Schild’s Ladder

your whole way of life determined by some senseless accident that has nothing to do with anything.

“When I arrived on Har’El, there was a genuine renaissance going on. People were reexamining their own traditions, not having them undermined by external events. Everything was fluid, everything was being questioned. It was the most exciting place I’ve ever lived in.”

“Really? For how long?”

Mariama shrugged. “Nothing lasts forever. You can’t have a whole world in perpetual upheaval.”

“No, but when the upheaval ended the result was apparently not a world you were prepared to live in.”

“My marriage broke up,” she said. “And Emine wanted to travel. If she’d stayed on Har’El, I might still be there. But those are personal, idiosyncratic reasons. You can’t start treating my decisions as some kind of measure of whether or not a whole society deserves to exist.”

“That’s true,” Tchicaya conceded. He was beginning to feel both battered and invigorated; she’d always had to push him to the edge of defeat before he got his second wind. He’d forgotten how much he’d loved arguing with her, when they’d taken the opposite sides back on Turaev. The only part he hated was the very thing that made it so exhilarating: there was always far too much at stake.

He said, “But even if Har’El and all the other worlds deserve to be left in peace, that right isn’t absolute.” He gestured at the border. “How can you mourn the loss of Zapata, and then turn around and destroy something a thousand times more beautiful?”

“I’m not mourning Zapata,” Mariama replied. “I’ve never been there. It means nothing to me.”

“So because no one has been through the border, whatever lies behind it is worthless?”

Mariama thought for a moment. “That’s putting it crudely. But however beautiful, and challenging, and fascinating it is, it’s not worth losing what we already have.”

“And if someone gets through and lives there for a day? Or a week? Or a century? When does the magic thing happen? When does their right to their home become equal to everyone else’s?”

“Now you’re just being jesuitical.”

“I think that’s the cruelest thing you’ve ever said to me.” Tchicaya smiled, but she didn’t soften.

“Freeze the border,” he pleaded.

Mariama said, “You freeze the border, if that’s what you want. If you do it soon, and if you do it properly, maybe that will convince us to leave it at that.” She inclined her head, and he could see her assessing the idea, judging it to be the farthest she was prepared to go. “Freeze the border before we do anything more, and you might just save whatever lies behind it.”

She turned and walked away.

Tchicaya watched her go, trying to untangle the negotiations he’d just stumbled through unwittingly. Without revealing any secrets, she’d all but declared that Tarek’s Planck worms were visible on the horizon. The fanciful notion was finally taking real shape, and she’d responded by giving him one last chance to put his own case, and to listen to her own. One last chance to sway her, or to be swayed himself.

She had given as much ground as she could. Neither of them were envoys for their factions; their decisions counted for nothing with anyone else. Between the two of them, though, there’d be no more engagement, no more discussion.

Just this challenge. This ultimatum.

This race.

Chapter 10

“I’ve already designed the vehicle you’re looking for,” Yann insisted. “I just need some help to describe it in more palatable terms, so I can sell it to the others.”

Rasmah said, “It’s not a vehicle. It’s software. And it’s software for a nonexistent computer.”

Yann shook his head. “That’s just the mathematical formalism I’ve used. It’s the best way to describe it?—? the most elegant, the most transparent. All we have to do now is disguise it.” He added, deadpan, “You can obfuscate, can’t you? Physicists have been taking simple mathematical ideas and obfuscating them for centuries. It must have been part of your training, surely?”

Rasmah took a swipe at him, and he flinched away from her. No doubt this was a habit he’d acquired during embodiment, when he’d managed to elicit a similar response from people on a regular basis.

With the queue for bodies growing ever longer as new arrivals flooded in, Yann had decided to remain acorporeal. Tarek had responded to this news at the weekly interfactional meeting with a long, paranoid dissertation on Yann’s self-evident intention to use his new position to “corrupt” the Rindler's processor network, infiltrating the Preservationists' communications and data storage systems, spying on them and undermining all their efforts. Fortunately, Sophus had spoken next, gently guiding Tarek back into contact with reality. Many things in the universe remained difficult and mysterious, but the casual structure of computer networks was not one of them. It would have required an act of cartoonish incompetence on the part of the Rindler's designers to create a network in which any of the abuses Tarek feared were physically possible.

Tchicaya said, “So you shift dynamics, once you’re through the border? You navigate between them?” He had arranged for the three of them to meet in his cabin so that Yann could try out the idea on Rasmah and refine his pitch, before taking it to a meeting of all the Yielders. “The dynamic laws are like stepping-stones that only need to last for as long as you use them?”

Yann grimaced. “That sounds ugly enough, but it’s not even close to the truth. The algorithm never obeys a sharply defined dynamic law; if it tried to do that, it would be doomed from the start.” He thought for a while. “You know how a Gaussian wave packet can keep its shape in a harmonic oscillator potential?”

“Yes.” Tchicaya felt a burst of confidence; that was just elementary quantum mechanics. In empty space, a particle’s wave packet would always disperse, spreading out without limits. But if the particle experienced an attractive force analogous to the tug of a spring in classical physics, there was a certain shape?—?a certain Gaussian, like the bell curve of statistics?—?which was stable. Any tighter, sharper wave packet would necessarily have a range of values for momentum that made it spread out; that was just the uncertainty principle. The right Gaussian, though, in the right environment, was the perfect compromise between uncertainty in position and momentum, allowing the shape of the wave to remain unchanged as it moved.

“This isn’t really the same,” Yann admitted. “But it might sound persuasive if I put it that way.”

Rasmah glanced at Tchicaya, exasperated. He made puppydog eyes back at her, pleading on Yann’s behalf.

She laughed, and relented. “Why don’t you just give me the description of the graph you want to scribe, and I’ll grind through the calculations using my own picture of Sophus’s model. If I can demonstrate that we’d get some inforamtion back through the border?—?something more than we put in?—?that might be enough to persuade people. I’ll make sure I phrase my results in the ugliest possible way.”

Yann said, “That’s wonderful. Thank you!”

He passed something to Rasmah?—?Tchicaya’s Mediator saw the fact of the exchange, but not the content? —?and then vanished.

Rasmah sighed. “You really think he’s on to something? A quantum computer can simulate any quantum process; that’s old news. It doesn’t mean that there is a quantum computer underlying anything.”

“No,” Tchicaya agreed. “But qubit network theory doesn’t claim that. It just says that when you get to a low enough level, you have nothing left to lose by treating the system as if it were software. It’s like all the proofs in applied algorithmic theory that are based on imagining Turing machines. No one complains that the real universe is conspicuously devoid of paper tape.”

“Old habits die hard,” she confessed. “I’m still in mourning for the Sarumpaet rules, and they were disproved before I was born. They’re what I was brought up on, they’re what I’ve thought of all my life as the template for a physical theory. It’s not easy adapting, even to Sophus’s model.”