Schild's Ladder

by Greg Egan

  Out of the full force of the wind, the geometry of both the Colonists and their architecture became more stable. The walls of the tunnel were formed from a basic layer population, but hundreds of other structures adorned them. Apart from the “air-conditioning” and “light sources,” Tchicaya couldn't guess what purpose most of the structures served. They looked too complex to be decorations, but mere endurance required sophistication here; the air-conditioning wasn't perfect, and anything incapable of responding to the weather risked being scoured away by the Bright.

  The tunnel branched; the procession veered left. The air-conditioning was becoming more aggressive about removing impurities; the ship and the toolkit had to work harder than ever to keep the hull intact and the probes viable in the presence of all the new cleaning vendeks. Tchicaya had contemplated a number of unpleasant fates since the anachronauts had blown him out of the Rindler, but being scrubbed from the environment like an unwelcome speck of dust was one of the most insulting.

  After a second fork, and a section that zigzagged and corkscrewed simultaneously, the tunnel opened out into a large cave. The physics here was more stable than anything they'd seen since the honeycomb; the weather had not been banished, but the turbulence had been subdued by an order of magnitude compared to the open Bright.

  A stream of vendeks crossed the cave, rendered pitch black by the scape for most of its length, where the probes found it impenetrable. Near the center, the stream mingled with the surrounding free vendeks, expanding and becoming diluted before contracting back to its original width and continuing on its way. The probes could enter this region, which they portrayed as a sphere of gray fog; not all of them were coming back, though, and those that did reported that they'd almost lost control over their trajectories. Moving through the Bright had been difficult from the start, but some extreme, systematic distortion here was interfering with their attempts to navigate.

  The toolkit collated all the evidence and reached its own conclusion. “There's curvature engineered into the graphs here. You can invade these vendeks where the current opens out, but in the process they reorient your time axis.”

  It took Tchicaya a moment to digest this. Patterns in a quantum graph persisted by replicating themselves in future versions of the graph, but “the future” could only be defined by the orientation of the pattern itself. If you sliced the space-time foam one way to find a graph with vendek A in it, but needed to take a slice at a different angle to find vendek B, the two vendeks would see time as lying in different directions, and mere persistence, on their own terms, would put them in relative motion.

  So “reorient your time axis” was toolkit-speak for “change your velocity.” The vendek current couldn't sweep anything along the way a river did, with pressure and momentum, but it could twist the local definition of being “stationary” progressively further away from its original orientation. In a sense it was like ordinary gravity, but on the near side the symmetries of the vacuum imposed a rigid austerity on the possibilities for space-time curvature. Here, the curvature had been tailored on the spot, woven directly into the graphs by the choice of vendeks.

  “These people engineer space-time the way we do polymer design,” he marveled. “Choose the right monomers, get their shape and reactivity right, and you can create whatever properties you desire.”

  Mariama smiled. “Except that they're more like microbes than monomers. Everything comes down to breeding and blending the right vendeks.”

  “So what is this? A waste-disposal system?” If they wanted to toss the banner away, they could have done that from the surface with their towing bubble, but this accelerated sewer might send it further, faster.

  The Colonists had paused at the entrance to the cave, but now they began to move along a shallow spiral, inching their way down toward the velocity gradient. They weren't discarding the banner in the black river. They were going with it.

  Tchicaya groaned. “I know what this is! We saw the rest of it, from the outside. It's a transport system. We're on the entry ramp to a highway.”

  Mariama agreed. “Maybe this whole place is just a tiny outpost, and the artifact is such a big deal that they're rushing it straight to the nearest expert.”

  The conga line of Colonists was winding its way toward the axis of the cave, actively fighting the effect of the black vendeks in order not to get dashed against the wall where the current exited. The Sarumpaet was still obediently following the towing bubble; if they wanted to break away from the convoy, they'd have to do it in the next few seconds.

  There was no way of knowing how long the journey would take. They'd seen this highway disappearing into the haze, into the depths Xof the far side. This outpost was where the danger would strike first, where the people needed to be told what was coming so they could fight it, or evacuate.

  But if the banner was being taken to the Signalers themselves, that could be the expedition's one opportunity to meet people with the knowledge and motivation needed to understand the warning at all.

  Mariama said, “You don't want to back out?” Perhaps she was afraid that if this turned out to be the wrong choice, he'd hold her responsible for urging him down here in the first place.

  Tchicaya said, “No. We have to trust these people to take us to someone who'll work hard to communicate with us. If that's not what they're planning, then we're screwed—but if we hang back and miss the chance to meet the experts, we're screwed anyway.” Ahead of them, the banner was blinking feebly; undamaged still, but it had never been designed to modulate all the forms of illumination that filled the cave.

  The bubble arced smoothly down into the gray fog of the entry ramp. As they followed it, the fog around them actually seemed to grow thinner; once the Sarumpaet began to surrender to the highway's demands, the probes had an easier task finding their way back to it—though the rest of the cave rapidly vanished from sight. Tchicaya felt a pang of frustration that he was insulated from any sense of the dynamics at play here. What would it feel like, for a native, to be whisked into motion like this? Would there be something akin to tidal effects, as different parts of your body were brought up to speed? It was a trivial thing to ponder, but he needed to cut through the barriers that separated him from the Colonists. He needed to imagine himself inside their skins, any way he could.

  The convoy straightened out. They were in the center of the highway now, portrayed by the probes as a narrow tube of clarity surrounded by fog. The Colonists themselves had begun emitting some of the parasprites that had illuminated the tunnels and the cave; the bubble and its cargo blocked the view ahead, but Tchicaya could still catch glimpses of them, shy luminescent starfish waving their four legs lethargically. They were probably relaxing, free from the arduous demands of the Bright—or if those demands were trivial, perhaps this trip was so dull for them that they'd entered something close to suspended animation. The Sarumpaet was doing absolutely nothing to keep up with them; as far as it was concerned, everyone was motionless. The highway had them all free-falling effortlessly toward their destination.

  Mariama asked the toolkit, “Can you tell how fast we're moving?”

  “I have no direct access to the Bright around us, and interpreting the acceleration process we've just been through is difficult.”

  “Don't be such a killjoy; take a wild guess. In the broadest, most naive, near-side terms.”

  “We might be doing something comparable to relativistic speeds.”

  Mariama looked around the scape, her eyes shining. “Do you remember what Rasmah said?” She was addressing Tchicaya now. “When she spoke to the Preservationists before the moratorium vote?”

  “Of course.” Tchicaya had to make a conscious effort to summon up the memory, but he'd had a few other things on his mind.

  “She was right,” Mariama declared. “Her whole vision of this place was exactly right. Not in the details; she couldn't anticipate half the things we've seen here. But she understood precisely what the far side could me
an for us.”

  Tchicaya experienced a twinge of irritation, bordering on jealousy. What right did she have to share Rasmah's vision? He was ashamed of himself immediately; she'd earned it, at least as much as he had.

  “You've had a change of heart,” he observed mildly.

  “I told you I'd never fight for an exotic wasteland,” she said, “but that's not what this is. And I'll fight for the Signalers because they deserve our help, but that's not the end of it. Not anymore.”

  She took Tchicaya's hands. “Some astronomically rare event created sentient life on the other side of the border, but that's all it was: bad luck, an accident of birth. We've found ways to live with all the hardships: the distance, the loneliness. That's a great achievement, an amazing feat, but that's no reason to sentence ourselves to repeat it for eternity.

  “How can we go on living in that wasteland, when even space is alive here? This is where we belong, Tchicaya. I'll fight for this place because it's our home.”

  In the eerie calm of the highway, Tchicaya felt himself losing his grip on reality. A whole universe was at stake, and here he was playing stowaway on a road train? Unknown multitudes would die, because he lacked the nerve to tap the driver on the shoulder and make his presence known. He could get his message across to anyone, if he put his mind to it. He'd managed to converse with twenty-third-century zealots with flesh for brains; how much harder could a glowing starfish be?

  When the highway began to disgorge them after barely two hours, he almost wept with relief. His gamble might yet fail to pay off, but at least it hadn't irrevocably sunk the whole endeavor.

  As they spiraled out of the darkness, the Sarumpaet steeled itself for the worst contingencies the toolkit could imagine. The Bright had been a challenge, but there was no reason to believe that it was the most extreme environment the far side could contain.

  Probes began returning. Parasprites flooded in. The convoy slipped out of the ramp into a vast, tranquil space. The toolkit analyzed the vendeks around them; the mixture was not honeycombstable, but it was like the Bright tamed, domesticated. The airconditioning in the colony had gone a short way in the same direction, but it was like the difference between a mesh cage in the open ocean, keeping the largest predators at bay, and an aquarium of hand-picked species that could coexist and thrive with a minimum of drama.

  The six Colonists were not alone here; the scape showed hundreds of similar four-branched xennobes moving around them in a multitude of neat, loosely defined rows, as if the place was crisscrossed with invisible escalators. Compared to the crush of the outpost, though, conditions were far from crowded. Layer walls undulated gently in the distance, dotted with parasprite lamps, but there was none of the density of structure they'd seen in the tunnels. High above Tchicaya—“above” according to the random orientation in which the Sarumpaet had emerged—other dark highways were visible.

  “I believe we're in a railway station,” he said. “The question is, where?”

  Mariama declared confidently, “This is the big smoke. All space and comfort.”

  “Where we came from wasn't exactly a ghost town.”

  “No, just a small village with no entertainment, and no contraception.”

  Tchicaya scowled, but then he realized that she was being neither serious nor entirely flippant. Tossing a few anthropomorphic parodies at the least important of the ten thousand unanswered questions they faced might at least stop them wasting energy trying to fill in the same blanks with earnest hypotheses that were just as likely to be wrong.

  As the Colonists crossed the atrium, alien cargo and its wouldbe puppeteers in tow, Mariama mimed cracking a whip. “Take me to your linguists,” she said. “And don't spare the vendeks.”

  If they were in a city, they had no way of judging its size from within, no way of knowing if they were moving from building to building through something like open air, or merely navigating through the rooms of a single, vast, hermetically sealed structure.

  They passed through narrow apertures and wide corridors; they wove through denser crowds; they encountered structures as baffling and varied as the machinery—or artwork, or gardens—of the outpost in the Bright. The probes gathered information, and the toolkit puzzled over it, but even when it made sense it was just another tiny piece of a vast mosaic. Grabbing hints of how the vendek populations were interacting inside some gadget—or pet—that they passed was all grist for the mill, but it was not going to make the whole city and its people snap into focus in an instant.

  Still, Tchicaya clung stubbornly to the notion that it was better to observe whatever he could, and provisionally entertain some wildly imperfect guesses, than to close his eyes and surrender to the verdict that he might as well have been a flea aspiring to understand the culture of a great metropolis. The scale in that analogy was right, but nothing else was. Both he and his hosts possessed general intelligence, and however mutually foreign their needs and drives, there was nothing—including each other's lives, customs, and languages—that could remain incomprehensible to them, given time, patience, and motivation.

  Time, they did not have, but he'd leave it to the Planck worms to declare when the supply was exhausted.

  Mariama drank in the sights like a happily dazed tourist. She treated their purpose at least as seriously as he did, and she'd confronted every problem they'd faced with ferocious energy and clarity, but something in her temperament refused to admit that the corollary of that dedication could ever be despair at the thought of failure. They'd accepted a burden that was constantly on the verge of crushing them both, but he'd rarely seen her so much as tremble beneath the load.

  The procession came to a halt in a huge chamber, containing a structure resembling a cluster of grapes the size of a whale. The surface of this object was like nothing the probes had seen before, and the interior proved even more surprising, killing them off completely. Other, slightly more familiar techology was arrayed around this bizarre leviathan.

  The Colonists broke rank; three of them fussed around the towing bubble, while the others went to one wall of the chamber and returned with some kind of small device, or creature. Whatever they were fetching didn't need to be towed; it followed its summoners back under its own power.

  When the Colonists burst the banner's bubble and lured their apparatus closer to it, Tchicaya moved the Sarumpaet away. He didn't want the ship caught up inadvertently in whatever they were about to do.

  Sprayed by vendeks, the apparatus began to shine. It emitted sprites, not the related vendeks the Colonists seemed to favor.

  Mariama said, “They're illuminating the banner with the right kind of lighting. The signal is encoded in its transparency to sprites; they understood that much.”

  “I think you're right.” There was always a chance that they were misreading the action, but Tchicaya felt hopeful.

  He surveyed the scene, trying to guess what would happen next. The banner was positioned between the sprite source and the giant bunch of grapes. Meaning what? This was their expert linguist? Another species of xennobe entirely, or some caste of the Colonists who sat motionless in this chamber like a bloated termite queen? He dismissed the notion immediately. They'd seen no other “castes.” A few teeming xennobes in a crowded “hive,” and he was starting to invent ridiculous insectile non sequiturs.

  The Colonists moved back from the illuminated banner, and did nothing more. They floated at the edge of the chamber, branches twitching lazily in the gentle currents.

  The toolkit said, “I've found a way to get probes into the unmapped structure now. This is very strange.”

  Mariama said, “We'll be the judge of strange. Just tell us what they've found.”

  “Take a cluster of protons and neutrons, and compress it by a factor of a hundred million. That's what this is.”

  Tchicaya blinked, disbelieving, “We're looking at a nugget of squashed near-side matter?”

  “Yes. It's wrapped in some complicated vendek-based layers that a
re helping to stabilize it, but basically it's a pile of ordinary nucleons with most of the empty space squeezed out of them.”

  Mariama turned to him. “It could be a kind of meteorite. With all the matter that's passed through the border, some microscopic speck might have encountered conditions that preserved it.”

  Tchicaya didn't welcome the conclusion this suggested. “So this room could be nothing but a museum display? I can't believe they'd go to the trouble of building the signaling layer, only to take the reply—proof of intelligent life behind the border—and stuff it in a cabinet for people to gawk at.”

  “Or study. People will come to study it.”

  “When?”

  Mariama said, “If you want to draw crowds, maybe it's time we changed the loop.”

  Tchicaya sent instructions to the banner. It stopped counting out primes, and switched to a simple, ascending sequence of integers.

  The Colonists responded with a flurry of activity: moving around the chamber, summoning new equipment. Tchicaya watched them, his hopes rising again. They had to realize that the banner was as good as alive, and ready to talk. Surely they'd reply now.

  He was wrong. They aimed no shuttered sprite lamp back toward the banner, they flashed no answering sequence.

  He switched to the Fibonacci series. This stirred the Colonists' branches a little, as if they welcomed the stimulation, but whatever the purpose of the equipment they'd gathered after the first change of message, it continued to be all they required.

  They were happy to watch, but they had no intention of replying. They were politely, respectfully observing the alien emissary, but too cautious to engage with it and speed up the process of understanding its message.