great-filter

If the galaxy has 100 billion stars and is 13.8 billion years old, where is everyone? Eleven serious answers to the Fermi Paradox.

The Milky Way holds 200 to 400 billion stars and we have found no sign of another civilization. The Great Filter proposes that one step on the road from chemistry to spacefaring is almost impossible, and we do not know whether we have already passed it.