Humans have often looked at the night sky and wondered if there’s anyone else out there. But stare into that darkness long enough, and many wonder instead: how did we get here? What were the odds, in a universe so enormous and chaotic, that humans should have come to exist at all? Is life, let alone intelligent life, such a wildly improbable occurrence that we’re the only ones here? Or are we an inevitable consequence of the laws of physics?
Life exists on Earth (assuming we’re not living in a computer simulation). Therefore, the universe must exist in such a way that we are possible. That’s the essence of the anthropic principle. On the one hand, it sounds tautological. By that, I mean, I’m just saying the same thing twice. But cast another way, it can lead us to important truths about the universe. It means any version of the universe we can fathom has to allow for life to exist at least once. When there are things we don’t understand about the universe — how dark energy works, how the cosmos formed — all our theories have to include the fact that we exist. The universe must allow us.
