Quote:
Originally Posted by Van Rijn
Assuming we did somehow find lots of dead civilizations, even then it could be tricky finding a common cause for limited lifespan, because we would have to generalize between (probably) very different species. Conceivably there might be a common theme, or there might be a variety of themes, some species lasting longer than others, and some continuing on. Would we be one to continue on? Who knows?
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If there are a lot of dead civilisations out there, and they all died from different causes, then it simply becomes a matter of chance. And such chance disappearances begin to look a little improbable. Once a civilisation spreads to more than just a few stars, it is insulated from any localised disasters. The possibilty that a large number of interstellar civilisations have each been removed in turn by chance alone is difficult to explain.
I did at one time think that Gamma-Ray Bursters might sterilise whole volumes of a galaxy on a regular basis; but the current theory suggests that GRBs send out tightly focused beams of death, which are great for observing across the universe, but not so good for sterilising a galaxy.