Note: There's some equation which was solved by some smart scientists and a lot of guessing which suggests that there are about 20 intelligent alien civilazations in the universe.
1) There's still a
lot of guessing, making the error-bars quite huge
2) The equation itself actually limits itself to civilisations that we would communicate with via radio (which clearly the Avatar abrogines are not), as well as limiting itself to basically M-Class Planet life (which at least the Avatar world basically is), ignoring all the other possibilities that we could imagine, and doubtless many others that even the SF-community has no concept of.
3) I've never
ever seen any use of the Drake Equation suggestion anything like there being a mere 20 alien civilisations in the entire universe. (Except for the ones where values have been used that suggest none at all, making even
our existence unlikely!) Even "20 in our own galaxy" is a little on the low side. Wikipedia has Drake's original range of estimate of 1,000 to 100 million in our galaxy. Although its "worst case of values" scenario does tend drift towards zero (universe-wide), that's an extreme outlier. (The "Best of the best" scenario" says 180 million in our galaxy, if I read it correctly, but that's also an outlier.)
Life (even (or indeed especially!) of the restrictive type the Drake Equation predicts) wouldn't necessarily be evenly distributed, in the Universe (or Galaxy). Stars are clumped (in galaxies, when considering the universal scale!), and interstellar conditions vary across any given area in so many other ways. When considering (say) Alpha Centauri as a potential contemporary co-evolver of life, consider that it is a star(-system) of very similar age to ours ('only' 250 million years adrift, out of a few billion or so total life), and probably from the same star-birthing grounds (with the same intermix of basic elements from which to build planets and the chemical processes upon them), in an area of the galaxy that has certainly been free of catastrophic radiation surges from a nearby supernova, at any critical point in our (pre-)history, and even (possibly!) whether it had been subject to the same hail of intragalactic panspermia-propagating interstellar space-debris (
if that's got anything to do with how life arises). Being close to us means that it's got several good chances of having the same sort of pre-biological conditions and (if not panspermia-induced) elements to kick off with whatever form of abiogenesis might have arisen.
OTOH, the whole Centauri system is a lot more complicated than ours, but with it being an "AB-C" system (Alpha Centauris 'A' and 'B' being binary, with 'C'/Proxima also being relatively close), so whether a suitably
life-supporting rocky planet is even more doubtful than the possibility of such a planet having accreted.
Which is not to say it might not be possible, and life on binary-orbiting planets is frequently seen in fiction (everything from Tatooine, of Star Wars fame (a hand-waved, 'this is an exotic planet (of entirely one biome!)' filmic shortcut, at least in its original conception and prior to any retroactive attempts to justify) to the Helliconia series (by Brian Aldiss, who actively
employed the vagaries of having a planet in a long-period binary-system as a major story-arc plot-point, essentially, and in an attempt to run with a viable setting for this largely non-terrestrial storyline), and
some fiction gets these things right, even before the science is willing to stand up and counted on the same point. OTO(O!)H, there's a lot more rubbish (or bad misses) out there than that which is accurately prophetic of yet-to-be-confirmed scientific realities.
(i.e. I get your point about Avatar's planet, but you can't just point at Drake and use
that to discredit its existence.)
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Topic: Nitpicks that Ruined Movies (Read 137790 times)