Schild’s Ladder

As Cass passed within a few kilometers of one of the counter-sources, she could see the aggregate rocky surface that betrayed its origins in Mimosa’s rubble of asteroids. Every scrap of material here had been dragged out of that system’s gravity well over a period of almost a thousand years, a process initiated by a package of micron-sized spores sent from Viro, the nearest inhabited world, at ninety percent of lightspeed. The Mimosans themselves had come from all over, traveling here just as Cass had once the station was assembled.

The scooter’s smooth deceleration brought her to a halt beside a docking bay, and she was weightless again. Whenever she was close enough to either the station or the Quietener to judge her velocity, it seemed to be little more than that of a train, giving the impression that in the five-hour journey she might have traveled the width of a continent on Earth. Not to the moon and back, and more.

One wall of the bay had handholds. As Cass pulled herself along, Rainzi appeared beside her. The Mimosans had dusted projectors and cameras all over the walls of the places she visited in the Quietener, rendering guest and host mutually visible.

"This is it!" Rainzi said cheerfully. "Barring untimely supernovae, we’ll finally get to see your graph complete." The software portrayed him with a jet pack, to rationalize his ability to follow her uneven progress up the wall without touching anything.

Cass replied stoically, "I’ll believe it when it happens." In fact, from the moment Ilene had scheduled the run, twelve hours before, Cass had felt insanely confident that no more hurdles remained. Eight of the fourteen previous targets had been achieved at the first attempt, making the prospect of one more tantalizingly plausible. But she was reluctant to admit to taking anything for granted, and if something did go wrong it would be easier to swallow her disappointment if she’d been pretending from the start that her expectations had always been suitably modest.

Rainzi didn’t argue, but he ignored her feigned pessimism. He said, "I have a proposition for you. A new experience you might like to try, to celebrate the occasion. I suspect it will be against all your high-minded principles, but I honestly believe you’d enjoy it. Will you hear me out?"

He wore a look of such deadpan innocence that Cass felt sure he knew exactly how this sounded in translation. If that was his meaning, the idea wasn’t entirely absurd, or unwelcome. She’d grown fond of Rainzi, and if he’d never been quite as solicitous or as eager to understand her as Darsono, the truth was, that made him more intriguing. If they could find enough common ground to become lovers, it might be a fitting way to bid Mimosa farewell: sweeping away the mutually distorted views they had of each other. To remain loyal to the ideals of embodiment, here, she’d been forced to adopt a kind of asceticism, but that was definitely not a quality to which she’d ever aspired, let alone one for which she hoped to be remembered.

She said, "I’m listening."

"For special events like this, we sometimes go nuclear. So I thought I’d ask whether you’d like to join us."

Cass froze, and stared at him. "Nuclear? How? Has someone solved all the problems?" Femtomachines built from exotic nuclei had been employed as special-purpose computers ever since the basic design had been developed, six thousand years before. For sheer speed, they left every other substrate in the dust. But as far as Cass knew, no one could make a femtomachine stable for more than a few picoseconds; they could perform a great many calculations in that time, but then they blew themselves apart and left you hunting through the debris for the answer. Gamma-ray spectroscopy could only extract a few hundred kilobytes, which was orders of magnitude too small even for a differential memory — a compressed description of experience that could be absorbed by a frozen reference copy of the person who’d actually lived through it. Cass might have missed the news of a breakthrough while she’d been on her way here from Earth, but if word had reached Mimosa Station at all she should have heard by now.

"Nothing’s changed in the technology," Rainzi said. "We do it freestyle. One-way."

Freestyle meant implementing your mind on a substrate that underwent quantum divergence. One-way meant none of the end products of any version of the computation could be retrieved, and transferred back into your usual hardware. Rainzi was asking her to clone herself into a nuclear abacus-cum-time-bomb that would generate a multitude of different versions of her, while holding out no prospect of even one survivor.