SC: So the way that you describe probability distributions over quantum wave functions is a little bit different than the way you describe probability distributions over classical configurations. In the classical configuration case, like we said, there is always an answer to the question, what is really the particle's positions and momenta? Quantum mechanically, if you have a state that is entangled with the rest of the world, there may not be any answer to that. And so in that case, we describe the system using a mixed state. This is the quantum version of a statistical distribution over states. It's kind of like, but not exactly a probability distribution over quantum wave functions. And you can do statistical mechanics in that kind of framework, also known as a density matrix, I should say.

1:14:40.6 SC: And so you can say, just like in the box of gas at a certain temperature, what is the probability of seeing an electron to move at a certain velocity? Well, it's possible, but if it's very high velocity, it'll be exponentially suppressed, things like that. That translates into a certain form for the mixed state in quantum mechanics that is dependent on a parameter, which we call the temperature. So the new way we think about temperature in quantum mechanics is as a parameter in a mixed state that tells you the relative abundance of states of different energies. And you can show that the predictions from that way of talking map nicely onto the predictions you would make in classical statistical mechanics for macroscopic things like the equation of state and the PV = nRT, things like that. But there's a huge important difference, which is that quantum mixed state doesn't necessarily mean that under the hood really deep down, there's a whole bunch of things moving around.

1:15:48.1 SC: There's a new thing that can happen in quantum mechanics, and for whatever reason, plenty of people who are super experts in quantum mechanics don't... I don't wanna say they don't understand this. Maybe they understand it. They never admit it, they never talk about this fact. The fact is you can have a temperature, you can have a mixed state describing a thermal distribution with some temperature that is completely static, that is completely not changing over time. You can't have that in classical mechanics. In classical mechanics, whenever you talk about a temperature, just as you say in the question, you're talking about a probability distribution over states that are moving, that are individually dynamical, and their average is not moving, but it's an average that is a sum over individually moving things. And that is not true anymore in quantum mechanics.

1:16:40.9 SC: In quantum mechanics, a thermal state is a sum over states that are not moving themselves. So that's a whole new thing, and people never talk about it. It's very relevant for Boltzmann brains. It's actually not that relevant for measurements. That's why people don't need to talk about it 'cause when you actually say, "Okay, what is the probability of getting a measurement outcome in this thermal state?" You still get very similar results in classical mechanics or quantum mechanics. But for the Boltzmann brain problem, we're not thinking about measurements, we're thinking about what happens intrinsically to the system. So suddenly that difference becomes very, very important. Artem Voroshitov says, "Is it possible that during the Big Bang and its aftermath, the volume of our universe is infinite, but only a finite volume is contained within our past light cone? How accurately do we understand the function volume as a function of time after the Big Bang?"

1:17:32.6 SC: It's 100% possible. In fact, it's very, very, very possible. We don't know whether the volume of our universe is infinite. If you're a stickler, there's no such thing as the volume of our universe, because volume applies to space. And the universe is spacetime. So when you have in general relativity an expanding universe, there are different ways to slice spacetime into three-dimensional space as a function of time that could give you very different answers for the question, what is volume as a function of time? For example, in a very simple universe like De Sitter space, De Sitter space is an example of a cosmological spacetime with a positive vacuum energy and nothing else in it, you can slice that spacetime in such a way that the volume as a function of time is finite 'cause it's a three-dimensional sphere, basically. But it increases toward the future and the past without bounds. So the finite volume gets infinite.

1:18:34.7 SC: But it's also possible to slice exactly the same spacetime so that the volume of space is always infinite. So you can slice it one way so it is finite, one way that it's infinite. That's because it's not a well-defined thing. But our observable universe is certainly finite. So observable universe is finite. We just don't know whether it is possible to slice the universe outside what we observe in a way that is infinite or finite. Jeffrey Seagal or Seagal says, "I really appreciated the conversation with Samuel Bowles. One point that struck me when he mentioned that group selection could work if the genetics of the groups was distinct enough, as he discussed this as a possible evolutionary mechanism for the development of racism as a recognition of different group genetics." I don't know whether he has discussed that or not. You would have to ask him.

1:19:28.3 SC: Of course, there are genetic factors that help define different groups, whether that its appearance or anything else. Presumably you've all heard various things about this, the similarities between different groups of human beings are way greater than their differences. Differences are correlated or not correlated in different ways. The categories that we usually think of as race do not map on straightforwardly to any genetic differences. There are genetic differences, but they don't easily map on to how we define things as a function of race. I think a better way of thinking about it is if you go back to the podcast we did with Nicholas Christakis, human beings as part of their basic make up, or at least it seems very, very common in human history for groups of people to have a slight in-group bias. We tend to define groups somehow, and we tend to like the people who are in our group, and we don't like as much the people who are outside our group. When we invent races as a social category, we don't know anything but genetics when we did that. We were not very good at that.

1:20:38.3 SC: So it's not surprising that the categories that we invent are not exactly reflective of any underlying genetic truth. But there are differences, differences in appearance, differences in other things. Like we said, it's a social fact that we choose to take some differences as really, really important, like what's our skin color is, and other differences, like what our hair color or eye color is less important, or the pitch of our voice or whatever. There's a million differences we could have chosen to focus on, but skin color is one that we do, and that's a very social fact. There are genetic realities underlying the differences between people, but social choices have a huge role to play here.

1:21:27.5 SC: Ryan Santos says, "Priority question, I believe I've heard you affirm unity of knowledge in prior conversations, which seems to me at a minimum that valid methods of discovery ought not to contradict each other, and when they do, it's a mistake of process rather than a contradiction of reality. My question is about confrontations of different methods in practice that lie somewhere outside the family of natural sciences. For instance, religious historians will often claim that purely academic historical methods validate their particular scripture, sometimes contradicting the current consensus of physics or biology. Another example might be DNA evidence used to overturn criminal convictions. Would you simply take such situations case by case, or is there some kind of hierarchy by which you give one means of investigation more authority than another?"

1:22:18.2 SC: Well, so I certainly have never, I'm pretty sure, have never used the words I affirm unity of knowledge. I do think of knowledge as different ways of talking about the same underlying physical reality. I do affirm the unity of underlying physical reality, and we have different mechanisms, as you say, to get to it. So I think that there's actually... There should be more or less common criteria for when those methods are trustworthy, when they are reliable, et cetera. Of course, within a certain sphere, whether you're doing archaeology or literary textual analysis or particle physics, the particular problems that you are faced with will be different compared to other areas, and therefore, you can use different criteria as a matter of practice. Just for example, in many sciences, certainly in social sciences and elsewhere, people talk about a three-sigma result. If you can get a certain P value greater than 0.99, then you have a statistically significant result.

1:23:28.9 SC: In particle physics, we say that you need a five-sigma result, which is a much higher level of statistical significance than in the social sciences. That's not because of any fundamental difference in what the two areas are trying to do. It's a difference in the amount of evidence that you can gather, and the cleanliness of the evidence that you get. In other words, in particle physics, you can get five-sigma worth of evidence, and if you don't have it yet, you can just keep doing the experiment, and hopefully, eventually you'll get it if the effect you're looking for or the particle you're trying to detect is really there. In the social sciences, that would mean there were no results if you asked for five-sigma statistical significance. So because you do want to get some results, you have a lower threshold of significance, but you also realize that you're sort of less surprised when some of those results are not replicated.

1:24:26.5 SC: In particle physics, if we discovered that actually we haven't found the top quark, it's not there, that would be weird. That would be almost impossible to make sense of because it's so firmly established, whereas there are almost no results in sociology or psychology or economics that are like that. I think that, yeah, we should... When there are overlaps, when there are questions that can be addressed using different methodologies, probably you have to go on a case by case basis in the real world as a practical matter. But in principle, it's all just trying to figure out how the world works. I think it is common. I don't think that we should certainly throw out the results of some kinds of analysis just because they disagree with the kind of analysis we like better. We should think carefully about what is appropriate to the question we're trying to ask, and which has been more reliable and so forth. You have to take all of it into account at the end of the day.

1:25:20.9 SC: Steve Sheridan says, "In late July, a paper was published in The Astrophysical Journal by Kyu-Hyun Chae from Sejong University in Seoul. The paper purports to provide strong evidence within graded in five-sigma significance. See, as we just talked about, pre-modified Newtonian dynamics gravity theory at low acceleration conditions of widely separated binary stars. The Sagan standard that extraordinary claims require extraordinary evidence would appear to apply here. Do you believe this paper provides sufficient evidence to support a breakdown of standard gravity at weak accelerations, and if not, why?" No, I do not. And this has something to do with what you mean by extraordinary evidence. A single paper is never extraordinary evidence. It's only one paper. You better have some back up to that paper to get extraordinary evidence. And when it comes to exactly this question, what's going on here is in certain theories of modified gravity, the Newton's law of gravity is effectively altered when the gravitational acceleration becomes very, very low. The difficulty, the obvious difficulty with testing an idea like that is when the gravitational acceleration is very, very low, there's other forces in the world that can get in the way, and suddenly make it look like your gravitational acceleration is something different than it really is. The gravitational acceleration from other things than you're looking for.

1:26:45.2 SC: So people are looking at binary stars that are very, very far apart and trying to measure their motion around each other. But guess what, that's a very hard measurement to make 'cause they're very far apart. They're moving slowly. It's gonna take them a long time to orbit or whatever it is they're going to do. There was a paper, I haven't read the paper, but there was a paper that claimed that in some certain subset of stars that people looked at, the fit to the data was better from Modified Newtonian Dynamics than other things. But guess what, there are other papers that look at very, very similar systems and claim that the fit is better for ordinary gravity. You don't hear about those papers as much 'cause they're a little bit less exciting, and that's why the fact that it is nominally a five-sigma detection does not make it extraordinary evidence because there are selection effects here. Which stars did you look at? How did you make sure that you didn't have false positives or misidentifying things? There's a whole bunch of work that needs to be done.

1:27:45.2 SC: So for huge results like this, you would know. The world would tell you if the scientific community actually thought that this had been established, we would not hide it from you. You would definitely hear. It's not enough to get one paper by one set of people getting one result. In my career, I've seen results appear on the front page of the New York Times that were completely bogus, and I've even written the paper that explained why they were bogus. So just be patient when it comes to these extraordinary claims. It takes time to really go through them part of... A better quote is extraordinary claims require careful examination of multiple results over time by different groups. How about that? Professor Beautiful says, "The Hubble tension, why are measurement differences from vastly different time epochs and inconsistency rather than just the Hubble constant changes over time? After all, inflation came and went, and dark energy is presumably changing the expansion rate."

1:28:50.4 SC: A couple things going on here. Number one, there is something called the Hubble tension. We did a whole episode about it with Adam Riess, a while ago. He wasn't at that time my colleague, but now he is. We're both at Johns Hopkins together. It's not that the Hubble constant was different. That's not the tension. The tension is that there are different ways of measuring the current Hubble constant. You can sort of do it directly, but you can also do it indirectly by measuring features of the universe, and then best fitting to what the Hubble constant needs to be to explain those measurements. The problem with the Hubble tension is the different ways of measuring the current Hubble constant disagree with each other, or more broadly, different ways of measuring cosmological parameters are incompatible with each other. Of course, yes, the Hubble constant does change as a function of time. The Hubble tension is the fact that it doesn't change in the right way, according to our theoretical understanding.

1:29:50.0 SC: The one little extra thing I wanted to say is, 'cause you're saying dark energy is presumably changing the expansion rate. It's actually exactly the opposite. If you had a universe with nothing but dark energy in the form of a cosmological constant, that is when what we call the expansion rate would be constant, because the expansion rate is not a speed. The expansion rate as measured by, for example, the Hubble constant, is basically a time scale. If you think about the Hubble constant, it's in units of meters per second, kilometers per second per megaparsec. So that's distance divided by time, and then that whole thing is divided by distance. So the units are just one over time. We use units of kilometers per second per megaparsec 'cause that's convenient for our brains. But the thing we're measuring has units of one over time. It's not a velocity, it's not even an acceleration, okay. It's basically the amount of time it would take for the universe to double in size, or slightly more carefully, for the university exponentiate in size to increase by an e-fold, one factor of Euler's constant e 2.7.

1:31:00.1 SC: Anyway, that's the point, if the universe is constantly expanding at a fixed rate, then that is equivalent to saying the universe is growing exponentially. That's what the acceleration of the universe refers to. If you find that confusing, it's because we're using words that we know from our ordinary lives to discuss velocities and accelerations when we're really discussing the expansion of the universe, which is a different kind of thing. So anyway, the expansion rate, as measured by the Hubble parameter, is decreasing with time. We all know that, it is decreasing more slowly and approaching a constant value because of dark energy. Bits Plus Atoms says, "In one of your mystery of time lectures on the great courses, you say that ABL, who are Aharonov, Bergmann and Lebowitz, argue that we perceive a time asymmetry in wave function collapse because we are asking a time-asymmetric question. If we pose the question symmetrically, the time asymmetry disappears. I struggle to understand this in the many worlds interpretation since the prepare again phase would seem to happen after decoherence. Can you help me understand this better or at all?"

1:32:10.2 SC: Probably not [chuckle] This is a tricky one to understand, but I can do a little bit to help you get it, which is that this is not within the many worlds interpretation really. ABL are really not advocates of the many worlds interpretation. Now, every experiment or every thought experiment or real experiment that they propose can be understood within the many worlds framework, but that's not what they are actually trying to do. And the second thing is, there's sort of a useful part and a less useful part in my mind of the whole discourse around what I was talking about in that particular lecture. This is the idea of pre-selection and post-selection. For those of you who've not, I don't know if there's anyone out there who has not listened to my teaching company lectures on the mystery of time, but it's a subtlety of quantum mechanics where the typical thing we do is we prepare a state. So we start and we say, "Okay, this wave function is in a superposition of spin up and spin down."

1:33:09.1 SC: And then subsequently, we measure it, and that we measure it either spin up or spin down. That's all you have. So Aharonov, Bergmann and Lebowitz figured out a way formally, which is 100% fine, to say, "Well, what if you post-selected after the measurement on a quantum state? Then you could have a different formula." And they have a formula for what the probabilities are of getting different outcomes at the measurement in between. The question is how you in practice post-select. The universe doesn't give us a way to post-select in the way that we can pre-select exactly because there's an arrow of time. So in practice, what you do is you just measure again at the end of the experiment after you've already measured once, you measure again to try to see whether or not the state is compatible with this post-selected state that you want it to be in. And if it's not, you throw it away, you ignore that measurement outcome.

1:34:03.9 SC: And then you do that many, many, many times, and you can build up statistical information about what happens in between. It's all 100% compatible with many worlds. If it were not experimentally, then I would have told you that a while ago. It's driven by a desire to have a different way of understanding things. And I don't think the world needs a different way, so I'm not... I don't follow it. I think that the idea of post-selection and related ideas of weak measurement in quantum mechanics are very interesting. I don't think you need any of them for understanding the foundations of quantum mechanics. Robert Parks says, "In your episode with Tim Maudlin, Tim spoke of what he considered to be an obviously erroneous understanding of Newton's third law, an understanding he's often presented as an objection to the wave function guiding how you're acting on particles without a reciprocal action. Could you help me understand why in quantum mechanics the action of a wave function to particle would not require an action of particle to wave function?"

1:35:06.1 SC: Well, it depends on what you mean by in quantum mechanics. This is not supposed to be a claim about quantum mechanics in general. This is supposed to be a claim about Bohmian quantum mechanics or pilot-wave theories, where you have the wave function and you also separately have particles. It is just a fact that if you want to have a pilot-wave theory, you're stuck with the real world problem that the Schrödinger equation works really well without any modification. So the way that they have both the Schrödinger equation for the wave function and some particles is to say the particles are pushed around by the wave function, but the wave function is not pushed around by the particles. Now, two things are simultaneously true. One is that seems weird. It seems weird to our physical intuition to imagine that the particles are being pushed around by the wave function, but not vice-versa. The second thing is, but there's no law against it.

1:36:04.8 SC: Bohmian mechanics is a proposal for a different kind of fundamental laws of physics. So it seems weird. That's fine. You're 100% willing to say, "It seems weird to me. I don't like it." You're not allowed to say, "Therefore, it's wrong. Therefore, it can't be right." It's a theory, it's a proposal for a physical theory that you can think about and you can decide whether or not it fits the data and so forth and so on. But it's not supposed to be compatible with some very naïve formulation of Newton's third law, to every action, there's an equal and opposite reaction. Tis Jansen says, "WIMPs are a very probable candidate for dark matter, where the M stands for Massive. Massive particles decay into lighter particles, unless there's a conserved property, and conserved properties are linked to symmetries. So if a massive dark matter particle doesn't decay, there should be at least a symmetry to discover, maybe even a new force. I don't hear anyone talking about this in popular science media, like magazines or YouTube, even though quantum mechanics is a hot topic to discuss. Or sorry, even though dark matter is a quantum... Is a hot topic to discuss, DM rather than QM. What am I missing here?" You're not missing anything. It's just not a popular topic to discuss. We don't know a lot about dark matter.

1:37:22.0 SC: We know a lot about its phenomenological Astro-physical properties, but we don't know a lot about its astrophysical properties, it's darn it... We don't know a lot about its particle physics properties, so you're right, WIMPs are a probable candidate, in the sense that they are a popular candidate, I should say there's probably a better way of saying it, WIMPs are supposed to be heavy, heavier than a proton typically, so they could very easily decay. In fact, one context in which WIMP models are often studied or supersymetric models, and if you just wrote down a supersymetric model without trying too hard, you would get a WIMP-like particle, but it would decay away pretty quickly, way too quickly to be the dark matter. So there is a subset of all the possible super symmetric models you can write down which have a new symmetry called R-symmetry or R-parity capital R, the letter. And that basically something that you just put on your theory and it prevents the lightest super partner, whatever that might be from decaying because that is a new symmetry.

1:38:23.9 SC: But it doesn't give rise to a forest 'cause actually in the simplest versions is just a discrete symmetry, it's not a gauge symmetry that would give rise to a new force of nature. So once you've said it's there, there's not a lot more to say about it. Of course, it's also possible to imagine that the thing that stabilizes the dark matter is a gauge symmetry. And then there would be a new force, in fact, I wrote a paper about that with Matt Buckley, Lady Arman and Marking Koki about dark electromagnetism. So U [1] gauge symmetry that stabilizes the dark matter particle. So you can talk.

1:38:52.2 SC: About that, but it's one of those things where it's possible, but it's really an extra complication on top of dark matter, and we haven't discovered it yet, so even I who wrote the paper would not get too excited about it until we had more reason to think it was on the right track. The Shannon Klide asks a priority question, I've already said this, but we've already had a priority question, but remember that priority questions are those that every Patreon supporter gets to ask once in their life, and I will make a good faith effort to answer it. So we get too many questions overall for me to answer all of them, but priority questions I will try to answer, I can not guarantee a satisfactory answer or satisfying one, but I'll do my best.

1:39:42.5 SC: In your July 17th podcast discussion, you and Dr. Joe Silk agreed that cosmic inflation has about a 50% chance of being right. Are there any alternative Big Bang speculations that populate the other 50% I.e. Hot big bang theories without Alan Guth, cosmic inflation. Oh, there are.

1:40:00.1 SC: They're absolutely are. The most popular ones are bouncing or cyclic cosmologies, but none of the others are anywhere near 50%, let's put it that way, in my own personal accounting, if inflation is 50%, something that we haven't yet thought of is probably 48% or comparable to inflation anyway, I don't think that any of the alternatives that I've seen to inflation or themselves anywhere near as compelling as inflation is, but there's plenty of FaceBase out there for theories we just haven't thought of yet, so you have to give some credence to those as well. Sean Bentley says My son Jack was wondering if you've heard of or read the three body problem series by Cixin Liu. We both really enjoyed it.

1:40:22.4 SC: Especially from a layman physics perspective, also curious if you have any thoughts on the book's name sake, the actual three-body problem in Physics, so I do know about the book... I'm very sad to say I've started to read it, but I haven't finished it, not because I didn't like it, just 'cause other things in life get in the way sometimes, so I can't comment on the book itself, it's a great title The Three-Body Problem because The Three-Body Problem refers to the question in Newtonian gravity of three objects orbiting each other, and it's a fascinating problem because of course the two-body problem, two bodies orbiting each other, that's perfectly solvable.

1:41:22.7 SC: Newton solved it back in the day, and The Three-Body Problem, which you would think might not be that much harder, is completely unsolvable, at least you cannot solve it analytically in terms of a closed form expression you can put on a computer and simulate it, but it turns out to be chaotic, as we later realized, probably Punk Ray was one of the first people to realize this, so it's an example of... Let's be very clear about what chaos theory here means, it's still deterministic.

1:41:52.4 SC: It's still Lapulse's demon has no trouble predicting it, if you know exactly what the system is doing right now, you can predict exactly what it will do next, the difference is what happens when you admit that you don't know exactly what the system is doing now, in a non-chaotic system, a small amount of ignorance now leads to a small deviation in your predictions about the future in a chaotic system, a small amount of Ignorance now leads to potentially large deviations about your predictions in the future, essentially, because we always do in the real world, have some small amount of ignorance, some small amount of uncertainty, you cannot very carefully...

1:42:30.1 SC: Very, exactly, very precisely predict what's going to happen next, and that's true in The Three-Body Problem, think about it this way, in some regime, if you have three bodies and they're orbiting each other, the two bodies, there might be two bodies that are very close and orbiting each other nearby, and a third body that is far away, so for some intents and purposes, that third body just orbits the center of mass of the other two, so it looks like you can figure it out, but there's...

1:43:07.2 SC: Little protibations and those protibations grow, and when the three bodies are zooming right next to each other, one of the three is typically just kicked out of the system entirely and predicting exactly when that might happen is very, very hard, so it's a wonderful little metaphor for chaos theory in general, and a reminder how easy it is for a very simple dynamical system to exhibit that kind of unpredictability. Nikita Lawson... Lawzavoi sorry says. While participating in my first meditation course recently, a teacher hinted at a rather radical idea that could be shortly, shortly quoted as maybe we don't have a body at all, accepting that our bodies are nothing, then...

1:43:44.7 SC: I'm sorry I have trouble reading this. Is not your fault, Niki it is completely my fault. Accepting that our bodies are nothing more than just an exquisitely arranged array of particles and interactions between them, would you be willing to agree that the entire my body concept is indeed an emergent phenomenon?

1:44:01.4 SC: It's 100% in an emergent phenomenon... Yes, that is true. Everything is an emergent phenomenon that does not appear in the most fundamental laws of physics, okay? Now, we don't even know the most fundamental laws of physics, but our current version of the most fundamental laws of physics is the core theory of the standard model particle physics plus general relativity. And you can look at that all day long if you want, and you will never locate a body in there, everything, macroscopic, everything collective, everything constituted from many different little bits that are individually mentioned.

1:44:22.4 SC: In the core theory would be an emergent phenomenon and human bodies or other large systems absolutely qualify. Now, that doesn't mean you don't have a body. It's a silly to say that you don't have a body, in my personal opinion, just because something is emergent doesn't mean it's not real, if you had that attitude, then you would literally not know anything that was real, because like I said, you don't know the fundamental laws of physics right now, our best theory is the core theory, but it's possible that things like electrons and quarks are also emergent higher level phenomena we don't know.

1:45:07.2 SC: So if you have this strict construal of reality where unless it's fundamental, it's not real, then you don't think that anything is real as far as you know, and that's no way to go through life, in my opinion. Mark Smith asks, how did you pick the title and ending music for Mindscape? That's a pretty easy question actually, I didn't want to bother getting permission, I didn't wanna pay for any music, so I had a friend and former collaborator from my grad school days, Ted Paine, he and I wrote a couple of papers together on topological defects and on Microway backgound and isotropies and after graduate school, he formed a band called Euphonic... I think you could probably find them on the.

1:45:22.4 SC: Internet if you dug around, and they had a few CDs, and I asked Ted if I could use some of their music for the intro and outgoing outro music for Mindscape. And he said Yes. So all this is more or less explained, there is, if you go to the website postrusuniverse.com/podcast, you can click on About Mindscape and it will actually mention all these things. Diana David Roots says, always, I've been puzzled by the concept of inertia in Newtonian mechanics inertia is the tendency of an object to remain at rest if it's at rest or to remain moving at a constant velocity if it's in motion, unless acted on by an external force from the perspective of Einstein Theory of Relativity, objects with mass will prefer to move along straight lines in the curve space time, when we try to divert an object from the straight line path, we're effectively trying to make...

1:46:39.4 SC: It deviate from its natural motion, however, still in my mind, the question of why objects have a inertial property, I.e... This tendency of following the Geodesics remains. Is there something more fundamental that I don't understand? .

1:46:52.9 SC: I don't think there is something more fundamental that you don't understand other than when you are and are not allowed to ask questions about why something is true right in a mathematical context, if you wanna say, why are straight lines the short assistance paths in Euclidean geometry, or why are geodesics shortest distance paths and non-nuclear geometry, you can answer that in terms of other mathematical concepts, but when you're asking about the physical behavior of things, sometimes the answer is, that's just the way it is. I could quote other laws of physics from which you can derive the fact that test particles move on inertial paths in general relativity, but then you could ask, Well, why are those laws of physics true. So I'm not sure what use it is to quote those other laws of physics, in my mind, it's a law of physics, that's how nature behaves, our job is to discover it.

1:47:50.2 SC: It might be there's some deeper theory from which it's derived and that would be great, but right now, when it comes to classical gravity, general relativity is the deepest theory that we have, so we accept it until something better comes along. Walter E Miller says, I really enjoyed your conversation with Avi Loeb a while back and I found his speculations about oumuamua quite interesting, he has come under a lot of criticism lately in the scientific community, but that is not dampened his enthusiasm for his opinions. What do you think about his recent finds of spherical metallic particles scraped from the bottom of the ocean that might be of extra solar origin?

1:48:26.1 SC: I thought when I did the conversation with Avi, who I've known for a very long time. That we had a very good reasonable conversation, oumuamua is this object that zoomed into the solar system and zoomed away. By Zoom, I mean just traveled and it wasn't under rocket power or anything like that. But there was some anomalous acceleration of the object, which is something that makes perfect sense, because when objects pass close by the sun, pockets of ice and things like that, often outgas and push the object off of its trajectory, so that's not surprising, but Avi made the case that we should at least contemplate the possibility, this is an artificial object, an interstellar space ship.

1:49:22.5 SC: Okay, I think that's extremely unlikely, I think that his case was unconvincing, but I think it's perfectly reasonable thing to contemplate and you should certainly take the possibility seriously, just because it's kind of wacky and out there, it doesn't mean... We shouldn't think about it. The implications would be really big if you were important... So I was happy to have the conversation. I do think that since then, he has not been a careful scientist about this question, he has written papers and continue to push the idea that we should take very seriously the existence of artifacts pointing toward extraterrestrial intelligent origin, and a recent example are these little metallic particles scraped from the bottom of the ocean.

1:49:52.1 SC: Nothing that I've seen from the perspective of other scientists who are experts in this area, I think that he's on the right track about this, it's a pretty universal dismissal of these claims, and he seemed to be rushing into print and just not being careful and things like that... So he's still a good scientist, he's still writing papers and sending them to referee journals, so we'll see how things go forward, but again, as we said with the Mon stuff previously, what you want to take any of this seriously is multiple different sets of people reaching the same conclusion, ideally from different perspectives, but at least multiple people who might want to disagree with each other, ending up having to agree with each other because the data force them to... We're nowhere near that yet. So again, I would just not think that there's much reason to get excited about this. Nate WhatUPS says, has the rise of generative language models like ChatGPT led you to change the way you come up with tests or homework, or the way that you evaluate your students test results or homework results? .

1:51:00.0 SC: So far, not yet. But maybe that has to do with how I do things. Or maybe it has to do with the current state of AI in the courses that I tend to teach. I'm either teaching a seminar kind of course where the grading is papers rather than homework or in-class exams, I actually kind of hate in-class exams, I'm not sure if I've ever given an in-class exam in my many years of being a professor, I give problem sets and take home finals in more mathy physics courses, and I ask students tried papers and grade them on the performance on those papers and in class participation in the more seminar humanity kinds of classes. So.

1:51:44.2 SC: I'm not right now teaching a physics mathy-based class, so I don't have to worry about students answering those questions using that ChatGPT. I'm not sure if I would... Like if you're supposed to do a certain physics problem and you can do it using AI, maybe that's just fine, as long as AI is gonna be around for a long time. For the papers that's an issue, and I am confronting this issue, and it was interesting, I'm teaching two classes this semester, and I asked my students in both classes, and they... Maybe they're fibbing or not completely telling the truth, but they were very against the idea of using AI, they're like Ah, that's just cheating.

1:52:26.4 SC: It's just gonna be BS. I don't think that we should believe that stuff, so we're not gonna do that. Now again, maybe they're whistling Dixie or whatever but they didn't seem like, Oh no, I'm sad that I don't get to use AI. What I told them was they can use it, but number one, they certainly can't use it to literally write their papers or even parts of their papers, I don't want any cut and pasting from AI into papers, and number two, if they do use it, they need to be explicit, it's a source that they're using, so they need to credit it, they need to say, I used the chatGPT for this purpose.

1:52:52.2 SC: To point to some issues or to formulate a sentence or to find some references or whatever it is, because I don't think that you can just say, Don't use it when it's a tool that's out there in the real world, you're not doing your students the best possible service from pretending that something is not possible when it really is, and of course, I also think that the class participation is an important part of the grade also. So far, the short answer is it hasn't greatly affected my grading or assignment giving, but we'll see, it may be will in the future.

1:53:34.1 SC: Astro Nobel says, When I decide not to put cream in my coffee, do I postpone the thermal equilibrium death of the universe by a tiny bit? The way that you've stated the question, I don't know what the answer is, because you have... The point is that if you put cream in the coffee, you increase the entropy of the universe a little bit...

1:53:55.0 SC: That's true. It was a joke by John Wheeler that he felt guilty every time he put cream into coffee 'cause he was increased the entropy of the universe, and there's no going back. Okay, but that doesn't strictly speaking mean that you are in making it faster, the approach to equilibrium, because if the sun blows up or expands to a red giant and engulfs the earth, then it doesn't matter whether you put your cream in your coffee or not, it's gonna be that event that increases the entropy of everything on earth, okay. Of course, it's all just a joke, because the amount by which you arguably might be increasing entropy of the universe is completely negligible compared to the whole entropy of the universe, so I wouldn't sweat it in practical terms. Pablo Montilla says, "We know black holes should evaporate due to Hawking radiation, that being the case, is there any point during evaporation when the mass of the black hole is low enough so that light can escape thus ceasing to be a black hole?". So no there is no such point, the black hole just grows smaller.

1:54:58.7 SC: Remember, a black hole is a region of space. The region of spacetime really, it's a region of spacetime from which light cannot escape, there is a tricky technical question about how to think about that when there is such a thing as Hawking radiation because of the following. If you imagine throwing something into the black hole, let's imagine it's a kind of abstract thing, so it's not like a book or a rocket ship, but it's a bit of information.

1:55:29.2 SC: Given that the black hole eventually evaporates away, that bit of information will eventually escape to the outside world. So you could, in some very strict construal kind of sense, argue that when there is Hawking radiation, there are in tiny black holes Hawking himself said something along these lines, but the rest of the world is gonna shrug and go, Come on, you know what we mean? You can't escape right? Then you have to wait until the black hole evaporates to escape. It's not really what we have in mind. But anyway, the black hole is a region of spacetime from which light cannot escape and that region grows smaller as the black hole grows smaller, looses mass, and eventually it will reach zero, and there's.

1:56:07.2 SC: No black hole left anymore, but there's no point in which the event horizon disappears it just shrinks to zero size. Paul Conti says, In the matter of AI in common sense, would it at least help an AI to learn if there were a pair of... If they were given a pair of stereo cameras and stereo microphones and a pair of movable prosthetic arms and sensitive articulated hands, with such a peripheral attachment, the AI could see here and learn about different shapes, sizes, and even about basic gravity, although this would not actually lead to common sense it would surely be a great improvement towards that goal.

1:56:45.0 SC: You know, I'm not an expert, but my impression is that, yes, this is exactly true, people who do robotics have found that AIs... This is old news, so maybe it's different now in the Large language model era, but my impression is that embodied AIs begin to act more human than AIs that just talk to you through the computer screen. They have a set of gestures that can interact with other people and they can see their gestures, et cetera, so I would not be surprised if that were completely true. There's another thing that is missing in modern large language models, which I think is even more.

1:57:22.4 SC: Important, which is feelings in the sense that Antonio DeMarco and I talked about on the podcast, and... So not in a sense of like, Oh, you hurt my feelings. But in the sense that we are our bodies and our minds are constantly trying to maintain homeostasis, there's some form of equilibrium in which we're happy and content, and we are constantly departing from that form because we're too hot or we're hungry or we're tired or whatever, and we work to restore it. And this provides the motivation for us to do many things in life, and none of this exists for current AI models, so I do think that if you actually wanted an AI model that would approach something like human intelligence or consciousness, you would both have to embody... Not maybe have to, but it would help your case greatly, both to embody it and to give it some feelings, to give it some desires, some goals that it could fall short of, and it would try to fix itself.

1:58:22.6 SC: Current language model doesn't get bored if you don't talk to it, you need them to get bored before they will become conscious. I'm gonna group two questions together, Sheldon Silliman says I was wondering If you ever had entertained the idea of writing science fiction, the scientific accuracy of books like The Martian seem to help present scientists and engineers in a more positive light, we could use more books with that attention to scientific detail and Some Random Crack Pot. That is their given name, I did not invent that one, Some Random Crack Pot says, I enjoyed the Alice and Robert chapter in.

1:59:07.3 SC: Something Deeply Hidden. I was wondering if you've ever enjoyed writing fiction or if you'd think about enjoying doing so. At some point, a Sci-Fi story from you would certainly rock. I've absolutely thought about writing fiction, the specific idea of trying to write a science fiction tale that would be distinguished by being especially accurate or especially inspiring to a new generation of potential scientists is not actually my biggest motivation here, if I did write a fiction, the two kinds of things that intrigue me... Look, I have no time to do this right now.

1:59:34.2 SC: So we're not gonna call me back 10 years from now to see if I've done this. This is not something that is imminent in any way, but I could imagine doing either a mystery novel, I love mystery novels, as we talked about in the comfort food discussion before, and that would just be as... Something would be completely different in my brain, which would always be fun, or I could imagine writing an intellectual book in the form of a kind of dialogue in a sort of fictional scenario, like the Alice and Bob chapter in Something Deeply Hidden where there were characters talking about ideas but they were.

2:00:12.1 SC: Doing so in kind of a narrative way, I do I feel slightly bad that all of the trade books I've ever written are a little bit hard or a little bit high level, there's differences. The biggest ideas in the universe books are higher level in the previous ones, but all of my books are a little bit demanding compared to other people's books, there's no books that I would give that I've written to someone who not only was not an expert in science but actively didn't like it, for example, I would love to write a science book that would be enjoyed by people who actively don't like science, and maybe a narrative structure would be a good way to do that. Again, no imminent plans along those lines, but who knows life is short, got a lot of things that I gotta do.

2:00:55.7 SC: Anonymous says, I know you said that human needs are changing over time, however, the human need for shelter has been pretty stable for a while, would it be possible to get the amount of time every individual needs to spend to obtain shelter for themselves to go down exponentially? It actually seems to be going up globally with all of our automation and what is going wrong with automated utopia in this domain. So I'm not sure what to say about this, I debated whether to answer it, 'cause I don't think that my answer is gonna be very enlightening here, as I said earlier, I do think that as a species, we have enough resources right now to give every human being shelter we're making choices to have a kind of society where some people are unsheltered and that's just something that we're all responsible for right something that we all have to take that responsibility for making that choice when we could make another one. I don't know the numbers, I'm not at all sure that it's true, that it takes more and more time for each individual to obtain shelter or anything like that, these questions are very, very hard to answer because the human race is very heterogeneous, people who are sort of of my age, in my income bracket, are spending a lot more money on housing than they were when I was born.

2:02:09.9 SC: Okay, so housing prices have gone way up, there's an enormous number of complicated factors that go into that that I'm not an expert on talking about, So short answer is, I don't know why this is true, I do think that we could make it very different, we're choosing not to it is something we should at least recognize as a fact about the world, it could be a different way if we wanted it to be.

2:02:34.1 SC: Robert rocks and Rescue asks, we say that in the MWI, the Many Worlds Interpretation, once decoherence happens, the branches can't communicate with each other, or at least of the probability is very, very small, but not zero. What would happen to a conscious experience if two separate branches with two copies of the observer seeing an electron and position A and position B would unify back into a single one, would that person remember being in a superposition having experienced both the electron in position A and the electron in position B? . This is an interesting question.

2:03:07.2 SC: But I think I'm gonna give a not completely satisfying answer to it, 'cause I think that it's not quite a well-posed question as it is. I know what you mean. We have the situation in many worlds where when you make a measurement... What does that mean? To make a measurement, it really means that some quantum mechanical system that was in the superposition by our lights has become entangled with this environment, that's decoherence. And the whole point is that the environment is big, so in tangling with the environment means not only does the particular thing that you've measured gone out of superposition, but it's affected by becoming entangled with many, many other degrees of freedom in the environment.

2:03:49.0 SC: So the idea of branches coming back together is by itself not a well-defined one, what do you mean by coming back together, are you undoing all of that entanglement with the environment, are you changing all of those impressions? . If I measure the position of an electron and I see that it's in position A not position B then that memory, that fact distributes through my brain, it's not just like one bit that I can access, there's various parts of my brain that are aware that the electron was in position A. So I don't know what it means to sort of re-go back to unified branch anymore, and this is reflective of the fact that it's one of those questions where it makes perfect sense to form the question, but there are assumptions underneath that don't quite hang together. Things like having a memory of something.

2:04:43.8 SC: Only happen because of the arrow of time, because of increasing entropy, and the fact that there are facts about the current state of the universe, which in a world of increasing entropy imply something about the past. When you see a footprint on a beach, you imply the existence of a foot that was there not too long ago.

2:05:07.1 SC: In the space of all possible ways that footprints can appear on beaches, most of them have nothing to do with feet, but when you conditionalize on being in a very, very low entropy past, then it becomes overwhelmingly likely that a foot caused that footprint. So if you are imagining the two branches come back together, that is a fluctuation that decreases the entropy of the universe, you have temporarily ignored the arrow of time and push things back into alignment anyway, it's like un-separating or separating unmixing cream and coffee once again.

2:05:44.0 SC: So what that means is that the whole idea of having a memory is no longer quite valid because you've undone some of the things that go into what it means to make a memory anyway, so I just don't think that... I think that it is certainly possible mathematically to take two branches of the wave function and to put them back into some kind of superposition, but you have to be much more specific. Well, number one, it's not gonna happen as a realistic fact, but number two, even as a thought experiment, you have to just be a lot more explicit about what some of the details are here.

2:06:22.1 SC: Chris K asks a priority question, I agree with you, that consciousness is emergent and deterministically bound to the physics of the brain, but I struggle to understand how it isn't simultaneously a thing that exists and also a thing that is non-physical. Is it your belief that my thoughts, and conscious experience, are themselves made of waves particles in the same way a rock is, and that the thought in my mind has a location in the physical universe that can be pinpointed? . Well, I do think that consciousness is emergent, whether it's non-physical is gonna depend on exactly how you parse that, so I'm not gonna make too much of that.

2:06:56.6 SC: It is similar to the way a rock is a physical thing, it's made of waves particles, but when we have these higher level vocabularies, we use concepts that are much more flexible and abstract than simply referring to a physical object, If I say The Star Spangled Banner, the national anthem of the United States, does that exist?

2:07:22.7 SC: Yeah, I'm pretty sure that exists. I've heard it, I've sung it badly in the past. Does it have a physical location, the Star Spangled Banner? No, it's kind of an idea.

2:07:35.2 SC: It's manifested whenever you sing it or you at the beginning of the baseball game or what have you. Likewise, there's plenty of higher level concepts that play a useful role in our understanding of the world that have causal powers, that have implications when we talk about them, et cetera, but aren't embodied in some physical location, cause and effect relationships, or an obvious example. So you don't need to imagine that consciousness is located at a point, in order to imagine that it's a physical real thing that emerges at a higher level description, those are perfectly compatible things. Dave Grundgaiger also asks an emergence question, the macro world is emergent in the result of core screening.

2:07:52.4 SC: What do you think is the likelihood that there exist multiple orthogonal core screenings that are individually consistent, useful and result in complex worlds that are undetected by each other? I would love to know the answer to this at a detailed level, but my guess, my belief is that the likelihood is very, very small. I know what you mean. So basically what we're doing here is saying, Let's just keep it very simple, lets just keep it classical, and we're looking around and we have the world with a bunch of atoms, and I'm core screening it into things like tables and chairs and computers and stuff like that, so basically what I'm doing is I'm grouping together a whole bunches of atoms and calling them an object, so the question is, are there different groupings rather than this table right in front of me that has some physical coherent location in space, I can talk about this atom in the table, and that atom over in the other room as part of a different higher level core screened thing.

2:09:11.2 SC: The problem with that is that that thing I invented, that core screen object that involved some atoms in the table, some atoms in the atmosphere in another room somewhere, that doesn't help understand the world in any way, there's no simple pattern that is obeyed by that particular core screened structure, it doesn't have any causal efficacy in the world, the table... If I just say, I have a table in front of me, if I tell you right now, that I'm speaking into a microphone that is on a table.

2:09:22.5 SC: Looking at a computer with various questions on them, that is also sitting on the table, you kinda know what's going on, I'm actually giving you useful information, and the reason why in the real actual world in which we live, that certain things make more physical sense to core screen than others is mostly due to spatial locality. You core screened in a way that the table has a location, I can tell you where it is, and that makes sense to you in some immediate way, and in fact, that has solidity, if I touch the table on one end then it's gonna affect the table somewhere else, all of these down-to-earth physical properties make this the right core screening to use, is it possible? There's some very different course screening...

2:10:25.5 SC: Yes, you might even guess that in quantum gravity, AdS/CFT is an example of a weird different core screening. AdS/CFT is this duality that you get in String Theory between a, let's say, an N-dimensional quantum gravity theory with anti-De sitter boundary conditions and an N minus one-dimensional theory on the boundary with no gravity at all. But interestingly, people who have thought about AdS/CFT, so the two theories are supposed to be the same, even though they're in different numbers of dimensions, that's obviously gonna be some wildly non-local map between them, but people don't really think about core screening on either side. Does it make sense to core screen, does it make sense to have physical objects on both sides, 'cause there's strong coupling on one side, week coupling on the other side, this is a great question that I think philosophers should think about more philosophers of physics, but they don't because I am not the boss of the world and I do not get to assign homework problems to everyone within academia, but if I could... That's one that I would definitely assign...

2:11:31.1 SC: Paul Hes says, In an answer during your August AMA, you described a photon with the spherical way function, and you implied that it's pretty typical to be admitted that way. I previously conceptualized a wave function to be much more directional, usually with a large moving peak where the particle is most likely to be found. Can you clarify whether a spherical photon wave function is a special case, if it's not spherical as this concept specific to photons or many types of particles, it's actually the generic case, you get some kind of spherical-ish wave function when you emit a particle, if you have a particle that is trapped somewhere, right, a particle that is an electron within an atom, then its wave function is going to have a definite shape, but we're thinking here of particles that have been emitted either in radioactive decay or a photon or whatever... How do photons get emitted...

2:12:22.4 SC: Do you have an electron? And it gets shaken. Somehow you move the electron around up and down very quickly that emits a photon, but that up and down moving doesn't because it's going both up and down, it doesn't pick out of direction in space if you have a laser or something like that, that's very different. Lasers will pick out directions in space, even if you have a flash light, it's not intrinsically emitting light in a direction, you gotta sort of focus it there with either mirrors or lenses or something like that. The generic thing for light to do is to spread out in a spherical wave.

2:12:56.6 SC: That's true classically, and it just remains true quantum mechanically. Classically, you probably think you can visualize that pretty simply, if you just think about light waves, quantum mechanically, you tend not to visualize that because eventually you're gonna see the particle and you're not gonna see the whole wave... That's the difference between classical mechanics and quantum mechanics.

2:13:18.1 SC: So you can, for example, as we did talk about in the August AMA, you can look at the track of a particle at the detector, the LHC, or in a bubble chamber or whatever, and it looks like that particle has a point-like trajectory, but that's because you're measuring it, and before you measured it, that particle's wave function was spreading out in something like a spherical wave, not exactly spherical, the details will matter, but they will tend to spread out in other... In all directions until they are actually measured somewhere. George asks my question concerns the heat death of the universe. And I was recently speaking with a friend of mine who received his bachelors in physics a few years ago, he said he was talking with his professors, already, I'm skeptical 'cause there's like many chains here in the communication, but the professor was talking about how a new universe might be able to be created after the heat death of our universe.

2:14:10.8 SC: You know it's possible. I've written papers about it, the paper I wrote with, Jennifer Chen, on the arrow of time and spontaneous inflation is an example of baby universes being created in the far future, but look, we don't know. Not only do we not know in a sort of strict sense that we haven't observed it, but we have no very solid theories about this, we have... We're not completely clueless, we have some ideas that we push around, it's important to know when we talk about...

2:14:22.4 SC: We don't understand quantum gravity, that's true, but we understand a lot about Quantum mechanics, and we understand a lot about gravity, so it's not like anything goes when it comes to quantum gravity, there's still some things that are more reasonable, more likely than others, and it's absolutely possible to contemplate scenarios in which something happens in the far future of the universe that brings the universe back to life, either in some large region or in some tiny little baby universe type of region, but honestly, we don't know, we don't understand the physics well enough to say one way or the other. So it's fun to think about, interesting to think about, but don't rely on it for anything for any planning purposes.

2:15:22.8 SC: I don't know. Jeff B says, when we say that a region of space has a finite number of degrees of freedom, is this equivalent to saying that reality is fundamentally discrete or is there a more subtle relationship?

2:15:35.9 SC: It's a little bit more subtle relationship, again, this is quantum mechanics, we're talking about, it's not classical mechanics, quantum mechanics in its basic formulation with the Schrödinger equation, et cetera, is not discrete, it is just wrong to think that the fact that the world is quantum somehow implies some discreetness to it. I ramble on about this in the upcoming book, the upcoming volume two of biggest ideas in the universe on Quanta and fields, because in something like an atom where you have discrete energy levels for the electron, that's not because the laws of physics are discrete. The laws of physics are smooth, it's a wave equation. The Schrödinger equation is that the set of solutions to that equation in that particular setup is discreet, so quantum mechanics itself...

2:16:52.2 SC: So you just do regular quantum mechanics. Nature is not discrete. Full stop. I recently wrote a paper very recently, pointing out that in certain special cases, if things line up just right, you can take quantum mechanics and you can discreetize it. You can discreetize the evolution of the wave function in Hilbert space so that it is truly discreet, there are some cosmological issues to come up there, but otherwise it's fairly plausible that that could be the real world, but we have no reason to think it's the real world it was just sort of intellectual exercise in pointing out this is a possibility that we can consider, but anyway, I think that's not what you're getting at when you ask about the fundamental degrees of freedom, the finite number of degrees of freedom.

2:17:12.9 SC: Usually in quantum mechanics, what we mean by that is the dimensionality of Hilbert space... Hilbert space is the space of all quantum wave functions for any point particle moving in space or any quantum fields, the dimensionality of Hilbert space is infinite, so it is not discrete, but if you have just a spin, a single cubit, that's just a two-dimensional Hilbert space, that's finite, and there are good reasons from quantum gravity and black hole entropy and the Bekenstein bound.

2:17:52.2 SC: And words like that, to think that the physical number of degrees of freedom in the sense of the dimensionality of Hilbert space is finite within any finite sized region of space. But again, that doesn't mean that nature is discrete in the regular sense, because it is a vector, the thing that we're just using to describe the universe is a vector in a finite dimensional vector space, but the vector is still continuous, it still moves continuously through that vector space, so that in that sense, in those senses, there is a more subtle relationship there.

2:18:20.0 SC: Kyle Steven says, With the continued proliferation of seemingly existential threats to humanity such as pandemics underlined AI nuclear war climate change, I can't help but feel the philosophical doomsday argument continues to gain more credence with each passing day, given these existential threats, should we lend any additional credence to the possibility the doomsday argument accurately accounts for why we find ourselves to exist so early in the universe? . So for those who don't know, the doomsday argument is one of these arguments that is based on the assumption that we are somehow typical observers within some class, some reference class of observers, so if that reference class of observers is all human beings who ever live... Okay, well then in that case, it is very very unlikely that we are within chronologically the first 1% of human beings who ever live.

2:19:15.1 SC: Right, 'cause that would be only 1% chance, so therefore, you suddenly have a prediction for how many human beings could possibly live or at least probably live into the future, not so many. Maybe a few more generations, but pretty soon you're gonna hit that 99% mark and it's gonna become unlikely, so I think this is just a mistake like just obviously wrong this argument, because we are not typical observers, we're gonna talk about this again later in the AMA but I've mentioned this before, I talked about it a little bit of length in the solo podcast from a while ago on the philosophy of cosmology, someday I'm gonna write a paper about this 'cause I think everyone gets this wrong, to be honest. So I just have zero credence in the doomsday argument.

2:20:02.1 SC: Just to point out one obvious reason not to believe it, why did you say all human beings ever existing rather than all life forms, ever existing. You get very different answers if you said that, but you have to pick a reference class, you pick it arbitrarily and your answer depends very, very sensitively on that choice, when the answer to a purported objective question depends sensitively on a completely random and arbitrary choice. You are probably making a mistake.

2:20:52.0 SC: I would say, and I think in the doomsday argument, that's very clear, but you are correctly, Kyle, pointing out the fact that there is something new about humanity in recent generations, namely that we... In a way that we didn't 100 or 1000 years ago have the capacity to really do disastrous things to life on Earth, including all of human beings, so in that sense, the chances that we do something terrible that destroys life on earth or destroys all human life is much bigger now than it used to be. That's a perfectly reasonable argument, but that didn't make any assumptions about typicality or anything like that, that just said, through technology, we have a lot more leverage over ending lives here on Earth than we ever did.

2:21:18.0 SC: That's the route I would go down if I wanted to think about this kind of philosophical argument. Jared Sage says, is it on the table that dark matter isn't a fundamental particle against the standard model, but instead it's some quasi-particle that's an excitation in an abstract, non-fundamental field? . Sure, it's on the table. Many things are on the table. I don't think it's on the table that it's a quasi-particle in standard model fields, I do think that you need some degrees of freedom beyond the standard model to do it, with the obvious exception that it could be tiny black holes or medium-sized black holes for that matter.

2:21:58.0 SC: A black hole in some very real sense is a quasi-particle, it's a extended excitation of existing fields like the gravitational field and the matter fields and so forth, but that's probably not what you have in mind. I think that you would need other fields... I don't think the fields we know about in the standard model are up to the task of giving you some unknown quasi-particle excitations that could be the dark matter, especially because standard model fields tend to interact not be dark. They would...

2:22:28.3 SC: Most ways I could think of to make bound states of standard model particles would interact electromagnetically like hydrogen atoms interact electro-magnetically, even though they are themselves electrically neutral because they're made of electrically charged constituents. So I think that this kind of thing is in the realm of... You're welcome to think about it, but we have no great reason to suspect that it's on the right track, and it would be hard to constrain your own derising. Tomer Hachahan says, what is the relationship between the notion of time in general relativity and the thermodynamic arrow of time from my limited understanding of GR, the main difference between time and the other cordon of space times at the sign of the metric is negative for the 00 index can one in principle, start from the signature of the metric is minus plus plus plus and derive the zero the coordinate is the one along which entropy grows. No [chuckle] Well, because yes, in general relativity or in special relativity, or for that matter, in Newtonian mechanics.

2:23:34.3 SC: There is a difference between space and time, and that difference is reflected in the relativity versions in the fact that the metric has a different sign in the time-like direction than the space like directions. None of that has anything to do with entropy. Okay, you can imagine a box of gas that is in thermal equilibrium and the entropy is neither growing or shrinking, but time is still passing because all the molecules in the gas are still moving, the arrow of time is over and above the existence of time itself, that minus sign in the metrics says there is something called Time, there's a coordinate that is different than space, it does not say that there's any arrow pointing along that direction.

2:24:16.1 SC: Which you know because there's no arrow pointing in the spatial directions right, there can be. In fact, there is here on earth and there's an arrow pointing toward the center of the earth called where gravity is pulling you towards, we don't make a big deal about that arrow because its explanation is perfectly obvious, there's the earth beneath our feet pulling us down, we know it's not there in the fundamental laws of physics, and we know it's not out there in outer space, far away from the earth. The arrow of time is only different because it's everywhere, and it starts at the Big Bang, we don't know exactly why that happened, but it is like the arrow space here on earth, it is something that is not ingrained in the nature of spacetime itself, it's a feature of our local environment.

2:25:01.2 SC: Motio Fatea says, What are your three favorite cocktails and why would you consider developing a signature Mindscape cocktail for the drinking pleasure of your Patreon fans? . Well, that's a good idea, although I'll have to confess, my ability to create new cocktails is pretty limited, I've tried, I've done it. Sometimes more successful than others. Let's just put it that way. So I'll take suggestions within Patreon for what could be the best Mindscape cocktail or Mindscape cocktail list for that matter. You know, Jennifer did, for a long time have a blog called cocktail party physics, where she collected physics cocktails in the side bar, but they were all pretty horrible, you wouldn't wanna drink these things.

2:25:12.4 SC: They are either just regular cocktails with physicsy names or terrible concoction that were meant to reflect some physical principles that would not ever be served in a bar, let's put it that way. I'm much more standard. In fact, I'm kind of boring when it comes to cocktails, I like my cocktails not fruity or juicy or sweet, I like more spirit forward, as they say, so I like martinis and Manhattan and Negronis, and slightly more out there world. I like sazeracs and corpse reviver no.2 and stuff like that. But honestly, am martinis, my favorite cocktail is very simple, very easy to make... You can mess it up, people do mess it up, but I think it's pretty easy to make the regular version of it, I was just at a party with...

2:26:37.0 SC: Not a party dinner at a friend's house, and he made martinis and he didn't use ice or make the martini cold in any way, and I could not hide my disappointment, and he felt a little sad that I didn't like his martini that much, 'cause it was all room temperature, but one of the requirements says is it should be super duper cold, that's my advice out there to martini makers.

2:27:00.8 SC: Simon Graph says, "As a good Bayesian, what do you think of higher order defeat problems, for example, how should we conditionalize on evidence that our ability to conditionalize, I.e. Taking evidence into account is currently impaired or worse evidence that conditionalization is not the right rule for taking new evidence into account, some people who argue that finding out you are drugged tired or suffering from hypoxia puts us into situations like this". I think that is a great question, but I don't have a great answer, I haven't thought deeply about these problems, my immediate guess is you do your best if you were drugged but didn't know it at all, then I can't think of a better strategy than just trying to do the same thing that you thought you were trying to do, if you did know it, then that should be part of your calculation of both your priors and your likelihood function, right.

2:27:53.7 SC: If you are seeing a pink elephant and you're like, Oh, that's very unlikely, but then you go also, you're completely intoxicated, then it becomes more likely you change your likelihood function, right? . Now, I am a good Bayesian, I try to be a good Bayesian, but to be clear, to be a good Bayesian is to assign prior probabilities to things and to try to update them when new information comes in, it is highly impractical to actually do that in the real world on a comprehensive kind of basis, you can do that explicitly for certain claims, scientists do it. When I was a graduate student, they didn't.

2:28:33.0 SC: Astronomers and physicists were not Bayesians generally back in the 1980s, and big data came along and it became more clear we had to be better Bayesians, and so now when you read papers that are looking for the Higgs boson or using CMB data to constrain cosmotrical parameters, everyone is Bayesian from the start. And that's very helpful. But as a practical matter, no one really plugs in Bayes' Theorem when they learn new information in everyday situations, so just be and on, trying to say is that to be a good Bayesian is really about trying your best to admit that you have priors and to update them when you get new information as best you can, it's not literally plugging in the formula, and then if you're in these situations where conditionalization is not the right rule or something like that...

2:29:27.0 SC: If you're somehow cognitively impaired, you're probably gonna be an even worse Bayesian than a perfect calculator would be, if you go back to the podcast we did with Karl Friston about the Bayesian brain and the free energy principle, the Bayesian brain hypothesis is about minimizing surprise like trying like a brain is supposed to model the world in such a way that it says the least surprised that it can be when it encounters new information, but even those people admit that that's calculationly implausible for the brain to actually do it, that's why you met the free energy principle.

2:30:05.1 SC: The free energy principle is kind of a way to approximate being a good Bayesian, and so I think that the real world is a lot richer and a lot more complicated than the perfect Bayesian reasoner that we imagine that these higher order defeat problems or examples of that, I do not know of a particular correct strategy to take that covers all of them. Sorry about that. Henry Jacobs says, "I get the impression that unitary evolution in quantum mechanics is analogous to volume conserving evolution in classical mechanics". Yes, that is true. "Classically, when dissipation is introduced, we get phase space contraction, however, dissipation is secretly achieved, it's really two subsystems interacting where one is large and called the environment and typically suck energy from the smaller sub-system. Is there an analogous conception of dissipation in coupled systems in quantum mechanics and kinda deal in explanation for the parent collapse of weight functions during observations?".

2:31:02.0 SC: I would say yes, absolutely. And in some sense, okay, so yes. Absolutely, there's a conception of dissipation for coupled systems in quantum mechanics, quantum systems become entangled with each other, that's an example, okay, when you lose the purity of your quantum state because you're becoming entangled with degrees of freedom elsewhere, and there are equations to govern this, so if you aren't tracking the environment or whatever else it is you're becoming entangled with, if you're only tracking the system of interest, It's an open system. It is not going to obey the Schrödinger equation. So you do the same kind of thing morally, that you do in classical mechanics, which is you say, What is the best approximation, what is the most realistic dynamical equation I could pose it that would...

2:31:49.7 SC: More or less track the evolution of my open system in contact with the environment that I am not tracking, and this is... I'm sort of saying this slowly and hesitatingly because hopefully it should be clear, you can't get a perfect equation that would ever do this, because the thing is, you don't know what the environment's gonna do. By hypothesis, you're not tracking it, right. If you try to model the earth as an open system, but you don't know that we're about to be hit by an asteroid, you're gonna get your predictions wrong, the same thing is true in quantum mechanics, so you have equations, you have master equations or the Lindblad equation or various other things that try to do this kind of thing by making assumptions about the environment, the environment is a thermal bath, it's weekly coupled, whatever set of assumptions it is you need to make, and you can do that, and that often works correctly in certain situations, but you shouldn't be overly confident in its predictions, they're as good as the assumption...

2:32:52.0 SC: The conclusions are as good as the assumptions. Let's put it that way. Now, if you're asking whether it's an explanation for the apparent collapse of wave functions, it's half of an explanation, all you're doing and saying here, decoherence. Decoherence is the phenomenon that is predicted by analyzing things in these ways. Some people will say that decoherence provides a solution to the measurement problem of quantum mechanics. Why? , Because if you have an open system coupled to an environment, it can start in a superposition of a pure state, quantum mechanically, and it will evolve into a statistical mixture of states, and that statistical mixture of states described by density matrix will be a sum of states whose coefficients are non-negative numbers adding up to one, that is to say they look like probabilities, and in fact, they precisely are the probabilities that are predicted by the Born rule of quantum mechanics, okay.

2:33:54.0 SC: So people will say, Look, all I need to do is have decoherence happen and suddenly I have a probability distribution over different states, that is all true, but what you don't have is a statement that says, and you will find yourself in one of those states once the decoherence happens, the rules of quantum mechanics all by themselves, say that you would find yourself in a mixed state, you find yourself in a combination of all of these states and you'll find yourself. In a density matrix in order to successfully address the measurement problem and understand...

2:34:26.0 SC: The apparent collapse of the wave function. You have to make a set of additional substantive claims, your substantive claim might be, these different parts of the density matrix now describe different branches of the Wave function, and I'm on one of them and not others. A different claim might be, there are hidden variables that point to one of these entries in the density matrix, and that's the one where I live, other modifications might be, the Schrödinger equation is violated and the other entries in the density matrix no longer exist, whatever they are, but this is all why we need theories of the foundations of quantum mechanics, you can't explain what we see, just by saying that there is decoherence in the world. Michael says, "I am an atheist and certainly no expert on religion or Christianity, however, it does strike me that Jesus seems to have been a really good person, feminist even perhaps, and no toxic masculinity that I am aware of. I'm wondering what your thoughts are regarding Jesus as a good person and as a corrective to oppressive text found in the Old Testament, and if Jesus holds up today is a model of non-oppressive...

2:35:33.4 SC: Non-masculine toxic figures, et cetera". You know, yes and no. In some sense I've often said, I'm 100% open to the idea that we can find wisdom and examples and inspiration in texts, whether they are religious texts or secular texts or whatever. If you wanna read the New Testament and find that Jesus seems to you to be kind of like a role model, then go ahead. I have no objections to that whatsoever, it's only kind of partial because number one, it's very very hazy what the connection is between the description of Jesus in the New Testament and any actual human person. Right, there probably was a person named Jesus, et cetera, but the New Testament texts were written decades after that person died by people who are not eye witnesses to it, so what are you gonna believe? , this is a set of stories that were told within the community and passed down orally for a while before they ever got written down, so it's not clear that you're actually looking up to a person rather than a fictional character in terms of what we are actually told about them.

2:36:43.5 SC: And the other thing is, some of the things that Jesus said were really admirable and some were not, like most people. This is why I don't like hero worship in any sense for Jesus or for anybody else. It's true that he said a lot of good things about turning the cheek and helping the poor, et cetera. He also said a lot of things about going to hell if you didn't follow him, and maybe he was not as misogynist as some of his contemporaries, but he certainly didn't say women and men have equal status in my church, I don't remember that one anywhere in the New Testament, certainly wasn't followed in by his followers when they actually set up the church, so go ahead. I would say, find inspiration in Jesus and Buddha or Jana or whoever you want to be inspired by. That's fine. But there's plenty of people out there to be inspired by. Not just that one.

2:37:38.2 SC: Sid Huff says, "Many people have been taught that atoms are mostly empty space, this notion was stayed eloquently by none other than Carl Sagan, however, many physicists debunk this statement as a misconception, so what exactly is empty space? , do such a thing actually exist whether inside atoms or elsewhere?". Well, you have to define what you mean by empty space, and then you can decide whether it exists, I would not say that atoms are empty space, mostly because I think that atoms are wave functions, right, and the wave function is a size, you can literally plot it when you look at all those orbital diagrams in chemistry class, that's the size and shape of an atom, in my way of looking at it, I don't see how anyone can both really understand quantum mechanics and claim that atoms are mostly empty space, because you have to... In order to say that atoms are mostly empty space, you have to think of an electron as a little dot, which we just know it isn't.

2:38:35.7 SC: I don't know. I know people are clinging to this way of talking, I don't blame Carl Sagan at all because he was not a quantum physicist, that was not his area of expertise, but there's modern grown up quantum mechanics people who still talk that way, even though they really should know better. Then I really just don't know. There's other layers here because, of course, we know these days that quantum field theory is a better way of thinking of things than point particle quantum mechanics, and there the notion of empty space becomes even more fraught. Let's put it that way. The closest you have in quantum field theory to empty space is the vacuum state, so a state of your quantum field theory where there are no particles, no exitations, no energy of any sort or anything like that. And you can have that, that's a pretty good approximation to empty space to the vacuum in between the planets and the stars, it's not exact 'cause there's light and so forth, and that means it's not completely empty, but it's a good approximation. I'm not sure what else we want other than that.

2:39:34.7 SC: Keith says, "Say Laplace's dark demon is like Laplace's demon except only knows the exact state of dark matter, the dark demon also knows General Relativity and thus presumably will be able to infer the presence of the clumped up ordinary matter, similar to how we ordinary beings infer dark matter, however, the dark demon is not aware directly of the laws of physics governing the other interactions of ordinary matter, e.g. Electromagnetism. My question is, given these properties of Laplace's dark demon, should we expect the dark demon to still be able to infer the state of the ordinary matter and hidden laws just based on this perfect dark and gravitational knowledge?".

2:40:14.5 SC: Well, it would be hard. So to rephrase the question here, If you knew, if you were perfectly knowledgeable about what all the dark matter was doing, and Laplace's demon is supposed to be really smart, so perfect calculation abilities, the ordinary matter in the universe would have an effect on the motion of the dark matter so could you infer the physics of ordinary matter from just what the dark matter is doing. In some sense, of course, this is just what we're trying to do right now with the dark matter, we know about what the ordinary matter is doing. We're trying to figure out what the dark matter is, and we know there that there are things we can learn, how much dark matter there is, how it's distributed through the universe, but there are also things that allude us right now, is the dark matter heavy or light to say axions or WIMPs, or black holes or neutrinos, or who knows? So, of course, Laplace's demon knows a lot more than we do, so I think it could go pretty far, it would certainly know that ordinary matter has dissipation, right, so it has some way of shaking off energy by giving off photons and therefore clumping and coming to the bottom of a gravitational potential well...

2:41:26.9 SC: That might naturally lead it to understanding electromagnetism, maybe even atomic structure, but then there's other things it would not know like it would never learn about the top quark, because top quarks just decay away, heavy particles don't really stick there in the set of particles that we have existing in the universe right now. So that would be very, very difficult for Laplace's dark demon to figure out. It would probably even have difficulty with something like the Higgs boson or the Higgs mechanism, because I'm not sure that the dark demon would ever be able to figure out that there was parity violation in the standard in what we call the ordinary matter sector, and without parity violation, you don't really need the Higgs mechanism, right you can just have masses for particles just like Dirac did when he first wrote down the Dirac equation, so my guess is the dark demon would be able to learn a lot, but certainly not everything about our known laws of physics.

2:42:26.4 SC: Nikola Ivanov says, If the Second law of Thermodynamics is applicable only to isolated systems, how can we think it is applicable also to the observable universe as a whole, if we don't know whether the observable universe is an isolated system.? .

2:42:40.1 SC: Well, there's two things, for one thing, there are absolutely are versions of the second law that are applicable to non-isolated systems, if you have a system that is in contact with a heat bath, okay, that is not isolated, it's in contact with the heat bath, but it's a very simple kind of non-isolation, it's just sort of being lured into thermal equilibrium, so in those cases, you absolutely have a version of the second law that it says that the sum of the entropy increase plus the heat flow into the environment is greater than zero, so something like that might still apply to the universe.

2:43:16.9 SC: But also more importantly, the second law is not posited as an axiom of anything, it is derived from behavior of physical systems, we know about core screening and about the microscopic structure and things like that, and so if the universe is not an open system, it's not an open system, if our observable universe is thought of as not an open system, it's thought of as not an open system because things can escape from it, there's a horizon around us and things can leave the horizon, it's not because things are coming in to our universe and influencing us, so again, that's a very simple kind of non-openness and one that can pretty easily be accommodated by what we understand about the dynamics of the Universe, so we have every reason to think that within our observable universe, entropy is going up.

2:44:06.0 SC: Russell Wolf says, "It feels to like me more often than not, your response to priority questions is something along the lines of, I don't think this question makes sense or I don't have much to say about this, when I'm listening to an AMA and hear a priority question come up, my first reaction is to expect a less interesting discussion because usually you have more to say about the questions you select freely, how well do you feel the system of priority questions is working?". Well, I'd be happy to get feedback from Patreon supporters about the priority question system, but I think it's working okay. It is true that a priority question by its nature is one that I'm gonna answer, whether or not I think I have anything interesting to say about it, my first criterion for picking questions to answer is whether or not I have anything interesting to say. So if you remove that criterion from consideration, there's gonna be a negative correlation with me having interesting things to say.

2:44:58.1 SC: But that's not the only thing that matters. I want the AMAs to be useful, both for listeners who are not the question askers and for the question askers, right. Both of those criteria count, so when I'm trying to choose questions to answer, mostly I'm thinking about the listeners, I'm thinking about whether or not they will want to hear my answer to this question, possibly. I don't know why they wanna hear some of these answers but you know I give it a shot. Whereas when I'm thinking about the priority questions, I'm thinking about the person asking the question I do... In the early days of the Patreon when it was smaller, I could answer all of the questions. And I felt like I was giving back a very definite tangible benefit to Patreon supporters. I can't do that anymore. So the priority question system was invented as a compromise where if you have one burning question that you wanna ask, if even though I seem to not be willing to answer it, I'll give you that chance.

2:45:58.4 SC: You absolutely have that chance and probably you will learn that I wasn't answering it because I have nothing interesting to say, but that's okay, maybe I'll be able to point in some direction or something like that. So again, I'm open to people suggesting changes in the priority question system, but I think so far it's working more or less as I had hoped.

2:46:17.1 SC: Brent Meeker says, "What do you think of various systems of voting, such as rank choice or distributed points? . Have there been simulations or empirical tasks of how they work? Arrow's theorem says that all voting systems can be gained". I don't think Arrow's theorem exactly says that. Arrow's theorem says that, certain kinds of voting systems, which are a lot of them, but not all of them, in particular, it applies to rank choice voting, but not the sort of voting systems where we have a continuum of preferences, there are voting systems where you don't just rank your choices, but you assign a number to them, you grade them basically range voting. So you say, Well, this option, I give a 10 to, this I give a 7.3, this I give a 2 and so forth, Arrow's theorem doesn't technically apply in those cases, and furthermore, what Arrow's theorem says is not that all voting systems can be gained. It says that there are various things you would like to be true about a voting system, such as no dictator, there's not just one person who makes all the decisions, and if two people both rank A greater than B, then their combined ranking is A greater B or things like that, can't all be simultaneously satisfied, but I think you're probably thinking of is strategic voting, which is a related but slightly different concept, strategic voting is when you have a set of preferences, but the most likely way to get your favorite outcome is not to vote honestly...

2:47:47.6 SC: About what your preferences are. Right, so you might vote for a third party, you might not vote, I should say, for a third party candidate not because you don't like them, but because you don't think they're gonna win, if 45% of the people like one candidate and 50%. I'm not gonna get this true in real time if 40%, 45% and 15%... Right. Are the voting things... Then you might worry that if you give your money to a third party candidate, you're throwing it away 'cause they're not going to win, so instead you strategically vote for somebody else, so that's a true but slightly different thing than Arrow's theorem. Anyway, I have mixed feelings about different voting systems, I do think that our current voting system pluralistic voting or First-past-the-post is the worst, I think that's the consensus of people who thought about this, and I do think that Rank-choice voting is better. I think that range voting, like I just described, is even better, although it's still subject to strategic voting considerations. There was a study... You asked about a study, does anything work the best.

2:48:58.2 SC: Well, what does it mean to work the best, right? This is why I'm interested in these questions because it's not at all obvious how to define what it means to work the best, but if you Google range voting, there was a study, someone tried to do a simulation of many, many different voting systems and invented an idea called Bayesian regret. You know how sad is the individual voter that their preferred candidate didn't win, and then you sum over all the voters, and range voting came out the best in that particular set of simulation, so there is at least an attempt to be a little empirical about this it's not a... It's well, it's a numerical experiment, it's a thought experiment, let's put it that way, it's not an actual empirical investigation based on real voters, and that's why I'm a little bit skeptical because there is a trade-off that voting theorists don't wanna face up to, which is that complicated systems are bad. Complicated systems might help you achieve some ideal solution in a thought experiment, but real people don't like them. Real people know what it means to vote for a candidate, they might even understand what it means to rank candidates, but you can quickly get elections.

2:50:22.7 SC: Like I was in California where we had elections with over 200 people on the ballot, you think you're gonna rank all them? . You have to do something. You have to have some simplification, so I don't know how much work has been done about people just not voting or voting badly, when you have these more elaborate systems in place, that's what I would worry about, it goes back up to Linux versus Macintosh users, people want a simple user interface, and the voting system is an example of where that is an important consideration. I'm gonna group two questions together, Schlier says "Elon Musk is famously a fan of the simulation hypothesis. It seems to me that if I were a billionaire, I too would question the nature of my perceived reality due to the sheer unlikelihood of having that experience, it's not surprising that there is a richest person, but it would seem surprising for me to be that person. Is this bad reasoning or can the atypicality of one's own role in the system serve as useful information about the nature of the system?". And Casey Mahone says, "I often hear physicists reworking their ideas in order to avoid Boltzmann brain situations, but this seems to clash with another idea I've heard you express, namely that we can't think of ourselves as being uniformly selected among all observers, can't we just imagine that there are Boltzmann brains having their own experiences near the end of time while we are here now...

2:51:46.7 SC: Why would we change a theory just because it suggests the possibility of Boltzmann brains somewhere else in space time?". So the common thread here is something you already mentioned earlier, this episode, the idea that we are somehow typical observers within some group of people, I kind of am sympathetic with Schlier's suggestion that if you were a truly non-typical person and you thought that you should be typical, then that might suggest to you that something was going on. Right, but guess what, forget about billionaires. Typical people are not physics professors, so I should have that same kind of belief, and this is exactly why I don't think that we should think that we're typical people, because by the time we're grown up and trained well enough to have such thoughts, we're already not typical people. We're certainly not typical arrangements of atoms, just by being people at all. This whole thought experiment is a weird thing where you say, Okay, here I am as a real person with real facts and characteristics about my life, I'm going to pretend to forget all of them, I'm gonna pretend to forget that I know who I am in the world, pretend that I'm a typical person, and then real...

2:53:03.1 SC: Then you wake up and look around and notice that I'm not typical and be surprised. This just seems weird to me. Like, Why are you doing this? Why not just admit that you're not typical. Okay, so that's my reasoning there. Now, I'll confess very very quickly, I don't have a perfectly well-formed alternative, so I'm working on that, I'm trying to figure it out. One of the aspects of what I think is a much better alternative is that if you have a set of observers who have the same information about their situation, so if you literally have observers that if you ask them everything about who they were, would give you precisely the same answer, then you should imagine that you were typical among that ensemble of people, so if you think about a duplication experiment where you step into a box and then you're turning the two identical people and you don't know neither one of those two people know which ones, they are, then you should give 50-50 chance to be in either one. What else are you gonna do? Because they're in at this technically indistinguishable situations, and so that's why the Boltzmann brain problem is a big problem because it's not because there are random fluctuations into brains...

2:54:19.7 SC: Okay, I know everyone says that it's kind of evocative and picturesque, and people talk about that, but again, this whole line of reasoning that says, if there were lots of Boltzmann brains, I would be a Boltzmann brain, I'm not one, therefore, it is ruled out by the data. I don't think that that makes any sense at all. The problem in the Boltzmann brain situation is that when there are fluctuations into Boltzmann brains, there are also fluctuations into people with exactly your experiences, but people with exactly your experiences in much different actual circumstances. Okay. The most obvious case is imagine a fluctuation into exactly our universe that we see around us right now, but no more, if you want to fluctuate into our universe as we see it, you don't literally need to make other galaxies and stuff like that.

2:55:13.5 SC: Right, you need to make the photons that you and I and astronomers observe from those galaxies and use them to infer the existence of galaxies, it's much easier to fluctuate into a few photons than to fluctuate a whole galaxy, so the overwhelming majority of observers in that kind of fluctuating universe who see pictures of galaxies far away, tomorrow will not see those pictures anymore, those galaxies will disappear because there were no galaxies there, there were just some photons that randomly fluctuated into existence. That's the problem with this scenario, is that you make a strong prediction that you don't really believe. Now, you notice I didn't say a strong prediction that comes out false, that's a slightly different thing, is that you don't really believe that prediction because of the cognitive instability aspects of your situation, you have to believe in that situation that all of your purported information about the universe is just randomly fluctuated and therefore is completely unreliable, and therefore you can't actually make any predictions about anything, and that's no way to go through life. So the belief that we are not Boltzmann brains does not rely on the idea that we are typical observers, chosen among all observers in the universe.

2:56:37.5 SC: It does... I do think it is absolutely fair and indeed the only thing to do to assume that we are typical observers from the set of people with exactly our information, it's completely cheating to say that there are some observers in a nice well-posed universe like we think we live in or portion of the universe, and there are many more observers in the future or in the past with exactly the same epistemic situation, but we're not them because how do you know you're not them? What's so great about you? Why don't they have feelings too? Right.

2:57:13.9 SC: So I do think that random fluctuation scenarios should be excluded from our consideration, but not because of literal Boltzmann brains. Redman says, "After extraterrestrial contact requesting a meeting, the President, a Mindscape subscriber, asks you to lead the human team, the aliens who can speak English but not other languages and are far advanced in the art of meetings, limit human participation to five people. Who do you take?". Whom do you take. Sorry, so I'm not gonna answer this question literally. But I wanna say two things about it. The first thing is that the reason I'm not gonna answer it literally is because I'm just not into these kinds of questions, and I know that many people are, I'm not trying to denigrate these kinds of questions, but like, pick your five favorite people with characteristics X, those are just never my favorite questions. I'm just not into them.

2:58:10.5 SC: It kind of smacks a little bit of hero worship. I know it's not. I'm not trying to say that, but who are the five best people the five coolest people? I'm not about people in that way, but I like my friends, my personal acquaintances, I'm about those people, but people out there in the world who do great things for them, I'm about their great things, I don't know them personally enough to say, who are the five people in history you'd wanna have dinner with or whatever, I just don't think that way, and I apologize for it 'cause it makes me weird and it makes me sound like I'm being rude to people who ask that question 'cause that kind of question is very common here in the AMAs. Okay, so I'm not gonna give you literal answers to it, I feel like I'd be insulting all the people I didn't pick, but I do think that the question of what kinds of people you would send to talk to... Intelligent Aliens is a really good question. Forget about individuals and their names, what kind of team would you assemble... That's a great quest.

2:59:14.5 SC: And that's very interesting. And the short answer is, I don't know, because one of the rules of the AMAs here is, I don't do any work for them other than literally editing them and then reading and recording them, so that's a question that demands a lot of thought, and I haven't thought about it, that's why I like that aspect of the question. You would... It's smart that you put in there in the question that the alien somehow speak English but not other languages. Okay, I don't know what that happened, but I guess I do recognize that it makes the question much simpler, so we don't need to send the linguist right. I mean, clearly, you would want to send at least a very good physical scientist and a very good biological scientist. Right, you'd wanna talk to them about science. And I think that you would separately want to send someone who was really good at technology. Being good at technology is different than being good at science, so someone who can learn about from the aliens about the fundamental laws of physics, someone who can learn from them about their biology and someone who can learn about them from them about their technology, just saying those words out loud makes it very clear that even five people is not gonna be enough.

3:00:26.6 SC: Like what do you mean someone who can learn about technology, there's lots of different kinds of technologies, people who are good at Super conductors are not good at pharmaceutical advances or something like that, so it's gonna be a tough call, and then I think you want some more socially oriented people, maybe a social scientist and an artist. Artist in the broadest sense, literature, movies or whatever, but someone who has a more poetic narrative sensibility would be a good person to talk to the aliens and also someone who knows something about social dynamics to figure out what the society is like of the aliens and something like that. So that seems like me to be a pretty good first attempt at five different kinds of people, but I was leaving out people who are interested in diseases, people who are interested in astronomy, people who know about complex systems in general, people who are politically smart people who could negotiate very well, there's a whole bunch of skill sets not in that team, so I'm just gonna cross my fingers and hope that we get 10 people on our team when we finally meet the aliens.

3:01:36.2 SC: Adam Small says, "Priority question. This has to do with black holes, from what I understand, the effect of gravity move at the speed of light, so if the sun suddenly took off and jetted out of the solar system, the earth would still revolve for a while until the information arrived. This relates to black holes, because since the signal of gravity moves and starts inside the event horizon where the source of gravity is, how does the information of gravity escape the event horizon? Since gravity does move and reach an orbiting star, I thought no information can escape other than Hawking radiation?". So there's a whole bunch of things going on here that I'll try to talk about a little bit. First thing, it's not really relevant to the question, but it's useful information, these kind of thought experiments where you say if the sun suddenly took off and jetted out of the solar system, this already doesn't make sense because it violates energy conservation, like...

3:02:29.0 SC: What do you mean? Suddenly took off? , the whole mass of the sun, suddenly has a different momentum, so you're already violating the laws of physics and then you're saying, Well, what would the laws of physics have to say about this? That's an inconsistent question. You need a better... And you can fix it up, right? You say like, what if the sun exploded, but if it exploded in two blobs moving off in opposite directions, like the sun decayed into too many suns going in opposite direction, so that's a fixable kind of thing, but just so you know, that kind of thing would have to be fixed in order to ask a sensible question. But the other thing, the more important thing about the question is this idea that gravity is kind of a substance that moves at a speed, that's just not what gravity is, is for that matter is not what electromagnetism is. Both gravity and electromagnetism are fields that pervade space time and solve some equations, and so the right question to ask is, what is the solution to the equations with certain boundary conditions, in the case of a black hole or the sun, the boundary conditions are...

3:03:31.2 SC: There's some mass or some effective curvature of space time located at some part of the universe, and with that boundary condition, you solve the equations around it, and you find that there is a inverse square law for both gravity and for electromagnetism. It's not because there's some flux of stuff, when you have a charged particle with an electric field around it, it's not because electromagnetism forces are moving away from the particle and reaching out and grabbing other things, it's because at every point in space, there is an electromagnetic field and it settles down to a certain configuration, given that boundary condition, that there is a charged particle at that point. Likewise for gravity, there's nothing moving faster than the speed of light in a static gravitational field, there isn't anything moving at all, it's static. [chuckle]

3:04:24.2 SC: So it is true that if the sun changed its configuration dramatically, for example, by splitting in two and moving off, then the boundary condition for the gravitational field would change, and that change would not be noticeable to us in some reference frame, 'cause it's relativity until... What is it? Eight minutes later, 'cause we're eight light minutes away from the Sun. But that's completely compatible, right, that's just the equation for the gravitational field, now has a different boundary condition and those changes ripple out at the speed of light, so it all does make sense, but you have to make sure that your intuitive model of what gravity is is actually matching up with what the equations are telling you. Anonymous says, "Clocks that I care about are usually a flow meter for entropy, when I sit to think for a minute, I'm waiting for a minutes worth of entropy increase to happen in my brain and regardless of how light would travel in that time, but some clocks aren't in tropic, like the T take derivatives with respect to in Hamiltonian, can you say something smart and not the limits of my comprehension about these two kinds of clocks?". I think I can try to say something useful anyway, whether or not it's smart and at your limits, but I think that you're probably not right to think about clocks as flow meters for entropy.

3:05:46.6 SC: It is true that in some certain physical circumstances, clocks do participate in the overall increase of the entropy of the universe, but the thing about entropy increasing is it doesn't increase at a constant rate. Entropy can stay constant in some system for a long time and then start going up or whatever, there's no law of physics that says entropy goes up at a certain rate. The second law just says the entropy doesn't go down, 'cause sometimes it'll stay constant, sometimes it'll go up and so forth, and for precisely that reason, most clocks, they work very, very hard to isolate them from entropy, the simplest clocks in the world are the rotation of the earth, and so you see the sun going up and down, and that does not increase entropy at all, it's in the limit where you can ignore some very, very tiny effects, which is a very good approximation. It's completely reversible. We know where the Sun and the Earth were millions or billions of years ago. So clocks are usually not flow meters for entropy, they're usually periodic things that do the same thing over and over again in a way that is completely constant in entropy, so that's the actual time that you measure with clocks, if you think about what are the best clocks they're the things that are like a pendulum where you have no air resistance or a little tiny quartz Crystal or an atomic vibration, all things that are not actually spewing entropy out there into the universe.

3:07:25.1 SC: Robbie P says, "You've said that the question why is there something rather than nothing? Is not a sensible one, but in some sense, isn't nothing all around us or right around the corner in any possible regime, why aren't we forced to choose between necessary and contingent, whatever the universe?". Well, sure. When you say why is there something rather than nothing? It would be nice if you told us what you meant by the words something and nothing. I think that the most traditional interpretation of that question is, why is there anything at all, and things like empty space are not nothing at all, they're full of quantum fields and they have a metric and they have a dimensionality and all these characteristics. It's not like there's an absence of anything, okay? . So I do not think that it is true that nothing is all around us or right around the corner, of course, you're also welcome to ask that. Why is space not empty? That's a perfectly good question. There's the saying that goes around in certain circles that the reason why there's something rather than nothing is because nothing is unstable. This is an extraordinarily annoying saying, because generally the people who say it don't know what it means or what they're talking about, that was a little motto invented by Frank Wilczek former Mindscape guest, where he was specifically referring to the question of why there is more matter than antimatter in the universe.

3:08:50.7 SC: Why there is a baryon asymmetry. So it was kind of like a little joke. Why is there more matter than antimatter, because in his particular model, which we don't know is true by the way, he had a system where an equal amount of matter and antimatter was an unstable circumstance and unstable configuration of stuff, so it's a conjectural model, but it's also not at all what most of us have in mind when we ask why is there something rather than nothing, so like many big sounding questions, the very first thing you should do when you ask it, if you actually care about what the answer is, is to carefully define exactly what you mean by those terms. Christopher Matthews says, "I've noticed that occasionally you'll get groups of questions concerning topics or conclusions that you dismiss as misguided or even woo woo, and in these cases, I further notice that the questions often appear to have been inspired by a recent video from pop science YouTube series like PBS Space Time, what is your feeling generally about these sort of video series, do you think they do a good job communicating physics concept to a general audience, even if they apparently cause a rash of misguided speculation from time to time?".

3:10:03.3 SC: I think that's a probably reasonable question, I don't have a lot of data on the basis of which to answer it, I personally don't spend a lot of time watching pop science YouTube videos, and I say that slowly and carefully, because I don't want to disparage pop science YouTube videos and certainly not disparage the people who watch them, I love it that there are pop science YouTube videos, just like pop science TV documentaries or pop science books, et cetera. It's not my thing 'cause I'm a professional scientist, and therefore, if I'm reading science, it's probably gonna be a little bit more technical than those things, and if I'm reading popular fun things, it's probably not gonna have anything to do with science. Okay, that's just who I am particularly. So I don't have an educated view on which science videos are the good ones and which ones are not. Like I said, I like the idea that there are science videos and I'm glad that they're trying.

3:10:58.8 SC: I do think there's one possible criticism or potential criticism that a potential pitfall... Let's put it that way, the people should worry about because different science questions have different levels of straight forwardness to their answers, like let's think about our atoms empty space, like we were just talking about. That's not a trivial question. It's not like how big is a black hole of a certain mass.

3:11:28.3 SC: There, you just go to the equation, you plug it in, you get the answer, so you can have a mind-blowing, Popular Science video about the journey into a black hole, how long it would take when you'd get spaghettified, when you could reach a point of no return, what you would see as you were looking outside, all of those are interesting questions, but the answers to them are ultimately perfectly straightforward, there are other kinds of questions that sound similar, right, are atoms mostly empty space. How hard can that be? But in fact, they involve very deep, potentially controversial issues about the foundations of quantum mechanics or things like that, and I do think that sometimes in these pop science videos, it's not that they get them wrong, it's that at least not... They get them wrong because they're being sloppy, it's because they're addressing questions which are legitimately tricky, and a lot of professional scientists get them wrong, scientists are sloppy all the time when they're talking about science, scientists will say things that they know what the footnotes and the caveats are but are not immediately conveyed when they say those things, scientists will say, the universe on large scales is either flat or positively curved or negatively curved, if you really sat down and interrogated them, they would know that's not right.

3:12:53.5 SC: They would know that's a set of assumptions that you're making, and they're only approximately to like there's a whole bunch of caveats that they have in mind that they're not sharing with you, and so they're not lying to you, they're just not telling you the whole story and then someone goes and makes a video about it and someone else thinks it's just true. And all of the footnotes and caveats and careful wordings have gone away. Right.

3:13:15.7 SC: And so that is a danger in making these kinds of videos, and I say to someone, I have not made a lot of science videos on YouTube myself, but I've been in science documentaries all the time, and the people in Hollywood where they make these little one hour shows for the science Channel or the History Channel or the Discovery Channel. The people who are making these shows are on the one hand, entirely well-meaning, and on the other hand, know nothing about science, and I say that without any disparagement, their job is making TV shows, there are not people... In general, there's always exceptions, but for the most part, the director of a TV science show is not... His job is not... Or her job, not Director of TV, science shows. It's director of TV shows, and science just happens to be what their job is this day, that's even true for the writers and the producers and so forth.

3:14:15.9 SC: So you get a lot of situations where they saw something on Wikipedia or whatever, they don't really understand it perfectly they're trying their best to turn it into something visual, and they do understand visual things, so they'll try to make a nice fun visual demonstration of something and not really have a very good idea of what the thing is that they're demonstrating. So like anything else in the world, you should be skeptical, you should keep your wits about you when you watch these things, you should really think about, Okay, this is being said to me on the internet, does that necessarily mean that it's true? .

3:14:50.1 SC: Jake Zielsdof says, "Do you have opinions about Oppenheimer as a physicist? Was he a great one?". Well, I think that he has contributions in physics, he was not in the top tier in terms of contributions, you will hear again and again that people who knew him and met him claim that he was in the top tier in terms of just being brilliant, but that's a different thing, there's plenty of brilliant people who don't do anything at all, I would say that Oppenheimer did some pretty good things, but not earth-shattering things as far as physics is concerned, he did do an earth-shattering thing in leading the Manhattan project for better or for worse, that was an enormous accomplishment personally, so in that sense, he succeeded at doing something other than writing theoretical physics papers, and I think that's fine. There are ways to have an impact on the world other than writing physics papers. Tim Converse says, "An acquaintance of mine once looked at my bookshelves and declared that my interest looked a mile wide and an inch deep, which was mean but fair. As a person with an unusually large volume of interest, how do you think about the trade-off between breadth and depth for your interests and your intellectual work, or do you not think of it that way?". Well, I think there is a trade-off.

3:16:04.0 SC: I think there's a finite number of days in the week, years in your lifetime, cycles of activity in your brain, etcetera. So if you are going to educate yourself and think very very broadly about many different topics, then you will not be able to focus on any one of those topics as deeply as you would if you only focused on that one topic. I think you just can't deny that for any one person, saying that by itself certainly doesn't tell us whether it is better to hyper-specialize and focus on one topic or to cast your net more broadly for obvious reasons. There's an obvious benefit to hyper-specializing, which is you can just always be thinking about a certain kind of thing, dig very deeply into it, you can understand its nuances really, really well, and there's an under-appreciated aspect, which is that thing is what you're thinking about in your spare time, as you're brushing your teeth, as you're walking to work, you're just thinking about that one thing, and that constant concentration on something is very valuable to really making breakthroughs. There's just no doubt about that.

3:17:14.9 SC: There is also value in not falling into erupt, in being constantly exposed to different ways of thinking and different ways of conceptualizing things and putting things together, and so even if your ultimate goal is to understand questions in a certain particular field, one can make the argument for also thinking about other fields and learning about them, even if it cuts down on the time that you get to put in the particular field that you're most interested in. All of that is all true, and I just said it, it's all true.

3:17:48.7 SC: But honestly, I just like what I do. I kinda don't care whether other people think that I'm a mile wide and an in inch deep or anything like that. Am I? That's for other people to judge. What matters to me is that I have a job that, lets me do what I want to do. If I didn't, then I would feel bad. But now I do, so I'm happy. There you go. That's what I care about. Now, what is the broad scale best way to deploy our intellectual resources? I don't know. I think that it's not that different from what we do, which is that we have some people who are super duper specialized, and we have other people who like to be a little bit more broad and interdisciplinary and they talk to each other. I do think that probably if I were, again, the god emperor of Academia, I would tilt the scales a little bit more toward broad people, interdisciplinary people. 'cause it's just kind of easier and cheaper to stick to a field and just do the same thing over and over again.

3:18:54.4 SC: I think that there's low hanging fruit that gets missed by not rewarding people who try to make connections across fields. But it's a small effect. It's not like throwing, I don't wanna stop all those people who are specializing. I don't wanna denigrate their work in any way. I think, everyone should, like being, I always say this, being a professor, being in an academic, being an intellectual, you gotta do it because you love it. There's no, that's really the only reason. Like if you have other motivations in your life, there's better ways to have them fulfilled than being a professor in various ways. Of course, being a professor also involves teaching and things like that, which is also important. I'm just thinking about the research intellectual project aspect of them. And if you love it, you'll love it in different ways.

3:19:45.7 SC: Different people will, the love for knowledge and research and learning new things will manifest itself in different ways in different people. And I think that's good. I'm not really about ranking all the different ways and figuring out what is the right one. Some Dude says "Priority question. I've sometimes tried to explain quantum field theory to friends with the image, with the analogy of a TV or computer screen. The pixels on a monitor may be turned on or off, but they're always there. Basically pixels having the potential to be on, off is analogous to discrete pockets of individual field having the potential to be excited or not. Do you think this is an APT analogy?". Yeah, actually I think it's a very good analogy. I think that people, because we're used to in the classical limit thinking about particles and objects do tend to think of the world as stuff in the forms of object with objects, with empty space in between them and Quantum field theory, or for that matter, even classical field theory.

3:20:48.9 SC: The quantum really doesn't have that much to do with it. Field theory says the opposite. Field theory says that even in the emptiest of spaces, there still are fields. They might have their lowest possible value zero or whatever that is, but they're still there. So this kind of analogy with a TV screen where some pixels are just off, but the pixels are still there. That's perfectly good. I like it. Sean Miller says, "Evolutionary principles taken in their broadest sense to mean change over time, and selective pressures that favor certain kinds of change, arguably are as fundamental as the second law. In this sense, one can think of the second law as a demon favoring patterns of matter that favor increased entropy. Do you think there's any utility in thinking of the evolution of the universe with this lens? Or does fundamental physics and the principle of least action essentially render any notion of selective pressure at this level...

3:21:38.8 SC: Nonsensical?". This is a complicated set of questions here. You're... I'm a little worried in the phrasing of the question because you leap from entropy and evolutionary pressures to fundamental physics in the principle of least action. And, all these are good ideas, but they're ideas in different contexts. If you have fundamental physics in the principle of least action, you don't talk about entropy or evolution or selection. You just follow the laws of physics and you just do what they do. The idea of entropy and selection and evolution only comes about when you've course screened and you have an arrow of time, et cetera. I don't like, as I sort of implicitly said earlier, I don't like to think about the second law favoring patterns of matter that favor increased entropy. The second law is just an inequality.

3:22:33.5 SC: It's very very weak [laughter] It says that along a trajectory, entropy could either go up or go down and it goes up. It doesn't say that it tries to go up as fast as it can. It doesn't say what way it goes up. It doesn't say how rapidly it goes up. It just says it doesn't spontaneously go down. That's a very, very weak requirement. Okay? What we would like to do, and maybe what you're gesturing at, is we would like to go beyond the second law of thermodynamics to really understand the ways in which physical large scale configurations of matter evolve to both increase entropy, but also have other finer scale things going on. Complex systems interacting with each other, biological systems and things like that. That's something I'm very, very interested in. But you can't just appeal to the second law of thermodynamics. The second law is just like the dumbest, simplest thing in this context.

3:23:28.9 SC: You need to think beyond that, and it's not clear what the rules beyond that are. So these are open research problems, I would say. Nalita S says, "As a theoretical physicist, is there a roadmap as to how you creatively come up with new theories that is being followed by all theoretical physicists? Or does every theoretical physicist build their own roadmap into new territory, like individualized? How does that mind blowing creative process take off?". I think it's closer to everyone as an individual. In fact, if you think about the training of a theoretical physicist, right? You go to undergraduate, you take some classes, you do a bunch of problem sets, you go to graduate school, you have an advisor, you take some more classes, but mostly now you're trying to do research and get papers written and so forth, but there's no class you take about how to be creative, how to come up with new theories.

3:24:22.4 SC: I always think back to Zen and the art of motorcycle maintenance, which among other things, it's a long book, but there's a lot in there about the philosophy of science. And one point in there about the philosophy of science is the Baconian scientific method. Francis Bacon back in the day trying to explain how science works, he says, formulate a hypothesis. Use the hypothesis to make predictions, test the predictions, right? And Pirsig, Robert Pirsig in Zen in the art of motorcycle maintenance points out, other people have also pointed out, but he did it very vividly. Step one is a doozy, formulate a hypothesis. What do you mean formulate a hypothesis? How many... How do you do that? Who says the rules are formulating hypotheses? There's potentially an infinite number of them out there. How do you choose which ones to formulate? That's the creative process, and I don't think there's anything mystical or woowoo about it, but it's also not axhumatized or algorithmized.

3:25:18.5 SC: We don't have a uniform agreed upon way to formulate hypotheses. In fact, it's not even a single step. Formulating hypotheses is a process. It takes time. You sort of get a vague idea and you think about it, what does it mean? How can I write down equations that would represent this? Or how do I change it? Now maybe I have different equations. Maybe it refers to something different all before you get to the point of saying, okay, let's make predictions with it, test them, things like that. And I think consistent with things I just said, that different people do it differently, and that's good. I think you need a bunch of very different kinds of approaches. It's probably overly simplistic, but think of Einstein. He had a certain style, right? And at the moment when his contributions were called for in the years, from 1900 to 1920, his style was perfect.

3:26:14.9 SC: It was exactly what the moment called for. But then after that, even though I will defend his understanding of quantum mechanics and physics more generally, he was Einstein after all, but his productivity waned. And partly that's because he was busy doing other things, being a celebrity. But partly because the techniques he had used before were no longer that useful for the moment of time that he was in. I think this is very often true in theoretical physics, that it's a match between your personal style and what is out there to be discovered and formulated, right? And the, the latter, you have no control over. So all you can do is the best you can do given your personal style and your strengths and your individual toolbox, and hopefully the world is ready for what you have to offer to it.

3:27:06.7 SC: Anonymous asks a priority question. "Starting, I need to know if this makes any sense. Let's say we have an energy density that can be described by the equation Y=1 between zero and one. So if we integrate Y=1 from zero to one, presumably zero to one go from X equals zero to X equals one. So we have two variables. We get the sum of X from zero to one, which equals one. It's just the area under the curve. Y=1 between X equals zero and X equals one". I agree with that. That's all true. Now the question continues, "Let's change the energy density such that it follows the equation Y= sine X plus cosine X. The volume of the original total energy still equals one. Just how it is described has changed". So I'm...

3:27:57.7 SC: Pausing here, there's a lot more. I'm editing the question out. You're welcome to go read it on the Patreon page, but there's a lot of details here. But sadly, this, there, there's a, a flub right there. There's, it's kind of an issue We have to confront, Y= sine X + cosine X does not have an integral between zero and one that equals one. Maybe if it were sine squared x plus co-sine squared x, it would equal one because sine squared x plus co-sine squared X equals one at every point. So it's just the same curve that you've decomposed in some way. But sine x plus co-sine X does not have an integral that equals one. So mathematically, that's a booboo. And then there's a, some extra steps that I'm skipping, but it's along these lines of having some functions and integrating them and so forth.

3:28:42.6 SC: And then the question concludes by saying a proton can be defined as containing three quarks, specifically two up and two and one down. Properties of quark include up quark equals charge a minus one third spin of one half, et cetera. So I will, the priority question is, does this make any sense? And my answer is no. It does not make any sense, I think, but there's, I can do more than that. I hope I can be a little bit more constructive here. When you're trying to think about things like how quarks work, how energy works, things like that, this is, I mean, maybe this is not what you want to hear, but a lot of people have thought about this already, right? And they're not all dummies. They've said really important things like the whole existence of up quarks and down quarks, et cetera.

3:29:33.1 SC: And they have a way of thinking about them. And I understand, I don't really know specifically about the author, the anonymous author of this question, but I know lots of examples of people with similar ideas and almost never do they understand the basic mainstream view of how quarks and gluons and things like that work, the idea based on quantum field theory and Quantum chromodynamics et cetera. And there's a desire or an aspiration maybe just to skip ahead to some deep insight about particle physics and quarks and leptons and things like that. My personal view, which always could be wrong, but my personal view is you're not ever going to skip the hard part and get an interesting, surprising, truthful insight into how these things work. That's not because the conventional way of looking at it using quantum field theory and QCD etcetera, Feynman diagrams is necessarily right.

3:30:32.8 SC: Maybe there's a better way of doing it or a different way of doing it. I'm very open to that. But I strongly believe the chances of finding a better way of doing it without first completely understanding and conceptualizing the usual way of doing it, are negligible, are close to zero because the knowledge that we have, and it's not just, favoring the mainstream view, it's that the knowledge we have is very, very detailed and specific. When we talk about quarks and gluons to people who are not physicists, it doesn't sound that complicated. How many few quarks and they're bound together, et cetera, et cetera. And you might get the impression that you can sort of think this through yourself and come up with something new, but the physicists are hiding stuff from you. They're hiding entire books worth of knowledge about fermions and propagators and Feynman integrals and Fidya of Pop Off Ghosts and dimensional regularization and effective.

3:31:35.9 SC: And it goes on and on and on. Scaling behavior and things like that, asymptotic freedom. You need to understand that stuff. And so if you really want to make a contribution, if you really want to push our knowledge forward in some direction, then do the work. Do the work of understanding quantum field theory. Buy a book, buy the textbook. It's hard. I know that it's hard, but you can do it. Anyone can do it. Any person who is, more or less has their average scale mental faculties around them. If they really, really wanted to, they could learn Quantum field theory and QCD, it's a big project. It will take you a long time, it'll be very frustrating, but you could do it. I encourage you to do it if that's what you want to do. And if it, that's not what you want to do, then again, I will repeat my personal opinion, which is that the chances of hitting on some new useful way to think about the physics of those systems of quarks and gluons is very, very small, because we know a lot and you're starting at an enormous disadvantage by not figuring out what it is we already know.

3:32:50.4 SC: Sheamus Maxwell says, "This question is inspired by your advice to physics consultants on science fiction movies to treat the script as data. If you woke up tomorrow in a fantasy world, peopled by orcs, elves and dragons, and everything seemed as real to you as the world you currently inhabit, would, what would be your best guesses as to what was happening? Would there be any room in your credence spread for something other than dream/hallucination? And if so, what might it be?". Sure. I think that the initial credence would be very highly peaked on dream/hallucination or, being fooled, right? By being given some drugs or something like that or whatever. But of course, what happens in these situations is that it's not an all or nothing call in terms of what your credences are. The credences that you should have, as I say about being part of being a good Bayesian is essentially no propositions should get zero credence from the start.

3:33:47.8 SC: It might be a sufficiently small credence that you don't sweat it, that you don't really worry about it in your everyday life. But waking up tomorrow and being surrounded by Orcs & Elves is not my everyday life. So I would have to start thinking about the wilder regions of proposition space and yeah, the possibility that there's a multiverse and somehow my conscious perceptions got moved from a world of, people and cats and dogs to a world of dragons & Elves would be non-zero, right? Or maybe that's the true world all along. And I've been dreaming about this mundane world of podcasts and social media and what have you. So I don't know what my actual credences would be, but I absolutely would be increasing over time, my credence in something that I would now consider to be incredibly dramatic and unlikely.

3:34:47.6 SC: Philip Malinowski says, "I don't wanna get you in hot water. Sorry, I don't wanna get you in hot water, but I'm curious, where do you stand on letting your cats roam free outdoors? On the one hand, it's good to let the cats be cats, but on the other they are incredible killing machines and may kill a few hundred animals a year". I think that's true, but I think that's not the reason why I don't do it. So we do not let our cats roam free outdoors. I think that's a very highly context specific question. If I lived on a farm in the middle of nowhere or just in a cabin in the woods, then maybe I would let the cats roam outdoors. But even then I would have some concerns about it because domestic cats are, as the name says, domesticated, they're not attuned, they're not selected for a successful life outdoors.

3:35:41.5 SC: So yes, they will kill a lot of birds and squirrels and mice and things like that, and they will also be very vulnerable to being killed by coyotes or wolves or dogs for that matter or just having an accident. So all that is part of the cycle of life. Like I don't mind that, I don't mind that cats kill animals. I don't mind that cats are killed by other animals. We're all gonna die someday. That is not the thing to mind. The thing that I mind is that I have a personal connection to certain cats, my cats, and I want them to remain safe. So I personally would like my cats to just stay indoors, especially 'cause I do not live in the country. I live literally in the city of Baltimore, not too far away from highways and certainly right next to all sorts of streets and what have you that we actually, I live in a part of Baltimore that it's right next to the Johns Hopkins campus, but it's kind of leafy, it's kind of, there's a lot of trees and things like that and a kind of wild and a kind of a lot of wildlife.

3:36:42.5 SC: We've certainly seen both foxes and deer in, walking by our house. Okay, so there's a little bit of wildlife out there, certainly squirrels and birds all over the place. So the cats would be happy out there when they notice the squirrels and birds may be less happy when they notice the foxes and falcons also, we have a couple of falcons nearby, so it's kind of weird to live in a city and have all this nature around you but so be it. I grew up in the suburbs and we had cats and they were all outdoor cats and, and guess what? Their life expectancy is much shorter. I never had a cat die of natural causes when I was growing up, but, well one got leukemia I guess, but I guess that, I guess that's a natural cause.

3:37:23.3 SC: But usually, being hit by a car is how the cats die. So it just makes sense to me that if you are entering into this particular relationship where you take care of the cat and are, have responsibility for it, keeping it indoors is a much more sensible thing. Owe or however, one pronounces O-W-E says when Eternalist say that every moment of time is equally real, how does that intersect with relativity where there is no such thing as simultaneity and the moments of time for one observer are not consistent with other observers on different paths? That's perfectly fair question. Typically, relativity and Eternalism go very comfortably together. In fact, one argument against presentism, presentism is the leading alternative to eternalism. So a presentist, rather than saying that every moment of time is equally real, would say that only the now is real, right. Now is real in the past and future are just predictions and memories.

3:38:20.2 SC: That is what is very hard to reconcile with relativity because people don't agree on what now means once you extend yourself from one point in space to other points in space. So presentism and relativity are not happy with each other. Certain people manage to nevertheless, figure out ways to believe both at the same time. But eternalism and relativity are generally taken to be 100% compatible, except that the way that we say what eternalism means needs to be just a little bit more carefully said. So it's true that eternalism is often explained as every moment of time is equally real. Really what you should say is every event in space time is equally real. It's not that there is some preferred way of slicing space time into moments of time. That is a perfectly legitimate critique of the way that we talk about Eternalism.

3:39:14.5 SC: Benjamin Barbrel says, "I learned listening to your podcasts and videos that a black hole has a very large entropy. If entropy still means in this context, the number of micro states corresponding to a different a given macro state. I don't understand the nature of these micro states in the case of a black hole, it sounds incompatible with the statement that a black hole has no hair. I feel like if a black hole had many micro states, it would lead to a resolution of the information paradox since the state of another system thrown in the black hole would just end up encoded in those degrees of freedom". Good is a very good question. It does, entropy still does in this context mean the number of micro states corresponding to a given macro state. But [chuckle] let's think carefully about what that means and it's subtle.

3:40:01.4 SC: And we also have to remember something we said much earlier in the AMA that in quantum mechanics, the way that we talk about mixtures of states is a little bit different. Okay? So think about a box of gas that has a lot of entropy. It has a lot of micro states that look that way. There are a lot of ways of arranging the atoms and molecules and positions and in velocities that have the same general, density and pressure and temperature and things like that. But also a box of gas has no hair, right? Macroscopically, the box of gas is gonna look exactly the same as a different box of gas with the same temperature and pressure even in a different micro state. So quantum mechanically that becomes even more vivid. The fact that you can have no hair and yet you have a lot of micro states because you have a certain combination of those micro states that is the thermal equilibrium combination that is a combination of many many states and therefore it has high entropy.

3:41:02.3 SC: But it's a particular exact combination of those many, many states. So it's not like a classical statistical combination of things where there's literally different kinds of micro states and you, there sorry, I should say, where there literally is a micro state that is the real one and you just don't know it, right? In the quantum case, it truly is a mixture of many different micro states in a definite combination, and that's what the black hole would be like. So a black hole purportedly is a thermal mixture of a large number of very specific quantum states in a very specific arrangement. Now you are right to wonder what those micro states are because nobody knows, that's a big part of the puzzle of quantum gravity. The Cosmic No Hair Theorem is exactly the thing that made people kind of wonder about this. How can a black hole have so much entropy if all black holes are the same, if they have the same mass in charge and spin?

3:42:00.9 SC: But that's a... That's mixing up a classical way of talking. The cosmic no hair theorem with a quantum way of talking, the entropy, we hope the resolution is that quantum mechanically there is a large set of micro states, we don't know what they are. We did have Andy Stromenger on the podcast a while back and Andy and Kumunmbafa looked at this for a very, very simple kind of black hole, a highly super symmetric black hole in very special circumstances. And in string theory with D brains, they could actually identify the micro states. That is much harder to do in the general real world situation. So the short answer is we don't know, but I can say that even if there are that many micro states, it does not by itself resolve the information paradox because there's the extra question of where the information is. The information paradox is not just, we don't have enough room to put the information in the black hole.

3:42:56.9 SC: The information paradox is we need to get it out in the hawking radiation. So if I have a book and I throw it into the black hole, if it goes into the middle of the black hole and then in the future it will hit the singularity, how do I get that information out into the radiation? Even though the event horizon might be very far away from where the book is, right? That's an important part of the black hole information puzzle. Pete Faulkner says, "I've heard you and others state that microscopic black holes are a possible contender as the dark matter. Doesn't hawking radiation suggest that any such black holes would've radiated away quickly? Or is the suggestion that they're somehow being constantly created?", No, the suggestion is just that you have to run the numbers. Like for many questions like this, you can't just use words, you gotta [chuckle] kind of think about the numbers.

3:43:46.5 SC: It is true that a sufficiently small black hole will evaporate away in a timescale less than the age of the universe. But a larger black hole would take longer than that to radiate away. So you gotta sit down and ask yourself how massive does the black hole need to be for its lifetime to be longer than the current age of the universe? And I actually don't know what the answer is, but the answer is big but not that big. It doesn't need to be like the mass of the sun. If you have a black hole, the mass of the sun, it's lifespan is gonna be way, way longer than the age of the universe today. So you can have black holes that are quite a bit smaller than the sun that are truly microscopic in some sense, and yet, have not yet evaporated away in the age of the universe from hawking radiation.

3:44:34.4 SC: Red Antonov says, "If the tension between the measured magnetic dipole moment of the muon and its theoretical value is a sine of new physics, should we expect to see deviations in other precision measurements of electromagnetic properties? For example, would there be hints of it in electric dipole moment studies of neutrons or electrons?", Absolutely, yes, there should be, but again, you gotta run the numbers, you can't just say, well, it's a different thing, go measure it, right? Some things are easier to measure than others. The thing about the muon is it's heavier than the electron. So that means that it's coupling to other particles, especially the Higgs and so forth. It's a little bit stronger and therefore, and just heavier particles more generally. Therefore, new physics effects might very naturally show up more readily in a muon than in an electron.

3:45:27.0 SC: Electron is kind of shielded from effects of heavier particles just 'cause it's mass is lower. Neutrons on the other hand, they are heavier, but they're a mess. 'cause there's, lots of quarks going on inside. It's hard harder to make the predictions for what they should be. So a muon is sort of at a sweet spot where it's heavy enough that maybe there's new physics there. It is simple enough that you can actually calculate what you expect to observe. Even given that, by the way, it's not easy to make that calculation because part of that calculation is that there are strongly interacting particles that are virtual particles that will contribute to things like the magnetic dipole moment of the muon. That's why, there's different theoretical calculations that don't agree with each other, which is probably the reason why that's probably the reconciliation of the modern muon electric dipole moment issue.

3:46:20.5 SC: It's probably not that there's really new physics, it's probably just that the calculations are hard and we haven't done them correctly. I say that's probably true, it might not be true and hopefully it's not, fingers crossed that it's really new physics. But there's a simple non-new physics explanation on the table here, namely that the calculations are not good yet. Eric Wonglik says,"You've been tasked with coming up with a video game idea that heavily utilizes a concept from physics that is normally difficult for people to visualize because it is not part of our everyday life, for example, four dimensional space. What concept do you choose?". This is gonna be a very boring answer, but I choose four dimensional space [chuckle] I think that's a great thing. This is like, I've mentioned this before, that either in video games or even even more obviously in some truly immersive VR experience, I'm very curious as to whether you could train people to think in terms of four dimensional space to sort of visualize it, to move around.

3:47:20.0 SC: There's nothing in the laws of physics that say I can't visualize being in four dimensional space, but there is a lot in biology and and evolution that has trained me not to do that. So can video games get around it? I think that's a very interesting question. Sandro Stookey says, "What would you say is the most important difference between David Wallace's explanation of the Born Rule in many worlds and your own?". I don't think there's any important difference. I mean, they're stylistically very different, but just for those who don't know, I wrote a paper with Charles Siebens on deriving the Born Rule in Many Worlds, a few years ago, David Wallace and before him David Deutsch proposed a different way of deriving the Born rule in many worlds. There are, there have been other options. I do think that the two Davids David Deutch and David Wallace, they're derivation is sort of what is now the standard one in foundations of physics circles.

3:48:17.3 SC: And I'd like to think I believe it is true, but one's personal, vantage point is always biased. I think that Chip Siebens and my way of thinking about it is in second place in terms of how much attention that it gets. And the reason why we're in second place, even though there's been many other options put on the table, is it's always really hard at the boundaries of physics and philosophy to correctly construct an argument for a conclusion that you already know, right? You know that what you want is the probability of measuring something in quantum mechanics is the wave function squared. So it's really easy to get the right answer for the wrong reasons, to make some simple assumption that seems natural to you, but really isn't. That helps you get the right answer. So in the field, there's a lot of feeling that purported derivations of the Born rule are cheating because they assume something that gives them the answer rather than actually adding it.

3:49:22.6 SC: And I don't think that, our solution actually does that, although opinions might differ. The language that is used in the David Wallace David Deutsch approach is completely different than the language that Chip and I use, which is also our ideas based on suggestions by Lev Vaidman and others. In the Deutsche Wallace argument, you think about what rational observers would do, you use decision theory and you use basic features of quantum mechanics to argue that rational observers trying to maximize their utility or whatever, should act as if they are going to observe Born rule probabilities in the many world's interpretation. Whereas what chip and I say is there are conditions of self locating uncertainty. Like, so we don't use words about decision theory, et cetera. We say when the wave function branches, you don't know which branch you're on, therefore you need to assign credences to being on one branch or another.

3:50:18.3 SC: And then we argue that the only sensible way to do that is to use the Born rule. So they sound very different, but precisely as there are many wrong ways to get the right answer, there might also very well be equivalent right ways of getting the right answer, right. When you have a mathematical theorem and you wanna prove it, it's not like there's one correct proof and all the others are incorrect. We are very happy, we said this in the original paper, we're very happy to be compatible with other ways of deriving the Born rule. We're not trying to displace them or supplant them, we're just trying to offer a different angle on it. What I like about our way of doing it is that to me it truly addresses in more or less incontrovertible ways the basic question of why there are probabilities at all.

3:51:07.3 SC: So the Deutsche Wallace approach says, given that there are probabilities of some sort, I might not know what they are, but I'm gonna try to be rational and assign them in a certain way. It doesn't quite tell you why there are probabilities in the first place, but we are crystal clear about why there are probabilities. There will be a moment in time when you don't know what branch of the wave function you're on, and as a good Bayesian, there's an epistemic credence that you should be attaching to being on one branch or the other. If you don't like our way of deriving the Born rule, then that's the the part you have to attack and people have attacked it. People, like David Albert will say, no, I don't need to apply credences in that situation. I can just feign ignorance. I can just say, I don't know what branch I'm on, full stop.

3:51:52.2 SC: I think that's not a good way to do science. I don't think we do that in any other areas of science. So I don't think that's, that quite works. That's quite valid. But, anyway, I don't think that there's an incompatibility between the two ways of doing it. The Deutsche Wallace approach can be criticized on precisely the grounds that they're making assumptions that might not apply. In particular, there are questions about how you value things that are going on elsewhere, in particular other branches of the wave function. That's there's some version of saying that what matters to you is what matters is what happens on your branch, not what happens on other branches. And if you don't buy that assumption, then you can undermine the whole game. I think that, chip and, my self locating uncertainty derivation also has assumptions that you can call into question.

3:52:44.5 SC: So, at some point, I do think that having sat through many discussions about this, the question is not why is it the wave function squared, right? That's not the question anyone is debating. So when we say debate or derive the Born rule, that's a little bit misleading in terms of what's actually going on. What really is going on is why is a deterministic theory having probabilities show up at all? Once you have probabilities in there and you admit that you should try your best to assign probabilities in some sensible, rational way, it's obviously the Born rule. The Born rule is just obviously what works. That's not where the controversy lies. The controversy is, I would argue a mostly entirely philosophical one about where the probabilities come from, where the idea of probability comes from at all. Matt Grinder says, "I'm hoping you can clarify an issue I have with the arrow of time in the increase of entropy, suppose the universe ends in a heat death and the hypothetical observer would not now perceive an arrow of time because of the way particles now interact...

3:53:54.2 SC: Do physicists mean to imply that this would mean that time has stopped doing what it has been doing for billions of years, namely going forward?". So there's a couple things I gotta like undo the question here. There are no observers in the heat death of the universe. To be an observer requires a departure from equilibrium. So you can't say I'm in the heat death situation and a hypothetical observer sees this or that. There literally are no hypothetical observers by construction, okay? But we can take the God's eye view and say like, what would the world be like? And in that case, I would again undo the question about time going forward. That's not what time does, [laughter] time does not go forward any more than on the real number line. The numbers go forward. There's just an infinite number of numbers. There's the number minus one, there's the number plus squared of two.

3:54:48.7 SC: All these numbers exist on the real number line in this way of thinking about time. The same thing is true with time. It's not that time goes forward, it's that individual people in the part of the universe's history where there is disequilibrium and a strong arrow of time perceive time in a certain way. They perceive a passage of time because they have a memory of the past and predictions about the future. So the physics of time is completely unchanged once you enter the heat death part of the history of the universe. But the physics of observers is changed quite dramatically. Namely, there are no observers and there's no impression that time is going forward. Two more questions left here in the AMA Herbert Berkowitz says, "How do fundamental particles get rather odd names like strange and charm? Do the naming rights. Go to the discoverer? Have there been fights over who gets the naming rights and who in the end makes the name official?".

3:55:43.1 SC: Yeah, it's a mess. In astronomy, things are actually much more systematic. There are committees of the International Astronomical Union, the IAU, that lay down rules for naming astronomical objects and things like that. Similar, like to the committees that decided that Pluto wasn't a planet anymore. There's a lot of committees in astronomy, but there's also a lot more celestial objects than there are elementary particles. So for elementary particles, they just kind of grow organically. In particular for both strange and charm, they had kind of long, interesting histories. The idea of strangeness as a conserved quantity came about before the idea that there was a quark called the Strange Quark. It came about before we knew about quarks. Likewise for charm, that was a hypothetical idea, put forward by Bjork Kain and Glashow I believe.

3:56:39.5 SC: There was also the gym mechanism, so that's Glashow, Elly Opolis and Mayani. Maybe they said it first. I forget who said it first, but there was a bunch of theorists basically saying, look, we can explain some things if you give us a fourth quark called the charm. We're gonna call it the Charm Quark. 'cause they were having fun and that they turned out to be right. So since they turned out to be right, people, went along with it. Other cases, it's not so clear for Quarks, they were independently suggested by Gell-Mann and Zweig. George Zweig and Gell-Mann suggested calling them Quarks. Zweig suggest him calling them ACEs. And Gell-Mann won. He was more famous and it was kind of a good name. Other cases still not adjudicated. There's the famous J/psi particle, which was, I'm gonna get the names wrong of who did it.

3:57:31.1 SC: I believe that it was Sam Ting, who was one of the leaders of the collaboration who found that particle. And it's a composite particle, it's a meson. And maybe Burton Richter was the other one at Slack who also discovered it at the Spear Experiment. And so, Richter and the Slack people named it the Psi particle, Psi, P-S-I is supposed to be like close to spear [laughter], which is the name of the experiment that they were doing. And the J was Sam Ting's way of trying to name it after himself. 'cause he wanted to call it T for Ting. But like, you're not allowed to do that. So a J is very close Orthographically to a T. So he named it that. And they more or less did it at the same time, and they were both equally famous. And so nobody won.

3:58:18.3 SC: So to this day it is called the J/psi particle. What can you do? There you go. There's no systematic way of figuring it out. Final question, Simon Carter says, "After picking Einstein's equation as the main subject to present from your first book, have you decided what you'll be presenting for the second book?". So there's two different ways to interpret this question. I think I know the right way, but just so everyone is on the same track, the books in question, here are the biggest ideas in the Universe series. Volume one was space time in motion and I did all of classical physics. Volume two is quanta and fields and does quantum mechanics and quantum field theory. In both books, I do many topics, right? There is no one main topic. So just so that is perfectly clear, that would be a misunderstanding of the question.

3:59:05.7 SC: I think what Simon is getting at is when you write a book, you go around giving talks, right? You go on a book tour, the book tour thing is overrated or overblown. It's not like there's literally a tour, it's just that, you arrange some public talks to give. And so I did that for the first book. I will do that for the second book. The talk that I gave to advertise, the first book was Einstein's Equation, the Secrets of Einstein's Equation. So what that meant is over the course of an hour, I go through the math. I don't assume that you know any calculus or anything like that, but I give you the basics of differential geometry and gravity and tensors and lead you up to Einstein's equation in all of its glory. And then show you the Short shield solution, et cetera.

3:59:52.7 SC: And you can find versions of it online. I just recently did a version at the Royal Institute in London, Royal Institution. So I don't know if that's up yet, but it should be soon. And there's other versions, floating around. So yes, when book two comes out, when Quantum Field comes out, which will be sometime in the spring, I will need to have a talk to give about it. And I'm not sure what I will give, it's not gonna be about quantum mechanics specifically. I've done that, right? Plenty of talks I've given about that. I really wanna concentrate on the quantum field theory side of things. But I don't know whether I wanna, like how technical I wanna make it. It's the popular talk. So in terms of what the audience is, it's a popular audience, and that's what I wanna aim at.

4:00:34.0 SC: But one way to do it would be to talk about Feynman diagrams and renormalization and effective field theory. I think effective field theory is probably the most important idea that physicists have that we don't tell non physicists about. So that would be a very exciting thing to talk about. Another angle to take would be to talk about phases and gauge theories, right? The Coulomb phase, the Higgs phase, the confinement phase. How one underlying idea of gauge symmetry can lead to very different behavior in very different circumstances. That would be fun to talk about. I kind of did talk about things related to that back when I was talking about the Higgs-boson in the big, in the particle at of the end of the universe book. So even though it's an important set of topics, maybe it's not the obvious one, or I could, give the audience a break.

[laughter]

4:01:27.5 SC: At the end of the book, I take all that we've learned about Feynman diagrams and decays and so forth, and I explain why the ingredients of the universe are what they are, why we are made of protons and neutrons and electrons held together by electromagnetism and gravity. It's a very simple set of ingredients, right? Three kinds of particles, protons, neutrons, electrons, two forces, electromagnetism and gravity. That explains an enormous amount of stuff. It's not quite everything, even our everyday life. It doesn't explain nuclear fusion and things like that. How, why stars shine. But still, you and me and our chemistry and our biology are completely explained by that. Why are those the particles that survive once heavier particles decay away? Why do you still have neutrons hanging around, even though neutrons do decay by themselves? So, I mean, that's kind of like a fun thing.

4:02:19.0 SC: Why do... What is, where does the scale of things come from? Why are atoms the size that they are? There's a, whole bunch of things that are a little bit less conceptually abstract than talking about ultraviolet cutoffs in the Renormalization group, right? So that's another possibility. I don't know. Put your suggestions in, in the comment section here, all you Patreon listeners and I will take them into consideration. We'll see one way or the other. It'll be fun. I hope everyone buys the book. I hope everyone has enjoyed this AMA. Thanks as always for your support from Mindscape. I really appreciate it. See you next month. Bye-bye.