What is life? How do you define what things are living and what things are dead. You might look at a running cheetah and say that thing is clearly living, and you look at a chunk of granite rock and you say, okay, that thing is not living. But where do we draw the line? And when we land on other planets someday, what can we realistically expect aliens are going to look like? Will we even recognize strange forms of life or will we only have the capacity to recognize things that are very close to earthly life? And what does any of this have to do with Frankenstein or ancient Greek philosophers or the possibility of finding a cell phone on Mars.

What is life? How do you define what things are living and what things are dead. You might look at a running cheetah and say that thing is clearly living, and you look at a chunk of granite rock and you say, okay, that thing is not living. But where do we draw the line? And when we land on other planets someday, what can we realistically expect aliens are going to look like? Will we even recognize strange forms of life or will we only have the capacity to recognize things that are very close to earthly life? And what does any of this have to do with Frankenstein or ancient Greek philosophers or the possibility of finding a cell phone on Mars.

Welcome to Intercosmos with me David Eagleman.

Welcome to Intercosmos with me David Eagleman.

I'm a neuroscientist in a all third at Stanford, and in these episodes we dive deeply into our three pound universe to uncover some of the most surprising aspects of our lives. In today's episode, we're not only going to dive into our three pound universe, but into the larger universe that surrounds us to think about the question of what is life? So what do we mean when we say something is alive. This is one of the oldest questions that biologists have been asking, and it's a strangely tough one. So today we're going to take a run at this question from a completely different angle, from the point of view of theoretical physics. Joining me today will be physicist Sarah Walker, who with her colleagues is working to ask the question of what is life through a very different lens, And we're going to get into questions like what we might expect when we discover life elsewhere in the universe, and how we can prepare ourselves to even know what to look for. But first I want to say that this question about what is life is one that humans have been asking for about as long as we can tell. So in the fourth century BCE, you had Greek philosophers like Plato and Aristotle writing about this. For example, Aristotle wrote a book called de Anima, or on the Soul, and he says, look to be a living thing, you possess a soul. And Plato, his mentor, was on the same train, talking about a world soul that differentiates between living beings and inanimate matter. But you had people being more specific too. For example, several decades before Plato and Aristotle, the Greek philosopher Empedocles proposed a theory of life based on the interaction of four elemental forces earth, air, water, and fire. He suggested that life is created through just the right combinations of these elements, and this is one of the earliest attempts to understand life as a combination of natural forces, offering a way of distinguishing between living things and inert matter. And another Greek Hippocrates, he started to lay the early foundations for the biological study of life by focusing on the human body. And what he said is there's a balance of four humors that are critical to life. You've got blood and phlem and yellow bile and black bile.

I'm a neuroscientist in a all third at Stanford, and in these episodes we dive deeply into our three pound universe to uncover some of the most surprising aspects of our lives. In today's episode, we're not only going to dive into our three pound universe, but into the larger universe that surrounds us to think about the question of what is life? So what do we mean when we say something is alive. This is one of the oldest questions that biologists have been asking, and it's a strangely tough one. So today we're going to take a run at this question from a completely different angle, from the point of view of theoretical physics. Joining me today will be physicist Sarah Walker, who with her colleagues is working to ask the question of what is life through a very different lens, And we're going to get into questions like what we might expect when we discover life elsewhere in the universe, and how we can prepare ourselves to even know what to look for. But first I want to say that this question about what is life is one that humans have been asking for about as long as we can tell. So in the fourth century BCE, you had Greek philosophers like Plato and Aristotle writing about this. For example, Aristotle wrote a book called de Anima, or on the Soul, and he says, look to be a living thing, you possess a soul. And Plato, his mentor, was on the same train, talking about a world soul that differentiates between living beings and inanimate matter. But you had people being more specific too. For example, several decades before Plato and Aristotle, the Greek philosopher Empedocles proposed a theory of life based on the interaction of four elemental forces earth, air, water, and fire. He suggested that life is created through just the right combinations of these elements, and this is one of the earliest attempts to understand life as a combination of natural forces, offering a way of distinguishing between living things and inert matter. And another Greek Hippocrates, he started to lay the early foundations for the biological study of life by focusing on the human body. And what he said is there's a balance of four humors that are critical to life. You've got blood and phlem and yellow bile and black bile.

So this was not correct, but.

So this was not correct, but.

It started giving the earliest shape to this biological idea that life depends on balancing a certain physical state, and that's he suggested what separates the living body from non living matter. And people started to get more specific about things, a little closer to the way that we think about them now. For example, Epicurus suggested that all things, including living beings, are composed of atoms moving through the void. So for the epicureans life is the result of particular combinations of atoms, and death is just the dissolution of these atomic arrangements. So the difference between living and non living matter lies in the specific arrangement of the atoms. And then Lucretius in Rome some centuries later wrote a poem called on the Nature of Things, and he built on this idea, and he said, living beings are distinguished from non living things by their particular atomic configurations and the ability to move and reproduce. And by the way, even though I know Western thinkers the best, this question of what his life was being wrestled with around the world. So I know that in China in the fourth century BCE, the Taoist text called wang Xi reflected on the nature of life and existence. It looked at how life emerged from the interplay of natural forces, like what they called chi, which was their notion of life energy. And in first century India you have Iravedic texts discussing life in terms of the balance among three doshas, Vada, Pitta, and Kafa. This is all stuff that's not so relevant except for ritual purposes. But the idea that was being pursued was that somehow life is sustained by the equilibrium of different forces. Okay, so the point I want to make here is that the question of what is life is not a new question. And there's a sense in which all these thinkers and books they foreshadow later biological thought by asking this question what animates matter? What makes it alive? And we see the same question reflected all over literature. The most obvious example is Mary Shelley is Frankenstein, and you may know that tells the story of Victor Frankenstein, who's a scientist who sets out to create life by reanimating dead tissue. And the creature he brings to life is assembled from corpses, but becomes a sentient, feeling being, And so readers are challenged and thinking about the boundaries between living and non living matter. And this sort of mythology reaches back hundreds of years earlier. For example, Jewish folklore has the story of the Golum, which is a creature who is shaped out of clay, and when someone writes something on his head, he comes to life as a protector, and if you remove a letter from the word, he becomes inanimate again. And the myth of the Golam inspired ideas from Frankenstein to movies that deal with artificial beings like ex Machina, where you've got a robot that gets artificially intell gin and becomes something that we might call alive. So this question, what is the boundary between life and death? This is a question that has long been on the forefront of the human mind. But of course there's a deeper question also, not just about human life, but about all the life forms we find on this planet. Because when we look around the animal kingdom, we find all kinds of very strange life forms, like platypuses or jellyfish or sephonophores. Anyway, we look at these things and we think, wow, those are really strange. And then we look to plants and we say, well, they seem like to qualify as life also. And then we look at single celled bacteria, which we didn't even know existed until very recently in history, when lewand Hook made a microscope and found these little creatures which you called animacules, which we now call uni cellular organisms. Anyway, we look at those, we say, you know, that seems like life too, But what do these all have in common?

It started giving the earliest shape to this biological idea that life depends on balancing a certain physical state, and that's he suggested what separates the living body from non living matter. And people started to get more specific about things, a little closer to the way that we think about them now. For example, Epicurus suggested that all things, including living beings, are composed of atoms moving through the void. So for the epicureans life is the result of particular combinations of atoms, and death is just the dissolution of these atomic arrangements. So the difference between living and non living matter lies in the specific arrangement of the atoms. And then Lucretius in Rome some centuries later wrote a poem called on the Nature of Things, and he built on this idea, and he said, living beings are distinguished from non living things by their particular atomic configurations and the ability to move and reproduce. And by the way, even though I know Western thinkers the best, this question of what his life was being wrestled with around the world. So I know that in China in the fourth century BCE, the Taoist text called wang Xi reflected on the nature of life and existence. It looked at how life emerged from the interplay of natural forces, like what they called chi, which was their notion of life energy. And in first century India you have Iravedic texts discussing life in terms of the balance among three doshas, Vada, Pitta, and Kafa. This is all stuff that's not so relevant except for ritual purposes. But the idea that was being pursued was that somehow life is sustained by the equilibrium of different forces. Okay, so the point I want to make here is that the question of what is life is not a new question. And there's a sense in which all these thinkers and books they foreshadow later biological thought by asking this question what animates matter? What makes it alive? And we see the same question reflected all over literature. The most obvious example is Mary Shelley is Frankenstein, and you may know that tells the story of Victor Frankenstein, who's a scientist who sets out to create life by reanimating dead tissue. And the creature he brings to life is assembled from corpses, but becomes a sentient, feeling being, And so readers are challenged and thinking about the boundaries between living and non living matter. And this sort of mythology reaches back hundreds of years earlier. For example, Jewish folklore has the story of the Golum, which is a creature who is shaped out of clay, and when someone writes something on his head, he comes to life as a protector, and if you remove a letter from the word, he becomes inanimate again. And the myth of the Golam inspired ideas from Frankenstein to movies that deal with artificial beings like ex Machina, where you've got a robot that gets artificially intell gin and becomes something that we might call alive. So this question, what is the boundary between life and death? This is a question that has long been on the forefront of the human mind. But of course there's a deeper question also, not just about human life, but about all the life forms we find on this planet. Because when we look around the animal kingdom, we find all kinds of very strange life forms, like platypuses or jellyfish or sephonophores. Anyway, we look at these things and we think, wow, those are really strange. And then we look to plants and we say, well, they seem like to qualify as life also. And then we look at single celled bacteria, which we didn't even know existed until very recently in history, when lewand Hook made a microscope and found these little creatures which you called animacules, which we now call uni cellular organisms. Anyway, we look at those, we say, you know, that seems like life too, But what do these all have in common?

Well, of course, the weird part of the story is.

Well, of course, the weird part of the story is.

That when you look at what we are made out of, and what jellyfish and house plants and bacteria are made out of, it's the exact same stuff. It's the exact same stuff that makes our molecules, that makes their molecules, and by the way, the same stuff that makes rocks and oceans and so on. You got carbon and nitrogen and oxygen and calcium and the rest of the atoms. But it's all non living stuff that makes us. Somehow, life is built out of a bunch of non life. Now you may know that. In nineteen fifty two, a scientist named Stanley Miller showed that if you put a bunch of inorganic compounds together, like you put methane and ammonia and hydrogen and water, and then you zap that with electricity, you get amino ad acids, which are the building blocks of proteins. And this was such a striking result because it showed the way that molecules we see.

That when you look at what we are made out of, and what jellyfish and house plants and bacteria are made out of, it's the exact same stuff. It's the exact same stuff that makes our molecules, that makes their molecules, and by the way, the same stuff that makes rocks and oceans and so on. You got carbon and nitrogen and oxygen and calcium and the rest of the atoms. But it's all non living stuff that makes us. Somehow, life is built out of a bunch of non life. Now you may know that. In nineteen fifty two, a scientist named Stanley Miller showed that if you put a bunch of inorganic compounds together, like you put methane and ammonia and hydrogen and water, and then you zap that with electricity, you get amino ad acids, which are the building blocks of proteins. And this was such a striking result because it showed the way that molecules we see.

In living things, like the amino.

In living things, like the amino.

Acids, could emerge from dead stuff if you just have the right kind of atmosphere. And I wasn't alive in the nineteen fifties. But I imagine the mood was really optimistic that from there it would be a straightforward run to see how all the pieces and parts would come together to build life. But here we are over seventy years later, and we still don't know how the story comes together. But the problem is actually worse than that, because almost everything that we as biologists ask about life has to do with life on Earth, where everything is built on atoms like carbon and on big molecules like DNA and RNA, which carry the information to build creatures.

Acids, could emerge from dead stuff if you just have the right kind of atmosphere. And I wasn't alive in the nineteen fifties. But I imagine the mood was really optimistic that from there it would be a straightforward run to see how all the pieces and parts would come together to build life. But here we are over seventy years later, and we still don't know how the story comes together. But the problem is actually worse than that, because almost everything that we as biologists ask about life has to do with life on Earth, where everything is built on atoms like carbon and on big molecules like DNA and RNA, which carry the information to build creatures.

Small and large.

Small and large.

But there's no necessity that life elsewhere in the cosmos will be built of the same stuff and in the same way. And here's the way to think about this. In high school biology, we all learned that we call something alive if it's organized into cells or even a single cell, and it has to have metabolism, meaning it converts energy into stuff that it can use, and it can regulate its internal environment and grow and develop and reproduce and respond to things. And it has to have some sort of programming code like genetic material that says how to build new ones and so on. But no matter how carefully people try to define this they always get into gray areas like viruses which can reproduce but only inside the cells of a host, and they don't have metabolism or respond to stimuli on their own. So do you call them living or non living?

But there's no necessity that life elsewhere in the cosmos will be built of the same stuff and in the same way. And here's the way to think about this. In high school biology, we all learned that we call something alive if it's organized into cells or even a single cell, and it has to have metabolism, meaning it converts energy into stuff that it can use, and it can regulate its internal environment and grow and develop and reproduce and respond to things. And it has to have some sort of programming code like genetic material that says how to build new ones and so on. But no matter how carefully people try to define this they always get into gray areas like viruses which can reproduce but only inside the cells of a host, and they don't have metabolism or respond to stimuli on their own. So do you call them living or non living?

Well?

Well?

Who knows.

Who knows.

And currently we're seeing all kinds of advances in biotech which are creating synthetic life forms, which raises all kinds of strange questions about what criteria should define life. But I think the problem isn't even about blurry boundaries between living and non living. The problem is that the criteria we use in biology textbooks, it's not really thinking big enough when we consider life in other forms elsewhere in the cosmos. And you may know that there's a lot of effort going into finding signatures of other life forms and the cosmos. And generally when people imagine meeting some alien civilization, they generally think, oh, it probably looks.

And currently we're seeing all kinds of advances in biotech which are creating synthetic life forms, which raises all kinds of strange questions about what criteria should define life. But I think the problem isn't even about blurry boundaries between living and non living. The problem is that the criteria we use in biology textbooks, it's not really thinking big enough when we consider life in other forms elsewhere in the cosmos. And you may know that there's a lot of effort going into finding signatures of other life forms and the cosmos. And generally when people imagine meeting some alien civilization, they generally think, oh, it probably looks.

Sort of like us.

Sort of like us.

You got two eyes, even if those eyes are bigger, and it's got a head, even if the head's a little bigger, and maybe it's got pointy ears. And we say take me to your leader, and they say, okay, follow me. But this all may lead us to have a very difficult time recognizing other kinds of life in the cosmos if what we're looking for is a Hollywood actor with some green makeup. So what if we really expanded our thinking on this, What if we really thought about other ways that we could define or at least detect life. So I wanted to see how other people might be thinking about this question, And for that I wanted to look beyond earth biologists. When you're looking for someone who has a very big view of things, you generally look to physicists. Now, physicists have not always been interested in the question of life, although one of the most famous little books entitled What Is Life was a nineteen forty three series of lectures by Irwin Schrodinger, the quantum physicist.

You got two eyes, even if those eyes are bigger, and it's got a head, even if the head's a little bigger, and maybe it's got pointy ears. And we say take me to your leader, and they say, okay, follow me. But this all may lead us to have a very difficult time recognizing other kinds of life in the cosmos if what we're looking for is a Hollywood actor with some green makeup. So what if we really expanded our thinking on this, What if we really thought about other ways that we could define or at least detect life. So I wanted to see how other people might be thinking about this question, And for that I wanted to look beyond earth biologists. When you're looking for someone who has a very big view of things, you generally look to physicists. Now, physicists have not always been interested in the question of life, although one of the most famous little books entitled What Is Life was a nineteen forty three series of lectures by Irwin Schrodinger, the quantum physicist.

But generally the question of.

But generally the question of.

Life seems like the wrong sort of level of question for a lot of physicists. And that's why I was so pleased to come across the book of Sarah Walker, who's a theoretical physicist.

Life seems like the wrong sort of level of question for a lot of physicists. And that's why I was so pleased to come across the book of Sarah Walker, who's a theoretical physicist.

At Arizona State University.

At Arizona State University.

She wrote a book called Life as No One Knows It, and she looks at the question of how she could measure life so that we would know when we find it. So I called her up to hear her take on this, and here is Sarah Walker. Okay, So, Sarah, I want to get into this issue about how physicists think about things differently than biologists do. And you give this lovely analogy in your book about how a physicist thinks about let's say gravity, So.

She wrote a book called Life as No One Knows It, and she looks at the question of how she could measure life so that we would know when we find it. So I called her up to hear her take on this, and here is Sarah Walker. Okay, So, Sarah, I want to get into this issue about how physicists think about things differently than biologists do. And you give this lovely analogy in your book about how a physicist thinks about let's say gravity, So.

Tell us about that.

Tell us about that.

Yeah.

Yeah.

I like using gravity as a good example because it's pretty familiar to us, and we kind of accept gravity as a real objective feature of reality, and forget that people had to actually invent our concepts of gravity. The whole process of doing that was really trying to understand regularities that unify behavior across a huge diversity of objects. And so the kind of things that were of interest to early physicists were balls, rolling down, inclined planes, and planetary motion in the heavens.

I like using gravity as a good example because it's pretty familiar to us, and we kind of accept gravity as a real objective feature of reality, and forget that people had to actually invent our concepts of gravity. The whole process of doing that was really trying to understand regularities that unify behavior across a huge diversity of objects. And so the kind of things that were of interest to early physicists were balls, rolling down, inclined planes, and planetary motion in the heavens.

And you know what they.

And you know what they.

Realized was if they chose a sufficiently abstract representation, they could talk about those things in the same language. And prior to that, in human history, we had no idea that planetary motion was governed by the same principles that keep us on this planet. Right, So it was a huge conceptual leap made by our species, and it was really one about trying to find the right kind of representation that could describe a huge diversity of forms. And this is why it gets interesting when we're talking about biology, because in biology we have a plethora of diverse kinds of forms of life on this planet. And a critical question if you want to talk about whether there are governing laws or principles of life, is is there some simple unifying description that could unify all of that diversity of life on Earth and not just explain what we see her on this planet, but also on other planets, which is one of the key questions I'm interested in.

Realized was if they chose a sufficiently abstract representation, they could talk about those things in the same language. And prior to that, in human history, we had no idea that planetary motion was governed by the same principles that keep us on this planet. Right, So it was a huge conceptual leap made by our species, and it was really one about trying to find the right kind of representation that could describe a huge diversity of forms. And this is why it gets interesting when we're talking about biology, because in biology we have a plethora of diverse kinds of forms of life on this planet. And a critical question if you want to talk about whether there are governing laws or principles of life, is is there some simple unifying description that could unify all of that diversity of life on Earth and not just explain what we see her on this planet, but also on other planets, which is one of the key questions I'm interested in.

So we're going to get into that question of what is life? How would a physicists think about life? But how did you get interested in that question?

So we're going to get into that question of what is life? How would a physicists think about life? But how did you get interested in that question?

I wanted to be a cosmologist or a particle physicist.

I wanted to be a cosmologist or a particle physicist.

When I was an undergrad.

When I was an undergrad.

I fell in love with theoretical physics and its ability to describe nature abstractly and the fact that the human mind could come up with descriptions of nature we could go test, so things like gravitational waves that we had no knowledge about, we could go out and look for just because the theory predicted them, and then learn new things about reality or neutrinos or another example. Right, these are not things that are like, you know, privy to our daily perception.

I fell in love with theoretical physics and its ability to describe nature abstractly and the fact that the human mind could come up with descriptions of nature we could go test, so things like gravitational waves that we had no knowledge about, we could go out and look for just because the theory predicted them, and then learn new things about reality or neutrinos or another example. Right, these are not things that are like, you know, privy to our daily perception.

Right.

Right.

We didn't evolve capacity to sense these things. Yet we can build theories that allow us to build technology to sense them. And so I was deeply intrigued by that whole process and that whole sort of conception of nature that you know, underlies what physicists do, you know, at this sort of edge of developing new descriptions of reality. And it was the case that through my undergrad education I just really decided I want to be a theoretical physicist. When I got to graduate school, I was like dead set on it. And my PhD advisor, Marcelo Gleister, a really fantastic thinker, was just you know, later in his career as a cosmologist and thought, you know, wanted to be great if I did some projects I'm origins life. And so I was pretty resistant at first because because of you know, kind of what you were indicating initially, Like physics and biology are usually traditionally seen as totally separate, and in some sense physicists look down on biology as a lesser problem than the kind of grand sweeping things that physicists study. So it just wasn't on my radar from my education that there would really be fundamental problems of the kind I was interested in. And I always loved biological sciences, but like, I really loved this idea of deep, abstract, unifying principles and really understanding at a core, you know, the nature of physical reality. And so what really sold me on the original life and why I decided to dedicate my career to it is I realized it was like a major open question, and major in the sense it wasn't just that we didn't, you know, have the right tools to answer the question.

We didn't evolve capacity to sense these things. Yet we can build theories that allow us to build technology to sense them. And so I was deeply intrigued by that whole process and that whole sort of conception of nature that you know, underlies what physicists do, you know, at this sort of edge of developing new descriptions of reality. And it was the case that through my undergrad education I just really decided I want to be a theoretical physicist. When I got to graduate school, I was like dead set on it. And my PhD advisor, Marcelo Gleister, a really fantastic thinker, was just you know, later in his career as a cosmologist and thought, you know, wanted to be great if I did some projects I'm origins life. And so I was pretty resistant at first because because of you know, kind of what you were indicating initially, Like physics and biology are usually traditionally seen as totally separate, and in some sense physicists look down on biology as a lesser problem than the kind of grand sweeping things that physicists study. So it just wasn't on my radar from my education that there would really be fundamental problems of the kind I was interested in. And I always loved biological sciences, but like, I really loved this idea of deep, abstract, unifying principles and really understanding at a core, you know, the nature of physical reality. And so what really sold me on the original life and why I decided to dedicate my career to it is I realized it was like a major open question, and major in the sense it wasn't just that we didn't, you know, have the right tools to answer the question.

We didn't even know what questions to ask.

We didn't even know what questions to ask.

And these places where we have these sort of conceptually open you know, like like nobody knows how to think about it, Like those are the spaces that I love to be in because those are the ones where you really have this opportunity to do something new and also like to maybe discover something kind of deep that we didn't know before.

And these places where we have these sort of conceptually open you know, like like nobody knows how to think about it, Like those are the spaces that I love to be in because those are the ones where you really have this opportunity to do something new and also like to maybe discover something kind of deep that we didn't know before.

So the way that a biologist thinks about what is life is we look and we see all these cells, we see cell processeds, and we discovered DNA and things like that and we think, Okay, we're going to make a theory about life, but how do you, as a theoretical physicist start tackling the problem?

So the way that a biologist thinks about what is life is we look and we see all these cells, we see cell processeds, and we discovered DNA and things like that and we think, Okay, we're going to make a theory about life, but how do you, as a theoretical physicist start tackling the problem?

It was interesting.

It was interesting.

So my first, like, I really, what I'm interested in is how does non living matter transition to living matter? And in order to answer that question, you need to have some sense of what you mean when you say something is life or something is alive, or something as living matter. And so I've always been very questioned driven. I think a lot of people that ask the what is life question, that's their question. But the way I approach it is that question is in service of solving this other very big open question in science, which is where does life come from in the first place? And so I was actually early in my career I was steered away even by some biologists from working on the original life because they thought I could learn more about biology by studying biological forms as we already understand them. And I intrinsically felt that there was something really new and different to learn about the original life transition itself. And so the sort of traditional approach, as I said, has been to ask what is life and then try to answer that question directly, And I just don't think that that's actually useful exercise in these sort of more fundamental aspects or getting at the frontiers of detecting life elsewhere or origins of life, because what we end up doing is kind of having these descriptors life life is, you know, requires metabolism to sustain itself, Life needs genetics or these things that are very anthropercentric and base dating examples as we know it and might you know, and those examples don't apply to like the earliest life on Earth as far as we know, because we don't know if it had a genetic system or not, for example. So we need deeper descriptions to go further than the biology we know. And that's what I got interested in, and that needs to be driven by really having a compelling question that you're trying to answer to focus your effort.

So my first, like, I really, what I'm interested in is how does non living matter transition to living matter? And in order to answer that question, you need to have some sense of what you mean when you say something is life or something is alive, or something as living matter. And so I've always been very questioned driven. I think a lot of people that ask the what is life question, that's their question. But the way I approach it is that question is in service of solving this other very big open question in science, which is where does life come from in the first place? And so I was actually early in my career I was steered away even by some biologists from working on the original life because they thought I could learn more about biology by studying biological forms as we already understand them. And I intrinsically felt that there was something really new and different to learn about the original life transition itself. And so the sort of traditional approach, as I said, has been to ask what is life and then try to answer that question directly, And I just don't think that that's actually useful exercise in these sort of more fundamental aspects or getting at the frontiers of detecting life elsewhere or origins of life, because what we end up doing is kind of having these descriptors life life is, you know, requires metabolism to sustain itself, Life needs genetics or these things that are very anthropercentric and base dating examples as we know it and might you know, and those examples don't apply to like the earliest life on Earth as far as we know, because we don't know if it had a genetic system or not, for example. So we need deeper descriptions to go further than the biology we know. And that's what I got interested in, and that needs to be driven by really having a compelling question that you're trying to answer to focus your effort.

How you build theory.

How you build theory.

Okay, so you asked the question of how does non living stuff become living stuff? And how did you how did you go about it?

Okay, so you asked the question of how does non living stuff become living stuff? And how did you how did you go about it?

How did you start making progress on a question like that?

How did you start making progress on a question like that?

Yeah, so obviously I didn't know a lot about biology and chemistry when I started. You can pick up a lot reading and talking to people, but it wasn't it's not my training, it's not my field of expertise. I would I will always stay upfront. I have all of the cognitive biases of somebody that was trained in physics.

Yeah, so obviously I didn't know a lot about biology and chemistry when I started. You can pick up a lot reading and talking to people, but it wasn't it's not my training, it's not my field of expertise. I would I will always stay upfront. I have all of the cognitive biases of somebody that was trained in physics.

I really tried to fight them.

I really tried to fight them.

But you know, I'm very aware of my disciplinary training, and part of the reason I'm so aware of it is walking into origins of life as a PhD student. Almost everybody there comes from a different discipline, right, Like there's the organic chemists and they have a camp of how they think about it. There's the genetics and molecular biologists and they have a camp about how they think about the problem. And there's the physicists and they have a camp of how they think about the problem. And so each discipline or your perspective kind of had a hypothesis that was informed by their discipline but not the others. And so I really tried to abandon all of that and just really try to focus on what the fundamental nature of the problem was. But obviously, starting from physics, I wanted to start with, like, why can physics not explain the origin of life? And that led to focus focus on information and causation because it seems to be the case that in living systems information is causal. So for example, you know there's people listening to this right now, I could say raise your hand.

But you know, I'm very aware of my disciplinary training, and part of the reason I'm so aware of it is walking into origins of life as a PhD student. Almost everybody there comes from a different discipline, right, Like there's the organic chemists and they have a camp of how they think about it. There's the genetics and molecular biologists and they have a camp about how they think about the problem. And there's the physicists and they have a camp of how they think about the problem. And so each discipline or your perspective kind of had a hypothesis that was informed by their discipline but not the others. And so I really tried to abandon all of that and just really try to focus on what the fundamental nature of the problem was. But obviously, starting from physics, I wanted to start with, like, why can physics not explain the origin of life? And that led to focus focus on information and causation because it seems to be the case that in living systems information is causal. So for example, you know there's people listening to this right now, I could say raise your hand.

Some of you may raise your hands.

Some of you may raise your hands.

I'm raising my hand right, And so we're separated in space and time, and there's causation there, right, and it's carried by words which are you know, very abstract, but there must be some kind of physicality to them if they have some causation in the world with sort of my thinking. And obviously there's also like in genomes we talk about them carrying information, etcetera. So this language of information is all over biology. And so the first problem I identified, which I wrote this paper with my postdoc advisor Paul Davies in twenty thirteen called the Algorithmic Origins of Life, was the original life transition must have something to do with a transition in causation and information.

I'm raising my hand right, And so we're separated in space and time, and there's causation there, right, and it's carried by words which are you know, very abstract, but there must be some kind of physicality to them if they have some causation in the world with sort of my thinking. And obviously there's also like in genomes we talk about them carrying information, etcetera. So this language of information is all over biology. And so the first problem I identified, which I wrote this paper with my postdoc advisor Paul Davies in twenty thirteen called the Algorithmic Origins of Life, was the original life transition must have something to do with a transition in causation and information.

And physical systems.

And physical systems.

And I've used that kind of as the paradigm of most of my career. Actually all of my work is training answer a question I posed in that paper. And so now I've settled on this new approach that I'm very excited about because of the connection between deep connection between theory and experiment called assembly theory, which is an attempt to understand how information really is the sort of underlying mechanism for the existence of some objects, but doing it in a much more physical way.

And I've used that kind of as the paradigm of most of my career. Actually all of my work is training answer a question I posed in that paper. And so now I've settled on this new approach that I'm very excited about because of the connection between deep connection between theory and experiment called assembly theory, which is an attempt to understand how information really is the sort of underlying mechanism for the existence of some objects, but doing it in a much more physical way.

Cool.

Cool.

So, just before we get into assembly theory, so give us an exams example of information and causation. Give us an example. How do you think about that in terms of life.

So, just before we get into assembly theory, so give us an exams example of information and causation. Give us an example. How do you think about that in terms of life.

Yeah, an example might be something like a technological artifact like a cell phone. We don't expect them to spontaneously emerge from the geochemistry of Mars. So if we found a cell phone on Mars, for example, we would consider it a biosignature because it has so much history necessary to construct something like a cell phone. Right, So, cell phones, if they appear in the universe at all, you know, should be expected to emerge on planets that have evolution of life over billions of years and evidential evolution of intelligent beings that construct cell phones.

Yeah, an example might be something like a technological artifact like a cell phone. We don't expect them to spontaneously emerge from the geochemistry of Mars. So if we found a cell phone on Mars, for example, we would consider it a biosignature because it has so much history necessary to construct something like a cell phone. Right, So, cell phones, if they appear in the universe at all, you know, should be expected to emerge on planets that have evolution of life over billions of years and evidential evolution of intelligent beings that construct cell phones.

They don't happen for free, all right.

They don't happen for free, all right.

That's a key conjecture of the theory that I'm working on, is that those kinds of objects require information.

That's a key conjecture of the theory that I'm working on, is that those kinds of objects require information.

Tell us where this is landed with assembly theory, and how do you think about life.

Tell us where this is landed with assembly theory, and how do you think about life.

Yeah, So the sort of key conjecture of assembly theory is that there are some objects that are just too complex to form spontaneously ever in the history of the universe. So this is this is very sort of counter to the sort of standard paradigm in physics right now, which is the idea that any object of our arbitrary complexity can fluctuate into existence with very low probability. That's completely consistent with all of our current theories of physics. And yet we don't see you know, brains popping into existence spontaneously, right, they evolve in bodies, and so there's this famous argument about Boltzmann brains, you know, being spontaneous objects, and it raises all kinds of paradoxes in physics. So both my brains are this idea that due to spontaneous fluctuation in the laws of physics it could be thermodynamics or quantum fluctuations. You can spontaneously fluctuate particles to existence, for example, and quantum physics as long as they're a particle antiparticle, and they'll just you know, spontaneously fluctuate out of existence. So these kind of effects can happen. And if you run that and just say, you know, like as a logical experiment, you say, well, there's no sort of bound on what could fluctuate into existence. You lead to a sort of paradoxical situation where something like a brain could also spontaneously fluctuate into existence. And this is paradoxical because if you were such a brain, it's not clear that your experiences would be anything different than the experiences that we have. So for example, you know, you could have just fluctuated into existence right now hearing me influctuated out of existence, and then you wouldn't know if this moment is actually the one that you fluctuated into existence, and now it's you know, so it's like it's very it's and it's a problematic because if these things are a possibility, affects some of our cosmological models and some of the other areas of physics. And it's also related to other problems in physics, like fine tuning of the initial condition, which is another issue where physics directly confronts biology, because to describe complexity, it has to be in the initial state of the universe that there was you know, a precise amount of information necessary to construct things like us, and an assembly theory, we think that all of the information is actually constructed over time in the dynamics of the universe unfolding and in particular on planets to build things that are complex like us. And that's the phenomena that we call life. And so the sort of key testable conjecture that we have so far is that there's actually a complexity threshold in chemistry where and we actually talk about it in terms of an assembly index, which is sort of a minimal number of steps for constructing an object. So if you want to think about legos, you're sticking them together, and you can take parts you've already built and build up to a particular structure, you'd have sort of a minimal number.

Yeah, So the sort of key conjecture of assembly theory is that there are some objects that are just too complex to form spontaneously ever in the history of the universe. So this is this is very sort of counter to the sort of standard paradigm in physics right now, which is the idea that any object of our arbitrary complexity can fluctuate into existence with very low probability. That's completely consistent with all of our current theories of physics. And yet we don't see you know, brains popping into existence spontaneously, right, they evolve in bodies, and so there's this famous argument about Boltzmann brains, you know, being spontaneous objects, and it raises all kinds of paradoxes in physics. So both my brains are this idea that due to spontaneous fluctuation in the laws of physics it could be thermodynamics or quantum fluctuations. You can spontaneously fluctuate particles to existence, for example, and quantum physics as long as they're a particle antiparticle, and they'll just you know, spontaneously fluctuate out of existence. So these kind of effects can happen. And if you run that and just say, you know, like as a logical experiment, you say, well, there's no sort of bound on what could fluctuate into existence. You lead to a sort of paradoxical situation where something like a brain could also spontaneously fluctuate into existence. And this is paradoxical because if you were such a brain, it's not clear that your experiences would be anything different than the experiences that we have. So for example, you know, you could have just fluctuated into existence right now hearing me influctuated out of existence, and then you wouldn't know if this moment is actually the one that you fluctuated into existence, and now it's you know, so it's like it's very it's and it's a problematic because if these things are a possibility, affects some of our cosmological models and some of the other areas of physics. And it's also related to other problems in physics, like fine tuning of the initial condition, which is another issue where physics directly confronts biology, because to describe complexity, it has to be in the initial state of the universe that there was you know, a precise amount of information necessary to construct things like us, and an assembly theory, we think that all of the information is actually constructed over time in the dynamics of the universe unfolding and in particular on planets to build things that are complex like us. And that's the phenomena that we call life. And so the sort of key testable conjecture that we have so far is that there's actually a complexity threshold in chemistry where and we actually talk about it in terms of an assembly index, which is sort of a minimal number of steps for constructing an object. So if you want to think about legos, you're sticking them together, and you can take parts you've already built and build up to a particular structure, you'd have sort of a minimal number.

Steps to make that structure.

Steps to make that structure.

And you can imagine if you're shaking a lego table right and you're doing random kind of configurations of objects, you'll get like a couple pieces sticking together, and they might repeat those structures, but you're not going to expect to see lego hogwarts of the taj Mahal, you know, spontaneously assemble even in you know the amount of time the universe has has had to you know, potentially, like you know, thirteen point seven billion years of shaking is not going to get you there. So you can imagine, like where is the boundary between the things that are really likely those small couple of things stuck together that we should find ubiquitous in the universe and something like the taj Mahal, which you know requires a lot of cultural information, a lot of evolutionary you know, like well, billions of years of biological evolution to get intelligent beings and then thousands of years of cultural evolution to build something that complicated.

And you can imagine if you're shaking a lego table right and you're doing random kind of configurations of objects, you'll get like a couple pieces sticking together, and they might repeat those structures, but you're not going to expect to see lego hogwarts of the taj Mahal, you know, spontaneously assemble even in you know the amount of time the universe has has had to you know, potentially, like you know, thirteen point seven billion years of shaking is not going to get you there. So you can imagine, like where is the boundary between the things that are really likely those small couple of things stuck together that we should find ubiquitous in the universe and something like the taj Mahal, which you know requires a lot of cultural information, a lot of evolutionary you know, like well, billions of years of biological evolution to get intelligent beings and then thousands of years of cultural evolution to build something that complicated.

Right, So, so.

Right, So, so.

What we say in assembly theory is that there's actually a threshold and if we find structures above this threshold, where we find abundant highly assembled objects, then that's a signature of life. And this has all kinds of really interesting consequences because now you've made this history of construction in this way of building the object kind of a physical property that and we can go measure it in the lab for molecules, and we've done that, We've done tests on biological non biological samples, and it seems that there really is a threshold value in this sort of complexity assembly index above which things are only produced by life.

What we say in assembly theory is that there's actually a threshold and if we find structures above this threshold, where we find abundant highly assembled objects, then that's a signature of life. And this has all kinds of really interesting consequences because now you've made this history of construction in this way of building the object kind of a physical property that and we can go measure it in the lab for molecules, and we've done that, We've done tests on biological non biological samples, and it seems that there really is a threshold value in this sort of complexity assembly index above which things are only produced by life.

So let me unpack that just a little bit.

So let me unpack that just a little bit.

So when you talk about things being testable, so you test them with chemistry essentially, and you're asking how complex a molecule do I expect to get accidentally just from things bumping into one another, Versus what's some threshold over which I say, wow, you know what, that thing that molecule is too complex that that's not going to come about by accident.

So when you talk about things being testable, so you test them with chemistry essentially, and you're asking how complex a molecule do I expect to get accidentally just from things bumping into one another, Versus what's some threshold over which I say, wow, you know what, that thing that molecule is too complex that that's not going to come about by accident.

That yeah, that's exactly what we're trying to test for. And the way that you actually do it is with sort of standard instrumentation in a chemistry lab, so we can measure this feature of this minimal number of stepsi assembly index using mass spectrometry NMR and for reds, so it's possible to take samples and actually test this conjecture, and so far it's held up.

That yeah, that's exactly what we're trying to test for. And the way that you actually do it is with sort of standard instrumentation in a chemistry lab, so we can measure this feature of this minimal number of stepsi assembly index using mass spectrometry NMR and for reds, so it's possible to take samples and actually test this conjecture, and so far it's held up.

And the conjecture that holds up is that there's some threshold of complexity and you get things accidentally for a while, but it doesn't get more complex than that.

And the conjecture that holds up is that there's some threshold of complexity and you get things accidentally for a while, but it doesn't get more complex than that.

It doesn't build the cell phone.

It doesn't build the cell phone.

So the expectation is that planets that don't have life will only be able to build molecular objects or you know, any objects like you know, it won't be able to build a cell phone, for example, but that boundary of what it can you know, what it can produce, is tightly bounded. There's like an upper limit in the complexity of the molecules, and life is the only thing that can cross that. And so I think about it oftentimes in terms of like if you imagine that you can think about the space of all possible objects that the universe could generate, and they're stacked by how hard they are to build, by their sort of construction history, and what objects need to precede them in order for them to exist that physical Like, what assembly theory is doing is making that a physical space by tying that the structure of that space to something we can measure in the lab. And then we're saying that life is the only thing that you find beyond a certain boundary in that space.

So the expectation is that planets that don't have life will only be able to build molecular objects or you know, any objects like you know, it won't be able to build a cell phone, for example, but that boundary of what it can you know, what it can produce, is tightly bounded. There's like an upper limit in the complexity of the molecules, and life is the only thing that can cross that. And so I think about it oftentimes in terms of like if you imagine that you can think about the space of all possible objects that the universe could generate, and they're stacked by how hard they are to build, by their sort of construction history, and what objects need to precede them in order for them to exist that physical Like, what assembly theory is doing is making that a physical space by tying that the structure of that space to something we can measure in the lab. And then we're saying that life is the only thing that you find beyond a certain boundary in that space.

So how does that help you understand how non living things become living?

So how does that help you understand how non living things become living?

Well, what it does is it allows us first to measure whether this has happened, which means we can actually start a new experimental paradigm for the original life. So traditionally in my field, you know, the standard set of experiments that people have done is to try to look for, you know, a chemical system that could produce an amino acid because we use amino acids in our bodies and all biological life forms do, or things that could make components of DNA or RNA again, because we find that in you know, all life on Earth, and so those have been really targeted syntheses, and I think that that's a bit of a challenge because it's looking specifically for molecular structures that we find in life on Earth, so it's not general, as we talked about at the beginning. But also it's problematic because we're putting so much agency and selection in because we know the goal in mind of what we want to produce, that we're actually sort of biasing the space to already produce things, even if they're complex, by putting boundary conditions in the experiment. And so the sort of vision that I build in the book about these original life experiments really comes from my colleague Lee Cronin, who originally developed assembly theory and also has this very large experimental lab trying to develop new platforms for original life experiments. Is to try to do these sort of random soup chemistries where you actually just try to model, you know, geochemistry, and you don't constrain it, and you try to detect if you start getting complex things out and at what level you start getting.

Well, what it does is it allows us first to measure whether this has happened, which means we can actually start a new experimental paradigm for the original life. So traditionally in my field, you know, the standard set of experiments that people have done is to try to look for, you know, a chemical system that could produce an amino acid because we use amino acids in our bodies and all biological life forms do, or things that could make components of DNA or RNA again, because we find that in you know, all life on Earth, and so those have been really targeted syntheses, and I think that that's a bit of a challenge because it's looking specifically for molecular structures that we find in life on Earth, so it's not general, as we talked about at the beginning. But also it's problematic because we're putting so much agency and selection in because we know the goal in mind of what we want to produce, that we're actually sort of biasing the space to already produce things, even if they're complex, by putting boundary conditions in the experiment. And so the sort of vision that I build in the book about these original life experiments really comes from my colleague Lee Cronin, who originally developed assembly theory and also has this very large experimental lab trying to develop new platforms for original life experiments. Is to try to do these sort of random soup chemistries where you actually just try to model, you know, geochemistry, and you don't constrain it, and you try to detect if you start getting complex things out and at what level you start getting.

Complex things out.

Complex things out.

And so if this idea of this threshold is accurate, we should be able to detect when life spontaneously emerges through a random chemical search. And so we kind of think of like it almost is like a chemical search engine, Like we don't know how often alien life or any kind of life forms form in this huge space of chemistry, and so we want to build a machine that allows us to actually explore that space and look for living things. But we need to actual measure we can go and do in the chemistry.

And so if this idea of this threshold is accurate, we should be able to detect when life spontaneously emerges through a random chemical search. And so we kind of think of like it almost is like a chemical search engine, Like we don't know how often alien life or any kind of life forms form in this huge space of chemistry, and so we want to build a machine that allows us to actually explore that space and look for living things. But we need to actual measure we can go and do in the chemistry.

To look for it.

To look for it.

So this is a very big paradigm shift in the way we're thinking experimentally about origins of life.

So this is a very big paradigm shift in the way we're thinking experimentally about origins of life.

So let me summarize this.

So let me summarize this.

Where we are so far, so you're you and Lee are looking at this issue of okay, lots of chemicals together. You expect things to be under the threshold of what you would call, you know, a certain complexity threshold. But you're asking how many times does something pop above that threshold? Like when do we see something go above that? And when it does go about that, we'd say, okay, there's something that we'd call life about that.

Where we are so far, so you're you and Lee are looking at this issue of okay, lots of chemicals together. You expect things to be under the threshold of what you would call, you know, a certain complexity threshold. But you're asking how many times does something pop above that threshold? Like when do we see something go above that? And when it does go about that, we'd say, okay, there's something that we'd call life about that.

Yes, And one of the other key things that I'm working on is developing sort of a theory of the actual transition between those phases. So we have a lot of the sort of scaffold those theory worked out in terms of how we think about selection in assembly spaces, which is kind of the space of these kind of operations of building up objects, but which is a very abstract space, just like you know, we always talk about in physics these very abstract spaces. So I kind of think of it like we have, like you know, coordinate geometry for like gravity, we have this sort of space of possibilities and the sort of relationships between objects is an assembly space. It's kind of the space that this physics lives in. But the sort of idea there is exactly what you're saying that we want to be able to go and detect this transition. So we also need to be able to predict from the theory when it should happen, and so that's something that we're working on quite extensively right now.

Yes, And one of the other key things that I'm working on is developing sort of a theory of the actual transition between those phases. So we have a lot of the sort of scaffold those theory worked out in terms of how we think about selection in assembly spaces, which is kind of the space of these kind of operations of building up objects, but which is a very abstract space, just like you know, we always talk about in physics these very abstract spaces. So I kind of think of it like we have, like you know, coordinate geometry for like gravity, we have this sort of space of possibilities and the sort of relationships between objects is an assembly space. It's kind of the space that this physics lives in. But the sort of idea there is exactly what you're saying that we want to be able to go and detect this transition. So we also need to be able to predict from the theory when it should happen, and so that's something that we're working on quite extensively right now.

Cool. So we're still in very early days with this, but when you imagine, Yeah, when you imagine what a search for life on other planets would look like, what strikes you.

Cool. So we're still in very early days with this, but when you imagine, Yeah, when you imagine what a search for life on other planets would look like, what strikes you.

Yeah, So some of the things I really love about the development of new theories is also like the philosophy that comes along with it. So I imagine that, you know, we'll go look for high assembly index structures in abundance on other planets, right, So we'll take, you know, in the Solar System, we might go to Titan or Enceladus and you know, bring a mass spectrometer and try to detect molecules with many parts, you know, that have these kind of properties that I was talking about. And so that's a doable experiment, Like we're almost pretty much ready to fly those kind of experiments right now. But from the philosophical side of it, it's interesting to me to think about that what we're looking for when we're looking for living things in the universe is we're looking basically for causal structures that are very deep in time. So all of this causation in history is necessary to maintain the existence of these objects. And it's actually because we talk about it as a measurable, observable feature of an object. You can go in the lab and measure you know how deep in this construction history a particular molecule is. Now you've made evolutionary time quote unquote in some sense of physical attribute of objects, and this kind of really radically freeframes I think some of the ways that we need to think about the physics of life. So, you know, going back to gravitation, you know, one of the reasons that new In and Galileo and the generation could come up with theories of gravity is because they started being able to measure time and seconds with high accuracy, and they had a way of measuring mass, and those became the variables that informed their theory. And so now we have a way of going in the lab and measuring you know, assembled structure that's you know, associated with the history that goes into an object, the information that goes into an object. So now we can talk about that as a physical property.

Yeah, So some of the things I really love about the development of new theories is also like the philosophy that comes along with it. So I imagine that, you know, we'll go look for high assembly index structures in abundance on other planets, right, So we'll take, you know, in the Solar System, we might go to Titan or Enceladus and you know, bring a mass spectrometer and try to detect molecules with many parts, you know, that have these kind of properties that I was talking about. And so that's a doable experiment, Like we're almost pretty much ready to fly those kind of experiments right now. But from the philosophical side of it, it's interesting to me to think about that what we're looking for when we're looking for living things in the universe is we're looking basically for causal structures that are very deep in time. So all of this causation in history is necessary to maintain the existence of these objects. And it's actually because we talk about it as a measurable, observable feature of an object. You can go in the lab and measure you know how deep in this construction history a particular molecule is. Now you've made evolutionary time quote unquote in some sense of physical attribute of objects, and this kind of really radically freeframes I think some of the ways that we need to think about the physics of life. So, you know, going back to gravitation, you know, one of the reasons that new In and Galileo and the generation could come up with theories of gravity is because they started being able to measure time and seconds with high accuracy, and they had a way of measuring mass, and those became the variables that informed their theory. And so now we have a way of going in the lab and measuring you know, assembled structure that's you know, associated with the history that goes into an object, the information that goes into an object. So now we can talk about that as a physical property.

That's terrific.

That's terrific.

And so when you imagine, hey, we sent the mass spectrometer to these moons and we found something that's above this threshold of complexity, and we're going to call that life.

And so when you imagine, hey, we sent the mass spectrometer to these moons and we found something that's above this threshold of complexity, and we're going to call that life.

What's interesting?

What's interesting?

Of course, you know, we all have grown up with this history of literature that has very earth like creatures, you know, maybe with point to your ears or something, but otherwise they're about like us.

Of course, you know, we all have grown up with this history of literature that has very earth like creatures, you know, maybe with point to your ears or something, but otherwise they're about like us.

What do you think of.

What do you think of.

When you think about the size of the possibility space and what what we would even recognize as being something interesting to us.

When you think about the size of the possibility space and what what we would even recognize as being something interesting to us.

Yeah, I've always had a challenge.

Yeah, I've always had a challenge.

So it's interesting being an astrobiologist because a lot of people want to ask you the question.

So it's interesting being an astrobiologist because a lot of people want to ask you the question.

Like what will aliens look like?

Like what will aliens look like?

And I literally, you know, I think the space is so huge. I think we cannot anticipate it. And so, you know, I talked a little bit about the possibility space, but you know, you can actually put numbers on it for chemistry. We can't put it for all possible technologies, which is one of the reasons that you know, the search for techno signatures or signs of technology, which is a very big area of astrobiology and increasing enthusiasm for you know, like it's hard to imagine what other technologies will emerge on other planets, right, we can't even anticipate what technologies we're going to happen next year. But if you think about chemistry, you can at least kind of iterate. You can talk about, you know, how you stick bonds together and how many molecules there are. And so my favorite example, just to give you a sense of the size of the space is to think about the molecule taxi al I think it has I don't remember. It's more like our formula, but it's not that big. It's like something like forty or fifty carbon atoms and it's got oxygen and hydrogen. It it's an anti cancer drug. If you wanted to make every single molecule with that molecular formula, it would fill one point five universes in volume. That's one molecule or another sort of big numbers ten to the sixty molecules that are like small molecula weight like less than five hundred amy, which is about the size of two amino acids. So like the universe cannot make every possible molecule, keminformaticians that do drug design cannot even predict the structure.

And I literally, you know, I think the space is so huge. I think we cannot anticipate it. And so, you know, I talked a little bit about the possibility space, but you know, you can actually put numbers on it for chemistry. We can't put it for all possible technologies, which is one of the reasons that you know, the search for techno signatures or signs of technology, which is a very big area of astrobiology and increasing enthusiasm for you know, like it's hard to imagine what other technologies will emerge on other planets, right, we can't even anticipate what technologies we're going to happen next year. But if you think about chemistry, you can at least kind of iterate. You can talk about, you know, how you stick bonds together and how many molecules there are. And so my favorite example, just to give you a sense of the size of the space is to think about the molecule taxi al I think it has I don't remember. It's more like our formula, but it's not that big. It's like something like forty or fifty carbon atoms and it's got oxygen and hydrogen. It it's an anti cancer drug. If you wanted to make every single molecule with that molecular formula, it would fill one point five universes in volume. That's one molecule or another sort of big numbers ten to the sixty molecules that are like small molecula weight like less than five hundred amy, which is about the size of two amino acids. So like the universe cannot make every possible molecule, keminformaticians that do drug design cannot even predict the structure.

Of every possible molecule.

Of every possible molecule.

So this is like the frontier and pharmaceutical drug design is we don't know how to explore the space because it's just so big. It's unimaginably big. And so this is the issue with alien life. Alien life, you know, presumably will start in chemistry on planets, and the space of possible chemistries is so large we can't even actually computationally explore it on Earth.

So this is like the frontier and pharmaceutical drug design is we don't know how to explore the space because it's just so big. It's unimaginably big. And so this is the issue with alien life. Alien life, you know, presumably will start in chemistry on planets, and the space of possible chemistries is so large we can't even actually computationally explore it on Earth.

So what you're doing is putting a metric to say, look, there is life here on let's say and sell it us. But it might be so different from what we've ever even thought about.

So what you're doing is putting a metric to say, look, there is life here on let's say and sell it us. But it might be so different from what we've ever even thought about.

There's no meaningful communication with it.

There's no meaningful communication with it.

Yeah, and I think I think you know.

Yeah, and I think I think you know.

Step one is do we have a sense that we understand enough about what life is to detect it independent if we know what kind of substrate it's instantiated in. And that was really always the question for me, because we don't know what chemistries are possible, we don't know what technologies are possible. And this is really the value of the sort of abstraction that physicists do is because you're looking at something that's such a deep, universal, abstract layer, you can start talking about systems that you haven't anticipated and still be able to measure them and look for them.

Step one is do we have a sense that we understand enough about what life is to detect it independent if we know what kind of substrate it's instantiated in. And that was really always the question for me, because we don't know what chemistries are possible, we don't know what technologies are possible. And this is really the value of the sort of abstraction that physicists do is because you're looking at something that's such a deep, universal, abstract layer, you can start talking about systems that you haven't anticipated and still be able to measure them and look for them.

Right.

Right.

So it's that's why I think this kind of approach is so important for these problems, whereas it might not be important for a biologist studying life on Earth because they don't need to anticipate, you know, this huge possibility space for the chemistry of life because we have what chemistry on life?

So it's that's why I think this kind of approach is so important for these problems, whereas it might not be important for a biologist studying life on Earth because they don't need to anticipate, you know, this huge possibility space for the chemistry of life because we have what chemistry on life?

You know, life selected on Earth.

You know, life selected on Earth.

Yeah, no, I agree.

Yeah, no, I agree.

I think it's I think it's amazing to be able to quantify this and say, hey, look there's something happening here that wouldn't happen by accident.

I think it's I think it's amazing to be able to quantify this and say, hey, look there's something happening here that wouldn't happen by accident.

Let me ask you this I'm curious about. There's this notion of convergent evolution.

Let me ask you this I'm curious about. There's this notion of convergent evolution.

For example, you know, we and octopuses both seem to have intelligence, but they have mollusc brains. We have ammalian brains, totally different structures, and yet they've converged on this thing. Or you know, insects fly and birds fly with totally different wings, but evolution has converged on something. When you just speculate about finding alien life someday, do you think things like intelligence the way we think about it, or even consciousness is something that we would you find or look for.

For example, you know, we and octopuses both seem to have intelligence, but they have mollusc brains. We have ammalian brains, totally different structures, and yet they've converged on this thing. Or you know, insects fly and birds fly with totally different wings, but evolution has converged on something. When you just speculate about finding alien life someday, do you think things like intelligence the way we think about it, or even consciousness is something that we would you find or look for.

What's your middle of the night speculations on that?

What's your middle of the night speculations on that?

Uh, you know, with usual with tough topics, I change my mind daily, But which is good and healthy? And you know, as a scientist, I think we always have to be like constantly fact checking ourselves and just making sure that we're upfront about it. So, but my current thinking, uh, I think life is the process of generating complex structure over time. And you know, it's not always like a linear trend, right obviously, Like even on Earth, there there's periods where you know, like evolution doesn't seem to always go in a direction of increasing complexity. But I think if you think at a planetary scale of this process of it, you know, basically, you know, sort of the fundamental principle I have in mind about what life is is life is the mechanism of how the universe creates what gets to exist.

Uh, you know, with usual with tough topics, I change my mind daily, But which is good and healthy? And you know, as a scientist, I think we always have to be like constantly fact checking ourselves and just making sure that we're upfront about it. So, but my current thinking, uh, I think life is the process of generating complex structure over time. And you know, it's not always like a linear trend, right obviously, Like even on Earth, there there's periods where you know, like evolution doesn't seem to always go in a direction of increasing complexity. But I think if you think at a planetary scale of this process of it, you know, basically, you know, sort of the fundamental principle I have in mind about what life is is life is the mechanism of how the universe creates what gets to exist.

Because this possibility space is.

Because this possibility space is.

So large in finite time, finite resource, the universe cannot create every possible object. And so what happens is you get these orally contingent trajectories constructing more and more complex structures.

So large in finite time, finite resource, the universe cannot create every possible object. And so what happens is you get these orally contingent trajectories constructing more and more complex structures.

And as they have.

And as they have.

More and more information, they can make more and more complex structure. And so I think that's actually the universal feature of life, is this idea of information constructing possibilities over time. And it emerges on planets because chemistry is the first place that that's necessary even to explore the structure of chemistry. So if you take that as fundamental and you ask the questions about intelligence and consciousness. My take on consciousness is consciousness is something related to the depth and time of physical objects.

More and more information, they can make more and more complex structure. And so I think that's actually the universal feature of life, is this idea of information constructing possibilities over time. And it emerges on planets because chemistry is the first place that that's necessary even to explore the structure of chemistry. So if you take that as fundamental and you ask the questions about intelligence and consciousness. My take on consciousness is consciousness is something related to the depth and time of physical objects.

So things like us that.

So things like us that.

Are four billion years old have a lot of historical contingency and all of the structure wrapped up in the present moment. So you know, basically we've been constructed on our planet over four billion years, and all of that history is compactified into a very small volume which we call a human being, in a human brain. And so I think probably consciousness is somehow fundamental to that structure. Obviously, so we don't know yet and we don't know how to test for that, but that would be sort of my conjecture. And I do think intelligence is also fundamental to this process, because intelligence is a mechanism of making new possibilities physically realized. And so I give an example in the book of Thinking about like rockets. Right, So, rockets are fully consistent with the laws of physics. It's one of the reasons that we can build them. But we imagined them centuries before we learned the rules of the universe that enabled us to actually build rockets, and it took you know, inventing the laws of gravitation and also all kinds of engineering principles before they could become a physical actuality on our planet. So they're not forbidden by our laws of physics or our universe, but they require information over time in the form of evolutionary objects constructing other evolutionary objects, things like us intelligent things in order to exist at all. And so I think that's the key feature of what life is. And so intelligence and consciousness seemed deeply imashed in that structure and probably pretty fundamental to it.