Dichronauts

by Greg Egan

  «How is it possible that I don’t have a knife?»

  «What about the sighting bar?» Theo suggested.

  Seth pulled the screen away from the observation bay and reached down to the stone bar that held the sights of the alidade. He strained against it, and managed to snap it out of the instrument frame. It was stronger than a wooden pencil, but much blunter; his only hope was to get the angle right.

  He lay on his back and slid to the side until he could rest the bar against the top edge of the water tank. Then he shifted a little farther, in increments, tipping the bar to the south, bringing its far end closer to the underside of the balloon. When he finally made contact, the bar met the panel obliquely enough to present its corner to the fabric as a sharp point. Seth pushed as hard as he could, and felt something yield—but when he relaxed the pressure the bar rebounded. He was deforming the panel, not piercing it.

  He climbed to his feet and took a swig of water from one of the canteens. He’d been holding off, afraid that once he started he’d never be satisfied, but if he was weak from dehydration it would be better to remedy that and put up with the cravings. He lay down again and rearranged the bar so that it stretched all the way from the floor of the basket to the underside of the balloon. Then he scraped the low end across the floor, tipping the bar and driving the high end higher.

  The balloon remained intact.

  Seth wedged his left arm under the bar and used his right to brace himself against the side of the water tank. Then he spread his arms, forcing the bar to tilt. In Theo’s view, he could see that he’d carved a furrow into the basket’s wooden floor—stretching almost to the north side. That was the limit: if he reached it there’d be nothing more he could do. He strained against the bar; it skittered over the wood, but he could feel it threatening to force its way back into the furrow.

  «Next time, they’ll put a valve in the balloon,» Seth predicted. «That will be the first recommendation from the inquest.»

  Theo said, «What inquest? If the heat gets unbearable, you can slide down one of the anchor ropes.»

  «There’s a thought. Hang a chair from the rope with a hook and we could sell tickets for the ride down.» Seth lifted his shoulders from the floor and turned them, forcing the lower part of the bar a finger’s width farther to the north. Above him, the wheezing giant started whistling.

  He dropped his arms and lay staring up at the balloon. He couldn’t see the hole he’d made, but it wouldn’t take long to have an effect. Now they had to hope that someone was monitoring the ropes while the repair crew were focused on the ratchet.

  The basket began swaying gently. The balloon wasn’t falling, but the drop in tension was already freeing it from the need to sit precisely at the ropes’ taut lengths from all three anchor points.

  The undulations grew larger, punctuated by abrupt changes in direction that sent Seth sliding across the floor of the basket. «I think this is when I’d recommend closing the valve. Maybe I should write that down for the coroner?» The wind-tossed balloon now had time to pick up speed before bouncing off the invisible walls imposed by the new, less stringent constraints. That was surely as bad for the ropes as repeated braking down on the ground.

  Theo said, «You should pack up the slates, so they don’t get smashed.»

  «Right.» Seth got to his feet and grabbed the water tank to steady himself, then he gathered up the slates with the measurements and jammed them into the same box as the spares. He lay down again, holding the box tightly against his chest as the basket weaved and swayed. «If you had to go, which would you prefer?» he asked Theo. «Fall or burn?»

  «Fall.»

  «Good choice.» The drop would certainly be terrifying, but perhaps the fear would be accompanied by a liberating thrill. Drifting up toward the solar cone might have sounded lovely and ethereal back at midwinter, but Seth was already as warm as he wanted to be for the entire remainder of his life.

  The balloon lurched down, swung to the west, then hit the limits of the eastern rope and rebounded. But then gradually, over a minute or so, the motion settled into something so steady that it was barely perceptible.

  Seth reversed onto his stomach and opened the observation bay. The glare was painful, but so was the brightness of the land below; the balloon had already been dragged north of the cliffs.

  The trip back was not as smooth as the ascent, but Seth could tell from the long stretches that passed without anyone needing to brake the reels that the partially deflated balloon was proving easier to handle.

  When the landing site came into view, there were a dozen people waiting. They grabbed hold of the dangling restraint ropes and hauled the balloon all the way down.

  As Seth reached the top of the boarding ladder, Raina called out, “Are you all right?”

  Seth’s voice failed him, but Theo replied, “We’re fine.”

  “See anything interesting?” Amina enquired.

  Seth started laughing, though he wasn’t sure why. Theo said, “A long drop, then a forty-five-degree slope.”

  Raina frowned, impatient for more. “And then?”

  “That’s it,” Theo replied. “A forty-five-degree slope, as far as the eye can see.”

  12

  Jonas said, “i’ve asked you here to talk about your next job. You’ve served the Office of Surveyors with great distinction, and I’m pleased to say that we’re in a position to offer you no less than three choices.”

  “I’m honored,” Theo replied. Seth added an awkward nod to indicate that he felt the same way. But it was Theo’s ingenuity that had made the balloon observations possible, and it was Theo with whom the Director wished to discuss grand plans for the future of the migration. Jonas’s own Sider was so reserved that Seth didn’t even know his name, and in meetings like this Seth wished that he could make himself equally unobtrusive.

  “The first possibility,” Jonas continued, “is retirement on a full pension.” Seth’s desire for invisibility couldn’t keep his astonishment from showing on his face; Raina exchanged a glance with him, more amused than reproving, that told him exactly how he looked. “The Baharabad Council has approved the offer, in recognition of the extraordinary contribution you’ve made to the city’s interests.”

  Theo spoke, with a tone of bewilderment. “Why would we even think of—?”

  “Please,” Jonas raised a hand and cut him off. “Wait until you’ve heard all the options. And once you’ve heard them, don’t rush to decide.”

  “Of course not,” Theo said, courteous but unmistakably wary now.

  Since hearing that Jonas had arrived in the camp, Theo’s mood had been swinging wildly between anxiety and supreme self-confidence. With all the observations proving to be consistent with his theory, he had seemed convinced that anyone who saw the data—let alone the increasing number of surveyors who had seen the dark slope itself first-hand—would come around to his point of view. But at the same time, it had unsettled him that Jonas, like Sarah and Judith, had set out from Baharabad long before anyone knew what the observations would reveal. So what was the Director doing in this wretched outpost, whose sole function was to prove that all future efforts should be directed elsewhere?

  “The second possibility,” Jonas said, “lies at the western node.” Seth managed to remain stony-faced this time, though it might have helped that the proposal, so far, was not so much surprising as incomprehensible.

  “If the migration really is blocked to the south,” Jonas explained, “we’ll need to consider routes that the ancients believed were impassable. After all, the true width of the habitable zone is equal at every longitude. If the world was a smooth, featureless hyperboloid, there would be no obstacle to crossing the nodes.”

  Theo couldn’t help taking a stab at where this counterfactual statement was leading. “You want to flood the western node? Turn it into a giant lake, and cross it by boat?”

  It was Jonas’s turn to be taken aback. “Full marks for lateral thinking, but I beli
eve the water shortage precludes that.”

  «You could always make an offer to buy the Orico,» Seth joked.

  «Fuck off.» Theo wasn’t accustomed to the armchair surveyors being one step ahead of him, and nothing put him off balance faster than the threat that they might have out-reasoned him.

  “We can’t flood the terrain at the node,” Jonas continued, “but there’s another way to avoid the clash between the alignment of the habitable zone and the surface geology: stay high above the ground, where it doesn’t matter if you’re turned so far that each of your feet stretches across a thousand mountains and a thousand valleys. The plan is to build a bridge of balloons, from the westernmost point where the habitable zone lives up to that name on land, all the way across the node.”

  Jonas wasn’t making eye contact, so Seth risked an “Are they serious?” glance at Raina; her response seemed to imply that they were. Theo managed to hold his silence for a couple of seconds, but then his frustration overpowered his self-control.

  “Wouldn’t you need to burn a dozen forests a day, just to keep a structure like that aloft?”

  “It won’t burn a twig,” Jonas replied. “One of the observers of your own balloon project has proposed a way to keep the air heated by redirecting sunlight with slabs of polished stone. The construction will be a monumental effort on the part of surveyors, weavers, and engineers, but once it’s built, it should require only maintenance and repairs, not an ongoing source of fuel.”

  “I see.” Normally, Theo might have begged to hear the details of the new heating method, but Seth understood that all he cared about right now was confirmation that the best offer had been saved for last.

  “Your third option,” Jonas said, “would be to join the expedition to explore the chasm.” He paused to give Theo a moment to accept that his own grand scheme was not on the list at all. “With the cliffs shielding the floor from the sun, it should be possible to follow the rift west, well past the point where the higher ground is uninhabitable.”

  “It’s not a ‘floor,’” Theo replied bluntly. “A floor is close to horizontal.”

  “Let’s not quibble over terminology,” Jonas suggested amiably. “You’ve found an expanse of low ground, and it should be traversable, if not easily. Given the height of the cliffs and the angle of the terrain, there’s a chance to map the extent of this chasm long before it emerges from summer. While work on the bridge of balloons will continue for as long as any threat to the southern migration remains, this expedition has the potential to resolve all our doubts. Believe me, every surveyor in Baharabad wanted to join. But you and Seth have earned a place on it, and it’s yours if you want it.”

  Having been mentioned, Seth felt it was his duty to fill the silence that followed. “Thank you,” he said.

  “Take your time,” Jonas urged them. “Think it over, and give me an answer in five days.”

  He tipped his head away from them, and began conversing with Raina and Amina. Seth walked briskly out of the tent, not wanting to give Theo a chance to decide that he’d have nothing to lose by speaking his mind.

  «These people are idiots,» Theo declared sullenly. «Why did I ever think that I could trust them?»

  Seth kept moving past the dusty row of tents, picking up his pace—wishing that, just once, the children’s tale of The Boy Who Outran His Sider could come true, letting him escape into blissful solitude.

  “Seth! Slow down!”

  Seth tipped his head; Raina and Amina were approaching. He stopped and waited for them to catch up.

  “I know you’re upset,” Amina told Theo. “But did you honestly think that the cities’ merchants were going to agree to pay a hundred thousand laborers for six generations . . . to build mountains to trap the sun?”

  “They’re paying for a fucking ‘bridge of balloons,’” Theo retorted. “Which will probably kill a hundred thousand people just trying to make it work. And if they ever succeed, we’ll just be facing the same situation on the other side of the node: migrating north, following the sun, until we meet the northern edge of the world. At which point there really will be nowhere else to go.”

  “Even if that’s true,” Amina argued, “the northern edge might be a thousand generations away.”

  “Or it might have crossed the northern habitable zone a thousand generations ago,” Theo countered. “You’re right that there’s no reason that the solar latitude of the edges should be symmetrical, but that cuts both ways.”

  Seth found the prospect of crossing the node on a bridge of balloons quite audaciously wonderful, regardless of what lay on the other side, but he wasn’t feeling brave enough to say so.

  “All that anyone’s ever known is the migration,” Raina said flatly. “Even if they believed that it was possible to end it, that doesn’t sound like a solution, it just sounds like a new kind of disaster.”

  “So the edge is just something I dreamed up, is it?” Theo demanded bitterly. “A dozen people have seen it now, and it’s still possible to pretend that it’s some kind of hallucination?”

  “It’s not a hallucination,” Amina replied. “But that doesn’t prove that it encircles the world. The cliffs might still turn out to stretch no more than a few degrees east-to-west. The expedition is the only way to settle that question.”

  Theo said, “But what if it doesn’t settle it? What if they travel a few degrees west, but then the cliffs turn to the south? The ground won’t be in shadow any more, making it impassable, but that won’t prove that the change in direction is anything more than a temporary meandering.”

  Raina said, “They’ll find whatever they find, and that will be better than knowing nothing.”

  “Fine,” Theo replied. “But since I have a choice, I’d rather go back to Baharabad and try to think of some new way to deal with the drought.”

  They walked on through the camp in silence for a while. Then Seth asked Raina and Amina, “You’re going on this expedition?”

  “Yes,” Amina replied.

  “And Sarah and Judith?”

  “Yes.”

  Seth wasn’t surprised. “Who else?”

  Raina said, “That hasn’t been settled yet. There’s a certain amount of politics to be accommodated.”

  “What do you mean?”

  Before she could reply, the four of them were distracted by shouting coming from nearby. As they approached the source, Seth saw a crowd gathered outside one of the tents.

  “I want to talk to Catherine!” a man was insisting, holding a woman roughly by the shoulders. “Why can’t I do that?”

  “Leave me alone,” the woman replied angrily. “If she doesn’t want to speak to a fool like you, that’s hardly a surprise.”

  “She can’t tell me what a fool I am herself?” The man gestured at the onlookers. “She can’t tell anyone here to pass on the message?”

  “She’s given me the message,” the woman retorted. “That will have to be good enough.”

  “When did you poison her?” someone called out, a taunt that was quickly taken up and repeated. Seth’s gut tightened with dismay; it was like a Sleepwalker mob in reverse.

  The man said, “This is what will happen: you can stay in your own tent, but we’ll bring you all your food. Then after a few days, we’ll see if we can wake her.”

  “You can’t imprison me!” The woman pushed his hands away. “Who do you think you are? You have no authority to tell me what I’ll eat or where I’ll stay.”

  “You’ll stay in your tent, half-head!” a Sider yelled from the crowd.

  “Can’t we bring a doctor?” Amina suggested. She didn’t even raise her voice, but other people picked up on the suggestion and echoed it. Seth was encouraged; this was a sensible compromise. The woman’s Sider might be uncommunicative for any number of reasons. Allowing self-appointed experts to judge whether or not she’d been fed the Thanton puffballs would be a recipe for vigilantism and paranoia.

  But the accused woman wasn’t interested in com
promise. “You can’t force me to see a doctor,” she declared defiantly. “My health, Catherine’s health, is no one’s business but our own.” She began trying to shoulder her way through the crowd, but no one was willing to let her pass.

  Seth was unsure now where his duty lay. Harassing anyone in this manner was obnoxious—but if Catherine really was in danger from her own Walker, her friends were entitled to come to her aid.

  “Here’s the doctor!” someone announced. Seth saw a woman with a bag of instruments approaching, and people were parting to let her through, but when Catherine’s Walker began screaming at her to go back to where she’d come from, she stopped to reassess the situation.

  The doctor’s hesitation did nothing to mollify the besieged woman, who began punching her nearest accuser and yelling at the crowd. “You’re all hypocrites! You’d do it yourself if you had the chance! You’re all sick of your own parasites jabbering on, telling you what to do! Well, I have the legs, I decide where I walk! Stand up for yourselves, you cowards! It’s the easiest thing in the world now! Show some fucking pride, and reclaim your bodies from those mind-eaters!”

  Seth was expecting this rant to be drowned out by angry rebukes, but instead the crowd became silent as the woman continued her tirade. “Be honest for once! It’s what you all want!” She laughed and held her hands up. “Learn the code, ask for help, pass the message palm to palm where they can’t see it. We can free ourselves, all of us! We just need to have the courage!”

  when seth woke in the early hours of the morning, he could tell that Theo was already awake. He wasn’t pinging the tent, but the darkness that would have held his view was still imbued with his presence: seeing what Theo saw when he saw nothing was not the same as seeing nothing at all.

  «The sun trap isn’t a lost cause,» Seth said. «If the bridge at the nodes doesn’t work out, and the expedition finds no limit to the edge . . .»