Dichronauts

by Greg Egan

  Seth squatted down and scrabbled in the mud; eventually he found a stone the size of his hand. For a trial run he tossed it straight up, and though the thump when it landed—at a count of two—was soft, he didn’t doubt that Theo and Judith could pick up the same sound from a much greater distance.

  «Ready?» he asked Theo.

  «Yes.»

  He threw it to his right, and had no trouble tracking it past the edge of the pit before it dropped out of sight. But the pronouncement of landfall never came.

  Seth moved closer, but learned nothing new: all Theo could show him beyond the edge was rain falling through air.

  “How far away is dawn?” he asked Sarah.

  “It can’t be long now.”

  They struggled to set up their tent in the mud, to be sure they’d have shelter once the sun rose. The interior would be like an oven by noon, but for now there was no reason not to sit inside and rest. The rain on the cloth was deafening, and the floor was barely drier than the ground outside, but the sheer achievement of carving this artificial space out of the downpour raised Seth’s spirits a little.

  When the first hints of light showed through the seams, Sarah crawled out and Seth followed her. The eastern sky was brightening, with the glow of the impending dawn farther to the north than he had ever seen it. The rain was already much sparser than it had been in the night, but as they sidled toward the pit enough remained to imbue the scene with a sense of scale—and for as far as Theo could ping the droplets, they were falling unimpeded.

  Seth moved closer and looked to the west. In the distance, there was enough of a curve to the edge for part of the drop to become visible—and by the scattered light of the pale pre-dawn sky, the rock face appeared vertical. “We’re on a cliff?”

  “Apparently,” Sarah agreed.

  Seth sidled a few steps nearer to the edge, and set his feet wide to raise his head, but with the ground nearby blocking the view it was still impossible to see down to the bottom of the cliff. “How deep is this thing?” he marveled.

  “And how wide?” Theo added.

  Seth shifted his attention from the northern face to the empty space beside it. If they’d been standing on the edge of some kind of canyon, the laws of perspective should have brought the southern face into view eventually, more or less converging with its partner toward some vanishing point. But beyond the revelatory bend in the cliff, all he could make out between west and south-west was a pale haze, scarcely different from the sky above. Like the rock face, there was no bottom to it, just a point where it was obscured by the foreground. For all he could tell, the land might never return to its normal altitude.

  “So the storm was somewhere out there,” he mused, gesturing to the south, “hitting whatever’s at the bottom of this cliff. The drop can’t be as deep as it looks, then, or how would the sound of the rain have reached us?”

  Theo said, “What if the ground at the bottom slopes up to the north? We might not have been hearing the rain itself—we might have been hearing the runoff hit the cliff face.”

  “Maybe.” Seth pictured the downpour falling on the slope, running uphill and crashing into the natural dam of the cliff face, forcing it to spill back and cycle around. It would be a bit like the waterfall in Thanton’s forest, but all its energy would end up being used to pound the cliff. If what they’d been hearing was a trick of the topography amplifying the sound of the rain, there was no need for an actual storm.

  He felt the heat of the first rays of sunlight biting into his skin. The rain had stopped and the ground was already drying out. They moved back beside the tent and prepared to spend the day following its shadow; even at noon, the sun would be so low in the north that the modest structure would offer some protection.

  “Those cliffs would make perfect sunshades,” Seth realized. “If we could get to the bottom, there’d be no direct sunlight, any time of day.”

  “Get to the bottom, how?” Sarah replied. “Even back at the camp, there’s nothing like the length of rope we’d need.”

  “So we sit here all day, and then go back empty-handed?” Seth could hear the mud crackling around him as it surrendered its water to the heat.

  “As opposed to what?” Judith asked. “Walk the edge, looking for an easy path down, while your body dries to a husk?”

  Seth stared at the ground, frustrated. “You’re the one who wanted to find a place where we could maintain a healthy separation from Thanton.”

  “Not at the bottom of a cliff,” she retorted. “We don’t even know that there’s a storm here, let alone have any reason to think it will drift north. As the steamlands move south, they’ll take the rain with them, and this will be nothing but an obscure place on the map, marked as an obstacle to future migration.”

  Theo said, “But aren’t you curious as to just how big an obstacle it is?”

  “No one’s carrying a city over the edge,” Judith replied. “We don’t need to know precisely how tall the cliffs are, to be sure of that.”

  “So what would the alternative be?” Theo pressed her.

  “It might be a good idea to go around them.”

  “And what kind of detour would that entail?”

  Judith hesitated. “It will be important to know that, eventually,” she conceded. “But we’re in no position to follow the cliffs and see how far they extend. We seem to be at their northernmost point; if we pursued them much farther we’d be too deep into summer. We can send an expedition to map them once they’re more accessible.”

  “Suppose we do that,” Theo replied. “We wait until autumn arrives here, so it’s an easy journey following the cliffs west. But we find that they don’t come to an end, or turn to the south sharply enough to let us pass. They just keep on running geographically west, which takes them back into summer, but doesn’t allow any kind of detour that puts them behind us once and for all. Instead, we’re forced to keep veering to the west—until that becomes a problem in itself, because the habitable zone is too narrow.”

  Judith laughed. “So you think this escarpment could stretch so far that it would block the entire western half of the migration? That sounds unlikely, but even if it were true, there’d be tens of thousands of people prepared to build roads down to the lowlands.”

  “And if that proved impossible?” Theo persisted. “If the cliffs were too high?”

  “Then we’d just have to migrate to the east.”

  “Suppose the same thing happens to the east.”

  “Now you’re being absurd.”

  Seth looked up at the ground beyond the shadow of the tent. The night’s puddles and rivulets had been transformed into arid depressions, but between them in places were some oddly delicate structures: arches and domes of once-damp soil that had dried out and become hollow, but were yet to collapse. He raised his canteen to his mouth before opening the lid just enough to allow the water to escape; even as it ran down his throat, he pictured half of what he’d swigged vanishing into the air before his parched body could absorb it.

  Sarah said, “If these cliffs block our way from node to node, we’ll deal with them. It’s as simple as that. If it’s a matter of life and death, any feat of engineering would be worth the effort.”

  “Of course,” Theo conceded. “All I’m trying to say is that we need to determine exactly what we’ve found here.”

  Seth had been listening to the conversation without much interest; if they couldn’t offer Baharabad the prospect of a second river, everything else was idle speculation. But Theo was rarely so persistent or argumentative just for the sake of it; there was always some kind of logic behind even his wildest blathering.

  “Why do you think the cliffs could stretch so far?” Seth challenged him. “If you have some theory, spit it out.”

  Theo was silent for a while, as if the answer was a guilty secret that he was reluctant to disclose. Then he said, “Have we actually seen the bottom of them? Do we have any idea how deep that drop is?”

  “
No,” Sarah replied. “But you’re changing the subject: the question was how far they extend east and west.”

  “The thing is,” Theo insisted, “we don’t even know that they’re cliffs. There’s an edge to the level ground, then a drop. That’s all we can be sure of.”

  Sarah groaned with exasperation. “There’s an edge, and a drop . . . and then there must be lowlands, whether you can ping them or not. And if these aren’t cliffs, what else could they be?”

  “The edge,” Theo replied.

  “The edge of a plateau?” Sarah suggested.

  “No.”

  “The edge of the high ground, the edge of the tablelands . . .?” Sarah was losing patience. “Whatever you like, it makes no difference.”

  Theo said ruefully, “Believe me, this is not what I’d like. But we need to contemplate the possibility that we’ve reached the edge of the world.”

  PART THREE

  11

  Seth woke early but knew he was unlikely to fall back to sleep, so he headed out for a pre-dawn stroll, taking the opportunity to stretch his legs before the heat became too oppressive. On his way back, the sky had grown bright enough that he could see the whole encampment spread out before him, a patchwork of coarse fabric pinned to the dusty hillside.

  «There must be two hundred tents,» he realized. «When did that happen?»

  «You know what they say,» Theo replied. «It takes a village to raise a surveyor.»

  At this time of day, the food hall wasn’t crowded. Seth joined a group of artisans from Sedington, whom he’d seen before but never had a chance to talk to. They told him that they’d heard Raina and Amina speak about the project at a meeting in their town, and decided that it was worth the trip for the guarantee of work.

  “It’s a bit of an adventure for us, coming this far west,” James, the chattiest of the group’s Walkers, explained. “But I hope you fools know what you’re doing.” The remark sounded neither disdainful, nor simply a matter of good-natured teasing; rather, his tone carried a mixture of incredulity and genuine concern.

  “We trust your sewing,” Theo replied.

  “I’m a rope-maker,” James corrected him.

  “Then I hope we can trust that, too.”

  “Oh, here come the half-heads,” Margaret whispered. Seth glanced toward the entrance; four traders from Thanton had entered the tent.

  “Be civil,” James chided her. Seth wasn’t sure if this was a serious admonition, or a sarcastic recitation of the instructions they’d all received from their superiors.

  A single bench ran north-to-south along the hall. When the traders had collected their food they chose the northern end, as far from the artisans as possible, but any ordinary conversation by one group would still be well within the hearing of the others.

  The artisans began joking about the foibles of various members of their own community, so Seth did his best to grant them his full attention and listen with an air of polite amusement. Experience had taught him that if he allowed himself to take in any of the Thantonites’ small talk he’d be at risk either of hearing something so blatantly offensive that he’d struggle to conceal his revulsion, or of seizing upon something ambiguously sinister and spending the rest of the day obsessing about it.

  Theo inspoke, «I was watching closely, and I’m fairly sure they didn’t sprinkle puffballs over the buffet.»

  «I don’t like doing business with them any more than you do,» Seth replied. «But if we’d shunned all trade with Thanton, the whole project would have taken ten times longer.»

  «I know. And I’m glad they’re here, in person.»

  «Why?»

  «Because whatever we learn about the edge, it will be clear to them that they’re getting the same story as everyone else. If we’d tried to send a delegation later, armed with pronouncements about the likely future of their river, they could have dismissed all our claims as self-serving misinformation.»

  The artisans had finished eating, so they bid farewell to Seth and Theo and departed. One of the west-facing traders glanced in Seth’s direction, as if contemplating an introduction, but Seth lowered his gaze and concentrated on his food.

  “you must be excited!” Raina enthused, as they approached the work site. “All the doubters could soon be eating their words.”

  “Or it could go badly,” Theo replied, “and I’ll be a joke in thirty cities.”

  “The people who backed you are the ones who’d look most foolish,” Amina decided. “It’s one thing to come up with a wild idea that turns out to be wrong, but nobody forced those merchants to invest in it.”

  “I’m not sure that humiliating the wealthy would work in my favor,” Theo mused. “I believe there’ve been a few occasions in history where that didn’t turn out so well.”

  From a distance, to Seth the assembly of fabric panels laid out over the ground looked a bit like a second camp, smaller than the one they’d left but so crowded that it was impossible to tell where one tent stopped and its neighbor began. Almost anything was more plausible than a single piece of material the size of half a dozen city blocks, and his mind could only accept the truth once the evidence was entirely unambiguous. Today, as he drew nearer he could see that the furnace had already been lit, sending currents of hot air wafting into the structure, raising the panels in synchronized undulations that no tent village could possibly exhibit.

  They paused on the slope to watch the balloon fill out a little more. As the center rose the western rim was drawn in, while the other free edges pushed farther north and south, keeping the upper surface more or less taut. On the eastern side the balloon was attached to the furnace room, a long stone building into which a relay of workers could be seen conveying timber from a heap outside.

  “That’s got to be the toughest job of all,” Seth declared. “We should show our appreciation to those people.”

  “Of course,” Raina agreed.

  They walked down toward the furnace room, past the hill-sized wood-heap. The sheer scale of it was even more striking once it resolved into individual logs, which summoned up thoughts of all the individual ax blows that had been struck in the service of its formation. One of the suppliers had told Seth that each trial consumed more fuel than the Baharabad bath-house used in a hundred days, which had only compounded his discomfiting sense of the magnitude of the whole endeavor. Theo was afraid of being laughed at, but what weighed most on Seth’s mind was the possibility that they’d end up having wasted people’s time.

  Even a few paces from the building’s entrance, the heat was intolerable. Seth stood back, looking in toward the soot-encrusted vestibule, while a woman finished loading the feeder with wood and dispatched it into the furnace. Despite all the seals and interlocked doors working to ensure a one-way journey for the fuel, a gale of hot, smoky air rushed out of the chute, filling half the vestibule before slamming the empty feeder back into place and blocking its own egress.

  “We want to thank you for your hard work!” Seth shouted, struggling to make himself heard over the pounding of the flames on the furnace walls. “If we succeed tomorrow, it will be your efforts that raised us!”

  Most of the people in the relay ignored him, but the grimy-faced woman who’d just worked the feeder paused to regard the visitors with amusement. “Better you than me up there,” she said. Her Sider added, “I know which one of us is at the greater risk of being barbecued.”

  “The scamper survived uncooked,” Amina pointed out.

  “Did you ever try cooking one, to see what it took?” the Sider retorted. Seth was about to laugh, but then he realized that she had a point: no one really knew whether the animal’s heat tolerance was the same as a person’s.

  They left the furnace room and sidled north to check on the first anchor point. Seth had joined the rope team here for two of the trials, but as he walked between the tents, the people he’d joked with only days before—most of them movers from Baharabad, who’d abandoned any notion of professional rivalry
to welcome this mere surveyor into their ranks—now seemed guarded and ill at ease in his presence. He greeted everyone, but then made his excuses and joined Raina and Amina as they went through their usual round of inspections.

  The rope was coiled on a single flat reel, mounted on a spindle that pointed horizontally north-to-south at present, but whose bearings allowed it to tilt and swivel. Seth followed Raina up the stairs of the supporting frame, from where she proceeded to run her fingers along the curved wooden rails that enabled the spindle to tip, checking that nothing was loose, warped, or insufficiently lubricated. Any structure with so many moving parts seemed like an invitation for one of them to fail, but Seth could see no way around the complexity. It had been necessary to make the rope as stiff as possible in the axial direction, or it would have been useless at constraining the balloon’s range of motion: free to depart from a taut, straight line into one that curved to the north or south, a fixed length of rope would have been able to reach any altitude at all, with the axial detour’s negative contribution balancing the extra height. But this rod-like stiffness in the crucial dimension meant that the rope could not be wound into a more compact, helical arrangement on a barrel-shaped spool, and the entire flat coil needed to tip to accommodate the changing position of the rope’s endpoint. In a perfect world, the tilting mechanism might have coped unaided as the rope unspooled, but in reality it took half a dozen people watching over it to keep any problems in check—and for the reverse process, the whole team of twenty had to work non-stop to give the balloon a relatively smooth descent.

  “Everything seems fine here,” Raina declared. “But feel free to check it yourselves.”

  “I trust you,” Seth replied.

  “And the truth,” Theo added, “is that if we start fretting about everything we haven’t verified in person, we’ll end up far too anxious to step into the basket.”

  “Fair enough.” Raina descended the stairs, but Seth lingered on the frame, not so much belying Theo’s claim as taking comfort in the structure’s bulk and solidity.