"Sailors have their krakens and their sea serpents. **Physicists have white holes: cosmic creatures that straddle the line between tall tale and reality.** Yet to be seen in the wild, white holes may be only mathematical monsters. But new research suggests that, if a speculative theory called loop quantum gravity is right, white holes could be real—and we might have already observed them.

A white hole is, roughly speaking, the opposite of a black hole. “A black hole is a place where you can go in but you can never escape; a white hole is a place where you can leave but you can never go back,” says Caltech physicist Sean Carroll. **“****Otherwise, [both share] exactly the same mathematics, exactly the same geometry.”** That boils down to a few essential features: a singularity, where mass is squeezed into a point of infinite density, and an event horizon, the invisible “point of no return” first described mathematically by the German physicist Karl Schwarzschild in 1916. **For a black hole, the event horizon represents a one-way entrance; for a white hole, it’s exit-only.**"