The cryptoterrestrial hypothesis proposes that reports of flying saucers or UFOs are evidence of a hidden, Earth-based, technologically-advanced civilization.[1][2]
Aaron John Gulyas, a scholar of conspiracy theories, characterized the so-called hypothesis as "really more of a thought experiment designed to raise questions", while others note that "even people open to [the cryptoterrestrial hypothesis] remain sceptical".[1][3] In 2024, authors in a philosophy journal described the cryptoterrestrial hypothesis as a suggestion that "sounds absolutely crazy".[3][4][5]