AMA | July 2023

0:00:00.2 Sean Carroll: Hello everyone, welcome to the July 2023 Ask Me Anything edition of the Mindscape podcast, I'm your host, Sean Caroll. If you've been listening to Mindscape for a while you know the general idea here. Every Monday, we have a podcast. I'm usually interviewing somebody, sometimes I do a solo episode, and once a month, it's this Ask Me Anything episode. And I always mention that these are supported by Patreon supporters, so you can sign up to be a Patreon supporter yourself. Go to www.patreon.com/seanmcarroll and pledge a $1 or $2 or a $1 million, however you feel like for each episode of Mindscape. It's very easy to do, it's very easy to cancel if you lose interest and it's much appreciated by me as well as actually getting some tangible benefits. These questions for the AMAs come from Patreon supporters, those are the people who are allowed to ask the questions, also Patreon supporters get ad-free versions of the podcast.

0:01:01.1 SC: And the reason why I'm bringing this up front and center right now is because we are experimenting with a new benefit for Patreon supporters, which is that I'm going to try to do a little reflection video, also audio version immediately after every podcast. So every time I interview someone, the AMAs don't count. I'm not gonna do reflection after the AMAs, you just listen to me talk for two or three hours, you don't need that, but after I interview someone, I'm gonna try to do a little reflection on what I got out of the podcast that just happened, what I think about it, why I had it in the first place, whatever is on my mind at that time. Just a couple of minutes. Very informal, nothing very serious or anything, but it is there on Patreon. It is nowhere else. So if that's the kind of thing you might be interested in, that's one more reason to sign up as a Patreon supporter for Mindscape. As always, enormous gratitude from me to everyone who listens to the podcast, whether you are a Patreon supporter or not. Special gratitude for those who chip in a $1 or $2 to per episode. It is very much appreciated. And this month, lots of questions, lots of things, lots of science this month, so let's go.

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0:02:28.8 SC: Chris Mason says, it seems like everyday there's another article or news report highlighting the existential risk of AI, artificial intelligence, do you think there is a risk associated with AI development that is serious enough to warrant such media attention? It feels to me just like the LHC Black Hole scare all over again. Yeah, I think there are some similarities there. It's actually a very tricky question. I have opinions about it, but I don't wanna act as if my opinions are set in stone, I think this is something where we should be applying some thought process to this, maybe at a more calmed, libertine level than we've done so far. There's clearly an argument to be made about existential risk, by existential risk, we mean really not just something bad happens, but all of humanity is extinguished, the end of the human race. That's an existential risk. Now, this seems hard to imagine exactly what would happen, but I think that the argument goes something like AI is something very different, we don't know what its capacities would be if we work on an analogy with human beings, if we take seriously in other words, the idea that AIs are truly intelligent, then we can easily imagine making AIs that are more intelligent than human beings.

0:03:45.1 SC: And human beings are the ones who built the AIs in the first place. So these more intelligent agents will be able to do at least that and more, and that opens up a whole bunch of possibilities if the values of the AI are not aligned with our human values, they might not care about us, they might be indifferent or even absolutely against our existence, we don't know. And I think that the argument goes, even if it's a small chance, it's enough of a chance that it's something we should worry about just because the whole end of all humanity is pretty bad, so even if the chance is very small, if it's non-negligible then we should take it very seriously. So I have lots of problems with this argument, a couple of them just very briefly, are number one, the more or less... What is the word? The anthropomorphic way in which we are borrowing the word intelligence and applying it to AI. We use the word intelligence to talk about human beings in many different ways, it's a catch-all term for many different kinds of capacities, from the ability to be as successful in life, to the ability to do well in standardized tests.

0:05:00.9 SC: And I think it's a little bit of a mistake, a little bit too anthropomorphic to simply say, "Well, AI, if it gets to be intelligent and more intelligent than us will be like humans, but smarter and therefore, better than us. AI is a different kind of thing. They're not embodied necessarily, they didn't grow up through evolution, they don't have the impulses and motivations and feelings that we have, that's not to say that they're better or worse or less or more capable, but they're different." And so I do think that it's important to recognize what those differences are and not to be too glib about putting everything on a single unified scale of intelligence. Another thing that I worry about is the idea that, well, the harm is so huge that even if it's very unlikely, we have to take it very seriously. I get that argument, but I think it's a little too quick. I used the argument... Speaking of the LHC Black Hole scare all over again. I use the argument in my book, The Particle at the End of the Universe, I said, "Look, when you open a jar of spaghetti sauce to put on your pasta for dinner in the evening, is there a chance that in that jar of spaghetti sauce, there is, has been a mutation which has created a virulent pathogen that when released by you opening the jar of pasta sauce will spread out into the ecosystem and kill every living being.

0:06:32.0 SC: Well, strictly speaking, as we always say here, when it comes to scientific questions, if the question is, is there a chance or is it possible that, the answer is always yes. There is some chance that every time you open that jar of pasta sauce, you're gonna wipe out the whole human race, and how much benefit do you really get from that jar of pasta sauce? So can you make an argument that even though it's unlikely that that pathogen will be created, nevertheless, you should not open it because the consequences would be so dire. And no, that kind of argument doesn't work to stop people from opening their jars of pasta sauce. And part of it is that we don't have a very good way of consistently multiplying a big number by a small number. The big number in this case being the harm that would be caused by this particular action in principle, possibly, and the small number being the probability that that action is actually going to lead to that harm. We are very bad at that kind of mathematical operation.

0:07:36.6 SC: So I don't think it's okay to simply say AI has a chance of extinguishing the whole human race, and therefore we should take that chance seriously. You have to be a little bit more specific. And the people who are worried about these dangers are, in my experience, not very good at telling us precisely how AI is supposed to do this. What is the actual scenario that we are worried about? I do think, meanwhile, that there are many things to be worried about when it comes to AI, how it's going to affect our consumption of news and information, how it's going to affect careers and jobs for writers and artists and people like that, how it will help people in all sorts of different ways, all sorts of different conversations we should be having. I think that those very, much more plausible real world near-term dangers are what we should be focusing on, not the existential risk kind of dangers. Especially because I think that the kinds of safeguards we will put in place to make sure that medium-sized risks from AI do not happen, will also help us prevent the big risks from AI.

0:08:52.2 SC: So I don't see much point in worrying about the science fictionary, literally killing all human beings kinds of scenarios. Yes, if it happens, that would be especially bad, but the kinds of things that we can do to prevent it from happening can be motivated in much more reasonable, sensible, high-probability ways. So I don't personally worry about existential risk from AI, I worry about other kinds of risks from AI.

0:09:21.7 SC: Paul Torex says, "Brian Lowery on the recent podcast reminded both you and me of Hugo Mercier and his analysis of reason as a primarily social activity. Question. In your view, is there one true logic, that is, can one say the statements in set A imply B without adding according to logic system L were without implicitly expressing from my standpoint as an adherent of logic system L." No, it's clearly not just one true logic. Any logician will tell you that, there's all sorts of different kinds of logic that we use for different purposes under different assumptions and so forth. I am not a philosopher of logic or the foundations of logic or anything like that, so I can't go through all the arguments back and forth, but there absolutely are different kinds of logic. I'm not quite sure how that connects with the analysis of reason as a primary social activity, except that, just to be super clear here, when Hugo was talking about reason as a primarily social activity, it wasn't a reason that he was focusing on. It was reasons, plural. The difference being, by reasons, he means the fact that when you do something, you think of it as being done for a reason.

0:10:35.7 SC: Okay. So in other words, you offer an explanation. That's a little bit different than reasoning. When you're adding two numbers, you're reasoning, but you're not offering reasons, you're just going through some steps. What Hugo Mercier was mostly concerned with is the social activity of explaining to other people why, you're doing something or they should do something, or something should be done by society or something like that, even though we closely relate reason, reasons and reasoning, they're not the same thing, they're related to each other, but it's the reasons, the offering of reasons that he was really focusing on. Shaquille says, "Energy can neither be created nor destroyed. Rather, it can only be transformed to transferred from one form or another, that's the law of energy conservation. When space and time itself is evolving, changing, expanding and in a way, creating itself isn't energy also created in the time, cosmic time scale of the last 13.8 billion years."

0:11:34.5 SC: Yeah, absolutely. Created or it can increase or it can be destroyed, there is no rule, or at least it is not correct to state the rule as the total amount of energy in the universe is constant. I wrote a blog post about this years ago, so if you Google the phrase "Energy is not conserved," you'll probably find my blog post about this, and it's a tricky thing because when you have space, time itself being dynamical as you do in general relativity, there is more than one definition of the word energy. Some of those definitions have the property that the energy is conserved, but they are also usually trivial, like it's just the energy is always zero for a closed universe in general relativity, for example. So that's conserved at zero now, at zero then etcetera, but it's not actually telling you anything interesting about the physical configuration of stuff. There's another definition of energy, which is just the energy of the stuff within the universe, the matter particles, the radiation, the dark energy, all that stuff.

0:12:39.6 SC: That is a number that you can add up. And it is absolutely not conserved, simple fact, okay. It can go up or it can go down. When the universe is mostly dominated by radiation, that energy goes down as time goes on. When the energy is mostly dominated by dark energy, on the other hand, it goes up as time goes on. It turns out that there is still a rule that is obeyed, but the rule does not simply say energy can neither be created or destroyed. The total amount of energy responds to what spacetime is doing in a very particular way. There's also subtleties in quantum mechanics, you can also have energy of the quantum states that you are experiencing as an observer change when you do a quantum measurement. I think there might be a question about that later. Simpsons asks a priority question, recall that a priority questions are granted to every Patreon supporter once per lifetime. You can ask a question and I will do my best to answer it. So Simpsons is asking his.

0:13:40.4 SC: "I really enjoyed your conversation on the social self with Brian Lowery. When we use sentences like, I am/have a self body or mind, the obvious constant is that I is not X, which makes me feel that I is real." So I'm sorry, I'm trying to read the notation here, that's capital I equals tilde capital X. In logic, the tilde often would mean not, but in physics or math, it might mean approximately equal to, so I'm not quite sure what is being meant here. Anyway, the question continues. I've learned it in physics capital I stands for electric current, which in turn is a stream of charged particles. I find that heuristically, the Lorentz force formula, I equals Q, the electric charge times E plus V cross B. That's correct. No, actually, that's not correct. Sorry. [chuckle] That is the force for the, that is the, I'm in the middle of Simpson's questions here. Let me finish reading Simpson's question.

0:14:42.2 SC: Could that, could we describe a dual entity, a body and a contingent mind with the electrical term describing the current conducted by a neural network system one, and the magnetic term describing the induced current by an immersion magnetosphere like the B field system 2. For me Q moves, therefore B, B feels I, I feels B. I therefore feel that I am. And to paraphrase Einstein question says, to the seat of the South have no point. The question is, can the physical I stand for the psychological I, can I be reduced to I? There's a lot going on here. So the Formula qE+V cross B is not the formula for the electrical current, that is a formula for the force on a charged body with charge Q in the presence of an electric field E and magnetic field B when the particle is moving at velocity V, that's a different thing than the current. The current is the total amount of electric charge passing by any particular small area element per unit time. So the formula doesn't quite mean what we said there, and also that's a very specific formula within electromagnetism, there's other formulas for forces and for things that mean different things.

0:16:01.3 SC: So nothing in that formula has anything to do with bodies or minds, it all has to do with electricity in a very specific theory of the electromagnetic field that was written down by Professor Maxwell and his predecessors. I think it would be a mistake to try to analogize it too closely to the eye of the self or anything like that. The fact that the letter I is used for electrical current should lead you to think of that as being related in any way to the psychological I, as in myself. Paul Conte says, "I was wondering if you had any opinions or observations regarding a recent study suggesting that dark matter is composed of very low mass bosonic particles, which can behave as a Bose-Einstein condensate and take on quantum wave-like properties on large scales." This may be related to something known as fuzzy cold dark matter. So I don't have that many thoughts on the recent study. There was a recent study, I know it's being referred to. Sorry, let's back up.

0:17:00.2 SC: The most popular candidate for what the dark matter is is the weakly interacting massive particle, the WIMP. For many reasons, it would make sense if there was a particle that was weak... Sorry, weakly interacting, electrically neutral, stable and has a mass of about the Higgs boson mass or maybe a little bit heavier mass, something like that, hundreds of GeV, at least one GeV, at least the mass of the proton or much higher. But there are other examples of dark matter candidates that are not weakly interacting massive particles, one is the axion. The Axion is a very light particle, 10 to the minus 5 electron volts, whereas the proton is a billion electron volts. So the axion is much, much lighter, but it's produced in a very different way in the early universe, so that even though it's very low mass, unlike neutrinos that are very low mass but rapidly moving 'cause it doesn't take much energy to get them to move, the axion is very low mass and almost at rest in the very early universe. So Axion still count as cold dark matter, even though they're very low mass.

0:18:05.0 SC: The idea of fuzzy, cold, dark matter or other things like that, Bose-Einstein condensate dark matter, etcetera, are other kinds of hypothetical particles that are even lower in mass. And you might know that in particle physics, mass is inversely proportional to Compton wavelength. Compton wavelength is roughly speaking, the smallest size you can squeeze a particle into. So a very, very, very low mass particle will necessarily be spread out all over the place. And the relevance for dark matter is if the wavelength of these quantum particles is astrophysical in scale, then the dynamics of those particles will be very different than particles that are point-like and just move in different ways. So I think that that scenario overall is actually interesting and promising. The difference, yeah, the reason why it's maybe not as popular as axions or WIMPs, is that axions and WIMPs were both invented for completely other reasons, they were not invented just to be the dark matter, they solve other problems and then they have bonus duty as being the dark matter, whereas this fuzzy dark matter stuff is part of a large category of models where it was purely invented just to be the dark matter. And look, maybe that's how it is, we don't know. But if you have one hypothetical particle that can solve two problems at once that's considered to be better.

0:19:28.6 SC: Now the, finally the new result that came out was a claim that certain observations of galaxies and clusters of galaxies and their gravitational lensing properties is better fitted to fuzzy very, very low mass dark matter models than it is to ordinary WIMP or axion models. I have no real idea whether or not that study is correct or not, I will leave it... I think that this is the kind of thing where even if it is correct, it's gonna need more analysis, more careful thought about it, so I'm gonna wait until that careful thought and extra analysis happens. If more and more data come in more and more analysis are done, and they continue to move in that direction, I think it would be super, super interesting and important. Sean Miller says, "Whatever consciousness is, it seems to reveal itself in organisms capable of perception. From this perspective, Physics and Philosophy, matter and consciousness meet in perception, perception seems to add something new to the physical world, which is information for an agent to act on, e.g, a measure of surprise in Shannon sense. I'm wondering if you could say more about your thoughts on information as it applies to physics. For example, does information and by extension, surprise exist in a universe without perception?"

0:20:46.5 SC: I think of information conceptually as a kind of thing that is very similar to energy, it's not the same thing, I'm not saying information is energy or anything like that, but they are on the same conceptual playing field. If I ask the question, does energy exist in a universe without perception? Well, your first instinct is to say yes, they're still particles. They have energy or whatever. Forget about details of quantum field theory, let's just make our lives easier. Think about particles moving under the influence of forces and we can assign energies to them. Okay. Then you might think, Yeah, they're particles, they have energy, energy exists, whether or not there's anyone looking at it or noticing that it's there. But there's another thing you could say, which is that without people to talk about it, the particles just do what they do. They follow the laws of motion, they don't know they're following laws of motion 'cause they're just particles.

0:21:40.3 SC: But they move on their trajectories, they obey certain patterns that are built into the fabric of the universe, so they have certain behaviors. But you don't ever need to use the word energy to describe such particles, you could just say what the particles do where they are, what their velocities are, and so forth. Energy turns out to be a really useful way of thinking about the particles because it's conserved for closed systems, you can help yourself analyzing the behavior of things, if you think in terms of energy, so it is useful to us to ascribe energy to physical systems. I think information is exactly the same way, I think you could imagine the universe doing what it does without ever referring to information. You don't need to use that kind of vocabulary, but it's useful to use that kind of vocabulary, so does information exist in the universe without perception, it exists, but there's no one there to talk about it, so it's not really kind of necessary part of that description. I don't think it's anything spooky or even related to consciousness about information.

0:22:53.7 SC: When you see a footprint on the beach, you are able to infer that there was probably a foot that passed by, somebody probably walked on the beach, there is information contained in the footprint. The amount of information contained to the footprint, I would say is the same, whether or not you see the footprint there or not, but the usefulness of the information is very different. I think it is interesting to think about how information came to be used by conscious perceiving creatures over the history of the universe, but I don't wanna give those conscious perceiving creatures credit for the existence of the information in the first place. Ali Alavi says, some people prefer not to tell their thoughts because of others reactions, for instance, they avoid discussing specific religions, differences between males and females, or Palestinian and Israeli issues.

0:23:48.8 SC: I'd like to know your thoughts about this phenomenon and subjects you have such considerations for, if any. I hope that almost everyone takes other people's reactions into account when they prefer to tell or not tell their thoughts. That's just called being polite, being a considerate person, I don't say every single thing in my head at all moments in time, I choose certain things to express and certain things not to express. Maybe, I think that I have a thought, but it's not a very interesting thought. Maybe I have a thought, but it would be rude to say it out loud, there's nothing weird or wrong about that. The general theory of when to say things and when not to say things is undoubtedly complicated and subtle, and many considerations come into play. Sometimes it's right to be rude for whatever reason, sometimes it's right to hurt people's feelings, sometimes you wanna say things and you know other people are gonna disagree with you, but you just think is the right thing to do, and it's time to stand up. Sometimes people just like to be obnoxious and therefore they say things that they didn't really need to say, but they kind of like to get a rise out of people, all of these are real human-sized things that are important and valid to take into consideration.

0:25:03.8 SC: I think the only mistake to make here is to be un-reflective and overly simplistic about questions of when you should express your thoughts and when you should not. Farun Naroshimisha says, "You've repeatedly expressed your skepticism of invoking the typicality of our own perspective, e.g in cosmology." Well, I agree, that it amounts to a leap in logic, isn't it arguable that it is a Copernican way of uploading Occam's razor? There are any number of ways of being atypical, so we shouldn't... So we usually have no basis for assuming any one of them. On the other hand, there is basically one way of being typical, so we at least have something to go on when we say, for example, what would a distant region of the universe feel like, assuming our neighborhood is typical.

0:25:45.2 SC: Well, I think that this has to be just carefully adjudicated here because there's different notions or ways in which things can be typical. I am just not typical, I'm not a typical collection of atoms in the universe, I am not a typical environment in the universe, I'm not even a typical person on earth, that's blatantly obvious in many, many ways. So it's not that we have no information and are therefore trying to do our best, we have information. When I say, we shouldn't assume we're typical, I mean we should use the information we have. And there's no reason to assume that given that information, we are still typical even after conditionalizing over everything that we know, because that information tells us very blatantly a whole bunch of ways in which we obviously are not typical. If you knew no better, then I would see an argument for saying that in some sense we're typical, but we know better, so I wanna take that seriously. When you say, "What would the distribution of the universe feel like assuming our neighborhood is typical?" Well, our neighborhood is not typical, again, we are close to a star, most parts of the universe are not close to a star.

0:26:55.5 SC: So what exactly is meant by that? Do you mean is our observable universe typical among the set of all sets of observable universes? We have no way of knowing that. You might have a specific cosmological model, in which case you can make some probabilistic statements, but I have simply no way of knowing whether or not parts of the universe outside what I can actually observe are the same as mine in the absence of that particular cosmological model, so that's why it's important to have a model and then you can reason within it. But these blanket statements about our typicality, I think are leading us astray in various ways. Brendan says, "If your wife hypothetically became religious, do you think that you... That would put friction on the marriage, or is it possible that a married couple can still be loving and supportive despite the polar opposite views on religion?" I think that depends a lot on what you mean by become religious. There's many different ways to become religious and forgetting about me and my actual wife, just thinking hypothetically about a couple. There's a way to be religious where you kind of say you're religious, but it doesn't really affect your life in any way, it doesn't affect your behavior, but you just say, Yeah, I believe in God or whatever, but you're still the same person you are.

0:28:13.9 SC: I certainly think that an atheist and someone like that could get along and have a very loving relationship, unless the atheist side of the story was more of... The atheist person insisted on some internal coherence to their partner's world views. Yeah, I would absolutely be sympathetic to a view that said, "If you're religious at all, it should affect your life," of course, again, once it depends on what you mean by religious. There's a form of being religious where you believe that God is just the universe and doesn't intervene anything that happens, then you knock yourself out. But if you believe that there's a God up there that judges you and cares about you, and wants you to behave in certain ways, and you will get punished or rewarded depending on how you behave, in my mind, if you're that person, if you have that belief, then that would have a huge effect on how you lived your life. So I could imagine an atheist being a little worried about the hypocrisy of someone who claimed to believe that, but it didn't actually affect their lives. For a lot of ways of being religious, it does affect your life very much, and it could turn you into a different kind of person, there are people who believe terrible things, in my mind, and they justify them on the basis of their religious beliefs.

0:29:34.1 SC: I would not want be married to someone like that. So I think you have to be a little bit more specific about what kind of religious beliefs we're hypothetically invoking here. Astro Nobel says, "I just read a very interesting article about the information paradox in black holes. To my surprise, a statement was dropped out of thin air about the monogamy of entanglement, it was stated that one particle, one cubit can be entangled with at most one other," and then the question goes on, but I can answer it from here. Either of the article you're reading or your reading of it was a little bit casual there, I think, there is a principle called the monogamy of entanglement, but it does not say that one particle can only be entangled with at most one other, what it says is that two particles can not be maximally entangled with more than each other at the same time. So there's a certain maximal amount of entanglement that, let's say one spin, if you have two particles, both of which have spin, if they're both in separate super-positions of spin up and spin down, then there's zero entanglement there.

0:30:42.4 SC: Measuring one tells you nothing about the state of the other. If they are maximally entangled, then measuring one tells you everything about the state of the other. They can both be in superpositions, but if they're an entangled superposition, let's say with the spins aligned with each other, then by measuring one to be spin up, you know the other one is spin down, that is maximal entanglement, and you can only be maximally entangled with one other particle at the same time. That's the principle of the monogamy of entanglement. Very often you have partial amounts of entanglement that's crucially important in the world. In fact, in the vacuum, an empty space, every mode of every quantum field that you have is a little bit entangled with every mode of the quantum field everywhere else in the universe. So that's perfectly allowed, just not at the maximum level. The amount of entanglement goes down as you get further and further apart in the vacuum in the quantum vacuum state. Yuro Michelle says, "How sure are we at this point that the fine particle found at the LHC really is the Higgs Boson?"

0:31:47.6 SC: We're basically 100% sure to the extent that you can be. We're sure enough to not be worried about that question anymore. When we first... So one, I need to back up a little bit here. What do you mean by it really is the Higgs Boson? It's like saying, do Jews and Christians and Muslims believe in the same God? Well, what do you mean by God there? The Higgs Boson is a hypothetical construct that plays a certain role in the electroweak theory of nature, it breaks the electroweak symmetry, it provides mass to electrons and other kinds of fermions and so forth.

0:32:22.8 SC: So the particle that we found is doing that, therefore, it is the Higgs Boson. You can also, however, have more elaborate models where more than one particle is responsible for these features, there are supersymmetric models with several Higgs Bosons at once, so I would say that we know that we found a Higgs Boson, an a Higgs Boson, no, a Higgs Boson. This is a Boson. And it's doing Higgs-like things, it clearly seems to be coupling to other particles in the way that the Higgs Boson is supposed to couple. Okay, we've measured that. That was not true in 2012, we had indications when we first found it that we... So what you do is you never see the Higgs Boson at the LHC, okay. What do you see is it decays into other particles, and what you can do is predict the relative rate of decay and to other kinds of particles, and you compare that with the data, so that's what we do. We didn't just see Higgs Boson there on a photograph, we saw some extra photons, some extra other particles, and both the absolute and relative amounts of these other particles were consistent with what you would expect from the Higgs Boson. Nowadays, we have much more data and it keeps saying the same thing. It keeps telling us that the decays of this new particle are exactly what you would expect from the Higgs Boson, so we are pretty sure.

0:33:47.5 SC: Tim Gianitsos, I hope I'm getting that right. Gianitsos says, "If we could isolate a group of particles from its environment that was large enough for us to measure its gravitational effect, presumably we could observe how it's wave function/superposition is related to gravity. Do we know what would happen from such an election experimental set up or could this only come from a quantum theory of gravity? Is our inability to perform these experiments just because our lack of technology?" You don't need a quantum theory of gravity for that, unless there are some proposals out there that are very, let's say non-standard, and they try to treat gravity as purely classical, they just refuse to admit that there's something called quantum gravity, so I don't find that those proposals are very promising, let's put them aside. The details of quantum gravity, as long as there is quantum gravity, don't really affect how a large, massive object in a quantum superposition would gravitate. That is just pretty straightforward. From the point of view of effective field theories, which I have sometimes talked about, and we'll talk about a lot more in the upcoming volume two of the biggest ideas in the universe.

0:35:01.9 SC: I know I will talk about it because I've written that part, I've written the whole draft, it's in the publication process now. Sometimes next year, it will come out and will talk about effective field theories. The idea that you don't need to know all the details, you don't even know what would happen in extreme circumstances at the Big Bang or black holes, you can just talk about weak gravitational fields, and every gravitational field in the solar system is weak by these standards. Weak just means you're not close to making a black hole. Under those circumstances, we know perfectly well what quantum gravity predicts almost independently of the specifics of the model. So yes, the inability to actually perform these experiments is entirely because they are just too hard to perform. When we do measurements of gravitational fields, we struggle against the fact that gravity is a very weak force, we can measure the gravitational field of things with Avogadro's numbers of particles, macroscopic thing is measured in grams or more, we can measure those gravitational fields. But that's a huge number of particles, you're never gonna keep something with that many particles free from decoherence and collapsing its wave function.

0:36:13.8 SC: So to actually have a microscopically large self-gravitating system, be in a superposition of being in two different places is very, very difficult to even imagine doing any time in the foreseeable future. Mikel Venison says, "I don't quite understand your take on the anthropic principle. In your great courses on the arrow of time, you formulate the anthropic principle as follows, If there are many different conditions throughout our universe then intelligent beings like ourselves will only find ourselves in the middle of those conditions that are compatible with us existing. What I don't understand is why you need the first clause, if there are many different conditions throughout the universe. Why doesn't the anthropic principle apply even if there's only one universe or one set of conditions?" If I can imagine two sets of conditions, only one of which is conducive to life, then I wouldn't be surprised myself, I wouldn't be surprised to find myself in that one, even if the universe with the unsuitable conditions didn't exist.

0:37:11.0 SC: Well, sure, there is a principle, which you might call the super-duper week anthropic principle, which simply says, the universe we observe is necessarily compatible with our existence. That's true. [chuckle] That's not very useful though. That doesn't tell us anything at all about anything. We already knew that. The anthropic principle that I'm referring to has explanatory power. If you imagine there was just a single universe where the conditions were the same everywhere, and it was not compatible with the existence of intelligent life, then we wouldn't be here talking about it. But if you imagine a kind of a multiverse, or at least a kind of very big universes where conditions are different from place to place, then there is a different consideration that comes in. Namely that there is a selection effect, namely, that you as an intelligent observer are not going to be privy to an unbiased view of the universe. You are necessarily going to find yourself in the subset of the universe that allows for you to exist in it.

0:38:12.0 SC: So it's not that the logical conclusion that the universe is compatible with our existence necessitates some kind of multiverse or different conditions. It's that the explanatory role played by that selection effect is different, if you have many different parts of the universe versus just a uniform universe everywhere. Vicken Vorperian says, "Is it possible to conduct a hypothetical experiment where gravitational wave interference occurs, and where areas of constructive and destructive gravitational wave interference are present? If such were possible, would sampling of areas of destructive interference yield a finding of true zero gravity in the universe and where space time is not curved? Well, yes and no is the kind of answer here. Hypothetically, you could absolutely have gravitational wave interference. I'm sure that you actually do that. Real gravitational waves go up and down, they cross by each other, and they will interfere constructively or destructively. That's true.

0:39:15.3 SC: You're not gonna detect that anytime soon because again, gravity's a very weak force. It's hard to detect gravitational waves at all. Think about light. It was very hard. It took hundreds of years for people to measure interference patterns in light, but they had measured light a long time before that. So now we're in a situation where we've just measured gravitational waves. Measuring interference patterns in them is harder than that. Okay. Furthermore, to the second part of the question, if there were destructive interference, that would not be enough to say that there's truly zero gravity in the universe, because the gravitational field is complicated. This is why you need to learn Riemannian geometry when you learn general relativity, because the way that we describe the curvature of space time is mathematically very intricate. And space time curvature has many different components. So if you had destructive gravitational wave interference, you would be zeroing out some components of what we call the Riemann tensor, the curvature tensor that tells us all the different ways in which the gravitational field is measured, all the different ways in which space time is curved, but you wouldn't necessarily be zeroing out all of them.

0:40:31.2 SC: So if what you mean by true zero gravity is literally flat space time, in some region of non-zero extent, you would not quite get that just by doing destructive gravitational wave interference. You have to work harder than that. Nikola Ivanov says, "It seems to me that there are some unstated assumptions in the Boltzmann brain thought experiment." The explicit assumptions are for an infinitely large and forever existing universe that there are random thermal or quantum fluctuations in a featureless universe, in a state of heat death, and that small fluctuations are more likely than large ones. However, there's also the unstated assumption that functioning complex structures like brains or our observable universe can pop out of a vacuum in an instant without an incompressible history of their formation. If you assume that complex structures like brains need time to develop as functioning entities, and that this time is incompressible, it's their evolutionary history that would change... I think there's a missing word here in the question. Would their evolutionary history change the discussion around Boltzmann brains?

0:41:37.1 SC: So, no, it would not, because this is not an unstated assumption. This is just a true fact, that you don't need an incompressible, evolutionary history to make a brain or anything else complex and macroscopic. By the way, it is not true that these things, that even in the conventional Boltzmann brain story, it is not true that these fluctuations happen instantaneously. It takes a long time. You basically would most likely witness a very long series of individually unlikely events assembling the brain out of vacuum fluctuations, because the most common way, the most likely way for a brain to appear is just the time reverse of the most likely future of a brain that is out there in the middle of nothing. So the reason why this is a known fact rather than assumption is because we can certainly imagine a configuration that looks like empty space plus a brain or plus a living organism or plus whatever you want to have, plus a planet, whatever you wanna have, plus empty space around it.

0:42:39.7 SC: We can imagine that in an otherwise empty universe, and we can hypothetically imagine what happens to that toward the future. We can project a little bit forward in time. And the most likely way for that configuration that we started with to assemble out of thermal random fluctuations is just the time reverse of that. It looks like a movie being played backwards. I actually wrote a paper about this with former Mindscape guest, Anthony Aguirre and also Matt Johnson. We wrote a paper about exactly this. The most likely way to make these complex structures is as time reverses of their most likely future decay paths. And those will generally be long, but much, much shorter than evolutionary timescales, or anything like that. We, you and I live in a world that is entirely conditionalized on the existence of a very strong thermodynamic arrow of time.

0:43:37.2 SC: So when we see a brain, we naturally say, "Oh, that must have arisen out of some complex evolutionary process." Just like when we see an ice cube, we go, "Oh, yes, there's probably a freezer or something like that." When you see a book, "Oh, someone wrote the book." When you see a footprint, "Ah, someone's foot was there." All of these very intuitive, sensible impressions come about because you have an arrow of time. If you didn't have an arrow of time, all of those implications, inferences would be completely unjustified. The world is not like that in the absence of a narrow time. So you can do the math and you can find that far and away the best, most likely ways of making complex systems is by randomly fluctuating them into existence over the course of many, many little sub fluctuations.

0:44:27.1 SC: Chris V has another priority question. "I've heard David Deutsch say that quantum computing is a short proof for the many world's interpretation. I believe his case is that you can devise a computation that cannot be computed in a reasonable time, even if every particle in the visible universe were acting as a transistor in a classical computer. If the computation can be completed via a quantum computer, then it can only have been completed via interactions with other worlds or similar. Is this really the case or have I misunderstood?" I believe that David Deutsch has said things like that, and I don't actually agree with the statement. It depends on what your collection of alternatives is to many-worlds. I think what that... There is an argument being made there, but two things are going on. One is, I don't count other parts of the wave function as necessarily other worlds. In particular, I don't count them as other worlds until decoherence has happened. And when decoherence has happened, then you're not interacting with them anymore. And certainly in a quantum computer, the whole trick is to avoid decoherence. So I think the different parts of the wave function are interacting with each other, but I would not call them other worlds.

0:45:41.9 SC: Other people speak differently, and I know that David Deutsch speaks differently. So that's just a different choice about what to mean when you say other worlds. But the other thing is, I do think that there's an argument here, but the argument is in favor of the idea that the wave function is real. Okay. To have quantum computing work in the way that we normally think of it working, it sounds like you need the wave function to be real. I say it sounds like that because maybe there's some clever way around that, but you certainly talk as if the wave function is actually a real thing that is interacting, interfering with itself, mattering in some way. Okay. There are versions of quantum mechanics in which the wave function is not real. It's hard to say what to think about these 'cause they generally won't tell you what is real. But they do say that the predictions for what you're gonna observe at the end of the day are the same as in conventional quantum mechanics. So those versions, the epistemic versions of quantum mechanics would still claim to be 100% compatible with quantum computing, because they make the same predictions as every other theory does. The shortcomings, they're not telling you what happens along the way.

0:46:52.3 SC: But I think the real problem with this argument is that there are other interpretations of quantum mechanics where the wave function is real, but there are not many-worlds. Hidden variable theories are that, spontaneous collapse theories are that and so on. You're certainly not ruling out hidden variable theories or spontaneous collapse theories on the basis of the existence of quantum computers. So if by arguing for a proof for the many-worlds interpretation, you literally mean ruling out the alternatives. I don't think the quantum computers really do it. Chris Roat, R-O-A-T, says, "As a former ad engineer at Google, I really like that you offer a Patreon option for ad-free listening. Ads are great when you're searching, search ads, but terrible when you wanna do other things. Display ads like listening to a podcast, watch a video, read the news or use social media. The more a creator's bottom line is based on display ads, the more their business becomes a murky cesspool. Would you consider some threshold of Patreon subscription counts or subscription value, which would trigger a full ad-free experience for all listeners? So I appreciate. Chris is looking out for the rest of the world, the people who do not subscribe to the Patreon feed. He wants no one to have ads, whether they subscribe to the Patreon or not.

0:48:15.1 SC: Look, I get it. I think that in many ways my ad set up is better than most. Wondery has been very, very good. They allow me to turn down a whole bunch of prospective advertisers. I will not advertise people who make any health claims about supplements or anything like that. Not to mention various anti-sciencey things that come across the list of possible advertisers. And they've never complained. I've been in negotiations with different web hosting services and sometimes they demand that you advertise certain things, which I just don't wanna do. And it's not that many ads either. There's a certain number, once every 15 or 20 minutes, you get an ad and so forth. Again, some of these podcasts have a much higher number of ads than that. So I think that given that there are ads, ours are pretty lightweight and not too onerous. Having said that, it is a little bit onerous. I get the fact that it's a better experience overall when you just sail through the podcast without being interrupted.

0:49:20.1 SC: Sometimes our ads are useful. I still use PrettyLitter for our cat litter, even though they haven't advertised on Mindscape for years. But I get that overall, it's an interruption to the flow of the argument. And look, it's more time for me. I have to record the ad, I have to embed it in, and all that stuff. So I don't wanna quote a number, but certainly if the Patreon subscription count was way higher than it is now, the income from Patreon would be bigger than the income from the ads and at some point there'd be no point in doing the ads. So even though I don't know what that number would be, I can absolutely imagine the Patreon becoming so popular that there was no more point in me having ads. That's pretty hypothetical right now, but that absolutely could be a possible future. So by all means, tell all your friends to subscribe to the Mindscape Patreon. Roy Thompson says, "Assuming you record this episode after the NANOGrav announcement on Thursday, June 29th, do you have any comments on what they announce?" I'm actually recording this on June 29th. The NANOGrav announcement that Roy is referring to is a recent announcement, not just by NANOGrav but by some partner collaborations, which are doing pulsar timing.

0:50:35.0 SC: If you remember the episode we did with Chiara Mingarelli, who is a gravitational wave astronomer who works on the NANOGrav collaboration, they're using measurements of pulses from pulsars throughout the Milky Way galaxy, which are very, very precise clocks. Okay. The timing is really, really on the nose and very, very regular. So when a long, long wavelength gravitational wave comes by, light years in wavelength, it can slightly move the distance to the pulsars between us and different pulsars in a way that you can actually notice by simultaneously keeping track of all the signals that we're getting from many different pulsars scattered throughout the galaxy. And in principle, you can see gravitational waves that are light years in wavelength as opposed to the ones we see at LIGO, which are kilometers in wavelength, a much shorter distance. And the announcement is that, they have for the first time seen this, at a pretty good statistical significance, but not absolutely, completely 100% settled, but it's very, very likely they have actually seen this background of gravitational waves. So what LIGO sees is typically, most often what LIGO sees is the end of two inspiraling black holes.

0:51:58.0 SC: Okay. So you have some black holes, they are tens of times the mass of the sun and they spiral in very, very, very close and they coalesce. Okay. And what you're seeing is that chirp, right at the very end where these two black holes collide with each other at the end of a long and spiraling process. Now you might ask, why don't you see the whole spiraling in, which also does give off gravitational waves? Well, for one thing, the amplitude is lower. When the black holes are moving more slowly, the gravitational waves are smaller. They're lower amplitude than when they're nearby. But for the other, the wavelengths are different. When the black holes are far away, their wavelengths are longer and LIGO can't see them. LIGO is a four kilometer arm. It is tuned to that wavelength more or less. So NANOGrav has a much, much broader... Not necessarily broader, it is broader, but that's not the point longer baseline, the pulsars are far away, light years away.

0:52:57.2 SC: Okay. So you're looking at much lower frequency, longer wavelength gravitational waves. So you're not seeing individual events. You're not seeing two black holes spiral into each other and coalesce. You're seeing a background of many, many binary inspiraling black holes. And because the amplitude is lower when they're far apart, you're seeing binary, super massive black holes. You have to make up for the fact that they're further apart. Therefore, the gravitational waves are weaker by making them stronger, by having the black holes be bigger in order to be visible. So there are many such things, 'cause you're not waiting until that last moment. The thing about the LIGO events is you only get a moment to see them, right, then they're gone. Whereas the NANOGrav signal comes from binary black holes that are sort of in stately orbits, gradually doing the same thing for millions of years before they will eventually in-spiral and coalesce.

0:53:58.8 SC: So we're not seeing one or two pairs of black holes, as far as we know, we're seeing a background caused by many of them. I don't know actually the details. This is too soon after the announcement for me to have actually looked at any of the papers. So had I done this two days ago, this AMA, I would've had to say, well, I don't know, maybe it's this, maybe it's that, but my impression is that what they saw is what they hoped to see. Okay, so they're... Well, I shouldn't say hope to see 'cause maybe they hoped to see something much more dramatic and surprising and they didn't see that. What they saw was what they optimistically expected to see. Let's put it that way. Which is great. All of these kinds of things, including LIGO and NANOGrav, they're just the beginning. They're just the first detection of a new kind of thing.

0:54:48.6 SC: And in astronomy, when you look at the universe in a new kind of way, you always end up being surprised. I can't tell you ahead of time the way in which we will be surprised. Maybe there will be more such black holes or fewer or maybe they're closer or in different kinds of galaxies. Maybe we can follow them up with different kinds of observations to locate where some of the individual sources are. Maybe we will find different sources of a gravitational wave background, like a phase transition that is very violent in the early universe or something like that. Or cosmic strings. Who knows? We're just starting. So I think that the signal that's been seen is makes sense. It's the kind of thing that they were hoping to see and predicting. And we'll have to see what we learn from further measurements of that signal. Okay. I'm gonna group two questions together. One is from Dale Echo. He says, "Inspired by your podcast with Tim Nguyen. I often hear legitimate scientists say they have better things to do or they don't want to give questionable ideas a platform, conspiracy theories, anti-vax, etcetera. This seems reasonable, but do you ever fear that these things already have platforms and by scientists not directly engaging and exposing their flaws, it empowers some of the most negative parts of society?"

0:56:05.2 SC: And then Oleg Rodinsky says, "Regarding the latest controversy with Joe Rogan, do you think there is an obligation from a wider scientific community to stand up against crackpots with a wide reach? And should this be somehow better managed in some more structured manner instead of voluntary, like it is now? Because as you yourself mentioned, debate and public rhetoric is a skill one needs to work on, something for philosophy of science departments to take on perhaps. Yeah, I think that this is a difficult question. I absolutely think that there is a legitimate worry about giving obviously wrong ideas too much attention. Okay. And this is not just my opinion. This has been shown by people who study information and misinformation and so forth for a living. When you give attention to bad ideas, those bad ideas very often become more popular. But that's not universal or absolute. I think that there are right and wrong ways to do this, to counter bad ideas in ways where you're not just giving them attention, you're really undermining them and showing why they don't work. I do think that we should have, let's say, a little more activity on the part of scientists and pro-science people in combating these very publicly visible bad ideas.

0:57:28.8 SC: It might not be in the form of a public debate or something like that, but I do think that there's a danger that scientists don't wanna get their hands dirty, right? They don't wanna sully themselves by stooping to the level of these conspiracy theorists and so forth. And some people's minds are made up. That's absolutely clear. Some people are just not ever gonna change their mind about this or that conspiracy theory. And I do think that scientists do that... Make the following mistake. They see the people who are not gonna change their minds and they say to themselves, "See, people never change their minds, so we're gonna ignore them. We're just not gonna pay any attention." I think that's a mistake because there's other people out there who do change their minds. Just the fact that some people won't and some people are lost causes is usually not the end of the story. It's usually the case that there's a vast middle ground of people who haven't yet made up their minds. And I do think that those people are worth reaching out to.

0:58:29.1 SC: Scientists are accused sometimes of being elitist and aloof, and that's because sometimes they are, elitist and aloof. And I think that that's bad. But like you say, Oleg, in the question, there are bad ways to do this. There's plenty of scientists who are top-notch scientists and are really good at understanding how the world works and how, whatever, the landing on the moon or vaccination strategies or whatever, and yet would be bad at explaining them to people who are not necessarily open-minded about it or combating someone who wants to be against that in some obvious way. So you have to have the right skillset to do this. And I do think that, just like for other forms of outreach, the field has a responsibility to get its hands a little dirty in there and send its best out there to combat these ideas, but individuals don't because they would probably be doing more harm than good.

0:59:31.8 SC: I do think that news organizations have at least as much of a responsibility as scientists do. News organizations very often bend over a little bit too far to give equal time to good ideas and bad ideas. News organizations should serve a function of separating the good ideas from the bad ideas. And by all means, if there is a news story, cover it. But you don't have to act like people walked on the moon as equally viable to people didn't walk on the moon. [chuckle] You don't need to give both sides to that one. And that's complicated by the fact that the moon hoax conspiracy theory is not something that has a lot of support because there's no vested interests who are interested, have any incentive to support it. But things like anti-vax or climate change nihilism and things like that, these are bad ideas that have vested interests supporting them. So we need to do a little bit more to combat them. And I do think that maybe a debate can play a role in that, but it has to be under exactly the right circumstances. I certainly don't blame scientists who don't want to individually get involved with this, on the grounds that they would not be good at it. I think that good for them for having the self-awareness to know that that would be bad.

1:00:56.2 SC: Devin Jones says, "Can a black hole accretion disc be hot enough and have enough pressure to a trigger nuclear fusion? And if so, is there any value to thinking of an accretion disc as sort of a very flat, extreme star?" Well, the short answer is, I don't know. [chuckle] I suspect. I don't see any reason why in the laws of physics it wouldn't be hot enough to trigger nuclear fusion, so I suppose it's possible. I don't think that there's much value in thinking of it as a very flat extreme star. A star is more than a place where nuclear fusion happens. It is a gravitationally self-sustaining quasi-equilibrium place where nuclear fusion happens. So in other words, a star is very specifically a collection of matter, which is in what we call hydrostatic equilibrium. There is a force of pressure pushing out on the outer layers caused by the nuclear fusion at the center, and there is a force pushing in due to gravity and those forces balance each other. And that's why we say hydrostatic equilibrium.

1:02:00.9 SC: I don't think that anything like that is likely to happen in the accretion disc of a black hole. So even if there were nuclear fusion, I don't think it would really be very useful to think of it as a kind of a star. Adam Rotmil says, "In reflecting on the contributions of Einstein and his contemporaries at the Fifth Solvay Conference, are there any unresolved questions or untouched hypotheses from that era that remain not fully integrated into our modern understanding of theoretical physics? Is there a particular concept or theory posited by Einstein that you believe we haven't yet fully reckoned with?" Well, mostly the answer is no, there. I don't think that that's the right way to think about Einstein's contributions at Solvay Conference, etcetera. He was more or less... I will defend Einstein to the extent that he understood quantum mechanics, and I actually am on his side about most of his opinions about it.

1:02:57.0 SC: But his contributions, other than the EPR experiment, obviously the EPR thought experiment and the whole idea of entanglement, which is kind of a big deal, and Einstein should get a lot of credit for that. But in terms of model building, in terms of proposing an alternative to quantum mechanics, as it was understood at the time, I don't think he think that he made much progress. He was more of a gadfly, he was more... The whole point of the EPR experiment was not to say, here is the right way to think about quantum mechanics. It was simply to say you're thinking about it wrong. Okay. And that can be a valuable contribution, but I don't think that he offered a clear alternative that was very compelling. Nor do I think that I'm waiting for such an alternative, 'cause I think I have it in the many-worlds interpretation. Different people think they have different versions of it, but I think that we've gone beyond Einstein in those ways.

1:03:53.0 SC: As a little tiny footnote here, I just don't like... I think that this way of thinking is probably never very good, this way of saying like, "Oh, there was a brilliant person in the past. What were their insights that we're ignoring now?" Brilliant people in the past were brilliant, there's no doubt about that. But almost always we've moved beyond their thoughts because we've learned a lot. Einstein didn't know about Renormalization and quantum field theory. He didn't know about black holes. There's a million things he didn't know about. So why in the world would I be asking what Einstein had in mind and whether or not we've followed up on that? Einstein might be much smarter than I am, but I know a lot more about physics in the modern way of thinking about contemporary fundamental physics than Einstein did because he's been dead for a long time. So I think that the place I would much rather ask what ideas some smart 25-year-old graduate student has than ask what ideas Einstein had today.

1:04:56.4 SC: Arca Lokos says, Arca Loko, and I don't know, I can't read the Greek letters very well. "Are there any undergraduate level quantum mechanics textbooks that don't assume the standard textbook or Copenhagen approach, but rather assume another interpretation, such as hidden variables or many-worlds? And would this make much of a difference for one just learning the basics of quantum mechanics?" I don't think so. I doubt it. Certainly not if you're really looking at undergraduate level quantum mechanics textbooks that are meant to be pedagogical. Okay. I mean, you can read very easily something like David Wallace's book, the Emergent Multiverse, which will explain to you the many world's way of thinking about things. But it's not meant as a quantum mechanics textbook. It won't help you solve the hydrogen atom or something like that. As I've mentioned, I am slowly, slowly, slowly working on a quantum mechanics textbook myself, but even mine will not be beholden to many-worlds or any other interpretation of quantum mechanics because I don't think that we're done.

1:05:58.8 SC: I think that it's very, very likely that many-worlds is the right answer, but there are others smart people who think other answers are right. And so I'm gonna take that into consideration. I'm not... My opinions are not always the end all of these things. But there's a deeper issue here, which is that it doesn't matter, honestly. It doesn't matter which approach you have, which of your versions of the foundations of quantum mechanics is your favorite one when you are first learning quantum mechanics. What I call the textbook approach to quantum mechanics is completely inadequate as a fundamental theory of nature. But it is completely adequate as a way to learn quantum mechanics and a way to do calculations and figure out, okay, what is the set of electron orbitals in a hydrogen atom, or something like that. It's fine for that.

1:06:47.9 SC: So in my book, I'm not gonna be pushing people on many-worlds or anything like that. I will have... The current plan anyway is an appendix where I talk about some of the different possibilities. I think that a lot of current textbooks say bad, untrue things about the foundations of quantum mechanics. That's not good. I wanna do better than that. I wanna say correct things, but which one you choose doesn't matter. For the purposes of learning quantum mechanics and doing calculations, simply saying, when you make an observation, it appears like the wave function collapses according to the born rule is a 100% fine. All I ask is that you then admit that can't be the final answer. And when we want to be more precise and go beyond the level of calculating hydrogen atom orbitals or Higgs boson decay channels, then we need to think more deeply. Christian Hoffman says, "This question about black holes has been on my mind for some time. Suppose I'm orbiting a black hole just above its event horizon and I stick my hand in. No matter what I do, I will never be able to pull my hand out again. But what would I actually feel like if I tried? I'm imagining it as like my hand is encased in a large block of cement and it's simply pulling the rest of my body towards it. I know you've mentioned several times that one wouldn't notice it when crossing the event horizon, so I guess my intuition must be wrong here."

1:08:12.6 SC: It's a little bit wrong, your intuition, but that's okay. I mean, most of us don't have good intuitions about what happens near the event horizon of a black hole. It is true that if the black hole is big enough, super large black hole, you would not notice when you crossed the event horizon. But the thought experiment you're setting up is not crossing the event horizon. You are outside the event horizon and your hand is inside. That's a different situation because you can't just say, "I'm orbiting the black hole." There are no circular orbits of a black hole right outside the event horizon. If you want to be outside the event horizon, something has to keep you there. Some force, whether it's a rocket ship or a wire that's attached to something very far away holding you up. And in that situation, if you put half of yourself or part of yourself, your hand on one side of the event horizon, and you on the other side, there will actually be an enormously strong tidal force. A tidal force being the differential force between different parts of your body. So the short answer is your hand will be ripped off your body and you would definitely feel it, even though if your whole body just passed through, because then your whole body's feeling the same gravitational force. You might not notice anything at all.

1:09:29.9 SC: Anyway, don't do any of these crazy experiments when if you actually have a black hole nearby. Leland Beaumont says, "What banged? What is your best description of the energy from which the universe emerged? What was its source, its size and its nature?" The short and accurate answer here is that nobody knows. It's probably not even right to ask the question, what banged? Because the question being begged is, is there something that banged? [chuckle] And that's not the right way to think as far as anyone knows about the beginning of the universe. I've said this before, but I keep trying to say it using different words, 'cause it has different resonance for different people. We don't... We are not able to say what happened at the moment that we talk about as the Big Bang. What that moment is, is an extrapolation into the past using Einstein's theory of general relativity. And the extrapolation tells us that if we go into the past, there's a moment of time where the density of matter and energy is infinite. The curvature of space time is infinite and so on. But that does not mean that the density of matter was infinite, the curvature of space time is infinite or anything like that. It means that that's the prediction of general relativity.

1:10:49.2 SC: But you're making that prediction in a regime where you know general relativity is not right. So what are you doing? What are you expecting The right thing to say is that there is, if you extrapolate general relativity backwards into the past, you reach a point where you don't know what happens. That's it. That's all you can say. Now, if you're a theoretical physicist, you can imagine ways to go beyond general relativity, either with quantum mechanics or extra dimensions or whatever, different kinds of things that go beyond our current understanding and say, maybe it's this, maybe it's that. And that's perfectly okay. But we don't know, is the short answer. We don't know what, if anything, there were. We were able to trace empirically what things were like right after the Big Bang, a second after the Big Bang. We have a pretty good idea of what was going on because the world was doing nucleosynthesis, and we can see their reaction products from that. But actually at the moment we just don't know. We do know that there's no need for anything to have banged. As far as current theory is concerned, the universe could simply have had a first moment.

1:12:01.3 SC: As far as we know, once again, the total charge of the universe is zero. The total energy of the universe is zero. You don't need to source or anything external to make it happen. But like I said, we don't know what actually did. David Dubrow says, "In the last AMA, you said decoherence occurs when a system you are paying attention to becomes entangled with the environment, which is the degrees of freedom you're not keeping track of. It seems like this brings subjectivity back into the definition of decoherence, similarly to how entropy is described in terms of microstates that appear the same from a macroscopic point of view. I thought many-worlds got rid of such subjective macroscopic concerns. What am I misunderstanding?"

1:12:42.6 SC: I don't think it's true that many-worlds gets rid of a macroscopic element in, or a subjective element in how we describe the universe. At some level, many-worlds is simply the statement that there are wave functions that always obey the Schrodinger equation. That's it. There's no mention of worlds, there's no mention of decoherence, there's no mention of branching. But those things exist in exactly the same way that tables and chairs exist, even though they are not mentioned in the standard model of particle physics. That's why David Wallace's book about many-worlds is called the Emergent Multiverse. And when things are emergent in higher level, there will be subjectivity that it comes in when we talk about how we describe the macroscopic world, how we course screen it, what information we keep track of, what information we don't keep track of. God does not talk about branches of the wave function, of the universe. God just talks about the wave function, what it is, the whole thing all at once.

1:13:38.1 SC: But we human beings with much less information and much less calculational capacity, we find it useful to talk about branching, 'cause that's where we live. That's what we can observe. That's what we can see. But when branching happens is something that we describe much as we describe, like you say, how entropy increases in a way that involves some useful subjective choices. Once you make those choices, once you say what is the course grading that gets you entropy or what is your division of the world into system and environment, then everything is objective. Then everything just obeys the laws of physics. But in going from the microscopic world to the macroscopic description, there are some subjective choices involved and that's perfectly okay. We're subjective people. Joshua Hillerup says, "Do you know if there's research on whether studying moral philosophy actually makes people better able to make moral decisions for whatever better might mean?"

1:14:35.9 SC: I'm not super familiar with this, but I do know that there is research on that and the answer is it doesn't make people better. Now, the research is not comprehensive or anything like that, but I do believe that, as I vaguely recall, there are studies that philosophy professors who teach ethics are no better at being ethical in the real world than regular people are. And in some sense that's not surprising to me. I think that this kind of education doesn't make you better. It makes you better equipped to be better if you are already oriented toward being better, but maybe you're not. If you're not oriented toward being a selfless person, for example, then being taught philosophical theories of selflessness are not going to make you more selfless. I don't think that that should be expected even, I think that's not really... I don't think of the study of moral philosophy as intended to make people more moral. I think that it is intended to help people understand what it means to be more moral. Whether they're going to be more moral is up to them.

1:15:48.6 SC: Sean Virtue says, "I just played a couple of games one called Fez, in which a two dimensional character in a two dimensional world is granted the power to perceive a higher third dimension. And one called 4D Minor in which the three dimensional player character can... In which the three dimensional player character can create a pair of glasses that allows them to interact with a higher fourth dimension. I believe they've helped expand ability to complex geometry in spacetime. And I wanted to know your thoughts on the role of games in comprehending advanced concepts in physics." Well, it depends on what you mean by a game. I suspect that the important aspect of these games is the simulation aspect or visualization or virtual reality aspect. If we think of a game as something that has a goal that you can win or lose, that you're oriented towards doing something, I don't think that aspect of it, even though it's fun and I'm all in favor of it, is necessarily pedagogically helpful or harmful. It's just there. But I do think of the ability to simulate different circumstances can be very, very helpful in comprehending advanced concepts in physics.

1:16:54.5 SC: I haven't thought about it a lot. I've not put a lot of effort into thinking how one might do this. So I don't think that my thoughts are very well formed. But I wouldn't be surprised because alot of the difficulty in comprehending advanced concepts in physics is that they are falling well outside our everyday experience. So what a good virtual reality or visualization can do is help expand what we have as our experience background, so I'm all in favor of things like that. Aaron Bowden says, "Thomas Hertog discussed quantum effects at the beginning of the universe and beyond the observable universe. But will we return to a quantum fuzz at the end of time? You've discussed the big freeze in previous episodes, but do you think that there will be interesting quantum effects when energy densities fall to zero?" In some sense there are, but I don't think that fuzz is the right word. What's going to happen is that the universe will equilibrate. It's like a box of gas coming to its maximum entropy state. When you think about the macroscopic features of that box of gas, nothing is happening. It's just sitting there.

1:18:03.6 SC: So I think that the important quantum effect in the future of the universe, if you believe in many-worlds, is that there will no longer be a distinction between the different worlds, because all of them will look basically the same. All of them will look basically like equilibrium. So there'll be no sensible way to divide the worlds into different worlds with different past histories. Once again, I haven't thought about that too carefully, but I think that's the general thing that we would expect. I'm not sure what you mean by interesting quantum effects, so maybe that doesn't qualify. Bo Parizo says, "I understand your wife knows Brazilian jiu-jitsu. What do you know of jiu-jitsu ? And how do you or don't you understand/relate to it?" Yeah, I know very little about it. Like many kids, when I was young, I took some lessons in karate and judo, so I have that kind of very young, not very deep level of knowledge of martial arts in general. But I have not studied anything about jiu-jitsu. Jennifer has not tried to teach me anything. It's something that you have to dive into. It's not something you do casually. And I spend my time right now doing other things, like making podcasts, so I haven't gotten into that particular thing very carefully.

1:19:16.0 SC: Ahmad Cheaker says, "My favorite biggest ideas in the universe video was your last one about the philosophy of science. Do you ever think you would write a philosophy of science book?" Depends on what you mean by a philosophy of science book. Certainly books that I have written have an awful lot of philosophy in them, whether it's From Eternity to Here or Something Deeply Hidden or The Big Picture. Some books don't have that much like the Higgs boson book or even The Biggest Ideas books so far have been mostly straight forward science, but I mix in philosophy there. If you mean by a philosophy of science book, a more technical academic book like a monograph, a research book, I could imagine doing that. I have various ideas about things that I've written about at a sort of casual, popular level that would be served by taking more seriously and rigorously and treating them more academically, that could possibly happen. The philosophy of Cosmology, for example, is a field where I think there's lots of things to say that I could maybe say some of them anyway.

1:20:21.8 SC: Maybe there's something to be said about emergence or something like that. I'm not really sure. I haven't thought about it too deeply. If what you mean by a philosophy of science book is sort of more traditional philosophy of science as meta science, as taken as its study not the universe but science. Thomas Kuhn, The Structure of Scientific Revolutions, or Paul Feyerabend, Against Method or Karl Popper and his Falsifiability stuff. All of that is the philosophy of how science gets done. I don't think I'm gonna write a book like that. I think that's important and interesting stuff. It's not my biggest interest. My interest is almost always in how the universe works, not in the practice of science. Jason Brinkerhoff, says "While in Rome on my first vacation in 10 years, I had the great pleasure of seeing Joel Holmes play at Gregory's Jazz Club. When you travel, do you often visit jazz clubs? Do you have a favorite city or country to visit for music?" Not so much, to be honest. I'm trying to think if I've ever visited a jazz club in Europe or Asia or anything like that, and I can't remember, so it wasn't a very memorable experience, honestly.

1:21:34.2 SC: I do do music when I travel, but if I'm in Europe, it's much more typically classical music. I think that Europe is way better at classical music than we are. They will have random concerts in church or something like that that are free and candlelit, and it's beautiful and lovely to just stumble across something like that. So I do seek that out and I've had wonderful experiences there. I think probably the jazz is better here in the United States, as far as I know, or at least I know better how to find it, let's put it that way. I know where the good jazz is much better here. So as far as cities are concerned, I lived in Chicago for a long time, I very well know where to find the good jazz there, at places like Andes or the Green Mill or what have you, and other places like New York. It's just pretty easy. New Orleans, it's just pretty easy. So I am definitely interested in doing that. But yeah, if I'm going to Europe, then it's probably more classical music. If I'm going to Asia, where I've not been nearly as much, but again, I'm probably not going to go there for jazz. I did go my one trip to China, I went to the Beijing Opera, which is amazing, but I don't have any enough experience there to offer anyone else any advice about what to do.

1:22:50.3 SC: David Maxwell says, "Is there still space for individual genius to make intuitive leaps that change fundamental physics and cosmology, like classical mechanics, relativity, and quantum physics, or have our collective knowledge and resources advanced to the point that all intuitive questions have been asked and only iteration remains?" The thing is, you never know about questions like this. If you ask someone in the year 1800, is there still space for an individual genius to overthrow classical mechanics? Someone might have reasonably said, well, probably not. Classical mechanics works really well, they wouldn't have foreseen quantum mechanics. So it's possible that something like quantum mechanics will just be true, continue to be true indefinitely into the future. But it's also completely possible that something will come along that is much more deep and fundamental. Quantum mechanics is not going to go away, just like classical mechanics didn't go away when we invented quantum mechanics. It's a limit of quantum mechanics.

1:23:47.5 SC: Sometimes you have a good scientific theory that you're fond of, and it turns out to be 100% wrong. It's just gotten rid of. Ptolemaic astronomy just doesn't really have any useful remnants to it. But other times, you have a good scientific theory where it might be improved upon or there might be a deeper theory underlying it that is discovered. But the theory that you're fond of is not just going to go away. That's the case for classical mechanics, for relativity, for quantum mechanics. But it's still absolutely possible, like I said, that something deeper, something very, very fundamentally different will be discovered someday down the road. But maybe not. That's all we can say. Sorry. Tim Converse says, "As I understand it, the Bekenstein bound limits the information that can be stored in a region of space. Any attempt to store more information in that region would result in a black hole. Does this implicate occasion go the other direction? Is there a sense in which any black hole has had a maximal amount of information stored in it?" To be honest, I don't like the way of thinking about the Bekenstein bound or black holes in terms of information, because the word information means different things in different contexts.

1:25:00.6 SC: And there's a sense in which you can make these statements, but there's a sense in which they're completely the opposite of true. Like entropy makes sense to me when you talk about this. I do think that a black hole is the maximum amount of entropy that a region of space can have. And probably, we think there's good reason to believe that we can think of that as entanglement entropy. Entanglement between the degrees of freedom inside the black hole and outside. But is having a large entropy having a lot of information? In some sense, it's the opposite of having a lot of information. We know nothing about the system except that it's high entropy. There's nothing specific that we know about it. If you had specific arrangements, then you would have a lower entropy situation. But I know what they mean because also you can think of entropy as counting the number of degrees of freedom that could possibly be in this high entropy state. And in that sense, there is information contained in the thing.

1:25:57.0 SC: So I'm avoiding the question because I don't think it's the right set of words to attach to these issues. But if you switch the question to an entropy question, then I wanna say yes. I want to say that the black hole is the max amount of entropy you can have in a region. And then you're saying, is there a sense in which a black hole has a maximum amount of entropy? Well, we're not sure about that because we don't understand the microphysics behind the black holes. We don't understand what are the degrees of freedom that we are tracing over, or whatever you wanna call it, to talk about the macroscopic framework of the black hole. So it is certainly possible that it takes time after forming a black hole for it to become entangled with the rest of the world. It's also possible that it's pretty quick, that it's essentially instantaneous. That's something that I myself am not going to opine on. But as long as you let the black hole settle down into its equilibrium state, then, yes, a black hole has the max amount of entropy that you can possibly have in that region.

1:27:08.2 SC: Michael Shillingford says, "In one of your last podcasts you mentioned that neither of anyone's later multiversal descendants are the same person as the person before the multiverse split. Why do you feel it's that way, as opposed to saying both descendants are the same as the prior persons, or that they are all the same person, but only to a certain degree?" I think that this is just a matter of improving our understanding, our precision, when we're talking about self identity in a world where there is branching and multiple universes. If you thought there was only one universe, then personal identity would be a fairly simple thing. Not 100% simple, but at least you're born, you grow up, et cetera, and then you die, and you are one person at each moment in time. Now, strictly speaking, your different versions of yourself at different moments of time are not precisely the same self. They don't have exactly the same memories, exactly the same position in space. They're not even made up of precisely the same atoms. But there is a clear, convenient sense in which we can trace some continuity across the years of your life time.

1:28:15.7 SC: When you now have many-worlds and each individual person becomes multiple copies, that's no longer true. There is no longer a unique single person that you can trace from birth to death. So therefore, the fact that even in the original single universe way of talking, you really should distinguish between yourself at 05:00 PM and yourself at 06:00 PM as two different people, just with connections between them. That goes from being optional but inconvenient in the single world case to being necessary in the multiple world case, because otherwise you start asking, well, after this branching happens, which one of those two future people will I be? And that's not a sensible question to ask, 'cause there's no such thing as which one you're going to be. Those are going to be two people, and they're separate people. They can't talk to each other. They can't interact. They're not the same person by any stretch of the imagination. They've witnessed a different measurement outcome for whatever quantum measurement you're going to do. So it only makes sense to treat them as different people. And in that case you have to say that they're different than the person that they were a few hours ago.

1:29:24.8 SC: Again, you always should have said that if you were being careful. But in the many-worlds context, you have to be careful if you want to make sense of what you mean by personal identity in that many-worlds scenario. Robert Ruxton Drescue says, "I've been a materialist all my life, but lately I find idealism as a much better metaphysical ontological framework. Everything is mental, and the brain doesn't produce the consciousness. Its activity is just correlated with it. The brain simply localizes consciousness in space time. I know that you are a physicalist. But have you considered idealism yourself?" Sure, I've considered it. I find essentially nothing attractive about idealism as a point of view. So idealism for those of you who don't hang out on these particular street corners. That doesn't mean you're idealistic in the sense that you hope for the best in the world. It's idealism in the sense of taking mind or mentality as central to how we think about the universe at the deepest level, as opposed to physicalism, where you think of the world as a physical stuff and consciousness or thinking is just an emergent phenomenon that comes out of the collective behavior of certain parts of that physical stuff.

1:30:37.7 SC: So idealism to me, both leans in the wrong direction and helps with nothing. By leans in the wrong direction, I mean we have an idea of what a mind is. We have an idea that your mind is different than my mind. We have different thoughts. [chuckle] We have different ways of thinking about the world, different memories, all things like that. And we have different pictures of the world. We have different sensory impressions of the world, different models, different theories. But guess what? The models that we construct of the world, even though we're different people, are extremely compatible with each other. It's not like I have general relativity as the true theory of gravity and you have Newtonian gravity. And we're both right. One of us might be more upto date than the other, but the world that we claim to be describing is the same world. That just seems wrong. If mentality were first, why would it construct the same world for everyone? Why not have different worlds for everybody. Now, of course, you can fix that. You can say, well, my kind of idealism doesn't have that. Okay, fine, but you're already swimming upstream, is my point.

1:31:49.9 SC: And then the fact that it doesn't help with anything is the physical world obeys certain rules. The world has laws of physics. They describe what happens in the universe. So if I'm comparing two scenarios, one of which says there's just the physical world, it does what it wants to do, and the other is there's sort of some mentality, some consciousness that exists that is not simply supervening on the physical world and the physical world arises out of that, what does that get me? [chuckle] I don't think it gets me anything at all because I think that people under appreciate the extent to which consciousness is intertwined with behavior. When I think about consciousness, my consciousness affects my behavior in a very definite way. I am conscious of something, therefore I react to it. I can tell you what it is that I am conscious of. That is my behavior. And all of that behavior is 100% well described by physicalism. So I see no place for anything other than physicalism to affect that behavior. Unless you're really just going to throw out all the known laws of physics and change them in some way. In which case, more power to you. Good luck with that. I've seen no even halfway plausible suggestions to how that would ever work.

1:33:10.3 SC: But if you could do it, then that's fine. And if you don't do it, then your idealism is not doing anything. It's just going along, giving you a warm, fuzzy feeling about where all this physical stuff comes from. So I think there's plenty of hard work to be done in showing how the phenomena that we associate with consciousness and thinking and et cetera, are all generated by physical stuff. But that's doable. That's just science. That's the job that we have in front of us. There's no major obstacle to getting it done. Anonymous says, "Momentum and position can be swapped in Hamiltonians, I've heard you say. Does this mean there are analogies between derived quantities of position and derived quantities of momentum?" Well, this is a tricky thing, so I have said things like this. If you want to hear more about what all these words mean, pick up The Biggest Ideas in The Universe, Volume One, Spacetime in Motion. Because I talk specifically about how to think about position and momentum.

1:34:09.9 SC: And just the very, very brief version is we typically hear about momentum in our intro physics course. We say, okay, there's a particle, let's say, let's keep our lives easy particle classical mechanics. It has a position, it has a velocity. And then, you define the momentum to be the mass times the velocity, and you show that the momentum of a whole bunch of particles is conserved over time. In the Hamiltonian formulation of classical mechanics, those are not the words you say. And it's unfortunate that we use some of the similar words, but they mean different things. So in the Hamiltonian point of view, you don't say, "I have a position of the particle as a function of time. I take its derivative to get the velocity, and then I multiply by mass to get its momentum." What you say is, at every moment in time, you have both a position and a momentum. It says that one moment of time, it is not a derivative. It is not a little rate of change of anything. There is something called the momentum.

1:35:07.0 SC: And then it is not a definition that momentum equals mass times velocity. It is an equation of motion. It is something that the momentum does. It doesn't have to do it. In the world of the classical way of... The Hamiltonian way of describing what the world is, momentum and position are totally separate things. But just like the position of a particle overtime, there's many trajectories you could imagine for it, and only one obeys the equations of motion. In the Hamiltonian version of classical mechanics, there's many things that momentum could do, and only one of them is obeying the equation of motion, that is being the mass times the velocity. That's what it is. So in that way of thinking, in this Hamiltonian picture, at the deep down level of what Hamiltonian mechanics is, there is no preference for position versus momentum. These are two quantities that are on an equal footing. Okay, that's what I like to say. Position and momentum are on an equal footing. It's not quite that they can be swapped. That's not quite right. You can redefine new variables that effectively swap them. That is true. But what I'm really saying is that there's no preference for position and momentum.

1:36:18.7 SC: But that's always a prelude to saying, of course, in the real world, [chuckle] there is a difference between position and momentum. There's many differences, the most obvious one of which is interactions are local in position, billiard balls bump into each other when they hit the same position at the billiard table, not when they have anything to do with each other's momentum. Okay? So you have to be very, very careful about analogies between derived quantities of position and derived quantities of momentum. Maybe there are other possible laws of physics, other possible Hamiltonians, in which they're on an equal footing. But in the actual Hamiltonian of the actual world, there is a clear distinction between position and momentum. And that's okay. Nalita S says, "What do physicists mean when they say that space and time are on an equal footing in special relativity? Speaking of equal footings, it seems to me that they regurgitate the statement with little precision as to what they truly mean. Would you kindly clarify this point?"

1:37:17.6 SC: Sure. They mean something very, very precise. In fact, what they mean is there is a four dimensional spacetime. That's the universe, the classical universe, anyway. Forget about quantum mechanics. But when you and I talk about space and time in relativity, those are not things that have any objective reality. They are not absolute. In Newtonian mechanics, yes, there is something called space, and separately there is something called space. Sorry. There's something called space, and there's separately something called time. And you can kind of glue them together if you wanted to, to make spacetime. But everyone agrees on what is space and what is time. In relativity, that's not the way it works. There is one four dimensional thing which we call spacetime, and you can divide it up into space and time. But people will disagree on how you divide it up into space and time because there is no absolute fact of the matter what is space and what is time separately. So you see the distinction.

1:38:18.8 SC: In Newtonian mechanics, there is a fact of the matter what is space, what is time? You could, if you wanted to, glue them together. In relativity, the only fact of the matter is that there is spacetime. You can, if you want to, divide it into space and time, but you might not agree with someone else's way of doing it. There's an infinite number of ways to do it, all of which are equally good. That's what they mean by saying that space and time are on an equal footing. They're both coordinates on a four dimensional spacetime, and different people will choose different ways of expressing those coordinates. Michel Korbuko sorry, Korrupco says, "After years of listening to Mindscape, and especially these AMAs, I noticed that some of my opinions become more aligned with yours, not necessarily because I agree with them, but simply due to long exposure. I did have some priors, but they slowly drifted without my conscious effort, and I only notice it comparing my notes from the past. How do you oppose such a process yourself, especially when it comes to science? Is it necessary to balance exposure to different sources in order to keep a high degree of intellectual independence?"

1:39:25.3 SC: Well, maybe my opinions that you're agreeing with are just correct. You got to consider that possibility at least. But I know what you're talking about. To be honest, maintaining a high degree of intellectual independence is not my primary goal. It's a goal. My primary goal is being right. If somebody else is really, really right. And I listen to them talking and I find, wow, you're just right all the time. And for good reasons. Not just for random reasons, for explicable reasons that you can offer and I can think about and understand, then I'm very happy to take over their points of view that they've convinced me of. I think the point is not intellectual independence, but I think the point is knowing why you believe certain things. It's not where the belief came from or the confidence you have in that belief, it's being able to articulate reasons why those beliefs are yours. That's what I would consider to be important. And that's not a matter of disbelieving or being skeptical or whatever.

1:40:27.1 SC: As Hugo Mercier said, we're actually super good at being skeptical. We're too good at being skeptical because we're skeptical of things that we should take seriously too easily in the world. It's not a matter of being skeptical. It's a matter of knowing what the sources of support are for the beliefs that you have. And to be fair, we human beings are very finite, very burdened. Life is short. You can't know everything. So sometimes your reasons for believing things are, "Look, I'm not an expert in this, but I trust this person's point of view about it." That's perfectly okay. It shouldn't be everyone's reason to have certain beliefs about any certain topic, because some people's job should be to really think about every possibility and dig deeply and make sure they know what's going on. But there are just too many questions to ask in the universe to do that process for every single possible question you can ask.

1:41:25.2 SC: So again, I would not worry so much about intellectual independence as really understanding not only what it is you believe, but why it is you believe it. James Allen says, "When giving the Messenger Lectures in 1964, Richard Feynman had a brief aside while discussing falsifiability. He said some have asked whether space and time were truly continuous or whether at some fundamental scale it was discrete, probably what we'd now call pixelated, and that it was known that it couldn't be discrete 'cause it made predictions which are falsified by observation. But he was in a hurry and never said what those predictions were or what the observations that falsified them are. And I've never seen this claim anywhere else. As his desk mate, do you have any insight into what he was getting at? Was he right?" Well, the way that you say it here is not precisely correct, because of course it's possible that spacetime is discrete. When you put limits on something by doing an experiment, you only limit something up to a certain degree. There's a certain precision in your experiment.

1:42:23.9 SC: If you pixelate the universe at a sufficiently tiny scale, then you cannot have ruled it out yet. So you can't just say, It's been ruled out. Let's move on." You can say, "Here are the limits on something like that." And there are limits. But guess what? Those limits are going to be dependent on the details. So the simplest, most straightforward thing you can do is say, okay, I have space time. I'm gonna literally make it into a lattice. Okay? So there's a finite distance between points in space, a finite interval between points in time. I'm going to chunk it up into a lattice that violates Lorentz invariance. That you're choosing a frame of reference in which to define your spatial lattice. So as a result if you... And you can do this because you can do this on a computer or something like that, but you can also do it by hand. You can say, if I take a smooth equation of motion, like Maxwell's equation for electromagnetism, and I simply discretize them and put them on a lattice, what happens? And the answer is, because you're no longer relativistically invariant, different frequencies of light will propagate at different speeds. There will no longer be an exact once and for all thing called the speed of light.

1:43:38.4 SC: That's a manifestation of the fact that you are violating Lorentz invariance. And this is something you can look for in experiments. I don't know what the best limits were in 1964, but there were some limits. Today, we can do much, much better. You can look at... Generally, the thing to do is to look at something very far away. So if there is an effect that accumulates over time, you're getting the biggest possible effect. The problem is, when you look at something very faraway, you're saying, well, I want a signal in two different wavelengths of light to leave at the same time and get to me, and I'm gonna ask whether or not they arrived at the same time. How do you know whether a signal that came from very far away did leave at the same time in two different wavelengths? After all, if there's something like burst or supernova or whatever, it's possible that its temperature changes with time, so that it's giving different amounts of radiation off at different times. But nevertheless, you can do it. You can try your best. You can work with gamma rays, things that are very, very sharp and well localized in time, and you can look for what are called dispersion relations that are nonstandard. That's just a fancy way of saying different wavelengths travel at different speeds.

1:44:45.3 SC: So far, no evidence for this. The world looks completely the Lorentz invariance, completely smooth at small scales. Again, you're just putting a limit on it to some precision. You're not saying once and for all forever. That's the truth. The other thing is that's just the dumbest, most straightforward way of pixelating spacetime. You might be able to do it in a more clever way that doesn't violate the Lorentz invariance as much. That's also absolutely possible. And guess what? This is why falsifiability is not the right way of thinking about scientific progress. It's more nuanced than that. Rob Petro says, "In a recent Twitter exchange, you quipped that it's good to have a manual coffee bean grinder on hand just in case. This leads me to believe that you are perhaps a somewhat refined coffee drinker. What is your coffee setup and what recommendations would you make to someone who likes good coffee but who's not yet a connoisseur?" Yeah, I think that somewhat refined coffee drinker is just about exactly right.

1:45:45.1 SC: I'm not a super coffee snob, but I do like good coffee. And if coffee is very bad, like the giant metal Terrine that you get at a hotel in a conference setup or something like that, then it can be pretty disgusting and bad. But I can still accept and get pleasure out of a wide variety of different kinds of coffee. Espresso, American coffee, Starbucks, whatever. I have lots of different possibilities, so I'm not that high strung about it. I have, throughout the years, gone through just about every possible way of making coffee. And I've had automatic machines that grind the beans and then make espresso or whatever. I've had drip coffee makers, I've had French press and so forth. And I've settled on like just the simplest and easiest thing, which is the pour over. I literally have my mug, which is pretty big. I put the plastic cone on top, little filter in the plastic cone, pour the coffee on it, pour the hot water over that.

1:46:46.8 SC: So even though that's very simple, there area couple of pieces of equipment you need. I think it does make a difference if you grind your beans right there. If you buy pre ground beans, that's not gonna be as good as if you grind the beans and then make the coffee right away. So I have a coffee bean grinder. And then you also need a source of hot water. When I was young and romantic, I boiled water in a pot on the stove, that is both highly inefficient and bad for the environment. So now we just have a kettle, an electric kettle, like a good European would have in their home, right? And it's actually very convenient for many things, tea as well as coffee and all sorts of things. So that's the morning routine. And then the only remaining question is what is your source of coffee beans? And again, I looked around, I tried various things, and I'm not a super expert. I've not tried all the things. So maybe I'm missing something that would be even better. But this is kind of weird and goofy sounding, but there is a company called Kicking Horse Coffee in British Columbia that you can buy their coffee on Amazon, no problem. Or directly from them, I suppose.

1:47:52.2 SC: And of their blends or of their beans. My favorite is one called Kick Ass Coffee. And I literally resisted trying this one out because the name is so dopey. But then I tried out other things and the reviews were so good, I had to give in. I tried, I'm like, "Yeah, this is the best. This is the best one I've ever had." So that's what it is, Kicking Horse coffee. Again, Kicking horse, if you're out there listening, would love to sponsor you or you sponsor the podcast. I can say good things about that coffee. Josh Dobbin says, "I am a layman reader, listener with enthusiasm, but a relatively shallow understanding of physics. A semi clever glib thing I put in a profile description is quote, 'I currently travel 90 miles per second around the sun, 136 miles per second around the galaxy, and 185 miles per second within the local cluster of known galaxies. I accomplished these spectacular feats all while standing still.' But here's my question. Can I just add these per second motions up together, 96 plus 136 plus 185 equals 417 and multiply that by the number of seconds in a year and arrive at the conclusion that my body is 13 billion mile distant from where it was in space a year in the past? Or am I making some essential error?"

1:49:13.2 SC: You're making two errors. Sorry about that, Josh. One is serious and one is less serious. The serious one is that these are not just numbers you can add, they're vectors because you're moving, you have a velocity. So these numbers that you're quoting, 136 miles per second,185 miles per second, et cetera, these are the magnitudes or the speeds, but they're not the directions. If I am adding together two vectors that are both 100 in magnitude but are opposite in direction, then their sum is 100 plus 100 equals zero because their directions are oppositely aligned. So the same thing true for these vector quantities. You will have to add them up, taking into account the direction as well as the magnitude. That's the serious error. But you will still get an answer even if you did it correctly. Hundred or hundreds of miles per second. What is it? Miles per second? Yeah. Hundreds of miles per second is the order of magnitude that you will get. Now, the other thing that is a less serious error is relative to what? There is such a thing as relativity. And in relativity there is no such thing as an absolute velocity.

1:50:23.8 SC: So all of these are relative to something. So you can fix that mistake. You can say relative to the galactic standard of rest or something like that, but you would have to fix it. You have to sit down and think about, when I'm quoting these numbers, what am I measuring them with respect to? Perhaps with respect to the rest frame of the cosmic microwave background would be a perfectly valid thing to do. So that's actually fun. I encourage you to do it. Look up, what is your velocity with respect to the cosmic microwave background. In fact, it will be simpler than what you're doing because you can just measure it directly. Maybe you can't, maybe you can. Now, probably you can't. Can you measure the dipole of... The dipole anisotropy of the cosmic microwave background. I think you can. I think that's something like an experiment you can do without very advanced equipment. Like if you know what you're doing, you can go upto the roof of a building and try to do that. I think that's true. Maybe I'm making that up. You can certainly detect the existence of the microwave background, but the Doppler shift is one part in a thousand for the relative motion with respect to it.

1:51:26.5 SC: Anyway, you could look up the number, get an approximate value. The high numbers of significant figures here are, of course, just a fake. [chuckle] Don't take these significant figures too seriously. Daniel Donaldson says, "During your discussion with Brian Lowery, the concept of self in the many world's interpretation came up. The example you gave was a person can see a spinning particle as either up or down. Which one is me? The answer you gave was neither. We need to update our notions of self as we've already talked about in this AMA. I guess I didn't understand where you and Brian went after that. My own thought was that I am me at time zero. If I see it as spin up, that me continues in the world. Another me that saw it spin down shared my experience up to that point, then has gone off to another adventure. My sense is that, in the many-worlds interpretation, this is wrong. In the self I am asking for... In the end, sorry, I am asking for a more in-depth explanation of the notion of self in this context."

1:52:22.2 SC: I should have grouped this question with the previous one. But yes, you need a more nuanced notion of self. In many-worlds, you can take your current self and uniquely trace it backward. You know what happened to you in the past to the extent that your memories and records are accurate, which is always a thing. But in principle, that could be done. But there is no such thing as your singular self in the future. There will be multiple people in the future, all of which consider your past to be their past. What vocabulary words do you wanna use to describe that? Go ahead, go nuts. At any one moment of time, you can sensibly talk about your actual past and all of your possible futures. That's what you have to talk about. You cannot talk about, who will I be? In which universe will I end up? There is just no such thing as that. Simon King says, "If quantum mechanics represents the true nature of reality, why do we as humans only experience the world in the classical sense?"

1:53:22.0 SC: Well, that's a difficult question. Part of it is easy, which is that we don't only experience the world in the classical sense. If you've ever heard of Geiger counter, much less done a quantum experiment of any sort, then you've absolutely experienced the world in a quantum mechanical sense. But I get what the question is asking about, there's absolutely a classical regime in which classical mechanics is a very good approximation to the underlying quantum dynamics. Why is that true? I think that we actually don't give the right or at least a complete answer to this. When we teach quantum mechanics, when we talk about quantum mechanics, there's two things that we talk about. One is what is called Ehrenfest theorem. If you have a situation where the pushes and pulls on a system, the forces acting on it very slowly over space. Like if you're the Earth and you're orbiting the sun, the sun's gravitational field does not change dramatically from place to place. So if that's true and you are heavy like the Earth is, for example, then your quantum mechanical observables, your position and your momentum, do a very, very, very, very good approximation of obeying the classical equations of motion. So there's a very well-defined sense in which quantum mechanics gives you back classical mechanics in a well-defined regime.

1:54:47.3 SC: Now that's only going to be true... It's only going to be... It's always true. It's only going to be relevant if your quantum mechanical wave function already starts out localized. So, if the Earth's wave function were spread out all over its orbit around the sun, then the fact that its average value of position momentum behave classically would be irrelevant, it would still look very quantum mechanical. The reason why that's not relevant is of course, decoherence. If you did have spread out, as we talked about already before, if you had a large macroscopic object that is spread out all over some different macroscopically observable places, then you very quickly become entangled with the environment, de-cohere, and in each branch of the wave function it looks like you're in one particular place. That's also important. We don't talk about that when we teach people quantum mechanics, maybe we should.

1:55:40.3 SC: There's another level of the question though. Those two things together are the basic answer you would give. There's an approximation that is good, and we start out approximately classical because of decoherence. We stay approximately classical because of Ehrenfest theorem, if the system is large and so forth, macroscopic. But you can ask why the universe, both in its initial conditions and in its laws of physics allows for classical mechanics to be a good approximation. That is a much trickier question. We have specific laws of physics that do allow that specific energies and forces and so forth, the Hamiltonian and the technical way of talking about it. And not all Hamiltonians would allow for that. So I actually wrote a paper with Ashmeet Singh, the Quantum Mereology paper where we do exactly this. Where we use the criterion of looking for classical behavior in order to figure out how to divide up the quantum mechanical wave function into sub-systems or into system and environment, for example. And we find there are ways to do it as long as the Hamiltonian lets you do it, and the initial conditions let you do it. If they didn't, you wouldn't have a universe for which classical mechanics was a good approximation.

1:56:57.5 SC: So this is, by the way, another place where the arrow of time comes in. As we talked about before in this AMA, in the future, when we reach equilibrium and there's no arrow of time, there won't be anything that looks classical, everything will be in equilibrium, everyone will be smoothed out. Even the different quantum worlds will sort of all blend together, so if that were the world in which we were in to start, then classical mechanics would not be a good approximation. There's one final aspect of this question, because Simon says, "Why do we as humans only experience the world in the classical sense?" So I think the primary answer here is essentially anthropic in some sense, classical mechanics allows for complex systems to come together and interact in certain ways that can process information and become conscious and so forth. So basically, you could re-ask this question as if you believe that there were branches of the way you function in a many world sense, why do we count as individual observers, sub-systems on individual way functions rather than combinations of subsystems scattered across different branches of the wave function, right?

1:58:08.2 SC: And there, the answer has to do with the fact that these different parts of the wave function that are branched apart don't interact with each other, the things that you would naturally call observers are localized on individual wave functions where things look more or less classical. So that's a complicated answer, and if you get the impression that it's not completely polished yet, I think that's a perfectly legitimate impression to get. Kyle Steven says, "In a recent interview, Neil Gershenfeld, the Director of the MIT Center for Bits and Atoms, said one of my favorite questions you can ask a cosmologists to trip them up is to ask is information the conserve quantity in the universe, is there a straight forward answer to this question? Why might Neil find this a difficult question for cosmologists?" Well, it's not perfectly straight forward just because you have to tell me exactly what you mean by information. There's different senses of the word information, so maybe a cosmologists would hesitate answering this until you explained exactly what you meant, I think that's perfectly fair hesitation.

1:59:12.2 SC: If what you mean is the microscopic information that completely specifies the quantum state of the universe, then whether or not that is conserved depends on your favorite interpretation of quantum mechanics. In many-worlds, it is overall, but you don't see it being conserved 'cause you only observe one branch of the wave function at a time. In objective collapse models, it is just not conserved because collapses of the wave function don't conserve information. This is famously a question that comes up in black hole physics, and the black hole information loss puzzle, is information really lost? And most physicist think the answer is no. They're not thinking about measurements or collapses of the wave function, they're thinking about the underlying dynamics. And people disagree about that, but at least you would once again have to tell me what you think is the best formulation of quantum mechanics to give a sensible answer to that question.

2:00:06.9 SC: I suspect, though, that what Neil has in mind is not the micro-physical information that gives us the exact microstate of the universe, but something more like accessible macroscopic information. And of course, that can be lost and gained depending on different physical processes. Such information is lost if you just increase the entropy of something. Increased entropy means that there is a broader class of microscopic states that might be represented by your macroscopic state, and if all you know is the macroscopic state, then you have less information about the system that you used to. But you can also gain information mainly by observing the system. So it's not a question purely for the universe, it's a question for who is it, who has the information, how are they gathering it, how do they course grain? All of those things. So I think that it is not a challenging question at a deep scientific level, it's just a question that needs more clarification before you're going to give a precise answer to it.

2:01:03.3 SC: Leenu Miseara says, "Are quantum fields really vibrating all the time due to the uncertainty principle or do they only vibrate when they are observed?" They are certainly not vibrating all the time due to the uncertainty principle. Again, read book two of The Biggest Ideas in The Universe, or I probably even talked about this a little bit in Something Deeply Hidden. There is a quantum wave function for the quantum fields and in the vacuum or in any stable configuration like an atom or so forth, the fields are not vibrating in any sense, they're completely static, they're the same field configurations from moment to moment. You talk a language of vibrating. Exactly. Well, for two reasons. Number one, because the behavior of the field is not classical. So sometimes people use the language of vibrations or whatever to give you a colorful feeling for what they really mean by quantum corrections to classical behavior, radiative corrections, they will sometimes call them. The other reason is that if you were to observe, you were to make measurements repeatedly, then you would collapse the wave function and you would have unpredictable answers when you figured out what you were seeing, and so it would look like they were vibrating.

2:02:16.1 SC: But when you're not looking, there's nothing vibrating, most of the time. Of course, the fields could viral, if they're not in the vacuum or if they're not in the static state, there are things to change in the universe, but there's no intrinsic jigglyness to quantum fields. Tilo says, "Would you say that non-deterministic interpretations of quantum mechanics are compatible with the eternalist view of time?" Yeah, sure. I think everything is compatible with eternalist view of time. It's a slightly sticky question, because if you have a non-deterministic interpretation of quantum mechanics, that typically means something like the wave function objectively collapses for some reason. And the thing about wave function is that they are defined on states at a given moment of time, that is to say throughout the universe at one moment in time. And as we've already said earlier in the AMA, that's not a well-defined thing in relativity. Who says what is the universe at one moment in time?

2:03:17.8 SC: Different observers might interpret that separately. So I'm not... I don't believe in these interpretations, I don't study up on them very much, so I'm not worried about this problem 'cause I just think that they're wrong. But if I were an advocate for one of these interpretations, I would worry a lot about when exactly the wave function collapses as far as different observers in different locations in the universe who are concerned. Having said that, once you pick an answer to that question, you would certainly be perfectly legitimate in having an eternalist view of time, it's just that the transitions from the state of the universe from one moment to the other are not perfectly smooth and deterministic. So be it. Sometimes that's how things are. Sandra Sturkie says, "I wonder about the ontological status of density matrices in Mad-Dog Everettianism... " that parenthetically is the label that Ashmeet Singh and I gave to the idea of pure wave function vector in Hilbert space realism. So no other stuff in your fundamental ontology other than a vector in Hilbert space.

2:04:24.6 SC: So Sandra says, "Can we treat a density matrix as a fundamental part of the formalism, as real as a pure state, a vector in a Hilbert space, or are they just a convenient mathematical device for representing mixed states? Does it matter from a realist stance if we cannot distinguish different distributions of pure states that correspond to the same density matrix?" Yeah, the answer is, I don't know. I'm not even sure if it matters. There's a fact about quantum mechanics. So for those of you who are not quantum experts, a density matrix is how in quantum mechanics, we talk about situations where there is not a pure wave function for a system. In classical statistical mechanics, you have box of gas, you say things like, there is some particular arrangement, there's some particular state of all the particles, all their velocities, all their positions, we just don't know what it is. So we have some probabilistic distribution function over possible microstates, and that's enough to make predictions and things like that.

2:05:24.6 SC: In quantum mechanics, the role of that probabilistic distribution function is played by the density matrix. You could imagine saying, I don't know which quantum state the system is actually in, therefore, I'm gonna represent it as a probability distribution over different possible quantum states. And then there's a mathematical details as to why it is something called the density matrix rather than just a probability distribution over states having to do with the fact that quantum states are vectors and you can add them together. But the different thing in quantum mechanics is that you can have entanglement between sub-systems. If you have two subsystems, A and B, and they are entangled with each other, then even if there is a pure, single, well-known quantum state for both A and B, the combined system, in general, there is not any pure quantum state describing A or describing B. They are entangled, so you need the information in both to describe them both at once.

2:06:22.3 SC: But if all you wanna do or make predictions for what you will see when you measure sub-system A, you can do that, and the information you need to do that is precisely the density matrix of sub-system A. So, density matrices or these probability distributions have a little bit more of a necessary character in quantum mechanics. In classical mechanics, it's really just because we don't know all the details. In Quantum Mechanics for an entangled sub-system, you need to talk the language of density matrices. So anyway, that was all background. As far as fundamental ontology is concerned, there is a fact about density matrices that if I have a system that is not necessarily entangled, but I do describe it using a density matrix may be because I don't know it's exact system state, maybe because it is entangled and I'm just not sure, for whatever reason, if I am describing it by a density matrix, which I'm always allowed to do, I can always, what we call purify the density matrix by imagining that there is other things in Hilbert space other than the system I'm considering.

2:07:28.5 SC: And there is some pure quantum state of the combined system, the system I'm caring about and the rest of the world. There is always... For any density matrix of sub-system A, there is always a pure state for that sub-system plus other things that would give you that density matrix. So I suspect because of that fact that you never need to talk about density matrices, but maybe there's some other fact that I'm not taking to consideration and they really should, that gives us a reason to prefer to talk about density matrices at the fundamental level of ontology. I don't know if that's true, but I'm open to the possibility. Peter Blankenheim says, "Your recent book explains that symmetries dictate laws of conservation, for instance, a kinetic and potential energy experiment is the same if done today or tomorrow at one location or the other, and that gives us conservation of energy and momentum. Can you explain the reasoning that makes that necessary? Short answer is no, I cannot explain it here in the AMA, it's too complicated for that.

2:08:33.4 SC: I actually struggled with this in the recently completed book two of The Biggest Ideas in The Universe, because this result we're referring to is called Noether's Theorem, after Emmy Noether the famous mathematician who proved it in the early 20th century. And you can give a hand-wavy argument for why it's true, but it's kind of a mess. It kind of takes a few steps to get there, and the pay-off is Noether's Theorem, which is very easy to state. So it's sort of a little bit tricky to prove, but very easy to state. So at the end of the day, for the book, I just decided to state it without proving it. If you want more details, you can go to the video series on The Biggest Ideas in The Universe. I forget which video it is, but in one of them, I do that hand-wavy discussion, and it might... It's probably in the one called symmetries later in the course.

2:09:24.9 SC: If I'm trying to distill it down, it's just hard to do, but what you need is a continuous symmetry, so a discrete symmetry is not good enough for Noether's Theorem anyway. And also you need a dynamic that is based on an action principle, a principle of least action, either classically or quantum mechanically. The quantum mechanical version would be Feynman's path integral version, but... So you need a certain set of ingredients and then you can chug through, just taking some derivatives and some paths and things like that, and you find that, yes, there is a quantity that you can construct. So Noether's Theorem doesn't just say, "There is a conserved quantity," it tells you what it is, it gives you a formula for that conserved quantity. So you can even take my word for it or go to the video, Symmetries and The Biggest Ideas in The Universe.

2:10:13.4 SC: Siddhartha says... And I apologize, by the way, if you're hearing noise in the background, I'm not sure if you are, maybe it's filtered out, but there are people outside making noise. Leaf blowers, I suppose, something like that. I don't know who they are, what they're doing. But sorry about that. Siddhartha says, "I'm trying to understand how eternalism explains our sense of a flow of time. If all moments of time are equally real, how can we recover the smooth flow of experiences from moment to moment? Is it not better explained by a modifying growing block universe where the future is as yet determined as an eternalism, just not materialized yet?" I don't think so. I don't see why that would be really any benefit at all, because in the philosophical view of a growing block universe, you still end up at the end of the day, after sometimes passed, you end up with a part of a block, which is nothing more than a set of moments of time, physical configuration at different moments of time, and yet every person, every instantiation of a self in that big block that has already been constructed had the thought the time was passing, even though they're just lists of configurations at different moments in time, which is what they would have been in eternalism.

2:11:32.2 SC: So that doesn't explain the flow of time, the philosophical point of view that says that what is real is the current moment in the past, but not the future, doesn't help us at all in explaining why we psychologically have a feeling of the flow of time. That psychological feeling, I'm sure that there are subtleties here that we're not getting into, but it basically comes from... At every moment of time, you and your brain carry around an image of the world that has just passed and the world that is just about to come, you sort of predict a little bit into the future, and you remember a little bit into the past, and you were constantly at every moment updating those predictions and those memories. And it's that unequal comparison between the impressions we have of the immediate future and the projects into the... Sorry, the impressions we have of the immediate past and our projections into the near future. These are different, and that's what gives us the idea of the time is flowing in that particular direction, roughly speaking, many details there to be filled in.

2:12:33.7 SC: Edward Morris says, "Regarding your conversation with Brian Lowery, I'm trying to understand what the suggestion that the concept of self could be an entirely social construction is even supposed to mean. Presumably, even if you lived your entire life in solitary confinement with no human contact, the fact that you felt pain when you dropped something on your toe but not on the floor will still give you some, at least a rudimentary sense of being some kind of self behind your eyes, I.e, who specifically lived in your body and not the floor. So what is it that... What is... Sorry. So, is this not part of the concept of self that he's talking about or what?

2:13:08.6 SC: Yeah, I'm not the one to defend it 'cause it's Brian's idea, not mine. But I think that what he's focusing on is the fact that so many features of our identity as a self, as someone who is an author and physicist and podcaster and things like that, these identities play social roles, they help tell other people who I am, and I define myself in reference to what other people would want to know about me or expect from me given my various identifications. So I think that you're probably right, I'm not an expert on this, maybe you're not, but I'm probably right that there is some kind of sense of self that would still exist if you were raised in solitary confinement with no human contact, but it wouldn't be an identity in the same way that psychologists think about the self.

2:14:02.8 SC: That's my reading of it. But I try to understand it better. I think understand it much better after the podcast, but I still do not understand the idea 100%. Walter Miller says, "When an electron falls into a black hole, what happens to that electrons or electrostatic field?" Sorry, the question continues. "Obviously, the portion of that field beyond the event rising it is no longer visible to the external universe, does the black hole wind up carrying a frozen electrostatic field like the quills on a porcupine?" Short answer, yes, that's exactly what it does. By the way, same exact thing with the gravitational field. If I throw a rock with a certain mass into the black hole, the black hole gets more mass, its gravitational field goes up, if I throw an electron into the black hole, both its mass and its charge change and now it's electric field and its gravitational field both are different. The rule that black holes have no hair, has a foot note in it, except for unbroken gauge symmetries, [chuckle] which is a fancy high-brow way of saying long range force fields.

2:15:06.4 SC: We only know of two long range force fields in nature, which are gravity and electromagnetism. So those two things can both be things that black holes have and you can easily change them by throwing things into the black hole. Dori Vinette says, "My Bested who you wisely and previously noted, is a very good kitten who deserves all the treats has passed on. Once I'm ready for the next kitten, what traits would you look for in a tiny baby to help me choose among all the masses of kittens I want to take home?" I'm sorry to hear that Bested that has passed on, it's always very difficult when that happens, even if we know that it's inevitable, so I hope you doing okay. I don't have any specific suggestions about what kind of kitten to look for, because everyone's different and all kittens are different and all people are different and they're gonna match up differently. My strong suggestion is to try some kittens out.

2:16:02.7 SC: We got Ariel and Caliban by being foster fails. We fostered kittens. We've done it more than ones. They were the first time we tried fostering. So by fostering, what it means is, if you have a cat shelter, they will often be overwhelmed because there's far too many kittens in the world, and they don't have enough room to have all the kittens, especially to give the very, very youngest ones the care that they need. So they will ask for volunteers to take care of kittens for a month or two, just to get them used to eating solid food and things like that, litter trained, whatever it is, give them some love and affection until they're ready to go up for adoption. There is a whole syndrome called Foster fails where you say, "Alright, I will foster... Be a foster parent to these kittens," and then you don't give them back, [laughter] and you say, "No, these are my kittens now." And it was pretty clear from the moment that we got Ariel and Caliban that that was going to be the case.

2:17:00.9 SC: But we subsequently did it, we had other foster kittens during the pandemic when it was just tough to find people, we volunteered and we did give them back. Ariel and Caliban did not get along with the newcomers, not even a little bit. We were hoping for a little bit, but not at all, they're very, very territorial, they love each other and they love us, but that's about it. So we were able to find homes for those other kittens. And either... So I would say try fostering if you wanna do that, or just go to the cat shelter and play with the kittens and see who you bond with, sometimes the cat will choose you, sometimes you will be just... Your heart strings will be tugged at by the grumpy cat in the back, it doesn't wanna play with anybody, but secretly needs love and you can provide that love for them. So I would say don't go in to the process with any particular list of requirements, figure out what the connection is, when you actually make it.

2:17:57.9 SC: Kyle Hicks says, "If the direction of the arrow of time is determined by the flow of entropy from states of higher order to those of lower order, could biological open dissipative systems be considered localized regions in spacetime where the arrow of time seemingly reverses its direction?" No, they cannot be considered that because those open dissipative systems that are biological organisms or whatever are very, very, very heavily reliant on the fact that entropy is increasing all around them. There's different ways for entropy to go down. As I often say, if you put a bottle of champagne in the refrigerator and it gets colder, its entropy goes down, okay, just by the properties of fluids. And that doesn't mean that the arrow of time is reversed, the arrow time is more subtle than that. The arrow of time is not just entropy's increasing, but there's a particular way in which it's increasing with this past boundary condition of a very simple low entropy state in a completely unspecified future boundary condition, none of that would hold true in a biological system, even if it itself was going down in entropy.

2:19:05.6 SC: If you clean your room, you're not reversing the arrow of time, you're just increasing the entropy of the universe by putting in the effort to clean your room, and biological organisms are the same way. Mike Meyer says, "How sympathetic are you to the victims of the OceanGate submersible disaster given the high amount of risk that the passengers assumed?" Well, I'm very sympathetic. I am not on board with the people who are sort of cheering these people who are risk takers and had too much money that they knew what to do with, and so they ended up in a disaster. I think it's still a disaster and it's still sad, especially because some of those people were the children of grown-ups who made the decision and they were just trying to keep their parents happy, and it's overall a very tragic thing. Of course, people who do risky things bear some responsibility to understand that there is a risk there, and especially if you're doing something where it's unique and it is not a well-trodden path and you're spending a lot of money, then you should put in the work to figure out precisely how much precaution is taken in.

2:20:10.1 SC: In the aftermath of the disaster, this is the submersible that went to look at the Titanic and imploded and killed everyone onboard. In the aftermath, there's plenty of quotes from the people who had built and run that submersible, which were basically laughing in the face of danger and safety precautions and things like that. There were a million red flags saying that this was not a well-ordered, a well-run operation that would be safe to go on. But that doesn't mean that they should die. That doesn't mean that we should celebrate the end of their life, I'm just not... I'm not, I don't see what the gain is there, I think it seems a little bit crass to do that. David Wych, W-Y-C-H, says, "The structure/dynamics of science funding in the US leads to a few not so great downstream effects. Principal Investigators, PIs, often spend more time applying for funding than doing actual science. Getting a job in the first place will be more dependent on your skills as a grant writer than the quality of your work, etcetera.

2:21:10.4 SC: As a wild thought experiment, what do you think would be the benefits to a downsides of just compiling a list of all the competent scientific researchers in the US, distributing our vast scientific research budget to everyone equally and letting people coordinate on their own to fund large research projects or not, versus the way we do things now?" Well, I certainly do agree that the current system could easily be improved. I think this particular wild thought experiment would be disastrously bad. [chuckle] Just giving equal amounts of money to everyone. What do you mean by everyone? Literally, everyone who asks for the money, whether or not they have even an academic position or a lab or have ever written a scientific paper, they just want the money, presumably, you have some standards there. Right, so okay, now you're gonna start coming up with the standards, do you need to be in academia? Well, that's not very fair, because there could be good people outside academia, do you need to have written papers, you have to...

2:22:04.5 SC: It's more complicated than that's going to sound. And also, there's just different amounts of need for money on the part of different kinds of science. Certainly, I apply for money, and I want all the money I can get for grant proposals and things like that, but there's no sensible world in which I deserve as much grant money as someone who is trying to build a Gravitational Wave Observatory or a giant particle accelerator. Those things are more expensive. So I think you need to actually just do the hard work. One way or the other, you'll have to decide who deserves the money, there's no shortcut here, you have to make that decision somehow. I do agree that the current system is just far too bureaucratic, we have far too often apply for money and justify it, especially as theorist, where you're supposed to propose a three-year plan of what you're gonna do for the next three years, which is just laughable. No one knows what they're gonna do for the next three years.

2:23:03.9 SC: So everyone lies, everyone says, "I'm gonna do this, when they just did it, right. So it's a bit of a Kabuki theater there, and we could obviously do better if only by making the grants less frequent, [chuckle] and the need for grant renewal. It doesn't need to be every year, you could just slow it down. And also, I do think that there are some people who just every single year, they're doing great science, just give them money. If they're just doing great science every year, and that is perfectly clear from their track record and everyone in the community knows it, why are they spending time trying to pretend like they're saying, "Oh, here's the great science I'm gonna do." I think that there's two categories to which we should just give people money, The ones who are clearly already doing great science and the people who are young and just starting out, but very promising. And beyond that, we should all save extra money for people who, "Okay, you've not been doing great science for a while, but you have a really good idea, so let's try to make that happen too." But all of these little footnotes and caveats add a little level of bureaucratic necessity to it, so they see why a current system like ours comes to be, even if it's not an ideal system.

2:24:16.2 SC: Michael Kramer says, "Einstein General Relativity question says that the curvature of spacetime depends on the energy tensor at that point. But does this mean that light by itself, I.e, massless, but containing energy can cause gravity?" Yes. 100%. This is part of the principal equivalence that Einstein used to inspire himself to invent general relativity. The idea that everything causes gravity and is affected by gravity, there's no exceptions to that. Everything with mass or energy or existence causes gravity. And in fact, it's not just hypothetical. In the early universe, the energy density in photons was way bigger than the energy density in matter particles like atoms or dark matter or whatever, we live in a radiation-dominated universe. I already talked about the fact that we have data from primordial nucleosynthesis when the universe was using protons and neutrons and Helium and other light elements, and that is a period of time when the universe was radiation-dominated, and that fact is crucially important to getting the right predictions for the relic, abundance of helium and deuterium and so forth.

2:25:32.1 SC: So yes, it not only can, but it absolutely does, and that's super important. Gregory Cosmic says, "In an eternal inflation scenario... " Oops where did you go, "... Does the bubble or post-inflationary space that contains our observable universe have a fixed boundary so that all its expansion arises from the expansion of space already inside the bubble? Where does the boundary of the bubble propagate outward through inflationary space, converting more and more of it into post-inflationary space?" That's a good question, and it's gonna depend on details. Usually, the answer is that the region outside anyone bubble or post-inflationary space is still inflating space, so you have inflation where you have some very high energy density in this inflaton field, this form of temporary super high density, dark energy, and it rolls down some potential to become very low energy and reheats into ordinary matter and radiation, and that's our universe.

2:26:31.8 SC: An eternal inflation that rolling down happens in one little bubble, but outside the bubble, you're still in this inflationary phase dominated by this ultra high energy, dark energy. So energy likes to go down or at least energy and a low entropy form likes to convert into energy and a high entropy forms. So at the boundary where you have true vacuum, the field, the inflaton fields in this low energy state on one side of the boundary, and on the other side, you have false vacuum where the field is in its high-end energy state, the boundary between them will move into the inflating region, they will move in the direction of where the scaler field or the inflaton field has a large false vacuum energy. So that tends to remove space from the inflating regime, but of course, inside the inflating regime, the universe is inflating, so it's expanding very, very fast. So even though you're removing more and more space from the inflationary regime, you're also creating more and more space, and that's why inflation goes on eternally.

2:27:36.2 SC: Aurey Modi says, "Do you believe there is a first cause, a cause that there is nothing else before or does every case have a proceeding cause? If so, how is that even possible?" I think that this whole question is mis-asked, it's mis-formulated. I don't think that there are causes at all, as part of the fundamental nature of reality, I think that causes a higher level emergent phenomena. It's not the right vocabulary to use to discuss the foundations of physics or science or anything like that. And I don't wanna go into too many details here because I've written about it elsewhere. I wrote a paper called Why Is There Something Rather Than Nothing, and I detail exactly this, or if you want in a more combative version of it. I did a debate with William Lane Craig, where he uses this Aristotelian language of you need a cause for every effect and things like that, the principle of efficient reason. That's just wildly inappropriate in the world of modern physics, we just don't talk that way anymore.

2:28:39.6 SC: There are rules, there are laws of physics, but the rules do not take the form of a chain of causes and effects, the rules are a different kind of thing, they're patterns. The question to ask is not, Is there a first cause? The question is, what do the laws of physics say about the beginning of a nature of our universe? Dave Grohl Giger says, "Do you think we should teach Modern Physics in middle school? I feel like I had to unlearn my middle school science when I got to higher levels. My teachers gave me the impression that everything was precise and known in a particular way, but that turned out not to be true, e.g. The picture of an atom as a mini solar system is burned in my skull." I think it's okay, it would be fine to teach some modern physics in middle school, but that doesn't mean that you need to derive classical mechanics from quantum mechanics in middle school. I think it's perfectly okay to first teach simpler, but more intuitive approximate versions of reality rather than going right to the exact, the standard model of particle physics when you're in third grade or whatever.

2:29:44.3 SC: No one should be surprised when you just have to get to the right answer by a series of steps rather than just starting there. Now, having said that, you should teach the classical physics or whatever the approximations we use correctly. And that's just hard to do because middle school teachers don't know it, they're not trained for that. Whether or not they should be trained for it is a different question, having to do with how we train teachers and how we credential them and how we pay them and how much we value them, which in this country is not that much. But right now, they're doing their best just to teach baby little physics there, you're not gonna get them to teach quantum mechanics in any accurate way. Sean Bentley says, "My 11-year-old Charlie had a question about what happens to your acceleration when you approach the speed of light? Ignoring the amount of energy needed to accelerate at these speeds, if you're going 0.9C and accelerating at 0.1C per second, does your acceleration slow before the last second ticks off?" I'm pretty sure the answer is no. Instead, the last second would stretch on to infinity due to time dilation.

2:30:51.8 SC: Well, again, what are you measuring your speed with respect to? Acceleration is a real objective thing, that's part of classical mechanics. Position and velocity are not objective, they are relative. But acceleration is absolute. The truth is, there's a set of equations that were... Are part of relativity, they're part of special relativity, but they were actually derived before Einstein came up with this capstone of relativity by Lorentz and Fitzgerald and Poincare, and people like that. And yes, your notion of both space and time alter at least the way that you would measure them compared to someone you're moving with respect to at a very rapid rate. Both space and time change and you keep accelerating at what to you is exactly the same amount of acceleration, and if you're measuring the speed at which other things pass you by, they go from being 0.9 to 0.95 to 0.96 to 0.97, they never get to one.

2:31:56.3 SC: They never get to the speed of light. They go up and up and up. I should have said from 0.9C to 0.99 to 0.999 to 0.9999, etcetera. You get closer and closer, you get asymptotically there, but that is because the way that you're measuring space and time relative to people you're zipping by becomes a little bit different. Jeffrey Seagal says, "I was intrigued by your skepticism, if I interpreted your reflections common correctly, regarding the social self in your discussion with Brian Lowery. It seems to me that the capability of charismatic individuals to command on questioning obedience of a large fraction of the population irrespective of the fact strongly supports such a view. Such a social self could be a selective advantage in human evolution, where competing human groups needed to survive in the absence of scientific knowledge. Do you have an alternative view of what underlies the frequent formation of groups such as QAnon, Flat Earthers or MAGA?" I think it's a very complicated phenomenon.

2:32:51.6 SC: I'm very skeptical of any purported explanation for the success of such conspiracy theories, etcetera, which is too simple and cheap. Human beings are kinda complicated, different people might have different reasons for joining QAnon, and he need to take that into consideration. Having said that, I think that the closest I've come to hearing a compelling overall theory of it was in the podcast with Tim Nguyen, about games and the philosophy of games and how you sort of... There's attraction in human beings for simple clear ways of thinking. And that's not... That doesn't sound bad, right? Simple, clear, those are good things, but the point of these conspiracy theories is, that they offer clarity where it shouldn't be there. Sometimes, like I just said, things are complicated, and the thing about these conspiracy theorist is they have an answer for everything that is simple, and there's a set of people to blame. It's very compelling for exactly that reason.

2:33:53.2 SC: And I remember... I was gonna say, I remember very clearly, I remember reading, and I've used this example before, there was a biography, a little memoir by a woman who had been really new agey. She's into all these woo woo, psychic kinds of things, spiritual in this modern woo woo kind of sense, and, but she was interested about what, this is true, am I on the right track? So she talked to lots of people and she eventually became a hardcore physicalist or naturalist, whatever you wanna call it, I don't know if she would use those words, but non-spiritual in the sense I'm using it right now. And what I was interested... That's a common story, that happens to a lot of people. What I was interested in was, the reason that she gave for her conversion was that when she talked to science-minded people, there are questions she could ask to which their answer was, "We don't know." But when she talked to her New Age friends, every question she asked, they had an answer. And she asked herself, what is a chance that they actually have an answer to every single question that I can ask? Shouldn't we still be asking, seeking?

2:35:10.8 SC: Aren't there more questions out there? But that's the lure of a good overarching conspiracy theory. I don't know if you wanna call it new ageism conspiracy theory, but that kind of thing where you have clarity that you didn't earn, clarity that is reassuring, but not actually reflective of a deep understanding of anything. And I think that that coupled with various psychological desires to have your in-group be valerized or getting defensive about other people and coaching on your privileges and so forth, there's a whole bunch of aspects that go into why these syndromes are so common. Cubit says, "You mentioned that the entanglement of a wave function depends on its decomposition in Hilbert space. However, it also seems like two particles can be entangled in an objective way so that there is no classical explanation for their correlations, somehow entanglement seems to depend on the choice of basis, and at the same time it doesn't. Can you help?" Yes, I think I can help here. I think that the issue is that you are saying the words two particles can be entangled.

2:36:15.3 SC: The point is that in quantum mechanics, if you have a system that we would call a two-particle system, there are ways of describing that system that do not map on to the fact that it's two particles. I'm trying to be... Say a very precise language here, that's why it sounds a little awkward or clunky here. I can find a basis in Hilbert space where the fact that these particle A and particle B is completely obscured. I could find a... If I have two particles, to get a little bit more technical, and say I have two particles, they're both in the States 0 or 1, so I can have a basis where the basis elements are 0/0, so particle A is in state zero, particle B is in state zero, that's a basis state, so 0/0, 0/1, 1/0 and 1/1, those are the basis states. But there's another set of basis states, 0/0 + 1/1, 0/0 minus 1/1, 0/1 plus 0/1, etcetera. So I can distribute the entanglement such that the states that were basis states and would have seemed entangled are now new basis states. But the different things that I'm referring to as the sub-systems are no longer the particles. Okay.

2:37:36.1 SC: The reason why it sounds confusing is because you're taking as objectively true the fact that you're starting with two particles. Quantum mechanics is a little bit more subtle than that, it doesn't necessarily talk that way. Of course, if you start with two well-defined sub-systems, then asking whether they are entangled or not is completely objective. What I'm saying is you can change the basis so that the sub-system decomposition is completely different in the first place. Eric Stromquist says, "I think you argued in a 2021 paper, that quantum measurements do not necessarily conserve energy, although energy would be universally conserved under the Everett interpretation. My question is, do you think this also applies to measurements of angular momentum too?" No, it does not necessarily apply to measurements of angular momentum. It could, but it doesn't necessarily and probably doesn't. And the reason why is that energy is special in quantum mechanics.

2:38:30.7 SC: It's the thing that appears in the Schrodinger equation. The Schrodinger equations is H𝚿=ID by DT𝚿, and H is the Hamiltonian, the observable that corresponds to the energy of the system. So this idea that... This was, Jackie Lodman and I wrote a paper about it. We got that published. And the idea of the paper is that you can measure a quantum system, if that quantum system is a superposition of different states with different energies, then in general, the outcome of that super position will have a different energy than you had... The outcome of the measurement will have a different energy than the original superposition did. You might say, Well, what if I start with the superposition of states that all have the same energy and then it won't happen, then you're not gonna get a different answer after you do the measurement than before, 'cause you're just redistributing the same energy among different states.

2:39:28.0 SC: But the problem with that is that that's a system that is not evolving, systems that have a fixed constant energy don't evolve in quantum mechanics. According to the Schrodinger equation, the only states that interestingly evolve are those that are super positions of states with different total energy. Angular momentum or electric charge, where things like that don't work that way, you can just have zero total angular momentum in the universe or a zero total electric charge in the universe, etcetera, and that's a perfectly valid way of constructing a quantum state that doesn't say anything about whether it's gonna evolve or not. So energy really is special in quantum mechanics in that sense. Geodude says, "What are your thoughts on open letters, calling from moratorium on research topics like solar geoengineering, viral Gain of Function Research and building large AI models, do you think it is wise to help research on certain topics? And to what extent is it possible to shift the focus of the research community through top level research direct is prohibitions or through social pressure at the level of individual researchers?

2:40:37.9 SC: Well, there's a lot of questions going on here, a lot of issues going on here. One is, is it wise to hold research, but another one is, is a good way of doing that through open letters? I have mixed feelings about open letters. I've signed a few in my day, but I don't seek them out, I don't never write them myself, I think it's a very, very blunt instrument to use to make things happen, in part because there's a strong selection effect. The people who write an open letter are going to be the ones who are most dedicated, most enthusiastic, most really worked up about the issue that they're writing about, and then they're gonna get other people to try to sign it who maybe are less enthusiastic or whatever, and inevitably that's gonna be compromises about the exact wording of the letter and so on and so forth. And the people who are gonna win the discussions about how to word it are the most enthusiastic, the most energetically involved in these topics that doesn't always lead to the best letters.

2:41:36.8 SC: So I think it's kind of an instrument in that sense. On the other hand, it can work, maybe not because people read the open letter and then say, "Yes, we will do that, we'll do exactly what you say." That never happens. But you can get a conversation started. Open letters do for some reason, seemed like a pretty good track record at getting people to talk about these issues, certainly an AI that has happened, so maybe... Okay, maybe you can make that argument why it's a useful thing to do it. At least it's focusing people's attention on the questions that we care about here. Now, whether it's wise to hold research on certain topics. I think it depends. I think that a lot of people are just wildly unrealistic about what it would mean to hold research on certain topics. Like are you really 100% okay if your country holds research on this topic, but all other countries don't? 'Cause you don't have control over what the other countries are going to do. There are systems in place for international agreements and so forth, but that's usually not what is being thought of in these calls for open letters.

2:42:46.7 SC: I think it's very hard to really imagine a system that effectively stops every country from doing research that would very likely benefit from that... Benefit that country if they did that research. So I'm just not sure how realistic it is, at all. Going back to the previous discussion we had about existential risks, I think that this is... You're hurting your own case by going too far, by saying, "Don't do research on this topic," that's just not gonna happen. I'm not actually going to stop, and therefore you're doing nothing, 'cause you're saying... You're asking for too much, you're gonna get nothing. Why not just have some sensible safeguards in place, why not just talk carefully and realistically about how you can monitor the research that is being done, how you can funnel research money into productive areas rather than destructive ones, and so forth. I think that kind of real world careful thought about how to do this is more productive in an open letter calling for research to stop. But people are lazy. People don't wanna do that work. That sounds like work, man. Protocols to do research safely. That's boring.

2:44:08.3 SC: I just wanna say the world might end, let's stop doing work on this while I continue to do the work in my backyard so that I can win the race ultimately. So I'm a little skeptical about calls like that. Yeah. Anonymous says, "I'm looking to write some fun science fiction stories with an as accurate depiction of quantum behavior in the many-worlds interpretation as possible. With that in mind, here's a scenario I would love your thoughts about. Alice has two photons, A and B, they're each prepared in a superposition of up and down, she measures particle A and tangling herself with it, but keeps B in its superposition. In the many-worlds interpretation, perhaps one could say that there is a branching where Alice's photon A is the one... Is up in one world and down in the other. But what about photon B, still in superposition? Is it duplicated but thinner or unbranched and fat in each world?" The answer it is, if A and B are entangled... Maybe I'm reading the question incorrectly. Hold on, let me think about this again.

2:45:11.0 SC: Yeah, so you say Alice has two photons, A and B, each prepared in a superposition of up and down. Yeah, so it's a little bit ambiguous here. If A and B are separately in superpositions, then if you measure A, then they are now two worlds, one, which Alice saw up and Alice saw down, and B is still in a superposition, if they are initially unintended with each other. But if they are not... Sorry, if they are entangled with each other, then when Alice sees one, the entanglement now breaks, so if the two particles are in an entangled superposition where let's say they're both up plus they're both down, that's the superposition therein. Then after you measure... And let's say Alices sees spin up, now B is in spin up, and they're no longer entangled, they're both separately and unintended spin up states, so if what you're asking is... So anyway, that's a whole bunch of true statements here.

2:46:12.6 SC: Maybe what you're asking is what happens just to the thickness of the world as you do these superpositions. And this is a strange, counterintuitive but true fact, if you think about the thickness or thinness of the world, that is given by the amplitude of that world in the wave function, that amplitude, absolute value squared, that's the thickness of the world, so when you do a measurement of any particle that is in superposition, the thickness of the whole world goes down because the amplitude of the branch you're on now is thinner than what it used to be. So that is a global feature of the wave function, this is again, one of the weird things about quantum mechanics is that the amplitudes of the wave function are not located anywhere. They are part of the whole way function of the universe. This in fact is crucially important in understanding what is called Quantum teleportation. Quantum teleportation is a way of taking a qubit, so you have alpha times spin up plus beta times spin down, and if it's entangled, you can actually move alpha and beta, you can move the information about what qubit you have without measuring it or destroying it.

2:47:27.2 SC: Okay. That seems like magic, but the real reason why is because alpha and beta were never really located at your qubit, even if it's not entangled with anything else in the world, they're still part of the wave function of the whole universe, it's just a weird non-local feature of quantum mechanics. Patricia Paulson says, "I've heard you say how the question we should be asking isn't, why are things non-local, but it's amazing that there is anything that is local, why do you think the idea of locality is stranger than non-locality?" Well, the simple answer is that there are many, many more ways for hypothetical laws of physics to be non-local than for them to be local. Think about it this way, take space, chop it up into regions of space that are one cubic centimeter across, so you have many, many cubic centimeters in the world. You chopped it up into little regions, not literally chopped it up in your brain, you chopped it up, so you can talk about all the quantum fields in one cubic centimeter and other cubic centimeter and so forth.

2:48:23.6 SC: Locality says that the direct interactions between one cubic centimeter and all of the other cubic centimeters in the universe are only between nearest neighbors. When I poke the quantum fields in a certain cubic centimeter at a certain location, it directly affects the very closest other fields, but does not directly affect anything going on very, very far away, that's a very, very special set up that you imagine all the possible couplings between that cubic centimeter and all the other cubic centimeters in the universe, most of them, most of the possible sets of interactions have at least some interaction between what's going on here and what's going on far away. Being local is being very special. It's like saying I have a list of 100 numbers and they just happen to be in numerical order. Right. Well, that's fine, but it's very special. Like in all of the lists of numbers you could imagine, most of them are mixed up. When you have just local interactions, it's a very small subset of all the possible interactions you can imagine.

2:49:29.0 SC: Linus Mellberg says, "I've been thinking about the interview with Andrew Strominger, where you talked about the holographic plate at the boundary in the infinite future. This sounds like the Laplace's demon. The plate is the state of the universe in the space dimensions at fixed time, and Laplace's demon can calculate anything that happened. Is there something else needed to make a holographic plate? It seems like there's something I'm missing. Well, I'm not quite sure what you have in mind when you say this sounds like Laplace's demon. Laplace's demon is supposed to be a vast intelligence. Laplace didn't call it a demon, he just said a vast intelligence. The whole point was that you could be smart enough and knowledgeable enough to predict the whole history of the universe from what is happening at any one moment. Of course, the universe itself does that, according to at least classical or unitary laws of physics.

2:50:21.2 SC: If you know the state of the universe at one time, the universe does the job of telling you what's going to happen next. But that's not Laplace's demon. Laplace's demon is supposed to be an agent, a consciousness, something that is capable of knowing, where as the universe sort of just mindless lead chugs along from moment to moment. If there is a holographic dual to the whole history of the universe that is located in our future, that's not anything different than just saying the universe has a history, and that history can be encoded on a space like surface in the future. But it's not anything knowing it or calculating it or anything like that, so it's not really very demon-esque. Keith says, "In the Biggest Ideas, volume one, and on the podcast, you articulate the broad strokes of humanism and anti-humanism with respect to the laws of nature. One way you used to often refer to the laws... One way you used to often refer to the laws of nature is as unbreakable patterns. This resonated with my own humble attempts to understand the laws of nature largely influenced by a control engineering perspective. For example, in optimal control theory, physical laws are often directly formulated as hard dynamical constraints. My question is, where does this perspective sit in the human anti-human dichotomy?

2:51:35.6 SC: On the one hand, it fits well with a human view, but it seems that these natural constraints might have more on to them than mere commune ways of summarizing the world. At the same time, I feel inclined to stop short of the anti-human perspective that the laws are acting to bring the world into existence." Well, I think I'm not gonna be all that much here, I think that your impressions are right. If you have this perspective from optimal control theory, thinking of laws as constraints, I think that you are welcome to do that from either a human or anti-human perspective. I think that the existence of constraint laws doesn't naturally fall into one camp or the other. The tiny little footnote there is that most anti-humans are thinking of the laws as bringing the world into existence over time, helping to explain how the world goes from the state of one moment into the state at the next moment of time, whereas constraint laws do not tell you how to relate one moment of time to the other, they tell you what can be true at each moment of time.

2:52:41.3 SC: Like if you might have a constraint that the total charge in the universe, the total electric charge is zero, there's an equal number of positive charges and negative charges, that's not helping you explain how the universe evolves from moment to moment at all. It's just a fact at each moment. I'm kind of human myself, so I don't pretend to be an expert on what an anti-human would say, but they might... I don't know, they might have interesting views about constraint laws rather than dynamic ones. Ken Wolf says, "I recently had to do jury duty and I found the experience interesting, but it got me thinking about the parallels between the process of jury deliberation in the process of scientific investigation. I would like to hear about any experience you have had on a jury to the extent that you are able or comfortable. But my real question is whether you had any thoughts on how scientific method can inform the process of justice in general and the process of jury deliberation in particular, and what differences you see between the two."

2:53:38.7 SC: Well, yeah, unfortunately, I've never been on a jury. I've been called for jury duty a few times, I've gone. This is mostly when I was in LA, and I would go and I never got picked. It's not like they questioned me and send me away, I just sat there for a few hours and they said, "Okay, we're done for the day, we have enough jurors," so I guess I never served, so I can't really speak to any explicit experience here. I do think that science is about finding the true things that happen in the world through some kind of hypothetical deductive method based on empiricism. A lot of buzzwords there, but the idea is you explore different hypotheses for how the world can be and then you compare with the data. And you ask, which of these hypotheses best accords with the data, which is very similar to what a jury is supposed to be doing. There's extra considerations for a jury because you're not only trying to find the truth, you're trying to fit it into legal requirements, you're trying to assign responsibility or blame or reasonable doubt, probable cause, things like that, that scientists don't have to worry about.

2:54:45.5 SC: But in general, I do think that the overall way that science gets done and having credences of different ideas about how the universe works, updating them in the light of new evidence, being careful not to fall prey to your cognitive biases, doing blind experiments, all of those things, are just good general principles of reasoning, especially about things that happen in the universe, which you're not sure about. So how to actually implement something where juries are more trained in that, that I don't know. That's a more difficult social engineering question, I don't have a simple answer to. Rue Phillips says, "Is it common to consume... Sorry, it is common to consume violence and sex in the media." I shouldn't have paused there before saying in the media. Rue is talking about in the media, is not just saying that we all just consume violence and sex every day, some of us may be.

2:55:39.3 SC: "However, my anecdotal experience is that violence is far more acceptable to tolerate them sex. Think of how popular and widely promoted violent movies like John Wick are and how comparatively rare it is to see the equivalent acceptance and popularity of strong sexual content. Do you agree and have ideas on why murder a far greater immoral act is so much more acceptable to consume than sexual content? I think that the general impression you have is probably true. The way I would put it is, I think that at least here in the United States, I'm not gonna talk about other countries 'cause they're gonna be different, and I'm not as familiar enough to say, but here in the US, we are more uptight about sex than we are about violence or death or other big things like that. I don't think that there's necessarily any... But also, okay, so yes, I do think that there is some greater uptight-ness about sex, and that leads us to be a little squishy when it comes to allowing sex to be portrayed on a TV screen or a movie screen. That is true.

2:56:39.2 SC: Clearly, it's not that hard. There's plenty of it out there. But I also think that it's a slightly glib comparison, they're not the same kinds of things. The reasons why you might not want to portray violence on screen are different than the reasons why you might not want to portray sex on screen, it's not a simple one-dimensional scale of morality and say, "Well, this is immoral, therefore don't portray it on screen." Every movie or TV show has immoral things happening, that is where conflict and drama come from, okay, so it's not as if, well, we can't show this 'cause people will then go out and do it. There's difference as rules being invoked here. I don't have time, it's the end of the long AMA here, so I haven't thought through how to exactly articulate the ways in which they are different. But I would say if you care about this issue, I would think in a way that trial is to be fair to the people who are in favor of having violence, but not sex, having sex, but not violence, having both, having neither, all these.

2:57:48.3 SC: Try to be fair to all the different points of view and ask yourself whether or not you can come up with a internally consistent moral standpoint which stands behind these. It would be a more nuanced one than simply saying, "Don't show immoral things on screen," you might not want to make people uncomfortable, you might want to not give them ideas, you might want to be interested in the story and not something gratuitous. There's all sorts of considerations that you might have in mind. I don't have a completely well thought about the area of exactly how much you should be able to have. Eric Dovigi says, "A priority question. I am an English lecturer at the University of Arizona. We have a great astronomy program here, and I've become very interested in going back to school for something in the Space Sciences, but I can't decide between planetary sciences, astronomy, physics or math. Can you help me decide which field to choose?"

2:58:40.0 SC: I understand this is tricky since you don't know me, but any information you can give me about the job prospects of the different science fields will be super helpful. Yeah, I'm not even gonna be able to give you that much useful advice about the job prospects, I think that there's two things going on here, one is that you need to find your own match in terms of your own skills and interests, because something like astronomy and something like math are very different from each other. Math is... There's no data collecting in math. There's a lot of data collecting in astronomy, it's mostly data collecting. So the process is very different. The things you'll be thinking about will be very different. The problems you'll be solving, it's all very, very different, and probably you and your personality and your interests are obviously a better matched to one side of that than the other, but I don't know what that is, you gotta figure that out for yourself.

2:59:35.8 SC: The other is not only should you worry about your fit with the different intellectual activities they we're thinking of here, but you should also think about like you say the job prospects, how vibrant is the field, how interesting are the new results. Like maybe you think that math is super interesting, but the parts you think are interesting, were all solved in the 19th century. That's perfectly valid. In which case, becoming a professional mathematician is not the right thing to do. Planetary science is certainly a growth area right now, especially if you're in the exoplanet side of things. Though, we've talked about exoplanets several times, I think most recently with John Johnson. We're discovering a whole bunch of new exoplanets, and planetary sciences being revitalized exactly because of that. Astronomy is... Astronomy and physics and math, those three are very broad. There's very different kinds of Astronomy, different kinds of physics, different kinds of Math.

3:00:32.0 SC: So there, you would have to really take seriously the sub-fields, what kind of math or you being doing geometry or analysis or whatever. What kind of physics? Condensed matter, particle physics, gravity theory experiment? Astronomy, are you thinking more cosmology or you can still do planetary science within an astronomy department. And there's a million different things to do, so I think there's a lot further that you need to look in to figure out what would be a good match for you. Look at the advice I always give, which is, don't just think abstractly about the fields, really dig into where you might go for graduate school, so you say it might be at Arizona, for example, look at the actual professors who might be your advisors, and look at the papers that they have written over the last five years, because science proceeds by papers being written. Ask yourself which of these papers would you like to have been part of, writing or thinking about.

3:01:30.8 SC: I get the impression that in Math, collaboration is less common. In physics or astronomy, it's very common, so PhD advisors write papers with their students, whereas I think in math, the students... Like philosophy, for example, also students are more likely to write papers by themselves. So ask yourself about that also, but really dig into what is the specific work you would be most interested in being part of. And the last question is from Lagoja Allan Pieski who says, "My partner and I are having our first child." Congratulations. "To decide on whose last name it will have, we are using a quantum universe, a splitter. The idea being that we should both be happy in one branch of the universe, what do you think of this logic, especially for more serious issues than the fun one I mentioned?" Well, I will answer it in the context of the fun one because I think it matters that it's a fun one, I think that the logic is very good for the fun one of deciding which last name or even first name your child will have.

3:02:31.7 SC: The reason why is because either name is perfectly fine, no one's being hurt by this, and what will... As I very often say, you will not be able to talk to the versions of yourself that will exist, your co-descendants of your past self, that will exist in other branches of the wave functions, you will not be able to compare notes to see who was happy or anything like that. But the advantage of this method that you're using is that you will have a little bit of knowledge that you didn't have otherwise, and that knowledge can bring you happiness. So let's say, I'm not sure whether you'd be happier if your first child have your name or your partner's name, I really don't know, but let's say you'd be happier if your first child had your name and the universe later comes along and says, "No, your first child should have your partner's name," then it is perfectly valid for you to be happy knowing that if many-worlds interpretation of quantum mechanics is true, there is a version of you and your family where they have the different name. And it's completely harmless here in this world.

3:03:39.9 SC: For more serious issues where there really might be a difference in happiness levels, I would not use this method, I would only use it if there were really exactly a 50/50 uncertainty, and then you would do it just for fun, otherwise, do your best to make the right decision, otherwise you might be very unhappy if the decision doesn't come out your way. And with that, thanks very much for listening once again to the Mindscape AMA. Remember, the new goodies that we're experimenting with over on Patreon, the little video reflections, not gonna happen for the AMA, you've just listened to me for long enough, but in the real regular episodes, we're gonna start trying to do that. See how long it goes. Maybe it'll work, maybe it won't. Anyway, thanks once again for supporting Mindscape. Have a good month. Take care. Bye-bye.

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