Phoresis

by Greg Egan

  The furrows on the wheel declared that the light from Leander had begun to graze the upper atmosphere of Tvíburi. Rosalind waited; she didn’t expect a visible effect until the path cut deeper.

  At the halfway mark any dimming was still impossible to detect in isolation, but when she switched to the lamp and back a few times, she found she had to shrink the iris slightly before the two points of light appeared equally bright again. As Leander moved closer to the edge of the disk, she forced herself to stop trying to spot changes by anything other than the official method—but there was an unmistakable blurring of the star’s image, with the once-sharp point shimmering into a faintly trembling ellipse.

  Moments before the occultation, Rosalind flicked the comparator, adjusted the iris, checked and rechecked. She had matched the lights again, perfectly, she was sure of it—and then Leander vanished from sight.

  She lay back on the viewing bench, drained but elated. “Half done,” she muttered. Now all she had to do was measure the effect when the light from the same star took the longest possible path through her own world’s atmosphere—and then she’d finally know whether the most dangerous moment in her life was one she’d already lived through, or whether there was greater danger still to come.

  “I’ll race you to the next level,” Joanna said, tensing her body in preparation to start bounding up the stairs.

  Rosalind groaned. “Not today. If you’re bored, feel free to run ahead of me, but I just want to conserve my strength.”

  “But we’re almost there!” Joanna remained beside her, keeping step with Rosalind’s measured ascent, but she was fidgeting impatiently as she spoke. “The sooner we arrive, the more daylight will be left.”

  Rosalind didn’t reply; she had no intention of increasing her pace. Before a jump, she needed to be calm and unhurried. If she sprinted up the stairs, she might gain the advantage of a little more time before nightfall, but it would come at the cost of finding herself standing on the ledge feeling as if she’d been chased there.

  The sun had just come out from behind Tvíburi, and it was still so high that its light had to travel obliquely through the wall of ice around them, bringing a diffuse, bluish glow to the western half of the spiral staircase. As she emerged from the shadow of the central column into the soft blue light, Rosalind contemplated the roots embedded in the ice, most visible as backlit silhouettes, but breaking through the wall in places to sprout the flowers that kept the air replenished. The Yggdrasil had served them well, but they had deceived it horribly. If she’d been alive at the time the tower was begun, she would have bet anyone that the tree would get wise and stop cooperating, long before its roots had accreted a spike of ice stretching halfway to Tvíburi.

  “Can you imagine never having to climb stairs again?” Joanna asked. She made the prospect sound surreal.

  “You don’t think we’ll be raising a tower of our own?” Rosalind teased her.

  “Someone else can do that job.”

  “Really? Who exactly are you volunteering?”

  Joanna said, “The children. I’ll farm the crops, they can farm the ice.”

  “Why not?” They all had their own peculiar fantasies as to how the new life would be—and there was no point cautioning anyone not to get ahead of themselves. However solid its foundations, the tower itself had only kept rising through the sheer force of its creators’ endlessly malleable hopes.

  By mid-afternoon, a section of the wall had grown so bright that Rosalind was left half-blinded by its lingering afterimage each time she walked into the column’s shadow. The stairs were meant to be uniform, and she ought to have been able to climb them with her eyes closed by now, but though she knew roughly where the dozen or so mistakes were in every flight, she didn’t have the kind of flawless memory that would allow her to anticipate exactly when her ascending foot would need to land a little higher, or lower, or farther ahead. In any case, the occasional risk of a mis-step did nothing to make the journey less monotonous. The best thing about this trip was that she wouldn’t be taking the stairs back down.

  “You have to promise that you won’t follow me,” she told Joanna sternly.

  “I don’t even have my glider!” Joanna protested. “I’m just here for moral support.”

  “I wouldn’t put it past you to have something hidden up there.”

  “Only food,” Joanna replied. “But who doesn’t keep a few seeds stashed on every level?”

  “What kind?” Rosalind wondered. She hadn’t eaten at all when they’d rested at noon.

  “None of your business! You’re meant to be flying light!”

  “A handful of seeds won’t kill me.”

  “I vomited in midair once,” Joanna confessed. “It might not have been fatal, but it was certainly distracting. So don’t expect any last minute snacks from me.”

  Rosalind started laughing.

  “What’s so funny?” Joanna demanded.

  “I’ve vomited a lot more than once.” How was it that nobody knew that the team’s most experienced flier had heaved up the contents of her stomach—however meager it was—at least as often as she’d managed to keep it down?

  “At last!” Joanna pressed her hand gratefully against the sign on the wall promising the end of level thirty-six, then raced ahead and disappeared around the curve of the staircase. Rosalind felt a twinge of impatience herself, but maintained her pace; if she was going to break a leg today, she’d rather save that for a more appropriate moment.

  As she stepped onto the landing, she saw Joanna waiting by the exit. “You don’t have to come out with me,” she said.

  Joanna scowled. “I didn’t climb all this way to stay inside.”

  Rosalind hesitated. “What happened to your stash? Have you eaten it already?”

  “No, it’s…” Joanna gestured toward the connecting chambers for level thirty-seven; the pressure difference wasn’t much, but it would still take time to go through and back. “I’ll wait until you’re done here.”

  “All right.” Rosalind walked over to the exit and opened the first door; when she closed it behind her she was in total darkness. She squatted down and started checking the seal, probing it with her finger from bottom to top. A speck of grit had become caught in the strip, so she opened the door again and brushed it away, then repeated the procedure.

  There were six doors in total. The seals were good, but they couldn’t be perfect, and in combination they probably ended up leaking air at about the rate the root flowers were replenishing it.

  Rosalind emerged from the darkness of the final chamber into dazzling sunshine. It was late afternoon, but out on the balcony the light was much stronger than down on the ground. Her skin tingled oddly in the rarefied air, and she could feel the rigid muscles closing off her windpipe, more efficiently than any of the door seals. She’d taken her last breath for a while.

  She put her pack on the floor and slid the panels out, then set to work assembling her glider. Every individual panel had probably been replaced four or five times, and the bracing rods and runners even more often, but she still thought of it as the same one she’d used for her first serious jump.

  Joanna stepped through the door, squinting at the sunlight. They nodded to each other, then Joanna approached and clasped her friend’s shoulder. Rosalind squeezed her hand reassuringly: this had to be done, and it would be over soon enough. But it was a cruel irony that the cost of being here meant that Joanna would be the last to know the outcome, when all their other friends were already waiting at the base of the tower to greet the returning flier.

  Rosalind finished putting the glider together, then spent twice as long checking it. One of the rods felt stiff; she pulled it out and replaced it with a spare. After that, when she pushed against the frame it responded like a single object, precisely as supple and as strong as she needed it to be.

  She propped the glider up against the wall of the tower, turned her back to it, and strapped herself in, securing the belt around
her waist.

  All this time, she’d been so far from the edge of the balcony that the ground had remained out of sight. As she walked forward, the horizon took longer than she expected to appear: it was even farther below her eye-line than the last time. She was afraid to look up at Tvíburi, to compare the angles the two worlds subtended, as if that might drive the point home far more ruthlessly. She was still a long way from the top of the tower, but some kind of dream-logic tugged at her mind, whispering that if she wasn’t careful, she might end up falling toward the wrong world.

  Or rather, the right one, sooner than intended.

  Rosalind turned back and raised a hand to Joanna, who reciprocated, smiling. It had taken a lot of courage for her friend to be here beside her, and a lot of strength to make it seem that it had taken none at all. Rosalind was glad that they couldn’t speak now; there were no words for a moment like this. She reached up and grasped the glider’s handle bars firmly, then turned away and walked quickly through the opening in the balcony, onto the ledge, and into the sky.

  For a moment she descended almost vertically, but then the airflow grew strong enough to tip the glider, and she was facing straight down. Her body continued to harangue her for the unforgivable thing she’d just done, jangling her nerves like a terrified mother screaming at a child caught in an act of suicidal folly, even as the elation induced by the inexplicable lack of a timely impact and agonizing injuries did its best to argue its own case. Both responses were premature—and as the fall stretched on and on, with neither pain nor safety arriving to settle the argument, Rosalind’s instincts began to cede ground to her more considered judgment. Which was a cautious so far, so good.

  Below her, patchy red clouds floated above the ice field. The tug of the air on the glider was still weak, and through the handle bars she could feel how little the frame was stressed. It was hard to think of that as anything negative: how kind of the atmosphere to treat her so gently. But sparing her deceleration now could only have two outcomes: a rougher ride when the deeper atmosphere fought to bring her back to terminal velocity…or an even rougher end, if it failed to slow her sufficiently before the ground completed the job.

  So be it. This was what the light of Leander had demanded of her. Tvíbura’s atmosphere was much thinner than Tvíburi’s, so the fall that would demonstrate whether or not the gliders could land them safely on the twin world, if they dropped all the way from the halfway point, could start from a much lower altitude here to compensate for that disadvantage. If her measurements and calculations were correct, a jump from the top of level thirty-six would be precisely as dangerous as the crossing itself.

  As Rosalind fell past the clouds, the glider began to shudder, and then roll. She shifted her weight, trying to keep it level; it wasn’t tipping very far, but it was lurching back and forth at an alarming rate. Her own skin was oblivious to the turbulence; all she could feel was a pressure and a chill that barely touched her, as if she were lying face down on a slab of ice, but wearing enough clothing to insulate her from most of its effects.

  She surveyed the ground below, hunting for familiar features to note their scale and rate of growth, trying to judge her height and speed against the last jump. She spotted a jagged ravine in the ice, farther to her left than she was used to; had some chance wind pushed her to the east, or had the ground itself, whirling around the midpoint between the worlds, outpaced her own lateral velocity, diminished by altitude?

  A cluster of low gray hills rose up on her right, ancient rock that must have been fresh soil a million generations ago. A patch of whorled ridges appeared in the ice below her, raked by the low sunlight. Whatever her rate of descent, it was clear now that she was traveling faster over the land than last time. That did make some sense: the glider bluntly opposed her fall, but eased the air aside as she moved forward. And if it had diverted a greater portion than usual of the energy she’d gained into horizontal motion, that might spare her some of the force of impact.

  The glider’s rocking grew more violent. Rosalind could feel one of the bracing rods bowing and relaxing under the onslaught. Sustained pressure was one thing, but this repeated flexing was uncomfortably close to her own action when she was trying to snap a thick twig. She wondered if she should risk letting go of one of the handle bars in order to take hold of the threatened rod; after all, she still had the straps around her waist. But then the glider lurched suddenly, sharpening her sense of how dangerously contorted her body might end up if she left even one hand free.

  She could hear the rod squeaking now, the high pitch of its complaint cutting through the noise of the wind. The thickening air buffeted the glider with a relentless, random vigor, as if trying to fold and unfold it along every possible line of weakness, never persisting with the same attack for long, but never failing to return to it later.

  She coughed to open her throat and inhaled deeply, but even as she was savoring the sweetness of the air and the rush of strength to her limbs, the rod snapped, leaving its two halves dangling uselessly from their connecting points. The glider deformed, with two panels pushing inward just right of her head, then everting again under the force of the wind.

  She gazed down at the shuddering blur of the ice field, trying to take comfort from its proximity even as the speed of her descent drained that consolation away. The glider’s frame was twisting, losing symmetry under its new regime, and the wind was both amplifying and exploiting the result. As the glider rolled and pitched, every sudden shift of orientation imposed its own new stresses, distorting the frame a little more.

  And the angles were growing larger, the tilts more precipitous. If the glider overturned, it would break apart completely. She’d somersault with the debris for a while before it was scattered by the wind and she was left tumbling through thin air.

  Rosalind tightened her left-hand grip, then reached down with her right hand and loosened the strap around her waist. As her body swung down, she reached up and snatched at the right handle bar, catching the end and then forcing her clenched fist rightward into a more secure hold.

  She dangled from the handle bars, astonished equally by her own actions and the fact that they seemed to be helping. The glider was still rocking from side to side, but so long as she maintained her grip, she did not believe it would actually overbalance. Wrist straps, she thought, almost calm for a moment. The handle bars needed to be supplemented with wrist straps.

  She glanced down at the ground, but struggled to interpret the faint pattern of blue-white streaks rushing by. There were no hills or ravines in sight now, and she was moving across the ice too rapidly to catch any of the finer details she was accustomed to using to gauge her height. Then she felt the sting of wind-borne dirt on her skin, and understood just how near she was.

  She tucked her knees toward her head, and managed to force her feet onto the tops of the runners. The glider gleefully took the new distribution of weight as an excuse to start gyrating more wildly again, but before it could come close to overtipping, it slammed into the ice.

  It bounced, twice, almost breaking her grip, spraying fine chips of ice onto her face as the runners scraped over the surface like paring knives. Rosalind kept her body rigid, certain that she alone was holding the frame together.

  She tried to see where the glider was taking her, but one of the panels that had retained its position blocked her view. Abruptly, she was airborne again, tumbling, and when the glider struck the ice it was upside down. Rosalind felt an impossible tug on her right arm; she released the handle bar and let half of the glider tear itself away.

  She lay still in the wreckage for a while, afraid that if she tried to move she would discover that she couldn’t. Maybe the best thing would be to rest where she was, until the shock of the impact had passed. But what if she lost consciousness?

  She rose to her feet and took a few tentative steps. One of her legs had been cut, but not deeply. She felt battered, and when she flexed her right hand she knew she’d broken a fing
er, but her back and her limbs were intact.

  Rosalind looked up across the ice and saw the tower in front of her in the distance, glinting in the late afternoon sun. She knew where she was now, and how far she had to travel. It was going to be a long walk, but there was no chance of getting lost.

  As she set off, she turned back to survey the fragments of the glider strewn over the ice. She was going to have to think of the next one as new.

  “I’m convinced,” she said softly. “We can survive the crossing.” She marched toward the tower, repeating the words in her mind, hoping that she’d be able to speak them with conviction by the time she reached her friends. If she’d died, they would have had to go looking for another solution, but now there was no point believing anything else.

  6

  As she walked through the village toward her mother’s house, Rosalind couldn’t help but feel self-conscious at how well-fed she must have looked. Not everyone she passed was alarmingly emaciated, but no one was carrying any flesh in reserve. To be ashamed of the disparity would be foolish; there’d be no point sending the expedition to Tvíburi if they all starved to death waiting for their first harvest. And if the provisions and laborers the villagers had sacrificed to the tower for the last four generations had been a heavy price to pay, she wasn’t exactly taking an easy path herself. Still, she could not recall the last time she’d really been hungry, and she doubted that was true of anyone else in sight.

  When she entered the house, she saw that her mother had invited her paternal aunt, Marion, to the farewell meal, along with Marion’s daughter, Celine. Rosalind embraced them all in turn, though she’d never been close to her father’s side of the family.