Fermi Paradox + Great Filter.
hypothesisframeworkSETI & Technosignatures
The tension between a galaxy of hundreds of billions of stars and the total absence of detected ETI; the Great Filter is one proposed resolution.
Enrico Fermi's 1950 question 'Where is everybody?' contrasts the cosmic scale (200–400 billion Milky Way stars) with the lack of evidence for ETI. Robin Hanson's 1996 Great Filter proposes that at least one step from abiogenesis to interstellar civilization is highly improbable. Whether the filter is behind us (we are rare survivors) or ahead (self-destruction, e.g., AI/nuclear) is unresolved and speculative. Other resolutions include rarity of life, the zoo hypothesis, and short civilization lifespans.