- What kind of computation do you think the fundamental laws of physics might emerge from? So just to clarify, so you've done a lot of fascinating work with kind of discrete kinds of computation that, you know, you could sell your automata, and we'll talk about it, have this very clean structure.

It's such a nice way to demonstrate that simple rules can create immense complexity. But what, you know, is that actually, are cellular automata sufficiently general to describe the kinds of computation that might create the laws of physics? Just to give, can you give a sense of what kind of computation do you think would create the laws of physics?

- So this is a slightly complicated issue, because as soon as you have universal computation, you can, in principle, simulate anything with anything. But it is not a natural thing to do, and if you're asking, were you to try to find our physical universe by looking at possible programs in the computational universe of all possible programs, would the ones that correspond to our universe be small and simple enough that we might find them by searching that computational universe?

We gotta have the right basis, so to speak. We have to have the right language in effect for describing computation for that to be feasible. So the thing that I've been interested in for a long time is what are the most structuralist structures that we can create with computation?

So in other words, if you say a cellular automaton has a bunch of cells that are arrayed on a grid, and it's very, you know, and every cell is updated in synchrony at a particular, you know, when there's a click of a clock, so to speak, and it goes a tick of a clock, and every cell gets updated at the same time.

That's a very specific, very rigid kind of thing. But my guess is that when we look at physics, and we look at things like space and time, that what's underneath space and time is something as structureless as possible. That what we see, what emerges for us as physical space, for example, comes from something that is sort of arbitrarily unstructured underneath.

And so I've been for a long time interested in kind of what are the most structuralist structures that we can set up? And actually what I had thought about for ages is using graphs, networks, where essentially, so let's talk about space, for example. So what is space? Is a kind of a question one might ask.

Back in the early days of quantum mechanics, for example, people said, "Oh, for sure, space is gonna be discrete, "'cause all these other things we're finding are discrete." But that never worked out in physics. And so space and physics today is always treated as this continuous thing, just like Euclid imagined it.

I mean, the very first thing Euclid says in his sort of common notions is, you know, "A point is something which has no part." In other words, there are points that are arbitrarily small and there's a continuum of possible positions of points. And the question is, is that true?

And so, for example, if we look at, I don't know, fluid like air or water, we might say, "Oh, it's a continuous fluid. "We can pour it, we can do all kinds of things continuously." But actually we know, 'cause we know the physics of it, that it consists of a bunch of discrete molecules bouncing around and only in the aggregate is it behaving like a continuum.

And so the possibility exists that that's true of space too. People haven't managed to make that work with existing frameworks and physics, but I've been interested in whether one can imagine that underneath space and also underneath time is something more structureless. And the question is, is it computational? So there are a couple of possibilities.

It could be computational, somehow fundamentally equivalent to a Turing machine, or it could be fundamentally not. So how could it not be? It could not be, so a Turing machine essentially deals with integers, whole numbers, some level. And it can do things like it can add one to a number, it can do things like this.

- It can also store whatever the heck it did. - Yes, it has an infinite storage. But when one thinks about doing physics or sort of idealized physics or idealized mathematics, one can deal with real numbers, numbers with an infinite number of digits, numbers which are absolutely precise. And one can say, we can take this number and we can multiply it by itself.

- Are you comfortable with infinity in this context? Are you comfortable in the context of computation? Do you think infinity plays a part? - I think that the role of infinity is complicated. Infinity is useful in conceptualizing things. It's not actualizable. Almost by definition, it's not actualizable. - But do you think infinity is part of the thing that might underlie the laws of physics?

- I think that, no. I think there are many questions that you ask about, you might ask about physics, which inevitably involve infinity. Like when you say, is faster than light travel possible? You could say, given the laws of physics, can you make something even arbitrarily large, even quotes infinitely large, that will make faster than light travel possible?

Then you're thrown into dealing with infinity as a kind of theoretical question. But I mean, talking about sort of what's underneath space and time and how one can make a computational infrastructure, one possibility is that you can't make a computational infrastructure in a Turing machine sense, that you really have to be dealing with precise real numbers, you're dealing with partial differential equations, which have precise real numbers at arbitrarily closely separated points.

You have a continuum for everything. Could be that that's what happens, that there's sort of a continuum for everything and precise real numbers for everything. And then the things I'm thinking about are wrong. And that's the risk you take if you're trying to sort of do things about nature, is you might just be wrong.

For me personally, it's kind of a strange thing, 'cause I've spent a lot of my life building technology where you can do something that nobody cares about, but you can't be sort of wrong in that sense, in the sense you build your technology and it does what it does.

But I think this question of what the sort of underlying computational infrastructure for the universe might be, so it's sort of inevitable it's gonna be fairly abstract, because if you're gonna get all these things, like there are three dimensions of space, there are electrons, there are muons, there are quarks, there are this, you don't get to, if the model for the universe is simple, you don't get to have sort of a line of code for each of those things.

You don't get to have sort of the muon case, the tau lepton case and so on. - All of those things have to be emergent somehow. - Right. - So something deeper. - Right, so that means it's sort of inevitable that it's a little hard to talk about what the sort of underlying structuralist structure actually is.

- Do you think human beings have the cognitive capacity to understand, if we're to discover it, to understand the kinds of simple structure from which these laws can emerge? Like, do you think that's a hopeless pursuit? - Well, here's what I think. I think that, I mean, I'm right in the middle of this right now.

So I'm telling you that I-- - Do you think you're hit a wall? - Yeah, I mean, this human has a hard time understanding a bunch of the things that are going on. But what happens in understanding is, one builds waypoints. I mean, if you said, understand modern 21st century mathematics, starting from counting back in, whenever counting was invented 50,000 years ago, whatever it was, right?

That will be really difficult. But what happens is we build waypoints that allow us to get to higher levels of understanding. And we see the same thing happening in language. You know, when we invent a word for something, it provides kind of a cognitive anchor, a kind of a waypoint that lets us, you know, like a podcast or something.

You could be explaining, well, it's a thing, which this works this way, that way, the other way. But as soon as you have the word podcast and people kind of societally understand it, you start to be able to build on top of that. And so I think, and that's kind of the story of science actually too.

I mean, science is about building these kinds of waypoints where we find this sort of cognitive mechanism for understanding something, then we can build on top of it. You know, we have the idea of, I don't know, differential equations, we can build on top of that. We have this idea or that idea.

So my hope is that if it is the case that we have to go all the way sort of from the sand to the computer, and there's no waypoints in between, then we're toast. We won't be able to do that. - Well, eventually we might. So if we're, us clever apes are good enough for building those abstractions, eventually from sand we'll get to the computer, right?

And it just might be a longer journey than- - The question is whether it is something that, you asked whether our human brains will quote, "Understand what's going on." And that's a different question, because for that, it requires steps that are, for whether it's sort of, from which we can construct a human understandable narrative.

And that's something that I think I am somewhat hopeful that that will be possible. Although, as of literally today, if you ask me, I'm confronted with things that I don't understand very well. - So this is a small pattern in a computation trying to understand the rules under which the computation functions.

And it's an interesting possibility under which kinds of computations such a creature can understand itself. - My guess is that within, so we didn't talk much about computational irreducibility, but it's a consequence of this principle of computational equivalence. And it's sort of a core idea that one has to understand, I think, which is, question is, you're doing a computation, you can figure out what happens in the computation just by running every step in the computation and seeing what happens.

Or you can say, let me jump ahead and figure out, have something smarter that figures out what's gonna happen before it actually happens. And a lot of traditional science has been about that act of computational reducibility. It's like, we've got these equations and we can just solve them and we can figure out what's gonna happen.

We don't have to trace all of those steps, we just jump ahead 'cause we solved these equations. Okay, so one of the things that is a consequence of the principle of computational equivalence is you don't always get to do that. Many, many systems will be computationally irreducible in the sense that the only way to find out what they do is just follow each step and see what happens.

Why is that? Well, if you're saying, well, we, with our brains, we're a lot smarter. We don't have to mess around like the little cellular automaton going through and updating all those cells. We can just use the power of our brains to jump ahead. But if the principle of computational equivalence is right, that's not gonna be correct because it means that there's us doing our computation in our brains, there's a little cellular automaton doing its computation, and the principle of computational equivalence says, these two computations are fundamentally equivalent.

So that means we don't get to say, we're a lot smarter than the cellular automaton and jump ahead 'cause we're just doing computation that's of the same sophistication as the cellular automaton itself. - That's computational irreducibility. It's fascinating, and that's a really powerful idea. I think that's both depressing and humbling and so on, that we're all, we and a cellular automaton are the same.

But the question we're talking about, the fundamental laws of physics, is kind of the reverse question. You're not predicting what's gonna happen. You have to run the universe for that. But saying, can I understand what rules likely generated me? - I understand, but the problem is, to know whether you're right, you have to have some computational reducibility because we are embedded in the universe.

If the only way to know whether we get the universe is just to run the universe, we don't get to do that 'cause it just ran for 14.6 billion years or whatever, and we can't rerun it, so to speak. So we have to hope that there are pockets of computational reducibility sufficient to be able to say, yes, I can recognize those are electrons there.

And I think that it's a feature of computational irreducibility. It's sort of a mathematical feature that there are always an infinite collection of pockets of reducibility. The question of whether they land in the right place and whether we can sort of build a theory based on them is unclear.

But to this point about whether we, as observers in the universe, built out of the same stuff as the universe, can figure out the universe, so to speak, that relies on these pockets of reducibility. Without the pockets of reducibility, it won't work, can't work. But I think this question about how observers operate, it's one of the features of science over the last hundred years particularly, has been that every time we get more realistic about observers, we learn a bit more about science.

So for example, relativity was all about observers don't get to say when, you know, what's simultaneous with what. They have to just wait for the light signal to arrive to decide what's simultaneous. Or for example, in thermodynamics, observers don't get to say the position of every single molecule in a gas.

They can only see the kind of large scale features and that's why the second law of thermodynamics, law of entropy increase and so on works. If you could see every individual molecule, you wouldn't conclude something about thermodynamics. You would conclude, oh, these molecules just all doing these particular things.

You wouldn't be able to see this aggregate fact. So I strongly expect that, and in fact, in the theories that I have, that one has to be more realistic about the computation and other aspects of observers in order to actually make a correspondence between what we experience. In fact, my little team and I have a little theory right now about how quantum mechanics may work, which is a very wonderfully bizarre idea about how the sort of thread of human consciousness relates to what we observe in the universe.

But there's several steps to explain what that's about. - What do you make of the mess of the observer at the lower level of quantum mechanics? Sort of the textbook definition with quantum mechanics kind of says that there's two worlds. One is the world that actually is, and the other is that's observed.

What do you make sense of that kind of observing? - Well, I think actually the ideas we've recently had might actually give away into this. And that's, I don't know yet. I mean, I think that's, it's a mess. I mean, the fact is there is a, one of the things that's interesting, and when people look at these models that I started talking about 30 years ago now, they say, "Oh no, that can't possibly be right.

"What about quantum mechanics?" Right? And you say, "Okay, tell me what is the essence "of quantum mechanics? "What do you want me to be able to reproduce "to know that I've got quantum mechanics, so to speak?" Well, and that question comes up, comes up very operational actually, because we've been doing a bunch of stuff with quantum computing, and there are all these companies that say, "We have a quantum computer." We say, "Let's connect to your API, "and let's actually run it." And they're like, "Well, maybe you shouldn't do that yet.

"We're not quite ready yet." And one of the questions that I've been curious about is, if I have five minutes with a quantum computer, how can I tell if it's really a quantum computer, or whether it's a simulator at the other end? Right? And turns out it's really hard.

It turns out there isn't, it's like a lot of these questions about sort of, what is intelligence, what's life? - That's a boring test for a quantum computer. - That's right, that's right. It's like, are you really a quantum computer? And I think-- - Or just a simulation, yeah.

- Yes, exactly. Is it just a simulation, or is it really a quantum computer? Same issue all over again. But that, so, you know, this whole issue about the sort of mathematical structure of quantum mechanics, and the completely separate thing that is our experience, in which we think definite things happen, whereas quantum mechanics doesn't say definite things ever happen.

Quantum mechanics is all about the amplitudes for different things to happen. But yet, our thread of consciousness operates as if definite things are happening. - To linger on the point, you've kind of mentioned the structure that could underlie everything, and this idea that it could perhaps have something like the structure of a graph.

Can you elaborate why your intuition is that there's a graph structure of nodes and edges, and what it might represent? - Right, okay. So the question is, what is, in a sense, the most structuralist structure you can imagine, right? So, and in fact, what I've recently realized in the last year or so, I have a new most structuralist structure.

- By the way, the question itself is a beautiful one and a powerful one in itself. So even without an answer, just the question is a really strong question. - Right, right. - But what's your new idea? - Well, it has to do with hypergraphs. Essentially, what is interesting about the sort of model that I have now is it's a little bit like what happened with computation.

Everything that I think of as, oh, well, maybe the model is this, I discover it's equivalent. And that's quite encouraging, because it's like I could say, well, I'm gonna look at trivalent graphs with three edges for each node and so on, or I could look at this special kind of graph, or I could look at this kind of algebraic structure, and turns out that the things I'm now looking at, everything that I've imagined that is a plausible type of structureless structure is equivalent to this.

So what is it? Well, a typical way to think about it is, well, so you might have some collection of tuples, collection of, let's say numbers. So you might have one, three, five, two, three, four, little, just collections of numbers, triples of numbers, let's say, quadruples of numbers, pairs of numbers, whatever.

And you have all these sort of floating little tuples. They're not in any particular order. And that sort of floating collection of tuples, and I told you this was abstract, represents the whole universe. The only thing that relates them is when a symbol is the same, it's the same, so to speak.

So if you have two tuples, and they contain the same symbol, let's say at the same position of the tuple, the first element of the tuple, then that represents a relation. Okay, so let me try and peel this back. - Wow, okay. (laughing) - I told you it's abstract, but this is the-- - So the relationship is formed by some aspect of sameness.

- Right, but so think about it in terms of a graph. So a graph, a bunch of nodes, let's say you number each node, okay? Then what is a graph? A graph is a set of pairs that say, this node has an edge connecting it to this other node.

So that's the, and a graph is just a collection of those pairs that say, this node connects to this other node. So this is a generalization of that, in which instead of having pairs, you have arbitrary and tuples. That's it, that's the whole story. And now the question is, okay, so that might represent the state of the universe.

How does the universe evolve? What does the universe do? And so the answer is that what I'm looking at is transformation rules on these hypergraphs. In other words, you say this, whenever you see a piece of this hypergraph that looks like this, turn it into a piece of a hypergraph that looks like this.

So on a graph, it might be, when you see the subgraph, when you see this thing with a bunch of edges hanging out in this particular way, then rewrite it as this other graph, okay? And so that's the whole story. So the question is, what, so now you say, I mean, as I say, this is quite abstract.

And one of the questions is, where do you do those updating? So you've got this giant graph. - What triggers the updating? Like what's the ripple effect of it? Is it? - Yeah. I suspect everything's discrete, even in time, so. - Okay, so the question is, where do you do the updates?

And the answer is, the rule is, you do them wherever they apply. And you do them, the order in which the updates is done is not defined. That is, you can do them, so there may be many possible orderings for these updates. Now, the point is, imagine you're an observer in this universe.

So, and you say, did something get updated? Well, you don't in any sense know until you yourself have been updated. - Right. - So in fact, all that you can be sensitive to is essentially the causal network of how an event over there affects an event that's in you.

- That doesn't even feel like observation. That's like, that's something else. You're just part of the whole thing. - Yes, you're part of it, but even to have, so the end result of that is all you're sensitive to is this causal network of what event affects what other event.

I'm not making a big statement about sort of the structure of the observer. I'm simply saying, I'm simply making the argument that what happens, the microscopic order of these rewrites is not something that any observer, any conceivable observer in this universe can be affected by. Because the only thing the observer can be affected by is this causal network of how the events in the observer are affected by other events that happen in the universe.

So the only thing you have to look at is the causal network. You don't really have to look at this microscopic rewriting that's happening. So these rewrites are happening wherever they, they happen wherever they feel like. - Causal network, is there, you said that there's not really, so the idea would be an undefined, like what gets updated, the sequence of things is undefined.

- Yes. - Is that's what you mean by the causal network, but then the-- - No, the causal network is given that an update has happened that's an event. Then the question is, is that event causally related to? Does that event, if that event didn't happen, then some future event couldn't happen yet.

- Gotcha. - And so you build up this network of what affects what. Okay? And so what that does, so when you build up that network, that's kind of the observable aspect of the universe in some sense. - Gotcha. - And so then you can ask questions about, you know, how robust is that observable network of what's happening in the universe.

Okay, so here's where it starts getting kind of interesting. So for certain kinds of microscopic rewriting rules, the order of rewrites does not matter to the causal network. And so this is, okay, mathematical logic moment, this is equivalent to the Church-Rosser property or the confluence property of rewrite rules.

And it's the same reason that if you are simplifying an algebraic expression, for example, you can say, oh, let me expand those terms out, let me factor those pieces. Doesn't matter what order you do that in, you'll always get the same answer. And that's, it's the same fundamental phenomenon that causes for certain kinds of microscopic rewrite rules that causes the causal network to be independent of the microscopic order of rewritings.

- Why is that property important? - 'Cause it implies special relativity. I mean, the reason it's important is that that property, special relativity says you can look at these sort of, you can look at different reference frames. You can have different, you can be looking at your notion of what space and what's time can be different, depending on whether you're traveling at a certain speed, depending on whether you're doing this, that, and the other.

But nevertheless, the laws of physics are the same. That's what the principle of special relativity says, is the laws of physics are the same independent of your reference frame. Well, turns out this sort of change of the microscopic rewriting order is essentially equivalent to a change of reference frame, or at least there's a sub part of how that works that's equivalent to change of reference frame.

So, somewhat surprisingly, and sort of for the first time in forever, it's possible for an underlying microscopic theory to imply special relativity, to be able to derive it. It's not something you put in as a, this is a, it's something where this other property, causal invariance, which is also the property that implies that there's a single thread of time in the universe.

It might not be the case. That's what would lead to the possibility of an observer thinking that definite stuff happens. Otherwise, you've got all these possible rewriting orders, and who's to say which one occurred. But with this causal invariance property, there's a notion of a definite thread of time.

- It sounds like that kind of idea of time, even space, would be emergent from the system. - Oh yeah. - So it's not a fundamental part of the system. - No, no, at a fundamental level, all you've got is a bunch of nodes connected by hyper edges or whatever.

- So there's no time, there's no space. - That's right. But the thing is that it's just like imagining, imagine you're just dealing with a graph, and imagine you have something like a honeycomb graph, where you have a bunch of hexagons. That graph, at a microscopic level, it's just a bunch of nodes connected to other nodes.

But at a macroscopic level, you say that looks like a honeycomb, you know, lattice. It looks like a two-dimensional, you know, manifold of some kind. It looks like a two-dimensional thing. If you connect it differently, if you just connect all the nodes one to another, in kind of a sort of linked list type structure, then you'd say, well, that looks like a one-dimensional space.

But at the microscopic level, all these are just networks with nodes. The macroscopic level, they look like something that's like one of our sort of familiar kinds of space. And it's the same thing with these hypergraphs. Now, if you ask me, have I found one that gives me three-dimensional space, the answer is not yet.

So we don't know, you know, this is one of these things, we're kind of betting against nature, so to speak. And I have no way to know. So there are many other properties of this kind of system that are very beautiful, actually, and very suggestive. And it will be very elegant if this turns out to be right, because it's very clean.

I mean, you start with nothing and everything gets built up. Everything about space, everything about time, everything about matter, it's all just emergent from the properties of this extremely low-level system. And that will be pretty cool if that's the way our universe works. Now, do I, on the other hand, the thing that I find very confusing is, let's say we succeed.

Let's say we can say this particular sort of hypergraph rewriting rule gives the universe. Just run that hypergraph rewriting rule for enough times, and you'll get everything. You'll get this conversation we're having. You'll get everything. It's that, if we get to that point and we look at what is this thing, what is this rule that we just have that is giving us our whole universe?

How do we think about that thing? Let's say, turns out the minimal version of this, and this is kind of cool thing for a language designer like me, the minimal version of this model is actually a single line of orphan language code. So that's, which I wasn't sure was gonna happen that way, but it's, it's, that's, it's kind of, no.

We don't know what, we don't know what, that's, that's just the framework. To know the actual particular hypergraph, it might be a longer, the specification of the rules might be slightly longer. - How does that help you accept marveling in the beauty and the elegance of the simplicity that creates the universe?

That does that help us predict anything? Not really, because of the irreducibility. - That's correct, that's correct. But so the thing that is really strange to me, and I haven't wrapped my brain around this yet, is, you know, one is, one keeps on realizing that we're not special, in the sense that, you know, we don't live at the center of the universe, we don't blah, blah, blah.

And yet, if we produce a rule for the universe, and it's quite simple, and we can write it down in a couple of lines or something, that feels very special. How did we come to get a simple universe, when many of the available universes, so to speak, are incredibly complicated?

Might be, you know, a quintillion characters long. Why did we get one of the ones that's simple? And so I haven't wrapped my brain around that issue yet. - If indeed we are in such a simple, the universe is such a simple rule, is it possible that there is something outside of this, that we are in a kind of what people call, so the simulation, right?

That we're just part of a computation that's being explored by a graduate student in an alternate universe? - Well, you know, the problem is, we don't get to say much about what's outside our universe, because by definition, our universe is what we exist within. Now, can we make a sort of almost theological conclusion from being able to know how our particular universe works?

Interesting question. I don't think that, if you ask the question, could we, and it relates again to this question about the extraterrestrial intelligence, you know, we've got the rule for the universe. Was it built in on purpose? Hard to say. That's the same thing as saying, we see a signal from, you know, that we're receiving from some random star somewhere, and it's a series of pulses, and, you know, it's a periodic series of pulses, let's say.

Was that done on purpose? Can we conclude something about the origin of that series of pulses? - Just because it's elegant does not necessarily mean that somebody created it, or that we can even comprehend what would create it. - Yeah, I mean, I think it's the ultimate version of the sort of identification of the technosignature question.

It's the ultimate version of that, which is, was our universe a piece of technology, so to speak, and how on earth would we know? Because, but I mean, it'll be, it's, I mean, you know, in the kind of crazy science fiction thing you could imagine, you could say, oh, somebody's going to have, you know, there's gonna be a signature there.

It's gonna be, you know, made by so-and-so. But there's no way we could understand that, so to speak, and it's not clear what that would mean, because the universe simply, you know, this, if we find a rule for the universe, we're not, we're simply saying that rule represents what our universe does.

We're not saying that that rule is something running on a big computer and making our universe. It's just saying that represents what our universe does, in the same sense that, you know, laws of classical mechanics, differential equations, whatever they are, represent what mechanical systems do. It's not that the mechanical systems are somehow running solutions to those differential equations.

Those differential equations are just representing the behavior of those systems. - So what's the gap, in your sense, to linger on the fascinating, perhaps slightly sci-fi question? What's the gap between understanding the fundamental rules that create a universe and engineering a system, actually creating a simulation ourselves? You've talked about, sort of, you've talked about, you know, nanoengineering, kind of ideas that are kind of exciting, actually creating some ideas of computation in the physical space.

How hard is it, as an engineering problem, to create the universe, once you know the rules that create it? - Well, that's an interesting question. I think the substrate on which the universe is operating is not a substrate that we have access to. I mean, the only substrate we have is that same substrate that the universe is operating in.

So, if the universe is a bunch of hypergraphs being rewritten, then we get to attach ourselves to those same hypergraphs being rewritten. We don't get to, and if you ask the question, you know, is the code clean? You know, can we write nice, elegant code with efficient algorithms and so on?

Well, that's an interesting question. How, you know, that's this question of how much computational reducibility there is in the system. - But, so I've seen some beautiful cellular automata that basically create copies of itself within itself, right? So, that's the question, whether it's possible to create, like, whether you need to understand the substrate or whether you can just-- - Yeah, well, right.

I mean, so one of the things that is sort of one of my slightly sci-fi thoughts about the future, so to speak, is, you know, right now, if you poll typical people, you say, "Do you think it's important to find "the fundamental theory of physics?" You get, because I've done this poll, informally at least, it's curious, actually.

You get a decent fraction of people saying, "Oh, yeah, that would be pretty interesting." - I think that's becoming, surprisingly enough, more, I mean, a lot of people are interested in physics in a way that, like, without understanding it, just kind of watching scientists, a very small number of them, struggle to understand the nature of our reality.

- Right, I mean, I think that's somewhat true, and in fact, in this project that I'm launching into to try and find the fundamental theory of physics, I'm going to do it as a very public project. I mean, it's gonna be live-streamed and all this kind of stuff, and I don't know what will happen, it'll be kind of fun.

I mean, I think that it's the interface to the world of this project. I mean, I figure one feature of this project is, you know, unlike technology projects that basically are what they are, this is a project that might simply fail, because it might be the case that it generates all kinds of elegant mathematics, but it has absolutely nothing to do with the physical universe that we happen to live in.

Well, okay, so we're talking about kind of the quest to find the fundamental theory of physics. First point is, you know, it's turned out it's kind of hard to find the fundamental theory of physics. People weren't sure that that would be the case. Back in the early days of applying mathematics to science, 1600s and so on, people were like, "Oh, in 100 years, we'll know everything there is to know "about how the universe works." Turned out to be harder than that, and people got kind of humble at some level, 'cause every time we got to sort of a greater level of smallness in studying the universe, it seemed like the math got more complicated and everything got harder.

When I was a kid, basically, I started doing particle physics, and when I was doing particle physics, I always thought finding the fundamental, fundamental theory of physics, that's a kooky business, we'll never be able to do that. But we can operate within these frameworks that we built for doing quantum field theory and general relativity and things like this, and it's all good, and we can figure out a lot of stuff.

- Did you even at that time have a sense that there's something behind that too? - Sure, I just didn't expect that. I thought in some rather un, it's actually kind of crazy thinking back on it, because it's kind of like there was this long period in civilization where people thought the ancients had it all figured out and will never figure out anything new.

And to some extent, that's the way I felt about physics when I was in the middle of doing it, so to speak, was we've got quantum field theory, it's the foundation of what we're doing, and yes, there's probably something underneath this, but we'll sort of never figure it out.

But then I started studying simple programs in the computational universe, things like cellular automata and so on, and I discovered that they do all kinds of things that were completely at odds with the intuition that I had had. And so after that, after you see this tiny little program that does all this amazingly complicated stuff, then you start feeling a bit more ambitious about physics and saying, maybe we could do this for physics too.

And so that got me started years ago now in this kind of idea of could we actually find what's underneath all of these frameworks like quantum field theory and general relativity and so on. And people perhaps don't realize as clearly as they might that the frameworks we're using for physics, which is basically these two things, quantum field theory, sort of the theory of small stuff and general relativity, theory of gravitation and large stuff, those are the two basic theories, and they're 100 years old.

I mean, general relativity was 1915, quantum field theory, well, 1920s. So basically 100 years old. And it's been a good run. There's a lot of stuff been figured out. But what's interesting is the foundations haven't changed in all that period of time. Even though the foundations had changed several times before that in the 200 years earlier than that.

And I think the kinds of things that I'm thinking about, which are sort of really informed by thinking about computation and the computational universe, it's a different foundation. It's a different set of foundations and might be wrong, but it is at least, we have a shot. And I think it's, to me, it's, my personal calculation for myself is, is, you know, if it turns out that the finding the fundamental theory of physics, it's kind of low hanging fruit, so to speak, it'd be a shame if we just didn't think to do it.

You know, if people just said, oh, you'll never figure that stuff out. Let's, you know, and it takes another 200 years before anybody gets around to doing it. You know, I think it's, I don't know how low hanging this fruit actually is. It may be, you know, it may be that it's kind of the wrong century to do this project.

I mean, I think the cautionary tale for me, you know, I think about things that I've tried to do in technology where people thought about doing them a lot earlier. And my favorite example is probably Leibniz who thought about making essentially encapsulating the world's knowledge in a computational form in the late 1600s and did a lot of things towards that.

And basically, you know, we finally managed to do this, but he was 300 years too early. And that's kind of the, in terms of life planning, it's kind of like avoid things that can't be done in your century, so to speak. - Yeah, timing, timing is everything. So you think if we kind of figure out the underlying rules it can create from which quantum field theory and general relativity can emerge, do you think that'll help us unify it at that level of abstraction?

- Oh, we'll know it completely. We'll know how that all fits together. Yes, without a question. And I mean, it's already, even the things I've already done, there are very, you know, it's very, very elegant actually, how things seem to be fitting together. Now, you know, is it right?

I don't know yet. It's awfully suggestive. If it isn't right, it's then the designer of the universe should feel embarrassed, so to speak, 'cause it's a really good way to do it. - And your intuition in terms of design universe, does God play dice? Is there randomness in this thing, or is it deterministic?

So the kind of-- - That's a little bit of a complicated question because when you're dealing with these things that involve these rewrites that have, okay. - Even randomness is an emergent phenomenon perhaps? - Yes, yes. I mean, it's a, yeah, well, randomness, in many of these systems, pseudo-randomness and randomness are hard to distinguish.

In this particular case, the current idea that we have about measurement and quantum mechanics is something very bizarre and very abstract, and I don't think I can yet explain it without kind of yakking about very technical things. Eventually I will be able to, but if that's right, it's kind of a, it's a weird thing because it slices between determinism and randomness in a weird way that hasn't been sliced before, so to speak.

So like many of these questions that come up in science where it's like, is it this or is it that? Turns out the real answer is it's neither of those things. It's something kind of different and sort of orthogonal to those categories. And so that's the current, you know, this week's idea about how that might work.

But, you know, we'll see how that unfolds. I mean, there's this question about a field like physics and sort of the quest for fundamental theory and so on. And there's both the science of what happens and there's the sort of the social aspect of what happens because, you know, in a field that is basically as old as physics, we're at, I don't know what it is, fourth generation, I don't know, fifth generation, I don't know what generation it is of physicists.

And like, I was one of these, so to speak. And for me, the foundations were like the pyramids, so to speak, you know, it was that way and it was always that way. It is difficult in an old field to go back to the foundations and think about rewriting them.

It's a lot easier in young fields where you're still dealing with the first generation of people who invented the field. And it tends to be the case, you know, that the nature of what happens in science tends to be, you know, you'll get, typically the pattern is some methodological advance occurs.

And then there's a period of five years, 10 years, maybe a little bit longer than that, where there's lots of things that are now made possible by that methodological advance, whether it's, you know, I don't know, telescopes or whether that's some mathematical method or something. It's, you know, there's a, something happens, a tool gets built, and then you can do a bunch of stuff.

And there's a bunch of low-hanging fruit to be picked. And that takes a certain amount of time. After that, all that low-hanging fruit is picked, then it's a hard slog for the next however many decades or century or more to get to the next sort of level at which one can do something.

And it's kind of a, and it tends to be the case that in fields that are in that kind of, I wouldn't say cruise mode, 'cause it's really hard work, but it's very hard work for very incremental progress. (laughing) (silence) (silence) (silence) (silence) (silence) (silence)