The Filter Concept

Economist Robin Hanson proposed the Great Filter in 1996 to explain the Fermi Paradox. Somewhere between dead matter and galaxy-spanning civilizations, there must be an extremely improbable step — a filter that almost nothing gets through. If the galaxy should be full of civilizations but is not, something is stopping them.

The filter could be any of dozens of steps: the origin of life itself, the leap from simple to complex cells (eukaryotes), the development of multicellular life, the evolution of intelligence, or the development of technology.