I can find no rational reason for aliens to invade the Earth.
If they need energy, water, metals or radioactives there are plenty in space to mined or harvested without dealing with pesky natives. If some super-civilization needed all the metals, silicates and carbon from our asteroid belt, they could just haul it all away without ever visiting the Earth and, we could do nothing to stop it. If they needed to enclose the Sun within a dyson sphere to harvest all the energy from it, they could do so and our technology would so primitive in comparison that we could do nothing to stop it. If they wanted to mine all the silicates and iron from the Earth, they’d just pulverize it into manageable pieces by slamming a few other planets or moons into it.
In any case they’d never have to set foot on the Earth at all.
The key thing to keep in mind here is the enormous differences technology. Science fiction is often wildly inaccurate on this score because they only posit differences of a few decades or centuries. It would not be like British maxim guns versus Zulu infantry.
Either the alien creatures will be millions of years more advanced than us or we’d be millions of years more advanced than them. This is a difference that is simply impossible for us to imagine. The nearest instructive analogy would the difference between humans and mice or ants. At best the mice would be nuisance, never a real threat. HG Wells got it right the first time. There could be no more war between humans and aliens than there can be war between humans and mice.
(I have a few more thoughts about interstellar warfare which I’ll discuss later.)
Nor do they need slaves. They would have built robots and automation to do all their dirty work long before they expanded to the stars. Robots are cheaper than slaves and far easier to control.
Nor do they need to harvest rare proteins or biochemicals from us. Any rare, complex molecules they need could easily be synthesized with solar energy, local resources and nanotechnology. It’s a lot cheaper to make these molecules locally than to trek across light-years of empty space to get them.
Population growth is also a non-starter.
I do agree that colonizing other worlds is essential to a technological species to survive over very long time scales. This is because it increases redundancy. If some disaster strikes the home world, the colonies, once they are self-sufficient, and they’d have to be self-sufficient almost from their foundation, can carry on so the civilization and culture doesn’t die. I think for the best long term survival of a civilization, a species would have to differentiate into new species (More on this at another time.) and spread widely and thinly over the whole universe. They wouldn’t have to conquer the whole universe. They just have to spread little pockets of themselves everywhere. This ensures the best chances against supernovae, exploding galaxies, cometary strikes, stars evolving off the main sequence, colliding galaxies and so on.
Having said that colonizing other solar systems does absolutely nothing to control or reduce population growth in the home worlds. When humans colonized new lands in successive waves, this did almost nothing to reduce populations in the originating territories.
In fact if we don’t get our population growth firmly under control, we will never gather the resources needed to build the infrastructure needed to colonize nearby solar systems. To colonize another solar system would be an enormous strain on a local economy. It will be one of the hardest things we’ve ever done. I’m not saying it’s impossible, in fact I’m saying it’s likely in the long run. I’m just saying it’s expensive. Better to have our population under control first before having that issue drain money from our first stellar colonization effort.
So this leaves the irrational reasons.
- Perhaps they are sadists and they can’t abide intelligent, tool-using lifeforms living in freedom in neighboring solar systems.
- Perhaps they have some bizarre art form that requires inflicting cruelty on other species.
- Perhaps they have religious reasons. Perhaps their religion compels them to convert all intelligent life to one way of thinking and one way of life.
Invading other solar systems just to indulge these reasons would be extremely expensive.
The next thing to consider is how old the oldest technological civilization is. If this first civilization is as nearly old as the universe, then it’s likely that most planets are already colonized by offshoots from this prime civilization. This civilization would be so advanced that no one would be stupid enough to pick a fight with them. In such a universe, territory would have to be shared and negotiated for.
If the first civilizations are still very young, while still being millions of years more advanced than we are, there are probably plenty of empty worlds for them to colonize anyway. And if not, they can manufacture their own artificial worlds out of asteroid or cometary materials.
Again none of this supports any rational reason to invade the Earth. If aliens wanted the real estate, there several comparatively simple ways to sterilize the Earth of humans and then terraform the planet to their needs. Again, I’m thinking of nanotechnological weapons here.
How would the conquest of Earth look to us? Simple. Just one day we’d all fall to sleep.
The aliens would just dust the planet with small crop of nanorobots, probably sent down with a meteorite. These robots would reproduce, infect us and study our biology for a few days. Then, upon being sent a chemical or radio signal, they’d just make a few adjustments to our biochemistry to put us all into comas. We’d never wake up again.
Afterwards they could use nanorobots to completely transform the biosphere. Like I said, HG Wells got it right the first time: We wouldn’t stand a chance against this.
But again this is just my opinion. Do any of you out there have good reasons to think that aliens will invade the Earth?