Re: Have aliens visited earth?
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Moreover the probability of a planet supporting life can be so small that even given the vast number of planets in the universe the expected number of planets supporting life can still be small. Say for example there the probability that planet supports life is 10^-15 and there are 10^9 planets in the universe. It doesn't matter how close these numbers are to the actual numbers the point is this: the expected number of planets supporting life is 10^-15 * 10^9 = 10^-6 = 1/1000000.
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actually I don't think this is right. it's
1 - [probability of life not existing on all 10^9 planets]
which is
1 - (99999999999999/100000000000000)^9
and my calculator can't seem to handle that business. I think it's smaller than your estimate though.
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