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The Drake Equation is designed to estimate the number of Planets possibly having intelligent life forms existing in our Galaxy. But I don't see how it's justified. As far as we know, Earth is the only planet with (intelligent) life forms existing on it, apart from Jupiter's moon Europa and Neptune which have oceans that may or may not contain life. I wonder what Dr Frank Drake set as the criteria to obtain the estimate value. Can I get help with that?

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Not really an physics or astronomy question it it? I mean, the factors are defined such the product give the desired answer and owning to ignorance most of the values were guesswork at the time. Since then we've learn more about some of the values but there are still large zones of ignorance an they lie in the factors that have little to do with physics (i.e. the ones concerning the odds of life evolving at all, of life evolving intelligence, of intelligence begetting technological civilization ...). –  dmckee May 27 '12 at 14:46
    
I'm going to close this as "off topic" for the moment. Arguments to the contrary are welcome. –  dmckee May 27 '12 at 14:47
    
Actually, such questions are not welcome in any other site, and I'm just curious to know. –  Graviton May 27 '12 at 15:16
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The equation is designed to show how much improbability one can tolerate. The number of planets is enormous, so even if we're "one in a million" or "one in a billion", there are lots of us. But if we're "one in a googol", then there aren't any more of us. We're probably closer to one in a million, not one in a googol, but nobody knows for sure. The issue is the uncertainties in out understanding of evolution of life, intelligence, and civilization, as dmckee says, not in physics. Agree with closing, but not with downvote. –  Ron Maimon May 27 '12 at 22:49
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closed as off topic by dmckee May 27 '12 at 14:48

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Well, the mathematical basis for the form of the equation is the rule of product.

Which factors are taken into account can certainly be disputed, i.e. there are certainly more complicated models and more correlations you could come up with. But the Drake equation lists a couple of reasonable yes/no requirements. Certainly, some variables are fairly hard to evaluate quantitatively, which makes it harder to dismiss it as a method for a guess.

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