Daniel and Kelly’s Extraordinary Universe - What is the Physics of life?

Episode Date: August 6, 2024

Daniel and Kelly talk to Sara Imari Walker, author of "Life as No One Knows it" about what life is and what aliens might look like.See omnystudio.com/listener for privacy information.

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Listen to these women and more on She Pivotts, now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. the deep mysteries of the universe. Wow, right into it, huh? Unfortunately, we don't have that on our schedule exactly. It's going to be as long as it takes. You know, when I need to do something important, but I keep putting it off, I put it on

a calendar and give myself a deadline. I find that that actually makes it happen, so you should schedule it. All right, let's do it. I'm putting it on my calendar. Let's have a Zoom meeting to share our ultimate enlightenment about the universe. How about June 2029?

That work for you? Uh, you know, I feel like, when you come up with budgets and timelines, you always need to multiply by at least three. So let's do something in the 2040s and I think you'll have enough time then. So there, it's scheduled and that was easy. Yeah, well, you know, now I'm worried that scheduling our ultimate enlightenment is going to lead us right into the Hitchhiker's Guide to the Universe trap. Like, I'm going to forget my towel? That maybe, but more importantly, we might get the answer and have no idea what the question was.

Oh, yep, yep, that's a tough one. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I never forget my towel. I'm Kelly Weiner-Smith, and my kids are always annoyed with me because I'm the only mom at the pool. who always forgets the towels. And I'm adjunct faculty at Rice University. How can you be forgetting towels? I mean, you have these young kids.

They're always making messes. I mean, everybody's kids, not yours in particular. You've got to just learn to bring the towel wherever you go, right? I am resistant to learning, I guess. I should know by now. But I never, all the other moms have the big bags and they've got snacks and goldfish. My kids are always like, where are the goldfish, mom? Everybody else has goldfish.

And I'm like, tell it to your shrink in a couple years, kid. I'm sorry. at least they have something to complain about right my wife has one of those big bags but she doesn't just have snacks and goldfish in it she's got all sorts of random crap in there and my kids are always making fun of her for it until the moment where they're like hey mom wait do you have chapstick or do you have a spoon and she's like of course I do and she digs it out of that bag and then she's like the savior mom to the rescue moms are the best absolutely and so welcome the podcast that celebrates moms, but also asks the deepest questions in the universe. We want to know how everything works, where it all came from, how it all can possibly make sense to our squishy little brains. Welcome to Daniel and Jorge Explain the Universe, a production of iHeart Radio. So today we're going to be talking about a topic that's near and dear to my heart.

I've spent many hours arguing over this question with friends, but I'll let you go ahead and introduce it. I just wanted to preface that I'm excited. on this podcast we talk about some of the deepest questions in the universe how is everything made where it all come from what are the tiny little quantum particles how do they weave themselves together in order to explain this existence and where possibly did we leave our towels but today in the podcast we're going to talk about something maybe even deeper something much more personal something closer to our experience and that's the question of life itself what is it how can we

talk about it. How can we understand it and how possibly could we discover it on alien planets? Oh, there's nothing better than talking about biology on a physics podcast. Finally get into the good stuff. With a couple physicists, right? And so today on the podcast, we're going to be digging into the question. What is the physics of life? And we're going to be talking to Professor Sarah Amari Walker, author of the recent book, Life as No One Knows It, The Physics of Life's Emergence. How do you feel about talking about life with two physicists, Kelly? Wouldn't be my first choice, but no, I'm kidding. I'm very excited to hear a different perspective on the question.

Well, I hope you brought a towel because this is going to be messy. It's always fascinating when physicists try to walk into another field and explain things. And I feel like often we do that because we think maybe there's a sense. simpler explanation or because we think in these like fundamental grounding in the basic principles of the universe. How would you say that's typically received, Kelly? So you say fascinating. We say maddening. So often physicists, you know, seem to think that physics is up here and biology is a few levels below. If you know physics, you must also know biology and maybe also chemistry so you can just wade in and solve all the problems that the biologists are too silly to be able

to figure out. And so often there's, you know, a bit of condescension. in the answers. I saw Freeman Dyson give a talk once about group selection that was absolutely infuriating because he clearly didn't understand what we were actually arguing about. But anyway, today's conversation,

I read Life as No One Knows It by our author who we're talking to today and I really appreciated that she did not have that condescending biology as easy attitude. She clearly appreciated the nuances and was trying to meld it with physics. As a physicist married to a biologist, I've definitely learned to treat biology with great respect.

Good. And not just for the health of my marriage, but also just intellectually, because I appreciate it. And I think, you know, this dirty secret about physicists walking into biology or chemistry is that we became physicist not because we thought biology was too easy or chemistry was too simple, but because it's too hard. You know, we can think about simple objects and put them together to try to describe the fundamental nature of the universe, but now we need like 10 to the 40 objects to explain like a drop of rain. It's too complicated. I can't think about all of those things at once. That's why I like

to boil things down to like one particle touches one other particle. And that's my whole universe, man. I appreciate that you're trying to clean up the reputation for your community, but I don't buy it at all. But I do think that biology is complicated. You know, we got the human microbiome. That didn't solve all the disease-related problems we thought it was going to solve. Now we're working on the connectome for the brain. There's just many levels, man. It's complicated. We deserve respect.

Maybe one day we'll have an explanation for the human and brain that goes all the way down to the fundamental physics, but not yet. And so to take us on this journey through the physics of life, whether we can understand the nature of life, the meaning of life, how to look for life and how maybe even to discover life on alien planets, we had a fun conversation with Professor Sarah Amari Walker about her new book, Life as No One Knows It. And here's the interview. So then it's my pleasure to welcome the podcast, Sarah and Mari Walker. She's a theoretical physicist and deputy director for the Beyond Center for Fundamental Concepts in Science, as well as a professor at Arizona State University. And she's tackling some really hard questions about the nature of life and consciousness and free will using physics in her new book.

Sarah, thank you very much for joining us today. Yeah, I'm thrilled to be here. Thanks for having me. We're so glad to have you here. So before we dig into the topic of your book, I just wanted to get to know you a little bit better, especially because you're writing such a fascinating book. You're tackling really big, really hard, almost philosophical questions, but you're using physics as a tool to do it. So take us back to the beginning, like what got you into physics in the first place?

I did not know I wanted to be a physicist until I took my first physics class. So most of my childhood, I actually thought I was going to be an artist and I went to community college and I knew at the time I liked science. So I just took all the science classes I could and I just fell in love with physics. I just think it's absolutely amazing to think about the universe in these really deep, abstract ways and come to understand the world in a way that is almost existentially shocking to humans in some sense because it's so different than the way that we thought it was and the set of broad regularities that physics reveals, I think, really beautiful. And I guess I was really excited about transforming something about the way that we think about the world and the way that physics does that. So I decided I wanted to be a physicist. Awesome. So we just had an episode recently about thinking like a physicist, what that means and had a little disagreement with Jorge about whether physicists think differently than other

scientists. And so you say you're drawn to physics in particular because of the way they think about the world. How is that different? How does the physicists think about the universe different than a biologist? Yeah. And I'm not even sure if it comes down to training or who gets attracted to different fields. So I actually asked this question myself. But for me, I think a lot of the discussion about what physics is is mostly about what physics studies and not what physics is as a discipline. And so for me, when I think about the history of physics and also what I'm trying to do as a physicist moving into territory that's traditionally not thought of as physics, You know, the thread I see there that I think is the commonality of like what I think the core of physics is, is building new and abstract explanations for the world around us.

So I think physics to me is getting to like the very root of like the most fundamental explanations. And that process of doing that is, you know, very unique to physics, I think is a discipline relative to other sciences. I think other sciences also do that. But I think the kind of training and the way that we're taught to think and trying to embed these sort of abstract universal ideas and mathematics that are so broad is pretty unique to what we call physics. Now, whether it will stay that way and it doesn't become sort of more universal to the rest of science or even if that's the best way of doing sciences, you know, a whole other subject of debate. But for me, that's the essence of what physics is and why I still identify as a physicist, even though the problems I study are so different than what has traditionally. been studied in physics. When you've taken on a particularly, in my mind, complicated question to tackle, so my training is as a biologist. And in grad school, like, the thing that you stay up

late drinking and talking about is, you know, what is life and how do you define species? Those are like the two questions where at the end we're all like, I don't know, nature doesn't fit into categories. And we all laugh and go out dancing. And so what different perspective does a physicists have on that question. And why do we need an answer to this question as opposed to the hand wavy? Nature doesn't fit into nice categories. Let's just move on. Why do we need to do better than that? So I love the resolution that nature doesn't fit into categories. And so I love that that's like part of the conclusion. I think that's actually a brilliant insight because I think we have a tendency to put problems in boxes because certain disciplines might become more adept to answering certain aspects of

questions. But there are some questions on the frontier like what is life that, you know, as a biologist, maybe you don't need to know the answer to because you can study biology on Earth without ever having a resolution to that question. But this gets to your point that, you know, there are some questions like the origin of life that require an understanding of what life is because that is not even a precisely defined question unless we say that there's some category of nature, quote unquote, that is life that we're trying to explain the origin of. And the other one is alien life or designing completely radically new kinds of life, which I think are not really decoupled problems with this idea of like what other forms could life take besides

the ones that have evolved on earth besides the biology that we know it. And so I think those questions surprisingly enough don't seem to have answers that fall just within the discipline of biology as it's developed because of exactly what you're pointing out that the boundaries of disciplines are kind of historically contingent. And there's a lot of things that necessarily need to come from chemistry or even computer science or physics or all these other different disciplines. And so one thing I've really come to notice in my career is that whatever discussion we need to have about solving that problem doesn't fit in any discipline as it's currently structured. And in some sense, we might need to build a new discipline to really think about this problem

because it's beyond the boundaries of like the current confines of knowledge that we've defined them so far. And that's exciting because it just shows you that disciplines are kind of human centric categories of nature. We might have to rewrite them. Yeah. I mean, we might argue like what is a physicist anyway and people argue about that right and sometimes I just redefine that term too that sounds good to me and you begin your really fun book with this question and the sort of shocking suggestion that somebody made that life doesn't exist you know that if we can't categorize it if we can't define it then maybe it doesn't exist in the end what is your definition of life yeah so in my mind I usually keep, I think, a running list of maybe three to ten different definitions for life

because I think pinning yourself to one too early is a bit premature when we don't understand what we're talking about. So usually my process is, you know, I really want to have a theory, like a theory that explains the broad patterns and regularities that we see across living forms and is deep enough to help us understand the original life. That's sort of my modality of thinking about these problems. And so I've spent most of my career trying to figure out what the structure of such a theory would be and obviously it has to be guided by some concept of what you think life is. So it's a little circular, but you're constantly redefining everything. So I'm often very hesitant to pin one answer when people ask me what I think life is. But with all that caveat, I can give you kind of a conceptual framing of what I think it is, but I wouldn't want to call it a definition. And I think a lot of what the theory that we're working on and the kinds of experience, are pointing to is that life is something about how information structures matter across space and time is one way I say it, but I think in the theory that we're building, it's much more precise to say that life is the mechanism by which the universe generates complexity. And we have a very specific way of thinking about complexity and it becomes very historically contingent. And so I guess how the universe uses memory that build complex things in the future might be the way I say it today. And if you ask me tomorrow, I would say something else because we're still a work in progress about trying to get to the bottom of what it is.

we're actually talking about. So for a biologist, the argument almost always comes down to, well, are viruses alive or not? So using the definition that you just gave, are viruses alive or not and why? Yeah. So I think there's a little bit more nuance. So usually the way I talk about it is like, are we talking about the physics of life, our particular instances of things that are living? And it might be like, are you talking about gravitational physics and like the curvature space time? Are you talking about a gravitational body that was generated by these sort of fundamental mechanisms that we know that our universe works in. And I think there are slightly different categories. So when I say things are life, I mean anything that is the product of an

evolutionary process and requires memory and information from the past to be able to actually make that thing exist in the present. And I think viruses are certainly that. They require evolution to form. But the sort of active process of generating complexity and generating novelty and contributing to the sort of open-ended growth of complexity that we've observed in our biosphere. I think things that do that are alive. And I'm not sure that I would qualify a virus as an individual agent as part of that creative process. But it certainly is when you look at viruses as components of ecological systems, for example. So a lot of the things with issues about life is trying to pick a scale and say this thing is life. When really what you're talking

about is a much more abstract universal physics that even enables those things to exist. in the first place to be selected. I think the reason that viruses have been hard is because it's actually a category error to try to partition a boundary around a virus and say, is this alive or not? When you really should be looking at the continuity of the evolutionary process and what it constructs. Yeah, fascinating. I don't know that I agree that we need a definition of life, but I do think it's valuable to try to try to try to figure out what this is.

like if we agree or discuss, you know, what life is, that shapes the way we think about how to look for alien life and all these questions. So I think it's very valuable to dig into the question, even if we don't find an answer. And from that perspective, I was really interested in the discussion you had at the beginning of your book about, you know, the sort of philosophy of what life might be. And you were going through this discussion of like panpsychism. And there's this one particular line that jumped out at me. It said, quote, if life is not a proper of matter and material things are what exist, then life does not exist. I was wondering if you could expand on that thought.

You know, doesn't it sort of ignore the possibility that life could just be an emergent phenomenon? As you said, an arrangement, a complexity of basic bits that are not alive. Yeah. So part of the reason that I structure things in specific ways early on was to kind of set up some things that come later in the book. And one thing I've noticed being a physical. is trying to build new physics is that we take for granted things as being absolutely true

about the universe that were actually invented by human minds, trying to correlate the way that their theories behave with things they could actually measure. The example I'd like to give is to think about mass. It seems so obvious to us that mass is a physical property of objects. And it is a physical property we talk about in our theories of physics because we can measure it and because Galileo rolling balls down incline planes and other people of his generation and realize that that was the right variable to construct theories of motion. I think, of course, you can talk about life as just being an emergent property, but you're never going to get to an objective understanding of it as a physical phenomena,

unless you can tie it to a measurement, and therefore whatever that thing is has to become what we would call a material property in our theories of physics, because now it's something we measure that becomes a variable in our theory, therefore it's physical. And I think this has been the thing that's really hard about thinking, about the nature of life is it has forever been an epiphenomenon and something we couldn't regularize as part of a law of nature because we want to adopt this view that surely it's just these emergent informational patterns, but we can't measure them objectively. And so my point

saying that if you want to reduce life that way, then life doesn't exist because you don't have an objective measurement, you don't have a way of grounding whatever you're talking about and testing it against reality and saying this is the thing that emerges when life emerges. If I could just stop you there because I'm not sure I'm following. Like let's take a simpler example, you know, a thunderstorm. A thunderstorm is an emergent phenomena bubbling up from the, you know, the properties of particles and molecules and all this kind of stuff. Clearly thunderstorms exist, right? We agree.

We can make measurements of them, their intensity, all sorts of stuff. We can ground them. We can write even some, you know, mathematical expressions that describe them in some cases. How can we say thunderstorms exist and we can make physical measurements of thunderstorms, but we can't say the same thing about life? Well, what would be the measurement that you're taking about life, though? So the question with thunderstorms is, it's a good example because most of the measurements you're taking are things like wind velocity, you know, the temperature, like these are like

physical measurements you can go in and take. And then when you put those in some model of a thunderstorm, you can actually model the thunderstorms behavior. And that same physics works if you go on another planetary body and account for differences in pressure and differences in the particular climate, you know, in that gravitational field and things like that. The issue with life is, you know, most people want to say that like when you're talking about chemistry and like life as an organizational property of chemistry, when we look at its parts, we don't see the things that we associate to life. And so therefore,

life is an emergent property of those parts. It's some organizational feature. But the problem is we don't have the rules to go from the atoms and the parts to that organization, feature in a universal way that would allow us to go on another planet and measure that property. It's very subjective the way that we talk about it right now. And so it's okay if it's subjective and not a material property. It might be that there is no law of physics that allows us to understand what life is. And it might be that life is not a universal category of nature.

It might just be some weird emergent pattern that emerged on Earth and there's no universality to it. But the argument that I'm interested. in, and the one I think that will actually help us find alien life is out there because life is a universal thing if it is, is that we need to figure out what are the objective properties. And when you do that, in some sense, you're making that property material in a way that it becomes measurable. And so that's sort of the interplay, like life has not been a material property. We've had this sort of vitalism and the idea of a soul. But the question is, is that

actually something that we can quantify put into a theory and also measure? so that we can actually say this is a real universal law-like feature of our universe. But so then why go to life does not exist as opposed to we don't understand it well enough yet? Because the logical conclusion of the way that much of the discussion has been is that we should assume life does not exist. So in some sense, what I'm trying to do is actually provoke, you know, like if we run the way we talk about things to their logical conclusion, what are we really saying? And is this actually what we intend to say? Or do we want to say there's something missing from our descriptions of nature? And maybe we need to rethink from first principles what it is that we're doing.

So I actually think life does exist. I was always perplexed that a lot of my colleagues, if you really listen to the words they were saying, we're implying that it does not exist. And some of them even saying it outright, that like we should just not think about the problem of defining life at all. Life is not a category of nature. It's all reducible to chemistry and physics. And I think that there's something deeply missing in what life is and why we keep asking this question.

So why is it a question we ponder in bars at night? It's probably because we feel intrinsically we're missing something about, you know, the descriptions of the world around us. That's pretty fundamental. So that was always my perspective. Now, that might not be right. But I think the way to find out if that's right is try to go through the process of building a theory you can test against something you can measure and trying to see if empirically, you're actually getting the right results.

And if you're building a theory that is all explanatory of the data that we see in the observations we can make. Right. So you're not saying, I don't exist or you don't exist or my cat doesn't exist. You're saying that we don't have a clear and crisp definition of life that lets us do things that we typically do in physical theories like we do with thunderstorms and we do with cats because we can make measurements of them.

We can't, other than just like vaguely talking about sort of fuzzy conceptual, categories. Yeah. I mean, in part, you know, the book is an exercise of trying to turn a philosophical question into a scientific one. Right? So this has traditionally been a philosophical debate because we don't have the things that we can pin the debate into measurements to actually go test what it is that we're talking about. And I think that's really the critical transition that, you know, most interesting science starts as philosophical questions and the period where the philosophy transitions to science is always deeply interesting because we're asking exactly these like really basic questions. It forces you to even ask what science is. What is a

measurement? What is a theory? How do you build a new theory? Like what are we even talking about ever when we talk about things in science? So this is why it's exciting, but it is really challenging because you're confronting things that, you know, we haven't known how to think about. And you're saying, let's pin ourselves down and be precise and think about it and ask how would we actually quantify and measure this thing. And how will we build a theory that describes this thing? And And if you look at the history of science, what excites me about it and why I think any of the ideas that we're doing might be on the right track is, you know, every time that that process has happened in the history of physics, we come out the other side with a radically different conception of what's going on than we had before. And like my favorite example is like to think about, you know, saying terrestrial and celestial motion are the same thing. It's like, you know, humans had been around for hundreds of thousands of years seeing the stars and the night sky and planets moving across the sky.

And we never thought like that would be, you know, like the theory of gravitation, it took, you know, centuries of measurement and coming to, you know, track the regularities of heavenly motions and be able to get clocks that were precise enough timing to actually build into an understanding of a theory of motion and gravitation that allowed us to like look up at the sky and be like, oh, those things are actually moving in the same way that things on Earth move. I mean, these are radical conceptual leaps that our species has taken. And I think to. think that we're done doing that is really premature so so I get excited about life and when people say well isn't it just a pattern of motions and I'm like well of course it is but we've explained lots of those before in really deep and fundamental ways so maybe we should try again all right I have lots more questions about this squishy topic but first let's take a quick break The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

There's been a bombing at the TWA terminal. Apparently the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. terrorism law and order criminal justice system is back in season two we're turning our focus to a threat that hides in plain sight that's harder to predict and even harder to stop listen to the new season of law and order criminal justice system on the iheart radio app apple podcasts or wherever you get

your podcasts my boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him

because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I, I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy, which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be beneficial to you.

Because it's easy to say like, go you go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just like walk the other way. Avoidance is easier. Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship.

I'm Emily Tish Sussman, and on she pivots, I dive into the. the inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten, Monica Patton, Elaine Welterah. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes and gives you the inspiration

and maybe the push to make your next pivot. Listen to these women and more on She Pivot. Now on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Okay, we're back and we're trying to sort through the slimy questions of the physics of life with Professor Sarah Amari Walker, author of the book, Life as No One Knows It. Well, in terms of taking like radical, conceptual philosophical leaps, I was very excited to see you open the door. to getting rid of reductionism. I mean, especially as a physicist, you know, and as you described earlier,

physics is so ingrained in the idea of like, let's find the microscopic explanation for everything. Start with what we hope is the fundamental and everything will bubble up from there somehow, dot, dot, dot, right? Leave that as an exercise for the engineers. But in your book, you actually consider the other approach, the idea that like maybe not everything is determined from the smallest bits.

maybe what we see as like emergent phenomena at different scales. We actually have their own different fundamental description that like, you know, the universe isn't controlled by the tiniest. Can you talk a little bit about that? I think that's probably a very unfamiliar concept for our listeners who are used to, especially on this podcast, hearing us talk about how tiny particles weave together to make the universe. Yeah.

And I also love that view of reality. I think it's like incredibly romantic and I was trained in that tradition. But thinking about life and really trying to ask the question, whether there were universal laws of life, like, that speaks to me that we're looking for something fundamental because it has to be universal and broadly explanatory of any life in the universe. You start to ask questions about the nature of what's fundamental. And as I already alluded to before, a lot of the ways that we think about what's fundamental are what things we can go in the lab and test that build the structure of our theories. And so some of the most precise theories we have are these ones about microscopical physical motions. But it doesn't mean that they explain everything. And one of the points that I make in the book, which is related to this sort of evolutionary progress of knowledge that we've been talking about,

about disciplines changing over time, is the notion of what's fundamental has actually changed with our theories and with our measuring devices. And so I think, you know, like the canonical example I like to give is to think about atoms, which we thought for a long time, indivisible units of matter until we built better technology and we realized they had parts. And so I'm not sure that there's really a bottom to that process. If string theory is right, obviously all the elementary particles and things we think are, you know, the full description of reality are not right. But we can't validate theories that go smaller because we don't have the technology yet. So, you know, that becomes a horizon of our current understanding of reality, not something that's

intrinsic to reality itself. And if you flip that around and you look at what you're trying to do building a theory of life, life is built out of these what we think are fundamental building blocks. But the kinds of things that we want to understand about life are much more about how the universe builds complexity out of small parts. And it is the case that if we can think about things that we can measure there and build theories there, there's no reason to think they're not just as fundamental as these other descriptions of nature. So that's sort of like the baseline philosophy I'm operating from. But the sort of core of your question, I think, is more about the emergence reductionism debate, not the philosophy of measurement and what's fundamental, but I think

like those things are coupled. So I wanted to preface it. But the emergence reductionism, you know, Phil Anderson had this great essay, which a lot of people have read and love about this idea of more is different. You know, even if you had that fundamental description, it doesn't mean that as you go to these other layers like biology and mind and technology, you're going to actually be able to recover all the features of them. And so this has been deeply perplexing. And what I suggest in the book is one of the reasons you can't go between scales is there actually are separate laws that describe the idea of a hierarchy in the first place

that the universe is actually constructing complexity and that time needs to be a component of that process. So if you remove evolutionary time, you know, you can talk about me being an emergent property of my atoms, but I've missed almost all of the physics that's in my body. I am like the product of four billion years of evolution. And so if I want to talk about me as a fundamental structure, I need to talk about that feature, not the atoms in my body. And so it's really trying to invert the nature of like what is the thing that actually explains this. you can say I'm an emergent property, but it doesn't explain from those laws, those lower level laws, how I got here and why I exist. But does that mean that there is no explanation that you have to have fundamental laws at every scale, or does it just mean those explanations escape us currently or our current ability to do those calculations? And in some future where we have an amazing supercomputer, we can model everything from the tiniest bits.

I think it's both of the last things you said. So I think there you cannot produce things like us from the current structure, the laws of physics. I don't even think if you had a supermassive supercomputer, you could do it. And a simple reason to cite that is it would require more computation than is available in all of the resources of the entire universe. And yet the universe builds things like us. And so I think that right there suggests that something fundamental is missing because you could say in principle, you could simulate it and you could generate. you know, our conversation that we're having right now. But actually in principle is not in principle because it's not even physically possible. So those things to me suggest that there's a

huge gap in understanding. But I also think fundamentally that the physics of what describes living things is not encapsulated in the physics that we have of gravitational fields or elementary particles or any sort of state of the art in modern physics departments. I think it's just not in those equations. And the reason I think it's not in those equations is because life is very much about the causation and time that's built into physical objects that are complex. And if you think about what the laws of physics reveal, they are often designed for specific problems. And they tell you what's universal about a set of questions, like motion, for example, like all moving objects can be described by mass and acceleration. And you don't care about the color of them or how those

objects feel or other things. But that doesn't mean that those laws explain everything about every object. And so, you know, the question is, how many kinds of laws of physics do we need? What's the sort of universal set of things that they cover? And I think life is presenting some real challenges for the sort of current paradigm that we have in really fundamental ways. Again, as the biologist in the conversation. So I feel like what I'm hearing is that we don't really understand the physics stuff, but we know that life is something that comes about through the process of evolution. So I feel like we're back in an evolutionary biology lab. Yes.

How does a physicist study it differently? Like, is the question what process results in something that natural selection can then act on? Like when we, you know, put the pedal to the metal or whatever, like what do we do in a lab or on a board with equations that's different? So this is a great question because ultimately, like Daniel's question can, you know, what will ultimately resolve it is does providing a new explanation provide any new experimental tests and things we couldn't do otherwise? Because it does, I could tell you, you know, I could sit here all day arguing that there's other laws of physics in life and, you know, you could nod your head, okay, Sarah, but show me the proof, right? And I've been doing this most of my career because, you know, I have like some conviction it's there, but we have to do the hard work as scientists and show that it's useful for something. And I think, I think to your question, the challenge is, you know, for the most part, we think about evolution and selection as being things that life does, but that doesn't allow us to explain the origin of life because it has to be some spontaneous fluctuation with no mechanism, right? And so, or it's just a rare fluke, right? And then if it's a rare fluke, then, you know, none of this discussion is necessary because it's just something that happened and there's no. you know, explanation for it. It was just, you know, a rare fluke event. And I think this is

one of the challenges because that allows, you know, intelligent design and other things to be equivalent explanations, the scientific one, because we don't have an explanation. So if you really want to explain it, you kind of have to assume the origin of life is itself a process of selection and evolution. So it's the product of those kind of mechanisms, which means you need an understanding of evolution that doesn't require a cellular architecture. And this is the main challenge, right? So before replication, before natural selection, as we understand it now, in genes or the way it operates in biological populations, out of chemistry, how does an evolutionary system get constructed? And so this is really the question that we're trying to ask is,

how do you get complexity when there is none? And so that's where we need a new paradigm because we need a mechanism of selection that operates, starting from simple molecules, building building into the complexity of life. And that's really the theory that we're working on. This assembly theory is really an approach to talking about selection in the absence of like when selection emerges, how does selection actually start and how to selection build evolutionary systems

that we recognize as evolving things. And so it's suggesting a much more universal structure to the evolutionary process than the particular things that were selected and evolved on Earth to understanding what are the general principles of the kinds of systems that chemistry could generate that could lead to this process of evolution that we recognize. That's the question we're trying to answer.

And I think that one really does demand new physical principles because you're asking out of, I mean, people really don't understand how big chemical space is. It is like astronomically large. We also do a lot of stuff with drug design with the same theories that we're trying to sell the origin life, which is kind of crazy. So I deal with like, you know, pharmaceutical drugs and this kind of stuff. But like when chem informatics go in and they want to estimate the size of the chemical space, they have to search to look for new drug-like properties, it is insane.

It's not small. It's insanely large. You know, I think a really good example is like taxol is a molecule I use a lot of times when I give lectures that I picked up from my colleague Lee Kronin. That molecule has a molecular rate of about 853. You know, I think it has like 47 carbon atoms or 53 or something like oxygen. Anyway, like if you wanted to do all the molecules with that chemical, formula alone, it would fill a volume of 1.5 universes. So if you think about a planet generating

chemical chemistry in an unconstrained way, no selection, the space of molecules that could be, you know, just randomly synthesized is so astronomically large. You would never expect anything complex to recur twice. And so this is kind of a key argument of the way that we constructed the theory. When you start to see things that involve a lot of constraints in the space of possibilities to get these really complex, really improbable objects with a high abundance that they're happening a lot. That's evidence of selection happening and that selection is actually the physics generating those objects.

But it's got to be much deeper than what we just see in evolved architectures that we have like with the cell because that comes fairly late in the original life process. So I understand that the space is very large, right? Obviously there's lots of different combinations. Chemistry is complicated. But how do we know what's improbable or what's unusual? because the space is so large and we haven't explored it, right? And you say, for example, like the existence of rockets in the universe is a sign of like

conscious thought or whatever. But, you know, how do we know that that's the case? How do we know that other arrangements that our particular planet didn't explore don't lead to greater complexity or more interesting things existing in the universe? So your question is a good one. And I think a lot of us have sort of embedded in the way that we think about the world. And this actually comes from the way that we think about physics. It's sort of a heritage.

legacy actually from the 1800s and the development of statistical mechanics and the idea of spontaneous fluctuation, we have an idea in our minds that anything of arbitrarily complexity can spontaneously fluctuate into existence. And this is the whole impetus of the Boltzman brain argument, which actually was proposed by Eddington originally as kind of a mocking of Boltzman's ideas, but then became something that physicists took very seriously and tried to put in our cosmological models. And so the challenge there is, is, of course, we can say, you know, a planet can make an arbitrarily complex molecule, right? I can make that statement and it seems intuitively logical.

But if I said, you know, Mars is going to generate a cell phone tomorrow, you would kind of laugh at me, right? Like, that's a silly statement. Is there really a chance that we could just find the planet Mars generating a cell phone? And like, not a cell phone, but just something equivalent amount of organization and evolutionary processes, like a cell phone takes four billion years to make on a planet. It takes a lot of selection to get to that very specific object. It's really designed for our biology. The technology is built on our planetary resources. Like everything about that object is a direct consequence of the fact that we've had four billion years of evolution along a specific trajectory on our planet. And so to assume

an object like that can just form random chance somewhere in the universe, I think is a major, it's a major misstep in our reasoning about how reality works. We have no evidence that it can actually happen outside of evolution. And so a lot of people will try to challenge the way that we're building the formalism on this idea that something complex can just be made on a planet in the absence of evolution and selection. And I can just say back to that, like, give me the evidence. The universe builds me anything that requires, like, information to specify it.

Because to me, what that argument would entail is actually the equivalent. of intelligent designs as the universe has the design of every object at every point in the universe. What I'm suggesting is that selection and evolution are required to build information specific to objects before they can exist. Right. And I agree with that. I'm not arguing that cell phones should appear on Mars or that would be probable. And I appreciate that, you know, complexity comes as like the tip of the pyramid built on the base of like a huge amount of things that came before it. Absolutely. But what I'm wondering is whether we we can argue that life on Earth is unusually complex.

We don't know what the space of possibilities is. Maybe if we go out in the universe, we discover, wow, we're actually quite primitive. The complexity here on Earth is, we're in the backwater. I mean, compared to Mars, sure, but like you were saying that, you know, what we've achieved here on Earth or what's happened here on Earth is unusually complex. But how do we know that? Oh, where's the prior? I see.

So I was referencing that with respect to an abiotic prior. I imagine you don't have an evolutionary system, right? So I think we're talking cross purposes about the question. So I just want to kind of frame it precisely. So if you just look at, you know, a system that doesn't have evolution or selection, the sort of framing that we have, the key conjectures, there's a maximum complexity. A non-living system could build and it can't build any more than that until selection and sort of feedback on the structure and like self-reproducing systems emerge that actually

constrain themselves to be able to perpetuate, right? you're asking is if that process starts, are we more or less complex than that typical process? And I think we don't know the answer to that, obviously, but I think what I can say is from the sort of structure of the physical laws in the theory that we're building and testing, every evolutionary system will have to climb the ladder of complexity. So there is no like major jump where you just get to be like the most complex thing in the universe by skipping steps. So that becomes a question of did life start in the universe on any planets much before us or have an accelerated process moving through the sort of complexity cascade? And I don't think

anyone knows the answer to that question. That's one of the reasons that we want to understand this physics. So we can actually make predictions about what that process looks like on other planets. And I think we're at this stage where I'm hopeful, you know, in the next, I don't know, 10 years maybe we might be able to say something meaningful about the first steps from geochemistry using this kind of theoretical construction, like these kind of steps about like, what are the first mechanisms of selection that emerge in chemistry and what do they look like in different planetary context. But saying something about that whole cascade is basically simulating the entire evolutionary process, you know, from the geochemical origin of life into technology on another

planet. And I don't think that's actually computationally feasible. I think we have to discover other life to answer that question, which is why we need a theory to know what we're looking for. So would geologists come across molecules that look complicated or chemistry was the class I did not get A-Zing? So how do you know that you've got like a complicated molecule that's life or do you get similarly complicated molecules in a geology lab that are not alive? It's a non-trivial question, highly non-trivial. And I think part of it comes from the different uses of the word complexity. So I think a lot of my planetary science colleagues and geologists would say, of course, we find complexity in chemical systems. We see it all the time. The kind of complexity

that they're talking about is often what we see in prebiotic chemistry experiments also, which is oftentimes like the most problematic thing you see in prebiotic chemistry is if you just run an unconstrained reaction, you get what we call a tar, which is an undifferentiated mess of molecules. So these kind of systems can generate a lot of molecular diversity. but it tends to be things that would be low complexity as individual molecules. And for things that are higher complexity, you don't see a lot of them. And that's very different than what we see in life, which is we see, you know, there's a lot of diversity in molecules in life, but compared to the size of the chemical space

that that could be, you know, equivalent structure like molecular weight or, you know, number of chryl centers or, you know, number of elements in the molecule. like any of these features you might say as equivalent molecules, you see very, very, very, very low diversity in biology. And so what biology does is it builds molecules that are deep in the space of chemistry. Like they require a lot of parts to build the specific molecule. So that molecule is complex in an evolutionary sense.

It's found in high abundance, but there's not a huge diversity of exploring in an unconstrained way, the space of all molecules. So I think the kind of complexity we talk about, out in a planetary science sense doesn't discover the kind of complexity that biology generates. So let's dig into that a little bit because I think that's really at the core of the argument in your book, right? This concept of complexity and how we discover it and what it means for life to be complex. So you're saying that life is something that uses a relatively small number

of building blocks but puts them together in a way that's very complex, right? The complexity comes from the arrangements of a few bits, not from the inherent complexity of the pieces and that we've, of the chemical space that exists out there, as you were saying earlier, it uses a tiny little, very tiny, yeah, very tiny little aspect of that. And so again, I wonder like, how do we know how unusual that is or how special that is, how distinct that is, how do we know that it's not possible using other building blocks to create complexity? How do we know that complexity doesn't always arise if you start from, you know, basic bits? Yeah, this is the more exciting question.

And it's actually, you know, the one experimentally I'm really interested in. If you designed an original life experiment that was modeling a planetary environment and it was unconstrained and selection and evolutionary processes emerged in the system just by the dynamics of the chemistry, would it discover the same biochemistry? And I'm not convinced it would. I think chemical space is so large that there are a lot of potential. chemical architectures for life, that could be quite different. But we haven't discovered them yet because life on Earth had one solution that allowed it to perpetuate itself. And it's used

that architecture for billions of years. And the question is, if the origin of life happened again, would it discover the same architecture or not? And nobody knows the answer to that. I think that's an experimental question. And that's one that we want to ask because part of the thing I try to really highlight in the discussion in the book, but I'm also really trying to just pitch to people as an experimental program that we need to do because it requires a lot of investment of technology and resources is to think through how we would build an experimental program to discover alien life in the lab. And the idea there is exactly. In the lab. Yes, it's exactly what you're saying, though. Like we don't know if life could exist in other chemistries. If you do a proper origin of life

experiment and you really want to know the spontaneous probability for our universe to generate life, you can't just cherry pick and use the molecular structures that were selected on Earth and say, I'm going to make these because you're inducing selection based on what was produced on Earth, right? Prior knowledge of it, you really want to see from chemistry, what would it generate without any intervention from us as, you know, designers of the chemistry, knowing what we know of Earth life. So I think the original life problem is actually, that's exactly what it is, is an experimental problem to try to discover what is the mechanism. Chemistry generates living forms. And if you know that mechanism, is it universally going to converge on what

life on Earth did? Or are there many solutions because this space is so huge? I'm sure you could get a lot of evolutionary biologists very excited if you could repeatedly generate. We need their talent. So that's good. Yeah. I think, you know, part of my motivation with right, it's, it's hard. to write a book, right? And first and foremost, I'm about the science. Like, I just really want to solve the original life. So part of my motivation is to get people excited about, like, what are the actual critical challenges here? And I think, I think this one is, like, the main one is like, what does the experimental program look like that solves the origin of life? And how related is it to all these other questions that we're talking about? And for me, it is going

to require, you know, really intense technological infrastructure building digital chemistry and AI-driven robotic chemistry to actually search chemical space like a search engine and then looking for these kind of chemistries and when they undergo selection and they start emerging things that we might call life.

And the reason for having to build a theory in part, besides all the reasons I have as a physicist, is if the chemistry is radically different, how do you even know it's a living thing? And so we have to be able to measure evolution in molecules agnostic to what molecules evolution creates

and know that they have a comparable level of selection in them to say that, you know, this is past the threshold that we expect it to be a living form versus, you know, what we expect, abiotic systems that aren't evolving to be able to generate. And so this is sort of the core argument of your book. You describe assembly theory where you measure the complexity of something as the number of steps it takes essentially to build some of the shortest path to go from building blocks to this thing, right? And then you do this thing where you say, well, anything above 15 steps is life and anything below 15 steps is not life. And I was with you until I got to that point.

I found myself asking, as you actually did in the book, like, well, why 15? Doesn't this feel sort of arbitrary? How do we know it's 15? It feels like it should be 42, right? 42 would have been better. Yeah, give us a description of that thought process. No, it's a good question. So 15 is maybe an approximate bound, right?

But where that comes from is actually the experimental data. So it's not like anointed, you know, like the assembly theory cult said it's going to be 15. It's just like, you know, we built. How do I join the cult? I know, right? There is no cult. Actually, like it's really funny because, you know, there's a lot of challenges we're getting, developing this theory from people picking it apart different ways, which we love.

But I don't think anyone's harder on it than the people we have actually working on it. So it's like, which is the best kind of science, right? Like you pick apart every idea and you reevaluate everything you're doing at every step. Well, if you're denying the existence of the cult, that tells me that the cult definitely exists. Oh, sure. Yeah, I know, right? You're just, I'm going to wink, wink, wink. Anyway, tell us about the data that supports the choice of 15.

Yeah, so that comes from the data. So this idea of this minimal path. So it involves recursion. So the idea is like it's easier with Lego than chemistry, you know, because most of us aren't chemists. So it's like you think you're building a particular Lego structure. I usually use Hogwarts Castle, but people know, but like the Taj Mahal or whatever, you know, building you might prefer, you know, you wouldn't expect to form it by randomly shaking the

building blocks in the box, right? There's instructions that allow you to make it. In assembly theory, you realize if you take the instructions, there's actually lots of different ways of getting to the end route if you don't use the instructions, right? So in assembly theory, we have to ground it in something that's always there about that structure and not just because you had a particular set of instructions in a particular environment to make that. And so we do this based on this minimal path idea and the assumptions of the minimum path are you can only build things if you already built them and you want to try to find the shortest path where you're reusing parts you've built already to build the final structure so very minimal set of assumptions it turns out

that feature you can actually measure in the lab and we measured it in the paper that we tried to do about biosignature validation in using mass spectrometry but there was a later paper from Lee Cronin's group that came out showing that you can also measure assembly index this shortest path measure with NMR and infrared. So we have a strong sort of conviction right now as a running assumption with the theory that it's an intrinsic property of a molecule this feature. It's one that you can measure with independent measuring apparatus. It doesn't depend on where the environment, where the molecule is made. So that gives us some of the baseline criteria of something being an objective measure of the amount of selection in an object. And then what you have in a

molecule that you can go and measure in the lab. So, you know, if I went to Enceladus and I measured it, you know, the molecule would have the same value it would have on Earth. Okay. So that's important. And so the question is then if you use that, does it actually separate out things that are uniquely produced by life from not? And so to do this, Lee's lab took a bunch of samples, you know, abiotic and biotic, even some scotch whiskey.

And then they had some samples that were blinded from NASA that were both biological and non-biological, sort of an adversarial test case. And what they did is they use this mass spec method to measure assembly index on the actual samples. And they showed that using assembly theory combined with the mass spec data, they only saw molecules that were more than 15 steps in this minimal path being produced by living samples. And this gets to the complicated versus complexity issue because one of the adversarial samples that NASA sent was actually Murchison meteorite. which oftentimes in prebiotic chemistry literature, you will see as being like the most complex sample of prebiotic chemistry, and it was still below 15 for the molecules in the sample.

So what you see in Murchison is, again, this tar, you have a lot of molecules, but none of them are high abundance and a high assembly. And so it's not just that the molecule is high assembly. You actually have to have it in a high enough abundance to say that it was selected in that particular context. Right. But does that mean that if I find some sample on an alien planet and you measure its assembly index and it comes out to 42, you're going to be like, this is life? Are you proposing this as a definition of life, a way to decide? I think that would be the ultimate outcome based on the path that we're on. But I think we have a lot more work to do to be like definitively there is a threshold in assembly spaces above which you would say that a sample was life or not. And that's that's sort of where we're going. So right now I would. would be pretty high confident if you discovered something on Enceladus that was 42, that it could only be produced by life. But the sort of next steps are really actually theoretically predicting why it should be the number 15 and what number it should be if you have variations in your

elemental distributions or other things about the structure of the assembly space, which is the underlying mathematical structure that we build this whole formalism out of. And so one of the projects in my lab right now is actually trying to quantify why there's a transition in assembly theory at the particular assembly index values that we see and might see in different systems. Because as you say, the chemical space is very large and isn't it possible that there's structures out there that are quite complex, but that nobody would call alive? Right. So there are many such structures, right? So it's not necessarily that the threshold

must be at 15. That's where we have for the kinds of chemistry that we tested in the lab so far. When we have a general theory, which we're working on very fervently right now with our teams, we would be able to predict based on the sort of elemental composition and other features of your chemistry where that threshold should be. And then that allows us further tests to really validate that this works in different systems. And, you know, one place where it might be more challenging is actually with minerals, because minerals don't uphold all of the properties of molecules. They have very different structure, but they're also made out of elements bonding. And minerals, because they have very different structure to how you build up a mineral in this kind of way that we do this kind of recursive construction and what you would define as a repeat in a mineral, they might have a, you know, a threshold that's much higher than what we observe for aqueous molecular chemistry.

And so as with any new theory of physics, it's a process of suggesting an idea, testing it, iterating on the idea. And so, you know, the process of theory building doesn't happen overnight. It happens over a decade or two. And so these are some of the frontier questions that we're asking about, like, you know, is this actually, you know, the right approach? Then these things should work out. But we don't know the answer yet. So that's why it's exciting. Sometimes life gets overwhelming and sometimes conversations about life get overwhelming.

So I feel like it's time for a break. So let's go ahead and hear a word from our sponsors. LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene.

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Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate.

Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast.

Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy, which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be beneficial to you. Because it's easy to say, like, go you go blank yourself, right? It's easy.

It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort.

Listen to the psychology podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. In sitcoms, when someone has a problem, they do. just blurt it out and move on. Well, I lost my job and my parakeet is missing. How is your day? But the real world is different. Managing life's challenges can be overwhelming. So, what do we do? We get support.

The Huntsman Mental Health Institute and the Ad Council have mental health resources available for you at loveyourmindtay.org. That's loveyourmindtay.org. See how much further you can go when you take care of your mental health. I hope your brains are rested and ready for some more overwhelming conversation about incredible topics like the physics of life. It is exciting. One question I would have in my mind if I was working on this is like whether the value is 15 or 19 or 14 or whatever. How do we know that all the information is captured by this one quantity? You backed it up so far with like, well, we have a bunch of these examples and it seems to have work.

and you're working on the theoretical underpinnings. But, you know, I work on machine learning problems all the time where we convince ourselves that we've learned how to distinguish between A and B because we've only seen some kind of examples and then we go off into the world. We're like, oops, turns out that's just one dimension of a multidimensional problem.

You know, for example, if I was, you know, not intelligent about this and I said, well, look, I took a bunch of examples of living things that all have brown hair and non-living things that don't have brown hair. And then I developed my definition of life to be like, does it have brown hair, I could also come up with a way to distinguish between, quote, unquote,

living and unliving things because my sample was limited. And here, your sample is limited because you only have examples from, you know, life we've seen. And so how do we know that there is a number that distinguishes? So there's a couple of things there. One of them is, assembly theory is not a scalar theory. So it's not just about this number. It's actually about also the abundance of objects at different assembly indices. So it's higher dimensional than that.

The idea is you're talking about selection in this massive commentatorial space and you have to talk about the reduction of the size of the space represented in the objects you observe. And we have rigorous ways for thinking, like based on the mathematical formalism of the theory, why we're capturing the relevant features of that reduction of the size of the space. People usually do do exactly what you're saying, where they try to, you know, separate living and non-living things and then classify them. And it's becoming very popular in astrobiology right now to do machine learning on those

kind of problems. I don't think that that approach is generalizable. The reason I have confidence in what we're doing is because there's a whole theoretical infrastructure building in a whole bunch of ideas about the nature of information in life. What is causation in life? How do we measure these features and molecules? You know, what is it about these emergent properties of life? Like I, you know, I've spent my entire career basically working on every kind of biological system imaginable. And, you know, Lee's lab has worked on kind of every chemical system imaginable and putting all of that knowledge into one theoretical structure that we can really stand behind and say this captures the features we think are important, and we can measure it.

And we want to test it by actually building living things in the lab. So it's not ever going to be convinced by just this measure and the copy number. What you get convinced of is an explanatory paradigm that allows you to explain not just this one data set, but a whole bunch of different things. And so ultimately the proof of the theory is going to come from the generalizability and the new questions it allows us to answer, not what we've done so far. So I wouldn't hang my hat on it, the data we have so far,

but what I'm hanging my hat on is the potential things that this is opening up and the way it's allowing a unified explanation for a whole bunch of problems in astrobiology that have traditionally been considered completely separate. And also on what we talked about at the very beginning about what is physics and what does physics do? And for me, it's about the explanation

for the nature of life that's more important and then anyone experiment. That feels like a nice note to end things on, like a nice wrap-up. Did you have another question, Daniel? Yeah, I would love to hear just as a final vision, like how you think this could, in the best case scenario, come together.

Like, you talk in the book about building these computers that you could like search for the origin of life. And when I do science, I was trying to imagine, like what's the fantasy data I would have? Are you hoping that we discover like alien life here on Earth before we discovered on insouletis? Would it actually be your preference? Take us through your scientific fantasy.

Right. So my preference is that we just discover more life and we understand what life is. So my preference is understand what life is and have enough scientific evidence to support that explanation. The progress of science is that's never a single aha moment. It's like a cultural transformation in the way we understand a certain set of phenomena

mediated by a whole bunch of experiments and observations and a conciliance of like a whole bunch of things coming together, right? So I think that process is highly nonlinear. For me, the reason I really advocated more for this experimental approach in the lab is the idea that you could iterate between the observation and theory very quickly. So the challenge for looking for life on alien worlds is we don't know the prior probability for life and we don't know what we're looking for. And so we don't know how many planets we have to survey before we find something and nor is it the case that we can actually

rule out a planet is alive or not. And so I think by trying to to bring the paradigm of looking for alien life into an experimental paradigm and one where we were actually building large enough chemical search engines to look for alien life, we actually make it tractable to understand the mechanism of the origin of life, the probability it doesn't happen, and also build the theory and experiments to really test how it does happen at the same time. So to me, it seems the most efficient route to actually getting to the answer to the question. And so, and you know, part of it might be biased by my background in cosmology and just looking at the way that particle physicists and cosmologies have collaborated to really like,

you know, why do we understand the mechanisms of like the Big Bang so well? It's because we built particle accelerators. And so I think without an experimental paradigm for these questions, that really ties the planetary and the alien search to the origin of life. You have to couple those problems with the same problem at their core. And I also just like the radical idea that like alien life will discover it on Earth in an experiment because it's fun. But then we'll know what we're looking for.

So like it seems more obvious. find it elsewhere, right? So, like, to me, that just seems logical. But it's also fun because, you know, like, it means we can do the science really rapidly. And I want to see it solved. So I want the most efficient route to an answer. And then we'll have to argue about whether it's really alien, if it was on Earth after all. Right. That's a good problem to have, right? Because I think, yeah, a really good problem to have. Come full circle to good beer conversation. Yes. Yes. There you go. See, if you answer one of the beer questions, but you have a better of your question, it's not a problem.

Excellent. There you go. Well, thank you very much for coming on and talk to us about assembly theory and for giving us an advance peek at your book. Everyone, it's called Life As No One Knows It, the Physics of Life's Emergence. Congratulations on the book and best of luck. Thank you so much. Thank you both.

Yeah, thank you. All right. And that was our conversation with Sarah and Mari Walker, author of the recent book, Life as No One Knows It, which you can now pick up at all fine booksellers. Kelly, what's your takeaway? Is physics going to help us understand what life is? Well, you know, my takeaway is pretty similar to my takeaway many years ago when I was arguing with my fellow grad students, which is, wow, this is complicated, which is pretty much the

conclusion to every ecology paper you'll ever read is it's complicated and it depends. And anyway, so yeah, it's complicated. What do you think? I think it's a valiant effort and it's worth doing and we're going to learn things along the way. I don't know that we're going to figure it out. I don't know that this is the right approach. But I think thinking hard about it is the first step to figuring it out, no matter where it goes. Often you go down to the root of something and you discover something completely different than solving the problem you meant to or you make breakthroughs in other areas.

So I'm excited to see where this goes. I'm excited that people are thinking about these problems. I think it helps clear away some of the cobwebs and provides a little bit of clarity. But I guess I have to put it into like, we'll see category before I'm actually convinced that this is the right way to think about life. I mean, it would be pretty epic if, like, on demand, new life could be created in the lab and we could look at different evolutionary trajectories and stuff like that. I mean, the evolutionary biologist would go wild if that could be accomplished. I don't know where you start to do something like that, but it would be pretty exciting if it could be accomplished. Yeah.

And then, of course, the next philosophical question would be if you've created a new kind of living goo, in your lab, is it an alien or is it just another kind of earthling? And how long before it begins to eat human flesh? Day one, I'm hoping. I mean, if this movie's going to be any good, right? Yeah, no, it's going to happen fast. I mean, you could also flip the question around and, like, say that new kind of living goo becomes intelligent.

How do we know it doesn't call us aliens, right? And like, we're at home. How can we be aliens? That's right. That's right. Let's all just get along and be earthlings, am I right? That sounds good, exactly. I look forward to a big, cozy family meal, passing the bread and the corn cobs around with our fellow earth goo. I'm going to schedule it one week after our meeting where you tell me about how physics have solved all the problems of the world.

Sounds good, and I'll bring some towels. That's good because I'll forget mine. Bring extra, please. Katrina will have an extra one in her bag. No worries. All right, thanks everyone for joining us on this squishy discussion about the physics of life. Hope you learned something. I certainly did. And thank you very much. Kelly, my friend and co-host for joining me on today's episode. My pleasure. Thanks, Daniel. Tune in next time. For more science and curiosity, come find us on social media where we answer questions and post videos.

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