by Greg Egan
Zak exclaimed suddenly, "I'm outside!" A moment later he added, "There's an arc of light. I don't understand this."
"An arc?" What did he mean? "Zak?"
There was a long silence, then he replied in a labored voice, "I need to take some measurements. I'll explain everything when I get back down."
"All right." Roi was desperate to hear exactly what he'd witnessed, but she knew it was unfair to expect a running commentary. Zak didn't have much time, and he needed to concentrate on setting up the instruments and collecting the crucial data.
Whatever else there might be to discover in the void, the one possibility in which they had invested the most hope — and planning — was that Zak would be able to locate a distant object that he could track for a while, in order to obtain an independent measurement of the Splinter's motion. From inside the Splinter, there were really only two distinct numbers that could be measured: the ratio of the garm-sard and shomal-junub weights, and the ratio between the periods of the shomal-junub cycle and the turning of the plane of the Rotator's spinning bar. Those numbers were in agreement with Zak's principle, but beyond that they revealed nothing about the geometry through which the Splinter was moving. If the simple geometry that the team had found in their calculations was the right one, then the time it took the Splinter to orbit the Hub would be identical to the period of the shomal-junub cycle. If all orbits at a given distance from the Hub were the same, regardless of their angle of inclination — the assumption of symmetry on which the simple geometry was based — then a stone moving shomal and junub of the Null Line would take the same time to complete its orbit as the Splinter itself, and so it would return to its greatest distance shomal of the Null Line after exactly one orbit for both.
How could you mark a fixed point on an orbit, though, in order to measure the time it took to return to it? The idea that two orbits at an angle to each other always intersected at the same two points was the very assumption they were trying to test, so it could not provide the signposts. The only method anyone on the team had been able to come up with was to rely on a different assumption — that objects far from the Hub moved on slower orbits — and then to hope that, with the Incandescence out of the way, it would be possible to observe something in the void so distant that it was as good as fixed. The apparent motion of that distant beacon would then be due — in the most part — to the Splinter's motion around the Hub.
While Roi had paced, Ruz had been still, but now she heard him shifting, consulting his clock. "Zak?" he called. "It's halfway through the dark phase!"
A few heartbeats passed, then the reply came back, "I know."
Roi said, "We should have tied a rope around him. Then if he cut it too fine we could have just dragged him down."
Zak hadn't taken the light machine, because of its weight, but they had never imagined that such a device would be available. Ruz had made three clocks that could easily be read by touch, and Zak had practiced in total darkness setting up the most important instrument, the one that would allow him to measure the passage of an object across his field of view. Once that was in place, then so long as there was a beacon worth aiming at, he only had to be able to time the moments when it passed behind a series of metal wires. However dim or bright an object might be, whatever the color of its light, you always knew when it passed behind metal.
"An arc of light?" Roi said. "Do you know what that could be?"
"No," Ruz replied. "But be patient. We'll have the whole journey back in which to interrogate him. In fact, we should extract every detail and write it all down, so if the Splinter sinks back into the Incandescence and never leaves it again, we'll have a record of what lies beyond."
Roi struggled to imagine what it could be like, looking out into the void. "If the Splinter really did break in two, long ago, do you think we could ever find the other half? Ever see it, even if we couldn't reach it?"
Ruz pondered the question. "It's hard to know how far away its orbit might be. Until we know, in spans, how far away the Hub is, it's difficult to quantify anything else. At the moment, we're not even sure that our orbit is 'size eight', let alone what that would mean in terms of actual distances." He paused, then called out, "One-quarter of the dark phase remaining! Zak, you need to move now!" It had taken Zak almost a quarter-phase to ascend through the crack, and though it would be easier coming down they needed to keep a healthy margin of safety.
Roi waited for his reluctant assent.
There was nothing.
"Zak?" She pressed her body against the rock, straining to hear anything, a word or a footstep. "Zak?"
She climbed up into the mouth of the crack. "I'm going up there. Something's happened to him, I need to bring him back."
Ruz said, "If the void's harmed him, it will do the same to you."
"You know what his health is like! He's been sick even back at the Null Line. The effort of the climb would have been enough to weaken him."
"When we planned this trip," Ruz insisted, "we all agreed that only Zak would take the risk—"
Roi seethed with frustration. He was right, they had agreed, but she didn't care. She said, "I'm not going to waste time arguing."
She clambered up the inside of the crack as quickly as she could, forcing herself to ignore the instinctive urge to feel her way slowly through the darkness. The rock was sharp in places, and slippery with weeds, but she kept her footing, and kept advancing. She didn't try to judge the distance or the passage of time, she just willed herself forward.
When a hint of light appeared ahead, she made no effort to make sense of it. Moments later, she tumbled on to the surface of the Splinter.
A band of light was wrapped across the blackness of the void, an arc that stretched from a point high above the rock and swept around a quarter-circle before the Splinter interrupted it. The color of the light varied smoothly across the band from inner to outer rim; within it, small points of brightness slowly drifted, changing color as they moved. Roi looked away; the spectacle was baffling and hypnotic, but this was not the time to sink into the morass of questions that it posed. The illumination it cast on the rock around her was weak and shallow, barely more than that cast by the light machine, but she had no trouble spotting Zak.
She ran to him, and drummed directly on his body. "What happened? Can you move?"
He stirred feebly, but there was no reply.
"Climb on to my back. Can you do that?" She placed herself beside him and flattened herself against the rock.
Nothing. She waited a few heartbeats, but he didn't move.
"All right. I'm going to try to lift you. Relax your grip on the rock." She nudged his body and it shifted slightly; whether he'd heard her and complied, or had simply lost his hold along with his strength, he wasn't sticking.
Roi tilted her carapace and managed to get all four claws on her right side beneath him. The edge of her body was too blunt simply to slide under him, so she tried to raise him with her claws first. She was not so old and weak that his weight should be immovable, and she was sure that once she got him on to her back she would be able to move quickly enough.
She strained against the rock. The very posture that she was forced to adopt undermined her strength, but if she couldn't raise him she could at least make it easier for Zak to complete the action by his own efforts.
She kept pushing, clinging to the hope that in a few more heartbeats the balance of forces would shift, he would slide into place, and they would dash to safety together, but whether or not Zak was striving to assist her, between the two of them he was barely moving.
She'd made a joke to Ruz about a rope, but it was exactly what she needed. She looked up at the tracker that Zak had assembled, wondering if she could use it somehow to lever him up. Then she noticed a sudden brightening, an aura of true, strong light seeping around the rock in the distance.
Roi hesitated, trying to imagine some way in which she might yet save them both. If they both died here, then it would begin to loo
k as if the void itself was fatal, and Ruz would not be so foolhardy as to try to make the measurements himself. The chances were that nobody would leave the Splinter again.
Zak twitched, then tapped one claw against her.
"Run, you fool!"
She bolted for the crack and skidded over the edge, losing her grip by accident but then understanding that it was better this way, better to fall. She bounced painfully against the jagged rock, but kept her claws tightly closed, refusing to slow herself. The rock around her was brightening, and she could feel the heat of the raw, unfiltered Incandescence growing above her.
She hit the floor, bruised and aching, but forced herself to limp down the tunnel away from the searing light. Ruz appeared beside her and she climbed on to his back. She clung to him tightly as he sprinted to the intersection and around the corner.
He kept running until it was clear that they were sheltered by the rock, immersed in nothing but ordinary brightness. Roi listened to the pounding of their hearts. Ruz sounded almost as shaken as she was.
After a while, she spoke. "He was too weak to move. I couldn't shift him."
Ruz said gently, "He might have died in the Null Chamber instead, but it would have been soon, whatever he did. This was the risk he chose."
"I know."
"He did a lot in one lifetime. More than any of us. What he learned, what he taught, what he changed."
"That's true." Roi let the sadness sweep over her. In the end, there was only work, only the Splinter, only the next generation of hatchlings, and the next, on and on into the future. Nobody could live forever. But Zak had woken them all from a daze, woken them to a new kind of thought, a new kind of work, a new kind of happiness. Even if the Splinter itself had not been at stake, he deserved to be remembered for that.
Ruz said, "Are you badly hurt?"
"No. Give me one shift and I'll have my strength back."
"You want to go back there?" Ruz's tone was neutral; he wasn't going to pressure her to take Zak's place, but nor would he try to dissuade her.
"I've walked beneath the void once, I can do it again. And I'm sure there's something out there that we can track, something we can measure." Roi pictured the strange ribbon of colors stretched across the darkness; she had no idea what it was, but she had seen lights moving within it.
"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 characteriz
e 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.