Incandescence

by Greg Egan

  "We have no destination yet," Jos replied. "We want to know what's happening to the Splinter, so we've left our teams to search for answers."

  Roi could hardly believe what she was hearing. They'd left their teams? How? Had the Jolt shaken them free, like the rubble it had torn from the solid walls?

  She said, "We have some ideas about what's happening to the Splinter. We believe something has pushed it, and now it's falling back and forth, in and out of the Incandescence."

  Lud said, "Falling back and forth?"

  "If you throw something shomal from the Null Line," Ruz explained, "it will reach a certain distance, fall back to the Null Line, go past it some way junub, fall back again, and so on. We think the Incandescence ends if you go far enough shomal or junub, and that's why the light comes and goes."

  The group talked this over among themselves, then asked to hear more. Zak remained quiet, which usually meant that he was tired or in pain, so Roi explained his idea of the Splinter orbiting the Hub, and the experiments in the Null Chamber that seemed to support it.

  While they were talking the light from the machine faded, and its whirring sound died away. But the walls were already beginning to brighten, and soon Roi had a normal view of everyone. They had a small cart with them, full of metal parts.

  Cot climbed on to Lud's back and began turning a handle attached to the machine. Ruz could no longer contain himself. "It's spring driven, isn't it?"

  "Of course," Lud said. "Trying to crank it smoothly and walking at the same time would be impossible."

  "But what makes the light?" Ruz's tone was drenched with such longing that he might have been a starving child begging for food.

  Lud chirped with amusement. "Just two rough surfaces scraped over each other, under pressure. Rough enough to make a disturbance, but not so rough that they'll stick."

  Jos added, "I found the effect completely by luck. I was grinding plants into a powder between two stones, and I grew tired of stopping work every time it grew dark. When I ground stone against stone with nothing between them, a faint light seemed to come from the point of contact. At first I thought I was just going mad from the darkness, but the more effort I applied, and the less of the mush there was to smooth the stones, the stronger the light became."

  Roi said, "So you've left your old teams now? You've formed a new one, and you're looking for recruits?"

  "Not exactly," Cot replied, working briskly to ensure that the spring was fully wound before the darkness returned. "We still don't know what's the best thing to do. We'll form a team if that's necessary, but we're willing to join an existing one if they can make a good case that they know what's going on and that they're doing something useful about it."

  Every time Roi thought she could no longer be shocked, these people outdid themselves. It had taken a great struggle for her to tear herself free of her work team to join Zak. On that first journey to the Null Chamber she had never been able to admit her intentions, even to herself. Now here were five people roaming the Splinter, challenging every passing stranger to make a reasoned bid for their labor, as if the whole idea of recruitment had been turned inside out.

  Zak spoke softly. "Some people are trying to build a tunnel that will change the way the wind pushes on the Splinter. If they succeed, they hope it will carry us to safety. I'm sure they could use your skills."

  Lud said, "I can make no promises, but we'd be happy to talk to them, to hear their case."

  Ruz said, "We can draw you a map, give you directions."

  "You're not going there yourself?" asked Sad.

  "We have another task." Roi explained about the crack in the wall, and the observations that they hoped would clarify both the Splinter's ordinary motion and the nature of the Jolt.

  The idea struck a chord with the light-makers, and they seemed torn between joining Zak's expedition and heading for the sardside and the tunnel-makers. Zak, however, explained that he would be making the observations alone and that his two assistants were all that he needed.

  Cot said, "Then at least take this with you to help you on your way." He opened the cart and produced a second light machine. "We brought two spares, and plenty of parts. If you take this one, we will still have no trouble reaching the sardside."

  Zak said, "Thank you." Roi would have preferred an extra body or two to help pull Zak's cart; this was more weight to carry, and now they'd have no excuse to rest when darkness came. Still, at least this way they could choose their own pace.

  Roi drew a map for the light-makers showing the way to Bard's team, and the two groups parted. Ruz agreed to carry the light machine on his back; he took the rear harness so as not to obstruct Roi's view ahead.

  They toiled on toward the junub edge, resting as they wished and using the machine to enable them to travel through the darkness. At first Roi found the strange, shallow illumination it cast disorienting, but after a dozen cycles she was accustomed to it, her mind switching easily between the two ways of seeing.

  It was hard work winding the spring, though. "I want you to improve on the design," she told Ruz.

  "In what way?"

  "I want a version that works unattended, filling itself with light when there's light to spare, then releasing it in the darkness."

  As they approached the edge the tunnels became increasingly strewn with rubble and the walls ever more fractured. Some of this might have been due to the Jolt, but Roi had heard descriptions of the area that long predated that event. It was easy to believe in a crack in the outer wall here, if not so easy to reach it.

  Ruz, who had been timing the lengths of each stretch of light and darkness, reported that he'd finally started to detect a small asymmetry between successive times spent in the dark. Now that they were a significant distance away from the Null Line, when the Splinter moved junub of the Incandescence the darkness came earlier, and lasted longer, than when it moved shomal. Roi had already noticed a difference in the way the light penetrated the rocks, with the onset of brightness coming faster when it started from above than from below, but every sign that confirmed their guesses about the Splinter's motion through the Incandescence was important. Apart from anything else, they would be relying on the rock of the Splinter to protect Zak from any dangerous emanations; they did not want to misidentify the phases of the cycle and send him out in the wrong period of darkness, to find the Incandescence looming directly above him.

  Shifting enough rubble to allow them to steer the cart through the tunnel became an impossible task. Roi helped Zak pack the instruments into his cavities, then had him climb on to her back. According to Zak's map they did not have far to go, but the map contained no annotations about the ease of travel along the tunnels it portrayed — let alone an up-to-date account that included the damage wrought by the Jolt.

  Roi noticed a slight thickening in the sparse vegetation on the walls before she felt the faint hint of a wind, rising and dying with the light. This close to the Calm, that could only mean that the feeble wind had almost no rock to penetrate. She moved ahead cautiously, afraid that they might all be caught by surprise with no roof above them, but as they approached the intersection marked on the map as lying directly beneath the crack, the onset of light brought no blinding revelation. If anything, this place seemed less bright than the garm-sharq edge.

  Still, the vegetation on the roof was the thickest Roi had seen since they'd set out from the Null Chamber. She set Zak down and clambered up the wall to explore it. She hadn't walked upside down in weight like this for a long time, and the encrusted surface didn't make it any easier.

  She probed the surface gently with her claws. "The rock feels strong," she reported. "No gaps, no cracks."

  Ruz said, "Maybe the vegetation's repaired it."

  "All my maps are too old," Zak lamented. "We should have brought tools to cut our way out."

  "Tools, and a very large work team," Roi suggested. She'd heard it said that the outer wall was at least a dozen spans thick, though like much
common knowledge that claim might not have had much grounding in solid information.

  Ruz said, "If there's a system of cracks, there might be other openings. Even if the vegetation got to all the old ones, the Jolt might have broken a way through somewhere else."

  Roi climbed down to the floor. "Stay here with Zak," she said. "I'll take a look around."

  She continued along the tunnel by which they'd reached the intersection. When the darkness came she froze and looked back, but there was no faint glow in the distance; she hadn't bothered to rewind the light machine, and apparently Ruz hadn't either.

  As the light returned she advanced slowly, listening to the wind. The sound had an odd, resonant beat that she'd never heard before, and as she approached the next intersection it grew louder.

  She turned right into the cross-tunnel, pursuing the sound. The floor of the tunnel was piled high with rubble, and it reached the point where it became easier just to climb on to the ceiling and stay there. When darkness fell once more it hardly seemed to matter; there might be cracks here, but at least she couldn't slip on a loose stone. She inched her way forward through the blackness.

  When the wind rose up again, Roi could hardly believe that she was in the Calm. Even at the garm-sharq edge she'd felt nothing like this; her carapace tingled beneath the assault as if she was being pelted with fine sand.

  The light now was brighter than she'd ever seen it. Brighter everywhere, but ahead, opposite the mouth of a side tunnel, a patch on the wall was almost blinding.

  She dimmed her vision as much as she could, and approached the intersection cautiously. As she turned to peer into the side tunnel she saw the floor ahead awash with radiance, blazing too brightly to bear. She retreated, her heart racing.

  When the next cycle of darkness came and the light ebbed from the surrounding rock, the intersection did not lose its strange radiance entirely. Roi approached the entrance to the side tunnel again, and looked toward the place that had been intolerably bright before. She could see a hole in the ceiling, with a ragged patch of the floor illuminated beneath it. The Incandescence was far away now, but it seemed that a part of its light was still reaching through that hole.

  No doubt remained in Roi's mind: this was a crack in the Splinter's edge, leading out to whatever lay beyond. The next time darkness fell the Incandescence would lie safely on the other side, and the secrets of the void would be rendered visible to whoever dared step outside.

  15

  Rakesh was dreaming that he was a child on Shab-e-Noor, diving into a river with a group of friends, when Parantham appeared among them. She stood on the riverbank, smiling. "We've found an Ark," she said.

  "Is this real, or am I dreaming?" he asked.

  "Both," she replied.

  His friends seemed troubled by the news. "Don't worry," he told them, "I'll be back as soon as I'm finished with this." A sense of panic was rising in his chest. Why couldn't he remember any of these children's names?

  "If we let you come back," one said darkly.

  Rakesh woke. He had not imagined the claim about the Ark; the telescope's report had entered his skull and the discovery had seeped into the dream's scenario.

  He walked to the control room. Parantham said, "I was about to wake you."

  "The news did that itself."

  "What do you think?"

  Rakesh scanned the data. The neutron star where the Ark had been found was twenty light years from the galactic center. Even with ninety per cent of the telescope's mirror in place the image of the find was just a tiny dark blur against the glow of the accretion disk. The spectrum was unmistakable, though; the object in question was made from the same material as the failed Ark that had been left behind.

  This Ark would be immersed in powerful winds from the differences in orbital velocity across its length. In spite of the turmoil of its surroundings it had apparently managed to remain in place for fifty million years, kept from spiraling inward by a passive asymmetry in its structure that allowed it to gain energy from the wind if it ever sank too close to the neutron star. It was in precisely the environment for which it had been built. If its makers survived anywhere, surely it was here.

  "Is there anything to keep us here?" he wondered. They had already built a communications link that would allow the telescope to convey any further discoveries to Lahl's Promise; before departing they could aim it at their destination, and if they moved again from there they could leave a relay behind.

  "Nothing I can think of," Parantham replied.

  Rakesh felt a twinge of anxiety. "What if this one's empty, too?"

  "Then we wait for the telescope to find another one." Even if this neutron star had captured all of the successful Arks initially, that didn't mean it had held on to them all. If there had been enough of them to start with — or if the Arkmakers had flourished in their new environment and found a way to build more — then viable Arks might have ended up orbiting several different neutron stars.

  "And if it doesn't find another one?"

  Parantham walked up to him and put a hand on his cheek, an almost maternal gesture of tenderness mixed with exasperation. "Then our time here will be over. We'll move on." She took her hand away. "But it hasn't come to that yet, so can you please stop fretting? Whatever this Ark contains will be fifty million years removed from its makers, so I'm not offering any bets about the nature of its inhabitants. But even fifty million years of energy starvation didn't finish off the other one completely. We've already faced the worst-case scenario. We've seen the desert; now we're heading for an oasis."

  When their hosts rebuilt and woke them at their destination, the sky had turned from dazzling salt to luminous milk. Fifty times more crowded than before, it had lost every perceptible trace of black. The closer stars still outshone the bright backdrop formed by the crowd behind them, but the contrast was greatly diminished. Night had become day; it was almost as if they were back on Massa, where the stars of the bulge could be seen against the pale twilight sky long before darkness fell.

  When the accretion disk came into view it outshone the sky around it, but it was not the kind of spectacle that it would have been against the black night of the disk. Then again, it could never really have existed out there. This was not a blazing X-ray binary, where a neutron star actively tore strips off a closely orbiting companion, but no star was truly isolated here, and the combined exhalations of thousands of neighbors kept the accretion disk aglow. The neutron star itself was almost lost in the bright center of the disk, where a narrow jet of plasma shot up from the plane. Its days as a conventional sun were long gone, but the chances were that it had never hosted life until it traded its own thermonuclear glow for this gravity-powered renaissance.

  The Ark was far too small to see with the naked eye from their distant vantage point, so Parantham aimed the shipboard telescopes while launching surveyor probes. The gray ovoid was six hundred meters long, the same size as the one they'd left behind, but its surface appeared far smoother. That might have meant better repairs by better-fed fungus, or it might just have meant that it had avoided more of the debris from the destruction of the home world.

  The Ark's rotation was tidally locked: it spun around its axis in exactly the time it took to complete an orbit, fixing its orientation with respect to the neutron star. This froze the stretch and squeeze of tidal forces into a stationary pattern, allowing the material of the Ark to respond to those stresses once and for all rather than suffering endless cycles of flexing; no doubt this had not always been the case, but the process of flexure would have stolen energy from the rotation until the spin finally did fall into synch. The fixed stance the Ark had achieved did not aim its long axis directly at the neutron star, though; the torque from the orbital wind produced a perceptible slant on the telescope's annotated image.

  Rakesh wondered if this leaning tower had been crafted to take account of its inevitable inclination. The interior of the Ark they'd visited had been essentially weightless, but
here the orbit, fifty thousand kilometers from the neutron star, was small enough for tidal forces to be felt. While they waited for the surveyor probes, he summoned up a map of that other Ark to see which directions its makers had expected to be "up" and "down". It looked as if they'd hedged their bets: most chambers tended to be almost spherical, with no special orientation required to make particular surfaces work as floors. Similarly, the tunnels sloped in all directions. The makers had been prepared for some uncertainty, but they had clearly not expected the tidal gravity to grow strong enough to dictate the lives of the inhabitants. They had trusted the wind-based buoyancy to keep the Arks in comfortable orbits, and in this case they'd been proven right: the strongest that the tidal gravity would reach here, augmented by centrifugal force from its spin, would be about one sixth the surface gravity of the home world.

  The surveyor probes reached their target. Rakesh watched anxiously as the neutrino tomograph slowly accumulated details, a solid labyrinth emerging from fog. The layout was not a tunnel-by-tunnel copy of the interior of the other Ark, but it was very similar, as were the density gradients in the walls. Here, those gradients could achieve their purpose: models showed the wind being scattered into the interior, spreading nutrients deep into the dead zone around the Ark's center where the plasma orbited at the same velocity as the habitat itself. In fact, the main difference the scan showed from the Ark they'd left behind lay in the center; where the last one had been full of rubble and unrepaired cracks, this Ark was in pristine condition.

  The probes added an analysis of the Ark's thermal budget, which showed that a substantial fraction of the energy from the wind was being degraded into heat, in a manner that turbulence alone could not explain. On that basis, the biomass within appeared to be at least ten thousand times more than its barren sibling had contained.

  Parantham said, "Let's see if anyone wants to talk to us." She broadcast a greeting from one of the probes, sweeping across the spectrum from the longest practical wavelengths down to far infrared. The plasma of the accretion disk stirred by the neutron star's magnetic field would not make for ideal radio reception, but shorter wavelengths would have no chance of penetrating the walls, and there were no visible external antennas or detectors that they could target. The other Ark had contained stretches of conductive wire, but if they had been part of the original design here they must have been broken up and dispersed. Perhaps that was a sign of technological change rather than decay or disrepair, with the old infrastructure being cannibalized for other purposes.