[js1138]

Suppose we find a signal from 3000 or 10,000 light-years away. That would mean, absolutely, that there are other civilizations having at least some correspondence to out level of technology. That would also imply -- considering the rather freakish history of biology on our planet, influenced by our unusual moon and well-timed asteroid collisions -- that there are many habitable planets with no technological civilizations. That would be an invitation to explore and colonize.

Now assume that the civilization at the other end of the signal thinks the same way. Where are they. If habitable worlds are only hundres of light-years apart, then travel to them is a workable engineering task. One could easily envision an empire expanding at a reasonable fraction of the speed of light -- say one percent, or 0.1 percent. (You could reasonably assume that technology continues to advance, making energy and manufacturing available and easy.)

At any reasonable rate of expansion, one could assume we would have been visited, colonized or contacted. So where are they? Unless we are they?

[RadioAstronomer]

At any reasonable rate of expansion, one could assume we would have been visited, colonized or contacted. So where are they? Unless we are they?

What I was trying to get across is that the distances are so vast an ET civilization may be "stuck" within their solar system just like we are.