A white hole is a black hole in reverse. Instead of absorbing all matter, energy and light outside of it as a black hole does, a white hole emits matter, energy and light, and cannot be entered from the outside. Once thought to be an impossible cosmological object, Carlo Rovelli and others have brought white holes back into contention. Alon Retter reveals the mistake physicists often make about white holes, and argues white holes play a vital role in the origin of the universe.