How does the Great Filter attempt to explain the Fermi paradox?

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artist's conception of Kepler-186f — extraterrestrial intelligence An artist's conception depicts Kepler-186f, the first Earth-sized extrasolar planet found in its star's habitable zone.

The Great Filter is a hypothesis proposed by economist Robin Hanson to address the Fermi paradox, which highlights the contradiction between the high statistical probability of extraterrestrial intelligence and the complete lack of evidence for its existence.

The concept suggests that in the evolutionary chain from the formation of a habitable planet to the development of a space-faring, colonizing civilization, there exists at least one step that is exceedingly improbable or impossible to overcome. This "filter" acts as a barrier that prevents life from progressing to the stage of interstellar expansion.

If the filter occurs early in the evolutionary process—such as the emergence of life itself—it would imply that humanity is rare or unique. Conversely, if the filter occurs late in the process, it suggests that advanced civilizations may frequently destroy themselves through their own technology or other catastrophic events before they can colonize the galaxy. Ultimately, the Great Filter attempts to explain the "Great Silence" by positing that the emergence of a detectable, long-lived technological civilization is statistically rare.1