Richard Feynman explains why our night sky is dark despite trillions of stars
A black patch of sky looks empty until you stop taking it for granted. That is the starting point of a theory from Professor Richard Feynman, built around what sounds like a child’s question, why the night sky is dark. The usual answer feels obvious. The sun sets, Earth rotates, and night falls. That explains why it is not daytime. It does not explain why the sky itself turns black. For centuries, astronomers and philosophers worked from a set of assumptions that seemed reasonable enough. The universe, they thought, was infinite. It had existed forever. And stars were spread through it more or less everywhere, even if they clustered in galaxies. Put those ideas together, and the darkness overhead starts to look strange. The way into the problem is visual. Picture yourself in a forest so vast it never ends. In a small forest, you can look between trunks and catch glimpses of open sky. In an infinite one, every line of sight eventually hits a tree. Shift your gaze slightly, and you miss the …
