by Greg Egan
She stared at the useless air blades atop the workbench, angry now. Ivo had seen his grandchildren; maybe the folk saying was right after all. That sense of completion had made him careless with his own life, and now his sloppiness was going to kill her too. She thought of grabbing the stupid tools and aiming them at the ground, going out in a blaze of glory that would carve her own name into the sagas.
She saw the whole scene from outside her body: she was silhouetted against the inferno she’d made, one blade in each upper hand, the tubes that fed them running down into the Mite. It was a striking image, no doubt about that—but there’d be no witness to record her defiant pose.
The tubes.
She turned to Ivo; he was slumped in his harness, eyes closed. What was she waiting for—his permission to tear the device apart? Carla wrenched the tube off the right-hand blade, then reached down and pulled the other end free from the outlet of its air tank. With her lower hands she groped inside the bottom of the Mite, finding the clock whose dials she’d been checking. The mechanism was completely exposed; Marzio, bless him, hadn’t sealed it away behind decorative panels that would only have made repairs more difficult.
She could feel the shafts that led out to the dials: she was disoriented for a moment, but the one for counting flickers was easy to distinguish by its speed, and the one for pauses not much harder. Once she had those two fixed in her mind, the shaft she wanted—the shaft that turned once every chime—was easy to find.
She probed the space between the back of the clock face and the gear at the base of the shaft. The separation was more than the thickness of the air tube. Better more than less—but the fit would not be tight enough to keep the tube in place by friction alone.
She felt her way deeper into the flying workbench and found a rack of vials, a stock of reagents that Ivo had intended to use in his calorimetry experiments. Each vial was sealed with a thick blob of resin. Carla sharpened her fingertips and sliced the top half off one of the seals, then daubed the sticky resin over the shaft. She did the same with a second seal, using it to coat the center of the gear. Her body was starting to protest against the heat now; mites were crawling beneath her skin, and some pointless instinct was trying to tempt her with visions of a cooling bed of sand.
She bent the air tube, bringing the two halves together so the corner was crimped to an impassably narrow fold—probably not air tight, but the flow it allowed would be a tiny fraction of the flow through the unobstructed width. Then she passed the tube down to her lower hands and pressed the folded end against the resin-coated shaft.
Laboriously, she began wrapping the tube into a spiral, threading the long tails in and out of the narrow spaces of the clock. The tube fought against the curvature and broke free. She sliced off more resin from two more vials and spread it over the gear and the tube. Her skin was stinging all over now, and points of light were moving across her vision.
The tube stayed in place, curled five times around the slowly turning shaft. Carla pulled apart the join between her cooling bag and its supply tank, and interposed the crude timer.
She opened the valve on the air tank slowly, afraid that too much pressure would tear the tube free. She stopped at the point she remembered by touch—well short of fully open, but where she’d last felt enough air flowing across her skin to make some difference. Nothing was coming through the pinch, and there’d been no tell-tale bounce of the tube unraveling.
She was dizzy now, too disoriented to trust herself to check anything she’d done, let alone try to change it. The lights behind her eyelids swarmed and chittered. She tried to picture Carlo, his body pressed against her, but then part of her refused to be fooled or comforted and the image of him spun away into the whiteness.
25
Carla shuddered and vomited a thin sludge into her helmet. She felt as if every scant of her flesh had been pounded with a mallet. She opened her rear eyes and looked down to see blue flames flickering over the gray rocks beneath her. Again? She was about to start buzzing hysterically, before her mind cleared enough for her to realize that the fire didn’t have to be a bad sign at all.
She reached for the clock, afraid that the tube might have become caught in the mechanism and jammed it, but far from being stuck the dials showed a later time than she’d dared to hope for. The Mite had passed its lowest point. She was alive, and she was moving away from danger.
She quickly turned Ivo’s air back on. The flames rose up in response, but she persisted until the heat became threatening, then she cut the flow back a fraction.
Ivo didn’t move. He’d shut off his air long before she had. Carla shivered but refused to start mourning him. A few lapses later the flames went out completely, so she set his cooling bag to full strength. The tube that had saved her life had broken away from the clock shaft and was floating around in front of her in an irritating loop, so she reconnected her tank directly to her bag and stowed the tube inside one of the Mite’s small storage compartments.
Ivo stirred and began rolling his head, as if trying to unkink his neck muscles. Carla let him be until he opened his eyes and appraised the situation for himself.
He reached for her hand. We’re ascending?
Yes.
He didn’t ask her to explain what had happened. After a while, he took his hand away and began loosening his harness.
Carla’s first instinct was not to intervene; if he’d been injured by the ordeal he might need to move to make himself more comfortable. It was only when he was entirely free of the harness and on the verge of pushing away from the Mite that she understood and grabbed hold of his arm. She was not at her strongest, but he was in no condition to resist her.
She took his hand again.
Better that I die, he wrote.
Carla didn’t know what to say to that, but she resisted the urge to slap him across the head. He’d made an honest mistake that had put them in danger, but they’d both survived. He’d undermined the Gnat’s chances of capturing the Object, but a future mission could always try again, better prepared. And though his reputation would be marred by this débâcle, he’d still been instrumental in the fact that the Gnat had flown at all.
The contamination was an uncharacteristic lapse. Carla had seen Ivo inspecting the air filters with a microscope, to ensure that there were no tears in them. But if the problem hadn’t arisen through carelessness, what had been its root? A misunderstanding of some kind. Which process was better understood, though: the filtering of dust from air… or the behavior of air in the presence of orthogonal matter?
What if the air is pure? she wrote.
Ivo didn’t dignify that with a reply. There was no better established fact in all of chemistry than the inertness of air. Nobody had a perfect explanation for this, but it had long been conjectured that each particle of the gas was a spherical cluster of luxagens, arranged in such a way that Nereo’s force canceled almost perfectly outside the cluster.
Still, when air bounced against rock it was Nereo’s force that made it bounce. Once an air particle actually made contact with something, the luxagens within couldn’t hide themselves completely. So it wasn’t inconceivable that orthogonal rock could react differently to air built from positive luxagens than it would to its own, presumably innocuous, swapped version. Let everyone on the Gnat and the Peerless share the blame, then, for failing to imagine that possibility.
Carla hadn’t thought to try to get a spectrum of the flames their spilt air had summoned, but she’d have bet anything that the same dominant spectral line as they’d seen before would have been present. Every mineral’s structure was complicated in a different way, and even a particle of air had its own elaborate geometry, but that one line screamed simplicity.
What was the UV frequency? she wrote.
Ivo gave her the wavelength.
No, the frequency.
I have no idea, he replied. His spectrograph was calibrated for wavelengths; it was the convention among chemists to express al
l their results in those terms.
You can’t work it out? Carla wasn’t so rattled that she couldn’t do it herself, but she wanted to keep Ivo engaged.
He humored her, carrying out the calculations on the patch of skin they shared. The spectral line’s wavelength wasn’t much greater than the minimum wavelength of light. Yalda’s formula put the frequency at near enough to three tenths the maximum; Ivo dutifully multiplied this out to get roughly a dozen and three generoso-cycles per pause.
Carla didn’t care about the final number; it must have been nice for the ancestors that a “pause” was a convenient fraction of the rotational period of the home world, but it had no bearing on anything else in the cosmos. All the real physics was in the pure ratios of numbers, untouched by the whims of history and convention.
The UV line they’d seen in every fire on the Object was three tenths the maximum frequency of light. Every photon of that frequency was traveling at a speed that tilted its energy-momentum vector steeply enough to make it lie at three tenths its original height.
But three to ten was the ratio Patrizia had found, when she’d fitted her curves for colliding particles to the data for light scattering off luxagens. A luxagen’s mass was three tenths the mass of a photon. So every photon in this ultraviolet line possessed the same energy as a stationary luxagen.
What if a luxagen became a photon? Carla wrote.
She could feel Ivo’s body shaking as he buzzed with mirth. Source strength? he replied.
He was right to object; a luxagen carried one unit of source strength, a photon had none. And from Nereo’s equation you could prove with mathematical certainty that source strength could never simply vanish.
Mathematically, though… it could cancel.
One positive luxagen, one negative, Carla suggested. Strictly speaking, the only quantity that had to remain unchanged was the total source strength: the count of positive particles minus the count of negative ones. The individual numbers didn’t need to stay fixed.
Ivo didn’t respond. Carla looked to his face; he appeared to be mulling it over.
She tried to imagine the process. Two luxagens came together, one of each sign… but instead of them simply bouncing off each other, the original particles were destroyed and two photons emerged.
It sounded absurd, but what principle did it violate? Source strength would be conserved, since the total was zero both before and after. Energy would be conserved, so long as each photon had the energy of a single luxagen. Momentum would be conserved if the photons were traveling in opposite directions, making the total zero before and after.
Is this charity? Ivo asked her.
Carla was taken aback. He thought she’d concocted the whole theory just to get him off the hook with Ada and Tamara. Of course not!
Luxagens vanish? Ivo’s face made it clear that he found this no more plausible than a conjuror’s claim to make a vole disappear from a sealed box.
Only in pairs, Carla replied, as if that were enough to make the idea respectable.
But no wonder it sounded preposterous: where else could they have seen positive and negative luxagens come together, with any hope of understanding the result? Not in the fleeting, uncontrollable events on the hull of the Peerless. Not in the light from the Hurtlers that menaced the ancestors; they hadn’t even known the luxagen’s mass or grasped the link between energies and frequencies.
Only here. Wherever this beautiful new physics carried them, it could only have begun here.
By the time the Gnat was fully re-pressurized and Carla had removed her cooling bag, she’d given Ada and Tamara a version of the Mite’s misadventures that never even raised the possibility of contamination in the air tanks.
“Air sets orthogonal rock on fire?” Tamara sounded every bit as skeptical as Ivo had been. “Are you sure there wasn’t some other—?”
“Air is made of positive luxagens,” Carla interjected. “Just like any other ordinary matter. That’s all it takes to set orthogonal matter on fire.”
She offered an illustration.
“The length of each line is the mass of the particle, and its height is the particle’s energy. Nereo’s arrow agrees with our time axis for positive luxagens, and opposes it for negative ones.”
Ada said, “Doesn’t a positive luxagen repel a negative one, close up?”
“It does,” Carla agreed.
“And the force pushing them apart goes to infinity as they get closer,” Ada added. “So how do they ever get to touch?”
“Luxagen waves don’t respect energy barriers absolutely,” Carla replied. “The wave for two luxagens with opposite signs will lie mostly in the energy valley where they’re far enough apart for Nereo’s force to become attractive—but it won’t be entirely confined to that valley, and it will allow some probability for the two luxagens to make contact. The fact that the probability is so small is why the process is relatively slow—why we had measurable delays before the flashes when we dropped the projectiles. But slow or not, once it happens, it happens.”
Ada looked dubious. Carla said, “Let me show you another process that’s worth thinking about.”
Ada stared at the new diagram. “A photon comes in from the left, a positive luxagen comes in from the right. They collide and bounce off each other.”
“Nothing too strange in that?”
“No,” Ada conceded.
“This picture is the same as the last one,” Carla said. “I just rotated it by a quarter of a turn. If a photon and a luxagen can bounce off each other like this, the version of events where two luxagens turn into two photons must be possible as well. It’s exactly the same thing, seen from a different viewpoint.”
Ada looked annoyed, but Tamara gave a chirp of delight.
“It’s an audacious theory,” Tamara said. “But where does it leave us? If we can’t even touch orthogonal rock with air, how are we going to get a sample to calibrate the reaction?”
“We can’t get a sample,” Carla replied. “But if these pictures are right, they tell us most of what we need to know. The UV line outshines everything else in the spectra, and if we dump a few hefts of calmstone onto the Object almost every luxagen in that heap of gravel will end up suffering the fate I’ve drawn. We know the energy and momentum produced by that reaction, so we can calibrate everything using that as our first guess.”
Tamara turned to Ivo. “What do you think?”
Ivo had been quiet since they’d returned to the Gnat, letting Carla give her version of events without comment.
“I don’t know what to make of this hypothesis,” he said. “But if we drop enough material to have a measurable effect on the Object’s trajectory—by Carla’s calculations—then we’ll have a chance to see how well her prediction bears out. If we’re going to be forced to work by trial and error, we might as well make the first trial count for something.”
Carla computed the total mass that needed to be flung onto the surface, but left the details of the orbit that would deliver it to Ada and Tamara. When Ivo had checked her arithmetic—and had her justify every assumption behind the numbers—she took on the purely physical task of winding the large catapult. Whatever damage the hyperthermia had wrought on her body, as she struggled against the wheel the pain and tenderness began to leave her.
Ivo loaded the catapult’s chamber, working the levers inside the hull that shifted measured scoops from the calmstone store. Compared to the tiny pellets they’d dropped before, this new bombardment was like a declaration of war. Carla had tried to balance the likelihood that some proportion of the material would be blown clear of the surface, unconsumed, against the possibility of an unanticipated process amplifying the whole effect. Though she’d never set eyes on Gemma, she’d heard the tale of the dark world that became a star repeated endlessly since childhood.
But Gemma had been ignited by a Hurtler, traveling at an infinite velocity relative to the rock of the planet. Sheer momentum would have carried the Hurtler deep
below the surface before the annihilation began, trapping much of the heat produced and rendering it far more damaging. She did not believe that an explosion that was open to the void would start a wildfire.
Ada wore the blindfold this time, but she followed a clock with her fingertips and called out the command to launch. When Ivo released the catapult, Carla could see the pile of brown rubble tumbling away in the starlight, receding almost as slowly as the Mite when it began its journey. But in five bells’ time the rubble would take a tighter curve around the Object than she and Ivo had done, and find a wall of orthogonal rock in its way. By then, the Gnat would be diametrically opposite the point of impact, shielded from the blast.
The wait was as tense as the Mite’s descent, but at least they could converse normally. “Who wants to break the news to Silvano?” Ada joked. “I don’t think he’ll be farming much wheat here.”
“Or mining much fuel,” Tamara added, “unless we can think of a way to handle it.” She turned to Ivo. “Is orthogonal rock a fuel, or a liberator?”
“There is no right word for it,” Ivo said. “Chemistry is about the rearrangement of matter. If matter disappears, that’s something else entirely.”
Half a bell before the impact, Carla handed out loaves, trying not to think about the fast she’d have to go through when she needed to return to her old mass. What mattered now was that they kept themselves alert, prepared to respond to any more surprises.
With one tap of her hand, Tamara deftly reversed the trajectories of the last crumbs that had been floating away from her mouth, then she took hold of the drive’s emergency start lever. If the reaction they provoked made a mockery of Carla’s guesses and blew the Object apart, the very alignment that had been intended to provide them with the most shielding from the blast would see the bulk of the flaming remnants propelled in the direction of the Gnat.