Sara Imari Walker on Making Sense of Life, the Universe, and Ourselves

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TRANSCRIPT

SPENCER BAILEY: Hi, Sara. Welcome to Time Sensitive.

SARA IMARI WALKER: Hi. I’m very happy to be here.

SB: First off, it’s a joy and an honor, really, to be here in Aspen with you. And I was at your talk at the Aspen Art Museum a few days ago, which was incredibly mind-altering, I would say reality-expanding, and I hope we can take it a little further with our conversation today. 

So I wanted to start with a quote from Life as No One Knows It, your new-ish book, and that’s, “By observing what is happening now in the present moment, we can infer what has happened already, even billions of years in the past.” Can you unpack this for me from a physics and time perspective—the now?—and perhaps even in the context of this room that we’re sitting in, here at the Aspen Institute, at this moment in time—I guess it’s almost 1 p.m. Mountain Standard Time—and we have microphones in our faces. [Laughs]

SW: Yes, and those are kind of odd objects that our universe has generated. 

Well, I think one part of it is, I think in some ways we take the past for granted in really interesting ways like, “The past happened and it’s in the past.” But all of the evidence we have about the past is actually in our present environment. And, as scientists, when we’re actually trying to study the past, we make predictions about the past just in the same way that we make predictions about the future. And then we have to test our theories against the objects that exist now. So all of the experimental tests we do are actually in the present moment. 

I find this very paradoxical. But we do have evidence of life on Earth being billions of years old, and that’s recorded in your cells. Subcellular structures are believed to be billions of years old; we have a lot of molecular evidence for that. And it takes billions of years of constructing more and more complex structures and evolving more variety of forms to get to something like a microphone. I’m just deeply interested in how that past history is wrapped up in the present moment in the objects that we observe.

SB: Well, here, I should say, your work—your lifeblood, really; that’s pun intended [Laughs]—is the study of the origins of life, which, as you’ve put it, remains one of the greatest puzzles in science. And this is a big question here, but: Why do you think, as much as we’ve advanced scientifically and technologically,are we still so in the realm of the unknown? Why do we still not know the origins of life?

SW: Well, I think the first thing to accept is, we can’t know everything. Even as we’re building supposedly superintelligent machines, they can’t know everything, either. Foundational principles developed in the last century say it’s not possible to know everything. But I think, more fundamentally, as history develops, you have a certain amount of knowledge and cultural history to actually understand certain problems of the world. And so, I think it’s really interesting, because physics as it exists now—so I’m trained in theoretical physics—really doesn’t take the contingency and the history as real physical features of the world. And the theory of life that we’re trying to develop really does take history as a physical feature of the objects that exist now. And I think this feature is quite interesting, because it’s not something that you might observe in the world until you see enough history pass.

So, as we see ourselves designing more objects, we see the imprint of our human agency in the world around us, we’re starting to realize that there are many more things that could exist, that we could create. And we see this happening over history and we see the agency of human culture actually transforming the planet. I think once you start to see that effect and you start to feel it as a lived experience of human beings, you can actually start to see the physics—that is, “life”—that I think emerges at the origin of life. So, I actually think that some problems we will not be able to solve simply because we haven’t had enough cultural history pass to actually recognize that the world works that way.

SB: So fascinating. [Laughs] I mean, we’ll get into your “assembly theory,” as you call it, shortly. But I first just wanted to mention that in your book you describe life as “the vaporware of chemistry.” I love this idea of “vaporware of chemistry.” Could you extrapolate that just a little bit?

SW: There’s this popular adage that life is an emergent property, so no atom in your body is alive, but you, as a living thing, are alive. And so, for a long time in my field, people thought you couldn’t reduce life to molecules, and you wouldn’t be able to know the imprint of life in a molecule. And actually, a lot of our work is saying actually you can, because some molecules require a history of an evolutionary machinery. I don’t think it’s actually machinery, but an evolving system to actually construct this particular molecule, because it’s just too complex to form by chance. But the historical viewpoint has been: Molecules are not alive, a single strand of DNA is not alive, and therefore, when you look at chemistry, you lose all the properties of life.

I think a lot of the history of physics has been coming up with new definitions for what we think of as physical. This comes out of our theories. So what are material properties? And one of the things I think becomes very relevant is realizing that many objects of our everyday experience carry with them this materiality associated with them being products of life. And that’s the feature I’m interested in, is that deep lineage, that deep history to construct these objects—that they don’t exist arbitrarily anywhere in the universe.

SB: Right. The microphones in front of us. [Laughs]

SW: Yes, that’s right. They’re a great example.

SB: You’ve made the case that we need an entirely new physics, and to achieve that, you’ve developed what you call assembly theory. Could you share with the listeners what assembly theory is, how it works, and why it matters for determining a new way forward, to figuring out what life is, where it comes from?

SW: It can be stated pretty simply, but I think underneath the simplicity of the statement, there’s a lot of complex layers and some very deep physics. But the simplest statement is just: The universe can’t make every possible structure, and it can’t make complex structures spontaneously. We conjecture that there’s actually a threshold in the complexity of an object, above which you need a living system to generate that structure and a living system being something that has a deep history, that is the product of evolution and selection. In some sense, you can think about life as objects making other objects. And the deeper that that chain of objects gets, the more alive we think it is in assembly theory, but actually that there’s an actual threshold in these contingent histories of these objects building objects where you say, “It has to be life, because nothing this complex can happen for free in our universe.”

SB: Right. These microphones started at the origin of life.

SW: They did, yeah. Information is accruing over billions of years to generate all the structure on our planet. And it’s not just that these microphones started their lineage at the origin of life on Earth; it’s that they don’t exist anywhere else in the universe, probably. This is also crazy, because actually it goes back to why is now the moment for the origin of life? There’s this great historian, Thomas Moynihan, who’s studying the history of how big history has been to humans. One of the things I think was most insightful from his work is just, for most of human history, people thought the world would repeat every few hundred years. So they would be back sitting in the same chair—

SB: Oh, wow.

SW: Repeating the… Because they thought the universe was so small. And so, as we’ve gotten, with geology and evolutionary theory, we started to realize the planet was very deep in time. And then, we invented telescopes and we realized how big the universe is in space. And now [that] we have all this compute, we realize how big the universe is in possibility. What’s super interesting about that is, once you start to realize how big the potential space of things the universe can build is, microphones are incredibly specific objects. They require billions of years of accrual of information. It’s very unlikely any evolutionary history anywhere in the universe is going to reproduce this conversation and have these microphones. And I think this is really a radical feature of our universe. It’s observationally consistent with all of our experience, but completely counter to what our theoretical constructions have told us about the way the world works so far, at least in foundational physics.

SB: I have to talk about time here, because time is essential to assembly theory, and in Life as No One Knows It, you write, “We must treat matter itself as information, which forces reconsidering the concept of what is material.” And elsewhere in the book, you note, “Standard physics treats time merely as a backdrop that objects move through, whereas in assembly physics objects have a size in time…” Could you talk about this concept of time as a material and also the relationship between time and information, as you’ve been calling it—or causality I guess?

SW: Yeah. And I guess, eventually, I hope to replace all those words with assembly because people will understand enough of what we’re trying to get at that there actually is a word for the things I’m saying. But when you’re inventing new theories, it’s quite hard because you have all these approximate words to describe the world, but none of them have exactly the meaning, because we haven’t discovered that meaning in the universe yet. That’s quite hard about these terms. 

But I’m pretty obsessed with time. It’s deeply fascinating to me that every hundred years we develop new theories of physics and they have new concepts of time, but we’ve never had one that actually really took time as a physical property of objects. And I think this is a really interesting, innovative insight of the theory that we’re developing. And it really just came by thinking concretely of the measurements that we do in assembly theory. So we actually have a way of measuring, in some sense, how much causation or constructive time is in an object. We call it the “assembly index,” and it’s just the measure of a minimum number of steps where you reuse parts. So there’s some kind of memory to reuse the parts to build up to an object.

We can go in the lab and measure it as a physical property of molecules. Thinking about that and how we build theories of physics, almost every theory of physics has taken measurement seriously as how we get at the materiality of reality. If we can measure something, we can codify it as an abstraction in our theory. And there’s this odd, very interesting conceptual loop in theoretical physics, because the things that become abstractions in our theory are the things that we think are materially and physically real. Like electric charge, because we can measure it, or mass, because we can measure it.

Assembly theory has this property of this causal depth, what we call the assembly index, which is a measurable property. This started to get us thinking about this idea that objects really do have a size and time, and they carry it with them. It’s a way to formalize this intuition. I have a wonderful colleague, Michael Lachmann, who if you ask him how old he is, he’ll say he’s 3.8 billion years old because some of the architecture in his body, the ribosome in particular, has been reconstructed on this planet for that long. We now have a way of talking about that property and it’s very different than the concept of time that we’re moving through time. We’re literally carrying time with us. And all of that time that is in you is why you’re not an emergent property. You’re actually just an object that’s very large in time. And this is why you behave very differently than atoms that are very small in time, because you have all of that constructed complexity built into you as a physical object.

SB: It’s funny, I’m turning 40 in a couple weeks, and it just feels like such an unremarkable age in this context. [Laughter]

SW: Well, actually, I’m around the same age, and it just makes you feel really great to be able to say I’m 3.8 billion years old instead of 42 or whatever it is. It sounds so much more glamorous. [Laughter]

SB: There’s this paragraph from your book that I’ve printed out in front of you. I was hoping you could read, because to me this says so much about your work, why it matters, and ultimately who we are as life—as living beings.

SW: Yeah. Life is pretty special. I’m happy to read it. 

“I am not my atoms, and you are not your molecules. We are part of the current instance in a several-billion-years-old lineage of propagating information that has structured matter on Earth since life first emerged on it. The first life never died. Not only did it not die, it bifurcated and generated all of us, from the diversity of trees to the diversity of minerals, to my coffee cup and my keyboard on this computer I am typing on, and your book (or device) as you read (or listen to) this. Individuals, and indeed species, are temporary aggregates of information as it persists in our biosphere.”

SB: Maybe continue that final sentence, the idea of us as temporary aggregates of information.

SW: Yeah, so I kind of avoided, when you asked me what information is and what time is and how are they related a little bit before, in part because I think information is a really important concept, but it’s really hard to define precisely in the way that I think is relevant to the physics. But we’re familiar with information from our everyday experience, right? Words are information; the internet is about how information is controlling our daily lives, with all these flows of information in our environment. The thing that’s kind of paradoxical about life versus how we think about things in physics is, in life, information seems to be a causal category. Me reading words can actually change something on the other side of the planet. And so it’s actually this propagation of this thing that seems very immaterial, but somehow constructs all this complexity that was so perplexing about the nature of life from the perspective that I started in in traditional theoretical physics.

So I started early in my career saying, “Information and causation were somehow critical to the origin-of-life transition. This is what life is doing, that nothing else we’ve observed can do.” And I think assembly theory, by thinking about this concept of actually embedding objects as having the size and time, actually gives a physicality to that. So the information in our environment—all of these abstract things that we see—is really just evidence of time and the fact that we live in a physical environment that is much larger in time than it is in physical space. This, to me, is such a beautiful visual, but it really helps bring all these things that we think are very abstract and not physical and things into the realm that physics can talk about them in a concrete way. And I like that. I like thinking about life having this longevity and this actual fundamental feature to it. Because I feel like, if we’re inventing theories of physics, there’s no deeper theory than the thing that describes the thing inventing the theories. So I get excited about those ideas.

SB: Well, and pulling back or maybe expanding from this: As a theoretical physicist and as an astrobiologist, how do you more generally or philosophically think about and/or define time and temporality?

SW: Time, for me, is very deeply tied to causation. My colleague Lee Cronin and I have been talking about this quite a lot, because it’s really interesting if you look at the philosophy of physics, causation is a concept that basically has been banished from physics. We’re not supposed to talk about causation. There’s brilliant quotes by Bertrand Russell about how sciences have no need for causation.

SB: Where did that come from? Why?

SW: I don’t really know. I think, if you go all the way back to Newton, a lot of the causation was put outside the universe, right? So, when you think about the way Newton structured laws of physics, he talked about an observer outside the universe that set the law and there was an initial condition for the universe. All of the description about the causation is outside the universe that it describes. 

I think that’s a very teleological view. It invokes that there has to be something outside the universe to even imprint these patterns on our universe. And I’ve always been interested in trying to build a physics that has no need for anything outside the universe. The universe just is the thing and we are inside it and we’re trying to understand how we emerge from that structure. And actually, even the concept of the universe as an emergent property of the human mind, what is the collection of all things? That’s what we call a universe. But we think the universe is fundamental and somehow we’re just sitting on top of it, but it’s actually a self-constructing system.

From my perspective, I think time in assembly theory is actually the same as causation. And basically what we’re conjecturing is that there is an order to reality in the sense that some things have to exist before other things can exist. And because the space of possibilities is so huge, you get these historically contingent paths being carved into this very large, exponentially expanding possibility space of possible structures the universe could construct and a biosphere, like what exists on our planet, is a constructive process exploring that space of possibilities and just generating lots of different structures.

You can see that in our technology, with the way we’re building machines that are deeper and deeper in time, because they’re encoding more and more information. All of our social information, our language, is now accessible in a dynamic way from a hard drive. But it took billions of years to get there. Those things don’t exist, and all they’re doing is encoding larger possibility spaces in smaller volumes of physical space.

SB: I’m so glad you mentioned technology, basically my next question, which is: Where does technology come into this origin-of-life conversation for you?

SW: I wrote an essay a few years ago called “A.I. Is Life,” which I think… I don’t mean it in the way that people usually do. I don’t think we’re building human-like intelligences. It’s something else entirely. But the idea of technology not being fundamentally different than biology, I think is an interesting concept. So, if I think about some of the earliest technologies on our planet, it would be something like the ribosome I already mentioned, which is a molecule inside every living cell, and it’s the molecule that’s responsible for translating the information from DNA into protein. So it’s like the molecular hub for allowing the genetic code to actually work.

That seems like a major technological innovation in early life. We’re just thinking, life had to invent something so that it could reliably store coded information in this way. If you extend that, the idea that life is objects building more complex objects, and you think about this idea of lineages, the fact that we are pushing a lot of our creativity into technologies we’re creating, and those technologies wouldn’t exist without humans first existing, which wouldn’t exist without multicellularity first existing, they’re just part of the lineage of information constructing more material possibilities. 

I see a real continuity between biology and technology that doesn’t have to do with the technology being a mirror of us or mimicking us in some way, but actually that the existence of these things is predicated on our existence. That kind of continuity, I think, is super interesting and it allows you to think about these structures in really different ways. Like if you could just imagine you were outside of us, which is what I have to do actually as a sort of… I always take the alien’s-eye view of Earth and think, how would they understand what the structure looks like from the outside?

It’s a nice view to think about this continuity of this constructed complexity through biology into technology. And then, maybe there’s subsequent phases we can’t even imagine yet that are post-technological. I don’t even know what that means. I just made that up, but…

SB: Well, in the context of this, as I was preparing for this, I was just thinking about the device in all of our pockets, the smartphone, the iPhone. How do you think about the iPhone, say, from an assembly theory perspective?

SW: An iPhone is definitely a biosignature. So if you found an iPhone on Mars, you wouldn’t sit there and say, “Wow, the geochemistry of Mars is doing something really interesting. It made this little metal box, and it looks like it’s got electronic circuits in it.” You would think some human put it there, or it’s evidence of some kind of alien technology. Let’s say it’s some technology parallel to an iPhone, but not invented by us, although, actually, we have a hard time even imagining that. But I think the point is that the cellphone already encodes a lot of history. There’s a lot of architecture that goes into the design of that from the circuit design to the way that the phone is actually… its morphology and all of these features.

We have this way of quantifying that constructed complexity, what I mentioned already is the assembly index. But the other key feature of the theory is this idea of copy number. And this goes back to the whole Paley’s watch argument, if people are familiar with that. There was a really big debate in the early days of evolutionary theory, where we went from natural theology and this idea that there was a designer that built the universe to thinking now that evolution is doing a lot of the work and the universe is kind of designing itself. That’s how I think about it. So I think we live in a universe that permits design, which I think a lot of your audience knows. And the fact that we can engage in design, actually, I think is evidence of much more fundamental principles.

But the evidence of design is really hard. Especially if it’s something you’ve never confronted—how would you know if it was a designed object or not? And that’s actually what assembly theory formalizes, is the evidence of design. It does it with this constructed complexity. But the copy number part is important, because if you see the same very constructed object—requires a lot of design to go into it—and you see multiple copies of it, it means that there was something in the environment that could produce it. Could have been a human; could have been a microbe; but it had to be something that itself was an evolved structure. 

It goes back to this idea of objects building other objects. You have some kind of complexity built up. That becomes something that’s abundant and high copy number, and then those structures actually can build more complex structures. It’s this cascade of these events that I’m really interested in, and that’s a foundational principle for thinking about life being an open-ended process of constructed complexity or creativity.

SB: Well, partially why I asked this question, too, is because we’re sitting in Aspen, this place where Steve Jobs famously, in the eighties, presented a Macintosh computer and was speaking to that work that then went on to—not literally change everything, like they like to claim it did, but—

SW: It changed a lot.

SB: It changed a lot. And, you know, we’re only eighteen years into the iPhone. It’s sort of mind-boggling to think how much has shifted in that period of time and the assembly it took to create that device, right? 

SW: Yeah, and there’s an interesting thing, because we do tend to reuse the same technology in a lot of ways. So that reuse of parts is also very fundamental because it gets into this copy number. It’s hard to generate new things. Like any creative person knows, a genuine act of creativity is hard, but reproducing it once it’s made is not as hard. I think this feature is really interesting and actually is one of the deepest principles about the nature of life, that generating true novelty in the universe is quite hard. It takes very long lineages to be able to access these really new things that the world could create. But once we figure out how to do it, we can do it again.

SB: I was looking at your book about the importance of merging technology and chemistry, and you spoke a little bit about it, but maybe you could go a little deeper. Where do you see that merging going? Where could the merging of chemistry and technology lead us?

SW: So there’s a few places. Mostly I’m inspired in my thinking on that by my colleague Lee Cronin, because he’s a chemist and he’s developing a lot of technology, mostly aimed at solving the origin of life, but because of these fundamental questions that we work on together. So he’s the one that also originated assembly theory, and I’ve been working with him on it for a number of years. Some of the technology there that I’m really excited about is this idea of what he calls “chemputation.” [Laughs] Which is kind of a funny thing. But it’s interesting, because chemistry is still very much an artisanal science. What I mean by that is, every molecule that we use, every pharmaceutical drug you take, is almost always made by a human chemist at the lab bench, making every molecule by hand. It’s kind of crazy in an age of automation that chemistry is still very much a human manufacturing job.

With the origin of life, we can’t just have a bunch of humans trying to make every single molecule and exploring all the chemical diversity on a planet. We need a machine that actually can automate chemistry and allow exploring all of this combinatorial diversity that chemistry can do. Lee would talk about it as a search engine for chemistry. And he’s actually built that. That’s a “chemputer.” He has a company [called Chemify] that’s trying to do drug manufacturing and actually on-demand printing of molecules. I think the company’s really brilliant and will really transform chemistry by making it a digital science.

But the idea there is, if you actually build that as a platform technology—say, for the pharmaceutical industry—then we have the same technology we can use for origin of life, selfishly, which is good. So that’s one. 

There’s also chemical brains and things like that. If you actually could build a brain that was physically instantiated and teach it the kind of algorithms that we’re teaching computers right now, I think the capabilities would be much more impressive than what we see now. So there’s a lot of ideas in this space of embodied intelligence, but you have to go all the way back down to chemistry to get there.

SB: Yeah. And just going back to technology, or at least the word technology, you’ve hinted at how language is such an important part of what you do, how you describe things. 

SW: Mm-hmm. Yes.

SB: And I happened to stumble upon an opinion piece that was published in the Financial Times this week by a systems engineer [Guru Madhavan], and it’s headlined “It’s Time to Retire the Word ‘Technology.’”

SW: Oh, interesting.

SB: In it, he argues that, “‘Technology’ has become a bloated umbrella, spanning too much and clarifying too little.” 

SW: Oh, it’s like artificial intelligence, too.

SB: I wanted to ask, do you agree with him on that? And how do you think about this word technology? How do you define it?

SW: Well, I think I’ve always thought of technology as kind of a blurry concept anyway. I tend to think about technology as artifacts that life creates that potentially open up new possibilities… 

So I think about the universe as a set of… The set of all possibilities can’t exist, but we’re at a particular—on this planet, we have a biosphere, we have a certain set of structures that exist, and we’re constantly reaching for the opportunity to create novel structures. And I think technology really mediates that kind of trajectory, that kind of way of navigating the space of what’s possible. I see it very much as part of the infrastructure of life. 

I think all words are poor at describing most of these concepts, so I tend to actually—I really like listening to what people really mean, not what they say. I think a lot of times we fail in communication, because we take the words too seriously, and we’re not actually looking at the way that people are constructing words together to try to get at the meaning they actually mean. And I think people that are very creative and very intelligent do this all the time, because language is this very discrete map of the world that doesn’t cover the world. And we’re constantly trying to patch together these words to actually describe the things that we see in our environment. And we have to do that, because that’s how we communicate with each other, but it’s never the whole story of what we’re trying to communicate. I think, any chance we can to change the meaning of a word, or recognize that the word is changing, is good. Because the meanings of words, they’re evolving very rapidly, actually, all the time. People that study language know this well.

SB: You’re kind of describing a physics of language, which is—

SW: Yes. I have a very embodied experience of language, though. I think of it as a physical object. And I think it’s really important for us to recognize that, because it’s another pattern that’s very deep in time, that’s actually part of the structure of life on this planet. And I think, if we recognize it as that, it’s a lot easier to understand when we’re swimming in that pattern, what it actually is, and then maybe not get so confused by words or get confused by large language models and things like this and thinking that they have properties they don’t. Or we have properties we don’t, because we confuse each other all the time, too.

SB: Yeah. [Laughs] I mean, how do you see this work, this origins-of-life work and assembly theory, playing into our understanding of ourselves in, say, a hundred years from now? Maybe this is too hypothetical, but what could physicists—or maybe everyone—in the year 2125 potentially be thinking about the outcomes of your work?

SW: Oh, that’s such a crazy question, because I have no idea how to anticipate that. I don’t know what they would say. I think I can tell you what I’d hope they’d say, which is a little bit different. But I think the things that are most significant to me is this re-centering of the actual significance of life on a cosmic scheme. So we have the whole Copernican Revolution, and most people in my field are like, “Oh, life is some epiphenomena. The universe is grand. There’s no need for having free will.” And you can quote any popular physicist communicator that basically puts life in this tiny box as this end state of what particles do. But it’s not very interesting. Like, “Look at elementary particles!” I’m just like, “No! Actually, look at life. Life invented the concept of elementary particles and figured out how to measure them.” I do think there are objective elementary particles, but you get my re-centering.

I think the fact that the universe generates structures like us is deeply significant, and I think understanding what that process is is deeply significant. I just would want people to really appreciate how amazing it is to exist, because most things won’t get to. And also that existing actually gives you causal agency—you really do have an impact on the future. Literally, it is constructed by the things that exist now. The future is entirely open. Obviously, there’s a lot of history getting to where we are, so it’s open in a historically dependent way, but it’s open nonetheless.

I think I hear a lot of people nowadays just having very closed views of the future. You hear the word inevitable a lot, or, “We live in a deterministic universe,” is kind of the foundational view in physics. I think that percolates all the way up through different levels of society to the way we culturally talk about the future being closed. And I think assembly theory is very much about the future being open, and life as the mechanism that constructs the future. I hope people take that seriously and make good choices about what future they want.

SB: Do you view assembly theory…? And I know that it’s very much in progress, it’s very much a deep-in-it kind of thing, but do you view it as a potential paradigm shift? How far away do you think we could potentially be from that?

SW: I think, if the research program is successful, it would have the features people associate with paradigm shifts. I think some of the things that the theory suggests about the nature of reality are really different than the way we think about it now. So, for example, I mentioned, you know, current physics says the universe is deterministic. Assembly theory would say the universe is not deterministic; it’s not determined until it happens, because you actually need the physical things to exist that can cause other things to happen. So it’s very much, again, a constructive process. The future is bigger than the past, so you have this expanding set of possibilities. The more complex things get, the more complex they can get, which is very paradoxical compared to standard physics.

Things like agency and free will are just very natural features of this physics. So there’s just a lot of things that are really different. And then this idea that you have a formal theory for life, and that you have a way of detecting alien life, independent of how different it might be in its physical instantiation—like, radically different molecules, radically different technologies—you now have a technology in this theory, theories being technologies themselves, that allows you to see the world in a different way and to discover those things. 

So, in the scientific community—I’m told this all the time—assembly theory is very “controversial.” And scientists apparently don’t like controversy. It’s so funny, because you look at the history of physics, every time we had a new thing come along, it was a lot of controversy. I love the hundred scientists against Einstein. There was actually literally a thing, it was like a hundred scientists against it. We have a lot of scientists against assembly theory, so we’re always joking, “Is that a positive sign or is that not a positive sign? What’s going on?” But I think it is challenging the way people think about things in a lot of different ways. It’s merging several fields in a way that doesn’t look familiar to any of the fields it’s merged and all kinds of things.

SB: Yeah, you’re combining biology and chemistry and philosophy. It’s not just a physics game. It’s all these different—

SW: And there’s some—

SB: And language.

SW: Yeah, language. And there’s some similarities to some things in the foundations of computer science, but I don’t think the universe is computational. I think actually assembly theory is very much not a computational theory, and I have lots to say about why fundamental physics couldn’t accommodate computation as a fundamental description of the universe. Also, evolutionary theory, right? The evolutionary biologists really don’t like assembly theory as a program, because they think evolution is a solved problem. 

It is a solved problem once you have an architecture that can evolve. So if you have a cell and you apply current evolutionary theory to it, it works great. But how do you get a cell? This is the problem. We need a deeper theory that actually allows us to get from no evolutionary system to an evolutionary system, and that’s what assembly theory is trying to get at. It exists in this really complicated web of lots of ideas from lots of fields. Nobody knows exactly what to do with it. I find that exciting, but it can be challenging.

SB: And I think the “why now” of it, which your book answers in a number of different ways, one of which I really appreciate, which is that we are entering this new age of artificial life and artificial intelligence, and if we don’t understand ourselves or the origin of life, then how are we going to fully understand what we’re building, right?

SW: Yeah.

SB: That’s such a great point.

SW: I walk around, and there’s lots of problems that people talk about [that are] popular; artificial intelligence is very hot right now and all this kind of stuff, or consciousness and these things. And I’m just like, I mean, I love all those questions. But I sometimes just want to shake people. I’m like, “Why don’t you care about the origin of life?” It’s the question. If we can’t answer this question, we can’t answer anything else about ourselves, ever. [Laughter] And I’m dead serious about it. I think it’s so fundamental, and I’m obsessed with trying to understand what we are on all the levels, because I just think it’s so profound to exist and to even have any of the things that we have and the way we have them. I just would love to understand it a little.

SB: Well, I would love to go back to your origin story here, at least in terms of your parents and growing up in Connecticut.

SW: Sure.

SB: Could you share a bit about your youth and what that environment was like, how it shaped you? And maybe also how you view it in your assembly theory/physics perspective.

SW: It’s always funny, because you have a reinterpretation of your own history as you grow older, right? My dad is a hairstylist. My mom is an interior designer and collects antiques, and I grew up in my mom’s house. It was a very old house in Connecticut. It was built in 1730, and I was just surrounded by old stuff all the time. And my mother would have stories about every artifact in her house. She just knew where everything came from, its whole history. And she had been a cosmetologist before, so that’s how my parents met. 

I grew up in a childhood setting that was very deeply steeped in history and aesthetics, which is super interesting being in Aspen and in this environment, but also in the work I do, because the more I think about how I think about life, its history, it’s a lot of aesthetics—I think those things very deeply permeated me, for sure.

SB: Even this notion of time as material.

SW: Yes, I know, very material in my household growing up. It’s so crazy. Everything had a story.

SB: Well, and your trajectory as a student and then professor in higher education is so remarkable. From Cape Cod Community College to the Florida Institute of Technology, to Dartmouth College, to Georgia Institute of Technology, to the NASA Astrobiology Institute, to, finally, Arizona State University, where you’ve been teaching since 2013?

SW: Yeah, that’s correct.

SB: Could you speak about your time in academia and how, looking back, you see this path from community college to Ph.D. to—

SW: Yeah, it’s always—

SB: Now running a lab, basically? It’s incredible.

SW: It’s easy when you post-select to be like, “Oh, yeah, it was a linear trajectory.” But absolutely, it wasn’t. Because of my history—my parents didn’t go to college, and I didn’t have a lot of people in my family that went to college—I went to our local community college, because I didn’t know what I wanted to do. But I had liked my biology class my senior year of high school, and I always liked math, so I thought I’d just take the science classes. And I just absolutely loved physics. 

So I took physics at community college and pretty much everything that is in my bio subsequent to that is just, “I want to be a physicist. I want to be a theoretical physicist.” I think this is the most amazing job you can have, to have the capacity to come up with new abstract descriptions of the world that actually match how the world works. I thought that was the ultimate creative act that humans do at this really deep, deep level. And I just wanted to do that. 

So I went to undergrad to do particle physics and physics. I wanted to do fundamental physics, which, as I was taught as a physics student, was particle physics cosmology. So I did that in my undergrad, and then I got to grad school at Dartmouth and I wanted to be a cosmologist. And my Ph.D. advisor wanted to work on origins of life. He was a much more senior physicist, studied origin of matter most of his career, figured he’d move on to the next problem. And I was just like, “Take me as your student. I want to work on origins of life.” I mean, I didn’t want to work on origins of life, but I took the… now I do.

SB: Yeah, it’s worth saying here that this was a risk because, at least in the physics community, it was sort of like, “Oh, that?”

SW: Actually, it’s really funny, I don’t even know how I navigated it all, because my PhD advisor was great. He was like, “Well, astrobiology probably has more jobs than cosmology, so you should do that.” But really what I wanted to do was be a theoretical physicist studying origins of life, and there were none. So it was really risky. 

When I was going to conferences as a PhD student, you know, it would be all chemists and a couple biologists, and then I’d be like, “Where’s the theory? Who’s talking about the transition from non-life to life? Like how do we talk about that problem? You’re doing some chemistry over here, you’re doing some bioinformatics over here…” 

I think the thing that drove me through was I was just really obsessed with this question. I think it’s just crazy that we don’t know. And it’s not even that we don’t know. It was like people didn’t know how to know. So it’s very interesting when you enter an area where people don’t even know what question to ask.

SB: Yeah. Well, I love… There’s the “ph” of your work, which is the philosophy and the physics, and that, to me, is so key to the process. If you’re not asking big philosophical questions, you’re not going to get big philosophical answers.

SW: No, absolutely not. And I think, in some ways, the philosophy has to go hand in hand with the physics, because you have to come up with the new idea. If the origin of life was going to be solved by any of our current frameworks, I think we would’ve done it fifty years ago, when people first started doing prebiotic chemistry experiments. But we haven’t, and we don’t have a clue how to do the right experiments. So I think assembly theory is opening up an entirely new way of thinking about origin-of-life experiments in theory, and that gets me really excited.

SB: Do you engage with philosophers in your work? Could you talk a little bit about that? Because I don’t think philosophers and scientists interact as much as they should. Maybe more philosophers and technologists these days, but I’d love to hear your take on just how you engage philosophy.

SW: Yeah, I mean, I think it’s just a part of what I do. I have a lot of philosophy colleagues that I talk with informally. I don’t really write papers with philosophers. I suppose I could, but it’s a little like—the work touches so many areas. Like, “What am I doing here this week [at AIR] in an art—?” Sometimes I have the most enriching conversations with artists about thinking deeply about these problems. So I think I don’t really parse the disciplines. It’s much more like, “What is the question?” And the question—it’s not even like there’s a boundary around science. 

I think people have pigeonholed science to be something people do in the lab, and they’re wearing white coats. And science is actually a cultural mode of inquiry about the way the world works, and scientists have cultural systems associated with that. But also, our interactions with those fundamental questions should bleed out into other fields, and they should be collaborative with all of these things.

I think this is why I feel like the public discourse is so important, because I get so much out of the work I do by having these kinds of conversations. It’s not just like I’m going to talk about what we’re doing. If that’s what I was doing, I would just be back trying to write the papers and stuff. But it’s actually because this active, ongoing conversation with people across different ways of thinking and knowing is essential to understand this question, “What is life?” Because we’re all experiencing it, and we’re experiencing it in different ways. So it’s not just a philosophy thing, I think.

SB: No, for sure. I should say this is our 136th episode of Time Sensitive, and you’re the first physicist we’ve had on. I’m not proud of that.

SW: I’m so honored by that though, so…

SB: I’m not proud of that. I definitely want… Carlo Rovelli, if you’re listening, I want to come to Marseille and interview you. But I do think physics and time is such an enduring subject and one that I could probably only interview physicists and keep the show going for a long time.

SW: You could. There’s volumes and volumes on how physicists think about time.

SB: But what I love about having you on the show is that you’re now in the context of these artists and architects and philosophers and chefs and others who all, in their own way, deal with what it is that you deal with.

SW: Yes, yes. And that part’s really fun. And actually, one of the things that’s really cool about assembly theory—because I mentioned it was controversial, we had this really big paper come out and it went viral, and it’s very unusual for a scientific paper to go viral. It was kind of crazy. I was like, “I don’t know what’s going on.” But we get all these emails from people trying to apply the theory in really interesting, unexpected ways, like to pieces of music, or to lock mechanisms in the history of locking architectures, or to art pieces. They really are trying to apply the mathematics of the theory in all these different spaces. Even architecture.

SB: Lineages.

SW: Yes.

SB: Last year, we had the sculptor Thaddeus Mosley on the podcast, and he’s a sculptor who works in wood, and I see the direct link from Brâncuși to Noguchi to Thaddeus Mosley. And that’s assembly theory.

SW: I know. The lineages are amazing. I see lineages everywhere now, which was kind of crazy. We talked about this in a conversation earlier this week, but the way that doing this kind of science becomes an embodied way of interacting with the world and seeing the world I think is super interesting. But I think I have to live it to do it, so that’s also an odd feature.

SB: Well, before we finish, we have to talk about aliens. You mentioned them—or the idea of the alien, but I guess, first, how do you define the word alien? What is alien to you?

SW: Well, this is so interesting, because I gave this whole talk once where I had all the different definitions of alien in the English dictionary. We could talk about “illegal aliens” or “alien” as in other, we have lots of ways to use it. And it’s super interesting, because alien is supposed to have this otherness to it, this unknown-ness to it, as a concept in the English language. But of course—

SB: It feels like far away, right?

SW: Yeah. But of course, if we discover aliens, they will no longer be that. So I find it a very paradoxical word for the thing that we’re trying to accomplish, right? Because if you’re really interested in alien, you’re basically making alien a not-alien concept. And so, I feel like I’m on the boundary of what is alien all the time in human culture. This is one of the reasons I like putting myself in uncomfortable spaces, intellectually especially, but—

SB: I guess you’re like the physicist-alien who transported down into Aspen this week, right?

SW: Yeah. I am an alien everywhere I go. [Laughter] But I think it’s really important if you’re studying alien life, right? I love the layers of words, and language is amazing, but I am deeply interested in whether there is life on other planets. The technical way I think about it is: Life, for me, is a planetary-scale phenomenon. So life emerged from the Earth as a biosphere, and so we’re looking for another planet that makes a transition to life and starts carving a trajectory through the possibility space of things that could be structured by an evolutionary process or an assembly-theoretic construction process. 

I expect those trajectories to be very different for other worlds. And that difference is what I would call “alien.” A different origin of life is an alien. There’s nothing alien on this planet by that definition that we know of, but it is a real possibility that there’s alien life elsewhere that made the transition from the space that the universe can explore easily to the space that is very hard for it to explore in a different way than we did.

SB: What do you think understanding a form of alien life, or just the idea of an alien, would tell us about life as we know it, or life as we could know it, and ourselves?

SW: I think it’ll tell us a lot. I also work on exoplanets, which are planets identified around other stars, and the community is having a really hard time thinking about how to look for life on these planets, because we only get a tiny bit of data from them. It’s atmospheric data, and it’s like, “How do you find the imprint of life in the molecules in an atmosphere?” Atmospheric molecules are very simple, because they actually have to be simple enough to be lightweight and be able to be gaseous in the atmosphere. 

So you’re not going to detect things like DNA in an atmosphere or something like that, right? It’s going to be something that’s like oxygen, molecular oxygen, O2. I always had a deep problem with looking for individual molecular biosignatures, which is what most of the field does. They’re like, “This amino acid is indicative of life,” or, “Molecular oxygen is indicative of life.” I find that doesn’t tell me anything about what life is.

We have a whole project in my lab looking at the assembly of the atmosphere, like how much causation is imprinted in the composition of the atmosphere as a whole, a planetary-scale signature of living complexity on a planet. I feel like if you detect something like that in the universe, you’re actually detecting another causal structure that’s deep in time. Like that says something fundamental about the nature of the phenomena that you’re interested in looking at. 

I am looking—and I have my whole career, which is a little unusual for people interested in alien life. People just want that “aha” moment. I want the moment when we can validate a theory about what we are by seeing another example of it. So for me, it’s the circle back to saying, “Oh, yeah, we actually do understand ourselves, because we have found another example of that thing in the universe.” That’s what gets me excited.

SB: So, your work is all about pulling out, but I want to pull out even further.

SW: Whoa. [Laughs]

SB: And really think about the collective us, I guess, however you define that—every living being, life form, individual organism. So your work is about that, but it’s also about these lineages that we were talking about, and you write “the entire structure of information patterning matter on this planet.” That’s sort of how you put it. Do you see your work then on some level as a way of bringing people together, despite difference?

SW: Yeah. 

SB: And showing how connected we all are, even though we’ve put up all these borders around ourselves, real and artificial. I feel like your work is actually kind of, at its heart, that was when I was thinking, “What would this work say to us in a hundred years?” I was almost thinking that. just wanted to put it out there: Do you think about it in that context as a potential means of bringing people together?

SW: I have not thought about that as an explicitly directed goal, but I do feel that. When I think about the ideas, I feel very connected to this planet and to all the life on it. It’s part of… my creative process is using the feeling, the intuition to guide the ideas. It goes back to the embodiment. So I guess I’m vigorously agreeing with you, but from a felt, lived experience, not from a, “I’m on my soapbox, here’s the ideas that you should…” So it’s maybe a little bit deeper than just verbal agreement. I think it’s fascinating to me that there’s really one example of life on this planet, and we’re all these very short, temporal experiences of it that are just part of that continuing structure. It makes me happy to be alive right now. I think it’s a pretty incredible time to be alive, actually. For lots of reasons.

SB: I think it’s incredible to just be alive, period.

SW: Yeah, that too. That too. [Laughter] But I think time creates you when the time is right for you, in some sense, which is kind of a funny thing to think, but yeah.

SB: Well, Sara, thank you so much. This was really a pleasure.

SW: Yeah, it was a lot of fun. Thank you so much for having me.

This interview was recorded in a studio at the Aspen Institute in Aspen, Colorado, on August 1, 2025. Special thanks to our episode sponsor, the Aspen Art Museum. The transcript has been slightly condensed and edited for clarity. The episode was produced by Ramon Broza, Olivia Aylmer, Mimi Hannon, and Johnny Simon. Illustration by Paola Wiciak.