by Greg Egan
As Yalda wandered among the guests, she struggled to keep her feelings from turning into grief or self-pity. It might have been better to have vanished without ceremony, but if it was too late for that she could still try to make the break as painless as possible. The day before, she had bid farewell to Lucio, Claudio and Aurelio in a final letter—short and simple, as Lucio had never learned to read as well as his co—but even without this parting note they would not have been expecting to see her again. When Giusto died and she did not visit the family to join them in mourning, they would have understood that she was never coming back. She still wished her brother and her cousins well, but she could not be part of their lives. Now she had to start thinking of her friends in Zeugma the same way.
Daria found her in the courtyard, and instead of offering distracting small talk chose to tackle the subject head-on. “In the old days,” she said, “every dozen generations, families would split up and the travelers would move a whole severance away. With no mechanised transport, that was it: no hope of visits, no hope of returning.”
“Why?” Yalda had heard of the custom, but she’d never understood its purpose.
“They thought it was healthy, to bring new influences to the children.”
“A separation wasn’t enough?” The new farm her father had bought had been that far from the one where she’d grown up.
Daria said, “There was less travel then, less mixing of people for other reasons. This was a way of forcing it.”
Yalda buzzed skeptically. “Was it worth the effort? Were the children any healthier?”
“I don’t know,” Daria admitted. “It’s difficult to study that kind of thing. But every biologist accepts that influences spread from person to person; some make us sick, some make us stronger. I’m glad your travelers will be coming from every city; at least they’ll be starting with a good mixture.”
“So what do we do if the mixture grows stale?” Yalda wondered.
“Learn enough about the things themselves to make new ones of your own,” Daria replied smoothly.
“Ah, as simple as that.” Was an influence a kind of… gas? A kind of dust? How did it leave and enter the body? What exactly did it do when it encountered your flesh? Nobody had the faintest idea.
Daria said, “If the Peerless comes back without that trick, I’ll just have to hang on long enough to work it out for myself.”
“What are you waiting for?” Yalda scolded her. “The Peerless isn’t an excuse for everyone else to take a four-year holiday. You should think of it as a contest; you should be trying to beat the travelers to as many discoveries as possible. We might have the advantage of time, but you’ll always have the advantage in numbers.”
Daria was amused by this idea, but not dismissive. “It would be a matter of some pride,” she conceded, “if we could greet them with at least one triumph of our own.”
Lidia entered the courtyard, accompanied by Valeria and Valerio.
“You missed the speeches,” Daria informed them.
“I’m glad to hear it,” Lidia replied. She embraced Yalda. “Is it true that you’re going to be a Councilor on the flying mountain?”
“Dictator, I think,” Daria corrected her.
Yalda said, “More like a factory supervisor: as far as I’m concerned, my main job will be to ensure that all the machinery is being operated safely. For the first year or two that’s likely to take precedence over everything else, but once the technical issues are under control we’ll have to make arrangements for… ongoing governance.”
“That sounds promising,” Lidia enthused. “In a city of runaways, no one is going to settle for anything less than a fair division of power.”
“Do you want to come and organize that for me?” Yalda pleaded. “Right now, I’m just hoping that any heated disputes can wait until after I’m dead.”
Lidia pretended to be taking the invitation seriously, but it was clear what her answer would be.
The children had been hanging back, waiting for Lidia to finish her greeting. Valerio embraced Yalda awkwardly then went looking for food, but Valeria didn’t flee.
“Are you enjoying your studies?” Yalda asked her.
“I like lens design,” Valeria replied.
“It’s an important subject.” Eusebio had promised to hire Valeria to work on the fire watch project—and cheap, light, wide-field telescopes would be part of the equipment every village would need.
“I brought a gift for you,” Valeria said. She handed Yalda a wooden tube.
“Thank you.” Yalda removed the cap and pulled out a sheet of paper.
“It’s beautiful,” she said, touched and intrigued. “What is it?”
“Do you remember Nereo’s equation?” Valeria asked her.
“Of course.” Yalda had not had the time to do any original work in optics for years—and Nereo himself had died soon after she’d visited him in Red Towers—but she’d been longing to pursue his ideas about the interactions between light and matter.
“You explained it to me,” Valeria said, “three years ago, when I’d just started at the university. And you showed me the solution for a source consisting of a single point—a ‘luxagen’.”
“I remember.” Yalda had been trying to convey to her just how little was still known about the subject, while offering a glimpse of one crack in their ignorance that might yet be widened.
“Not long after that,” Valeria continued, “we were studying gravity. And I learned that the first thing Vittorio did after guessing the potential energy for a mass concentrated in a single point was to calculate what that meant for a mass arranged as a spherical shell.”
“Ah.” Yalda examined the sheet again, overcome with pride and delight. “And this is the equivalent, for the light field?”
“Yes.”
Yalda studied the results. “These sizes you’ve written, they’re the radius of each shell?”
Valeria said, “Yes. Vittorio showed that, outside the shell, the gravitational potential energy was exactly the same as it would have been if all the mass were just concentrated at the center, so I was hoping the light field would follow the same rule. When it didn’t, I thought I’d made a mistake, so I had to wait until I’d learned a different technique that I could use as a cross-check.”
Yalda was still trying to absorb the implications of what she was seeing. “For some sizes of shell… the external field vanishes completely?”
“That’s right,” Valeria confirmed. “That happens whenever the radius is a multiple of half the minimum wavelength. And when it’s an odd number of quarter-wavelengths, the interior field vanishes.”
Yalda would never have guessed that the undulating field from a myriad of point sources could cancel exactly over any extended region—let alone an infinite one, and from such a simple geometry. No wonder Valeria had doubted her first calculations; it was as if someone had claimed that a gross of clanging bells could be rendered inaudible merely by arranging them in a circle of just the right size.
“Have you shown Zosimo and Giorgio?”
Valeria said, “I wanted you to see it first.”
Yalda held the sheet aside and embraced her. “It’s a beautiful gift. Thank you.” Your mother should have been here to see this, she thought, but the words were too strange to speak aloud.
Lidia said, “I don’t want to risk annoying you both… but are these pictures of anything real?”
Yalda started to explain about the light field around the hypothetical particle Nereo had dubbed a luxagen, and how Valeria had added up that field for a multitude of luxagens arranged in a shell, but Lidia hushed her. “I meant something we can all see and touch.”
Yalda thought for a while. What did it mean that luxagens were normally surrounded by furrows in the light field, but in the right configuration the landscape around them could become perfectly flat?
She said, “How about something you can feel, but never see?”
“What, thin air?”
Lidia joked.
“Exactly.” Yalda exchanged a glance with Valeria; she looked baffled for a moment, but then she understood.
“Nereo hoped that the light field might account for all the properties of matter,” Yalda explained. “Not just burning fuel and glowing petals, but how a rock holds together instead of crumbling, and how it resists being crushed down to a speck. Why dust is sticky, and fine dust even stickier… but an inert gas like air, which everyone thinks of as the finest dust of all, doesn’t stick to anything, not even itself.”
“And these pictures are the answer?” Lidia was bemused.
“Not to everything,” Yalda said, “but perhaps they’re a clue to the last puzzle. It’s not hard to see how solids could be built from luxagens: the particles would sit in the troughs of each others’ serrated fields, which would hold them a certain distance apart from each other in a kind of array. Two stones you pick up off the ground won’t stick to each other—even if you polish them flat—because with such vast numbers of particles you wouldn’t expect them to form a single, perfect array. But a speck of dust is lighter, and small enough for the internal geometry to be less of a mishmash; there’s more chance for everything to line up and make two specks adhere. So if gases are built from luxagens too—and are so fine as to be invisible—why don’t they stick together even more strongly?”
Lidia still didn’t see it; Yalda looked to Valeria for support.
“Suppose you arrange the luxagens in a spherical shell of just the right size,” Valeria said. “Then the force that makes most regular arrangements of luxagens sticky will vanish outside the shell. A shell like that won’t stick to anything—so maybe that’s what gases are made of.” She hesitated, then turned to Yalda. “I don’t think that quite works, though. If you look at the potential energy curves at the edge of the shells with no external field, they always slope in such a way as to produce an outward force—so wouldn’t that tear the shell itself apart?”
Yalda checked the diagrams. “Ah, you’re right,” she said. “So there must be something subtler going on.”
“See, we don’t have the answers here,” Daria joked. “We need the Peerless to go out and fetch them for us.”
“But this is close,” Yalda insisted. “If it’s not the whole story, it’s still a powerful hint.”
Yalda could have talked optics with Valeria all night, but that would only have made parting more difficult. “Have you seen your brother recently?” she asked.
“Two days ago,” Valeria replied. “I looked after the children while he went to the factory.”
“But you need to study!” Yalda hadn’t meant to blurt out a rebuke, but she couldn’t bear the thought of Valeria jeopardizing her own chances. “You can’t afford to do that all the time,” she added.
“I don’t; Valerio helps too. And Amelio has other friends as well.” Valeria was beginning to look uncomfortable; Yalda let it drop. Lidia and Daria would have helped with the children if Amelio had allowed it, but he was still angry with them for trying to persuade him and Amelia to wait. Yalda would never see Tullia’s grandchildren, but she suspected Amelio would relent in the end and heal the rift with his other honorary Aunts.
Lidia said, “I’m glad I missed the speeches, but I hope I haven’t missed all the food.” Yalda led them indoors, where Giorgio’s children were still running back and forth from the pantry, keeping everyone fed.
Yalda tried to keep the conversation from growing too solemn; she had no intention of making some kind of earnest declaration to each one of her friends, summing up and attempting to put right everything that had passed between them—as if they were business partners settling accounts. She had apologized often enough to Lidia for the unequal share she’d taken in the burden of raising the children, thanked Giorgio and Daria for their help at the times she’d received it, and offered encouragement to Valeria and Valerio whenever it had seemed likely to be well received. There was nothing more she could achieve with a few rushed words, and the last thing she wanted to do was sound like someone making death-bed reparations.
Around midnight, guests began making their excuses. Dozens of people from the university and the Solo Club—acquaintances with whom Yalda had played dice or argued some point of philosophy or physics—bid her good luck with the flight then departed without any fuss.
With the house almost empty, Giorgio approached her.
“Can we see you off at the station?” he asked.
“Of course.”
Yalda had no luggage; everything she owned was in Basetown already, and everything she’d need was in the mountain itself. The six of them walked together down the quiet streets, with Gemma high above them lighting the way.
On the platform, with just a lapse to departure, Valerio started humming and wailing. Yalda was bemused; they hadn’t been close since he was three. She bent down and embraced him, trying to quieten him before anyone else joined in.
“I’m not dying yet!” she joked. “Wait a year and a day, then you can mourn me. But don’t forget that I’ll have had a long life by then.”
Valerio couldn’t really make sense of this, but he recovered his composure. “I’m sorry, Aunty. Good luck with your journey.”
“Look after your brother,” she said. And try not to imitate him.
With her rear gaze, Yalda saw the guard scowling at her; the engine was already running and sparks were rising into the air. She released Valerio, raised a hand to the others, then leaped into an empty carriage as the train began to move.
She sat on the floor, eyes closed, braced against the shock of amputation.
From a distance, Mount Peerless appeared almost unchanged from its pristine state. As the train brought her closer, Yalda struggled to identify anything more than a slight thinning of the vegetation since the first time she’d set eyes on the peak. The mountain roads that had been widened and extended were still invisible from the ground, and even the mounds of excavated rubble from the new trench were lost in the haze.
Basetown was the end of the line. When Yalda walked out of the station the main square was deserted; where the markets had stood just two stints before there was bare, dusty ground. All the construction workers and traders had departed, and though there were probably dozens of Eusebio’s people still around for the final cleanup, on her way to the office she encountered only fellow travelers. As well as inducing an eerie sense that she’d already parted company with the rest of the world, this raised the problem that, out of the six gross or so on the final list of recruits, she’d only managed to memorize a tiny fraction of their names.
“Hello Yalda!” a woman called from across the street.
“Hello!” That she knew the woman’s face only made it more embarrassing.
“Not long now,” the woman said cheerfully.
“No.” Yalda resisted the temptation to take a bet on, “Time to tell your co to buy a telescope!” However good the odds were that this would be apt and welcome, it wasn’t worth the risk of alienating someone who was actually bringing her co along for the ride.
Eusebio was in the office, poring over reports with Amando and Silvio; Yalda didn’t disturb them. Her own desk was almost empty; before she’d left she’d been double-checking calculations for the navigational maneuvers the Peerless would need to perform if it encountered an unexpected obstacle. It looked as if they’d found the perfect route for the voyage—an empty corridor through the void, oriented in the right direction and long enough to take an age to traverse without coming close to a single star—but once they were above the atmosphere it was possible that fresh observations would reveal a hazard that needed to be side-stepped.
She worked through the details one more time. If the obstacle wasn’t too large, they’d be able to swerve around it and still reach infinite velocity—albeit with even less fuel remaining for the rest of the journey than originally planned. There was no way of guaranteeing the Peerless’s triumphant return, but if the travelers failed to attain an or
thogonal trajectory—with the Hurtlers tamed and time back home brought to a halt—they would have no advantage left at all.
When his assistants had left, Eusebio approached Yalda. “How did it go with your friends in Zeugma?” he asked.
“It was fine.” Yalda didn’t want him struggling to empathize, telling her that he understood how she must feel. She said, “I think we need name tags.”
“Name tags?”
“For the travelers. Something we can all wear on necklaces, so we know who’s who.”
Eusebio looked harried; Yalda said, “I’ll organize it myself, don’t worry about it.”
“All the workshops are empty,” he said, spreading his arms to take in the whole ghost town. “Not just of people, of tools and materials.”
“Not inside the Peerless, I hope.”
The suggestion appeared to take Eusebio by surprise, but then he found himself with no grounds to object to it. “I suppose that makes sense.” He checked a wall chart. “Workshop seven?”
“Yes.”
Yalda found a spare copy of the recruits list. When she and Eusebio had first set out to sign up volunteers she could never have imagined filling a dozen sheets of paper with their names, but even this final census amounted to less than the population of her home village.
There were still trucks shuttling between Basetown and the Peerless every bell, but they were no longer in high demand; she ended up alone save for a driver she didn’t really know, so she sat in the back by herself and watched the town receding into the haze. She wondered what would happen if she went to Eusebio and said: I’ve changed my mind, I’m staying. There were other people with the skills to take her place in everything she was expected to do; the project would not fall apart on the spot. But she knew she was caught in the trap she’d used herself on so many others: she was vain enough to believe that her presence might make the difference between success and failure. And if the thought of deserting the Peerless to while away four years on the ground waiting for the world’s problems to be solved elsewhere made a thrillingly delinquent fantasy, the one thing she found more terrifying than the prospect of a journey through the void was the possibility of those four years of anticipation ending in silence.