Stephen Wolfram: Fundamental Theory of Physics, Life, and the Universe | Lex Fridman Podcast #124

Lex Fridman 0:00 The following is a conversation with Stephen Wolfram, his second time on the podcast. He's a computer scientist, mathematician, theoretical physicist, and the founder and CEO of Wolfram Research, a company behind Mathematica, Wolfram|Alpha, Wolfram Language, and the new Wolfram Physics project. He's the author of several books, including A New Kind of Science, and the new book, A Project to Find the Fundamental Theory of Physics. The second round of our conversation is primarily focused on this latter endeavor of searching for the physics of our universe in simple rules that do their work on hypergraphs and eventually generate the infrastructure from which space, time, and all of modern physics can emerge. Quick summary of the sponsors: SimpliSafe, Sunbasket, and MasterClass. Please check out these sponsors in the description to get a discount and to support this podcast. As a side note, let me say that, to me, the idea that seemingly infinite complexity can arise from very simple rules and initial conditions is one of the most beautiful and important mathematical and philosophical mysteries in science. I find that both cellular automata and the hypergraph data structure that Stephen and team are currently working on to be the kind of simple, clear mathematical playground within which fundamental ideas about intelligence, consciousness, and the fundamental laws of physics could be further developed in totally new ways. In fact, I think I'll try to make a video or two about the most beautiful aspects of these models in the coming weeks, especially, I think, trying to describe how fellow curious minds like myself can jump in and explore them either just for fun or potentially for publication of new innovative research in math, computer science and physics. But honestly, I think the emerging complexity in these hypergraphs can capture the imagination of everyone, even if you're someone who never really connected with mathematics. That's my hope at least, to have these conversations that inspire everyone to look up to the skies and into our own minds in awe of our amazing universe. Let me also mention that this is the first time I ever recorded a podcast outdoors as a kind of experiment to see if this is an option in times of COVID. I'm sorry if the audio is not great. I did my best and promise to keep improving and learning as always. If you enjoy this thing, subscribe on YouTube, review it with five stars on Apple Podcast, follow on Spotify, support on Patreon, or connect with me on Twitter @lexfridman. As usual, I'll do a few minutes of ads now and no ads in the middle. I try to make these interesting, but I do give you timestamps so you're welcome to skip, but still please do check out the sponsors by clicking the links in the description. It's the best way to support this podcast. Also, let me say, even though I'm talking way too much, that I did a survey and it seems like over 90% of people either enjoy these ad reads somehow magically or don't mind them at least. That honestly just warms my heart that people are that supportive. This show is sponsored by SimpliSafe, a home security company. Go to simplisafe.com to get a free HD camera. It's simple, no contracts, 15 bucks a month, easy setup. Even I figured it out. I have it set up in my apartment. Of course, I also welcome intruders. One of my favorite movies is Leon or The Professional with Jean Reno, Gary Oldman, and the brilliant young Natalie Portman. If you haven't seen the movie, he's a hitman with a minimalist life that resembles my own. In fact, when I was younger, the idea of being a hitman or targeting evil in a skilled way, which is how I thought about it, really appealed to me. The skill of it, the planning, the craftsmanship. In another life perhaps, if I didn't love engineering and science so much, I could see myself being something like a Navy SEAL and, in general, I love the idea of serving my country, of serving society by contributing my skill in some small way. Anyway, go to simplisafe.com/lex to get a free HD camera and to support this podcast. They're a new sponsor and this is a trial run, so you know what to do. This show is also sponsored by Sunbasket, a meal delivery service. Visit sunbasket.com/lex and use code Lex to get $30 off your order and to support this podcast. This is the last read of the trial they're doing so this is the time to get them if you're considering it, and if you do, it'll help ensure that they decide to support this podcast long term. Their meals are healthy and delicious, a nice break from the minimalist meals of meat and vegetables that I usually eat. Maybe on a personal note, one of my favorite things to do is watch people cook, especially people who love cooking, and hang out with people over amazing meals. I still tend to be strict in my diet no matter what, even in fancy restaurants, but it brings me joy to see friends and family indulge in something like a cake that has way too many calories or ice cream or whatever. My mom, in fact, for much of my life made this cake called an anthill on my birthday that brings me a lot of joy and way too many calories (laughs) . I was thinking of doing a video with my mom as she makes it. I thought it'd be a fun thing to, to do together. Anyway, go to sunbasket.com/lex and use code Lex. Do it now so they sign a long term contract with this podcast. This show is also sponsored by MasterClass. Sign up at masterclass.com/lex. 180 bucks a year, you get an all-access pass to watch lessons from Chris Hadfield, Neil deGrasse Tyson, Tony Hawk, Carlos Santana, Garry Kasparov, Daniel Negrano, and many more brilliant world experts.Masterclass has been a really special sponsor. They believe in this podcast in a way that gives me strength and motivation to take intellectual risks. I'm thinking of doing a few solo podcast episodes on difficult topics, especially in history, like the rise and fall of the Third Reich, or Stalin, Putin, and many other difficult topics that I'm fascinated by. I have a worldview that seeks inspiring positive insights even, and perhaps especially, from periods of tragedy and evil that perhaps some folks may find value in if I can only learn to convey the ideas in my mind as clearly as I think them. I think deeply and rigorously and precisely, but to be honest, have trouble speaking in a way that reflects that rigor of thought. So, it really does mean a lot, the love and support I get as I try to get better at this thing, at this talking thing. Anyway, go to masterclass.com/lex to get a discount and to support this podcast. And now, finally, here's my conversation with Stephen Wolfram.

Lex Fridman 7:14 You said that there are moments in history of physics, and maybe mathematical physics or even mathematics, where breakthroughs happen and then a flurry of progress follows. So, if you look back through the history of physics, are, what moments stand out to you as important such breakthroughs where a flurry of progress follows?

Stephen Wolfram 7:34 So, the big famous one was 1920s, the invention of quantum mechanics, where, you know, in about five or 10 years, lots of stuff got figured out that's now quantum mechanics.

Lex Fridman 7:45 Can you mention the people involved?

Stephen Wolfram 7:46 Yeah.

Lex Fridman 7:46 Like, key people?

Stephen Wolfram 7:46 It was kind of the Schrodinger, Heisenberg, you know, Einstein had been a key figure. Originally Planck, then Dirac was a little bit later. That was something that happened at that time. That's sort of before my time, right?

Lex Fridman 7:59 (laughs)

Stephen Wolfram 8:00 In my time was in the 1970s, uh, there was this sort of realization that quantum field theory was actually going to be useful in physics, and, uh, QCD, quantum chromodynamics theory of quarks and gluons and so on, was really getting started. And, uh, there was again, sort of big flurry of things happened then. I happened to be a teenager at that time, and happened to be, uh, really involved in physics. And so I got to be part of that, which was really cool.

Lex Fridman 8:29 Who- who were the key figures, aside from your young selves at that time?

Stephen Wolfram 8:33 You know, who won the Nobel Prize for QCD, okay? People, David Gross, Frank Wilczek, you know, um, David Politzer. The people who were the sort of the slightly older generation, Dick Feynman, Murray Gell-Mann, people like that, uh, uh, who were Steve Weinberg, Gerard 'Hoft, he's younger. He's, he's in the younger group, actually. But, um, these are, these are all, you know, characters who were involved. I mean, it was, uh, you know, it's funny because those are all people who were kind of in my time, and I know them, and they don't seem like sort of, uh, these historical...

Lex Fridman 9:08 (laughs) Einstein figures.

Stephen Wolfram 9:08 ... you know, iconic figures. They seem more like, uh, everyday characters, so to speak. Um, and, uh, so it's always, you know, wh- when you look at history from long afterwards, it always seems like everything happened instantly, um, and that's usually not the case. There was usually a long build-up. But usually there's, you know, there's some methodological thing happens, and then there's a whole bunch of low-hanging fruit to be picked, and that usually lasts five or 10 years. You know, we see it today with machine learning, and, you know, uh, deep learning neural nets and so on. You know, methodological advance, things actually started working in, you know, 2011, 2012, and so on. And, uh, you know, there's been this sort of rapid, uh, picking of low-hanging fruit, which is probably, you know, mm, some significant fraction of the way, way done, so to speak.

Lex Fridman 10:00 Do you think there's a key moment? Like, if I had to really introspect, like what was the key moment for the deep learning, quote unquote, revolution? I mean-

Stephen Wolfram 10:08 Th- it's probably the AlexNet business

Narrator 10:10 Yeah.

Lex Fridman 10:10 ... with ImageNet.

Stephen Wolfram 10:11 Yeah.

Lex Fridman 10:11 So, is there something like that with physics where... So, deep learning neural networks have been around for a long time.

Stephen Wolfram 10:20 Absolutely. It's the 1940s, yeah.

Lex Fridman 10:22 There's a bunch of little... There's a bunch of little pieces that came together, and then all of a sudden everybody's eyes lit up. Like, wow.

Stephen Wolfram 10:28 Right.

Lex Fridman 10:28 There's something here. Like, even just looking at your own work, just your thinking about the universe, that there is simple rules can create complexity. You know, at which point was there a thing where your eyes light up? It's like, wait a minute, there's something here. Is it the very first idea, or is it some moment along the line of implementations and experiments and so on?

Stephen Wolfram 10:54 Yeah. There's, there's a couple of different stages to this. I mean, one is the think about the world computationally. You know, can we use programs instead of equations to make models of the world? That's something that I got interested in in the, at the beginning of the 1980s. You know, I did a bunch of computer experiments. Uh, you know, when I first did them, I didn't really, I s- I could see some significance to them, but took me a few years to really say, "Wow, there's a, a big important phenomenon here that lets sort of complex things arise from very simple programs." Um, that kind of happened back in 1984 or so. Then, you know, bunch of other years go by, then I start actually doing, uh, a lot of much more systematic computer experiments and things and find out that the, you know, this phenomenon that I could only have said occurs in one particular case is actually something incredibly general. And then that led me to this thing called principle of computational equivalence, and that was a, a long story. And then, you know, as part of that process, I was like, "Okay, you can make... Simple programs can make models of complicated things. What about the whole universe?" That's our sort of ultimate example of a complicated thing.

Lex Fridman 12:03 Yeah.

Stephen Wolfram 12:03 And so I got to thinking, you know, could we use these ideas to, to study fundamental physics?... a you know, I happen to know a lot about, you know, traditional fundamental physics. My, um, uh, my first, you know... I, I had a bunch of ideas about how to do this in the early 1990s. I made a bunch of technical progress, I figured out a bunch of things I thought were pretty interesting, you know, I wrote about them back in 2002. Um-

Lex Fridman 12:26 With A New Kind of Science and The Cellular Automata World and-

Stephen Wolfram 12:29 Right.

Lex Fridman 12:29 ... there's echoes in The sem- Cellular Automata World with your new, uh, Wolfram Physics Project world. We'll get to all that. Allow me to-

Stephen Wolfram 12:38 Yeah.

Lex Fridman 12:38 ... sort of romanticize a little more on the philosophy of science. (laughs) Uh,

Lex Fridman 12:43 so Thomas Kuhn, a philosopher of science, describes that, you know, the progress in science is made with, uh, these paradigm shifts. And so to linger on the sort of original line of discussion, do you agree with this view that there is revolutions in science that just kind of flip the table?

Stephen Wolfram 13:03 Yeah. What happens is, it's a different way of thinking about things, it's a different methodology for studying things, and that opens stuff up.

Lex Fridman 13:11 There's this idea of, uh... (sighs) He's a famous biographer but I think it's called The Innovators. The biographer of Steve Jobs, of Albert Einstein-

Stephen Wolfram 13:22 Oh, yeah.

Lex Fridman 13:22 He also wrote a book, I think it's called The Innovators, where it, he discusses, uh, how a lot of, uh, the innovations in the history of computing has been done by groups. There's complicated group dynamic going on. But there's also a romanticized notion that the individual is at the core of the revolution. Like, where does your sense fall? Is, is, um, ultimately, like, one person responsible for these revolutions that, that creates the spark? Or one or two, whatever, but... Or is it just the big mush and mess and chaos of, of people interacting, of personalities interacting ...?

Stephen Wolfram 14:01 I think it ends up being like many things. There's leadership and there ends up being... It's a lot easier for one person to have a crisp new idea than it is for a big committee to have a crisp new idea.

Lex Fridman 14:10 Yeah.

Stephen Wolfram 14:10 And, um, I think, you know... But I think it, it can happen that, you know, you have a great idea but the world isn't ready for y- for it. And, um, you know, you can, you can... I mean, this has happened to me plenty, right? It's, you know, you have an idea, it's actually a pretty good idea but things aren't ready. Either, either you're not really ready for it or the ambient world isn't ready for it, and it's hard to get the thing to, to get traction.

Lex Fridman 14:37 It's kind of interesting. I, I mean when I look at A New Kind of Science, you're now living inside the history so you can't tell the story of these decades. But it seems like The New Kind of Science has not had the revolutionary impact I would think it, uh, might. Like, it feels like at some point, of course it might be, but it feels at some point people will return to that book and say, "There was something special here. This was-"

Stephen Wolfram 15:10 Well, look, wha- what happened-

Lex Fridman 15:11 "... incredible." So... Or do you think that's already happened?

Stephen Wolfram 15:13 Oh, yeah, it's happened except that people aren't, you know... The, the sort of the heroism of it may not be there. But the, what's happened is, for 300 years people basically said if you want to make a model of things in the world, mathematical equations are the best place to go. Last 15 years, doesn't happen. You know, new models that get made of things most often are made with programs, not with equations.

Lex Fridman 15:38 Mm-hmm.

Stephen Wolfram 15:38 Now, you know, was that sort of going to happen anyway? Was that a consequence of, you know, my particular work and my particular book? It's hard to know for sure. I mean, I am always amazed at the amount of feedback that I get from people where they say, "Oh, by the way, you know, I started doing this whole line of research because I read your book blah blah blah blah blah." It's like, well, can you tell that from the academic literature? You know, were, was there a chain of, you know, academic references? Probably not.

Lex Fridman 16:05 One of the interesting side effects of publishing in the way you did this tome is it serves as an education tool and an inspiration to hundreds of thousands, millions of people. But because it's not a single, uh, is, it's not a chain of papers with spiffy titles, it doesn't create a splash of citations. Like-

Stephen Wolfram 16:28 No, it's had, it's had plenty of citations. But it's, it's, you know, I think that the, it... People think of it as probably more, you know, conceptual inspiration than, uh, than kind of a, you know, this is a line from here to here to here in our particular field.

Lex Fridman 16:45 Right.

Stephen Wolfram 16:45 I think that the, you know, the thing which I am disappointed by, and which will eventually happen, is this kind of study of the, this sort of pure computationalism, this kind of study of the abstract behavior of the computational universe. That should be a big thing that lots of people do. ... get to-

Lex Fridman 17:04 You mean in mathematics purely, almost like for some-

Stephen Wolfram 17:06 It's like pure mathematics, but it isn't mathematics.

Lex Fridman 17:08 But it isn't. It, it isn't.

Stephen Wolfram 17:10 It's different.

Lex Fridman 17:10 It's a new kind of mathematics is, is it... (laughs) And the title of the book-

Stephen Wolfram 17:14 A new kind of science. Yeah, right. (laughs)

Lex Fridman 17:15 (laughs) It's a good title.

Stephen Wolfram 17:15 That's why the book is called that, right?

Lex Fridman 17:17 (laughs)

Stephen Wolfram 17:17 That, that's not coincidental. (laughs)

Lex Fridman 17:20 Yeah. It's interesting that I haven't seen really rigorous investigation by thousands of people of this idea. I mean, you look at your competition around Rule 30. I mean, that's fascinating if y- if you can say something...

Stephen Wolfram 17:34 Right.

Lex Fridman 17:35 Is there some aspect of this thing that could be predicted?

Stephen Wolfram 17:38 Right.

Lex Fridman 17:38 That's the fundamental question of science. That's the core-

Stephen Wolfram 17:41 Well, that has been a question of science. I think that's a, that is a, some people's view of what science is about, and it's not clear that's the right view. In fact, as we, as we live through this pandemic full of predictions and so on, it's an interesting moment to be pondering what, what science's actual role in those kinds of things is.

Lex Fridman 17:58 Oh, you think it's possible that in science, clean, beautiful, simple prediction may not even be possible in real systems? That's the open question ... question I don't know.

Stephen Wolfram 18:08 Right. I don't think it's open, I think that question is answered and the answer is no. (laughs) I mean-

Lex Fridman 18:12 (laughs) Well, no, no, no answer could be just humans are not smart enough yet.... like we don't have the tools yet.

Stephen Wolfram 18:17 No. No. That's, that's the whole point. I mean, that's, that's sort of the big discovery of this principle of computational equivalence of mine, and, um, the, uh, you know, this is something which is kind of a follow-on to Godel's theorem, to Turing's work on the Halting problem, all these kinds of things. That there is this fundamental limitation built into science, this idea of computational irreducibility that says that, you know, even though you may know the rules by which something operates, that does not mean that you can, uh, readily sort of be smarter than it and jump ahead and figure out what it's going to do.

Lex Fridman 18:51 Yes, but do you think there's a hope for pockets of computational reducibili- computational re- uh-

Stephen Wolfram 18:58 Reducibility.

Lex Fridman 19:01 ... reducibility.

Stephen Wolfram 19:01 Yes. Yes.

Lex Fridman 19:01 Like, that's... so, and then, and then a set of tools and mathematics that help you discover such pockets.

Stephen Wolfram 19:07 That's where we live, is in the pockets of reducibility.

Lex Fridman 19:09 Right.

Stephen Wolfram 19:10 That's why, you know, and this is one of the things that's sort of come out of this physics project, and actually something that, again, I should have realized many years ago but didn't, um, is, uh, you know, the, it, it could very well be that everything about the world is computationally irreducible and completely unpredictable, but, you know, in our experience of the world, there is at least some amount of prediction we can make. And that's because we have sort of chosen a slice of, um, probably talk about this in, in much more detail, but, I mean, we've kind of chosen a slice of how to think about the universe in which we can kind of sample a certain amount of computational reducibility, and that's, that's sort of where we, where we exist. Um, and, uh, it may not be the whole story of how the universe is, but it is the part of the universe that we care about and we sort of operate in, and, um, that's, you know, in science, that's been sort of a very special case of that. That is, science has chosen to talk a lot about places where there is this computational reducibility that it can find, you know, the motion of the planets can be more or less predicted, you know, the, uh, uh, something about the weather is much harder to predict, something about, uh, you know, other kinds of things the, the, um, are much harder to predict and it, it's, um, uh, these are- but science has tended to, you know, concentrate itself on places where its methods have allowed successful prediction.

Lex Fridman 20:35 So, you think Rule 30, if we could linger on it, because it's just such a beautiful, simple formulation of the essential concept underlying all the things we're talking about, do you think there's pockets of reducibility inside Rule 30?

Stephen Wolfram 20:48 Yes. But it's a question of how big are they, what will they allow you to say, and so on, and that's, and figuring out where those pockets are, I mean, in a sense, that's the, that's sort of a, a, a, you know, that is an essential thing that one would like to do in science. Um, but it's, it's also, the, the important thing to realize that, that has not been, you know, is, is that science, if you just pick an arbitrary thing and you say, "What's the answer to this question?" That question may not be one that has a computationally reducible answer. That question, if you, if you choose, you know, if, if you walk along the series of questions and you've got one that's reducible and you get to another one that's nearby and it's reducible too, if you stick to that kind of, stick to the land, so to speak-

Lex Fridman 21:36 Yeah.

Stephen Wolfram 21:37 ... then you can go down this chain of sort of reducible, answerable things. But if you just say, "I'm gonna just pick a question at random. I'm gonna have my computer pick a question at random-"

Lex Fridman 21:47 Yeah.

Stephen Wolfram 21:47 ... uh, you know-

Lex Fridman 21:47 Most likely it's gonna be irreducible.

Stephen Wolfram 21:49 Most likely it will be irreducible. And, and what we're throwing in the world, so to speak, uh, we, you know, when we engineer things, we tend to engineer things to sort of keep in the zone of reducibility. When we're throwing things by the natural world, for example, not, not at all certain that we will be kept in this kind of zone of reducibility.

Lex Fridman 22:08 Can we talk about this pandemic then-

Stephen Wolfram 22:11 Sure.

Lex Fridman 22:11 ... (laughs) for a second?

Stephen Wolfram 22:13 A little bit. Yeah.

Lex Fridman 22:13 Is, so how do we... so there's obviously huge amount of economic pain that people are feeling, there's a huge incentive and medical pain, uh, health, just all kind- psychological, there's a huge incentive to figure this out, to walk along the trajectory of reducible, of reducibility. Uh, there's a, there's a, a lot of disparate data. You know, people understand generally how viruses spread, but it's very complicated because there's a lot of uncertainty, uh, there's, uh, there could be a lot of variability, like, so many, obviously a nearly infinite number of variables that, uh, that represent human interaction, and so you have to figure out inter- from the perspective of reducibility, figure out which variables, uh, are really important in this kind of, uh, from an epidemiological perspective. So, why aren't we... you kind of said that we're clearly failing. (laughs)

Stephen Wolfram 23:16 Well, I, I think it's a complicated thing. So, so, I mean, you know, when this pandemic started up, you know, I happened to be in, in the middle of being about to release this whole physics project thing-

Lex Fridman 23:24 Yes.

Stephen Wolfram 23:24 ... but I thought, you know-

Lex Fridman 23:25 The timing is just, uh, cosmically absurd.

Stephen Wolfram 23:28 A little bit, a little bit bizarre.

Lex Fridman 23:29 Yeah.

Stephen Wolfram 23:29 But, but, um, but, you know, but I thought, you know, I, I should do the public service thing of, you know, trying to understand what I could about the pandemic and, you know, we'd been curating data about it and all that kind of thing, but, but, you know, so I started looking at the data and started looking at modeling, and I decided it's just really hard. You need to know a lot of stuff that we don't know about human interactions. It's actually clear now that there's a lot of stuff we didn't know about viruses, um, and about the way immunity works and so on. And, um, it's, you know, I think what will come out in the end is there's a certain amount of, of what happens that way you just kind of have to trace each step and see what happens. There's a certain amount of stuff where there's gonna be a big narrative about th- this happened because, you know, of T-cell immunity. This ca- happened because there's this whole giant sort of field of, of, of asymptomatic viral stuff out there. You know, there will be a narrative, and that narrative, whenever there's a narrative, that's kind of a sign of reducibility. But when you just say, "Let's, from first principles, figure out what's going on," then you can potentially be stuck in this kind of, uh, mess of irreducibility where you just have to simulate each step, and you can't do that unless you know details about, you know, human interaction networks and so on and so on and so on. The thing that has, has been very-... sort of frustrating to see is the mismatch between people's expectations about what science can deliver and what science can actually deliver, so to speak. Um, because people have this idea that, you know, it's science, so there must be a definite answer, and we must be able to know that answer. And, you know, this is, it is both, uh, uh, you know, the- the- when you've- after you've played around with sort of little programs in the computational universe, you don't have that intuition anymore. You know, it's- it's- I always- I'm always fond of saying, you know, the- the- the- the computational animals are always smarter than you are. That is, you know, you look at one of these things and it's like, "It can't possibly do such and such a thing." Then you run it and it's like, "Wait a minute, it's doing that thing. How does that work? Okay, now I can go back and understand it."

Lex Fridman 25:29 But that's the brave thing about science, is that in the chaos of the irreducible universe, we nevertheless persist to find those pockets, that's kind of the whole point. That's- like, you say that the limits of science, but that, you know, yes, it's highly limited, but th- there's a hope there. And, like, uh, there- there's so many questions I wanna ask here. So one, you said narrative, which is really interesting. So obviously from a- at every level of society, you look at Twitter, everybody's constructing narratives about the pandemic, about not just the pandemic, but all the cultural tension that we're going through. So there's narratives, but they're not necessarily connected to the underlying reality of these systems. So our human narratives, I don't even know if they're... I don't like those pockets of reducibility 'cause we're, um, it's like constructing things that are not actually representative of reality-

Stephen Wolfram 26:32 Well, but-

Lex Fridman 26:33 ... and thereby not giving us, like, good solutions to how to pre- predict the system.

Stephen Wolfram 26:39 Look, it- it gets complicated because, you know, people want to say, "Explain the pandemic to me. Explain what's gonna happen."

Lex Fridman 26:45 In the future, like predict-

Stephen Wolfram 26:46 Yes, but- but also, can you explain it? Is there a story to tell?

Lex Fridman 26:49 What already happened in the past?

Stephen Wolfram 26:51 Yeah, or- or-

Lex Fridman 26:51 Just- just in general.

Stephen Wolfram 26:52 ... what's going to happen. But I mean, and- and, you know, it's similar to sort of ex- explaining things in AI or in any computational system. It's like, like, you know, explain what happened. Well, it could just be this happened because of this detail and this detail and this detail and a million details, and there isn't a big story to tell. There's no kind of big arc of the story that says, "Oh, it's because, you know, there's a viral field that has these properties and people start showing symptoms, you know, when- when the seasons change, people will show symptoms," and people don't even understand, you know, seasonal variation of flu, for example. It's a- it's a, um, uh, it's something where- where, you know, there- there could be a big story or it could be just a zillion little details that- that mount up.

Lex Fridman 27:33 See, but... Okay. Let's- let's, uh, pretend that this pandemic, like the coronavirus resembles something like the 1D Rule 30 cellular automata, okay? So, I mean, that's how e- epidemiologists model virus spread.

Stephen Wolfram 27:51 Indeed, yes.

Lex Fridman 27:52 Is there some graphs-

Stephen Wolfram 27:52 They sometimes use cellular automata, yes.

Lex Fridman 27:54 Yeah. So... Yeah. And, okay, so you could say it's simplistic, but... Okay, let's say it- it is- it's representative of actually what happens. Uh, you know, the- the dynamic of you have a graph, it probably is closer to the hypergraph, uh, model.

Stephen Wolfram 28:10 It is, yes. It's- it's actually...

Lex Fridman 28:11 (laughs)

Stephen Wolfram 28:11 That's- that's another funny thing.

Lex Fridman 28:12 Yeah.

Stephen Wolfram 28:13 As- as we were getting ready to release this physics project, we realized that a bunch of things we'd worked out about- about foliations of causal graphs and things were directly relevant to thinking about contact tracing-

Lex Fridman 28:23 Yeah, exactly. With contact-

Stephen Wolfram 28:24 ... um, and interactions with cell phones and so on-

Lex Fridman 28:25 That's really-

Stephen Wolfram 28:25 ... which is really weird. Um-

Lex Fridman 28:27 But like, it just feels like, uh... It feels like we should be able to get some beautiful core insight about the spread of this particular virus on the hypergraph of human civilization, right? Like-

Stephen Wolfram 28:40 I tried. I didn't- I didn't manage to figure it out. I mean, I-

Lex Fridman 28:42 But you're one person.

Stephen Wolfram 28:43 Yeah. But I mean, I think actually it's- it's a funny thing 'cause it turns out the, um, the main model, you know, this SIR model, I- I only realized recently was invented by the- the grandfather of a good friend of mine from high school. So-

Lex Fridman 28:55 (laughs)

Stephen Wolfram 28:55 ... that was just a... You know, it's a weird thing, right? The question is, you know, okay, so you know, you know, on this graph of how humans are connected, you know something about what happens if this happens and that happens. That graph is made in complicated ways that depends on- on all sorts of issues that where we don't have the data about how human society works well enough to be able to make that graph. There's actually, um, uh, one of my kids did a study of sort of what happens on different kinds of graphs and how robust are the results, okay? His basic answer is, there are few general results that you can get that are quite robust. Like, you know, a small number of big gatherings is worse than a large number of small gatherings.

Lex Fridman 29:35 Mm-hmm.

Stephen Wolfram 29:35 Okay? That's quite robust. But when you ask more detailed questions, it seemed like it just depends. It depends on details. In other words, it's kind of telling you, in that case, you know, the irreducibility matters, so to speak. It's not... There's not gonna be this kind of one sort of master theorem that says, "And therefore, this is how things are gonna work."

Lex Fridman 29:57 Yeah. But there's a certain kind of, from a graph perspective, there's a certain kind of dynamic to human interaction. So, like, large groups and small groups, I think it matters who the groups are. For example, you can imagine large... Depends how you define large, but you can imagine groups of 30 people as long- like, as long as they are, uh, cliques or whatever. Like-

Stephen Wolfram 30:22 Right.

Lex Fridman 30:22 ... as- as long as the outgoing degree of that graph is small or something like that, like you can imagine some beautiful underlying rule of-

Stephen Wolfram 30:31 Right.

Lex Fridman 30:31 ... human dynamic interaction where I can still be happy, where I can have a conversation with you and a bunch of other people that mean a lot to me in my life and then stay away from the bigger, I don't know, not going to a Miley Cyrus concert or something like that an- and- and f-... figuring out mathematically, some nice-

Stephen Wolfram 30:49 See, this is an interesting thing.

Lex Fridman 30:51 ... rule of behavior.

Stephen Wolfram 30:51 So, I mean, in, you know... This is the question of... What you're describing is kind of, uh, the problem of, um, many situations where you would like to get away from computational irreducibility.

Lex Fridman 31:02 Right.

Stephen Wolfram 31:02 A classic one in physics is thermodynamics. The, you know, the second law of thermodynamics, the law that says, you know, entropy tends to increase, things that, you know, start orderly tend to get more disordered. Or which is also the thing that says given that you have a bunch of heat, it's hard... Heat is, you know, the microscopic motion of molecules. It's hard to turn that heat into systematic mechanical work. It's hard to, you know, just take something being hot and turn that into, oh, the, the, you know, the... All the atoms are gonna line up in the bar of metal and the piece of metal is gonna shoot in some direction. That's essentially the same problem as, how do you go from this, this computationally irreducible mess of things happening and get something you want out of it?

Lex Fridman 31:43 That's right.

Stephen Wolfram 31:43 It's kind of mining, you know, you're, you're kind of... Now, you know, actually I've, I've understood in recent years that, that the story of, of thermodynamics is actually precisely a story of computational irreducibility. But it is a, um, it is already-

Lex Fridman 31:56 It's interesting.

Stephen Wolfram 31:57 ... uh, an analogy th- you know, you can, you can kinda see that is can you take the, um... You know, what you're asking to do there is you're asking to go from the, um, uh, the kind of, um, the mess of all these complicated human interactions and all this kind of computational processes going on. And you say, "I want to achieve this particular thing out of it. I want to kind of extract from the heat of what's happening, I want to kind of extract this useful piece of sort of mechanical work that I find helpful." I mean-

Lex Fridman 32:25 Do you have a hope for the pandemic? So we'll talk about physics, but for the pandemic, can that be extracted do you think?

Stephen Wolfram 32:31 Well, I think I-

Lex Fridman 32:32 What's your intuition?

Stephen Wolfram 32:33 Look, the, the good news is the curves basically (laughs) , you know, for reasons we don't understand, the curves, you know, the, the, the clearly measurable mortality curves and so on for the Northern Hemisphere have gone down.

Lex Fridman 32:46 Yeah, but the bad news is that it could be a lot worse for future viruses. And what this pandemic revealed is we're highly unprepared for the disc- discovery of the pockets of irreducibility (laughs) within a pandemic that's much more dangerous-

Stephen Wolfram 33:02 Well, my, my guess-

Lex Fridman 33:03 ... and destructive.

Stephen Wolfram 33:03 ... is the specific risk of, you know, viral pandemics, you know, th- that, that the pure virology and, you know, immunology of the thing, this will cause that to advance to the point where this particular risk is probably considerably mitigated. But, you know, it's... Uh, you know, does... Is, is the structure of modern society robust to all kinds of risks? Well, the answer is (laughs) clearly no. And, you know, it's, it's surprising to me the extent to which people... Uh, you know, as I say, it's, it's, it's a... It's kind of scary actually how much people believe in science. That is, people say, "Oh, you know, because the science says this, that, and the other, we'll do this and this and this," even though from a sort of common sense point of view it's a little bit crazy (laughs) . And, and people are not prepared and it doesn't really work in, in society as it is for people to say, "Well, actually we don't really know how the science works." People say, "Well, tell us what to do." And-

Lex Fridman 33:58 Yeah, because then, yeah, what's the alternative? The... For the masses, it's difficult to sit, it's difficult to meditate on computational irreducibility. It's difficult to sit-

Stephen Wolfram 34:09 Yeah, yeah, right.

Lex Fridman 34:10 To... It's difficult-

Stephen Wolfram 34:10 It's... No,

Narrator 34:10 you have to know what to do.

Lex Fridman 34:11 ... to enjoy a good dinner meal-

Stephen Wolfram 34:13 Right.

Lex Fridman 34:13 ... while, (laughs) while knowing that you know nothing about the world (laughs) .

Stephen Wolfram 34:15 Well, I th- think this is a, this is a place where, you know, this is, this is what politicians, you know, and political leaders do for a living, so to speak, is you gotta make some decision about what to do. And it's, um-

Lex Fridman 34:25 Tell some narrative that, uh-

Stephen Wolfram 34:27 Right.

Lex Fridman 34:28 ... while amidst the mystery and knowing not much about the, the past or the future, still telling a narrative that somehow gives people hope that we know what the heck we're doing.

Stephen Wolfram 34:39 I... Yeah, don't get society through the issue, you know, even, even though, you know, the idea that we're just gonna, you know, sort of be able to get the definitive answer from science and it's gonna tell us exactly what to do. Unfortunately, you know, uh, that... It's, it's interesting because let me point out that if that was possible, if science could always tell us what to do, then in a sense our, you know... That would be a big downer for our lives if science could always tell us what the answer is gonna be. It's like, well, you know, it's kind of fun to live one's life and just sort of see what happens. If one could always just say, "Let me, let me check my science. Oh, I know, you know, the result of everything is gonna be 42. I don't need to live my life and do what I do. It's just we already know the answer." It's actually good news in a sense that there is this phenomenon of computational irreducibility that doesn't allow you to just sort of jump through time and say, "This is the answer," so to speak.

Lex Fridman 35:32 (laughs)

Stephen Wolfram 35:33 Um, and that's... So that's a good thing. The bad thing is it doesn't allow you to jump-

Lex Fridman 35:37 (laughs)

Stephen Wolfram 35:37 ... through time (laughs) and know what the answer is. Um-

Lex Fridman 35:39 It's scary. Do you think we're gonna be okay as a human civilization? You said-

Stephen Wolfram 35:45 Absolutely.

Lex Fridman 35:45 ... we don't know.

Stephen Wolfram 35:46 Absolutely.

Lex Fridman 35:46 D- (laughs) Do you think it's... Do you think we'll prosper or destroy ourselves as a-

Stephen Wolfram 35:53 In general?

Lex Fridman 35:54 In general.

Stephen Wolfram 35:55 I'm an optimist (laughs) . The... No, I think that the... You know, it'll be interesting to see, for example, with this, you know, pandemic. I, you know... To me, uh, you know, when you look at, like, organizations, for example, you know, having some kind of perturbation, some kick to the system, usually the end result of that is actually quite good, you know. Unless it kills the system, it's actually quite good usually. And I think in this case, you know, people... I mean, my impression, you know... It's, it's a little weird for me because, you know, I've been a remote tech CEO for 30 years. It doesn't... You know, this is bizarrely (laughs) , uh, you know... And the fact that, you know, like this... Coming to see you here is, is, is the-

Lex Fridman 36:34 Yeah. It's one of the rare moments of human interaction (laughs) .

Stephen Wolfram 36:36 It's the first time in six months (laughs) that I've been, like, (laughs) you know, in, in a building other than my house, okay? So-

Lex Fridman 36:41 (laughs) That's amazing.

Stephen Wolfram 36:42 So, so, you know, uh, it's, it's... I'm, I'm a kind of ridiculous outlier in these kinds of things.

Lex Fridman 36:47 But overall y- your sense is when you shake up the system and throw in chaos that you, you, you, uh, challenge the system, we humans emerge better.

Stephen Wolfram 36:57 ... seems to be that way. Who's to know? But I think that, you know, people, uh, you know, my, my sort of vague impression is that people are sort of, you know, "Oh, what's actually important?" You know, what's, uh, what, what is worth caring about and so on, and that seems to be something that perhaps is, is more, you know, emergent in this kind of situation.

Lex Fridman 37:16 It's so fascinating that on the individual level, we have our own complex cognition. We have consciousness, we have intelligence, we're trying to figure out little puzzles, and then that somehow creates this graph of collective intelligence where we figure out... And then you throw in these viruses of which there's millions different-

Stephen Wolfram 37:36 Uh-huh.

Lex Fridman 37:36 ... you know, there's an entire taxonomy. And the viruses are thrown into the system of collective human intelligence, and we little humans figure out what to do about it. We get like, we'll tweet stuff about information. There's doctors, there's conspiracy theorists, and then we play with different information. I mean, the whole of it is fascinating. Um, I, I am like you, also very optimistic. But, uh, there's a fe- just you said, uh, the computational reducibility, there's, uh, always a fear of the darkness of the uncertainty b- before us.

Stephen Wolfram 38:09 Well, yeah. Yeah, no, I mean-

Lex Fridman 38:10 And it's scary.

Stephen Wolfram 38:11 I mean, the thing is, if you knew everything, it would be boring.

Lex Fridman 38:14 (laughs) Yeah.

Stephen Wolfram 38:15 And, and it would be... And, and then, um, uh, and, and worse than boring, so to speak. It would be, you, it would reveal the pointlessness, so to speak. And in a sense-

Lex Fridman 38:25 (laughs)

Stephen Wolfram 38:25 ... the, the fact that there is this computational irreducibility, it's like as we live our lives, so to speak, something is being achieved. We're computing what our lives, you know, uh, uh, you know, what happens in our lives.

Lex Fridman 38:36 That's funny. So the, the computation irreducibility is kinda like, it gives the meaning to life. It is the meaning of life. Computational reducibility is the meaning of life. There you go.

Stephen Wolfram 38:46 It s- it, it gives it meaning, yes.

Lex Fridman 38:47 (laughs)

Stephen Wolfram 38:47 I mean, it, it, it, it's, it's what, it's what causes it to not be something where you can just say, uh, you know, "You went through all those steps to live your life, but we already knew what the answer was."

Lex Fridman 38:58 Right.

Stephen Wolfram 38:58 Hold on one second. I'm going to use my handy Wolfram|Alpha sunburn computation thing, so long as I can get a network here. There we go.

Narrator 39:07 Answer's

Lex Fridman 39:07 sunburn.

Stephen Wolfram 39:08 Oh, actually, you know what? It says sunburn unlikely.

Lex Fridman 39:11 (laughs)

Stephen Wolfram 39:11 This is a QA moment.

Lex Fridman 39:14 (laughs) Ah. This is a good moment. Okay. (laughs)

Stephen Wolfram 39:16 Okay. (laughs) Well, let's, let me just check what it thinks there.

Lex Fridman 39:20 (laughs)

Stephen Wolfram 39:20 I would see why it thinks that. It doesn't seem like my intuition. This is one of these cases where we can... The question is do we d- do we trust the science or do we, um, use common sense?

Lex Fridman 39:30 The UV thing is cool. The...

Stephen Wolfram 39:32 Yeah, yeah. Well, we'll see. This is a QA moment, as I say. It's, uh, it's like-

Lex Fridman 39:36 (laughs)

Stephen Wolfram 39:36 ... (laughs) do we trust the product? Yes, we trust the product. So, if I'm-

Lex Fridman 39:39 And then there'll be a data point either way.

Stephen Wolfram 39:41 Yeah, but if, if I'm desperately sunburned, I will send bin it in a angry feedback.

Lex Fridman 39:46 Because we mentioned the concept so much and a lot of people know it, but can you say what computational irreducibility is?

Stephen Wolfram 39:54 Yeah, right. So it's, I mean, the, the question is, if you think about things that happen as being computations, you think about the, uh, some process in physics, something that you compute in mathematics, whatever else, it's a computation in the sense it has definite rules, you follow those rules, you, uh, follow them many steps, and you get some result. So then the, the issue is, if you look at all these different kinds of computations that can happen, whether they're computations that are happening in the natural world, whether they're happening in our brains, whether they're happening in our mathematics, whatever else, the big question is, how do these computations compare? Is, are there dumb computations and smart computations, or are they somehow all equivalent? And the thing that I kind of, uh, was sort of surprised to realize from a bunch of experiments that I did in the early '90s and now we have tons more evidence for it, this thing I call the principle of computational equivalence. Which basically says when one of these computations, one of these processes that follows rules, doesn't seem like it's doing something obviously simple, then it has reached the sort of equivalent level of sophisticate... of computational sophistication of everything. So, what does that mean? That means that, you know, you might say, "Gosh, I'm, I'm studying this little, tiny, you know, tiny program on my computer, I'm studying this little thing in, in nature, but I have my brain and my brain is surely much smarter than that thing. I'm gonna be able to systematically outrun the computation that it does, because I have a more sophisticated computation that I can do." But what the principle of computational equivalence says is that doesn't work. Our, our brains are doing computations that are exactly equivalent to the kinds of computations that are being done in all these other sorts of systems. And so what consequence does that have? Well, it means that we can't systematically outrun these systems. These systems are computationally irreducible in the sense that there's no sort of shortcut that we can make that jumps to the answer. Now, the-

Lex Fridman 41:50 In a general case.

Stephen Wolfram 41:52 Right. Right. The, but, but the... So, what has happened, you know, what science has become used to doing is using the little sort of pockets of computational reducibility, which by the way are an inevitable consequence of computational irreducibility that there have to be these pockets scattered around of computational reducibility to be able to find those particular cases where you can jump ahead. I mean, one, one thing, sort of a little bit of a parable-type thing that I think is, is fun to tell. You know, if you look at ancient Babylon, they were trying to predict three kinds of things. They tried to predict, you know, where the planets would be, what the weather would be like, and who would win or lose a certain battle.

Lex Fridman 42:31 (laughs) Yeah.

Stephen Wolfram 42:32 And they had no idea-

Lex Fridman 42:33 Yeah.

Stephen Wolfram 42:33 ... which of these things would be more predictable than the other.

Lex Fridman 42:36 That's funny. (laughs)

Stephen Wolfram 42:37 Uh, and, and, you know, it turns out, you know, where the planets are is a, is a piece of computational reducibility that, you know, 300 years ago or so we pretty much cracked. I mean, it's been technically difficult to get all the details right, but it's basically we, we got that. You know, who's gonna win or lose the battle? No, we didn't crack that one. That one-

Lex Fridman 42:55 Not yet.

Stephen Wolfram 42:55 ... that one, right. The, the, the-

Lex Fridman 42:57 Game theorists are trying.

Stephen Wolfram 42:59 Yes.

Lex Fridman 42:59 And then the weather...... how are we-

Stephen Wolfram 43:01 It's kind of halfway on that.

Lex Fridman 43:02 Halfway? (laughs)

Stephen Wolfram 43:03 Yeah. I think we're, we're doing okay at that one. I, uh, you know-

Lex Fridman 43:05 So do you think-

Stephen Wolfram 43:05 Long term climate, different story.

Lex Fridman 43:07 (laughs)

Stephen Wolfram 43:07 But the weather, you know, we're-

Lex Fridman 43:08 But-

Stephen Wolfram 43:08 ... we're much closer on that.

Lex Fridman 43:10 But do you think eventually we'll figure out the weather? So, do you think eventually most thing... we'll figure out the local pockets in everything, essentially, the local pockets of reducibility?

Stephen Wolfram 43:19 No. I think that the... it's, uh, it's an interesting question, but I think that the... you know, there is an infinite collection of these local pockets. We'll never run out of local pockets. And by the way, those local pockets are where we build engineering, for example. That's how we... You know, when we... if we want to have a predictable life, so to speak, then, you know, we have to build in these sort of pockets of reducibility. Otherwise, you know, if we were, if we were sort of existing in this kind of irreducible world, we'd never be able to, you know, have definite things to know what's gonna happen. You know, I, I have to say, I think one of the features, you know, when we look at sort of today from the future, so to speak, I suspect one of the things where people will say, "I can't believe they didn't see that," is stuff to do with the following kind of thing. So, so, you know, if we describe, oh, I don't know, something like, um, heat, for instance. We say, "Oh, you know, the air in, in here, it's, you know, it's this temperature, this pressure." That's as much as we can say. Otherwise, just a bunch of random molecules bouncing around. People will say, "I just can't believe they didn't realize that there was all this detail in how all these molecules were bouncing around, and they could make use of that." And actually, I realized, there's a thing I realized last week actually (laughs) was, um, was a thing that people say, you know, one of the scenarios for the very long term history of our universe is the so-called heat death of the universe, where basically everything just becomes thermodynamically boring. Everything's just this big kind of gas and thermal equilibrium. People say, "That's a really bad outcome." But actually, it's not a really bad outcome. It's an outcome where there's all this computation going on, and all those individual gas molecules are all bouncing around in very complicated ways, doing this very elaborate computation. It just happens to be a computation that right now, we haven't found ways to understand. We haven't found ways... you know, our brains haven't, you know, and our mathematics and our science and so on, haven't found ways to tell an interesting story about that.

Lex Fridman 45:18 (laughs) That's, uh-

Stephen Wolfram 45:18 It just looks boring to us.

Lex Fridman 45:20 There's a... you're saying there's a hopeful view of the heat death, quote unquote, of the universe, where there's actual beautiful complexity going on-

Stephen Wolfram 45:30 Absolutely. Absolutely.

Lex Fridman 45:30 ... similar to the kind of complexity we think of that creates rich experience in human life and life on Earth?

Stephen Wolfram 45:38 Yes.

Lex Fridman 45:38 So, those little molecules interact in complex ways that, that could be intelligence in that, there could be-

Stephen Wolfram 45:43 Absolutely. I mean, this, this is the, this is what you learn from this principle.

Lex Fridman 45:46 Wow. That's a hopeful message. (laughs)

Stephen Wolfram 45:48 Right. I mean, this is what you kind of learn from this principle of computational equivalence.

Lex Fridman 45:51 Yeah.

Stephen Wolfram 45:52 You learn it's both a, a message of, of sort of hope and a message of kind of, you know, there's... you're not as special as you think you are, so to speak. I mean, because, you know, we, we imagine that with sort of all the things we do with, with human intelligence and all that kind of thing, and all of the stuff we've constructed in science, it's like we're very special. But actually, it turns out, well, no, we're not. We're just doing computations like things in nature do computations, like those gas molecules do computations, like the weather does computations. The only, the only thing about the computations that we do that's really special is that we understand what they are, so to speak. In other words, we have a... you know, to us, they're special because kind of they're connected to our purposes, our ways of thinking about things and so on. And that's, um... but so, so-

Lex Fridman 46:41 That's very human-centric. That's... we're just-

Stephen Wolfram 46:43 It is.

Lex Fridman 46:43 ... attached to this kind of thing.

Lex Fridman 46:45 So let's talk a little bit of physics. Maybe let's ask the, uh, the biggest question. What is a theory of everything? In general, what does that mean?

Stephen Wolfram 46:56 Yeah. So I mean, the question is, can we kind of reduce what has been physics as a... something where we have to sort of pick away and say, "Do we roughly know how the world works?" To something where we have a complete formal theory where we say, "If we were to run this program for long enough, we would reproduce everything." You know, down to the fact that we're having this conversation at this moment, et cetera, et cetera, et cetera. We-

Lex Fridman 47:22 Any physical phenomena, any phenomena in this world?

Stephen Wolfram 47:25 Any phenomenon in the universe.

Lex Fridman 47:26 Yeah.

Stephen Wolfram 47:27 But the... you know, because of computational irreducibility, it's not... you know, that's not something where you say, "Okay, you've got the fundamental theory of everything, then, you know, tell me whether, you know, uh, lions are gonna eat tigers or something." You know, that's a... no, you have to run this thing for, you know, 10 to the 500 steps or something to know something like that. Okay. So at some moment, potentially, you say, "This is a rule, and run this rule enough times, and you will get the whole universe." Right? That's, that's what it means to kind of have a fundamental theory of physics, as far as I'm concerned, is you've got this rule, it's potentially quite simple. We don't know for sure it's simple, but we have various reasons to believe it might be simple. And then you say, "Okay, I'm showing you this rule. You just run it only 10 to the 500 times-"

Lex Fridman 48:18 Mm-hmm.

Stephen Wolfram 48:18 "... and you'll get everything." In other words, you've, you've kind of reduced the problem of physics to a problem of mathematics, so to speak. It's like... it's as if, you know, you'd like... you generate the digits of pi. There's a definite procedure. You just generate them. And it'd be the same thing. If you have a fundamental theory of physics of the kind that, that I'm imagining, you, you know, you get a... this rule and you just run it out and you get everything that happens in the universe.

Lex Fridman 48:46 So, a theory of everything is a mathematical framework within which you can explain everything that happens in the universe kind of in a unified way. It's not there's a bunch of disparate modules of-

Stephen Wolfram 49:01 Right.

Lex Fridman 49:03 Does it feel like if you create a rule, and we'll talk about the Wolfram Physics model, which is fascinating, but if- if you, if you- f- have a simple set of rules with a, with a data structure, like a hypergraph, does that feel like a satisfying Theory of Everything? Because then you really run up against the, uh, irreducibility, computational irreducibility.

Stephen Wolfram 49:32 Right. So that's a really interesting question. So I- I- I, you know, what I thought was gonna happen is I thought we, you know, I thought we had a pretty good, I had a pretty good idea for what the structure of this sort of theory that's sort of underneath space and time and so on might be like. And I thought, "Gosh, you know, in my lifetime, so to speak, we might be able to figure out what happens in the first 10 to the minus 100 seconds of the universe."

Lex Fridman 49:57 Mm-hmm.

Stephen Wolfram 49:58 And that would be cool, but it's pretty far away from anything that we can see today and it will be hard to test whether that's right and so on and so on and so on. To my huge surprise, although it should've been obvious, and it's embarrassing that it wasn't obvious to me, but- but, um, to my huge surprise, we managed to get unbelievably much further than that. And basically what happened is that it turns out that even though there's this kind of bed of computational irreducibility that sort of, uh, these, all these simple rules run into, there is a, there are certain pieces of computational reducibility that quite generically occur for large classes of these rules. And, and this is the really exciting thing as far as I'm concerned, the- the- the big pieces of computational reducibility are basically the pillars of 20th century physics. That's the amazing thing, that general relativity and quantum field theory are sort of the pillars of 20th century physics turn out to be precisely the stuff you can say. There's a lot you can't say, there's a lot that's kind of at this irreducible level where you kinda don't know what's going to happen, you have to run it, you know, you can't run it within our universe, et cetera, et cetera, et cetera, et cetera, et cetera. Um, but the thing is, there are things you can say and the things you can say turn out to be very beautifully th- exactly the structure that was found in 20th century physics, namely general relativity and quantum mechanics.

Lex Fridman 51:24 And g- general relativity and quantum mechanics are these pockets of reducibility that we think of as the, that, you know, 20th century physics is essentially pockets of reducibility. And then it's, it is incredibly surprising that any kind of model that's generative from simple rules would have, would have such pockets.

Stephen Wolfram 51:48 Yeah, well, I think what, what's surprising, uh, is we didn't know where those things came from. It's like general relativity, it's a very nice mathematically elegant theory. Why is it true? You know, quantum mechanics, why is it true? What we realized is that from this, that they are, these theories are generic to a huge class of systems that have these particular very unstructured underlying rules. And that's the, that's the thing that is sort of, uh, remarkable, and that's the thing to me that's just, it's really beautiful. I mean, it's-

Lex Fridman 52:21 It is. True.

Stephen Wolfram 52:21 And the thing that's even more beautiful is that it turns out that, you know, people have been struggling for a long time, you know, how does general relativity, theory of gravity relate to quantum mechanics? They seem to have all kinds of incompatibilities. It turns out what we realized is at some level they are the same theory. And that's just, it's- it's just great as far as I'm concerned.

Lex Fridman 52:41 (laughs) So-

Stephen Wolfram 52:41 Yeah.

Lex Fridman 52:41 ... maybe, like taking a little step back from your perspective, not from the low, not from the beautiful hypergraph Wolfram Physics model perspective, but from the perspective of 20th century physics, what is general relativity? Wha- what is quantum mechanics? How do you think about these two theories from the context of the Theory of Everything? Like just even definitions.

Stephen Wolfram 53:05 Yeah, yeah, yeah, right. So, so I mean, you know, a little bit of history of physics, right?

Lex Fridman 53:09 Yeah.

Stephen Wolfram 53:09 So, so I mean, the- the, you know... Okay, very, very quick history of physics.

Lex Fridman 53:13 Yes (laughs) .

Stephen Wolfram 53:13 Right? So, so I mean, you know, physics, you know, in ancient Greek times, people basically said, "We can just figure out how the world works. As, you know, we're philosophers, we're gonna figure out how the world works." You know, some philosophers thought there were atoms, some philosophers thought there were, you know, continuous flows of things. People had different ideas about how the world works. And they tried to just say, "We're gonna construct this idea of how- how the world works." They didn't really have sort of notions of doing experiments and so on quite the same way as developed later. So that was sort of an early tradition for thinking about sort of models of the world. Then by the time of 1600s, time of Galileo and then Newton, um, sort of the big, the big idea there was, you know, you know, title of Newton's book, you know, Principia Mathematica, Mathematical Principles of Natural Philosophy. We can use mathematics to understand natural philosophy, to understand things about the way the world works. And so that then led to this kind of idea that, you know, we can write down a mathematical equation and have that represent how the world works. So Newton's, one of his most famous ones is his universal law of gravity, inverse square law of gravity that allowed him to compute all sorts of features of- of the planets and so on. Although some of them he got wrong and it was, took another a hundred years for people to actually be able to do the math, uh, to the level it was needed. But, but, um, but so that, that had been this sort of tradition was we write down these mathematical equations, we don't really know where these equations come from. We write them down, then we figure out, we work out their consequences and we say, "Yes, that agrees with what we actually observe in astronomy or something like this." So that tradition continued and, um, then the first of these two sort of great 20th century, uh, innovations was, uh, well, the history is actually a little bit more complicated, but let's- let's say-

Lex Fridman 54:58 (laughs) Yeah.

Stephen Wolfram 54:58 ... that the- the, um, the- the- the- the, there were two, quantum mechanics and general relativity. Quantum mechanics had kind of, 1900 was kind of the very early, uh, stuff done by Planck that led to the idea of photons, particles of light. Um, but let's, let's take general relativity first. One, one feature of this story is that special relativity, thing Einstein invented in 1905-... was something which, surprisingly, was a kind of logically invented theory. It was not a theory where... it was something where given these ideas that were sort of axiomatically thought to be true about the world, it followed that such and such a thing would be the case. And it was a little bit different from the, the kind of methodological structure of some, of some existing theories in more, in the more recent times, where it had just been, we write down an equation and we find out that it works. So what happened there-

Lex Fridman 55:51 So there's some reasoning about the light.

Stephen Wolfram 55:53 The basic idea was the, you know, the speed of light is, appears to be constant. Uh, you know, even if you're traveling very fast, you shine a flashlight, the light will come out, e- even if you're going at half the speed of light, the light doesn't come out of your flashlight at one and a half times the speed of light. Um, it's still just the speed of light. And to make that work, you have to change your view of how space and time work, um, to be able to account for the fact that when you're going faster, it appears that, you know, uh, length is foreshortened and time is dilated and things like this.

Lex Fridman 56:26 And that's special relativity.

Stephen Wolfram 56:27 That's special relativity. So then Einstein went on with sort of, uh, vaguely similar kinds of thinking. In 1915, invented general relativity, which is a theory of gravity. And the basic point of general relativity is, is it's a theory that says when there is mass in space, space is curved.

Lex Fridman 56:49 Mm-hmm.

Stephen Wolfram 56:49 And what does that mean? You know, you, y- y- usually you think of, uh, what's the shortest distance between two points? Like in a, uh, ordinarily in, on a plane in space, it's a straight line. You know, photons, light goes in straight lines. Well, then the question is, is, uh, if, if you have a curved surface, a straight line is no longer straight. On the surface of the earth, the shortest distance between two points is a great circle. It's a circle. Um, it's, uh, so, you know, Einstein's observation was maybe the physical, uh, structure of space is such that space is curved. So the shortest distance between two points, the, the path, the "straight line" in quotes, won't be straight anymore. And in particular, if a, if a photon is, is, you know, traveling near, near the sun or something, or if a particle is going, something is traveling near the sun, maybe the shortest path will be one that is, is, uh, is, is something which looks curved to us because... it seems curved to us because space has been deformed by the presence of mass associated with that, that, uh, massive object. So, so the, kind of the idea, uh, there is, um, think of th- the structure of space as being a dynamical changing kind of thing. But then what Einstein did was he wrote down these differential equations that basically represented the curvature of space and its response to the presence of mass and energy.

Lex Fridman 58:13 And that u- ultimately, it's connected to the force of gravity, which is one of the forces that s- seems to, based on its strength, operate on a different scale than some of the other forces. So it operates at a scale-

Stephen Wolfram 58:26 Yeah.

Lex Fridman 58:26 ... that's very large.

Stephen Wolfram 58:27 What happens there is, is just this, this curvature of space which causes, you know, the paths of objects to be deflected, that's what gravity does. It causes the paths of objects to be deflected. And this is a, an explanation for gravity, so to speak. And the surprise is that from 1915 until today, everything that we measured about gravity precisely agrees with general relativity. And that's, um... uh, and that, you know, it wasn't clear black holes were sort of a predi- well, actually, the expansion of the universe was an early potential prediction. Although Einstein tried to sort of patch up his equations to make it not cause the universe to expand, 'cause it was kind of so obvious the universe wasn't expanding. And, um, uh, you know, it turns out it was expanding and he should have just trusted the equations. And that's a lesson for, for those of us, um, interested in making fundamental theories of physics is, you should trust your theory and not try and patch it because of something that you think might be the case that, um, uh, that, that might turn out not to be the case.

Lex Fridman 59:25 E- even if the theory says something crazy is happening?

Stephen Wolfram 59:28 Yeah, right.

Lex Fridman 59:28 Like the universe is expanding.

Stephen Wolfram 59:29 Like, like the universe is expanding, right? Which is... but, but, um, but, you know, then it took until the 1940s, probably even really until the 1960s until people understood that black holes were a consequence of, of general relativity and so on. But that's, um... you know, the big surprise has been that so far, this theory of gravity has perfectly agreed with, you know, these collisions of black holes seen by their gravitational waves. You know, it all just works. So that's been kind of one pillar of the story of physics. It's mathematically complicated to work out the consequences of general relativity, but it's not... there's n- there's no... I mean, and, and, and, and some things are kind of squiggly and complicated. Like people believe, you know, energy is conserved. Okay, well, energy conservation doesn't really work in general relativity in the same way as it ordinarily does, and it's all a big mathematical story of how you actually nail down something that is definitive that you can talk about and not specific to the, you know, reference frames you're operating in, and so on, and so on, and so on. But fundamentally, general relativity is a straight shot in the sense that you have this theory, you work out its consequences. Um-

Lex Fridman 1:00:35 And, and that, that theory is useful in terms of basic science and trying to understand the way black holes work, the way the creation of galaxies work, sort of all these kind of cosmological thing. Understanding what happened, like you said, at the Big Bang-

Stephen Wolfram 1:00:49 Yeah.

Lex Fridman 1:00:49 ... like all those kinds of... well, no, not, not at the Big Bang actually, right? But, uh...

Stephen Wolfram 1:00:53 Well, features of the expansion of the universe, yes.

Lex Fridman 1:00:55 Features of the expansion-

Stephen Wolfram 1:00:55 I mean, and th- and there are, there are lots of details where we don't quite know how it's working. You know, is there... you know, where's the dark matter? Is there dark energy? You know, et cetera, et cetera, et cetera but, but fundamentally the, the, you know, the testable features of general relativity, it all works very beautifully. And it's, uh, just in a sense, w-... it is mathematically sophisticated, but it is not conceptually hard to understand in

Stephen Wolfram 1:01:16 some sense.

Lex Fridman 1:01:17 Okay. So that's general relativity. And what's-

Stephen Wolfram 1:01:19 Okay.

Lex Fridman 1:01:19 ... its friendly neighbor? Like you said-

Stephen Wolfram 1:01:21 Quantum mechanics.

Lex Fridman 1:01:21 ... there's two theories, quantum mechanics.

Stephen Wolfram 1:01:22 Right. So quantum mechanics, the, the, the sort of, the way that that originated was one question was, is the world continuous or is it discrete? You know, in ancient Greek times, people have been debating this. People debated it in, you know, throughout history. "Is light con- made of waves? Is it continuous? Is it discrete? Is it made of particles, corpuscles," whatever. Um, you know, what had become clear in the 1800s is that atoms that, you know, materials are made of discrete atoms. You know, when you take some water, the water is not a continuous fluid, even though it seems like a continuous fluid to us at our scale. But if you say, "Let's look at it smaller and smaller and smaller and smaller scale," eventually you get down to these, you know, these molecules and then atoms. It's made of discrete things. So the question is sort of how important is this discreteness? Just what's discrete, what's not discrete? Is energy discrete? Is, you know, is, wha- what's discrete, what's not? And so-

Lex Fridman 1:02:18 Does it have mass? Those kinds of questions.

Stephen Wolfram 1:02:21 Yeah, yeah, right. Well, well th- th- there's question, I mean, for example, is mass discrete is an interesting question, which is now something we can address. But, but, um, you know, what, what happened in, um, uh, the, in, in the, uh, coming up to the 1920s, there was this kind of mathematical theory developed that could explain certain kinds of discreteness in, in particularly in, in features of atoms and so on. And, uh, you know, what developed was this mathematical theory that was a theory, the theory of quantum mechanics, theory of wave functions, Schrodinger's equation, things like this. That's a mathematical theory that allows you to calculate lots of features of the microscopic world, lots of things about how atoms work, et cetera, et cetera, et cetera. Now, the calculations all work just great. The, um, uh, the question of what does it really mean is a complicated question. Now, I mean, to, to just explain a little bit historically, the, you know, the early calculations of things like atoms worked great in 1920s, 1930s, and so on. There was always a problem. There were, uh, in quantum field theory, which is a theory of, uh, uh... In quantum mechanics, you're dealing with a certain number of atom, a certain number of electrons, and you fix the number of electrons. You say, "I'm dealing with a two electron thing." Um, in quantum field theory, you s- allow for particles being created and destroyed. So you can emit a photon that didn't exist before. You can absorb a photon, things like that. That's a more complicated, mathematically complicated theory, and it had all kinds of mathematical issues and all kinds of infinities that cropped up, and it was finally figured out more or less how to get rid of those. But there were only certain ways of doing the calculations, and those didn't work for atomic nuclei among other things. Um, and that led to, oh, a lot of developments up until the 1960s of alternative ideas for how, how one could understand what was happening in atomic nuclei, et cetera, et cetera, et cetera. End result, in the end, the kind of most, quote, "obvious" mathematical structure of quantum field theory seems to work, although it's mathematically difficult to deal with. But you can calculate all kinds of things. You can calculate to, you know, a dozen decimal places certain, certain things. You can measure them. It all works. It's all beautiful. Now you say-

Lex Fridman 1:04:30 By the way, the underlying fabric is the model of that particular theory is fields. Like you keep saying fields is-

Stephen Wolfram 1:04:36 Uh, tho- those are quantum fields. Those are different from classical fields. A, a field is something like you say, um, there's, like you say, the temperature field in this room. It's like there is a value of temperature at every point around the room. That's, um... Or, or you can say the wind field would be the, the vector direction of the wind at every point.

Lex Fridman 1:04:56 It's continuous, a field.

Stephen Wolfram 1:04:57 Yes. And it's a, that's a classical field. The quantum field is a much more mathematically elaborate kind of thing. Um, and I should explain that, that one of the pictures of quantum mechanics that's really important is, you know, in classical physics, one believes that sort of definite things happen in the world. You pick up a ball, you throw it, the ball goes in a definite trajectory that's the, where it has certain equations of motion, it goes in a parabola, whatever else. In quantum mechanics, the picture is definite things don't happen. Instead, sort of what happens is this whole sort of structure of, of all, you know, many different paths being followed, and, um, we can calculate certain aspects of what happens, certain probabilities of different outcomes and so on. And you say, "Well, what really happened? What's really going on? What's the sort of, uh, what's the underlying, you know, what's the underlying story? What, how do we, how do we turn this, this mathematical theory that we can calculate things with into something that we can really understand and have a narrative about?" And that's been really, really hard for quantum mechanics. Uh, my, my friend Dick Feynman always used to say, "Nobody understands quantum mechanics," even though he'd made his, you know, whole career out of calculating things about quantum mechanics. Um, and, uh, you know, so, so it's a little-

Lex Fridman 1:06:11 But nevertheless, it's, uh, what the quantum field theory is very, uh, very accurate at predicting a lot of the physical phenomena. So it works.

Stephen Wolfram 1:06:21 Yeah. And, but there are things about it, you know, it has certain... When we apply it, the standard model of particle physics, for example, we, uh, you know, which we apply to calculate all kinds of things, it works really well. And you say, "Well, it has certain parameters." It has a whole bunch of parameters actually. You say, "Why is the, you know, why does the muon particle exist? Why is it 206 times the mass of the electron?" We don't know. No

Stephen Wolfram 1:06:46 idea.

Lex Fridman 1:06:46 But, so the standard model of physics is, is, is one of the models that's very accurate for describing three, three of the fundamental forces of physics, and it's looking at the, the world of the very small.

Stephen Wolfram 1:06:58 Right.

Lex Fridman 1:06:58 And then there's back to the neighbor of, uh, gravity, of general relativity. So, and then in the context of a theory of everything, what's traditionally the task of the unification of these theories? And why is it hard?

Stephen Wolfram 1:07:15 Well, I mean, the, the issue is you try to use the methods of quantum field theory to talk about gravity and it doesn't work.... just like there are photons of light, so there are gravitons which are sort of the particles of gravity. And when you try and compute sort of the properties of the, of the particles of gravity, the kind of mathematical tricks that get used, um, in working things out in quantum field theory don't work. And, um, that's, um ... so that's been a sort of fundamental issue. And when you think about black holes which are a place where, uh, sort of the, the structure of space is, um, uh, you know, has, has sort of rapid variation and you get kind of quantum effects mixed in with effects from general activity, things get very complicated and there are par- paradoxes and things like that. And people have, you know, there've been a bunch of mathematical developments in, in physics over the last, I don't know, 30 years or so which have kind of picked away at those kinds of issues, and got hints about how things might work. Um, and but it hasn't been, uh, uh ... you know, and the other thing to realize is, as far as physics is concerned, it's just like, here's general activity, here's quantum field theory, you know, be happy.

Lex Fridman 1:08:25 Yeah. So do you think there's a quantization of gravity, quantum gravity th- ... what, what do you think of efforts that people have tried to ... yeah, what do you think in general of the efforts of the physics community to try to unify these laws?

Stephen Wolfram 1:08:39 So I think what's ... it's interesting. I mean, I would've said something very different before what's happened with our physics project. Um, I mean, you know, the remarkable thing is, what we've been able to do is to make from this very simple, structurally simple underlying set of ideas, we've been able to build this, this, you know, very elaborate structure that's both very abstract and very sort of mathematically rich. And the big surprise as far as I'm concerned is that it touches many of the ideas that people have had. So in other words, things like-

Lex Fridman 1:09:13 Mm-hmm. That's-

Stephen Wolfram 1:09:14 ... string theory and so on, uh, twistor theory. It's like the ... you know, w- we might have thought, I had thought, we're out on a prong. We're building something that's computational-

Lex Fridman 1:09:22 Right.

Stephen Wolfram 1:09:22 ... it's completely different from what other people have done. But actually, it seems like what we've done is to provide essentially the machine code that, you know, these things are, are various features of domain-specific languages so to speak, that talk about various aspects of this machine code, and I think there's a ... this is something that to me is, is, is very exciting because it allows one both for us to provide sort of a new foundation for what's been thought about there, and for the, all the work that's been done in those areas to, you know, to give us, you know, more, more momentum to be able to figure out what's going on. Now, you know, people have sort of hoped, oh, we're just gonna be able to get, you know, string theory to just answer everything. That hasn't worked out, and I think we now kind of can see a little bit about just sort of how far away certain kinds of things are from being able to explain things. Some things ... one of the big surprises to me actually, I literally just got a message about one aspect of this, is, um, uh, the, uh, uh, you know, it's turning out to be easier. I mean, this project has been so much easier than I could ever imagine it would be. That is, I thought we would be, you know, just about able to understand the first 10-100 seconds of the universe, and, um, you know, it would be 100 years before we get much further than that. It's just turned out, it actually wasn't that hard. I mean, we're not finished but, you know, w-

Lex Fridman 1:10:42 So you're, you're, you're seeing echoes of all the disparate theories of physics in this framework of ...

Stephen Wolfram 1:10:47 Yes. Yes. I mean, it's a very interesting, you know, sort of history of science like phenomenon. I mean, uh, the best analogy that I can see is what happened with the early, early days of, of computability and computation theory. You know, Turing machines were invented in 1936. People sort of understand computation in terms of Turing machines, but actually there had been preexisting theories of computation, combinators, general recursive functions, lambda calculus, things like this, but people hadn't ... those hadn't been concrete enough-

Lex Fridman 1:11:18 Mm-hmm.

Stephen Wolfram 1:11:18 ... that people could really wrap their arms around them and understand what was going on. And I think what we're gonna see in this case is that a bunch of these mathematical theories, um, including some very ... and one of the things that's really interesting is, one of the most abstract things that's come out of, of sort of, uh, mathematics, th- higher category theory, things about infinity groupoids, things like this-

Lex Fridman 1:11:40 Mm.

Stephen Wolfram 1:11:40 ... which to me always just seemed like they were floating off into the stratosphere, uh, uh, ionosphere of mathematics, um, turn out to be things which our sort of theory anchors down to something fairly definite, and says are super relevant to the way that we can understand how physics works.

Lex Fridman 1:11:59 Give me a sec. By the way, I just threw a hat

Lex Fridman 1:12:01 on. You've said that, um, this metaphor analogy that, uh, Theory of Everything is a big mountain, and you have a sense that however far we are up the mountain, that the f- the Wolfram Physics model view of the universe is at least the right mountain.

Stephen Wolfram 1:12:25 We're the right mountain.

Lex Fridman 1:12:26 (laughs)

Stephen Wolfram 1:12:26 Yes. Without question. So I'm, I'm-

Lex Fridman 1:12:29 So, which aspect of it is the right mountain? So for examp- ... I mean, so th- there's so many aspects to just the way of the Wolfram Physics Project, the way it approaches the world, that's, um, that's clean, crisp, uh, and, uh, unique, and powerful. So, you know, there's a, there's discreet nature to it, there's a hypergraph, there's a computational nature, the, uh, there's a generative aspect; you start from nothing, you generate everything. Which ... do you think the actual model is actually a really good one? Or do you think this general principle of from simplicity generating complexity is the right? Like, what aspect-

Stephen Wolfram 1:13:07 Well, I think-

Lex Fridman 1:13:07 ... of the mountain is the correct-

Stephen Wolfram 1:13:08 Yeah, right. I mean, I, I think that the, the kind of the meta idea about using simple computational systems to do things, that's, you know, that's the ultimate big paradigm that is, you know-... sort of super important. The details of the particular model are very nice and clean and allow one to actually understand what's going on. They are not unique. And in fact, we know that. We know that there's a, a, there's a large number of different ways to describe essentially the same thing. I mean, I can describe things in terms of hypergraphs, I can describe them in terms of higher category theory. I can describe them in a bunch of different ways. They are, in some sense, all the same thing, but our sort of story about what's going on and, and the kind of, uh, kind of cultural mathematical resonances are a bit different.

Lex Fridman 1:13:54 Yeah.

Stephen Wolfram 1:13:54 I mean, I think it's, it's, it's perhaps worth sort of saying a little bit about kind of the, the, you know, foundational ideas of, of, uh, of, uh, uh, you know, of these- of these models and things.

Lex Fridman 1:14:04 Great. So, can you maybe, uh, can we like rewind? We've talked about it a little bit, but can you say like what the central idea is of the Wolfram Physics Project?

Stephen Wolfram 1:14:16 Right. So, so the question is, we're interested in finding a sort of simple computational rule that describes our whole universe. That-

Lex Fridman 1:14:24 Can we just pause on that? It's just so beauti- uh, that- that's such a beautiful, that's such a beautiful idea.

Stephen Wolfram 1:14:30 Yeah.

Lex Fridman 1:14:30 That we can generate our universe from a sim- from a, uh, from a data structure, a simple s- structure, a simple set of rules, and we can generate our entire universe.

Stephen Wolfram 1:14:42 Yes. That's the idea.

Lex Fridman 1:14:44 That's awe-inspiring. (laughs)

Stephen Wolfram 1:14:44 Right. Uh, but, but so, so, you know, the question is how do you actualize that? What might this rule be like? And so one thing you quickly realize is, if you're gonna pack everything about a universe into this tiny rule, not much that we are familiar with in our universe will be obvious in that rule. So, you don't get to fit all these parameters of the universe, all these features of, you know, this is how space works, this is how time works, et cetera, et cetera, et cetera. You don't get to fit that all in. It all has to be sort of packed in to this, this thing, something much smaller, much more basic, much lower level machine code, so to speak-

Lex Fridman 1:15:20 Mm-hmm.

Stephen Wolfram 1:15:21 ... than that. And all the stuff that we're familiar with has to kind of emerge from the operation of-

Lex Fridman 1:15:26 So, the rule in itself, because of the computational reducibility is not gonna tell you the story. It's not gonna give you the-

Stephen Wolfram 1:15:34 Right.

Lex Fridman 1:15:34 ... answer to a... It's not gonna let you predict what you're gonna have for lunch tomorrow-

Stephen Wolfram 1:15:40 Right.

Lex Fridman 1:15:40 ... and it's not going to let you predict basically anything about your life, about the universe.

Stephen Wolfram 1:15:44 Right. But, and you're not going to be able to see in that rule, oh, there's the three for the number of dimensions of space and so on.

Lex Fridman 1:15:50 Right.

Stephen Wolfram 1:15:51 That's not gonna be there.

Lex Fridman 1:15:52 So space-time is not going to be obviously-

Stephen Wolfram 1:15:54 Right. So, and the question is then, what-

Lex Fridman 1:15:56 ... present in there?

Stephen Wolfram 1:15:56 ... what is the universe made of? That's- that's a, it's a basic question. And we've had some assumptions about what the universe is made of for the last few thousand years that I think in some cases are just turned out not to be right. And, you know, the most important assumption is that space is a continuous thing. That is that you can... If you say, let's pick a point in space. We're gonna do geometry. We're gonna pick a point. We can pick a point absolutely anywhere in space. Precise numbers we can specify of where that point is. In fact, you know, Euclid, who kind of wrote down the original kind of axiomatization of geometry back in 300 BC or so, um, you know, his- his very first definition he says, "A point is that which has no part." A point is this- is this, you know, uh, this indivisible, you know, infinitesimal thing. Okay? So, we might have said that about material objects. We might have said that about water, for example. We might have said water is a continuous thing that we can just, uh, you know, pick any point we want in- in- in some water. But actually, we know it isn't true. We know that water is made of molecules that are discrete. And so the question, one fundamental question is what is space made of? And so one of the things that's sort of a starting point for what I've done is to think of space as a discrete thing, to think of there being sort of atoms of space just as there are atoms of material things, although very different kinds of atoms. And by the way, I mean, this idea, you know, there were ancient Greek philosophers who had this idea. There were, you know, Einstein actually thought this is probably how things would work out. I mean, he said, you know, repeatedly he thought this is the way it would work out, but we don't have the mathematical tools in our time, which was 1940s, 1950s and so on, to explore this. He-

Lex Fridman 1:17:42 Uh, like the way he thought, y- you mean that there is something very, very small and discrete that's underlying-

Stephen Wolfram 1:17:51 Space.

Lex Fridman 1:17:51 ... space?

Stephen Wolfram 1:17:52 Yes. And that- that means that... So, you know, the mathematical theory, mathematical theories in physics assume that space can be described just as a continuous thing. You can just pick coordinates and the coordinates can have any values, and that's how you define space. Space is this just sort of background, uh, sort of theater on which the universe operates.

Lex Fridman 1:18:13 But can we draw a distinction between space as a thing that could be described by, uh, three values, coordinates, and how you're... Are you- are you using the word space more generally when you say...

Stephen Wolfram 1:18:29 No, I'm- I'm just talking about space as in-

Lex Fridman 1:18:31 Like literally three-dimensional?

Stephen Wolfram 1:18:31 ... what we experience