It’s the most basic terror that science fiction can provide – not only are there aliens out there, but they want what’s ours and will stop at nothing to get it. Alien Invasion stories are a staple of the genre, but they’re often undermined by the failure of the writers to do some basic preparation before they begin – such as understanding the laws of physics. Or biology. Or economics. Or common sense…
So I’m going to go over a few of the major problems and suggest solutions writers could use when building an invasion – solutions that are less about an excuse for cool CGI, and more about writing a compelling and surprising story.
PROBLEM ONE: THE DISTANCE
The first major problem is that it’s an unimaginable distance to even the nearest stars. At our present level of technology, it’s taken us 34 years just to get a probe out to the edge of our solar system – 0.18% of a light year. The nearest star is 4.2 light years away. It’s not a journey we’re likely to be making soon. Alien invaders will have to overcome exactly the same problem, probably magnified because they’re unlikely to come from the very nearest star. So here’s some solutions…
- Faster Than Light Travel
- Instantaneous Travel
- Invaders from Another Dimension
- Invaders from Another Time
- Energy Lifeforms
Travel time to the nearby stars would take many thousands of years at present speeds, but a decent amount of technological advance might bring that down to a hundred years or less – something doable in a human (or alien) lifetime. It’s still a very long journey if you’re launching an invasion, though – if you assume that an invasion has to have some kind of political support back home, is that going to last for decades? Would radio signals reach the invasion fleet halfway to their goal, recalling them because their homeworld has had a massive social revolution? And of course, we’re still only talking about the nearest stars, a mere handful of light years away and unlikely to be inhabited, so longer journeys from the vast bulk of the galaxy might not be worth considering.
Once you reach truly fast speeds, though, another factor comes into play which makes the journey a little more possible: relativistic time dilation. As anyone who’s read Einstein’s papers (or, more likely, Joe Haldeman’s The Forever War) will know, time travels differently depending on how fast you’re moving. A ship travelling at a significant percentage of lightspeed might take five hundred years to make a journey, but the people on board might only perceive it as five years. The invaders might be fresh and ready for the fight, but everyone they ever knew at home will probably be dead. Maybe they've had to abandon their own world – which actually works quite well if they’re coming to stay and have no interest in returning home.
On a really long journey (far beyond human or alien lifespans), there are two obvious ways to keep the inhabitants going: either they don’t age in some kind of suspended animation, or they do grow old and die, but their descendants keep running the ship and will be the ones to conduct the invasion at the end of the journey. If they’re in suspended animation, then they’ll likely be up and ready for the invasion, unless there have been some problems along the way like losing all their personalities in a computer failure, which could create extremely confused and unpredictable invaders (as in Douglas Adam’s Mostly Harmless). If the invaders have come on a generation ship, they may have tired of the whole purpose of the journey somewhere along the way – or they may have become religious fanatics even more insanely dedicated to wiping us out. Indeed, they might not even have started out as invaders in the first place.
Essentially, the point is: no matter what you do to alleviate the effects of a long journey, humans (and aliens) might not be the same once they reach their destination, leading to a certain unpredictability that can make things interesting.
But why restrict ourselves to invasions from beings quite so similar to us? Humans have evolved (and are still evolving) to meet the demands of our environment. Might not space travelling aliens adapt to the requirements of a spacefaring life? Including, most importantly, the vast gulfs of time that space journeys require?
These kinds of aliens are likely to be vastly more advanced than us, and may not be biological at all, meaning they may have vastly greater control of not only their bodies but their minds. If there’s any kind of life to be had in space, then adjusting time perception so that they can experience long journeys in the blink of an eye will be a vital adaptation. Or maybe they are simply capable of enduring the boredom without going mad or changing into something completely different along the way.
Of course, this level of advancement will put them so far beyond us that they might not have any interest in planets, let alone the antlike beings on the surface of a little blue-green world. Or they may see us much as we look at a farm on our world: something to be managed lest some dangerous growth gets out of control. They might decide that our whole biosphere needs pruning, or that we simply need to be removed and placed somewhere else. It all depends on their perspective, and the trick here is figuring out exactly how a vast alien intelligence will think. A difficult choice, but perhaps a refreshing one.
Of course, there’s one thing we do that already travels at the maximum speed of the universe: radio. Our signals have travelled more than 100 lightyears out into the galaxy, and (though very faint) will continue to travel on, possibly alerting aliens to our presence, and, as time goes on, providing a vast wealth of information about us.
What if their ‘invasion’ is one not of military might, but of information? We can’t expect them to link to the internet and hack our systems directly if they’re transmitting at the same speed as us, but human systems can be hacked in other ways: by ideas. Carl Sagan’s Contact shows what happens when a benevolent elder race sends us a package of information to give us a technological boost. Sagan, however, was an optimist; what might a malevolent alien race send us?
The first temptation is to say reality TV, but (if I’m serious for a moment), the aliens wouldn’t be able to respond adequately to our own culture without being laughed at – they’d be years, decades or even centuries out of date. So they have to send something that can destabilise our world without much reference to our own transmissions. But that can be surprisingly easy; on our own world, we’ve seen stone age societies disrupted by the cargoes transported to distant Pacific islands during World War 2. If similarly advanced cargoes of information were dumped on us, these too could disrupt our world – maybe causing wars, maybe making us dependent on their transmissions for continued survival, maybe lying to us about what to expect from galactic society so we’re unprepared for the real invasion. Ideas themselves can be very dangerous sometimes…
The main purpose of FTL in fiction is to turn interstellar travel into an analogue of either sea or air travel on Earth – something we can understand and cope with. Planets then become distant lands across the sea rather than strange unknown worlds, and it seems possible to walk around on any of them without instantly dying from the lack of breathable atmosphere. In other words, it gives us a way to ignore how different alien worlds, species and cultures are likely to be; alien invaders become more like foreigners from our own world - weird but understandable.
That’s fine if you just want a way to get the aliens from A to B and don’t much care how they do it. But it can be a bit dull just to wave a wand and say ‘hyperspace’ or ‘warp drive’ or whatever: that's essentially magic. FTL should have a cost, and it's the cost that can make it interesting. One obvious example is the folding of space in Dune, where interstellar travel is accomplished with the help of the drug Spice, which makes the navigator prescient and thus able to operate the hideously complex systems that actually fold space; the enormous value of Spice then drives interstellar conflict. Or another example, from Iain M Banks' Culture series: FTL travel has long become routine to the point where no-one particularly thinks about it, but there's still a basic rule: the size of the engine you use has a direct effect on the speed a ship can travel. This then becomes a critical point in the plot of Excession as one particular ship races to prevent two invasions threatening the Culture at the same time. Or what if the systems that travel between the stars are somehow biological, and the invaders have either harnessed them somehow, or perhaps are living within them? Maybe such a lifeform would want to pause in our solar system to feed – most likely on something manageable like an asteroid or a comet, but this could then present an opportunity for the aliens living on them to make forays against us.
So when you're building an FTL system, bear in mind a simple principle: nothing in this universe comes for free. Sometimes it might seem as though it does, but there are always hidden costs somewhere...
Another way to avoid the problem of distance altogether is literally to avoid the problem of distance altogether - by connecting two parts of the universe with a portal that lets you travel from one to another with minimal effort. Maybe you're piloting a ship through a wormhole, or perhaps simply walking between two rooms that actually exist in different star systems - either way, you're making life easy for the aliens.
Much of how an invasion using this system would go really depends on how you set up the rules of how the system works. Can invaders just turn up in the middle of London with no warning, or must they engineer a wormhole that manifests somewhere in the solar system and forces them to use some kind of basic space travel as well? If the former, then some of the reasons for invasion that are usually absurd suddenly become viable – a need for planets to colonise, for example. Because if you can travel from planet to planet without the trouble of going into space, then you’d probably wouldn’t bother with space travel at all.
And this leads to more interesting possibilities. It could mean a vastly skewed technological approach, especially if these portals turn out to be somehow natural in origin and societies using them have been able to develop with no concern for actual space travel; we could see steampunk-style invaders, or ones whose technology relies exclusively on genetically altered creatures, or any kind of strangeness (or maybe just cheap copies of Egyptian warriors).
And, of course, this kind of interstellar travel should still have a cost. If not an economic cost, then maybe a social one; for example, when two societies on Earth get to know each other, their cultures soon start to leak across the divide, and a good deal is often lost. In the end, maybe an alien race could turn us into copies of them simply by having a more advanced culture and being willing to share. Not your typical alien invasion, but a very effective one in the long run.
But why should the invaders come from another star? There’s another situation that could lead to alien invasion – an incursion from another universe entirely. Parallel universes are a common enough trope in science fiction, usually intended as a way of exploring an alternative version of our own world. But if the technology exists, and those worlds aren’t able to travel to distant stars, then the temptation for an invasion in search of living space, minerals, water, and maybe even slaves becomes very possible. An interesting idea would be to show a culture similar to ancient Rome stumbling across portals to our world, then launching raids against us for all the things ancient peoples would have wanted: loot, people to enslave, and then weapons and technology once they realised we were more advanced.
Or, of course, there’s nothing to stop this other world being rather more alien than that. Nor is it necessary to make it an actual alternate earth; it could be another kind of universe altogether – maybe some kind of hell dimension where the demons have decided it’s time to spread their empire of pain to our world. Or maybe even an invasion from heaven because God decided we needed to be taught a lesson.
And all this is only for universes that are side by side and equally real. You might also consider invasions from universes that are created within ours as simulations, where the inhabitants we created break loose and try to claim some kind of place in a more real world. The opposite is also possible: if it turns out that our universe is only a simulation within some greater universe, the what’s to stop people from the world above just simulating an invasion happening to us, from any direction they care to imagine? Or entering our world themselves and playing with us as though we were toys?
Once you start playing with other realities, virtually anything becomes possible – the main trick is to find something interesting and then follow through on the implications without just using it as a gimmick.
It gets even stranger once you allow for time travel, because then you could have invaders coming from the past or future of our own world – our ancestors or descendants. The first thing you have to decide is how time travel works: can time be rewritten, or can’t it? If it can, then that offers an instant reason for travelling back into time: the invaders are from the future and want to make some change in the history of the world. Most of the time we see stories about individual travellers or small groups trying to accomplish a change, but why not have an entire civilisation facing extinction in some future time come back to try and make it right – at our expense? And what if they make mistakes and found reinforcements coming back in time, each from a different, changed future, leaving to another conflict among the various groups of time travellers? This could get very messy, and very interesting.
If time cannot be rewritten, then time travel can still be useful. Firstly because you could always be going forwards in time – maybe we’re being invaded by beings who existed here millions of years ago, or maybe it’s an enemy from our own past coming forwards in time, with no way of returning home and a desperate need to conquer us in order to survive. Secondly, you can always invoke the many worlds hypothesis, in which a journey to another time means you end up in a parallel universe that’s exactly the same as ours was at that moment, allowing access to the past without any way of affecting the present. But why they would come to our time when they could skip back a few thousand years and find a world much easier to conquer? Why not hop back to the Dark Ages and rebuild Rome, or supplant the ruling dynasty of China (as so many invaders did)? There’s nothing to stop this being a historical story as well as a science fiction one, and that could make it even more interesting.
Finally, here’s a pretty weird idea for a way to get between the stars: become the only thing we know of that makes this journey on a constant basis – light itself. If we have aliens that are composed entirely of energy, and especially if they can transform themselves from one kind of energy to another, then they could take advantage not only of lightspeed, but also a time dilation effect that would make the journey seem almost instantaneous. Quite why they’d bother invading is another question entirely, but they’d certainly be a bugger to fight.
(I did actually find a reason why such a race might invade and exterminate humanity in The Last Man on Earth Club, but I won’t spoil it here).
IN PART TWO...
We'll look at some reasons for alien invasion that make sense. Unless the invasion starts first. In which case it's already making sense.