One of the oldest cliches of science fiction is the “alien invasion.” Often enough it’s used as a metaphor for whatever’s going on in the world. But when used as straight serious storytelling, the problem always becomes an issue of “how the hell do you explain how an invasion across interstellar distances makes any sort of sense.”
There are two contradictory issues:
1) Anyone powerful and advanced enough to mount a military action across lightyears would kick our asses in a heartbeat.
2) Anyone powerful and advanced enough to mount a military action across lightyears would have no good reason to kick our asses.
A discussion on Fark produced this succinct explaination courtesy user “Tofu:”
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Bendal: 1. Show up in alien battle cruiser with asteroid in tow
2. Get on the radio “Hey guys, we want X tons of the following metals in orbit when we came back in 2 months.”
oh by the way, it just occurred to me why this is funny. Pick any metal. One moderately sized asteroid contains more of that metal than has ever been mined on Earth in all the history of civilization. Ya really.
Also, a couple of good-sized comets contain more water (at least more fresh water) than exists on Earth. Saturn’s rings contain perhaps a thousands times as much water as exists on Earth.
There’s really nothing that you can get on a planet, that isn’t easier to get elsewhere, from a more shallow gravity well (except possible hydrogen if you need an assload of it). If you have the technology to travel between the stars, planets are useless to you.
This is the genius of Sagan’s book, Contact. The aliens say, “the only thing that makes the emptiness bearable is each other.” The only use that an alien civilization would have for us is to be amused by our quaint folk songs and monkey dances. So, we’ll give them our Beibers and our “rap stars” and our season 3 of It’s Always Sunny in Philadelphia and in return, they’ll give us resources that are trivially easy for them to acquire (like hundreds of tons of gold or copper) – to them that would be like giving a New Guinea tribesman your pocket mirror in exchange for a shrunken head or something. He finds the shiny thing amusing, and you get to put the head on your coffee table and joke about it with your friends.
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Unless somebody invents a way to send armies across interstellar distances essentially instantly and virtually free – perhaps some form of *extremely* unlikely easy wormhole system – then interstellar invasions seem very unlikely. By the time humans gain that sort of power, the bulk of us probably will not be living on planets anyway, but on asteroids, comets and free-floating stations. While interstellar wars might be barely conceivable (if you have a relativistic starship, you’ve got a dandy weapon for destroying planets and, conceivably, whole solar systems), invasions just don’t make sense for most of the reasons invasions are usually held for. There is, of course, one exception: the purely irrational. In human history, nothing has inspired quite so many truly insane wars as religion, or religious-like irrational ideology. A close second is probably an absolute ruler gone bonkers. So if the aliens get it into their heads (or whatever) that their gods, their king, their Fuhrer, their Supreme Soviet hates humans… watch out.
