In Plato’s Republic, written around 380 BC, he describes a group of prisoners who have been chained inside a cave since birth. They cannot turn their heads. Behind them, a fire burns. Between the fire and the prisoners, people carry objects — figures, animals, shapes — and their shadows are cast onto the wall in front of the prisoners. The prisoners have never seen anything else. So naturally, they believe the shadows are real. This is their world. This is their truth. The shadows have names. The prisoners have opinions about them. Some are even considered experts in reading the shadows. One day, a prisoner is freed. He turns around. The fire blinds him. Slowly, painfully, his eyes adjust. He is dragged out of the cave into the sunlight. At first he can only look at reflections in water — the direct light is too much. Gradually he sees trees, people, the sky. Finally, he is able to look at the sun itself —...