Text 1: The 'Great Filter' hypothesis suggests that if advanced civilizations are common in the universe, we have not detected them because some developmental step—from simple life to interstellar expansion—is exceedingly difficult or impossible to clear. If the Filter lies in our past (e.g., the origin of life), we may be rare survivors; if it lies in our future (e.g., self-destruction), our prospects are grim. Text 2: Some astrobiologists argue that the Great Filter might not be a single event, but a series of subtle energy constraints. A civilization might reach a technological plateau where the energy required for interstellar travel is so vast that it is never economically or physically viable to leave their home system, even if they avoid self-destruction. This suggests that the 'silence' of the universe is a result of resource limitations rather than biological rarity or inevitable collapse.