Greg Egan - The Eternal Flame

“Tamara, Livio.” At least Ada’s introduction was discreet.

“Pleased to meet you,” he said.

“Likewise.” Tamara faltered. Forewarned, she might have had a chance to think up a suitable topic of conversation, but after Ada’s minimal briefing what could she ask this man about? The death of his wife?

Livio said, “It must have been exciting, going out there in the Gnat .” His enthusiasm seemed genuine, and Tamara was grateful that his opening gambit hadn’t been to offer his commiserations on more infamous events.

“It was glorious,” she said. “The experience of a lifetime.” She glanced at Ada, willing her equally experienced co-navigator to chime in with some anecdote from the journey and take the pressure off her. “I’m hoping to do some more flights soon—but I doubt I’ll ever see anything to compare with the first big explosion we raised on the Object. There was so much burning smoke stretching out from the impact site that it was visible from the opposite side.”

“I’ve worked out on the slopes a bit,” Livio said. “It’s beautiful, just looking down into the stars. But I hope my children get a chance to cross the void. We can’t stay cooped up in this rock all the time.”

“No.” Tamara didn’t want to believe that he’d feign these sentiments merely to put her at ease. “It was just dumb luck that I saw the Object first,” she admitted. “That’s the only reason I ended up on the Gnat . But what I’m trying to do now is make travel away from the Peerless as easy as possible. Maybe for the next generation, instead of the lotteries it will simply be a birth right: everyone gets to make at least one trip.”

Livio chirped approvingly. “I like that idea.”

Tamara said, “I should let you get on with your work.”

“All right.” Livio hesitated. “Can we meet up again? Share a meal, perhaps?”

He didn’t suggest a time, knowing she’d have her own schedule for eating. “Tomorrow, around the sixth bell?” Tamara proposed.

“That would be good. You know the food hall, about halfway to the summit from here—?”

“Yes.”

“Can we meet there?”

“That would be fine.”

“I’ll see you then,” Livio said. He tipped his head in thanks to Ada, then returned to his workbench.

Tamara was silent most of the way to the observatory. Livio seemed charming, civilized and enlightened. He would send their children out across the void, reveling in the starlight. Even if it was all an act, it was a more appealing performance than Tamaro’s endless lectures on her familial obligations.

But she couldn’t help feeling a twinge of claustrophobia at the thought of where she was being led. However genuine Livio’s virtues might be, the ultimate purpose of their alliance would be the same: one day, they would come together to end her life. This charming man might never coerce her—but she would still be expected to make the choice herself before her co-stead grew too old to raise children, and before any other fate befell her own borrowed flesh.

31

Carla looked up from her desk to see Romolo approaching, dragging himself across the workshop. Shafts of light escaping from the sunstone lamps crisscrossed his path, bright enough to be delineated clearly by the dust in the air, flaring into dazzling patches of radiance as they fell on his skin. She had been told to stay alert for warning signs, defects in her vision that might presage a relapse, but how would she tell? Everyone working in this maze of light was blinded momentarily a dozen times a day.

“I think I might have found something,” Romolo said cautiously. He offered her a strip of paper from his spectrograph.

The single dark line standing out against the background was in the far ultraviolet. For an instant Carla came close to panic: if this was the signature of annihilating luxagens, whatever was behind it could kill them all. But the line’s position against the calibration marks made its wavelength even shorter than the UV Ivo had recorded on the Gnat —and the notion that Romolo might have shaken some dormant cache of negative luxagens out of a lump of clearstone would have been fanciful at any frequency. Sharp, monochromatic UV didn’t have to come from the destruction of matter. All it would take would be stimulated emission between two closely spaced energy levels.

Carla freed herself from her harness and followed Romolo back along the guide rope. Across the workshop, five other students were working on their own samples. The ancestors who’d stocked the warehouses of the Peerless had made an effort to be comprehensive; more than three gross varieties of tinted clearstone were represented. Under the microscope about half of these had turned out to be variegated, with the hue they presented to the naked eye just a blend of the colors of various inclusions, but the remainder, the apparently pure specimens, would still take years to test.

Romolo’s current candidate was a dark green cylinder the size of Carla’s thumb, carefully polished so the ends were flat and parallel, held in place between one full mirror and one thin enough to be partially transparent. Making the search even more laborious was the need to try out each sample of clearstone with a dozen different pairs of mirrors. The lowest grades of mirrorstone produced small but measurable alterations in the hue of the light they reflected, but the same effect had the potential to ruin a coherent light source even when it was too small to measure. For now, the only solution was sheer force of numbers, with the hope that random variations among the highest quality mirrors would produce a few that were good enough to allow the device to function.

Romolo had shut off the sunstone lamp before coming to fetch her, but at her urging he lit it again, then quickly pulled the housing closed around the apparatus, leaving most of the lamplight to fall upon the sides of the clearstone. If they really had stumbled on a substance with just the right pattern of energy levels, this light would be pumping luxagens from their natural state in the highest level, down to one from which three separate jumps would take them back to their starting point, completing the cycle.

From the end of the cylinder, a diffuse, wan green disk fell onto the screen at the entrance to the spectrograph. To the naked eye, there was certainly no sign here of a perfectly aligned coherent beam. “Why couldn’t it be a longer wavelength?” Romolo lamented.

“Ha! Don’t be ungrateful.” An invisible light source wouldn’t please the navigators, but Carla would accept vindication of the underlying theory in any form. “The spectrum shows a strong, monochromatic signal,” she said. “Stronger than the UV of the same frequency in the sunstone’s light. So at the very least, you’re shifting energy into that line somehow. What we need to check next is the coherence length.”

She reached into the cupboard below the bench top and found a suitable double-slitted screen. It was a nuisance not being able to see the results immediately, but Carla mounted the slitted screen and a UV-sensitive camera in the path of the beam.

The image from the camera showed a clear pattern of interference stripes, as expected from any monochromatic light source—even a single hue filtered from the chaotic mixture emitted by a lamp. So long as the tiny difference in travel time that arose when the wave passed through one slit or the other didn’t exceed the lifetime of each wave train, the light from the two slits would interfere this way.

“Now, what would clinch it?” Carla waited for Romolo; she hadn’t spelt out every possible confirmatory step in the protocol the students were following, but she was sure he could think of something.