> I don't think this is the _only_ sort of alien technology we should be
> looking for, but it's certainly a good scenario. List members tend to assume
I think it is exactly the right sort of alien technology to look for.
Only this kind of civilisation creates huge, durable artifacts/high-visibility signatures, and quickly at that. Such civilisations are extremely expansive (because they get selected for aggressive expansiveness while propagating across the cosmic Petri dish). To sum it up, they are highly expansive and highly visible. They would overrun any stagnant civilisation. There cannot be any long-term stable stagnant civilisation, because it either dies out (either from intrinsic reasons (which?!) or external events: asteroid impact, vicinal supernovae & GRBs) or explodes into a supertechnology culture. A civilisation below nanotechnology level is essentially incapable of interstellar travel. I don't consider >10^4 year journeys in vast ecology bubbles to be interstellar travels.
> that "exotic" ventures like interstellar colonization will necessarily rely
> on all kinds of fancy nanotech, but don't forget that the idea of traveling
It's not fancy, it's simply economical.
> to other stars isn't as exotic as it used to be, in a way. If our history
> had gone just slightly differently (and I'm not refeering to our space
> program, but to world history in general) we might have already sent out
> craft using ramjet and ion proulsion.
> While the nano-alien scenario is intriguing, I'm not ready to say we've never
> been visited just because we don't see any evidence of this specific kind of
I'm really at a loss why we are here at all. From what (little) we know, life nucleation events are not that rare. Evolution is nonlinear, yet coevolutionary factors favour intelligence emergence.