Sara Walker: belief

Transcript context

…Can you explain assembly theory to me? I listened to Lee talk about it for many hours, and I understood nothing. No, I’m just kidding. I just wanted to take another… You’ve been already talking about it, but just what from a big picture view is the assembly theory way of thinking about our world, about our universe. Yeah. I think the first thing is the observation that life seems to be the only thing in the universe that builds complexity in the way that we see it here. And complexity is obviously a loaded term, so I’ll just use assembly instead because I think assembly is more precise. But the idea that all the things on your desk here from your computer, to the pen, to us sitting here don’t exist anywhere else in the universe as far as we know, they only exist on this planet and it took a long evolutionary history to get to us, is a real feature that we should take seriously as one that’s deeply embedded in the laws of physics and the structure of the universe that we live in. Standard physics would say that all of that complexity traces back to the infinitesimal deviations and the initial state of the universe that there was some order there. I find that deeply unsatisfactory. And what assembly theory says that’s very different is that, the universe is basically constructing itself, and when you get to these combinatorial spaces like chemistry, where the space of possibilities is too large to exhaust them all, you can only construct things along historically contingent paths, like you basically have causal chains of events that happen to allow other things to come into existence. And that this is the way that complex objects get formed, is basically on scaffolding on the past history of objects, making more complex objects, making more complex objects. That idea in itself is easy to state and simple, but it has some really radical implications as far as what you think is the nature of the physics that would describe life. And so what assembly theory does formally is try to measure the boundary in the space of all things that chemically could exist. For example, like all possible molecules, where’s the boundary above which we should say these things are too complex to happen outside of an evolutionary chain of events, outside of selection. And we formalize that with two observables. One of them is the copy number, the object. So… … is that with two observables. One of them is the copy number of the object. How many of the object did you observe? And the second one is what’s the minimal number of recursive steps to make it? If you start from elementary building blocks, like bonds for molecules, and you put them together, and then you take things you’ve made already and build up to the object, what’s the shortest number of steps you had to take? tary building blocks, like bonds for molecules, and you put them together, and then you take things you’ve made already and build up to the object, what’s the shortest number of steps you had to take? And what Lee’s been able to show in the lab with his team is that for organic chemistry, it’s about 15 steps. And then you only see molecules that the only molecules that we observe that are past that threshold are ones that are in life. And in fact, one of the things I’m trying to do with this idea of trying to actually quantify the origin of life as a transition in… A phase transition and assembly theory is actually be able to explain why that boundary is where because I think that’s actually the boundary that life must cross. The idea of going back to this thing we were talking about before about these structures that can reinforce their own existence and move past that boundary, 15 seems to be that boundary in chemical space. It’s not a universal number. It will be different for different assembly spaces, but that’s what we’ve experimentally validated so far. And then-…

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