Filter Theory

In xenology, a class of theories regarding the Fermi Paradox which states some mechanism or mechanisms ("filters") exist which prevent dead matter from giving rise to spacefaring civilizations whose effects on the universe could be observed.

During the Second Interstellar Period scientists learned they had been too optimistic about the detectability of alien civilizations across cosmic distances, partially explaining some of the mystery which filter theory tries to answer, but the relative paucity of intelligence compared to other forms of life, the lack of extant star-god civilizations with eons of history, and evidence of technological species slipping into extinction lend it enduring weight.