Greg Egan - The Clockwork Rocket

Paolo said, “I understand.” He was silent for a while. “But how large a rocket would be large enough? No one knows. It’s a very big risk to take, based on nothing but guesswork.”

“If it stops the Hurtlers from destroying us,” Eusebio replied, “how could it not be worth it?”

“But that judgment depends not only on the travelers succeeding,” Paolo reasoned, “but also on an absence of other solutions. The same resources spent here on the ground might solve the problem more efficiently. I can’t speak for others, but I do like having my own money doing its work somewhere nearby, where I can watch over it.”

“Yes, sir.” Eusebio lowered his gaze. The rejection could not have been clearer.

Paolo turned to Nereo. “So, perhaps the Eternal Flame could be made real?”

“Perhaps,” Nereo conceded reluctantly. “But there are a number of subtleties to be considered, some of which we barely understand.”

“What if I hired a gross of chemists to go out into the desert and start testing every possible combination of ingredients? Somewhere far from any people they could harm?” Nereo didn’t reply immediately, but Paolo was already warming to his own vision. “We could require that each experiment take place at a location on the map that encoded the particular choice of reagents. That way, it would be apparent from the positions of the craters which reactions should never be attempted again.”

“Ingenious, sir,” Nereo declared. He was being sarcastic, but Paolo chose to take him at his word.

“The credit,” Paolo replied, “should go to our guest, who delivered this inspiration to me.” He bowed his head toward Eusebio.

Throughout their second, final show in Red Towers, Eusebio kept up an admirably professional veneer of optimism, but as soon as they were back in Nereo’s guest room he slumped against the wall.

“It’s too much,” he said numbly. “I can’t do this anymore.”

“We can find someone else to take over the recruitment drive,” Yalda suggested.

“I’m not talking about the recruitment drive! The whole project is impossible. I should give up this idiocy and go back to the railways; let someone else worry about the Hurtlers. I’ll probably be dead before the worst of it, anyway. Why should I care?”

Yalda walked over to him and touched his shoulder reassuringly. “So Paolo won’t invest in the rocket. He’s not the only wealthy person on the planet.”

“But Red Towers is as good as it gets,” Eusebio said. “Journalists here understand the whole message. People listen to our plan and offer intelligent, constructive criticism. But no one here will volunteer to be a passenger, and the man who owns half the city would rather try to resurrect alchemy as his weapon against the Hurtlers than watch his money disappear into the void.”

“It’s a setback,” Yalda admitted. “But don’t make any decisions right now. Things might look different after a few days.”

Eusebio was unconvinced, but he tried to receive her advice graciously. “Don’t worry,” he said. “I couldn’t throw this all away in an instant if I wanted to. It’s not as if someone’s going to walk up to me tomorrow and offer to buy the mining licenses.”

Yalda woke in the night, unsure for a moment where she was. She raised herself up on her elbows to look around the room. Soft-edged shadows tinged with spectral colors stretched across the floor from beneath the window, framing Eusebio’s sleeping form.

He was beautiful, she realized: tall and strong, perfectly shaped even in slumber. How had she never seen that before?

But it was the thought of him that had woken her. If they brought their bodies together now, she was sure she could extract the promise from him. Her flesh wouldn’t die; she’d let her mind and its anxieties fade away, leaving her children with a devoted protector. He was the closest thing to a co she could hope for, and she did not believe he would refuse her. Not here, alone with her; not if she insisted.

She rose to her feet and stood watching him, imagining his skin pressed against her own, rehearsing the words that would convince him. If Paolo could have six sons, why should Eusebio limit himself to two? She would not say a word against his co; she wasn’t asking him to betray his lifelong partner, only to enlarge his prospective 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.”