The Eternal Flame

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.

“We delay one of the paths,” he suggested.

“Yes!”

He took a small rectangular slab of clearstone from the cupboard, its faces polished to optical flatness, and mounted it against the screen so that it covered just one slit. This setup would leave the geometry of the light paths much the same, but the extra travel time through the clearstone would be more than enough to destroy the interference pattern from any ordinary source.

Romolo loaded the camera and made the exposure. When he retrieved the paper, Carla’s skin tingled with excitement. The interference pattern was shifted off-center, but the stripes were almost as sharp as before. The wave’s oscillations were following a regular sequence of peaks and troughs that persisted for so long that the delay couldn’t scramble the smooth variation of phase shifts responsible for the pattern.

“Coherent light,” she said. “Invisible or not, the principle’s the same. Congratulations!”

Romolo seemed unsure what to make of his achievement. Carla said, “In all of history, no one’s seen light like this before.”

He managed a self-deprecating chirp. “But do I get to tell my grandchildren that I helped to solve the fuel problem?”

“Maybe. Let’s see where this takes us.”

Carla gathered the whole team to watch the next test, checking the beam’s collimation. A truly parallel beam was impossible, but images of the UV light emerging from the end of the green cylinder showed a disk with no detectable change in size across the entire width of the workshop.

“The wavefront speed of this beam will be tiny!” Patrizia enthused. “Trap some luxagens in the valleys, and we might even have time to watch them jump levels.”

Carla said, “Slow down. Anything trapped in these beams will only be confined in one direction. That’s not enough to force the luxagen waves to take on discrete energies.”

Patrizia hesitated. Romolo said, “Couldn’t you use three beams, for the three dimensions?” He gestured with his hand, sketching three orthogonal planes in the air. “Combine three waves, and you can hem the luxagens in on all sides.”

“Perhaps,” Carla conceded. If the wave trains from all three beams were long enough, the pattern they formed together could persist for a significant time. And as Patrizia had said, the wavefronts themselves would be moving relatively slowly. This weird array of hills and valleys—like the energy landscape of a solid, but floating ethereally in the void—would drift backward through the beams that created it, carrying any cargo they managed to load into it.

Carla set Romolo to work testing all the mirrors in the workshop with the same slab of clearstone. Seeing whether the device still worked after the substitution would finally reveal which of the mirrors were good enough for their purpose—sparing his colleagues years of wasted effort.

At the end of the day she took Patrizia and Romolo aside. “I think the beam trap is an idea worth trying,” she said. “If we can arrange things so the majority of the valleys end up containing at most one luxagen, that would be the simplest possible system to study—maybe even simple enough for us to map out a direct connection between its spectrum and its energy levels.”

Romolo looked daunted. “How will we know what energy state the luxagens are in to start with? I don’t see how we can control that.”

“I don’t think we can,” Carla agreed.

Patrizia said, “Suppose we feed the luxagens in at one end—we don’t just scatter them into the valleys everywhere. Then we can sample the light that’s emitted at various distances from that starting point, which will tell us what’s happening at various times after the luxagens are dropped in. Every transition will take place at a different rate, so at least that should spread things out, making it easier to untangle what’s going on.”

The three of them worked together, sketching a preliminary design for the apparatus they’d need. The new project would not be simple, but Carla hoped the detour would prove to be worthwhile. Luck had delivered them a coherent light source that nobody could see, but if they could leverage that into a deeper understanding of the rules that dictated the behavior of every solid, they’d have a chance to make the rest of the search far more systematic.