Wednesday, February 25, 2009

Do multiple Earths equate to multiple civilizations?

If [the planets] be inhabited, what a scope for folly; if they be not inhabited, what a waste of space. -- Thomas Carlyle

This is exciting and all, to think that there may be other Earths in the millions out there someplace. Yet I think most of the analysis of this possibility is incomplete.

In order for life as we now know it to arise, there need to be certain conditions. A moderate sized yellow sun, for one: a small red sun would grip a planet in tidal lock, and a giant white or blue sun wouldn't live long enough for life to evolve. A small rocky planet with liquid water at or near the surface--although extremophiliac life might exist under harsher conditions. And then possibly a disproportionately large satellite along with tides, oxygen and or carbon dioxide in the atmosphere, and etc.

And then life has to evolve, onwards from unicellular and acellular life, into multicellular life of increasing complexity and sophistication. There is probably nothing automatic about this. Fast, torpedo-shaped sea creatures have evolved any number of times: ichthysaurs, tuna, marlins, orcas, but sentient primates with binocular vision and opposable thumbs have come along very rarely. Indeed, we seem to be the last of only a handful of such creatures ever to arise.

Most analyses I've seen stop here, but it seems to me that there are further improbabilities to be overcome. The rise of intelligent life doesn't mean the rise of civilization, or even technology. What if intelligent life on another world never got beyond the hunter/gatherer stage, or the agricultural stage. What if the industrial revolution never happened? Or more frustratingly, what if the aliens were like certain civilizations here, which did not lack knowhow, but did lack curiosity.

Of course, it could be that Earth is the exception, and that advanced technological civilizations are the rule elsewhere in the cosmos. But given the chain of improbabilities that have led from the primordial scum to our present state, it's fairly easy to to doubt that anyone Out There is listening to our call.

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