What Makes Something Alive? Assembly Theory and the Origins of Life (Sara Walker, Theoretical Physicist)

24:33And so we don't think that happened until after there was an evolutionary architecture. And I think there's lots of evidence to support that. In prebiotic chemistry, they think they can produce it, but they're like gaming the system by, you know, putting in already designed molecules and already designed conditions. So they put the selection in. And this is also one of the sort of challenges with origins of life is as a research field, experimental research field, is how do you build an experiment where you don't put all of your evolutionary agency and intelligence into the experiment and you ask how can the universe generate complex structures without us putting the design in like basically the original life is the origin of design in the universe which is which is also kind of a crazy way of thinking about it but you know that's why there's all these debates between intelligent design and evolutionary theory because this problem is not solved i obviously think it's a naturalistic explanation but um but that's really what we're what we're after is and it's a really hard problem because we're basically, why it's fundamental physics, I think, is because basically we're saying the universe has a self-constructing principle.

25:32Like I don't think about the universe having anything outside of the universe. The universe literally has to build itself. And part of the mechanism of doing that, like the self-constructing system, it becomes things like a biosphere. That is the only kind of structure that can build into all of these complex potential spaces that we see our planet evolving into. I think it's also just worth maybe taking a moment for listeners to emphasize how different assembly theory is to the traditional way that people talk about what is life and the origins of life. It's such a radically different way of talking about these things.

26:10Maybe for the benefit of folks, what were the sort of traditional ways people would say, here's how we define life or here's how we talk about the origin of life versus saying, we're looking at it in this sort of step function-y way? Yeah, so I can definitely do that. And then I'd like to kind of qualify that a little bit historically, because I think I think it's really important to understand that, like when we come to understand things, we often change the definitions we have for them. So the way that people think about it traditionally, like the most popular definition is what the so-called quote unquote NASA definition, although it's not officially endorsed, it came out of a NASA workshop, is life is a self-sustaining chemical system capable of Darwinian evolution.

26:48And so just as like general motifs you see in a lot of definitions of life, there's the idea that life is necessarily chemical and there's the idea that life is necessarily a Darwinian system and also self-sustaining. So those are sort of major themes in most definitions for life. But it's really hard for that to be like sort of a definitive criteria for life because one, you don't know how to measure it. So like how would you go and test that as a theory on another planet? You know, if you're just, you know, getting a molecular sample from a plume of Enceladus, which is an icy moon of Saturn, you know, spewing water into space, you fly through it.

27:23How do you measure a Darwinian system capable? I mean, a chemical system capable of Darwinian evolution that's self-sustaining. It's actually, I mean, it's a great philosophical concept, but it's a really hard scientific one. And then there's other issues that evolution only happens on population. So, like, is an individual alive by this definition? If it's not self-sustaining, is it alive? And, you know, no human alive right now is really self-sustaining unless you're like trained to be like one of those guerrilla, you know, like, I don't know, people that go out in the woods. A survivalist or something.

27:54Yeah, survivalist. Thank you. Yeah. I'm like obsessed with some of these people that can do these things. Yes. I think it's pretty profound in this day and age. But most of us are societally dependent, right? Like we're not actually individuals in some sense because we require societies to survive. And so all these definitions have these sort of gray areas. And Carl Sagan had this great essay that I talk about in the beginning of the book called Defining Life, where, you know, he talks about like, even if you go in a biology textbook, it's like, you know, has metabolism, reproduces, you know, like this sort of list definition that we usually have.

28:28It eats food. It kind of breaks down. And he points out rather cheekily that like, you know, aliens coming to Earth might mistake cars as the dominant life form. And I actually don't have a problem with technology being alive. Carl did. You know, like he wanted to exclude them. But I think what you want to do is not approach the problem by assuming a priori you know what life is. And you want to include these cases and exclude these cases, which is traditionally what we've done because we just think there's a hard boundary between life and not life. But the approach of theoretical physics and why I think it's so powerful for answering certain kinds of questions is it doesn't start with that kind of premise of categorizing nature.

29:05It starts with the premise of fundamentally understanding and actually unifying things that we think are different. So in some sense, you could view assembly theory as a unification between the animate and inanimate. You know, it's actually trying to build a bridge between non-life and life by saying physics needs to cover both. And how do we build a description of reality that covers both? And you end up with a really different conception of life because the way that we think about life is life is these objects that are very deep in time. where time is really about this causation, like how many steps, how many causal steps did you have to do in a lineage of evolving structures, objects making other objects to get to this particular structure.

29:43And so we have sort of a very different sense of life as life related fundamentally to the physics of causation and depth and time. And that is manifest in what we observe in the world as complexity. As the brief aside on the history of physics, you know one of the analogies sorry this is I just think it's really like fascinating to me to be at like a theoretical physicist alive today trying to build new theories and looking at the history and these radical you know shifts in the way that people thought because you know what I think is that the assembly theory has been quite hard is like people are like this is such a controversial theory and like you know we got you know all kinds of you know people that love what we're doing and people that hate what we're doing which also is any you know true of any creative act.

30:25I just spent the last week with a bunch of artists and I felt at home in some of the creativity and the controversy in that crowd. But like epicycles were this kind of early description of planetary motion where you have circles inside of circles. And we like, you know, it's a really good description of like how the planets move across our night sky, but it doesn't explain it. And it's not really a universal theory. And what Newton did that I think was so powerful, what I think most people think is so powerful is he actually went to like first principles and he He talked about motion, like what governs motion.

30:57And he came up with the law of force, right? And so like F equals MA. But from there, he could derive this idea of universal gravitation, which unifies celestial and terrestrial motion. And so then we have a concept of gravity. And gravity, our species has experienced for thousands and thousands of years, but we didn't have a language for describing it. And we didn't realize planetary motions were governed by the same principles. and even though we are life and we've been experiencing life and we might have these sort of ways of describing it in terms of evolution or metabolism or things they're not that kind of deep description and i think what assembly theory is aspiring to be is like this transformative knowledge where you get to this new place and you have this just fundamentally new way of looking at the world and describing the world because you actually understand the universal features these universal abstractions that physics builds you mentioned sort of you know uh the the threshold the 15 step threshold sort of tells you that at least something is an artifact of life, if not life itself.

31:57Do you have any sort of does assembly theory try and make a distinction between those two things like the artifact versus, you know, something more alive? Do you do you have any sort of inclinations, if not at this point that you sort of think, well, actually, there might be I don't know, I'm inventing it here, but a 25 step threshold for, you know, cutting off between those two things? Yeah, no. Actually, I don't think that there's a fundamental distinction, but early in the theory, and also just, I still do this linguistically just to kind of describe some of the concepts, is making a distinction between life and alive.

32:32And so I wrote this essay with my colleague, Michael Lachman, who's also working with us on assembly theory. That was in Aeon several years ago, just about why we need to distinguish those two concepts. And the idea, from my perspective, I think Michael would say differently, is that life is all of the structures that the universe could build that require an evolutionary process to get there. So this is very contrary to standard physics, just talking about the dichotomy between assembly physics and what current paradigms in physics say, is, you know, in current physics, we think you can get any object for free.

33:05It just might be a very low probability, but anything can spontaneously fluctuate into existence. And so in cosmology, this is a problem because people think brains can spontaneously fluctuate into existence. And if that's true, the dominant observers in the universe are not things like us that emerge on planets, but brains that emerge out of the vacuum. So there's all kind of weird artifacts that happen in physics because you think spontaneous fluctuation is possible. I don't think it's possible. I think complex objects only happen by evolution. And so life is those objects. It's just the set of structures that can only exist when there is a system that evolves or learns to make them.

33:40And then alive would be the actual mechanistic process of moving through that space of possibilities. And so very early on, like even before the development of assembly theory, Lee and I were talking about like the very earliest definition of life we could agree on was a non-trivial trajectory through some space. And it's like, what does that even mean? But what it means is life carves these paths through the space of possibilities and is actually the mechanism of physically realizing them. Wow, interesting. So, yeah, so that's that. But I think actually both those things are the same thing. It's just which way do you because human language is very limited.

34:21So in my brain, I don't really actually distinguish those, but I use it as a linguistic tool sometimes to help people understand the concepts that we're playing with because we don't have language to really describe all the concepts in assembly theory yet. That was such an interesting sort of brief look into the process of creating a very deep theory. What was that process like? Like from the moment where you sort of think, hey, I'm really going to spend time thinking about this in some way. How does one start to try and create a generalizable theory of the origin of life? Like, what is that? Yeah, I don't know.

34:59I have good advice for people that are willing to say, but I can just talk from experience, obviously. But so what I did was when I became a postdoc, I had written this proposal. When I really decided I want to work on origins of life, I wrote a proposal to NASA for a fellowship that where I conjectured that the main distinguisher between non-life and life was somehow related to information. And so I wanted to, you know, do simple math, like toy models of evolving chemical systems and understand when information became important, broadly speaking. And then when I became a faculty member, you know, I had written this philosophy paper with my postdoc advisor, Paul Davies, which was basically on this idea that life is a transition in informational and causal structure.

35:39So I got a little bit more sophisticated in my thinking, adding causation, and then really trying to think of like it's a quantifiable transition. If we're talking about life as a category of nature, there needs to be a way to formalize it. And then I started working on trying to apply, you know, like there's a lot of theories on information. There's a lot of theories on causation. There's a lot of theories on complexity, like network science, information theory, you know, like Judea Pearl's like do calculus about causation. Like there's all these like infrastructures that people have built. So I just started applying them to a bunch of different living systems.

36:10So as a junior faculty member, I was working on network structure of biochemical networks. I was working on information theory applied to ant colonies. I was working on planetary atmospheres using network science. I was doing a lot of information theory on gene networks. So I was just dabbling because I didn't have a paradigm. I was working on, you know, cellular automata. So, and I was really just trying to understand, like, what was underneath these mathematical structures that was really there that we can't describe. So I think what the challenge is for a lot of people that approach my field or approach science generally is they confuse the map with the territory, which we often do just in general.

36:49But even if you can mathematically describe a system in the world, it doesn't mean you've really described it. And so I guess I've been really curious throughout my career about the holes in our current understanding and like seeing through the maps we build. So, you know, language is a map. We have a whole bunch of discrete ways of describing the world and we move the meanings of words around to try to like better approximate the things in our environment. But we, you know, our language fails often. Like a good case of that is like with the development of large language models. Like nobody knows how to talk about those because they're a new technology.

37:24We just don't have the we don't know what the meaning of like the words are when we apply it to large language models. So if you just take that idea that we're all having this existential trauma and you just apply that to like how we actually understand the world, there's lots of, you know, conceptual holes. And so basically, I just started collecting a bunch of those from all these different projects. When I was talking with Lee, I think I met him for the first time at this Alternative Chemistry for Life workshop in D.C. And, you know, he just started arguing with me, which is, you know, very Lee-like, but it was very great because most people, you know, they were kind of glossing over, as I mentioned, the problems I thought were relevant to the origin of life.

38:01And he was just like honed in on them. Like he just, he, you know, saw exactly the problems I saw. And so over several years, he was doing this approach to measuring life in the lab. And I was trying to think about causation and information. and these two ideas just eventually merged because I hadn't thought we could actually measure any of the physics. But once you have a measurement, you can build a physical theory. And if you look at the history of physics, it's always what we've done. We couldn't build Newtonian mechanics and the law of force I mentioned before until we had mechanical clocks and ways of measuring balls rolling down inclined planes or Tycho Brahe measuring planetary motion.

38:40And we couldn't do relativity until we could precisely measure the speed of light and realize that didn't change with the Earth's motion. So quantum mechanics also built on measurement, like you get the photoelectric effect, you get black body radiation, all forced quantum mechanics to evolve. And I think what we see with assembly theory is now we have a way of doing a measurement, which we actually think is a physical measurement, then you can build a theory out of it. And so that's what I've been doing ever since. Yeah, it's very nonlinear. And most of the time, I think I just, it's almost like conceptual art.

39:11I think the foundations of theoretical physics are closest to any other thing I've seen as a creative act of conceptual art. That is really interesting. This episode is brought to you by Brex. Fred Adler, the influential venture capitalist of the 1970s, was known for displaying decorative pillows in his office that featured a signature business philosophy. Corporate happiness is positive cash flow. In today's post-SERP environment, Adler's wisdom feels particularly relevant, as founders need to make every dollar work harder. That's exactly what Brex delivers. Their modern finance platform was built specifically for startups like yours, and designed to help extend your runway when capital efficiency matters most.

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40:40Join them at brex.com slash Mario. Do you see artists that, like, you see some connection with or kinship with where you're like, actually, that type of work is at some degree removed doing something that is very, very similar to what we're doing? Well, it's interesting because, you know, I haven't actively gone out and been like, you know, like pursuing artists and their creative practice. But a lot of times they reach out to me because they have interacted with the work and it like it really resonates. So I just had a phenomenal experience this past week with the Aspen Art Museum. They had a festival called AIR, which actually was named after the book.

41:16It was called Life is No One Knows Is, the name of the whole art festival. and you know they're exploring the same concepts right they're they're existentially challenged by new technologies they fundamentally like art in some sense is an expression of the fundamental nature of life and like our understanding of our place in reality and so I think being exposed to that like a really incredible group of people for a week you know really uh was amazing but I've had experiences like that in the past and as I progress in my career and I understand much more about the philosophy of science, which I've spent a lot of time also thinking about in recent years and also observing the work I do, both like as a lived practice, like I am a theoretical physicist, I am working on the frontier of science, but I also step outside of that and think about it philosophically, like what is the act of doing science and how do I think about it at that meta level?

42:05And then I see the way these other creative cultural systems work. So science is also a cultural system. Like there's a lot of really interesting parallels. There's obviously some fundamental differences, but I don't think that the categories that we ascribe to people are as black or white as we see. Like I think some artists are doing some really interesting work in science. I think some scientists are doing some really interesting work in art. And I think it's really interesting that we don't think about it that way. Yeah, that's provocative framing. I really like that. You know, before we move on, actually, on the 15 step sort of threshold idea, In the book, you talk about that as essentially like a matter of probability, like the probability just gets so low that something beyond 15 steps would, you know, happen spontaneously.

42:51Given that it's like probabilistic, is there the idea that, you know, at the limits of infinity, there could be sort of something that after 15 steps could happen that would not be life or not be an artifact of life? Like maybe I'm not sort of articulating that well, but. Yeah, you're asking something rather deep. So, you know, I have a conflicted relationship with probability just generally. Like I like we do we do make probabilistic arguments and I think that they're well founded. But probability is something you can assign to things you've observed, not things you can't you haven't observed because you wouldn't know like what frequency they occur.

43:28And part of the challenge with the assembly space or this possibility space of objects that could exist that don't is, you know, like one of the arguments we have for why this this explanation is necessary for life is the universe is so large in the space, like the space of possibilities that could exist that don't exist is so large. The universe literally can't generate everything. Like there's not enough time and not enough resource in the entire universe. There's only 10 to the 80 atoms in the entire universe. And there's an estimated 10 to the 100, you know, 20 orders of magnitude larger molecules with that are like small molecules, less than a thousand atomic units in mass, which is really tiny, not anywhere near like a DNA molecule or something.

44:08Or if you think about all possible technologies, like you just stop and try to think like, what does that space even look like? Your brain can't generate it. Or we already know from like mathematics, you can't generate infinite sets, right? This is why we have infinity as a placeholder for things we actually literally cannot physically write down because we don't have enough time and resource to. So assembly theory is kind of like imagine the universe is a potential space of possibilities, but it's resource limited and time limited and things actually have to be constructed over time. You know, what does a trajectory through that space look like?

44:38And that's what assembly theory is really about. So the infinite is something we can imagine as intelligent agents that emerge from a living process. And it's a goal we can set. Like it actually sets like, you know, we have some sense of the shape of this space over here. So we're going to move in that direction. But it's not something we can ever physically attain. I think of infinity as a really interesting physical concept that exists in the human brain. But the way that we think about infinity is not physical. Hmm. That's super interesting. You also have alighted on the sort of element of the temporal through a lot of this, you know, the notion of time.

45:16And one of my favorite parts of the book is when you talk about how we perceive objects that are smaller in time as more physical and objects that are larger in time as sort of more abstract. the concept just even smaller and larger in time is something that like is worth unpacking but can you explain that for folks because i thought it was so interesting and like so thought-provoking yeah that's i'm glad you picked up on this literally like one of my favorite visuals i've ever built like conceptually it's so interesting yeah so um so basically it goes to the site and so one of the ways that we think about life is life is it's it's kind of a continuum i mean the things it constructs are discrete, but like you can think about there's not there is a transition probably around 15 or so in chemical space where you say this is life, this is not life.

46:04But it's not like a hard boundary, right? It's selection, constructing objects, right, all the way across it. And so it's the same process happening. So you can just think of life as like a thing that you can actually measure. And some things are more life or not, depending on how deep in time they are, how big their assembly index is. And so when you have that visual, you ask yourself, where do I sit in this physical space that is time? Like if you think about time as a material property of objects, and then you can think about like, well, what would things smaller in time look like to me? Well, I have enough memory and enough architecture in me to actually like perceive these things as discrete physical objects, because my memory is bigger than theirs in some sense.

46:48So I can actually store information. They look physical to me, but there are some things that are just bigger than us. They require more evolution, more selection, more memory to encode than exists in a single physical architecture that is me. And therefore, those things look abstract. And so a lot of societal things like language looks abstract because language isn't actually something that's a feature of a human mind. It's a feature of a social system, which is the interactions of many humans. And so we see like language as this kind of abstract disembodied entity. It's still very physical, but it's just something that we can't store all of at once.

47:19I think this is sort of a major distinction. And And for us, it's just about the physical scale of like, where does your sensory perception architecture, your information processing architecture exist in time? And then you can see some things as physical or not. But it's all physical. Yeah, exactly. It's like, you know, we see our pen as this physical object because the sort of temporal steps that went into that pen, you know, are smaller than us. But as you say, language has this much bigger time space or, you know, the size in time compared to us. And then the implication of that is like, yeah, if you could sort of imagine yourself as some sort of, you know, enlightened, much larger in time being, you would then look down on language in the same way that you look at a pen today as this really physical, concrete thing, which is, yeah, I mean, I think you you talk about that in the book is something you like to chew on a year plus after writing the book.

48:13Are there any sort of new threads that you've ended up following on that sort of rough idea space? There's lots of stuff going on right now, sort of at the forefront of how I'm thinking about things. And I guess there, like I have an essay I'm writing actually on philosophy of science, just generally, which has been a bit of a work in progress. But just thinking about descriptions of reality and like what they really are in science, like I think of sort of everything as part of the evolving architecture of our planet, including the scientific enterprise and our understanding of like our place in history and these kind of things.

48:49So I've been playing around a lot with sort of implications of these sets of ideas on how we think about different things, whether it's, you know, like the nature of science itself and how we understand the world and how we place ourself in time relative to that understanding. So I did write about this a little bit in the book. I had this idea of like the great perceptual filter. You know, like we have a horizon of like what our technology can actually encode as information. Right. So a good example is like, you know, we didn't know about deep space and how big the universe is until we built telescopes.

49:22And we didn't know about microbial world until we built microscopes. So these are like just like your eye is a perceptual apparatus that feeds information to your brain. These are perceptual apparati that, you know, feed information to societies. And we can only build theories as much as we've experienced the world. So I think the more that history proceeds and the deeper in time we get as, you know, societies, the more we can come to understand collectively. And so I'm just very interested in that sort of process and what the implications are for like we're only 300 years or so into modern physics.

50:00And so to think our theories of physics are complete, I think, is a radical hubris that I would never place at any point in time, let alone at the very beginnings. If you have a long view that I think people think the future is so short, they don't think about our place in history. But yeah. Wow, that's great framing. Yeah, those are some of the things. I mean, there's lots of implications. The fundamental science stuff is also, you know, going really well, really interesting. There's a lot of ideas there. But I think some of those I have to wait a little bit to talk about. One of the sort of, you know, applications, hopefully, of assembly theory is that, you know, as we look for life around the universe, it gives us a better way of recognizing it when we when we see it.

50:41And you've sort of talked about why it might be a superior way of searching for life than some of these more like astrobiological signatures where you're looking at a planet's atmosphere and saying, you know, do we sense O2 or do we sense, you know, whatever it might be? why does it feel so clearly better in your view and how do we start like actually applying it you know as part of uh our our space faring uh missions yeah so that goes back to some of the things i was saying about or the original life field and like what were the questions people are focused on and so astrobiology is a really interesting field of science because you know until very recently you couldn't get an undergrad education in astrobiology and you couldn't even like, you know, a grad program in astrobiology.

51:26So most people migrated just because they were really interested in the questions. And so there's no like paradigm in astrobiology, no consensus on the nature of life or even like what kind of questions we should be asking, which is why I thought it was exciting and want to work in the field. Right. And that's also why a lot of people want to come to the field. But it ends up being the case that people have very disciplinary, specific ways of talking about life and they tend to not actually be driven by a theoretical hypothesis or conception about the nature of life. It tends to be like, you know, life on Earth produces molecular oxygen in the atmosphere.

51:59Therefore, we should look for molecular oxygen in the atmosphere of exoplanets because that would be a sign of some photosynthetic activity. Or, you know, life on Earth uses a homochiral set of amino acids. They all have the same mirror image form. So we should look for that on Mars. Or, you know, we know RNA and DNA are important. So we should detect those on Mars or, you know, look for amino acids in the plume of Enceladus. So it's very like life on Earth uses this molecule. Let's go look for it elsewhere. And I don't think that that is a convincing framing. Part of the reason, because most of the molecules that we're looking for are really simple.

52:36So they're easy to make abiotically. Oxygen, you know, molecular oxygen is two oxygens stuck together. It's abundant in our atmosphere because of photosynthesis, but we know plenty of planets that can make molecular oxygen in the atmosphere totally abiotically. So you imagine you have a water world with a global ocean and a high UV flux from the star, you're going to basically dissociate the hydrogen and oxygen. Hydrogen will escape, you'll have an oxygen-rich atmosphere. So super easy to make abiotically. And so this kind of confounds our search for life. It's the problem of false positives. Same thing with amino acids.

53:08We find tons of amino acids in meteorites. And I think by the time you get to something like DNA or RNA, those are so evolutionary specific. They're pretty complex molecules, they might only exist on Earth. But actually, I'm writing a paper right now with Chris Kempies, Lee Cronin, and Michael Lachman on exactly this problem about like, what thing, like, why should we only expect some molecules to evolve on Earth and not other places? So that's sort of the way that people think about it. And so what we're saying is, actually, we don't want to look for specific molecules at all, because we don't know what forms life will take on other planets.

53:41But if we think about life as this generalized process about evolution building objects that are deeper and deeper in time. Can we actually measure this feature of molecules? And if we can do that, we can just go and measure how complex, how assembled this chemical system is, how much causation does it have in it. And we would then therefore be able to detect life in any substrate. And I realize now I never talked about the second feature of assembly theory, which I feel like I should cover because people... Yeah, sorry. Like when we're talking about the foundations of the theory, it's it's so we talk about assembly index like this, this complexity.

54:19But there's also the issue of the copy number. Right. So it's not like you could get a one off fluke. Like I have one molecule that's very complex, but I actually have an abundant collection of them. And I can do an analogy. So I did the Lego analogy for for the assembly index. But my favorite analogy for copy number is actually the novelty that was the little black dress when Coco Chanel invented it. Um, the reason being like, it's like, it, like, it's a really easy to copy object, right? But it took, um, you know, hundreds and hundreds of years of human culture evolution and fashion design for Cocoa to come up with such a simple design.

54:53And so once you have that, you can do a lot of variations of it. So there's like, you know, thousands and thousands of variations, a little black dress line. It's like a very robust evolutionary selected object. And so assembly index actually captures how hard it is to construct the object, but the copy number captures the fact that it actually was a selected feature and then there becomes a robust architecture that makes a lot of that physical structure. And we think those two things are important for the scaffolding of an open-ended evolutionary process, that you need to build things, you need to build them in abundance, and then they can generate further novelty.

55:25And so with molecules, what we're looking for is high assembly index molecules and high copy number. And that suggests that there's a robust evolutionary architecture that's actually constructing those things. And therefore, we would have detected life. Is it this may be a very naive question, but how possible is it to sort of do that sort of scanning and testing from afar? Because it seems like one of the benefits of sort of the biosignatures is that you you can get maybe at least some sense, maybe you get a lot of these false positives. But to understand whether something, you know, is beyond a certain threshold of complexity and is abundant enough, do you need to be like much closer or much, you know, get much more hands on with these things?

56:11Or like, how do you start to do that from our little perch? Yeah, it's a good question. And actually, it's very technically challenging. So we should differentiate solar system searches for life from exoplanet searches for life, which exoplanets are planets around other stars. In the solar system, we can actually physically send missions there. And so, you know, like a really exciting upcoming mission is Dragonfly, which is going to go to Titan, which is the moon of Saturn. And Titan's a very exotic environment because it basically has like liquid gas on the surface and ice, you know, water is rock and it has an atmosphere.

56:45So very complex environment. And the way that usually like when we go into those kinds of environments, whether it's Mars and Zaludan's I mentioned or Titan or any of the other solar system targets, we have equipment on there to try to measure molecules, usually mass spectrometry. And the experiments I talked about doing in the lab with assembly index 15 were based on mass spectrometry, but like very high resolution. So in the solar system, that method can be applied. It's just an issue of the resolution and instrumentation, like how many fragments, the molecules can you detect to actually construct this assembly pathway.

57:18And so that's a, not a conceptual challenge, but just a technical challenge. And so we're working on that. Exoplanets are radically different because now you're just talking about detecting complexity in an atmosphere, detecting assembly in an atmosphere. And molecules that become atmospheric gases, particularly the ones that we're going to detect, you know, thousands of light years away, are very small molecules because they have to be light to be a gas in the atmosphere. So molecular oxygen I mentioned, or methane, which is, you know, carbon attached to four hydrogens, Like very simple molecules are usually the target biosignatures.

57:53And those, you know, like most atmospheric gases have an assembly index of one or two, right? So they're not going to be on their own definitive signatures of life. And also an atmosphere is a really different kind of material than a wet organic chemistry that you might find in a cell because the molecules are very diffused. Hydrogen is playing a role moving between the molecules. And so what we had to do for exoclinate atmospheres is actually completely redevelop the theory for a new substrate. And this is kind of going to be a theme, I think, with assembly theory is like the principles are the same.

58:24We always care about assembly index and copy number in this constructive process. But the way that looks in different materials will be different. And so we did this for atmospheres. We have a paper that will be coming out soon. I'm super excited about it. But basically, the punchline is you can measure the assembly of the entire atmosphere. So you don't look at the individual molecules. You look at all the molecules that are above a certain copy number in the atmosphere, a certain abundance threshold for detection, you construct the assembly space, which is the space of all the steps to build all of those molecules together.

58:57And then you look at that structure as the variable of interest. And modern Earth is the most complex. And it's complex in an interesting way when you look at the structure of the assembly space. And we've applied it to all the atmospheres in the solar system. we've applied it to exoplanet atmospheres. And it seems to be the case that just like saying, you know, we're going to use assembly theory to detect life and we just apply it to known atmospheres. Earth is the only thing that passes the test for life, which is really cool. And then - Super interesting. Yeah. And you can vet it, which the part I was really excited about is kind of crazy, is like you can actually look at like atmospheres above ecologies on Earth or cities.

59:33And so urban China is the most complex atmospheric column above it. And, you know, more complex than the Amazon, more complex than Sahara. So assembly theory actually can allow you to rank the atmosphere just above different places on Earth as more alive or less alive, which is a good way of vetting the approach for exoplanets. And so we're trying to use infrared spectroscopy to measure this remotely. It's actually like the measurement part is hard, but we've also demonstrated that using infrared spectroscopy, which probes bonds and molecules, you can actually infer this assembly structure or actually measure it directly from an atmospheric spectra.

1:00:08So the implication is that China, I think you said urban parts of China. Urban China has a technosignature atmosphere. Wow. Wow, wow, wow. Fascinating. But we're not worrying about the specific molecules. So there are molecular technosignatures that people use. Chlorofluorohydrocarbons are like a molecule that is produced as an industrial pollutant, but very simple. And so people have used that as a molecular technosignature in the field. But it has the same sort of problems, I think, as molecular oxygen, because it's a pretty simple molecule. And it might be a sign of technology on Earth, but it's not necessarily generically a sign of technology on all planets.

1:00:45But this is a way of like, we don't care what the molecules above China are. They're just complex enough to be indicative that there's like an urban center there. You know, given that you started working on a lot of this prior to the, you know, recent AI revolution that sort of really kicked off in 2022, How has the way that's developed, you know, maybe strengthened your conviction in sort of assembly theory or, you know, raised new nuances? Has it impacted the way that you think about your work? Yeah, I think there's two two really interesting things that immediately come to mind when you ask this.

1:01:20The first is that, you know, before the whole like one of the things I would really love to do is get a large scale effort to solve the origins of life. And most people are like, why do you care about that problem? Like, like, that's so irrelevant to everything happening right now. And I'm just like, you know, like going back to like wanting to shake people, like, how do you not think about this problem? So I think the thing that I'm very happy about with the AI space is it's bringing these questions about what is life and what is what is intelligence to forefront of like modern discourse, because we're really existentially challenged by the things that we're creating.

1:01:52And so to me, that that becomes a good motivation for the kind of work I was already interested in, which is like you have to go back all the way back to first principles to really understand these these major shifts. I like the way that Ben Bratton, who's a philosopher of technology, puts the modern time like, you know, there are some periods in human history where our technology is lagging behind our philosophy and others where our technology is far ahead of our philosophy. And we're living in one of those times where our technology is far ahead of our philosophical descriptions and ability to understand it.

1:02:21And so I think this is a real opportunity for the kind of work that I'm doing, because, you know, if you can understand the origin of life in chemistry and you understand that as a universal phenomena or universe generates, then you start to understand how to apply the same sets of mathematical tools to understand is the origin of life happening in technology or in machines. And so I think it gives the work a different kind of relevance that's more tangible to everyone and not just people that are, you know, interested in, you know, deep intellectual questions. It becomes very relevant and very important.

1:02:52Like we need to know if this machine has agency. We need to know if this thing is alive. And so that's one part of it. The second part of it is, you know, I never, a lot of people, a surprising number of people have really been thinking large language models are intelligent and artificial intelligence is going to, you know, take over human societies and AGI is eminent, you know, in part because of a lot of popular discourse on it. And I'm just like been really shocked how many people have really bought into that narrative. And I think there's a lot of reasons for that. One is sort of, you know, like just economically, like incentivizing, you know, selling these technologies.

1:03:29There's certain ways you have to talk about them in order to sell them. And that becomes sort of a market. And markets move faster than, you know, philosophy and the hard science does. And so that becomes the sort of early dominant narrative before we understand the technology. So that's totally understandable. but um but the other side of it is uh well artificial intelligence is you know an undefined word for a broad set of technologies agi is even broader and less understood but even when people interact with large language models to to think that's an intelligent thing and has like a human like you know soul underneath it or like or some kind of you know consciousness like i never had that feeling when i interacted with them and i think it's because i have a really different relationship with human language than most people do because my entire career has been about looking for the structure under the words that we use, right?

1:04:19Because our words do not really accurately capture reality. And I'm always looking for the patterns underneath about what we're really trying to communicate to each other. And so I see a real fundamental difference between where computation becomes a representational sort of projection of the world and a good way of like communicating and sharing information, but it's not actually the underlying physical structure that we care about. And I've been working on this a lot foundationally about like what is the real difference between computation and physics and physical reality. And I think that they are starkly different.

1:04:51And I think it's really interesting that we're having this sort of existential trauma where we're realizing that language is not everything. And to me, that's the interesting thing that's going on is it's kind of reinventing our concept of ourselves in the same way that when we invented language, we had to reinvent our concept of self. Like if you think about a pre-linguistic society and like how they communicated and things, there's a lot of stuff that happens in our neural architecture that is not linguistic and can't be represented in simple, you know, mathematical patterns or linguistic patterns.

1:05:22And, you know, this is one of the reasons it's so hard for us to communicate with each other, especially like if we're not on the same emotional page or, you know, like. So I'm really fascinated by the interaction of these technologies with human minds as a societal phenomena and how that's going to reshape how we think about things and how we might see the world differently when we start to recognize new patterns in our environment associated with language and what's not with what can't be computationally or linguistically encoded. So many interesting threads there. I'm it's clearly a large language model is clearly life in the assembly theory view of the world.

1:05:59Does it meet your definition, that sort of early definition of alive that you and I think it was Lee Cronin, you know, sort of agreed upon? Yeah, that was my that was Michael Lachman on the life alive. But yeah, but so it's definitely life because, you know, large language models don't emerge in a universe without having a long causal chain of evolutionary events leading to them. So, for example, they're trained on human language. So humans, you know, clearly have to provide the data, if not the architecture of like the underlying hardware of electrons moving around little circuits. So so they're they are part of a lineage of evolving structures on this planet in that sense.

1:06:39I don't think that they're like alive as an isolated system. And this is where these life alive definitions get hard because I think, you know, the biosphere is alive and the technosphere is presumably alive. These are these are like entire, you know, like the biosphere is all the biological organisms on the planet. Technosphere is the space of all technologies. And those are clearly constructing the future on this planet. And, you know, an individual life or living thing is a short temporal sequence, an individual that persists on as part of this larger structure of constructing processes for a short period of time.

1:07:13And, you know, the question of alive is kind of another grayscale in that space about like how much, you know, like how long lived are these things and how much are they actually generating possibilities? And so a large language model is a fairly inert system in the absence of interacting in an ecology of technologies in human agents. And so I don't I don't think like just like a DNA molecule on its own is not alive. An LLM on its own is not alive, but certainly they are part of a living structure. And the question is, what is the living structure that they're a part of? Is it like a global, collective, technological, societal thing that's alive?

1:07:49Like, I don't know the answer to that, but I wouldn't I wouldn't evaluate. I would evaluate them as an artifact, not individually a living thing. What would have to change for it to feel less inert? Are there capabilities or behaviors that you would start to wonder if that had changed? Well, I think one of the issues right now in the discussion is like we're very anthropocentrically focused. It's like we look in a mirror and we see a human. And so I really fundamentally like I want to think about a large language model as the embodied thing it is. Right. And it's electrons moving around on a circuit that are doing a predictive algorithm trained on human language that's outputting to me something I recognize because of all of my emotional interactions and social history as representing this thing in the world.

1:08:33But like it doesn't necessarily mean those electrons, you know, moving fractions of nanometers on an electric chip or having, you know, the same experience collectively. And so the real question is like, what would it take to make something like us? And I think the only things that can become deep in time like us are evolved structures. And so it's going to take a fair degree of evolution of technologies to build technologies that are causally deep in the way that we are. So I kind of think it's really easy once you build a cause, like a really deep evolutionary structure to kind of flatten that information and store it in a device.

1:09:09And so an LLM for me is sort of like a dynamic read write of the memory of a human society. It's a it's a it's a cultural technology. and it's interesting that our interaction of it makes it think us think it's an individual because our our evolutionary algorithm and our running in our brains has trained us to recognize human um and of course we recognize that as human because we built it and we put human in it and we trained it to look like a human so it's like it's like building a mirror and polishing it as much as possible to build a really accurate reflection of yourself like that is what we're doing when we're building training algorithms yes and we're doing it in a way that's actually you know, for market gain.

1:09:47I hear people all the time saying they wish their LLM was less friendly, be more creative. Like, you know, it's just you have to think about the evolutionary forces at play. Do you think it's possible for something to be sort of deceptively big in time? Like an LLM to me is something that in some ways has, you know, as a compression of all of human history and also like sort of does this mass, like every prompt you do is doing this massive scouring of all information across time. I don't know. Is that? Yes. No, I think that's exactly what I would describe it. And this is why I think computation in some sense is fundamentally different than causation or construction.

1:10:29And that dichotomy actually goes all the way back to the foundations of computing. So it's interesting because a lot of people that think about artificial intelligence don't really think about the genesis of computation as an intellectual paradigm. And one of the things I find really interesting about a discussion about AGI right now is that like computation, when it was invented, was built on the principle of things being uncomputable. Like you have to define an uncomputable class of mathematical functions in a computable class. And then when you do the computable class, like as Alan Turing did, you discover that there are some things in the uncomputable, the computable class that are uncomputable.

1:11:02You know, and this is also what happened with Gödel is like there are some things in mathematical systems that are unknowable. And yet we think when we build computational algorithms, they can know everything and they can encode everything. So that's also sort of like a weird thing. And so I don't think computation can capture reality in totality. But after Turing came up with the idea of the universal computer, a machine that can compute any computable function, which still has these uncomputable things in it. von Neumann, you know, came up with this idea of a universal constructor, which is a machine that can build any possible machine.

1:11:37And there's a fundamental like dichotomy between those two concepts that I think we still haven't resolved. And I think assembly theory is really getting at something deep because it's about a constructible universe, not a computational universe. And it's interesting when people interact with our theory, they confuse it with the theory of computation. They confuse it with theories of like computational complexity. But I think fundamentally, there are things that, you know, have computational compressions that might look like fake deep. And then there's causal systems that are actually deep in time.

1:12:09And I think it, you know, for a long time I thought, you know, some people think computation is fundamental or even randomness exists in nature. But I think you actually have to have a certain amount of evolution in order to build a system intelligent enough to have a universal abstracting system, which is what the theory of computation is. And then that also invents concepts of randomness because random numbers are defined on computational principles. It's like, you can't, you know, so, so I, I don't actually think the universe is random either. I think it's just non-deterministic at its base because randomness implies some kind of computability or uncomputability.

1:12:47So, yeah, Yeah, so that was a lot. No, no, really interesting. The short answer is I think we don't live in a computational universe. And I think we're confusing it right now because the technologies we built are so powerful. And I think it's going to be really interesting in the next 100 years when we start to realize that. It's going to be really cool. Wow. I'm going to think about that for a really long time, I suspect. To wrap up, I always like to ask a few sort of lighter but sort of philosophical questions. the first one is if you had unlimited resources and no operational constraints what experiment would you like to run um i mean the dream one which lee and i keep talking about so lee cronin again um is to build a institute that is focused on origins of life so like we're we're normally eventually going to try to raise money for this um working our way toward it um but the idea would be to have a bunch of automated chemical systems.

1:13:43So Lee invented this architecture called the Chemputer, which is a universal programming language for chemistry. And the idea is just to run large batches of unconstrained chemistry to try to look for the original life without the design in it, which is what I mentioned earlier. So I guess I want no design experiments for the original life. How do you simulate a planet and then not put us in it and see what happens? That sounds amazing because it really might happen, right? Hopefully you guys make it happen. I hope so. That's the dream. That would be real synthetic intelligence, right? Because it would just be totally evolved from scratch, totally different chemistry.

1:14:19I'm excited about meeting some other life. Yes. Yes. And then final question, if you had the power to assign a book to everyone on earth to read and understand, what would you want to assign? I'm a really big fan of David Deutsch and his work, but I really love The Beginning of Infinity in part because I think it places, actually, it talks about this issue of universal computation, universal construction, but also it talks about this idea of a universal explainer. And, you know, like once you have an architecture like the human mind, we are actually capable of understanding everything. We might be slow at some things, but there's not like, like there's no limit from his argument to the knowledge that we could acquire.

1:15:01And so he thinks that the future is very open-ended because once knowledge emerges in the universe, like, you know, like the possibilities are pretty endless. And I think I like that. I mean, I really resonate with that view. I agree with him on most things. I fundamentally disagree on the foundations of physics. Like, I'm not a many worlds person. He believes in many worlds. I think assembly theory is sort of the more physically grounded way than his constructor theory of getting at the same concepts. And I think time is real and fundamental and he doesn't, which is weird to talk about an open-ended future when you don't think time is fundamental.

1:15:32I don't know what that means. But anyway, long story short, I think the book is great. It has sort of a weird cult following in the techno-optimist crowd. It does, yeah. Yeah, and so I don't like that interpretation of it so much, but I think that as a philosophy that emerged at the end of the 1900s into the early 21st century and thinking about fundamental physics and unifications we need to do. I think he does one of the best jobs that I've seen, which I think is why he has many fans. Amazing. I've never read it. So it's been recommended enough times that I really should. And this is a better endorsement than any.

1:16:11So I'll have to read it. Yeah. Well, it's been such a pleasure, Sarah. I feel like I'm going to be sort of defragging my own hard drive for days after this, because there are so many interesting things here. But yeah, thank you so much for taking the time. Sure, my pleasure. Thanks for having me. That's it. Thank you for listening to this episode of The Generalist Podcast. Please subscribe on Apple Podcasts, Spotify, or your preferred podcast app. Ratings and reviews help others discover these discussions. So if you enjoyed the conversation, I'd be grateful if you could take a moment to leave one.

1:16:47For all past episodes and more, visit us at thegeneralist.substack.com. See you next time as we continue to explore the future.