What is life, really? Despite scientific progress, we still don’t really know.
Lee Cronin, a professor of chemistry at the University of Glasgow, explains that there is a significant disconnect between the physics of the universe and the biological processes we observe. This discrepancy makes it difficult to understand how inanimate matter evolves into living, breathing, thinking forms.
The solution? Cronin proposes assembly theory, which involves using large-scale complexity to assemble all the components that work together to create adaptable life. Assembly theory suggests that life emerges through two key processes: copying and existing. These two simple words, Cronin explains, are the essential essences of life as we know it.
Thanks to Cronin, this theory has been put into practice by NASA in its search for life on other planets. Together, we are getting closer to understanding the mystery of life: how it began, what it looks like, and how it might evolve.
Lee Cronin: We don’t know what life is, which is an insane situation right now. We still don’t know what life is, even life on Earth. There’s a gap in current physics as we define it, or in current physics as we think of it, as some kind of timeless universe. The universe unfolds kind of like a mechanical music box, where you play music and it all happens, right? And you can go backwards and forwards. And that doesn’t really explain how life started or the novelty and openness of biology.
On the other hand, biology does all sorts of crazy things. New species are invented all the time, humans are developing new technologies, new cultures, new add-ons, new memes. We have a huge gap between the physics of the universe, what we understand to be the physics of the universe, and what happens in evolution. The fact that evolution exists in the physical universe and is defined by the same reality or rules means that there may be a space to figure out how to bridge the gap between physics and biology.
My name is Lee Cronin. I’m a professor of chemistry at the University of Glasgow and I do research, exploring everything that’s going on in the universe that has to do with chemistry, the origin of life and the creation of life. There are two strange universes: the universe of physics, where we understand the Standard Model, gravity, time and quantum mechanics, from the Big Bang to the formation of stars. Then we have the evolution of biology that happened on Earth, about 4 billion years ago. Since then, there’s been innovation, right up to the technology that humans have produced.
I noticed an interesting problem: the physics of the Universe doesn’t really predict the emergence of biology and doesn’t really explain why biology started to evolve. Although we have Darwin’s theory of evolution, and in fact, Darwin did a fantastic job of understanding the slow variation that occurs, there hasn’t been a moment to bridge the gap between physics and biology in one leap. What “assembly theory” does is it actually allows us to explain how inanimate matter becomes evolutionary and how we can literally turn sand into cells through the process of selection.
What does life actually do? To put it very succinctly, life creates complicated things on a large scale. I can give you a simple example: take a weird object, like an iPhone. If you went to Mars and found a single iPhone, you might be curious, maybe it was a random event. But if you find two iPhones, three, ten, a hundred, and they all work, you can start to be more and more confident that these iPhones were produced by a technological process connected to a living system. That’s basically what assembly is all about – this ability to generate complexity on a large scale, across a large number of different things.
As a chemist, I think about molecules all the time. A molecule is a series of atoms connected by things called bonds. When I developed the idea of the “assembly index” and applied it to molecules, I imagined that I could take a molecule, cut out different atoms, and keep cutting and cutting until all that was left was atoms. Let’s say I had a molecule made up of carbon, nitrogen, and oxygen. I would simply cut all of these things out, and at the bottom of my tree I would be left with a base, where I would have carbon, nitrogen, and oxygen atoms. To get the molecule back, I would put them together in the right sequence to form the molecule. The assembly index is simply a matter of taking a molecule and cutting it up: what is the minimum number of cuts I need to make to turn this molecule 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 that drove me to develop assembly theory in the early days was to help NASA try to see if we could find life elsewhere in the solar system. NASA wanted to understand assembly theory and the assembly index as a universal marker of biology. I wanted to challenge the current approach that NASA was taking, which is very Earth-centric. They were looking for molecules that we would find on Earth in biology, and I think that’s fundamentally wrong. Molecules on Earth are not necessarily universal signatures of life, but complexity is. When I started to convince NASA of that, they started to get involved and said, “Okay, we’re going to give you samples of meteorites, from different places in the universe, so that we can really map not only Earth but parts of space.” Right now, the only place we know there is life in the universe is Earth. We want to compare life on Earth using this technique, and then go further and see if we can find life on Mars and in the outer solar system.
Can I explain how matter became life? Yes, from rocks to dinosaurs is one, yes. The assembly theory challenges the idea that life is completely impossible because it explains how rocks, step by step, as they assemble, undergo selection and produce complexity, step by step by step. It’s something that we are able to quantify very carefully. The environment on planet Earth that gave rise to life created the chemistry and the environment; the cooking began. There is only one thing that is key to the origin of life, and life in the Universe, and that is one word: existence. For an object to exist, it must outlive its natural life. This process of copying an existence to defy the law of erasure is how life begins to emerge. It is the battle to emerge from the maelstrom of chance and persist, and it is so simple. It’s like the simplest observation: copy and exist. That’s all life is. Life is an extremely fragile chemistry that has found a way to copy itself and continue to exist. We living beings are the oldest artifacts on Earth, older even than some rocks, because we are able to copy ourselves and continue to exist, which is very interesting. So it’s just existence and copying, these two things that give you biology.