Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - AMA | May 2022

Episode Date: May 12, 2022

Welcome to the May 2022 Ask Me Anything episode of Mindscape! These monthly excursions are funded by Patreon supporters (who are also the ones asking the questions). I take the large number of questions asked by Patreons, whittle them down to a more manageable size — based primarily on whether I have anything interesting to say about them, not whether the questions themselves are good — and sometimes group them together if they are about a similar topic. Enjoy! Support Mindscape on Patreon.

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They negotiate, coordinate, advocate for you, close the deal with you, and hand the keys to you. They bring you home. Realtor's are members of the National Association of Realtors, right by you. Hello, everyone. Welcome to the May 2022, Ask Me Anything Edition of the Mindscape Podcast. I'm your host, Sean Carroll. Things have been a little hectic around here at Mindscape World International Headquarters, writing some science papers, giving some talks, preparing to move from Los Angeles to Baltimore, which is a big deal. And, of course, working on the copy editing and proofreading for the book, The Biggest Ideas in the Universe, Volume 1, Space Time in Motion, be out in September. A lot of copy editing. A lot of making sure the figures look right and stuff like that. But anyway, it's all refreshingly normal kind of stuff. So I'm not going to dwell on it, tell any stories, anything like that. Let's just remind everyone that the AMAs, the Ask Me Anything episodes are brought to you by supporters on Patreon. You can become such a supporter yourself

by going to patreon.com slash Sean M. Carroll. Patreon supporters pay for nice things like the transcripts for all the episodes and they help with the sound quality a little. bit in some ways. And by being a Patreon supporter, you get ad-free versions of every podcast, plus the ability to ask questions at these AMAs, as well as the usual warm, fuzzy feeling for doing a nice thing and being part of something bigger than ourselves. That's it. Let's go. Dave La Judice says, do you think our current electromagnetic sensing abilities rule out local alien visitors? I'm surprised at the near-zero credence given to the possibility that aliens are in our solar system in Fermi paradox discussions?

Well, no. I mean, as you ask the question, the answer is no. I do not think our current sensing abilities rule out local alien visitors. It would be completely trivial for aliens with very, very high technological abilities to be in the solar system without giving off a signal that we could notice. All they have to do is hide on the far side of the moon, and then it would be very difficult to notice them. But certainly if they hit out on Pluto, it would be even easier. But I also don't really think that's the issue. And this is the kind of backwards pseudobasianism that gets you in trouble when we think about things like aliens. The question being asked is, you know, can you think of a way? Can we cook up a scenario in which there are aliens there, but we haven't noticed them? Sure. That's easy to do. It's not that difficult to imagine. But it's also not the question we should be asking. The question we should be asking is, in the two different hypotheses, one of the which there are aliens here in the solar system, and the other which there aren't, what do you expect? What are the predictions, the expectations, the likelihoods in the technical Bayesian

jargon under each one of those hypotheses? And then we compare that to the data. And the point is if there's no aliens in the solar system, we expect exactly what we see, namely no evidence for aliens. If there are aliens out there, why would they be hiding? Right? Under the vast majority of versions of aliens in the solar system I could think of, they would be easy to find. And therefore, the fact that we don't have any evidence for them is strong evidence against their existing. It's never 100%, so maybe they're out there,

but given that it would be very, very easy to notice them under the vast majority of circumstances that we can imagine, the absence of such evidence is strong reason to decrease whatever prior you have. If you're prior that there are aliens in the solar system is 0.9999, it won't matter. you'll still think that, but that's the slippery problem of being a principal Bayesian when you try to pick your priors in a good way.

Eager Parskin says, can you convince me to vote? I've never voted my life because I know that I don't know enough about what's going on behind the curtains to make an informed decision. Anyone who just reads the news, gets biased opinions that do not reflect everything that's going on. Also, if, say, I lean left and you sit me down with a smart politician from the right and I'm open-minded enough, I'm 100% sure they can change my opinion. So how can I vote based on my values when I know that there are definitely things I'm overlooking and things I can't possibly know because they're happening on the inside? So this is an interesting question because the usual question can you convince me to vote is more about the unlikelyhood that anyone vote would matter.

We talked about this with Herb Gintis, right? When you talk about elections with enough people voting, the probability that any one person's vote is going to be the deciding factor is so incredibly tiny that it might as well not. matter at all. But Igor's question is a little bit different. He's saying, I just don't know enough to vote, right? And therefore, maybe I shouldn't. And, you know, honestly, I'm not going to try to convince you to vote. I think it's okay if you don't vote. We talked to Andrew Lee, who is a working politician in Australia where they have mandatory voting, and he thinks it's a good system. And, you know, he thinks that because people are supposed to vote in that country, they actually pay closer attention to the media. But if you don't, I'm of the opinion that if you don't want to vote,

that's okay. I do wish that more people would vote. So I think it's a legitimate question. Can I convince you to do it? But I don't know really what to say to the question, except I don't buy the argument. I don't buy the argument that you can't get good information in the news media at all. You can get bad information from the news media. That's perfectly true. But also there's good information out there. And I think it's a little bit of an abdication of responsibility to just shrug your shoulders and say, well, who knows what's going on? I think we have to develop our skill set of being able to distinguish between good information and bad information. If you're 100% sure that talking to someone on the other side can change your opinion,

that's, you know, in some sense, good for you. But in another sense, it means that you need to do that talking to both sides and figure out which side you agree with more. I hope it's not the case that if you talk to two people on different sides alternating a hundred times in a row, that you would change your mind a hundred times. That would be, well, at least it would be very strange. I don't think most people are like that. I think that most of us have values. We get information and not only are there factual matters about, you know, what a certain policy is, et cetera, But there's also value alignment, right? There's the idea that certain political figures are just talking the talk that resonates with how you want things to be.

The reason why we vote for people rather than do direct democracy and vote on every single bill or issue coming up is because we aren't supposed to be experts. We're supposed to vote for people who, I mean, ideally they would be experts, but in the real world, things are so complicated that they hire staff members who are experts. themselves. But the point is you vote for people who will represent your values, who if they care about the environment, if you care about the environment, you can vote for someone who clearly cares about the environment. If you care about gun rights, you can vote for someone who cares about gun rights, and all those different ways of going down the line. Of course, there will be misinformation and people will lie about things, but you know they have a record for voting, right? You can see what they actually vote for and against. If you're really,

interested. If you don't care, that's one thing, okay? But if you're interested but you don't think that you have enough information, I'm just skeptical that that's true, because I think there's a lot of information out there. A lot of it is pretty objective, right? You can choose to get information from biased sources, but a lot of information is actually pretty reliable. Like where someone voted on some bill, just, you know, look up in the congressional record or whatever. I think that's pretty reliable. There's a lot of news sources out there who are perfectly reliable. Not is perfectly reliable, but quite reliable, and who are nevertheless denigrated by one side or the other because they don't like what they're saying, but that's something we have to learn to get beyond.

So I don't have any specific either advice or arguments to convince you, but I do will, I will put forward the opinion that we all have values and we all have a responsibility to figure out what we think is true about the world. and that's the stuff on the basis of which we vote. It's not an easy thing by any means, but that's what I think that we're supposed to try to do. Kevin O'Toole says, I really enjoyed your book from eternity to hear. One question, though, is still bothering me.

In the first two chapters, you described time asymmetry from two different perspectives. There's a physics-based asymmetry, where entropy was low in the past and will be high in the future. There's also a cause and effect asymmetry, where, from the perspectives of people and other agents of change, and agents action cannot change the past, but can change the future.

It seemed like the point there was to say that one asymmetry implied the other. But unfortunately, I just don't see any good reason why the two asymmetries should be related at all. Is there some fundamental contradiction, either intuitive or in the math, in imagining a time-reversed agent who remembers the high-entropy future and whose actions change the high-entropy past? Yes, there is a fundamental contradiction in that. And it's kind of too long of a story to tell you right here in the AMA. I will point to the fact that I just gave a talk on this at Berkeley, which is going to be mentioned in the very next question, but in a different context. So the title of the talk was the arrow of time in causal networks. It's on YouTube. You can find it. Where I talk about exactly this. I talk about the connection between the increase of entropy and the causal arrow, the fact that causes precede effects.

Now, there's a footnote, there's many footnotes there. Different people have different ideas about what you mean by cause and effect. So you can have a certain construal of the idea of a cause by which causes and effects are simultaneous, et cetera, et cetera, et cetera. So forget about all of those details. I mean the usual thing. I mean that if I swing my arm and knock over a glass of wine, I say the glass fell down because I swung my arm. I do not say I swung my arm because the glass was going to fall. That's explicable because entropy has been increasing. tropic arrow of time, the fact that entropy was low in the past and is increasing toward the future,

that, in my view, is the single fact underlying all of the asymmetries between past and future and our macroscopic universe. So what is the connection, you know, very, very briefly, if you didn't have entropy at all, if you were Laplace's demon, you know exactly the micro state of the universe, right, then there's no such thing as cause and effect, and there's no such thing as an arrow of time. It's just the state of the universe at every moment, and it exactly implies the state of the previous moment and the next moment in a deterministic universe. We can also argue about determinism, but that's, again, another kettle of fish to talk about. But in the deterministic assumption, like the Schrodinger equation or Newton's Laws of Motion, every moment has all the

information that implies all the previous moments and all the next moments. So just by construction, the existence of something like an arrow of time, and including causes preceding effects, must come about because somehow you coarse grain, right? Because you're not Laplace's demon. If you know the exact microstate of the world, then you predict both the future and the past with perfect fidelity and doesn't make sense to talk about causes and effects.

The information contained in the universe at every moment of time fixes every other moment in this deterministic model. So you can't pinpoint whether something is a cause happening first or in effect happening after, okay? But we don't have that information. We are not Laplace's demon. We have very incomplete information about the universe. We coarse grain. We look at the universe and we notice some observationally accessible features of it.

And there's other microscopic features that we do not notice. And so what I argued in my talk in Berkeley is that you can actually use this fact in the context of what are called causal networks. This is a way of thinking about cause and effect relationships that is very, very popular in both computer science, artificial intelligence right now, but also all over the social sciences. A way of stringing together different facts about the universe, which they will call random variables, because they're facts with certain probabilities attached to them, drawing lines between them, and making a little network, and then saying, okay, where are the causes and where are the effects? And there's certain features of where you can

draw those arrows connecting the different random variables, the different features of the universe, like I'm swinging my arm, the glass is falling down, so that means it's a certain probability that I swing my arm, a certain probability, the glass falls down, and a mutual relationship between them, right? Conditional probabilities and so forth. And all of that can be used to talk about causes and effects if you also add in some counterfactual information. If I consider what happens if I hadn't swung my arm, would the glass have still fallen down, right? That's where you can get a true handle on causality. And so the thing is that you can do that going forward in time. You can draw arrows from past features of the universe to future features of the universe purely based on the

macroscopically available information. That's what we do all the time. We predict the future probabilistically, not deterministically, because we don't have all the information, but we predict what's going to happen in the future on the basis of the present state of the universe. This is a feature of physics, is that you don't need to also know the past. You might need to know certain relics of the past that are embedded in the current moment, but the point is you only need to know the current moment. Okay, this is called the Markovian property in computer science and statistics and elsewhere, in random processes generally.

Markoviness is the fact that you can predict. what happens next just on the basis of the current moment. And so you can make a causal diagram going from events to other events forward in time, that is to say, from the Big Bang to today and toward the future. But the point is you can't do it backwards. You cannot make a causal diagram with the arrows pointing in the other way. And the reason is because when you go backward in time, the current state of the universe is not enough to predict the past state of the universe. You also need to assume a low entropy past. That's what's called the past hypothesis.

Otherwise, if that were not true, then the kinds of reconstructions we do of the past and the future would be the same, right? We'd have the same access to things about the future and things about the past from the present. But we don't. We have things like memories and records and fossils and photographs, right? We have information about the past. Why? Because there's an extra thing going on.

namely that the universe started with a low entropy past, that gives us extra information about the past that we don't have about the future. But we need to assume that low entropy past to really make that information be reliable. So therefore, the evolution from today to yesterday is not Markovian. It's not you know today and therefore you can retradict yesterday. It's that you know today and you know the big bang. You know the very, very low entropy past. Those two facts are enough to reconstruct what it is possible to reconstruct about the past.

Okay. So anyway, the very short answer here, which I'm not necessarily sure is going to make sense if you're not already familiar with this jargon, but I'm trying to give you the very short version of the argument. You can make a causal diagram with arrows moving toward the future if entropy is increasing, but you cannot do it with the arrows going to the past if entropy was lower in the past, because there's an extra fact that you need. And now, you can argue whether or not the notion of causality in these causal networks is the right one. The notion basically is that if I were able to keep everything else in the universe fixed,

but change one fact, change whether I swing my arm, does that have effects downstream? So the glass is being knocked over, or the glass is not being knocked over. The classic example is, you notice a correlation in the data that if, People are outside and it's sunny, they do not have umbrellas up. If people are outside and it's raining, they do have an umbrellas up. So in the data, you don't know whether rain causes umbrellas to go up or putting umbrellas up causes rain, right? There's just a correlation between them.

So you need this information that is not in the data, this counterfactual information. If you could imagine putting a person there, raising their umbrella, would it start raining? No. If you imagine it raining and someone who didn't have their umbrella up, would they raise their umbrella? Yes. So that's the direction in which the causality goes. And that's a story you can tell forward in time because entropy is increasing. It's not a story you can tell backward in time.

Related question comes from Liam McCarty, who says, in your recent lecture at Berkeley, the Arrow of Time in Causal Networks, and then he gives the YouTube address, if you want to check it out in the comments. You mentioned that the smoothness of the cosmic microwave background is dependent on the past hypothesis. That is, without stipulating that the early universe was low entropy, we couldn't say that the cosmic microwave background is smooth. This is a fascinating point I hadn't heard before, but I'm still struggling to understand exactly what you meant. Can you discuss this here? Yeah, this is a very, very important point because it's part of recognizing that how we reason about the world, physics and other things, is always sort of assumes the past hypothesis,

even before we knew what it was, or you knew there was such a thing as entropy. We assume the arrow of time, I think is probably a better way of saying it. So we put a telescope like WMAP or Planck out there in the sky, or we do observations here on the ground or in balloons, et cetera. We map the cosmic microwave background. We find that this leftover radiation from the Big Bang is pretty smooth. It looks more or less the same in different directions, but not exactly. There are small fluctuations, one part in 10 to the 5, okay?

And we say, look, therefore, the early universe, the moment from which this radiation was emitted, which is only like 300,000 years after the Big Bang, the physical world was smooth, right? That's why the radiation that we're seeing now look smooth, because the actual primordial plasma was smooth, more or less the same density and temperature at different points in time, at different places, sorry, throughout the universe. But that's not what we see. We don't see the primordial plasma. What we see is photons, microwave photons, landing in our telescope here on Earth. We see the radiation field locally right next to our telescope.

That's what we actually see. We use our brains to reconstruct what the early universe must have looked like based on that radiation field impacting our telescope here and now. But of course, when we do that, we're assuming that entropy has been increasing along the way. So think about it. The photons that come to us from the microwave background, their wavelengths depend on many different things. Their wavelengths depend on what the temperature was at the cosmic microwave background.

But it also depends on the velocity of the fluid, right? There's a Doppler effect going back and forth. And it also depends on the gravitational field that it is. is going around because there's a gravitational redshift that can blue shift, redshift or blue shift, depending on how the gravitational field goes, it can change the frequency of that photon. Okay. So if you just ask the question, given the photons that we see here in our telescope, but we make no assumption about the low entropy of the Big Bang, we allow it to be super duper high entropy,

and you say, in all the different ways that we could have gotten, that image that we we get in our telescopes, what does a typical reconstruction of the early universe look like? And the answer is, it is wildly in homogeneous. There's very different densities and temperatures and velocities and gravitational fields from place to place. But they have all conspired exactly to cancel out so that we see a very smooth radiation field in our telescope today. And if you ask yourself, well, if you think to yourself, that seems very unlikely. Why in the world would there be some massive conspiracy where all these very different effects exactly cancel out or almost exactly cancel out to give us an isotropic, smooth cosmic microwave background? Well, there's no good reason for them to do that.

But that's not the question we asked. We asked the question conditionalized on the fact that we have a smooth image in our telescope and no other fact. what is the likelihood that the early universe looked one way or another? So without the past hypothesis, the early universe is overwhelmingly likely to be very, very, very high entropy, right? Because you didn't make it be low entropy, and there's more ways to be high entropy than low entropy. It is unlikely, given that high entropy state, that we would see a smooth CMB today, but it's less unlikely than that there really was a low entropy state in the early universe just by accident. So if you don't have the past hypothesis, you have to imagine that with overwhelming likelihood,

the smoothness of the CMB is just a conspiracy, it's just an accident. It is a downward fluctuation in entropy because without the past hypothesis, we right now are at the minimum moment of entropy in the history of the universe. It would be higher in both the past and the future. Now, no one believes that's true. There's zero reason. It just doesn't make sense to think that that's true. The actual universe was low entropy, is the right way to think. And therefore, you can use ordinary scientific reconstruction to understand that the pictures we take in our telescope really are evidence that the early universe was smooth. But it's only evidence because we can and do and should assume the past hypothesis of low entropy. Okay, Mr. Fu says, looking back 500 years in the past and how we managed to disprove so many scientists of that era,

do you think that 500 years in the future, all of our understandings of quantum mechanics and mathematics could be proven completely wrong by scientists of the future, which might in case invalidate many worlds and other important concepts? Well, you know, I think it's actually, there's two things going on. One is that by picking 500 years in the past, you've gone a little bit further. than the scientific revolution. So there weren't scientists back in that era, okay? Once we had the scientific revolution, once we had people like Galileo and Copernicus and Kepler and Descartes and Newton and so

forth and hook and whatever, they said a lot of things that are true, that we still think are true today, right? Now, they're not fundamental truths. Newtonian mechanics is not fundamentally true. It's been superseded by quantum mechanics and relativity. but there is still a limit in which it's a very, very good description of what happens. There are situations in which it is correct. You don't need to know general relativity to fly a rocket to the moon.

Newtonian mechanics and gravity works perfectly well. That's what I expect will be the case going forward. Sometimes we have ideas in science, even post-scientific revolution, that turn out to be wrong. That's absolutely true. You know, the plum-putting model of the atom is everyone's favorite. example. But, you know, the plum-putting model of the atom was never something everyone believed. It was just an idea out there that we knew perfectly well we weren't certain about, or even very, very high credence. So I think that the thing is that the something like quantum mechanics, something like

general relativity, even the standard model of particle physics, the core theory, if you like, these are really accurate effective theories. And they're not going to go away. They might be replaced by better theories, but there will still be a regime, a domain in which they work perfectly well. Whether or not many worlds is going to survive or not, I have no idea. I mean, I have a credence. I think it will survive, but I could be wrong about that. Eric Speckhard says, you've mentioned several times that Humian constructivism lets you be judgy. Can you elaborate on what you mean by that? If moral beliefs are contingent and specific to an individual, as I understand the case to be in Humane constructivism, in what sense can you be justified in being judgy? So I think all the work here is being

done by the word justified in that last sentence. So for those of you who don't know, I talk about human constructivism in the big picture and elsewhere. It's a view of morality where you say that there is no once and for all universal, rational way to be moral. What there are are individual ways of deciding what you think is moral. And then in the world, you get out of the world, you get out there and talk to other people and try to work with them the best you can, given that you don't necessarily agree on how morality works. And as I like to point out, that is what actually happens. So that is how the world actually works. So if your objection to this view is, well, if that were true, it would just be chaos and calamity and nothing would work, it's just the world. I'm just describing

what actually happens in the world. So I'd like to talk about constructivism as opposed to relativism, because moral relativism, as I understand it, and everyone has slightly different definitions of these words, so I'm not that interested in debating the definitions, but moral relativism posits that morality is, inheres in a community or a set of individuals, and is only relevant to that community and those individuals, okay? But I didn't say any of those words when I just described human constructivism. I construct a moral theory, and I think my moral theory is the right one. For me, it's the one I constructed, but I'm definitely going to use it to judge other people's behavior, right?

That's one of the things you do with a good moral theory. The crucial thing, like I said, in the end of the question is, can you be justified in doing that? And I'll say, I think that this hope is a relic of the days when we were all moral realists, moral universalists. Most people still are. But back in the days, when we thought that there was a morality out there in the sky or whatever, or that we could just perceive by pure reason or whatever. We had a justification that was universal, that was objective, that you could just logically tell people, you know,

either God says this or Emmanuel Kant says this or whatever, the Golden Rule says this, and then that's the way to move forward. But I think that was a mistake. I think that thinking that that's the kind of justification that morality needs, it was just a mistake from the start. It's sort of antiquated these days. So what do you mean by being justified? I think that, you know, when I say, like, for example, men and women should have equal rights, okay?

This is my judgment. I do not think that this is a universal truth, because I don't think there are any moral universal truths. But I will also judge someone harshly if they discriminate against men or women in any very obvious way. And they will say, well, no, my morality is different, okay? And what I can do is judge them. What I can't do is use logic to convince them that they're wrong. What I can do is try to use their own views to convince them that they're wrong. Like, are you sure you believe that?

Is it really consistent with other things you believe? Knowing things that maybe you didn't know about men and women and their status in the world, maybe you'll change your mind. Like, I can do the things people actually do when they're trying to make a moral case to a different person. But there is no absolute ground to stand on to say that they're making a mistake, right? Like if they say 2 plus 2 is 5, an ordinary arithmetic, that's a mistake. If they say men and women do not deserve equal rights, that's not that kind of mistake. I'm still going to judge them for it.

It's just not going to stop me. And I'm happy to admit I don't have that objective justification that I might have had if I could appeal to God or reason or anything like that. Okay, I'm going to group two questions together. Joshua Hillerup says, What do you think about having a university having a rule that a certain percentage of professor slots have to be cross-discipline

with two or more departments having to work together to do the hiring? Obviously, there's lots of details that could make specific setups bad, but what is your opinion on the general idea? And then Tomer Hockoen says, how would you design your dream university or research institute,

given the budget of a big university like Harvard or Yale, what sort of professors would you hire, on what subjects would you focus, what would the curriculum look like, et cetera. So Tomer's question is too big for the AMA, but some of it will be addressed by trying to answer Joshua's question. I don't really have a grand design for university slash research institute because, you know, there is no such thing as my dream university or research institute. I actually think that if anything, the problem with the set of universities and research

institutes that we have is they're too much alike. they have more or less the same model rather than trying to experiment and do different things, focusing on different things. They're pretty homogeneous. They have like the same way of doing things. And if you think that's the perfect way of doing things, that's fine.

But we don't know what the perfect way of doing things is. And, you know, at fact, I'm leaving Caltech, but I have huge admiration for Caltech for being different than other places. That doesn't make it right for everybody. I'm very, very happy to tell prospective undergraduate. it's Caltech is not right for some people, as great a place as it is. For some people, it's the perfect place. For many people, it's a terrible place. And I think that a lot of places should be

like that, right? I think a lot of places should have a little bit of personality and be a little bit different. So I don't have a dream university or research institute. Also, research institutes are very different than universities. I mean, universities are weird things, trying to combine research and teaching in the way that they do. It's a, 500-year-old model in some sense, or a thousand-year-old, I don't know when it goes back. It goes back quite a ways, 1,200s, maybe, 800-year-old model, when research was a different thing than it is now, as was teaching. And I wonder if, you know, how long the perfect, the model that we have right now will actually last.

But having said all that, with all those caveats in mind, you know, I'm a huge fan of the traditional arts and sciences curriculum. I like that. History and English and physics and biology. You know, as an astronomy major at Villanova, I had to take a huge number of astronomy and physics and math courses, and because it was a university with very, very broad distribution requirements, I had to take a lot of humanities and social sciences also. I didn't take any biology and chemistry. Maybe I should have. I don't know. Maybe it shows up in the podcast I'm doing right now. but I think it deserves careful thought this question. So when I'm not answering it, I'm not answering it because it's not a good question, because it's a huge question, how to make different kinds of research universities

and institutes that would optimize across a whole bunch of different things. Many that are very good at teaching, some that are good at, you know, science, some that are good at humanities, some that are four years, some that are eight years, some that are two years, you know, some that are all people living on campus, some that are, you know, people not living on campus, and a whole bunch of different ways to sort of be, have a personality and be a university. Anyway, that didn't answer your question, but it rambled on about it. Joshua's question is a little bit more focused on the idea that universities should have a certain percentage of faculty that are specifically cross-discipline.

I do like something like that. I'm not sure if that's exactly the way to do it. You know, in my, as I just said, in the universe that I would like to have where there's many different kinds of universities, I would love to see some universities without any departments at all, right? Where faculty could just do the research they wanted to do, students could in consultation with faculty, design their own courses of study, people could be hired and promoted via ad hoc committees with different kinds of people, so that the question of, you know, if you want to hire an economic historian, do they belong in the history department or the economics department? That's a terrible question that should never come up. You know, that's a huge failure mode of

universities. And the way that it happens is, you know, if you're super good, if you're a very productive, senior level person, you can be interdisciplinary, right? You can get your own grants, you can find your own little institute, get your own group together and whatever. There's plenty of interdisciplinary research institutes at universities. What there isn't is a path for young people who are interdisciplinary from the start to get hired, right? The path to become a professor is to excel in a discipline and get hired in that discipline and then branch out later. And that works pretty darn well for many people, but for other people it just doesn't. So I do like the idea that one way or another, it should be possible to hire people as professors in a way that is not

the individual departments doing all the work. That is the way it is right now. For those of you, maybe you're not in universities or don't know. At universities, it's departments that have the power, roughly speaking, to hire and promote people. It's not the president of the university or the provost or any, or the deans or whatever. They will assign a slot. I mean, they'll say, okay, you have money, to hire somebody. And the negotiation is more or less the department will say, okay, we would like to hire a biophysicist. And the president and the dean will say, okay, you have money to do that, or no, you don't. Or, you know, make a case. Why is biophysics interesting, et cetera? And so there's a back and forth there. But when it comes to choosing the person, 98% of the work is done by

the department. And what that means is, if you have a physics department, a biology department, and economics department, a history department, and they know that jobs are scarce, right, that they're not going to get to hire that many people, they will, as a department, almost always decide to hire people who fit well in the boundaries of that department. And that just leaves out people who don't fit well into those boundaries. And I think it's a huge mistake. I think it's a huge opportunity cost for universities that want to do better, right? University should always be competing with each other, to hire the best people, do the best research, to be the best educators of the best students.

This is a clear way, I think, that you could snap up a bunch of really great people who are young and imaginative are going to change the world, but don't fit exactly into individual departments. That's how I would put it anyway. I'm never going to be a university administrator, though, so this might not ever happen. Andrew Goldstein says, in your blog describing the move to John's Hopkins, you make reference to two seminars. The one is entitled Physics of Democracy, which sounds disparate but very intriguing, even hopeful given current events. The other includes complexity and emergence, which is a passionate interest to me. So as an outsider, might it be possible to hear or read about any of the discussions that will transpire during these seminars?

I would gladly up my membership to the quantum tier for the privilege. So yeah, the second one that you're referring to is an upper-level undergraduate seminar just called topics and philosophy of physics. So I will do a little bit of quantum mechanics, a little bit of the arrow of time, a little bit of the anthropic principle and things like that. I think that's what you're referring to. And I'll also be talking about complexity in the physics of democracy class. But neither one of these seminars are going to be videotaped or online or anything like that. And I think that's correct. I think that's the right thing to do.

You know, there's a big place for videotaping things and handing them out freely. as hopefully you know, because I do it all the time. This podcast is audio taped, which is then handed out freely, and that counts. But the biggest ideas in the universe videos were also handed out freely. But the place for that is kind of broadcasting, right? When the role of having a video and having people watch it is you have a person talking. A person with knowledge is trying to spread that knowledge to the rest of the world. That's when that model works very well.

But a seminar is not that model. A seminar at the university level, we're going to have like 15 students or fewer in the room. Much of the conversation is going to be the students talking, not me talking. And it's got to be a little protected from criticism from the outside world. You have to feel like you're free to say some stupid things because you don't know. And if you're worried about saying things in the world making fun of you, then you might not speak up when maybe you should. So I think there's a perfectly good place for having seminars that are not recorded, that are just ephemeral. You know, there's a moment there in the classroom, sitting around the table, people are talking to each other.

It's fun. It can be life-changing and it's important, and it's not for external consumption. There's other cases where I don't think that cameras should be allowed also. Like if you have some really focused workshop among your own research group where you're bouncing back and forth ideas that are not yet completely baked and you want to build on them and write papers and so forth, you know, that's not for public consumption either. So I'm a huge believer in filming things and letting them be shared, but that's not for everything. Some things are like that and some things are not. The good news is that for the physics of democracy, I certainly hope to write a book on the subject at some point, and that will hopefully appear. For the Foundations

of Physics seminar, I don't know whether I would ever write anything about that, but certainly individual topics within that are things that I write papers about, including complexity and emergence, the anthropic principle, the arrow of time, quantum mechanics, things will get ridden about that, one way or the other. Rob F says, do you think progress in answering the biggest questions of modern physics will be primarily achieved iteratively

through collaboration of large teams of scientists, or do you think it will progress via a paradigm shift sparked by a handful of genius individuals? The popular history of science seems to say, suggest, perhaps wrongly, that great leaps and understanding were made by exceptionally gifted individuals, Newton, Einstein, etc. But modern science seems more of a collaborative effort. Put another way, do we have to wait for the next Einstein in order to make the next great leap forward? I love this question. I think it's very important because the answer is in between.

There have been studies that have purported to show that super-duper smart people are way more influential in the history of science than the average person. I actually don't believe the these studies because I think that there's a methodological flaw in them. I think that what happens is there are very, very smart people out there in the world, but those people absolutely lean on the efforts of the other people who they talk to and collaborate with. I mean, I understand there's history behind the remark, but when Newton says he saw further than others because he stood in the shoulders of giants, he stood in the shoulders of all sorts of people, of different Heights. And that was really, really important. I mean, in the biggest picture, sorry, in the biggest

ideas book that is going to come out, I tell the story of how, very, very briefly, how Newton was inspired to write the Principia, Mathematica, right? You know, the greatest work in the history of physics, where he proposed Newtonian mechanics and the inverse square law for gravity and a bit of calculus. You know, there were other people who had most of those ideas. In particular, Robert Hook had the idea that there was an inverse square law of gravity, okay? And he had the idea that would explain Kepler's laws of motion and the planets moving in ellipses. He wasn't as good at math as Newton was. So he couldn't quite prove it. He couldn't quite derive that the motion in an inverse square potential or inverse

square law, force law, would be an ellipse. And so Hook and Christopher Wren and Robert Halley, of Halley's Comets fame, they used to get together and talk about these things at the coffee shop. and they eventually, you know, engaged Hallie to go visit Newton, who was up in Cambridge. All these other people were in London and asked Newton, because everyone knew even at the time, before the Principia, the word had gotten out that Newton was the smart one around here. And, you know, when Hallie asked him, he said, yeah, no, it'll be an ellipse. And Hallie's like, how do you know? He said, I calculated it.

And Hallie says, well, why didn't you write anything? He's like, yeah, I can't really be bothered to write these things. But, you know, Hallie provoked him to write about it, and then eventually that turned into the Principia, which tells us both that if it hadn't been Newton, it would have been somebody else. I mean, given that the idea of the inverse square law was already there, someone else would have put it together. Galilean relativity, conservation of momentum, they were all already there. Leibniz invented calculus, not long after Newton, you know, et cetera, et cetera. But Newton was there, and he was extraordinarily smart, and he did the greatest single achievement in the history. of physics, okay? So I think it's both. I think that super talented people play an outsized

role, but they wouldn't be able to do it without all the work of everyone else. And that is even more important today when we have these large collaborative efforts. It's sometimes hard to see the impact of the smaller incremental steps along the way, but they're important. They're important for the whole story. Joelle Curtis says, do you think the fact that our most successful theories explain interactions and forces in terms of local gauge symmetries is explanatory in any deep sense. Does it tell us something very important about nature or our relationship to it? Well, I have no idea. That's a very good question. I honestly don't know. And I think that, I think my credence for answering questions like this is less now than it was 10 years ago. Because I've been thinking about

quantum gravity in the meantime, and gravity changes everything a little bit. So for folks who are not experts in these buzzwords, our best current theories of the world in terms of predicting things and being accurately mapped to data and so forth are quantum field theories, so quantum mechanical theories of fields that pervades space. And in particular, they have different kinds of fields. And the forces that we think of, electromagnetism, the weak nuclear force, the strong nuclear force, and gravity for that matter, are all a certain kind of field defined by a certain kind of symmetry called local gauge symmetries. Okay? We won't go into what that means, but there's a certain symmetry property that helps explain the features of the forces of nature.

Did it have to be that way? Could it have been some other way? Is it telling us something deep? I don't know. And one of the reasons why I don't know is because just being a field theory, I don't think is right. I don't think the world is a field theory. And the reason why is because in field theory, there's an infinite number of things going on in any one region of space. And to me, that means that there could, in principle be an infinite amount of entropy in any region of space, right? Because entropy counts the number of things that could be going on in a region. given its macroscopic features. And so if field theory were right, then I claim that you could imagine states in the universe

where there's arbitrarily large amounts of entropy in any region. But we know that's not true, or we think that's not true, because if you keep putting things in a region of space, the energy keeps going up, and eventually you collapse into a black hole. And black holes have entropy, but that entropy is not infinite. It's a finite number. So that tells us there's only a finite number of things that can, can happen in any one region of space, and that tells us that nature is not described by a quantum

field theory. Now, we're still working on understanding the implications of that, because certainly the local gauge theories that we use are really super-duper successful, but once gravity becomes important, it seems that they can't be fundamental, even though they're very successful. How that all fits together, I don't know. So it's very, very possible that the success of gauge theories in our low-energy, accessible world is not an accident, does reflect something really deep going on at a profound level, but it's also possible that in some sense it's an accident. In some sense, it's epiphenomenal, something that would be true in some approximation, but is not very deep or fundamental. I honestly just don't know. It's worth thinking about.

Lester Sue says, are you able to explain the context implications of the latest Fermilab results on the W boson? So for those of you who don't know, Fermilab, the giant particle accelerator facility just outside of Chicago, recently published a paper where they measured the mass of the W boson. W boson is one of the two kinds of bosons we have carrying the weak interactions. It's a boson that is an excitation of a local gauge field, as we were just talking about. The Z boson is the other kind. Z bosons are neutral, W bosons are charged, their masses are similar, but a little bit different. and it's hard to measure the mass for many, many reasons,

but people have been trying to do it and people have been doing it, and then the question is, keep doing it and get more and more accurate results. The reason why it's an especially interesting thing to do, not only you saying, well, that's the constant of nature, the mass of the W boson that would be nice to know, but other features of the world feed into the measured mass of the W boson. This is a feature of quantum field theory that all fields kind of vibrate,

around in the background and affect the properties of all the other fields. This shows up when you think about Feynman diagrams and the fact that the mass, what is the mass? It's just the property of inertia of a particle moving all by itself, right? The mass you would think doesn't have anything to do with interactions. If you just have a particle not interacting, just move in, it still has a mass, right? Or even just sitting there, it has a mass. But in quantum field theory, the Feynman diagrams are telling you that as that particle is just sitting there, it is interacting with all the other fields around it, and these are quantified by little loops that you can draw in the vitamin diagrams, and those loops will eventually connect the properties of that particle sitting

there to all the other properties of all the other fields in the universe. So, in principle, by measuring things like the mass of the W boson and other particles, you can tell whether there are other fields that we haven't yet directly detected in any other particle accelerator. You can say that there are consistency relations between things like the mass of the W. boson, the mass of the Higgs, and the mass of the top quark. Okay. And so this new result from Fermilab seems to be telling us that at a statistically significant level, the mass of the W boson is a little bit bigger than we thought before and is not consistent with the standard model of particle physics, but would be consistent if there were somehow some other particles that were feeding into the W

and giving it a little bit of extra mass. I'm not going to tell any details about what those models look like. You can check out Matt Strassler's blog where he talks about those things or other, if you just go to archive, I'm sure there's many, many models have appeared since this happened. But here is the context which should make you be cautious about the whole thing. You know, it's Fermilab that is getting this result, right? It's not the large. Hadron Collider, that's at CERN outside Geneva in Switzerland. I didn't even know Fermilab was still running, you might say to yourself, and you'd be correct because Fermilab's accelerator, the Tevatron, turned off in the year 2011. So this analysis is not because Fermilab has collected new data,

it's because it has been analyzing more carefully the data that was collected in 2011 and before, which is fine. You're allowed to do that. But this, This result is not compatible with previous results, either from Fermilab itself or from the LHC in Switzerland. Maybe it's like close to being compatible in the error bars or whatever, but it's clearly not precisely compatible. And so it's both based on old data and it's incompatible with previous results. So if there is some amount of credence you have, that this is just a goof, that somehow there is some systematic effect in the accelerator or the detector or the data analysis pipeline, this would be a, you know, above average chance for something like that to happen. And, you know, if they had just

measured it and gotten the right answer, the answer everyone thought was the correct one, they would, people would think it would be perfectly fine. But it is okay to be more skeptical about dramatic claims, right? And this is one where, you know, that there's sort of a root to skepticism, if that's what you want to take. At the same time, the people who are actually doing the analysis, et cetera, they know what they're doing. You know, they're not dummies. They know their detector pretty darn well, better than anybody else does.

And they wouldn't say something dramatic like this unless they thought that they had double-checked every possible single thing that would cause this to happen. So we'll have to wait. We'll have to see if better data or experiments from LHC or elsewhere are able to pin it down. Otherwise, I would not get too excited just yet, but it would be very cool if it were true. Kathy Seeger says, how best to argue with people who claim that Ukraine should surrender because they can't win on their own and an active involvement of NATO would maybe lead to a third world war or nuclear strike?

I get the argument in a way, but it still feels flat out wrong to let me, to me, to let Russia win the war and get away with atrocities. From a moral philosophy point of view, what would you say? So I don't know if Kathy, you yourself were inspired by this, but a claim close to that claim was famously debated just a little while ago because Noam Chomsky, of all people, said it. You know, Noam Chomsky famous for many things, linguistics most prominently, but also as a leftist critique of imperialism, et cetera. And there's a worry that, you know, you get so interested in critiquing American and European imperialism that you sort of, take it easy on imperialism from other places, from China or Russia or whatever. So that was the counter argument to Tomsky, because Tomsky is basically saying, look, Ukraine can't win. They should just, you know, take it. Rather than sacrificing themselves, they should,

you know, let Russia basically win. I don't know exactly the words, so don't quote me on that. You can go look it up. But there are certainly people who have that point of view. There's no question. I do not see any justification for... for me to tell Ukraine what to do about this. I think that throughout history, there have been stories of countries or people who've been attacked against overwhelming odds and have resisted.

And sometimes their resistance has worked, and sometimes it hasn't. But there is something, since you ask from the moral philosophy point of view, there is something intrinsically noble about the resistance, about fighting for your country, for your freedom against a authoritarian oppressor who is invading you.

So I think there's something noble about what Ukraine is doing. And I'm not going to give them advice. Look, what I mean when I say I'm not going to give them advice is, if they wanted to surrender, if they said, look, it is, you know, we're hurting ourselves, too many people are dying, too many atrocities, we have to end this even if it means surrendering to the imperialist aggressor, I would not criticize them for doing that, but I certainly won't criticize them for continuing to resist. I mean, go them, go Ukrainians. They have shown enormous courage and pluck, and the whole world is rooting them for very good reasons.

The harder thing to do is to say what other countries should do. And, you know, I have no influence over what Ukraine does. I also have no influence over what the United States does. So it's just me talking. I, you know, I don't have any policy levers to pull. on this one. But it's an interesting, weird kind of dance, isn't it? Because, of course, as I said, in the last AMA, World War III would be bad. You know, having literally hundreds of millions of people die is an outcome, because of nuclear weapons throwing back and forth, is an outcome to be avoided at all costs, I think. So that is why NATO and the U.S., etc., do not want to send troops to the Ukraine because then those troops would fight Russian troops and it would be war between NATO and Russia and that war could escalate to nuclear weapons. I'm completely on board with that worry. I think that's a very reasonable worry. But what's weird about it is we are allowed to send weapons,

right? Like somehow we, by we, I mean, like the collective humanity, have decided that if we send weapons or food or resources of some sort to Ukraine, and they use them to fight against Russia, that's not an act of war. So I think it's okay. I'm not arguing against it, but just the philosopher in me wants to say, that's a particular place that you've chosen to draw a line between two things. And I bet that that line would not stand up under very, very strict scrutiny. Helping Ukraine one way versus another seems to me to be the issue. But as long as it prevents a nuclear war, I'm happy to go along with the conventional understanding. Anyway, I'm very, very happy that we give Ukrainians resources to fight against the invading army. Robert Ruxendrescue says,

Imagine I write to you a sentence in Romanian, my native language. For you, it will look like a random sequence of letters with no meaning or information in them. For me, that sentence would be meaningful and have a lot of information. What then can be said of the relationship between information and entropy? It seems like what we call low entropy is arbitrary. So I like how you are assuming that I don't speak Romanian. In this case, your assumption is completely correct, because I do not speak a word of Romanian. But this is a perfectly good question, but there are perfectly good answers to this. I don't think this is a very mysterious at the fundamental level. It becomes mysterious because we use the word information in different ways.

So there is a sense of information that Claude Shannon introduced, where it really is a perfectly objective quantitative thing based on the frequencies of different symbols coming your way, right? So if someone sends you a text in Romanian, you can look at the frequency with which different letters are used or different words are used, et cetera, and talk about the entropy of a message in the sense that, given that language, even if I don't understand it semantically, even if I don't know what it's supposed to be telling me about the world, I can still say that within this language, a certain message is information-packed or not very informative at all. That's a purely mathematical statement.

And how you should think about it is certain sentences are surprising. They don't appear very often. They therefore convey a lot of information. If someone says the sun rises in the east versus saying the sun rose today in the west, even though the length of the sentences are the same, one conveys much more information. Because we already knew the sun rises in the east. Telling me it rose in the east this morning doesn't give me any more information that I didn't already have. Telling me it rose in the West, which is not a common sentence that you would hear people say, would, if it were true, convey a lot of information.

So in that sense of the word information, doesn't matter whether I can speak Romanian or not. I can still talk about the entropy. There's another sense, though. I mean, like you say, there's this connection between the words and the meanings of the words out there in the world. And there, it's still an answerable question. The point is that there's different ways of course-graining, right? The same exact text might have no information content from the perspective of a certain observer and a lot of information content from the perspective of another observer.

Let's say that there's an observer who interprets it as Romanian and understands what it means, and another who interprets it as English and therefore gets nothing out of it. They have different ways of course-graining. They have different ways of dividing the space of letters up into words, et cetera, and calculating its entropy. And so they would get different answers for that. So in that sense, it's not arbitrary, but it's relative to the course

graining. It's relative to the way that you're looking at the world. When it comes to actual physical systems, not strings of text letters, there are ways that we all, as human beings, look at the world and we course grain it in the same way. That's why using the ideas of information and entropy and the connection between them is not arbitrary in practical purposes. Sean Corum says, can photons have arbitrarily high energy, or would an energetic enough photon turn into a black hole? Nope, photons cannot turn into black holes.

Why? Because there's no such thing as a photon having an arbitrarily high energy. Why? Because energy is not an intrinsic concept to the photon. The energy is not Lorentzen variant, right? You know, we know that objects have kinetic energy, as well as rest energy. Rest energy equals MC squared plus kinetic energy.

But the kinetic energy depends on their velocity, depends on their motion, and that's relative to who's observing it, right? If I'm in the rest frame of the object, it has zero kinetic energy. Likewise, for a photon, even though it moves at the speed of light, I can still change my reference frame and observe its energy in different reference frames.

And there's always a reference frame in which the photon looks like it's low energy. There's always another reference frame in which it looks like it's high energy. So there's no such thing as a photon just having high energy once and for all, and therefore there's no danger that it turns into a black hole. Brad Dowden says, do you recommend that we say the arrow of time is entropy increase, or instead, is whatever the entropy of the universe does? I recommend that we say the arrow of time is all of the ways in which the past is different from the future. Okay. So one of those ways is that entropy is increasing, entropy one of

was lower in the past, will be higher in the future. But there are other ways. We already talked about causality. There's memory. There's aging and biology and evolution of the universe and evolution of the ecosystem, things like that. Okay, those are all defining versions, not versions, but features of the arrow of time.

The next correct statement is that the reason why there are all of these arrows of time is because entropy is increasing. So that is the single thing that enables all of these other asymmetries between past and future. So the fact that entropy is increasing is the reason why there is an arrow of time. I would not say that it is the arrow of time. Alex Ellis says, more than once I've heard statements along the lines that many worlds is the only interpretation of quantum mechanics that doesn't add anything. It just follows directly from the math.

What does that mean? No equation or mathematical process means anything unless you attach meanings to the mathematical. entities involved. Sure. So that's not a very accurate or at least somewhat sloppy statement that you have quoted. Many Worlds is the only interpretation of quantum mechanics that directly follows the math. What the correct statement is that the ontology and dynamics of many worlds are the simplest ones. It says that there is nothing but a quantum state, which is an element of Hilbert space, and the quantum state evolves according to the Schrodinger equation. That's what many worlds says. It says, in other words, there are not other degrees of freedom. There are not

other dynamical laws. There are not other ways of thinking about it involving agents or experiences or anything like that. So, of course, just like any other physical theory, you have to be able to explain how this mathematical formalism accounts for the world, right? So like, if you tell me the Earth goes around the sun, how do I get that from a state evolving in Hilbert space, right, according to the Schrodinger equation? Of course, you have to do that, but that's no different for many worlds than anything else. The correct statement is the minimal ingredients that are part of everyone's theory of quantum mechanics, namely wave functions in the Schrodinger equation, are the only ingredients you need for many worlds. There's no statement that is especially

mathy or antimathy about many worlds. It's no one. more or less than any other physical theory. Claudio says, I notice that wormholes are being mentioned more often lately. What's the current understanding of wormholes and what would be evidence of their existence? I don't know what social media you're listening in on, where wormholes are being mentioned more lately, but, you know, wormholes are a hypothetical construct that were made famous by Einstein and collaborators, but there are other people talking about them, where you can basically use the fact that in general relativity,

space time is curved to imagine building a tunnel through space time. So building a little wormhole, as it were, connecting two different parts of the universe. And the really cool part about it is in this imagination space where we're just making things up. We're not worried about what actually happens

in the real world. You can imagine wormholes that are shortcuts. So even though I'm here and someone else is on Alpha Centauri, I can imagine a version of space time in which there is a wormhole where it would take me four light years to get to Alpha Centauri the usual way going near the speed of light, but it would only take me a day to get there through the wormhole. The distance would be shorter, okay? So the short answer is, I don't think there are any wormholes. I don't think this is a part of the real world.

People have tried, and they have not completely succeeded in saying it's impossible to make a wormhole. What they have shown is that if you try, lots of bad things happen. Generally, speaking, if you try to make a wormhole, what actually happens is everything collapses into a black hole. It's very, very similar to the cosmic censorship conjecture. Cosmic censorship says that the only singularities appear beyond event horizons of black holes. It's a similar thing with wormholes when you get right down to it, but there are technical details that we don't need to go into. But from the thought experiment point of view, they're very, very interesting. A lot of work being done these days in the ADS-CFT correspondence uses wormholes.

of various kinds. But they're not trying to model the real world. They're trying to learn general principles that might somehow tell us about it. And of course, as Kip Thorne and others realized long ago, if you have a shortcut through space, you can go backwards in time. So wormholes are useful both to travel great distances through space and also maybe to enable time travel, which might be, depending on your stance on these things, a reason not to think that there are any wormholes because time travel would be a mess in its own right. Taroon says, where do you stand on Hume's skepticism toward the principle of induction and what this means for the validity of science?

Well, you know, I'm a basian. So I don't think that there's any principle of induction that is any hard and fast rule. You know, the principle of induction, if we, what was it ever supposed to be? I'm not sure. If you see a white swan and a white swan and a white swan, when do you reach the point where, therefore there are no black swans. I mean, you just get more and more credence, right? Like, like Good Bayesian has just no problem with this. You say, well, if we live in a world where half the swans were white and half were black versus a world where they were all white and none of them were

black, the probability of seeing a hundred white swans in a row would be very high in one and very low in the other, so I'm going to increase my credence in the one that is more likely to be true. But I admit that the next one I see might be black, right? So that's one. sort of the cheap and easy part of the answer to that question. Like the principle of induction was never supposed to be, never had any good reason to be taken completely seriously as a way to get reliable knowledge of the world. The other, of course, like hiding here,

is the issue that any Good Bayesian has about the priors that you have for all of your credences. So, you know, this is the Nelson Goodman, is a philosopher who pointed out, look, you know, when we're trying to do induction, what are we inducting on? Like, what are the properties that we're measuring? So when we talk about the swans, it was either white or black, right? And you say, it's white is white, it's white, every swan I've ever seen is white, therefore they're probably all white. Even a good Bayesian would be tempted to say something like that, right? Not 100%, but if you see a million white

swans in a row, you become pretty confident. So what Goodman says is, for some reason he went with blue and green instead of white and black. But he says, look, let me define a property called grew. And grew is green up until the year 2100 and blue after the year 2100, right? That's a property, absolutely true. And he says, look, so far when I see, you know, my, I don't know, Shoshito Pepper, every shishito pepper I've seen is green, and therefore I'm tempted to say it'll be green forever. But it's also true that every shishito pepper I've ever seen is grew, right?

Because they're all green before the year 2100, and it's compatible that they'll be blue after the year 2100. So how do I know which conclusion to draw? And from the Bayesian language, what this is saying is, what are the priors that you put on different propositions? And your prior might be much higher that the wavelengths of light reflected by this by this vegetable, remain constant versus changing into something else, right, or something like that. But you still have to ask where those priors come from. And I'm very happy to say that they're a little bit subjective, right, that we human beings invent priors because we have a preexisting image of the world, the manifest image that gives us certain predilections towards certain ways of thinking

that the world behaves, and that's where our priors come from. And different people will have slightly different priors, et cetera. But that is where the subjectivity comes in. And and that's okay. Like, you know, the short answer to all of these questions is, pre-Hume, there was a real effort to put everything on a firm foundation, right? You didn't really have knowledge unless it was kind of like math. Like it was kind of like absolute truth descended from completely believable postulates or axioms. And I think that the usefulness of what Hume did was to undermine that program.

and to soften people up, even though Hume didn't have all the final answers, he softened people up for accepting the idea that knowledge is a little bit more fallibilistic, a little bit more approximate, a little bit more probabilistic in some sense, something that we worked toward getting higher and higher credences and things, rather than getting them true once and for all. Jeffrey Segal says, I enjoyed everything everywhere all at once, but I need to defend the everything bagel as my favorite bagel,

as my favorite bagel. What is your favorite bagel and do you have an alternative candidate for the bad bagel? So I don't want to know. No spoiler alerts but there isn't everything

bagel in the movie. Everything everywhere all at once. It plays an important role. And I love everything bagels. I don't think that you should need to defend it and I don't think that the movie is necessarily anti-everything bagel.

Still not a spoiler. Don't worry. I also just like garlic bagels or onion bagels. They like the savory bagels. So my alternative candidate for bad bagel would be something

sweet, right? But, you know, in the right circumstances, a blueberry bagel with some, you know, strawberry cream cheese or something like that is perfectly fine. So I don't think there are any bad bagels. There are just bad bagel eaters. Bruno Teshera says, after the podcast with Nicole Younger Halpern, do you still stand by the statement that we have already discovered all the laws of physics that affect our everyday lives? Well, technically no. I do not stand by that statement, but I've never made that statement. It is not a statement that I would ever make. The statement I actually make is that we know,

we completely understand, the laws of physics underlying the everyday world. And all of the words in that statement matter. You can't just kind of leave some words out and get a statement that is equally true. In particular, the word underlying is very, very true. Nobody in their right mind thinks that we understand all of the laws of physics at all of the levels

of analysis you might want to think about. We don't understand, I don't know, why bumblebees fly, how they fly. I'm not even sure that's true if that's an urban myth. We don't understand high temperature superconductivity. We don't understand what the dark matter is. Plenty of things we don't understand. And the specific statement that I've tried to make is that we understand the laws of physics in one domain at one level.

And that level is the standard model of particle physics plus general Relativity, the core theory. Nothing that Nicole and I talked about is in any sense incompatible with the standard model plus general relativity. So there's no reason why I would change my stance on that particular statement. Brad Malt says, we, your loyal listeners, I appreciate the loyalty, Brad, thank you, seem to be continually asking questions reflecting our confusion about improbable branches of the multiverse. In the April AMA, this took the form of a question about the meaning of making moral choices. And you counseled us not to be discouraged because the bad branch of the wave function was improbable. I think we would stop asking this question if you could articulate

why thin worlds are any less real. For instance, if there is a 99% chance of a good world and a 1% chance of a bad world, aren't there just two worlds, 50% of which are bad? You say the worlds don't count equally, but why not and in what sense? This is a perfectly good question. As you say, versions of it have been asked many times. I predict that I can articulate it very well, and it will not stop people from asking the questions. And that's not because people are stubborn. It's because it's a very different kind of thing. This is an issue that arises in the many worlds interpretation that just doesn't arise in other theories, and therefore, you know, it's okay to struggle with understanding what is going on here. The mathy way to say it

is that in quantum mechanics, in many worlds quantum mechanics, the quantum mechanics, the quantum The quantum state of the universe is a vector, and the different worlds are components of that vector. So if you imagine a simple example where there's a vector in X, Y, plane, right? I draw an arrow going from the origin to some point, X, comma, y, and I could project it down to the X axis and over to the Y axis to get its components. Now, let's say that my coordinates of the tail, the head of the vector, I don't know which one is which. The arrow is X equals 1, Y equals 10. Okay?

So I have two components. The X component has length 1. The Y component has length 10. But you would not be tempted to say there's two components. They're equal. I think that these two components matter the same, right? One component is 10 times longer than the other one is. And that's what the world is in quantum mechanics.

The world is a vector, and these different components are the different. The world, the quantum state of the universe is a vector, and the different individual worlds are components of that vector. Components can be bigger or smaller. That's the basic fact. That's the mathy version. If you want a more sort of physical version, think of it this way. We want to be able to compare different worlds. We need to be able to say that some worlds do count more than others.

And the reason why we need to be able to say that is because we do want to assign more probability to seeing some result. And if you don't think that's possible, if you just take a stubborn view where it says, I'm not allowed to assign different amount of worlds, then you don't believe many worlds. So you don't have an issue. You can't make many worlds work. unless you're willing to make that metaphysical step. And then if you are willing to make that metaphysical step, the question is, okay, how do I do it? How do I assign amounts of umph to the different worlds with thickness, whatever you want to call it?

Should it just be 50-50? Should it just be equal for every world? And the answer is that that possibility of trying to give equal umph to every world just fails. It just fails right away. And one way of seeing that is think about if I were to split, one world into three. Okay. So now I have three worlds and you're going to say, well, I'm going to give them equal for equal thickness, equal width. So it's one-third, one-third, one-third, right? But now instead of splitting into three, so let's keep that in mind, now let's imagine I just

split into two. Okay, so I measure a spin or something like that. I get two outcomes. I have now two worlds and I split into two. But I agree ahead of time that if I get spin down, I'm going to split again, right? If I get spin up, I'm not going to split again. So in that case, I first split into two worlds, and now you're saying, well, I'm going to give them one half, one half, right? And now I split again the other world. Now, the choice is either I give that world that is now split

one quarter, one quarter for each of its successors, right? Because it was half for the first splitting, and then another half for the second splitting, so it's one quarter, one quarter. So the spin-up world gets a half and the other two worlds get a quarter. Or I say, okay, let me say why that doesn't make sense. The reason why that doesn't make sense is if I take the limit, as that second splitting happens closer and closer and closer to the first one, then I can't tell the difference.

There becomes no difference. That limit should be continuous. It should be smooth. There's no difference between splitting into three all at once and splitting into two and then conditionally splitting into another two really, really, really, really quickly. I better get the same answer. So one quarter, one quarter, one half is a different answer than one third, one third, one third. So that doesn't work.

So instead you might say, oh, okay, when I do the second splitting, I will update, I will redo my idea of what the thickness of all the worlds is and I'll give it one third, one third, one third. But then, you know, for those of us were on the spin-up world, we had thought that our world was half of all the thickness, and now something that happened in a completely different world reduced us to one-third of the thickness. And that doesn't make sense either, right? You're like, oh, my goodness, none of this makes sense. Whatever are we to do? Well, the answer is given amount of thickness that is given by the born rule, given by the wave function squared, the, you know, X squared plus Y squared equals the length of the arrow squared. That is the conserved quantity that is there all the time.

So I know it's very different than what you're used to, but if you accept many worlds at all, you have to count the worlds unequally. Let me give you a third way of thinking about this, or a third justification for doing it this way. Let's say that you do, you want to treat some worlds as equally thick or equally important, okay? Well, you know, since it is the component of a vector, maybe you say, well, at least I will treat worlds equally thickly if they have the same amplitude, right? If the component has the same length, then I could treat it equally, right? If it's spin up and spin down, it's literally one over square root of two spin up plus one over square root of two spin down, and then I make that measurement. Now I should treat it equally.

So that's okay. Yes, you are allowed to do that. But then what does that imply when the amplitudes are not equal? What it implies is that if I have two unequal amplitudes, then I could ask for the two different components, the two different worlds, what if I subdivide them unequally, right? What if I subdivide them until they're subdivided into a number of worlds such that their amplitudes are equal, right?

So I keep slicing until they have equal slices of the pie. So I get, you know, two-thirds of one world and one-third of the other world, but then I take the two-thirds world and I split it one more time, right? And so then I get worlds with equal amplitudes. I assign them equal width or thickness, and I ask, what does that imply pre-splitting? What does that imply before I did that extra splitting? Well, what it implies is the width of the two-thirds world was two-thirds, right? That's what works. So if you want to assign equal width to worlds with equal amplitudes, that means you should use the born rule, the wave function squared, when you don't have equal amplitudes.

So no matter what way you slice it, from matter what way you come at the problem, if you want to make sense of the worlds in many worlds, you have to assign a meaningfulness, thickness, umph, whatever you want to call it, which is proportional to the wave function squared. If you don't think many worlds make sense, That's a different question, but that's what you need to do in many worlds.

Ford Prefect says, in principle, could there exist a particularly lucky configuration of massive objects in the universe that would happen to bend light in such a way so that by observing it we could snoop into our past and see how dinosaurs are being wiped out by an asteroid? Well, in principle, there could be, but let's emphasize precisely how impractical it is. For one thing, when you have things like stars and planets, which have gravitational fields that do bend light, the amount of light bending is really, really tiny. If you want anything close to several degrees of bending, you're going to need something like a black hole, okay? So you have black holes out there in the universe, but what's happening is the Earth is sending light out in all directions, and that light is spreading out as it goes further and further away from the Earth. So even if there was like a configuration of black holes somewhere out there in the galaxy many light years away, which had exactly the property that a single beam of light precisely targeted could zoom out from the earth, wrap around. So the dinosaurs were what, 65 million years ago? So it would have to be 32.5 million light years away, very, very far in another galaxy. So some photon could go exactly in the right configuration and come exactly back to us. But think about it. What would the photon next to it do?

Well, it's so thinly spread out that it would not come anywhere close to following. It would be in a different path. It would be diverging because all the photons are moving apart as they leave the Earth. Think about it this way. Think about taking a picture of the Earth from the orbit of Pluto just with a video camera. You're not going to see that much. The Earth will be a little tiny dot. That's all it's going to be.

In fact, that's literally the pale blue dot image that was taken. by the Voyager spacecraft. It's just a dot. You're not going to get any images. And that's just the orbit of Pluto. That's not 35 million light years away, right? So for all intents and purposes, this is not really going to happen. The other thing is, you know, this is an elaborate setup to do something pretty simple.

Like if you really want to capture images from the past, just take a picture. Let's take a photograph. Now, admittedly, we don't have any photographs from 65 million years. ago, but we have other records. We have fossils, right? We have footprints. We have bones and things like that. And you might say, well, that's not as detailed as we would like. Yeah, it's not, but it is much, much, much more detailed than we would ever get from light that was sent off to some black hole, 35 million layers away, 32.5 million layers away, and then sent back to us. Tom says, I enjoyed your recent conversation with Daniels and subsequently saw the movie. I'm curious. if you ever had any ideas for movies or creative projects of your own. I know you've consulted on the physics portrayed on film, but what about a screenplay of your own?

Yeah, I've absolutely thought about it. I've even, I don't want to say collaborated. That sounds too, gives me too much credit. I have talked to friends of mine who are screenwriters about maybe collaborating. It's never really gotten off the ground entirely my fault that it's never really gotten off the ground because there's too many other things going on. And I've had situations where, let's put it this way, if I had really devoted myself to getting this screenplay written, it would have been written. I'm not going to say the movie would be made.

The vast majority of screenplays never get made in this town. But I think that would be a lot of fun. I'm very much interested in it. I'm not giving up on it yet. But still, there's plenty of other things I've got to get done first. Ken Wolf says, I think one of the key questions in the future of artificial intelligence is whether or not something like human-level artificial general intelligence can be developed without creating a conscious entity. I'm not asking whether you think this is possible, since I don't think anyone can answer that at this point.

My question is, whether you think an advanced AGI with or without subjective conscious experience represents a greater existential threat to humanity and why. Well, I have a couple of comments here, and none of which are going to be really satisfying answers to your question. I don't know what it means to say that a certain AGI artificial general intelligence has consciousness or not. Not that I'm saying it's impossible to answer. So I'm not saying that in the sense of saying, oh, I don't know what that means because I don't think it makes sense. I just mean I don't know what it means. I'm not exactly sure how to draw that line.

I'm perfectly willing to believe that AGI could be conscious. I just don't know what the criteria are. So I have no idea. I just don't have a good answer to the actual question of whether an AGI with or without consciousness is the bigger threat. Also, you know, I don't know what the origin of the threat is. This is a slightly different issue than what you're asking, but how does the super intelligent conscious AI actually threaten me? Like, I can imagine if we turned over all of the levers and buttons that controlled our economy or our military, that would be a threat, but maybe we could have

an AGI but didn't give it any access to the economy or the military. So I'm, I'm, not exactly sure what the precise scenario to worry about is. I think that it's all a little vague. I would be more interested in this issue if it were a little bit more specific, what it was I should be worrying about. Henry Jacobs says, perspective, free will is a bad theory, not because it's false, but because it's not a theory. Thoughts. Follow up, so this is a parody of a quote of you, roughly replacing free will with God, and I suspect even the explanation logic is isomorphic. Am I being lazy? So, yes, I think you're being lazy, or at least you're being very wrong. Sorry about that, Henry, but you know, you ask the questions, so you kind of open yourself up for it. Look, I've given a

talk called God is not a good theory. You should watch the talk, because in the beginning of it, I tell the amusing story of how you can find on YouTube. It was at a conference at Oxford on cosmology and theology and the intersections between them. And in the program for the conference, the title of my talk was listed incorrectly. It was listed as, God is not a theory. And I tell the story of how that is exactly the opposite of what I think. That is why the title of my actual talk was God is not a good theory. If it's not a good theory, it is a theory. It's just a bad theory. That is exactly the point that I was trying to make. So you seem to be under the impression that I think that God is not a good theory because it's not a good, because it's not a theory, but that is the opposite of what I believe. So I do not think that the cut and replace that you are suggesting has much of whatsoever. Sorry. Cooper Veit says priority question. Remember, I keep forgetting to mention this, but priority questions are every.

person who is a Patreon of Mindscape gets to ask a question once in their life that I promise to answer, or at least try to answer. I do not promise the answer will be satisfactory, but I will not ignore it. There's too many questions, so I have to delete some questions, and therefore sometimes, you know, you're really interested in a question that I'm not. This is the way that you can get your question answered, by labeling it as a priority. But you only get to do it once in your life, so make it good. So Cooper says, on the issue of morality, Adam Smith talked about a sympathetic observer, someone who would be able to sum up the net most preferable alternative outcome or macro state. Do you think net preferability is remotely scientific?

I have mixed feelings about this one. I think this is a good question. So, again, my mixed feelings are because they're really mixed, not because I think it's an ill-posed question. Let me say two things. One thing is that if you have some decision procedure, if you have some way of saying, in this, circumstances, these circumstances, you should act in a certain way, okay? This is the moral thing to do. You can always translate any decision procedure into a procedure of maximizing some function,

right? Even if it's the very trivial thing of the function equals one on decisions that you should make and the function equals zero on decisions you shouldn't make. So there's always some way to mathematicize and to think of a decision procedure or a theory of morality of what is right and what is wrong as assigning numbers to things. So that can't be the objection to this kind of thing. But there can be an objection, namely what kind of number are you assigning? The idea, and this is sort of proto-utilitarian consequentialist, right, summing up the net most preferable alternative. What exactly is it, if I understand your question correctly, Cooper,

you're asking what exactly is it that I'm summing up? And is the thing that I'm summing up something that is sensibly summed up? You know, just because we can use words like summing things up doesn't mean that it makes sense to sum things up. You cannot add up the number three to the coffee cup in front of me. It doesn't make any sense. Yeah, you're adding two things in different spaces that do not have an addition operation defined on the set that is their union. So that's a real worry, right? that the idea being there's something called preferability that we can attach numbers to and then we can

add them up. I do think that, again, maybe there is a trivial sense in which this is always possible in principle, but I have big worries about it as in practice that there is, I mean, there's assumptions being made here, you know, maybe about the linearity, for example. You know, if I have two people, that for some reason their preferences or their utility or whatever we want to call it is one-half each, and that's equal under some calculation to a person with preference one and another with preference zero. I'm not sure that does make sense, but I can't rule it out. I don't think it's the practical way to go about doing these things. I think that it's sort of, maybe this is what you're getting at with your question.

I think that it sounds more rigorous and quantitative and sciencey than it's, really is. I think that the right thing to do is not necessarily phrased in those terms. That would be my position, but it's not a position I hold very strongly. I'd be willing to talk to into something better with a convincing counterproposal. David Colbert says, I've recently dipped my toe into exploring ancient Greek schools of philosophy, or perhaps more accurately life philosophies, like stoicism, or at least its more modern incarnation, appeals to me. Do you find any such life philosophy is intriguing, or do you eschew adherence to things like this in much the way, same way as you dislike hero worship? Well, I think it's a different thing than hero worship,

but there is a similarity. So a school of thought or a philosophy is a set of ideas. Adhering to a set of ideas is not the same as hero worship in my mind. I'm very much in favor of adhering the set of ideas that makes sense. I'm a naturalist. There you go. I'm a many worlds person. And you can attach all sorts of isms to me. I think that there's a certain kind of person that says, oh, I don't like isms. But I think that isms are really helpful. You know, they, they are, if they're well designed and you don't, you know, take them overly harshly, that is to say you don't insist that everyone adhere to the rules in some kind of overly precise way.

They convey information when you say someone is a socialist or a fascist or whatever. Hopefully information is contained by saying those things. Likewise, with schools. thought of ancient Greece or anywhere else, East Asia or indigenous Americans or whoever, these are philosophies that you are welcome to adhere to if you want to. Now, personally, maybe this is what you're getting at. I wouldn't take these schools of philosophy as looking for the right one, as a set of things that one of them is right, and we should figure out which one is right and then follow that. I think that any of them are worth looking at four good ideas. You know,

for that matter, religious traditions are also perfectly good sources of good ideas, just as they are sources of bad ideas also. What matters to me is the quality of the idea much more than where it comes from. So if you can read texts from ancient Stoics or, for that matter, Epicureans, or whoever, and get good ideas for living your contemporary life, and I think that's great and good for you. Chris says, I think you've talked about morality as being emergent but not scientific. So I'd like to ask how you view these as compatible. It seems by emerging you mean that it's built from things described by the fundamental laws. So if this view is taken for morality, why would that not be investigated scientifically too? Like how the emergent physics of fluids is studied scientifically.

Wouldn't it seem that either morality is not emergent or it has to be able to be studied scientifically? So certainly I've never said words like morality is not scientific. The words that I might have said are that morality is not a science. You cannot derive moral conclusions from the same way that you can derive scientific conclusions. Namely, you put forward hypotheses and then you test them experimentally, right? That's how you derive scientific conclusions. That's how you figure out what is the correct scientific point of view. That is, because in science, there are alternate worlds, right? Alternate possibilities. Like maybe there's a world in which Newtonian mechanics was right. Maybe there's a possible world, not actual worlds necessarily, but hypothetical worlds in which

the axiom is the dark matter, another hypothetical world in which a weakly interacting massive supersymmetric particles, the dark matter, and we're trying to do observations to figure out which world we live in. It's not that one can be driven to the right conclusion just by thinking about it or talking about it. And that's just not how morality works, right? You know, no one is saying, well, here's a moral possibility and here's another moral possibility. Let's do an experiment to see which one fits the data. It's just how it works for morality. I do, so I'm not a moral realist, so that's why I don't think that you can study morality scientifically. I do think that morality is part of the level at which we describe the world

that is emergent, the level involving human beings and their interactions, because human beings describe the world in moral terms. And they say, this is good, this action, this is bad, et cetera. Human beings do that. So it's not fundamental. It's emergent in that sense. But my point about morality is that, I mean, there's two things, there's two questions to ask about morality. One is, what are the morals that people have? That question can be studied scientifically, right? We can say, well, if people have these morals, they will do this or they will say that, and then we can go investigate it. The other question is, what are the morals that people should have? That question cannot be investigated scientifically. Different people have different morals. They're

going to make them up on the basis of different things, and there's no once and for all right answer. Again, scientifically, there's a once and for all right answer, but in morality, there's not. So you can study aspects of morality scientifically, but you can't find the right morality by doing science in the same way that you can find the right dark matter candidate by doing science. Peter Solfess says, when I hear the heat death of the universe described, it is usually described roughly as a giant void with some lonely low-energy photons floating around. If that's the case, what would have happened to all the lumps of iron? Are they just not mentioned, or is there some decay process that would also wipe them out at

some point? It's definitely the decay process. It will take a very, very long time, but even lumps of iron will eventually go away. We don't exactly know how. So one possibility, and maybe the most likely, the most popular one, is that protons are not perfectly stable. Protons have never in the real world been observed to decay. There are limits on the proton lifetime that are something like 10 to the 35 years,

but there are also theories that predict that the proton lifetime is 10 to the 36 years. So that's very, very plausible that iron nuclei are not perfectly stable, they just decay. When the protons decay, because the protons would decay into lighter particles that would then fly away, and eventually that would happen to all the protons and all the neutrons. Once you got rid of some protons in the iron, when I say protons decay, neutrons will also decay. We don't say that because we know the neutrons decay. Neutrons all by themselves out there in the world have a lifetime of something like 10 minutes. But protons observed in the world, as far as we know, are stable.

But maybe they're not perfectly. Maybe also those theories, especially grand unified theories in which protons are not stable, are not correct. Again, we have no experimental evidence for them. But even then there is something called gravity, right? So an iron nucleus could, in principle, decay to a black hole. And that black hole would evaporate away. Or maybe we don't know what it would decay into because we don't understand quantum gravity, but there could be some gravity-like process by which the nature of the iron nucleus changes into something else.

That would be super, super rare, much slower than the decay of the protons by gran unification or something. something like that. But the good news is that we know gravity exists, right? So if you wait long enough, it would happen. The iron nucleus would decay into other things. I have no idea how long it will take, but eventually it would happen. And likewise, for bigger things like rocks and so forth. And all of this is hypothetical. All this is speculative. We haven't been around for 10 to the 100 years or whatever. But it's based on very straightforward physics. It's pretty solid stuff. I'd be surprised if there were any individual collections of protons and neutrons and so forth that were perfectly stable in our universe. Brendan says, when you write your trade books, do you have a process for determining the right balance between being too technical and being too general?

Short answer is no, and a longer answer is that every book is different. In the biggest ideas series that I'm writing right now, it's pretty technical. There's a lot of equations in them. The from eternity to hear was was not as technical, but it was still a little bit demanding, both in physics and philosophy, whereas I think the big picture and the Higgs boson book were less demanding in terms of technicality. So I'm sorry, I should mention something deeply hidden on quantum mechanics along with from eternity to hear were both a little bit demanding in terms of the concepts being talked about. The Big Picture and the Higgs boson book were a little bit less demanding, but neither one of them is like quantum mechanics for babies. They're both involving some ideas that are tough to wrap your mind around a little bit. I'm very open to the possibility of someday writing a book that is much less technical or much less demanding than either one of those books were.

I don't know whether that would happen or not. They don't have any immediate plans. Maybe the physics of democracy, for example, will work out to be that way. I could make that one technical. I'm not sure about that. I hope not. I hope that's not overly technical. I hope to make it a fun gripping read. That's what I'm always aiming for. So it's more about keeping the level uniform and consistent within a book, rather than making any one book aim at some imaginary, perfect balance between being too technical and too general. Vladimir Bellick says, what are some of the skills that aren't directly related to science

but are very useful to have for a professional physicist? For example, I've been wondering if being a good salesman or marketer in the broadest sense of the term could be useful for a researcher in physics. Also, thank you very much for the advice you gave regarding giving talks and being engaging last AMA. So I kept that little lessons in there, Vladimir, because before I read it,

I was going to say the single best advice I could give is learn to give good talks. It's right up there. The second best advice is learn to write good papers, okay? The basic advice is that there is science that we do to become a professional physicist, but there's also telling other people what science we have done. And you'd be surprised at how often that, how important that is, you know, both for better and for worse. There are very good examples of people, you know, saying something in such a compelling way that everyone caught onto it very, very quickly. They're also examples where someone had a good idea and they wrote about it and no one paid attention. And it's not because that person wasn't famous. For other reasons, I was just looking over the transcript of the podcast I did a while back with Leonard Suskind. He's one of the co-inventors, among other great accomplishments. Lenny's one of the co-inventors of the holographic principle. The other co-inventor is Gerard de Tuf, another famous Nobel Prize winning scientist.

Sorry, Lenny is not won the Nobel Prize, although he's at that level. But a tuft was one of the single most important theoretical physicists of the second half of the 20th century. A huge name in quantum field theory really just revolutionized the field in the 70s. And Lenny tells the story that, you know, in some sense, in some very real sense, the holographic principle first appeared in a Tuft's paper. And Suskin wrote another paper about it, not knowing about a Tuft's paper, second, but no one read a Tuft's paper. because the title of the paper was about dimensional reduction in quantum gravity, and dimensional reduction has a separate meaning to physicists, and they didn't think that that was an interesting thing to read about, okay?

So just because the title of the paper was not exactly on point, not enough people read and absorbed and understood that crucially important point about the holographic principle, at least, you know, according to Lenny's retelling, which I think jibes with my experiences as a very young postdoc at the time. So, and a toft is pretty clear, you know, often, and he's a very good writer. He's fun to read. And there's many people who are just not good to read at all or fun to read at all.

And that affects whether people are going to read your papers, right? Likewise for giving talks. Some people, you know, you always want to go to their talks, even if you're not interested in the subject matter, because you know you'll learn something. It'll be fun. And other people, you never want to go to their talks, even though you're super interested in the subject matter. So I think the single most important thing is communication. And I don't want to call that being a salesman or marketer because that's a slightly different thing. The point of being a salesman, a salesperson, is that you want someone to buy your goods.

That is disconnected from the question of whether or not your goods are any good. You want people to buy them. So what I'm emphasizing is not selling your goods, but explaining to people what the goods are. Let them decide whether not they're interesting or not. That's what I think is the most important other skill. Flying Waffle says, aren't superfluidity and superconductivity examples of strong emergence, i.e., to understand those systems from a macroscopic point of view, we can't just break them down into the behavior of individual particles.

So I know what you mean, but no, I do not think that these are examples of strong emergence. And for those who are not quite following along, the idea of strong emergence is that you can't just take a microscopic theory, right, a theory of the fundamental constituents of a thing, put it on a computer and let it run. That would be, if that process, if that procedure did tell you always exactly correctly what happened, there might be weak emergence, there might be a way of talking about the system at a higher level, but still the way of talking about it at the lower level is complete and comprehensive and gives you everything. That's weak emergence. Strong emergence says that you can't just do that.

You cannot just take the microscopic theory simulated and get the right answer because something new comes in at the macroscopic level. So in quantum mechanics, the world is not made up of little things. That's just not how quantum mechanics works at the fundamental level. There is one wave function for the whole universe. And usually you can get away with ignoring that, or let's say, either think of things as truly separate or separate but entangled with each other. In the examples of superfluidity and superconductivity, you can't do that. You really need to take seriously the fact that there is just one wave function for the whole system. So that might seem to be a challenge to the idea of weak emergence.

But I think it's a fake challenge because I think that most people who think about emergence are not really familiar enough with quantum mechanics, as they should be, and they make this mistake of conflating the idea of a microscopic theory with a theory of microscopic things. To my mind, a microscopic theory is just the more comprehensive theory. It's the theory that works in a wider domain of applicability, including ones where individual systems are microscopic. But it doesn't necessarily mean that the system is comprised of little pieces. So I just think that there's a sloppiness in the way that many, people define what is meant by emergence. If you define it in the conventional way with little pieces

making up big things, no quantum mechanical system counts as being emergent. And I think that's just a mistake because people are still embedded in a classical way of thinking. I haven't actually written this up. I've been writing about this for a little while, but I haven't actually completed a paper or anything like that. But we're working on it. We're trying to get there. But I think the the fundamental issue of strong emergence is not about quantum mechanics versus classical mechanics. So superfluidity and superconductivity don't really qualify as what the people who like strong emergence really want to be talking about. Tim Kennedy says, at the very end of a black hole evaporating, does it explode in a blaze of glory?

And if so, is it at all similar to the Big Bang, given there will be pretty much nothing around it? It does explode, but it's not much of a blaze of glory. You know, the black hole gets smaller and smaller over a tremendously long period of time. And as it gets smaller, it gets hotter. So its rate of evaporation increases. And you can go down to like the plank scale, right? And that's the last burst of energy is when the black hole is down to the plank scale. And you can calculate how much energy is given off when a plank scale thing explodes.

It's not that much. It's like a grenade going off. If I remember correctly. I haven't thought about this in a long time, so I might be misremembering. but it's not some big world-shattering kind of thing, because most of the energy has already been transported away much earlier. Eric Stromquist says, the universe appears roughly homogeneous and isotropic reflecting the translational and rotational symmetries of physics. However, the third space-time symmetry

of Lorentz symmetry seems observationally broken by there being a preferred inertial frame. For example, that of the CMB or even the ordinary matter of the nearby universe. My question is, what is the significance of this, and in particular, is the existence of a preferred frame related to concerns raised about exactness and fundamentallyality of Lorentz symmetry? I've never seen any doubts raised about either translational or rotational symmetry in the laws of physics. I wanted to answer this question, not because of any great wisdom about it, but because I have written papers about violating translational and rotational symmetry with Mark Wise and some other collaborators, Lottie Ackerman and Chen Yonge. saying we wrote papers on violating rotational invariants or translational invariants during inflation. So how would you see the impact of that in the cosmic microwave background? But I don't think it's likely that that's true. We just wanted to figure out this is a very common thing to do in

physics. We said, if it's true, how would you know? So now people can go and look in the microwave background because they weren't looking before our papers came out. But the basic question, I think is an interesting one, but I don't have a pithy answer to it. I do think. think that it is a fact that our universe seems to have a preferred, at least approximately preferred rest frame, being at rest with respect to the cosmic microwave background. And in fact, this was an issue in the early days of inflationary cosmology. People pointed out that a lot of the models that people were throwing around had perfect Lorentzen variants during inflation, you know, basically something that was to sitter space, so not quite Lorentzen variants, but at least no

preferred rest frame, okay? Sorry about all the jargon words here, but no preferred rest frame during inflation, and then one somehow got established when inflation ended, and that didn't quite make sense. And there is a resolution to this problem, and the resolution is basically that it's not ever perfectly free of a preferred rest frame. There is always during inflation some inflaton field doing the inflating, and that field does pick out a preferred rest frame. Now, why was it ever there? That I don't know. That's a more difficult one.

It was always there, as far as we know, so it's not a matter of, you know, creating it, such as understanding why it was always there. But I don't think that that's a puzzle that people have really thought about very carefully. So, sorry about that. No helpful answers for that one. John says, thanks for answering my question about positronium during a previous AMA. I have a follow-up during... You said that positronium-hydrogen...

don't have the same spectrum because of the difference in mass between a proton and a positron, this must involve gravity, right? No, it has nothing to do with gravity. Mass has something to do with gravity, that's true, but mass also just has something to do with inertia, right? I mean, the idea of mass is there in F equals M.A., Newton's second law, even if the F has nothing to do with gravity. It's just a matter of the average energies or the total energies involved in binding two particles together with different masses. The energies all come, from the electromagnetic force. There's a little bit of quantum mechanical play there,

but the electromagnetism is the force that is holding together, the proton and the electron or the positron of the electron. Gravity has nothing to do with it. Jesse Rimler says, in the realm of foreign policy, do you agree with the principle that it is most important for a citizen to be critical of the actions of their own state? Well, I think that's a little bit too vague

to be a principle that I agree with. most important in the universe, the most important thing ever written down. Maybe what you mean is it's more important to be critical of one's own state than of other states. I don't even agree with that. What I would like is just to be correctly critical of everybody. You know, I do think that in practice, so not in principle, but in practice, one tends to know more about the pros and cons of one's own state. And I do think that, I mean, maybe the implication is you don't want to give your own state a free ride just because it's yours. That I agree with. Yes, absolutely. But there's no idea, I would not agree with an idea that until I fix all of my own state's problems,

I'm not allowed to criticize other states. I think that's going too far. Frank Lehman says, What do you make of the academic job market for recent PhDs in STEM or any other fields? Are the woes that come with it these days reflective of a profound shift in the prospects for young scholars, or was it ever thus? It's always very hard for me to tell, to be very honest, about questions like this. There are some numbers and data out there, but there's a lot more feelings. And people's feelings are inevitably kind of shaped by their own personal circumstances and what they're familiar with, right? And I recognize that, and therefore I'm not going to try not to project my own feelings onto things like that. I mean, the job market is not very good in the sense

that there's always many more people who want to be professors than there are jobs for professors. So that's true. But that's a weird kind of thing to complain about. I mean, if the job, the number of jobs stayed the same, but suddenly overnight, twice as many people wanted those jobs, suddenly the job market is a lot worse. But it doesn't reflect some flaw in the system or anything like that. I mean, the job market for PhDs is much better than the job market for NBA basketball players. Many, many, many more people want to be basketball players than would get hired doing that. So I think that's kind of the wrong way to look at the problem. I mean, Frank, in part that I didn't read of his question, he mentions adjuncts,

and that's a problem. This is, for those of you who are not in academia, there's an increasing reliance at many colleges and universities on not having the professors teach most of the courses, but not having the full-time professors teach most of the courses, but rather bringing in part-time adjunct professors. People who don't have tenure, who are not on tenure track, who have no chance of being promoted or anything like that, who have no time or resources to do research, they're just basically hired guns to teach a course. And I can imagine that on occasion that might be a useful thing for university to do, but

it's way, way overdone in the current market. I don't worry about the overproduction of PhDs because I think that getting PhDs is a good thing. It's an individual choice. I think that people coming into PhD programs and applying for them should be told in no uncertain terms what the job market is like. I've gotten flack, actually, from my colleagues because sometimes I'm too honest about the difficulties of the job market. And they're like, no, you should be encouraging the young people. And I don't want to encourage young people. I want to be honest with the young people.

If that encourages them, that's great. But I'm not encouraging them for the sake of encouraging them. I want people to know what the situation really is. And the situation really is that the vast majority of people who get PhDs are not going to become tenured professors someday. But if they still want to get a PhD knowing that, I think that's awesome. I think that's great. And we should allow them to do it.

So I actually think there's an overproduction of postdocs, if you ask me, that's postdoctoral thing, if you're a PhD student, the thing you do next is you apply for postdocs, at least in scientific fields, and then eventually you become a faculty member. And that's great if you do succeed at eventually becoming a faculty member, because it means that you've had some time to practice and do research without all the extra burdens of being a faculty member, etc. But very often, people don't only just get a PhD, but then spend, what, six, nine, ten years as a postdoc and then still don't get a faculty job. And that, I think, is much, much less justifiable from the point of view of that researcher, because getting a PhD is clearly,

like I said, a good thing. It trains you, it gives you some credential, et cetera. The extra marginal benefit of being a postdoc for eight years is very tiny in my mind, unless you go on to become a professor, in which case it can be substantial. But for other jobs, it's very tiny. So I don't think the problem is overproduction of PhDs. I think that we, the problem is that we let PhDs linger around without giving them permanent jobs. I think that's the problem. Carlos Nunes says, Do you have a specific argument for why you don't want to have kids? Are you familiar with the philosopher David Benatar? And if so, what's your opinion on his anti-natalist view? Benetar argues that we should avoid bringing more people into this world due to the inherent suffering

of being alive. So I think that Benatar's argument is very wrong from my point of view. I do not think there is inherent suffering of being alive, I kind of think being alive is pretty awesome. It has its ups and downs, but I think it's part of it being awesome. If there weren't downs, we wouldn't appreciate the ups as much to vastly oversimplify a very complicated set of issues. I just don't want to have kids. That's it. It's not a deep philosophical position.

I have other things to do. I have other things that I want to spend my time doing. People, some of my best friends, they have kids. It's great. I don't actually mind kids as such. It's just that with my lifestyle and with what I'm. I want to do. I would like to put my time and resources elsewhere. I think it would be terrible to be a parent and then not spend time, spend effort to spend resources being with your kids. And I

don't really have the resources to do that myself. Justin Walcott says, my five-year-old son, Nicholas, see, there's a good kid right here. Nicholas, I'm sure is an awesome five-year-old kid. Nicholas and his friends at school are debating whether infinity is the largest number or not. Nicholas says it can't be since it's not a number because infinity plus one equals infinity. Ah, very good for Nicholas. But sadly, the answer to this is it depends. I mean, obviously, as soon as you ask this question, right, you're going to know that the answer is, it depends on what you mean by number, right?

So there are systems of numbers like the integers where infinity is not a number. Infinity is not an integer because, like you say, infinity plus one is not, is still equal to infinity. But there are other systems of numbers that are bigger than the integers, and you can add infinity and include that in your system of numbers. You have to change a little bit the rules for what happens when you add numbers to each other, etc. But the point is, depending on how you define number, you can accommodate infinity, but you don't have to. Not a perfectly satisfying answer, but it should inspire you to go Google around different systems of numbers and how infinity fits into them. Joseph Williams says, do you think our seemingly advanced mathematical abilities, along with our pre-examination, of the beauty and elegance of math is an involved trait. If so, why and how? Well, in some sense,

everything is an evolved trait. All of our traits are evolved, right? So in that sense, sure. I would also kind of question the assumptions of the question. I don't think our mathematical abilities are all that advanced. You know, compared to cats, the mathematical abilities of humans are quite advanced. But, you know, I make mistakes all the time doing math, even in elementary arithmetic. So I'm hesitant to give myself a lot of credit for advanced mathematical ability. So the real question is, is there some, I think what do you mean by the question is, is there some adaptive advantage to having much more mathematical ability than a cat has, right, or than a chimpanzee? Well, I tend to think probably not. I mean, there might be an advantage, but I don't think that the use of mathematics has arisen sufficiently long ago in evolutionary history that that particular trait was selected for. You know what I mean? A lot of things that we're able to do, were able to do just sort of as a side effect of some of our features or traits.

or whatever you want to call them, being selected for completely other reasons. So I can easily imagine that our brains developed in certain ways, and those developments were evolutionarily advantageous, and as a side of fact, we got better at doing math. I suspect it's more like that. I cannot imagine really that a lot of group theory or differential geometry was useful to hunter-gatherers on the plains tens of thousands of years ago. Richard Cashdan says,

I have a serious problem with the way people always seem to talk about simulation theory, the idea that we are living in a simulated universe. They generally say that the universe is 13 billion years old, and therefore there is plenty of time for civilizations to grow up, to the point that they can build simulations, and therefore the probability is that we are in a simulation because there would be many more simulated universes than the one original universe. I wonder if you would agree with me that this argument is nonsense,

because we have no clue how old the actual universe is. all we would know is that our simulated universe feeds us signals includes to make us conclude that if our universe were real, it started with the Big Bang some number of years ago. What does that have to do with how and when the real universe started? So there's two things going on here. One is, is it conceivable or likely that if we are in a simulation, the simulators have tricked us into thinking that the universe is 14 billion years old when it's really not? So that is possible, but I think it's not likely, and I'll explain why. So it's completely possible. You could arrange.

It goes back to what we were saying about the low entropy of the Big Bang vis-à-vis the smoothness of the cosmic microwave background, right? In some sense, what you're thinking about is the simulators are tricking us into thinking that there was a low-entropy Big Bang 14 billion years ago because the cosmic microwave background is smooth. But they could easily set up a radiation bath near. our telescopes here that would trick us into thinking that, okay? Except, even though it's possible, it's not the best way to do it. It's not the simplest or algorithmically most straightforward way

to do it. If you wanted to make us think that the universe was that old, you would just simulate the whole universe because the starting point is enormously simpler, right? The starting point of a hot big bang that is smooth and dense and rapidly expanding, that's easy to put into your computer. all of the specific details about the universe today in order to match that very simple beginning are incredibly complicated. You're asking your computer simulator to do much more work than is necessary if you want to make them trick us into thinking the universe is old. Now, maybe they want to do that. It's possible. Sure, it's possible. But I'm just saying that it's not the sensible way to do it. If you think that our simulators are very smart, then they would just run it from the Big Bang onward. But more importantly, for your actual question, I think that your logic is a little bit shaky here, Richard, because basically what you're saying is, if we live in a simulation, then the universe might not be 14 billion years old.

Sure, that's true. But the argument is supposed to be that if we don't live in a simulation, we could still build a lot of other simulations, and therefore there would still be a lot of people living in simulations. and then the question comes about why aren't we one of them, right? I don't agree with that argument, to be honest, but not for this reason, because basically you're already assuming we live in a simulation, so they've already won by the standards of your version of the argument. So I don't think that that's a good objection to the simulation argument. Casey Mahon says,

sometimes I find it really odd that I happen to be born human. After all, it seems far more likely that I'd be born a bacteria or an insect. Of course, the answer is that someone has to be born. had to be me, but that feels unsatisfying, can you offer any insight? Maybe. So this is actually related to what I just said is why I don't believe the regular simulation argument, because there's a presumption, a premise of this kind of reasoning that said that somehow there's this thing called I, me, myself, right, that had some probability of being something in the universe. And if that probability was equal with all kinds of things, then there's a lot more bacteria or insects

than there are human beings. I mean, clearly, just by saying it out loud, by spelling it all out loud, I hope the craziness of that chain of reasoning becomes clear. There is no you that exists outside your physical body that becomes embodied in either a bacterium or an insect or a human being. That's just not the way it works. What happens? What happens? is that a lot of bacteria and a lot of insects and a lot of human beings come into being through the physical evolution of the universe and the biological evolution of the species. And there's just no sense in which you are randomly selected from all possible living beings. Why would we ever think that, right? And this is why I think that a lot of anthropic reasoning is incorrect, that we

somehow tend to reason as if that were the case. But it really, it just isn't. You're just you. There's nothing to be explained there. There's no sense in which you could have been someone other than you. Someone else could be someone other than you. And in fact, if you took a vote among all the bacteria and all the insects and all the human beings in the world, which one of them, how many of them are bacteria, they'd mostly be bacteria. That's true. But all the humans would say that they're human. That's just how it works.

Igor Velotik says, in what way has conversation with Justin Clark Donne affected the way which you think about the reality slash obfutable? of mathematics. So, yeah, I've been continuing to talk to Justin, who was on the podcast a little while ago, who's an expert on these foundations of mathematics questions. And he hasn't convinced me yet. I'm not a mathematical realist. I'm a reality realist. I think that the physical world exists, and that mathematics is something that we human beings use to talk about the physical world. I don't want to go into all of the details, but let me just say sort of one thing that Justin keep saying and one thing that I keep worrying about. The thing that Justin keeps saying is, it's not an original argument with him, but it's one of the arguments for mathematical realism

is we need to believe in the consistency of our theories. If you make a statement like the standard model predicts the following result, you believe that there are predictions of the standard model, which is to say that you believe that the theory itself is consistent. It doesn't predict everything. If you have an inconsistent mathematical formalism, it can predict anything. So you have to assume that your systems are consistent in order to do science, et cetera. But making statements about consistency of theories is a higher level thing that you can't prove. And this is a consequence of Gertl's theorem and subsequent work in mathematics. You can't prove the consistency of your theories. In fact, you could choose to add extra axioms to sufficiently

powerful theories that either say, and this axiom system is consistent or, and it's not consistent, okay? So the argument is that you have to accept in order to believe in the consistency of your theory, you have to accept some extra non-provable fact about the theory, namely that it is consistent. And since that's not provable, you're basically accepting some mathematically real fact that just exists as truth, okay? I don't quite buy that argument because I don't quite think that, I mean, I think I can just assume my system is consistent and keep using it without accepting the existence of some objective fact of the matter outside of human invention about whether it is consistent or not. But I'm not 100% certain about that. So that's the thing I wanted to say about my own point of view is that if I were to criticize myself, I would say that in some sense I want my cake and eat it too.

I want to be able to use math and trust it and think that if people in a completely different physical reality had invented arithmetic, they would still think that the twin prime conjecture is either true or false in that world, while still not believing that it's a separate part of reality. I want the math to be true but not real. And I think that is a distinction worth drawing, but I couldn't actually promise you that it's worth drawing. So maybe eventually I have to give in. I'm not sure about that. But, I do think that people are using words like realism and existence a slightly different ways when they talk about these different things. That's the heart of my objection. Chris Murray says, when planning to dine at an very expensive restaurant, how do you prepare? Besides dressing for the occasion, are there other steps you take? This is a fun question, but the answer is no. There's really no other steps that I take. I do think it's nice to dress nicely when you go to a nice restaurant. But, you know, some people, People will try to like check out the menu online, see what is going on. Other than sharing some food allergies with a restaurant ahead of time, I just like to show up and have no spoilers ahead of time, right? Just see what's going to happen. You know, different restaurants are very different.

You know, there's some fine dining restaurants that are still following the paradigm of appetizer, entree dessert. Others have like 20 little tiny courses that are one bite each and things like that. So there's many ways that the paradigm can work, and that's part of the playfulness and part of the fun of it. Some are very stuffy and formal, some are much more playful, et cetera. And, you know, so I just like to wallow in the experience. Let it happen. I don't do any preparations. No. Jimmy Summer says, I was reading a quantum article, and it said that when speaking about space time emerging from quantum mechanics, you could essentially construct an equivalent theory where quantum mechanics instead emerges from space time.

So in that construction, space time is ontological, and everything else is emergent rather than the other way around. And these emergent theories based on correspondences, it would be difficult to know which way reality is actually set up. Does this make any sense, or am I misunderstanding this, or is this just wrong? I'm not exactly sure what was being referred to in the Quanta article here. Probably it's referring to ADS-CFT, which is this correspondence between quantum gravity in antigenesis. to sitterspace, that's ADS, antidesitter space, and quantum field theory without gravity in one dimension lower. That's the CFT, conformal field theory, CFT. And the CFT side of the duality, the idea behind the duality is that these two theories are supposed to be equivalent to each other,

okay? You can start with one and derive the other or vice versa. But the fact is, the CFT side of the ledger where there is no gravity is much easier to define rigorously, okay? And so in practice, when you really want a full description of the theory, you start with a CFT and you derive the quantum gravity side from it as an emergent holographic phenomenon, because the quantum gravity side has one more dimension of space time than the conformal field theory side does. And I'm not even sure that the gravity side by itself has a full rigorous description. So I'm not quite sure this really is a duality. I'm not a super expert here, but there's been enough mumblings in talks that I've gone to in papers I've read to make me a little suspicious that there's a full 100% super accurate correspondence between conformal field theories and anti-decidder space quantum gravity.

I think that there's probably a restricted correspondence in the sense that many emergent descriptions are, right? There's a domain of applicability for them that does not extend over the complete theory. But anyway, both of these sides of the duality are quantum mechanical, and both of them also have space time. The difference is that one side has gravity and the other doesn't. Okay. So if that is what is being referred to by the article that you read, I would certainly not say that you, derive quantum mechanics from space time. You derive space time from quantum mechanics either way that you go. But maybe I'm missing it. Maybe I'm not, maybe referring to some other idea.

I don't see any possible way that you could get quantum mechanics to emerge from space time. Space time is classical. I mean, when you say space time, you need to have a theory of what space time does, like Einstein's general relativity or whatever. That's a classical theory. You're not going to get quantum mechanics to emerge from that as far as I could tell. David DeClert says, in your recent talk about the arrow of time, this is referring to the talk I gave at Berkeley at the Simon's Institute for the Theory of Computing. It's amazing that I was invited to give a talk at the Simons Institute for the Theory of Computing, giving that I know nothing about the theory of computing, but there was a workshop there at the time on causality, and I know a

tiny bit about causality, much less than most of the other people there, but I know a lot about the Arrow of Time, so I could talk about the Arrow of Time. So I could talk about the arrow of time and causality. So in this talk, David goes on to ask, you mentioned that we believe that entropy was low in the past because of a very strong bias in our brains, and that without the past hypothesis, it's much more likely that air molecules randomly push the wine glass off the desk than your swinging arm did. But now that we know that we're biased, shouldn't we correct for our bias and choose to believe whatever we know to be more likely, given that we know we're biased, why should we should we continue to believe the past hypothesis? Well, this is a case where a bias is a good thing,

because our bias is correct. Or our bias is certainly, yeah, our bias is correct. Let's just put it that way. And this is an argument. I've talked about it before, but it's articulated most clearly in my paper called why Boltzmann brains are bad. The point is that if you didn't have the past hypothesis,

you only had, let's grant you some information about the current universe. You know, we could argue in detail about what you would know and not know about the current universe if there were no arrow of time, but let's just say you know the current universe. But there's no past hypothesis so that you extrapolate from the current state into both the past and the future, and the entropy increases in both directions.

That's what you would predict if you didn't have the past hypothesis. But as a result of that, what you're saying is that your current moment, including your current self, are the results of a random, unlikely fluctuation downward in entropy from a high entropy past. And that's very possible, but what it means is that the stuff inside your brain, not only your knowledge of the past, but all your knowledge of physics and logic and math and reason, just randomly fluctuated into existence. And it's equally possible for incorrect ideas to fluctuate into your brain randomly as for correct ideas. In fact, honestly, it's way easier to fluctuate a wrong idea than to fluctuate a correct idea.

randomly into your head. So the point being that if you accepted that past view of the universe, if you accepted that history of our universe, you would have no reason to accept the past history of the universe because you would have no reason to accept your own views on anything at all. So this is cognitively unstable, this point of view. This is a point of view which you cannot simultaneously hold and believe you have good reason for holding because in virtue of holding that view, you shouldn't believe that view, okay? So therefore, the way to get out of it is just to say, I don't believe that view. You can say, look, maybe it's true, just like maybe we're a brain in a vat or being taunted by an evil demon, like any other skeptical hypothesis, but it's no way

to go through life. In order to have a view of the universe that makes sense and makes it possible to make progress, et cetera, you have to assume the past hypothesis. And then you check it. You say, okay, I assume that the entropy was low in the early universe, and then you look at our maps of the microwave background and so forth, and you go, yes, this is consistent with that assumption I made. I think I'm on the right track. That's how it works. Rue Phillips says, can you please expand on the meaning of it from bit that John Archibald, Wheeler said decades ago. Chalmers seems to take it quite literally in his latest book on virtual worlds. What's the real insight here and how speculative is it? Well, I don't know. It's the

short answer. John Wheeler famously was better at coining pithy provocative phrases than at spelling out all the details of the implications for these phrases. So it from bit is probably his most inscrutable phrase. In some sense, what it's supposed to mean is that information is key to understanding what happens in the universe. Rather than thinking of the world as just stuff it, right, bumping into each other, think about the information contained in that stuff. And the implication would be that if you had very different stuff, but following the same pattern, containing the same information, standing in the same relation to other stuff in the universe, etc., then it would for all intents and purposes qualify as the same thing going on. Okay. So a down-to-earth way of saying

this is the substrate independence of consciousness or cognition. It doesn't matter in this point of view if it's in a computer or in a brain or whatever. If the same kinds of information processing events are happening, they are equivalent to each other. So it's not, you know, a principle that you can test or anything like that. It's a perspective. that you can take on what is going on in the world. So you can take it quite literally or not. I mean, I think that if you're careful, there are both differences and similarities

between what happens in a biological brain and what happens in a computer. For some purposes, the differences will matter. For some, they will not. And I'm not trying to dismiss the question. I think these are very important questions, but I think that a pithy slogan is not going to be the final word on those questions.

Brian Tidmore says, my 12-year-old son has stated that he wants to invent teleportation. I explained to him why it's impossible, delved a little into the physics of what we know of matter and how the universe has rules, but I felt my answer was discouraging him. What are your thoughts on encouraging creativity and interest in science, but keeping a young mind grounded in reality? This is a great question, and you know, it doesn't stop when your son is 12 years old. It works with graduate students and postdocs and even colleagues and maybe even yourself. going on that line between explaining why something doesn't sound to you like a good idea,

while still encouraging them to try. I mean, I think everyone, certainly I, everyone who has gone up through theoretical physics, has had this experience of having an idea, taking it to some wiser elder person, running it by them and being told why it wouldn't work, and believing them and going away and then realizing either because you figured it out or because someone else scooped you on it, that it would have worked if you had just tried harder on it. So in my own role sometimes as an advisor or something, I try to have exactly this balance between saying, well, you know, here's the problems with that idea, but I don't want to

discourage you. And then sometimes you just got to discourage them because the idea is so obviously wrong that you think it's not worth it. And that's a risk. This is just the risk of doing science. But okay, at the level of talking to a 12-year-old, you know, for one thing, are you sure the teleportation is impossible? You know, I get that there are very good arguments for it. How well do we know that those arguments are true? How well we know that energy is conserved or that information cannot travel faster than the speed of light? These are things that we know, that we think we know. And in fact, I think that they're probably true, some construal of them.

But you can ask how well we know. Why do we know, right? And also you can sort of steer from the original idea to a related idea. Like, okay, why do you want to invent teleportation? What's important about that? Given the constraints of physics, as we currently understand it, maybe the original idea didn't work, but maybe there's some other idea that does the job just as well or is more interesting.

you can explain that, okay, here's what we are able to do. Here's what people are thinking about now. You know, here are ways to get around very fast from place to place. You can talk about wormholes, for example. You can talk about quantum teleportation, all the things you can just Google. I'm not going to explain them all right now. But you can say, look, there are things we think we understand quite well. There are things that we don't understand nearly as well.

sometimes it's a little tricky to clearly discern the boundary between them. And so, you know, encourage him to go look it up and think about it. And the other thing is that this is just inevitable, and I don't know any way around this, to really understand what's going on in these issues, right, deeply into the heart of physics, it takes time. It takes a lot of work. It takes a lot of prerequisites where you have to learn things and a lot of math is involved. And that can be really discouraging.

When you're 12 years old, you want to skip to the answer. You don't want to learn differential geometry and quantum field theory. You want to know why you can't build a teleportation device. And that's very, very, very, very frustrating. At some level, you just have to be honest and say, sorry, you have to learn all this stuff. At the other level, you can say, look, your good news is there's all this stuff that you get to learn. And other people have already figured it out. So you don't have to invent it for yourself.

You can just learn it, and that's possible to do. and it will take time, but it's enormously fun and rewarding to do that. So you have to preach a little patience. You have to look for the chinks in the armor of what you think is true, and you have to encourage people to really think through the ways in which their crazy ideas may or may not work. And then, you know, there's a crucial divergence at some point in a young person's life where they decide to become a scientist and really think about things and give up on some favorite ideas when they don't work out but still keep working on others if they're promising. Or they become a crackpot.

And the difference is that the crackpots don't listen and learn. The crackpots have zero interest in learning from you. They think they know the answer already and they just want to tell you. And that's what you want to avoid letting your children become. Mama, don't let your babies grow up to be crackpots. encourage them to keep learning, to accept that their ideas might not be right, but maybe they can make them better by working on them, learning more, and listening to others, and thinking about it all.

Vakintas Morkvenas says, do you have any handcraft hobbies? No, it's the short answer. I don't even have that many hobbies. I don't know what counts as a hobby. You know, a lot of my time is spent either thinking or talking or writing about physics and philosophy and other ideas out there in the world. And I like it that way. I'm not going to apologize for that. I'm very, very fortunate to be in a situation where I can do this, and an enormous amount of my energy goes into doing it, and I get paid to do it. It's my job. I have a job title, you know.

So no complaints about that. But not a lot of time do I spend on, you know, puttering around, building things or whatever. I have painted in the past. I was never any good at that. as I mentioned earlier on the podcast, I bought a bass guitar during the pandemic. I still have every plan to learn that, but it's been slowed down by other obligations. Maybe after I move to Baltimore, we'll have a music room, who knows. But building things or creating things or, you know, quilting or crocheting and things like that, no, I've never really taken that up. Let a thousand flowers bloom. Let people do different things. I love it when people do it, but I can't offer any wisdom from my own perspective.

Ray Fuchillo says, doesn't the holographic principle place an upper bound on the size of the universe? I've heard you say that the universe may be infinite, but it seems that at some large size, there'd be insufficient space on the boundary to account for the density of information that we observe around us, since the surface to volume ratio decreases with size. So, no, not quite. the trick is that there's less information around us than you think. So the holographic principle says that if I have a region of space and I surround it by a boundary, the amount of information inside the region,

the amount of information characterizing the region itself can be encoded or is no greater than the area of the boundary as measured in plank units. So you don't need a very big region before there are far, fewer plank units on the boundary than there are plank volumes in the region. But the point is of the holographic principle that what is happening in all those parts of the region of space is not independent. What's going on in one region is sort of redundantly encoded with what's going on in other regions. That's the only reason holography is possible. Now, you have to understand that the plank length, the plank volume, the plank area, these are really, really tiny. So you can fit a

of information on a plank-sized boundary surface around you. So the limitations of doing that in terms of what you see around you literally, like planets and stars and galaxies, that is nowhere close to saturating the amount of information that you can encode on the boundary, according to the holographic principle. Rafael Buso has, you know, nicely formulated the holographic principle in a completely rigorous way, and it works differently in different kinds. of cosmological space times, if you have a sufficiently rapidly expanding universe, then there's sort of no limit to the amount of information you can put on, because it's really not, when you technically go into it, it's not about the area of the boundary, it's about the, well, sorry,

it is, the relationship is not between the area of the boundary and the information inside. It's between the area of the boundary and the information that ultimately flows through the future light cone of that region. But that future lightcomb can be infinitely big if you live in an expanding universe of the right form. So there's tricky subtleties there. But anyway, the short answer is no. There's no upper bound on the size of the universe. In Minkowski space, where there's no expansion of the universe, it can be infinitely big, holographic principle can still apply, no problem. Jonathan Goodson says, when I see two particles exchange a photon on a Feynman diagram, it looks like it's a simple matter for the photon to find the target particle.

But given their size, their spatial separation, and the fact that the photon could be emitted in any direction, the exchange seems extraordinarily unlikely. Is the photon's trajectory constrained by an electromagnetic field? And if not, how do we account for its incredible navigation skills? So yeah, in that first question, you're sort of, you're almost there in getting the right answer. Remember, the world is not made of particles. The world is made of fields. So particles are a convenient way to talk about what we see when we observe the quantum fields.

a tiny fluctuation, vibration in the field looks like a particle. And even better, Feynman discovered that we can talk about the interactions between the fields in terms of an infinite number of particles that we're summing over. So when you see that image in a Feynman diagram of a particle being exchanged between two different particles, a virtual particle, right, that's a shorthand for vibrations in the fields. And the fields are everywhere. The particles look like they live on some line, on some world line, traveling from one place to another, but it's a representation of what is actually happening in the field, and the field is everywhere.

So the field doesn't have to find the target particle. Every little vibration in one field is sort of sympathetically causing vibrations in all of the other fields, and all of their combined feedbacks lead to these interactions that you're talking about. So you just have to keep in mind that Feynman diagrams are just shorthand, for what quantum fields are actually doing. Kuhn al-Menda says, how do you envision the many-worlds interpretation winning out? Will it forever be an argument based on parsimony,

or are there any experimental findings that might help us? Well, I think both, you know, I mean, I think that many worlds is both simple and it fits the data, and if that continues, then it will look good for many worlds. But there's two other things that will happen. One is that there's also the question of fruitfulness. You know, Thomas Kuhn, long after he had,

done his famous book, The Structure of Scientific Revolutions, where he talked about paradigm shifts and so forth. He was accused of being a relativist about scientific truth, and he wasn't. So he explained in a later paper that, no, there's absolutely criteria that we use to choose between scientific theories. The problem is that the criteria are not quite an algorithm. There's different criteria that weigh differently. And one of them is the fruitfulness of an idea. So I think that what will really cause people to get on the many worlds bandwagon is when you can make some money with many worlds, when you can use that perspective to understand other puzzles in physics, like quantum gravity, for example. So that's exactly what I am trying to do.

So if you show that the many worlds perspective is really, really useful, I mean, arguably it helped lead to the mention of quantum computers with David Deutsch and others. So that's already a useful version of it. But if you can keep showing that it is the most productive way of thinking about quantum mechanics, then people will begin to accept it more. But on the question of experimental findings, you know, that's where you're going to be able to distinguish between many worlds and other competitors, like pilot wave theories or whatever. Well, it's not the only way. I suspect that other versions of quantum mechanics just don't make sense, ultimately. Pilot wave theories or objective collapse theories, I think that they're ultimately ill-defined,

especially in the context of quantum gravity. They always help themselves to some pre-existing classical notion of location and space and things like that, which won't be appropriate once you quantize gravity. So support for those alternatives might just wither away anyway. But I would love to be able to find experimental differences. There are obvious experimental differences between many worlds and objective collapse theories, and those experiments are ongoing. People are looking for evidence of objective collapses. They haven't found any yet, but who knows. eventually, hopefully they will be able to rule out all of the promising models. For pilot wave theories, there is this idea, there's a claim that there are no differences

in the predictions between pilot wave theories and many worlds. I'm a little skeptical of that claim. You know, it's a theorem that you can prove, but like any theorem, there are assumptions that you make that go into that theorem, and I'm a little skeptical of the assumptions. So I would love to develop an actual killer here is the experiment you can do. to distinguish between many worlds and pilot wave theories. But I haven't done it yet, so I'm not sure whether it's possible or not. Now I'm going to group two questions together.

One is from Charles Murrow, and it's a priority question, and he asks, if each semi-classical branch of the wave function instantiates a different real universe within its own space time, it seems that for non-interaction between the branches, both space and time must be emergent from the quantum formalism. But this doesn't seem to be the case. Also, it's hard to understand how decoherence can create. create new space times because it is a dynamical phenomenon that spreads outward in a light

cone within the present space time. So the question is, how is this possible, the dynamical process of decoherence, creating different non-interacting space times? And Paltorek says, can you sketch an outline of how ever-ready in quantum mechanics leads to each branch having its own space time, i.e. one that lacks any curvature that will be due to massive objects in the other branches. So, yeah, I am someone who believes that when you have an Everettian branching of the worlds, each world has its own space time.

And one sort of question that is lurking in the background here is, what do you mean by a space time? So I think there's two different ways you could slice it. You know, and the point of space time is that it has a metric. There's a metric on space time that tells you where the light cones are, what the curvature is, what distances are, All of that stuff, right? That's the geometry of a space time is encoded in the metric. So if you wanted to, you could say there is only one space time, but there are two different metrics, right? So let's imagine you do something like an experiment where, because Don Page has actually done this experiment.

You know, just for fun. He said, you know, let's take a Geiger counter or, you know, let's take some, I don't know exactly what he used, to use some quantum measurement device that can give you two different answers, up or down, left to right or whatever. And if it's one answer, he takes a bowling ball and moves it to the left. And if it's the other answer, he takes a bowling ball, moves it to the right, and then use a Cavendish experiment, which measures the gravitational field of a nearby object to say, you know, did the gravitational field follow the bowling ball? And of course, the answer is that the gravitational field followed the bowling ball,

exactly as it would if the world were just classical, right? And if you thought that somehow the gravitational field of the bowling ball in the other branch of the union, could still be felt in your branch, that should not happen. You should observe a gravitational field that was halfway in between the two bowling balls. Okay? Now, no one expects that to happen, but that would be what you should expect if you think that the force of gravity in one could leak into the other branch. But if you think of it in terms of the metric, the metric defining the curvature of space time, the metric is just another field, just like the electromagnetic field or the electron field or whatever.

So it's conceptually not hard at all to imagine that there are two branches with two different metrics on them, right? And what we would call that is two different space times because space time is defined by what the metric is doing. But it's not that conceptually difficult. So in Charles' question, I think I would like to undo a lot of the assumptions here.

Number one, space and time can be emerging from the quantum formalism. some of us, like myself, have written papers saying exactly that. So I think that that's pretty straightforward. We don't know that it's true in any obvious way, but it's certainly possible, certainly conceivable. I happen to think it's very promising. And then also you say decoherence is a dynamical phenomenon that spreads outward in a light cone within the parent space time.

That's not true either. That is an option that you have in Everardee in quantum mechanics, how to define the splittings of the universe, whether or not you want to localize it inside a light cone, or whether not you just want to say, in some frame that you choose, you describe splitting as happening instantaneously in that reference frame. Either way of doing it is perfectly legitimate, gives all the same experimental predictions, et cetera, et cetera. So branches of the wave function are like, are a higher level immersion phenomenon, okay? They are like entropy or temperature or things like that. They are not something that exists at the fundamental level. They are higher level constructions

that are useful for human beings to talk about. It's human beings who care about the classical limit. It's not the universe that cares about the classical limit. So we can choose, we're given this option in many worlds, to define branching as either being confined to a light cone or being instantaneous. John Eastman asks a priority question. I accelerate charge particle A, causing virtual photons to travel to distant charged particle B, which feels a force proportional to A's acceleration. Is there an inertia-like reaction force acting back on particle A? Could a weak field-gravity analog of this effect explain inertia itself?

I'm sorry, I know there's a priority question, but I think that the words are a little bit too vague for me to understand what is being asked. I don't know what an inertia-like reaction force is supposed to be. It is true that there are radiation reaction forces for all long-range forces, which I guess basically is E and M in gravity. Namely, when you accelerate a particle that has charge or mass, then the field around it responds, and that changes what you might naively think would be the acceleration of the original particle. It doesn't really affect, it doesn't really depend on whether or not there is another particle, charged particle B, far away. This radiation reaction effect can happen just with one particle in the universe. If you have other particles, then there will be other forces going on.

Yes, indeed. However, I would say that none of this explains inertia itself. It's an extra tiny little correction onto the fact that there is inertia. And also, I don't know why you want to explain inertia. inertia is just a fact about the universe. F-equals MA in the Newtonian limit. you know, at some point you say this is how the world works and you don't try to explain it. Or if you really are devoted to explaining an idea, what you really have to do is imagine that the idea was wrong.

Right? So you don't just say, I would like to explain inertia. You say, I would like to compare two different universes, one of which has the notion of inertia in it and one of which does not. These are two different hypothetical universes. And now I will explain why we seem to live in one rather than the other. That is a sensible program to undertake. And I don't think the radiation reaction has any impact on either one of them. Paul Hardy says, I watched a discussion on entanglement, and they suggested that entanglement could be closely related to the creation of space, so space isn't fundamental. Would this mean that our entanglement might play a crucial role with the Big Bang when our universe was created? Yeah, possibly. I mean, as I mentioned, I've written papers on space arising from quantum entanglement, and I did write one paper with collaborators called quantum circuit cosmology,

where we talked about how the expansion of space, you know, in a view where space is an emergent feature of a bunch of entangled quantum degrees of freedom, then what does it mean for space to expand? Well, it means that more degrees of freedom are becoming entangled. So we have this picture where you start with a large number of unentangled cubits or other quantum degrees of freedom, and you have a quantum circuit that describes how those unentangled cubits become entangled with the rest of the world and now become part of space time. And if you play that movie backwards, you reach a point because of the holographic principle. There's only a finite number of cubits in our current universe.

So if the number of cubits is increasing as time goes on, it was decreasing in the past, and you reach a point where there's the first pair of entangled cubits. and it's basically at the beginning of inflation in our picture that we wrote about. So in some sense, it's not the Big Bang. You know, I want to, maybe I should have started this answer by saying that, what do you mean by the Big Bang? The Big Bang, of course, there's a difference between the Big Bang model, which is just a hot, expanding universe that we live in, and that's true.

There's also the Big Bang event, the singularity at the beginning of the cosmos. That doesn't exist. There is no singularity at the beginning of the cosmos, okay? that is a prediction of classical general relativity, but classical general relativity is not right. So it's a stand-in for whatever happened at that moment, okay? It's not a singularity. So in this picture, what happened at that moment,

the first thing that happened in our universe was two qubits became entangled. Now, why did that start? Why did that happen? What happened before that? Were they just unentangled forever or what's going on? All very good questions, none of which we tried to answer in our paper. in that particular paper. I tried to answer them in other papers.

But we don't know. So to your direct question, would this mean entanglement might play a crucial role at the Big Bang? Sure. It's completely possible, but we don't know. This is all very speculative right now.

Anders Hanson says, quantum electrodynamics, QED, is considered to be one of the most accurate theories in the history of science. However, there are opinions about it that it is wrong in different aspects. What is your option and opinion and why? So I'm not sure the sense in which you mean that it is wrong.

It's a little vague to say there are opinions that it is wrong. I'm not quite sure what that refers to. It's clearly wrong in that it's incomplete, right? There are particles other than the ones that are described in QED. Strictly speaking, QED is the theory of photons, electrons, and positrons, and that's it, right? Electrons, anti-electrons, and the photons that give forces between them. That's the original definition of QED. So if you believe there are neutrinos and quarks, if you believe there's the strong interactions and the weak interactions, then QED is wrong.

But really, we don't usually say it's wrong. We say that it's just part of a bigger structure. Electromagnetism has become unified with the weak interactions and the electroweak theory. We also know there are the strong interactions and so on. Maybe all three of those forces are unified in grand unification, but we just don't know right now. There's another sense, a much more subtle and interesting sense, in which QED might be wrong. When we understood finally, you know, it wasn't until the 1970s, we really understood quantum field theory. And part of that understanding was renormalization group flow.

So renormalization has this reputation as being about hiding infinities, okay? And it was originally, that was in the 40s and 50s, the idea that we had infinities in quantum field theory. we had to get rid of them, we renormalize them. But it was understood much better through the work of Wilson and previously Gelman and Lowe and Katanov and others in the 60s and 70s, where we understood the renormalization

is really a way of looking at physics at different scales, including the effects of different processes at different energy and time and length scales. So what Wilson in particular was able to show is that you can take a quantum field theory and cut it off. you can say, I'm just not going to include effects above a certain energy scale.

And because energy is inversely proportional to length, that's like I'm not including effects below a certain wavelength. And you might say, well, who chooses that wavelength? That sounds important. You're just arbitrarily cutting off your quantum field theory. And the renormalization group is a way of dealing with that of saying, I can choose whatever cut off I want to not include a product. processes at very high energies, and by letting the other parameters of my theory change with respect to that cutoff, so the mass of the electron and the charges of different particles, all these

things depend on the cutoff. I can make everything vary together in such a way that my low energy predictions remain unchanged. That's the renormalization group. So when we finally figured out that there was a feature of QCD of the strong interactions, which is that it is asymptotically free, that at higher energies, the interaction becomes weaker and weaker. That was good. That made QCD our best defined theory of fundamental physics, because all of the problematic aspects of of any quantum field theory, the problematic aspects are always at high energies. And in QCD, UCD, the interactions turn off at high energy, so it's really not problematic at all. QED is not perfectly well defined at high energies, and there is, in fact, a very subtle kind of

blowing up singularity called the Landau Pole of QED, and it's very, very much higher energy than the plank scale. It's not anything you have to worry about in practice, but it is a sign that you can't just take QED and extend it to arbitrarily high energies or short wavelengths. Maybe that is what was meant by QED being wrong. You can cure that by embedding QED in a bigger framework. I don't think the standard model is sufficient because there's still that U1 in SU3 cross-SU2 cross-U1. That U1 is basically an electromagnetism-like theory. But if you embed it in a grand unified gauge group, then you can solve that land-up pole problem. So QED is certainly right for describing what goes on in computers and in your biology, even if it's not right at these super-duper high energies.

Saykar Rabbala says, it is fair to say that you are quite successful outside of physics and academia, that you think of quitting academia and research before you moved to Johns Hopkins University. Is your motivation and drive to do physics academia research the same say as it was 10 years ago? Yeah, I thought about quitting academia,

but I'd not thought about quitting research. Research is the thing that makes me the happiest. It keeps me the most intellectually engaged, and I have a million ideas of things I want to do, research-wise. So if anything, The drive to do research is higher now than it was 10 or 20 years ago. I mean, I always sort of abstractly loved doing research and thinking about the universe. But I think now I have a much better idea than I did decades ago about where the interesting questions are and how I can make progress answering them.

So if I was going to leave academia, it was so that I could do more research and the research of the kind that I precisely wanted. The reason why I'm going to Hopkins, other than the fact that they offered me the job, was because it's a job that is suited to let me do that, to let me do exactly the kind of research I want to do with the people I want to do it with, et cetera. So it's worked out very, very well that way. I'm not going to stop doing the non-academic stuff. That'll still go on. Tyler Whitmer says, you're really good at remembering former guests and cross-referencing

them on the fly when topics overlap with your current guest. Do you have a cheat sheet or something or just a really good memory? I think that I neither, I certainly don't have a cheat-eat, and I don't have a good memory either. In fact, I think it's the opposite. It's interesting that it is often the case that I don't remember interesting tidbits of former podcasts because while I'm podcasting, while I'm, you know, the questioner live there with the guest, I'm thinking about what question comes next. Did I hit the record button? How is the sound quality? How much time is left? All of these things, right? And, and, And I try to make it also seem like a real conversation. Like I'm not just listing, I don't have a prelisted set of questions to ask. I'm trying to respond mostly to what the person just said. There's some talking points that I want to reach. There's some things I want to get to.

So I might sometimes change the topic for that reason. But usually I'm just trying to actually act like it's a conversation and ask questions. But of course, I do some preparation for each episode, which involves, you know, reading or listening or whatever. and while doing that, I might be reminded of previous podcasts. The thing is that for a podcast like this, I'm the one inviting the guests, right? I mean, that's the difference between this and a talk show on radio or TV, where someone books the guests and some different person asks them the questions. So if I'm inviting someone on the podcast, it's because I'm interested in what they have to say

for some pre-existing reason. So I'm not just, you know, thinking, well, this is the question I'm supposed to ask. I'm thinking, this is the issue I want the answer to. And often those are connected with previous podcasts that I often also had issues I wanted the answer to. So to me, it all does kind of fit together in a way. So it's not a matter of having a really good memory. It's a matter of having reasons why previous guests were there and relating them to what the current guest is saying. Jason Worell asks, is the bigger motive for physics mainly to comprehend the place of humanity in the vast cosmos?

or is it mainly to advance the place of humanity in the vast cosmos? I don't think that there is a bigger motive, honestly. I'm not sure that that's a competition that there's going to win. Different physicists will have different reasons, and different people will have different reasons. My own interest is mostly in understanding, in comprehending the cosmos. I'm very interested in advancing the place of humanity, making the world a better place, both here on Earth and in the cosmos.

but I do have this conviction, two convictions. Number one, that advancing humanity is easier when you understand the world in which you live. And number two, there should be an ecosystem, a balance between people who are purely trying to make things better in advance humanity and people who are trying to lay the groundwork for doing that in a more comprehensive way down the road. I think that my skill set of my interests are more aligned with the understanding big picture kinds of questions than with advancing this process. particular local issue right now. Jeff B. says, occasionally when I study physics, I can feel my woo-woo side, longing to break free. As much as I want to understand the truth of the universe,

another part of me wishes that we live in a world with angels, demons, and gods that play tricks. Do you ever have this wish? Are you ever able to satisfy it through fiction? Well, you know, I did have that wish when I was younger, and I was very much interested in science fiction and fantasy and movies and comic books and things like that. And even, you know, it strikes me now that comic book characters are movie stars, that the comic book characters that I liked when I was a kid in comic book age were the ones who were most supernatural in some sense, the most cosmic, the most spooky.

Doctor Strange, Green Lantern, Thor were much more interesting to me than Batman and Superman and Spider-Man ever were. So, and I think the same thing, you know, remains true, except now that I know that it is purely through fiction. You know, when I was a kid, I was very interested in parapsychology and ESP and telekinesis and UFOs and all that stuff. Now I know more about the world. I think that the chances that any of that are real are very, very tiny. And so that's okay. I'm very happy to tickle that itch, scratch that itch. You don't want tickle an itch to scratch that itch through fiction of various sorts. And by the way,

I just realized I said, comic book reading age, what I meant by my mind. what I meant by that was my comic book reading age. People of all ages are very, very welcome to read comic books. I still do it myself sometimes as an indulgence. But when I was a kid, I was into it and I knew what was going on. These days I had no idea what's going on in comic book land. Speaker Ukraine says, to explain science to people, scientists often dumb it down using approximations and analogies. People take these simplifications at face value and build crazy theories around them, arriving to crazy or at least false conclusions. How would you dissuade any conspiracy theorists of their being wrong. Sometimes you have to challenge them anyway as they are

decision makers or influencers, et cetera. Well, I think there's two things that are being smushed together here that maybe I'm not quite willing to smush together. Yes, scientists absolutely simplify. They use approximations and analogies. And yes, it is absolutely a danger that people can listen and hear the analogy perfectly, but then presume that parts of the analogies, that weren't meant to be taken seriously, should be taken seriously, and therefore end up misunderstanding some delicate, nuanced scientific point. That is absolutely a danger. I think that it is something where that's something that people have to watch out for, because scientists know when they're using an analogy, which parts of the analogy are real and which parts are not,

the person listening might not know that. That's why I am very much against things like the balloon analogy for the expanding universe, right? Because we know as scientists that there's no inside the balloon or outside the balloon. There's just the surface of the balloon. But the people who you're showing that analogy to have trouble appreciating what that really means. So I just don't use it. I just use like expanding raisin bread or something, something where it's three-dimensional from the start. The other thing you're asking about are like conspiracy theorists and decision-makers. And I do not think that people become conspiracy theorists because they listen to scientists, explain things, and take the simplifications to literally. I don't think that's why. you become a conspiracy theorist. I don't know. I don't have a fully fledged out theory of why people do become conspiracy theorists. I encourage everyone to listen to the podcast with T. Wen, who really has a wonderful theory of the valorization of clarity. You know, conspiracy theorists like the fact that their conspiracy provides an answer to everything, and it provides an answer that is crisp and clear and immediately understandable and black and white and rigorous.

And the world is not. The world is a mess. The world has things we don't understand, et cetera. And so a real correct understanding of the world is less complete than a good conspiracy is. And I don't know the way to talk conspiracy theorists out of their conspiracy theorizing. But one thing to point out is you have to be willing to accept ambiguity and uncertainty in your decision in your picture of the world. And also the other thing to point out is one problem. with conspiracies is that they often don't really think through how they were going to happen. They sort of imagine actors with infinite superpowers pushing things around out there in the world, whereas really it's people, you know, all these people with their own flaws and their own hopes and their own ways of working, and there's some collective emergent behavior that comes out of all of that. And it's very hard to imagine a small cabal of ultra-powerful people pushing around the world. in any realistic kind of way.

I don't know if pointing that out actually changes the minds of any conspiracy theorist, but I think that's a real reason to not be a conspiracy theorist yourself. De Pankar Bose says, In our universe, all matter and thus all life forms, including us, are made up the first generation of particles in the standard model.

That is to say, this is me now talking. Electrons, electron neutrinos, up quarks, and down quarks. And, of course, the up and downs make protons and neutrons. So that's the first generation of particles. The next generation is muons and their neutrinos, charmed in strange quarks. The third generation is tau's and their neutrinos, top and bottom quarks. And all those heavier particles just decay away, leaving us with the first generation. So anyway, resuming the question, I was trying to imagine some other universe that has matter

and life made of entirely of particles from the second or third generation. Is this possible? Or does the question not even make sense because the standard model only applies to our universe? Well, no, I think the question makes sense. No, sorry, I don't think the question makes sense, but not because the standard model only applies to our universe. I think it's perfectly sensible to ask if we didn't have the standard model, but something like it but slightly different,

how would the universe be different? That's a perfectly sensible, counterfactual question to ask. The problem is that by definition, the second and third generation is made of the heavier particles, right? So very similarly to if we define the past, to be the direction which entropy was lower, ex post facto, we define the first generation of particles to be the particles that are the lightest. And it's just a feature of quantum field theory that heavy particles decay into light ones. Why do they do that? Ultimately, it's because entropy

increases. Because when a heavy particle decays into light particles, it decays into several particles, right? One particle cannot decay into one particle if the two particles had different masses without conserving energy. So when the neutron decays, for example, it decays into a proton plus an electron, a neutrino and an antineutrino. So there's more particles and therefore more entropy. You can imagine a process by which several particles come together, several light particles come together to make a heavier one, but that would decrease the entropy of the universe because there would be fewer particles. Sometimes it happens, but the overall tendency is for heavier to decay into light. So anyway, the answer is, in whatever universe you're in, if that universe obeys the laws of quantum field theory and has an ordinary arrow of time, you're going to make whatever matter you have out of the stable light particles.

So if you think about it, I talked about this in the biggest ideas in the universe in the video about either atom. I think it's atoms, that video. Basically, all the particles, there's many, many, many particles in the standard model, they're all produced in the early universe, but they all decay until you hit the last. lightest set of particles that contain some conserved quantity. So neutrinos are just the lightest particles, period, the lightest particles with the lightest fermions, okay? Let's put it that way. Massless particles, like photons are, of course, lighter, but you can't turn a fermion into a boson. Electrons are the lightest particles with charge, protons are the lightest particles with barion number, and so forth. Neutrons are not the lightest particles with anything, but neutrons are also not stable. They decay.

When you combine neutrons with protons, you can make metastable nuclei. That's what atoms are made out of. Jim Murphy says, were you a gifted student in grade school, and do you think that the U.S. school system does a good job, good enough job, at helping these students reach their full potential? I was, I was a gifted student. I was in the gifted classes. In fact, I was a student when that idea of having gifted classes first came into existence. I remember very vividly that when the idea first happened,

in my local Pennsylvania public school system, they had no idea what to do. And we kind of did arts and crafts for a year as gifted students. But eventually, it just turned into, you know, advanced courses in the same kind of thing. We had, you know, gifted English, gifted math, or whatever. It was sort of a, they, in principle, you know, why the letter of the law did what the mandate said to do, but it wasn't anything special. Do they do a good enough job at helping these students reach their full potential? No, of course not.

But the same thing is true for not gifted students or for average students or for any students. The U.S. system, as I know it, does not do a good enough job at helping students reach their full potential. And different, so I don't think of it in terms of, you know, gifted versus non-gifted. All students are different and we can't invent a new educational system anew for each student. Therefore, it will always be the case that whatever the system is, is going to make compromises to try to optimize teaching as many students as it can as well as it can. So some students are going to not get as much out of that as other students, and that's a shame, and we should try to do it better.

I don't think any students are fully served by the current system, especially because some students will have secret talents, right? We'll be very bad at taking whatever standardized test you're using, but really good at something else, and the system is not built to really find those talents and encourage them. It sort of bulldozes you into a certain way of being, which is not the ideal thing. I don't know how to fix it either, though. So, you know, there's one thing to complain about it.

There's another thing to try to make it better. Brandon Lewis says, what is your favorite subset of mathematical notation? And what is the least? And how is the notation you use regularly evolved over the course of your career? This is a funny question, but that's why I took it because I had not really thought about it. The short answer for favorite mathematical notation is tensor notation in general relativity. And I've always had like a pet theory for why it is so good, namely that general relativity was kind of useless for a long time. Einstein invented it in 1915, and it didn't really become

heavily used in astrophysics until relatively recently. You know, the number of Nobel Prize is that lean heavily on general relativity was very tiny. It was like one before the year 1980, and it's like half of them in the most recent 10 or 15 years. So general relativity has finally become really, really important. So basically, again, pet theory, I have no idea if this is true or not. I think that the physicists who did care about general relativity during the early days had enough time to like really make a notation really good and agree on what they, what they said. Whereas in quantum mechanics and quantum field theory, they were so busy leaping to the next puzzle and trying to solve it that they never had good time to figure out.

what the good notation was. So that is my story. I'm not necessarily sticking to it, but that's what I think is true. Richard Graff says, in your podcast with Nicole Younger-Helper on Quantum Steampunk Thermodynamics, she described how information could perform work. Compared to a classical example, like a spark fuel moving a piston, the steampunk example appears less direct. It's not so much the knowledge that moves the weight as what the experimenter does with that knowledge. And the effort required of the experimenter requires additional work input that seems more directly tied to the weight movement than the knowledge does. Have I tangled myself up into much nuance here? And if so, can you help untangle and clarify? Well, I can try to explain what is going on.

So in some sense, I don't think, let's put it this way. Information and its role in physics is both a very old topic and a hot new topic. Like we've always known that there was a relationship there, but people are really becoming more and more impressed with how important that relationship is. But we haven't yet settled on the once and for all cleanest, clearest, best way of both explaining what that relationship is and putting it to work. So this means both that sometimes we miss the importance of information and other times we exaggerate the importance of information. So people will often say, and I think I probably said, that you can use information to do work. What does that mean? So the typical example is you have a piston, on one side of the piston, you have some fuel, you spark it, it expands and heats because of combustion and it pushes the piston.

That's the standard thing to do. What Richard is referring to is the idea that if I have just one particle inside a box and the particles moving around, right? So it has a lot of velocity, but it's bouncing around in different ways. if I don't know where the particle is, I can't do anything with that. There's no way, if I put a divider in the box, half the time the divider will move to the left, half the time will move to the right. If I do that many, many, many times, it will do a random walk, and that's not doing a lot of work, okay?

It's doing very, very little. Whereas, if I have the information of knowing exactly where the particle is and how it's moving, then I can wait to put the divider in at exactly the right time so that I know the particle will bump into the divider and move it in the direction I want to move it. Okay, so if I know that for many, many particles, I can do that many, many times and coherently add all of those pushes

because I had that extra information. I'm basically being Maxwell's demon in this case. I'm extracting work from a high entropy set of particles because I have information about it. So people say, look, in some sense, information is doing the work. Clearly, it's not doing the work. What's doing the work is the particle, bumping into your divider. But information enables you to do that work. Now, if I were a little bit cynical, I would say, look, information also enabled you to do the work when you burn the fuel in the regular piston, because you knew the fuel was in a low entropy state where you could release some of that free energy by sparking it. Okay. So it's always information in some sense that is allowing you to do the manipulations. that extracts work from a physical system. And it's always the physical system that is actually doing the work. But there is a an interplay here. Knowing more information lets you do more work, lets you do more interesting things. That is perfectly clear. So what, again, we want to be able to do is to say once and for all what that relationship is in a clear, crisp way. We're not quite there yet, but it's not wrong to say that knowing that information is helping you do a little bit of work. Lewis B says, one of my favorite parts of listening to you and other scientists is the quickness and freeness with which you will admit you don't know or we don't know something. I've even heard you say we have lots of ideas but you don't have high credence in any of them. That said, are there some places, e.g., many worlds, where you do seem to assign relatively high credence. I wonder what differentiates these for you. What about these ideas capture you? Well, that's complicated, but there's many things. You know, it's based. It's

for whatever sets of reasons, I'm assigning high credence because of some combination of priors and likelihoods and data that comes in, right? So I have a high prior as a scientist on a simple explanatory theory. That's one reason why many worlds is one of my favorite theories. But then I will modify that credence based on the data that comes in and I learn more things about it. So the only reason why people switch from classical mechanics to quantum mechanics was because they were forced to do so by an overwhelming amount of data. And some things we just don't have the data. So, you know, my favorite example is always dark matter.

I think we have very good data that says there is dark matter. And we have very good data that tells us certain properties of the dark matter, that it is cold, there has a certain density, that has a certain distribution through the universe. We have essentially no data about what it is within that set of properties. There are many different kinds of particles you could imagine that would be cold, that would be dark, et cetera. So we don't know whether it's axions or wimps or something else. So it makes perfect sense to me to have high credence that there is dark matter and low credence that the dark matter is axions, etc. Right?

I don't think it's any more deep than that. But maybe what you're referring to is the idea that sometimes people do have very different credences, even when there's no data. So let's still think about axions versus wimps as dark matter candidates. For a long time, wimps were the leading candidate to be the dark matter, wimps being weakly interacting massive particles. And axions were like the second leading candidate. And there were many, many other candidates. But people didn't give equal credence to every candidate.

They liked some better than others. Why do you do that if the data do not distinguish? Well, the answer is that some of those theories fit well with other, ideas, some of those theories are more explanatory than others. So WIMPs are extremely popular because they fit perfectly well with many other ideas about physics beyond the standard model. Supersymmetry is an idea, but extra dimensions, strong coupling, there's a whole bunch of ideas for physics beyond the standard model that would naturally lead you to a weekly interacting massive particle. And there's even what is called the WIMP miracle, that if you ask if you have

a particle that was in thermal equilibrium in the early universe, and eventually it stopped annihilating and sort of froze in, what would the interaction strength have to be for that to happen? And roughly speaking, the answer is the weak interactions of particle physics. So that was sort of a miracle that gave people more credence that this theory was on the right track. So it fit in with other ideas. Axions likewise were not predicted. They were not invented to be the dark matter. Axions are a hypothetical particle that were invented. I mean, the original idea came from Pache and Quinn, Pache and Helen Quinn, when they were trying to solve a problem in quantum field theory called the strong CP problem. CP is a potential symmetry of particle physics, which unlike many times

in particle physics, you think that there should be a symmetry and you find that it's broken. In the case of CP, what we found was that the strong interactions should break it, but they don't. That's that sort of the opposite kind of problem. And so Pache and Quinn invented a mechanism that explained how you could add one extra field, and you could explain why CP was not broken by the strong interactions. And then both Frank Wilczek, former Minescape guest, and Stephen Weinberg, pointed out that the Pachequin mechanism predicted the existence of a new particle. And people were very optimistic. They would find the particle because it was very easily findable. They did not find it. So they did, you know, the next sensible thing. They expanded their parameter space a little

bit, right? And they said, well, okay, maybe let's be less choosy about what symmetry breaking scale is involved with this particle. And once they did that, they realized, oh, if we pick the symmetry breaking scale appropriately, we can get a dark matter candidate, and the axiom could be the dark matter. And so that's a pretty good dark matter candidate, because it's a particle that was invented for a completely different reason, but it's not perfectly good because you have to, like, make up this energy scale to fit the data, whereas with WIMPS, the energy scale just comes along for free. But at least it was not invented to be the dark matter. And other candidates for dark matter were just invented to be the dark matter, right? They were not even trying

to solve any other problems. So you see that there is kind of a hierarchy of how the idea fits in with other ideas and whether it's solving problems or creating them and so forth. And these are all perfectly good reasons to have high or low credence in different ideas before the data come in and decide the question once and for all. Brian Charlebois. says, first-time question asker here, and since you want to write a book on democracy, I'm calling this a priority question. Do you wish or hope for some form of direct democracy to exist worldwide in the next thousand or 10,000 years? No, I have zero hope for direct democracy to exist ever in any group of people, more than like 20 people. Because as we talked

about before. Direct democracy is the idea that issues that come up before the nation or the state or whatever group of people you're talking about, every person votes on every individual issue, as opposed to representative democracy, where you vote for a representative and the representatives have the job of really devoting their lives to understanding these issues and deciding what to do. That latter system just seems much better to me. It's still democracy. It's still people voting and the authority and the authenticity. What is the word I'm looking for? I don't know. I'm losing the word. But the justification for the power being held by these representatives is that the people vote for them. That's the essence of democracy. It's the people's will that is giving government its legitimacy.

But representative democracy is just infinitely more sensible for any system that is even a little bit complicated. And the modern world is extremely, extremely complicated. So the idea of ruling the world by direct democracy seems crazy pants to me. In fact, if you're interested, you can go back to the podcast I did with Edward Watts about the fall of the Roman Republic. The Roman Republic fell, and we talked about why that happened. But first, the question is, I mean, not the question, but the point that should be appreciated is the Roman Republic lasted for 500 years and was very, very, very successful over those 500 years before it eventually collapsed. So that's a pretty good run. And there is a very clear comparison to be done between the Roman Republic and Greek democracy, because the Greeks

were often much more invested, the Athenians, I should say, in direct democracy, where you would vote on everything. And it led to complete chaos because, you know, you would vote to send out the naval fleet, then a week later you would vote to bring it back. And it was not a good way to run a country. And so the Romans kind of were much more successful because they voted for representatives and the representatives did the work. Representatives, if they're good, of course, you can always question whether or not you're having a system that elects good representatives, but if they're good, they will be much more able to understand the complexities of the world and guide the country through them. Huberto Nani says, may you please comment about your favorite places on the internet? I'll go first,

all the nooks of preposterousuniverse.com. So thank you, Umberto. I don't really have a great answer to this. I just wanted to give Umberto a chance to advertise my website, preposterous universe.com. So there are a lot of things. There are a lot of nooks and crannies on the website that you can spend hours of fun reading and watching videos and things like that.

But, you know, other favorite places on the internet, look, my internet use is not that sophisticated in some sense. I'm on the internet all the time, but I use it for email. I still use Feedly to read blogs. If you're a long-time listener, you remember Neha Narula, one of the very first podcasts I did talked about cryptocurrency. And we talked about the different ways that people use the Internet. And I said that I still read blogs using a feed reader. And she was kind of shocked and appalled that there are still people who do that.

So I still do that. I'm on Twitter, YouTube, Imager for just wasting my time or Reddit or whatever. I often lurk on the Sixers subreddit, much more interesting than the physics subredits to me, et cetera, but nothing very profound. I don't have any special places that you haven't heard of that I would go recommending, to be honest, sorry. Niccolo Musmesi says, regarding Bayesianism, you've often argued that the potentially subjective nature of priors is not an issue, and I agree with that.

But what about the fact that often we can't list all possible priors in the first place? Like, for example, in theoretical physics, this is precisely the case, since listing all possible priors would imply coming up with all the possible theories before being able to update from evidence. Doesn't this issue limit the application of Bayesianism to less speculative settings? Yeah, I think that this is a very important issue. I mean, I wouldn't put it exactly in the words that you put it in, because any good Bayesian, especially when you're doing something like theoretical physics, and let's say you're trying to explain the dark matter, right, like we were just talking about, you have different credences on different theories. But you should

put a certain amount of credence on the set of theories I haven't. explicitly listed. The set of ideas I haven't come up with yet, right? I mean, that's obviously always an open possibility. So that's easy to say. Like, that's not, that's not the problem. There should be some credence on stuff you haven't thought of yet. That's easy. The problem is that the whole point of Bayesianism is that not only you have those priors, but then you update them when new data comes in. And you update them on the basis of these likelihood functions. You say, well, if this theory is right, how likely is it that I would have gotten that data? That's easy to do when you have a theory, but that's very hard to do when the proposition

you're talking about is, I don't yet have a theory, right? In the space of all theories, I haven't yet invented, what is the chance I would see this data? That's really hard to specifically say. So I don't, you know, in practice, you can very often get around this, but, well, you can think you get around it, but it's not perfectly clear at a principled, rigorous level that you're making sense. So we saw this at the very beginning of this AMA with aliens in the solar system, right? You need to ask yourself, what is the likelihood that aliens in a solar system would act in a certain way? And so you say, you fool yourself into thinking, I have a theory called aliens in the solar system. But that theory is not very specific. What kind of aliens? How long

have they been there? Are they aggressive? Are they, you know, made of biological materials? You know, there's a million things that you haven't answered. And therefore, it is a lot of. It is, difficult to answer questions about what the likelihoods are. And I do think that that is an issue for Bayesian reasoning. And I'm sure people have debated it to death in the depths of the Bayesian literature, and I don't myself really know what the answer is. I would like to know more. Anyone out there who has some ideas or knows some literature about that, that would be fun to read. Oleg Rovinsky says, I am an Israeli who was born in Ukraine, so I've been following the war very closely, and it made me reconsider what I thought about the severity of our conflict in

comparison to the scale of what happens in Ukraine. I wonder whether you had similar thoughts about the severity of U.S. internal political conflict and the threat it poses to U.S. democracy in comparison to the gradual slide over the years of Russia into totalitarianism. Do you still think U.S. democracy is going through a severe existential crisis? Well, yeah, I do, but I mean this is a good set of issues to be thinking about. For one thing, one correction, I'm I don't think there's any gradual slide of Russia into totalitarianism. Russia was part of the Soviet Union, which was totalitarian from the start, okay? I would say that there was a brief moment when maybe in some sense Russia was trying to be democratic, okay?

But there was never a time, you know, to me that you know that your democracy is working when the ruling political party tries to win but loses and hence over power. And as far as I know, that's never happened in Russia. You know, you have to be able to lose and you have to be able to hand over power when you lose in a peaceful transition. That's what really makes you democracy, not the voting part. Okay. And so I think it's a very different situation from the start comparing the U.S. to Russia. I mean, there's no one-to-one comparison. They come from very different historical trajectories. Having said all that, the U.S. is a much healthier democracy right now. It's been around a long time. It has established institutions. And therefore, it is not the same kind of worry that you have in China or Russia or other places that have a totalitarian history. That doesn't mean there's no worries, though.

We just talked about the fall of the Roman Republic. It lasted 500 years and then became an empire, a dictatorship, right? And the U.S. could do the same thing. And maybe every single year, the chance is small, but there's an accumulated effect. And the effect, you know, the result of losing democracy in the U.S. is enormous for not only the U.S. but the world. Part of why I worry about the U.S. is because I live here. This is my country. And so I can, I have some voice here in a way that I think that other people should have voices in their countries. But also, you know, it's not just you say there's some chance that democracy could fail per year and it's small. You say, well, how is this year different than last year or 10 or 20 years ago? And I think that there are many, many objectively true facts about the current situation that make it clear that democracy is more fragile right now than it used to be.

You know, I just said that the real test of democracy is a peaceful transfer of power and we just had a major political party that tried not to hand over power. And rather than those people being thrown in jail, they're still in the government. They are still trying to be a ruling political party. And we're trying to treat it as business as usual, right? just politics, people disagree with each other, blah, blah, blah. I don't think it is business as usual. I think it is a true undermining of legitimacy of democracy. And even though it's not nearly as bad, the Democrats have another problem with democracy, namely that they look at what Republicans are doing and they cease to think of Republicans as partners in the Democratic project. They think that they're not really legitimate people in the system anymore. And the whole point of democracy is you have to work with the people, you don't agree with. And I think that's breaking down. And that breakdown of the ability to work with the people you don't agree with might ultimately be much more important to the failure of democracy in the U.S. than anyone's politicians attempts to seize power or change their vote outcomes or

anything like that. You need buy-in. You can only have a successful democracy if everyone in the country wants to be in a successful democracy. I think that is evaporating in the United States. That's a huge crisis. And I can't say too much about what a big problem. problem, that is, in my view. Tomas Sedevich says, are there plans for audiobook versions of the biggest ideas books? I've thoroughly enjoyed the previous ones, but the equations would likely make that difficult. Could this be solved by a supplemental PDF or something similar? There will be audiobook versions, yes. I'm not exactly sure how we're going to solve the obvious problems here. There usually are PDF supplements for figures in books. There's many more figures

in the biggest ideas books than there were in previous books because it's more, you know, I have a lot of graphs and things like that, as well as the ordinary, you know, illustrations. So what I tentatively think is that there will be an audiobook and I will narrate it, but it won't be an exact translation. In other words, when I did my other audiobooks, they're very fussy, the producers of the audiobooks. You need to say exactly every word, no more or no less than what was in the book. I can easily read the equation out loud. That I can do, no problem. But figures are a little bit harder, and sometimes the meaningfulness of the equation is a little bit less clear if you can't

stare at it with your eyeballs. So what I would like to do is negotiate an ability to improvise a little bit while reading the book and be a little bit more wordy and explanatory about what's going on in the figures and the equations rather than just reading it word for word. I have no idea whether the, you know, I don't make the audiobook. I read it, but there's a company that produces and sells them. And so I have to see what they think. I will, I will try to do that, but we'll have to see. So there can't be really a supplemental PDF with equations because that would just be the book. That would just be by the book, which I encourage you to do, the hard copy of the book, even if you get the audiobook, I still encourage you to get a hard copy exactly because

these are deep, difficult ideas, and you're going to want to look back at the, at the, at the paper and say, oh, yes, I see. I mean, either hard copy or, you know, e-book version. That's, that's okay. There will definitely be an e-book version. And again, we'll try our best to make sure the e-book version has the equations presented correctly, et cetera. But when I say we, it's not me. People always come to me and like, you know, this equation was typeset badly in your book. Like, I don't do that. They don't even ask my input about that. So you have to talk to the company that makes the books. Okay, I'm going to group two questions together. One is from who says, do you think there's value in making the basic math of physical theories more constructive

slash computational? Right now, a lot of it builds on things like the real numbers. Their whole existence is not proven constructively, and only an infinitesimal fraction of them are computable. This seems like a bit shaky as a foundation. And then Rollo Burgess says, this is a question I've been thinking about since coming across an observation in Scott Aronson's book, Quantum Computing since Democritus. Basically, mathematically, the set of computable numbers is a subset of the reels of measure zero. This means that if the universe is continuous, almost none of its states can never precisely be calculated using any set of physical laws. The laws must be continuous, but our calculation procedures can only yield computable answers. Erringson thinks this point

makes it seem likely the universe isn't truly continuous in a mathematical sense. Do you think this kind of point is potentially sound or flawed in some way, and if the latter why? Well, I don't know. So both questions are asking, you know, are our difficulties of various forms in coping with the continuum, the real numbers, right? That particular uncountable infinity of numbers that we have in the real numbers. Every theory of physics that is very successful right now is based on continuum numbers. Quantum mechanics, classical mechanics, relativity, whatever you want, quantum field theory, etc. real numbers or complex numbers or the equivalents, vector spaces, manifolds, these all are smooth, continuous things. There are problems both conceptually and in the foundations of math with dealing with these things. And therefore, it's very natural to wonder, you know, maybe nature doesn't actually use that. Maybe it's just that we approximate it that way because there's some

discreetness or granularity or something like that, but it's too small for us to see. So, I I don't know. I don't have strong feelings about this. I think that one thing that I would emphasize is that our difficulties don't matter to the world. Our difficulties in calculating some state that the universe is in or our difficulties in understanding the definition of the continuum or the continuum hypothesis, etc. Nature doesn't care about any of these things. So the only motivation for me would be is if you could really show the continuum, theories were just incoherent, right?

We're just impossible. If they're possible, then nature can do it. And maybe that's true. I don't know, one way or the other. It certainly would be easier in a lot of ways if nature were not continuous. And by the way,

one thing to emphasize very strongly here is that the opposite of continuous is not living on some kind of lattice. The simplest way to take the world and make it discreet is to literally take the smooth, space time around us and map it onto a set of points, a lattice of points in space and time. There's very good reason to think that that is not how the universe works. There's no length scale,

like the plank length with little bits connected point by point. Quantum mechanics just doesn't work that way. And certainly holography and black hole information, et cetera, do not work that way. But there still could be some kind of discrete, countable structure underlying everything. So I'm very open to people who think that, but it's a challenge because quantum mechanics isn't that. The Schrodinger equation is defined on a vector space, which involves smooth evolution. So you are potentially changing quantum mechanics. And I do have ideas about this, by the way, but let's be honest, there is no empirical motivation. There's no data that says we should change quantum mechanics right now.

Andrew Harris asks a priority question. Isaac Newton was no doubt a very clever intellect. If you could magically revive him and he was your student, how long do you think it would take him to get up to speed with current day physics? What would be the main obstacles you as his tutor face in accomplishing this task? Yeah, Einstein, or Einstein, I said, Newton, he was very smart. He invented calculus. So he would be fine, I think, in the modern world.

It would absolutely take him time to come up to speed. You know, roughly speaking, if you just did the dumbest thing in the world and said, given Newton's knowledge of the world, how would he correspond to a modern-day physics student? And roughly, it's some kind of first-year undergraduate, right? Because first-year undergraduates learn Newtonian mechanics and calculus, and he invented those things. Now, admittedly, we have slightly better notation, and we have slightly better concepts. Like, he never talked about energy, for example. That was not something that he understood very well.

certainly didn't talk about vectors. That's something they didn't know about at all. But by the second half of your first year student studies, as a physics student, you're learning about electromagnetism, which he certainly didn't know about. And in your second year, you're onto relativity in quantum mechanics and things like that. So roughly speaking, he's a first year undergrad, give him three years to catch up on the undergrad stuff, two more years in grad school, and he's a working modern physicist. But I suspect that he's a better. than average working modern physicist. So let's give him four years overall, three or four years to catch up. If you really devoted yourself to doing nothing but learning physics, which maybe Newton would do, make it one or two years. But it's something like that, something roughly. He was very, very smart, but he was not superhuman. He was not an alien, and he needs to learn the notation and do the problems. That's just like everybody else. I don't think there would be any deep conceptual issues. He would have to unlearn some cherished beliefs that people had in the 1600s about the nature of reality. But, I mean, that was what made him very good, is I bet he

could relearn that stuff pretty quickly. Crather-Luca says, how do you believe a person should weigh their feelings versus rationality in decision-making? Emotions are usually so random and unreliable, yet a life trying to avoid passion barely seems like a life worth living. So, I don't think that there is any weighing between feelings versus rationality. I think they do two totally different things. It's like saying, which is more important in driving a car, pushing down the gas pedal or turning on the ignition key? You need to do both.

Likewise, your feelings, and David Hume was very clear about this. Reason is and always should be the slave of the passions. What he meant was passions tell us. what we want. Reason tells us how to get it. Those are compatible operations. Those are not incompatible operations. I think it's a mistake to say that, you know, acting passionately and emotionally is somehow the opposite of acting rationally. You can let some subset of your passions override your rationality and get in trouble that way and find out that ultimately your passions are being undermined because you were not rational enough. So my philosophy

is absolutely 100% that what you should do is not weigh one versus the other, but let your emotions and your cognition work together rather than work against each other. Cooper says, the question why is there something rather than nothing, appears to presuppose that nothing is a more natural state than something, and thus the presence of something demands explanation. I'm not sure why that should be, as the concept of true nothingness is difficult for me to philosophically wrap my head around. Do you have any thoughts on the matter? Yes, I have thoughts, you can read them. On the internet, you can Google, why is there something rather than nothing and my name, and you will find a paper that I wrote with exactly that title. It appears

in some Rutledge companion book, you know, major, I forget the name of the book, but it's like, you know, current controversies in physics or the Rutledge companion to the philosophy of science or something like that. It was an invited chapter. And I wrote about, why is there something rather than nothing? And you're right. The language steers us a little bit wrong. I wouldn't say that asking why is there something rather than nothing necessarily presupposes that nothing is more natural state. I mean, maybe there is no natural state, but there are alternatives. You know, there could have been something or there could have been nothing, and maybe there's some reason why. But honestly, what I ultimately come down to say is there probably isn't a reason why there is something rather than nothing, because there isn't really such an alternative.

What does it mean to say there could have been nothing? nothing is not something that can be. Nothing is not a state of existence. It is a state that nothing exists, right? So I think that the most likely thing is that this is not a question that has some answer that it will satisfy everyone. It's just a question we are tricked into asking because of the way that we talk, not because of the way the explanatory matrix of the universe is actually arranged. Okay, the very last question for this AMA comes from Emmett,

who says, have you thought about doing a live Mindscape episode, perhaps a Zoom session that patrons could attend and submit questions to the chat? It could be a fun experiment and a good way to get together with this highly diverse group of Mindscape patrons. I'm sure some of us would be willing to help facilitate if that would be of interest. You know, I've thought about lots of things, including things like that. I've thought about, you know, having a live event with former guests. I've thought about bringing old guests back on to, you know, talk to each other rather than just talk. to me. I've talked about having a live call and event like you're talking about. And there's two things that prevent me from doing it right now. Number one, it seems like work. Even if the actual event

isn't work, it had to put a lot of thought into how to do it right. And that's work. And there's lots of ways to do it wrong. So it does require some thought and some arrangement. And the other is, like, I haven't really thought of any particular way of doing something very different than what I'm doing now that would be better or even good in a different way compared to what I'm doing now. I mean, we have certain goals in, I have certain goals with the Minescape podcast. Your mileage may vary. But, you know, I want to get to people's ideas. I want to be able to interrogate them and increase our understanding of them. Ideas that are a little bit subtle and systematic and require some time to dig out and explain and think about the consequences of. The AMAs, what we're doing right here,

this is a perfect kind of off-the-cuff thing. I don't do planning for the AMAs. So I can be sloppy and say, I don't know. That's perfectly fine in AMA land. But a live thing is just a different thing. It's not systematic. There will be very good questions and some not so good questions. Some questions will be more interesting to others, et cetera, et cetera. So I don't know how to do that in a way that would be clearly better than what is going on right now. So maybe I could. I will keep thinking about it. I'm very happy to keep suggesting things like that.

I'm not, I don't want to dissuade people, even though I haven't done anything radical like that. I'm still very open to the possibilities. So who knows? That's the great thing about having your own podcast. I can do whatever I want. I could make it all me talking to my cats from now on. Maybe that would double my listenership. I don't know.

but the cats don't tend to talk back unless I just literally put them in their little cat carriers and then they'd be making noises but it would not be talking to me in a comprehensible way so it's not really in the spirit of the podcast per se that's how we are that's where we are right now

hope you're enjoying the podcast as it is and I'll see you next month bye-bye