"I have a friend called Tio," Haf said, without looking up from his frame. "He told me that the best way to think about curved geometry is to imagine it as lots of little flat pieces stuck together. I mean, a cube is just six flat pieces, but it's not that far from the shape of a sphere. And if you use more pieces, you can get closer."
"That's true," Roi said. "You can shift all the curvature into the corners between the pieces. But I'm not sure where that gets you. Who did Tio study with? Kem? Nis?"
"I don't think it was either of them. He spoke to a lot of different people. Picked things up here and there."
Roi kept staring at the frame, but her mind was blank. Having exhausted all the elegant tricks she knew, she had finally attacked the problem directly, with no subtlety but all the diligence she could muster, hoping that somewhere along the way an opportunity to simplify the mess would appear before her eyes. It hadn't happened yet.
There must be something simple
, Zak had declared. But he'd found that once already, in the principle of the weights. In a void full of Jolts and Wanderers, and countless distant lights that for all Roi knew could be wrapped in curvature of their own, how much more simplicity could they expect?
Sen, one of Neth's students, appeared at the entrance to the chamber. "We're opening the tunnel now," she said.
Roi put down her frame. Haf made ready to heft the light machine on to his back, but Roi said, "I don't think we'll need that." The dark phase was almost over, and Sen knew the area so well that she'd come to them without any light of her own. Roi was getting better at following people by the sound of their footsteps, even when she was in an unfamiliar place, a skill that seemed to come naturally to Haf and the others hatched since the Jolt.
They followed Sen down a narrow, sloping tunnel toward the rarb-sard edge.
By the time they reached their destination, there was enough light to see Neth, Bard, and a few dozen others gathered in the plug chamber adjoining the new tunnel. The outer wall where the tunnel approached the surface had been thinned and weakened to the point where it had almost certainly broken apart during the last light phase. From this chamber, the first of the sets of stone plugs that were keeping the tunnel sealed would be pulled aside, at the same time as eleven others further downwind were withdrawn. If everything went as planned, the wind would flow freely across the width of the Splinter and strike the sharq end of the tunnel with enough force to break through the thin crust that had been left by the workers there, opening up a third unimpeded channel from Incandescence to Incandescence.
Roi approached Neth. "Surely your work's done here now," she joked. "We'll be waiting for you to join us at the Null Chamber." In fact the Null Chamber was empty of theorists and Roi had no reason to visit it any more, but no other place had the same ring to its name.
"When the tunnels have steered us past the Wanderer, I might take you up on that," Neth replied, in all seriousness. "I want to work with someone who's interested in a deep understanding of the changes we've seen in the density of the Incandescence as we've moved away from the Hub. There are many mysteries there. We understand weight and motion pretty well for rocks like the Splinter, I think, but when it comes to anything else we're still just gathering data, and guessing."
Bard consulted a clock, and called out to the plug operators. There was no need to send a light-message to the operators in the other chambers; they'd be following prearranged instructions and clocks of their own.
The plug operators, lined up in rows, began hauling on their ropes, which ran through a system of pulleys to the huge stone sitting at the far end of the chamber. Although this single stone was probably close to the limit of what could be moved with a wheeled cart and metal tracks, it was only about a sixth of the size of the tunnel's aperture; six separate plugs inserted from their own separate chambers came together to block the tunnel at this point alone.
As the stone moved Roi could see a halo of light shimmering around it; though she wasn't gazing directly into the Incandescence through the small gap between the stone and the chamber's walls, even the reflection from the tunnel wall was dazzling. There was scarcely any wind leaking out through the gap, though; the path straight ahead through the great tunnel was so much easier for it to take.
The halo shrank and dimmed as the plug came closer, though the light remained visibly brighter than that flowing through the stone itself. It occurred to Roi that they could have put void-watchers here after all, in spite of the inconvenient direction of the weight; with one of Cho's contraptions poking out into the void, the observer would not have needed to cling to the surface. It was only the historical accident of the order in which various things had been invented that had kept the void-watchers at the junub edge. With the present system working smoothly, though, and all the teams accustomed to it, she couldn't bring herself to suggest rearranging everything for the sake of efficiency. Light-messages reached their destinations quickly enough.
It would be a few shifts yet before the void-watchers could tell them precisely what the new tunnel had achieved. The further they moved from the Hub, the less powerful the wind became, but they were also ascending a gentler slope as they struggled toward the fateful distance of the Wanderer's orbit.
As they headed toward the exit together, Haf said, "We should find a way to capture the wind and then push it out ourselves, with a strength that suits us. Why should we be hostage to the speed it travels naturally?"
Neth assumed a posture containing a mixture of respect and amusement. "That's a nice idea, but where does the 'strength that suits us' come from?"
"Give me time," Haf replied. "There must be a way."
Roi heard a deep groaning sound coming through the rock. She had no idea what its cause was, but she had never heard anything like it when she had visited the other tunnels. Perhaps they were experimenting with a new configuration of flow-control baffles, but if that was the case then this ominous noise suggested that the wind was making short work of them. She looked to Neth for an explanation, but it was Bard who shouted for all of them to run.
The noise grew louder as they reached the exit tunnel, and as they clambered up the slope an intense light rose up behind them. It could not be the baffles; Roi hoped it might just be a single plug coming loose, but she didn't waste time looking back and trying to weigh up various scenarios. She saw that Haf was far ahead of her, his youthful vigor carrying him to the front of the pack. Amid the chaos and fear, and her own determination to outrace the danger if she possibly could, a small part of her relaxed, resigned to anything so long as he survived.
As they passed the chamber where she'd waited with Haf, the ground rasped and screamed like a susk in agony. The tunnel flattened, making progress easier, and the light from behind dimmed even as the sound became unbearable. Roi finally paused to look back and saw a fissure opening in the rock behind her, separating the tunnel they'd ascended a few heartbeats ago from the one they were now following. It was the kind of terrible spectacle that she had once imagined a division of the Splinter might bring, but the weights had done nothing but ease as they'd moved away from the Hub. If rock was parting from rock, the curvature of space-time was not to blame. As she bolted on down the tunnel, she understood that the most likely cause was not a fresh Jolt from the Wanderer, either; the timing would have been too much of a coincidence. This was a disaster they had brought upon themselves.
They ran until the rock fell silent and the glare of the Incandescence was left behind. When they finally paused to take stock of the situation, Neth was nowhere to be found. Roi couldn't remember seeing her at all during their panicked flight, but it was possible that she'd split up from them at some point, taking a different turn once they'd had a choice. More than a dozen other people from the chamber were missing.
Bard led them to a point where a terrified light-messenger was still standing at her post, though the next station to her rarb was now deserted. It was still possible to send queries skirting around the tunnel in the other direction, and Bard was slowly able to build up a picture of what had been lost and what remained.
It seemed that a large piece of rock had sheared off the side of the Splinter. What was gone included the original mouth of the new tunnel, and all six of the first set of plug chambers. The next set, downwind from that, remained intact. Many dozens of people had certainly been killed, some of them carried off into the Incandescence inside the fragment that had broken away, others seared by exposure. The ordinary system of tunnels was now open to the Incandescence, but that in itself wouldn't cause any more harm if people kept away from the damaged region.
Roi had sent Haf to search for Neth, but he returned with no news of her. She tried to set aside her fears for her friend, and think through the other ramifications of the disaster. The tunnel was still open, and could still be controlled by the remaining plugs and baffles. If the cracks caused by the construction ran deeper, if more of the Splinter's rock was threatened, it was hard to imagine any easy solution to that now. Leaving this tunnel open, and closing down the other two instead if they needed to adjust the balance of forces, was about the only strategy Roi could think of to minimize the risk; shutting off the flow was just as likely to trigger another failure in the rock.
Haf said, "Why is the wind blowing from rarb-junub?"
"What?" Roi had become disoriented. She looked to the nearest wall sign; Haf was right. She found Neth's student, Sen, huddled against the rock and asked her if she could explain the anomaly in terms of the damage, the local density of the rock, the possibility of a redirection of the flow.
Sen had trouble concentrating; she was still in shock from their brush with death, and Neth's disappearance. She did her best to analyze the problem, but she couldn't rule anything in or out.
Roi asked Bard to send a message to the void-watchers, asking them if they'd noticed any changes in their latest observations. When the reply came back from Ruz, it was exactly as she'd feared:
"The Splinter has gained a spin around the garm-sard axis. Direction is junub to rarb. Period about seventeen times shomal-junub cycle."
The slow spin would be rotating the tunnels in and out of alignment with the wind, slashing their effect to a fraction of what it had been. If it could not be corrected, they would be left with far less speed and manoeuvrability than when the first tunnel had been opened.
Bard said, "If we have to cut more tunnels, we can do that."
"And lose more rock? More people?"
"What choice do we have?" he replied. "Can we pass the Wanderer safely in this state?"
"I don't know. I don't know how much power we will have lost, I don't know how the whole picture will have changed."
Roi sent a message to Kem, to be sure that she knew exactly what had happened, and was thinking about these problems. Then she approached Sen again.
"I need your help," Roi said gently.
Sen still couldn't get out of her flattened defensive posture; she wanted the walls to hide her, to swallow her.
"The Splinter is spinning," Roi told her. "The only way I can think of to correct that is to use the baffles in the tunnels, and try to modulate the flows to provide a torque to bring us to a halt."
Sen struggled to focus. "I think the most stable alignment for the Splinter with respect to the wind would be with the tunnels running rarb-sharq again. In time, we should settle back to that naturally."
"That sounds likely," Roi said, "but we can't rely on it happening in time. We need to get stabilized as soon as we can."
"We never planned for this," Sen replied. "Neth and I. We never did the calculations."
"But you understand her ideas? You can work it out?" Roi had only the crudest notion of Neth's work herself. Even if she found the written notes, it would take her thirty-six shifts to begin to master the theory of wind flow.
"Perhaps I can do it," said Sen. "Perhaps."
Bard found a chamber for them to work in, close to an existing light-message route, and set up a control post with Roi, Sen, Haf, and a dozen checkers.
As the great tunnels swung around, the wind would strike first one side wall, as they approached rarb, and then the other as they turned away from it. If there was any natural effect that would favor one wall in a manner that could halt the spin, Roi couldn't see it operating on the kind of time scale they needed. They would have to try to take control of the flow, using the baffles to ensure that the wind hit the rock with the maximum possible force when it could retard the spin, but passed through the tunnel as smoothly as possible at all other times. Like the imbalance between the garmside and sardside that had carried them away from the Hub, they could try to break the natural symmetry of the situation to work to their advantage.
Sen struggled with the calculations. There was no shortage of people around her to help with the raw template manipulation, but she was the only one who really grasped Neth's ideas. When her mind grew stale and she needed a diversion to clear her thoughts, Haf did his best to cheer her up, babbling away about his schemes for the future.
"When we're past the Wanderer, we should build a wall around the Hub," he suggested. "To make sure that whatever happens, no future generation ends up where we are."
"A wall around the Hub?" Sen made a sound of delighted incredulity. "Made out of what, exactly?"
"I don't know yet," Haf replied. "But we should move right outside the Hub's curvature, and put the wall so far out that there's no chance of the Hub capturing anyone again."
"How can we go past the Hub's curvature?" Roi protested. "Even if the Incandescence stretches that far, the wind will be too weak to move us."