David: Plato's Cave. The philosophers and scientists love telling us about Plato's Cave.

BO: Why? It's such a great, great story.

Ard: Do you want to tell us that story?

BO: Well there are many sides to the story. I want to know why they like the story first.

David: Well it's this sense that people like Roger Penrose particularly, or Greg Chaitin, the mathematicians, they say, ‘Look, there are the truths, there are things which are just absolutely true. Just because we can't see them, doesn't mean they're not there. We've just got to not get fooled by thinking that there’s just the flickering images we're seeing on the wall. That is to limit your imagination.’ And that's why they tell it.

BO: Shall I tell the story? Okay. My telling of the story is, of course, going to be imperfect. I think every storyteller… It's the beauty of story that we bend it a little bit in accordance with how we’re perceiving the world in that particular moment.

Anyway, these people have been in this cave. Let's think of them as prisoners, or they they've been in this cave for a while. The light comes from behind them, and they're in this cave in such a way that they can only see in the cave and see the images passing by on the cave wall.

And one of the things that I think people have taken from it is a great question of illusion and reality. The things that we're seeing, that they're seeing on the cave wall, is that truth? That's what you're saying. Or is that which creates the shadows, is that truth?

David: And what do you think of it? What does it say to you?

BO: I think it's one of the greatest stories, and it's a story rich with truth. It's one of those stories incredibly soaked in the truth of life, because that's what we do: we're constantly looking at things and taking them for absolutes. I think the story is one of the great… it is an allegory. It is an allegory of knowledge, but I think it's also an allegory of perception. And I think it's also an allegory of ultimate truths. And I think this allegory tells us that, actually, we can't know ultimate truth. We, in our mortal condition, at best can deduce what that is like from what we're seeing on the cave walls.

David: Yeah, that's what science says it does.

BO: If we were to turn round and walk out into what is creating that reality – what's creating the shadows on the wall – we now have to leave all of the orders of knowledge as we know it and enter into the orders of enlightenment of higher kinds of spiritual ecstasy, visionary states: things that don't belong to the conversation of science. And yet, at the same time, how is it strange that some of the great scientists were visionaries themselves?

Ard: And do you think in Plato's Cave we're looking at these shadows, and so that's all we see, and they can be distorted? Do you think that people find that sometimes a frightening thought? That all they are seeing are the shadows? Or do you think that people, maybe, sometimes also think that the shadows are all that there is?

BO: I think we have come to think that that is all there is. And I think atheism, at its worst, tells us that that is all there is, because you can see it. I mean, one of the great arguments of atheism keeps coming back to: ‘I can't see it. There's no evidence for it. I can't touch it.’ It goes back to evidence, and once we start to deal only with evidence, we're talking about shadows on the wall. We can see them; we can't see what's causing it. We can't deal with the source of the images on the wall. Evidence ends up being its own limitation.