Грег Иган - Schild’s Ladder

Suljan said, "I think it’s moving." Successive pulses were coming back with slightly different delays. The reflective layer was more or less keeping pace with the expanding border, but the signal showed it drifting back and forth. "Vibrating, maybe?"

Rasmah replied, "It’s probably something changing in the border region, messing with the propagation speed." That explanation made more sense to Tchicaya; the signal was crossing a vast tract with potentially variable conditions, so it was more economical to attribute any delay to the vendeks it encountered along the way.

Suljan gave her a withering look. "More expert commentary from the peanut gallery. The returns are too clean, and too sharp; that much variation in propagation speed would broaden them detectably."

"Hmm." Rasmah didn’t argue, but her eyes glazed over; she was checking something. When she emerged, she said, "Okay, you’re right. And the changes are too fast and too regular; the source of the variation would have to be fairly localized, so it must be the reflector, not the medium."

Tchicaya turned to Umrao. "Any ideas?"

"I didn’t see anything like this in the simulations," he said. "But then, I just remixed the vendeks from the border region. This layer might hold completely different ones."

The vibrations stopped.

Yann stared at the plot on the screen. "Just like that? No decay curve?"

The vibrations resumed.

Tchicaya looked around the room. Several people had left; apparently, the ringing of the far side’s equivalent of a planetary ionosphere was of no interest to them. Anything that influenced signal propagation was of crucial importance, though, and if this layer could move, it might even break up and reveal something deeper.

The vibrations halted again, only to restart a few seconds later. "One hundred and thirty-one oscillations," Yann noted.

Rasmah said, "What’s that going to tell us?"

Yann tapped his fingers against the table, one hand in time with the returning pulses, the other beating out the rhythm of the reflecting layer itself. Tchicaya resisted an urge to tell his Mediator to stop rendering Yann’s icon; the constant drumming was annoying, but he’d never edited anyone from his sensory map before, and he wasn’t about to start.

"One hundred and thirty-seven," Yann announced.

Tchicaya said, "You think there’s some longer-period cyclic process, modulating the faster one?"

Yann smiled enigmatically. "I have no idea."

Suddently, Rasmah groaned. "I know what you’re thinking!"

"What?" Tchicaya turned to her, but she wasn’t giving anything away.

She said, "I’ll bet you anything that you’re wrong."

Yann shook his head firmly. "I never gamble."

"Coward."

"We have no mutually beneficial assets."

"Only because you threw yours away," she retorted.

Umrao said, "I’m completely lost. What are you people talking about?"

"One hundred and thirty-seven," Yann counted. "One hundred and thirty-eight. One hundred and thirty-nine."

He fell silent. The vibrations had stopped.

Tchicaya said, "The slower cycle is varying, a little. Maybe lengthening. What does that tell us?"

Rasmah had turned pale. At the console, Suljan, who’d been paying no attention to the conversation at their table, suddenly leaned into a huddle with Hayashi. Tchicaya couldn’t hear what they were whispering about, but then Suljan let out a long, loud string of obscenities. He turned to face them, looking shocked but jubilant.

"You know what we’ve got here?" he asked.

Umrao smiled. "I just worked it out. But we shouldn’t jump to conclusions."

Tchicaya pleaded, "What conclusions?"

"Three consecutive primes," Suljan explained.

The vibrations had resumed, and Yann was calmly tapping them out again. Tchicaya calculated the next number in the sequence, and thought about trying to quantify the odds of the first three occurring by chance, but it would be simpler just to wait for the pattern to be broken or confirmed.

"One hundred and forty-seven. One hundred and forty-eight. One hundred and forty-nine."

On cue, the vibrations halted.

Yann said, "I wouldn’t rule out nonsentient processes. We don’t know enough about the kinds of order that can arise in this system."

Umrao agreed. "There’s no reason evolution couldn’t have stumbled on something useful about primes in the far-side environment. For all we know, this could be nothing more than an exotic equivalent of cicada calls."

"We can’t rule out anything," Suljan conceded. "But that has to cut both both ways. It has to include the possibility that someone is trying to get our attention."

"It looks as if the Colosseum is about to welcome us in," Rasmah said. "You first."

"I don’t think so." Tchicaya held up his hand; it was shaking. They’d spent almost two hours sitting in the corridor outside the impromptu amphitheater where the Preservationists were meeting, and now the blank, soundproof wall in front of them was beginning to form a door.

"Turn down your adrenaline," she advised him.

"I don’t want to do that," he said. "This is the right way to be. The right way to feel."

Rasmah snorted. "I’ve heard of traditional, but that’s ridiculous."

Tchicaya bit back an irritated reply. If he was going to harness his body’s natural agitation, he could still keep his behavior civilized. "I don’t want to be calm," he said. "This is too important."

"So I get to be the rational one, and you get to be impassioned?" Rasmah smiled. "I suppose that’s as good a strategy as any."

It had taken Tchicaya six days of arguing to push a motion through the Yielders' convoluted decision-making process, authorizing disclosure of the recent discoveries to the opposition, and he had hoped that it would be enough. The Preservationists would repeat the experiments, see the same results, reach the same conclusions. He’d set the chain of events in motion, and it would have an unstoppable life of its own.

Then the Preservationists had announced that two Yielders would be permitted to address them before they made their decision on a moratorium, and he’d found himself volunteering. Having worked so hard to create a situation where they were apprised of the facts and prepared to listen, it would have been hypocritical to back out and leave this last stage to someone else.

The door opened, and Tarek emerged, looking worse than Tchicaya felt. Whatever the body did in times of stress could be ameliorated at will, but Tarek had the eyes of someone whose conscience was robbing him of more than sleep.

"We’re ready for you," he said. "Who’s first?"

Rasmah said, "Tchicaya hasn’t smeared himself in goat fat yet, so it’ll have to be me."

Tchicaya followed her in, then hung back as she approached the podium. He looked up at the tiers of seats that almost filled the module; he could see stars through the transparent wall behind the top row. There were people here that he knew well, but there were hundreds of complete strangers, too; the ranks of the Preservationists had been swelled by new arrivals.

The audience was completely silent. There was an expression of stony resentment on some faces, an unambiguously hostile gaze, but most people just looked tired and frayed, as if the thing they hated most was not the presence of Yielders bearing unpalatable revelations, but the sheer burden of having to make an invidious choice. Tchicaya could relate to that; part of him longed for nothing more than a turn of events that would render all further effort irrelevant, one way or another, so he could curl up and sleep for a week.

Rasmah began. "You’ve seen the results of our recent experiments, and I’m going to assume that you’ve replicated them successfully. Perhaps someone will correct me if that’s wrong, and the raw data is in dispute."