Alien invasion motives

[Aghanim]

Lets say we have an alien race that have advanced technology like interstellar spaceship, FTL travel and advanced robotics thingy. Is there any logical reason why they want to invade Earth and kill humanity like in most science fiction? Space already contains infinite natural resources in the form of asteroids, then with their advanced technology they can search for planets that they can inhabit without any sentient lifeform, or if that fails they can use their advanced interstellar spaceship tech to build orbital colonies.

Basically most of the science fictions that I have read tells me that most of alien invasions are caused by either misunderstanding or that alien species hates us somehow because of some religious or political belief (Covenant), or that they just love war (Klingons), and I have a hard time finding a good logical reason of why aliens should invade us and Earth instead of finding an unused planet in the infinite-ish outer space...

[Tex_NL]

You're right about the resources. Pretty much everything is easier to find elsewhere. Living space is a very good reason to invade and occupy earth. Currently we have no idea of how common a liveable planet actually is. Actual earth like planets (water, oxygen, etc. everything that makes earth liveable) might be extremely rare. An orbital colony, however huge, still remains rather limited. Both physically and emotionally. Nothing beats real ground and real air.
It could be a pre-emptive strike. They might worry we someday could become a threat to them.
Or they might have simply developed a taste for man flesh. An interstellar species could harvest us as easy as we harvest cattle.

Edited September 13, 2016 by Tex_NL

[Nuke]

the aliens want our bacon!

[DDE]

I'm backing up preemptive strike. Don't even need FTL for that, Relativistic Kinetic Kill Vehicles are non-SF planetbusters. And they are nigh-unstoppable.

They make preventive extermination of every possibly sentient lifeform the only wise course of action.

 

[SargeRho]

Nature-worshippers might whack us for screwing up the environment. Food is also an option.

[Signo]

"Battlefield Earth" precondition was that the "aliens" found one of our Voyagers/Pioneers with all the directions to come here encased in a wonderful and precious gold disc. And they had an option to mine any other body in the solar system due to the contract the had with their bank.

So basically they came here and killed us all with gases just to pay their mortgage.

[Emperor of the Titan Squid]

Because they have come to earth to start another branch of civilization, and avert the destruction of their species. This planet turns out to be habitable to them, so they come here. Also, their ultra planetary chauvinists, and will only live on earth. (Footfall)

[PB666]

Nope, they cannot expect Earth will be a good place, the best places to go are to planets coming into main sequence (their parent star) that have undeveloped life, less risk of a culture kiling diseases. Since these bugs can live deep in the earth and at elevated temperatures is would be difficult to eliminate them.

If you have the ability to go interstellor, then I think for certain you want the extraplanetary resources, a system with alot of comets and asteroids will do (assuming you have fusion). Occasionally as an insurance colony you would terraform a orange star early in its mainstage, but mostly as a safety.

The reason they would attack earth is because of risk we create, and they would want to learn our technology and explore our biota, robotically of course, first.

 

[SinBad]

I think it wont be an intentional effort to exterminate us. Consider a slower than light civilisation bent on expansion. Each star has a maximum carrying capacity for life due to limited energy and mass. Because they dont have ftl, before they leave their own system they explore every option for getting the most out of thier own star. Planets are an inefficient use of mass when it comes to supporting a large population, the habitable surface area only increases with the square of radius whereas the mass required increases with the cube of the radius. Oniel cyliners have a much better surface area to mass ratio. So their original planets would eventually end up as a swarm of habitats in solar orbits. Once a population fills that, any surplus population must be shipped out to find a new star. Every year each populated planet sends out its surplus in the form of habitats retro fitted for interstellar travel. the more stars doing this, the closer the total yearly surplus is to the carrying capacity of the new star. If we are unfortunate enough to be in the way of such an expansionist culture, we may find a fleet of construction ships arriving to start building orbital colonies (and more ships) out of any matter they can find. If we get hit by a fleet thats already nearing the maximum capacity of our star, they would have to choose between a primitive surface dwelling alien species selfishly hoarding mass, or their own children. We get bulldosed without hesitation. Absolute worst case is if they go for automation in a big way. Even if their race eats itself to extincion, their machines may carry on. Thats assuming they hang around to inhabit the systems they have already mined out, instead of a slow trickle of surplus, we might face the entire population of their home star migrating all at once, and probably getting here within a few hundred years of each other. Sure they would start with the easy to get mass in the asteroides, then move on to the larger bodies. Thats assuming there are enough easily mined volotiles around and they dont just start stipping atmospheres. In the face of a ravenous hoard, we are just small sacks of indignant water.

[Bill Phil]

Harvesting biomass. It might be very hard to make complex molecules.

6 hours ago, Tex_NL said:

You're right about the resources. Pretty much everything is easier to find elsewhere. Living space is a very good reason to invade and occupy earth. Currently we have no idea of how common a liveable planet actually is. Actual earth like planets (water, oxygen, etc. everything that makes earth liveable) might be extremely rare. An orbital colony, however huge, still remains rather limited. Both physically and emotionally. Nothing beats real ground and real air.
It could be a pre-emptive strike. They might worry we someday could become a threat to them.
Or they might have simply developed a taste for man flesh. An interstellar species could harvest us as easy as we harvest cattle.

Orbital colonies are, if anything, less limited, especially for a species that's very advanced. They aren't limited by habitable zones, they're constructed for the explicit purpose of creating a comfortable environment, and with the resources available in the solar system you can get much more surface area than the planets and moons can provide.

It is real air and real ground. Not terra firma, but anyone who's looking at colonizing space should do away with planets. The only advantage to them would be the resources buried deep within it, and even then, you can use that to make more colonies and support more people. Of course, that's assuming you have super technology to mine entire planets.

Since we haven't built orbital colonies yet, we can't say whether or not there would be major psychological issues. And if they are present, they will fade with time, as people get used to it.

A pre-emptive strike wouldn't have to be an invasion.

[magnemoe]

Making orbital colonies from that you bring in the starship would be way harder than build it in the home system, as we have seen no dyson swarms they have enough space and resources.  

Some reason for an alien invasion, first you want planets with an oxygen atmosphere an advanced ecosystem would be an benefit, you might even find some useful species or useful genes. 
This is the only thing who is valuable enough to skip back slower than light. 
Now having an primitive alien civilization on the planet would be an benefit as you could either trade with it or take it over kzin or footfall style, both is far faster than build an civilization from nothing. 

Now for an fun story assume an travel time of say 50-100 year,  You would not know earth had intelligent life unless you had very good telescopes and understood that the changes was farming. 
then they discover it, you are committed and its up to the captain.

[magnemoe]

5 hours ago, DDE said:

I'm backing up preemptive strike. Don't even need FTL for that, Relativistic Kinetic Kill Vehicles are non-SF planetbusters. And they are nigh-unstoppable.

They make preventive extermination of every possibly sentient lifeform the only wise course of action.

 

This has an major issue, time from you receive the first radio signals to the target has an independent asteroid civilization is not so many hundred years. 
It would be an very bad idea to hit somebody to kill of 9/10 of their population while taking out 1/10 of their industrial capacity, would make them very angry while leaving lots of capacity to militarize fast wile expanding their industry exponential for more military capacity.
My response would not be to kill their planet, just a dinosaur killer level impact from time to time to tie up resources trying to help the people on the planet while I build the invasion fleet. 
Making an relativistic kill vehicle would require significant space infrastructure so the aliens would realize this. 

Yes it could be worse, you could hit an outpost to an empire

[kerbiloid]

Maybe they have developed humanity as a hunting reserve?

Also we can be a favorite toy of their hated neighbor, even if we have no clue about this.

P.S.
Flesh-eating aliens would just take a pack of humans and clone them.

Edited September 14, 2016 by kerbiloid

[KSK]

If life has independently arisen in different star systems (as opposed to life-forms with a common biological origin being seeded across the stars by something), then the chance of a terrestrial ecosystem harbouring anything useful to an invader, whether that be genetic material or delicious tender man-steaks, is pretty remote. At best, Terran biochemistry will be so completely different as to be utterly incompatible with the alien's biochemistry and at worst, to them Earth is a nightmarish world of poisons and strange diseases.

I agree with @Bill Phil Acquiring real estate just isn't a compelling reason for a starfaring species to invade Earth and likewise acquisition of resources. Similarly, I'm having a hard time believing that an alien species would invade over incompatible political or religious beliefs - even assuming they have such things, they're likely to be so far removed from Terran beliefs that any differences are meaningless or literally incomprehensible.  Of course you could posit an irrationally xenophobic race (such as the Daleks) who's only mission is to wipe out anything alien but by definition that isn't a logical reason to invade Earth.

Containment of humanity is a possibly logical reason to invade I suppose, if we were posing a threat to galactic peace or some such reason. Frankly that seems laughable at the moment - right now we're more of a threat to ourselves than anything else.

Edited September 14, 2016 by KSK

[magnemoe]

5 minutes ago, KSK said:

If life has independently arisen in different star systems (as opposed to life-forms with a common biological origin being seeded across the stars by something), then the chance of a terrestrial ecosystem harbouring anything useful to an invader, whether that be genetic material or delicious tender man-steaks, is pretty remote. At best, Terran biochemistry will be so completely different as to be utterly incompatible with the alien's biochemistry and at worst, to them Earth is a nightmarish world of poisons and strange diseases.

I agree with @Bill Phil Acquiring real estate just isn't a compelling reason for a starfaring species to invade Earth and likewise acquisition of resources. Similarly, I'm having a hard time believing that an alien species would invade over incompatible political or religious beliefs - even assuming they have such things, they're likely to be so far removed from Terran beliefs that any differences are meaningless or literally incomprehensible.  Of course you could posit an irrationally xenophobic race (such as the Daleks) who's only mission is to wipe out anything alien but by definition that isn't a logical reason to invade Earth.

Containment of humanity is a possibly logical reason to invade I suppose, if we were posing a threat to galactic peace or some such reason. Frankly that seems laughable at the moment - right now we're more of a threat to ourselves than anything else.

If the life chemistry is totally alien you would be very safe from diseases, you would be pretty safe anyway as diseases are linked to species. Yes they can jump species if they are in close contact but an alien would be as likely to get an disease on earth as you are from getting an disease who only hit plants even if biochemistry is the same. 
Poison is an far more likely problem 

[PB666]

1 hour ago, KSK said:

If life has independently arisen in different star systems (as opposed to life-forms with a common biological origin being seeded across the stars by something), then the chance of a terrestrial ecosystem harbouring anything useful to an invader, whether that be genetic material or delicious tender man-steaks, is pretty remote. At best, Terran biochemistry will be so completely different as to be utterly incompatible with the alien's biochemistry and at worst, to them Earth is a nightmarish world of poisons and strange diseases.

I agree with @Bill Phil Acquiring real estate just isn't a compelling reason for a starfaring species to invade Earth and likewise acquisition of resources. Similarly, I'm having a hard time believing that an alien species would invade over incompatible political or religious beliefs - even assuming they have such things, they're likely to be so far removed from Terran beliefs that any differences are meaningless or literally incomprehensible.  Of course you could posit an irrationally xenophobic race (such as the Daleks) who's only mission is to wipe out anything alien but by definition that isn't a logical reason to invade Earth.

Containment of humanity is a possibly logical reason to invade I suppose, if we were posing a threat to galactic peace or some such reason. Frankly that seems laughable at the moment - right now we're more of a threat to ourselves than anything else.

An exceptionally foolish occupation

[todofwar]

Most earth species don't like eating us because we don't have allot of calories to offer, so I doubt an alien would want to. As for resources, any species that advanced will see Venus next door and terraform that instead of wasting time attacking us. And they can strip Jupiter's moons for water and volatiles all they want, again without touching us. The idea of a Dyson swarm based civilization might result in the destruction of earth, but it would be a few small ships at first. 

I think what we really need to be worried about is those plans on display in the local planning office on alpha centauri.

I think it's likely the species will have environmentalists who insist on preserving us. Maybe let us have one habitat with our most precious monuments (that would be an interesting argument as to what do we save) and enough resources to support a few million of us. Also, as time has gone on we've outgrown the whole rope and pillage phase, maybe all species evolve towards altruism with time.

[RainDreamer]

Replace the human with an alien.

Sometimes it is not about an invasion as much as nonchalant accidental destruction without any sort of hostilities. Some aliens may simply not care about our existence at all or even notice it, just as much as we care about random bacteria in the air.

One day they might accidentally stop too close to earth with a warp drive and blast us with deadly radiation because one of them had to pee so bad.

[LN400]

One reason could be the same reason we squash flies whereever we see them. Flies don't mean much to most of us, we might be as significant to any alien as flies are to us. It's not like we are hellbent on squashing flies, it's just that we don't care and if a fly gets in our way or is of any niusance, then we squash it. We use insect repellants and poison to get rid of mosquitos, they might use whatever they find practical to get rid of us for the same reasons we have.

Humans are not necessarily significant in the grand scheme of things.

Food source? Doubt that. Evolution on other planets have no obligation to follow the carbon path and the substances that make up living things here might be deadly poison to other life forms. Heck, even the oxygen rich atmosphere here might be a poisonous hurdle impossible for them to overcome.

Resources: See the first point.

Other than that

Because it would look as awesome as in the movies.

Because they are interstellar psychos, a travelling Bates' Motel.

Because our existence goes against what their beliefs dictates.

Because they're clowns who don't know when to quit.

Edited September 14, 2016 by LN400

[kerbiloid]

... Because they are Happy Tree Friends.

[softweir]

52 minutes ago, LN400 said:

...

Because our existence goes against what their beliefs dictates

...

I feel this is an idea worth exploring! Humans are very good at finding things "disgusting", whether those things are concepts (religious or otherwise) cultural practices, or even appearance. While it is going far too far to suggest that all hypothetical alien races would have a similar behaviour, it is not implausible to hypothesise that in a sufficiently crowded galaxy at least one race might finds other intelligent races are disgusting or offend their beliefs simply by existing. The might be offended by the fact we are intelligent when their religion demands that they are the only intelligent race, they may be offended by some detail of our biology, they may be offended by some detail of our emotional, cultural or religious behaviour.

I have for a while been considering a situation where humanity might encounter aliens, only to discover that they find us objectionable because we can choke on our food, since (in this scenario) we are the only intelligent race to have evolved with crossed respiratory and digestive tracts. Also that they also find our uniquely bipedal locomotion extremely disturbing, or at least pathetically ridiculous! Though I had not taken that scenario to the extent of having them try to wipe out the object of their objection.

[Kerbart]

10 minutes ago, softweir said:

I feel this is an idea worth exploring! Humans are very good at finding things "disgusting", whether those things are concepts (religious or otherwise) cultural practices, or even appearance.

At the same time, as a species we've already evolved beyond that and we're hardly a space-faring race, let alone interstellar travelers. Of course a different species *could* find us reprehensible beyond repair, but I'm going with Sagan on this, and assume that they would not have gotten where they are with such a mindset.

we do no longer baptize kannibalistic tribes. Hell, we try to leave any untouched tribe as much untouched as possible these days. Aliens, visiting our world as tourists “A unique opportunity; observe tribes that are on the brink of spaceflight. Witness how your civilization was 2 million years ago*” (units translated for clarity) would more likely to prefer it untouched.

[Scotius]

18 minutes ago, softweir said:

I feel this is an idea worth exploring! Humans are very good at finding things "disgusting", whether those things are concepts (religious or otherwise) cultural practices, or even appearance. While it is going far too far to suggest that all hypothetical alien races would have a similar behaviour, it is not implausible to hypothesise that in a sufficiently crowded galaxy at least one race might finds other intelligent races are disgusting or offend their beliefs simply by existing. The might be offended by the fact we are intelligent when their religion demands that they are the only intelligent race, they may be offended by some detail of our biology, they may be offended by some detail of our emotional, cultural or religious behaviour.

I have for a while been considering a situation where humanity might encounter aliens, only to discover that they find us objectionable because we can choke on our food, since (in this scenario) we are the only intelligent race to have evolved with crossed respiratory and digestive tracts. Also that they also find our uniquely bipedal locomotion extremely disturbing, or at least pathetically ridiculous! Though I had not taken that scenario to the extent of having them try to wipe out the object of their objection.

Well, considering that our bipedal mode of locomotion is actually very efficient and effective (one of the best on this planet in fact), it should be the other way around. We should consider all other crawling, slithering aliens as pathetic mistakes of the evolution It is a joke of course

[LN400]

8 minutes ago, Scotius said:

Well, considering that our bipedal mode of locomotion is actually very efficient and effective (one of the best on this planet in fact), it should be the other way around. We should consider all other crawling, slithering aliens as pathetic mistakes of the evolution It is a joke of course

Best as in how we determine best. It does have some drawbacks though. 2 legs require a more sophisticated brain that requires more energy, it requires a sturdy skeleton where other solutions could get away with a less resource hungry skeleton, more muscles just to stay upright. We stumble and fall if we're not careful, one leg out and you have a disadvantage.

From an energy and resources point of view, 2 legs may not be all parade and confetti. Since the existence of aliens is purely speculative, one can speculate that there are other possibilities that we just can't envision since our ability to envision is limited by our experiences here on earth.

[magnemoe]

33 minutes ago, LN400 said:

Best as in how we determine best. It does have some drawbacks though. 2 legs require a more sophisticated brain that requires more energy, it requires a sturdy skeleton where other solutions could get away with a less resource hungry skeleton, more muscles just to stay upright. We stumble and fall if we're not careful, one leg out and you have a disadvantage.

From an energy and resources point of view, 2 legs may not be all parade and confetti. Since the existence of aliens is purely speculative, one can speculate that there are other possibilities that we just can't envision since our ability to envision is limited by our experiences here on earth.

You have two restrains, first you need manipulators as arms, you also need an decent speed for one just to move around, your big brain needs lots of high quality food. 
Without challenges as hard to get food, hunting or avoiding predators its very unlikely you would become intelligent in the first place. 
Outside of the upright walking like we do, you also have the dinosaur body plan where an heavy tail counterbalance the upper body. An centaur like body plan should have an benefit as it would be easy to free up the front limbs. 
Can other come up with more who would work as well or better? 

Note that on earth small animals come in all sort of shapes, large ones come in fewer as its fewer good solutions who works with an one ton animal. 
Edit many of the two legged dinosaurs had small brains, compare with being intelligent balancing on two legs are no issue, four legs is not dynamic stable either. you are less likely to fall if you slide but not much more. 
 

Edited September 14, 2016 by magnemoe