Ard: I wanted to ask you something else. You wrote, ‘We have a compelling need to lend form to the universe without destroying its mystery.’ Do you think we can destroy its mystery by science?

SG: No. I think that science only… well, again we’re talking about that religious… I think we’re talking about the same thing: that sentiment of wonder, and awe, and terror. And I think, for me, one of the greatest moments of making peace with science was to realise that rather than taking away the mystery, it added to the mystery, only in the sense of that experience.

I’m calling mystery the sense of that experience, not a lack of clarity about what’s going on. But when you understand something, in all its clarity, that adds to the experience. Maybe I shouldn’t call it mystery.

Ard: No, I think that people sort of think that mystery is only about things we don’t understand. In fact, religious people sometimes think that in order for them to have God in science, they have to have bits they don’t understand, but I think that’s just the wrong way of thinking about it.

I think part of what makes science so beautiful, or that sense of the beauty of science being close to the sense of terror, is that you do see something more clearly and it’s very beautiful, but it seems to point to something beyond itself, and that’s what generates that sense of being at a precipice, where you think it’s beautiful, but it’s also actually making the mystery more. There’s more of a mystery rather than less of a mystery, even though…

SG: It intensifies the mystery.

Ard: It intensifies the mystery, even though you understand it better. And that sounds a bit fluffy, but…

David: No! Surely not, Ard!

Ard: I was accusing him of being fluffy.

David: All the time!

Ard: But I think if as a scientist you have that experience, and you do understand something, actually it intensifies the mystery.

David: Why did you say ‘I made peace with science’? When did you have to make peace with it? What do you mean?

SG: Well, I suppose… I don't know. I never thought I’d say that, but…

David: Well, you did.

SG: .You made me say it; or it came out. So what does that mean? Maybe at some point I was a bit suspicious of science. I thought, maybe, it would take away from my appreciation of the universe.

David: The sort of picking-the-butterfly-apart effect.

SG: Yes, exactly. So while I was fascinated by what I was learning, perhaps part of me feared that once it was all explained, it would get rather dull.

So it was hugely reassuring to me that when I understood something, that it actually created in me the same sentiments, the same emotions emerged as when I didn’t fully understand something and simply wanted to take delight in it.

It gave me a better understanding of what mystery – which I think is a very basic emotion, almost – was actually all about. So that must be why I said ‘I made peace with science.’

David: Is mystery aligned with meaning? With thinking this means something? That it makes sense of it?

SG: Well I suppose what I think we’re both trying to say is that there is no contradiction between making sense of it… between finding meaning and preserving mystery.

Ard: It reminds me of a quote by Henri Poincaré, a very famous French mathematical physicist, who says, ‘A scientist does not just only study science because it’s useful; he studies it because it’s beautiful. And if nature were not beautiful, it would not be worth studying, and life would not be worth living.’

It’s very French. But I think there’s something about ‘you study it because it’s beautiful’. And if it weren’t beautiful it wouldn’t be worth doing.

David: Yes. And you’ve already defined beauty as being, at least in part, that sense of it pointing forwards, beyond itself, as you would say. So that when we say nature has to be beautiful, and if it wasn’t I wouldn’t study it, it’s another way of saying, if it wasn’t always expanding, pointing to new things that it might generate. Because I think, sometimes, and maybe it’s us in the media, the popularisers, we give this impression that there’s a big mystery. But don’t worry, there’s an army of people in white coats who are clearing up the mystery, like clearing up the knick-knacks in a room. And before you know it, it’ll all be squared away like a Prussian dining room and…

SG: That’s a particular aspect of science, and what scientists do, practitioners of science do. But then there is also the exhilarating part of understanding the universe, which, for me, is what drew me to science.

David: A friend of mine’s a mathematician, Greg Chaitin. He described, I think, what you’re talking about. He said, for him, he would have small ideas: just a small idea, like sitting on your chair. Then, he said, he had certain huge ideas, and for him it was like climbing up a mountain. And the exciting thing was not just getting to the top of the mountain, but from there he could see a whole range of mountains out in the distance, which he hadn’t been to, obviously, but suddenly he realised they were there. Is that the same sort of thing?

SG: Yes. For me that’s definitely how it works. A lot of my work is built on an idea and a model that I came up with 20 years ago. And I remember that moment of watching it do something I didn’t expect it to do, which is on a computer screen. I’d written down some simple equations, and I expected it to behave in a particular way, and it didn’t. And it showed me something that then became the basis of pretty much what I do in science.

David: How did it feel?

SG: It felt amazing! It really did. And this was in the day when you could actually watch the computer simulation happening, because computers were very slow 20 years ago, and so I did actually watch this simulation.

David: So what were you actually seeing? I’m just fascinated.

SG: I wanted to see how populations of pathogens would evolve under selection from host immunity: by host, I mean us. So when a malaria parasite enters my body, I will, of course, mount immune responses to this parasite. So parasite populations evolve under this selection pressure. What’s interesting about a lot of parasite populations is that they seem to exist as these, sort of, discrete tribes ‒ different strains ‒ and this is the mystery, because there’s no reason why they should be doing that.

And what this model showed me is how, under selection pressure from host immunity, these populations would self-organise into these discrete tribes, simply in order to avoid competing with each other.

David: And nobody knew that before?

SG: Nobody had done that before.

David: And it’s not what you were expecting?

SG: No, it wasn’t. I thought they’d be a big mush, and that we’d have to think of ways in which we’d have to impose structure. So, at a fundamental level, I was setting something up where I expected there to be huge mush, and then we’d have to come up with ways to impose structure, and instead the structure emerged on its own. So that was fun; that was great.

Ard: That’s amazing.

SG: It was quite a moment.

Ard: It must have been amazing to see.

SG: It was. And so what I’ve been doing since then is trying to validate that. So I’m interested, obviously, in whether this is truth, in the sense of being a useful metaphor, or a useful framework for understanding what happens in infectious diseases, because it does have practical implications.

So that’s what I’ve been doing for the last 20 years: trying to validate that theory.