I've never understood why the Fermi paradox is considered to be a paradox at all. Alien civilizations could be as common as dirt, and how would we be aware of them? For practical purposes, almost the entire galaxy might as well be infinitely distant. The mean distance of stars from earth, and therefore, planets, is on the order of thousands of light years. It takes extraordinary effort to transmit information even to the Voyager 1, which is now 0.0025 light years away, which is 1/1800 of the distance to the nearest star, and perhaps 1/2,000,000 of the distance to the average star in our galaxy. Even at the distance of the nearest star, our most powerful radio signals would be indistinguishable from the cosmic background radiation even if one knew what to look for! And conversely, essentially nothing an alien civilization broadcast would be visible to us. It's not just a question of tech--the signals would be far weaker than the background noise everywhere but a tiny bubble around a given planet.