Why the Universe Keeps the Lights Low

Imagine walking into a forest so dense that no matter which direction you look, your line of sight hits a tree trunk. Now, translate that to the night sky. Since the universe is home to trillions of stars, shouldn't every single point in the heavens be occupied by a shining beacon? If so, our midnight sky should be blazing with the collective, blinding light of a gazillion suns. Yet, we get a lovely, quiet velvet dark.

This cosmic puzzle is known to science enthusiasts as Olbers' Paradox. For centuries, stargazers wondered if the light was simply getting tired or blocked by space dust. But the real answer is far more poetic. The universe is not infinite in age, and it is actively stretching. Because the universe had a beginning, the light from the most distant stars simply hasn't had enough time to reach our eyes yet. They are still en route, traveling through the deep dark to meet us.

Furthermore, because space is expanding, the light waves traveling toward us get stretched out. By the time this ancient starlight reaches Earth, it has shifted out of the visible spectrum and into infrared. The universe, it turns out, is actually glowing, but it is doing so in a wavelength we cannot see with the naked eye. It keeps the nursery lights dimmed so we can get some sleep, while secretly bathing us in the invisible warmth of the cosmos.