Incandescence

by Greg Egan

  Rakesh felt the jolt of the chute unfurling, followed by a persistent deceleration. The heat shield slowly dimmed and his weight diminished as the package drifted down into the troposphere. There was some gentle buffeting, but the descent was uneventful, with nothing to presage the sudden thud of landfall. The plateau was some ten kilometers above the average surface elevation, not quite the highest point on the planet, but close.

  The shield split open. A whirring sound followed as the chute was reeled back in. Rakesh restored his vision to the usual wavelengths and looked out across the surrounding terrain, a heavily corrugated igneous landscape. It conjured up fanciful images of boiling lava frozen into glassy black rock, sandblasted for an aeon but still not rendered flat. They were about a meter from the edge of the metallic patch. Had he been his normal size, the ground here would have looked merely dimpled.

  Parantham's avatar rose to its feet, and he joined her. The rover purred and advanced beside them on its flexible treads. Rakesh doubted that their diminished stature would cut much ice if there were locals watching from hidden strongholds who held some strange reverence for this site; treading lightly or not, trespass was trespass. Still, at least if these avatars were crushed out of existence their bodies on Lahl's Promise would stand a chance. The last backup Rakesh had made for himself was on Massa, and he had no idea what, if anything, the Aloof were retaining of their guests as insurance against misadventure.

  They tramped across the undulating lava field. According to the rover, the black rock beneath them contained almost no iron, and there was no obvious cavity marking out a distinct body of ferrous ore that the putative microbes might have mined. The layer of dirty metal ahead of them looked as if it had been sprayed on to the surface.

  They reached the diffuse edge of one of the six lobes. The iron was stained green and brown, presenting no silvery sheen, but it still looked more like a layer that had been deposited on top of the igneous rock than something created by converting a pre-existing source in situ. Models of the planet's surface evolution lent no weight to the idea that this elevated place had once been the bottom of a mineral-bearing sea, though they couldn't entirely rule out six small, iron-rich puddles at the edge of a muddy alpine lake.

  The rover probed the layer across the spectrum, then sent an invisible wave of nanomachines forward to gather more information and sharpen its tentative spectroscopic estimates.

  Parantham displayed the evolving isotope data in a shared visualization in front of them. «This has been refined by smelting three or four different ores from different sources,» she said. «It's not geological in origin, and it's not biogenic. Iron, nickel, chromium. it's an artificial alloy. This is steel. Designed to resist corrosion.»

  «Can we date the smelting?» Rakesh wondered. «Aha!» There were minute traces of radioisotopes. The models suggested that the metal had been refined between one hundred and twenty and one hundred and eighty million years ago.

  Rakesh's thoughts hovered between astonishment and bemusement. Had the cousins just become a great deal smarter, or was he staring at a mirage? They had yet to find a single biological molecule here. Could life have flourished on this desolate planet, to the point of giving rise to a steel-making culture, and then shrunk back down to nothing, leaving this single, shriveled artefact as its only witness?

  The nanomachines advanced, probing the composition of the deposit in all directions. It was not homogeneous. Time had blurred what might have once been sharp distinctions, but hints of structure survived as complex veins of impurities threading the six lobes.

  Parantham said, «What was it? A sculpture of an insect?»

  Rakesh glanced away from his avatar's vision to a virtual schematic, a map of the impurities overlaid on an aerial view of the site. «It's a robot,» he declared. «A six-legged robot.»

  «Perhaps.» Parantham was pondering the isotope analysis again. She said, «There are markers in this metal that fit the meteor data far better than anything else on this planet.» She hesitated. «It's a probe, Rakesh. From the meteor's world. This planet isn't the parent world, but the parent world sent this probe.»

  Rakesh tried unsuccessfully to pull his jelly-baby face into a scowl of disbelief, but then everything fell into place.

  The cousins had made steel, and mastered interplanetary flight. They had sent this six-legged robot to explore their barren sister world, more than a hundred and twenty million years ago. Out in the disk, a species with a head start like that might have circumnavigated the galaxy before Rakesh's ancestors had touched a stone tool, and built a civilization to rival the Amalgam before humans had sent a single spore to a neighboring star.

  This wasn't the disk, though. Grand histories, here, were prone to truncation. A neighboring star had come too close, and either captured the planet or ejected it into interstellar space.

  Rakesh said, «The meteor is about fifty million years old. The interloper passed through this system perhaps a hundred million years before then. That's why the meteor's path didn't match its chemistry; the whole planet had been traveling away from its home star for a hundred million years before the meteor was blasted off it.»

  «Yet the meteor still bore life,» Parantham said. «That DNA was the same age as the meteor itself, not a remnant from an earlier epoch. Whatever the parent world endured for those hundred million years, it wasn't enough to sterilize it.»

  Rakesh looked out across the stained patina of metal. «Microbes survived. But what about the probe builders?» It seemed too cruel a coincidence to believe that the interloper had come along just as they were developing the technology that might have allowed them to survive the encounter. Perhaps that had even been a trigger; perhaps they had been locked in some kind of cultural stasis until their astronomers realized that their world was in peril.

  «We'll scour the system,» Parantham declared. «There might be some more clues here, they might have left something on one of the gas giants' moons.»

  Rakesh agreed. «And then we go after them.» They would follow the meteor back to its source, and retrace the path of these unlucky exiles, deep into the crowded heart of the bulge.

  10

  As Roi launched herself across the Null Chamber, it struck her that she had never seen the place so alive with activity. She counted seven distinct groups, each numbering six people or more, gathered together on the walls and along the web, making measurements, adjusting machinery, talking excitedly, testing ideas.

  She and Zak had scoured the Splinter from garm to sard in their hunt for recruits, braving libraries and workshops, abattoirs and storage depots, risking ambush every step of the way. Now the hard times were over; they had built their team, and its numbers bolstered their loyalty in a way that mere reason never could.

  Near the Null Line, Ruz and his apprentices were working on their new clock, tinkering with the mechanism as they calibrated it against a cycling pair of shomal-junub stones. Zak had set them a wildly ambitious target: to create something small enough for a traveler to carry anywhere in the Splinter, oblivious to the varying weights and accurate enough to be trusted for thirty-six shifts without recalibration. After trying out many unwieldy designs, they had devised a system in which two spiral coils of metal ribbon were joined at their centers to small shafts. The first and larger of the coils was tightened by turning its shaft with a lever, and then the force as it unwound was eked out slowly and employed to feed a gentle, to-and-fro rocking of the other coil's shaft. Rendering this complex mechanism perfectly regular was a serious challenge, but the team never seemed to be short of new ideas to try, and each refinement so far had improved on the last.

  Ruz had been a metalworker for most of his life. It had taken Roi more than a dozen shifts to recruit him, but he had later admitted that the instant he'd seen Roi's «Rotator» — her contraption for demonstrating the Splinter's spin — he had been hooked in equal measure by a fascination with the idea that the world could be secretly turning, and a conviction that he could do a
far better job at making the kind of gadgets needed to quantify that motion. Happily, his conviction had turned out to be entirely justified.

  Roi drifted past the clockmakers and landed against the wall, close to the point where Tan was talking with a small group of students. «What is natural motion?» he asked. «Looked at closely, and in the absence of spin, it seems as if a weightless stone is trying to follow a straight path. Yet over large enough distances, that path can curve around into a circle, or other kinds of curves. What's happening?» He lifted up a complicated patchwork he'd made by gluing together dozens of fragments of skin. «See this line, marked across this surface?» He indicated a path he'd dyed in ink. «On every small piece of the surface, it's a straight line. But the line as a whole isn't straight; it can't be, because the surface itself isn't flat. So how can we determine exactly which paths can be made by small, straight lines joined together in this way? That will depend on the way the parts of the surface are connected to each other. We need a precise, mathematical expression of the nature of that connection, in order to understand which paths are as straight as they can be, given the geometry of the surface.»

  Roi listened closely. She, Zak and Ruz had lured Tan away from the sign-age team where he'd honed his geometrical skills. Calculating distances through the tunnels of the Splinter had given him both an extraordinary facility with numbers and a powerful sense of how they could be used to analyze paths, shapes and motion.

  «Keep in mind,» Tan continued, «that there is one ingredient in the idea of natural motion that doesn't show up when we study a surface like this. Zak has argued that the natural path for any stone you throw from a given point depends, not just on the direction you throw it, but also upon its speed. The natural path of the Splinter appears to be a circle, but an object that starts out on that circle and travels in the same direction as the Splinter will still follow a path with a different shape if it's moving faster or slower than the Splinter. So we need to find a way to incorporate that into our geometrical scheme. We need to merge the idea of speed with the idea of direction.»

  Roi had to make an effort to tear herself away. She had heard Tan explain these ideas many times, but on each occasion the concepts became a little clearer, a little bit more precise. If he ever reached the point where they were defined with sufficient mathematical rigor to allow her to start making calculations, she hoped she could find a way to merge them with Zak's other principle — that the true weights everywhere summed to zero — and then she might finally be able to start mapping the possibilities for the Splinter's past and future.

  She clambered across the wall to the crevice where Zak was resting. She tapped the adjacent rock gently, and after a moment a single claw emerged from the crack.

  «It's Roi,» she said, «I've brought you some food.»

  «Thank you.» Zak slid out on to the wall, awkwardly. Roi opened her carapace and took out a bundle of food. She'd spent half the shift collecting it, but she did not begrudge the effort. Zak was old, his body was failing, but she had no intention of letting him starve to death.

  Zak ate slowly, in silence. Roi no longer asked him what hurt and what didn't; she gathered that almost everything did.

  When he'd finished, he surveyed the activity in the chamber with a satisfied air. Roi could see the meal dissolving smoothly inside him, unhindered by the obstructions she'd noticed the last few times. Clearly the rest had done him some good.

  «How are you finding things on your travels?» he asked.

  «What do you mean?» She'd returned from the last recruiting expedition with two young students, but that had been several shifts ago, and she'd reported the result to him then.

  «How do people think of us? Word must have spread out from the Calm by now, that there's a new team here, doing a new kind of work.»

  «Ah.» It was a good question, but a difficult one to answer. «I wouldn't say that there's any particular resentment directed against us. Nobody likes having their team-mates taken, but recruitment is recruitment, it's a fact of life.»

  «And work is work?» Zak pressed her. «The mere existence of a team is its own justification?»

  Roi replied cautiously, «It seems that way. Most people don't consider themselves experts in the history of the Splinter, to the point of declaring 'There has never been a team like that before'. Work is whatever a group of people do, and most of us take it for granted that what other teams do is useful in some way. There might be only five or six jobs that literally everyone knows about and understands, but that doesn't mean people are hostile or suspicious toward all the rest.»

  Zak pondered this. «I've been wondering at what point we'll need to let some of our own members get poached.»

  Roi was startled. «Can we afford that? Our numbers are still very low.»

  «Can we afford not to?» Zak replied. «It's not just a matter of being sure we play the game, being sure our existence is accepted. It would also be of value if some of our ideas could spread outside the team itself. Almost every child learns writing and simple arithmetic; they're parts of the culture that have managed to move beyond the specializations where they originated. Imagine if the facts about weight and motion could acquire the same status.»

  Roi could see where this was heading. «So by the time the next division of the Splinter is imminent, everyone will have at least a basic understanding of what's going on. It won't be necessary to try to educate them from scratch.»

  «Is that too ambitious?» Zak wondered.

  «I don't know. Tell me when the next division is coming.»

  Zak emitted a sarcastic rasp. «I have a feeling you'll know that before I do.»

  «Don't count on it.» In truth, the idea of being able to predict the event still seemed almost as strange and metaphysical a prospect to Roi as the thing itself.

  «When is the next overview meeting?» Zak asked.

  «Two shifts from now.»

  «I think I'll attend.»

  Roi was pleased. «It will be good to have you there. You've been away for too long.» She hadn't been close to anyone near the end of their life before, and she was never sure what to expect. Zak's strength came and went, and every time it declined she was afraid he was dying, but a few shifts' rest, some good news about the team, and a problem worth thinking about were often enough to revive him. He'd never travel all the way to the garm-sharq edge again, but he might survive at the Null Line for dozens more shifts.

  She bid him farewell, and launched herself across the chamber to the point on the web where her own equipment was set up. Every shift, she counted a few cycles of the three periodic motions to see if anything had changed in their relationship. Once Ruz's clock was declared trustworthy as a standard in its own right she'd start using it to measure the absolute durations of the cycles, but until then she was content to record the ratios between them.

  She set everything in motion and then watched patiently, counting the passage of the cycles using a trick she'd picked up from Gul, a recruit who'd worked in a storage depot: sliding a series of stones threaded on wires, rather than trusting everything to memory or wasting precious skin by making a scratch for each event. Though all three motions slowly diminished over time — however thin the air the stones were moving through, however well-greased the pivots on the Rotator's spinning bar — the periods she was measuring were unaffected, and as long as each cycle could be clearly tracked this gradual decay caused no problem.

  As Roi watched the stones, in her mind's eye she pictured the way their paths might have looked to some impossible cosmic observer, floating in the Incandescence high above the Splinter's orbit. The problem of how these paths wrapped around the Hub entranced and infuriated her. If the Map of Weights could be believed, then long ago — and, presumably, further from the Hub — anything falling freely would have traveled endlessly along the same closed curve. Whether it was simply going around in a circle, or whether it was also detouring up and down or in and out made no difference, because the period
s for all three motions were the same. Now, it was as if something had taken that simple pattern and squeezed and twisted it, forcing the different cycles to break ranks, and yet miraculously preserving Zak's balance of weights.

  She finished her count. In eighty-five cycles of the shomal-junub stones, the plane of the rotating bar turned sixty-eight times, and the looping stone completed forty-five loops. These numbers hadn't changed since she'd begun measuring them.

  Roi recorded the results with the usual mixed feelings. Any change would be the cause of great excitement, the start of a new opportunity to prise apart the mysteries of weight and motion. The numbers had spoken eloquently when she and Zak had first identified the three cycles, but their silence since then had been disappointing.

  At the same time, she knew that any change would mean far more than an intellectual impetus for the team. If the weights increased, the strength of the rock beneath her would be tested, and everyone in the Splinter would be at risk. However great her hunger for revelation, she could not deny a powerful sense of relief that the numbers continued to seem immutable, and that she might yet live out a quiet life merely contemplating their mysteries without ever feeling their sting.

  The overview meeting was held in a chamber a few dozen spans from the Null Line. This place was large enough for the whole team to fit, clinging to the walls, but not so large that people could split up into individual project groups with the members audible only to each other.

  Tan spoke about his group's continued efforts to explain natural motion geometrically. «First, we need to extend the idea of direction to include speed. We can understand the direction 'three spans garm for every one span rarb', so why not also include the idea of speed, and talk about 'three spans garm for every heartbeat that passes'? But then, if we talk about the garm direction, the rarb, and the shomal, there is a fourth simple direction we must add to the list: time. In fact, every path that's traveled includes some component in that direction; we can't travel garmwards a single span without some time also passing.