DEATH’S DOOR

 

ALASTAIR REYNOLDS

 

SAKURA BECAME AWARE that he had an audience. He dipped his brushes in liquid ammonia and set them down on the easel, turning from his canvas and the landscape beyond it.

“Still dabbling?” asked the figure that had been watching him paint.

“Everyone needs a hobby, Tristan.”

“I sat down at a piano recently,” the figure answered after a moment’s reflection. “Not in this anatomy, obviously. But my hands moved to the keys and I stumbled my way through a late Rachmaninov. Until then I barely remembered that I could play.”

“That’s procedural memory for you. Other than smell, there’s not much that gets into our brains quite that deeply.” Sakura extracted his brushes from the ammonia solvent, sniffing at them before beginning to dry them on a rag. He wondered why ammonia always made him feel melancholic, burdened by something he could not quite identify.

“You don’t have to stop on my account,” Tristan said as he picked his way nearer. Like Sakura he had adopted centaur anatomy, by far the most practical option for coping with Titan’s combination of high gravity and treacherous footing.

“I’m done,” Sakura said with a sigh of resignation, stepping back from the easel. “It wasn’t going very well, anyway. Is there any reason why you’ve come here, Tristan?”

“No law against looking up old friends, is there?”

“If only it were that.”

“We’ve both come,” said a second voice, higher and more fluting than the first. A transparent sphere bobbed down from a low escarpment of frozen methane, with a winged angel floating within it.

“Gedda,” Sakura said with only mild surprise. “I should have guessed Tristan only ever came as part of a double act.”

“If your friends can’t intervene in a time of need, what good are they?” Gedda’s sphere touched down next to Tristan. They were indeed old friends; he had known both for at least four hundred years, through adventures, wild times, joys and sorrows and more anatomies than any of them could count. Somewhere in his winnowings he had lost the specifics of how they had met, but it hardly mattered to him now; it was enough that the three liked each other (while occasionally testing the limits of that union) and had many shared experiences.

Gedda was examining the canvas, shaking her head slowly. Her skull was small and sleek, bird-light in its cranial architecture. Her body form was diaphanous, with her core nervous system embedded within layers of translucent anatomy, with her veined and colour-tinted wings folded back on themselves.

“Is that your idea of composition, Sakura? That mountain’s all wrong. You’ve got it much too far over.”

“Clearly no one ever told him about the rule of thirds,” Tristan said confidentially, cupping a hand to the side of his mouth.

“It’s a methane berg, not a mountain. Look, I appreciate seeing both of you—I really do. But you can forget any ideas about talking me out of my decision.”

Gedda rolled closer to the canvas. “I see you’ve put her in the picture again?”

“Her?” Tristan asked.

“His nameless watcher. The woman he shoves into every one of his landscapes, as if he can’t bear to let the composition stand on its own merits.”

Tristan cocked his head, reappraising the canvas. “I suppose the colours aren’t too bad. We shouldn’t be too hard on him. It can’t be that easy getting paint to work in this ball-freezing cold.”

Sakura began to unloosen the screws holding up the easel. “Now that the art critics have had their say, can we agree that the door threshold is my business alone?”

“It’s too low,” Tristan said.

“One in a thousand? Don’t be such a hypocrite. You face worse odds than that when you go prancing around on cliff faces. Same with Gedda with her flying.”

“That’s different,” Gedda said. “Tristan chooses his sports, just as I chose to fly. There’s a risk, which we’ve both done our best to minimise, and that’s the price we pay for having fun. But you’ve instructed the door to kill you.”

“Did you argue with Sartorio this way, when he set his threshold ten times lower than mine?”

“No,” Tristan said. “But we should have. There isn’t a day when I don’t miss him.”

“Me as well,” Gedda said. “And we’re not going to make the same mistake twice.”

“She’s right,” Tristan said, moving to help him pack away the painting equipment. “Undo the setting, Sakura. This is just a phase. You’ll get over it soon enough, and realise that there’s still plenty to live for.”

“And if I don’t?”

“You’re not really committed,” Gedda said. “You wouldn’t be painting if you didn’t think there was a reason to go on.”

“You don’t understand,” Sakura said.

“Damn right we don’t,” Tristan answered.

“I’m older than either of you. That’s plain just from the memories that came through my winnowings. I remember bits of history you two have only read about. The argosies. Cities on Venus. The Change Wizards and the Great Dominions. The fact is that I’ve seen and done more than either of you, and I’ve started to sense the limits.” Sakura finished boxing the canvas, protecting the still-wet paint. “There are only so many permutations of experience a human nervous system can process. I don’t ever want to be bored. I’m not bored just yet, but I can feel boredom stalking me, and I’m not going to give it a chance of catching up.”

“We have to argue him out of this,” Gedda said urgently, rolling forward. “My flying tournament on Jupiter is in six months—it’s the reason I’m locking in this anatomy for the time being, so that I can get an edge over Malec. But between now and then we can show Sakura the sights again—shake him out of his rut.”

“It’s more than a rut.”

“We’ll see about that,” Tristan said, clapping his hands. “You just need to let your friends take care of you. It’s settled, old man—you’re ours until Jupiter!”

“Nothing’s settled!” Sakura exclaimed, but with the exasperated good humour of someone well aware that they were on the losing side of an argument.

His friends looked each other. Tristan hoofed at the ground. Gedda flexed her beautiful wings, facets of pastel colour splintering out of them. “We’ll turn you,” she said, with a fierce conviction. “Come with us, and you’ll remember that life’s worth living until the last bitter drop.”

 

 

GEDDA EXTENDED A hand through the membrane of her excursion bubble, touching the destination panel on the left side of the door. At her touch, coloured motifs and symbols glowed against the door’s black surface, becoming a blur as she sped through branching menus. Worlds, dwarf planets, moons, minor bodies flickered by in an ever-accelerating shuffle.

Sakura, standing a few paces behind, politely averted his gaze. He had agreed to indulge his friends.

“There,” Gedda said, withdrawing her arm and rolling back. “It’s locked in for the next three transits.”

“Do you know where we’re going?” Sakura asked Tristan.

“My idea, this one, actually—the timing was too good to resist. But Gedda approved, and she gets to choose the next one.” Tristan settled a confiding arm on his shoulder. “Don’t worry, old man—I won’t inflict anything too weird on you.”

Gedda went through first. Her excursion bubble contracted by about a third, allowing her to roll into the doorframe, through the yielding grey surface, until it puckered tight. Tristan and Sakura stepped back from the upright cylinder of the door, looking up at the glass column that stretched into the lowering clouds. A few seconds passed and then a bright bolt shot up the column and away, gathering tremendous speed in the few instants that it was visible.

Sakura waited a few heartbeats. She would already be beyond the atmosphere, her nervous system buffered against the acceleration, speeding to some other place in the system.

The doorway chimed and pulsed to indicate readiness for the next transit, with Gedda’s settings still holding.

“Go,” Tristan said.

“After you, I think,” Sakura answered. “Trust me—I’m not going to back out this early in the game.”

Tristan accepted this pledge and walked through the surface. After a few moments he also shot up the tube and away into space, close on Gedda’s metaphorical heels. Knitters would already be dismantling and reforging Tristan’s anatomy, remodelling neural connections so that the transition from one body form to another felt entirely seamless.

Sakura, alone now, had the door to himself. It was just him, the door, the raised area of ground on which it had been constructed, the winding staircase leading up to it, a landscape of low hills and lakes stretching away into misty, sepia-stained distance, a little drizzle touching his skin from the east.

The rain was composed of long-chain hydrocarbons; the atmosphere was cold and poisonous, the thick clouds reducing the daylight to a sullen orange. To Sakura’s senses, though, the rain was invigorating, the temperature pleasant, and the quality of light restful, suggestive of morning mists in the hills of Honshu or Tuscany.

There had been a time when Sakura had resisted these adaptive tweaks, regarding them as somehow false or counterfeit, but in recent centuries his views had softened. No alien organisms had evolved on Titan—or anywhere in the Adaptasporic Realm besides Earth—but if they had, and over time had gained senses and minds, then surely they would have ended up apprehending Titan in distinctly similar terms, enjoying its gentle rains, soothing airs and mellow light.

Sartorio had been a purist, Sakura reflected, and would not have approved. In Sartorio’s view, you either met the solar system on human terms, with all its beauty and ugliness unfiltered, or you were indulging in tragic self-deception.

“Why not make the sky blue, and be done with it?” Sartorio would ask, mockingly.

Sakura was thinking of his old friend—their old, mutual friend—as he stepped through the door.

There was the usual instant of disconnection, an abeyance in his thought processes that was both briefer than sleep and oceanically deeper, and then he was elsewhere in another body, knitted for him during the transit.

He stepped out into darkness. He felt rocky ground under his soles. Two legs this time, ending in feet rather than hooves. His friends were present, although it took a few seconds for his eyes to adapt to the darkness. Gedda was unchanged, still a winged angel in an excursion bubble. Tristan was bipedal, reverting to something close to baseline anatomy. He was a glassy stick-figure, echoing Gedda’s core anatomy, with layers of translucence shrouding their central nervous systems.

Sakura inspected his own forearm, seeing the same translucence: skin, muscle, bones and nerve turned gel-like with a tinting of different hues.

Overhead was a bowl of stars. Nothing to smell or taste, just vacuum beyond the synthetic membrane of his skin and an invigorating coldness when he tried to draw in a breath.

“All right, do I get twenty guesses? Somewhere rocky, not ice-dominated. Callisto, maybe, but since we’re going to Jupiter soon enough, I don’t think you’d bring me there immediately. And is that Mars overhead? I think we must be quite a bit closer to the Sun. Ceres, maybe, except that horizon looks a little too far away—assuming you haven’t shrunk me down to a doll. Earth’s moon, then, or just possibly...” Sakura bent down and scooped up a loose pebble, watching it drop back to the ground. “Mercury, if I had to stake my life on it.”

Gedda pouted. “You’re no fun.”

“Don’t blame me for being good with worlds—I’ve seen enough of them.”

“We’re near the terminator,” Tristan said. “The Sun will be rising very shortly, and we don’t want to miss it.”

Gedda raced ahead, rolling and bouncing from one low ridge to another. Tristan strode on, and Sakura followed. After a few minutes of gradual ascent, they reached an overlook with a series of ledges poised over a near-vertical cliff face, and far below them a flat black plain stretched all the way to the horizon.

“Sit down here,” Tristan said, picking his way to one of the ledges, precariously close to the sheer drop of the cliff. He squatted with his legs dangling over the edge, and Gedda rolled to a halt with her bubble just fitting in the available space.

Sakura settled down between his friends. “I hate to break it to you, but this won’t be my first Sunrise.”

“Sunrise is the end of the show, not the start of it,” Gedda said, in a gently chiding tone. “For now, just sit still and wait. Keep your eyes at the default amplification level too—you’ll thank me for it later.”

“All right.” Sakura forced patience upon himself. “About your tournament, by the way. Is winning against Malec really the only thing that’s driving you?”

“Malec thinks he’s better, and he hasn’t been shy about advertising his opinion. Mouthing off at every chance. At Jupiter I get the chance to even the record.”

“Until the time after that. Sooner or later he’ll beat you in some other tournament and you’ll be back where you started. Where’s the end to it, Gedda?”

She examined him with a puzzled look. “Does there need to be an end?”

“She enjoys her flying,” Tristan said. “Better to indulge in an activity that was already pointless from the start, like competitive flying, rather than one that only turned out to be pointless much later on, like figuring out your Null Model.”

“And what keeps you going, exactly?”

“Insulting my friends. Making new ones, to compensate for the ones I already insulted just a bit too much. You’d be surprised how much work those activities demand of me—it’s practically a full-time occupation.”

“In fairness, you’re getting very good at it.”

Tristan tensed, leaning forward. “It’s starting, Gedda.”

“Yes,” she answered. “Very definitely.”

“What, exactly?” Sakura asked.

“Just look,” Tristan said.

It began incredibly faintly, with a barely perceptible blue-green glow playing on the arc of the horizon. Slowly it pushed fingers of light towards them, extending across the dark plain. They were not straight, like radial spokes, but rather approached in a series of angular, dog-legged progressions, like the trail left by a lightning strike in an atmosphere. The blue-green fingers faded. But almost immediately, a ruby-pink aura was forming on the horizon again, and beginning to extend itself across the plain.

“What are they?” Sakura asked.

“The entire plain’s riddled with primordial lava tubes,” Tristan said. “Very old, for the most part—billions of years, probably as far back as the Late Heavy Bombardment. There’s glass in some of these tubes, shock-formed silica, and in places the veins are thick enough, and extensive enough, to function as natural light-pipes. The Sun pumps light into them over the horizon, and it leaks around the curve of Mercury and reaches us ahead of the Sunrise itself. Where the tubes are broken, or the glass veins lie very close to the surface, the light escapes back into space. You’d never get an effect like this on a planet with an atmosphere, since the airglow would smother it long before the Sun pushed above the horizon. That’s half the mystery. What no one really understands—yet—is why the colours vary, or why the show’s never the same from one ’rise to the next.”

The ruby-pink fingers had reached nearly all the way to the base of the cliff under them, and still more colours were brewing on the horizon. Emeralds this time, and as his eyes became better accustomed, Sakura began to pick out branches and forks of other hues, chasing away from the main display.

“Isn’t it lovely?” Gedda asked. “Strange and unpredictable. How wonderful to have something we don’t fully understand, this late in the day.”

“I wouldn’t go that far,” Sakura said. “Just because we haven’t figured out how something works, doesn’t mean that we couldn’t. I could take a stab at it right now. Those glassy veins are probably doped with impurities, filtering the light to varying degrees. As for the unpredictability—well, it’s Mercury, it’s still seismically active, so there are bound to be ever-changing stress patterns in that plain, and I wouldn’t be surprised if the light has to take a different path from one cycle to the next, never mind the fact that the Sun angle will change due to the axial tilt...”

“Spoken like a true Null Theorist, crushing the joy out of life,” Gedda said.

“I never said it wasn’t beautiful,” Sakura replied, putting on an affronted look. “It is. I didn’t expect this.”

“They found it about a thousand years ago,” Tristan said, standing up. “During one of the early exploration missions, I think. Then it was forgotten by the time they built cities across half of Mercury.”

Sakura nodded, remembering—dimly—a time when the inner worlds, from Mercury to Mars, had been dense with human settlement. The vogue had shifted, though. Over the last few centuries there had been a move to return these places to something closer to their pristine conditions. There was room for trillions of people further out, with no need to swelter so close to the Sun.

“Where are you going?” Gedda asked as Tristan began to climb up and off the ledge.

“Over to that finger,” Tristan said, pointing to a spur of rock jutting out from the cliff at right angles, a couple of hundred metres to the right. “I think I can get to it without too much difficulty.”

“Watch your step,” Gedda said.

While the play of colours continued, and with Tristan picking his way to the finger, Gedda moved her excursion bubble next to his crouched form. “We go back quite some way, Sakura,” she said, dropping her voice so that the conversation would be local. “Not as far as some, I know. But long enough for me to think I had some sense of what made you tick.”

“You do. I’m a very simple soul.”

“Do you remember a talk we had once? It would have been on Oberon, I think, or maybe Nereid. I was the one feeling listless and you told me you’d never have that problem, not while you had the great edifice of the Null Model to drive you on.”

Sakura tucked his knees tighter to his chest. “I don’t remember that conversation.”

“I’m offended. It meant a great deal to me.”

“If it happened at all, I must have lost it in one of my winnowings. Don’t blame me for that: I know you’ve had your share.”

“Perhaps winnowings are the solution, then. Instead of setting that door threshold so low, and rolling the dice on death each time you step through, you could just submit to a harsher degree of winnowing.”

“And lose myself in a series of little deaths, rather than one big one?”

“At least we’d still have you.”

After a silence he replied: “I was wrong about the Null Model—I just didn’t see it at the time. None of us did. We were so hung up on constructing our perfect system of knowledge that none of us stopped to think what we’d do when we were finished.”

Gedda flicked her attention to Tristan, who was working his way along a very narrow traverse to reach the finger.

“Do you know for sure that you’re done?”

Sakura shook his head slowly, smiling. “I could take apart that plain and work out what makes it behave as it does, why it varies from cycle and cycle, and I’d stake my life and yours that there isn’t anything in it that contradicts the Null Model.”

“But then there wouldn’t be a plain anymore.”

“There’s that,” Sakura admitted.

Tristan had reached the finger. They could only just make out his translucent form as he monkeyed out from the cliffside.

“Don’t fall!” Gedda called.

“I think I’m just in time,” Tristan answered, arms spread wide for balance. The finger narrowed along its length, and he had to step gingerly for the last few paces.

“Exactly how old are you, Sakura?” Gedda asked.

“I don’t remember. I lost track in one of my early winnowings, and I never bothered running a self-audit. Does it matter?”

“I’d like to know why you keep putting that watcher in your paintings. Then maybe we’d know you a bit better.”

“And know what to fix?”

“Watch this!” Tristan called.

A fiery yellow glow swept in across the plain, following a jagged, branching path. It was brighter than any of the patterns they had seen before and Sakura guessed that the Sun must be close to the horizon, pumping more and more light into the glass channels, but also close to overwhelming the display with its own intensity. Now Tristan arched his back and threw back his head, and between one instant and the next he became consumed by the same fiery yellow. It was glowing out of him, turning him into an exultant human star.

“What’s he doing?” Sakura asked, amused and intrigued.

“He must be standing in the path of a light beam, coming up from the plain,” Gedda said. “We can’t see it until ittouches him, then it bounces through his body in a million directions and lights him up like an ornament.”

“Like a flashy, cheap ornament.”

“But you have to give him credit for the timing. He must have done his homework for once. I bet that light beam doesn’t hit that finger every time the Sun comes up, or even one in a hundred times.”

“All right, Tristan,” Sakura called. “You’ve impressed me. You can climb down now. You’re making me nervous just watching you.”

“Show’s over anyway,” Tristan said, starting to fade, as if a battery inside him were losing charge. “Here comes the Sun, anyway, spoiling everything.”

“Without the Sun you wouldn’t have been able to show off!”

“You have a point, old man.” Tristan started to backtrack, reversing his steps to the relative safety of the cliff and its ledges.

“Admit it,” Gedda said. “We surprised you with his phenomenon. You didn’t know about it, and you’d certainly never seen it.”

Sakura made to contradict her, some faint nagging memory insisting otherwise, but he was wise enough to nod gracefully. Tristan had gone to some trouble to make this work, and it would have been churlish to ruin the moment.

“It was lovely.”

“Good. But we’re not done with you. Not by a long margin.”

 

 

THEY WENT TO Venus next. Sakura guessed where they were without too much trouble: not many worlds had rocky surfaces, gravity similar to Earth, and atmospheres hot, dense and corrosive enough to test even the sturdiest anatomy. Tristan and Sakura waddled around like upright lobsters, knitted into armoured skin, while Gedda accompanied them in her excursion bubble, breaking off only to put in some flying practise in the high atmosphere, where the pressure and wind forces approximated those at the Jupiter tournament. They were there to visit an artist friend of Gedda’s, a personage called Ossian who curated a menagerie of strange mechanical sculptures, huge walking and ambulating constructions driven only by the wind. No one knew who had made these ungainly, scuttling entities, nor their purpose, but Ossian had set her mind to rebuilding the broken ones, and after a century and a half of painstaking effort, she had overseen the rehabilitation of twenty-two of the shambling artefacts. Many more remained to be fixed, though, and before they could be restored to life, they needed to be organised, their parts separated and categorised into bonelike piles, spread out on a level plateau near Ossian’s dwelling. Gedda, knowing that Sakura had a tinkerer’s mindset, had decided that it would be therapeutic for them all to spend a few weeks helping Ossian, and so it proved.

Venus was a backwater place now, with fewer than a million permanent inhabitants, most of whom lived far from Ossian’s place on the northern foot slopes of Ra Patera. There had been billions once. People had come to the sky first of all, dwelling in floating cities dozens of kilometres above the sulphurous, heat-haze crush of the surface. Eventually, the cities, straining with over-population, had pushed anchoring taproots down to the surface, and those taproots had become the seeds for the rampant conurbations of the second wave. Finally, there had been efforts at localised terraforming—first with domes, and then with glass-walled cylinders whose open tops projected beyond the upper atmosphere, so that the jewel-hulled argosies of the third wave could come and go with ease.

The argosies were no more, though, and those paltry terraforming projects were now regarded as the quaint vanities of an earlier age. The governing philosophy of the Adaptasporic Realm was minimum local intervention. Worlds could be colonised, but it was people who had to be shaped to the environment, not vice versa. Humility and coexistence, rather than arrogance and dominance.

Ossian was a good host, and by the time they left her—and discarded their lobster-bodies—Sakura and his friends had helped resurrect three more sculptures, and Sakura expressed his sincere intention to return and continue the work. Deep down, though, he knew that he had made a thousand similar promises, and rarely held himself to them. He had never been good with promises.

From Venus, Tristan took them to Mars, where they spent two weeks rambling around a network of Pre-Adapt ruins, marvelling at the glory and hubris of those ancient days. Their anatomies (Gedda excepted, of course) were striding, giraffe-like forms, perfect for picking their way through the dust mounds that had nearly consumed the old settlements. After the busy work of Venus, it was a lazier time, and Sakura was glad to find moments where he could drag out his canvas and paints, held by the doors until he summoned them. Tristan pranced around reciting Shelley, obscurely pleased to have memorised Ozymandias.

It was Gedda’s turn again after that, and since she needed some atmospheres to play in, they spent a month around Uranus—Sakura and Tristan visiting the moons while Gedda dipped in and out of the cloud decks. Then onto Neptune, and finally Pluto and its environs, where there were salty oceans, and Sakura and Tristan adopted various aquatic or amphibian body plans, depending on local preferences and customs.

Sakura hardly dared voice it, but somewhere in the fourth month, somewhere between Charon and the lakes of Nyx, he felt a turning in himself. It was a small thing, like the tiniest shift of light on an overcast day, but he registered its change all the same.

Registered it, noted it, and yet forced himself to hold the door’s threshold at the level he had locked in before Titan.

It was not time to change it—not yet. But he was at least opening himself to the possibility. Perhaps his friends had been right after all.

 

 

IN THE FIFTH month, not long before they would have to turn back to Jupiter, Tristan pulled strings to get them a close-up view of the Luminal Minds.

They came out into vacuum and weightlessness, three friends in close-formation excursion bubbles. A dusky radiance lit their bodies, all that remained of the Sun’s glare by the time it had struggled its way out to the frosty, vault-like margins of Trans-Neptunian space. It was a cold yellow eye, still brighter than any star but becoming unquestionably starlike.

“I don’t see anything,” Gedda said, swivelling around.

“You won’t—not until we’re much nearer. The Luminals are very dark, despite their name. Crank up your eyes a few logarithmic steps.”

Tristan had played a minor role in negotiations with the Luminals, helping to draw up a treaty that barred the opening of any more doors between ten and twenty light hours from the Sun for at least the next thousand years. In return for the peace and quiet offered by this gesture, the Luminals agreed to run theoretical simulations of Null Model consequences and also conduct high-redshift observations of early galaxies and proto-galaxies for clients in the warmer parts of the Adaptasporic Realm still clinging to the idea that there was life beyond the solar system.

They powered into darkness. Sakura and Gedda adjusted their visual sensitivity, taking pains not to look back at the Sun. There were no bright worlds beyond this point, just ice and darkness and then the unthinking void between the edge of the system and the next star, a gulf which had been crossed by a few machines but no living organisms larger than bacteria.

Gradually, though, something emerged.

There was a cluster of them—three Luminal Minds in close proximity. Each was fifty thousand kilometres across, and the space between them was about twenty times as great.

They were spheres made up mostly of nothing. Hundreds of billions of tiny elements organised into a shoal or cloud of distributed processors, with no physical binding. There was a dark, purplish flickering from the Luminal Minds—subliminal straylight from their private cognition.

Or perhaps a gentle welcome or warning.

“They have names,” Tristan said. “But if I were to start naming them, we’d be here to the middle of next week. I called them Indigo, Violet and Ultramarine, but that was just my private shorthand. We’re heading into Indigo.”

Sakura’s eyes strained at the limit of their detection threshold, swarming with photon noise and cosmic ray hits.“Is Indigo friendly?”

“Oh, they’re all friendly. Up to a point. Just don’t say anything rude. Oh, and don’t think anything rude either.”

“They can read our minds?”

“I’d rather not find out.”

Indigo loomed, planet-sized and silent. Stars shone through the vast interstices between its mainly invisible processors. On the glass wall of the excursion bubble, a thickening network of yellow lines showed guestimated structures and avoidance points. The bubble steered itself obligingly.

Music began to play.

“What’s that?” Gedda asked.

“Rachmaninov,” Tristan answered. “I thought you could use a little accompaniment to settle your jitters.”

“We’re entitled to be a little edgy,” Sakura said.

“No need, old man. Indigo’s just a baby—barely a hundred years old, which is nothing in Luminal terms. They start really small. To begin with, their nervous systems are fully human, just as complicated and compact as our own. Then they open themselves up, like galaxies spreading apart on a surf of dark energy. The knitters dismantle and convert their biological neurones one by one, making them self-sufficient and vacuum-hardy. Instead of electrochemical signals, they bounce their thoughts around with photons. Gradually, the space between the neurones opens wider. At the same time, they’re adding more and more processing capability, transforming raw matter into additional neurones. Most of these Luminals needed to tear a few comets apart just to get the building materials.”

“They get more powerful,” Sakura said. “But also slower.”

“It’s a trade-off they’re willing to make. Luminals are really only interested in talking to other Luminals, so it doesn’t really bother them that they’re thinking at a different rate to the rest of us.”

“We’re just a nuisance,” Gedda said. “A fast, scurrying nuisance—rats in the basement.”

“So long as we respect their needs, give them room to think and grow, we can easily coexist—even benefit from each other. I formed quite an attachment to Indigo.”

A blue flash washed over Sakura.

“What was that?”

Tristan laughed. “I think we just ran into a thought! I was trying to avoid getting in their way, but there are so many connection pathways that it’s all but impossible not to intercept the odd transmission. I wouldn’t worry, though. Indigo won’t miss it. If the thought was critical, it’ll wait and re-send once we’ve unblocked the pathway. Probably wasn’t a complete thought anyway, just a constituent process.”

“Are you sure you got permission for this?” Gedda asked, nerves pushing through her usual sanguinity. “It feels wrong to be inside another person’s mind. I wouldn’t want some tiny organism drifting through my brain, crashing into my thoughts.”

“They’re used to it,” Tristan said breezily. “The largest and oldest of the Luminals are already more than a light-second across, easily big enough to swallow Earth and its Moon. On that scale, you can’t really legislate against trespassers. Bits of rock and ice are sailing through them all the time.”

“Exactly how big do they intend to get?” Sakura asked.

“There’s no danger of them rubbing shoulders just yet, old man. There’s a lot of space out here—a lot of room. Even if the Luminals confine themselves to the space between ten and twenty light hours from the Sun, there’s room for trillions of them—more than all the human beings that have ever lived. They’ll run out of building materials long before they run out of elbow-room.”

“Let’s hope they don’t turn their eyes to the gas giants,” Gedda said.

“Or the Sun,” Sakura said. “They barely need the Sun at all, do they, other than something to orbit?”

“You two are such worriers,” Tristan said, shaking his head. “They’re already hitting the limits, anyway. The largest of them have to deal with non-negligible self-gravitation. They start to collapse under their own mass. The only way around that is to use their own thoughts as light-pressure, counteracting the inward pull.”

“Like stars,” Sakura said. “Thought-pressure, instead of fusion-pressure. Actually, that’s rather lovely. Your own thoughts, keeping you alive. Never stop thinking, never stop dreaming, or you start to die.”

“Too weird for me,” Gedda said, giving a theatrical shiver inside her excursion bubble.

Tristan pushed them further and further into the depths of Indigo. He had some diplomatic business that still needed fine-tuning, some small but necessary closure of detail, and Indigo was the designated ambassador, tasked to speak back into the world of normal humanity. Presently, their excursion bubbles were surrounded by a swarm of macroscopic knitters, congealing closer and exchanging a constant flicker of purple transmissions. Tristan urged calm: these knitters were merely the means by which Luminal Minds such as Indigo gathered additional raw material, harvesting primordial objects as they drifted between the neurones.

The knitters engulfed the excursion bubbles, blocking out any view of the Sun, the worlds, the stars or the rest of Indigo. Sakura was tense, but he set his faith in Tristan’s reassurance. Tristan might take insane risks with his own survival in the pursuit of thrills, but he would never jeopardise his friends.

Colours flooded the bubble. Symbols and images jostled against the glass sphere, projected from outside. In places, the bubble began to buckle inward, as if resisting some titanic external pressure.

“It’s all right,” Tristan called, sounding very distant. “Indigo’s just taking a polite interest in my friends.”

“Tell Indigo to take a bit less of a polite interest,” Gedda said.

Structures penetrated the bubble. They burst through without breeching vacuum: radial spikes of self-knitting matter, projecting inward like stalactites. Sakura stiffened, but he had no choice but to surrender and accept his own powerlessness in the face of Indigo’s scrutiny. The spiked structures closed in until they were almost touching his skin, leaving only a Sakura-shaped void between their tips. Then they jabbed, and he felt an instant of cold contact that was too brief and strange to be pain, and in the very next instant Indigo withdrew. The spikes dismantled themselves, retreating back through the bubble, and the bubble’s membrane healed itself without fuss.

“That was...” Sakura started saying, simultaneously affronted and exulted that he had been the object of such close attention. But he trailed off, lost in wonder at the images now playing across the outside of his bubble. Worlds, cities, bodies—a torrent of experience. Scenes from a life.

His own.

 

 

AT LAST IT was time for the tournament.

Sakura, Tristan and a dozen or so close friends were gathered on the observation deck of one of Jupiter’s floating cities, keeping close to the railings and looking down into the turbulent depths far below. Through many flavours of vision they tracked the glittering specks of moving fliers, sculling over the billowing, wind-torn peaks of mountainous cloud formations, six sheer kilometres beneath the city’s keel.

“Go, girl,” Tristan exclaimed, pumping a fist—he and Sakura had both reverted to baseline anatomy—as Gedda hairpinned one of the aerial marker buoys, executing a very tight and skilful turn.

“She cuts it fine,” Sakura said, with a knot of apprehension in his stomach.

“Just fine enough. She’s done well to keep that anatomy locked in; she knows the limit of her wings better than anyone else in the contest. You can’t pick up that sort of thing in just a few days—you’ve got to live and breathe a body to really know it.”

“I don’t know what drives her.”

“At least she’s driven by something. Isn’t that enough, just to have something that pushes you on, even if it’s just some petty rivalry with another flier? You watch Malec now.” Tristan leaned over, pointing down to the flier just behind Gedda. “He’s all bluster, but when it comes to putting his neck on the line, he hasn’t got the nerve. He won’t dare swing in so close to that marker, and he’ll lose about a second on the return because of it. All Gedda has to do is keep making those tight loops and she’ll gain half a circuit on him over the next dozen laps.” He passed a glass to Sakura. “Hold my drink, old man. I’m going to up my wager.”

“Haven’t you bet enough?”

“Are you kidding? I’m just getting started.”

Tristan swaggered off to increase his stake, leaving Sakura alone for a few moments. Looking down at the fliers, tracking their looping circuits, he held one arm outstretched with the thumb and forefinger at right angles, forming half a rectangle. He tilted it around, trying to find a pleasing composition. The colours and formations of the cloud structures were impressive enough, but there was no land down there to anchor the view. Besides, he would not have known where to place his signature watcher.

Sakura took a sip of Tristan’s drink. He swallowed it into his mouth and throat, detecting a distinct smokiness, followed by an immediate neural buzz. It could not be anything as simple as alcohol, Sakura felt certain, but whatever was in it had been tailored to fool the receptors in his throat, and his brain was quite willing to be dragged along for the ride, a co-conspirator in the age-old ritual of deliberate intoxication.

For a second he saw himself from outside, like the figure in his paintings, lost in a vaster landscape. His body looked and felt humanoid, but the only authentic part of him was his nervous system, and even that was adulterated. When was the last time he had been biologically human, he wondered? He could take a trip to Earth some time, and have the door knit him a body that was flesh and blood all the way out to the skin. It would be good for old time’s sake. The Himalayas, maybe.

He allowed himself a smile. It was a small plan, no more than a vague, ill-formed intention, but it was the first time in six months that he had entertained a desire of his own rather than being led along by his friends. He had something to look forward to: a reason to hope that the doors would treat him kindly. Perhaps that was all that it had taken: to be jolted out of his routines, forced to see the miracle of his own existence afresh.

He made a quiet pledge with himself. The next time he went through a door he would raise the threshold a little, just to balance the odds a little more in his favour.

“Where is she?” Tristan said, returning.

Sakura had taken his eye off the tournament. Feeling a giddy sort of elation, he handed Tristan back his glass and began to sweep the clouds, looking for the telltale glints of the fast-moving fliers. “I don’t know. Maybe they finished that heat.”

“No, they still had fifteen circuits left when I went indoors. Something’s off—they aren’t competing.” Tristan gave him a warning look, as if to say that he had trusted him with one thing, to keep watching the race, and Sakura had not even accomplished that one task. “Maybe they’re gathered at the far marker.”

They crossed to the other side of the observation deck, something of Sakura’s good humour already dissipating. Most of their friends and associates were already there, a carnival of anatomies pressing against the railings. Centaurs, sphinxes, seahorses (in liquid-filled excursion bubbles), winged angels, a person like a baby elephant with six legs, another like a large crab or spider, two lime-green mantises with cocktail glasses, a trio of severely minimalist geometric forms who relied on force-effectors for traction and manipulation. All were peering—or directing batteries of sensors—into the underlying cloudscape.

“They’re regrouping,” Sakura said, spotting a cloud of bustling, gyring glints near the other marker.

“I see Malec, but not Gedda.”

One of the geometric forms swivelled around with a stonelike grinding sound. A human face pushed out from a flat facet. “Gedda clipped the marker, Tristan. She buckled a wing and dropped hard. That’s not Malec either.”

“Malec’s gone deep,” chirred one of the mantises. “He’s trying to reach Gedda. But it gets thick and hot quickly down there.”

Tristan swallowed. “She’ll be all right.”

Footsteps thundered behind them. Sakura and Tristan turned in time to see a phalanx of black-skinned fliers dash to the railing, pouring over it like a tide. They dropped like arrows, keeping their wings tight to their bodies. Sakura tracked them until they had dropped below the level of the tournament, into denser clouds.

“Malec will reach her,” Tristan said, very softly. “And if he doesn’t, the rescue fliers will.”

“Why weren’t they already at altitude, ready for this?”

“Tournament rules,” said the seahorse. “High purse, but high risk too. It was one of the stipulations.”

“We should rebody, go after her,” Sakura said.

Tristan shook his head. “Have you any idea how long it takes to knit a pair of wings? We have to trust in Malec and the rescuers. There’s no other way.”

They waited. The clouds boiled below. A few of the other competitors went in pursuit of Gedda, but before very long they had returned to the tournament level, exhausted by the descent. Their bodies were highly optimised for flight at a particular altitude, and to go much deeper was a strain on their muscles and cardiovascular systems. They had to land on the buoys to recuperate, draped over them like a mass of weary bats.

The black-skinned rescuers came up soon after. They had gone a few kilometres deeper than any of the competitors, but they had also hit their limits, wing movements growing sluggish and uncoordinated. Tristan proposed calling for an excursion bubble, so that one or both of them could venture after Gedda. Before any arrangements could be made, though, Malec was already signalling back from the depths. He had turned back at six kilometres beneath the tournament level, far further than anyone else had made it.

“I saw her,” he reported, breathless and dispirited. “She was dropping much too quickly, three or four kilometres under me. It looked like she’d torn a whole wing off. I couldn’t get to her. I had to turn around just to make it back to the shallows.”

Nothing more needed to be added. Given the limits of her physiology, Gedda would have been dead by the time Malec gave up on her rescue.

Somewhere below she was still falling, approaching some dark equilibrium. But she could not be saved; she could not be restored.

 

 

A WEEK AFTER her death, Sakura and Tristan were at a door in Europa. They had doored once since Jupiter, and only as far as this nearby moon and its lulling ocean. It had been at Sakura’s insistence. He could no longer tolerate the sight of those swallowing clouds.

There were many doors in Europa, but the majority were built into castles of spiralling ice, daggering down from the ocean crust. Sakura and Tristan had picked one of the more out-of-the-way doors for their farewell.

“You only have to stay another six months,” Tristan chirped, steadying himself with a flick of his tail. “Is that so hard? You don’t even have to go through another body. We can attend the memorial in excursion bubbles.”

In the event of her death, Gedda had stipulated a six-month delay between the time of her passing and any memorial service that her friends might care to arrange. It was a custom among competitive fliers, one that gave sufficient time for interested parties to converge from across the Adaptasporic Realm, as well as permitting the rescheduling of other tournaments. Such arrangements were not uncommon—no more so than death itself, at least—and Sakura knew that he had probably lodged a similar condition with his own executor at some point. But like so much else, the exact details had been lost in one of his winnowings.

“I have to go,” he said, repeating the elements of a conversation they had been through a dozen times in that week. “I don’t trust myself, Tristan. If I stay here, with you—with our other friends—I’ll lose the nerve.”

“You really mean to go through with this?”

“I’m settled in my choice.”

Tristan cast a dispirited look at the door. “We were better off not interfering. If Gedda and I hadn’t tried to shake you out of that rut... damn it all, Sakura. I thought one in a thousand was bad enough. How far have you taken it now?”

“One in ten. The lowest threshold the door will accept.”

“I’ll knit you a pistol with a revolving chamber and a bullet. At least you’d be honest about what you’re doing to yourself.”

“I am honest. But don’t blame yourselves. If it’s any consolation, you had begun to change my mind.”

Tristan chirped a mirthless laugh. “Begun.”

“But then Gedda changed it back. She didn’t mean to, of course, but there’s nothing like a stupid, accidental death to remind you of the supreme futility of everything.”

Tristan extended a flipper, touching the limit of Sakura’s own. “I’ve lost one good friend this week. Don’t leave me all on my own. I’m begging you, Sakura. For me, if not for yourself. Leave that threshold at one in a thousand if you must, but not this low.”

“I’ll door twice between now and the ceremony. Odds are that I’ll still be around.”

Sakura flicked his tail, preparing to swim into the door.

“No,” Tristan said, with a sudden forcefulness. “No. Not this time. You’ll hate me for this, but I have to do it.”

“Do what?”

“Naomi Cheng.”

Sakura was silent. They were words that connected together to make a name, a human name, and they struck within him like some huge, soundless submarine gong.

Memories loosened, unspooled. Things that he had forgotten—things he had forgotten he had ever known—were uncoiling into daylight.

“What have you done to me?” Sakura asked.

“A terrible thing,” Tristan said. “Something a friend would never do to another friend. But you’ve pushed me to it, Sakura. If it was the only way to save you, it needed to be done. You’d never run an audit on yourself, and I could never do it for you. But Indigo could. It’s why I took you to the Luminal Minds—that ambassadorial stuff was just a ruse. So that Indigo could crack you open like an egg, and sift through the memories you don’t even know are still in your head. That’s how winnowing works, you know. It severs the connections to memories, but the structures are still in place. And sometimes all it takes is a name, a single name, to unlock them.”

Sakura was still awestruck. Awestruck, gong-struck, horror-struck. “Who was she?”

“You know, my friend. You’ve known all along. She’s the one in your paintings. The watcher.”

“That doesn’t answer...”

“There were two of you,” Tristan answered, with a desperate calm, as if Sakura had a knife to his throat. “On a ship. A very primitive ship, sent out only a couple of hundred years into the spacefaring era. It crashed on Mercury.”

Some faint thing prickled his nose. Flashes of memory. A buckled hull, the feeling of life support modules under his hand, the prickle of sweat on his skin.

“The smell of my brushes. The solvent I had to use on Titan.”

“Liquid ammonia,” Tristan said. “Leaking out of the refrigeration circuit of your crashed ship.”

Sakura closed his eyes, permitting himself a moment of introspection. He thought of the smell, the charge of sadness it had carried with it. Sadness and something else he now understood. The burden of a solemn promise, carried across centuries, but which he had allowed himself to neglect.

“What did I do?”

“You lived. It’s that simple. Only one of you stood any sort of chance of surviving long enough for rescue, and you drew straws. Naomi administered an overdose from the medical rations, killing herself so that you might survive. You’d have done exactly the same thing, but that doesn’t alter the fact that you were the one who got to live, and that you made a commitment to Naomi. Do you remember it?”

The ship, the smells, the memory of her body, welled back into him. Naomi Cheng, lying on her side, black hair sprayed out around the base of her neck, her face to the fogged oval of a window, the blaze of Mercury beyond.

“I said I’d live for the two of us,” Sakura answered. “I said I’d carry her life within my own, that I’d see and do all the things she couldn’t. That I’d never stop living, never stop remembering, never stop being grateful for the gift she gave.”

“And yet you let it slip.”

“I never meant to. There were just too many centuries, too many memories. Somewhere along the way I dropped the thread. I forgot Naomi.”

“You didn’t,” Tristan said, moving to drift him away from the door. “Not really. You carried her inside you, and you lived up to that vow. Now all you have to do is hold to it.” He paused. “I shouldn’t have done it, Sakura. Violating the sanctity of another person’s memories goes beyond any bond of friendship. I expect you to hate me for it, and in truth I don’t blame you. But if that’s what it takes for you to reconsider, I consider it a price worth paying.”

Sakura freed himself from Tristan’s gentle embrace. “You’d lose a friendship rather than lose me?”

“If I’d thought there was any other way.” Tristan averted his eyes. “I’m going now. I’ll let you go through that door on your own, and I won’t wait to see if you change the threshold. But in six months I’ll be back to honour our friend, and if her life meant anything to you—and I know it did—then I expect to see you there.” He dipped his beak. “Hope, I should say. I hope to see you there.”

Tristan swung around and began to swim off into the blue murk of the Europan ocean. His tail left a backwash that quickly faded into stillness. Stillness and silence. Sakura waited a decent interval, alone in his palace of ice, and then turned back to the door, his mind made up.