This is just a bunch of idle speculation. We can't speculate on the motives of aliens at all. Look at how hard it is to discern the motives of other humans, an

This is just a bunch of idle speculation. We can't speculate on the motives of aliens at all. Look at how hard it is to discern the motives of other humans, and now tell me you're going to discern the motives of something biologically completely unlike us? You can't assume they're rational motives either. Why should aliens be incapable of something like religion, egotism, mass delusion, or hedonic desires? As far as the feasibility of star travel: it's hard, but not impossible. The thing that makes it hard really isn't the propulsion problem. You can go to the stars using technology contemporary with the Beatles white album: http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi... A thermonuclear Orion could achieve around 10% the speed of light... according to figures computed using 60s assumptions of vehicle mass. With very lightweight materials and more efficient thermonuclear charges higher fractions are certainly achievable. (Though the acceleration would be rough!) What you can't do with 60s-70s tech is survive the trip. The biological, structural, psychological, and engineering robustness challenges outweigh the challenge of propelling yourself at meaningful fractions of the speed of light. But those are all things that will yield to incremental progress. (BTW: the same is true for Mars. The Apollo rig could have, with very minor modifications, sent astronauts to Mars. They would have been dead when they got there. The life support tech to keep a human in a can alive that long did not exist. Propulsion isn't the hardest problem.) The fact is that we simply don't know. We don't even know if there is other complex life in our galaxy, let alone what it might be capable of or what it might do.