Sara Walker: Physics of Life, Time, Complexity, and Aliens

You have an origin of life event. It evolves for 4 billion years, at least on our planet. It evolves a technosphere. The technologies themselves start having this property we call life, which is the phase we're undergoing now. It solves the origin of itself and then it figures out how that process all works, understands how to make more life, and then can copy itself onto another planet so the whole structure can reproduce itself. The following is a conversation with Sara Walker, her third time in this podcast. She is an astrobiologist and theoretical physicist interested in the origin of life and in discovering alien life on other worlds. She has written an amazing new upcoming book titled Life As No One Knows It, The Physics of Life's Emergence. This book is coming out on August 6th, so please go pre-order it now. It will blow your mind. This is The Lex Fridman Podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's Sara Walker.

You open the book, Life As No One Knows It: The Physics of Life's Emergence, with the distinction between the materialists and the vitalists. So what's the difference? Can you maybe define the two? I think the question there is about whether life can be described in terms of matter and physical things, or whether there is some other feature that's not physical that actually animates living things. So for a long time, people maybe have called that a soul. It's been really hard to pin down what that is. So I think the vitalist idea is really that it's a dualistic interpretation that there's sort of the material properties, but there's something else that animates life that is there when you're alive and it's not there when you're dead. And materialists don't think that there's anything really special about the matter of life and the material substrates that life is made out of, so they disagree on some really fundamental points.

What exactly are we missing by focusing on such a short span of time? I think we're missing most of what we are. One of the issues... I've been thinking about this really viscerally lately. It's weird when you do theoretical physics, because I think it literally changes the structure of your brain and you see the world differently, especially when you're trying to build new abstractions.

Yeah. You mentioned just the technosphere, and you also wrote that the most, the live thing on this planet is our technosphere. Why is the technology we create a kind of life form? Why are you seeing it as life?

No. Physics hardly even acknowledges that the universe is random at its base. We like to think we live in a deterministic universe and everything's deterministic. But I think that's probably an artifact of the way that we've written down laws of physics since Newton invented modern physics and his conception of motion and gravity, which he formulated laws that had initial conditions and fixed dynamical laws. And that's been sort of become the standard canon of how people think the universe works and how we need to describe any physical system is with an initial condition in a law of motion. And I think that's not actually the way the universe really works. I think it's a good approximation for the kind of systems that physicists have studied so far. And I think it will radically fail in the longterm at describing reality at its more basal levels. But I'm not saying there's a base, I don't think that reality has a ground, and I don't think there's a theory of everything, but I think there are better theories, and I think there are more explanatory theories, and I think we can get to something that explains much more than the current laws of physics do.

So what do you think is the origin of life on earth and how can we talk about it in a productive way? The origin of life is like this boundary that the universe can only cross if a structure that emerges can reinforce its own existence, which is self-reproduction, autocatalysis, things people traditionally talk about. But it has to be able to maintain its own existence against this sort of randomness that happens in chemistry, and this randomness that happens in the quantum world. And it's in some sense the emergence of a deterministic structure that says, "I'm going to exist and I'm going to keep going." But pinning that down is really hard. We have ways of thinking about it in assembly theory that I think are pretty rigorous. And one of the things I'm really excited about is trying to actually quantify in an assembly theoretic way when the origin of life happens. But the basic process I have in mind is a system that has no causal contingency, no constraints of objects, basically constraining the existence of other objects or forming or allowing the existence of other objects.

Yes. Can you explain assembly theory to me? I listened to Lee talk about it for many hours, and I understood nothing. No, I'm just kidding. I just wanted to take another... You've been already talking about it, but just what from a big picture view is the assembly theory way of thinking about our world, about our universe.

That's our best feature. I don't know how we got to the wiggling required given the constraints of language because I think we started about me asking about alien life. Which is how many different times did the phase transition happen elsewhere? Do you think there's other alien civilizations out there? This goes into the are you on the boundary of insane or not? But when you think about the structure of the physics of what we are, that deeply, it really changes your conception of things. And going to this idea of the universe being small in physical space compared to how big it is in time and how large we are. It really makes me question about whether there's any other structure that's this giant crystal in time, this giant causal structure, like our biosphere/technosphere is anywhere else in the universe.

Well, one of the things you described that you already spoke to, you call it the great perceptual filter. There's the famous great filter, which is basically the idea that there's some really powerful moment in every intelligent civilization where they destroy themselves. That explains why we have not seen aliens. And you're saying that there's something like that in the temporal history of the creation of complex objects, that at a certain point they become an island, an island too far to reach based on the perceptions? I hope not, but yeah, I worry about it. Yeah.

You tweeted, "If one wants to understand how truly combinatorially and compositionally complex our universe is, they only need step into the world of fashion. It's bonkers how big the constructable space of human aesthetics is." Can you explain, can we explore the space of human aesthetics? Yeah. I don't know. I've been obsessed with the... I never know how to pronounce it. It's a Schiaparelli. They have ears and things. It's such a weird, grotesque aesthetic, but it's totally bizarre. But what I meant, I have a visceral experience when I walk into my closet. I have a lot of...

Wow. What do you think beauty is? We seem to... Underlying this idea of playing with aesthetics is we find certain things beautiful. What is it that humans find beautiful? And why do we need to find things beautiful? Yeah, it's interesting. I mean, I am attracted to style and aesthetics because I think they're beautiful, but it's much more because I think it's fun to play with. And so, I will get to the beauty thing, but I guess I want to just explain a little bit about my motivation in this space, because it's really an intellectual thing for me.

Let's jump from beauty to language. There's so many ways to explore the topic of language. You called it, you said that language, parts of language or language in itself or the mechanism of language is a kind of living life form. You've tweeted a lot about this in all kinds of poetic ways. Let's talk about the computation aspect of it. You tweeted, " The world is not a computation, but computation is our best current language for understanding the world. It is important we recognize this so we can start to see the structure of our future languages that will allow us to see deeper than the computation allows us." What's the use of language in helping us understand and make sense of the world? I think one thing that I feel like I notice much more viscerally than I feel like I hear other people describe is that the representations in our mind and the way that we use language are not the things... Actually, this is an important point going back to what Godel did, but also this idea of signs and symbols and all kinds of ways of separating them. There's the word and then there's what the word means about the world. We often confuse those things. What I feel very viscerally, I almost sometimes think I have some synesthesia for language or something, and I just don't interact with it the way that other people do. But for me, words are objects and the objects are not the things that they describe.

What do you think about computation as a language? I think it's a very poor language. A lot of people think is a really great one, but I think it has some nice properties. But I think the feature of it that is compelling is this kind of idea of universality, that if you have a language, you can describe things in any other language.

One of the possible titles you were thinking about originally for the book is The Hard Problem of Life, reminiscent of the hard problem of consciousness. You are saying that assembly theory is supposed to be answering the question about what is life. Let's go to the other hard problems. You also say that's the easiest of the hard problems is the hard problem of life. What do you think is the nature of intelligence and consciousness? Do you think something like assembly theory can help us understand that? I think if assembly theory is an accurate depiction of the physics of life, it should shed a lot of light on those problems. In fact, I sometimes wonder if the problems of consciousness and intelligence are at all different than the problem of life, generally. I'm of two minds of it, but I in general try to... The process of my thinking is trying to regularize everything into one theory, so pretty much every interaction I have is like, "Oh, how do I fold that into..." I'm just building this giant abstraction that's basically trying to take every piece of data I've ever gotten in my brain into a theory of what life is. Consciousness and intelligence are obviously some of the most interesting things that life has manifest. I think they're very telling about some of the deeper features about the nature of life.

Is there shortcuts we can take to artificially engineering, living organisms, artificial life, artificial consciousness, artificial intelligence? Maybe just looking pragmatically at the LLMs we have now, do you think those can exhibit qualities of life, qualities of consciousness, qualities of intelligence in the way we think of intelligence? I think they already do, but not in the way I hear popularly discussed. They're obviously signatures of intelligence and a part of a ecosystem of intelligence system of intelligent systems. But I don't know that individually I would assign all the properties to them that people have. It's a little like, so we talked about the history of eyes before and how eyes scaled up into technological forms. Language has also had a really interesting history and got much more interesting I think once we started writing it down and then inventing books and things. But every time that we started storing language in a new way where we were existentially traumatized by it. The idea of written language was traumatic because it seemed like the dead were speaking to us even though they were deceased. Books were traumatic because suddenly there were lots of copies of this information available to everyone and it was going to somehow dilute it.

So do you think the universe has an end, if you think it's a book with an end? I think the number of words required to describe how the universe works as an end, yes. Meaning I don't care if it's infinite or not.

Why does anything exist at all? Ag, I don't know.