Phoresis

11

Petra lay harnessed to her sled, tense in the airless silence, stealing quick glances to either side to reassure herself that her mute companions hadn’t taken their eyes away from their telescopes. The catapult would only be released if Kirsi and Rada tugged on the two levers at exactly the same time, in a unanimous vote that was meant to spare them all the consequences of an ill-timed attempt. But if any kind of error was possible, that included a lack of consensus that would prevent her from being launched at all. Waiting six days for the next opportunity would be unbearable.

She was spared the anti-climax: the sled shot forward and she was in the void. She turned and looked back toward the tower, elated. The rope trailing behind her lay in an almost perfect straight line, but the tug of the harness on her shoulders was as gentle as she could have wished. Ingrid and Lena were working the crank so smoothly that the rope they unwound was neither slack nor tense, neither holding her back nor looping dangerously ahead of her.

She quickly returned her gaze to the view ahead, determined not to be taken by surprise. However accurate the predictions of the libration had become, the team’s ability to aim and calibrate the catapult remained the greatest source of uncertainty. The target might appear on her left or her right, outracing her or lagging behind. The only thing she was sure she could rule out was a head-on collision; they couldn’t have achieved that themselves if they’d tried, and their errors were hardly going to conspire to make it happen.

A star blinked, then another, and another. Petra registered the events but couldn’t yet extract any real sense of the occluding object’s position and motion. Kirsi had spent more than a hundred nights staring through her telescope before she’d managed to record a sufficient number of occultations to be sure that the old tower was even standing; until then, for all anyone knew it might have crumbled to the ground. Petra had been in awe of her then, but now that she was actually approaching the thing and still couldn’t interpret the fleeting evidence it offered for its existence, her admiration only increased. She would never have had that much patience.

Slowly, a dim gray thread emerged against the blackness, slightly to the left of the sled’s forward bearing. From this distance, it seemed as remote and unreal as it did through the telescopes: more like a flaw in the lens than a solid object. But now there was no lens to bear the flaw, and when Petra closed each of her eyes in turn, the blemish remained.

As she watched, the thread thickened slightly, but it was also moving away to the left. She needed to change her trajectory, but acting too soon or too late would ruin the encounter. She estimated the angular speed of the target, then waited and did it again. Waited again. Estimated.

She pushed the lever on her own small catapult and sent a rock flying into the void to her right, at the same time loosening the brake on her rope spool. The sled responded with a brief, satisfying jolt, and the extra rope began playing out beside her. When the spool was half unwound, she tightened the brake again, and the right-angle bend she’d created began to deform. There was a huge amount of rope laid out along her original trajectory, and the rock she’d ejected hadn’t possessed anything like the momentum needed to realign it all neatly behind her, but if she’d judged the timing correctly she’d have a good chance to make it to the tower before too much of the rope got the message that she’d changed direction.

The thread was a gray sliver now, slowly growing wider. Petra could discern a sharp boundary at one end—the “bottom,” by her parochial reckoning—but when she followed it “up” toward Tvíbura, it just narrowed and dimmed until it had no visible effect on the stars behind it.

The tower passed by on her left, but they weren’t done with each other yet. She looked back anxiously and watched the gray sliver cross over to her right. She’d overshot it twice now in different directions, but it was speeding up in the first direction, as it moved away from the closest point in the libration cycle, so it was only a matter of time before it overtook the rope she’d laid across its path—

The sled shuddered alarmingly, swung from side to side, then settled. When Petra looked back along the rope, the part she could see was pointing straight toward the tower. If everything had gone to plan, she was effectively tethered to her target now, with the tower’s own acceleration keeping the rope pressed taut against it. And so long as nothing slipped or broke, she would keep on circling it, drawn ever closer as the rope wound her in.

She could feel a gentle tension in the rope, conveyed to her as a slight pressure from the harness. The stars wheeled slowly across the sky, but even when they’d come full circle it was hard to feel any sense of progress. It was only by the time she’d completed half a dozen orbits that she was able to convince herself that the cycles were growing shorter.

When Rada had suggested this method for the crossing, Petra’s first instinct had been that conservation of angular momentum would impose an ever greater velocity on the traveler as she spiraled inward, which would either lead to the rope snapping from centrifugal tension, or deliver her to her destination with a speed she’d have no hope of countering or surviving. But that hunch had proved to be misplaced. The curious geometry of the spiral involute meant that the pull of the rope, while slowly changing the direction in which she was moving, would never increase her speed. The time it took her to loop around the tower was only shrinking because she was drawing closer—and rather than feeding her energy, the tower and Tvíbura were helpfully draining away her unwanted angular momentum.

She needed to be patient now, but vigilant too; with no real idea of her precise distance from the tower when it had snagged the rope, counting orbits wouldn’t tell her much. All she knew for sure was the general character of motion along the involute: the distance from the center would change at an almost constant rate for a considerable time, only to start falling precipitously at the end.

The turning of the stars, with the same familiar constellations rolling into view over and over, risked lulling her into a state of dreamy torpor, but the slow revelation of the tower itself held her attention, however frustrating the pace. The walls of her own world’s newer version were hardly perfect geometrical forms, but the old tower looked almost as if it had melted and flowed at times, or at least that its underlying vegetative skeleton had started to rebel and go wild. Petra did not expect anyone to have tended to it for a very long time, but she tried not to extrapolate too far from these undeniable signs of neglect. One forsaken structure was no fair measure of the state of a whole world.

When the rush finally came she was more than ready for it. The tower seemed to spiral in toward her, spinning as it approached, revealing ever richer details in its warped and pitted surface but moving too fast for her to dwell on any one feature. The extent of her motion “upward” toward Tvíbura had seemed quite small to her before, but now she could see that the helix she’d wound was pitched more steeply than she’d expected, and when she tried to find the point where the rope had first touched the wall, it was too distant to discern.

She’d already rewound her catapult and prepared it for its final task. Before the relentless spiraling left her disoriented, she ejected a second rock to oppose her motion, and suddenly the sky was all but still.

The sled had not been perfectly halted: it continued upward along the length of the tower, while also trying to pull away from it. Then the rope caught it and stopped it, briefly, before it rebounded inward and swung toward the wall. Petra was ready; she raised the baffle at the side of the sled, and when it struck the wall there was a thud she could feel through her bones, but no pain, and no apparent damage.

She waited for a while, prepared for the worst: for the helix to start unraveling. But gravity here was still negligible; it was not as if the coiled rope was having to support any real burden to stay in place. And in the tests on her own tower, the rope of tangler fibers had ended up not just wrapped around the ice, but bonded to it in places, the friction of the encounter having partly melted it.

Petra checked that her pack was secure, then untied her harness from the frame of the sled, leaving it joined only to the rope on a second spool. She released the brake on the spool—allowing it to turn almost freely, but with a governor to slow it if it spun too quickly—then clambered off the sled and floated beside the wall of the tower.

Now that she was no longer swayed by the notion of lying on her stomach on the sled, her sense of the vertical changed. The bulk of the tower, the part beyond the helix, was clearly below her. Tvíbura was the only way down.

She gave the sled a firm upward push, which had little effect on it but sent her body downward at the speed of a brisk walk. She watched the bumpy, mottled wall of the tower move past her.

She knew that the balcony couldn’t be far, but it was a relief when she finally spotted it below her. She waited for it to come closer, then reached out and placed a gloved hand against the wall, careful not to apply pressure and push herself away. The friction wasn’t much, but nor was her weight. She bent her knees as she struck the floor of the balcony; she bounced up again, but clawed at the wall and halted her ascent. The encounter pushed her away from the wall, but downward as well, and the balcony’s outer, protective wall stopped her and sent her inward again. Petra forced herself to stay calm as she bounced from surface to surface; so long as she did nothing to gain energy, and nothing that sent her over the balcony, she’d have to come to a halt eventually.

When she was still, she lay on the floor for a while, grateful and amazed. The bridge might be far from complete, but the first strand was in place. The worlds would be joined, for anyone to cross between them at will. They had proved that it was possible.

The ice was gone around the seals of the entrance from the balcony into the tower, which made it easy to get through the six doors, but meant at least one level of the tower would be devoid of air. Petra was unfazed; anything less would have left her resentful that she’d wasted so much time training in the void. The seals could be repaired eventually, the whole journey made infinitely easier, but the world would not begrudge her the satisfaction of being among the few prepared to go first.

Inside, the staircase looked almost familiar in design, but hallucinatory in detail. The Yggdrasil roots had had their way, retreating and advancing, laying down mounds of ice in one place, resorbing it in another. The stairs were still traversable, but the endless variation of bumps and pits rendered every footfall a surprise.

Petra descended as quickly as she could, taking advantage of the low gravity. She would be cautious once a fall might actually injure her, but if she dawdled now that would only make her more impatient later, and more tempted to take foolish risks. Apart from the breach at the entrance, the walls themselves appeared to have retained their integrity; for all the strange distortion and dimpling she encountered, there were no outright holes in the ice. As the sun dropped lower and came directly through the walls, it cast strange bright spots and twisted caustics over the central column. It was like the dappled light in one of the shallower tunnels through the tanglers.

She reached the bottom of the level just as night fell, and found the seals of the connecting chamber not just intact, but blocked by outgrowths of ice. She took the chisel from her pack, but then thought better of trying anything in the fading light. If she ruined the seals and lost all the air from another level, that would be unforgivable. So she spread her blanket on the floor beside the chamber, and slept.

Standing in the open air at the top of the final staircase, with the wind and dust of the ancestral world blowing in her face, Petra felt her brothers begin to stir.

The stairs she could see in front of her weren’t any more malformed and bulbous than the thousands of helical ones she’d already negotiated, but the unbroken line from the landing to the still distant ground did induce a new kind of vertigo: if she slipped and fell, it wasn’t clear how far she might descend before she came to a stop. The swollen ice on the side walls had spat out all the railings to which she might have hooked a safety rope; all she could do was keep her hands on the walls to steady herself, and take scrupulous care with where she placed her feet.

As she prepared to step off the landing, she felt her brothers rebel, all but paralyzing her with fear. She only had one more pessary left, and whatever progress her friends might have made on the rope bridge by the time she came back, she was fairly sure that her need to exercise unfettered judgment would be even greater then. “What would you have me do?” she muttered. “Stay here forever and starve to death?”

She still had food in her pack, of course. And whether her brothers were aware of that or not, she wasn’t really arguing with them, so much as with a kind of conspiracy they’d formed with her own, more ancient instincts. Ancient Petra certainly knew about the food.

Modern Petra took off her pack, pulled out the sack of dried meat and tanglers, and tossed it down the stairs. It came to a halt before it vanished from sight, and it did not appear to have split open. She hadn’t really intended the gesture as an experiment to test her own vulnerability, but the results were encouraging: even if she did fall, it might not be too terrible.

The conspiracy was appalled, but it was also hungry enough to be disinclined to walk away from food. Petra put her pack on and started making her way down, promising everyone that she’d start chewing on a tangler once she reached the sack—and hoping that it would seem easier and safer by then to continue down the stairs than it would to turn back.

The ice field around the base of the tower was desolate. If there had ever been tents or other buildings here, no trace of them remained.

Petra inhaled the thin, dusty air and contemplated the task ahead of her. The hemisphere visible through the telescopes contained no farms or grassland, and everything that wasn’t ice resembled outcrops of bare rock, or pits of gray dust. But if Tvíburi had proved anything, it was that a food source didn’t always look the way it was expected to look.

Evening was approaching, so she set up her tent in the partial shelter of one of the tripod legs. Whatever else had befallen Tvíbura, the ocean must still be thriving if the Yggdrasil that held the tower up hadn’t withered and died. If only the people of the surface could have found a way to live down there in the sweltering darkness, sheltered from the vagaries of the sun and the geysers, floating through the molten ice.

In the morning, she set off east, guided by the sun but also looking up often at Tvíburi to impress the meaning of its features on her so she’d have no trouble reading them, day or night. The idea that she might somehow fail to find her way back to the tower did not remain unthinkable for long; by the end of her first day walking, it had vanished from sight, and while the maps in her pack were as detailed as she could make them from Tvíburi, down on the ground, for stride after stride, the only phrase her surroundings evoked was: ice is ice.

On the second day, it rained heavily, and she filled a bottle with ethane. When she squatted down to inspect the rivulets running over the ground, she saw fine dust pinned by surface tension to the top of the liquid, but no matter how closely she squinted at the surface she could not make out a single struggling insect.

On the third day, she reached a cluster of hills. She clambered over the rocks, in and out of shallow, sheltered valleys, but they concealed nothing she could recognize as living.

On the fifth day, with Tvíburi low in the sky, Petra came to a place that was known to have been farmland. The topography had kept the degraded soil from dispersing across the whole surrounding ice field, but the swirls of gray dust through which she strode did not remain still enough to make a home for any conceivable form of vegetation.

The fields were long gone, but where the center of the village must have stood, she found the remains of half a dozen buildings, with stone or wooden foundations set in pits hewn into the underlying ice. Petra knelt down between the ruins, covering her face against the dust. At least some of the people of this village had reached Tvíburi safely; that much was recorded in the archives. But what would she tell their descendants when she returned? That there had been no invisible salvation, no revolution in Tvíburan agriculture that could keep people fed as the soil blew away. No one had any right to be surprised by that, but she could not blame them for hoping otherwise.

When she set out on the seventh day, Tvíburi hung bisected on the horizon behind her. Petra felt a sense of panic at the prospect of losing sight of her own world; once it vanished, she might find herself wandering endlessly beneath an empty sky. But she stared down her fears and kept walking. Every place where she’d set foot until now had been scrutinized for generations, and all that anyone had seen through their telescopes had been farm after farm dying. But half the world had remained hidden, and from the day the last migrants had alighted on the Tvíburian ice, no more news of its fate had been forthcoming. Many people had made the Great Walk on Tvíburi—and at least in the past, on Tvíbura too. If she wanted to return with a final answer on the fate of this world, the only way was to revive that tradition.

12

Petra didn’t expect the old maps of the far side to tell her much; when she’d compared migration-era maps of the visible hemisphere with current, telescopic versions, four out of every five villages had vanished entirely. But with nothing else to guide her, she sought out the places where people had once lived.

Sometimes it was difficult to know if she’d reached the right site and found nothing, or simply failed to pin down the correct location. Unlike farmland and grassland, hills and mountains didn’t blow away in the wind, but it was rare that they could serve as reliable signposts.

By her thirteenth day on Tvíbura, all her food had run out. She’d been expecting that, and as an abstract idea it didn’t worry her; all her training told her she could keep up her strength and complete the Great Walk in thirty days, at which point Rada would be waiting for her at the base of the tower with fresh supplies. But starving herself by choice, as an exercise, within half a day’s walk of her own village back home, was not the same as marching empty-handed over an endless expanse of barren ice on the most distant part of a world that for all she knew was entirely lifeless.

On the morning of the fourteenth day, as Petra was disassembling her tent, she noticed a strange bulge on the horizon. It looked like a small mountain range, except that it was the color of ice, not rock. To explore it, she would need to detour to the north, and it seemed to correspond to nothing on her map. But then, either she was lost and this landmark would help to set her straight, or it was something genuinely new that merited investigation.

By mid-afternoon, the formation had come into clearer view, but that only made it less comprehensible. The “mountains” really were made of ice—or at least covered in it—but their shape was neither that of any rocky structure Petra had ever seen, or anything the elements had been known to carve out of the ice field. For a long time, she simply doubted that she was perceiving their geometry correctly; with a single viewpoint, changing so slowly, she lacked the cues to verify the full, three-dimensional forms that her mind kept proposing, then rejecting, then stubbornly returning to. But before night fell and she was left with nothing but starlight, she’d almost convinced herself: someone had tried to grow half a dozen separate Yggdrasil towers in the ice, all side-by-side. And then either by mishap, or by very strange design, they had all ceased growing vertically, and stretched out instead in more or less the same horizontal direction.

Dawn revealed nothing that made Petra change her mind, apart from one minor refinement: while five of the towers had remained upright, supporting the weight of their eccentric offshoots, the second from the left had toppled over in the direction of the overhang, but then rather than falling sideways as well it had come to a halt leaning against its neighbor.

She packed up her tent and strode toward the deformed towers as fast as she could. The wind was blowing strongly against her, but she had no intention of passing another night without resolving the mystery.

The only reason she could think of to grow an ice tower on the side of the world facing away from Tvíburi was in the hope of creating a geyser. But the stories all declared that Freya had proved such efforts futile—and while Petra could understand people doubting that those old fairground experiments had been conclusive, seeing the full-scale version stretching up into the sky without sinking its own foundations had surely been a great deal more persuasive.

Something touched her face, and she slapped at it instinctively. When she examined her palm, there was a soft, dark smear: the body of an insect.

Petra broke into a run, but her destination was too far away for a single burst of optimism to carry her there, so she slowed to a walk and conserved her strength. Sprinting to the point of collapse only to find a tiny patch of grassland clinging on behind the towers would not be worth it.

The sun was setting as she approached the feet of the towers. To Petra’s eye, they looked infinitely more misshapen and neglected than the one she’d descended, but if no one had ever been meant to climb them, different standards applied.

To the west, the sun was framed by the ramshackle arch of the fallen tower. Petra headed for the gap between the central pair, anxious as she passed below one of the overhangs, as if it might choose this very moment to tear itself free and crash to the ground. Staring up at the huge, horizontal column of ice, she thought of the tree branches she’d seen in the picture books passed down through her family. But no tree had ever stopped and sprouted a single branch of the same girth as its trunk.

She’d swatted a few more insects along the way, but she had to be ready to find herself among ruins as grim as any of the dead villages she’d passed through. When she reached the base of the tower, twilight had already descended, and whatever lay ahead was lost in the gloom. She stopped and prepared to set up camp.

“Who goes there?” a voice demanded.

Petra froze, unable to reply, though the tone had been more curious than threatening.

“Who is it?” The woman sounded annoyed now, rather than aggressive, as if she’d decided that a friend was playing a joke on her.

“My name’s Petra,” Petra called back into the darkness.

“Who?”

“Petra. Can I ask your name?”

A figure strode out of the shadows. “I’m Ebba,” the woman replied irritably, as if that ought to have been obvious. “Why don’t I know you? Which village are you from?”

Petra said, “I’ve come from far away.”

Ebba snorted. “Far away? Nothing’s far away.”

“I’ve come from Tvíburi,” Petra explained.

She couldn’t really see Ebba’s face, but the woman seemed to be scrutinizing her strange, coarse clothing. “What kind of nonsense is that? Are you telling me you flew here?”

“No. We finished our tower, and joined it with yours. There was some rope involved, but no untethered flight.” Petra was starting to wonder if she was dreaming, or had simply lost her mind. “We were afraid that everyone here might be dead.”

Ebba walked right up to her and grasped her shoulders, as if to check that she was awake herself, and that Petra was not her own hallucination.

She said, “We were afraid you were all dead, too. We thought the first travelers must have starved to death, along with every crazy woman who followed them on the basis of nothing but a scrawl on a fragment of a broken glider.”

Petra started sobbing. Ebba embraced her clumsily, hushing her. “Well, neither world is dead, so there’s only good news.”

“But what do you eat?”

“The usual kind of food.”

“Grown how? How do you still have soil?”

Ebba released her. “You didn’t see it, as you were approaching?”

“See what?”

“You must have been too far away.” Ebba caught herself. “And you must be very tired and hungry.”

Petra followed her through the darkness. She could smell the soil now, and some complicated scent carried on the breeze that she could only assume was a melange of old-world vegetation: grass, crops, trees. Ebba led her into a house, to a lamplit room, where two other women were preparing food. The three of them conversed in whispers, then Ebba introduced her friends as Laila and Tone.

“You came down through the old tower?” Laila asked, as if that were the most surprising aspect of Petra’s journey.

“Yes.”

“I went there once. I started walking up the stairs to see if I could get a nice view, but then I changed my mind and came down.”

Petra said, “Quite right. The stairs have lost their shape and they’re very slippery.”

She sat at the table and ate, in a daze, confused by the peculiar flavors and textures but not repelled; some part of her body welcomed every mouthful, more than it had ever welcomed her chewing on a tangler. She answered the women’s questions as best she could, though some words in their dialect were utterly opaque to her. When she tried to think of sensible questions of her own, her mind shrank away from the task. After a while, her eyelids became heavy, then Ebba led her to another room and gestured to the blanket on the floor.

When Petra woke, she could tell from the light that it was long after dawn. For a moment she felt ashamed, as if she’d failed to attend in a timely manner to some important duty, and betrayed herself to her hosts as lazy and ungrateful. But as her mind cleared, she decided that she had no reason to reproach herself. She’d come a long way; she could be forgiven for sleeping till mid-morning.

When she left the room where she’d spent the night, she found the rest of the house empty, so she walked outside, squinting at the brightness. Stretched out in front of her was a row of similar houses; beyond them, an expanse of green fields full of low, leafy plants, interspersed with what she took to be orchards.

Past the fields, there were more villages, and more fields, and on it went, until behind the most distant fields there was a row of ice towers. At first Petra thought they were the ones she’d seen as she’d arrived, but that made no sense; she hadn’t walked that far. As she turned her gaze to take in the whole impossible, idyllic scene, she realized that there was a ring of towers, encircling all of the agricultural land. Maybe twenty or thirty in total.

There were women walking along paths between the fields, and when Petra caught their gaze they raised their hands in greeting. No one came scowling to inquire about her origins; they must have been told already. Petra found a bench and sat, taking in the morning sun.

Ebba approached, carrying a basket full of something that looked disturbingly like tangler nodules, but were probably actually edible. “How did you sleep?” she asked Petra.

“Deeper than I’ve ever slept before.” Petra wanted to thank her for her hospitality, but then thought better of it; it might be insulting to suggest that she would ever have treated a stranger otherwise. “Can I ask you something?”

Ebba said, “Of course.”

“Where does all the soil come from?”

Ebba turned and looked out across the fields. “If you can be patient for a moment longer, you’ll see for yourself.”

Petra didn’t mind waiting. Ebba joined her on the bench.

“You came all this way thinking that we might be clinging to life, desperate to join the migration?”

Petra said, “Can you blame us? Nothing we could see through the telescopes looked good.”

“We were desperate,” Ebba conceded. “In my grandmother’s time, a lot of people starved. This place is beautiful, but it took generations of work to complete, and it can only feed so many of us.”

“Your grandmother worked on the towers?”

“Yes.”

Petra heard a faint hissing sound, somewhere in the distance. She turned toward it, and saw a slender column of white ascending from the middle of the fields. Compared to the geysers on her own world, it was ridiculously modest, as if the crack in the ice through which it flowed might be barely a hand’s breadth wide. But then, if it ran slowly and never rose high, whatever soil it delivered would not be scattered uselessly across the distant ice fields. It would all rain down upon the farms.

“The towers are so small,” she said.

“Yes,” Ebba agreed. “But they’re unbalanced in a way that puts the ice under stress—and more so at a distance than directly beneath them, so the effects of several towers can be combined. We found a spot where the ice was weak already, where an old geyser had once flowed. Freya showed that you can’t punch a hole through a slab of flawless ice just by piling up weight on top of it. But where there was a crack before, there’s a chance. We built rings of towers like this in seventeen different places. This is the only one that worked.”

Petra piled up all those towers, failed and fruitful, in her mind’s eye; nothing had come easily to anyone. She said, “Everyone will have the chance to walk on the two worlds now. We can travel, we can trade, we can bring the most distant cousins together. The hard times are over.”

The white column rose higher, summoned by the sun. Petra closed her eyes. She’d stay here and rest for a few more days, meet Rada to share the good news, then climb back to the void she loved, and join the others working on the bridge between the worlds, strand by strand, until it was complete.