The Clockwork Rocket

family.

Eusebio opened his eyes. She saw him register her presence, her gaze. She expected to be questioned, but he remained silent, as if everything between them was clear to him already. If she lay beside him now, it would not take much persuasion. They both wanted the comfort of this, and the promise of life for their children.

But as she took a step toward him, Yalda felt a chilling clarity spread across her mind. She wanted comfort —not oblivion. And whatever Eusebio wanted, it was not the encumbrance of her children. Nothing in this beguiling vision had any connection to their real plans, their real needs, their real wishes. The oldest part of her believed it could survive this way—as her mother had survived in her—but even that blind hope was misplaced. Eons of persistence would count for nothing when the sky lit up with orthogonal stars.

She said, “The Hurtlers woke me. I’m sorry I disturbed you.”

Eusebio said, “That’s all right, Yalda. Just try to sleep.” He closed his eyes.

Yalda returned to her bed, but she was still awake at dawn.

After breakfast, Amando came in his truck to take Eusebio to another test launch. Eusebio didn’t demur; the sheer momentum of the project still counted for something. At least until the money ran out.

Nereo walked Yalda to the station. “I’m sorry we didn’t have a chance to talk optics,” he said. “I’ve been tinkering with your light equation recently, trying to find the right way of adding a source.”

“Really?” Yalda was intrigued. The equation she’d come up with five years before described the passage of light through empty space, but said nothing about its creation. “How far did you get?”

“I took some inspiration from gravity,” Nereo said. “Think about the potential energy of a massive body, such as a planet. Outside the body, the potential obeys a three-dimensional equation very similar to the one for light: the sum of the second rates of change along the three directions of space is zero. Inside the body, instead of zero that sum is proportional to the density of matter.”

“So you think I should add a similar term to the light equation, to represent the light source?” Yalda thought about this. “But a light wave involves a vector with four components; the source would have to be the same kind of thing.”

Nereo said, “What about a vector that’s aligned with the history of the light source—pointing into its future —with the length of the vector proportional to the density of the source?”

“That’s the right kind of vector,” Yalda conceded, “but what would this ‘density’ actually be describing?” He didn’t mean mass; this was something else entirely.

“Whatever property matter needs in order to produce light,” Nereo replied. “We don’t have a word for it yet; maybe ‘source strength’? But assuming we can put a number on it, we can talk about how tightly it’s packed: the ‘source density’.”

“Hmm.” Yalda worked through the implications as they entered the station. “So if we’re looking at the simplest case, where everything is motionless, only the time component of the equation would be non-zero, and it would have solutions a bit like gravitational potentials.”

“But not quite the same,” Nereo stressed. “These solutions oscillate as you move across space.”

Yalda’s train was boarding; they didn’t have time to take the discussion further. Nereo said, “I’ll send you a copy of my paper when I’ve written it.”

On the journey back to Zeugma, Yalda managed to find one solution to Nereo’s equation herself: the equivalent of the potential energy around a motionless, point-like mass.

For gravity, it had been known since the work of Vittorio an era and a half ago that the potential was inversely proportional to the distance from the mass. For light, the overall strength of the wave diminished with distance in exactly the same fashion, but it also underwent an oscillation with the smallest possible wavelength— that of a wave traveling at infinite speed. All of this was just an idealization—the need to wrap around the cosmos smoothly would impose additional constraints and complications—but it was a start.

Yalda pondered the curve. Perhaps there was something like this present in everything from sunstone to a flower’s petals. Light at the minimum wavelength would be invisible, so when the source was motionless the petals would be dark. But a system of oscillating sources, suitably arranged, might well be able to twist the original pattern into a set of tilted wavefronts, corresponding to light slow enough to lie in the visible realm.

Exact solutions when the source was in motion wouldn’t be easy to find, but the general idea made sense; to generate a wave that moved energy around, something had to feed in the energy in the first place, whether that meant jiggling the end of a string or vibrating your tympanum in air. That the creation of light would draw true energy out of an oscillating source—increasing its kinetic energy, rather than draining it—was a peculiar twist, but that was rotational physics for you.

There was, Yalda realized, another strange twist, arising from Nereo’s choice of a vector aligned with the particle’s history as the term to add to the equation. If you accelerated a light source long enough to curve its history around a half-circle and send it backward in time… then once it was settled on its new, straight trajectory it would be surrounded by a wave that was the opposite of the original. Compared with its earlier self, the pattern of light the source generated would now appear upside-down.

But how could a featureless speck of matter tell which way it was traveling through time? The arrow of time was meant to come solely from entropy’s rise; a lone particle couldn’t grow disordered. A wave changing sign wasn’t as dramatic as the difference between a stone being smashed and the shards spontaneously reassembling, but it did imply that there might be two distinguishable kinds of source, at least when they weren’t moving too rapidly: one “positive”, one “negative”.

It was evening when the train pulled into Zeugma. Yalda didn’t have the energy to face the four squabbling brats at bedtime, so she wandered around the city center for a while, killing time until she was sure they’d be asleep.

When she finally braved the apartment, she was surprised to find Lidia sitting in the front room, in the dark.

“I thought you’d be at work,” Yalda said. “Did they change your shift—or was there some problem with the helper?” The whole point of asking Eusebio to pay her had been to hire someone to watch the children in her place.

“The helper was fine,” Lidia said, “but we didn’t need her tonight.”

“So you’re working mornings again?”

“No, I’ve lost my job.”

“Oh.” Yalda sat beside her. “What happened?”

“Did I tell you about my new supervisor?”

“The idiot who kept asking you to become his deserted brother’s co-stead?” Yalda didn’t believe the rumor that Lidia had murdered her own co, but there were times when it might have been helpful if more people had taken it seriously.

Lidia said, “Two days ago he came up with a new offer: either I hand the children over to his brother, or he tells the factory owner that I’ve been stealing dye.”

“But you only ever took from the spoiled batches. I thought everyone did that!”

“They do,” Lidia replied. “But he told the owner I was taking good jars as well. He had some kind of paperwork prepared, inventory records that made it look plausible. So the owner believed him.”

“What a piece of shit.” Yalda put an arm across her shoulders. “Don’t worry, you’ll find a better job.”

“I’m just tired,” Lidia said, shivering. “I used to think everything would be different by now—by the time I was this old. But what’s changed? There aren’t even women on the Council.”