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What are the chances that we will encounter some alien form of life as we explore the galaxy? If the argument about the timescale for the appearance of life on Earth is correct, there ought to be many other stars whose planets have life on them. Some of these stellar systems could have formed five billion years before the Earth—so why is the galaxy not crawling with self-designing mechanical or biological life forms? Why hasn’t the Earth been visited and even colonised? By the way, I discount suggestions that UFOs contain beings from outer space, as I think that any visits by aliens would be much more obvious—and probably also much more unpleasant.
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