Three Body Problem
When the Culture coalesced from a clutch of space-dwelling humanoid species nine-and-a-bit thousand years ago, by a chance of timing it found a relatively quiet galaxy around it. There were various other mature civilisations going about their business, traces and relics of civs variously Sublimed, retired to quiet Elderhood, abated, gone extinct or otherwise not making themselves apparent to anybody, and - due to the fact nobody else had bothered to go wandering on a grand scale for a comparatively long time - lots of interesting 'undiscovered' star systems to explore.
Exploring the unknown parts of the galaxy - at least, those regions unknown as far as the Culture was concerned - was now the principal concern of the Contact section. Nevertheless, in the swallowingly vast distances between the stars, it was very easy for something to remain hidden, unidentified and unknown for aeons, even if it was not actively trying to conceal itself. It was in these enormous dark spaces that interesting things tended to turn up; things perhaps unknown to any of those actively in-play Involved and Aspirant civilizations.
For this reason, Culture Contact ships frequently took less-than-direct routes across the Galaxy, often acting on obscure theories, deep research in ancient archives or hints exchanged in inter-Mind gossip, or sometimes just on a whim.
A hundred or so years before, the GCU Pretentious Twaddle had accidentally discovered an enigmatic construct during an eccentrically indirect route between stars, situated in a very sparsely-populated section of the galaxy a considerable number of light-years from any stellar system.
The artifact consisted of a cloud of several hundred spherical objects, in numerous different sizes but all hundreds of kilometres across, and all polished smooth to sub-millimetre precision on the outside. The spheres were presumed to be habitats of some kind, although they were all empty of life or even the sign of ever having been inhabited, and every one was pierced from surface to core with innumerable passageways - some barely wide enough for a human and others capable of accommodating a starship - linking spherical chambers with a similarly bewilderingly vast range of sizes. Their material composition seemed to resist a complete analysis; whatever it was, it was extremely dense and was almost certainly not conventional matter at all. Thanks to their mass and consequent gravitational attraction, the objects were in constant chaotic motion, unpredictably whirling and swirling around one another but - and this was the key observation - never, ever colliding with one another.
The Pretentious Twaddle and its crew studied the inexplicable artifact for a week, becoming increasingly puzzled, and named it the Delphic Chaosarium. It then called for help.
The Chaosarium was a perfect example of a truly, hideously, ineffably complex and entirely insoluble problem in mathematics, at least as far as the understanding of the Culture was concerned. Indeed, it looked like it had been deliberately set up to illustrate a perfect solution for this kind of intractable problem, as some kind of final signature statement by whatever civ assembled the thing in the first place.
The laws of motion determining the future position and velocity of each body in the cloud of objects were of course well known, but they depended on the distance and direction to each body from all of the others. But all of the other bodies were themselves in constant motion, so solving the entire set of equations for all objects for the next second, the next instant, was a problem without a precise mathematical solution. So imprecise, approximate mathematical methods and tools had to be used instead, which were capable enough to give good solutions for short time intervals, but tended to quickly diverge from the real behaviour over longer periods. The upshot of all this was that the movement of the spheres was effectively unpredictable for more than a few days ahead, even with the prodigious computational and Mind-modelling capacity available to the Culture.
In theory, though, a chaotic cloud of objects ought to be subject to the occasional impact. This was the principal way in which stars and their stellar systems coalesced out of a chaotic primordial dust cloud: collisions causing particles to stick together, converting the kinetic energy into heat and boot-strapping the process of nuclear fusion at the heart of every sun. But, even more worryingly, the spheres in the Delphic Chaosarium somehow never collided with each other, even over periods measured in millennia. The objects themselves didn't seem to have any sensory or propulsion/course-correction capability - none had ever been observed in use, at least - which suggested that the equations of motion had been worked out to a frankly impossible degree of accuracy when the artifact was created in the first place, carefully and precisely arranged so that the objects never collided.
The inference, which had made itself apparent to the Pretentious Twaddle after a prodigious amount of close observation, was that there was - or had been, at least - a species or creature or construct very significantly smarter than anything the Culture could manage. Whoever they were, they were unique, in the Culture's not-inconsiderable experience, in being able to see the future: not in some mystical metaphysical sense, but they could actually, mathematically, predict the outcome of complex events whose outward appearance was completely random and arbitrary.
The tangible proof that some ancient civilization could do something that the Culture could not was, naturally enough, the kind of enticing lure that just could not be ignored. As it had to be studied in-situ - since it could not, by definition, be recorded or modelled satisfactorily - the Delphic Chaosarium became a place of special study for the Culture, almost the destination for a pilgrimage, for those seeking a predictable future or wishing to pull some sense of order from apparent chaos. It tended to attract intense, thoughtful people, and intensely introspective Minds, too; it was a place for quiet contemplation of the structure of the universe, to ponder the ineffable nature of chaos and the indefinable characteristics of the infinity of space and time.
For this reason, there had been a continuous Culture presence at the Chaosarium since its discovery.
"So, it's a way of telling the future?" he asked.
"Not quite," the drone replied gravely, "It's a demonstration that, at least in some cases, the future can be foretold with astonishing, indeed impossible accuracy. Something we, the Culture, can't do. Can't get even close. Much to the annoyance of certain Minds I could mention."
"Whoever it was that made this thing," the woman added, "If they could predict the motion of a system of this complexity, perfectly, for unknown aeons, what else could they predict?"
Qu-el Histoker was a squat but powerfully-built homunculus of a man, more hirsute, perhaps, than human-basic norms but certainly unremarkable in a society where physical appearance, or even basic body plan, was optional, usually a fashion statement and could be changed on a whim. He eyed his companions clustered around in the accommodation section of the ex-Very Fast Picket Negotiation Is Overrated, now rapidly being re-commissioned as a full warship and re-re-designated as a Rapid Offensive Unit.
"Okay, I appreciate that the Chaosarium is unique, unprecedented," he said, "But why do we have to go there? Surely the Culture already has a presence in the locality?"
Roosh Formali-Kai had once been a state-of-the-art Special Circumstances drone. But that had been centuries ago; inevitably, technology and manufacturing capabilities had moved on, and more modern equiv-tech espionage-level drone models had vastly superior capabilities in almost every area. With the state of emergency, it had rapidly been refitted with such upgrades that could be achieved without a total rebuild. Not like it was anything like enough of an improvement, it had thought pessimistically.
Nevertheless, the ancient machine had retained its outward appearance: a gunmetal ovoid, now displaying the yellow-green aura field of mellow approachability, bisected by a narrow sensor band currently swirling with an iridescent sheen like oil on water. The old drone was acutely aware that its selection for this particular mission was not on the basis of its capabilities, but more on the fact that it just happened to be on the Continent-class GSV Absolutely No You-Know-What which, entirely by chance, was heading in the general direction of the Chaosarium and could get them, and the Negotiation Is Overrated, in the general volume in the next few days. The Culture Contact section had a saying for this: "Utility is ninety percent proximity".
The Absolutely No You-Know-What was in a state of extreme activity, converting, re-commissioning, upgrading, refitting, and just generally cobbling together every ship available in its hangers, as well as building as many new ships as it could. This demanded the full-time attention of the GSV's Minds, so it was leaving the briefing for the crew of the Negotiation Is Overrated to the ROU itself.
"Of course there is a Culture presence there," Formali-Kai replied, its aura briefly flickering rosy-red, "But it is hardly on a war-like footing. They may not even have heard that the Culture is now at war or, even if they have, decided that it has nothing to do with them. Frankly, they're a bunch of introverted tourists barely able to see anything beyond their metaphorical navel."
"Actually, they are a formal Contact mission, and they are well aware of the declaration of war," the ship interjected, sounding amused, "What they don't yet know is the importance that has been attached to the Chaosarium, or why."
Foklane Valbada was lithe and athletic, taller than her male companion and quite noticeably strong around the shoulders; she looked like one who regularly swam a great many kilometres. She had been in Contact for a long time, and had experienced an immense variety of missions and encounters along the way. Being bounced at short notice into what was almost certainly some kind of SC response to the current emergency was, she privately considered, almost certain to end in tears, but she found she had no moral basis to refuse the assignment she had been offered.
"So what exactly," she demanded, "Is the supposed military importance of the Chaosarium?"