What is Olbers’ paradox?

Modern theories of the universe begin with the simplest of observations — that the night sky looks dark. This darkness implies that the universe is not infinitely old, as scientists once thought. If it were, starlight would already have seeped into all corners of space, thus giving a hot and uniform glow across the sky. This insight is known as Olbers’ paradox, after the 19th century German astronomer Welhelm Olbers.