The Eternal Flame

Carla heard the click of the lever. “The red light’s gone,” Romolo said. “There’s nothing.”

“Lift the shutter again,” Carla suggested.

“Yes. Now the light’s back.”

“You must be blocking the visible light, not the IR!” Carla declared. She slipped past the students in front of her, then felt her way around the edges of the bench. She could see a faint splotch of gray where the beam came to an end, and once she was oriented she knew where everything was.

She put one hand on the lever that would bring the shutter down over the visible beam, then reached for the IR lever; Romolo’s hand was still on it. He buzzed in surprise and pulled his hand away. “Did I have the wrong one?” he asked, embarrassed.

“No,” Carla replied. “You didn’t.”

She asked Romolo to move aside, then she peered through the eyepiece herself and tried blocking each beam in turn. Shutting off either one made the reddish glow disappear. There was no escaping the conclusion, then: something that the infrared light was driving off the mirrorstone into the vacuum was scattering the visible light through a small angle—and showing a preference for red in the process.

Luxagen scattering was predicted to be stronger at the red end of the spectrum, but the small angle made no sense. Perhaps the mirrorstone was giving off a very fine dust, reactive enough to be absorbed by the container walls as soon as the IR was shut off. If these dust particles were transparent they could be refracting some light away from the beam axis.

Carla explained her hunch to the students, then swung the eyepiece around by almost half a revolution, in the hope of seeing some backscatter reflected off the dust. There was nothing. She went back to the light Romolo had found; as she moved the eyepiece even closer to the beam axis, the red tinge became less pronounced while the overall brightness grew a little.

But it was hard to quantify the changes in this complex mixture of hues. Carla asked Patrizia to relight the firestone lamp. “I don’t know what we’re seeing here,” she admitted, “but I think it will be easier to study if we try scattering a single color at a time.”

Following her instructions, Palladio and Dina fitted a prism and a color-selecting slot into the visible beam. “Let’s start with green,” Carla suggested.

With the workshop in darkness again, Carla bent down and looked through the eyepiece. She’d left it in the position where the scatter had first appeared, as far from the axis as you could go while still seeing anything at all. It took almost a lapse for her eyes to adapt sufficiently to pick up the weaker glow now that most of the beam was being blocked, but the glow was still there.

And it was red. Pure red. The green light crossing the container was being scattered—and in the process it was turning red.

Carla felt utterly lost. If nature had deliberately set out to mock her—to prove to her students once and for all that their optics teacher knew nothing about light—it could not have done a better job.

She steadied herself. This would make sense, somehow; she just needed to be patient. “Who’s got good vision in low light?” she asked. After a moment Eulalia replied, “I’ve been doing fire-watch shifts lately, if that’s any help.”

“Perfect.”

Carla had Eulalia take her place at the eyepiece.

“What do you see?” she asked.

“Red light,” Eulalia confirmed.

Carla found the lever for the visible light shutter and closed it about halfway. “What now?”

Eulalia was silent for a pause or two. “A dimmer red light.”

“Is the color any different?”

“Not as far as I can tell.”

Carla addressed the students in the darkness. “Why did I reduce the intensity?” she asked.

Patrizia replied from the corner of the workshop. “If the luxagens were getting trapped in the light wave’s energy valleys, they’d be rolling back and forth in those valleys—giving off light of their own at a different frequency to the frequency of the beam.”

“So what does it mean that the scatter remained red when I made the beam dimmer?” Carla pressed her.

Patrizia said, “It means that explanation can’t be right. The exact shape of those valleys would depend on the strength of the light. A weaker beam would have made the valleys shallower… making the luxagens roll back and forth more slowly, reducing the frequency of the light they emitted.”

“Exactly,” Carla replied. But she knew of no other way that one pure color could give rise to a completely different hue. White light could end up being filtered selectively, changing its appearance in all kinds of ways, but when you started out with a wave of a single frequency it was supposed to make everything it touched oscillate at the very same pace, generating more light of the very same hue.

Carla opened the shutter fully again. Then she groped her way around the bench and adjusted the slotted screen in front of the prism that determined the color of the visible beam, changing it from green to blue.

“What do you see now?” she asked Eulalia.

“The light’s turned green.”

She pushed the slot back in the other direction, until the beam was yellow.

“And now?”

“Nothing,” Eulalia replied. “It’s gone dark.”

Carla buzzed, delighted in spite of herself. “Blue becomes green, green becomes red, yellow becomes infrared.” At least the shift was in the same direction each time. She’d given up all hope of impressing the class with a simple explanation for these strange results. They’d found a completely new anomaly, a mystery to rank with the stability puzzle itself. There was nothing to be done now but to accept that.

And to gather more data.

She called for the workshop to be lit again, and asked Palladio and Dina to add a second prism to the light path, this time directly behind the eyepiece. Then for each color beamed across the container, she had the students take turns measuring the frequency of the light that was scattered at a variety of angles.

The experiment had one more surprise for her. At the smallest angles, violet light produced two distinct colors in the scatter: one only slightly altered in hue, the other shifted far toward the red. At larger angles the two colors moved closer together—just before the scatter disappeared completely. Blue light showed signs of doing something similar, though in that case the second color moved beyond the visible range, at a point not far below the maximum scattering angle.

Carla plotted all the measurements on her chest, then dusted her skin with dye and made copies for the students to keep. “Think of this as a souvenir,” she told Romolo. “Maybe by the time your grandchildren are studying optics, this experiment will be as famous as those Sabino did to measure Nereo’s force.”

“I’m confused,” Romolo said. “Did we find free luxagens in the container, or didn’t we?”

Carla said, “Ask me that again in six years’ time.”

10

Carlo stiffened his tympanum to keep himself silent, then plunged the probe deep into the flesh of his wrist. As he struggled to force the needle all the way down to the calibration mark the pain became excruciating, but once the thing was in place and motionless the sensation was tolerable.

“The voles of the Peerless thank you for your sacrifice,” Amanda said wryly.

Carlo managed a dismissive buzz. Loath as he was to inflict needless suffering on the animals, he was stabbing himself more out of expediency than compassion. The current version of the probe was so large that he could not have expected the creatures to endure it without an elaborate routine of anesthesia and recovery—and by