Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - AMA | September 2023

Episode Date: September 4, 2023

Welcome to the September 2023 Ask Me Anything episode of Mindscape! These monthly excursions are funded by Patreon supporters (who are also the ones asking the questions). We take questions asked by Patreons, whittle them down to a more manageable number -- based primarily on whether I have anything interesting to say about them, not whether the questions themselves are good -- and sometimes group them together if they are about a similar topic. Enjoy! Blog post with questions and transcript: https://www.preposterousuniverse.com/podcast/2023/09/04/ama-september-2023/ And you can now pre-order The Biggest Ideas in the Universe Vol. 2: Quanta and Fields!

Hello everyone. Welcome to the September 23 Ask Me Anything Edition of the Mindscape podcast. I'm your host, Sean Carroll. We're approaching, it occurs to me, episode 250 of the Mindscape podcast. I just published 248 last week. And I'm not going to do anything special for the 250th episode. It 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 fifth anniversary at the beginning of, 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 done, 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 Minescape over the last five years. That's a lot of episodes. 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. 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 my Mindscape is not the most controversial or action-packed or even, you know, G-Wiz podcast out there. But there's a lot of cool ideas to talk to. 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 huger number of people who I've not yet had as guests. It would be easier for me to have guests on over and over again, no doubt about that.

But I never know when I'm going to discover something new and interesting by just having someone who I've never talked to. You know, most of the guests by now that I have on Minescape 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. You know, some episodes will resonate with some people and some won't, but that's part of the excitement. So very proud of what we've done here. 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 slash Sean M. Carroll. And, you know, five years is a long time. Will 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. You know, then I will easily say, like, this isn't worth it anymore. But, you know, five years, I think that there's two mindscape guests who have, are deceased now, which is very sad to me. Herb 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 months ago. Very sad, but you know, 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 Minescape. Otherwise, but she was a uniquely good person at making a different kind of thing, palatable and exciting and interesting to other audiences. 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 going to happen to all of us. So it's just a reminder that we've been around for a while now, doing the podcast. 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 web page at Reposterous 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. Jason Richiarty says, I've heard you mention that Twitter is dying several times on Minescape, 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 want to 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 brand. X, whatever it's going to be called, it will exist, I think, in the years to come, at least as long as this podcast does, would be my guess.

But it's changing and it's absolutely changing for the worse in many noticeable ways. You know, the most obvious way 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. 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, you know, 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. 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, 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 polled said that they'd either left Twitter or were using it a lot less now. So, you know, that just makes the platform less enjoyable, less fun, et cetera. So looking for alternatives is the current mode that I'm in. There's another article, by the way, I think Washington Post maybe, that mentioned there's a lot more disinformation on Twitter now than there ever was before. And, you know, these are studies. These are people collecting data.

This is not vibes. This is not, you know, 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 checkmark system. For those of you who are not on Twitter, bless your hearts, there used to be this thing called being a verified user, and you get a little blue checkmark by you. And it was originally because, you know, people like Shaquille O'Neal, who was a, big celebrity user in the early days, well, 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 checkmark, 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, 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, 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 an 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 an authority in some subject. You know, 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 have not heard of them before, but you could find them. 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 want to mouth off, you know, people who embody the Dunning Krueger 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. You know, 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, you know, who followed who and how you could find people and things like that, 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 unmistakingly making it harder to use Twitter. The way that I read Twitter used to be something called tweet deck. Now that is removed. I can't use it anymore, right? So that is. just a much worse experience overall. The statement is that going forward, they're going to 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, you know, to try to find something interesting. So for many, many reasons, I think that Twitter is seriously declining. And again, it's not just, you know, the vibes are bad. 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 going to happen next. I am personally spending most of my time on blue sky to the extent that I'm doing anything at all. But I can't really push Blue Sky 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 Blue Sky 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. 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 kind of 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. It's something for, you know, Mastodon is Twitter for Linux users. I used to have a Linux box on my desk and, you know, in my office, and there's a certain kind of person who loves Linux as an operating system rather than MacOS or Windows

because they can really get in there and they can fiddle with it and they can make it exactly what they want, 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. You know, 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. I think that it was very important to me. You know, I've certainly connected with many of the Minescape 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 going to 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? 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 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 I think you see the relationship between these two questions, you know, 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. You know, 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. I don't think so. You know, I do think that your reflections change. I hope that they do. I 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. You know, we're always, I hope, thinking about our thoughts, right? Thinking about where we're coming from and hopefully we can reinterrogate 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 or frequency of these reflections has changed. I want to know what the universe is, what it's made of, how long it's going to last, where it came from, our place in the universe.

I think about all these things. 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 is, what would be better would be an acknowledgement that our everyday intuitions trained as they are by evolution and our lives and things like that just aren't up to the task of thinking about eternity pro or con, right? 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, you know, 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, you know, I thought it should be this way, but it's not that way. You know, I think that it would be more satisfying to me or more rewarding if it were this way, but it just isn't. You know, that's the kind of, you know, that's the kind of, you know, attitude I want to take in my reflections on these deepest questions. Amad Chaker says, I just watched your video on renormalization. This is referring to from a couple years ago, the biggest ideas in the universe videos that are leading into the books that were in the process of putting out. So Amad 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,

2EV and 3EV, 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 our 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. 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 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 in find a diagram 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, and it turns out it is not fixed by the external conditions, by just momentum, conservation, et cetera. So you integrate over all 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 and 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 1 over x squared, forget zero. How about integrating 1 to 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, you know, the integral gets bigger and bigger and bigger and

just gets, you know, 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, Amad'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 momentum is we don't know what's going on,

infinitely big momentum. Momentum is inversely proportional to distance in quantum mechanics and field theory. So you're effectively talking about infinitely short distances where spacetime 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 a mod correctly says, just between two electron volts and three electron volts, there are an infinite number of momentum 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 in getting a finite answer. because really you're adding up zero times infinity, okay? And that's ill-defined, as it is simply stated baldly 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.

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 going to 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 and Leibniz who taught us how to do this, which is to discretize, 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 is nothing different than that. You get a finite answer for the integral over this loop momentum of all the possible momentum between 2EV and 3EB. That's just not a problem. That's just calculus. The only problem comes when you're considering momentum that go infinitely

big, and that's a whole other story. Cooper says, has your thinking on complexity changed at all in light of your recent conversations with Sam Bowles and David Crackauer? Both emphasize 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, well, I guess the way that I would put it is, I had not thought that anyone would use the feature teleological behavior or telenomic 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. 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 subsystem? I think it'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. You know, our galaxy is pretty darn complex. It is not telenomic 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 such a big difference once matter becomes telonomic, once a complex adaptive

system has goals. And, you know, back in the day, you would in Santa Fe Institute's circles, hear a lot more talk about complex adaptive systems than you do now. 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

telonomic 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. And you're absolutely welcome to do that. That's a fine thing to do, but you wouldn't want to 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 plumping 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 arrow of time, so I don't want it ruled out from this whole area of inquiry. Rob Gebelah says, I have a question about your confidence in the claim that all physical laws relevant for our everyday life are known. 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 look at a higher order perturbation, 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 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. 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,

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, you know, 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, you know, 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 an absolutely conceptually allowed thing to think about, but the data have spoken on that one. They're not there. 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 want to say too much about this because 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, you know, 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. Let's talk about the worries. The unpredictable things, you know, 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. You know, 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. And if, you know, 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.

You know, we can worry about that. That's much more plausible than extinction level events. And it 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, yeah, 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 bioweapons, pandemics, good old-fashioned nuclear war, right? 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, you know, the frequency with which these things happen are sufficiently rare that human beings are not good at planning for them. You know, it hasn't happened to last five years.

Of course, the pandemic thing did. I get that. But otherwise, you know, 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 time scales longer than 10 years between when they generally happen that I think are very good to worry about.

Sunspots and solar flare is another one that I've talked about before. In terms of hopes, you know, I don't know, I have mentioned recently the podcast 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 like electricity and things like that, not political power. We might even, arguably, be getting better protecting the environment if we really put our minds to it. 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? 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. You know, 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. 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, 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. 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, there's nobody who dies as a child unnecessarily, etc. 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 Minescape podcast can possibly do. 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 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? You know, 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.

Even my literal set of graduate students who I work with and who I know, they either, quote unquote, 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 going to 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. You know, the idea like, I'm going to work and work and work and get tenure. That's the goal that 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. 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, you know, 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 system so that maybe some people who kind of liked it one way could go to different universities or different research institutes. But guess what? This has been tried. There have been universities and research institutes that have tried to not have tenure. Nobody wants to go there. Or people go there and say, please, you know, 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 by a 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 like to read it, whatever. 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. And I never knew. So I was like, oh, this is kind of flattering. I didn't really agree with anything that was in the paper, but, you know, still, it's kind of nice to know the people are taking it seriously.

So I don't know. Maybe it should be more common to let people know. but maybe you don't want to 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 because 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. 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, 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, you know, ego surfing. I'm not like, oh, happy that someone cited me. I want to 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. 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, we're going to group two questions together. One is from Fabian Rostalin. By the way, before I actually answer this, I should have said this in the intro,

but a couple things. Number one, we're getting a lot of questions and 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're, you know, you've been asking questions and have never gotten one through, 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 applied either of these questions. 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? And the other questions by Gauta Aynabal, 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 worlds interpretation of quantum mechanics. For Fabian's question, I think this is the more straightforward answer here. 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 many worlds is your favorite theory, that's how you have to behave. So, you know, 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 Siebens and I had a way to do it that I kind of like.

but the implications go way further than just deriving the probability rule. The implication is that the worlds count by a certain amount that is weighted by their wave function squared. So to skip to the answer here, even though there are, in some sense, more people in the future, each one of them counts less. I don't mean to disparage them, but they count as much as, you know, a person, 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 Gerlock 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's 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, because there is a whole, another universe, 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 the theme. and therefore I don't think it matters that there are more people, more copies of me in the future. And likewise, for Gautus question, this idea of, you know, 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, 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're 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, because it's not going to work out for you in various ways. Lothian 53 says, in the many worlds interpretation of quantum mechanics, how do we know that the other worlds continued 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, right? Like, 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 want to think that, you are welcome to do so. Stevie CpW says, how do you feel about data science being accepted as an alternative to algebra and calculus and higher education admission requirements? Well, I have 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 that people are talking about this, it's usually the high school level that people most care about this question. You know, 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 the statistics also deserves a place at the table, and that means that something has to go. You know, whatever that is, that might be different for different people, et cetera. But I think reasoning about probabilities and uncertainties is very, very important, and is also mathy. You know, it doesn't

have to be just, you know, here's a coin flip. You can get really deep into serious math and solving equations if you study probability carefully. And I think 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? Central limit theorems, 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, you know, 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 socioeconomic 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. You know, if people aren't learning algebra and calculus as well as they should,

dump money on the problem would be my solution. You know, 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

of 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. You know, 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. Like when I've had a really long day or a really long week or whatever, it's going to 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, you know,

I know that the pizza in 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. Macaronian 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, you know, we have a routine where we work really, really hard during the day. And then we kind of collapse. And, you know, we don't want to do anything challenging.

Like, you know, we'll read, of course. But usually, like, once it's late at night, we're reading fun. simple things. You know, the simplest things for me, the most fun things that are still rewarding are just, you know, reading these science fiction stories or the science fiction authors that I grew up with as a kid. So Heinlein and Zelasny and Liguin and the Dragon Writers of Pern or something like that, you know, I can just read that stuff over and over again. And I've discovered newer ones. Ian Banks is really difficult to read the first time. But upon rereading, it's fun because 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 because it's, you know, fun and, you know, whether it's Poirot or Colombo, murder mysteries, or, you know, recently, I'll tell you a story. I was recently, as part of Johns Hopkins, you know, 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, you know, finally at this advanced age that I have reached, living the dream of being an interdisciplinary academic scholar. 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 Jan Nizmael, we founded a natural philosophy forum. I'm also on the faculty board for something called the Alexander Gross 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 are 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 are doing the social sciences and democracy, people who are doing engineering, and it's just, you know, like a kid in a candy store, as it were. I'm having an enormous time,

like finally, I feel like an undergraduate again, right? 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. Anyway, why am I telling you this? Because at the Humanities Institute, I ran into and made friends with a woman Virginia Jewess, who is an Italian scholar. You know, 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 U.S., at Hopkins, she taught a course, first-year seminar course on the, prestige TV era, right? 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, you know, response was, Jane the Virgin, huh? That doesn't fit in to the pattern that has been established with these other shows. And she says, yes. And when she was telling me this, I'd 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 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, right? These, you know, ridiculous plots, secret twins, dead people coming back to life, people being married, people being brother and sister, you know, all these, you know, crazy tropes. And so Jane the Virgin is kind of a, not really a parody, 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. 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, you know, this show, even though it's extremely lighthearted and fun and it's basically a comedy, dromedy maybe, whatever you want to call it, but it hits a huge number of really deep issues. For

one thing, it's a bunch of immigrants in the United States. So they're dealing with, you know, it ran from what, like 2015 and 2019. Guess who got elected president of the United States in that era? And that was a, there was a serious set of issues that have not gone away for people who might be undocumented or family members are undocumented, but also questions of religion because Jane and her family are Catholic, questions of, you know, 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 lighthearted and fun way when they're not tugging on your heartstrings. Anyway, the point is that we have been watching Jane the Virgin and just loving it. It's great. 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, right, but it needs to be good. Like, 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, you know, 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's awful. It was really bad. It's just, I don't know whether the quality of Kentucky Fried Chicken. 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. 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 a mood to be challenged, it still has to be quality writing, you know, 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 Nunez 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.

You know, I don't want to give economists' 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. 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 Minescape many times. I think that the standards have to be adjusted to be realistic. You know, 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, right? 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. I do think that when things are complex, like they are in economics and maybe arguably even more in psychology, sociology, et cetera, 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, right?

So there's a challenge there, and maybe progress will be slower because of that. 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, right? 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 in causal networks, you can find a talk I gave on that. And Kevin continues, explaining in broads, 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? 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, right? I mean, maybe there's some Q&S.

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 because someone says something in a talk doesn't mean the audience agreed with it, certainly. In this case, well, you know, also maybe they're not telling me, but I always do try to figure out. I try to ask people like 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 where we talk about entropy and the arrow time and things like that, and the other from causal network research, 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 arrows point in, especially they always point from past to future. 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, you know, 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 about the second law of thermodynamics? I know that, but when I explained to them, you know, Judea, Pearl and causal 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 it was an interesting kind of thing. I think that different people will care more or less about it.

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.

Linio Miziaris says, in the latest AMA, you told us that Boltzman 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 the Boltzman brains are not possible. It's that it is possible that they're not possible.

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 will recalapse or crunch or anything like that, the fact that the universe will be empty and will 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 a

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's 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. So it is in the case where the universe just settles down once and for all, then there will be no Boltzman 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, you know, isn't the very concept of temperature based on the movement of atoms? And the answer is no. I mean, 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 physics, mechanics, of course, you can have a circumstance where you literally have a bunch of atoms moving around with different velocities, and then you go 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, like I said, what we call a density matrix or a mixed state. What does that mean? Ordinarily in quantum mechanics, when you hear a little bit about quantum mechanics, you're talking about wave functions, right? 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, well, we would have known if classical mechanics had been true, that there really were particles with definite positions in momentum. 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, right? Maybe you, 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 in momenta in classical mechanics. But in quantum mechanics, you can add and subtract. By the way, sometimes people think that you should be able to add positions. You can add momentum 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 pre-existing 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 because 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. 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 particles, positions, and momentum. 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.

And so you can say, you know, 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. Okay?

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, you know, the equation of state and the PV equals 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. 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 want to say they don't understand this. Maybe they understand it. They never admit it. They never talk about this fact, okay? 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. That is not true anymore in quantum mechanics. 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, right? That's why people don't need to talk about it, because 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 Boltzman 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 Boryshtov 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? It's 100% possible. In fact, it's 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 space time, right? So when you have in general relativity an expanding universe, there are different ways to slice space time 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 DeSitter Space. De Sitter Space is an example of a cosmological space time with a positive vacuum energy and nothing else in it. You can slice that space time in such a way that the volume as a function of time is finite, because it's a three-dimensional sphere, basically, but it increases toward the future in the past without bound.

So the finite volume gets infinite. But it's also possible to slice exactly the same space time so that the volume of space is always infinite. So you can slice it one way so that it's finite, one way that it's infinite. That's because it's not a well-defined thing. But our observable universe is certainly finite. Okay, so our 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 Segal, or Siegel, 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. of course, there are genetic factors that help define different groups, right, whether it's appearance or anything else. Presumably you've all heard various things about this. You know, 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 makeup, 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 to the people who are outside our group. When we invent races as a social

category, we don't know anything about genetics when we did that, right? We were not very good at that. 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 like really, really important, like what our skin color is, and other differences, like what our hair color or eye color is, less important, or, you know, 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. 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? 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, etc. Of course, within a certain sphere, whether you're doing, you know, 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, right? You know, if you can get a certain P value greater than 0.99, then you have a statistically significant result. In particle physics, we say that you need a 5 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, cleanliness of the evidence that you get. In other words, in particle physics, you can get 5-sigma worth of evidence, and if you don't have it yet, you can just keep doing the experiment, and hopefully eventually you will 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 ask for 5-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. In particle

physics, if we discovered that, you know, 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 that 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 a 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. Steve Sheridan says, in late July, a paper was published in the Astrophysical Journal by Qin Chen from Sejong University in Seoul. The paper purports to provide strong evidence within greater than five sigma significance, see, as we just talked about, for a 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, right? It's only one paper. You better have some backup to that paper to get extraordinary evidence. And when it comes to exactly this question, what's going on here is, you know, 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, okay, 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. 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 because they're very far apart. They're moving slowly. It's going to 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 because they're a little bit less exciting. And that's why the fact that it is nominally a 5-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. 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. Okay, you would definitely here. 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, you know, just be patient when it comes to these extraordinary claims. It takes time to really go through them. I mean, 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. A couple things going on here. Number one, there is something called the Hubble Tension. We did a whole episode about it

with Adam Reese 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 measure. 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. The one little extra thing I wanted to say is because you say 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 cosmontal 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. You know, if you think about the Hubble constant, it's in units of meters per, 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, because 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 universe to exponentiate in size, to increase by an e-fold, one factor of oiler's constant E, 2.7. 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 Adams says, in one of your mystery of time lectures on the great courses, you say that ABL, or Aron-O Bergman and Leibovitz, argue that we perceive a time asymmetry and 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 world's interpretation, since the prepare again phase would seem to happen after decoherence. Can you help me understand this better or at all? Probably not. 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-referencing and post- selection. For those of you who have 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, right? So we start and we say, okay, this wave function is in a superposition of spin up and spin down, and then subsequently we measure it. And if we measure it either spin up or spin down, that's all you have. So Aronov, Bergman, and Labovitz, 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.

You know, 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, 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 difference. different way of understanding things. I don't think the world needs a different way, so I'm not, I don't follow it down. 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 is often presented as an objection to the wave function guiding, i.e. 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? Well, it depends what do 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 Bohemian 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 Schrodinger equation works really well without any modification. So the way that they have both the Schrodinger 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, okay? Bomi 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 naive formulation of Newton's third law to every action. There's an equal and opposite reaction. Tise 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 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. We know a lot about its phenomenological astrophysical properties, but we don't know a lot about its astrophysical property. 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're a popular candidate, I should say. That'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 are supersymmetric models, and if you just wrote down a supersymmetric 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's a subset of all the possible supersymmetric models you can write down,

which have a new symmetry called R-symmetry or R-parity, capital R, the letter. And that's basically, you know, 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. But it doesn't give rise to a force, because actually in the simplest versions, it's 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, Lottie Ackerman, and Mark Kimi-inkowski about dark electromagnetism, so a U-1 gauge symmetry that stabilizes the dark matter particle. So you can talk about that, but it's, you know, 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 Clyde 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 cannot guarantee a satisfactory answer or a satisfying one, but I'll do my best. In your July 17 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 Goose's cosmic inflation. Oh, there are. There 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 are themselves anywhere near as compelling as inflation is. But there's plenty of phase space 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 Sinchen Liu. We both really enjoyed it, especially from a layman physics perspective. Also curious if you have any thoughts on the book's namesake, 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 because 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. 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 it on a computer and simulate it, but it turns out to be chaotic, as we later realized, probably Ponkeray 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. It's still Laplace'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, 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 intense 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 little perturbations, and those perturbations grow, and when the three bodies are zooming right next to each other. 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 Lozavoy, sorry, says, while participating in my first meditation course recently, A teacher hinted at a rather radical idea that could be shortly quoted as, maybe we don't have a body at all. Accepting that our bodies are nothing than... I'm sorry, I have trouble reading this. It's not your fault, Nikita.

It's 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? It's 100% 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 in the core theory

would be an emergent phenomenon and human bodies or other large systems absolutely qualifying. 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 a merge entire level phenomenon. We don't know. 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 Minescape? That's a pretty easy question, actually. I didn't want to bother getting permission.

I didn't want to pay for any music. So I have a friend and former collaborator from my grad school days, Ted Pine. He and I wrote a couple of papers together on topological defects and on my growing background and isotropies. And after graduate school, he formed a band called Euphonic. I think you can probably find them on the 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 music. 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, preposterousuniverse.com slash podcast, you can click on About Mindscape, and it will actually mention all these things. Diana David Ruse says, Always I've been puzzled by the concept of inertia. In Newtonian mechanics, inertia is the tendency to 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's theory of relativity, objects with mass will prefer to move along straight lines in the curved space time. When we try to divert an object from this straight line path,

we're effectively trying to make it deviate from its natural motion. However, still in my mind the question of why objects have inertial property, i.e. this tendency of following the geodesics, remains. Is there something more fundamental that I don't understand? 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 want to say, why are straight lines the shortest distance paths in Euclidean geometry, or why are geodesics shortest distance

pads in non-Nuclidean 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. 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 Lobe a while back, and I found his speculations about Umamuma quite interesting. He has come under a lot of criticism lately in the scientific community, but that has not dampened his enthusiasm for his opinions. What do you think about his recent vines of spherical metallic particles scraped from the bottom of the ocean that might be of extra solar origin. You know, 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. Umamuma 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 spaceship, okay?

I think that's extremely unlikely. I think that his case was unconvincing, but I think it's a perfectly reasonable thing to contemplate and you should certainly take the possibility seriously, just because it's kind of wacky and out there, doesn't mean we shouldn't think about it. The implications would be really big if it 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 continued 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, scrape from the bottom of the ocean. Nothing that I've seen from the perspective of other scientists who are experts in this area think that he's on the right track about this.

And it's pretty universal dismissal of these claims. And he seemed to be rushing into print and just not being careful and things like that. So, you know, 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 forced 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 What Ups says, has the rise of generative language models like chat GPT 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? So, 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. You know, 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 math-y physics-y courses, and I ask students to write papers and grade on the, on the, performance on those papers, and in class participation, in the more seminar, humanity, kinds of classes. So I'm not right now teaching a physics-math-e-based class, so I don't have to worry about students answering those questions using chat GPT. 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 going to be around for a long time. for the papers, that's an issue. And I am confronting this issue. And it was interesting. I am teaching two classes this semester. And I asked my students in both classes. And, you know, 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. It's just going to be BS. I don't think that we should believe that stuff. So we're not going to do that. Now, again, maybe they're whistling Dixie or what. 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 use the chat GPT for this purpose, you know, 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 so far, the short answer is it hasn't greatly affected my grading or assignment giving, but we'll see. It may be it will in the future. Astroaubel 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, that's true. It was a joke by John Wheeler that he felt guilty every time he put cream in a coffee because he was increasing 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, you know, if the sun blows up or, you know, 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 going to 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. Remember, a black hole is a region of space, a region of space time, really.

It's a region of space time from which light cannot escape, okay? 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, a, a, a, kind of abstract thing. So it's not like a book or a rocket chip, but it's a bit of information. Given that the black hole eventually evaporates away, that bit of information will eventually escape to the outside world. Okay. So you could, in some very strict construal kind of sense, argue that when there is hawking radiation, there aren't any black holes. Hawking himself said something along these lines. But the rest of the world is going to, you know, 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. That's not really what we have in mind. But anyway, the black hole is a region of space time from which light cannot escape, and that region grows smaller as the black hole grows smaller, loses mass, and eventually it will reach zero and there's no black hole left anymore. But there's no point at which the event horizon disappears.

It just shrinks to zero size. Paul Conte says, in the matter of AI in common sense, would it at least help an AI to learn if it 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 toward that goal. You know, I'm not an expert, but my impression is that, yes, this is exactly true.

people who do robotics have found that AI's, 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 important, which is feelings in the sense that Antonio Demosio and I talked about on the podcast.

So not in the 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, right? 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, or 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. You know, a 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 going to group two questions together. Sheldon Sillyman 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 crackpot, that is their given name, I did not invent that one, some random crackpot says, I enjoyed the Alice and Robert chapter in 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 fiction, the two kinds of things that intrigue me, look, I have no time to do this right now. So we're talking, 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'd love it. I'd love of mystery novels, as we talked about in the comfort food discussion before, and that would just be something that would be completely different in my brain, which would always be fun. Or I could imagine,

you know, 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 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, are a little bit high level. I mean, there's differences, the biggest ideas in the universe books are higher level than the previous ones, but all my books are a little bit demanding, you know, 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, you know, who knows? Life is short. Got a lot of things that got to do. 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. 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 because I don't think that my answer is going to 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?

It's 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, right? 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, okay? So housing prices have gone way up. There's 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 that could be a different way if we wanted it to be. Robert Ruxendrescue asks, we say that in the MWI, the many world's interpretation, Once decoherence happens, the branches can't communicate with each other, or at least that 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 in 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, but I think I'm going to give a not completely satisfied answer to it because I think that it's not quite a well-posed question as it is. I mean, I know what do 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 a superposition by our lights has become entangled with its environment. That's decoherence. And the whole point is that the environment is big, right? So entanglement 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. 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 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, right? 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 a 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 only happen because of the arrow of time, right, 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 world of

a foot that was there not too long ago. 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 unseparating or separating, unmixing, cream and coffee once again. 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 way you function and to put them back into some kind of superpillar. position, but you have to be much more specific. Well, number one, it's not going to 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. Chris Kay 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 going to depend on exactly how you parse that, so I'm not going to make too much of that. It is similar to the way a rock is a physical thing. 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, right? If I say the Star-Spangled Banner, the National Anthem of the United States,

does that exist? 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, right? It's manifested whenever you sing it, or, you know, 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 are 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 Grundgeiger also asks an emergence question. The macro world is emergent and the result of coarse-graining. What do you think is the likelihood that there exist multiple orthogonal coarse-graining 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 detail 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.

Let's just keep it classical, and we're looking around, and we have the world with a bunch of atoms, and I'm coarse-graining it into things like tables and chairs and computers and stuff like that. So basically what I'm doing is I'm grouping together whole bunches of atoms and calling them an object. So the question is, are there different groupings? You know, 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 coarse-grained thing. The problem with that is that that thing I invented, that coarse-grained object that involves 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 coarse-grained 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, looking at a computer with various questions on them, that is also sitting on the table, you kind of know what's going on, right? 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 coarse grain than others, is mostly due to spatial locality, right? I mean, we've coarse-grained 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, it has solidity, right? If I touch the table in one end, then it's going to affect the table somewhere else. All of these down-to-earth physical properties make this. right coarse-graining to use. Is it possible there's some very different course graining? Yes. I mean, you might even guess that in quantum gravity, ADSCFT is an example of a weird, different course-graining. ADS-C-F-T is this duality that you get in string theory between a, let's say, an N-dimensional quantum gravity theory with antidecidder boundary conditions, and an N-minus-1-dimensional

theory on the boundary with no gravity at all. But interestingly, people who have thought about ADS-C-F-D, so the two theories are supposed to be the same, even though they're in different numbers of dimensions. That's obviously going to be some wildly non-local map between them. But people don't really think about coarse-graining on either side. You know, does it make sense to coarse-grained? Does it make sense to have physical objects on both sides? Because there's like strong coupling on one side, weak 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. Paul Hess says, in an answer during your August AMA, he described a photon with a spherical wave function, and you implied that it's pretty typical to be emitted that way. I previously conceptualized a wave function to be much more directional, usually with a large moving peak where the particles most likely.

to be found. Can you clarify whether a spherical photon wave function is a special case? If it's not spherical, is 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? You have an electron and it gets shaken somehow, right?

You move the electron around, up and down very quickly, and that emits a photon. But that up and down moving, because it's going both up and down, it doesn't pick out a 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 flashlight, it's not intrinsically emitting light, in a direction, you know, you've got to 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. 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 going to see the particle and you're not going to see the whole wave, right? that's the difference between classical mechanics and quantum mechanics. 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, at 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.

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 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 bachelor's in physics a few years ago. He said he was talking with his professor, so already I'm skeptical because 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. 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. You know, it's important to know when we talk about 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. 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? It's a little bit more subtle relationship. You know, again, this is quantum mechanics we're talking about. It's not classical mechanics. Quantum mechanics in its basic formulation with the Schrodinger equation, etc., is not discrete, okay? 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 it, 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 Schrodinger equation. It's that the set of solutions to that equation in that particular setup is discrete. So quantum mechanics itself, if you just do regular quantum mechanics, nature is not discrete,

full stop. I recently wrote a paper, very recently, pointing out that in certain, certain special cases, if things line up just right, you can take quantum mechanics and you can discretize it. You can discretize the evolution of the wave function in Hilbert space so that it is truly discrete. There are some cosmological issues that 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 an 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. you ask about the fundamental degrees of freedom, the finite number of degrees of freedom,

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, right? 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. there are good reasons from quantum gravity and black hole entropy and the Beckenstein bound 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 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, right? So in that sense, in those senses, there is a more subtle relationship there. Kyle Stevens says, with the continued proliferation of seemingly existential threats to humanity, such as pandemics, unaligned AI, nuclear war, climate change, I can't help but feel that 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 that

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, right? Because that would be only a 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. I mean, maybe a few more generations, but pretty soon you're going to hit that 99% mark, and it's going to become unlikely. So I think that this is just a mistake, like just obviously wrong this argument because we're not typical observers. We're going to 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 going to write a paper about this because I think everyone gets this wrong, to be honest. So I just have zero credence in the doomsday argument. Just to point out one obvious reason not to believe it, why did you say, say all human beings ever existing rather than all life forms ever existing, right? You'd 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, 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 1,000 years ago, have the capacity to really do disastrous things, to life on Earth, including all of human beings, right? 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. 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 is 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.

A black hole in some very real sense is a quasi-particle, right? It's an 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, most ways I could think of to make bound states of standard model particles would interact electromagnetically. Like hydrogen atoms interact electromagnetically even though they're themselves electrically neutral because they're made of electrically charged constituents, right?

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'll be hard to constrain your own theorizing. Tomer Hakkonen says, Hakohen, sorry, Hakohen, says, what is the relationship between the notion of time and general relativity and the thermodynamic arrow of time? From my limited understanding of GR, the main difference between time and the other coordinates of space times is that the sign of the metric is negative for the 0-0 index. Can one in principle start from the signature of the metric is minus plus-plus, plus, and derive the 0-th coordinate is the one along which entropy goes. grows. No. Well, because yes, in general relativity or in special relativity or for that matter, in Newtonian mechanics, 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.

You can imagine a box of gas that is in thermal equilibrium, and the entropy is not. And the entropy is neither growing nor shrinking, but time is still passing because all the molecules in the gas are still moving, right? The arrow of time is over and above the existence of time itself. That minus sign in the metric 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, which you know because there's no arrow pointing in the spatial directions, right? There can be, in fact, there is here on Earth. There's an arrow pointing toward the center of the Earth called where gravity is pulling you toward. 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, right? 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. of space here on Earth, it is something that is not ingrained. In the nature of space time itself, it's a feature of our local environment. Moshefader says, what are your three favorite cocktails, and why? Would you consider developing a signature Minescape 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 Minescape Cocktail or Minescape 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 sidebar, but they were all pretty horrible. You wouldn't want to drink these things. They were either just regular cocktails with physicsy names or terrible concoctions 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. You know, I like my cocktails not fruity or juicy or sweet.

I like more spirit forward, as they say. So, you know, I like martinis and Manhattans and Negronies. In the slightly more out there world, I like Sazirax and Corpse Survivor No. 2 and stuff like, that. But, you know, honestly, a martini is my favorite cocktail. It's very simple, very easy to make. You know, you can't, 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, 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 because it was all room temperature. But, you know, one of the requirements is it should be super duper cold. That's my advice out there to martini makers. Simon Graf 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. take new evidence into account, is currently impaired. Or worse, evidence that conditionalization is not the right

rule for taking new evidence into account. Some people have argued that finding out you are drugs, tired or suffering from hypoxia puts us into situations like this. I think this 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? 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 basian. I try to be a good basian. But to be clear, to be a good basian is to assign prior probabilities to things and to try to update them when new information comes in. It is highly impractical to actually, 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. You know, when I was a graduate student, they didn't. Astronomers and physicists were not Bayesian's generally back in the 1980s, and big data came along, and it became more clear we had to be better Bayesian's, and so now when you read papers that are looking for the Higgs boson or using CMB data to constrained cosmological 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 to be, all I'm 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 if you're in these situations where conditionalization is not the right rule or something like that, if you're somehow cognitively impaired, you're probably going to be an even worse Bayesian than a perfect calculator would be. You know, if you go back to the podcast we did with Carl Fristin about the Bayesian brain and the free energy principle, the Bayesian brain hypothesis is about, you know, minimizing surprise. Like trying, like a brain is supposed to model the world in such a way that it's as the least surprised that it can be when it encounters new information. But even those people admit that that's calculationally implausible for the brain to actually do it. That's why you invent the free energy principle.

The free energy principle is kind of a way to approximate being a good Bayesian. So I think that the real world is a lot richer and a lot more complicated than the perfect Bayesian reason that we imagine. These higher order defeat problems are 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 a cheat. It's really two subsystems interacting where one is long. large and called the environment and typically sucks energy from the smaller subsystem. Is there an analogous conception of dissipation coupled systems in quantum mechanics, and can it yield an explanation for the apparent collapse of wave functions during observations? 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 entangle 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 Schrodinger 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 posit that would 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 is going to 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 going to 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, you know, 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 a 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 a predictions. They're as good as the assumptions. 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, right? All you're doing is 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 a 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? 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 find yourself in a density matrix. In order to successfully address the measurement problem and understand 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 am 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 Schrodinger 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, a 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 as a model of non-oppressive, non-masculine, toxic figures, etc. You know, yes and no, in some senses, 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 want to 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 were not eyewitnesses to it. So what are you going to believe? You know, this is a set of stories that were told within a community and past 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. And the other thing is, you know, some of the things that Jesus said were really admirable and some were not, like most people, you know? This is why I don't like hero worship in any sense for Jesus or for anybody else. It's true that, you know, 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, you know, 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 by his followers when they

actually set up the church. So, you know, go ahead. I would say, you know, find inspiration in Jesus and Buddha or Zhuangza or whoever you want to be inspired by. That's fine. But, you know, there's plenty of people out there to be inspired by, not just that one. Sid Huff says, many people have been taught that atoms are mostly empty space. This notion was stated eloquently by none other than Carl Sagan. However, many physicists debunk this statement as a misconception. So what exactly is empty space?

Does such a thing actually exist, whether inside atoms or elsewhere? Well, you know, 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 has 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. 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, you know, 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 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 excitations, no energy of any sort, anything like that. And you can have that. You know, that's a pretty good approximation to empty space, to the vacuum, in between

the planets and the stars. It's not exact because there's light. and so forth, right? And, you know, that means it's not completely empty, but it's a good approximation. I'm not sure what else we want other than that. 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 would 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? 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, okay, so perfect calculational 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?

Is it 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, 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 that Dark Demon would be able to learn a lot,

but certainly not everything about our known laws of physics. 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? Well, there's two things. For one thing, there 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 a 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. But also, more importantly, the second law is not posited as an axiom of anything. It is derived from the behavior of physical systems. We know about coarse-graining 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, right? 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-opomeness 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. Russell Wolfe says, it feels to me like 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 going to 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 going to be a negative correlation with me having interesting things to say. But that's not the only thing that matters.

You know, 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 want to hear some of these answers, but 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, you know, 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 want to ask, even though I seem to not be willing to answer it, I'll give you that chance. You absolutely had that chance. And probably you will learn that I wasn't answering it because I have nothing interesting to say, but that's okay. You know, maybe I'll be 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. 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. Arrows 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 to sort of voting systems where you have a continuum of preferences, right? 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 than B. Things like that can't all be simultaneously satisfied. What I think you're probably thinking of is strict. 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 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 going to win. You know, if 45% of the people like one candidate and 50%, I'm not going to get this true in real time, if 40%, 40%, 45% and 15% are the voting things, then you might worry that if you give your money to the third party candidate,

you're throwing it away because they're not going to win, so instead you strategically vote for somebody else. So that's a true but slightly different thing than arrows 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? 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 the, 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, 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 want to 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, right? 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. Like, I was in California where we had elections with over 200 people on the ballot. You think you're going to rank all them? You have to do something, right? You have to have some simplification. So I don't know how much work has been done about, you know, 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, you know, Linux versus Macintosh users, right? People want a simple user interface and the voting system is an example of where that is an important consideration. I'm going to group two questions together. Schleyer 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 likelihood 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 a 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 Boltzman brains having their own experiences near the end of time while we're here now? Why would we change a theory just because it suggests the possibility of Boltzmann brains somewhere else in spacetime? 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 Schleyer'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, you know, 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 going to pretend to forget that I know who I am in the world, pretend that I'm a typical person, and then, you know, 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, you know, if you think about a duplication experiment, right, where you step into a box and then you're turning into 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 being either one. What else are you going to do, right? Because they're in epistemically indistinguishable situations. And so that's why the Boltzman brain problem is a big problem, because it's not because there are random fluctuations into brains. 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 Boltzman brains, I would be a Boltzman 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 Boltzman 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, 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, you know, 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. It's 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 Boltzman

brains does not rely on the idea that we are typical observers chosen among all observers in the universe. 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? So I do think that random fluctuation scenarios should be excluded from our consideration, but not because of

literal Boltzman brains. Redmond says, after extraterrestrial contact requesting a meeting, the president, a Minescape 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 going to answer this question, literally, but I want to say two things about it. The first thing is that the reason why I'm not going to answer it literally is because I'm just not into these kinds of questions. And, you know, 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. It's, it kind of smacks a little bit of hero worship. I know it's not, I'm not trying to say that, but, you know, who are the five best people, the five coolest people? I'm not about people in that way. You know, I like my friends, my personal acquaintances. I'm about those people, but people out there in the world, you know, who do great things, for them, I'm about their great things. I don't know them personally enough to say, you know, who are the five people in history you'd want to have dinner with or whatever. You know, I just don't think that way. And I apologize for it because it makes me weird and it makes me sound like I'm being rude to people

who ask that question because that kind of question is very common here in the AMAs. Okay, so I'm not going to give you literal answers to it. I feel like I'd be insulting all the people I didn't pick, you know. 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. You know, forget about individuals and their names. What kind of team would you assemble? That's a great question. That's very interesting.

And, you know, the short answer is, I don't know, because, you know, one of the rules of the AMAs here is I don't do any work for them other than literally, you know, editing them and then reading and recording them. So that's a question that demands a lot of thought, you know, and I haven't thought about it. That's why I like that aspect of the question. You know, you would – it's smart that you put in there in the question that the aliens 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 a 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 want to talk to them about science. And I think that you would separately want to send someone who was really good at technology. You know, being good at technology is different than being good at science. So, you know, 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, you know, makes it very clear that even five people is not going to be enough. Like, what do you mean someone who can learn about technology? Like, there's lots of different kinds of technologies. People who are good at superconductors are not good at, you know, pharmaceutical advances or something like that. So it's going to be a tough call. And then I think you want some more socially oriented people, you know, maybe a social scientist and an artist,

artist in the broadest sense, you know, literature, movies or whatever. But, you know, 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 to me to be a pretty good first attempt at five different kinds of people.

But it's leaving out people who are interested in diseases, people are interested in astronomy, people who know about complex systems in general, people who are politically smart, people who could negotiate very well. you know, there's a whole bunch of skill sets not in that team. So I'm just going to cross my fingers and hope that we get 10 people on our team when we finally meet the aliens. 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've 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.

You know, 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, 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 two mini suns going in opposite directions. 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. For that matter, it's not what electromagnetism is, right? 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 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.

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. So it is true that if the sun changed its configuration dramatically, for example, by splitting into 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 because it's relativity, until, what is it, eight minutes later, because 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, like, 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 minute's worth of entropy increase to happen in my brain, regardless of how light would travel in that time. But some clocks aren't entropic, like the T you take derivatives with respect to in Hamiltonians.

Can you say something smart and at 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. 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, right? 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. 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, right? 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, right? 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.

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, you know, 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, you know, 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. You know, there's this 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 Minescape guest, where he was specifically referring to the question of why there is more matter than antimatter in the universe, why there's a baryon asymmetry. So it was kind of like a little joke, you know, 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 a, a, a, a new, a, a, you know, equal amount of matter and anti-matter was an unstable circumstance, an 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 spacetime. What is your feeling generally about these sort of video series? Do you think they do a good job communicating physics concepts to a general audience, even if they apparently cause a rash of misguided speculation from time to time? I think that's a perfectly 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, etc. it's not my thing because I'm a professional scientist and therefore if I'm reading science, it's probably going to be a little bit more technical than those things. And if I'm reading popular fun things, it's probably not going to 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. I do think there's one possible criticism or potential criticism that, or potential pitfall, let's put it that way, that people should worry about, because different science questions have different levels of straightforwardness to their answers, right? Like, let's think about our atoms empty space, like we were just talking about. That's not a trivial question. It's not, you know, it's not like how big is a black hole of a certain matter.

There you just go to the equation, you plug it in, and 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 would get spaghettified, when you could reach a point of no return, what you would see as you were looking outside. All 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, you know. 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, you know, 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. They would know that's a set of a assumptions that you're making, and they're only approximately true. 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 the footnotes and caveats and careful wording have gone away, right? 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 on I've been in science documentaries all the time. And, you know, 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, you know, 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, right? 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. So you get a lot of situations where, you know, 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? Jake Zielsdorf says, Do you have opinions about Oppenheimer as a physicist? Was he a great one? Well, I think that, you know, he has contributions in physics.

He was not, you know, 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, right? 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, you know, in that sense, he succeeded at doing something other than writing theoretical physics papers. And I think, you know, 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 interests, how do you think about the trade-off between breadth and depth of your interests and your intellectual work, or do you not think of it that way? Well, I think there is a trade-off. You know, I think that there's a finite number of days in the week, years in your lifetime, cycles of activity in your brain, et cetera. 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. You know, 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 underappreciated aspect, which is that thing is what you're thinking about in your spare time, you know, 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. There is also value in not falling into a rut, 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. You know, all that is all true, and I just said it, you know, it's all true. But honestly, I just like what I do. I kind of don't care whether other people think that I am a mile wide and

an 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, you know, lets me do what I want to do. If I didn't, you know, 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, you know, the god emperor of academia, I would tilt the scales a little bit more toward broad people, interdisciplinary people, because it's just kind of easier and cheaper to stick to a field and just do the same thing over and over again. 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 want to stop all those people who are specializing.

I don't want to denigrate their work in any way. I think, you know, everyone should, like, being, I always say this, being a professor, being an academic, being an intellectual, you got to do it because you love it. There's no, that's really the only reason, you know, 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. 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 objects with empty space in between them.

And quantum field theory, or for that matter, even classical field theory, 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 nonsensical. You know, this is a complicated set of questions here. You're a little worried in the phrasing of the question because you leap from entropy and evolutionary pressures to fundamental physics and the principle of least action. And, you know, all of these are good ideas, but there are ideas in different contexts. You know, if you have fundamental physics and 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 coarse-grained 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. It's very, very weak. It says that along a term, 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, 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. 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. I mean, in fact, if you think about the training of a theoretical physicist, right? You know, 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. 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 Boconian scientific method, Francis Bacon, back in the day, trying to explain how science works. He says, you know, formulate a hypothesis, use the hypothesis to make predictions, test the predictions, right? And Perzig, Robert Persig in Zen and 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 of 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 woo-woo about it, but it's also not axiomatized or algorithmatized. We don't have a uniform agreed-upon way to formulate hypotheses. In fact, it's not even a single step, you know.

Formulating hypotheses is a process. It takes time. You sort of get a vague idea and you think about it. You know, what does it mean? How can I write down equations that would represent this? 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. You know, 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, you know, from 1900 to 1920, his style was perfect. 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 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. 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 equals 1, between 0 and 1. So if we integrate y equals 1 from 0 to 1, presumably 0 and 1 go from x equals 0 to x equals 1,

so we have two variables. We get the sum of x from 0 to 1, which equals 1. It's just the area under the curve, Y equals 1 between x equals 0 and x equals 1. 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 equals 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 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, there's a flub right there.

There's kind of an issue we have to confront. Y equals sine x plus cosine x does not have an integral between zero and one that equals one. Maybe if it were sine squared x plus cosine squared x, it would equal one because sine squared x plus cosine 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 cosine x does not have an integral that equals one. So mathematically, that's a boo-boo.

And then there's some extra steps that I'm skipping, but it's along these lines of having some functions and integrating them and so forth. And then the question concludes by saying a proton can be defined as containing three quarks, specifically two up and one down. Properties of quark include up quark, equals charge of minus one-thirds, spin of one-half, et cetera. So I will, you know, the priority question is, you know, 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, etc. 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, et cetera, Feynman diagrams, is necessarily right. 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. You know, when we talk about quarks and gluons to people who are not physicists, it doesn't sound that complicated, you know, 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 Fadai of Popov, ghosts, and dimensional regularization, and effective, and it goes 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, 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, you know, 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 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. Seamus 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, 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 slash hallucination? And if so, what might it be? Sure, I think that the initial credence would be very highly peaked on dream slash hallucination, or, you know, 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 part of being a good Bayesian is, essentially no proposition should get zero credence from the start. 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 and elves is not,

my everyday life. So I would have to start thinking about the wilder regions of proposition space. And yeah, you know, 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 and 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. Philip Malinowski says, I don't want to get you in hot water. Sorry, I don't want to 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. You know, they're not attuned. They're not selected for a successful life outdoors. 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 going to 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 because 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. We actually, you know, 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 lot of wildlife. We've certainly seen both foxes and deer in, you know, walking by our house, okay? So there's a little bit of wild life 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, maybe like, you. less happy when they noticed 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 guess what? Their

life expectancy is much shorter. I never had a cat die of natural causes when I was growing up. But, you know, well, one got leukemia, I guess. But I guess that's a natural cause. But usually, you know, 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 have responsibility for it, keeping it indoors is a much more sensible thing. O-A, or however one pronounces O-W-E, says, when eternalists 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 and the past and future are just predictions and memories. 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. Benjamin Barbrell 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 microstates corresponding to a given macro state, I don't understand the nature of these microstates 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 microstates, 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 microstates corresponding to a given macro state. But, you know, let's think carefully about what that means, and it's subtle, and we also have to remember something we said much earlier in 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 microstates that look that way. There are a lot of ways of arranging the atoms and molecules in 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 going to look exactly the same as a different box of gas with the same temperature and pressure, even in a different microstate. So quantum mechanically, that becomes even more vivid, the fact that you can have no hair, and yet you have a lot of microstates, because you have a certain

combination of those microstates that is the thermal equilibrium combination that is a combination of many, many states, and therefore it has high entropy, 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 microstates, and there, sorry, I should say, where there literally is a microstate 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 microstates 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 microstates 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? But that's mixing up a classical way of talking the Cosmic No Hair theorem with a quantum way of talking de-entropy. We hope the resolution is that quantum mechanically there is a large set of microstates. We don't know what they are. We did have Andy Strominger on the podcast a while back, and Andy and Kermunvafa 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 microstates. 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 microstates, it does not by itself resolve the information paradox, because there is the extra question of where the information is. The information paradox is we don't have enough room to put the information in the black hole. 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 eventorize and

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 have radiated away quickly? Or is the suggestion that they are somehow being constantly created? No, the suggestion is just that you have to run the numbers. You know, like, for many questions like this, you can't just use words. You got to kind of think about the numbers. It is true that a sufficiently small black hole will evaporate away in a time scale less than the age of the universe. But a larger black hole would take longer than that to radiate

away. So you've got to 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 of the mass of the sun, it's, lifespan is going to 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 had not yet evaporated away in the age of the universe from Hawking Radiation. Red Antinov says, if the tension between the measured magnetic dipole moment of the muon and its theoretical value

is a sign 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 got to 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, is a little bit stronger, and therefore, and, you know, just heavier particles more generally,

therefore new physics effects might very naturally show up more readily in a muon than in an electron. Electron is kind of shielded from effects of heavier particles just because its mass is lower. Neutrons, on the other hand, they are heavier, but they're a mess because there's, you know, lots of quarks going on inside. It's hard 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. 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 Woonlich 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 going to be a very boring answer, but I choose four-dimensional space. I think that's a great thing. This is like, I've mentioned this before, that either in video games or 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. 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 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 Stuckey 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 Seabins 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 have been other options. I do think that, you know, the two David's,

David Deutche and David Wallace, their derivation is sort of what is now the standard one in foundations of physics circles. 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 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, you know, 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 Bourne rule are cheating because they assume something that gives them the answer rather than actually adding it. 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-Deuts approach is completely different than the language that Chip and I use, which is also our ideas based on suggestions by Lev Weidman and others, In the Deutsch-Wallis argument, you think about what rational observers would do. You use decision theory and 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 worlds interpretation. Whereas what Chip and I say is there are conditions of self-locating uncertainty. So we don't use words about decision theory, et cetera. We say, when the way function branches, you don't know which branch you're on. Therefore, you need to assign credences to being on one branch or another. And then we argue that the only sensible way to do that is to use the Bourne 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 want to prove it, it's not like there's one correct proof and all the others are incorrect. We're 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.

So the Deutsche Wallace approach says, you know, given that there are probabilities of some sort, I might not know what they are, but I'm going to 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 part you have to attack, and people have attacked it. People, you know, 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. 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 quite works. That's quite valid. But, um, Anyway, I don't think that there's an incompatibility between the two ways of doing it. You know, the Deutsche Wallis 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. 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 branch.

And if you don't buy that assumption, then you can undermine the whole game. I think that, you know, Chip and my self-locating uncertainty derivation also has assumptions that you can call into question. So, you know, 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. 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 Grindr says, I'm hoping you can clarify an issue I have with the arrow of time and 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. 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've got to 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 gods 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. 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 square root of two. 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 the 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 the 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? 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 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 Bjorkane and Glashow, I believe. There was also the gym mechanism, so that's Glashow, Iliopolis, 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 going to call it the charm quark because, you know, they were having fun.

And that turned out to be right. So since they turned out to be right, people, you know, went along with it. Other cases, it's not so clear for quarks. They were independently suggested by Gelman and Zweig, George Swig. And Gelmong suggested calling them quarks. Swig suggested them calling them aces. and Gelman won. He was more famous and it was kind of a good name. Other cases still not adjudicated. There's the famous J-slash-Sai particle, which was, I'm going to get the names wrong of who did it. 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 mezzan. And maybe Burton Richter was the other one at Slack, who also discovered. it at the Speer experiment.

And so Richter and the Slack people named it the Psi particle. Psi PSI is supposed to be like close to spear, 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 because he wanted to call it T for Ting, but 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.

So to this day, it is called the J-slash-Sci 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, and motion and 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. 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 know, 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 Schwarzschild solution, et cetera. 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 2 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 going to be about quantum mechanics specifically. I've done that, right? Plenty of talks I've given about that. I really want to concentrate on the quantum field theory side of things. But I don't know whether I want to like how technical I want to make it. It's a popular talk. So in terms of what the audience is, it's a popular audience, and that's what I want to aim at.

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 Kulam phase, the Higgs phase, the confinement phase, how one underlying idea of gauge symmetry, It 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 particle 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, you know, give the audience a break. 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, why stars shine. But still, you know, you and me and our chemistry, in 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. Why does it, where does the scale of things come from? Why are atoms the size that they are?

You know, 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? 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 for Minescape. I really appreciate it. See you next month. Bye-bye.