"There must be something simple," she said. "We have to keep searching for it."
Zak's body had been seared beyond recognition. Roi had seen many corpses in her life, most of them half-eaten by murche, but she had never faced a choice before about the fate of a friend's remains. Though everyone expected to be consumed by scavengers, as it was normally as inevitable as death itself, was it her duty to Zak to ensure that end? It seemed more fitting to leave him here, where the Incandescence had claimed him.
The tracker, made of metal and susk cuticle, was pitted and tarnished but appeared to have survived intact. Roi went to it and adjusted the aim, sighting a bright point of light at the edge of the colored arc. She took the clock Ruz had made for her from her right cavity, and held the moving wheels against her claw so she could time the occultation of the light by the tracker's wires.
As the light moved, its color changed smoothly. It didn't take long for it to cross the whole width of the band and vanish completely. Roi had no idea how to explain this peculiar behavior. Was the light now being hidden by something in the void — something opaque, like metal — or had it been destroyed?
She recorded the time it had taken for the light to cross a small portion of the view, but she didn't trust that number to tell her much about the Splinter's motion. The lights weren't merely changing color, they were moving apart as they flowed across the band. To expect the time it took for them to cross one thirty-sixth of a circle to be directly proportional to the whole journey seemed absurdly optimistic.
Ruz called to her anxiously, and she returned to the interior with plenty of time to spare. When she was safe in the shelter of the side tunnel she explained what she had seen.
"I have to go out again," she said. "Maybe we'll think of an explanation for all of this, and find some way to calculate the Splinter's orbital period from this data, but since we don't really know what we're measuring, the more observations I can make, the better."
Back on the outside, Roi confirmed a hunch that she'd had before: if she confined her measurements to one part of the band, all the lights took the same time to move through the same angle; when she reoriented the tracker and looked elsewhere, though, the time was different.
Halfway through her second stint, Roi thought she recognized some familiar patterns among the points of light, appearing again in the same part of the band. She wasn't sure, though; she hadn't made an effort to commit the patterns to memory.
The third time she returned, she was certain that some patterns were recurring. By the fifth time, she was convinced that everything she could see in the void was following the same periodic motion. Her first impression of the lights drifting across the band had been that they were like motes of dust, never the same twice. That wasn't true, though. Notwithstanding the strange distortions of color, angle and speed that accompanied their passage, and the fact that they regularly disappeared from view, she was seeing the lights arranged in exactly the same patterns, again and again. The view as a whole was as cyclic as clockwork.
The period was certainly longer than the window of time she was able to spend making observations during each junub dark phase; it was not, however, equal to the shomal-junub cycle itself, as the lights were not the same each time she returned. Her first guess was that three cycles of the moving lights was close to two shomal-junub cycles, and once she knew what she was looking for her observations bore this out. The two-thirds ratio was not exact, though; it was closer to thirteen parts in twenty.
So much for the simple geometry.
"If we understand anything about orbital motion," Ruz ventured, "then this period has to be coming from the Splinter. There's no way that the orbits of all these other objects could conspire together to give the same result."
Roi would have been happier about attributing everything to the Splinter's motion if the pattern of lights had moved rigidly across the sky, like the view when she leaped from one side of the Null Chamber to the other, tumbling as she went.
"If these things really are motionless," she said, "then why does their appearance change all the time?"
Ruz pondered this. "If they're very distant from us," he said, "then the natural paths of the light that's reaching us from them might be affected by the geometry. This isn't like seeing something that's right in front of us, when we can reach out and confirm by touch that what we're seeing is what's really there. If the geometry can bend the Splinter's natural path to wrap it around the Hub, why shouldn't it bend light as well?"
"Ah." Roi couldn't see how this could explain the whole strange vision that the void presented, but it did make some sense. They'd been used to thinking of light as traveling in straight lines, like a rapidly flung stone crossing the Null Chamber before anything could divert it. It seemed the void was too big, and even light was too slow, for the comparison to be sustained.
"We're going to need to do a lot more calculating," she said. Ruz's suggestion was both daunting and encouraging; daunting because it complicated the way they needed to interpret the observations, but encouraging because it meant that the same data provided a far richer means of checking new theories about the geometry than the single number — the Splinter's orbital period — that they'd anticipated gathering.
The eighth time she climbed out into the void, Roi felt her body beginning to falter. Though she'd given herself time to recover from the battering she'd received after fleeing the Incandescence, she hadn't rested again since she'd started making observations.
Her work here was almost complete. Although the motion of the lights wasn't rigid, and varied in a complex way across the band of color, there were only so many measurements required to characterize it; she believed she was getting close to the point where further data was merely confirming what she had already recorded.
She chose a bright light that would be easy to follow, and aimed the tracker toward it. It was only halfway through the measurement, when the times for the successive occultations were beginning to diverge from those she'd seen before for this part of the band, that it struck her that she should have noticed this bright object before. She recognized the pattern of lights around it, and she was sure that in the past they had not included this luminous interloper.
Which meant what?
Perhaps this object was not as distant as the others. It could be orbiting the Hub closely enough for its own independent motion to show up against the synchronized rotation of the background.
Could this be their lost half, the other Splinter?
It was an appealing notion, but why should another Splinter moving through the void be bright enough to see at all, when their own was in darkness? Roi fought her tiredness and tracked the object carefully, until Ruz shouted a timely reminder.
When Ruz heard the news he was excited. "I have to see this for myself," he insisted. Roi was too tired to argue; it was still possible that the void was causing her harm that would only show up in the long run, but it seemed overly cautious to deny Ruz one quick trip when she had survived so many herself.
"When I've rested," she said. "I think I know when it should be visible again. We can go up together."
Roi found a comfortable crack in the wall and shut off her vision, leaving images of the arc of lights wheeling through her mind. The understanding they needed seemed to be forever retreating beyond their grasp, but if she thought about how much had been learned since Zak's first experiments in the Null Chamber, she felt a surge of optimism. Even the Jolt, the source of as much threat and disruption as anything she'd known, had brought them this rich new vein of information.
Sometimes she felt as if there were two people fighting inside her. One longed for the time when she'd tended the crops, basking in the uncomplicated bliss of cooperation, and wished for nothing more than a return to that changeless routine, and a sense of belonging so strong that it extinguished everything else. It was like the Incandescence itself: endless light, endless sustenance.
The other part of her recoiled from that memory. She still reveled in the joys of belonging to a team, but the work she had chosen was utterly different. Instead of being blissfully content with the same healthy crop at the end of each shift, she could only claim success now from something new: a revelation, a contradiction, a twist that turned their old guesses inside out. If they ever did reach the end of the mysteries of weight and motion — and if Zak's legacy finally granted his people the power to steer their fate — she would welcome the return of ease and safety like everyone else, but she did not know how that second part of her would go on living.
Ruz was younger and far more rested than she was, so Roi let him climb ahead of her. She heard his exclamation of delight when he emerged on to the surface. By the time she joined him, he was already beside the tracker.
"Let me get oriented," he said. "This way is rarb, around the Splinter's orbit." He swung the tube of the tracker toward the center of the arc. "And this way is garm, toward the Hub." He turned it to the left, away from the arc. "So the garmside of the void appears completely black, while on the sardside this arc of light is wrapped around the rarb direction." He had heard the same basic facts from Roi, but finally seeing the void's peculiar geometry for himself seemed to compel him anew to seek an explanation. "A quarter of a circle. Why a quarter? The Splinter beneath us is blocking half the view, but why should we be seeing light in only half of what remains?" He hesitated, then answered his own question. "The missing half is in the direction of the Hub. So the Hub must be responsible."
Roi said, "Do you seriously believe that we're almost as close to the Hub as we are to the Splinter — to the rock beneath our claws?" That was a terrifying prospect. She had always imagined the Hub as something small and distant, not a looming presence they were on the verge of swiping, like some careless runner scraping against a tunnel wall.
"Maybe not the Hub itself," Ruz replied. "But suppose we're close to the point where orbits become unstable. Imagine that region as a huge ball around the Hub. There's nothing solid in it, but presumably light can't cut across it to reach us, because it spirals in and hits the Hub instead. There's no rock, no metal, beside us the way the Splinter is beneath us, but
the geometry
still blocks the view."
"That does make sense," Roi admitted. She tried to picture the paths that the light might take as it flowed in from the distant reaches of the void. "The light's not moving in circular orbits, though, so where it gets caught by the Hub might not correspond to the point of instability for the Splinter. I wish I knew
exactly
where rarb and garm lay from here; if we measured the angle from rarb to the start of the arc, that might tell us something."
"Tan can probably think of a way to do that; the signage teams make trickier calculations all the time." Ruz surveyed the arc. "And that's the bright light you mentioned? To the far right, just above the Splinter?"
"Yes."
"We need to get some new recruits here," he suggested, "making measurements constantly, shift after shift. Between the orbit of this Wanderer, and the paths of the light through the void, there must be enough information to pin down the geometry exactly."
"Let's hope so." Roi wasn't sure how complicated the geometry might yet turn out to be. Now that they knew that it lacked the perfect symmetry they'd hoped for, in principle it could be as messy and irregular as the walls of a tunnel.
Ruz timed the Wanderer as it moved across the width of the arc. Roi looked out into the void, freed of the tracker's narrow view, wondering what these lights might be. Small pieces of the Incandescence, severed from it somehow? She didn't understand why the Incandescence was confined to a plane at all, but perhaps there was some way that parts of it could break free, over time.
Or perhaps it was the other way around. Perhaps these points of light began by moving freely, their orbits aligned in all manner of directions, and over time the geometry around the Hub gathered them together and dragged them down into the plane. If that was the case, then these lights were not the offspring of the Incandescence, but its source, its replenishment.
Roi felt giddy, but she could almost picture it: a void full of lights that spiraled in toward the Hub, which swept them together into a plane of wind and radiance. That was the world the Splinter had been immersed in before the Jolt, and from within it had seemed boundless and unchanging. Gradually though, even particles of wind would drift close enough to the Hub to fall, irretrievably. So there would need to be more of the lights coming in, endlessly feeding the Incandescence.
She was tempted to share her ideas with Ruz, but that could keep until they were inside again; better to let him concentrate on his measurements. As she watched the lights drifting across the arc, the Wanderer suddenly grew brighter. A luminous spike transected it, and a second point of brilliance blossomed at the tip of that spike and moved away.
Ruz said, "Did you see—?"
"Yes."
"What was
that?"
The smaller bright point had vanished; Roi wasn't sure if it had traveled beyond the band of visibility or simply become lost in the crowd, but she couldn't see anything moving.
"The weight must have torn a piece off it," Roi said. "Like the Splinter dividing."
"It's still there," Ruz said. "As bright as ever."
"It's not rock," she said, "it won't break up the same way. Rock by itself is dark; this is wind and light, it's all the things that become the Incandescence."
"What strength does wind and light possess, to hold together at all?" Ruz protested.