This is all that needs to be said.
But the zombie apocalypse is just around the corner… :eek:
No. 1 , All the world does not have to be like the US. Perhaps the Chinese with their American industry granted wealth and power will try peaceful space exploration. War is our top export. It does not have to be theirs. If they do decide to start taking over, the world could be an ugly place indeed.
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Civilizations might choose to channel their aggression to other races or may just be violently xenophobic. Or, you know, have completely alien motivations.
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Given what we currently know of physics, yes. Suppose alien invaders had some strange device (let’s hypothetically call it, I dunno, a Star Gate) that let them instantly travel from one location to another. Then, all bets regarding interstellar invasion would be off.
Also, there're incredibly expensive methods of space travel that mandate invading other solar systems. Consider, for example, the book "Footfall" by Niven and Pournelle. As I recall, the aliens travel to a new solar system in slower than light macrostructures. But it's a hail mary pass. Once they get here, they need all the resources they can get to either settle or keep moving on. If we don't want to share our resources, they have no choice but to take them. After traveling for 100's of years and finding a planet that supports life, the aliens might just prefer to take it rather than get back in the car for another millennia or two.
I happen to know of a planet where this is true. The four footed furry ones, with a tail. The Earth bipeds, not so much. Tongues are much too small.
Well, sure…now it’s unlikely. I scared em off with this thread.
Nor would it be such a task for such creatures to create a virus that only affects humans. No dust to wait for settling. I wonder is that is what all the anal probing is about? Rather than just the redneck way of saying they secretly desire back door shenanigans, that is.
To say that “we’re on the verge…of interstellar space travel,” is a reach. We may be able to travel to other systems in the next one hundred years, or not within ten thousand, all depending on what kind of paradigm-transforming discoveries in physics that may or may not occur. We almost certainly are not going to be bodily traveling to other systems with an extrapolation of any existing technology, including fusion-based rocket propulsion, as the specific impulse requirements to transport any appreciable payload (and decelerate it on the other end) are just to large; at best, we may be able to send small, self-replicating probes to explore other systems, and even this would require substantial (but physically plausible) extensions of nanotechnology and machine intelligence, perhaps by combining them with biological molecular engineering, i.e. something akin to Freeman Dyson’s Astrochicken concept.
As for an alien species invading the Earth: why would they bother? It is unlikely that the conditions on Earth would be such that they would be optimal for supporting an alien lifeform, and there are vastly more mineral and elemental resources to be found in space, readily accessible in the form of asteroids and comets that are far easier to extract than having to pull them back out of a deep energy well. Any alien species that has developed the infrastructure to survive indefinitely in space and has access to enough energy to be able to transit between star systems is probably going to be far beyond a dependence on living on a planet’s surface. The only reason I can see for an “invasion” is an evolutionary imperative to quash all competition, in which case it is still far easier to destroy complex life on Earth from afar (dropping asteroids, radioactive dust, et cetera) rather than land in troopships and start blowing blue flame out their arses.
Stranger
And to make it even more unlikely take a look at where the Earth is in relation to the whole Milky Way galaxy. Not only do we orbit a mundane star, we are situated pretty much near the ass end of our galaxy.
We are located in our galaxy’s version of Siberia.
Well, that’s one way of looking at it. On the other hand, we may be in just the nice temperate Mediterranean area, free of high stellar density zones with supernovae exploding every few eons, washing the nearby area with lethal radiation, and yet close in enough to be cushioned from being cast into a hazardous region with objects with high proper motion and in a region with a high heavy metals concentration to support life.
There is a good argument to be made—even from our limited empirical data set–that even within a relatively confined region of space, the formation of life is either very, very common (i.e. the random processes that result in the formation and stability of self-replicating molecular structures can be found all over the place in the habitable regions of F, G, and K spectral class stars and must occur with high frequency), or that the formation of life is very, very unlikely (i.e. that it takes more than just the right conditions and a few billion years of time; some special conjunction of fates has to occur in a very specific order). We can say this because while we’ve been able to produce all of the precursors to life in a fairly simple laboratory experiment that spontaneously produces amino acids under primordial conditions that are likely common, we’ve only see one clear lineage of DNA-bearing life on Earth, which means that life either only formed once, or it emerged statistically many times but one particular form came to dominate.
Now, complex, much less sentient life, on the other hand, we have no basis to say anything substantive, other than it appears that modern life went through a series of bottlenecks (multiple endosymbiotic transitions, multicellular speciality, sexual reproduction, et cetera) in order to get to a point of developing bother vertebrate and invertebrate species that have some nascent means of tool manipulation and self-awareness. How common or likely these are to occur independently is difficult to say insofar as we have very little insight into how these occurred even in our own evolutionary history, much less extrapolate what the probability might be in a different environment.
Stranger
Not as big a barrier as you may think.
The Fermi Paradox has it that, even assuming sub-light “slow” spaceships a species should be able to populate the entire galaxy in around 10 million years (this assumes time to find a new planet, setup shop and develop industry sufficient to send a new bunch of settlers on their way some centuries later). It’s slow in the beginning but in time the growth becomes exponential.
Ten million years may seem a long time but it really isn’t. Considering the earth is a few billion years old all you need is some species out there to have a minor (cosmically speaking) head start and they could be all over the place.
Actually, the Fermi paradox is what makes me strongly believe any alien contact is going to be immediately hostile to humans.
If a alien happens to be peaceful, they are not going to expand. We’ll probably never hear from those ones. They will probably never go much of anywhere, maybe just expand and live in space as Stranger suggests.
But the intersteller travelling alien that decides to expand - watch out. These are the one’s we are most likely to meet. As you point out they could colonize the galaxy within 10 million years, and planets like Earth will be just another stepping stone. Another ‘egg’ in their basket.
I actually wonder if humans will eventually start to expand this way (starting many centuries from now of course). One reasoning would be that if we don’t, eventually some other alien will. And if we don’t build up our planetary count as early as possible we’re weak. Only by having enough ‘eggs’ in the basket can a species like ours last as long as the stars do.
But perhaps any advanced aliens out there stop once they feel they have enough ‘eggs’ and security. Getting back to the Fermi paradox, the fact that no alien has steamrolled through our solar system so far makes it seem likely that interstellar travel is not ecessarily worth the effort. Hence, our greatest defense is still the distance of space itself.
Funny thing about this is that the species becomes fragmented. If in the process of colonization, a fiftieth-generation colonist encounters a member of his species that didn’t leave the original planet (representing a few thousand years of separation), they might appear as aliens to each other.
This is highly unlikely since, unlike Star Trek, the odds of stepping out into an alien biosphere and having it sustain and nurture a biology that will pretty much inevitably will not be adapted in any way, shape, or form to it are about as astronomical as the journey here would be. If you are actually flying to other solar systems in your own body and surviving the trip your level of technology is probably so high that any material needs you have can be found using the resources of your own solar system and perhaps the next couple near yours. It might be more easy to terraform any other system that is in the Goldilocks range than to practically start from scratch eliminating and terraforming ours. In fact, doing so around one of the many, many, many more red dwarf stars out there would also have the benefit of a star on a main sequence that might continue for many more billions of years than ours. The odds of finding one in such a system, such as the one harboring Gliese 581g would also be greater than coming here as they are likely to be common. There would be doubious material or habitable gains to be made by traveling to Earth.
You also make a huge assumption that our own history and motivations are the only reasons any alien civilization might have to travel anywhere. An alien biology and culture, especially if they have technology which would likely be advanced enough to us that they would be perhaps sentient to us as we are to lesser animals on Earth could have motivations that we could not begin to consider. And perhaps there are no good options for traveling far beyond one’s solar system in the end, even for beings who have the tech and can afford to do so.
If an alien civilization has found a way to travel across the stars, they very likely have a level of technology that’s difficult for us to comprehend. The energy and technology required to get here would also give them anything they needed. Earth doesn’t have a special gooey center - we’re not geologically or metallically all that unique. Aliens aren’t going to invade us for iron or wood. And they aren’t going to take us for slaves because their robotics are almost certainly more practical than owning alien slaves. There’s almost no reason to try to invade earth.
Destroy us, on the other hand, maybe. When you get to the level of technology where you’re zipping around the galaxy (if it’s at all possible), you probably have access to such huge amounts of power that destroying entire planets is practical. If you can move a ship across 50 light years, you can probably move a giant asteroid at relativistic velocities across a solar system. Once the ultimate destruction is available, the universe becomes a very scary place to live in. One species who got out to the technological lead first may think that allowing any other species to achieve a similar feat would be too big a threat to their very existance. So they may proactively travel the universe crushing out any life they find in self defense.
Earth’s atmosphere may well be poisonous to aliens, but as you say, terraforming is a definate possibility. Furthermore, if we can assume that liquid water is important for at least some significant portion of aliens, then they would hardly be starting from scratch with earth.
Consider inherent advantages of Earth that might make it a good place for hypothetical aliens versus any other number of other potential planets in goldilocks zones.
- It rotates, causing uniform distribution of temperature within its surface area. You don’t get that with Gliese 581g, which is tidally locked to its sun.
- It is in a solar system that has been around long enough to clear out the asteroids, and the earth has very infrequent hits. Granted, an advanced alien could probably deflect asteroids anyways, but it is extra work/energy they don’t have to expend.
- Our sun is going to be stable for another billion years or so.
- Our system is not a binary or multiple star system, which potentially have orbital disturbances or extreme planetary temperature variations.
- We have an atmosphere. Aliens might have to heavily modify it but at least the basic organic molecules are already present to do so.
- We have a lot of liquid water.
- Our weather is managable. Other planets, such as Gliese 581g might have completely insane storms due to their extreme hot/cold areas.
Hypothetically advanced aliens could add water & atmosphere to any old rock in a goldilocks zone via asteroid collision - but how long would it take for the water/atmosphere to stabilize and form. I was under the impression it would take millions of years.
Compare that to travelling a few hundred years, maybe a few thousand years to reach earth which already has all of the basics mentioned above.
Now, I hate bug-eyed monsters as much as everyone…but do you have to be so mean?
Several theoretical designs have a reasonable sized fusion rocket reaching 10-20% of the speed of light. That would easily bring anything within 10 light years within reach. Fusion is not I think a paradigm-transforming discovery. Antimatter would make it faster or the fuel requirements smaller. I don’t think antimatter is paradigm-transforming discovery either, as it is a well examined phenomenon. As such I don’t think it is unreasonable to assume we will have mastered fusion and antimatter technology within the next 1000 years.
My personal, pulled out of my butt, opinion is that life is very common. However, multi-celled (or equivalent) is extremely rare.
What is the limiting step?
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Life forming?
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Multi-celled life?
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Intelligent life?
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Technological civilization?
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Interstellar travel?
I think it is multi-cellular life…though it could also be intelligent life. I think, and hopefully am wrong, that if we ever ‘get out there’ we will find only bacteria and no even close to inhabitable worlds. A desert. THAT is why we have never been invaded.