Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - AMA | December 2020

Episode Date: December 9, 2020

Getting into the swing of things here with monthly Ask Me Anything episodes. If you missed the explanation last month, there is a Patreon page for people who wish to support Mindscape with a small donation per episode. Benefits include a warm feeling, social status, access to ad-free versions of the podcast, and the ability to ask questions once per month, which I answer over the course of a hilariously long podcast. Thanks to the generosity of Patreon supporters, we are now making the fruits of these monthly adventures available on the regular podcast feed. Here is the December 2020 edition. Note that there won't be a January 2021 edition, as I take a break from podcasting for the holidays. Have a good one everybody! Support Mindscape on Patreon.

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On the I-Heart Radio app or wherever you get your podcasts. Hello, everyone. Welcome to the December 2020. Ask Me Anything Edition of the Mindscape podcast. I'm your host, Sean Carroll. As you probably know, last month's AMA, which is done for Patreon supporters, you can always support Mindscape at patreon.com slash Sean M. Carroll. Patreon supporters get to ask questions for the monthly AMA, and they voted to release the answers to the general public. So we sort of tentatively did that half-heartedly a few months ago on YouTube. but it wasn't really quite part of the regular podcast feed. Last month was the first time we did it for real on the podcast feed. And so the good news is that got a few more Patreon supporters,

all of whom want to ask AMA questions, which is great. So we have some new listeners here. And this is the first month where it'll be exactly the same podcast being released, the episode, including this introductory part. So hello, everyone, who is a new supporter, and thank you to all of the support. that we've had for a while. This is a great tradition we have. And also, just so you know, we're not going to have a January 2021 ask me anything. I take a couple of weeks off from the whole

podcast thing for the end of December beginning of January. We all need to take a break, even podcasters like myself. So the next AMA will be, I will put up the post asking for questions at the end of January and be releasing the episode in the beginning of February. So hopefully that makes perfect sense. Anyway, lots of questions, as you might expect today, because we have some new listeners and askers of questions. Not everyone knows the rules. The biggest rule being you only get one question to ask, okay? So I know some people ask more than one. If you do, it's actually perfectly okay to ask more than one question, but I'm only going to answer one of the questions. Any topic is okay, but nothing that requires me to do work. That might be read a

paper, watch a video, read some document or anything like that. This is just an opportunity to get information or opinions from my brain without me doing any work. Me doing no work is a very common criterion for things I try to do in the world. What was the other thing? Anything else? Oh yeah, you know, the number of questions is large. This episode will be long. So to the extent possible, try to aim for concision in one's asking of questions. I do edit the questions down, but that takes time for me. And, you know, everyone else wants to listen to the answers to their questions. So I know that there's a temptation to, you know, tell a story, develop your characters,

have three-act structures with conflicts and heartbreaks and points of no return. But the AMA questions are best when they're short and sweet and to the point. And, you know, most of them are. But I'm just giving you a reminder of that that's how it successfully works. Otherwise, yeah, so here we are, beginning of December. Hope everyone had a good Thanksgiving if you celebrate that. Good hoping ahead of time that you will have good winter holidays, whatever your favorite winter holiday might be. Good news being that we might have a vaccine.

I mean, there's good news because Donald Trump is not going to be president anymore, but you all knew that. The other good news is that there might be vaccines coming for COVID-19. The lockdown pandemic has had its toll, taking a toll on all of us, myself and included, I've been, as I'm very happy to say, I suffer from the pandemic lockdown way less than most people do, given my job, et cetera, but still, you know, ready to get out there, ready to travel again. There's a lot of places I would have visited this year that I didn't, including spending a lot more time in Santa Fe, where I'm now an external professor and talking to the people there. And so I hope that everyone listening is doing more or less okay in the pandemic, and I'm hoping

that things will return mostly to normal. I know that people have talked a lot about, will it really be normal if we get a vaccine and everyone's vaccinated? And maybe it won't be. Maybe everyone will still be wearing masks. Maybe they won't allow concerts or bars or whatever. I actually am optimistic that we will get mostly back to normal.

But as you know, especially if you've listened to the podcast episodes we did with Tara Smith and David Baltimore, developing a vaccine for something like this is very, very tricky. you know, testing it, figuring out that there's no terribly deleterious side effects and so forth. It can take a long time. I'm optimistic about the vaccines, but I'm sure that there will be snafus down the road. So it's hard to predict exactly when it will go into wide-scale circulation. But still, I think it's okay to be a little optimistic.

We've been pessimistic for a while. Things have been tough right now here in L.A., as well as the rest of the United States, certainly. We're in the middle of a wave again, you know, I guess the third wave by now. We're locking down, no more restaurants anymore, anything like that here in L.A. So hopefully that will do a good job, and even before the vaccine comes, we'll be able to return somewhat to normal. Anyway, with all that, so many questions about the universe and life and everything. So let's go. Sam Barta says, I've heard you say both that in the many worlds interpretation of quantum mechanics,

the observer and detector are treated as quantum, and at other times that macroscopic objects are treated classically due to decoherence. How can macroscopic objects be in superpositions if their amplitudes are spiked due to being measured by the environment? Can you please help me understand this tension and or my confusion? Sure. It's just a difference between what you perceive on a single branch of the wave function versus what's going on in the wave function of the universe, the collection of all the branches

considered together. So when a Geiger counter goes off, right, because it's measured some quantum mechanical event, whether or not you are Schrodinger's cat or just a person carrying a Geiger counter, that means that some little nucleus of an atom has its quantum state become entangled with the rest of the world. It is either decayed or not decayed. And so the world has branched in two, but also macroscopically, you heard the Geiger counter go off, and therefore you have branched into. But you have to change what you mean by the word you.

There's now two different people, one of whom heard the Geiger counter go off, one of whom didn't. So when we say things like the person is a quantum system and they're in a superposition, that's completely true in the wave function of the universe. There's one person who heard the Geiger counter and responded appropriately and one who didn't. But you can also say that a person is localized spatially and in other quantum mechanical variables, but that means on a single branch. So that's the thing about the emergence of the classical limit in quantum mechanics is that not only is their branching, but that on individual branches, physics behaves more or less classically. So on individual branches, we expect people and planets and things like that to have more or less well-defined locations in the universe, more or less well-defined. Velocities up to some error, but still pretty well-defined.

And that's completely compatible with the wave function of the universe, including superpositions where those people are in very different positions or velocities or whatever. Rakesh Patel says, any tips on time management? There are so many books, podcast, YouTube, blog, side projects, etc. Have you found a way to manage this? Well, you know, I'm actually not someone who is very formal about these things. You know, when it comes to productivity tips, time management tips, things like that. I joke about it, but honestly, I don't have much of a system. And partly that's because in the kind of work that I do, whether it's, you know, solving equations or thinking about physics or writing or whatever.

that kind of work, you can't do it on demand. You can't do it on schedule, right? You know, I have moments when I'm very inspired and I want to do it and that you would have trouble tearing me away from it. And other times where I'm sitting there and I know that I should be doing some writing or some physics or whatever and it's just not coming, right? So I find it almost impossible to plan those things ahead of time. You know, podcasting, you have to plan ahead of time. You had to actually make an appointment with another person. Very annoying. But, you know, that's also something I could try to plan ahead for. for. So no, I do not have any dips on time management. I just try to minimize the bad things, the distractions, and, you know, carve out room for everything else. But as I've said before, on the podcast and elsewhere, I'm the kind of person who likes to have a million things going at once in different areas. So what works for me is not necessarily going to work for somebody else. Sorry about that. Robert Ruxendrescue says, we know a black hole is a region of space time where the entropy is very high and gravity dominates. Is there any mathematical reason why the Big Bang universe, why the Big Bang slash the universe can't be a white hole? It's actually very similar

to a white hole. It's almost exactly the same with one possible difference. So a white hole is just a time reversed version of a black hole. So in a black hole, if you have like a star collapsing or something like that, the star collapses, its density increases, and also the metric that measures the curvature of space, time becomes singular at a moment in the future of the black hole, which we call the singularity. And that's almost exactly the same as what happens at the Big Bang, plate in reverse. At the Big Bang, we nominally start with an infinite, at least that's what the equations say. We don't really believe it physically, but we imagine that there's something taking the place of infinite density and curvature that then expands and dilutes so that you get a more or less sensible classical Big Bang. But the difference is that as far as we know, the Big Bang was everywhere.

But the Big Bang event, that moment of time extended throughout the universe, everywhere in the universe, again, as far as we know, because we don't know for sure. But in the models that we play with, we imagine the Big Bang started all throughout space at whatever moment of time that was. So there's no such thing as outside the Big Bang. That's the difference between a white hole and the Big Bang. A white hole, if you really literally take it as a backwards in time, black hole, has an inside and outside, right? There's an event horizon. For a black hole, the event horizon is something you can go into but not come out of. For the white hole, the event horizon is something you can go out of but not come into.

But there's still, you imagine that there is the white hole and there's something called outside the white hole. And for the Big Bang, as far as we know, there's no such thing. Otherwise, they're very, very similar. Christian Dobo says, as a lay person, I'm still not totally confused. I understand what it means that according to special relativity, one cannot talk about what is happening now on Kepler 452B. What if the United Federation of Planets were to designate a zero coordinate in space time, then send ships with perfectly synchronized clocks to numerous planets? And then it goes on from there.

So the point is, sure, you can absolutely lay out what we would call a reference frame in relativity, special relativity, general relativity, or whatever. The only claim on the part of relativity is that there's nothing special about your reference frame. If the United Federation of Planets wants to lay out one reference frame upon which we can draw upon to talk about what is happening at one moment on this planet and some other planet, there's nothing to stop the Klingons or the Romulans from laying out a completely different reference frame, which is, you know, tilted in the space time with respect to the first one. So either one of those is perfectly okay.

There's nothing in special relativity. It says we can't talk about simultaneity. It's just that it's not objective. It's not universal. It's not built into space time itself. It's just a choice individual people choose to make. Stephen Noble says, have you considered any guests who would talk to your audience

about advances in programming languages? I haven't thought about that. I have thought about computer science in different ways. It's always a little bit tricky because, you know, number one, you want to make it accessible to people who know nothing about programming languages. And number two, what I'd like to talk about in the podcast are the big ideas behind what's going on, not the specific implementations thereof. So I'm not sure that I would be able to pull that off in terms of talking about advances in programming languages in a way that is user-friendly and also big picture-oriented.

But, you know, I'm always happy to take suggestions for possible guests, if you have any in mind. Sam Bartah asks another question. I just said that you only had to have one question, but he sneaks in another one, which is, who would you rather trade Ben Simmons or Joelle Embed? So I don't have to answer that because it's your second question. So therefore, I'm not going to say who I'd rather trade, although I think the answer is actually pretty obvious. Damien Alexiev says, does the relativity of simultaneity in the theory of relativity allow for a frame of reference from which the temporal direction of events in our frame of reference appears reversed? Sure, 100%.

I mean, nothing special about relativity there. Newtonian space time has the same thing. Just use a time coordinate which counts down instead of goes up. We actually do that, right? When we launch rocket ships, 10-9, 876, 5, 4, 3,21, right? That is a reversed time coordinate. So you could easily imagine a time coordinate with respect to which you would say the change of entropy is negative with respect to that time coordinate.

No problem doing that either in Newtonian mechanics or in relativity. Alon G says, aren't you afraid to live on top of the San Andreas' fault? So, no, not really afraid of that. For many reasons, number one, I don't live on top of the San Andreas fault. You know, it runs nearby, but I'm not on top of it. Number two, you know, there's always worries that you can have anywhere in the world, whether it's weather or natural disasters or diseases or whatever. I think that Southern California is actually relatively safe compared to a lot of places.

Number three, you know, we have been, you know, places like California that have been subject to earthquakes for a long time. Other places also like Japan or other places in the Pacific Rim have come up with strategies for dealing with them. You know, the structural integrity of buildings, for example, it's really, really good here in Southern California. In fact, if there were a really, really big earthquake, which is absolutely a worry that you should take serious, Seriously, the thing to worry about is not like your house would fall down or your apartment building would fall down or even that it would be set on fire or anything like that. The thing to worry about is it could shear the electrical and water supplies to the Los Angeles basin, right?

So that's a big problem because you know, you just have an earthquake that moves two plates with respect to each other. Los Angeles, love it though I do, is very much dependent on the outside. world for electricity, of course, but also just for water. And so that would be a big problem. And therefore, like any good, well-prepared Los Angeles, we have an earthquake kit that has some, you know, power generating, just solar power generating things. We don't have like a gasoline power generator, but we have enough food and enough water to get by for at least a couple weeks here. And so other than that, you know, you have to choose your poisons in terms of bad things that

can happen anywhere, and I think Los Angeles is not much worse or better than most places. P. Walder says, following on from the David Eagleman podcast, if a congenitally blind individual received visual signals translated into a set of vibrations in a vest or some other device, would that person actually have the same or similar visual experience that a sighted person experiencing the same signal directly would have? I'm not exactly the person to ask, not being a neuroscientist myself. I think it's a very good question. My guess is no. It would not be the same experience.

I'm not even sure, though, what it would mean to say that it's the same experience, right? This is the old philosophy problem of is my experience of the color red as a cited person, the same as your experience of the color red if you were also a cited person. And I think that part of the answer to that question is, what do you mean the same? What would that even entail? There could be some operational similarities in terms of how you react, how you respond to the impulse that you get sensory input from the outside world. Naively, of course, I would guess that it's very different because what you're directly feeling

is some touch or electrochemical stimulation from the gadget that is very different than what your eyes do. But in principle, I guess, since I'm not an expert, I could imagine that things get wired up in your nervous system so that those impulses go right to what would be the visual cortex in other people. So I think that the interesting question here is how far could you go in arranging it that these other sensory modalities actually gave you exactly or a very, very good approximation to literal vision? I don't know. I think it's certainly the current state of the art not very far, but maybe someday that will be possible. Paul Hess says,

Please help me reconcile the concept that the laws of physics are completely reversible and not dependent on the arrow of time with the concept that quantum information is destroyed upon measuring. Well, it depends on your favorite interpretation of quantum mechanics, right?

If you think that wave functions in quantum mechanics truly collapse, as some people do, whether because you've measured it or just spontaneously or because of some physical trigger. There are people who believe all three of those things.

Those are three different things. One, wave functions collapse because they're measured. Two, wave functions collapse randomly. Three, wave functions collapse when some threshold is reached. Okay. There are theories of quantum mechanics that rely on all of those different things. But in every one of those options, the laws of physics are not reversible. In the many world's interpretation, or for that matter, in pilot wave theories,

boean hidden variable theories, the laws of physics are reversible, but quantum information is not destroyed upon measuring. It might be lost. It might be lost in either version, even though boeomians don't like to talk about other branches of the wave function,

the wave function still evolves according to the Schrodinger equation, and no information about that is lost. It is still true that if you knew everything there wasn't about the wave function, and you know the Hamiltonian, the polygon to Schrodinger's equation, then you would have the information you need

to evolve the wave function forward and backward in time. What happens when the wave function branches is that you have access to less and less of the wave function because you only live on one branch at a time. But that doesn't mean the information is really destroyed. It's just hidden from you. Chris Rogers says, In my fruitless efforts to understand general relativity,

I keep hearing that on Earth, objects don't fall due to the pull of gravity, but instead the ground accelerates up. What's up with that? If this is the case, what is driving the acceleration? So, yeah, I mean, this is an optional but very recommendable shift of perspective when you go from Newtonian physics to general relativity. In Newtonian mechanics, the force of gravity is a force that acts on objects and accelerates them, much like the electric force or whatever, other kinds of forces you can imagine. In general relativity, it turns out to be way more convenient to define a, uh,

At rest, or not, I shouldn't say at rest because that's not well defined, but unaccelerated, right? An unaccelerated, unforced motion through the universe is defined as freefall. Trajectories that just move without feeling anything, right? When you're standing on the ground or sitting on a chair, you feel something. The ground is pushing up against you or the chair is pushing up against your butt, okay? That's not an inertial trajectory, what we would call in general relativity. you're being pushed on. So the general relativist would say it's only freefall that we should think of as an unforced trajectory,

and zero acceleration means you're in freefall. And if that's the case, since we're not in free fall standing on the earth, then clearly the earth must be accelerating us. And in order for that to happen, the surface of the earth must itself be accelerating. So if you want to know what's driving it, it's just the pressure in size. the earth, right? You're just asking, what is holding up the earth? Why is the ground I'm walking on not freely falling toward the center of the earth? Well, the earth is solid, and there are pressure forces inside, and those are pushing, and you feel the push. You feel it on your feet when

you walk around, okay? It's actually not such a difficult change of perspective to get into once you're used to it, even though the language is a little bit different than maybe what you were grown up with. Stephen Berniger says, I asked you about the presidential elections before the elections, and I'm now asking you again, not only about who won, but about the state of U.S. society post-election.

From the outside, it looks like a weird theater performed by a split society where the two sides have a very different perception of reality. Do you believe there's a way for the new administration to bring the two sides closer together, or will we have to learn to live with a deeply split society in the United States? Well, I do think that there is a split in the United States.

If you're interested, I did a podcast episode with Will Wilkinson on exactly this. And it's not just another one with Ezra Klein on exactly this. With Ezra, I was talking about polarization as a political phenomenon. With Will, I was talking about the urban rural divide and how that is the single biggest driver of the polarization. And so, you know, it's vastly oversimplified, but the two countries that you have in the United States are the ones who live in cities and suburbs and the ones who are more. rural. And in some, again, extremely simplistic diagnosis of why Biden won in 2020, but Trump won in 2016, it's because people in the suburbs switch from being Republican voters to Democratic voters a little bit. So the urban democratic sphere widened a little bit to include some suburbs.

I don't, and, you know, so the point of both those podcasts was, again, in the very mindscapey tradition. We aren't just trying to place blame on this side or that side. We were trying to understand, is there some reason why this polarization seems larger now than it used to be? Without being a value judgment, just trying to understand it. And there are reasons why. I mean, in some, you know, as Ezra points out, you know, in some sense, it was surprising 40, 50 years ago when we weren't as polarized as we are right now. That's the surprise. In some sense, we're returning to a support of more natural state. Now, that is enormously complicated by the change in the media landscape, right, by the fact that people get their news in very different ways than they used to. So

that provides an engine for increasing the partisan divide to the point where, as you say, it's almost like they have a different perception of reality. So, but the other thing, which I talked about with Ezra was that, you know, politicians are just becoming better game theorists in some sense. And they're realizing that, Some of them are realizing that the way to win the political game of being elected over and over again, if that's your goal, is not always the way to make the country better. So if all you ever want to do is get elected and that's what politicians want to do, if that's true, then you're in trouble. Then you can gain the system and the country will suffer thereby. So that's the question to ask.

You know, as we've seen the attempts to overturn the election results fail miserably, on the one hand, we can be happy that a lot of local officials, even Republicans, have been very firm in not allowing fair election results to be overturned. But at the same time, we can be disappointed that a lot of national Republican officials seem to be perfectly happy with the attention. even if the attempt fails, right? It certainly seems as if, you know, if the election had been a lot closer, then they would have been perfectly happy to overturn the results. And it's just it did fail because the beatdown was pretty bad. And so that's a worry going forward, absolutely. And I think that this is why I've talked about democracy on the podcast and we'll continue to talk about it, because doing democracy right isn't easy. It's not obvious. And as we're learning, we're not very good at it.

And that is something for which I can say, you know, both sides are to blame. I think that saying both sides are to blame in general is a bad strategy because often it's just one side. But the idea that we should listen to the other side and take their desires into account and try to reason with them is an important one. And both Democrats and Republicans are bad at it these days. Nerves are raw, right? and people are very upset with other family members and so forth. So I don't know. I'm not super-duper optimistic about bridging divides,

but I know that we have to keep trying. That's the only way to go forward if we're going to keep this democratic experiment going strong. Clyde Schechter says, let's imagine that closed timeline curves really exist. I get to my rocket ship and follow a trajectory, arriving back where I started before I left. Wouldn't it also follow that my brain would be in the earlier state as well,

and I would have no memory of the journey. So no, that's it. I can actually answer this one. It's a rare time travel question where the answer is perfectly unambiguous. No, you personally move forward in time. That's the idea of being on a closed time like curve. You go back in time as far as the history of the universe is concerned.

So you can go back to, you know, I don't know, 1950. But in your personal timeline, you are only getting older. There's no part of you that reverse. ages or anything like that. So it is absolutely not true that you, your brain or your memories would be back in an earlier state. That's one of the reasons why time travel is hard to understand and probably not possible because it breaks the connection between time is viewed by the universe as a whole and time is viewed by you personally. Jamie Tan says, a photon of lights proper time is zero. A photon of lights proper time is zero. I should

pronounced it. That means that for a photon, time and consequently distance do not exist, making its speed from his own perspective infinite. But we measure the speed of light to be 186,000 miles per second, which is a finite value. Now, what makes for the differential? So I always, you know, there's a tricky thing to do when you talk about the perspective of a photon. Photons don't have perspectives, not just because they're single particles, although that's more than enough reason to say they don't have a perspective, but also because they don't experience the passage of time. Photons don't experience anything at all.

If you don't experience time, then you experience nothing. When we say that the speed of light is such and such a thing, clearly that's not from the photons perspective. That's from our perspective. We use miles and seconds or centimeters and seconds or whatever you want. So that velocity is what we would measure

using our measuring apparatus. And this causes a lot of puzzles with photons, not experience. time because we experience time and we sort of imagine taking the limit as things slow down more and more and more, but that's not how it is. There's literally zero experience when you're a photon. Duncan Palmer says, as the pandemic has advanced, I've noticed many of us have adjusted our sartorial preferences. In the privacy of your homeworking environment, what is your daily outfit of choice and has it changed much since the beginning of the year? It hasn't changed much

since the beginning of the year. You know, I go back and forth a little bit. You know, usually it's pretty casual, you know, sweatpants, t-shirts, hoodie, that kind of thing. Sweater or whatever. But, you know, it's, I don't like it. I know that there's a lot of smart people, whether they're scientists or business people or whatever, who, you know, they're extreme examples, of course, but they literally just wear exactly the same clothes every day because they say, well, that saves me from waste.

some of my precious mental resources on deciding what to wear. That is not me. I actually enjoy things other than just doing the science or whatever. And one of the things I enjoy is aesthetic pleasures, looking good and looking at other things that look good. I like it when people wear good clothes, interesting clothes, whether it's casual or formal. It doesn't really matter to me. But the idea of wearing clothes and having a look, I think, is a part of what makes life interesting and fun. And so at the same time, I can't quite bring myself to dress up or even dress as nicely as I would if I were going into the office when I know I'm just going to spend all my time sitting here at home. So part of me keeps telling myself I should dress a little bit nicely, if only for Jennifer and the cat's benefit or maybe for my benefit. So I haven't gone quite as slob-oriented as some people, but I'm definitely dressing down more than I had before.

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That's ODOO.com. Humberto Nani says, how are things in California? Like, are students able to learn? Is the election topic settled down? How are you able to go out and feel safe with regard to health and things like that? You know, look, it's mostly normal here in California. Like I said at the beginning of the podcast, we've locked down again in terms of going out at night. Restaurants for a long time now were doing outdoor dining.

and I'm really, really incredibly supportive of local restaurants and heartbroken that they're going to be suffering so much. So we have been going, you know, try once a week or two out to a local restaurant and ordering in, take out a delivery when we can. But the going out has now gone away, right? There's just no more of that for the next, from between now and I guess three weeks, three or four weeks, because things have gotten bad here in L.A. And that also, you know, that I don't, I will confess, I do not follow very much the whole school situation since even at Caltech, I don't teach courses. I think most of the courses online are online now at Caltech and other universities in California. But it doesn't affect my life very much since I'm not teaching. And so I don't even know whether pre-college courses, schools are open or not. I don't think, you know, it's been a little disappointing how local municipalities around the country and around the world have chosen to sometimes do things for what is more political reasons than for scientific reasons.

And sometimes that criticism is oriented toward not shutting down. People don't shut down as nearly as much as they should because it's politically bad. But other places, they shut down too many things or the wrong things, right? I mean, it's just, it just seems hard to get it right. But anyway, yeah, I mean, the election is still bubbling along on Twitter and the news media, but life goes on. We all know that come January 20th, Biden's going to get inaugurated. It'll be difficult for him. There'll be a lot of challenges.

Let's just put it that way. There's a lot of, you know, regulations that are being rapidly undone in the last couple weeks as people try to cause harm on their way out. but mostly things are, you know, going on. Life is going on, and we're going to try our best to pick up the pieces next year. Seamus Maxwell says, I was sad and learned of the recent death of David Graber, anthropologist and author of debt, the first 5,000 years, and bullshit jobs. Was he ever on your radar as a potential mindscape guest?

You know, I knew about David Graber, and I was aware of his work, and I think that, you know, he's the kind of person who I would think of as a potential guest, but I wouldn't say that I got very close to inviting him at any point. Of course, when so many people who knew and loved his work said so many nice things after he died, I did feel regretful that I never had that chance. So there's some lesson in there for living life to his fullest, but you don't know who is going to be around next year or five years from now. So it's not a very helpful guide to inviting people on podcasts.

Sharon says, like many people, I'm worried about global rise in right-wing national. nationalism and authoritarianism, climate change, global wealth, and resource inequalities, etc. I'm on the final leg of a PhD in physics, and while I love my research topic, it doesn't have a lot of practical applications. Lately, I've been wondering what the ethics of working in such a non-practical field are, when my skills can be useful elsewhere. For instance, while I can't personally do much about the global rise in authoritarianism, I know that I have a skill set to switch to working on climate modeling and things like that and help fight the good fight. Have you ever felt anything similar about working in an abstract field? You know, I'm sympathetic to the impulse that, you know, the work that we do in so much as it's

possible, it's nice that that has a tangible positive effect on the world. And I'm also perfectly aware that most of the work I do is pretty darn abstract with no immediate to tangible benefits. But I do think, but there's a couple things going on. One is, I think that it's important that we have a lot of things going on. So even when there are big disastrous things, whether it's authoritarianism or climate change and so forth, I am absolutely not of the belief that everyone should drop everything and work on those things.

Because that's kind of self-defeating, right? I mean, the reason why those things are bad is because they get in the way of doing the good parts of living life and being a human being. So, and part of those good parts are learning about the world. So I think that, you know, not just being a physicist, but being a musician or an artist or a writer are things that are important to keep doing for some fraction of the human population, even as we face important crises. And the other thing is, I think that there is some positive aspect of the work that I do, whether it's understanding how the universe works at a deep level might lead to some future scientific breakthroughs, even though it's a little loose of a connection. but also I can have an educational impact, right?

I mean, and that is part of the reason why I don't just do scientific research and write papers, but I also write books and do podcasts and give talks and things like that. That's also a reason why the podcast is not just about physics, because I think there's more than one message to get out there. So if anyone who is going into physics or planning to go into physics decides that, you know what, I want to have a more immediate, tangible right-away impact to make the world a better place, then I'm completely on board with that. I think that's a wonderful reason to switch fields.

But I don't think it's necessary. I don't think you're a bad person. I mean, what would I say, right? But I don't think you're a bad person. If you continue to think about the way you function of the universe, even as the globe is getting warmer due to human climate change-induced kind of things. I guess I did. I ended that sentence badly, not climate change-induced.

whether because the climate is changing due to human activity. Paul says, are there any proposed solution to the vacuum catastrophe that you find compelling? Paul, I'm honestly not sure what you mean by the vacuum catastrophe. Do you mean the cosmological constant problem, which says that we think that the vacuum energy should be much bigger than it is, or do you mean a possible vacuum decay or other things? So you need to be, give me more details before I can answer that one. Sorry. Maxime Alexandrovich, but sorry, to any of the answers that I can think of, to any of the meanings I can think of, to vacuum catastrophe, no, I do not find any of the solutions compelling. But I might not understand what do you mean. Maxime Alexandrovich says, there is currently huge social resistance in Poland, including massive public demonstrations and protests. It is caused by the sentence of highest court. It is a new interpretation of Polish constitution, which says that it is not constitutional to abort a pregnancy.

The court argues that the life should be protected at all cost, even if there are huge chances, that this life will end very quickly after birth or a child will be deformed, etc. What is your approach to abortion? When a human starts to be human and is active compassion to abort a life? When is it an active compassion to abort a life if according to a series of tests, it's almost sure that it won't be a normal healthy life? So there's a couple of different questions that are sort of mixed in together here. I mean, there's the question of, does the mother of a child, does the woman who is pregnant have a right to have an abortion? And there's a separate question of, is it better for the child to be aborted if it's not going to have a normal, healthy life? You know, I'm, for these kinds of questions, the default answer is that the mother should decide in my point of view. I'm not the one carrying around this baby.

I certainly don't think that it's a moral mistake to give birth to a child, even if you know that it will be disabled or unhealthy in some way. I think you have every right to do that, and then you should, you know, you do have a responsibility once it happens to try to make sure that that child's life is as pleasant as possible. But, you know, no, but I don't, there's so, I mean, again, this is too much, I'm stumbling because there's too much to say here. One big question is, are you deontologist or consequentialist about morality, right? So I think that a lot of the discussion of abortion has this, well, a lot of the rhetoric from people who are against abortion has this kind of deontologist perspective where they think that there is a sacredness to life. And ending life in any way, even a potential life, is a moral mistake. And I completely don't share that conviction. I think that there's nothing sacred about life.

I'm also not consequentialist. I think that I'm sort of a half and half when it comes to morality. And I don't think that my moral system is very well articulated. So I couldn't even give you the explicit guidelines. But I don't think that there is some number out there like utility that we should just add up. So I don't think that giving birth to as many people as possible is a good thing either. I know that Peter Singer and among other people have made arguments that it is better not to give birth to people who will suffer once they're born than to give birth to them. But yeah, I just don't buy that.

I think there is some value in existing, but I don't think that we should work to maximize that value. So, but for the down-to-earth practical questions, let the mother decide. It would be my rule of them. Dan O'Neill says, if you could snap your fingers and instantly have the same level of not. knowledge and expertise in some field of science outside physics, what would you choose and why? Yeah, I thought about that. Yeah, I mean, it's a good question. There's just too many.

It's just very hard to pick. And, you know, the secret problem with this question is it's not multiple choice. You didn't give me a list of options. So, you know, is all of biological science count or is just, you know, paleontology count, right? I mean, the answer would be very different. Possibly, you know, if I could choose all biological science, I'd probably choose that. Because biology is, you know, on the one hand, we've learned a lot and we know a lot. On the other hand, there's a lot more to learn.

And maybe, you know, combining that with some physics knowledge would lead to great things. Whereas with, you know, psychology or sociology or political science or economics, we know, I think, relative to what there is to be known a lot less than we do with biology and physics. So it would be fun to know that stuff. but maybe a little bit less tangible progress could be made for someone like me who likes to write down theories and make predictions and stuff like that. But I reserve the right to completely change my mind

about this question if I think about it more because it doesn't have an obvious answer to me. Good question. Nathan Egan says, as I understand it, black hole evaporation is caused by matter-antimatter pairs forming near the black hole with one entering and one leaving.

Wouldn't the antimatter particle reduce the mass of the black hole and the matter particle increased the mass, with a 50-50 chance of either particle entering or leaving the black hole having a net zero effect on its mass. So no. Both matter particles and antimatter particles

have positive mass. There are no particles that have a negative mass. But a particle can have a negative energy from a certain perspective in general relativity. So I think what you're getting at here is the difference between matter and antimatter, and for these purposes, there is zero. Okay?

The only question, the reason why black holes lose mass is because, from this perspective of particle, anti-particle being created, one going in, one going out, from the point of view of an outside observer, the particle coming out has a positive energy, and the particle going in has a negative energy. And you might think,

well, how can a particle of a positive mass but a negative energy? The mass of a particle, e-equals mc-squared says, because what you should do to think of what do you mean by the mass of a particle is, go to its rest frame, okay, stand next to the particle, and ask how much energy it has. And however much energy it has, divide that by C squared. We're going to call that parameter the mass.

E divided by C squared is the rest mass of the particle, okay? But to the point of view of someone very far outside the black hole, the particle falling in, they're not in the rest frame. In fact, they can't be in the rest frame. The particles on the other side of an event horizon. So that's why it's okay in some sense for that infalling particle to have negative mass. Sorry, negative energy, not negative mass. That's the whole point.

It has nothing to do with matter versus antimatter. It just has to do with this weird quirk of general relativity that a particle inside an event horizon can have a negative amount of energy from the perspective of a person outside the black hole. Nikos Sakharagas says, do you believe that uploading our consciousness, thus copying it, would ever really work? Meaning that even if we are able to fully copy our mind in the cloud,

doesn't that mean that there would be just an identical mind, but with a different first-person experience? So it will never be the initial you, but a copy of you. So I think, again, there's two issues, two sets of issues colliding here. One is, could you upload, forget about copying just for a second. could you upload your brain state into a computer and essentially continue on your life, your perceptions and your memories and your feelings and so forth in a computer?

And I think that that's possible in principle, but I think it's super duper hard, way harder than a lot of people suspect it is going to be. But I do think it's impossible. It is possible in principle. There's no objection to that from the point of view of the laws of physics or something like that. The second question is, you know, if it is copying rather than destroying your brain and uploading the information, then is there another copy of you? Sure. But, you know, I think that this is something that is driven home by thinking about the many worlds interpretation of quantum mechanics, which is that we should think of you as existing differently at different moments of time in the first place. You now is not the you of 10 minutes ago or the you 10 minutes from now. And they have. a relationship to each other. There's a reason why we can usefully think of you 10 minutes ago as being the same person in some sense as you 10 minutes in the future, but they're not the same,

right? You have 10 more, 20 more minutes worth of memories. So if you take that seriously, the idea that there's a copy of you that's living in a computer, and therefore there are now two of you, shouldn't be any problem at all. Like there's one of you before, now there's two of you. What that means is there are two people who share the same past, but they're different now. So it's exactly like the many worlds interpretation in that sense. Paul Torek says, this is a follow-up to Gregory Kusnik's question from last time about the protein crystal that computes a universe simulation. The crystal starts at some plane, call at the bottom, which represents the initial conditions of the simulated universe, then each successive layer represents the next state. Gregory didn't say anything about entropy in this simulation.

Suppose we can group items in each horizontal plane into macroscopic objects, and suppose entropy increases for those macroscopic states as we proceed further from the initial plane. Suppose this increasing entropy has a lot to do with how the people of the simulated universe can remember earlier states but not later ones, etc. Does this satisfy your requirement for a time-like aspect so that the people in the simulation could experience something? So I think, well, so let me be perfectly honest. My commitments to questions like this are not very strong. I am not sure what the right answer is to questions like this. I think there's a good question.

You know, I've thought about it a little bit without, you know, absolutely landing on an answer. Here is my tentative answer. There is a sense in which. So I think, let me just rephrase the thought experiment in different words to just make sure that I'm answering you the same question. Well, you can tell me, if I'm answering the same question you're asking. If you believe that there's a four-dimensional block universe that we live in, right? Three dimensions of space, one dimension of time. If you believe, like I do, from an eternalist perspective, that all instances of time are equally real,

that in some sense, the four-dimensional universe is like a stack of three-dimensional slices of time with things in slightly different places. So could you then create a stack? of things that exist that extend through space rather than through time, but have all of the characteristics of, you know, evolving one leading into the other, obeying some patterns that we would recognize as laws of physics and so forth, even though they're extending just through space, not through time. And then would it also be okay to think of the little parts of that stack that you've created

as experiencing things, having consciousness, and so forth? So my tentative answer is, yes, in some sense, it would be okay to think of them in that way. But not in a very useful sense, not in our sense, because our experience of the world and consciousness and time is entirely intertwined with the fact that we experience time passing in some way, that we, that when we talk about ourselves, we mean some instantiation of matter in a certain configuration, at a certain configuration, certain moment of time. So our experience of being conscious and making choices just relies on the actual time coordinate that we have, or the actual time direction, or the arrow of time, or however you want to put it. So something that is analogous to that and similar to that, but which from our perspective only extends in space and not in time, wouldn't be conscious or experiencing in our sense. There might be another sense in which it is, but it would be so different.

from ours, that it's not clear to me what use it would have. Okay? And, you know, you're tempted to say, well, okay, I had this stack of things. I'm going to, like, poke at it and change it. But then you're automatically introducing some change over time, which is cheating by the rules of the thought experiment. So I think that's my answer. But I don't think it's a very sophisticated philosophical view. So this is one of the things I'm definitely willing to be open-minded about.

The Vermilinin says, do you believe? space time is continuous or discreet? How do you think that could be tested and maybe eventually proven? I don't think, you know, so the deflationary answer is it's neither one. I think space time is an approximation, right? I think space time is a limit in the classical limit to a quantum mechanical wave function. So when you say the words is space time continuous or discrete, you're secretly already talking classically. You're acting as if there's some thing called space time, but could be either continuous or discrete, right? And I don't believe in that thing. I believe in the wave function of the universe. And I believe that

there are different ways of describing parts of the wave function of the universe that, to us, are described in the language of classical physics. Oh, look, there's space time, there's some fields, there's some objects, things like that. So I think of the very question of whether space time is continuous or discrete, is ill-posed, because space-time is not a fundamental thing. You do ask, how could it be tested or experimentally proven? There's a related thing. So from my perspective, where you should always start with wave functions and quantum states first, rather than asking, should space-time be continuous or discrete, you should be asking,

is the Hilbert space, is the space of all possible quantum wave functions, infinite-dimensional, which is kind of like continuous, or finite-dimensional, which is kind of like discreet. And I'm very hopeful that there could be experimental testable consequences if Hilbert Space is finite dimensional. I think it probably is finite dimensional. The obvious experimental consequence is a violation of Lorentz invariance, a violation of Einstein's sacred principle, that there aren't rest frames in the universe, okay? And we're looking for those violations, but we don't yet have a really reliable theoretical prediction for what the violation should be. So I'm open-minded about that too. I think this is something where people should be

putting a lot more brain power into asking what those violations might be. Sean Morris says, can you help me understand how photons are massless, yet they have an energy associated with them? If energy is equivalent to mass, how do massless particles like the photon and gluon exist? So, as I said, in a different context a little while ago, energy is not equivalent to mass. Mass, you should think of mass as one kind of energy. Energy is a broader concept, okay? The equation E equals MC squared does not say energy and mass are equivalent. It says that there are certain specific situations in which the energy of an object equals its mass times the speed of light squared. Namely, when what you're talking about is an object,

okay, so it's like not a field pervading all of space, but as an object with a object with a in an extent, and it's at rest. If that object starts moving, its energy is bigger than MC squared, because it has some kinetic energy as well as the rest energy. Also, it can have potential energies. The object sitting on the floor or on a desk or on a mountain, it has other forms of energy over and above its rest energy. So what we mean by mass is just the energy something has at rest divided by C squared.

Okay. So the thing about photons and gluons, massless particles, is that they are literally never at rest. They are always moving at the speed of light. To anyone who is not moving at the speed of light, that's how fast they're going. So this question, how much energy does the thing have when it's at rest, doesn't apply to a photon. And therefore, the best we can do is just say its mass is zero. Danielle Cortesi says, how do you reconcile your experience as a conscious observer with the many worlds interpretation of quantum mechanics. In particular, how do you explain experiencing

only a single branch? Since all branches objectively exist, it seems to me that you can't say that the original before branching consciousness continues its experience because it would mean ascribing a special status to one of the branches. So yes, that's true. As I just said, and as I go on a great length about in my book, something deeply hidden, the way that conscious observers work in many worlds is that they start out as one observer and they become more and more observers. When the way function branches, what was one observer is now multiple observers. So it is certainly not true that there is any one particular path through that branching tree that you call the real observer. There's nothing more real about one than any of the other ones.

But once the branching has happened, each one of them is an observer experiencing only a single branch. This is something that is different in the many world's interpretation of quantum mechanics versus any other theory of physics ever. Namely, it's a little bit trickier to identify what you mean by an observer living in a semi-classical world. It has to be different because it's not surprising that it's different is what I should say, because every other theory of physics before quantum mechanics, the classical world was just the world. And now many worlds comes along and says, well, there are multiple classical worlds existing in parallel. And that means that that gives you a whole new thing that can happen where one observer can evolve into multiple observers in the future. So I don't think it's weird, but you have to get used to it if you're going to buy into many worlds. That's how it's going to have to be.

Amman Nilapa says, I was listening to a recent talk of yours where you laid out a research agenda for mad dog everettianism. In response to a question, you speculated that it may turn out that while space is emergent, time may be fundamental. I know this is probably speculative, but if such a picture were to be true, will that also imply the block universe eternalist view may be replaced by a more presentist picture, or did you have something else in mind? So this is a good question, but I think in my mind, the answer is no. So I know that for many people, the reason why eternalism is a good idea is because of relativity. Because once Einstein comes along, as we've already discussed, there's no unique special objective way to slice space time into different three-dimensional spaces evolving with time. And therefore, once you get that, how in the world can you be a presentist? I know people who still are presentists, but if we can't even define the present in any unique objective way, then how are you supposed to do that? Okay?

However, I'm not one of those people. You know, I am an eternalist, but I would have been an eternalist even in the Newtonian universe. Even if you could uniquely divide space and time into space and time, to me the important thing is that the laws of physics don't specify any one moment as real. The laws of physics relate what is going on in the universe at different moments, but they don't have a special finger that points to one moment says, here's the real moment, okay? That's just not how the laws of physics work. That finger wouldn't be doing anything. So to me, whether time is emergent or fundamental is completely beside the point

about being presentist versus eternalist. I mean, it's true that if time were not fundamental, the whole debate over being a presentist versus an internalist would lose some of its force because what exists would be a different kind of thing than what we're usually used to thinking about. But if time is fundamental, that doesn't mean I'm suddenly a presentist.

It just means that the whole four-dimensional block has a way of being described in terms of a time parameter. And by the way, so footnote here, which is a little bit more technical, Just because time is fundamental in my way of saying it, and maybe this is not a good way of saying it, but this is the way that people talk, so it's how I talk.

Time being fundamental doesn't mean that a certain time coordinate is preferred, okay? That's the lesson of relativity, which I do take on as important, which is that different time coordinates are equally good. So when you start with the Schrodinger equation, for example, there's a time coordinate right there in it. It says ID by DT,

the time derivative of the wave function exists there in the Schrodinger equation. And so someone can say, well, isn't that a preferred time coordinate? But the answer is no. You have a Schrodinger equation in QED, quantum electrodynamics, or other theories we know are perfectly Lorentz invariant. So it's just that you can describe exactly the same situation as a different wave function evolving with respect to a different time coordinate, but it's physically the same four-dimensional universe.

So in that sense, time being fundamental doesn't privilege one moment of time in any way. Sam says, it's my understanding that one must always be able to normalize a wave function of any system. And I know that one way to state this mathematically is that if you integrate the wave function over all possible values of the variables, you should get exactly one. It seems to me if your system had an infinite number of particles so that your wave function depended on infinite number of variables, such a normalizing integral would not converge. So my question is, when you talk about the wave function of the universe, are you making an assumption about the number of particles, or is there a way to get around this? That's a very good question, but no, we're not making an assumption about the number of particles. And I think, again, like many questions at this time have had, there's two things going on, okay? One thing going on is that when you do quantum field theory or even when you do quantum mechanics of an infinite number, infinite dimensional Hilbert space, the math is way harder.

You know, it's weird to me, and I'm writing a quantum textbook now, and I'm going to try to highlight this weirdness. The first thing we do, for most quantum mechanics examples, are something like a particle in a box, or the simple harmonic oscillator or something like that. And these are all infinite dimensional Hilbert spaces, which you can roughly think of is just corresponding to the fact that if you have one particle in a continuum, you know, in a line or a plane or a volume, There are literally an infinite number of points where that particle can live. And every one of those points, every one of those physical locations, corresponds to a different dimension of Hilbert space in the quantum version of the thing. So right away, when we teach people quantum mechanics, mathematically we're teaching them the hardest examples, right?

But there's also a good reason why we're doing that, because physically a particle in a box is something familiar, and trying to do it quantum mechanically is a natural place to go. So anyway, when we do something like quantum field theory, it's still true that wave functions need to be normalizable, but doing it is often something people skate around because the math is just really hard. But the short answer to your question is, yes,

things need to be normalizable. The second aspect here is, does this have something to do with the number of particles in the universe? So, number one, universe is not made of particles. It's made of fields, or at least the configuration space, is field space, not particles. space. So it's the values of the fields all throughout space that matter. Number two, the way that we

usually do it is to say, sure, space could be infinitely big, but we just divide by that. We divide by the volume of space. So when you do your integrals, you take a limit, right? So when you actually, I don't know, Sam, if you've taken quantum field theory yet, but when you do, you will often find, depending on how careful your instructor is, you will often find that you do what we call working in a box. This is really a very, very common quantum field theory technique. We start in a box of space, and we say, here is a fixed box, not a physical box, but a region of space where we're going to start doing things like letting fields evolve and whatever

and quantize them in the whole bit. And then, and only after then, do we take the limit as the box gets infinitely big? And when we do that, we take it in such a way. so that all the interesting quantities we want to calculate remain finite, like the density of something, okay, or the energy density at some point, the number density of particles that you might observe, stuff like that.

So there are ways of accounting for the fact that the universe could be infinitely big, while still remaining loyal to the principle that wave functions should be normalizable. By the way, again, another technical mathematical point, the thing that you integrate to get one is not the wave function, it's the wave function squared. In fact, in particular, it's the wave function complex conjugate times the wave function, so psi-star-si.

So the adjective we apply to this is square-integrable. So wave functions need to be square-integrable, psi-star-si integrated over everything needs to equal one. Kirkbrigg says, what do you think of prospectival realism as a topology for eternalism? So I didn't, I think that I understand perspectival realism. I think I understand eternalism, and I think I understand topology. But I was not able to figure out how these words are fitting together, so I'm not going to be able to answer your question. So in particular, I have no idea what it would mean to have a topology for eternalism.

Do you mean a topology for space time? I mean, a topology tells me the properties of a mathematical space that are invariant under smooth deformations. So I really don't know exactly what you're asking. Sorry about that. David Lang says, does the many world's interpretation predict that at least one version of you will endure eternally? The answer is, it depends. It's possible that there's a version of me that he endures eternally. But it's not definite.

And this is one of the sad things about many worlds is that we haven't done enough research on it. And so there's a lot of things we don't know about it. Part of the lack of clarity here is that we don't know whether or not Hilbert's space is, infinite dimensional or finite dimensional, like I said before. If Hilbert space is infinite dimensional, then the infinite number of things can happen, and things can grow increasingly unlikely or increasingly thinner in the wave function of the universe while still not ever fading all the way to zero. Whereas if it's finite dimensional, there's only a finite number of things that can happen,

and enduring eternally is not guaranteed. Another thing is that, you know, many worlds does not say that everything happens. Many worlds says the Schrodinger equation is obeyed. So another formal technical answer to this question is, well, you have to tell me what the Hamiltonian of the universe is and the Schrodinger equation and everything that I can ask, and the limit, as time goes to plus infinity, is there any branch of the wave function where I exist?

And, you know, that's a technical question that we'd have to answer. And I don't know, I don't have the technical ability to do that since we don't have the Hamiltonian for the universe. And the final point is, we don't even know if time is fundamental or not, right? So if time is not fundamental, if it's emergent, then there might not be any such thing as eternally.

There might not be an infinite amount of time left in the history of the universe. So many worlds could still be true in some generalization where time is not explicitly evolving, but the number of ticks on the clock that the universe has to experience could still be finite. So these are all really, really good questions. I'm not trying to blow them off, but we honestly just don't know the answer.

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Joaquin Iverson says, I don't understand what it means when you write in your book that according to the many-worlds theory, one branch can be thicker than another. And it gets especially strange when it has moral implications. Why would it be more important

to reduce suffering for a thicker future branch than for a thinner future branch? So I don't want to go too far where it's important to reduce suffering. So if you read the chapter that I have in something deeply hidden about morality, everything is phrased in very conditional terms. If you believe this, then you should believe that.

Like I said, I'm not a utilitarian. I don't think that your moral choices should be made by adding up utility in some way. But I did try to make arguments that if you were a utilitarian, here's how you should think. The point is, in many worlds, the world is described by a wave function,

in the world, in the grandest sense, all the worlds, there's a wave function, okay? And wave functions assign amplitudes to what will become different branches of the wave function. So if you have a spin that is in an equal superposition of spin up and spin down,

we say that it is 1 over the square root of 2 times spin up, plus 1 over the square of 2 times spin down, and then the probability that you would find yourself observing one or the other is that amplitude squared. So 1 over the square to 2 squared, is 1 over 2, so it's a half, okay?

But they don't have to be 1 over squared or 2 and 1 over square to 2. They could be any 2 numbers whose squares add up to 1. So you could have a particle that is in a superposition of square root of 2 thirds spin up and square root of 1 3rd spin down. And when that happens empirically, what we find is that 2 thirds of the time we see the particle being spin up when we measure it, and 1 third of the time it's spin down. So there's long argument over how to make that make sense with the Everettian point of view, but it's there. It is absolutely there.

And what I would say is that the way to make that make sense in the Everettian point of view. So the anti-Everdians would say, look, there's no such thing as probability in the Everett version of things. There is a branch where it's spin up and there's a branch where it's spin down and there's a hundred percent chance that there will be those two branches. There's not a two-thirds chance of one branch and a one-third branch of another branch. So what the Everettian has to say is, you don't know what branch you're on when the wave-function branches, and so you need to assign credences, and then you make an argument that the credence should be proportional to the wave-function squared. And one of the arguments is, if you were on the square root of two-thirds branch, you could branch again, right? You could branch again, you could measure another spin that was 50-50, and then you would have three-thirds.

three branches. So if you agreed ahead of time that if you measured the spin up, you would branch the universe again in a 50-50 measurement. And if the spin were down in the first measurement, then you just left it there. Okay. So you first branch into a square root of two-thirds spin up and then square to one-third spin down. And then you branch again, and now you're left with three branches. All of them have an amplitude of square root of one-third. And that's the point, if you're a good Everettian, the point you try to argue for is that only when branches have equal amplitudes should they be treated equally. And I'm not going to go in right now into why you do that. There's lots of arguments and you debate which is the best argument, decision theory or some epistemic rationality or some principle of indifference or other different kinds of things.

But the point is that that's what gets you the right answer. Okay. You treat branches of the wave function equally when they have equal amplitudes. And it immediately follows that you don't treat branches of the way you function equally when they don't have equal amplitudes. Because if you did, then you could split one of them again, and now there's two of them. And you can't, you're changing ex post facto the way that you treat those worlds. Okay. And by the way, this goes along perfectly with how we think about things like energy conservation. Where does the energy come from when you branch into multiple worlds?

well, the amplitudes that those square root of 1 3rd and square to 2 thirds outside the branches, those get squared and multiply the energy. So if your two branches

have equal energies, then you don't create twice as much energy by branching the universe. You create square root of 2 thirds squared times the energy plus square

1 3rd square times the energy and that's the same amount of energy that you had before. So whether it's probability or energy, or utility, a self-consistent happy Everettian will wait what goes on in branches of the universe as the wave function squared. It's the only way to be a good Everettian, okay?

And you can justify that again. There's many ways to justify it. You can say, well, imagine that I did a maximal amount of branching, and then I just count, right? The number of branches you could fit into the wave function. The universe is proportional to the amplitude squared. That's one thing. That's just Pythagoras' theorem. That's why if you go back to something deeply hidden,

I say that it ultimately just comes down to Pythagoras' theorem. But anyway, the very short answer to your question is, everything to an Everettian has to be proportional to the amplitude squared. Ken Wolf says, do you think there is a way that a Dyson sphere could be surrounded by some sort of parabolic mirror that directs all the waste heat in one direction, such as into a black hole, as a stealth measure? I like how you're thinking, how to hide the Dyson spheres.

You know, with 30 seconds of thought having gone into it, yeah, that seems plausible to me. I mean, there will always be some waste heat because your mirrors will also give off heat. But I think that, and I'm not saying that your scheme with the mirrors is necessarily the most efficient way of doing that. But the general idea that in principle, you could take the, so the idea for any of the you who have been living lives somehow did not come into contact with this, this thought, if you build a Dyson sphere, that is to say if you surround a star in all four-pie star radians, you know, in all directions, you build a sphere that completely encompasses a star. So you're trapping a lot of energy, right?

Stars giving off energy, and it will heat you up. And so on the other side of the sphere, outside of the star, you will necessarily radiate into space. And so this is thought to be a way to look for Dyson spheres out there in the sky by looking for these large but dully radiating objects that are otherwise star-like. So, you know, you could just, I mean, make your life easier, surrounded by, I don't know if it's easier or harder, but surrounded by a whole bunch of more spheres, right, and continually degrade the radiation to lower and lower frequencies, higher and higher, larger. higher and higher, larger, larger wavelengths. So you need to emit the same amount of energy, but if you shift it all to longer and longer wavelengths,

that maybe it's harder to detect, I don't know. Maybe it's easier. Or maybe it would be easy if you knew where to look, but you don't know where to look. But I think in principle, there are things you can do to try to hide your Dyson spheres from nosy astronomers, yes. Jose Ignacio Alcantara says, I wonder how you feel about graduate students

taking on a teaching load. Do you think this could be beneficial for them, or might you be concerned that in their eagerness to please senior faculty members they might be taken advantage of. Well, there's always a possibility of graduate students and their eagerness

to please senior faculty members being taken advantage of. That's something that graduate students should look out for and departments should look out for in a more systematic way. I actually think that it is useful for graduate students to do some teaching.

After all, many of them, certainly many of them in physics, are going to want to eventually become professors where teaching will be part of their job. I think that we do a terrible job overall in teaching students how to be good teachers, which would be an important thing down the road. On the other hand, you know, you can get a lot more work done, a lot more research, I should say, done if you're not teaching. So there's definitely a place for fellowships that release graduate

students from teaching at some point. So there's a balance there. You know, I was on fellowships when I was a grad student, but I taught a couple times voluntarily because it's good experience and I enjoy doing it. Frank Lehman says, to what extent do most working theoretical physicists keep up with new developments in higher mathematics? Has any of your own work relied on truly cutting-edge maths research? I think it depends very much on exactly what kind of theoretical physicists you are. I think people will be surprised at how many theoretical physicists do not keep track of new developments or even old developments in higher mathematics. You know, a lot of theoretical physics.

Let's say you're a particle physicist who wants to, you know, suggest some new set of fields that are interacting with each other and calculate their decay rates and stuff like that. There's a certain set of tools you need, which is a lot of math, a lot of complex analysis and integration and group theory and things like that. But it's the same stuff year to year. You don't really require more math as time goes on. There is a small part of theoretical physicists who are very, very mathy, right? typically people we think of as string theorists, the Ed Wittins of the world, who is basically creating new math as he goes along. But that's a small proportion of them.

And I think that there's also a whole bunch of people, which I would include myself, where it's not that we're learning new math or keeping track of new math for its own sake, but sometimes we're trying to learn new things. And to learn new things, new areas of physics, that often requires. requires learning new mathematics, right? When I want to learn information theory or something like that, I will have to learn new math along with the physics. That's, I think, something that you're trained to do.

But you're doing it for a purpose to learn this new bit of physics, not because it's cool new math. Who knows? Maybe it'll be interesting someday. Richard Koshdan says, can you explain the acceleration aspect of the twin paradox? I heard it once, but don't remember it and don't really understand it. and I edited down that question a little bit.

I think at one point about the thing I edited, Richard, is that you use the phrase aging slower, and I would never use that phrase. I don't know what it means to age slower. You age at one year per year. That's the amount by which you age. I think if people want to understand the twin paradox, it's very, very helpful to do it right,

to think about it correctly. Individual people, no matter what trajectory they're moving on in the universe age at one year per year. The amount of elapsed time on two different trajectories might be different, right? But it is really exactly like moving through space. And I've used this analogy before and I will continue to use it. When you're walking from point A to point B, you could go in a straight line or you could go on a curved path. You're always traveling at one meter per meter, right? You're not moving at a different rate of space per space,

but you will take a different amount of distance depending on whether or not you go in a straight line or a curved line. It's exactly the same thing for traveling through time, except with the one difference, that the shortest path in space is a straight line, and the longest time in time is a straight line. So the fact that you age less when you zoom out on a rocket ship, turn around and come back, then if you do, if you just sat here and didn't move,

is not because of the acceleration. It's because you're not taking a straight line path. Now, admittedly, the only reason you can not take a straight line path is because you did acceleration, right? So there's a relationship there. But Tim Maudlin in one of his books on the foundations of physics, when he's talking about space time, you know, he points this out, if you take two twins, and they start at the same point, and one immediately accelerates off in a rocket ship, zooms out a long distance, immediately accelerates back, whereas the first one just stays put. So in space time, they're forming basically a triangle, right? Then there can be a big difference in the amount of time elapsed between the two trajectories.

Whereas if the second twin, sorry, if the twin that leaves, if the twin that zooms out, zooms out very quickly, but then immediately turns around and comes back, they can do the same acceleration, right? They're doing it at different times. They're doing the return acceleration sooner. But if you think about, you know, just accelerating off, freely floating, accelerating to turn around and come back, if you do that quicker, and then you get back to where you started quicker and you decelerate to stop, then the difference in time elapsed is much shorter than if you

are traveling near the speed of light for almost that whole time and do your acceleration only at the halfway point. The point of this example is, the difference in time does not in any sense come from the acceleration. The difference in time elapsed comes from the fact that you're taking a different path through space time, a path that is very close to being a straight line or a path that is very far away from being a straight line. That is what matters. Peter Benham says, is there such a thing as zero velocity in the absolute anywhere in the universe or is it all just relative? How can we determine who is taking the slowest path through time if there is such a thing?

So again, there's no such thing as the slowest path through time. Everyone is one year per year, one second per second. The total amount elapsed can be different for different people, but it doesn't depend on zero velocity because velocity is not well defined. Velocity, according to relativity, is something that is only relative to an observer. But there's a huge difference between velocity and acceleration. There's no such thing in relativity as absolute velocity, but there is such a thing as an absolute acceleration. And you know that, because if you imagine yourself out there in a rocket ship, you have no idea, if you don't look outside the rocket ship, how fast you're moving.

But you absolutely know how fast you're accelerating because you can feel the push on your feet if the rocket is accelerating. That's what determines whether or not you are on what we call a geodesic, a straight line trajectory through space time, or whether you are not on a geodesic. And it's those geodesics, those straight line paths, that will experience the longest time between any two events. Nathan Simmons says, thanks to your book, The Big Picture, whenever I put creamer into my coffee,

I think about complexity, swirls, and entropy. What is another fun, similar metaphor for a physics concept that involves something we do every day? That's one of my favorite ones, so I'm not sure, but the only one that comes to mind right now is the one I just used. the analogy between traveling on different paths, whether you're walking or in a car or whatever,

versus doing the twin paradox experiment. You know, the twin paradox is about the different amounts of time elapsed, moving on different paths in space is about the different amounts of spatial distance you traverse, but it's a very good analogy, and I think that one that people find very helpful. Hughes Math says, I wish, sorry, I would think if you took the derivative of volume of a sphere,

you should get the surface area, does not work like that of a circle and the circumference. I'm not going to sit down and look at the formulas, but when you take the derivative of anything, you've got to say, like, with respect to what? And you ask why the derivative of something should equal something else. So you have to think through these things before you plug in the numbers or see that the formulas don't work correctly. There's different things that you can differentiate with respect to other things. Matthew Caffrey says, I'm a science fiction writer who uses multiple worlds as a plot device. I wanted to run a fictional scenario by you.

If there was a room, box, or planets sufficiently separated from the rest of the universe, so that there was no significant physical interaction with the quiet spot and the outside world, could the wave function of that quiet spot be considered separate from the universal wave function? Well, yes and no. Certainly it is absolutely possible to imagine subsystems of the universe that are unentangled with the rest of the world. I think that's what you mean by separate. you might mean by separate just non-interacting, but in this quantum context,

what matters is are two things entangled with each other? And we find unentangled things all the time. You know, again, to go back to a previous discussion we had, there's a difference between living on a branch and considering the whole wave function of the universe. Two things can be unentangled on a single branch, but entangled on the whole wave function as a whole or vice versa. So it's a little bit complicated when you say,

are two things entangled with each other or not. But having said that, typically when we measure something, so you measure the spin of a particle and it's spin up. Now, you're entangled with that particle, but on your branch, it just is spin up. It's not still entangled with you. In the wave function of the universe, it's entangled, but on that branch it is not.

So having said that, the question is, can you, in the wave function of the universe, have a subsystem of the universe that is so isolated so that it's unentangled with everything else. Yes, you absolutely can imagine that in principle, in practice it'll be really hard to pull off. I mean, you talk about sort of isolating a box under the Earth or in a quiet room or whatever,

but, you know, photons count. Photons are emitted by any object at a non-zero temperature, and photons do interact with other things. So even if you built a room in a box and put it out in outer space in the desolate cold of intergalactic space, it is still constantly being bombarded by photons from the universe. You know that because you look outside and you see the galaxies.

If you had a radio telescope, you can see the microwave background, etc. So it still wouldn't be 100% isolated in that true sense. Fador Indutti says, endutni says, most physicists agree that gravity is quantum in its nature. Given that the main field in relativity is the metric tensor itself, Would you agree that quantizing gravity implies the existence of a minimal distance, such as the punk length? If so, does it mean it's space time has to be discrete?

So, no, I don't agree with that at all. I mean, maybe it's true, but there's no logical derivation of a statement like that. And keep in mind, quantum has nothing to do with discrete. These two words are completely separate. I know that before quantum mechanics came along, the idea of a quantum was, in fact, a discrete lump of something. but quantum mechanics by itself does not imply discreetness. Again, this is something I talked about at great length in something deeply hidden. What quantum mechanics implies about space time is that there is a wave function,

and the wave function assigns different amplitudes to different ways that space time could be. That's it. That's what it implies. Just like if you quantize an electron, it doesn't imply that the electron only has certain locations it can take. If that electron is stuck inside a potential, like the electrical potential caused by an atom, then maybe there are discrete energy levels it could be in, but the number of places that the electron could be seen if you look for its position is still infinitely big. So there's no direct route to go from quantizing gravity to minimal distance in any sense.

Philip Myman says, is it fair to say that measurement resulting from true quantum randomness like spins and locations of particles are new information in our observed branch of the universe in a way that non-quantum random measurements like the outcome of a coin toss are not. If so, then does that become new information at the earlier moment of decoherence with the environment or at the later moment when an observer

at the edge of the environment finally becomes entangled with it? So I think that the short answer to your question is the observer is completely irrelevant here. Who cares about observers? There are physical processes going on in the universe and decoherence is one of them, and that's what matters. Now, when de-coherence happens, you go from a situation where, let's say, to make our lives easy, you had one branch of the wave function before, and then you have two after. So the transition from the one to the two is completely smooth and uniform and according to the Schrodinger equation.

But the evolution from the one wave function to either one of the two, which is what an observer would measure, is not smooth and continuous. That's why we fool ourselves into thinking that wave functions collapse. Okay. So the wave function changes in some discontinuous way from the point of view of an observer. But again, the word observer doesn't mean like a human being. It just means any big macroscopic classical thing. Does that count as new information or old information? You know, and the answer I would say is, you know, who cares?

It just is up to you whether you want to call it that. It's different information. so it's new in that sense, but all the information that was there was somehow encoded in the wave function of the universe as a whole before that event actually happened. Johnny says,

after your podcast about democracy, you got me thinking, if we had someone truly admirable and virtuous to take charge, would you ever consider a benevolent dictatorship scenario? This is just a thought experiment out of curiosity.

So I can certainly admit that if we were infinitely smart, and able to, if we were omniscient, and we knew that a certain person was infinitely good and wise, then that person would be better in charge of the country or the world than any democratically elected legislator would be. But we're not like that.

It's like imagining that we're being Laplace's demon. In the real world, you can trick yourself into thinking that someone is perfectly good or even pretty darn good and wise and be terribly, terribly wrong. And besides which, I think in the, You know, in the real world, it's just crucially important that the authority of the government comes from the people, right? And a lot of people will say, you know, well, people aren't very good decision makers. People like the Hoypolloy, you know, they're not very smart, not very informed, not very educated, they're not very rational.

Why should we give them the right to decide what's going on? And the point of democracy never was that it was the best decision-making process. It's not as if you let millions of people vote and you're most likely to get the right answer in some sense. The point is that people care about their own interests. People are going to stand up for themselves and in ways that people in positions of power who are just given that power over other people are not going to do so. So I don't think that realistically there is ever any benevolent dictatorship scenario that I'd be in favor of, both because I don't think we could do a good job picking the benevolent dictator, and because I think that it's not the right in-principle way to govern a country.

Nathan Morgan says, if a black hole is fully described by its angular momentum, charge, and size, to me, that suggests very low entropy. We know everything. There's no uncertainty. If it's possible, high entropy is related to what's going on inside, so are black holes high or low entropy? So, yeah, I mean, this is exactly the reason why Hawking and Beckenstein's discovery of black hole entropy was surprising. In classical general relativity, which is where it is

true that a black hole is fully described by its angular momentum charge and size, then there's not a lot of micro-states, as we would say, right? So if you go back to when Boltzmann invented the modern concept of entropy, it was based on the fact that if you have a box of gas or a cup of coffee or whatever, you can think of that as a collection of many, many atoms or molecules arranged in different configurations. In classical general relativity, there's nothing inside a black hole that is being arranged in many, many different ways, and therefore you would not expect it to have any entropy at all. So when Hawking-Bekinstein derived the fact that it had entropy, it seems to be implied by that, but we had to be a little bit careful because we don't know. You know, this is an area of physics

that is not completely understood, but it seems to be implied by that that there are many, many different little microstates that the black hole could be in, and that what we're observing as the big macroscopic black hole is some superposition or combination of all these microstates. So what are they? Well, that's the good question. That's what we would like to know. We'd like to know what they are and how they work to make black holes make a bit more sense. Justin Bailey says, what if the speed of light was 10 times faster?

Would the universe behave any differently? So I'm going to be a crumagine here. when you say 10 times faster, I would have to ask, compared to what? You know, the speed of light is one light year per year. It can never be any faster than that. It can't be any other number. What you really mean is, if you think of the speed of light

as 300,000 kilometers per second, would you really mean is, what if seconds were longer, or what if kilometers were shorter? And when you say it that way, it's clear how very human-centered that kind of thing is. Now, you could imagine,

and people have imagined, for whatever reason, you could imagine changing all of the laws of physics so that you change the size of atoms and the speed of atomic transitions and chemical reactions and the size of elementary particles

and the masses of elementary particles and the interaction strength of elementary particles you change everything exactly in the right way in concert so that what you would call a meter does really change, so that in fact the speed of light is 3 million kilometers per second rather than 300,000 kilometers per second. So that's how, that's the answer.

Would it be different? Yeah, I mean, you're changing all the laws of physics in some way to make that happen. And what the results would be, you know, how life would be different. I'm really not sure. That is not something I really thought about. Pete Harlan says, you and your loved ones and a few friends have an opportunity to travel to Earth a thousand years in the future. If there are people there, you are among them, they're friendly, they're expecting you, and they will know where and when you came from.

You can't return and nobody else can make the journey forward. Would you do it? What if it were 10,000 years, 100 or a million years? I actually don't know. I think my first impulse is that I would not do it. And the point is that I am, I live here. I'm embedded in the world as it is right now. I have, you know, a lot of friends, right?

And I can bring a few friends. I'd be leaving other people behind. But I also, I understand the current world to some extent. I'm doing work, pushing back the frontiers of knowledge and things like that. I know where to go, to have a good time, all those things. I understand this world. I understand that this world as it is right now is extremely. extremely flawed in many, many ways, but I know how to deal with that and try to make it better.

Whereas the world a thousand years from the future, I guess I'm allowed by this thought experiment to bring a few friends along, but there's still a whole bunch of people I'm leaving behind. I don't know the world. And I could learn it, but I would always feel like a stranger in a strange land in some sense. I mean, having said that, I do get the attraction of the thought experiment because I'm hopeful that the world will be a much better place a thousand years from now. You know, if you do the same thought experiment

thinking of someone a thousand years ago, would they like to be moved up to here? Certainly, you know, sanitation and health care and education are much better now than they were back then. But the other consideration is, you know, there's no guarantee that the world a thousand years from now

is anything like our current world, right? You know, a thousand years ago, things were very, very different, but they're still kind of like the world we have now, right? There are still people and horses and stuff like that. Whereas technology is changing so rapidly that in a thousand years, things could be dramatically different. You know, maybe we live all in a simulation or maybe we've destroyed ourselves. We're all living on different planets or, you know, we're all changed our genomes so that we live forever. Who knows?

Like, the world could be much different between now and a lot. a thousand years in the future than it is from now to a thousand years ago. So it's not at all clear that a thousand years from now would be hospitable to people like me. Even if there are people there and they're friendly, maybe the world would have changed so much that I wouldn't enjoy it anymore. I just don't know. So my guess is I would try to make the most of the world we have right now. This is Jacob Goldstein from what's your problem. When you buy business software from lots of vendors, the costs add up and it gets complicated and confusing.

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Brad Malt says, in your view, possible outcomes exist in superposition until they become entangled with their environment. whereupon the wave function decoheres and the outcomes are represented by separate worlds. But we can never communicate with or observe any of these many worlds except our own. Instead of all these many worlds, an alternative explanation might be that the wave function represents probabilities, and when it collapses, the outcome is the world we experience. Why isn't this one-world explanation a simpler, more intuitive, better explanation,

or at least an alternative possible explanation? So you can try to develop theories like that, and people have, but the short answer as to why it doesn't work is because wave functions seem to be physical things. They don't just represent probabilities, and we know that because wave functions interfere with each other, right?

That's what the double slit experiment tells us. You put the wave function of a single particle through two slits, and the wave function seems to be like a wave. It goes up and it goes down, and it constructively or destructively interferes on the other side. If there was such a thing as just,

the probability that the particle goes through one slit or the other and lands somewhere on the other screen, then you would just add up the probabilities. There'd be no interference pattern between that. It's experiments like that that make us think that wave functions are real physical things, not just ways of talking about probabilities. Gregory Cusnik says, suppose your future self steps out of a wormhole, shows convincing proof of his identity, and tells you to rob a bank. You have no reason to want to rob a bank, and every reason not to, since you'll most likely get caught, go to prison, and ruin your life. Indeed, your future self tells you that's exactly what happened to him to his everlasting regret.

He can't believe he let himself be talking to such a hairbrained venture. Nevertheless, he fully expects to talk you into it, and the single consistent world model of time travel says he must succeed, even though he has no real argument to offer beyond the fact that he was talked into it. Is that fact sufficient to convince you and whose idea was it to rob a bank in the first place? So, this is a very good question because it sort of highlights, the conflict between time travel and single consistent world versions of time travel and our everyday intuitive experience of free will, right? In this thought experiment, why can't I just choose to not rob the bank?

And indeed, I think in this thought experiment, I would choose not to rob the bank because I don't want to rob the bank. So what would happen? Well, either for some unknown reason that is very unclear to me, the universe would conspire to force me to rob the bank, or I would learn that the guy was lying to me. My future self was not telling me the truth. He was trying to test me to see whether or not I'd be smart enough

to realize that he might not be telling the truth. And so I would try to do that. So I don't think that, you know, one thing about time travel is, even if you believe, I guess the third possibility is maybe the metaphysics is wrong and it's not a single consistent world. I could change things. Who knows?

But even if I thought that there was just a single consistent world, if there was time travel in that world, there's no obligation on my part to try to make it a single consistent world. It just will be a single consistent world no matter what I try to do. Like there's lots of dumb ways to do time travel, but the dumbest way is to imagine that we have to not disturb the timeline. Okay? the timeline is going to be the timeline. You're not going to disturb it. So if it's your scenario is exactly like a prophecy, right?

A prophecy that says on this date, I will rob the bank. And it's by someone who has foretold the future many times and has 100% accuracy, right? That's just not the way the real world works. And so we're not used to it. The question is, what would we do if we were faced with that? And I still think I would try not to rob the bank and see what happened. Antonio Justino says, You've obviously thought a lot about entropy and the second law of thermodynamics.

To me, it's always seemed incomplete, like we're missing a corollary. Usually the patterns we see when we study the world are described with equalities, but here it tends to inequality. That being, I think that the point being that entropy increases, but the amount by which it increases is not specified by the second law. Could it be that we're not capturing the true measure of the low entropy of states such as my memory, my computer's hard drive, or the use of the use of the amount? uniqueness of the arrangement of atoms in my AMA question to you. Could the increasing entropy of the universe on one hand be balanced with the increasing order that we see in parts of it? So I think, I mean, I know what you mean. The second law is a much more loosey-goosey law than other things that we think of as laws of physics, right?

It is, like you say, an inequality, not an equality. So, yes, there is an equality behind it all, but that equality is just, the exact underlying microscopic laws of physics. So the point is not that we increase the entropy here and balance it with increasing order somewhere else.

That's not part of anyone's law of physics. The point is if you describe the universe microscopically, so you describe the exact quantum state of the universe or the exact classical state or whatever laws of physics you're going to believe in for the moment,

then the word entropy doesn't apply. Because the whole idea of the word entropy is that we've forgotten something. We've coarse-grained, or we have incomplete access to the information about the microscopic state of the universe.

That's the only situation in which entropy becomes a useful concept. So it's not true that the second law is just incomplete in and of itself. It's trying to describe

a situation of incomplete information, and therefore it tells us something incomplete about the future. Chris Shaw says, my question is, everything in space-time

is a product of some form of energy through E equals MC squared. All mass matter, radiation, anti-matter, dark matter, even dark energy. That's literally everything in the cosmos. All that's left is space. Is it possible that space is a product of energy as well or the side effect of reactions between different kinds of energy?

I don't think so. So I think that this is not how a modern physicist thinks about it. I'm hesitating because, you know, maybe there's some other way of thinking about it. But the very hypothesis of the question, everything in space time is a product of some form of energy through E equals MC squared is not exactly right. As we said just before, E equals MC squared

is an equation that applies to a very, very restricted set of things. It applies to things that are objects, so they have both locations and extent in space, and they are objects that are at rest. Okay. So it doesn't apply to things like fields or dark energy, There's E equals MC squared is just meaningless in the concept of, in the context of dark energy. It doesn't apply to radiation because radiation is moving at the speed of light.

It cannot possibly be at rest, okay? So, you know, energy is important, but it's not everything. There are other things. There are other important ideas that you need. In fact, I would honestly go to say the energy is one of the less important things. Energy is a derived quantity. If you tell me what everything else in the universe is doing, I can tell you its energy,

but if you tell me it's energy, I can't specify what all the things are, right? KC says, might entanglement decay? That's a curious question if time itself might emerge from entanglement. So, you know, entanglement can decay if you do things to a system, but there's no rule that says entanglement has to decay.

If you have two particles that are entangled, let's say maximally entangled, and you just let them sit there, you keep them isolated from the rest of the world, the entanglement between them does not change over time. It does not either increase or decrease in general. Again, you can perturb it. You can change it with an influence from the outside world,

but there's no reason for entanglement to decay all by itself. It's not like two people holding hands where they get tired, okay? It's really just not like that. It's a different kind of thing. Trevor Villawak says, what do you suspect the implications of eternalism are for consciousness? What does it mean for our conscious self? to in some sense exist eternally at every moment in our timeline.

And how do you reconcile this with the phenomenon of consciousness being tied so closely to individual present moments flowing forward in time? Well, I don't, you know, I have trouble understanding what presentists really think. So I'm not always very good at explaining what eternalists think because it's always in contrast with a view I don't understand. So eternalists think that what exists is the four-dimensional world. All of the moments in time have some equal amount of existence. But when you talk about what a person is believing or thinking or experience at any one moment of time, then you're taking a slice through that four-dimensional world and picking out what is going on at that moment. And, you know, as I discussed various times, various places, for example, in the podcast with Jananne Ismail,

we talked about the psychological aspects of the arrow of time a little bit. And the point is that that person at any one moment of time has a memory of the recent past and also is trying to predict the immediate future, right? And so even though they exist in principle at one moment of time, they are constantly making reference to changing moments of time, to moments in the immediate past and their environment around them is changing as well as their internal changes. So it's really a give-and-take kind of thing. You are sort of interacting with and being influenced with the world around you while entropy is increasing all along. So, of course, consciousness is something we don't completely understand, but the fact that consciousness seems to experience this flow of time is related in exactly that way to the fact that entropy is increasing. Now, having said that, there's an enormous amount of work remaining to be done to spell this out. And if you thought that the words I just said

sounded kind of vague and incomplete, that's because they are. So there's plenty of research yet to be done in thinking to make this connection between the arrow of time and consciousness perfectly clear. Brian Tidmore says, does information have mass? Does information create mass?

Or does information rearrange existing energy mass? So I would go back to what I just said about energy kind of being less important than other things. I think information is exactly the same way. think of both energy and information as ways of characterizing the stuff of which the universe is made. Okay. And you can debate, depending on your particular fundamental ontology, what is the stuff of which the universe is made?

But energy and information are on very, very much the same level in terms of what their role is in the physical playing out of the world. That is to say, in some sense, you don't need them. If you just told me what the quantum state of the world was and the Hamiltonian, the plug into Schrodinger equation, that's all I need. Or if you're a Newtonian kind of person, all you tell me is the position and velocity or the point in phase space of every little bit of the universe, that's all you need. Then you can run that forward and backward. And words like information and energy and entropy for that matter would never enter your vocabulary. But as human beings, we find it enormously helpful to attach words like energy and information to different physical configurations. It's an example where that kind of conceptual handle on what's going on gives us enormous insight.

So that's my way of thinking it. I think that information is secondary. It's parasitic on the stuff. But having said that, you know, I say that very hesitatingly because it can be really. really, really useful to think that way. Even if it's parasitic on stuff, it's a very useful concept. You know, I wrote a paper with several collaborators on the Bayesian Second Law of Thermodynamics, which is part of this research program that is going on in various circles to understand the

relationship between information and entropy and thermodynamics and work and energy and things like that. And by knowing something about a system, you can manipulate it in such a way. to extract energy from it. Okay, see, there's an interplay between energy and information. My point is just that I don't need to know any of those words. If all I knew was that there was stuff

acting in a certain way, that's a complete description in some sense. Fran Plaas says, which were the coolest Christmas gifts that you ever got, either as a child or a teen? Ah, so this is a tough one. You know, to be perfectly honest,

I don't rank my Christmas gifts or even have very vivid memories of them. You know, I remember getting gifts and I couldn't even tell you which of them were for Christmas versus other times. Like, used to like playing with model rockets when I was a kid and things like that. The one Christmas gift that I actually remember very, very vividly, and this is going to really, it's going to be like the nerdiest thing I've ever said on this podcast, which is saying something. The Christmas gift I really remember getting was a desk. And I loved having a desk.

I wanted a desk, you know, I wanted someplace to sit and read and write and things like that. That's what I really wanted more than anything else. And I got it. But I think I suspect that as important and as good as it was for me to get the desk, one of the reasons why I remember it so vividly is it was really hard to hide that desk under the Christmas tree. So it was, you know, under a big blanket or whatever, and I knew perfectly well what I was going to get ahead of time. So that played a big role in me remembering it to this day.

Paul Hardy says, wondering about the model that says the universe might expand, then contract, expand, et cetera. In the big crunch, I know all the matter would collapse in on itself, but what would cause space itself to collapse? Why wouldn't only the matter collapse due to gravity? Well, the basic answer is that space goes along with matter according to the rules of general relativity.

You know, there's a more subtle answer, which is that when you say space is collapsing, what does that supposed to mean, right? Especially because there's no rule that says space can't be infinite and yet still collapse, okay? When we say space is collapsing, we're kind of using a metaphorical language because, I mean, here's how the actual cosmologists are thinking about this. I have a universe. It has a metric, a way of describing the geometry of space.

And it also has stuff inside, okay, particles, galaxies, or whatever. So think about, in particular, a cosmology. So not just a random collection of particles, but particles that are uniformly distributed through space, either expanding or contracting. Then the easiest way to describe that is by choosing coordinates on space such that

the particles basically don't move with respect to those coordinates. Okay? So the coordinates have a distance between them that changes over time because the particles are coming closer and closer if the universe is collapsing. And therefore we attach words to that,

namely that space is collapsing. But we don't have to do any of that. We could choose completely different coordinates. We could choose coordinates in which space wasn't changing at all, but all the particles are moving within space, rather than having their spatial coordinates tied to where the particles are. That would be clumsy. It would be hard to do it. The equations would not look very pretty, but you could do it if you wanted to. The physical reality is that the density of matter is increasing, and there's another physical reality in that the curvature of space is increasing when you collapse to a big bit.

big crunch, or when you come out of the Big Bang, going to the past. So that's basically, I hope that's a useful answer. Like, part of it is there's a physical thing happening, namely the curvature of space time changing, but also part of it is there's just a way of speaking that we have that is convenient. Anders says, you've said that the recent particles decay is an increase of entropy. A neutral meson decays into two photons, and there are more ways to arrange two photons than one meson. But wouldn't entropy increase even more if the meson

decayed into four photons shooting off at right angles, and repeat that reasoning until we have mesons decaying into an infinite number of photons shooting off in all directions. Why doesn't that happen? So the very short answer here is that there is no law of nature that says that entropy has to increase as much as it can, right? So the process, I mean, I'm not sure exactly what my words were, but it's not quite right to say that the reason particles decay is increase of entropy. Increase of entropy is the reason why it is more often for a particle to decay than to a bunch of particles to come together and form one particle, okay? That irreversibility, that difference in rate. It's not a strict irreversibility because sometimes particles can come together and form just one. But it is much more common for single particles to decay. That's because that increases the entropy of the universe. That's what makes it more likely, but not what makes it possible.

Okay. But anyway, there's no rule that says that entropy increases as fast as possible or as much as possible. So the processes that do happen will increase the entropy of the universe. But to figure out which processes happen, it's not enough to just say, well, what would increase the entropy? You have to figure out what the actual laws of physics say happens. Paul Cousin says, do you know when the quantum physics textbook you're working on is going to be ready approximately? well, it's not going to be for a while. Let's put it that way. It's not even due for more than a year from now. Okay. So I think it's due in early 2022. So if it's published by later in 2022, I'd be happy. But I can't promise that for sure. You know, books, both writing and publishing books just takes a really long time. I mean, I guess it's been a while since I published a textbook. So it might be a shorter turnaround time for the textbook. because presumably I will write it up in latex and they will just sort of copy edit that file directly

rather than typesetting it and all those things that the trade books do. But anyway, 2022, very, very soonest. Sorry about that. Gary Miller says, in many worlds theory, are there countless universes that are identical but for one quantum particle somewhere in that universe?

And wouldn't most of them hew to some similar mean state because changing a few particles here and there wouldn't seem likely to dramatically change an entire universe even over billions of years. Yeah, absolutely. No, there's no rule in many worlds says the worlds are very, very different from each other. One particle being different is unlikely because, you know, typically momentum is conserved or something like that. So you can say that one particle has decayed or not decayed.

And that absolutely, as long as that decaying particle becomes entangled with the rest of the world, that would qualify as making a new universe. Yeah, I think that's part of many worlds. You have to learn to accept that if that's the route you're going to go down, which I encourage you to do. David asks, what implications does quantum entanglement have for how we understand human relationships? Zero. None whatsoever. Human beings are deeply within the classical regime. We're not entangled with each other. Sorry about that. Entanglement is not like, as we said, a physical force pulling us together, pushing us apart, anything like that. It's just, a feature of the quantum wave function that is really

inapplicable to big macroscopic things like human beings in the real world on individual branches of the wave function. Gustavo Chavez says, when you interviewed Tyler Cowan in episode 19, I hoped it would be like a live performance of Tom Murphy's delightful exponential economist meets finite physicist's blog post.

In it, the author recounts a dinner conversation between a physicist and an economist about the hard limitations physics imposes on the idea of exponential economic growth. The basic rational, is that our rate of economic growth so far has always depended on an equal or higher rate of energy consumption growth

and that the Earth only has one mechanism for releasing heat to space and that's via infrared radiation. We understand the phenomenon perfectly well and can predict the surface temperature of the planet as a function of how much energy the human race produces. The upshot is that a 2.3% growth rate at a 2.3% growth rate

we would reach boiling temperature in about 400 years. Do you agree with that? 400 years seem so soon, is there any way out of this fate for us? So there's a few things here. I think that I'm not sure if I agree with it or not. I would have to redo the calculation, which is against the rules of the AMA. And I'm not sure that it's calculating the right thing.

Well, I'm not sure what it is calculating in particular because I'm not sure what is meant by energy consumption or energy usage. I mean, if that's just sort of burning fuels or something like that, then that's. that's one thing, but solar energy comes into us and then we give it back. So there's a net zero energy consumption. If we switch entirely to solar, would that count as zero energy consumption under this calculation? So I'm just not sure. I'm not exactly sure what's going on. I do think that one could do a kind of calculation analogous to this.

The important thing is actually, guess what, the entropy production, less than the energy consumption. You know, energy is conserved in the universe, but we take useful, low entropy forms of energy and turn them into useless high entropy forms of energy. And there's different ways you can do that. And there are limits on the efficiency of doing that. So maybe there's some calculation like that. But I have no intuition for how quickly we're going to reach that. But also, you know, this big assumption that the rate of growth is somehow exactly proportional to the rate of energy consumption seems very unlikely to be true to me. This is why physicists doing economics is always kind of a shaky thing.

Like you can derive conclusions from your assumptions, but it's the assumptions that should be questioned here. When I was interviewing Tyler, you know, I'm not that interested in doing science fiction-y, apply physics ideas to economic stuff. I really wanted to understand the rationale and the implications of his idea that the most moral way to organize an economy is to maximize growth because everything else is second. That seems like an unrealistic claim to me, but it's interesting to try to pinpoint exactly why one thinks that it is. Casey Haskins says, if you were granted the power to change one thing about the way academic science is practiced today, what would it be? You know, that's a hard question to ask. I don't necessarily have a ready-to-hand answer because academic science is a very complicated thing with a lot of moving parts. Let me mention two things. I know you said one thing. Let me mention two things that. I think are sort of semi-plausible changes in the way things could be done.

One is in the way that grants are given out. You know, science requires grant money. You need it to pay graduate students, postdocs, traveling, you know, buying equipment. Of course, people not like me, but real experimentalists require a lot of grant money for setting up labs, building experiments, things like that. Theoretical physicists don't need that much, but even we need a little for students and stuff like that. And it's just a pain to get the grant money. I mean, I think the system works pretty well.

It'll never be perfect. But having served on committees to hand out grant money, I know from experience that the people on those committees are really sincerely committed to trying to make sure that the best proposals get funded. You know, I've absolutely been on grant proposal committees where some big shot, who is very famous and very successful and very smart and very. and very talented, you know, kind of phoned in their grant proposal and basically said, you know, I'm smart, give me money, whereas a young person who's also smart put in a grant proposal that really had some ideas in it. And we funded the young person and not the big, famous person. But I really think there's a huge inefficiency in the fact that it just takes so much time. This might be because we're in grant renewal season right now at Caltech.

But there's just so much work put into this. And I don't think it needs to be for something. like theoretical physics. It's just crazy that we're spending time because the grand proposal is set up. The whole idea of it is set up for something much more experimental where you say, well, I'm going to build this thing and then I'm going to try to do this experiment with it. And that's a very sensible thing to ask for a proposal for. But theorists don't know from month to month what they're going to be working on. So we have to pretend to say, well, okay, next year I'm going to do this. And the year after that, I'm going to do that. And it's just,

It's just bizarre. And so I think that, you know, there's a certain class of people and theoretical physicists fit into them, but other people fit into them, where you do a much better job just asking, you know, how many interesting things has the person done over the last five years? Have they been productive? Have they been doing good work? If so, continue to give them money. Of course, you have to figure out extra categories for brand new people, young people, whatever. And there should also be categories for people who haven't been doing good work, but do have a good idea. need money to do it.

But I think that, you know, rolling funding for people who have been productive over and over again would both be easier, more accurate, and save a lot of time. That's one idea. The other idea, much more radical, is I think that there should be universities that don't have departments. In other words, every university has a physics department, a history department, and economics department, and I think it has even much more of a chilling effect on interdisciplinary work than we talk about. You know, like, and I've seen this in action where I'm in a physics department and we're thinking about hiring a new person who does biophysics.

And rather than asking, you know, is the work good? We're constantly asking, is it physics, really? And the same thing I'm true is, I'm sure is true for, you know, an economic historian. I'm sure that there's an economics, economics department that is saying, but is it really economics and a history department is saying, is it really history? And there's just a million examples of this. And so I can envision a utopian university. doesn't have departments, that it has professors, and professors have their specialties,

but rather than the department deciding to hire people that sort of continue on their favorite kind of research, there are ad hoc committees that say, like, what kind of person do we want to have here at the university? And individual students could sort of carve out their own specialty and their own major by picking and choosing different courses to take. That might be too utopian, but I think that something like that, you know, we have a lot of universities, at least some place, should try it. Simon Carter says, does your work deriving space time

from quantum mechanics work for other interpretations or just many worlds? The answer is I'm not sure. It's certainly a much easier fit in many worlds than other interpretations. So I'm not going to say what is or is not possible

in other interpretations. But the thing about many worlds is exactly because it is so simple and austere. There's just a vector in Hilbert space evolving with time. It doesn't make a lot of assumptions to start

with about what it is you're quantizing, right? Whereas as far as I know, every other version of quantum mechanics has a vision from the start about what it is your quantizing, you know, particles or fields or whatever. And so therefore, you kind of have to know the answer ahead of time. When it comes to quantum gravity, there's a different kind of thing. Like you can start with space time, but if you're saying, well, space time isn't the fundamental ingredient, if it's somehow emergent from something we don't know what it is, then you're reduced to just guessing. And that's what we, you know, we guess that string theory is right, or loop quantum gravity is right. And then you try that out.

And that's perfectly sensible way of moving forward. But it's not a model independent algorithm for saying, well, here are the properties it would have to have, no matter what the right guess is. That's something that many worlds is set up to do in a very nice way, I think. John says, I have a question about quantum gravity in the double-slit experiment. Consider an atom on edge, on the edge. There's some mistypo here. An atom on edge of the left slit and an atom on the edge of the right slit.

As an electron passes through both slits, is there any tug from gravity on these two atoms? I realize humanity will likely never have instruments sensitive enough to test this, and then I'm basically asking you for the correct theory of quantum gravity. Not necessarily the correct theory of quantum gravity needed here. This is the kind of question you can certainly imagine asking. independently of the specifics of quantum gravity. Any theory of quantum gravity better give you classical gravity in the correct limit. So, yeah, I think that there will be a gravitational pull. You know, that's the thing about gravity, according to Einstein, is that everything

causes a gravitational pull. You know, there's a small number of contrarians who think that gravity can be classical while quantum mechanics will matter and everything else is still quantum mechanical, to me, that makes absolutely zero sense because gravity says there's a certain amount of energy in some place, and that energy causes space time to curve. But if in quantum mechanics, you don't even know where an object is, you know, if it can be the superposition of being here and being there, then how do you calculate where the energy is? It kind of just doesn't fit together very much. So I think the gravitational field has to be quantized, and therefore, yeah, you'll definitely have a gravitational impact on the double slit experiment. When you run the next,

numbers, you find, the effect is so tiny that it's never going to matter, like you say. So no one needs to worry about that. There's other forces, just the radiation from light in the room, is enormously greater than the force due to gravity from an atom. Lou Argears says, how does a rotating universe work? Do you take a baby big bang and spin it like atop? What is the axis? These are all very good questions.

I don't think that, in fact, the idea of a rotating universe makes perfect sense. In other words, there are universes that make perfect sense or cosmological models that make perfect sense that people describe as rotating, but they don't map cleanly on to the notion of a spinning top that you have in mind. Typically, what they involve is something like galaxies in the universe all rotate individually, or essentially all galaxies have some rotational axis. What if all those axes were lined up together, right? We think that in the real world, the galaxies sort of have spin axes that are randomly distributed with respect to each other, or at least far away galaxies. But if they were all lined up, that would sort of impart some effective average non-zero angular momentum vector to the mass in the universe as a whole. We don't think that that's how it is. So there is no axis in the real world, as far as we know.

Anonymous says, could you explain what temperature is? unlike the usual macroscopic definition, which states that it is a measure of a quality of a state of a material, I'm interested in a microscopic definition on a particle level. Can a single isolated particle from the standard model have a temperature? Well, the answer is basically no. Temperature is an emergent feature of large collections of particles. There's no such thing as the temperature of a single particle. One classical definition of temperature is just the average kinetic energy of particles in a gas.

So you could, you know, the thing that it comes to close, to the temperature of a single particle is the kinetic energy of the particle. But it's not really the temperature, because temperature implies the idea that different particles have different relative kinetic energies. For a single particle, the kinetic energy depends on your reference frame in which you measure it, but the temperature doesn't depend on the reference frame. So that's okay. You know, temperature, it's like pressure.

Pressure is exactly the same way, or just density of matter. There are certain things that do not make sense at a particle level but become interesting and relevant at the emergent level when you have many, many particles. Pat Gallagher says, is the arrow of time relativistic in that different observers may experience different sequences of events? No, it's not relativistic in that sense, at least again, as far as we know, many of these questions are have a caveat as far as we know. So in the world, as we know it, where there are no time machines, right, where there are no closed time like curves, you can slice the universe into moments of time. And the arrow of time has, as one of its features,

that there's a function of those slices called the entropy, the entropy of the universe at that moment of time, and it increases monotonically in a certain direction. So relativity says that there are different ways of slicing the universe into moments of time. Different observers would naturally define different reference frames. But it remains the case that no matter how you slice it, according to any observer in a universe without closed time-like curves, you will have the feature that entropy increases monotonically in the same direction on all of them. So the arrow of time is invariant in that sense. John Eastman says,

The doomsday argument assumes that we are equally likely to be born in any position within the unique list of all humans who will ever live. But if the many world's interpretation is correct, then our birth position is simultaneously within many different lists of humans, branching through our present into different futures. Thus, our birth position is no longer correlated with the size of a unique list of humans and therefore the doomsday argument fails. Is this correct?

I think it's on the right track, honestly, but, you know, look, I don't believe the doomsday argument. I think the doomstay argument does fail. So once you think it fails, there's probably more than one reason you think it fails. I think the idea of assuming that we are typical observers within the population of all human beings to ever live is just not a good assumption. We're not, I'm not a typical observer. I'm me. And, you know, I'm very specific, actual observer. But this is, as you'll recall, if you listen to the podcast with Nick Bostrom, this is a controversial issue. People are not clear on the best way to do

this. There's a, there's a school of thought that says that when you're comparing theories with large numbers of observers to theories of cosmology with small numbers of observers, you should favor the theories that have large number of observers because it's more likely you're in that theory than in the other theory. I don't think that's right. I think that you can favor theories in which it is more likely that you, specifically you, come into existence. So therefore, it might effectively be true

that universes with large numbers of observers are more likely. But I don't think you should weight your prior probabilities by the number of observers. If you did think that, then you'd, get into a complicated situation in many worlds because now you have multiple worlds, but they have different weights, right? They have different amplitudes, different thicknesses. So I would think that you should then weight the number of observers by the amplitude squared of that branch of the wave function.

But I don't think that's the first thing, the right thing to be doing anyway, so I haven't really given a lot of thought to that. Siddhartha says, I want to spark yet another discussion on the question of free will. My takeaway of your views is that free will is emergent, but we're not Laplace's demon and in our everyday lives, we cannot help but make choices because we have very incomplete information. But how about free will in the stronger sense? Asked another way, given the physical laws and initial conditions of the universe, was it inevitable that 13.8 billion years later, a biological entity called Sean Carroll will experience a series

of life events that will lead him to start the Mindscape podcast and monthly AMA questions in exactly the manner you have done? Well, you know, I think that it's an underposed question because it depends on what your view is about the laws of physics, okay? In particular, quantum mechanics kind of gets in the way here, right? You know, quantum mechanics says that there are probabilities of different things happening, and if you played the movie backwards or re-ran the film of the universe starting from the beginning again, you would not get the same outcomes, and that has nothing to do with free will whatsoever.

It just has a question of whether or not the laws of physics are deterministic or indeterministic. Many worlds is deterministic, so the multiverse is the same. but people might be in different branches of the wave function experiencing different things. So there is a question about whether or not the laws of physics are deterministic and indeterministic that has zero to do with the question of free will. The strong sense of free will, the libertarian sense of free will, has to do with whether or not you personally can violate the laws of physics just by thinking about it. And I don't think that's true, but whether or not it's true has nothing to do with whether or not the laws are

deterministic or indeterministic. A universe governed by indeterministic laws of physics has exactly as much free will as a universe governed by determined laws of physics if those laws of physics are always obeyed even by people. Joseph Tungretti says, I have a hard time wrapping my head around the notion that a gravitational field doesn't decay down to zero given enough distance between two massive objects. If the only matter in the universe consisted of two neutrons located a million light years apart, Does general relativity imply that given enough time, they'd move closer and closer to each other until they eventually collide?

It does. I mean, you need to tell me what the velocity of the neutrons is. If the neutrons start at rest with respect to each other, then in general relativity or Newtonian gravity or anything else, there's a gravitational pull between them and they would eventually come together. Neutrons were not a good choice for you because neutrons decay within like 10 minutes. So they would decay long before they came together. Neutrinos would work if you had two neutrinos at rest. They'd be even more vivid example. They're even lighter in mass and they're stable. But they would eventually pull each other together. Yeah.

John Bach says, given the state of the evidence today, would you put your money on the traditional Big Bang or the Big Bounce? Are there some theoretical issues that the big bounce solves that make it more appealing than the Big Bang? Well, you know, I don't know. I certainly don't have strong feelings one way or the other. I don't think that the big bounce is the right way to talk about the alternatives to the Big Bang. I mean, presumably by big bounce, you mean the universe that collapses and then bounces and we're in the expanding phase. If that only happens once, then it's almost impossible to solve what I think is the most important problem,

which is where the arrow of time comes from, why the entropy was so low near that bounce. If it happens cyclically many times, then that problem is even worse because you're pushing it back to T. equals minus infinity. So I don't like bouncing cosmologies very much at all for exactly that reason, but you can have other ways in which there is space time before the Big Bang, but just not a bounce. And that's what Jennifer Chan and I proposed in 2004, where baby universes could spontaneously nucleate out of an empty space time pre-existing. So I think that I'm very open on the question of whether or not there was a universe and space time before the Big Bang, but the specific scenarios of bouncing cosmologies

I'm not a big fan of. Brent Meeker says, imposing the black hole information paradox, it is commonly noted that Hawking showed the radiation spectrum to be a black body, and then it is inferred that the outgoing radiation can contain no information except the temperature parameter of the Planck spectrum.

That seems like a big leap to me. Is there no way to have a black body spectrum that is not produced by an array of random radiators? So, yeah, this is just a case of sloppy, science communication, to be honest. So it's not true that Hawking shows that the spectrum of radiation is the black body, and then we infer from that that there's no information in the outgoing radiation. What Hawking actually infers in his calculation is the specific state of the outgoing radiation,

namely that is a thermal density matrix. So if that doesn't mean anything to you, it means that the wave function of the individual, of the set of all the radiation particles is not a pure single wave function. It's a mixture of multiple possible wave functions in exactly the same way that in ordinary statistical mechanics, we talk about the probability distribution of particles in a box to have certain velocities and positions. We talk about the probability distribution for the quantum state to be in different wave functions. And the thermal, and so that whole thing, that mixed state, as we call it, combination of many different weight functions is called a density matrix, okay, for technical reasons,

which you don't have to get into. But there is a specific density matrix called the thermal density matrix, which is something that has the spectrum of a black body and no other information in it. That is the status, that is the characteristic feature of the thermal density matrix. And that's what Hawking's calculation predicts the photons should be in. So Hawking's calculation doesn't just predict that the spectrum should be a black body. It predicts specifically that there is no information hidden in secret correlations in the outgoing photons. And that's why people don't believe that Hawking's radiation is the right final answer if you believe that information eventually gets out.

You need to actually have secret correlations in that outgoing set of photons, while still having the spectrum of a black body but not exactly a thermal density matrix. Edward A. Morris says, does the expansion of the universe, affect the wave functions of electrons and other elementary particles? In other words, do these particles experience a kind of redshift like photons do? And if so, what is the practical effect? I think the answer is it depends. You know, it's, these are hard questions to answer because we talk in words about the expansion

of the universe, but it's the equations that matter, right? So the correct answer to any question like this is, give me the equation for the physical system you want to describe, like the wave function of an electron or something like that, couple it to the expanding universe metric tensor of general relativity, and solve for its behavior, okay? And then the answer is given to you, full stop. For photons, you do that. I mean, you can pick up my general relativity book. We do that for photons, and that's where you get, you're solving Maxwell's equation for the evolution of photons.

because they're electromagnetic waves, so it's not photon particles, it's classical electromagnetic waves, and that's where the redshift comes from. So what you would want to do is take the Schrodinger equation for the wave function of an electron and allow it to be evolving in the background of an expanding universe. And I'm sort of having and hoeing about what the actual answer is because it depends on what's going on with the condition of your particle. If it's just one particle, okay, if it's just the way, function of an electron, it has nothing, whether or not the universe is expanding, the, that

electron's wave function will spread out. This is what wave functions do. They spread out, okay? So a, um, a, a, a, a plain wave will be spread out all throughout the universe, right? But that's just, uh, uh, what should I say? It's an idealization, right? So you can have a plain wave that is oscillating like a perfect sine wave spread out all throughout space, but that's not, as we already talked about earlier, a normalized

wave function, okay? So to create what we call a wave packet, which is a wave function or any other wave that is localized in space with different wiggles in it, that wave packet can be thought of as a superposition of parts of energy that move at different velocities. So all of this is to say in a fancy way that if you start with a wave packet for an electron or a photon or anything else, it will spread out over time. Okay. So that's not quite the cosmological redshift. The equivalent of cosmological redshift for something like an electron, a massive particle,

is just that its momentum changes, right? If you, instead of emitting a photon from one galaxy to another one, if you throw a photon, throw, not a photon, photons always move the speed of light, throw an electron or throw a baseball for that matter, from one galaxy to another. and you set it up so that in the rest frame of the throwing, it has a certain momentum, then in the rest frame of the person catching it in the other galaxy, its momentum will be less. And that will be because of the cosmological redshift. So there are debates, I'll admit it, there are debates in the general relativity literature

about whether or not that's really a different thing than the ordinary Doppler shift. I think it is. But at some level, you can absolutely predict. Everyone agrees on the prediction of what you observe, right? all they disagree about is whether or not it's worth attaching certain words to it and that I feel less strongly about personally. Jared Kosulich says, if there were two of you and you could coordinate your activities to learn from each other, how would the other you spend their time? So I think in these questions, you know, it's related to my thoughts about many worlds. If there are two of me, there aren't two of me.

There are two different people who might be identical. They might both look like me and have the same memories as me. and all that stuff, but they're two people. So it's not like, you know, Calvin and Calvin and Hobbs where you duplicate yourself and have all your duplicates do the messy work, do your homework and do the dishes and things like that, because those are people and they live a life too. So there's no sense in which it's fair to like make one person do all the learning and the other person just goof off and have a good time. That's because there's two different people. So I think that what you're asking is, you know, could we split up the responsibilities and the fun equally or? or something like that, but honestly, I don't know.

So I'm a little worried that these sort of thought experiment questions are not tied down by reality well enough. So I'm not trying to avoid your question, but I honestly don't know how to answer it in an honest way. Sorry about that. Scott Fenton says, what do you think our best physical theories, sorry, why do you think our best physical theories still rely on constants of nature?

And to what degree is progress in physics related to elimination or sublimation of physical constants? It seems that major paradigm shifts often come with new ways of seeing, reducing the number of required constants. So I'm not sure that's true. I mean, I know there are sometimes when you can reduce the number of required constants. So, like, when all you knew about was chemistry and you knew about elements, you had to separately specify all the chemical elements, right, in their masses and their charges,

isotopic abundances, things like that. And certainly, you know, understanding there was just protons and neutrons. made your life a lot easier and the fundamental theory has fewer constants in it. But then, you know, we went and found the muon and the top quark and the Higgs boson and they require more constants to specify their details. So I don't have any special feeling that the best theory would have no constants or something like that. I mean, that would be nice if there was a way to just from pure numerology, I guess, derive all the constants of nature. But we're not anywhere close to like that happening anytime soon. So I think you should just be open-minded when you're moving from

our current theories to better theories, whether or not the number of parameters or constants of nature will increase or decrease. I think that's not something we have the right to guess right now. West Clyburn says, who was your favorite Muppet? You know, I'm of an age. Those of you, I hope that there's some of you out there that are of the same age. My experience with the Muppets was mostly from Sesame Street. You know, my Muppet watching years, as it were, was before the Muppets had their own TV show. I mean, probably I could have watched the Muppet show and did, but it wasn't like one of my favorite things. When I was a young kid, it was definitely Sesame Street that I was watching. So I think that do the big ones count? Like, do the human beings in costumes count as Muppets? I'm

not sure. Because if that's allowed, then I will definitely vote for Snuffellupicus to be my favorite Muppet. I always liked it when he was on the show. He rarely appeared. And of course, none of the humans on the show could see him, so I thought that was cool. Michael Lacey says, in last month's AMA, you said that there would be many branches of the wave function in which Donald Trump was not reelected. If branching is caused by quantum decoherence, but human behavior can be explained using classical physics, what would cause branches to have different election results? Would differences result from a Schrodinger's cat scenario, where quantum measurement can

trigger different macroscopic outcomes, or would they result from a butterfly effect where very small differences in the initial conditions of each branch evolve into large differences over time. Well, I want to say both because those two things are not really different from each other. You know, the Schweringer's cat scenario is exactly set up so as to take a tiny quantum measurement outcome and amplify it to a big macroscopic difference. Cats alive or cats dead or cats awake or cats asleep, however you want to do it. So that is what is needed for any of these things to be true. So if you want a quantum fluctuation where a whole bunch of people vote differently, for example, that could happen by, you know, random but coordinated changes in the brains of a whole bunch of voters, right?

And it's unlikely, but it absolutely could happen one way or the other. So my thing about human choices and quantum branchings is, you know, I keep thinking that I say it very clearly, but people, not you, not you, Michael, but people keep misunderstanding me. So let me say it again. What I try to say is human choices do not cause branching. But branching can absolutely cause human choices. Okay? In other words, quantum events like a certain chemical reaction not happening, even though it's overwhelmingly likely that it happens,

but maybe there's a quantum fluctuation and it doesn't happen. We could interpret the effects of that in the macroscopic world as a different decision being made by a human being, okay? Because human beings are just collections of particles. the rules of quantum physics. So it's not that we could we can never have different branches, which we would interpret ex post facto as saying, well, different decisions were made on these branches. My point is simply that the branching was not caused by the decision making. It's the other way around. James Kittick says, reversibility in principle versus reversibility in practice is sometimes explained

through examples like scrambling an egg. But I got to thinking about a lot of of dominoes set up on a table. When the dominoes get knocked down by a chain reaction, I'm struggling to see how this is reversible, even in principle, for at least two reasons. So there's two reasons. I'm just going to read one, because I think it's the same answer for both. The reason is, how would the last domino ever stand up again? Well, I can imagine some random fluctuations of the atoms in the table somehow conspiring to give the domino an upward push. My understanding is that waste heat can't do work, so how would there be enough energy to stand the domino back up. So I think the reason why you can't understand it is because you're using a rule from

macroscopic physics. Waste heat can't do work and trying to apply it to a wildly improbable microscopic situation in which a huge number of atoms randomly fluctuate their velocities in just such a way as to push a domino back up. So the point is, if you allow yourself to imagine these very, very far-fetched microscopic scenarios, there's no such thing as waste. heat anymore. All there is is atoms, right? From this microscopic point of view, there are atoms, and they have velocities, and they have positions. And to reverse something like a domino falling, like, you don't need a whole bunch of domino. Just take one domino. It falls and it makes noise. And you say, well, how in the world could that domino just spontaneously pop back up?

Well, when it fell, you know, it created noise, it created heat. It shook the atoms in the table and in the air around it. So just wait a second after it fell, and then thought experiment-wise, you can never do this in practice, but in principle, imagine reversing the momentum of every single atom. So you just send it backwards.

That's all you need to do. And that is an extremely, incredibly, precisely, finely tuned situation. But in that situation, all those atoms would come up and exactly undo the falling of the domino to put it exactly back up, stationary where it started. It's not very likely, but it could happen. Christoph Pironsky says,

we programmers tend to care for code efficiency. Many worlds interpretation requires copies of the full universe for the tiniest differences in single quantum outcomes. It's almost not possible to imagine something less efficient. Would it be possible to devise a variation on many worlds, which would keep most of the universe in a single copy and branch just different results of quantum outcomes? So I think that this is a little bit backwards. I think that programmers who care for code efficiency should be the biggest fans of the many worlds interpretation of quantum mechanics because the code is not the universes. The code is the Schrodinger equation, right?

The code is not the outcome of doing the calculation. You should distinguish between the code and the output of the calculation. I could write a very short code that gives a huge output, right? I could just list all the real numbers. Or, well, I couldn't do that. I could list all the integers in principle or the integers up to some bound, whatever you wanted to do

with a very, very short amount of code. That's what many worlds is. The code is extremely short. There's a wave function and there's the Schrodinger equation. How short could you be? How more efficient could you possibly be? So that's the point that there are plenty

of other variations of many worlds, but their code, their instruction manual, is always less efficient because it says, because many worlds says, there's a wave function and there's the Schrodinger equation. Every other version says there's a wave function and the Schrodinger equation, and there's this other stuff that stops other worlds

from being made. So that's where you have to take your choices. Guillermo L.C. says, can shadows travel faster than the speed of light? And the idea here is, this is a kind of a famous thing. You know, like if you cast a shadow in something very, very far away, like the moon, cast a shadow on the moon.

you can move it back and forth much faster than the speed of light. And for that matter, you don't need to think about shadows. Just take a laser and point it to the moon. You jiggle it back and forth across the face of the moon. And yes, the place where the laser hits the moon or the edge of a shadow being cast on the moon can move fast in the speed of light

because it's not a thing. It's not a thing that can convey information or any, no individual particles or other things are actually moving fast in the speed of light in that experiment. But the edge of the shadow or the point of the laser absolutely can appear to be doing that. Josh says, how did the scientific community treat Werner Heisenberg after World War II? Was he able to reintegrate into the scientific community?

Yeah, he absolutely was. You know, I'm not the best person to ask about the history of some of these things. Like, honestly, you know, no false modesty here. You would do better just going to the Wikipedia page for Werner Heisenberg. But he absolutely was still part of the scientific community after World War II. in fact, he was a big deal, you know, especially in Germany. And, you know, he served as the director of various institutes and, you know, various international meetings and things like that. So he absolutely was part of it.

You know, I think we have a slightly different view now because it is much, they didn't know in, you know, 1950s or 60s that Heisenberg had tried really hard to build an atomic weapon for the, for Germany during World War II. So that wasn't counted against him. Now, it was, you know, you can ask, well, what were his spoken opinions about what was going on? And I'm, again, not the world's best person to ask about this. My impression is that Heisenberg, like many people, sort of danced carefully along an edge of saying, you know, I'm not really for the Nazis. But on the other hand, we're in a war. and I would rather Germany win the war than the other side. In particular, a lot of Germans were very worried that the Russians,

that the Soviets would win the war and take over and install communism or something like that. So I think that's where Heisenberg came down, but that left him after the war not being treated as, you know, a nasty ex-Nazi, just, you know, a German who had been too patriotic like many others had. I'm not passing any judgments, and I'm sure that my information and knowledge here is not very detailed, so again, you should check better sources than me. Linneumizhira says, in something deeply hidden, you taught us a perfectly good explanation for the Bourne rule that it makes sense if we understand it in terms of the Pythagoras theorem.

Why can't David Albert accept it would be really the most reasonable explanation for self-locating probability in many worlds? So, you know, there's, you know, David Albert's objection. You can see it in the podcast I did with him. We had a more recent YouTube dialogue that you can also check out. You know, David knows perfectly well that there is a natural measure to put on your credences in many worlds given by the Bourne rule. He just doesn't see what forces you to do that, right? So I think that David has a view of the philosophy of probability in which is more frequentist in orientation than Bayesian, more abysian, more abys.

objectively chancy rather than subjective and knowledge-based. So he doesn't think it's a probability when you have this situation where there's one person on one branch and one person on the other branch. That's not the kind of thing that adapts itself to be thought of as the frequency of an experiment done over and over again, okay? Because no matter how many times you branch the wave function, any possible set of outcomes will be experienced by somebody. So David's objection is not that Pythagoras' theorem doesn't give you the right answer, is that he doesn't think there is such a thing as an answer that everyone should be obligated to use. I disagree with him, obviously, but plenty of people agree with him. So there you go.

Santiago Torres says, no question this time. Merry Christmas. Thanks for your great podcasts. Usually, you know, people do leave little messages here in the AMA, and I appreciate all of them and I read all of them, but I usually don't read them out loud as questions. But I thought that, you know, just a nice Merry Christmas to everyone out there, it was a nice thing to do. So I'm reading this out loud. Merry Christmas, happy Hanukkah,

happy Kwanza, happy, what do the Romans call it? The Saturnalia, right? All sorts of holidays happen over this time of year, and I hope everyone out there listening has some good ones. Joy Colbeck says, have you ever spent Christmas outside of the United States? And if so, where? If not, where in the world would you like to have a Christmas holiday and why? I don't think that I've ever spent Christmas outside the U.S., you know, in fact, this is going to be the first year, the first Christmas of my life that I've not spent it with my mom. Almost always I go to visit her. Sometimes she's come to visit me, but she's in Florida and I'm in California and we're in the middle of a pandemic. And it's bursting out all over and airports and air travel is especially

bad right now. So we have made a mutual decision to not do it this year. We'll make it up later. Don't feel bad for us. We can celebrate Christmas. some other day. But therefore, no, I'm not really been outside the United States to celebrate it. If I did, where would I want to do it? You know, I think that for something like Christmas, which I absolutely enjoy as a secular holiday, I would like to be some place that wasn't too exotic because, you know, I love visiting exotic places, but look, you know that it takes a certain energy, right? It takes a certain amount of effort to sort of negotiate places. where you don't speak the language

and you have no idea what's going on. And so that's a fun thing to do, but it doesn't seem very Christmasy to me. And I think that Christmas also, I wouldn't want to be in a very warm climate, especially if I'm traveling for a holiday. Like, I love being in Los Angeles for Christmas and it's beautiful every day

and I can go walk outside without wearing a coat. But if I'm actually traveling somewhere specifically for Christmas, then a little snow or at least chill in the air would be nice. So I'm thinking given that probably something, place like London or Edinburgh is one of our favorite cities. I would love to go in Edinburgh and visit the Highlands and so forth in the middle of December. That sounds like it would be great. You know, there's plenty of places that I know and love, Montreal, Paris would all be good places to go. So no immediate plans to do that, but it's something fun to think about.

Jessica Napier says, both determinism and simulation theory come up quite a bit in your conversations. The former makes me feel melancholic and unmotivated, and the latter freaked out. You don't seem phased by either, though. Do you have any words of comfort or advice? I think that, again, I try to give the short answer and then delve in. The short answer is no, I don't have any special words of comfort or advice. Not because I don't think you should be comforted, but because I was never close to being unmotivated or melancholic or freaked out by these things.

I, you know, the, there's your life and how you experience it and how you live it and how the people around you experience it and live it. And there's what you learned about the larger universe, right? And if I learned that, you know, God exists or God doesn't exist or determinism is true or indeterminism is true or there's a multiverse or there's Boltzman brains, all that, none of that is directly affecting my actual life. I mean, maybe God existing would affect my life if it were some specific religion that gave me instructions. Okay, that's true. But sort of a non-interventionist God out there who just created the universe and left it alone wouldn't affect my life at all. So why should that freak me out? You know, I think that the powers that I have to affect things at this higher emergent level where I'm a person making decisions and affecting things seem to me the same in all of these different scenarios as they were before.

I think that the only reason why you might be freaked out is if you had some maybe subconscious, intuitive feeling of something like a strong form of libertarian free will, right? Where you thought of yourself as not part of the physical world, but as something that was sort of special and separate. And I don't mean that in a disparaging way. Plenty of people think this going back to, well, Kant obviously. Emmanuel Kant famously, but going back much further than that. But I never was tempted by that point of view. I always thought of myself as part of the universe. I'm trying to understand a little bit better.

But the fact that I, you know, my atoms are obeying the laws of physics, whether I like it or not, never threatened me, never threatened to make me melancholic or freaked out. Pablo's Papa Georgi says, please choose one. And then Pablo's, you've typed physics, but then you didn't type another one. You didn't give me any other option. So physics or nothing, I think you just left it out. So I'm just mentioning this, maybe next time. we get an AMA, you should finish the question. Robert Grenise says, in order for particles to become entangled, do they have to at some point be near each other?

Well, this is a yes or no question. The short answer here is no, they do not. Certainly, the existence of entanglement has nothing to do with the distance between different particles. And as I've said already earlier in this AMA, entanglement doesn't fade away with either space or time necessarily. It can if you bump into it. The footnote here is that, of course, entanglement is caused by some physical process, and the laws of physics are local, right? Particles interact with each other when they are at the same point in space time, not when they're very, very far away. Of course, two objects like the Earth and the Sun can interact with each other when they're far away, but only via the intermediary of a local field, the gravitational field, stretching between them.

So that's the secret. So you might say, well, in order to become entangled, particles have to interact, therefore they have to be at the same place or at least near each other. But that's not quite right. If particle A wants to become entangle with particle B, it could do that by particle C interacting with A and then interacting with B, right? So there could be some other particles that take the entanglement and stretch it between them. So you could entangle A with C and then move C across the universe or whatever, and then see. C becomes, transfers its entanglement to be. In fact, that's actually something very much like that happens in what is called quantum teleportation.

Okay. So if you Google quantum teleportation, you can see things like that in action. Gerald Dr. Gerard Drovin says, I don't know, but I read on the internet that the earth is flat. And here you are telling us there's a universe and fields and something called space time. That's probably your opinion, but the internet tells us different things. So why do you tell all these fairy tales to the public? while you know it's all just a lie.

It could be that you skipped my question yet. I hope you'll know it's not a serious question. But I wonder how you feel as a person and a scientist about these kinds of remarks, about people who believe in all sincerity that the Earth is flat and things like that. Well, you know, look, I have a mixed set of feelings here because I think that scientists see people getting science wrong

and they both take it too personally and also take it too simplistically. you know, the fact that people have incorrect opinions about science, whether it's the Earth or Flat or anything else, I don't want to excuse it. I don't want to tell them that it's right to do that, but it's usually not a straightforward matter of scientific literacy. If anything that we should have learned in the past couple decades, it's that people's beliefs about things do not flow directly from knowledge to belief, right? There's plenty of things that go into forming people's beliefs. It could be their political polarization affiliation, but it could also be where they grew up, their feelings about all sorts of things. You know, we tend to believe things that are said by people we trust, disbelieve things that are said by people we don't like. There's a whole bunch of things going on here. And I think that, you know, a classic example was the creationism debates that were very strong in the 80s and 90s and so forth. People were trying to get creationism taught in public schools, and scientists fought against it.

in a way that was, you know, took it seriously as like, well, these people believe this view of the world. We have this view of the world. Let's debate them on the merits. But they didn't understand that for a lot of local school districts that were actually interested in teaching creationism, the people there couldn't care less about creationism or Darwinism. What they wanted was to not be told what to think by a bunch of elites from big cities and coasts and universities and things like that. And so in response, what the, what the scientists did is to talk down to them as big city elites, right? And so it usually backfires in that way.

I think that at least some large fraction of people who believe the earth is flat don't really care if the earth is flat in some very real sense. They are performatively expressing their distrust of institutions, okay? If you want to put it in a slightly pompous terminology, they're rejecting the, the idea that they should be told what to think. The thing about the earth being flat or round is not that they have some idea based on experiments or observations. It's that they want to reject the conventional wisdom. Okay.

And that's also bad, but it's bad for a different reason than, oh, these people just haven't been taught science. Okay? So what we have to think about is where trust in scientists comes from, in addition to thinking about where scientific knowledge comes from and how we share that. So that's how I feel. I feel that we really need to do more not only in informing people about science, but in getting people to trust the right sources and distrust the sources they should be distrusting. Matt Faw says Einstein said that speed is measured relative to one's frame of reference, and general

relativity allows for frame-dragging the moving of space timing around a spinning massive body. So is it possible that when Vera Rubin saw, what Vera Rubin saw were galaxies in which their local frame of reference itself was moving relative to us? So no, because what Einstein said is that inertial trajectories, unaccelerated trajectories, are all equivalent to each other in special relativity. Okay? So speed is measured relative to one's frame of reference. That's true. but when someone like Vera Rubin looks at the

rotation curve of a spiral galaxy, it's not just measuring the speed of one particle, right? You're measuring the rotation of a galaxy. And that's a real physical thing. That's not dependent on one's frame of reference. Whether a galaxy is rotating

or not rotating is an absolute thing. You know, this is Isaac Newton's famous bucket experiment. You can take a bucket and you can spin it and you can instantly observe the fact that it is spinning from the fact that the water in the bucket

begins to creep up the edges of the bucket. What that means is there's a real physical effect of that spinning. So that is not something that simply depends on one's perspective. So there's a long-winded way of saying that when you are measuring the velocities of stars or radioactive, not radioactive,

using radio waves to measure the gas and dust inside galaxies, you're measuring a real physical thing, not a frame-dependent thing. Tom Hawkins says, do you think that sending humans to the moon and Mars is a wise use of resources, or would it be better to continue with robotic exploration? Well, you know, robotic exploration is absolutely more cost-effective.

Okay, so, you know, I'm very bad at answering questions about how we should divide up the money. Because I'm not sure how much money we have. You know, it's not something that I'm really well-versed in. or how best to spend it or things like that. It's certainly true. I'm happy to say that for given scientific return, robotic exploration in the solar system

is currently way more cost-effective than sending human beings. But look, I get the fact that sending human beings has a romantic side to it. Forget about cost-effectiveness. The world is not all cost-effectiveness, or we just wouldn't send robots at all. I just stay here on Earth, right? We have this drive to understand things.

we also separately and, you know, coincidentally and synchronously, have a desire to go there. And that's okay. So I'm all in favor of human exploration of the solar system. I just don't want it to cut into the budget for scientific exploration, which is cheaper to do just using robots. Dan Inch says, I understand that some people in the U.S. declaw their cats. This is unheard of here in the U.K., and I think it's actually illegal. Without passing judgment, are your cats declawed? So no, Ariel and Galban very much had their claws.

You can see the evidence for that on my legs and arms. They're very, very sweet cats. And, you know, they would never strike out in anger, but they do sometimes get spooked. And clawing happens, right? So, yeah, you know, look, I grew up with cats and some of them were declawed. You know, when I was a kid, when I was not the decision maker in the family. But also, I'm not sure what, you know, the state of. of knowledge about declawing was at the time.

You know, now I understand that it is a bad thing to do. And, you know, I think that when you get cats, on the one hand, I'm made happy by people adopting cats from their local shelter, et cetera. But on the other hand, it's a responsibility, right? Like, you have to take the good with the bad. You have to take care of the cats. They're depending on you now. And so part of that is, you know, the cats are going to claw some things.

Like, again, Ariel and Caliban are actually incredibly. well-behaved compared to many cats. I grew up with cats. I know what I'm talking about. Our furniture is in very good shape. They do not claw on the furniture. They do not try to eat human food. You know, we can sit there eating dinner, fish, chicken, whatever, and, you know, they'll walk

around and they don't even try to eat it from us. They don't usually knock things off of desks and tables. Ariel sometimes does that strategy, but again, less often than my other cats did. But you don't know, right? if they had grown up with different personalities where they were clawing the furniture all the time. You know, we would try to dissuade them from doing it, but yeah, you have to live with that. That's a decision you have to accept. Blake Sewer says, as a mechanical engineer, I had myriad classes in classical thermodynamics,

but I never really developed an intuitive feel for the field until I studied statistical mechanics. Why don't we start with that statistical mechanics? So thermodynamics is the, you know, science that arose in the first half of the 1800s. with ideas like entropy and work and the efficiency of different heat transfers and so forth, whereas statistical mechanics, which arose in the second half of the 1800s, was about explaining all of those features of thermodynamics

by thinking of fluids and gases as actually made of atoms, made of particles, made of molecules, which had a statistical distribution of their velocities and so forth, thus statistical mechanics. So, yeah, I mean, I sympathize with the idea that there are certain intuitive understandings that you get from statistical mechanics. And it is, after all, true. But there are things that are very understandable in terms of thermodynamics that you just don't need all that machinery to get, right?

I mean, the ideal gas law, pressure times velocity is proportional to the temperature, right, times the amount of stuff. that's a simple thing you can understand. You can understand why a gas inside a piston heats up when you push it without going into details about atoms and distribution functions and things like that. So it's always a choice when you teach physics or when you learn physics, do you do it exactly right from the very start? Or do you, you know, take a level of analysis and study that and then learn later about a deeper level of analysis? I do not think that you should teach quantum mechanics first, and classical mechanics just take the limit to quantum mechanics. I just think that would be, I mean, quantum mechanics is harder than classical mechanics. Why not give people classical mechanics right away?

And I think that it's a less clear case, I admit, with thermodynamics and statmec. But I do think that you can learn some things about thermodynamics perfectly well without knowing statmec. Look, if you really want to understand thermodynamics, you need to study differential geomodynamics. That's the secret they don't tell you. If you really want to know, like, where are all these partial derivatives coming from and all these rules and it doesn't make sense? It's all because the secret of thermodynamics is thinking of it as different coordinate systems in a high-dimensional manifold, right? All those partial derivatives and Maxwell relations are just super simple in the language of differential geometry, but no one learns differential geometry first and then thermodynamics second, okay? So, in fact, most people learn thermodynamics that never learn.

differential geometry. So you always make those sort of sacrifices when you learn things in the real world. Chris Fhotas says, is the universe finite or infinite? And if the answer is infinite, since it started from a singularity with a finite shape, at one point did it become infinite? So we don't know whether the universe is finite or infinite. We honestly don't know. So it's not like I'm hiding anything from you. It might be finite. It might be infinite. It might be infinite. We just don't know. There's only a finite amount of it that we can observe, but that tells us nothing about whether or or not the part outside is finite or infinite. And you say, if the answer is infinite, if it started from singularity with a finite shape,

at one point did it become infinite? But it didn't. If the universe is infinite, it did not start from a singularity with a finite shape. If the universe was infinite, it was always infinite, okay? So I've said before, maybe you've heard me talk about this before or not, but the big bang, the singularity at the beginning of cosmology, is just a place where we don't know what's going on. We don't even have the language to talk about it. Classical general relativity fails, okay?

So the singularity itself is not something we have any right to proclaim knowledge about. All we can talk about with any sensibility is a certain amount of time, even if it's a very short amount of time, but some amount of time after the singularity. And the point is in Big Bang cosmologies, in solutions to Einstein's equations of general relativity that come from an initial singularity, there are plenty of solutions of the form where at every single moment after the Big Bang singularity, space is infinitely big. There's just no problem with that. And that's one of the features of general relativity, that there's no problem with that. You can have space infinitely big. Richard Young says, I understand that the universe in many worlds only branches when quantum systems and superpositions become entangled with their environment.

But I wonder about something like a large Hadron Collider, where we monitor almost countless resolutions of quantum entanglement in an experiment like Atlas. Does each resolution of a particle's path or decay cause a branching? Yeah, absolutely. It does. I mean, but again, that's not that many compared to other things going on in the universe. There's a lot of specific things going on. So think of it this way.

You know, when a, when two particles crash into each other in a particle physics experiment, the prediction of quantum mechanics is that the wave functions of the new particles being made, move out away from that collision in more or less a spherical wave. Okay? Not exactly. In fact, depending on the details, it might not even be close to that. But in principle, it could be moving out in all directions. That's never what you see.

What you see is a trajectory, a curve of an actual particle in your detector. And this goes all the way back. This was, in fact, called someone's paradox or someone's puzzle. I forget the guy's name. But back in the early days of quantum mechanics, the predictions of the Schrodinger equation was that when an atom decays, a radioactive decay, the electron or whatever alpha particle that gets emitted has a wave function that is emitted in a spherical wave. But you never observe that. You observe a track. And the many worlds explanation for that is as soon as that wave function interacts with the detector around it, it branches. It branches into many, many different copies.

And in every different copy, the wave function is the particles observed to be in a particular place going in a certain direction. The good news is that once that happens, once that initial branching happens, and you have now a localized wave packet in that branch where the particle has been detected as a particular place and it's moving in a certain direction, then it just keeps bumping into the rest of the detector and leaving a track. And you can show this, you know, using math. So the fact that you see a line corresponding to the trajectory of a particle isn't surprising even in many worlds, but yes, there's a lot of branching, just like there is with all sorts of other radioactive decays.

Simon Tulloch says, why doesn't the cosmic microwave background radiation give us a universal standard of rest against which all velocities can be measured absolutely? It does. In fact, we call it the cosmological rest frame. This is something that cosmologists talk about all the time. And I think I know what's in the back of your mind, namely, what's in the back of your mind is, aren't we taught that there is no absolute rest frame? But what really, again, you know, there's details that get left out sometimes when we talk about these things. The real thing is the vacuum, empty space, space time itself doesn't have a rest frame, okay? The fact that the universe is full of photons in the form of the cosmic microwave background, and we can measure our rest frame with respect to that is no different. than saying I can measure the velocity of my car with respect to the ground. Okay? Of course, individual objects in the universe can define the standard of rest with respect to them.

And it just so happens that cosmologically we have one that we can share all over the universe. But it doesn't affect the features of relativity that in empty space, the laws of physics don't depend on your velocity with respect to anything at all. Saraj Raj Rajan says, is Hilbert space a real thing? or is it something invented for the math of physics to work? What is a good analogy you use to explain it to someone at an undergrad level? You know, I never know exactly how to answer these questions because they involve deep questions in the philosophy of mathematics that I don't have strong opinions about.

You know, in some sense, what I'm tempted to say, but I won't stand up to absolute belief in it because I'm not an expert of this, what I'm tempted to say is, Hilbert Space is an abstract idea. there's only one real thing, which is the universe. The other real things are things inside the universe or parts of the universe or aspects of the universe, okay? In our way of thinking about quantum mechanics, Hilbert space is the space of all possible wave functions.

It has the mathematical character of a vector space, as John von Neumann pointed out a long time ago. And so even in that perspective, even if we wanted to think of the universe as a wave function, It's only one vector. It's only one element of a Hilbert space, which has an infinite number of elements. So the whole Hilbert space doesn't exist, at least not at any one time. But of course, there are people, mathematical platonists, who think that abstract mathematical objects do exist, have a sense of existence separate from the kind of existence that physical stuff has. So I don't necessarily buy into that, but very, very smart people do.

So if you are a mathematical platonist, then Hilbert space exists. Otherwise, it's a mathematical tool that we use to understand the real physical world, which is what actually exists. Dead Baby Seal says, I have been starting to learn a little bit about quantum field theory, and to be honest, canonical quantization feels sort of arbitrary. Do we know of other ways of performing quantization in QFT? If so, are they useful, and what are they used for? So, yeah, there's absolutely other ways in quantum field theory or not in quantum field theory, right?

You can do things via path integral. That's a different thing than canonical quantization. There's other sort of operator-based methods and things like that. But, you know, in some ways, I want to say, who cares, right? I've said this before. I'm going to say it again. Nature doesn't start with classical theories and quantize them. The idea of quantization is a way of discovering quantum mechanical theories.

But the quantum mechanical theories exist all by themselves. However, you go about discovering them. Even when you do canonical quantization, there's still some arbitrariness in how you go, ordering operator ordering ambiguities and things like that. But hopefully, you know, most of the time, you get more or less the same answer, and that's true in quantum field theory. So, yeah, different textbooks will use different ways of doing it, but you'll end up in the same place, more or less, with QFT.

Jan Lushik says, is the universe 13.8 billion years old everywhere, or just from our local perspective? Well, I don't know about everywhere. You know, again, we can only observe part of the universe, some finite bit of it. Outside the part we can observe, things might be very, very different, including the Big Bang and all that associated with that.

Also, as we've been, there's been a bunch of special relativity questions here. Just saying is the universe 13.8 billion years old everywhere implies a certain choice of reference frame. In fact, it's the reference frame given to us by the cosmic background radiation, the cosmic rest frame, okay? In that rest frame, from that perspective, the statement that the universe is 13.8 billion years old is just the statement that the time from now in that rest frame to the Big Bang is 13.8 billion years from the perspective of every particle that is at rest in that rest frame. And roughly speaking, that means all the massive particles in the universe, right? particles don't travel near the speed of light.

If they move a little bit, it doesn't affect their perception of time very much. So 13.8 billion years old everywhere in the visible universe is a perfectly legitimate thing to say. Christopher Stanford says, does time stop in a black hole? It would have its own laws of nature within its own confines its own universe. So no, time does not stop in a black hole, at least as far as we know. No one's been inside a black hole. So what do we know? We could get burned up by a firewall when we come close.

but according to the standard theory of black holes in general relativity, et cetera, if you pass by the event horizon and are in a black hole, time still flows for you, you might not even notice. If the black hole's big enough, you wouldn't even notice

that you were inside a black hole. Steve M. says, what do we know about the Higgs field beyond its existence and the boson? Can it be affected as we affect the electromagnetic field? Giving mass to particles doesn't tell me much.

Yeah, of course it can be affected just as we affect the electromagnetic field, it is a field out there and affecting it is how we discovered it at the large Adderon Collider. When we collide quarks together that are inside protons, they started the Higgs field vibrating.

And we saw that as an excitation of the Higgs field and detected its decay products. That's how we know that it's there. The problem is that unlike the electromagnetic field, the Higgs is very massive. Okay. So when a particle is massless, like the photon, the particle associated with the electromagnetic field,

what that means is, you know, we've already said earlier in the AMA, the mass of a particle is how much energy it has at rest. And if it's moving faster, if it's not at rest, then it has more energy. So you can think of the mass of a particle is really the minimum amount of energy it takes to make it. So low-mass particles, it doesn't necessarily take any energy at all to make them. That's why it's easy to make electromagnetic fields. because they're associated with massless particles.

Every photon has some energy, but there's no lower limit on what that energy could be. As the wavelength gets bigger and bigger, the energy gets less and less. Whereas with the Higgs boson, it takes a huge amount of energy in a very tiny amount of space to create even just one Higgs boson,

and then it decays away very quickly. So just writing down the equations, the Higgs is exactly like every other field, but in practice, it's very hard to push it around or notice that it's there. Lee Foucher says, why is it the people who live in rural areas tend to vote Republican and people who live in urban areas tend to vote Democrat? That's a good question. I did a whole podcast on it if you want to talk to Will.

If you want to listen to the Will Wilkinson podcast or if you did listen to it and want more information, he wrote a mini book about it, a very long paper that is linked in the show notes for that podcast. You know, any question like that is hard to answer. There's probably many, many factors that go into a lot of things. But Will tried to do a little psychology, right? He compared people in urban areas and rural areas on measures of the Big Five personality inventory. And he made claims, like, there were certain Big Five personality traits. I'm going to forget what they are. So I shouldn't try to reproduce them here.

But some personality traits naturally go along with living in urban areas, others with rural areas. And those personality traits also, to some extent, do line up with political affiliation. So maybe that's part of it. You know, roughly speaking, people in urban areas are more comfortable in kind of an environment where there's new experiences going on all the time. You know, you go to your favorite ethnic restaurant. You know, there's different languages on the signs around you. There's people you don't know and all that stuff. Whereas people in rural areas are more comfortable with knowing what's going on, like knowing what kind of food they're going to get at their local restaurant.

and it's sort of comforting that there's a routine that is predictable. They don't need to sort of worry about getting things wrong and stuff like that. And neither one is good or bad, but it's very natural that that would line up both with where you live and with how you vote. That makes sense to me. Iric says, I have a feeling the answer is no, but have you ever played the video game The Outer Wilds? I completed it more or less at the same time as listening to last week's time travel episodes, and it strikes me as a perfect example of a time travel story where your name, not necessarily trying to change things.

So, no, I've not played it. Nothing against playing video games, but I have not actually gotten into that. I was, look, I was an OG video gamer. Like, I went to the spaceport and played all the asteroids and Lunarlander and space invaders, and I had a little Atari when I was younger. But, you know, the video games are so much more sophisticated now. And part of me worries that if I got into it, it would suck up a lot of time. And I have other things to do.

So I'm trying not to have that possibility be presented to me. Tim Kennedy says, in your biggest ideas of the universe, number 22 cosmology, you talk about the universe having no center. In a thought experiment, if right at the time when the universe was the size of a grapefruit, there was one cubic micrometer right in the middle of the grapefruit, and another on the outer edge of the rind, wouldn't the first be more in the center than the one that was on the rind? Well, there was never any time when the universe was a great fruit.

grapefruit. When we talk about the size of the universe, and again, this is totally our fault. When I say us, I mean, you know, popularizers of science. We talk about the size of the universe, we usually mean the size of our observable universe. So, as we've already said in the AMA, we don't know whether the universe is infinite or finite, okay? Even if the size of our observable universe was the size of a grapefruit, almost 13.8 billion. years ago, the universe itself might have been infinitely big at that time. And it's certainly, at least, you know, again, as far as we know, it was not that there was matter in a grapefruit sized region of space and then empty space outside. That's conceivable. You can imagine that, but we have zero reason to think. That's how it was. So the universe could be closed, that is, say, it could be the three-dimensional version of a sphere, and then it could literally have a finite size, and that size could be that of a grapefruit,

but it wouldn't have any middle. There's no middle to a sphere, because when we say in math or physics, when we say the sphere, we mean the surface of a two-dimensional sphere. So the surface of a two-dimensional sphere has no middle. What you're thinking of as the middle is inside,

and that doesn't count. That's not part of the sphere. And the universe could be a three-dimensional version of that. So it could be a closed, positively-curved, three-dimensional, manifold that is spherical in its geometry, but again, nothing in the middle. So I think that the thought experiment starts from a place where we don't actually think that applies to the real universe. Andy Val says, why do you do what you do? Is it is the quest for knowledge and understanding

enough to keep you fulfilled along your journey, or is there some greater goal you're attempting to accomplish? So I presume what you mean by what I do, you know, professionally, in the broad sense of, you know, including talking about science and doing podcasts and things like that. You know, look, I think that any answer to a question like that that doesn't start by saying because I enjoy it is probably not completely honest, right? I think that very few people do things that they absolutely don't want to do, but they think it serves a greater goal. You know, most people get personal satisfaction from pursuing greater goals. So I think, you know, I do enjoy it. Like, I mean, figuring out the universe, thinking about it, doing science and philosophy and, you know, talking to people in other fields and biology and neuroscience and design and cooking and climate and all these things.

It's just enormously fun for me, not necessarily for everyone. And that's also cool. And so, you know, I like learning new things. I like being the first person in the world to figure something out for the first time. and I like figuring out how to say those things and then saying it. And I like talking to other smart people who have learned things and are talking about them. I don't know if you can hear Caliban meeping in the background. I don't know why he's meeping right now.

But certain times of day, they want attention. They just got fed. So Caliban wants pets right now, but I've got to finish the AMA. So, you know, just like a cat, I have things that make me happy. Caliban would like to be petted right now. I like figuring out the laws of nature. You know, that naturally fits in to greater goals, to have a complete understanding of the laws of nature,

to make the world a better place by spreading both knowledge of science and an appreciation for a certain way of apprehending the world and learning about it and being kind to each other and all those things. But I think that if I attached a greater goal to it, it would be ex post facto. I think that, you know, honestly,

the best answer to a question like that is I'm doing it because I enjoy it, and I enjoy it a great deal. Peter Whaley says, what advice would you give to someone who wants to enter the world of physics? I already graduated, but have a thirst for knowledge about our physical world. How can I know if I'm up to the task, especially on the mathematics side? You know, the only thing you can do is try, right? You can apply for a job. Doing physics is a weird thing because it depends a lot on what kind of physics you're trying to do.

Like, you know, my familiarity is with very theoretical, speculative kind of physics, right? Not applied physics. And so the kind of physics I do, basically every single person who is employed doing it is almost always for university, sometimes for a laboratory or think tank, right? The Institute of Rans Study or Fermulab or someplace like that. But that's it. And that's a very small number of jobs. So it's hard to get these jobs. But there are plenty of physicists who are in other areas of physics that are much more applied and are much more useful to the outside world who work for industry or for the government in some other capacity.

And there's an even larger number of physicists who learn physics and do something else with it, whether it's going to Wall Street or working in a completely different sector, something like that. but I have no idea how, you know, your particular background or anything like that. So, yeah, apply for the jobs, is what I would say. If what you want to do is write physics papers, then, you know, try it out. Write some physics papers. Put them up on, I don't know, Reddit or Quora and say, like, what do people think about my physics papers? You know, it's very easy to fool yourself into thinking you have a great new idea about the world, but you need reality checks.

You need other people, people who are in the field and have been following it. And ask yourself this. You know, every morning on archive.org, there are dozens and dozens of papers appearing being written, right? Is there one category within the archive, whether it's, you know, AstroPH or HepPH or whatever, where you, number one, can download those papers and read them? and understand them, and number two, enjoy doing that? If those are both the case, then you're probably good enough to create some of your own. If that's not the case, then I would concentrate more on learning more and catching up rather

than trying to create new physics yourself. William E. Clark says, you say that the best mathematical description of the universe we have is that of a vector in Hilbert space. Why do we need the whole Hilbert space when just a single vector describes the whole universe? Well, because the universe at a single moment of time is described as a vector in Hilbert space, but then it evolves in time. The vector changes to a different vector. So we kind of need at least as much of Hilbert space as we would have to elect the vector,

which is the state of the world right now, change over time. That's the only reason. James Hancock, sorry, I shouldn't say. That's a little bit cheap. That's not the only reason. We very, very often care about subsystems of the universe. right? So it's not just the whole universe, which is a vector in Hilbert space, but subsystems are parts of Hilbert space. And since we almost always deal with little parts of the universe one at a time rather than the universe as a whole, knowing the mathematics of Hilbert Space more generally is an important part of being able to do that. James Hancock says, I just found out that no one has ever measured the one-way travel time of light, and thus we don't know if direction has an impact on its speed. Could it be that the speed of limit of light is relative? How would this?

affect or understanding of relativity. You know, look, as I've said before in these AMAs, whenever a question is of the form, you know, could it be that something is true? The answer is probably yes, it could be. If there are no observational consequences of that fact, then I'm not sure why I should care. And if there are observational consequences of that fact, then I suspect we would have known a long time ago. So I haven't thought very deeply about this particular phenomenon. So maybe there's something I'm missing here, but it's not something that I personally think of as an important question that is open to us in relativity right now.

Mekhella Chan says, do you podcast with your eyes open or closed? My eyes are open right now because I'm reading this question. But so something about your reply to Lisa Feldman Barrett's request to do so suggested to me that you might usually interview eyes closed. Nope, I don't know what I said to give you that impression, but I don't think it's true. And my eyes are usually open. You know, if I'm thinking hard about something, I might close my eyes for a second. But generally, when I'm doing the interviews, my eyes are open. Just FYI, when I do the interviews, you know, I, if in a perfect world, I would do the interviews in person, you know.

And in fact, I tried, I used to try to do that a lot. And here is the downside of that, that, you know, if you try to do it in person, you go to someone's office, for example. And so you can set up microphones and so forth. Not everyone's office is very acoustically good, and not everyone is good at, you know, moving close to the microphone, etc. So even though it counterintuitively, like being in the office, can often lead to worse acoustics than doing it remotely. All this is leading up to it, something relevant to your question. So these days, I do it, of course, all online. And again, I tried, since I believe that being able to see the other person and is actually really helpful,

which means that your eyes better be open, to the conversation, right? Like, sometimes you'll notice in the conversation just because of delays in the internet and so forth, like one person will try to ask a question and talk over the other person. It's just an inevitable consequence of the technology we're using to do these interviews.

So there is a service called Squadcast that lets you do interviews with video. So not recorded, They don't record the video. It's just an audio recording. It's still just an audio podcast, but they let each other, each of the two interviewees see each other on screen. But Squadcast just turned out not to be a very workable solution for me for lots of reasons, one of which was you could only use it with Google Chrome, I think. And guess what? Not everyone has Google Chrome. So these days I'm just using Zencaster, which is purely audio. So this is the long way to get

to a relevant fact to your question. I could do the interviews totally eyes closed because they're not looking at me, I'm not looking at them. But no, I do not tend to do that. Alexander Cordova says, I just watched the podcast episode with Neda Englehart and find myself to still be confused about the initial premise of the black hole information paradox, namely why it's even a paradox in the first place. Why do we exactly do we insist on the fact that information must be conserved? So I don't like calling it a paradox, actually. I call it a puzzle.

But the reason why you might expect information to be conserved is because that's what quantum mechanics. says, if you believe in the many worlds interpretation of quantum mechanics and you believe that there's just a Schrodinger equation where there's a wave function that evolves, as we say, unitarily, which is a fun way of saying it obeys the Schrodinger equation at all times, then there is a, that's a consequence of that information is conserved. So it would represent some kind of violation of the Schrodinger equation if black holes turn pure quantum states into mixed quantum state, which is what Hawking's calculer. seems to imply. Now, maybe you need to modify quantum mechanics, or maybe there's a different version of quantum mechanics, that's okay. But then extra evidence accumulates if you try to invent a theory

where in our tangible reality, information is not conserved, that information conservation tends to ruin, lack of conservation tends to ruin other things. Energy is not conserved and other things like that. Quantum coherence is lost. Bad things happen. And finally, you know, we have the example of the ADSCFT correspondence, where it is clear on one side,

ADSCFT is a relationship between two very different theories. One is just a quantum field theory without gravity. One is a quantum gravity theory that has black holes in it. And on the black hole side, the black holes can form and evaporate. And on the quantum field theory side, you can just use the Schrodinger equation to evolve the quantum state forward in time. And so information is conserved in that. theory, even though it's supposed to be exactly equivalent to a theory where black holes are being created and then evaporating. So there's lots of sort of indirect reasons to believe that information is conserved.

None of that is 100% certain, right? So people have absolutely taken seriously the idea that information is not conserved, but those options don't seem to fit very well with other things we understand about physics. Oria Biddle says, Sam Harris spoke with Judea Pearl about cause and effect and asked him about downward causation. emergent phenomena like minds that abstract and have causal efficacy over and above the physics of things. He stipulated that abstraction must have causal power because the software, the governance behavior, can be platform independent. Pearl said he didn't think about it in top-down terms, and as an engineer, he was more interested in the clash between the two levels of description as a means to programming it into a robot. I would like to probe your philosophy around this area of emergence, downward causation, and their relation to artificial intelligence and consciousness. So that's not really an AMA question.

That's like a whole several podcasts worth of discussion. You know, roughly speaking, I don't like the idea of downward causation. I think that it is overused to simplify things, well, to cheat around some things that could be better described in other terms. I don't even really like upward causation in a very real sense. I think that, you know, if you have levels of description of reality, there's a level where it's all quantum field theory, a level where it's chemistry and molecules, a level where it's people and planets and chairs and tables. I don't think personally about the relationships between those different levels as being causal ones. I think if you have a well-defined level, causal efficacy happens within the level, not between different levels.

There are other relationships between the levels. You could have supervenience relations. You could have explanatory relations. You could have coarse-graining relations and things like that. Emergence relations, obviously. But I don't think the causation is the right way to think about it, not in the sense of, you know, cause and effect that today a pearl would ever care about. So that's the very short version.

There's subtleties there. Lots to think about. My own ideas are not completely settled, but that's the short version. Okay. The last question for this long AMA is from Clint Atmar. In light of the COVID vaccines coming out soon, will you be one of the first in line to get one, or will you wait some period of time to see if there are any side effects? And if you do wait, how long?

That's a good question, important, relevant real-world question. I don't think I will try to wait long. The question in some sense is, how well do you trust the people who have been testing the vaccine? So as you know, from previous podcasts, vaccines could be good at killing off the virus. but yet also have bad consequences down the line. So you have to be careful. It's not just a matter of making the vaccine. You really do have to test it.

It's perfectly sensible in my mind to worry that they will rush the vaccine, right? It's also perfectly sensible to worry that the vaccine approval process will be too slow because we're just not used to moving quickly. So I have no idea where to come down in, you know, are they rushing it and therefore being sloppy? or are they being overly careful because they're in a bureaucratic mindset or whatever? But I suspect, you know, that probably it will be fine. And anyway, the world will be a much better place when a lot of people are vaccinated with a good vaccine, which I hope that they're going to get.

And, you know, I have no idea also, you know, what the process will be for people being vaccinated. Like, do you just sign up and go to Walgreens and they shoot you with it? Do you have to, like, get in a queue? There's certainly going to be a rush when the vaccines come out. So I'll be perfectly honest. I am not someone who follows every in and out of that particular process. It's one of those things where I judge that it's crucially important to the world, the vaccine, the COVID vaccine, but it's not something that I personally have special understanding of or any influence over myself.

Therefore, I'm going to wait for it to appear. And at that point, I will try to judge whether it seems, reasonable to take it or not. My suspicion is it will be reasonable to take it and safe. I haven't really dug into that very deeply, so don't trust me on that particular issue. Other things you should absolutely trust me on. But that one, I would do your own homework and find some reliable sources. That's what I'm going to be doing myself. Hopefully, next time we have an AMA, everyone will be vaccinated and the world will be somewhat back to normal. That's probably over the optimistic, I think. But, you know, that's okay. We can be optimistic.

Good. No new AMA coming out at the end of December. So, but anyway, if you have holidays, hope you have a good holiday. If you don't, hope you're hanging in there. 2020 will be over. See you on the other side. Woman, and I wear Ashtro. To me, that means I know who I am. I trust what I like. I don't second guess it. I show up bold, intentional, and fully myself every single day. My style is timeless. It's beauty grows and gets stronger with time. Ashtro isn't just what I wear. I express who I am, unapologetic, confident, whole. I know who I am. I trust what I like, and I don't second guess it. I'm a black woman and I wear Ashera. Discover your style at Ashero.com.

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