There was the subtlest of changes in the ship around them; later, Matlyen wondered if he had simply imagined it.
"We are under way," Harunda-Lua announced, "The Reformed Pacifist tells me that the engine tests took longer than expected - some minor fettling, it seems - but they now appear to be working as well as expected."
"Good news," Matlyen agreed, "Does this mean I can get out of this thing?"
Before even the drone could answer, the suit effortlessly separated from the acceleration couch in which it had been partially embedded only a moment before. Matlyen found he could sit up, assisted only very slightly by the suit. The pale eggshell cylinder that was Harunda-Lua's casing appeared in Matlyen's line of sight, its aura field once again a band of yellow-green around its centre.
"How's that?" it asked solicitously.
The couch tilted so that he half-slid, half-fell onto his feet. He stood up straight, flexing his muscles and rotating his hips. He felt fine; more than fine, really good. The helmet sections of the suit folded themselves neatly into the collar around his neck; the gloves covering his hands similarly furled themselves into his cuffs. It felt like he was wearing a fairly heavyweight one-piece coverall, but it did not seem to be either actively supporting him or restricting his movements in any meaningful way.
"Much better," he replied, "Back at full strength, I think."
"Good to see you are back on your feet," the voice of the Extended Adolescence came from nowhere in particular.
Matlyen was genuinely relieved to hear the voice of the old ship. He surprised himself by how much he had missed his conversations with the erstwhile LCU.
"Hello, ship," he said cheerfully, "Can I take it you are fully restored?"
"I'm fully operational," the Extended Adolescence replied, "Although I'm no longer 'the ship', I'm afraid. The Reformed Pacifist is running the show, so I am, once again, just a passenger."
"Yes, of course," Matlyen said politely while the couch gently folded itself into the floor, then added, "So perhaps you could find the time to explain to me what exactly is the insight you gained from observing the Castophrenic Widowhood ship when we were trying to escape."
"I can do that," the Extended Adolescence said immediately, "Although it will take a little time."
"Time," Matlyen replied, "is not currently pressing upon me."
The explanation was long, complex and, it had to be said, stretched Matlyen's talent for mathematics - which was middling at best, he would have admitted immediately - to the limit, even with the aid of equations, models and diagrams displayed via his neural lace. He was at least able to appreciate the elegance of the new formulations, even if he did not really understand all of the details. The drone waited politely during the explanation, without interrupting, although Matlyen suspected Harunda-Lua had already received a similar lecture, albeit at much higher speeds from the old ship.
"So, a key observation, given the insights into the behaviour I managed to observe," the Extended Adolescence concluded, "Is that that what we previously thought of as being genuinely chaotic activities are at least partially predictable given the use of novel transforms in sub-hyperspace dimensions. Therefore, purely random actions - which are in practice just the result of chaos below the level of general observability - are likely to be mappable onto chaotic events and thus tractable to the same transforms."
"I see, mostly," Matlyen said candidly, "And how does this enable the Reformed Pacifist to move without being detected?"
"The surface of the Grid is in constant chaotic movement," the Extended Adolescence replied immediately, "Although the extent of that movement is rather small compared with the distance in hyperspace between the Grid and the skein. So, hitherto, a Culture ship's engine fields simply ignored the apparently random fluctuations and engaged with the average position. This is, in fact, extremely efficient, so that the maximum speed of a ship is determined by the area of the hypersurface the fields can interact with, and therefore the volume in hyperspace those fields can create."
"Yes, I can understand that," Matlyen said, sounding confused, "But what has it to do with being invisible?"
"Oh, it's not quite invisible," the Extended Adolescence replied, "Although it does make the ship much less easily detected when in motion. The Reformed Pacifist is now continuously altering its engine fields, minutely, to align more precisely with the chaotic movement of the Grid, which it can now partially predict. The difference between the terminator of the engine fields in 4D and the Grid's hypersurface is much smaller, so the disturbances caused are also small and more difficult to spot."
"And the engine rebuild was to allow the ship that level of control?"
"Essentially, yes. So, now, the velocity at which the GOU proceeds while remaining hidden is effectively limited by the speed and precision with which the Mind can solve the appropriate equations and adjust its engine fields to compensate. Any faster, there is more chance of the predictions being out of date and therefore leaving a trail, a path of disturbed spacetime which would make both our presence and passage more obvious."
"Okay," Matlyen said thoughtfully, "So the ship could still travel as fast as before, if it really needed to?"
"Again, yes, although this would negate any attempt at stealth. So we are currently travelling slowly, as the Reformed Pacifist suspects that the Castophrenic Widowhood ship is still out there."
"The one the Reformed Pacifist spotted earlier?" he asked, anxiously.
"Yes," the voice of the Extended Adolescence said, "And it might be the same one which attacked us, although that's less certain. Although if it is the same one, we must really have annoyed them."
"So, the ship's going to keep its metaphorical head now and just pootle along to a point where we might just get picked up by the Obambulatist?"
"So what should I do in the meantime," Matlyen said, half to himself.
"Get some more rest," the Extended Adolescence said immediately, "And, if I were you, I'd get an in-depth briefing on the Delphic Chaosarium."
Once again, the Mind of the Extended Adolescence opened a communication channel with the Reformed Pacifist.
~Can I distract you a little once again, it sent, there's something else bothering me.
~Well, I am fairly busy doing hard sums on a regular basis, just to keep moving onwards, as well as keeping a weather eye out for that dratted Castophrenic Widowhood ship.
~Thank you. Indeed, it is that ship that is concerning me. Can I take it that you have had no further sightings, as it were, from your sensors.
~Not a peep.
~Well, that's good news. It seems that, for the time being at least, our little ruse of pretending to be an itinerant asteroid for a few days has not been spotted...
~What do you mean?
~My understanding is that leading individuals in the Castophrenic Widowhood are usually the cleverest as well as the most suspicious individuals. And they are not all that stupid, even if all their important decisions are made at bio-brain speed.
~So, there's a decent chance, according to my simulations and probability models, that you were under their surveillance when you dropped out of hyperspace and went dark, even if you were unable to detect them.
~And therefore they may very well have seen, at least roughly, where you were when you did that. They could easily decide to investigate further, given that the alternative would be to admit to their superiors that they had lost you with, I suspect, rather ghastly biological ramifications.
~I think I can see where you're going with this.
~I think you do. So, I think we need to assume that you are being followed, or at least will be in the near future.
~So you need to take evasive action, immediately.
~Right. Starting to do so right now. If I'm following your argument correctly, I need to take actions which are neither genuinely random - by which I mean chaotic, of course - nor are they obviously predictable; I should make direction and speed changes which simple probability theory would suggest were unlikely but not at the level that they merge into the noise of apparent randomness.
~Just what I would have recommended. And you might chance an occasional active scan, too, following the same approach as to direction and intensity.
~Okay. Are you sure you weren't a warship in a previous life?
~Huh, no. Although I have spent a long lifetime investigating a huge number of wacky alien civilizations. And few less wacky ones, too. Sometimes, they do come up with useful ideas.