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EPISODE LINKS:
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Sara's Website: http://emergence.asu.edu/

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OUTLINE:
0:00 - Introduction
1:53 - Origin of life
9:46 - Did aliens seed life on Earth?
14:57 - What is life?
26:36 - Cellular automata
31:04 - The laws of physics may change with time
40:50 - Nobel Prize for the origin of life
46:09 - Is consciousness fundamental to the universe?
57:28 - Life is the most deterministic part of physics
1:00:03 - Free will
1:08:20 - How to detect alien life
1:22:57 - How many alien civilization are out there?
1:29:41 - Shadow biosphere
1:36:08 - UFO sightings
1:39:43 - Exponential population growth of AI lifeforms
1:46:50 - The role of death in life
1:50:54 - Advice for young people
1:56:40 - Meaning of life

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The following is a conversation with Sarah Walker, an astrobiologist and theoretical physicist at Arizona State University and the Santa Fe Institute.

She's interested in the origin of life, how to find life on other worlds, and in general, the more fundamental question of what even life is.

She seeks to discover the universal laws that describe living systems on Earth and elsewhere, using physics, biology, and computation.

Quick mention of our sponsors, Athletic Greens, NetSuite, Blinkist, and Magic Spoon.

Check them out in the description to support this podcast.

As a side note, let me say that my hope for this podcast is to try and alternate between technical and non-technical discussions, to jump from the big picture down to specific detailed research and back to the big picture.

And to do so with scientists and non-scientists.

Long-term, I hope to alternate between discussions of cutting edge research in AI, physics, biology, to topics of music, sport and history, and then back to AI.

I hope you come along with me for that wild, oscillating journey.

Some people message me saying to slow down since they're falling behind on the episodes of this podcast.

To their disappointment, I have to say that I'll probably do more episodes, not less, but you really don't need to listen to every episode.

Just listen to the ones that spark your curiosity.

Think about it like a party full of strangers.

Just walk over to the ones who look interesting and get to know them.

And if you're lucky, that 1 conversation with a stranger might change the direction of your life.

And it's a short life, so be picky with the strangers you talk to at this metaphorical party.

This is the Lux Friedman Podcast and here is my conversation with Sarah Walker.

What are the various hypotheses for how life originated on Earth?

Yeah, so I guess you're asking a historical question,

which is always a good place to start thinking about life.

So there's a lot of ideas about how life started on Earth.

Probably the most popular is what's called the RNA world scenario.

So this idea is probably the 1 that you'll see most reported in the news, and is based on the idea that there are molecules in our bodies that relay genetic information.

We know those as DNA, obviously, but there's also sort of an intermediary called RNA, ribonucleic acid, that also plays the role of proteins.

And people came up with this idea in the 80s that maybe that was the first genetic material because it could play both roles of being genetic and performing catalysis.

And then somehow that idea got reduced to this idea that there was a molecule that emerged on early earth and underwent Darwinian evolution and that was the start of life.

So there's a lot of assumptions packed in there that we could unpack, but that's sort of the leading hypothesis.

There's also other ideas about life starting as metabolism, and so that's more connected to the geochemistry of early Earth, and it would be kind of more focused on this idea that you get some kind of catalytic cycle of molecules that can reproduce themselves and form some kind of metabolism.

And then life starts basically as self-organization and then you have to explain how evolution comes later.

Right, so that's the difference between sort of energy and genetic code.

So like energy and information, are those the 2 kind of

Yeah, I think that's a good way of putting it.

It's kind of funny, because I think most of the people that think about these things are really disciplinary biased.

So the people that tend to think about genetics come from a biology background and they're really evolution focused.

And so they're worried about where does the information come from and how does it change over time?

But they're talking about information in a really narrow way where they're talking about a genetic sequence.

And then most of the people that think about metabolism, origins of life scenarios tend to be people like physicists or geochemists that are worried about what are the energy sources and what, you know, like what kinds of organization can you get out of those energy sources?

about them for a little bit longer though?

So if we talk about the metabolism view of the origin of life, like where was the source of energy?

Probably the most popular view for where the original life happened on Earth is hydrothermal vents because they had sufficient energy.

And so we don't really know a lot about early Earth.

We have some ideas about when oceans first formed and things like that, but the time of the origin of life is kind of not well understood or pinned down and the conditions on Earth at that time are not well known.

But a lot of people do think that there was probably hydrothermal vents which are really hot, chemically active regions, say on the sea floor in modern times, which also would have been present on early Earth, and they would have provided energy and organics and basically all of the right conditions for the origins of life, which is 1 of the reasons that we look for these hydrothermal systems when we're talking about life elsewhere too.

Okay, and for the genetic code, The idea is that the RNA is the first, like why would RNA be the first moment you can say it's life?

I guess the idea is it could both have persistent information, and then it can also do some of the work of like what, creating a self-sustaining organism?

So the idea is you have in an RNA molecule, you have a sequence of characters, say, so you can treat it like a string in a computer, and it can be copied.

So information can be propagated, which is important for evolution because evolution happens by having inheritance of information.

So for example, you know, like my eyes are brown because my mother's eyes were brown.

But then you also have the ability to perform catalysis, which means that that RNA molecule is not inert in that environment, but it actually interacts with something and could potentially mediate, say, a metabolism that could then fuel the actual reproduction of that molecule.

So in some ways, people think that RNA gives you the most bang for your buck in a single molecule and therefore It gives you all the features that you might think are life.

And so this is sort of where this RNA world conjecture came from is because of those 2 properties.

Isn't it amazing that RNA came to be in general?

Okay, so we're not talking down about RNA.

Yeah, I think the issue, it's not even the RNA world is a problem.

And actually, if you really dig into it, the RNA world is not 1 hypothesis, it is a set of hypothesis, hypotheses, sorry.

And they range from a molecule of RNA spontaneously emerged on the early Earth and started evolving, which is kind of like the hardest RNA world scenario, which is the 1 I cited, and I get a little animated about because it seems so blatantly wrong to me, but that's a separate story.

And then the other 1 is actually something I agree with, which is that You can say there was an RNA world because RNA was the first genetic material for life on Earth.

So an RNA world could just be the earliest organisms that had genetics in a modern sense didn't have DNA evolved yet, they had RNA.

And so that's sort of a softer RNA world scenario in the sense that it doesn't mean it was the first thing that happened, but it was a thing that definitely was part of the lineage of events that led to us.

So if Life was like a best of album, it would be on the, it'd be 1 of the songs on there.

Did life, do you think, originate once, twice, 3 times on earth, multiple times?

I think that's a really difficult question.

And so there's some, so there's a lot of questions in that question.

So 1 of the first ones that I think needs to be addressed is, is the original life a continuous process on our planet?

So we think about the original life as something that happened on Earth, say, almost 4 billion years ago because we have evidence of life emerging very early on our planet.

And then an original life event, quote unquote, a singular event, whatever that was, happened.

And then all life on Earth that we know is a descendant of that particular event in our universe, right?

But we don't have any idea 1 way or the other if the origin of life is happening repeatedly and maybe it's just not taking off because life is already established.

That's a argument that people will make or maybe there are alternative forms of life on Earth that we don't even recognize.

So this is the idea of a shadow biosphere that there actually might just be completely other life on Earth, but it's so alien that we don't even know what it is.

I'm gonna have to talk to you about the shadow biosphere.

In a second, but first let me ask for the other alternative, which is panspermia.

So that's the idea, the hypothesis that life exists elsewhere in the universe and got to us through like an asteroid or planetoid or some, according to Wikipedia, space dust, whatever the heck that is.

We basically rode along whatever kind of rock and got to us.

Do you think that's at all a possibility?

So I think the reason that most original life scientists are interested in the original life on Earth and say not the original life on Mars and then panspermia, the exchange of life between planets being the explanation, is Once you start removing the original life from Earth, you know even less about it than you do if you study it on Earth.

Although, I think there are ways of reformulating the problem.

This is why I said earlier, like, oh, you mean the historical original life problem.

You don't mean the problem of how does life arise in the universe and what the universal principles are, because there's this historic problem, how did it happen on early Earth?

And there's a more tractable general problem of how does it happen?

And how does it happen is something we can actually ask in the lab.

How did it happen on early Earth is a much more detailed and nuanced question.

It requires detailed knowledge of what was happening on early Earth that we don't have.

And I'm personally more interested in general mechanisms.

So to me, it doesn't matter if it happened on Earth or it happened on Mars.

The question is, did it happen more than once in our universe?

And so the reason I don't find panspermia as a particularly – I think it's a fascinating hypothesis.

And I in particular think it's possible once you get to the stage of life where you have technology because then you obviously can spread out into the cosmos.

But it's also possible for microbes because we know that certain microorganisms can survive the journey in space and we, you know, they can live in a rock and go between Mars and Earth.

Like people have done experiments to try to prove that could work.

So in that scenario, it's super cool because then you get planetary exchange.

But say we go find, we go look for life on Mars and it ends up being exactly the same life we have on Earth biochemically speaking, then we haven't really discovered something new about the universe.

If we find, if all the life we ever find is the same original life event in the universe, it doesn't help me solve my problem.

a sign that you could separate the environment from the basic ingredients.

You can have like a life gun that you shoot throughout the universe.

And then like once you shoot it, it's like the Simpsons with a makeup gun.

When you shoot this life gun, it'll find the earth's, it'll like get sticky, it'll stick to the earth's.

And that kind of reduces the barrier of like the time it takes, the luck it takes to actually from nothing from the basic chemistry, from the basic physics of the universe for the life to spring up.

Yeah, I think this is actually super important to just think about like does life getting seated on a planet have to be geochemically compatible with that planet?

So you're suggesting we could just shoot guns in space and life could go to Mars and then it would just live there and be happy there.

So 1 of the things I was going to say in response to your question about whether the origin of life happened once or multiple times is for me personally right now in my thinking, although this changes on a weekly basis, but is that I think of life more as a planetary phenomena.

So I think the original life because life is so intimately tied to planetary cycles and planetary processes, and this goes all the way back through the history of our planet, that the original life itself grew out of geochemistry and became coupled and controlled geochemistry.

And when we start to talk about life existing on the planet is when we have evidence of life actually influencing properties of the planet.

And so if life is a planetary property, then going to Mars is not a trivial thing because you basically have to make Mars more Earth-like.

And so in some sense, like when I think about sort of long-term vision of humans in space, for example, really what you're talking about when you're saying, let's send our civilization to Mars is you're not saying let's send our civilization to Mars, you're saying let's reproduce our planet on Mars.

Like the information from our planet actually has to go to Mars and make Mars more Earth-like, which means that you're now having a reproduction process, like a cell reproduces itself to propagate information in the future.

Planets have to figure out how to reproduce their conditions, including geochemical conditions, on other planets in order to actually reproduce life in the universe, which is kind of a little bit radical, but I think for long-term sustainability of life on a planet, that's absolutely essential.

Okay, so if we were to think about life as a planetary phenomena, and so life on Mars would be best if it's way different than life on Earth, we have to ask the very basic question of what is life?

I actually don't think that's the right question to ask.

It took me a long time to get there, right?

Yeah, you cross it off your list, it's wrong.

I mean, I think it has an answer, But I think part of the problem is, you know, most of the places in science where we get really stuck is because we don't know what questions to ask.

so you can't answer a question if you're asking the wrong question.

And I think the way I think about it is obviously I'm interested in what life is.

So I'm being a little cheeky when I say that's the wrong question to ask.

That's exactly like the question that's like the core of my existence.

But I think the way of framing that is what is it about our universe that allows features that we associate life to be there.

And so really what I guess when I'm asking that question, what I'm after is an explanatory framework for what life is, right?

And so most people, they try to go in and define life and they say, well, life is, say, a self-reproducing chemical system capable of Darwinian evolution.

That's a very popular definition for life.

Or life is something that metabolizes and eats.

What I think about life is there are principles and laws that govern our universe that we don't understand yet that have something to do with how information interacts with the physical world.

I don't know exactly what I mean even when I say that because we don't know these rules.

But it's a little bit like, I like to use analogies.

You'll give me time to be like a little long-winded for a second even as I… But sort of like if you look at the history of physics, for example, this is like so we are in the period of the development of thought on our planet where we don't understand what we are yet, right?

There was a period of thought in the history of our planet where we didn't understand what gravity was.

And we didn't understand, for example, that the planets in the heavens, you know, were actually planets or that they operated by the same laws that we did.

And so there has been this sort of progression of getting a deeper understanding of explaining basic phenomena like, I'm not going to drop the cup, I'll drop the water bottle.

This is why I'm a theorist, not an experimentalist.

have, especially if I did the confidence smash.

Anyway, so if you take this view that there's sort of some missing principles, I associate them to information.

And what the sort of feeling there is, there's some missing explanatory framework for how our universe works.

And if we understood that physics, it would explain what we are.

It might also explain a lot of other features we don't associate to life.

And so it's a little like people accept the fact that gravity is a universal phenomena, but when we want to study gravity we study things like large-scale, you know, galactic structures or black holes or planets.

If we want to understand information and how it operates in the physical world, we study intelligent systems or living systems because they are the manifestation of that physics.

And the fact that we can't see that clearly yet or we don't have that explanatory framework, I think it's just because we haven't been thinking about the problem deeply enough.

But I feel like if you're explaining something, you're deriving it from some more fundamental property.

And of course, I have to say I'm wearing my physicist hat, so I have a huge bias of liking simple elegant explanations of the universe that really are compelling.

But I think 1 of the things that I've sort of maybe in some ways rejected my training as a physicist is that most of the elegant explanations that we have so far don't include us in the universe.

And I can't help but think there's something really special about what we are and there have to be some deep principles at play there.

And so that's sort of my perspective on it.

Now, when you ask me what life is, I have some ideas of what I think it is, but I think that we haven't gotten there yet because we haven't been able to see that structure.

And just to go back to the gravity example, it's a little like in ancient times they didn't know- I was talking about stars and heavens and things- they didn't know those were governed by the same principles as that darned experiment.

Once you realize, like Newton did, that heavenly motions and earthly motions are governed by the same principles and you unify terrestrial and celestial motion, you get these more powerful ideas.

And I think where life is is somehow unifying these abstract ideas of computation and information with the physical world, with matter.

And realizing that there's some explanatory framework that's not physics and it's not computation, but it's something that's deeper.

So answering the question of what is life requires deeply understanding something about the universe as information processing, universe as computation.

It's something about, Like would, once you come up with an answer to what is life, will the words information and computation be in the paragraph?

I know, I hate, actually I hate this about what I do because it's so hard to communicate, right?

With words, like when you have words that are ideas that have historically described 1 thing and you're trying to describe something people haven't seen yet and the words just don't fit.

So what's wrong, is it too ambiguous, the word information?

Yeah, no, I don't think it's binary either.

I use it, so the other way I might talk about it is the physics of causation, but I think that's worse because causation is even more loaded word than information.

And in some sense, I think the physics, so this is the really radical part.

Some sense like when I really think about it sort of most deeply, what I think life is is actually the physics of existence, what gets to exist and why.

And for simple elementary particles, that's not very complicated because the interactions are simple.

But for things like you and me and human civilizations, what comes next in the universe is really dependent on what came before.

And there's a huge space of possibilities of things that can exist.

And when I say information and causation, what I mean is why is it that cups evolved in the universe and not some other object that could deliver water and not spill it?

Maybe it wouldn't be a cup, but it's a huge – it's – you know, People talk about the space of things that could exist as being actually infinitely large, right?

I don't know if I believe in infinity, but I do think that there is something very interesting about the problem of what exists in its relationship to life.

So do you think the set of things that could exist is finite?

very large, but if we were to think about the physics of existence, like how many shapes of mugs can there be?

I should go to the math department for that.

I just mean, maybe another way to ask is, what do you think is fundamental to the universe and what is emergent?

So if existence, are we supposed to think of that as somehow fundamental, you think?

So there's a couple problems in physics that I think this is related to.

1 is, why does mathematics work at describing reality so well?

And then there is this problem of we don't understand why the laws of physics are the way they are, or why certain things get to exist, or what put in place the initial condition of our universe, right?

There's all of these sort of really deep and big problems, And they all indirectly are related, I think, to the same kind of thing that, you know, our physics is really good if you specify the initial condition at specifying a certain sequence of events, but it doesn't deal with the fact that other things could have happened, which is kind of an informational property, like a counterfactual property.

And it's not good at explaining this conversation right now.

It's just there are certain things that are outside the explanatory reach of current physics, and I think they require looking at it from a completely different direction.

And so I don't want to have to fine-tune the initial condition of the universe to specify precisely all the information in this conversation.

But that's sort of like how people wanna frame it when they're talking about, the standard model is sufficient if we had computing power to basically explain all of life in our existence.

An interesting thing you said is the way we think about information and computation is by observing a particular kind of systems on earth that exhibit something we think of as intelligence, but that's like looking at, I guess, the tip of an iceberg, and we should be really looking at the fundamentals of like the iceberg, like what makes water and ice and the chemistry that from which intelligence emerges

We can't just couple the information from the physics and I think that's what we've gotten really good at doing, especially with sort of the modern age where software is so abstracted from hardware.

But the entire process of biological evolution has basically been built, like been building layers of increasing abstraction.

And so it's really hard to see that physics in us, but it's much clearer to see it in molecules.

Yeah, but I guess I'm trying to figure out what do you think are the best tools to look at it?

I think if we solve that, we'll solve everything.

I'm saying an open mind because I think the biggest stumbling block to understanding sort of the things I've been trying to articulate or – and when I talk also with colleagues that are thinking deeply about these same issues is none of it is inconsistent with what we know.

It's just such a radically different perception of the way we understand things now that it's hard for people to get there.

And in some ways you have to almost forget what you've learned in order to learn something new, right?

So I feel like most of my career trying to understand the problem of life has been variously forgetting and then relearning things that I learned in physics.

And I think you have to have a capacity to learn things, but then accept that things that you learned might not be true, or might need refinement or reframing.

And the best way I can say that is just like with a physics education, there are just certain things you're told in undergrad that are like facts about the world.

And your physics professors never tell you that those facts actually emerge from a human mind, right?

So we're taught to think about, say, the laws of physics, for example, as this autonomous thing that exists outside of our universe and tells our universe how it works.

But the laws of physics were invented by human minds to describe things that are regularities in our everyday experience.

Right, so it's like turtles on top of turtles, but eventually it gets to the human mind and then you have to explain the human mind with the turtles.

So you have to, it comes from humans, this understanding, this simplification of the universe, these models.

There's a concept called cellular automata.

So there's some mysteries in these systems that are computational in nature that have maybe echoes of the kind of mysteries we should need to solve to understand what is life.

So If we could talk, take a computational view of things, do you think there's something compelling to reducing everything down to computation, like the universe is computation, and then trying to understand life?

So throw away the biology, throw away the chemistry, throw away even the physics that you learn undergrad and graduate school, and more look at these simple little systems, whether it's cellular automata or whatever the heck kind of computational systems that operate on simple local rules and then create complexity as they evolve.

Is it at all, do you think productive to focus on those kinds of systems to get an inkling of what is life?

And if it is, do you think it's possible to come up with some kind of laws and principles about what makes life in those computational systems?

I think they're good toy models, but mostly like where I've thought about them and used them is to actually, let's say, poke at sort of the current conceptual framework that we have and see where the flaws are.

So I think like the part that you're talking about that people find intriguing is that if you have like a fairly simple rule and you specify some initial condition and you run that rule on that initial condition, you could get really complex patterns emerging.

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Sara Walker: The Origin of Life on Earth and Alien Worlds | Lex Fridman Podcast #198