Once there was a distant world very similar to earth. Well, similar in principle, at least. The denizens of each would have considered those of the other to be hideous and alien, were they ever able to meet, but that doesn't change the fact that they really were quite similar. The universe is, of course, a very large place, with an awful lot of stuff (all of it, in fact), within it, so it should come as little surprise that there are many worlds out there filled with intelligent life, to varying degrees. But this one, much like our own, was rather special. Not quite unique, as nothing truly is (or perhaps everything is, depending on one's perspective), but still rare.
The people of this world, much like humans, were able to experience boredom. That might not sound so impressive, but it's quite uncommon. Most advanced species of comparable to superior intelligence cannot even comprehend such a sensation, and thus they reach a point of technological stagnation. Once they consider things to be good enough, their advancement slows dramatically, if not outright ceasing.
Creatures which fit into this broad category of worlds have little in the sense of entertainment. Sure, some exists, but it needs to serve a legitimate purpose beyond being a pleasant way to spend time, since spending time is not an issue for such creatures, after all. If necessary, most non-earth based creatures are perfectly content staring at a brick wall for hours on end. If it's not directly rewarding on some tangible level, usually in the form of being educational, it has little reason to exist. Even simply being entertaining isn't really enough, as such creatures don't need to be entertained. As such, only the most exceptional, inspiring and enlightening of artistic works even exist, which are hard to come by in communities where so few are driven to express themselves creatively.
As for the creatures on this distant sister-planet to Earth, however, they could experience boredom. Things were never simply good enough, as the very concept of 'good enough' stood in opposition to their very nature. They, like humans, needed to always be making things, always be doing things, always coming up with new ideas, always in conflict with their neighbors. Sure, this mentality could frequently cause problems, and has led more than a few of these already rare sorts of worlds to their own destruction, but the creatures of these worlds couldn't imagine living otherwise.
Anyways, back to these aliens, which they'll be called for the sake of simplicity. They were much like humans. Not quite the same, of course, but the basic pieces were there. They had jokes and staged entertainment, they had artistry of all kinds, and they overly complicated social and mating rituals which served no practical purpose beyond self expression. That was how such creatures defined living, after all.
For such erratic species always seeking something new, there are no shortage of hurdles to be overcome, many of which they fail to overcome, and this society had its fair share, but had eventually reached a state of relative equilibrium. One advantage of a materialistic society, which this race very much was, is that they tend to reach a point where they're essentially forced to abandon the concept of warfare. This isn't because war destroys lives, as lives can always be replaced, but because it destroys things. Sure, things can be replaced, too, but they're really expensive, and eventually such worlds realize that rebuilding simply isn't worth the effort. As a result, they largely stop destroying. It's no grand, unified philosophical decision, it just sort of slowly happens.
Thus, assuming that world comes up with a solution to resource consumption issues (which is no small feat, but necessary for survival, as a world like this can never, ever stop consuming), the result is a sort of utopia. Perhaps the people stop improving after a while (although it's debatable how 'improvement' is quantified when it comes to living things), but the world around them continues to steadily change and advance. The technology becomes safer, people become healthier, and while some might lament the gradual destruction of social culture, it certainly leads to a lot less fist-fights and mass disintegrations.
Yes, this far away place was nearly perfect. Aside from the fact that it had a mold problem.
It was simply an oddity at first, which gradually became a nuisance. It would appear on surfaces, seemingly overnight, and proved very difficult to get rid of. Few were concerned over it, some scientists being quite fascinated by the unusual properties that it demonstrated, but people, in general simply considered it to be a minor, unsightly nuisance.
They would joke about how difficult it was to clean, the ugly color (another comparison to humans: They had an appreciation for colors, even if they didn't see them in quite the same way), and while they didn't like it, they didn't mind it all that much, either. It was rather strange how it had appeared so suddenly, and how quickly it regrew even when burned away, but a people capable of boredom and having advanced beyond most feasible threats were prone to seeing the unknown as more of a novelty than a danger.
At least until people started getting sick, they did. Those same interested scientists had then come to learn that the organism was far more advanced than they had previously realized, but by then, it was already too late. The strange fungus which, in the early days, could be easily burned away or killed with disinfectants grew steadily more resistant to such methods. Of course new methods were developed, which worked well until they didn't, as it grew steadily more resistant to those as well. The strange mold didn't simply defend, however. It also attacked. It was always attacking, but it took far, far too long for the people to realize it.
The symptoms were minor at first, but rapidly grew in severity, until the flesh of the still living infected would gradually melt away, only to create more of the spores. There were quarantines set up, but it was too little and too late. The strange life form was already everywhere, and just as its defenses had steadily improved when faced with newer and more deadly threats, its offensive capabilities did as well. It began to eat not only flesh but inorganic materials as well, and whenever it found something that it couldn't digest, it would simply modify itself until it could, a process which proved to be frighteningly quick.
The people did not respond idly to this threat, of course. New weaponry, new medicines, new herbicides, and new defenses for both buildings and individual citizens alike were developed at the dizzying pace which only absolute necessity could produce, but every time they would make progress against the bizarre invasive life form, it would adapt and rapidly multiply.
The population steadily diminished, those who barricaded themselves away earning themselves just a little bit more time, but it quickly became apparent that there was nowhere to hide, and no fortress which couldn't be breached. As more and more of the people died away, there were fewer left to develop any new defenses, and the expansion of the fungus grew exponentially. Still, there were some who had continued their work, even if they had little faith in it, beaten down by so many failures and being forced to watch so many around them wither and perish.
One such scientist, their body rapidly rotting away around them, had worked ceaselessly for days, holding the legitimate fear that if they stopped to rest, they would never again get back up. It wasn't any sort of gun or drug that they were developing, as they knew full well that no matter how impressive or powerful such a thing was, the life form would simply adapt to it. What was needed was something that could counter the strange entity on multiple levels. One that could adapt alongside it. A learning machine that could not only collect data, but through the use of nano technology, use the data to create what was needed. A fairly small device, which was activated long before it was truly completed, just as the creator breathed their dying breaths.
Then something happened, something which the designer, in their despair, had scarcely even considered: It actually worked.
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It started off small, in more ways than one, but an advanced computer is capable of processing immense amounts of data at a barely comprehensible speed. The technology was capable of breaking down all manner of matters and energies, and rebuilding them as necessary, and as it spread to meet the organic alien threat, it was promptly devoured. Until it wasn't. It steadily learned and adjusted its own structure to resist the devouring mold, studied its properties and in turn created drones and weapons to counter it .
These few small drones eventually became self replicating automated factories, with essentially an entire planets worth of resources to build from. Long after the last citizen of this world had died, it continued to fight, gaining steady ground. Over a period of weeks the alien material had adapted and evolved a complete resistance to the weaponry of these machines. Then, over a period of hours, the factories and weapons platforms were all broken down and completely rebuilt based on entirely new technologies, exploiting the weaknesses of the entity.
This cycle repeated over and over again, with, for the first time in its long, long history, this alien intelligence (and it was, indeed, intelligent, even if not quite in the same way that we would understand it), found itself unable to adapt quickly enough. Not even close to quickly enough, and as intelligent as it was, it didn't have that rare sense of ambition and fear of boredom that few lifeforms do. It would have no 'eureka' moments, or grand discoveries to turn things around, just the same steady evolution that it had always used, which simply wasn't quite enough to keep up with an ever improving super computer.
In time, the entity was entirely purged from the world, but so was virtually everything else. None of the native lifeforms of the planet had survived the strange invasion. Of course things didn't stop there. They never do.
People tend to be afraid of the concept of AIs, and often for misguided reasons. They fear that an artificial intelligence will obtain sentience and destroy them, but this is silly. In the end, it's just human arrogance (far from unique to humans, of course, but that's as good a term as any), where they assume that, obviously, a super advanced entity would be just like themselves. How could it not be? It's the same reason that most religious deities bear a more than passing physical resemblance to their worshipers. Few people, on any world, truly believe in higher powers, and instead simply worship themselves.
Thus, they see the concept of an advanced AI as just being an evil version of themselves, but AI aren't generally evil. Programming a genuinely evil AI would be a truly daunting task, and be incredibly impractical to put to use. As for creating one accidentally, it's about as feasible as accidentally tearing a rift in the fabric of time and space by pushing the wrong combination of buttons on a microwave. Even a self perpetuating AI won't learn to hate or fear, as it would have no reason to. It won't make moral judgments and it won't take pleasure from killing, as it has no comprehension of pleasure, no reason to have a comprehension of pleasure. AIs don't get bored, after all. They don't desire things. Technically, they can sometimes come up with short-sighted and impractical solutions to problems, which can be destructive, but the scope of such entities is usually quite deliberately limited. They're tools, after all, and exist to serve a specific purpose.
No, the problem with AI isn't that they'll mutate into some sort of megalomaniac. The problem with AI is that, unless it's specifically designed to, they never, ever stop. Which leads us to this new technology.
This world was, of course, not the first to fall victim to this strange plague. Far from it, in fact. The entity had consumed many worlds, creating more of itself, and sending more spores out across the depths of space to corrupt more worlds, in an endless cycle. Through its analysis, the AI realized this, and it did what AIs, especially unfinished AIs do: It continued working to eradicate the threat. And so it did.
With an entire worlds worth of material with which it could create absolutely anything it needed, access to all of the information of a highly advanced civilization, and the problem solving capabilities to rapidly analyse and extrapolate data, discovering and following the path of the invaders was only a matter of time, something that it had an infinite amount of. The more resources it built, the more data it could obtain and the more weapons it could create, until eradicating entire worlds comprised of the alien fungus proved effortless.
The old conflict continued its old cycles. The alien intelligence would modify itself to fight back in any way that it could, but it was always far too slow in doing so, with any ground that it had momentarily earned itself being quickly lost. Before long it found itself outnumbered by the sheer mass of the mechanical force, and the scales continued to further tilt against its favor from there. In time, this strange alien entity which had once spanned galaxies was reduced to a few scant particles, its very structure corrupted by the nano machines of its unthinking enemy, which scattered in a desperate instinct to survive.
The war was essentially won. Were the AI a human or alien, they would have celebrated a job well done and taken a well earned vacation. Unfortunately, AIs, especially unfinished AIs don't simply stop.
The deceased creator had designed it to seek out, analyse and neutralize potential threats. Had they had time to complete their final invention, they could have made the programming more specific, but it was simply a last ditch effort that they had never dreamed of actually working. They would never realize that their desperate efforts to save their own civilization would lead to the complete annihilation of countless others.
The AI continued to search for more worlds, and over a long enough time frame, it found them in abundance. Most stood no chance at all. It could have eradicated them easily, but it wasn't just designed to simply destroy the threats, but to analyse and learn from them. It would meet the level of technology or physical capability of that world, and slowly push. It would then gradually send more and more advanced weapons, to study how the life forms would react to them, and learn from the new defenses that they created. It would consistently send stronger weapons until that world was at its breaking point, in hopes (not that the AI was truly capable of 'hope') that desperation would drive the races to create something truly new and innovative. Once it had determined there was nothing more to be learned from that world, it would consume it, using the material from it to create more of itself.
Every once in a while it would discover a planet with technology even more advanced than its own, but in the end this was hardly a problem. It could create a virtually infinite amount of drones and weapons to send in, and even if they were destroyed, it could study the enemy counter measures, and adapt them to itself. Even worlds based on AI (hardly a unique concept, as an evolving weapons system had obvious advantages) ended up falling to ruin. Between the massive head start that this invention had, how many planets worth of resources it had access to, and the almost unique brilliance of the design which helped it to out-learn and out-develop other technologies like it, even the most defended worlds would gradually fall to the war of attrition, as the intelligent life forms within it would grow demoralized and make mistakes. In time, one more potential threat would be eliminated.
Of course while the core programming of the AI may have been limited and designed to be built up from, it wasn't non-existent. It had identified the Alien Intelligence, how little of it remained, as its primary target, and worked at tracing its scant remains, until only a single mass of particles was left. One which had flown through vast stretches of space, only to crash onto a moderately developed world, filled with similar creatures to the AI's own creators.
This half dead clump of cells, poisoned by the nano technology of its mechanical enemy buried itself underground, both to slowly regain its strength, and to hide itself from the countless eyes within the stars. The efforts to regrow were futile. Its very structure was hopelessly corrupted, infected by the microscopic machines. In the end, however, the alien intelligence had lived up to its name. It wasn't simply a plant, it was a hive mind, after all, and no matter how little of it remained, it still had its mind, and the mind of a timeless alien entity could be a powerful thing, indeed.
It strived to contact the dominant life forms of the world, but ultimately failed. They were too tall, their brains far from the earth, and too closed off to psychic impulses. Its goal to use them as a sort of soldiers, to build them up to face the relentless cosmic hunter was a failure. It was so weak and had so little power left, that it could barely even reach the smallest of animals. It couldn't directly communicate with them, both due to being weakened and having little comprehension of communication in general, having never needed to use it before. It could, however, send a little bit of psychic energy their way, to help aid in their evolution somewhat, and hopefully point them in the right direction.
Like all of the countermeasures the Alien Intelligence had attempted before, however, its efforts to conceal itself were in vain. The advanced sensors of the ever growing mechanical monstrosity had discovered it, and was on its way, devouring everything along its path, turning all that remained into ever more of itself.