If the universe is infinite and filled with stars, why isn’t the night sky lit up like a Vegas strip? That’s the brain-teaser at the heart of Olbers's Paradox, named after 19th-century astronomer Heinrich Olbers. His midnight musings asked why the dark expanse above us isn’t wall-to-wall starlight.

The answer? Space isn’t just vast—it’s busy. Expanding galaxies, light-dimming dust clouds, and the fact that some stars are so far away that their light hasn’t even reached us yet—thanks, speed of light! And don’t forget the big one: the universe had a starting point, the Big Bang, meaning there hasn’t been infinite time for light from every star to fill the sky. Even the cosmic microwave background radiation, the faint afterglow of the Big Bang, has cooled to near invisibility.