Today, there is no point to arguing about the plurality of worlds, the notion of a cosmos populated by other inhabited worlds like the earth. The idea is as old as antiquity and contradicts the authority of the Greek philospher Aristotle, who limited the universe to one world, the earth. Through the telescope, the solar system's planets became worlds and places scholars could imagine harbor life, but planets in orbit around other stars were not discovered until 1992. Recent advancements in the precision of ground-based astronomy now put the number of extrasolar planets over 400. None of them, of course, is considered habitable, but now it is a lot easier to believe earthlike planets will be spotted.
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