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> We can never prove that aliens are not out there, only that they are. No, he's just saying if we don't find them by 2035 he owes the Internet coffee. Pretty

• AnimalMuppet 9y ago
  But the contrapositive is logically equivalent to the original statement. "If aliens exist, we'll have evidence by 2035" is logically equivalent to "If we don't have evidence by 2035, aliens don't exist". But it won't be taken that way. Now, I'm overstating the attention-grabbing headline to reflect a greater degree of certainty than Shostak genuinely believes. But he's stating it with more certainty than he genuinely believes, at least in the headline. If he really believed the headline, he'd say, "If we don't find them by 2035, I will believe that they don't exist" instead of "I will buy everyone coffee".