I never bought the theory that, as in the flying saucer movies of the 1950s-1960s the gentle space aliens were coming here because they were alarmed about nuclear bombs.
I believe they (or the empty ufos which make dead stops, move in one direction, then another, then shoot out of sight——which would splatter any living creature pilot like a raw egg) are merely waiting for the smartphones, video game addictions, ipads, notebooks, laptops and social networking to set up humanity to be replaced someday soon. AI could travel from one solar system to another using wormhole networks.
Very interesting hypothesis: That AI on other planet(s) is or are waiting for the framework to be established so that the AI can occupy this planet next.
VERY interesting hypothesis.