[lhorie]

Sure, but that doesn't really address the point. Suppose aliens got really lucky and managed to achieve interstellar travel in just 1 billion years since the big bang. That still leaves the entire area outside of a 12 billion light years radius from us invisible, i.e. they would have to be somewhere within that radius within the next 12 billion years, for us to be physically able to see them. But that radius is like less than 1% of the known universe.

And in actuality, they would need to sit there detectably within the narrow period of a few hundred years or so that humanity is actually looking at that spot in the sky. So, for example, if they were galaxy hopping every few million years rather than cancerously leaving dyson spheres everywhere, and just happened to temporarily brush into our radius of visibility during their nomadic travels, we wouldn't necessarily see them if they got within view too early or too late.