The Clockwork Rocket

having paid so much for my education—but I can’t see Acilio and his cronies patiently following the trail of evidence from the velocity-wavelength formula to the passage of time for fast-moving travelers.”

“No.” The mention of Acilio reminded Yalda of someone else she’d been trying not to think about. “How do things stand with the university?”

“I’m negotiating a payment for them to relocate the observatory,” Eusebio said. “It’s not finalized, but given the amount we’ve been discussing they’ll be able to build a new telescope twice the size.”

“But not at the same altitude.”

“You can’t have everything. Don’t you think this is more important?”

“It’s not me you’ll have to convince,” Yalda warned him. “Have you ever heard of a man called Meconio?”

“Meconio? I thought he was long dead.”

“Not in spirit.” Perhaps the university would take Eusebio’s money and accept the deal before Ludovico discovered the connection between this “mining project” and the loathsome subject of the new physics.

“How much of the mountain do you think is sunstone?” she asked.

“Maybe two-thirds, by mass.”

Yalda did some quick calculations on her back. “That might be enough for one quarter-turn in four-space, but there’s no chance at all that it will cover the whole voyage.”

Eusebio glanced at her, surprised. “You expect the yield to stay the same, after half an age working on improvements?”

“Maybe not, but if there’s barely any sunstone left over from the acceleration stage… what kind of yield are you hoping for?”

“I don’t expect the travelers to burn sunstone for the later stages,” Eusebio replied.

Yalda was startled. “You want them to turn hardstone and calmstone into fuel?”

“Either that,” he said, “or move beyond the need for fuel entirely.”

Yalda waited for a sign that he was joking; none came. “So you’re counting on this rocket riding the Eternal Flame? Is that what you told your father to expect?”

Eusebio hunched his shoulders defensively. “Just because Ninth Age charlatans wrote a lot of nonsense about a similar idea doesn’t mean it’s actually impossible.”

“A flame that consumes no fuel?”

“Tell me why it can’t exist!” he demanded. “Not the version the philosophers imagined: some magic stone that would sit on your shelf, creating light and nothing else—that would violate conservation of energy. But if light and kinetic energy are created together there’s no reason they couldn’t balance each other precisely, without any change in chemical energy to plug the gap. Fuel doesn’t need to be consumed; that’s just the way it works with the kinds of fuel we have right now.”

Yalda had no argument about the energy balance, and while she couldn’t calculate the relevant entropies on the spot, creating light generally meant an increase. In conventional flames the hot gas formed by the spent fuel also contributed to the rise in entropy, but there was no reason to think it was essential. On the face of it, then, a slab of rock could create a beam of light—balancing the energy and momentum of the beam by recoiling in the opposite direction, but suffering no other change—without violating any principle she could name.

Accepting that statement of theory was one thing. Being stranded in the void with an infinite velocity, exiled from your home until you conjured the Eternal Flame into existence, was a different proposition.

“I can’t tell you it’s impossible,” Yalda conceded, “but you still need to ensure that there’s a useful amount of sunstone left after the acceleration—even if you have to throw away half the rest of the mountain to eliminate some dead weight. Give them something they can make more efficient, not a choice between bringing a Ninth Age myth to life, or never coming back!”

“Let’s see what the detailed surveys tell us,” Eusebio said, trying to sound conciliatory. “Two thirds was just a conservative guess.”

Yalda stared out across the desert. Who was going to volunteer to ride on this folly if it looked harder to survive than the Hurtlers?

She said, “Please tell me you’re not expecting the travelers to invent their own means of dealing with waste heat.”

“Of course not.”

“So…?”

“I’m planning to divert some of the exhaust gas,” Eusebio said. “Letting it expand and drive a piston while it’s thermally isolated will cool it down and supply some useful energy—then decompressing it further while it’s circulating around the habitation will draw in heat. Most of it will then be released into the void, but some will be used to maintain the pressure in the habitation, which would otherwise decline over time as the original atmosphere leaks out.”

“So you’ll be burning some sunstone for these purposes, even when the rocket isn’t in use?”

“Yes—though compared to the amount used for propulsion it won’t be much.”

Yalda couldn’t fault this scheme, or suggest any obvious refinements, but that wasn’t good enough. “Now that you’ve proved that you have no fear of explosions,” she said, “how about a detour to Amputation Alley?”

Eusebio regarded her suspiciously. “Why?”

“There’s a man there called Cornelio who knows more about heat than either of us. You should ask his advice on this.”

“Can he keep a confidence?”

“I have no idea,” Yalda replied, irritated. Cornelio had always treated her honourably, but she wasn’t going to vouch for his willingness to go along with Eusebio’s whims.

“Never mind,” Eusebio said. “I’ll hire him as a consultant, have him sign a contract.”

Yalda lost patience. “Do you honestly think you can send a whole mountain into the void in secret? Just you, and a few dozen advisers? Maybe you could get that much dead rock off the ground through sheer trial and error, but we’re talking about risking lives! You need the best people in the world to know about this, to think about it—to criticize all your ideas, all your systems, all your strategies. And I do mean the best people, not the best you can afford to put on your payroll and subjugate to a vow of silence.”

“I have enemies,” Eusebio said pointedly. “People who, if they knew of these plans, would happily spend a good part of their own fortune just to see me fail.”

“I don’t care,” Yalda replied coolly, resisting the urge to remind him that she’d suffered far more from his enemies’ pique than he had. “If the travelers are to have any hope of surviving, you’re going to need every biologist, agronomist, geologist, chemist, physicist and engineer on the planet as worried about their fate as you are.”

“And why should they fret about the lives of a few strangers?” Eusebio retorted. “You didn’t seem too eager to spread news of the catastrophe that this trip is intended to forestall.”

“I was wrong,” Yalda admitted. “First I didn’t take my own reasoning seriously, and then I was vain enough to think that if I could see no remedy myself, there was none. You’ve shown me otherwise, and I’m grateful for that. But it can’t end there.”

Eusebio said nothing, his gaze fixed ahead.

“No more silence,” Yalda declared. “I need to make the case for the problem, and you need to make the case for the solution. Let people argue, correct us, support us, tear us down. It’s the only hope we have to get this right.”

When Yalda arrived home Daria was in the apartment, helping Valeria and Valerio infuse some anatomical realism into their sketches of giant lizards laying waste to Zeugma.

“Lizards can rearrange their flesh almost any way they like,” Daria explained, “but they have five favorite postures, which are used in different places for different tasks. If they were on the ground, smashing buildings like this, you can bet they’d have a lot of flesh in their rear legs and their tails. It’s no good drawing them the way they’d look running along a slender twig.”

The children were entranced. Yalda sat and listened, not saying too much, hoping that merely sharing their interest would be read as a sign of affection. When she tried too hard Valeria reacted with scorn, but if she kept her distance she was punished later with accusations of indifference. It was exhausting having to be so calculating