Dichronauts

by Greg Egan


B B   A A A A A

This is an excerpt from the novel Dichronauts by Greg Egan. Copyright © Greg Egan, 2017. All rights reserved.

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1

On the day the movers zigzagged the museum, Seth’s whole family woke before dawn. They ate a quick breakfast then set out across the city to join the crowd gathering to watch the spectacle.

By the time they arrived the sky was bright, and all the vantage points to the east and west of the museum were taken, occupied by a good-natured but impenetrable throng. So they sidled north into the border precincts thinned by the encroaching summer – and found themselves on a deserted hill overlooking the building itself.

“Not from the north!” Elena complained. Irina responded indignantly, “I can make it twice as clear as you can!”

«What do you think?» Theo inspoke. «I’m not even pinging the scene myself – there’s so much bouncing around from the crowd that it wouldn’t make any difference.»

«This is fine,» Seth replied. He didn’t know if Elena was just being spiteful, or if she and Irina had a real problem sharing views.

Seth’s mother said firmly, “We’ll watch from here, it’s as good a spot as any.”

The movers had finished their preparations inside the building, and were assembling into four rope teams outside: two near the south-west corner, two at the north-east. There must have been fifty Walkers in each team, but a part of Seth’s mind still refused to accept that they stood any chance of shifting the huge structure. He’d seen the wheels and pivots under the floor once, in a tour of the ancient building that had treated it as an exhibit in its own right, but the sheer size of those hidden components, however well-designed they were to aid the movers’ task, had only made it seem more fanciful that anyone could set them in motion.

“There’s a career for you, Seth,” Theo’s father suggested.

“Maybe.” Seth wasn’t sure if he was joking or not. “I think Theo would get bored, though.”

“That’s not important. He can still enjoy his own work. It’s like that with all of us: give and take.”

«What is it with your father?» Seth asked.

«He wants me to study business law – so he’s hoping you’ll pick something that he thinks I’d hate, as much as he thinks you’d hate his choice for me. If we’d both be suffering equally, it would be harder for you to complain.»

«Do you want to study law?» Seth’s gut tightened at the thought of spending half his life, even as a scribe, on anything so soul-sappingly tedious.

«No.» Theo sounded amused that he’d needed to ask. «Do you want to be a mover?»

«I don’t know. I doubt I’ll ever be strong enough.»

The teams had taken hold of their ropes and were beginning to strain against the impossible load. The two groups at each corner were pulling at slightly different angles, but all four directions required an awkward stance. Seth noticed that a few of the movers at the north-east corner were west-facers, which had to make their work even harder.

«You see that?» he asked Theo.

«If they were upside-down, I’d be impressed.»

Seth laughed and did a half backflip, landing on his hands, west-facing himself now. His own vision was undisturbed – the world itself no more seemed upside-down than when he tipped his head back to see westward – but his arms were blocking Theo’s view, and the thought of trying to manoeuvre them out of the way made him fear he’d lose his balance, risking a dangerous uncontrolled fall. He hadn’t hand-walked since he was a kid; it had seemed easy then, but he was seriously out of practice. He completed the flip, and brushed the soil from his palms.

“What are they doing?” Elena asked irritably. “Nothing’s happening!”

“The hardest part is getting the wheels moving,” Seth’s father explained. “But once they start—”

The museum began to turn. It stretched out along the grand avenue that cut diagonally across the city, growing ever more slender, taking up ever less of the width of the road. The centre of the building, the pivot, stayed fixed, while the opposing teams of movers ran ahead of their ropes’ anchor points: half of them heading north-east, half south-west.

“See anything now?” Irina asked sarcastically. Elena said nothing, but when Seth glanced her way she seemed rapt.

«Are you sure you don’t want to be a mover?» Theo teased him. Seth could feel his own face contorted into an expression of delighted stupefaction. The parallelogram below them was insanely skinny now; he’d turned pebbles about as far as this, but nothing larger.

«Only if I get to ride inside the buildings, and see all the rooms remain normal while the city turns around me.»

«You can always turn yourself and get the same view.»

«You think so? Who’s going to clear the streets for me?»

The museum’s far corner, needle-thin, slid past the bakery, the grain store, the bath house. It crossed the bridge over the brook and pushed on into the northern residential precinct. The movers themselves were barely visible now, stretched out along the road into surreal slivers of flesh. Despite what he’d said to Theo’s father, Seth doubted that their Siders were feeling bored. Strength and agility were not the only skills at play here: to execute a manoeuvre like this, you’d need the clearest possible sense of your surroundings in all directions, demanding a flawless collaboration between Walker and Sider.

The corner itself became too narrow to discern, but then Seth noticed some of the movers reorienting their bodies and heading back down the avenue. They’d turned the massive building as far as they needed for the first step, so now the central pivot would be raised and a new one, almost at the corner, lowered, as the wheels were reconfigured to facilitate a counter-turn that would end with the museum one-eighth of the way to its destination. It would take the whole day to bring it to its new location at the city’s southern edge.

Seth’s father handed out the stone-fruit he’d brought, and everyone sat on the dusty ground of the abandoned lot, chewing the sweet, heavy pulp while they waited for the second act to start.

Theo said, “We should halt the sun, not move the cities.”

His mother laughed. “One day, maybe.”

“I’m serious.”

Seth’s mother tipped her head back and scowled, unable to resist taking Theo at his word. “And survive on what? Do you think you could farm the same plots of land forever?”

“And what about quarries?” Seth added. “Whatever happened with the crops, you couldn’t dig up the same stone twice.”

“How much new stone would we actually need,” Theo countered, “if we weren’t leaving a trail of rubble behind?”

“Hmm.” Seth paused to give the question due consideration. Theo had a habit of blurting out these absurd, dream-like propositions and then defending them with such sincerity that everyone’s scepticism began to waver.

“And how exactly do we halt the sun?” Theo’s father asked.

“There’s a mover for every job, isn’t there?” Theo replied. “So surely there’s an un-mover for this one.”

This assertion was so strange that it hung in the air unchallenged.

Seth looked down across the city. Much as he admired the movers, the truth was that the best he could hope to be if he joined them was some kind of minor assistant, checking ropes or carrying tools. He was healthy enough to be a stonemason or a farm labourer, but he did not have the strength to fling buildings around like toys.

Theo inspoke, «You know who goes before the movers?»

Seth wasn’t sure he understood the question. «Road-builders?» Theo clearly wanted to escape the law, but there had to be limits to what he would put up with.

«Before the road-builders.»

Privately, Seth ran through a list of ever-less-appealing preparatory trades – then as he pictured the untamed ground that the very first of these workers would confront, a wilderness untouched by leveller or plough, he finally understood what Theo had been hinting at. Why hadn’t he thought of it himself? He’d always wanted to work outdoors, and there was no job less confining.

«You’d be happy with that?» he asked. «We’d do it together?»

«Why not?» Theo replied. «We could study something real, and do something useful.»

«While we wait for the un-movers to catch the sun?»

«Of course. And not a statute, a contract, a lease, a trust or a lien in sight.»

Seth’s mother was facing away from him, but he caught his west-facing father’s eye.

“We know what we’re going to do,” he announced. “Both of us.”

“Is that right?” Theo’s father asked warily.

«Fuck, yes,» Theo inspoke. Seth struggled to keep a straight face, waiting for his Sider to find the courage to express the same sentiment out loud, but then he found himself unable to keep silent any longer.

“We’re going to be surveyors,” he said. “Movers are indispensable – but even they need someone going ahead of them, to find the best route for the city to take.”

2

“The possibility that the world might be infinite was recognised by people as far back as the Siseans.” Maria’s Walker, Samira, wrote the name beside the timeline she’d sketched; Seth copied it, wondering abashedly if he was the only person in the class who’d never heard of this entire civilisation before. “But many other cultures assumed that the migration was ultimately cyclic. There were two main variants of that mythology: one in which constant southwards travel would eventually take you back to where you’d started – as if north and south were no different than east and west – and another, more elaborate, version, in which the advance of the sun regularly slowed, halted, then went into reverse, allowing the migration to change direction. Of course, the last occasion on which the reversal was meant to have happened was always taken to be so remote as to be the stuff of legend rather than history, and the absence of any signs of past habitation required the proponents to believe in summers so fierce as to transform buildings into sand, while mysteriously permitting the same kind of stone in its natural state to survive intact.”

Seth resisted the urge to share a silent joke about the halting sun with Theo. There was no prohibition on inspeech during lectures, but if they didn’t discipline themselves and limit its use to helping each other follow the material, they’d end up constantly distracted.

“Later,” Maria continued, “as geodesy began to develop into a true science, doubts arose as to whether an infinite assembly of matter was physically possible. The sun was understood to be orbiting the world under the influence of the same gravitational attraction that we feel here on the ground – but then the sun itself, a finite body, was seen to exert a tidal pull on the water in every river. If the world was infinite in extent, how could its gravitational pull fail to be infinite too?”

Seth contemplated this disturbing notion. If you could measure the tides raised by the sun, and then measure the tug of the world upon your body, hadn’t you, by implication, measured the world itself and discovered its limits?

But Maria had a far less radical solution. “In the generations following Siméon’s Treatise on the Tides, geodesists reached a consensus on this question. There is, in fact, a simple shape the world could take that would allow it to be infinite, while giving rise to a finite gravitational force.” Samira sketched four hyperbolas on the drawing board, symmetrically arranged around a central point. “Imagine that these curves go on forever. Take the area between them and spin it around the north-south axis to make a solid. The one-sheeted hyperboloid that wraps around the axis is the ground on which we stand. The two dish-shaped surfaces at the north and south are unreachable to us, but if anyone lived in those sunless places they would feel the same kind of gravity holding them to the ground as we do.”

Samira began writing a familiar equation below the sketch, while Maria reminded the students of its role. “Siméon’s Law of Gravity says that if you add the second rates of change of potential energy along the two ordinary directions, then subtract the same quantity along the axial direction, the result will be proportional to the density of matter. Though this shape has an infinite volume and, in its entirety, an infinite mass, you can satisfy Siméon’s Law while still producing a finite force everywhere – in fact, a force that’s of equal strength everywhere on the surface.

“Your task, to be completed by tomorrow, is to find precise expressions for the potential energy in each distinct region. You may assume, for the sake of simplicity, that the density of the rock is the same everywhere.”

«This gets better every day!» Theo enthused as they headed out of the classroom. «All the things they never explained properly in elementary school are starting to make sense now.»

«I’m going to need your help with this,» Seth confessed. Geodesy delighted him, too, but some of the technicalities were frightening.

«Remember the formula they gave us for the point mass?»

«Vaguely.»

«You wrote it down,» Theo assured him. «I think we’ll just have to ... spread that out over a larger volume.»

«An infinite volume!»

«Yes,» Theo conceded. «But the shape is so symmetrical that there’s bound to be some kind of trick to make the problem simpler than it sounds.»

Seth went to the study hall and sat scribbling formulas, trying out Theo’s suggestions. In the empty space around a point mass, the potential energy was proportional to the inverse of the true distance from the point, with the force the inverse squared. But when matter was spread out at a uniform density, there was a solution that was even simpler, with the potential energy proportional to the square of the true distance from some point, and the force proportional to the distance.

«Some point?» Seth could follow all the algebra, but the symbols meant nothing until he knew what they were measuring. «Which point?»

«Whatever makes things simplest,» Theo proposed.

Seth liked that rule. «The centre?»

When they followed through with detailed calculations, everything began to fall into place. On the ground, and in the space above it, the gravitational pull of the entire, infinite world was no different from that of a certain finite mass at the world’s centre. It was as if all the vast plains and mountain ranges that stretched on forever to the north and south had been replaced by a single pebble – an absurdly heavy one, but not boundlessly so – that acted as their gravitational proxy. But there was a further, equally astonishing twist: although an idealised point mass produced infinite forces along its cones – where the true distance from the point fell to zero – in the solid rock between the hyperboloids, those forces weren’t merely hidden, they were tamed: reduced to finite quantities. The pebble at the centre of the world was a useful fiction, from a sufficient distance, but if you could actually burrow down into the rock, instead of being torn apart as you approached the cone, you’d find the force of gravity decreasing.

«Well done, Surveyor Theo.»

«Well done, Surveyor Seth.»

Walking home, they passed a playground where half a dozen kids were sledding up a northwards ramp. Seth paused, tempted but a little embarrassed.

«Go ahead,» Theo encouraged him. «We’re not that ancient yet.»

The group were friendly and one of the kids let Seth take a turn on her sled. He lay on his stomach on the polished stone, gripping the worn handles. Three Walkers sidled up the start of the ramp, pushing him to get him started. Seth could feel the changing forces in his gut as his helpers’ task grew easier, then superfluous, and as they stepped away he cried out in abandon at the rush of acceleration. The sled shot up the slope; Theo showed him the edge drawing closer. Then they were truly flying, off the ramp, through the air, down into the straw heap.

«Isn’t gravity glorious?» Theo’s words sounded muddy and his view appeared blurred; the jolt of landing must have shifted him a little. Seth waited for him to squirm back into place before replying, «It is.»

He rose to his feet and picked up the sled, sidling back to return it to its owner.

With the sun low in the western sky, it was hard to believe that it could ever threaten anyone, let alone blast abandoned cities into dust. Seth stood for a moment, savouring the smell of the hay that still clung to his sleeves, then he bade the children goodbye and set out for home.

3

«Something’s wrong,» Theo said as they approached the house. «Can you hurry?»

Seth broke into a run – though they were coming from the west, so if he couldn’t see anything amiss himself, nor could Theo. «What’s the problem?»

«My sister’s in trouble.»

«How do you know?»

«I can hear her.»

Seth had reached the porch. He unlocked the door and stepped inside. “Elena?” he called out. She didn’t reply. «What’s Irina saying?» he asked Theo.

«It’s muffled. But I think they’re in their room.»

Seth climbed the stairs, bracing himself, unsure what to expect. He knocked gently on his sister’s door. “Elena? Are you all right?”

“Go away! I’m busy!”

“Can I talk to Irina?”

“We’re both busy.”

“Can’t she tell me that herself?”

“Just leave us alone.”

Seth stayed by the door. Theo said, «You need to do something. She’s crying out for help.»

Seth didn’t doubt him, but the claim was confusing. «Why doesn’t she pitch it so everyone can hear?»

«Something’s constraining her.»

Constraining? “Elena?” Seth called again.

“Go away!” she shouted. “I’m trying to study!”

«Just open the door,» Theo urged him.

«She’ll have locked it.»

«There’s a key in our parents’ room.»

«For emergencies.»

«This is an emergency.»

Seth said, “I need to talk to Irina! It’s important!”

“She’s asleep.”

“I thought you said she was busy.”

“She’s busy sleeping, I’m busy studying. You might want to listen to Theo yammering away all day, but normal people work out a better way.”

“I know she’s not sleeping,” Seth replied. “Theo can hear her.”

Elena fell silent. Seth could hear movement in the room. He waited for his sister to come to the door.

«Get the key! Now!» Theo’s tone had turned frantic.

«Why?»

«She’s hurting her!»

Seth ran to his parents’ room. «Where is it?»

«By the window.»

Seth grabbed the key and sprinted back to Elena’s door. He pushed the slotted card into the lock, then tugged on the handle until the door unlatched and the counterweights flipped it up against the ceiling.

Elena had a band of cloth fitted tightly around her head from chin to cranium, covering every visible part of her Sider. But she’d slid the longest left finger of her right hand under the binding, deep into the place where—

Theo screamed at her, “Stop!

The word left Seth’s skull ringing. Beyond all the rage and anguish it carried, the sheer force of it made him feel like he’d been punched.

Elena pulled her hand away and sank to her knees. Seth steadied himself and approached her. He took hold of the cloth and started easing it forward; there was blood on the material, spots and streaks in yellow and red. When the whole thing was free he dropped it on the floor and gazed down at Irina.

The membrane of her right pinger was torn, and there was a dark unnatural space between her damaged flesh and the tunnel through Elena’s skull. Two rivulets were seeping from the cavity, entwined but immiscible.

Theo said, «They need a doctor.»

Seth stood in silence, swaying.

«Seth? They need help.»

«I know.» He put a hand on Elena’s shoulder. “Do you think you can walk to the clinic with me?”

Elena started sobbing. “I didn’t have a choice! She didn’t give me any choice!”

“We can fix this,” Seth promised. “But you need to come with me.” He couldn’t leave her alone while he fetched the doctor; he had no idea now what she might do. Their neighbours wouldn’t be home yet, and there was no one else nearby on whom he could call for help.

He took her hands and pulled her to her feet, then tipped his head and started backing out of the room. Elena resisted for a moment, but then she let him lead her into the corridor and down the stairs. On the porch, Seth scrawled a note on the message board, then they set out into the twilit streets.

Lamps showed in a few scattered windows, but as Seth headed west the paving stones beneath his feet were all but lost in the gloom. Elena kept her face to the east and followed him by touch alone. When they finally reached the corner and began sidling south, it was like stepping halfway into daylight again, with Theo’s crisp vision revealing every crack and bump on the path well enough for Seth to plan his movements. But this was the side of Irina’s injury; to Elena, they were walking into darkness. Seth did his best to steer her past the hazards, and offer a cue when she needed to take a larger step than usual, but he couldn’t bring himself to offer verbal advice. Avoiding the humiliation of advertising her condition to passing strangers was only part of it. So long as no one spoke, everything he’d seen in her room felt contained by the silence.

When they entered the clinic the lamplight was dazzling. Seth counted at least twenty patients waiting on the benches, huddled miserably, alone or with companions who glowered at him as if he’d come to usurp them from their places in the queue. He got Elena seated, then took a numbered card from the dispenser by the door.

The doctor’s assistant approached and bent down to examine Elena and Irina. “This is urgent,” he said sternly. “Come with me.”

The assistant took Elena by the arm. Seth started to follow them, but when he reached out for his sister’s hand she pulled free. “Just wait for me,” she said.

Seth sat on the bench. Theo hadn’t spoken to him since they’d left the house, and he didn’t know what to say himself. The silence made him feel hollow; Theo was still sharing his view, but everything Seth saw, by light or by echo, seemed dead and empty.

When their parents arrived, Elena and Irina were still with the doctor.

“What happened?” Seth’s father asked.

“They were bleeding,” was all Seth could say. “Both of them.” He wondered if Theo was talking with his own father at a higher pitch, beyond any Walker’s hearing.

Irina’s mother spoke quietly with the doctor’s assistant, then the assistant led the four parents in the direction of the consulting rooms. Seth leant back on the bench and closed his eyes, then shut out Theo’s view.

In the darkness of his skull, Theo finally spoke.

«Elena’s pregnant.»

Seth had no wish to follow this partial revelation to its logical conclusion, but Theo always chose his words with care. «Just Elena?»

«Irina refused. Elena went alone.»

The claim was surreal; if not for the night’s horrors, Seth would have laughed and called Theo’s bluff. No playground know-it-all, let alone biology teacher, had ever raised such a possibility.

«So what will happen with the baby? She’ll have a side-blind child?»

«They’ll try to adopt an unpaired Sider,» Theo guessed. «I don’t know how easy that is, but it happens.»

Seth felt as if he was sinking into the darkness. He didn’t want to open his eyes and face the crowd of strangers, who had by now all surely guessed his family’s bizarre affliction.

But the strange, curdled shame he felt had nothing to do with Elena and Irina. What disturbed him the most was the sense of his own naïveté. How could it never have occurred to him that a Walker and a Sider could disagree on their choice of partners? That the idea hadn’t been put to him long ago by some giggling schoolmate or sober adult was no excuse: what kind of idiot could fail to imagine the dilemma, unprompted?

Theo’s father was always prattling on about give and take, always talking down the notion that both Walker and Sider could ever get their own way and be entirely happy. And though his son had proved him wrong about that once, it wasn’t the last choice the pair would face. There was a lifetime more to come.

Theo said, «They’re back.»

Seth opened his eyes. Their parents were walking slowly between the benches, holding Elena’s hands. There was a bandage on her head, covering the wound but not entirely blinding Irina’s right side. Seth stood and waited for them, then led the way to the exit.

No one spoke aloud in Seth’s range of hearing on the way home, but Theo said, «They’re going to be all right. The doctor told them there’s no permanent damage.»

«Good.» They reached the corner and headed east. Seth looked up into the warm yellow light from the windows of the houses. No permanent damage.



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