Why on earth--okay, why in the UNIVERSE--would aliens invade?

In My Humble Opinion
41

Slight hijack - but it’s worth pointing out that this is a crucially important stipulation, because without FTL, or comparable magic-tech, there’s just no way at all to successfully invade Earth. And oddly enough, it’s Harry Turtledove (not one of science fiction’s Great Minds) who probably did one of the best jobs of illustrating this point, in his WorldWar series. (Aliens with slower-than-light starships invade during WW2).

Let’s say that I’m the leader of a super-advanced alien culture on Gliese 581 C, the nearest terrestrial world we know of outside our solar system. It’s a bit over 20 light-years away - next-door neighbors in astronomical terms. Say that I don’t have FTL, but I do have the capacity to build large starships. (Maybe my crews hibernate, maybe these are generation ships, maybe my species just has a thousand-year lifespan - whatever). These starships almost certainly are going to be large, because they can’t be resupplied from my home system, so they need to be self-sufficient. Even so, space is going to be limited. (The ships have to be big - but the bigger they are, the harder it is to get them moving, as I discuss more a bit later. And there are other issues…)

How fast are these ships? Well, they probably aren’t going anywhere close to the speed of light. Remember, I’m not using magic-tech, so I’m more-or-less playing by Newton’s rules - if I want to accelerate beyond what slingshot-orbits can give me (not even close to a fraction of the speed of light), I need to carry some way to generate energy, and I need reaction mass to push against. Even if I’m, say, building an Orion nuclear pulse-drive (setting off nukes behind my ship to move it), that means I’ve got to carry a lot of fuel to get up to speed. I also need to carry a lot of fuel to slow down again - the exact same amount, more or less. (I can play with fly-by orbits and solar sails to shed some speed once I reach the Solar System, but there’s a limit to what I can do there.)

There’s also the issue of shielding - space is mostly empty, but even hitting a tiny speck of dust at, say, 5% of light-speed is probably something that’s going to leave a mark. There are relatively inexpensive ways to deal with this problem - Arthur C. Clarke would suggest building an ice-shield on the front of your ship - but remember that this still adds mass, which means you need more fuel to accelerate/decelerate. Further - your fuel has mass of its own, whether its a bunch of nukes or hydrogen for your nifty fusion reactor or what-have-you. Carrying more fuel increases your fuel requirements all by itself…

You see the problem. Building a big ship that moves fast is damned hard - and absent magic nano-tech or replicators or something like that, you don’t dare build small, because all your invaders are going to have is what they take with them. So, as the God-Emperor of Gliese, I may be able to build starships with sizable crews and resources - but they’ll almost certainly be much slower than anything you’d see in most science-fiction. However, I’m going to be extremely generous and posit that Gliesan warships can cruise at about 5% of light-speed. That means they can travel the 20 light-years from their homeworld to Earth in about 400 years.

Think about what this means for our brave Gliesan warriors. An invasion ship arriving today would have departed during the Renaissance. Even if we posit that the Gliesans have magic telescopes that can achieve any resolution they want across the light-years, they wouldn’t have seen anything on Earth that could have come close to harming anyone with starship-level tech. Black-powder weapons and chain-mail would fare poorly against a WW1 infantry brigade, let alone this kind of technology - and the starship would be equipped accordingly. Oh, sure, it would be insane if they didn’t have some kind of manufacturing ability on-board - but do you really think that people expecting to fight a war against people armed with pointy sticks and pop-guns are going to bring along their own culture’s equivalent of an armored brigade, “just in case”? Remember that every super-tank or scramjet-bomber they stick in that starship is room (and mass!) that can’t be used for additional colonist/invaders, or food supplies, or slower passenger transport aircraft, or anything else that you might actually need, badly, if you’re invading and colonizing a low-tech world. Every kilogram your people carry is potentially a matter of life or death.

“Right, right,” you might say. “But surely, your God-Emperor-ness, the Gliesan invaders would make some provision for technological advancement? You won’t expect the Terran sheep to simply stand still for 400 of their Earth-years, will you?”

Well, let’s think about that a second. (And if you’re read Turtledove’s stuff, you know where I’m going with this.) Assume that the invasion of Earth was very carefully planned. Before I sent my fleet, I directed my scientists to study the Earth for, oh, a thousand years. (That would be the period 600-1600 AD). Our telescopes are so powerful, we see everything that happens. And what do we see? Well, not a whole hell of a lot. In 600 AD, most transport is by horse, walking, or sail - and that’s still true in 1600. Over that thousand-year span, most human weapons technology remains a variation on the theme of “stab/bludgeon/slash the other guy before he can do that to you”. There are certainly improvements in metallurgy, and the emergence of gunpowder weapons is interesting - but why would I anticipate anything remotely like the Industrial Revolution? For that matter, why would I anticipate anything like the 20th-century leap from horse-and-buggy to spaceship in a single freaking human lifetime?

I wouldn’t. There’s nothing going on in 1600, or for a thousand years before (or two thousand, for that matter) to suggest that any big change could happen that fast. So, my crews might leave Gliese anticipating some changes - but nothing like what they’d actually encounter.

This means that the invading starship will reach the Solar System horribly, horribly under-equipped for War With The Humans. This starship is not magic, and the human governments have many, many high-yield nuclear warheads at their disposal - woe betide the unwary starship that enters low Earth orbit! As for the invaders on the ground - well, that’s when things get really nasty. There are over 6 billion of us, and we have the industrial resources of entire continents to bring to bear. I’m not saying the humans would necessarily get off without a scratch, but it’s hard to imagine these under-equipped invaders, in their limited numbers, failing to be swamped by human armies that number in the tens of millions. (Assuming that Human governments ally against the invaders).

“But wait!” you might say. “Your Imperial Highness, your warriors can still prevail! They could mine the asteroid belt, or the Jovian moons, and build a larger industrial base, and use that to craft a war machine to put the human scum in their place!”

I admire your enthusiasm - but you’re probably wrong. Remember, this starship was built to conquer a low-tech world, and exploit a planetary resource base. Why in the world would I have also wasted huge amounts of cargo capacity on the much more complicated (and expensive) gear required for deep-space mining? Every asteroid-mining boat I attach to the starship means that I can’t throw in as many of the Giant Terran Mining Robots that I expect to actually be using.

The take-away message is this: Any invading starship moving at non-magical speeds, equipped with non-magical technology, would almost certainly arrive unprepared and under-equipped for a war against humans equipped with thousands of nuclear warheads, jets and tanks in Ford knows what numbers, and powerful hand weapons. This deficit would be something they wouldn’t be able to fix.

42

Um… okay. That’s why I stipulated it. Otherwise we have to confine ourselves to wondering why would the Martians invade, and given the events of my last time travel trip, the answer is clearly “revenge.”

43

Simple really, to further the species. The more inhabitable planets they take over, the easier it is to assure the safety of the species.

44

But, Your Ineffableness, Sir. Who’s left on Mars to avenge themselves?

45

Not that I’m admitting anything, but it’s conceivable that, while I was in the Pleistocene hunting cockatrices, there may have been a slight and unforeseeable misalignment in the verniers of my Burroughs-Libby continua device, resulting in a mis-application of the hyperspace gyros, which resulted in the entire intelligent population of Mars, including their arsenal of 455,366,209 planet-cracker bombs being thrust into the Null Void.

As I said, I’m not admitting anything.

But it’s nothing to worry about anyway, as the null-void portal cannot be opened again until Tuesday the 25th of November, and on Monday the 24th I will be heading to Earth-1, 2987, Century, to perform a panty-raid on the headquarters of the Legion of Super-Heroes. (Those of you who who know what I’m talking about will understand why this is a desirable activity.) I won’t be back until after Thansgiving, I’m sure you guys can handle a little Martian invasion without.

46

Can you maybe talk the Martians into joining your panty-raid?

47

Not that I’m admitting anything, but as they’d obviously be looking to nuke me, personally, that’s gonna be a “No.” Half the point of the panty-raid is to be on a planet guarded by Mon-El, Wildfire, Ultra Boy, & their buddies.

But I’m not terribly worried, as I had the foresight to use the aliases “OtakuLoki,” “Mr. Excellent,” “Chimera,” and so forth whilst among the Martians.

48

You appear to be assuming that the invading species is only going to be a couple hundred years more advanced than we are, tops (i.e, the common Star Trek aliens). However, given the age of the galaxy/universe, alien cultures are far more likely to be **tens of millions **of years more advanced than we are (imagine if, in an alternate timeline, velociraptors in the cretaceous period managed to fast-track to civilization within a million years, then spent the next 70 million years developing science and technology, and just now decided to go out and conquer the galaxy). Somehow, I think an alien race that advanced isn’t going to see nukes as much of a threat, even if they weren’t expecting them.

49

I’ve got news–we’ve already invaded. I’m an alien (at least that’s what all my acquaintances think). Alas, I don’t know why I’m here any better than anybody else does.

50

…or, Battlefield Earth - summarised in four words (leaving out nothing important).

51

I was thinking about something last night. Here we are on Earth, looking up at the stars going “Ooh, gosh, isn’t it pretty? Big and black and mysterious with lots of sparkly things!” and hoping we might pick up an extra-terrestrial radio signal sometime.

When in actuality there are spacecraft all whizzing around in space from planet to planet, killing, saving, or chatting with each other. The spaceways are a virtual hubbub of activity, like it’s always rush hour.

We are completely blissfully unaware just how busy and active things are out there, because from this distance and this technology it’s impossible for us to detect.

We’d feel such a fool when we finally got to see what’s really happening.

52

Not that you’re admitting anything, of course.

But could you have made this announcement just a tad bit sooner?

I’d had some weaponized sour dough sponge just sitting in the lab fridge - until this morning. It would have been perfect, if I’d known to expect guests.
Now I have to start another one, and you know how finicky a good San Fran sourdough can be, esp. once it’s been weaponized.

53

Well, there’s problem with your argument right there; you put the bar for plausible technology much too low. No, you won’t see change-stuff-fast-with-no-limits nanotech in the real world, but you’ll see some - life is proof of concept for molecular machinery, just as birds are for flight. And there’s no reason at all that you can’t build replicating machines and the AIs to run them.

So for an advanced culture without magic tech, the invasion force could consist of one guy. One alien and his Von Neumann replicator/manufacturing unit, which he could drop on Mercury and tell it to replicate over the surface and to turn the top mile or so of crust into combat robots, factories, and warships. The rest of his species might not even be involved; just him, out on a lark.

Because most likely, that’s exactly what happened on their homeworld. Humans advancing unusually fast is a plot point to make the invasion something other than a short story about human primitives getting stomped, but there’s no reason to assume that real aliens will conveniently be slower to advance than we have.

Slow, fragile chemical fueled missiles. A decently advanced interstellar culture should be able to just laser them out of the sky or outfly them.

Except that they could drop a few billion - or many billions - of replicated combat robots. And simply destroy any and all armies that try to mobilize from orbit.

Most likely everything you need to build an industrial infrastructure would be a small Von Neumann machine, and patience. Just as all you need to grow a continent wide forest is a few seeds, and time.

54

Because they think we are terrorists and threaten them. They know we have the bomb are they are afraid of the mushroom cloud.

55

That’s pretty much what I was going to post. A few details might be different (if the events actually happened, which no one is admitting) - it wasn’t Mars nor the entire population (which is part of the problem, if there was one, which there isn’t). But the most important thing to remember is that some of them alien bastards have no sense of humor. At freakin’ all.

But don’t worry, Skalds panty-raid should fix everything. That’s why I stay out of his way. Well, the panty raids and the rule-the-world thing…

#

Friends are just enemies that don’t have the guts to kill you.

56

Your analysis is the equivalent of Admiral Nelson attempting to extrapolate what a ship of the line might be like in 200 years based on the wood hulls and sails of his day and then formulating a defense against such a fleet. He would likely shit himself as his entire fleet exploded around him. Destroyed by Tomahawk cruise missles fired from a single Aegis radar equiped Ticonderoga class missle cruiser he would never see just over the horizon.

You seem to be leaving out that such aliens are probably at least 1000 years more advanced than we are now. Our tanks and planes would likely be as effective as a Roman legeon would be against a modern mechanized brigade.

At the very least they would have energy weapons or rail guns. We are close to having them now. EMPs, sonic or microwave weapons. Particle beams. (And they can probably fire most of it from space.) Advanced armor orders of magnitude stronger than anything we have now. Scramjet powered aircraft capable of speeds several times faster than a SR-71 Blackbird. Shit, a single aircraft (probably unmanned, like a super smart version of a Predator drone) with a laser 50 years more advanced than the Boeing YAL could wipe out an entire wing of modern fighter aircraft as soon as they rose above the horizon.

57

To see if the center is chewy or chocolate cream.

58

Why should aliens think that we’re anything more than ants? Even giving them a hypothetical technological level a few hundred years beyond ours, why should that mean that they think we’re sentient? Because we make jet planes? Big deal. We don’t worship the same deity they do, don’t look like them, don’t act like them, they might well reason we’re no more sophisticated than the chimps who use sticks to fish ants out of mounds. And their religious philosophy might be such that anyone who says something to the contrary is a heretic.

That doesn’t explain why they’d come here, of course (I’ll get to that in a moment), but it does explain why they might have no moral or ethical problems about knocking us off our perch.

As for picking Earth, over another solar system, or even other planets in our own solar system, that’s a bit more complicated. One thing that we know from our study of the cosmos is that the types of matter known to exist aren’t evenly distributed over it. The planets around second generation stars are lacking in material which our own system has, but there’s probably third generation stars whose planets don’t have the same amount of say, iron, as our own do.

So maybe our closest neighbors look in our direction and see that we’ve got all this iron laying about, so much so that we’re just leaving huge amounts of it outside in the rain, while they’re forced to account for every picogram they have. Their technology is more advanced than ours, but the ability to transmute carbon into iron (for example) is so cost prohibitive that sending out an invasion force to wipe us Earthlings out and take the entire system is a bargain in comparison.

Additionally, we don’t know what the physics of FTL travel might be, or even really what the make up of interstellar space outside our system is (yet). If there were limitations on the kind of travel you could do (say anything over an X-number of lightyears jump is bad for the crew, or takes too much energy) or because of the makeup of interstellar space, if you want to go to any point outside the area, you have to pass through our solar system, then you’ve got a powerful reason for them to want to come after us.

After all, if ET is forced to make a stop over in our system (say they need to get a refill at Jupiter or something), we’ll figure it out sooner or later. Now, some of us are going to want to try and trade with the aliens to get their more advanced tech, but others of us, probably a good many, are really going to care about how we get that tech, just so long as we get it. Yeah, it might be like fleas trying to bring down an elephant, but eventually even the elephant gets annoyed and does something about it.

59

A couple points here. First - I agree, it’s certainly possible that our hypothetical Gliesan invaders experienced a period of rapid technological development akin to the past couple of centuries we’ve enjoyed. Here’s the thing, though: how do you know that it’s coming? Our civilization two hundred years before the Industrial Revolution looked a whole lot like our civilization a thousand years before it. So, if you’re the Gliesans, do you really bring all the extra gear you need to deal with an advanced civilization, on the off-chance that you happen to arrive after an industrial revolution? Or so you figure, “eh, it’s probably not going to happen before I get there”, and take your chances? Recall that there are plenty of human civilizations that never developed technology much beyond Stone Age level.

Of course, you’re quite right that if the Gliesans have nanotech, a single guy can come prepared for anything - but I’m very skeptical on that front. Sure, life is a proof-of-concept that “machines” on that scale can work - but what do we know about machines on that scale? They work best when they’re fairly soft, mostly water, and very simple.

A lot of what you’re saying here is “our weapons would be useless against arbitrarily powerful technology.” Well, sure. That’s true. But if the alien technology is less than fantastically superior to our own, then it can’t defeat us - even if it’s still very, very good. A man with an AK-47 could probably hold off a Roman legion for a good long time - but if their morale didn’t break, they could eventually kill him. The AK would run out of ammo, or they’d flank him, or some other facet of the fog of war would rear its ugly head.

That’s a little beside the point, though. I’m not saying that these guys wouldn’t have scramjets, or laser-fighters, or super-tanks. I’m saying they wouldn’t bring them, at least not in big enough numbers to make a difference. Invading aliens would be very, very unlikely to make the right choices about what to bring on an invasion of Earth, because their information at launch-time would be hopeless out-of-date by the time they arrived. So long as they don’t have FTL or extremely powerful nanotech, they need to make hard choices about what to spend payload on - and the weapons they’d use in a war against their own species aren’t likely to make the list when they’re planning a war on nearly-unarmed savages.

Even if they did bring limited numbers of super-weapons - what of it? Say you’re right, and they’ve got planes that can take out dozens - hundreds! - of ours before we can even engage them. Well, we can accept those losses - we have lots of planes, the industrial capacity to replace them, and plenty of potential pilots to train. These poor bastards would be at the very, very end of their “supply train” - and ours is right here.

60

What? I’m sending a platoon of monkeys to bodyguard you. You’ll be perfectly safe as long as the Martians decide to assassinate you in particular rather than just nuking everybody from orbit.

ETA: Just to be safe, maybe you should all go out and confiscate every copy of Alien. We don’t want the Martians getting any useful advice from our cinema.