If aliens composed of conventional matter (especially carbon-based lifeforms) invaded Earth then they would have observed us already, for long enough to know how we live, what our capabilities are and what might be useful to them. Not only would they have inter-star travel technology but they would have been sneaky enough to avoid being observed by our probes, satellites and telescopes, including radio ones. Their last stop before invasion would probably be the far side of the Moon, which we do not look at very often except for lunar satellites. We would do the same if we intended to establish a colony in the future.
This means they would know we were unable to defend ourselves against a hostile invasion if that was their intent. We might wonder what their aim was if they were invading a planet far from home; one possibility is that they had wrecked their home planet and decided to establish a new colony. Given what we are doing to the Earth, they might struggle to justify that our planet had much life left for such a colony to be feasible in the long term; they would be best to share ecosystem-saving inventions with us until the Earth had stabilized, before they chose to take over.
If they were that technologically advanced that they had sneaked up on us over such a long distance (several light years at least) and had enough lifetime to make it worthwhile (or a new generation on their ship), then it would be easier for them to use their hyper-speed to go back in time and invade Earth in an earlier century, perhaps just prior to the industrial revolution.
Then we would be absolutely defeated.
There would be no resistance. There would be no saving the day. We would be absolutely, utterly obliterated, with no hope of victory.
0 Comments