Sara Walker #3

You have an origin of life event. It evolves for 4 billion years, at least on our planet. It evolves a technosphere. The technologies themselves start having this property we call life, which is the phase we’re undergoing now. It solves the origin of itself and then it figures out how that process all works, understands how to make more life, and then can copy itself onto another planet so the whole structure can reproduce itself.

The following is a conversation with Sara Walker, her third time in this podcast. She is an astrobiologist and theoretical physicist interested in the origin of life and in discovering alien life on other worlds. She has written an amazing new upcoming book titled Life As No One Knows It, The Physics of Life’s Emergence. This book is coming out on August 6th, so please go pre-order it now. It will blow your mind. This is The Lex Fridman Podcast. To support it, please check out our sponsors in the description. And now, dear friends, here’s Sara Walker. Definition of life

You open the book, Life As No One Knows It: The Physics of Life’s Emergence, with the distinction between the materialists and the vitalists. So what’s the difference? Can you maybe define the two?

I think the question there is about whether life can be described in terms of matter and physical things, or whether there is some other feature that’s not physical that actually animates living things. So for a long time, people maybe have called that a soul. It’s been really hard to pin down what that is. So I think the vitalist idea is really that it’s a dualistic interpretation that there’s sort of the material properties, but there’s something else that animates life that is there when you’re alive and it’s not there when you’re dead. And materialists don’t think that there’s anything really special about the matter of life and the material substrates that life is made out of, so they disagree on some really fundamental points.

Is there a gray area between the two? Maybe all there is is matter, but there’s so much we don’t know that it might as well be magic. Whatever that magic that the vitalists see, meaning there’s just so much mystery that it’s really unfair to say that it’s boring and understood and as simple as “physics.”

Yeah, I think the entire universe is just a giant mystery. I guess that’s what motivates me as a scientist. And so oftentimes, when I look at open problems like the nature of life or consciousness or what is intelligence or are there souls or whatever question that we have that we feel like we aren’t even on the tip of answering yet, I think we have a lot more work to do to really understand the answers to these questions. So it’s not magic, it’s just the unknown. And I think a lot of the history of humans coming to understand the world around us has been taking ideas that we once thought were magic or supernatural and really understanding them in a much deeper way that we learn what those things are. And they still have an air of mystery even when we understand them. There’s no bottom to our understanding.

So do you think the vitalists have a point that they’re more eager and able to notice the magic of life?

I think that no tradition, vitalists included, is ever fully wrong about the nature of the things that they’re describing. So a lot of times when I look at different ways that people have described things across human history, across different cultures, there’s always a seed of truth in them. And I think it’s really important to try to look for those, because if there are narratives that humans have been telling ourselves for thousands of years, for thousands of generations, there must be some truth to them. We’ve been learning about reality for a really long time and we recognize the patterns that reality presents us. We don’t always understand what those patterns are, and so I think it’s really important to pay attention to that. So I don’t think the vitalists were actually wrong.

And a lot of what I talk about in the book, but also I think about a lot just professionally, is the nature of our definitions of what’s material and how science has come to invent the concept of matter. And that some of those things actually really are inventions that happened in a particular time in a particular technology that could learn about certain patterns and help us understand them, and that there are some patterns we still don’t understand. And if we knew how to measure those things or we knew how to describe them in a more rigorous way, we would realize that the material world matter has more properties than we thought that it did. One of those might be associated with the thing that we call life. Life could be a material property and still have a lot of the features that the vitalists thought were mysterious.

So we may still expand our understanding, what is incorporated in the category of matter, that will eventually incorporate such magical things that the vitalists have noticed, like life?

Yeah. I always like to use examples from physics, so I’ll probably do that. It’s my go-to place. But in the history of gravitational physics, for example, in the history of motion, when Aristotle came up with his theories of motion, he did it by the material properties he thought things had. So there was a concept of things falling to earth because they were solid-like and things raising to the heavens because they were air-like and things moving around the planet because they were celestial-like. But then we came to realize that, thousands of years later and after the invention of many technologies that allowed us to actually measure time in a mechanistic way and track planetary motion and we could roll balls down inclined planes and track that progress, we realized that if we just talked about mass and acceleration, we could unify all motion in the universe in a really simple description.

So we didn’t really have to worry about the fact that my cup is heavy and the air is light. The same laws describe them if we have the right material properties to talk about what those laws are actually interacting with. And so I think the issue with life is we don’t know how to think about information in a material way, and so we haven’t been able to build a unified description of what life is or the kind of things that evolution builds because we haven’t really invented the right material concept yet.

So when talking about motion, the laws of physics appear to be the same everywhere out in the universe. You think the same is true for other kinds of matter that we might eventually include life in?

I think life obeys universal principles. I think there is some deep underlying explanatory framework that will tell us about the nature of life in the universe and will allow us to identify life that we can’t yet recognize because it’s too different.

You’re right about the paradox of defining life. Why does it seem to be so easy and so complicated at the same time?

All the classic definitions people want to use just don’t work. They don’t work in all cases. So Carl Sagan had this wonderful essay on definitions of life where I think he talks about aliens coming from another planet. If they saw earth, they might think that cars were the dominant life form because there are so many of them on our planet. Humans are inside them, and you might want to exclude machines. But any definition, classic biology textbook definitions, would also include them. He wanted to draw a boundary between these kind of things by trying to exclude them, but they were naturally included by the definitions people want to give. And in fact, what he ended up pointing out is that all of the definitions of life that we have, whether it’s life is a self-reproducing system or life eats to survive or life requires compartments, whatever it is, there’s always a counterexample that challenges that definition. This is why viruses are so hard or why fire is so hard. And so we’ve had a really hard time trying to pin down from a definitional perspective exactly what life is.

Yeah, you actually bring up the zombie-ant fungus. I enjoyed looking at this thing as an example of one of the challenges. You mentioned viruses, but this is a parasite. Look at that.

Did you see this in the jungle?

Infects ants. Actually, one of the interesting things about the jungle, everything is ephemeral. Everything eats everything really quickly. So if an organism dies, that organism disappears. It’s a machine that doesn’t have… I wanted to say it doesn’t have a memory or a history, which is interesting given your work on history in defining a living being. The jungle forgets very quickly. It wants to erase the fact that you existed very quickly.

Yeah, but it can’t erase it. It’s just restructuring it. And I think the other thing that is really vivid to me about this example that you’re giving is how much death is necessary for life. So I worry a bit about notions of immortality and whether immortality is a good thing or not. So I have a broad conception that life is the only thing the universe generates that actually has even the potential to be immortal, but that’s as the sort of process that you’re describing where life is about memory and historical contingency and construction of new possibilities. But when you look at any instance of life, especially one as dynamic as what you’re describing, it’s a constant birth and death process. But that birth and death process is the way that the universe can explore what possibilities can exist. And not everything, not every possible human or every possible ant or every possible zombie ant or every possible tree, will ever live. So it’s an incredibly dynamic and creative place because of all that death.

This is a parasite that needs the ant. So is this a living thing or is this not a living thing?

Yeah.

It just pierces the ant.

Right.

And I’ve seen a lot of this, by the way. Organisms working together in the jungle, like ants protecting a delicious piece of fruit. They need the fruit, but if you touch that fruit, the forces emerge. They’re fighting you. They’re defending that fruit to the death. Nature seems to find mutual benefits, right?

Yeah, it does. I think the thing that’s perplexing for me about these kind of examples is effectively the ant’s dead, but it’s staying alive now because piloted by this fungus. And so that gets back to this thing that we’re talking about a few minutes ago about how the boundary of life is really hard to define. So anytime that you want to draw a boundary around something and you say, “This feature is the thing that makes this alive, or this thing is alive on its own,” there’s not ever really a clear boundary. And these kind of examples are really good at showing that because it’s like the thing that you would’ve thought is the living organism is now dead, except that it has another living organism that’s piloting it. So the two of them together are alive in some sense, but they’re now in this weird symbiotic relationship that’s taking this ant to its death.

So what do you do with that in terms of when you try to define life?

I think we have to get rid of the notion of an individual as being relevant. And this is really difficult because a lot of the ways that we think about life, like the fundamental unit of life is the cell, individuals are alive, but we don’t think about how gray that distinction is. So for example, you might consider self-reproduction to be the most defining feature of life. A lot of people do, actually. That’s one of these standard different definitions that a lot of people in my field like to use in astrobiology is life as a self-sustaining chemical system capable of Darwinian evolution, which I was once quoted as agreeing with, and I was really offended because I hate that definition. I think it’s terrible, and I think it’s terrible that people use it. I think every word in that definition is actually wrong as a descriptor of life.

Life is a self-sustaining chemical system capable of Darwinian evolution. Why is that? That seems like a pretty good definition.

I know. If you want to make me angry, you can pretend I said that and believed it.