Adam Brown – How Future Civilizations Could Change The Laws of Physics

Today, I'm chatting with Adam Brown, who is a founder and lead of the Blue Shift team, which is cracking mass and reasoning at Google DeepMind and a theoretical physicist at Stanford. Adam, welcome. Delighted to be here. Let's do this. OK, we'll talk about AI in a second. But first, let's talk about physics. OK. First question.

What is going to be the ultimate fate of the universe? And how much confidence should we have? The ultimate fate is a really long time in the future, so you probably shouldn't be that confident about the answer to that question. In fact, our idea of the answer to what the ultimate fate is has changed a lot in the last hundred years. About a hundred years ago, we thought that the universe was just

static wasn't growing or shrinking, was just sitting there statically. And then in the late 20s, Hubble and friends looked up at massive telescopes in the sky and noticed that distant galaxies were moving away from us and the universe is expanding. So that's like big discovery number one. There was then a learned debate for many years about

you know, the universe is expanding, but is it expanding sufficiently slowly that it'll then re-collapse in a big crunch, like a time reverse of the big bang and that'll be super bad for us? Or is it going to keep expanding forever, but just sort of ever more slowly as, you know, gravity pulls it back?

but it keeps it's fast enough that it keeps expanding and there was a big debate around this question and it turns out the answer to that question is is neither of them is correct in possibly the worst day in human history sometime in the 1990s we discovered that in fact not only is the universe expanding it's expanding faster and faster and faster it's what we call dark energy or the cosmotional constant is this

the word for uncertainty is making the universe expand at an ever faster rate, accelerated expansion as the universe grows. So that's a radical change in our

understanding of the fate of the universe. And if true is super duper, bad news. It's really bad news because the accelerated expansion of the universe is dragging away from us lots of distant galaxies. And we really want to use those galaxies. We have big plans to go and grab them and turn them into

vacation destinations, or computronium, or in any other ways, extract utility from them. And we can't, if the cosmological constant is really constant, if this picture is correct, because anything close enough, we can go out and grab it, obviously. But if it's further away than about a dozen billion light years, the expansion of the universe is dragging it away sufficiently rapidly that even if we send probes out at almost a speed of light, they will never make it. They will never make it there and make it back.

They'll never even make it there if it's sufficiently far away. And that means that there's a finite amount of free energy in our future. And that's bad. I mean, that means we're doomed to a heat death, if that's true. But is it true? Is it true? I mean, that was the second ask for your question.

First of all, we keep changing our minds about these things over the last century or so. So on first principles grounds, you may be somewhat suspicious that we'll change our minds again, and none of this is settled physics. And indeed, it may be that the cosmological constant is not constant, and you should hope with all your heart that it's not. It may be that it naturally bleeds away. It may be, in fact, that our fate is in our hands, and that our distant descendants will go and

bleed the cosmotional constant away, will force it to go to zero. They will be strongly incentivized to do it, if they can, because otherwise we're doomed to a heat death. How would they bleed this away? Oh, well, again, this obviously depends on physics that we're not totally sure about yet. But it seems pretty consistent with the known laws of physics, that the cosmotional constant, what we perceive it as being a constant, this dark energy quantity that's pushing the universe apart from each other,

In many very natural extensions of the known laws of physics, that is something that we have the ability to change. In fact, it can change. It can take different values. It is not just totally fixed once and for all. In fact, you have what's called different vacuum, different regions of parameter space that you can transition between, in which the cosmological constant can take different values.

And if that's true, then, well, you can either sort of wait around and hope to get lucky, hope that the universe just sort of spontaneously moves from one of these vacuums to another, one with a lower cosmological constant, to tending towards zero asymptotically, or you could take matters into your own hand. Or you could imagine our descendants deciding that

they're not going to just suffer the heat death, that they're going to try and trigger a vacuum decay event to get us from one vacuum we're in to another vacuum with a lower cosmological constant. And our distance descendants will

be forced to basically to do that if they don't want to suffer a heat death, proceed with caution. But definitely proceed with caution. In these theories where there's lots and lots of vacuums out there, and most of those vacuums are incredibly inhospitable to life as we know it. In fact, seemingly they're just completely inhospitable to all forms of intelligence. So you really, really don't want to end up in them. However,

Again, if our best theory is correct, it seems as though there should be some of them that are much like our own in many ways, but have a lower value of the cosmological constant. And so what we'd want to do is engineer that we end up in one of those vacuums. Sorry, what is a vacuum?

Ah, great question. A vacuum is like a possible, well, what we would perceive as a possible set of laws of physics as we see them. So what it really is is a minima in some higher dimensional abstract laws of physics space in which you can find yourself in a minima, but these minima may just be local minima. In fact, according to our understanding, the minima which we live today

is that gives us all of the laws of physics that we see around us is in fact just a local minimum and there's a lower minimum, in fact there's many lower minima out there to which we can transition spontaneously or because of our own deliberate action. Okay, I'm just going to throw all my confusion at you and you figure out which one is worth dealing with first. What is the nature of the loss function that makes one value of minimum and one higher

what is exactly the ball rolling up on when it gets out or into a valley here. And then you're hinting at the possibility that there are other places in the physical universe or in some hypothetical universe where the vacuum could be different.

As in in reality, there are other pockets with different vacuums or that hypothetically they could exist or that no, our universe kind of factually could have one of these. I don't know. This is the kind of thing I like throw into like, you know, just like put everything I can into like a cloth from them. See what it comes at the other end. Good. Well, I'm happy to be your your your thought.

The loss function is the energy density. And so maybe a good analogy would be water. Water can exist in many phases. It can be steam. It can be water. It can be ice.

And even if it's in a cloud, let's say, it would rather be water than be water vapor, but it's having a tough time getting there because in the middle there's a barrier. And so you know that's just spontaneously, it can eventually do sort of a thermal process, turn from steam into water. These will be like the two minima in this lost landscape. And or you can go and do cloud seeding to turn it from

water from water vapor into water. And so those would be the equivalent to the the minima here. The existence of different minima in general is a very well established part of physics. The possibility that we could engineer going from one minima to another in a controlled way is a more speculative branch of physics speculation. But it seems totally consistent with everything we know that our distance attendants would try to attempt it.

What would it take to do this? Probably you'd want something that would look a bit like a particle accelerator, but it would be considerably more controlled. You need a very controlled way to sort of collapse a field and make a bubble of this new vacuum that was big enough that it would continue to expand.

rather than just re-claps under a zone surface tension, you'd have to do that in a very careful way, both to make sure that you didn't, you know, accidentally make a black hole instead by the time you concentrated all those energies. And also, you know, worse than making a black hole would be ending up in a vacuum that you didn't want to end up in, would be ending up in a vacuum in which you would not only bled off the cosmological constant in some way, but that you had changed, let's say, the electromagnetic constant or the strong

nuclear force or any of these other forces, which would be seriously bad news. Because if you did that, your life, as you know it, is extremely well- attuned to the value of the electromagnetic constant in your evolutionary environment. It will be very, very bad indeed if we changed those constants as well. We'd really just try and target the cosmological constant and nothing else, and that would require a lot of engineering prowess.

So sorry, it sounds like you're saying that changing the laws of physics is like, it's not like some crazy, it's not even like Dyson sphere level crazy. It's like, yeah, somebody could do it on like some planet in the middle of. I think it's definitely substantially harder than Dyson spheres as far as the tech tree goes, but it's not.

Yeah, what do we mean by changing the laws of physics? Like that just sounds like magic. We're not actually changing the laws of physics. We're just changing the laws of physics, the sort of low energy laws of physics as they present to us. In this scenario, again, this is speculative, but it's not like super duper crazy. It's a natural consequence of our best theories of, or at least some of our best theories of quantum gravity that they allow for this possibility.

There is a meta law of physics, the true laws of physics, be it string theory or whatever else, that you're not changing. That's just the rules of the game. What I'm describing is changing the

the way that the universe looks around you, changing the cosmological constants. So I think again, changing water into, water vapor into water is a great analogy here. There's nothing actually, the laws of physics are still the laws of physics, but the way it feels to live in that universe, the value of the electromagnetic constant is perhaps not an absolute fixed value. It can

vary in different places. And one, similarly, the density of water around you, the viscosity, would change. It'll be an environmental variable like that. Yeah. So one question you might have is, if this is the thing that could sort of, I don't know if organic is the right way to describe it, but maybe spontaneous, if this is the thing that can just like kind of happen,

There's something really interesting about where, like, if a thing can happen, you kind of see examples of it happening before. So even with nuclear weapons, I don't remember the exact phrase. I'm sure you actually probably know what it is. But wasn't it the case that early in Earth's history when there was a higher fraction of 238 isotopes that there were spontaneous nuclear explosions? There probably was spontaneous nuclear

reactors, not nuclear, they've discovered a seam in Africa where it looks like there was a fission reaction that naturally happened. It didn't explode, but it did do the same thing that happens in our nuclear power plants. Yeah. You know, when we can look at like nukes is like, oh my gosh, this is like, this thing just would not have been possible if like some intelligent beings hadn't tried to make it happen. But you know, like something like this happened before.

because the laws of physics allow it. Is there any story you can tell here where this vacuum decay is like in one sense, maybe it takes like a super intelligent species to coordinate to make it happen, but also because it is the thing that the laws of physics can manufacture or can allow for it has all it has happened before or is happening or something.

Yeah, I mean, absolutely. Almost certainly. And I think that humans can do can happen without humans. It's interesting to reflect on what aspects of human behavior nature has a tough time doing without us and what it just does on its own. For example, we make colder things in our laboratories than really exist naturally in the universe, but the universe certainly could make anything colder just by chance. But

Yeah, vacuum decay is something that if it is possible, will in our future definitely happen. That's just like a feature of the world that eventually due in our distant future, if it's possible at all, it will happen due to a quantum fluctuation.

Our descendants may not wish to wait around for a quantum fluctuation to happen. They may wish to take the fate into their own hands, since a quantum fluctuation can take exponentially long times to happen. And if they even happened, you'd end up in an unfavorable vacuum, not hospitable for life, rather than trying to steer the cosmological constant in a happy direction.

But they certainly can happen in our future, and indeed definitely will happen if they're permitted. According to our understanding of quantum mechanics, if they're permitted, they must eventually happen. Furthermore, there are, again, speculative but not wild theories of the early universe in which this happened in our past.

in which we transitioned far, far in the past, maybe into what's called a bubble universe. So we started off in some other much higher vacuum long in the past. And then what we see as the big bang was in fact just a sort of local

vacuum decay that then gave rise to the bubble in which we live everything we see around us. Who would be in a position to seed these bubbles? Usually people are thinking that something just spontaneously happens. In the same way that rain spontaneously happens in a cloud that somebody didn't go and seed it deliberately to make it happen. But you could more than free to speculate that somebody seeded it to make it happen as well. How does this respect the conservation of energy or the conservation of energy? Energy is not conserved.

in general relativity. Energy is not conserved. It's conserved locally at things you can do at a local level. But in an expanding universe, energy is not conserved globally. This is one of the big surprises. That is not a speculative statement. That is a statement that goes all the way back to Einstein and general relativity is energy is simply not conserved at the global level. It's conserved at the local level. You can't do something in your lab that will

generate free energy. But if you can participate in the expansion of the entire universe, then energy is not conserved. So if you were to spawn a bubble universe in your lab, you've theoretically created a lot more matter and energy. And what would be the thing that offsets this or that makes this viable?

Energy is conserved in a universe that's not expanding. A static universe. A universe that is expanding, energy is not conserved. It can just appear, and general relativity is quite clear on that. General relativity, Einstein's theory of space and time, one of our most beautiful and best tested theories, is quite clear on that point. Energy is not conserved to ask what happened to the energy. You can ask at a local level what happened to the energy density, but at a global level, energy is simply not conserved.

then do our future descendants have any constraints in terms of, because earlier we were mentioning, I was a catastrophe we found out about the cosmological constant, because it limits our cosmic horizon, and that limits the free energy that our descendants would have access to. But if you can just make entire universes,

Yeah, this is a matter of extreme interest, I would say, to us. It won't be relevant for tens of billions of years, probably, because that's the time scale on which the cosmological constant operates. But if the cosmological constant is truly constant,

And we've only known about it for 25 years, and there are, you know, astronomical observations that seem to be intentional with that. But like, if it is truly constant, then there is a finite amount of free energy in our universe. If it's not constant, if we can manipulate it, or even if it naturally decays on its own, then there is the possibility of an unbounded amount of free energy in our future, and we would avoid a heat death scenario.

The situation you mentioned earlier were, somebody seated our universe. They've created a bunch of energy. Correct. It would be extremely obvious. And that's related to them having something equivalent to a positive cosmological constant in there. Yes, in any of these scenarios in which our universe is a bubble that formed in a sort of bigger, multi-verse, or a

That's a loaded term, but a sort of larger universe in which our universe is just one bubble. The higher the meta universe also has a cosmological constant and it is higher than the value in our universe. That is the one sense in which there's some version of energy conservation is that you can go down from high from high to low. It is considerably harder to go from low to high.

So the idea is that you would recursively have universes in which the bottommost one would immediately implode because of a negative cosmological constant and the biggest one is exponentially increasing. Correct. The rate at which the universe is exponentially increasing is set by the cosmological constant, which the volume of the universe is exponentially increasing. So you can imagine a scenario in which there was a high cosmological constant that you have a

bubble universe that has a lower value of the cosmartial constant, it continues to expand. You could make new bubble universes or new regions in that universe that have a lower cosmartial constant, either naturally and spontaneously or due to action that we might take.

As long as that cosmoshal constant is non-negative, is zero positive, that universe will not implode. If it goes negative, that universe will eventually implode. So you could imagine a cascade in which you go to lower and lower values of the cosmoshal constant. There are a lot of engineering details to be worked out, but what I'm describing is a scenario that is not inconsistent with the known laws of physics. How likely do you think this is? If the laws of physics are what we believe them to be,

And if we do not blow ourselves up in some other way, this is a issue that our distant descendants will eventually have to confront. No, no, there's like other bubbles, not about something our descendants might do, but the fact that the Big Bang was the result of a bubble within some other metastable state. That's a tricky question.

But since you asked it, I'd say probably 50%. There's a lot we don't understand about any of these questions. They're all like super speculative. It's an active area of research how to combine quantum mechanics and expanding universes. On the other hand, it seems pretty natural when you do combine quantum mechanics and gravity and try and fit them all together in a consistent picture. If universes can expand a lot, then the

At all, according to the gravitational theory, then quantum mechanics will naturally populate those bits that can expand a lot. And so you'll naturally end up with an expanding universe. So I would say probably in my heart, slightly higher than 50%, but I'm going to round it down to 50, epistemic humility.

It's funny because there's often the way people talk about their AI timelines. Really, I think it's like 2027, but if I'm taking the outside of you, I'm going to say 2030. Okay. And is there any way, given a current understanding of using bubble universes to do useful work for the people outside of it? So to have do some computation within it or to

gets some sort of actual energy out of it for the people outside of the bubble. So the thing about these bubbles is that they tend to expand at the speed of light. So even if you start off outside, you're probably going to end up inside them in short order, unless you run away very quickly. So this isn't something that we make in the lab, and then just remains in a box in the lab, and then we use to do things. This would be something that we would do, or maybe we would just happen to us because of spontaneous vacuum decay. And it would engulf

all of our future like home. And so it's not a box that you're using to do things. It's a new place that you live. You better hope that you've engineered stuff so that that new place is still hospitable for life. So look, if it's a case that you can set up some apparatus, not now, but not in this room. But eventually that if some individual wants to change the constants of nature,

They can not only do this, but then the repercussions will extend literally as far as like and expand. You might have some hope that, you know, future civilizations, individuals or AI's have tons of freedoms that they can do all kinds of cool things. You can have your own galactic cluster over there. And if you want to, you know,

Go do whatever you want, right? Go live your life, and there's gonna be some libertarian utopia. But if you can literally destroy the universe. Yeah, it's a different story. That is a big negative ex-anality destroying your future light cone. And in a world with big negative ex-analities, libertarian fantasies can't really happen. It has pretty good big governance implications, is that if it is possible for people just to wipe out

their entire future like home, not only themselves, but everybody else who wishes to participate in that future like home, then we're going to need a government structure that prevents them from doing so. I mean, the worst case scenario is even worse than that. Not just that, you know, they could do it, but that they, in some sense, be incentivized to do it. You could imagine really adverse laws of physics in which

Maybe you could speculatively build some power plant that just really makes use of just sitting on that edge of instability. And then each person individually might say, oh, I'm quite happy to bear one in a trillion chance that I wipe out the future like home because I get so much benefit from this power plant.

But obviously, the negative exality means that people really shouldn't do that. So I hope the laws of physics don't turn out that way. Otherwise, we're going to have to have some super arching control. I've done a couple of these interviews, actually. These end up being my favorite interviews, where a normal person who has just had great school education can think of course I understand this, right? Or if you've just seen enough YouTube videos about PopSci.

give you a concrete example. When Andrew and David Reich, the geneticist of ancient DNA, I feel like we have a sense that we understand the basics of how humans came to be. What is the story of human evolution? And just like the episode revealed to me that the main questions we might have about like how humans came to be, where did it happen? When did it happen? Who did it happen with?

In fact, the last few decades of insights of totally revolutionized our understanding. We have the sense that we understand what basically cosmology implies. But this idea that, in fact, there's this underlying feel, which not only implies very interesting things about the distant past, about the Big Bang, but also what our future descendants

you know, what kinds of civilizations they'll be able to set up both from a governance and a practical like energy perspective. It's like totally changes your understanding. Yeah, it just keeps changing. I mean, not just your idea. Our idea, everybody's idea has changed a lot in my lifetime and may continue to change. And in some sense, it's because you have the lever arm, the long lever arm or of asking about the very, very distant future that makes even small uncertainties today pan out to absolute change, normal distances in the distant future.

I think you earlier said, I wouldn't be that crazy, but also it's not as easy as a nice and spear. What are we talking about here? How much energy would it take to? The energy requirements are probably pretty small, much more than we can currently make in our particle colliders, but much smaller just in terms of MC squared than the energy in your body, for example. The energy is not going to be the heartbeat. The heartbeat is going to be concentrating it together in a really small

little bubble that's shaped exactly right in order that it doesn't form a black hole expands in just the way that you want it to expand and lands in the vacuum that you're aiming for. So it's more going to be a control issue than just a pure energy issue. But you think this is just table stakes for like, you know, distant descendants who are like colonizing the stars? It's not inconsistent with the known laws of physics, which means

that is just engineering. I feel like that the most sort of a dirty phrase business can occur is, your proposition is not inconsistent with a lot of physics. Not this. If we lived in a world of intelligent design and these were the laws we found ourselves with,

At a high level, what is the creator trying to maximize? What is the other than maybe us existing? Does it seem like something that is being optimized for? What's going on here? If you just throw a dot in laws of physics space, in some sense, there are some properties of our universe that would be somewhat surprising.

including the fact that our life seems to be incredibly hospitable for complexity and interestingness and the possibility of intelligent life.

which is an interesting fact. Everything is just tuned just so that chemistry is possible. And perhaps in most places you would throw the dart in possibility space, chemistry would be impossible. The universe as we look around us is incredibly rich. The structure at the scale of viruses, all the way to structure at the scale of galaxies, there's interesting structure at all levels. This is a very interesting fact. Now, some people think that

actually interesting structure is a very generic property. And if we threw a dart somewhere in possibility space, there would be interesting structure, no matter where it hit, maybe it wouldn't look like ours, but there'd be some different structure. But really, if you look at the laws of physics, it does seem like they're very well attuned for life. So in your scenario, where there's an intelligent creator, then they would probably be, you'd have to say they'd optimized for that. It's also the case that you can imagine explanations

full Wyatt so well-tuned for life that don't involve a intelligent principle. Is there any explanation other than the anthropic principle for why we find ourselves in such a universe? Well, you suggested one with an intelligent crater, but yeah, the usual one that people like to talk about is the anthropic principle. So is it like 99% that basically the reason we find ourselves in a universe like this is the anthropic principle?

Like, what probability do you put on, like, enthalpy principle is a key to explaining why we find ourselves in the kind of universe we find ourselves in. I think it's going to depend on what quantity you're asking me about. Yeah. So if you ask me, you know,

99% of the matter in the solar system lives in the sun or on Jupiter. And yet, we live in this really weird corner of the solar system. Why is that? I'm pretty confident that the answer to that is anthropic, that if we live in the central, the sun would be dead. And so one should expect intelligent life to live in this weird place in parameter space. So that's perhaps my most confident answer to that question. Why do we live

where we live, then if we start talking about different constants of nature, we start getting different answers to that question. Why is the universe tuned such that the proton is just a tiny bit more stable than the neutron? That seems like that's begging for a prophic answer. Of course, if that's true, that demands that there be different places somewhere in the multiverse where, in fact, the neutron is slightly heavier than the

Yeah, the protons decay to neutrons rather than vice versa and people just don't live there. So that if you want to go down that road, you end up being naturally drawn to the existence of a of these variables scanning over space. Is there some way for the anthropological principle to exist that doesn't involve these bubble universes?

Yes, all you need is that there is different places in some larger possibility space where these quantities scan, where they take different values, bubble universe is just one way to do that. We could just be different experiments simulations in some meta universe somewhere. What part of this is the least sort of logically inevitable, right? Some theory seem to have this

feeling of like it had to be this way. And then some are just like, why are there these like 16 fields and hundreds of particles and so forth? We're part of the, the, the, our understanding of physics. Yeah. I would say that there's three categories. There's things like quantum mechanics in general relativity that are not.

logically inevitable, but do seem to be a tractors in some sense. Then there are things like the standard model has 20 fields and it has a mass of the neutrino. Why do those masses of the neutrino have the values that they have? The standard model was just fine.

before we discovered that the neutrinos have mass in the 1990s. And those just seem to be just totally out of nowhere. Who ordered that was a famous Nobel Prize winning physicist said about the muon. In fact, longer ago than that, they just seem to be there, but without any particular reason. And then there are these quantities that are somewhere in the middle that are not logically necessary, but do seem to be necessary for a life as we know it to exist.

How confident are we that these different properties of different universes would actually be inconsistent with intelligent life? Yeah, I think that's a great question. And this line of thought starts to is a

is a skeptical response to the anthropic principle. An example that sometimes people use is a puddle that's sitting in some depression in the ground reflects on how wonderful the universe is, that this depression in the ground seemed to have maybe made the perfect shape for the puddle to exist. And our view would have said, no, the reason the puddle has that shape is because it is itself adapted to the hole in the ground. So maybe no matter what the laws of physics

there would be something that emerged there. And suddenly, if you go to, you know, there's all these weird bacteria at the bottom of the sea or in nuclear reactors or in various other places, this kind of life will find a way philosophy seems to be adapted at least there, where it's very different from the surface of the earth, where we find ourselves, and yet they're able to be certain

Life is able to live in undersea vents and is able to adapt itself to those environments. I think I basically buy that life is quite adaptable, but whether life is adaptable enough that a universe with a cosmological constant that ripped it apart every microsecond, that seems implausible to me.

Or even closer to home, the center of the sun. It's not clear exactly what, whether we get intelligent life living at the center of the sun, even though it has the same laws of physics as us. It just has a different environmental variables. What is the most underappreciated discovery in cosmology in our lifetime?

We have sort of in the 2000s and before, very carefully studied the cosmic microwave background, this what's sometimes called the echo of the big bang and the inhomogeneity of the net. The fact that it's not quite the same in every direction. And doing that discovered like a super interesting fact that was definitely not known in my lifetime anyway, which is the quantum origin of all of the structure we see in the universe. So if you look out in the universe,

The density is not the same everywhere. You know, the density on Earth is much more than an interplanetary space, which is itself much more than an intergalactic space. And the sun, you know, central sun is all the more denser. It is inhomogeneous. It is not the same.

And if you look back to the early universe, it was considerably more homogeneous. It was homogeneous to one part in 10 to the five, 10 to the six. Super almost everywhere. Every point had almost exactly the same density. And so then there's kind of an easy part and a hard part. The easy part is understanding how if you have

very small inhomogenities, how they grow into large inhomogenities. That's already quite well understood by classical physics. Basically, the idea is this. If you have a place that's denser and a place that's less dense, then the gravitational force pulls stuff

towards the high density stuff. So if you have a small inhomogeneity, they naturally grow under that effect, where they just gravitationally fall towards the denser thing. If you start seeded with small inhomogeneities, that will grow large inhomogeneities. And that's well understood. The thing that we now understand much better than we did is where those small inhomogeneities come from. Like why, just after the Big Bang, was the universe not perfectly inhomogeneous? Because if it was perfectly homogeneous, there's no opportunity for it to

for anything to go. And we now understand with a high degree of confidence, something that we didn't understand, which is that those inhomogenities were seeded by quantum fluctuations, that when the universe, just after the Big Bang was considerably smaller than it is today, the effects of quantum mechanics were correspondingly more important. And those quantum fluctuations produced tiny little fluctuations

in the density of matter in the universe. And all of those tiny little, one part in a million fluctuations grew into all of the structures in the universe, all the galaxies, you, me, everything else.

Is it a meaningful question to ask what level of structure each individual discrepancy corresponds to each individual one in 10 to the five part? Is it a galactic super cluster? Is it a galaxy? It depends. We believe that these were generated during the drill period of the chord inflation, very poorly understood, very early in the universe.

There were fluctuations made not just at one scale in those days, but at all scales, well, many, many scales. So there were fluctuations made at a scale that nowadays corresponds to 10% of the distance across the visible universe, all the way down to

structures that were in homogeneity that were much, much smaller scale that correspond to a galaxy today, all the way down to, now this is speculation, but in some models of inflation, they were tiny in homogeneity, very small scale in homogeneity that would give rise to primordial black holes, like tiny little black holes left over from the big bang. There's no actual evidence in terms of observational evidence, no strong observational evidence for those, but those are a possibility that's allowed by our theory, and people think about them and look at them.

Super excited to announce our new partner, Scale AI. Adam is, of course, a lead of Blue Shift, which is cracking maths and reasoning at Google DeepMind. DeepMind, along with all the other major AI labs, like Meta and Thoropic and OpenAI, partner with Scale. For many of them, Scale supplies high-quality data to fuel post-training, including advanced reasoning capabilities.

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What makes general relativity so beautiful? I think general relativity is really an extraordinary story. It's pretty unusual in the history of physics that you, to first approximation, just have one guy who sits down and thinks really, really hard with lots of thought experiments about jumping up and down in elevators and beetles moving on the surface of planets and all the rest of it. And

At the end of that time, writes down a theory that completely reconceptualizes nature's most familiar force, and also speaks not just to that, but speaks to the origin and fate of the universe, and almost immediately achieves decisive experimental confirmation in the orbits of

astronomical observations of the orbits of planets and the deflections of lights during the klipses and stuff like that. It's a pretty beautiful theory and it completely changed our idea of gravity from being a force to just being an artifact of the curvature of spacetime.

Actually, this is actually a good point to chat about your actual day job. So there's these open debates about the kind of reasoning that these LLMs do. Does it correspond to quote-unquote true reasoning or is it something more procedural?

It sometimes gets into a definition game, but this is maybe a good way to test our intuitions here. The kind of thing that Einstein was doing where you start off with some.

thought experiments, you start off with some seeming conceptual inconsistencies and existing models, and you trace them through to some beautiful unified theory at the end, and you make incredibly productive use of these intuition pumps. That kind of reasoning, how far are our EIs from that?

Like it said, and I kind of agree with this, that maybe the very last thing that these systems will be able to do, these LLMs will be able to do, is given the laws of physics, as we understood them at the turn of the last century, invent general relativity from that. So I think that's probably the terminal step, and then once it can do that, if it can do that, then there won't be much else to do as far as humans are concerned.

It's pretty extraordinary. I mean, particularly coming from a physics background in which progress is pretty slow to come to the AI field and see progress being so extraordinarily rapid day by day, week by week, year by year. Looking at it, it certainly looks like these LLMs and these AI systems

In some sense are just interpolators, but the level of abstraction at which they're interpolating keeps going up and up and up. And we keep sort of writing up that chain of abstractions. And then presumably, from a sufficiently elevated point of view, the invention of general relativity

from Newtonian physics is just interpolation at some sufficiently grandiose level of abstraction that perhaps tells us something about the nature of intelligence, human intelligence, as well as about these large-language models. If you ask me how many years until we can do that, that is not totally clear, but

In some sense, general relativity was the greatest leap that humanity ever made. And once we can do that, perhaps in 10 years, then we will have fully encompassed human intelligence. Will it have the same

Will it be of the same character as what Einstein did? Clearly, there are many disanalogies between human intelligence and these large language models. But I think at the right level of abstraction, it may be the same. Do you see early examples of the kind of thing it was? Obviously, not the little difficulty, but you just start off with like, hey, here's something funny. Go think about it for a while. Is there something especially impressive you see when you run that kind of experiment?

At the moment, these tend to be, you know, the systems tend to be doing more elementary material than that. They tend to be doing undergraduate level material.

Yes, I haven't seen anything that jumps out to me like inventing generative TV or even a toy version of that, but there is in some sense creativity or interpolation required to answer any of these problems where you start with some science problem, you need to recognize that it's analogous to some other thing that you know and then sort of combine them and then make a mathematical problem out of it and solve that problem. Do you think AI mathematicians, AI physicists,

will have advantages over humans just because they can, by default, think in terms of weird dimensions and manifolds in a way that doesn't natively come to humans. You know, I think maybe we need to back up to in what sense the humans do or don't think natively in high dimensions. Obviously, it's not our natural space. There was a technology that was invented to think about these things, which was

notation, tensor notation, various other things that allows you to, using just even writing as Einstein did a hundred years ago, allows you to sort of naturally move between dimensions. And then you're thinking more about manipulating these mathematical objects than you are about thinking in higher dimensions.

I don't think there's any sense in which large language models naturally think in higher dimensions more than humans do. You could say, well, this large language models have billions of parameters. That's like a billion dimensional space. But you could say the same about the human brain that it has all of these billions of parameters and is therefore billion dimensional. Whether that fact translates into thinking in

uh, billions of spatial dimensions. I don't really, I don't really see that in the human. And I don't think that applies to another, let me know. Yeah. I guess you could imagine that, um, you know, if you were just seeing like a million different problems that rely on, uh, doing this, uh, uh, uh, weird tensor math, then in the same way that maybe even a human gets trained up through that to build better intuitions, the same thing would happen. They, they, I just sees more problems and then develop better representations of these kinds of weird geometries or something.

I think that's certainly true that it is definitely seeing more examples than any of us will ever see in our life, and it is perhaps going to build more sophisticated representations than we have. Often in the history of physics, a

breakthrough is just how you think about it, what representation you do. It is sometimes jokingly said that Einstein's greatest contribution to physics, which is a certain notation he invented called the Einstein summation convention, which allowed you to more easily express and think about these things in a more compact way that strips away some of the other things.

Penrose, one of his great contributions, was just inventing a new notation for thinking about some of these space times and how they work that made certain other things clear. So clearly, coming up with the right representation has been an incredibly powerful tool in the history of physics and many incredibly large developments. Some are analogous to coming up with a new

experimental technique in some of the more applied scientific domains and yeah one would hope that

as these large language models get better, they come up with better representations, at least better representations for them that may not be the same as a good representation for us. We'll be getting somewhere when you ask Gemini a question and it says, ah, good question. In order to better think about this, let me come up with this new denotation and then we can show. We've been talking about what AI physicists could do.

What could physicists with AI do? That is to say, are your physicists colleagues now starting to use LMS or you yourself using LMS to help you with your physics research? What are they especially good at? What are they especially bad at? Yeah, so what?

Physicists don't do, or don't productively do, is just say, LLM, please quantize gravity for me, go. That doesn't get you anywhere. But physicists are starting to use them in a big way, but just not for that. More of an assistant, rather than agent.

Three years ago, there was totally no value whatsoever in them. Low-hanging fruit uses include doing literature search. If you just say, I have this idea, what are some relevant papers, they're great about and it's semantically greater than any other kind of search. The other thing that they're extremely useful for now that they were useful for is just as a tutor.

If there is a huge amount of physics that a physicist would be expected to, that has already been done and no human has ever read the whole literature or understands everything or maybe there isn't even something that you feel you should understand or you once understood that you don't understand. And I think the very best thing in the world for that would be to phone up a colleague and say,

If you knew exactly who to phone, they'd probably be able to answer your question the best. But it's certainly, if you just ask a large language model,

you get great answers, probably better than all but the very best person you could phone. And they know about a huge amount. They're non-judgmental. They will not only tell you what the right answer is, but debug your understanding on the wrong answer. So I think a lot of physics professors are using them just as personal tutors. And it fills a hole because there are personal, if you want to know how to do something basic, there is

typically very well documented. If you want to know quite advanced topics, there are not often good resources for them. And talking to these language models will often help you debug and understand your understanding. And it'll explain to you not only why what the right answer is, but what you thought was wrong. And I think it'll be a pretty big deal, sort of analogous to the way that

chess players today are much better, even when they're playing across the board without the benefit of computer, just having to be able to be tutored by chess machines off the board. And this is the same. You want to understand this thing about group theory, go and ask the machine and it'll explain it to you, and it won't judge you while it's doing it.

There's an interesting question here. Clearly, these models know a lot. And that's evidenced by the fact that even professional physicists can ask and learn about fields that they're less familiar with. But doesn't this raise the question of we think these things are smart and getting smarter?

if a human that is reasonably smart, had memorized basically every single field and knew about the open problems, knew about the open problems in other fields and how they might connect to this field, knew about potential discrepancies and connections,

What you might expect them to be able to do is not like Einstein level conceptual leaps, but there are a lot of things where it's just like, hey, magnesium correlates with this kind of phenomenon of varying, this kind of phenomenon correlates with headaches. Therefore, maybe magnesium supplements cure headaches. These kinds of basic connections you would, anyways, does this suggest that LLMs are as far as intelligence goes even weaker than we might expect given the fact that

Given their overwhelming advantages in terms of knowledge, they're not able to already translate that into new discoveries. Yes, they definitely have different strengths and weaknesses than humans. And obviously one of their strengths is that they have read way more than any human will ever read in their entire life. I think maybe again, the analogy with chess programs is a good one here. They will often consider way more

possible positions as a Monte Carlo research than any human chess player ever would. And yet even at human level strength, if you fix human level strength, they're still doing way more search so that their ability to evaluate is maybe not quite as natural as a human. So the same, I think, would be true of physics. If you had a human who had read as much and retained as much as they had, you might expect them to be even stronger.

Do you remember where the last like, uh, uh, uh, physics query that you asked in a little more? The last physics query, well, a recent one was I, I asked it to explain to me the use of squeezed light at LIGO, which is a topic that I always felt like I should understand. Um, and then try to explain it to somebody else and realize that I didn't, uh, understand it and went and asked the LLM that blew me away that it was able to like,

exactly explain to me why what I was thinking was incorrect. So why do we use this particular form of quantum light in interferometer used to discover gravitational waves? The reason that's a good topic is perhaps because it's an advanced topic, not many people know that, but it's not a super advanced topic. There are

out of a physics literature of millions of papers, there have got to be at least a thousand on that topic. If there was just a handful of papers on a topic, it's typically not that strong at it. Do you reckon that there is a, among those thousand papers is one that explains why the initial understanding or thought you had about it was wrong because if it just intuited that, that is actually quite like, that's pretty fucking cool.

Yeah, I don't know the answer. That is an interesting question. I think it might be able to debug even without that. If you do much simpler things like give these language models code, it will successfully debug your code, even though presumably no one has made that exact bug in your code before. This is at a higher level of abstraction than that, but it wouldn't surprise me if it's able to debug what you say in that way.

It just falsifies a lot of stories about their just fuzzy search or whatever. Scott Aronson recently, or it was a year or so ago, he posted about the fact that the tribute before got like a B or an A minus or something on his intro to quantum computing class, which is definitely a higher grade than I got. And so I'm already below the waterline.

But yeah, you know, you teach a bunch of subjects, including GR at Stanford. I assume you've been querying these models with questions from these exams. How has their performance changed over time? Yeah, I am.

I take an exam I gave years ago in my graduate general relativity class at Stanford and give it to these models, and it's pretty extraordinary. Three years ago, zero. A year ago, they were doing pretty well, maybe

a weak student, but in the distribution, and now they essentially ace the test. In fact, I'm retiring that. That's just my own little private eval. It's not published anywhere, but I just give them this thing just to follow along how they're doing, and it's pretty strong. It was maybe easy by the sense of a graduate

courses, but a graduate course, in general relativity, and they get pretty much everything right on the final exam. That's just in the last couple of months that these have been doing that.

What is required to ace a test? Obviously, they probably have like read about all the generality textbooks, but I assume to ace a test, you need something beyond that. Is there some you'd characterize? Physics problems compared to maths problems tend to have two components. One is to sort of take this word question and turn it using your physics knowledge into a maths question. And then

solve the maths question. That tends to be the typical structure of these problems. So you need to be able to do both. The bit that's maybe only LLMs can do and wouldn't be so easy for other things is step one of that is like turning it into a maths problem. I think if you ask them hard research problems, you certainly can come up with problems that they can't solve. That's for sure. But it's pretty noticeable as we have tried to develop evaluations for these models that

as recently as a couple of years ago, certainly three years ago, you just scrape from the internet any number of problems that are totally standard high school maths problems that they couldn't do. And now we need to hire PhDs in whatever field. And they come up with one great problem a day or something. The difficulty as these LLMs have got stronger, the difficulty of evaluating their performance has increased.

How much do they generalize from these difficult problems to not only that domain of physics, but just generally becoming a better reasoner overall? They just see a super hard GR problem. Are they better coding now? Generally, you see positive transfer between domains. So if you make them better at one thing, they become better at another thing across all domains.

It is possible to make a model that is really, really, really good at one very particular thing that you care about. And then at some stage, there is some pre-to-front here, and you start degrading performance on other metrics. But generally speaking, there's positive transfer between abilities across all domains. We've got these literally exabytes of data that we collected from satellites and telescopes and other kinds of astronomical observations.

Typically, in AI, when you have lots of data and you have lots of compute, something, something, large model, great discoveries. Is there any hope of using these extra bytes of astronomical data to do something cool? Yeah, great question. People are trying that. There's an effort

Shirley Ho and Flatiron, which is basically that exact plan, is they take the pipeline of all of the data that comes out of these astronomical observatories, they big and plug them into a transformer and see what happens.

you can come up with all sorts of reasons in advance, why that might not be something that will work, but you could also come up with reasons in advance why large language models wouldn't work and they do. So I'm very curious to see what happens. I mean, the dream there would be that, you know,

There's lots of things hidden in the data that no human would ever be able to tease out. And that by doing this, you could just revolutionize the amount of these astronomical observatories incredibly expensive. If we can just have a computer, better parse all of the data from them in a way that no human ever could, that would be a tremendous improvement. These things are very good at finding patterns, and maybe they'll find patterns that are not particularly interesting to a human.

Okay, so going on the QR thread again, maybe one advantage these models have is obviously you can run a lot of them in parallel and they don't get fatigued or dazed. And you could imagine, again, naively you would imagine some sort of setup. I assume you're doing much more sophisticated things, but naively you could imagine a setup where

Look, it seems like what special relativity, which is something that maybe is easy to understand, is just like you start off with, let's just randomly select a couple of observations. Obviously, they were randomly selected. And let's just think about what's going on here for a while. Let's just do a bunch of chain of thought for a year or so. And you could just imagine

doing this and doing some sort of best event across like a thousand different randomly selected parts of the current model of the universe. And just seeing like at the end of it, which one comes up with some especially productive line of thought. Yeah, I mean, I think that could be productive. One challenge in that would be how do you evaluate whether you had a good theory at the end?

That's going to be the tricky bit. For things that are most easily paralyzed are things in which, if you get the right answer, it's clear you got the right answer. Perhaps things in NP, one might say. Whereas in this case,

is special relativity, how would your computer know if it generated special relativity that it was on to a winner? There are various ways in which it could know, it could check that it was mathematically self-consistent and various other facts, but the evaluation is going to be a tricky part of this pipeline that you might wish to set up.

Is there a no experimental way that you could detect time dilation or something? There is an experimental way that you could detect time dilation. But that would involve sending out probes or doing something in the real world. Whereas I thought you were just trying to run this data. But now today we have these exabytes of information. So you could just have some sort of like ability to search or query. Like, I come with this theory. Maybe this is a philosophical difference where you maybe think that the way that a theory is good is that it best matches the

it best predicts the data with some loss minimization. That's not always how new theories, particularly revolutionary theories, come up. There's this famous fact, even when they were moving from a geocentric.

world view to a heliocentric world view that it was so beautiful, the theory by the time they were finished with the epicycles, I mean, not beautiful, it was so ornate by the time where these planets were moving around the sun but moving on epicycles that actually the data didn't any better fit the heliocentric world view than the geocentric world view, especially since they didn't

properly understand the elopicity of the Earth's orbit around the Sun. So it wasn't. Why does one theory replace another? One reason is obviously that it's more consistent with the data, but that's by no means the only theory. And if you just optimize for being consistent with the data, you're going to end up with

If you optimize only for being consistent with the data, you're going to end up with epicycles. You're not going to end up with some beautiful new conceptual thing. Part of the reason people like these new theories is that even though they may be not better at matching the data, they are more beautiful. And we'd have to teach.

And that's been a reliable guide in the history of science. And we'd have to teach these LLMs beauty. So this actually raises an interesting question, which is, look, in some sense, we have the same problem with human scientists, right? And so there's all these people who claim to have a new theory of everything. And I guess there's not an easy verifier that everybody agrees to because some people call them cranks. Other people think they're geniuses.

But somehow we've solved this problem, right? Well, we've sort of solved it. I mean, we haven't solved it in the same way that if you have some new sort algorithm, you claim as fast in everybody else's sort algorithm. There doesn't need to be any dispute about that. You can just run it and see if physics is not the same way. It is definitely the case. So there's a number of people who think they have great theories.

there are even perfectly respectable people who are professors at prestigious universities who have very different opinions about what is and isn't worthwhile.

direction to be exploring. Eventually, you hope that this gets grounded in an experiment and various other things. But the distance between starting the research program and the community reaching consensus based on data and other considerations can be a long time. So yeah, we definitely don't have a good verifier in physics.

Even if we did some day get superhuman intelligence that could do, they could try to find all the remaining sort of high level conceptual breakthroughs. How much of a room is there for that? Basically, it was just like 50 years of like, here's all the really advanced great physics. And now we just bogged through additions to the standard model.

You know, if you look at Nobel Prizes a year after year, they get less and less, at least in physics, they tend to get like less and less significant. And in fact, this year, the Nobel Prize in physics was worth it too. Yeah. Hopfield and Hinton for their work in AI. So apparently... Yeah, maybe it takes things to come. Yeah. I don't think there's reason.

I don't think we should be pessimistic about that. I think they could easily be room for completely new conceptualizations that change things. I don't think it's just turning the crank going forward. I think new ways to think about things have always been extremely powerful. Sometimes they're fundamental breakthroughs. Sometimes they are breakthroughs in which you even take regular physics. This is a story to do with renormalization that maybe is a little too technical to get into, but there was a sort

amazing understanding in the 1970s about the nature of theories that have been around for forever or for years at that stage that allowed us to sort of better understand and conceptualize them. So I think there's good reason to think that there's still room for new ideas and completely new ways of understanding the universe.

Do you have some hot take about why the current physics community hasn't, I mean, the cosmologies may be a very notable exception where like, it does seem like the expected value of the, like coq slits switching back and forth. Well, if you take particle physics, I think it's because we were a victim of our own success is that we wrote down theories in the 1970s. And those theories were, but

It's called the standard model. And those theories were too good in the sense that we won, in the sense that we could predict everything that would come out of a particle accelerator, and every particle accelerator that's ever been built, and every particle accelerator that's likely to be built

given our current budget constraints. So particle physics, there were some questions around the edges, but this model that we wrote down in the 70s and into the 80s, basically completely cleaned up that field. We wish to build bigger, more powerful particle accelerators to find stuff that

that goes beyond that. But basically, we won, and that makes it difficult to immediately, if you get too good, then it's hard to know where to push from there. That's as far as particle physics is concerned.

Is there some, so it sounds like the problem with these colliders is that the intro, like the expected entropy is like not that high of like, yeah, we, because the reason it's not that useful is because like we kind of have some sense of what we'd get on the other side. Is there some experimental apparatus that we should build where we in fact do have great uncertainty about what would happen? And so we would learn a lot by what the result ends up being. With the problem with particle colliders is in some sense that they got too expensive. And

CERN is tens of billions of dollars, a small number of tens of billions of dollars to run this thing. It's super interesting, however, everybody talks about how academics can't possibly compete with the big labs. But the cost of CERN is larger than the cost of a big model training run, so by a lot. So that's just academics pulling their money. So that's an interesting fact. But

Yeah, they got so expensive that it's difficult to persuade people to buy a new one for us that's even bigger. It's a very natural thing to do to build an atom smasher that just smashes things together to higher energy. It's a very natural thing to see what comes out. People were perhaps somewhat disappointed with the output of the LHC, where it just, it made the Higgs, which was great, and we found it, but we also expected it to be there. And it didn't make anything

else any of these more fanciful scenarios that or anything basically unexpected but people had speculated we see super symmetry there or we see extra dimensions and basically that was a null result we didn't see anything like that.

I would say we should definitely build another one if it was cheap to do so. And we should build another one once AGI has made us also rich that it's cheap to do so. But it's not the obvious place to spend $50 billion if you get $50 billion to spend on science.

Often, it's these smaller experiments that can be looked for things in unexpected places. A decade ago, there was Bicep, which is a reasonably cheap, tens of millions of dollars experiment at the South Pole that thought it had seen some hints in the cosmic microwave background of gravitational waves. That would have been revolutionary, if true. Not worth doing Bicep if it costs $10 billion. Definitely worth doing Bicep if it costs $10 million. So there's all sorts of experiments like that, often observational. What is the value of seeing these memorial gravitational waves?

Oh, it gives you hints. You're just examining the night sky very closely and seeing hints of what happened at the Big Bang. This is a different approach to doing high-energy physics, which is

Why do you want to build a big collider? You want to build a big collider because the bigger the collider, the more high energy you can smash it together with. And Heisenberg's uncertainty principle says that high energy means short resolution. You can see things on very small scales. That's great, except the cost to build them is there's some scaling laws and the scaling laws are not particularly friendly. There is another

sort of approach that one might say, which is, you know, there was a ginormous explosion that happened, which was the big bang. You know, if you imagine,

If we look at after the universe, it's expanding. If you sort of play the tape backwards, it's contracting, eventually it all contracts at 13.8 billion years ago in the Big Bang. And so that's a very big particle-clider indeed. And so by just examining very closely the Big Bang and its aftermath, we're able to hopefully probe some of these quantities that are very difficult to probe with particle-claters. The disadvantage is that you can't

Keep running it and adjust the parameters as you see fit. It's just like one thing that happened once and now we're having to peer backwards to With our telescopes to see what happened, but it can give us hints about things that would be inaccessible with any future information about the distant past that is in principle inaccessible Probably not in principle. So something happened to the universe In it in its evolution, which is that

The very early universe, just after the Big Bang, was opaque to light. We can only see light past about 300,000 years after the PewDiePie Big Bang. Before that, everything's so dense, it's like just a dense plasma that light just gets absorbed by. It's like trying to look through the sun.

And so we cannot see directly anything from before 300,000 years. Nevertheless, we can infer lots of stuff that happened from before 300,000 years. In fact, looking at that light, what's called the cosmic microwave background that was emitted at that time, we infer lots of stuff about just due to the patterns of anisotropy that we see in the sky. We can infer a great deal about what was happening earlier. And most of our confidence about modern cosmology comes from a number of

experiments that starting the 80s, but accelerating under 2000s, really very carefully measured that unizotropy and allowed us to infer stuff before that. At the information theoretic level, there's nothing inaccessible.

I guess that makes sense. The conservation of information. Maybe you'll tell me that that also isn't true. Well, that's a great question. I mean, there's been a lot of debate in the black hole context about whether information is conserved by black holes, but the modern consensus is that it is. Look, if you're enjoying this conversation, you should consider working for my sponsor, Jane Street. They're a very successful quantitative trading firm.

Physicists do particularly well in trading because they can combine hard applied mathematics with a bunch of empirical and theoretical considerations. In fact, Adam once filed for a patent using quantum entanglement and violation of Bell's inequality to do relativistic arbitrage.

I don't understand what that means. Maybe I should have asked Adam. But if you do, you should go work for Jane Street. Jane Street is keen to hire smart, curious, and rigorous people who want to work on interesting technical problems. You can join Jane Street, not just from physics, but also other technical fields like maths and CS. They're always hiring full-time, and their summer internship applications are open for just a few more weeks, and they're filling up fast.

If you really want to stand out, check out their Kaggle competition. Go to janestreet.com slash Dwarkesh to learn more. And there's also a really interesting video there about their ML work that you should check out. All right, back to Adam. All right, Adam, what are your tips for hitchhiking? Oh, good question. So I hitchhiked a bunch around America and Europe. I've done oxygen Morocco when I moved from

Princeton at Sandford, I hitchhiked a bunch of other times down to New Orleans, various other places. I think probably the biggest tip for hitchhiking is to stand in a good place. Some counter-party modeling, imagine the person who's picking you up, they need time to see you, to evaluate you, and to decide they're gonna pick you up, and then to safely stop, and that all needs to happen. So stand somewhere where people can see you, possibly at a stoplight, and where there's a place for them to safely pull over.

How do you model the motivations of people who pick you up? What are they getting out of this? I think it's different for different people. I think about 20% of people will just always pick up hitchhikers, no matter what, even if I'd...

you know, it was dressed very differently and presented very different. I think some people would just pick people up no matter what. I basically fall into that category now. Well, it was hard coded into my brain that I will 100% pick up hitchhikers always under all circumstances, just because enough people have generously picked me up down the years that I just feel as though it's my duty and sort of not not subject to a cost benefit analysis. Just it's in there.

Many other people are evaluating you and just trying to decide what you're in for. Some people are lonely and want somebody to talk to. Some people have a just spirit of adventure and find it exciting to pick people up. Certainly, it's not a representative cross-section of people, I would say. There's definitely a selection bias in who picks you up. They tend to be more open and more risk tolerant. What was your motivation for?

Were you just in need of a car or what was going on? No, I enjoy meeting people. I enjoy the experience of meeting people and weird episodic sense of which, you never know what's going to happen. I think I have a very high tolerance for ambiguity and I enjoy that.

What was the percentage of we just had a normal conversation? They went in the general direction I was going and that was that versus I've got a crazy story to tell about X incident, a whole percentage is each. Hmm. I think some people are just totally normal people.

families moving their trial to college and you get there and you help them, you know, move some stuff into the door room just to thank you all the way through to absolutely wild cases, probably 20%, just like this is one of the craziest things that ever happened in one way or another. Yeah, any particular examples of the wildest things? Oh, yeah, huge. I mean, it's just

absolutely firehose of wild things happening. I tell so many stories, like I remember once there was a trucker who picked me up in the desert outside Salt Lake City and who drove me to Battle Station Nevada and who

as we were talking, the truckers are always in fact the most interesting of all. It's typically illegal or any way in violation of their employment contract for them to pick people up. So those guys are really, and it's always guys, are really pushing the envelope in terms of picking you up.

The truckers often will say, you are the first person I've had in my cab in 20 years of trucking or something. And then they tell you about 20 years worth of things that have been on their mind. So I'd say that those are often the really interesting ones. As I said, there's this one in Utah who was just talked from the moment I got into the cab until we got to Nevada. And I kind of got the feeling that he had sort of excess

mental capacity and that this was his, you know, he was now just going to dump it on me. And he was telling me all about his life. And I remember this very well, how his brother-in-law thought he was a loser, his sister's husband, but like now he had the hot fiancé, so who was the loser? And then just gradually over the course of the six hours, it just suddenly occurred to me that his fiancé was doing advanced fee fraud.

on him and the whole thing was some ginormous and he was being scammed by his fiancé and very unfortunately for them they tried to execute the scam while he had me in the cab and he never had anyone in his cab so now he had me in his cab and they were trying to do some fraud on him and I was able to they had some wheat factory in Wales, United Kingdom that they had some British High Court document saying that he was entitled to if he paid off the lien on it there was some long complicated story

that was totally flagrantly false. And I kind of felt like I had a moral obligation to him to break the news to him. On the other hand, we were in the middle of nowhere in Nevada and I was clearly a very important part of his personality that this was so. So I kind of waited until we got close and said, is it possible that your fiance is being scammed by these people and sort of

raise the notion of scamming, and I was willing to intellectually entertain the possibility, and then we got a bit closer. Is it possible that you were yourself being scammed by your fiancee? And then he was like, no, no, no, I can't be. And he had all these documents to show that it was all legit. And they were just somebody from a British legal background, sort of transparent forgeries. And he did eventually accept it, and was just crying on my shoulder in some

truck stop. That was quite a high pathos moment. And then said, this happened before, and it turned out he previously been scammed in the same way

Or a similar way, through somebody he'd met through the same match.com profile. There was this lucky profile, because people kept messaging him through it. So we talked through that and worked through that. And I felt in some ways I'd been his guardian angel. But he'd also be my guardian angel and picked me up in the middle of the desert. So there was some great exchange there. That's crazy.

I hope he closed down that profile. I did chat to him about that possibility and he wasn't fully brought in on it. What's the longest you've been stranded on? That would probably be one time in Richmond, Virginia, in some not particularly good neighborhood trying to hitch out of there. I think that was about

a day, which is really bad. That's really bad. Like sometimes if you get a good spot, that's worth 1000 miles. Just don't give it up just for a short hop anywhere. If you get a bad spot, get out of there on any means necessary because there's because

There's probably a thousand ex variants and how high quality hitchhiking spots are, I would say. How did you find the time to get stranded for a day at an end? In terms of intensity, it doesn't really take that much wall clock time. As we say, it's coast to coast is...

You know, like a week or so, it's pretty fast because you're not yourself driving. In that sense, it's easier. You could do it to wait. And there is definitely high variance how long you can be. But in terms of sort of incidents per minute, it's a pretty good way to see the world. And you see such a cross-section of people who I might never otherwise meet and such a sort of high variance cross-section. Everything from sort of idle millionaires cruising around the country looking for adventure to

people who just got out of prison to in one memorable incident. Well, it eventually transpired as we were going along that they were actually just teenagers. And I didn't somehow didn't clock that when getting in the car. And they had stolen the family car and were driving west without a plan. And yeah, there I gave them a talk, talking to and bought them dinner and some life advice. So that was some stuff I forgot.

Did you make them call their parents? I did make them call their parents, yes. Heavily encouraged them to call their parents. Is there a law to get the professor? None of these people typically realize that your academic background never really comes up in conversation typically. Sometimes it does, but typically that's not the nature of the conversations. Was there any time you felt particularly unsafe?

I have definitely felt more unsafe picking up hitchhikers than I have hitchhiking. Maybe I just got lucky, but picking up hitchhikers, there it tends to be, no one really picks up hitchhikers anymore. And there's definitely a selection effect on who's hitchhiking. I have definitely felt more in risk of my life with hitchhikers I picked up than I ever did hitchhiking. But it's possible I just got lucky. You don't see the other branches of the wave function.

What are the other interesting insights from just getting this random cross-section? Yeah, all sorts of facts. A lot of people just like to talk. There's a lot of people out there, and I like to talk too, so it's mutually beneficial.

Well, the truckers, I imagine, are especially key to those guys. They're really interesting. Yeah, they're all they're all cheating their logs. They have certain logs about how long they can travel for at least every single one has ever picked me up. Maybe it's correlated with their willingness to pick up hitchhikers is all been in some way or another gaming the system of their their logs about how long they're allowed to drive for.

and playing games with time zones and stuff like that. And they typically, yeah, they're smart people, and they just have a lot to say and don't really have anybody to say it to, so they're very grateful. What are they especially insightful about? They tend to have listened to a huge number of audiobooks. They have a ginormous amount of information stored in their brain, but nobody to tell it to. Also,

Many of them tend to have had

unlucky romances at some stage in their past that they've never really got over or spoken to. And I really feel as though many of them would do well to speak to a therapist, but you are the therapist in that case. So, you know, in many ways, people will tell you things that frequently people will say things like, I've never told anybody else this in my life before. That's common, not just the truckers, other people as well. I mean, sometimes it's, you know, family is picking you up and so they're not going to say that. But often it's just, um,

Often it's just single people picking you up, and they'll say, I've never said this before to anyone else in my life, and they'll tell you some story of their life. And I do think it's, obviously, I'm very grateful to them for driving me down the road, but I think also it's an exchange. They're also getting quite a lot out of the conversation. I remember one case going to New Orleans, somebody just meant to only take us

I think it was just that some state trooper had come along in South Carolina and was going to arrest us because it's illegal in some states to hitchhike and North Carolina. And so I was like, I could just take the next ride. And it was just 10 miles down the road. And he ended up getting so into it that we ended up driving up.

maybe a thousand miles out of his way, but at home we'd gone and he'd had this, you know, having great conversations, just absolutely sort of wonderful time and he just wanted to keep going and going and drive us through the night and then we ended up going through the deep south in the middle of the night and arriving near New Orleans around.

and he'd had a father who had been in the military, but he'd kind of had a difficult relationship with and ended up going and visiting his father's grave in Baton Rouge. Never having done that in the 20 years since his father died, but just as this sort of turned, I mean, he just was driving along, expecting to go home, and then it just turned into the sort of spiritual quest for him. So, you know, stuff like that can be pretty gratifying. It's also sort of cheating. You're not

In my way of thinking about it meant to be taking people out of their way, like they're meant to be going where they're going and you go with them when they take you no further, but in this case, I think he needed to go there, so that was good for him. Did you stay in contact with any of the people? Your rhetoric? Typically no, and I would almost consider it for form to do so, but actually there was

There was one lady who came to stay in New York later, and she was going down to Haiti to be a doctor there. She was a doctor, and so I stayed in contact with her a bit. But typically, it's just the nature of the interaction, is that you have this beautiful moment in time together, and then that's it. Any other tips that somebody should know? I mean, should they do this anymore, given that it's

largely uncommon and so uncommon types of people might pick you up. I think it used to be very common in the United States. It's still reasonably common in Europe. It used to be very common in the United States, and then there were some mass murderers who drove the popularity down by targeting hitchhikers.

Maybe this is just pure cope. In my mind, you need to worry about that less, because if you are a mass murderer, it's really in a serial killer. It's not really a high expected value strategy to cruise around looking for hitchhikers, since there's so few of them. But that just might be pure cope in my head. I've never refused a ride for safety grounds, but I would. I hope I would, if necessary.

Sometimes you would refuse a ride because somebody's only going a short distance in a really good hitchhiking spot. It's kind of bad cometer of refuse a ride, but sometimes you should do that. Other tips. Don't write your exact destination on your sign. Write the sort of direction in which you're going. The reason is maybe two-fold. One, a lot of people, if they're heading towards that place, but not going to that place,

will not stop because they think, oh, I'm not going to wherever it is, I better, I better not, you know,

I'm not going there, so I won't pick you up, even though you'd very much appreciate a partial write there. The other reason is if you do want to decline a write, it's certainly a lot easier to do so if the person says, oh, I'm going to that city. That's hard. If they say they're going to that city and you're writing something more vague on your sign, then it's maybe easier to decline a write. If you want to get out of the car, the classic and the

is to say that you get in and you feel unsafe, is to say that you're car sick, because even serial killers don't want vomit in their car, so that's a good reason to get out. And then you just say, OK, I'll just stay here. That's another trick I've never had to deploy that.

I never had to deploy that. Typically, there's a moment of anxiety in the first minute, but then after a minute, it's clear that everybody's... I mean, they're also anxious about you. In many ways, you can tell that they're quite nervous about you. And then after a minute, it's clear that everybody's, if not a sensible human being, that at least a safe human being, and everything's super relaxed for the rest of the right, typically. Any other strange people who put you off, they're going to mind.

Not necessarily strange, but just like memorable. So many different kinds of people. Yeah, I remember there was one like seemingly very successful cowboy, but you know, cowboy, some driving some fancy truck in Wyoming and had a big herd of cattle and all the rest of it and was just asking me actually somewhat unusually to ask me what I do. And so, you know, at that time,

Oh, he's doing cosmology. So I sort of trying to explain to him and just had no totally disconnecting with anything. Just didn't understand a word I was saying all the way through. And eventually we landed on the fact that the stars in the sky are just like the sun only much further away. And this was a fact that in his life up to that stage, he just never encountered. And that was extremely gratifying because he

He was blown away by that fact. He was totally intellectually capable of understanding it. He just never, in his 50 years of existence, up to that moment, ever heard that fact. And his mind was just totally racing. This was reorienting his picture of his place in the universe must be so big. It was a stars out there. And he phoned his wife, I think, a somewhat less excited and then took me to a gun store and brought me lunch. And it was a good time.

He was a ranch. He was seemingly a very successful rancher based on everything about him, but he had some prized high quality bulls that were some rare high quality bulls. I can't exactly remember the details, but yeah, he just never really contemplated what the night sky meant for him.

There's a Sherlock Holmes story where Holmes learns that actually the sun is the center of the solar system. Interesting. And then the logic is Watson tells him this and Holmes is like,

Fuck, why did you tell me this? I tried to like reserve mental space for things that are actually relevant to my work, and now I gotta like forget this. Yeah, the hitchhiker's going to the galaxy. Yeah. What did you learn from studying the first-hand accounts of the Nagasaki bombers? Oh, yeah, that was... Okay, so during the pandemic,

My landlord has a big library, and I just started reading, you know, during deep lockdown, some books in the library, and I was just sort of, so where do you stay that you're a landlord? Oh, I... You've got an apartment complex library. I live in a house that was used to belong to the chair of the English department at some Stanford, and then it was heard by a grandson, he rents it to me, and it was some...

He has a very extensive library. It's very interesting. And I was like, you know, going through it during first lockdown and came across this like super enigmatic statement in some book about the history of Japan and

was super fascinated by it and started, for reasons that I'll explain in a moment, then just became obsessed for a few months on reading absolutely everything I could about the bombing of Nagasaki, which is the most recent nuclear weapon ever to be set off during wartime, and was reasonably controversial because people questioned whether we should have done it or not.

And that wasn't the question I was looking at, actually. The question I was looking at wasn't, should they have ordered it to be done? But were the people who did it, even following orders? And it's a pretty wild story that I didn't know, certainly before any of this happened, which is

It was never meant to be a mission to Nagasaki. It was meant to be a mission to bomb Kokura, a different Japanese city, but they got there and it was clouded over and they had like very strict instructions. Do not bomb if unless you can see the target. And that was the order. Do not bomb unless you can see the target. And they got to this other city and they passed over a bunch of times and they couldn't see the target. It was covered in the clouds. So then they went to their secondary target, Nagasaki, and it was again covered in clouds and they did a whole bunch of passes.

And they'd made various mess ups the bomber crew had beforehand including getting lost and

They'd made a number of mistakes, personal flying mistakes on their part that meant that they didn't have enough fuel once they got to Nagasaki to carry the bomb back to base, basically. And they probably have ended up in the ocean had they tried. So they were extremely motivated. At this time, this was the only nuclear weapon that existed in the world. We'd had two and then it went up to one and now there was one and they were just about to

drop it in the ocean and lose it. So according to the official account, after having done all this, on the third and final paths over Nagasaki, there was a miraculous hole in the cloud that suddenly opened up.

and then they dropped it. And that story is a bit sus. If for no other reason that they actually missed a little known fact, they missed Nagasaki. They were aiming for one point and they hit another point that was on the other side of the hill such that the original thing they were aiming for was reasonably untouched by comparison for the fact that a nuclear weapon had been dropped. They missed by much more than you would miss if you were doing visual bombing and they would be told to do

visual bombing. So this kind of suspicion is that they were doing a little bit of radar bombing against direct orders. So is it possible that 50% of all of the nuclear weapons ever dropped in combat were in fact dropped against direct orders? Which is, you know, if true, that's a pretty striking

fact about nuclear war, since people are somewhat worried with nuclear war that someone will launch nuclear weapons without being ordered to do so. And it does kind of look like 50% of all the nuclear weapons ever dropped in combat or dropped against direct orders. And when they got back,

Curtis Lamay was going to feel, was going to core marshal them and was like super mad but then the war ended and they didn't want to do it for PR reasons. So I just ordered and found every account ever written by every person super fascinating to do that because all these different people had completely non-overappling lives. You know, some of them were

were on the Manhattan Project and were their observers and waited later when Nobel Prizes physics and some of them were just people who were just there for one moment. I knew we all were on the plane. On every, there was typically a

a physicist, a representative of the Manhattan Project on the plane, just in case. So Louis Alvarez was someone there. He actually wasn't on the Nagasaki mission. He was on the Hiroshima mission. But in his biography, they said they saw a hole in the clouds.

I don't think I believe them. So like, that was like, I think one of the hints, it was maybe reading his, you know, at some stage reading his biography that was one of the big hints. The other people insist there was, but what's super clear is that whether or not there was a hole in the clouds, and probably there was a hole in the clouds, just because of some of the technical things to do with the discussion, though it's definitely not obvious, what's clear is that whether or not there was a hole in the clouds, they certainly, you know, had decided in the cockpit on that final run.

that no matter what they were gonna drop it. So even if there wasn't a hole in the cloud, was a hole in the clouds, wasn't a hole in the clouds, they had decided to drop the nuclear weapons against direct orders. And as they had written, like, basically, like, oh, we totally still hold the clouds, but even if we hadn't, we would have dropped it. That basically is, yeah, so different people write different things. There's about 10 people on these plays. But not all of them were

Some of them are some ways away from where the action is happening. There's the bombardier who says that he saw a hole in the clouds. There's the pilot who says something, but everyone has their own different perspective and some of the perspectives are just totally... This is something that I guess I'd always been told by my history. She's just been never really appreciated until I'd done this 360 view of history that people can describe the same events and just they have flat key inconsistent memories of each other. Nobody who was on the plane said that they faked the hole in the cloud story.

But some people who were on the plane said they were determined to drop the bomb, no matter what. And they were highly incentivized to do it. Because if they had not done it, they'd have probably, as it was, they only barely made it back to their emergency landing spot in Okinawa. They would have definitely ended up.

in the drink and certainly the bomb would have ended up in the drink. Have they not done it? So I don't know. I mean, I'm not a professional historian and maybe there'll be a difference of opinions, but it's clear there was something highly sus about at least 50% of all the nuclear weapons dropped in combat.

I mean, the interesting thing is that the reason nuclear war was averted in other cases is also because they refuse to follow direct orders, right? So in this case, or in the case of Petrov, he didn't report the seeming exciting of nuclear America. And that obviously contradicts orders.

Yeah, there's kind of nuclear insubordination in both directions. That's right. That's like the good kind, where they sort of maybe should drop the bomb according to their orders and refuse to. And then there's the other kind. Yeah. I also want to ask, so you've had not only one remarkable career, but two remarkable careers. So in physics, you've

you're close-collaborate or people like Leonard Saskin, and you've done all this interesting research. Now, you're helping do the reasoning work that Google DeepMinds is working on in AI. Is there some chronology you have in your head about how your career has transpired? Oh, I don't impose narratives on it like that. It's certainly a big

very big contrast between doing physics and writing retail papers, as it were, retail, doing one by one, writing physics papers, and then doing AI, which moves just tremendously faster, and trying to contribute to the wholesale production of knowledge in that way. And they have very different

impacts in terms of counterfactual impact. Physics, like you write some papers and you're like, I've not written that paper, no one will written that paper for years, or ever, perhaps. Computer science doesn't feel like that. It feels like if you didn't do it, someone else would do it pretty soon thereafter. On the other hand, the impact, even a few days of impact in computer science, these things are going to change the world.

hopefully for the better to such a large degree that that's much bigger than potentially all the physics papers you have wrote. So that's interesting. You say that about you feel that physics is physicists are not fungible in the same way.

The story about why physics has slowed down is usually that in fact there isn't any low hanging fruit and the idea that you would discover something that somebody wouldn't have written about for many years to come. I had a couple of double negatives there, but basically like you're not gonna, you know, we've like found all the things that are, you can just like write a paper about it and you're not just gonna like think about something and find something that somebody else wouldn't have written about otherwise.

But here you're saying the field that's moving way faster, which is computer science. That's the one where all of these people are going to come up with your algorithms if you hadn't come up with them yourself. And it's physics where if you had more Leonard Suskins and Adam Browns, you would have a much faster progress potentially.

Well, partly, there's just so many more people working on the problems in computer science than there are in physics. There's just the number of people is part of what makes the counterfactual impacts it. I mean, like, how many theoretical physicists are there versus how many people are working on, like, AI research? AI research around the world. There's, you know, I don't know how many people are... No, but they're not in a matter. Like, thousands and thousands and thousands. They're in a matter where, like... Physics, it's 100, 200, 300. Really?

in the narrow domain of high-energy theoretical physics. There's many more physicists than that if you include people more generally, but they're sufficiently specialized. That's partly part of the reason, is that it's much more specialized field. In a very specialized field, the number of people who would actually write that paper is a much smaller number.

How much do you ascribe the slowness of physics to these kinds of things that are just intrinsic to any field that is as specialized in as mature versus to any particular dysfunctions of physics as a field?

Yeah, we look back on the golden era of physics from the 1900 through 1970s or something as a period when things happened. I do think there is a low-hanging fruit aspect to it. I mean, we already talked about how the standard model is so successful in terms of particle colliders that it's just hard to make rapid progress thereafter.

So I don't really see it as a dysfunction of a field, so much as being a victim of our own success. Having said that, does physics have fads? Does physics have fashions? Does physics have any of these other things? Absolutely it does. But quite how much counterfactual progress we'd make if that weren't true, I don't know.

How well calibrated are the best physicists? It doesn't necessarily pay to be well calibrated, and that incentive structure is perhaps reflected in the poor calibration of many of the best physicists. First of all, because physics is a sufficiently mature field, all the good ideas that look like good ideas have already been had, or many of them.

Where we're at now is the good ideas that look like bad ideas. So in order to motivate yourself to get over the hump of get through the get over the barrier and actually explore them, you need a little bit of.

irrational optimism to sort of ride out the initial discouraging things that you'll discover as you go along. So I would say that typically theoretical physicists are not particularly well calibrated and tend to be in love with all their own theories and make highly confident predictions about their own theories. Before the LHC turned on, there were certainly a lot of

high energy theorists making extremely confident predictions about what we'd see at the LHC, and it was typically their own favourite particle that we'd see. And while I'd loved to have found supersymmetry, it would in some sense felt somewhat unjust to reward the hubris of people making overcompet and poorly calibrated predictions. So yeah, that's definitely a thing that happens. But I wonder if poor calibration on the individual level is somehow optimal on the collective level. Yeah, I think that's basically right. I mean, the same is kind of true of

in other domains of life as well, of course, startups. If you were properly calibrated about how likely your startups succeed would be, maybe you wouldn't do it, but it's good for the ecosystem that certain people are willing to give it a go. Yeah, I think it's good for the ecosystem and perhaps bad for the individual to be well calibrated.

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Learn how Stripe Billing can help your business at Stripe.com slash billing. All right. Back to Adam. Another topic I know you study a lot is how one might mind a black hole. Oh, yeah. Right. I'm going to pay for that. Yeah. Tell me about it.

Okay, so what do you mean by mine black hole? Mine black hole means take the energy out of a black hole that used to be in a black hole. Obviously, if our distant descendants have used up all of the energy and stars and everything else, the black hole might be the last thing they turn their eye to.

Yeah, so can you get energy out of black holes at all? The old story, pre-1970s is known. Black hole is one way matter falls in and that becomes out. It's stuck. The thing that Hawking and Beckenstein discovered in the 70s is that once quantum mechanics is involved, that's not true anymore. Once quantum mechanics is involved, in fact, energy, even without you doing anything, starts to

leave black holes. The problem, as far as resistance descendants will be concerned, is that it leaves black holes extremely slowly. So if you took a solar mass black hole, same mass as the sun, just collapsed to form a black hole, there'll be this little quantum, what's called a Hawking radiation nowadays, a little quantum Hawking radiation in which the energy will leach out again, very, very slowly. And the temperature of a solar mass black hole is measured in nano kelvins, so very

low temperature. So the energy leeches out when something like cold, you know, so cold, you couldn't even see it in the cosmic OK background. It leeches out incredibly slowly back into the universe. And that's bad news, because it means the energy comes out super duper slowly. So the mining question.

is, can you speed that up? Solar mass black hole, if you don't help it, will take about 10 to the 55 times the current age of the universe to have given out all its energy back into the universe. Can you make that faster? And there were these proposals stretching back a few decades that you could, you could do what's called mining black holes, where

We see the Hawking radiation that escapes from a very long way away from the black hole, but actually, mathematically, it's known that much of the Hawking radiation doesn't escape. It just sort of makes it a little bit out of the black hole and then falls back in again. And there was this proposal that you could have got to reach in with a mechanical claw, obviously not crossing the horizon, because otherwise you've lost the tour and you'll

somewhat counterproductive, but like just just outside the horizon, just grab some of that Hawking radiation and just drag it along way away from the black hole and then and then feast on it or do whatever it is you want to do with it. And in that way, you could what's called mine a black hole, you could speed up the evaporation of a black hole by a huge factor. So in fact, the lifetime would no longer go like the mass cubed, like it does with just unaided Hawking radiation of what would scale like just a mass. So considerably faster for a

large black hole. And so this was these proposals, and I had some sort of pessimistic contribution to the story, which is that the existing proposals did not work. They didn't work to speed it up. And in fact, you can't speed it up. You can't get down that M cube down to M. You can't, in fact, get anything less than M cubed. It still scales like the mass cubed. The length of time you need to wait to get all the energy out of a black hole still scales like the mass cubed. And

What goes wrong is ultimately a material science problem.

So this scoop that comes down really close to the horizon. Now from one point of view, that's just like a space elevator, albeit a very high performance space elevator. Space elevators, you'll remember these ideas for how we might get things off the surface of the earth without using rockets. And the idea is that you have some massive orbiting object, sort of very long way way beyond geostationary orbit. And then you dangle off that rope down to the surface of the earth. And then you can essentially just climb up the rope.

to get out. That's a space elevator idea. And already around Earth, it's hitting pretty hard material science constraints. So if you want to make a space elevator, the trouble with making a space elevator isn't so much supporting the payload that you're trying to have climb up. It is merely just the rope supporting its own weight, because each bit of the rope needs to support not only its own weight, but also the weight of all of the rope beneath it. So the tension that you require keeps getting more and more and more as you as you go up.

At the bottom, there is no tension effect. It doesn't even touch the earth. It's not like a compression structure that's like a skyscraper that's pushed up from below. It's a tension structure that's held up from above. But as you go up, because you need more and more tension, you also need to make the rope thicker and thicker and thicker. And if you try and on Earth or around Earth, build a space elevator out of steel, say, it just doesn't work. Steel is not strong enough. You need to keep doubling the thickness until by the time you get to

geostationary orbit, the thickness of the steel rope is more than the size of the earth, like the whole thing just doesn't work at all. But carbon nanotubes are this material that we discovered that are much stronger than steel. So in fact, around earth carbon nanotubes will just about work if we can make them long enough and pure enough and

then they will be strong enough that we will be able to build a space of ratio around Earth in maybe sometime in the next century that you only need a couple of doublings of the thickness of the carbon nanotubes along its entire length. So carbon nanotubes work great around Earth, but they are totally inadequate.

for black holes. For black holes, the critical material science property you need for this rope is the tensile strength to mass per unit length ratio. It needs to be strong, high tensile strength, but low weight, light, low mass per unit length. And that's the critical ratio. And carbon nanotubes is 10 to the minus 12 or something on that scale. And that is simply not strong enough at all. In fact,

What I showed in my paper is that you need a

tensile strength, the weight ratio, that is as strong as is consistent with the laws of nature. So in fact, the laws of nature bound this quantity. The finarness of the speed of light means you cannot have an arbitrarily strong rope with a given mass per unit length. There is a bound set by the c squared in some units that bounds the maximum possible tensile strength that any rope can have. Any rope, in fact, that has that. An example of a rope that has that is a string. So a string is

I mean, a fundamental string for a string theory is an example of a hypothetical rope that is just strong enough to violate, to saturate that bound, that strength bound. And then the problem is the following. The problem is that if you have a rope that saturates the bound as strong as any rope can be, it is just strong enough to support all of its own weight.

exactly on the edge there with exactly no strength left over to support any payload it might wish to carry. And that's ultimately what dooms these mining black holes, these rapid mining black hole proposals. And what happens if you try to make the rope stronger? Well, you can't. One example of a thing that goes wrong is the speed of sound in a rope is

goes up with the tension and down with a mass-ponet length. And if you try and use a rope stronger than this or some hypothetical rope, you would find that the speed of sound is greater than the speed of light. And that's a pretty good indication. So if you just take a rope, stretch between you and ping it, there will be little vibrations that head over towards you. And those vibrations

a sub-luminal, if it's just a normal rope, or move at the speed of light for a string or something that saturates analogy by analogy condition, and would be faster than the speed of light for some, you know, that'll be an example of why you know there's something wrong with that proposal. So it just happens to be the case that the rope cannot mine black holes.

I think we've mentioned a couple other bounds like this where there's no, in principle, reason you might have anticipated X and T Y there would be such a bound that prevents something that just like kind of gets in our way. But it just so happens to be this way.

Does this suggest that there's some sort of like deeper conservation principle we'd be violating and then like the universe conspires to create these engineering difficulties which limit that? Yes, nothing is ever a coincidence. So usually, you know, from the perspective of the story I just told to do with mining black holes, it's not clear what exactly will be broken about the universe. If you could mine black holes somewhat faster than we can. There are other symmetry

There are other ways of thinking about it, in which if you could make a string that was strong enough to actually do it, if you could make a rope that was stronger than this bound, that various other things would go wrong. There are various symmetry arguments that that can't happen. But yeah, usually, often it turns out, if we have these bounds, that there's something that sort of saturates the bound or gets very close to the bound. And that's a sign that you're on the right lines with some of these bounds.

on the right lines in what sense? As in, if you have a bound, but you can't think how to get closer to the bound, that's usually an indication that you need to think closer, because often these bounds are often these bounds, if you're clever enough, there's a way to get to the bound. There's no rule that has to be so, but that's often the case that someone will come up with a bound, someone will come up with, and there'll be a gap between the bound and how close we can get. And usually,

more ingenuity will take you up to the bound. I guess the thing I'm curious about is why it would be the case that, like, essentially bound would exist in the first place. And how often do you run into these things where, basically, are you expecting to discover something in the future about, like, why it had to be this way that you can't mind black holes? Like, something would be violated about, like, that tells us something important about black holes that they can't be mined. And it's deeper than the tensile strength of the string that would be required to mine it.

Yeah, good question. I started these investigations because it offended my intuition for various information theoretic reasons, the idea that black holes could be mined with parametric speeds ups.

When I thought harder about it, the reasons why I thought that couldn't happen didn't really make sense. So in this particular case, maybe someone will come up with a reason. I don't actually have a particularly strong reason where they can't be mined anymore, except that they can't.

OK, so we can't get the material out of the black hole in a piece that would make it reasonably useful to us. What can we do with black holes? What are they good for? If you have a small black hole, you can get stuff out of them more rapidly. The temperature of a black hole is inversely proportionate size. So one thing that people have talked about with black holes is using them to extract all of the energy from matter.

So, as you know...

Most chemical reactions are pretty inefficient. You burn gasoline and you extract, as a function of the rest mass of the gasoline that you started with, you extract one part in 10 billion of energy from the gasoline that you started with. So that's bad from the point of view. You have MC squared in a gallon of gasoline. You've got a full MC squared worth of energy in there, and you can only get out one part in 10 to the 10. That's a pretty unsatisfactory

situation. Roughly speaking, the reason that all chemical processes are so inefficient is that they only address the electromagnetic energy in the electrons, and very small fraction of the electromagnetic energy in an electron in atoms is stored in the electromagnetic interaction between the electrons and between the nucleus and the electrons. Most of it is stored in the nucleus itself, in the strong nuclear forces, and particularly in the rest mass of the protons and neutrons that constitute it.

So you could do much better if instead of doing electromagnetic interactions, you use nuclear interactions that that can probe the energy in turning protons into neutrons. That's why nuclear power plants are so much more efficient on a per mass basis than chemical

power plants, like coal plants or gas plants, because you're getting a much higher fraction, you know, best case scenario, you're getting one part in 10 to the three, or 10 to the four of the rest mass of the uranium that you start with, you're extracting as energy. But even there, even in that process, it's still only, you know, absolute best one part in the 1000, the rest mass. And the reason is that you are

Using where much more of the energy is stored, which is the strong and weak interactions between the protons and the neutrons, so much more is available to you. But still, at the end of whatever the process you finish with there, there's a number that'll be conserved. And that is the, what's called the burial number. So it's the total number of protons plus the total number of neutrons. You can transmute protons into neutrons or vice versa in nuclear processes, which is partially the reason they're so much more

using much more better energy than things that just affect the chemistry. But it's still most of the energy is stored in the rest mass of the protons and the neutrons. And you want to get that and nuclear processes conserve that.

beta decay will maybe turn a proton into a neutron or vice versa, but the total number of protons plus neutrons is not changing, and so therefore 99.9% of the energy is inaccessible to you. So what you need to do to get that energy and try and get most of the MC squared out of the matter that you have, what you need to do is use a process that eats

barrier number that can, in which you can start off with a proton and a neutron and end up with no proton or neutron. And instead all of that energy unleashed in high energy radiation that you can use for an emphasis. So electromagnetic interactions won't do that. Strong interactions also won't do that. Weak interactions won't do that. The only

force of nature that will do that with a small caveat. The only force of nature that we know that will do that is the gravitational interaction. And so it is a property of black holes that you can stand outside the black hole and throw protons and neutrons into the black holes. And then it'll process it and then spit out photons at the end in Hawking radiation and gravitons, such as

going to be slightly annoying to have to capture and neutrinos, but they're there in principle. And in principle, you could capture them. So one thing that black holes might be technologically useful for in the future is you start off with a much smaller black hole than what I've just done the size of the sun. Be very careful about making sure it doesn't grow. Yeah, you could be super, super careful and throw in protons and neutrons and then get out photons.

In principle, if you could capture everything that's emitted from the black hole, including the gravitons in the neutrinos, that gets rid of the barrier number conservation problem and allows you to build power plants that approach 100% efficiency. By 100%, I mean not the way we measure gas turbine efficiency, where we talk about the total available chemical energy in the gas. I mean 100% of the embassy squared of the entire gas you're putting in.