It seems no less plausible that what spreads outward at a sizable fraction of lightspeed is a wave of "terraforming" agents, altering all planets in the neighborhood into more suitable colony planets. Meanwhile colonization spreads at a rate roughly bounded by the ratio of reproduction rate to death rate, which might well be significantly slower than that.
That scenario would be enough to ensure that if an intelligent species evolves, it is necessarily far from any spreading interstellar empire (since otherwise the terraforming agents would have destroyed it), without having to posit such a fast colonization wave.
That said, though, why assume that a colonization wave is astronomically detectable? Being detectable at this range with our instruments is surely an indication of wasting rather an enormous amount of energy that could instead be put to use by a sufficiently advanced technology, no?
That said, though, why assume that a colonization wave is astronomically detectable? Being detectable at this range with our instruments is surely an indication of wasting rather an enormous amount of energy that could instead be put to use by a sufficiently advanced technology, no?
Waste heat is one thing there's not much one can do about. Even a Dyson sphere will have it. In the case of Dyson spheres there have been active attempts to find them. See here although some other work suggests that Dyson spheres are just not that likely(pdf). Most largescal...
If it's worth saying, but not worth its own post, even in Discussion, it goes here.