Carla moved slowly down the empty corridor, listening to the twang of the guide rope, waiting for the flaw she’d missed to reveal itself. When it finally hit her, she could buzz ruefully at her foolishness and drag herself back to bed. What about cooling? This rocket would still need a separate cooling system, burning fuel of its own… but there was no law that required the heat it generated to be as much as a conventional engine produced. And the right choices in the design could help: the faster the ultraviolet photons the device was able to emit, the less kinetic energy the mirror would need to remove from the other photons—which meant less energy ending up as heat.
Carla didn’t need to search for a clock to know that it was still early, but the only person in the mountain there’d be any point in waking was also the only one who’d understand why she couldn’t wait a few more bells to resolve this.
She reached the precinct easily enough, but she had to check the names on a dozen doors before she found the right one; she hadn’t paid a visit since Patrizia had started living apart from her co. Carla knocked tentatively, wondering belatedly if her behavior would appear completely deranged. But the door opened before she had a chance to change her mind and retreat.
“Good morning Carla.” Patrizia looked puzzled, but if she was annoyed at being woken she hid it well. “Come in, please!”
The apartment smelled of paper and fresh dye. There was a lamp burning in the front room, revealing walls stacked with books and tied bundles of notes. The gravity was very weak here, but Carla clung tightly to the guide rope.
“I won’t waste your time,” she said. “I’ve had a wild idea, and I need to hear your opinion.”
She described the basic principle of the mirror trick, then went on to explain how it might be used in a real device. When she’d finished speaking she braced herself for a barrage of objections, but Patrizia remained silent, gazing thoughtfully into the middle distance.
“So have I lost my mind?” Carla pressed her. She’d gently put Patrizia straight when the girl had fallen prey to her own kind of nonsense; it was time for Patrizia to return the favor.
“I don’t think so. Why would you even say that?”
“Because it can’t be this easy! The Eternal Flame—from a few mirrors and a slab of clearstone?”
Patrizia buzzed softly. “In the sagas, the Eternal Flame doesn’t do anything; it just sits there being cool and inscrutable. Your version would be more like the process plants perform every day: extracting energy from the production of light without incinerating themselves. Nature must have found a trick a lot like yours—shuffling luxagens around a closed cycle—even if it puts it to a very different use. Crossing the void with minimal fuel wasn’t something a flower was ever going to find helpful, but that doesn’t mean it’s impossible.”
Carla felt no sense of reassurance. If Patrizia had found a glaring flaw in the plan that would have settled the matter, but the fact that the idea had survived her brief scrutiny proved nothing. “And no one else thought of this? Not Yalda? Not Sabino? Not Nereo?”
“They all thought energy was continuous!” Patrizia protested. “Would this scheme work at all, without discrete energy levels?”
“I don’t know,” Carla admitted. Certainly the whole idea was easier to grasp when the luxagen could cycle repeatedly between a few fixed states.
“I think Yalda had hopes that we’d master the creation of light by studying plants,” Patrizia said. “And maybe that will give us the best insights into the process, eventually. But someone had to be the first to spell out the kind of steps that would make this possible. You’re the first, Carla. You’re not losing your mind, I promise you.”
“Thank you.” Carla did trust her to give an honest opinion, and not to indulge in flattery. “But I won’t believe I’m right until we’ve proved it.”
“So where do we begin?” Patrizia asked. “We’ll need to find varieties of clearstone with the right energy levels, but we’ll also need to calibrate mirrors for their red shifts.”
“This is going to be a whole new project,” Carla said. “I’ll have to go to the Council to get their approval for the change of plans.”
“Hmm.” Patrizia was impatient to get started. “Surely I can reanalyse a few absorption spectra without waiting for the Council? When Romolo and I went through them the last time, we were looking for very different properties.”
“That’s true.” The search for the perfect clearstone would start all over again, and there was a chance that once again it would succeed. But even the navigators’ modest needs would require the entire inventory of the clearstone Romolo had used in his visible light source. For this new application—
“It won’t be enough,” Carla realized. “Even if we can make this work in a demonstration rocket, there isn’t the slightest chance that we’ll have enough material to replace the engines.” The mountain’s stocks of exotically tinted minerals weren’t miserly, but the ancestors had only intended them to provide representative samples to be studied for the sake of materials science. They had never anticipated the possibility that one particular variety would become more valuable than sunstone.
Carla buzzed with grim satisfaction, glad that she’d caught her own mistake before making a fool of herself in front of the Council. “What was I thinking? Anything less than a full replacement for the engines would be worthless. If we can’t accelerate the Peerless at close to one gravity, it will take too much of the ancestors’ time for us to get back to them.” Returning to the home world a few years late—by the ancestors’ clocks—would mean arriving just as collisions with the orthogonal cluster began in earnest.
Patrizia regarded her with bemusement. “Everything you say is true,” she said.
“Then why didn’t you tell me? That’s what I came here for!” Carla dragged herself back along the guide rope, confused. “I needed to know where I’d gone wrong.”
“There’s nothing wrong with your plan,” Patrizia insisted. “Not as far as I can tell. But as you say, the proof will be in the demonstration.”
“And then what?” Carla hummed with frustration. “If we succeed, we’ll have the satisfaction of knowing that if half the mountain had been made of exactly the right kind of clearstone, that would have solved the fuel problem? And that the ancestors are likely to have all the resources they’d need to evacuate the home world—with the only problem being the lack of any way to tell them how to do it?”
“If we succeed in making a photon rocket,” Patrizia replied, “then it will be the start of an entirely new endeavor: working with the chemists to learn how to make the right kind of clearstone, in the quantities we need, from the materials we actually possess.”
Carla was incredulous. “You want the chemists to make a mineral on demand, now? You mean the way they solved the fuel problem by transmuting all our spare calmstone into sunstone?”
Patrizia said, “Now you’re being crazy. First, the quantities we’d need would be much, much smaller: we’re talking about making engines that will run for years, not fuel that will be used up in an instant. Second, I suspect that different kinds of clearstone are chemically and energetically far more similar than calmstone is to sunstone. And third… if we can make your idea work, even on a modest scale, that will give us a new energy source. Burning sunstone to provide the energy to make sunstone would have been a losing proposition. But whether it’s heat or photons the chemists need to nudge one kind of clearstone into another, if we can pull off your trick and make an Eternal Flame on our own—even once—then we ought to be able to supply that energy without consuming anything.”