The Clockwork Rocket

by Greg Egan

  Only stubbornness kept her going, and it kept her going too long. When she was forced to stop, retching and shaking, she finally understood what she’d done to herself. She’d brushed the symptoms aside, treating them as ordinary signs of fatigue and telling herself that she could overcome them with sufficient resolve.

  Cursing her stupidity, she lay on the path, trying to cool herself against the uneven slabs of fractured rock, too weak and queasy to go looking for a proper bed of soil. She could feel the heat moving through her flesh, a stinging presence probing for an exit like a swarm of trapped parasites. The thought of dying here embarrassed her; she’d been told what to do, she had no excuses. Triumphantly pointing to her dissected corpse, Ludovico would ban all women from using the observatory. “Look at the size of this bloated creature! With a ratio of surface area to mass less than half that of a man, how could she be expected to survive the rigors of altitude?”

  When night fell, Yalda tried climbing to her feet; on the third attempt she succeeded. She was still nauseous and trembling. She took a trowel from the cart and stepped off the path; there was no bare soil, but there was a patch of shrubs that she believed she could uproot. In good health she could have done it with her fingers alone, but the flesh she extruded now to follow the roots down was too weak to dislodge them. She hacked at the plants with the trowel, severing enough of the woody cores to free a shallow layer of soil. She lay in it and rolled back and forth, crushing worms and scraping her skin on broken roots, trying to maximize her area of contact.

  Some time later she found herself lucid again, gazing up at the stars through a gap in the trees. Fragments of hallucinations lingered; she remembered thinking that she was already in the observatory, adjusting her equipment and wondering why the colors in the star trails were refusing to merge. She’d thought the glowing blossoms above her were flaws in the optics, surfaces chipped in the bumpy truck ride scattering stray light everywhere.

  Contemplating the flowers’ cool radiance, Yalda wondered why nature hadn’t stumbled on some easier way to rid her body of its heat. Why couldn’t thermal energy simply be converted into light and tossed into the sky? Plants were believed to turn the chemical energy they extracted from the soil into light, a small amount of heat, and a new, more accessible store of chemical energy in their seeds and other structures. Animals, burning that secondary fuel, used the energy to move their muscles and repair their bodies, and to make a little light for internal signaling—but the rest became a wasteful, burdensome dose of heat. Why couldn’t they shift more of it into light, instead? Why had her grandfather’s glowing skin signified a fatal pathology, when every living thing would surely have had an easier time if it could shine like a flower?

  Yalda clambered to her feet and returned to the path. Her mind was still a little askew; she found it odd that the cart had sat there for so long, undisturbed. By now, shouldn’t someone have chanced upon it and come looking for its owner—or failing that, ransacked it for valuables?

  Well, no.

  She took a loaf from the cart, sat on the ground, and ate half of it; at that point her body indicated abruptly that it had had enough. She rested for a lapse or two to make peace with the meal, then she set out again, moving slowly, vigilant for warning signs.

  The sun was setting over the plains below, complicating the dusty brown channels with shadows, as Yalda approached the observatory. Renato was sitting outside; he’d not known exactly who’d be coming to replace him, but he’d known the schedule, and Yalda was late.

  She couldn’t help calling out a greeting to him, though even to her the words sounded muffled and distorted, and she’d been told that her speech would be inaudible to any intended recipient. As she drew nearer, she saw the words on his chest: What took you so long?

  Too much stopping to admire the view, she replied.

  I’ll need to show you everything tonight. Renato waited for her to acknowledge that she’d read this, then he replaced it with: I have to leave in the morning. Yalda doubted that Fosco would abandon Renato if he didn’t show up precisely when he was expected, but the delay was her fault, and it would be unfair to put any pressure on Renato to rush his descent.

  Renato showed her the living quarters first. There was a pantry, which she’d replenish from the cart, an inside bed—which she had to admit would be easier to keep free of weeds—and a storeroom with lamps, fuel, and an assortment of tools. No toilet, Renato wrote. Sorry.

  I’m a farm girl, Yalda replied.

  The office was still well-stocked with paper and dye; Yalda had brought a little of both. She was used to doing all her scribbling and jotting and rough calculations on her skin, saving paper for the final, polished results.

  The telescope itself was not housed; the ten-stride-long box that held the heavy clearstone lens in place, its sides built of struts and crossbeams, had only a few skinny, strategically placed boards to block scattered light from entering the optics. The machinery that drove the mount, and the observer’s station, sat inside a kind of swiveling hut at the instrument’s base.

  They entered the hut. In the dwindling light, Renato pointed out a printed maintenance schedule; Yalda replied that she’d read a copy back in Zeugma. Tullia had already told her most of what she’d need to know, though it was something else to have the tracking drive right in front of her, with its terrifying plethora of mirrorstone cogs and springs. The prospect of having to repair it if it broke seemed about as daunting as trying to bring one of Daria’s mutilated arborines back to life.

  There were no lamps in the hut, but Renato moved about confidently, and apparently he could still read Yalda’s skin; maybe all astronomers ended up with eyesight like Tullia’s. When an indistinct gray smudge appeared on his chest, Yalda tentatively gestured that she’d need to touch him, and he spread his arms, granting permission. She moved her palm quickly over his body. Let’s see you line up a star and follow it, he’d written. I’ll feel better about leaving if you know what you’re doing.

  Yalda had used a much smaller telescope at the university, but the principles were the same. Standing by the observer’s bench, she checked the clock by touch. Sitha would be high above the horizon; she had memorized its celestial coordinates, and she scribbled the conversion to altitude and azimuth for two separate times: the coming chime, and the one after. She cranked the telescope to point to the first location; it was well balanced and surprisingly easy to move, but there was something surreal about the walls of the hut turning on their rails as she labored against the azimuth wheel. Then she calculated the changes in the two angles that the star’s location would undergo between the successive chimes, and set them into the tracking drive.

  She wound the drive’s spring, lowered the bench to make more room for herself, then lay down beneath the telescope. A selection of eyepieces sat in a rack beside her; she picked one with a modest magnification that would allow her to view Sitha’s trail all at once, and inserted it into the holder.

  With three eyes closed, she peered through the telescope, adjusting the focus. So soon after sunset, most of the sky would just look gray, but she’d expected a little of Sitha’s trail to be showing in her field already. She checked the time again, and did a few calculations; she should have been seeing something. She reached over and put her hand on the azimuth wheel; there was some play in it, rendering the narrow engraved markings she’d carefully aligned nothing more than rough landmarks. Painstakingly, she nudged the wheel back and forth, until a wisp of red and orange appeared in the corner of the field. The time was getting closer; she kept making adjustments until the whole trail was visible.

  The clock chimed; Yalda released the brake on the tracking drive. The mechanism was not sophisticated enough to follow the star for an indefinite period as it circled the celestial pole, but the telescope’s steady movement from the current location to the predicted one would take most of the burden off the observer for one chime, allowing her to keep the trail centered with just a few corrective
nudges.

  With the hard work done, Yalda finally relaxed and let herself marvel at the telescope’s power. Even in the gray twilight, Sitha’s trail was already brilliant and clear. Most bright stars were bright because of their proximity, and that in turn usually meant that their trails were short; a close neighbor of the sun was rarely rushing by with great haste. But Sitha was an exception, a brilliant oddity fast enough to spread its colors wide. When she made her measurements, it would be her first choice.

  Yalda squeezed out of the way and let Renato check the result of her efforts; he needed to prop himself up on the bench to reach the eyepiece. He remained there, perfectly still, for what must have been a full lapse. Then he climbed out and put a hand on Yalda’s shoulder.

  On his palm he’d written, Well done. You’ll be fine.

  Renato insisted on sleeping outside and giving Yalda the debris-free bed in the living quarters; she would have had no qualms about sharing it with him, but she decided it would be presumptuous to expect him to feel the same way. The clean white sand had a peculiar, slippery texture, but the stone base certainly kept it cool, and Yalda surrendered to her weariness with luxurious rapidity.

  She woke before dawn and unpacked the cart so Renato could use it to take his own notes and equipment back down the mountain. When he had departed, the muffled sound of her footsteps in the thin air took on an eerie, distant quality; she could not expect to see another person for the next three stints. She’d asked Ludovico for four stints, assuming that he’d grant her two at the most, but he must have mistaken the curious familiarity of her Meconio essay for some kind of genuine resonance with his own views. Either that, or he was wise to the whole scam and simply enjoyed watching people scrambling about trying to satisfy his whims.

  Yalda set up her equipment in the observing hut, and spent the morning testing and aligning it; there were parts of the task that were actually easier in daylight. In the afternoon she forced herself to sleep; she needed to nudge herself into a cycle of nocturnal wakefulness, but it was hard to relax when her first observations were just a few bells away.

  She woke around sunset, ate half a loaf, then went to the hut while it was still light. In time, she hoped to be able to operate the telescope’s machinery by touch and memory alone, but for now she was better off starting each session with a clear view of her surroundings, giving her a chance to get oriented.

  With her own bulky contraption clamped over the telescope’s eyepiece holder there was no longer room for the observing bench; she’d taken it out and put it in the office. She cued up Sitha and checked the image by flipping down a mirror that diverted the light into an ordinary eyepiece; it didn’t take long to center the trail, as she’d done the previous night. Then she raised the mirror and let the same light pass into her purpose-built optics. Sliding her body around on the floor, she peered into the second eyepiece. In this view, the trail was replaced by a broad elliptical blur—more compact than the long streak she’d started with, but still multicolored and not remotely point-like.

  She reached into the side of the device and began adjusting the distance between two lenses. The principle was simple enough: if a clearstone prism spread a narrow shaft of white light into a fan of colors, the very same fan fed back through the prism would have to emerge as a single, sharp beam. Sitha’s trail provided a ready-made fan, albeit a far from perfect match. A system of lenses could magnify the overall angular width of the star trail, and then a flexible mirror could tweak the detailed progression across the colors. Yalda’s first task was to get the width right: to shrink the blurred ellipse as much as possible by changing the magnification alone. Then she could tinker with the shape of the mirror to perfect the transformation.

  That had been the plan; the reality wasn’t so simple. Once she started moving the pegs that deformed the mirror, she realized that she was still altering the overall size of the color trail. In theory, it might have been possible to make the two kinds of adjustment independently, but with nothing actually enforcing that the idealization was irrelevant.

  Yalda spent a few pauses cursing her stupidity, then reached back to adjust the lenses again. The ellipse became a little less broad, but also grew thicker in the other direction. The clock chimed; it was time to change the tracking parameters.

  Improvements came painfully slowly. When Sitha drew too close to the horizon to be followed—more than a bell before dawn—Yalda was still not happy with the results. Rather than choose another star and start again from scratch, she decided to call it a night; this way she could preserve all the Sitha-specific adjustments she’d made, ready for a further round of refinements.

  Trudging back toward the living quarters, she stopped to look up at the sky, at all the burning worlds rushing by. Sitha was just one transient neighbor among this staggering multitude. How could anyone hope to wrap the stars in mathematics and draw them into their mind? She was a child fumbling with a clumsy toy, pretending that it granted her magical powers, while this vast, magnificent procession continued on its way, entirely oblivious to her fantasies.

  Yalda slept until mid-afternoon, then she sat in the office planning a new strategy. If she disciplined herself when she reshaped the mirror—always making changes in pairs that largely canceled each other’s effects on the overall spread of the color fan—it might save her some unnecessary adjustment of the lenses.

  Two bells later, lying on the floor of the hut with her skin chafing and her fingers cramped, she allowed herself a chirp of celebration, unperturbed by its distorted tones. Sitha’s trail had finally shrunk to an almost circular patch of light, only slightly bluer on one side than the other.

  It was time to make use of Nereo’s trick. Yalda slipped a mask into the light path that blocked the center of the image, leaving only the faint halo that surrounded the bright core. As her eyes accommodated to the much dimmer partial image, it became easier to see the changes caused by each slight movement of the mirror’s pegs.

  Half a chime later, a single, fine adjustment plunged the view into total darkness. Yalda was ecstatic; Sitha’s image was now smaller than the mask that was blocking it!

  She slid the mask away, expecting to see a tiny, perfect disk of light, but the whole field remained black. She’d bumped the telescope, and it was no longer pointed at Sitha at all.

  Yalda found the star again, but it was hard to keep it centered for long without losing some of her dark adaptation. She tried switching to her left eye each time she had to pull away the mask to correct the tracking, then switching back to the right to resume shrinking the halo, but the two eyes were in cahoots, their pupils contracting in tandem even when only one of them was dazzled. Finally, she tried flipping onto her chest and letting one of her rear eyes take the glare. Amazingly, it worked: her front eyes retained their sensitivity.

  When Sitha dropped out of reach once more, Yalda realized that for the last three chimes she’d been unable to make any improvements; she’d simply been trying out small adjustments and then undoing them. But the halo was very faint now, and it was unreasonable to expect it to vanish completely. She had gone as far as she could with Sitha.

  And she had collected her first set of data.

  Yalda woke early and set about translating the positions of the two dozen mirror pegs into a set of wavelength and velocity values. It was a complex calculation; it took her until late afternoon to complete it, double-checking every step. She plotted the points on a sheet of paper that she’d prepared with a grid; there were some tasks that were just too difficult to perform on her own skin.

  The data curved down across the upper right corner of the plot: with increasing velocity, the wavelength fell. That general trend wasn’t news, but here at last was a hint at the detailed shape. Yalda contemplated some possibilities for the precise form of the mathematical relationship, but she knew that was premature. She needed to see if other stars gave her the same curve.

  Tharak was next, almost as bright as Sitha, though its trail was
less than half as long. Zento was faster, more distant. Yalda was learning what worked and what didn’t, acquiring an instinctive sense of the adjustments she needed to make to shrink the colored ellipses down to sharp white disks. On her sixth night of observations, she managed to peg two different stars, Juhla and Mina, before dawn.

  Laboriously, she added each star’s points to the plot. That the light velocities she was sampling were clustered together was no great achievement; that simply reflected the fixed positions of the holes in which the adjustment pegs sat. But the corresponding wavelengths weren’t scattered too widely, either. Her method was yielding the same pattern, star after star.

  As she ran out of bright targets, the observations became more difficult. After three nights of increasing frustration, Yalda gave up on Thero, unable to distinguish any change in its image despite wildly different settings for the pegs. She wondered if she’d grown sick from exhaustion: if she’d lost Thero’s trail, and was simply hallucinating blotches of light to fill the darkness.

  She rested for two days: doing nothing but eating, sleeping, and taking short walks along the access path. Tullia had warned her not to push herself; nobody was immune to heat shock. After her trouble with the ascent she should have been more careful.

  She tried a different star, Lepato. It took her all night, but her mind was clear now, and by dawn she’d shaped the mirror to conform to Lepato’s faint trail. Starlight was not as fragile or elusive as it seemed; with enough patience, you could even capture its likeness in stone and wood.

  Yalda had been on Mount Peerless for a stint and seven days, and she had data for a dozen stars. It was time to try to make sense of what she’d gathered. Curled up on the observation bench that she’d moved into the office, she contemplated the sweep of the curve across her plot.