Not long before his death in 1996, Carl Sagan said that he had been “captured by the notion of extraterrestrial life” since childhood and that discovering it would be an “absolutely transforming event in human history.” Exactly because the prospect was so alluring, however, Sagan warned that we should be skeptical about believing reports of UFOs or alien encounters.
As he put it in the documentary “Cosmos,” “extraordinary claims require extraordinary evidence”—an idea now known as “the Sagan standard.”
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