Great Filter

The Great Filter is a hypothetical explanation for why we haven't observed intelligent extraterrestrial life despite the vast universe. It suggests there may be a highly unlikely or difficult step in the development of life or civilization that prevents most life from advancing to detectable levels. This "filter" could occur at various stages, such as the emergence of life, developing intelligence, or surviving technological challenges. If the filter is behind us, it implies intelligent life is rare; if ahead, it suggests future civilizations face significant risks. Understanding the filter helps us grasp the rarity or commonality of advanced life in the universe.