Plato’s cave

The prisoners have been chained since childhood, facing a wall. Behind them a fire burns, and between the fire and their backs people carry objects along a walkway. The prisoners see only the shadows the objects cast, and hear only the echoes. So the shadows are their whole world. They name them, argue about them, get good at predicting which shadow comes next, and give out honours for it.

One prisoner is freed and dragged into daylight. It hurts. At first he can’t see anything. Then he sees reflections, then the objects themselves, and finally the sun. When he goes back to tell the others, his eyes haven’t readjusted to the dark. He’s worse at the shadow game, and they decide the trip has harmed him. Plato adds that if they could get their hands on him, they’d kill him.

Plato meant it as a story about education, and about the difference between opinion and knowledge. Read today, it sounds like a rendering pipeline. There’s a light source behind the viewer, and projected images that get mistaken for the objects. The people have never seen anything else, so they build a full science of the projection.

Two things carry over to a computed world. First, the prisoners aren’t irrational. Their science works, because it predicts shadows. A simulated physics would work in exactly that way. Second, the freed prisoner is worse off in the cave afterwards. Knowing what’s behind the projection gives you no edge inside it.

The cave is an early and influential version of the question this site asks, but not the earliest. The Bṛhadāraṇyaka Upaniṣad (4.3) was composed in India before the Buddha. It already describes the dreaming self making chariots, horses and roads where none exist. The cave is also honest about what an answer costs. The one who has seen the sun can’t prove it to the others. They’re the majority, and they’re hostile.