Idea of the day
Why Is the Night Sky Dark? Olbers' Paradox, Explained
For four hundred years a dark night sky was one of the hardest puzzles in astronomy. You learn why that darkness is a real surprise, which simple fact about time explains it, and why the most common explanations fail. You also pick up a habit for testing claims: ask what you should already see if they were true.
Physics & Chemistry6 min read · 3 questions









