by Greg Egan
The tiny dark point erupted with light as the Gnat’s sunstone engines burst into life. “We can still do it,” Pio said softly. The skills that had lofted the Peerless from the home world hadn’t been lost.
The dazzling speck of radiance stretched into a blinding streak of light, then the Gnat disappeared from view. Carlo looked up; at the opposite edge of the window, Ivo’s grandchildren were still gazing down from their father’s arms.
“That looked like a clean burn to me,” Addo opined, as if he’d spent his life watching events just like this.
Marzio said, “It won’t be long now.”
“I don’t think the relay clerks will be slacking off today,” Silvano joked.
The paper-tape writer clanged. Marzio walked over to it and read out the message from the observatory. “Intact and on course.” He let the tape fall from his hand. “Roberto is seeing light of the right size and brightness, from the right direction, heading the right way.”
Carlo wanted that to be enough, but he couldn’t keep silent. “And if the engines were damaged, we’d know? If anything had burned too fast or too slowly…”
“Everything is fine,” Marzio declared. “The launch was perfect. The Gnat is on its way.”
23
When the glare of the exhaust had vanished from the windows and her weight had died away with the shuddering of the engines, Tamara relaxed her tympanum and unhooked her harness. The starlit cabin was dark to her dazzled front eyes, and the only sound she could discern was the soft rhythmic ticking of the nearest clock.
She pulled off her helmet, which remained attached to her cooling bag on the end of a short cord. “Is everyone all right?” she asked. Ada, Carla and Ivo responded in turn, their hesitation sounding more like diligence than a lack of confidence: the answer was too important to be given without a pause or two of mental and physical self-inventory.
Tamara took hold of the guide rope beside her couch and dragged herself toward the center of the cabin, where the three mutually orthogonal ropes, offset slightly, didn’t quite meet. She opened her dark-adapted rear eyes; the view they added was so much crisper than the gray shadows in front of her that it felt as if she had a lantern strapped to the back of her head. She could see her fellow crew members clearly now; Ada had taken off her helmet, and Carla was in the process of doing so. The bright horizon line of the home cluster’s stars shone through the windows, its hoop tilted satisfyingly against the Gnat’s axis. That small geometric hint alone told her that they were not wildly off-course: it was unlikely that any serious mishap with the engines could have left the craft so close to its expected orientation.
“No pain, no dizziness, no hearing problems?” she asked.
“I’m fine,” Ada replied, propelling herself with her legs from the couch. She drifted across the cabin before grabbing one of the transverse guide ropes.
“I am too,” Carla said. Ivo took off his helmet before responding, “My right shoulder’s a bit sore. I think my arm got pinned in an awkward position when the engines fired. It’s not even worth resorbing though; a short rest will fix it.”
Tamara wasn’t too worried; Ivo’s age left him more vulnerable than the rest of them, but this sounded no more serious than the twinges he’d owned up to after the most strenuous of the safety drills. Resorbing and re-extruding a limb was difficult without removing your cooling bag, and though the cabin’s air was cooling them perfectly well, the ideal was to keep the bags on at all times in case there was an unexpected breach.
She said, “Ivo, I want you resting for the next six bells, but when Carla’s checked her own equipment you should talk her through the checks on your own.”
“Right,” Ivo agreed.
Tamara dragged herself away from the center of the cabin and took her place beside one set of theodolites, mounted within the polyhedral dome of a window. Ada, at the opposite window, had her own duplicate instruments, including a separate clock. Tamara began with some star measurements, establishing the Gnat’s orientation precisely, then she aimed the theodolite with the widest field in the direction where she expected to sight the next scheduled flash from a beacon.
“If we had sufficiently accurate clocks,” Carla mused, “we could find our distance from each beacon using the time it takes for the light to reach us.”
Tamara buzzed with mirth. “Accurate to what, a piccolo-pause? While you’re at it, why not use the geometric frequency shift to compute our velocity?”
“Who knows?” Ada interjected. “If people end up shuttling back and forth between the Peerless and the Object, do you think they’ll still be navigating like this after a dozen generations?”
“There’s only so much you can do to make a clock keep better time,” Tamara replied. “We’re already close to the limits of engineering.”
“But nature’s full of systems with their own rapid, regular cycles,” Carla countered. “Light itself, among others.”
“Very practical,” Tamara retorted. “Once you filter out a single pure hue from a lamp, the beam will still be made up of lots of short wave trains: a few cycles at a time, all with random phases compared to each other. Even if you had some way to count the cycles, it would be like listening for the ticking from a vast heap of clocks that started up at random moments, ran for a few pauses and then died.”
“That’s true,” Carla said. “But why not look for better ways to use the same clocks? The light given off by tarnishing mirrorstone as it spits out each luxagen ought to be in phase with the light that stimulated the emission in the first place. If you bounced that emitted light back onto the mirrorstone, looping the whole process around, you might be able to build a source that remained in phase over much longer periods than any kind of natural light.”
“Light that elicits light that elicits still more light?” Ada joked. “That’s starting to sound like the Eternal Flame.”
“Not so eternal,” Carla said ruefully. “The tarnishing would use up the mirrorstone just as surely as any flame consumes its fuel.”
“And you count the cycles… how?” Tamara pressed her.
Carla said, “I’ll have to get back to you on that.”
Tamara felt the dials at her fingertips reach the configuration she’d been waiting for. The beacon’s flash came a moment later—almost certainly from her own clock running slightly fast. But this wasn’t Carla’s brave new world yet, and it was the position of the beacon against the stars that mattered most, not the timing. She recorded the angles on her forearm, then turned the theodolite toward her second target.
“First sighting acquired,” she announced. “Well within the expected region.”
Ivo hummed with pain. “I’m sorry, I’m going to have to take the bag off. Just partly, along the right side.”
Tamara said, “Carla, can you assist him?”
“Of course.”
Tamara watched them without leaving her post. It was a simple enough maneuver, and even if the Gnat chose this moment to split apart and spill them all into the void, Ivo would still have his bag, helmet and two air cylinders with him like the rest of them.
Ivo chirped with relief as he resorbed his right arm, then he spent a lapse rearranging the flesh internally before extruding a new limb. Carla helped him refit it to the bag, running some air through as a test.
“Thank you,” Ivo said. “I think I can check the equipment myself now.”
“There’s no pain at all?” Tamara asked him.
“None. The new arm’s perfect.”
“All right.” With anyone else she wouldn’t have fretted over such a minor injury, but Ivo’s dexterity would soon be crucial.
Tamara turned back to the theodolite in time to catch the flash of another beacon. “Second sighting acquired,” she said. “Within the expected region.” Each flash, observed against the background of the stars, placed the Gnat on a line that passed through the beacon in question. Had the craft been stationary it could have been pinned down at the intersection of tw
o such lines, but even in motion three sightings would be enough to determine its trajectory, and any more would improve the accuracy of the solution. That was assuming that all the errors in the measurements were random, but she and Ada could compare their results as a check against any systematic bias.
“Still nothing?” Tamara asked Ada, puzzled that her co-navigator had yet to report a single sighting. Each beacon only flashed once a bell, but the times were staggered so that one beacon or another was visible every lapse.
“Either my first target’s died, or something on the window obscured it,” Ada explained.
“Why didn’t you tell me?” Tamara was confused. They needed to communicate everything clearly, but Ada knew that perfectly well. In all of the drills, she’d been scrupulous.
“Ivo was telling us about his injuries, I didn’t want to interrupt him.”
“But once he’d stopped—”
“I know,” Ada said. “I apologize.” Her tone was even, with no trace of resentment, but Tamara still felt awkward to be reprimanding her.
There were contingency plans for all the observations to be performed out on the hull if there was serious damage to the windows from an encounter with orthogonal dust, but that was an extreme measure that would make the whole procedure much more arduous. Stray particles from the Gnat’s own exhaust might have left a smattering of subtle defects in the clearstone, but Tamara had never really thought through the proper response to such a minor vitiation.
“Once we’ve finished with the beacons, we should do a systematic check for pitting,” she decided.
“Good idea,” Ada said. A moment later she added, “Ah, first sighting acquired! Within the expected region.”
An ache in Ivo’s arm. A few flaws on a window pane. Tamara had no intention of becoming complacent, but these were the kind of problems she could live with. In the drills, they’d rehearsed the complete disintegration of the Gnat’s cabin, flailing around the mock-up in their cooling bags until they’d learned to use their air cylinders as rockets to bring themselves together on the engine module, ready to make the flight home without a single wall to protect them. She should not be unsettled by anything less.
When they’d both computed their estimates of the Gnat’s trajectory, Tamara’s agreed with Ada’s to within the error bounds. The results implied that they would need to fire the engines again, briefly, in order to aim the Gnat squarely at the rendezvous point, but they could refine their measurements even further by waiting a few bells before repeating them.
To quantify the pitting on the windows, they each made observations of two gross stars that should have been visible from their respective posts, checking for any images that were obscured or distorted. Tamara found two cases where she could see a faint, blurred oval of light in place of a portion of one of the star trails—and by shifting the theodolite sideways while retaining its direction, she could move this aberration across the field, a sure sign that the flaw was in the window itself.
Ada found three. It was not a bad rate. And when the beacon Ada had missed was due to repeat, they were able to use the trajectory data to anticipate its location in the sky much more precisely. This time it did show up, in the dead center of the targeted star field. Whatever the original problem had been, the navigational procedure itself was proving to be as robust as Tamara had hoped.
Carla fetched four loaves from the storage cupboard and the whole crew ate together. The women had agreed to double their usual food intake; they could return to fasting once the mission was over, but for now nothing mattered more than a clear head.
“I’ve been thinking about your luxagen waves,” Ivo told Carla. “They’re not confined entirely to the energy valleys, are they?”
“Not entirely,” Carla agreed. “The bulk of the wave lies in the part of the valley where a particle with the same energy would be rolling back and forth—but at the point where the particle would come to a halt and move back toward the center, the wave doesn’t instantly drop to zero. It just becomes weaker as you follow it out past that point.”
She sketched an illustration, but no one could see it clearly in the starlight so Tamara lit a small lantern and aimed the beam at Carla’s chest.
“And the same is true for a luxagen outside the valley, trying to get in?” Ivo wondered. “The energy ridge around the top of the valley won’t keep out a luxagen wave entirely—even if that ridge would be insurmountable to a particle with the same energy?”
“Right,” Carla said. “Energy barriers aren’t absolute for these waves, the way they are for particles.”
Ivo chewed on his loaf for a while, thinking this over. “Then why are solids stable under pressure?”
“Under pressure?”
“You’ve solved the original stability problem,” Ivo said. “You’ve explained why luxagens in a solid don’t gain energy by radiating, which would blow the whole structure apart. But there’s another problem now: if you squeeze a solid hard enough, why doesn’t it collapse? With the old particle mechanics you could expect the energy ridge between two valleys to keep the neighboring luxagens out. But if a luxagen wave has some probability of getting past that ridge, then over time, under pressure, shouldn’t the luxagens be squeezed together into fewer and fewer valleys? Shouldn’t the rock at the center of every world end up as a tiny, dense core too small to see?”
Carla said, “If you pack more luxagens into each valley, the ridges grow higher, making it harder for the waves to get past them. But the valleys do grow deeper as well, which will help to draw the waves in. I’m not sure if those two effects balance out…”
“And the gravitational pressure grows stronger, as the rock becomes more dense,” Ivo added.
“Yes. So it’s complicated. Let me do some calculations when we get back to the Peerless.”
“Hmm.” Ivo seemed pleased that Carla had no immediate answer to his puzzle. “And in spite of all these new ideas, the power of orthogonal matter to act as a liberator remains as mysterious as ever.”
“It does.” Carla was beginning to sound a bit besieged. “An ordinary, plant-derived liberator must have a distinctive shape that allows it to bind to a particular solid and modify its energy levels—rearranging the rungs on the ladder so a luxagen can climb all the way to freedom, radiating just one photon at a time. A rare fifth- or sixth-order phenomenon becomes a first-order event; a faint trickle of light over eons becomes an instantaneous avalanche.
“But what are the chances that the orthogonal dust that fell on the Peerless before the spin-up had just the right geometry needed to modify the energy levels of calmstone? If you pick some mineral at random, that certainly won’t do the job. If you swap its positive luxagens for negative ones, its structure will be exactly the same as the original. It might interact with ordinary calmstone a bit differently—each will see the other’s energy valleys as peaks, and vice versa, so grains of the two minerals might stick together half a wavelength closer than usual—but that would still be a weak and distant bond. So I don’t see how it could compare to the kind of chemical tricks that plants took eons to learn… and in fact, no plant ever gave us a liberator for calmstone.”
Ada said, “How elusive can the answer be, once we have a mountain of orthogonal matter to play with?”
“We’ve been playing with ordinary matter for generations,” Tamara pointed out. “And we don’t have all the answers there.”
“If the Object turns out to be inert,” Carla argued, “that could mean that we do understand both kinds of matter reasonably well. We’ll just be left with the historical curiosity of the dust that threatened to light up the Peerless… and I suppose that could turn out to have been some kind of freakish bad luck.”
Tamara wasn’t inclined to argue when she had no better ideas herself. But she did not believe in that kind of luck.
Tamara gathered six new beacon sightings, then merged them with Ada’s to sharpen their estimate of the Gnat’s trajectory. A few brief squirts of air
from the attitude-control jets reoriented the craft so the engines could deliver a small push in the required direction. She set the parameters of the burn into the controlling clockwork, then the crew donned their helmets and strapped themselves into their couches again.
The glare from the exhaust through the windows was as bright as it had been at the launch, but Tamara had barely registered her weight against the couch when the burn was over. She’d been worried that using the engines again might exacerbate Ivo’s problem, but he assured her that he was completely unharmed this time.
A bell later, the observations showed their modified trajectory to be as good as they could have wished for. There was no point trying to aim the Gnat down to the last saunter yet, when they still hadn’t pinned down the rock they were aspiring to reach with the same precision. The infrared color trails taken from the Peerless could only tell them so much—but they’d soon be able to make a fresh determination of the Object’s trajectory, with the aid of some decent parallax at last.
Looking out at the familiar stars, Tamara realized that she’d never even searched the sky for the Peerless. It would have been invisible to the naked eye, but she’d felt no urge to hunt for it, no pang of separation at its disappearance. And why should she have felt lost? The light from the beacons and the stars formed a grid of intangible guide ropes, transforming the void around the mountain into a solid, traversable realm.
If they could find a way to hold this ground, building a permanent framework of beacons and observatories, the sky from the Peerless need never be flat again—need never revert to the kind of painted dome that befitted a pre-scientific culture. Whatever triumphs or disappointments the Object had in store, if they could just retain the hard-won benefits of parallax, at least her generation would have that much to its name.
“Four different kinds of rock, at least!” Ada declared excitedly. “Different hues, different textures, different albedos.”