I don't buy this argument. Let's pretend for a moment that there are currently 5-20 intelligent species in our galaxy, and everyone except us developed deep space ships and successfully colonized thousands of other planets (make up almost any numbers you want here; the results still hold).
What would our telescopes see? It seems like we would most likely see exactly what we see today.
The probability that one of those ships happened to fly anywhere close to our solar system, while we were looking, is still vanishingly small. Omnidirectional radio transmissions spread so quickly that they fall below the noise floor almost instantly over interstellar distances.
Space is really really really really big. We can see stars. We can just barely see some planets in a few very specific configurations. We can sometimes make coarse estimates of the chemical composition of those planets. And that's about it. We don't really know how to detect life on extrasolar planets. The ones we've already found could be teeming with life and we wouldn't know it.
What would our telescopes see? It seems like we would most likely see exactly what we see today.
The probability that one of those ships happened to fly anywhere close to our solar system, while we were looking, is still vanishingly small. Omnidirectional radio transmissions spread so quickly that they fall below the noise floor almost instantly over interstellar distances.
Space is really really really really big. We can see stars. We can just barely see some planets in a few very specific configurations. We can sometimes make coarse estimates of the chemical composition of those planets. And that's about it. We don't really know how to detect life on extrasolar planets. The ones we've already found could be teeming with life and we wouldn't know it.