Greg Egan - Incandescence

"I think they might be sleepwalking," he said. "Like your team-mates. I think they've done many things, learned many things, seen many things, but now they've had to find a way to live without needing what the world can no longer provide for them." He could understand the attraction of a strategy like that, for the Arkdwellers, for anyone. It was better than going mad with boredom. "Maybe there are one or two among them who are a bit like you, but a lot less restless. Sentinels, not quite awake, who can watch the world go by, and even intervene in it a little, but who can't, or won't, reengage with the universe until it has something new to offer them."

Zey absorbed this. "But they brought you here, just to wake us?"

"That's what I believe," Rakesh said. "But I'm not certain about any of this."

He waited until the last traces of Lahl's Promise had drifted out of sight, then he started the ferry's drive.

"Forget the Aloof," he said. "Let's go and find out if any of your team-mates are ready to engage with the universe."

The message from Ruz began, "Cho has found the Wanderer."

Roi read on, amazed.

While most of the void-watchers had given up their old job and come to join the geometry-calculators, Cho had refused to accept that the act of observation had become impossible. The junub edge had become useless; not only had the Incandescence hidden all the ordinary, distant lights that might have been used as guides to the Splinter's motion, once the Wanderer was orbiting in the same plane as the Splinter, the rock of the Splinter itself blocked any chance of a view of it from the junub edge.

So Cho had gone first to the sard edge, hunting for another crack in the rock through which he could extend his light-gatherer. He'd had no luck, though, in finding such an opening, or even a promising site where one could be made.

Once the Splinter crossed the Wanderer's orbit, the garm edge, facing in toward the Hub, became the only feasible observation post. Cho had journeyed back across the length of the Splinter, carrying all his metal plates, to search for a new vantage point.

He had found a suitable crack in the rock, and lowered his light-gatherer through to the surface. By blocking the aperture with punctured metal sheets to limit the amount of light transmitted, and then projecting what remained on to a smooth stone surface backed with roughened metal, he had been able to form an image which could be viewed safely.

The image was not sharp, but even through the Incandescence a dazzling smear of elevated radiance could be seen. It was the Wanderer orbiting the Hub, its intensity cycling dramatically. The emission of a flare or some other misadventure had apparently knocked it into an elliptical orbit, and on its closest approaches to the Hub it was now shining with an unprecedented brightness, which fell away again as it moved further out.

Roi conferred with Kem and Nis. "What does this mean?" she wondered. "How strong can this new light become?"

"I have no idea," Nis confessed. "I don't understand what's happening. The weight is squeezing the Wanderer, agitating its material somehow, but this effect is out of all proportion to that. It's as if. a child had teased a susk a dozen times, always getting a response as mild as their teasing, but then they found they'd crossed some kind of threshold and driven it into a fury."

Roi did not like the sound of that. What could the Wanderer do to them, in a fury?

Kem said, "We have two choices, I think. We could simply keep moving out, trying to put as much distance as we can between us and the Wanderer."

"That's getting harder, though," Roi replied. "And more perilous." Not only was the slower wind and the thinner Incandescence limiting their pace, if they ended up too far from the Hub there would be no hope of sustaining the crops. To survive the Wanderer only to die in a famine would be the worst thing she could imagine.

"The other choice is to take a different gamble," Kem said. "It's not too late to put ourselves in an orbit where we're constantly shielded by the Hub. The Wanderer's closest approach to the Hub is closer than we are now, but its furthest distance is still outside our present orbit. We can match orbital periods with it, and try to lock ourselves into a relationship where the Hub protects us as much as possible."

"Then what do we do when the Wanderer's orbit shrinks further?" Roi said. "We can't follow it back down toward the Hub in order to keep our orbital periods the same." She had had the idea, long ago, that perhaps Bard should have carved tunnels through the garmside as well as the sardside, granting the Splinter the ability to travel in either direction. If it came to a slow, drawn-out famine because they were too far from the Hub, that might yet be their only salvation, but there wasn't the slightest prospect of creating those tunnels in time to chase the Wanderer.

Nis held up the message sheet that contained Cho's observations. "Look how much brighter it's becoming already, just from the slight increase in weight when it reaches the closest point to the Hub along its orbit. When its orbit shrinks . "

He trailed off, but Roi didn't need him to complete the prediction. Either the process that was driving this radiance would come to a halt by destroying the Wanderer, or it would keep growing in the same spectacular fashion, and it would make no difference where the Splinter was. Unless they were shielded by the Hub, this light would be strong enough to outshine the Incandescence and sear them all to death.

Roi rejoined the geometry-calculators for one more task. Since the Splinter's orbit was essentially circular and the Wanderer's was not, they couldn't hope to track its motion perfectly, keeping themselves always in the center of the safe zone that lay roughly — but thanks to the twist, not precisely — on the opposite side of the Hub. However, they could find the orbit that gave them the greatest protection possible, given that the Wanderer's brightness was reaching its ominous peaks with perfect regularity.

In effect, they would try to hide the Wanderer behind the Hub, to make it disappear from view. As the instructions flowed from the calculators to the sardside tunnel, and the observations flowed from Cho to the calculators, Cho's data began to reveal a modified cycle. As well as dimming and brightening from its own mysterious dynamics, the Wanderer was now growing more or less obscured by the Hub, which was swallowing varying portions of its light. As the Splinter eased into its new orbit, the two cycles slipped into the desired, antagonistic relationship: the Wanderer's dazzling bursts were cut short by the Hub's intervention, and when the imperfect alignment of the orbits most prevented the Hub from hiding the Wanderer, it was, of its own accord, at its least radiant.

Roi signaled Bard to close the tunnels, and told Tio to let the calculators rest. There was nothing more to be done. If the orbits started slipping further out of alignment, moving further from the Hub would only worsen the disparity. Their fate was at the mercy of the Wanderer now.

Roi sent word to evacuate the edges, to bring everyone as close as possible to the center of the Splinter. Her first instinct had been to move people to the sard edge — doubling the amount of rock between them and the Wanderer compared to the center — but Kem had pointed out that while pure light straight from the Wanderer couldn't reach them from the opposite side, a flare might wash behind them while radiating heat and light of its own, rendering the sard edge vulnerable.

Cho refused to leave his observation point, as did the light-messengers who linked him to the center. Roi sent a message to him.

"Let me replace you." She was older, it was her time.