Incandescence

theorists had managed to keep recruiting. Even as people grew hungry, they had been driven not to ransack the diminished crops at the edge, but to gather around the seeds that Zak had planted, to tend and protect a very different crop.

Tan approached her. “Are you ready?”

Roi felt sick. She remembered the time at the junub edge, when Zak had gone silent. If they failed now, it would be the very same feeling played out in slow motion for everyone in the Splinter. Worse than a new division, worse than anything that had happened before.

“Absolutely,” she said.

In silence, side by side, she and Tan plunged into the world of geometry.

This time, there were not two but five unknown templates to feed through every step of the calculations. One was tied to the way the symmetries slanted around the Hub; another to the freedom they needed to express the size of orbits; another to the way the shape of space-time varied as you moved out of the plane of the Incandescence. Along with the other symbols they needed to wrap the whole space-time in unknown numbers, the total was so great that Gul’s beautiful frames had all needed to be hastily rebuilt.

Roi lost herself in the process. She worked slowly, satisfying herself that every step she took was valid before moving on to the next, so that when it came time to pass each frame to her checkers she felt no hesitation. As the dark phases approached, the newest recruits wound the light machine and kept the work going.

The stones clicked gently, the templates grew longer and more intricate. The third of her checkers called an error to her; she accepted the frame back, and corrected the mistake.

As well as the Splinter’s old circular orbit, it would be necessary to apply Zak’s principle to at least three other paths through space-time in order to unravel all the unknowns. To provide an extra degree of confidence in their results, she had not conspired with Tan on the choice of paths; the two of them would make their own separate decisions, and then see if their final answers still agreed.

Final answers? The prospect still seemed impossibly remote. The templates thickened like weeds. Someone brought Roi some food. She had lost count of the number of dark phases they had passed through. She finished her first analysis of the Splinter’s orbit, and chose the next path: an orbit that went backward around the Hub. In the simple geometry that would have told her nothing new, but with the strange new twist they’d added, it became an entirely different kind of motion.

Tan called a break; they all needed to sleep. Roi clipped protectors over the wires of her frame to keep the stones in place. She didn’t speak to Tan, to anyone, she just found a crevice in the wall of the chamber and shut off her vision.

When they resumed, she felt refreshed, but the intervening time melted away; it was if she’d never put the frame down at all. The templates were too big to be considered beautiful, but she was beginning to recognize similarities in some of the ugly knots writhing around within them, and she clung to the hope that these knots might meet up in a way that would allow them to untangle each other.

A chance came to use her own tool to unravel some of the ugliness: the free template linked to the size of the orbits. She hesitated, wondering if she was acting too soon; how could she know if a different choice, delayed, might not spare her even greater effort?

The knots were crowded around this one point right now, though. She let them join up, loosen, vanish.

She finished her third path, her fourth. She had applied Zak’s principle four times, and now there were no more decisions left for her to make; all she could do was keep smoothing the templates, following the internal logic of their forms.

Sleep again. Already?

Roi woke before anyone else, and walked softly back to her frames. She stared at the template locked on the wire, and saw in her mind’s eye what three or four steps would produce. Her tactic with the orbit-size template had paid off: the period of the Rotator, the period of the Splinter’s spin when judged against the path of a tossed stone, obeyed the square-cube rule exactly. The same had been true for the simple geometry, but she had never dreamed that such a relationship could survive all the complications they’d thrown into the mix.

Her checkers stirred, and patiently resumed their places. She dared to cast a glance at Tan; his posture seemed optimistic. She was not fooling herself, then. They had not become lost in this maze of symbols.

Roi pushed on to extract the other results. The period of the orbit, the ratios of the weights were much more complicated templates than before. Roi found them ugly, but that didn’t prove that they were wrong.

This time, as well as determining the size of the Splinter’s orbit—compared to a still unknowable natural unit—she would need to quantify the twisting of the geometry around the Hub. The two were entangled in the templates, but taken together, their newest observation, the ratio of the Splinter’s orbital period to the shomal- junub cycle, and their oldest, the ratio of the weights, could unlock the numbers.

Roi finished the calculation, but couldn’t bring herself to pass on the frame for checking. She was sure she had made a mistake. The amount of the twist, in natural units, was very close to one. She had no real idea what that meant, but at least it was simple.

The size of the Splinter’s orbit, though, was not eight, as before, but barely more than two. It was true that the orbits could not be compared directly between the geometries, but surely an orbit four times smaller was impossible. Wasn’t an orbit of size six unstable?

The answer turned out to be: not any more. In this new geometry, orbits in the direction of the twist remained stable right down to a size of one unit. The marker for danger remained the behavior of a looping stone, but the link between the shape of the loop and the size of the orbit had changed completely.

Roi didn’t know if this was good news or bad. They were four times closer to the Hub than they’d imagined, but they could survive a further halving of their distance, rather than losing a quarter of it.

She passed the last frame to her checkers and stretched out against the rock. She looked over at Tan; he’d finished too.

She waited for the final verdict. There was some confusion; she and Tan had expressed their results differently, because his way of describing the orbit size was not the same as hers. The checkers worked through the conversion, then announced a perfect concordance.

Roi was elated that they’d made it through the ordeal and emerged with answers that made sense, but she needed to remain cautious. They had shown that a geometry with rotational symmetry, and which obeyed Zak’s principle, was possible. That was a beautiful result that they had never been certain of before. However, the freedom to set the twist in the geometry to whatever number they wished meant that they hadn’t really subjected their theory to a meaningful test. One new observation, the period of the orbit, had been absorbed entirely by the need to pin down that new unknown, the twist.

Tan approached her.

“Well done!” he chirped.

“You too.”

“I’m glad we made different choices,” he said. “We should keep the two systems; it will allow us to cross- check everything between them.”

Roi said, “We need to start thinking about the other observations from the void: the lights, the motion of the Wanderer. Once we’ve thrown all those numbers at this geometry, we’ll know if it’s real.”

Tan let his legs sag comically. “I need a break,” he pleaded. “At least one shift doing nothing.”

The checkers dispersed to gather food. In spite of his protests, Tan lingered, poring over the templates with her, trying to understand what the new geometry meant.

He said, “When you carry the direction of the Rotator’s plane around a loop in curved space-time, it comes back changed. So the period of our spin is different from the period of our orbit; even the old geometry predicted that. But in this geometry, even if the Splinter didn’t orbit—if it was held at a fixed position, with the garm-sard axis pointing toward the Hub—we would still feel a spin weight, and the Rotator would still turn!”

Roi checked; he was right. If you took a direction pointing toward the Hub, and simply carried it forward in time, it turned away from the Hub. The only way to feel as if you were not turning was to spin along with it, like the Rotator.

“It’s all very strange,” she said. A little later, she noticed something else. “If your distance from the Hub is two or less, it becomes impossible not to move in an orbit! To try to stay still means moving faster than the fastest possible speed!”