Schild's Ladder (24 page)

Tchicaya looked away from the simulation to the mundane surroundings of the cafeteria. He was beginning to feel more optimistic than he had since he'd arrived, but this was all still speculation. To build a machine, a body, from anything like these “cells” was going to be a dauntingly complex endeavor.

He said, “We have to win time from the Preservationists. There has to be a truce, a moratorium, or this could all be wiped out before we learn anything.”

Rasmah said, “You think they could make effective Planck worms, without knowing what they're dealing with?”

“You're the one who's convinced that they have spies.”

“If they have spies, why should telling them anything buy us more time?”

“When did spies ever share their intelligence with the masses?” Tchicaya countered. “Suppose Tarek was looking over our shoulder right now, but everyone else remained in the dark?” He turned to Umrao. “I don't suppose you've investigated the possibility of Planck worms? A plague that kills the vendeks, and leaves a sterile vacuum in its wake?”

Umrao glanced around the table warily. “If any of what you just said was serious, I don't think I should answer that question.”

Suljan groaned. “Forget about politics. We need more data!” He slumped down across the table, drumming his fists on the surface. “I was playing around with something last night, before I stepped out for a snack and ended up mired in this discussion. I think I might have found a way to extend Yann and Branco's technique, pushing the range about ten thousand times further.” He looked up at Yann, smiling slyly. “The only way I could make any progress with your work, though, was to translate it all into my own formalism. Everything becomes clearer, once you express it in the proper language. It only took me a few hours to see how to scale it up, once I'd dealt with the mess you left us.”

Rasmah asked sweetly, “So what was the great conceptual breakthrough, Suljan? How did you sweep our Augean stables clean?”

Suljan straightened up in his seat and beamed proudly at them all. “Qubit network theory. I rewrote everything as an algorithm for an abstract quantum computer. After that, improving it was simplicity itself.”

On his way to the Blue Room, crossing the observation deck, Tchicaya spotted Birago standing by the starside wall. His first thought was to walk on by; minimizing friction by minimizing contact had become an unwritten rule of shipboard life. But the two of them had got on well enough before the separation, and Tchicaya was sick of only talking to Preservationists at the interfactional meetings, when the entire discussion was guaranteed to revolve around a mixture of procedural issues and mutual paranoia.

As Tchicaya approached, Birago saw him and smiled. He looked slightly preoccupied, but not annoyed at the interruption.

Tchicaya said, “What are you up to?”

“Just thinking about home.” Birago nodded vaguely in the direction of the blue shift, but Tchicaya knew which star he meant. It had been chosen by the people on Viro before they were scattered, and Tchicaya had had it pointed out to him by the evacuees he'd encountered on half a dozen worlds. The spore packages had already been launched from Gupta, and the evacuees—who'd spread out to many different intermediate destinations, to avoid overtaxing the hospitality of the locals—would follow within a couple of centuries. “We're not losing this one,” he said. “Not until the sun burns out.”

Tchicaya had heard the slogan many times before. Whether it was a matter of being the oldest community of evacuees, or some other factor in the original culture, people from Viro always appeared more focused on their new home than on the loss of the old. Birago himself had no clear memories of Viro—he'd left as an infant, and moved from world to world a dozen times—but if his family had wrapped him in any vision of permanence, any sense of belonging, it was anchored to their future, not their past.

Tchicaya said, “There's good reason to be hopeful now.” That wasn't giving anything away: the Preservationists would know, at the very least, that his side had had a series of breakthroughs. Their understanding was snowballing; a concrete plan for some form of stable compromise could only be a matter of time now.

Birago laughed. “
Hope
is for when you have nothing else. When I was a child, no one around me would ever look up at the border and say, ‘It's too big. We're too late. It's unstoppable.’ We had no plans, we had no remedies; the only strength we had came from refusing to give up. Which was all very laudable...but you can't go on like that forever. There has to come a time when hope turns into something more tangible.”

“Honey or ashes.”

“Ah, know-it-all travelers.” Birago smiled, but there was an edge to his voice. Picking up a few idiomatic phrases in passing didn't mean you understood anything.

“We'll both have certainty soon,” Tchicaya insisted. “I can't believe it will be much longer now.”

“
We
? What counts as certainty for you?”

“Safeguarding the far side.”

Birago was amused. “And you think that could ever be part of certainty for us?”

Tchicaya felt a chill of disappointment, but he persisted. “I don't see why not. Once we understand this thoroughly, we'll know what is and isn't safe. No one runs around extinguishing stars out of fear that they might go supernova.”

Birago gestured with his right hand, “There are tens of billions of stars to learn from”—then with his left, toward the border—“but there's only one Mimosa.”

“That doesn't mean it will remain a mystery forever.”

“No. But no one's patience lasts forever. And I know where the benefit of the doubt belongs.”

Tchicaya arrived late in the Blue Room, missing the start of Suljan's experiment. Many more people had chosen to avoid the crush and watch from their cabins, so the place was far less crowded than before, to the point where there was space for furniture.

As Tchicaya joined Rasmah, Yann, and Umrao at a table not far from the console, Rasmah was saying, “I'm not optimistic about seeing anything new, such a short distance in. If the outermost mixture of vendeks is converting our vacuum at the fastest possible rate, there could be light-years of them behind the border.”

“‘Light-years’?” Yann regarded her with amusement, as if she'd made some kind of category error: a liter of energy, a kilogram of space. The normal geometrical meaning of a quantum graph was intimately bound up with the presence of particles, and they were yet to unravel any simple notion of distance for the far side.

“You know what I mean,” Rasmah retorted. “Ten-to-the-fiftieth nodes' worth.”

Umrao said, “The hardest thing for me to wrap my mind around is the complete lack of Lorentz invariance. If you picture the graph's history as a foam—the edges all extending into surfaces, the nodes all extending into lines—you'd actually see
different
vendek populations if you re-sliced that foam in a different way.”

Tchicaya grimaced. “Doesn't that imply that there's a preferred reference frame? Couldn't you assign yourself an absolute velocity, just by seeing what kind of vendeks you were made from?”

Umrao gestured with his hands in a fashion that Tchicaya's Mediator translated as negation. “Without any external cues to guide you, you'd always slice your own world foam the same way, and see yourself as being made from the same vendeks.
Other people
moving past you might see your constituents change, depending on their velocity relative to you, but you'd see them change in the same way. And both of you would be entitled to claim that you were the best judge of your own composition.”

Tchicaya pondered this. “So everything ends up on the same footing as rest mass? It's as if speeding past an electron fast enough could make it look like any other particle at all—but in its own reference frame, it's still an electron?”

“That's right.”

Suljan shouted triumphantly, “We have an echo!”

Tchicaya turned to face the screen. It showed a simple blip, the plot of a returning pulse. Suljan's method had coarser resolving power than Yann and Branco's, but that was what allowed it to penetrate further: his signal wouldn't reflect back from the middle of a vast sea of vendeks repeating the same population mix, so any return at all meant that it had encountered a larger-scale change.

Hayashi was beside Suljan at the console. “There must be a layer population, like Umrao predicted,” she said. “Some ten-to-the-forty nodes from the border.”

Rasmah leaned toward Tchicaya and whispered, “A hundred kilometers, in good old reactionary language.”

Umrao was pleased. He said, “I wish we could tell exactly what the border mix changed into, though.” He looked around the table. “Come on, there's a challenge for you. Range
and
resolution. How?”

Rasmah joked, “I'm sure using the Right Hand as well would do wonders.”

Tchicaya said, “They'll be getting echoes, too, right now, won't they?” The two Hands themselves were about a hundred kilometers apart, so it was plausible that the scatter could reach them.

“Only if they know precisely what to look for.” Rasmah raised her hands defensively. “Don't say it: I'm the one who believes in spies.”

A sense of anticlimax had descended on the room; the result was important, but it didn't compare to their first glimpse of the Planck-scale structure of the far side. That there was macroscopic structure, too, was encouraging, but extracting further detail would be difficult. A hundred kilometers of solid rock would be no barrier to investigation, but a shift of vendeks was not like a change from crust to mantle, refracting and scattering seismic waves in a simple, predictable fashion. It was more like the boundary between two distinct ecosystems, and the fact that remnants of their expedition had straggled back intact after crossing a wide savanna didn't mean the adjoining jungle would be so easily probed.

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.”