Have We Already Been Visited by Aliens?

It’s often said that “extraordinary claims require extraordinary evidence.” The phrase was popularized by the astronomer Carl Sagan, who probably did as much as any scientist has done to promote the search for extraterrestrial life. By what’s sometimes referred to as the “Sagan standard,” Avi Loeb’s claim clearly falls short; the best evidence he marshals for his theory that ‘Oumuamua is an alien craft is that the alternative theories are unconvincing. Loeb, though, explicitly rejects the Sagan standard — “It is not obvious to me why extraordinary claims require extraordinary evidence,” he observes — and flips its logic on its head: “Extraordinary conservatism keeps us extraordinarily ignorant.” So long as there’s a chance that 1I/2017 U1 is an alien probe, we’d be fools not to pursue the idea. “If we acknowledge that ‘Oumuamua is plausibly of extraterrestrial-technology origin,” he writes, “whole new vistas of exploration for evidence and discovery open before us.”



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