Incandescence

by Greg Egan

  Call the shomal-junub weight one. The rarb-sharq and spin weights could be quantified now: they were sixteen parts in twenty-five (the square of the ratio of the shomal-junub period to the spin period). The total garm-sard weight was two and a quarter, according to the weight measurements taken throughout the Splinter, and supported by the fact that the looping stone calculations, based in part on that figure, gave the same rate of spin as Roi's new device.

  If you stripped away the complications of spin, the hidden rarb-sharq weight was revealed—sixteen parts in twenty-five—and the garm-sard weight was reduced, down to one and sixty-one parts in a hundred, which was just three parts in a hundred short of one and sixteen parts in twenty-five.

  The sum of the two weights that pushed things toward the center of the Splinter was, within the limits of the accuracy of their measurements, equal to the weight that pulled things away from it. The forces that squeezed and the forces that stretched were in balance after all. The number three was nowhere in sight, but of all its beautiful corollaries, the one symmetry that Zak had most admired had somehow outlived it.

  Zak said, «We don't know when the Map of Weights was drawn, or what its purpose was. It might be nothing but a guess, or a crude approximation, or a record of someone's wishful thinking. But suppose it's none of those things. Suppose it's an accurate record of the truth, of the weights as they once were.

  „This map can't tell us if the weights have grown stronger since it was drawn, because we don't know what scale was used to depict them. It does tell us two things, though: first, that the ratio between the weights has changed, and second, that a hidden relationship between them has stayed the same.“

  As Roi contemplated this she realized how unsettling it was. It was easy to invent stories about the world being torn apart: one time, many times, take your pick, the event happening for no particular reason and making no particular sense. Everything she'd seen or heard on the subject was either six generations removed from a reliable witness, or had many other explanations. But above and beyond the flimsiness of the evidence was the apparently arbitrary nature of the claims. When a disaster could be invoked without cause or constraint — at some fabulist's whim, as it were — it was easy to doubt its authenticity.

  Who would have fabricated a map, though, which secretly implied the very same symmetry as all the painstaking measurements that she and Zak had just made? This hidden thread of order didn't yet tell them why or when the weights might have changed, but the hint that they couldn't just shift any way they liked suddenly made the possibility of change seem far more real to Roi than it had ever been before.

  „What now?“ she said.

  „We have a candidate for a guiding principle,“ Zak said, „but it still needs to be checked, to be verified somehow. And we still don't know how it manifests itself in the rules of natural motion; we know the weights close to the Splinter, but we don't know the precise rules governing orbits in general.

  „We also need to discover, or deduce, the rules that govern the history of the Splinter, past and future. We need to know if the weights really could have changed, and when and by how much they will change again.“

  Roi could have recited the same demands herself, but hearing them spelt out this way made her feel as if she'd been loaded down with an impossible burden.

  „It's too much,“ she said. „Too much for your lifetime, and mine.“

  „Of course it is,“ Zak replied. „One solution to that would be to write down what we've learned, put copies in all the libraries, and hope that in the future someone curious, intelligent, and fiercely independent will come along, understand what we've written, and take up the task where we left off.“

  Roi said, „That might not happen for a hundred generations.“

  „Then we're left with no other choice,“ Zak said. „We need to recruit more people to help us, here and now. Then we can both see the job completed, and we can both die happy.“

  9

  Rakesh felt no change in his body, no disruption in the flow of his thoughts, but when he looked up from the console the pattern of stars through the window was different, and the meteor had vanished from its enclosure.

  «All right,» he said slowly. «I can live with that.»

  «This means. whatever they just did to us, they didn't feel entitled to do to the meteor?» Parantham frowned. «Or they just didn't want us mistaking a low-fi copy for the thing itself?»

  «So now I'm a low-fi copy of myself?»

  «Oh, don't get precious on me,» Parantham retorted. «We were counting isotopes atom-by-atom in that rock. Hardly the kind of thing your personality depends on. I suspect they maintained the standard we're used to in travel, but you know that falls far short of sending a few tonnes of matter at atomic resolution.»

  «Fair enough.» In fact, as far as Rakesh knew nobody in the Amalgam had ever attempted such a thing. «So how did they send us?» he wondered. «How long did it take?» He checked the console. The map told them that they'd traveled the two hundred and seventy-nine light years from their previous location in three hundred and twelve years. The excess time over line-of-sight distance didn't really prove anything one way or the other, though: those decades might have been spent adding a new node to the Aloof's network, or they might have been nothing but the necessary delay caused by a slightly zigzagged path between pre-existing nodes. «Did we ride mundane gamma rays, or the secret highway?» How could they tell the difference?

  Parantham didn't reply, and Rakesh let the question drop. The destination was more important than the journey, and the cabin was flooding with light as their chosen star swung into view.

  The window darkened to compensate, but a broad patch of bright sunlight still swept across the floor, bringing a palpable warmth as it touched Rakesh's skin, lighting up motes of dust as it crossed the cabin. He had almost forgotten that until now they'd had no sun to call their own; the starlight here had seemed more than enough for any purpose. Just as he was getting used to the change, a far greater surprise followed. A stark, slate-gray world appeared beneath them, sharply etched vistas of plains and canyons passing by, before the sliver of vivid dayside topography was replaced by a softer starlit version.

  «I take back every insult,» Rakesh proclaimed. The lack of planets on the Aloof's star map might have been perverse, but they hadn't played dumb with their guests this time. He had been expecting that he and Parantham would be dumped in a remote circumstellar orbit and left to scour the region themselves for specks of light. Instead, the Aloof had placed them just a few hundred kilometers above a rocky, terrestrial-sized world. Even if the system was packed with other planets, this was clearly a good place to start.

  Parantham said, «We'll need telescopes, spectrometers, radar.» Rakesh was already summoning up the interface with the workshop, and sending it suitable designs culled from the library.

  While the workshop labored, they stood by the window and waited impatiently for each new glimpse of the world below. Twice a minute, the sunlit landscape raced by; Rakesh would gladly have given up the convenience of centrifugal gravity for a steadier view, but he'd already programmed the workshop with designs for instruments anchored to the center of the spinning habitat, so with a little patience he could have both. At least their orbit around the planet was taking them further into the dayside, so the crescent beneath them was steadily growing.

  «What should we call this place?» Rakesh asked. The planet had never been detected from the disk, and though its sun had been catalogued a million years before it had never been allocated anything more than a number.

  «We haven't even named our ship yet,» Parantham replied.

  «Lahl's Promise?» The name slid off his tongue without a moment's thought, but on reflection Rakesh decided that it had a suitably admonitory ring to it. It would remind him that he'd vowed to treat the search for his cousins as seriously as Lahl had treated the need to find a child of DNA to take up the quest in the first place.

&nb
sp; «That's fine by me,» Parantham said. «But let's hold off on the planet until we know something about it.»

  The planet looked arid to Rakesh, though at least it wasn't visibly cratered, and the haze on the horizon made it clear that it possessed some kind of atmosphere. Back in the disk, the DNA panspermia was full of worlds like this, mostly populated with nothing but microbes who'd been hiding meekly in the soil for a few billion years. Lahl's Promise? Rakesh felt a twinge of guilt. Noteworthy as it would be to confirm that the panspermia really had stretched a tendril down into this perilous neighborhood, microbes were microbes, and he couldn't pretend that he wasn't far more excited simply to have found an excuse for the Aloof to release him from their usual strictures. According to legend, Leila and Jasim had been given a grand tour of the natural wonders of the bulge, but even if that was true, in three hundred millennia only a handful of travelers taking the short cut had claimed to have been woken en route at all, and no one had ever been handed a ship and allowed to go sightseeing.

  Within two hours the instruments were online, and solid data about the planet was coming through. It was a medium-sized nickel-iron-silicate world, with a weak magnetic field and a reasonably thick atmosphere comprising mostly nitrogen, carbon dioxide and methane. There was no obvious chemical disequilibrium, no unstable mix of gases in proportions that only ongoing biogenesis could explain. The temperature and pressure on the surface would permit liquid water in the tropics all year round, but there was none visible, and water vapor was present in the atmosphere only in trace amounts. Radar showed no signs of subsurface ice. This was a dry and dusty world, and there was no obvious reason to suspect that it had ever been much wetter. The topography showed evidence of tectonic activity and vulcanism, and such water as the atmosphere contained could easily be accounted for by volcanic eruptions.

  Still, the DNA panspermia had been known to gain a toehold on worlds as harsh as this. The microbes in the meteor had certainly appeared to be adapted to water-based chemistry, but that didn't have to mean vast rivers and oceans.

  The view from their low, near-equatorial orbit was limited. Rakesh had the workshop build a mapping probe, to sweep over the planet in a polar orbit, imaging the whole surface in successive slices. Parantham ordered the construction of a second telescope, to search the sky for sister planets.

  «Some of the isotope ratios look marginal,» she noted. «Nothing we've seen here says that the meteor could not have come from this system, but the data we've got from this planet so far isn't as close a match as I'd expect.»

  Rakesh laughed. «So maybe the Aloof have a sense of humor after all? They put us into orbit around this desert world, knowing there was a sibling with oceans and forests a few million kilometers away?»

  «Let's see if there are any siblings at all.»

  In fact, they knew from the Amalgam's catalog that there ought to be at least three, and Parantham's search quickly found them all. One was a «baked» gas giant, a ball of methane and hydrogen more than a hundred times heavier than the world below them, orbiting at less than half the distance from the sun. It possessed two rocky satellites, both far too small to hold atmospheres. The second and third gas giants lay in tilted, highly eccentric orbits, further from the sun. One had four significant moons, the other three, but none of these satellites looked promising either as hosts for life, or as geochemically plausible parent worlds for the meteor.

  «This is still our best bet, then,» Parantham said.

  «Assuming we're even in the right system,» Rakesh added.

  «I wouldn't give up on that yet. If nothing obvious comes from the mapping sweep, we'll have to think about looking for microfossils.»

  «Yes.» Rakesh's spirit sank; the promise was getting heavier by the hour. Here they were in the galaxy's vibrant core, and Parantham was talking about scouring a planet's worth of rocks for cavities that might once have been microbes. Still, if that was it — if this world was a bacterial graveyard, and the Aloof had invited them here merely to pay their last respects — once he'd done his duty they might yet reward him with the chance to see something more.

  He toyed with an image of the four planetary orbits. No two of the ellipses shared the same plane, and the planets' axes were all over the place. That was what came of living in such crowded conditions: a neighboring star must have passed by and wreaked gravitational havoc. Rakesh ran dynamical models, testing the stability of the present arrangement, trying to get a sense of how long it might have persisted. The outer two gas giants were slowly nudging each other's orbits into a resonant configuration in which one world would complete exactly three trips around the sun to the other's two, but the process hadn't yet reached that stable endpoint. This and other signs that the system was still settling down after a profound disturbance suggested that the event had taken place between one and two hundred million years before. The same encounter might well have altered conditions on the world below them, though the geology still offered no indication that there had ever been running water.

  «Metal!» Parantham announced.

  «What?»

  She pointed to the console. «The mapping probe just saw a glint of unoxidised, elemental metal. Mostly iron, with a number of impurities.»

  Rakesh reviewed the data. High on a plateau in the tallest of the planet's mountain ranges, a metallic patch a few square meters in area had registered on radar, along with other wavelengths. Its detailed structure had not been resolved, but its chemical state alone was significant. In theory, rare geological processes could be responsible for such a deposit, but the surrounding rocks bore no witness to the necessary conditions.

  They let the mapping probe continue its sweep of the planet, so as not to miss any further surprises, but they had the workshop build and launch a second probe tailored to investigate the strange glint more closely.

  Rakesh said, «There was nothing in the structure or genome of the microbes we saw in the meteor that suggested they could metabolize metallic ores.»

  «Viva diversity,» Parantham replied. «A microbial world is still a whole ecosystem. If this is biological, who knows what other niches there are that we haven't yet spotted?»

  The second probe swept low over the plateau, and sent back high resolution images. The metal formed a blotchy but weirdly symmetrical patina on the rock, concentrated in six roughly elliptical lobes arranged in pairs around a central axis. It was hard to see how any underlying ore body that might have been metallized by microbes could have taken such a shape, though perhaps microbial colonies could self-organize into this pattern for some other reason. Spectroscopy revealed no organic matter, but that didn't rule anything out; a similarly remote view of the Aloof's DNA-infested meteor would have portrayed it as equally sterile.

  They waited two full planetary days before taking the next step, allowing the mapping probe to image the entire surface. They passed the time arguing about the possibilities, cooking, eating, occasionally sleeping. Rakesh felt a strange mixture of urgent curiosity and an equally strong desire to prolong the unfolding process of discovery. Was this how it had been, to live in the Age of Exploration? Every world had held surprises then, when the ancestors of the Amalgam had still been slowly reaching out to find each other. Back in the disk, every planet he'd set foot upon had been visited by a hundred billion people before him, its every feature catalogued in more detail than he could hope to match with firsthand observations in a thousand years.

  The mapping probe found no more elemental metal, and no other chemical anomalies at all. To the limits of the probe's resolution and sensitivity, every other structure and substance on the planet's surface could be accounted for by geological effects.

  Rakesh knew exactly what he wanted to do next, but he was unsure where his obligations lay. «What are the rules about landing on a world like this? Just because we can't find a trace of life doesn't mean there aren't a billion software citizens buried in a processor somewhere.» The disk contained thousands of planets where all evid
ence of biological ancestry had been carefully wiped from the surface, out of a desire to avoid attracting attention. They were all catalogued now, and their inhabitants left in peace, but the earliest of the explorers who'd chanced upon such places had sometimes triggered substantial animosity.

  «If the Aloof don't want us setting foot here, I'm sure they'll intervene,» Parantham replied. «If this planet has custodians who are distinct from our hosts, it's the people who brought us here who have a duty to ensure that we cause no offense. As long as we act in good faith, it's their responsibility.»

  «I can't argue with that,» Rakesh conceded, «but it still doesn't feel right. Act at will and then see if you're restrained or rebuked, like a child?»

  Parantham said, «They chose their relationship with us. If they want to open up a dialogue, if they want to educate us, they can do that any time. Until then, what choice do we have? We can't intuit every cultural sensitivity from first principles. So long as we do no harm, if we blunder in where we're not wanted it's up to someone with local knowledge to give us a civics lesson.»

  «If you go back far enough in history,» Rakesh countered, «I can think of some civics lessons I'd rather not have.»

  They argued for hours, but finally settled on a compromise. They would send down a small collection of probes to investigate the anomalous metal. They would not literally set foot on the surface, but telepresence would still grant them most of the same advantages.

  Rakesh switched his senses to his avatar as it plummeted through the stratosphere, curled up inside the heat shield that protected the whole exploratory package. There was no light source within the ceramic cocoon, but when he shifted his vision to infrared the differential heating of the shield provided enough contrast for him to make out his immediate surroundings. Parantham's avatar was coiled snugly behind the laboratory/rover, his jelly-baby twin. Both of them were about a millimeter tall, and shorn of unnecessary extras, leaving torsos, pudgy arms and legs, and heads without mouths or noses. The lab's machinery would do all the smelling, and their real bodies could do all the talking.