Why is the Night Sky Dark?
via PopSci
The question barely makes sense the first time you hear it. “It’s like asking why is water wet,” says Will Kinney, a cosmologist at the University at Buffalo, currently on sabbatical at Stockholm University in Sweden. But for centuries the darkness of the night sky had astronomers stumped. They called the puzzle Olber’s Paradox.
Distant stars look weak, and very distant stars shine too dimly for you to see with your eyes. But when space telescopes like Hubble peer deep into the darkest spots of sky, they uncover bunches of incredibly faint galaxies. And the deeper they look, the more they find. If the universe went on forever with stars sprinkled evenly throughout—as many early stargazers assumed—the night sky would be full of so many points of light that it would never look dark.