This post from J. Storrs Hall at Nanodot, the blog of the Foresight Institute, offers a dystopian, and realistic, view of how mankind’s first encounter with extraterrestrial intelligence will likely play out.
Hall’s premise is the most likely first visitor will be a civilization commanding “full-fledged nanotech” and “hyperhuman AI.” Given that construct we won’t be welcoming emissaries of an alien race, we’ll be facing its resource seeking nanobots that will likely be looking to loot our solar system of raw material and harness the sun with a Dyson sphere. Kind of makes you long for little green men, hostile or not, eh?
From the first link:
Star travel is expensive; it costs on the order of a ship’s own mass in equivalent energy to get it up to relativistic speeds. Any culture capable of that will be at least a Kardashev Type I civilization, and most likely a Type II. And the reason they’ll be doing star travel is to work their way up towards Type III. Any sentient creatures that actually get here will be nanotech-based robots, not water-based organisms. They won’t have spacecraft, they’ll be spacecraft. They will be unlikely interested in thecarbon-poor mudballs of the inner solar system, but reap abundant carbon from the outer planets and carbonaceous asteroids to build Dyson-sphere-like structures around the orbit of Mercury.
We simply aren’t going to see less sophisticated visitors due to the starship paradox: send a starship out now with all Earth’s current technological resources behind it, and then wait and send one in 50 years with full nanotech. The second one gets there first.
For more background reading, here’s an explanation of the Kardashev scale cited above. And for a little reassurance Hall’s outcome isn’t all that inevitable read the comments at the linked post.