Space & Cosmic Mysteries

Anything beyond Earth's atmosphere: astronomy, planets, dark matter, interstellar objects, signals from space and the search for life elsewhere. Not for sightings or craft in Earth's skies.

• 024024Codex case fileFermi ParadoxThe Fermi Paradox is the tension between the apparent likelihood of extraterrestrial civilizations and the absence of confirmed evidence for them.12 sourcesOpen →
• 061061Codex case fileZoo HypothesisThe zoo hypothesis proposes that advanced extraterrestrial civilizations exist but deliberately avoid contacting Earth, preserving humanity as an uncontacted…10 sourcesOpen →
• 060060Codex case fileGreat FilterThe Great Filter proposes that one or more extraordinarily unlikely transitions separate lifeless planets from durable, detectable civilizations.10 sourcesOpen →
• 066066Codex case fileRare Earth hypothesisThe Rare Earth hypothesis argues that complex life requires an unusually restrictive combination of astronomical, geological, and biological conditions, even if…10 sourcesOpen →
• 063063Codex case fileDark Forest theoryThe Dark Forest theory treats cosmic silence as self-protection: civilizations hide because an unknown neighbor might destroy them first.9 sourcesOpen →