Home > Clement's Game > Science Fiction Round 50: The Fundamental Alien Invasion Problem

Science Fiction Round 50: The Fundamental Alien Invasion Problem

Inspired by reading The Three Body Problem recently, I decided to spend a few words on the central problem of that novel.

Specifically, the phenomenon of the alien invasion.

TVTropes as a nice do-it-yourself guide on the topic, but I’d like to confront one aspect that is rarely adequately addressed:

Why bother?

Setting Up The Playing Field

The most important problem of motivating an alien invasion is to turn the question on its head: rather than simply, “Why bother?” we need to ask “Is it worth the bother?”

Realistic space travel is slow and expensive.

For the purposes of this exercise, I’m going to assume that space travel takes a significant investment in time and resources, even if you’re using faster-than-light travel or physically impossible supertech.

Besides which, invasions are generally slow and expensive, requiring a large investment in time and resources.  Especially if you’re trying to take the whole planet in one fell swoop.

If you can just teleport all the inconvenient natives into space, and instantly take over everything with a snap of your fingers… this argument doesn’t work for you.  My discussion also assumes that the planet being invaded is the locals’ homeworld, and that they do not yet have interstellar travel capability.  (If they do, then we start hitting different issues than the more classic aliens-invade-Earth style plotline.)

We Needed the Resources

The resources desired by a group of invading aliens fit into several categories:

  1. Raw.  We’re talking minerals, water, oxygen… whatever.  It’s just sitting there, waiting for someone to snatch it.
  2. Processed or agricultural.  The aliens are coming to take your bubblegum or your cows (because they’re delicious, I guess).  These things wouldn’t exist if a civilization wasn’t there making them.
  3. Sentient.  You want slave labor, free technicians, or… something.

Unfortunately, none of these work.  At all.

  1. Raw materials are everywhere.  You’ve already drained your home planet?  Fine.  Check out a nearby asteroid belt, moon, or other planets in your home system.  Sure, it may be a little expensive to set up local space industry, but it’s going to be way cheaper — in resources and lives — than sending an invasion fleet to steal somebody else’s stuff.  Already mined out your own system?  Just copy your space industry to some other nice, uninhabited system.  It’s still expensive, but you already have the space industry stuff you need, and again, no need to fight the pesky locals.
  2. If you’re really into weird alien foods, have you considered trading with them?  It’s way, way cheaper than fighting.  They might even have suggestions for you, or ideas on what other things you might like, that you haven’t figured out from watching all their old TV broadcasts.  They’ll love your technology, but it’s also likely that they’ll be satisfied with resources you can reach that they can’t.  Or your weird alien foods.  Even better, now you have friends who may be willing to help you out in a pinch.  Win!
  3. Why do you want slave labor?  You have space travel.  Surely you can cobble together a half-decent robot for menial tasks.  If not, maybe you can trade us some of your space tech, and we can give you all Roombas.  As for alien slave labor that’s more skilled, you could just hire some.  If the aliens are that good, it’s likely they’ll jump at the chance to do cool things with you while traveling IN SPACE!!!!!  Especially if you pay well.  Finally, using the local sentients in extensive medical experiments to help your own species (or as incubators for your species) is not only going to make them super mad, but it’s also extremely unlikely that their biology is going to be at all compatible with yours.  At best, you’re going to end up with a lot of freaky corpses.  Not worth it.

Movies and books that fail in this aspect are almost too numerous to count: the humans in Avatar and the aliens in The Three Body Problem are among them.

Humans Are Delicious

This is a variant on the resources question, but I feel it needs to be addressed with a heading of its own.

First: Eating sentient things is mean.

Second: They don’t want to be eaten, and will fight back.  You’re better off abducting cows, and they probably taste better anyway, since the locals haven’t been breeding themselves for deliciousness.  (War of the Worlds, I’m looking at you.)  Besides, if the cows are tasty, we’re back to the resource problem again.

Third: Once again, your biology is not likely to be compatible with theirs.  They likely produce proteins that you’re allergic to or can’t digest.  If they have a different chirality for some amino acids, you may get some other side effects.  On the plus side, their microbes probably can’t infect you easily.  But, you know, you’re better off carefully testing the cows for edibility anyway.  And maybe cooking them to kill the bacteria, just to make sure.  (The aliens in War of the Worlds made this mistake, too.)

You Have Our MacGuffin

This is terrible.

You had a cool thingamabob that did important stuff, like explode or terraform planets or control the fundamentals of the universe, or it’s a precious, irreplaceable religious artifact of your civilization, and somebody… what, dropped it out an airlock?!

Look, if you’re invading because somewhere on their planet, the aliens have some object that is precious to you, why not just ask them nicely for it?  No need to tell them the truth — just say it’s a very important religious artifact (or historical artifact, which may work better for technological wonders) and that you would gladly pay them to get it back.  If they’re anything like humans, you’ll have ten different fakes plus the real one within twenty-four hours.  No muss, no fuss.  Sure, maybe you needed to sell your technology, or something else expensive, but… that was better than a protracted invasion, now, wasn’t it?

Admittedly, it would be annoying if they used it for something, or reverse-engineered it before returning it to you.  But it’s still probably better than wasting a bunch of resources on an invasion, and then having them get the MacGuffin first anyway… especially if they then threaten to use it on you or threaten to destroy it, depending on what it is.  This is not unlikely to happen — the locals aren’t stupid, and they know their own planet better than you.

Nice Planet You’ve Got There

Yup.  It’s the only planet with chocolate, after all.

In this case, the invaders aren’t after the locals’ stuff — they want to move in.

This motive is assigned to the Martians in The War of the Worlds, the Fithp in Footfall, the Boov in Home, the aliens in the Tripod series, and so on.

But, guys… space travel takes time, and you have great technology.  Why not just, say, terraform a convenient rockball somewhere?  There are no natives competing for space, and you don’t even have to worry about local biota.  This is particularly egregious in the case of the Tripods, since they are planning to terraform Earth, and have the technology to maintain enclosed domes until everything is the way they want it.  They should’ve just gone for Mars.

This is perhaps less serious for The War of the Worlds, since the Martians there don’t have terraforming capability, are (in interstellar terms) super nearby, and can get along with the terran environment just fine.  (Except for that issue with the microbes…)

Besides, even if you can’t terraform immediately, if you can do interstellar travel, you can clearly set up a suitable long-term life-support system.  Make yourself some nice domes somewhere, and start doing some research.

We’ve Got To Kill You First

This idea also appears in The Dark Forest.

In essence, no civilization ever contacts another, and if they discover another civilization exists, the discoverer with immediately destroy it… to avoid being destroyed by them.

Have none of these authors heard about game theory?

Fundamentally, wiping out a bunch of aliens who’d have to put a lot of effort into killing you… probably isn’t worth it, unless you’re sure they’re going to start something.

And, in a game theoretic sense, this is a suboptimal solution.  This scenario is a bit like the iterated prisoner’s dilemma: if you know the other player is going to screw you, you should always screw them (or try to screw them first) in order to avoid being utterly screwed.  However, if you try cooperating once, at the start… and the other player cooperates, too… you can get a much, much better outcome.

Admittedly, given that the penalty for trying to cooperate with someone aggressive could be harsh, a defensive stance is understandable.  However, in a setting like The Dark Forest, I would have expected somebody out there to get lucky, find a friend, and then, because the two civilizations are working together, have enough power to extend that cooperation to others.

Hello, galactic police.

In the absence of a larger-scale interplanetary association, paranoia could be a motivating factor… but I don’t find it very satisfying.

You Started It

This almost works.  For example, in Ender’s Game, the aliens attacked first (in a badly planned attempt at first contact), and so the humans felt it necessary to wipe them out in order to defend themselves.

But, it only pushes the question of “why invade?” one step back, from the secondary invaders to the primary ones.  Why did they try?  It still needs an answer.

And, in the particular case of Ender’s Game… wow, that was poorly executed.

We Are The Borg

This would be something like self-replicating probe death machines programmed to annihilate all life, an assimilationist threat like the Borg, or some powerful and xenophobic aliens bent on total galactic control.

Regardless, this means the invaders are being driven primarily by ideology (or fundamental programming), rather than by rational needs.  I also find this motive somewhat plausible, but if it shows up in your story, I want to see it in action.

I want to see the life-hating probes focus on sterilizing the surface, not rounding up humans for experiments or randomly shooting them.  Drop some asteroids on them.  Start (and finish) by using your superweapon.  Go big or go home.

For the other cases of Borg or expansionist totalitarian threats, let’s see some pompous demands for surrender.  Promises and demonstrations that resistance really is futile.  If you spook the natives enough, some of them will just surrender.  It’ll save you a lot of time.


Yes, you can have inscrutable aliens with blue and orange morality.

But all those potential rational reasons for an invasion still apply.

In short: What do they want?

If you want to have the aliens be characters at all, we’re going to have to see some development, like learning about the herd-mentality of the aliens in Footfall, or the lack of family ties for the aliens in Home.

Otherwise, they’re just the inhuman acceptable targets that the protagonists can murder en masse without feeling guilty.  You could swap them out for a horde of space zombies and get pretty much the same effect.

In Summary

Invading a planet is probably not worth the bother.  You should go home, rethink your life, and consider some less violent alternatives.

And if you really must invade somewhere… seriously, do your homework first.

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