Groundbreaking chemist defines all of life in 2 words | Lee Cronin

• We don't know what life is—which is a crazy place to be right now. We still do not know what life is, even life on Earth. There's a gap in the current physics as defined, or current physics as we think about it, as this kind of timeless universe. The Universe kind of unfolds a bit like a clockwork music box, where you play the music and it would just happen, right? And you could go backwards and then go forwards.

And that doesn't really explain adequately how life got started or the novelty and open-endedness of biology, and in contrast, biology, which is doing all sorts of crazy things. New species are being invented all the time; where human beings are developing new technologies, new culture, or add-ons, new memes. That we have this massive disconnect between the physics of the Universe, and what we understand is the physics of the Universe, and what's happening in evolution.

And the fact that evolution exists in the physical universe and is defined by the same reality or rules, if you like, means that maybe there is a space for understanding how we bridge the gap between physics and biology. My name is Lee Cronin. I am the Regis Professor of Chemistry at the University of Glasgow, and I'm doing research, exploring all things in the Universe to do with chemistry, origin of life, and the creation of life.

Well, so, there's kind of two weird universes: there's the physics universe, where we understand the standard model, and gravity and time and quantum mechanics, from the Big Bang to the formation of the stars. But then we've got the evolution of biology that occurred on Earth, starting about 4 billion years ago. And since the 4 billion years, there's been innovation, going right up to the technology produced by humans.

I noticed an interesting problem that the physics of the Universe does not really predict the emergence of biology and doesn't really explain why biology started to evolve. Although we have the Theory of Evolution that was put forward by Darwin, and actually, Darwin did a fantastic job at understanding slow variation that occurs, there was no kind of moment to bridge the gap from physics to biology in one leap.

What 'Assembly Theory' does, it actually allows us to explain how inanimate matter becomes evolutionary, and literally how we can turn sand into cells by the process of selection. What does life actually do? And put very succinctly, life creates complicated things at scale. And I can give you a really simple example, like just take an outlandish one, like an iPhone.

If you went to Mars and you found a single iPhone, you might be kind of curious, maybe it was a random event. But if you find two iPhones, find three, find 10, find 100, and they all work, you can start to be increasingly sure that those iPhones were produced by a technological process connected to a living system. And so that's really, in a nutshell, what assembling encapsulates—this ability to generate complexity at scale, over a lot of different things.

As a chemist, I think about molecules all the time. And a molecule is a series of atoms connected by things called bonds. So, when I was developing the idea of 'Assembly Index' and applying it to molecules, I imagined that I could take a molecule, just cut off different atoms, and keep cutting and cutting and cutting, 'til there's nothing left but atoms. So, say if I've got a molecule that's made up out of carbon, nitrogen and oxygen, I would just cut all those off, and at the bottom of my tree, I would be left with a base where I had carbon atoms, nitrogen atoms, and oxygen atoms.

And then to recover the molecule, I'd put 'em together in the right sequence to the molecule. And so the Assembly Index is just, take a molecule and I'd chop it up: what is the minimum number of chops I need to make to turn that molecule back into its building blocks? The Assembly Index is literally a measure of the minimum amount of information required to make that molecule.

One of the motivations for developing Assembly Theory at the beginning was to help NASA try and see if we could find life elsewhere in the solar system. What NASA wanted to do was understand Assembly Theory and the Assembly Index as a universal marker for biology. I wanted to challenge the current approach taken by NASA, which is very Earth-centrist. They were looking for molecules we would find on Earth in biology, and I think that's fundamentally wrong.

The molecules on Earth aren't necessarily universal living signatures—but complexity is. And so when I started to convince NASA of this, this is when they started to get involved and say, "Okay, we're gonna give you samples from meteorites, from different places in the Universe, so we could use this to really map not just Earth, but also parts of outer space." Because, right now, the only place where we know there is life in the Universe is on Earth. So, what we wanna do is benchmark life on Earth using this technique and then go further out and see if we can then find life on Mars and in the outer solar system.

Can I explain how matter became life? Yeah, rocks to dinosaurs is one, yep. Assembly Theory challenges the notion that life is vastly impossible because Assembly Theory explains how rocks, step-by-step, by grinding together, undergo selection and produce complexity, step-by-step-by-step. And this is something that really, we're being able to quantify very carefully.

And so, the environment on planet Earth at the origin of life created the chemistry and the environment; the cooking started. And really, there's only one thing that is the key to the origin of life and life in the Universe, and that is one word: existence. For an object to exist, it has to survive for a longer time than its natural life.

This process of copying an existence to defy the law of being erased is how life starts to emerge. It is the battle to emerge from the maelstrom of randomness and persist, and it's so simple. It's like the simplest observation ever: copying and existence. That's all life is. Life is extremely fragile chemistry that has found a way to copy itself to continue to exist.

And we are, as living things, the oldest artifacts on Earth, even older than some of the rocks, because we are able to copy ourselves and keep going, which is so interesting. And so it's just existence and copying—those two things give you biology.