Even if there is an advanced alien civilization in our galaxy they could be as much as 100,000 light years away from us, which means any alien asronomer zooming in on our planet would not find any sign of intelligent and complex society here on earth. At best they would see cavemen which are indestiguishable from other mammals on this planet. That would be a best case scenario. There may not be any other life in our Milky Way, but let's say there is some life, intelligent at that, in a galaxy far far away, 2 million light years away, or 50 million light years away, or a billion light years away. How would any civilization living there right now would even be capable of knowing that on our small rock across the universe there's us, waiting to be discovered? They wouldn't know. They would be seeing the version of earth accessible to them, which is the version that earth was millions or billions of years ago. They just wouldn't know.,(reply>), has the same idea. Maybe distance keeps us from hearing or seeing one another. Because of the great distances and the shift in ages or time periods of the respective planet in regards to the others planet.