Each time one of Livia’s staged targets had been achieved, Cass had dispatched a small army of digital couriers to pass on the news to seven generations of her ancestors and descendants, as well as all her friends in Chalmers. She’d received dozens of messengers herself, mostly from Lisa and Tomek, full of inconsequential gossip, but very welcome. It must have grown strange for her friends as the years had passed, and they no longer knew whether or not there was any point continuing to shout into the void. If she had traveled embodied, as a handful of ancients still did, she could have caught up with centuries of mail on the return voyage. Reduced to a timeless signal en route, though, she’d have no choice but to step unprepared into the future. Her homecoming was going to be the hardest thing she’d ever faced, but she was almost certain now that her time here would prove to have been worth it.
Half an hour before arrival, Cass rolled onto her stomach and poked her head over the edge of the couch. Her engine’s exhaust was a barely perceptible flicker, fainter than a methanol flame by daylight, but she knew that if she reached down and placed her hand in the stream of plasma, she’d rapidly lose any delusion that her Mimosan body was indestructible.
She watched the Quietener growing beneath her, the silvery sphere glinting Mimosa-blue. Surrounding it was a swarm of smaller, twinned spheres, unevenly colored and far less lustrous. Tethers, invisibly slender, allowed the twins to orbit each other, while ion jets balanced the slight tug of the Quietener’s gravity, keeping each pair’s center of mass fixed against the stars.
The Quietener made it possible to perform experiments that could never be carried out elsewhere. The right distribution of matter and energy could curve space-time in any manner that Einstein’s equations allowed, but creating a chosen state of quantum geometry was a very different proposition. Rather than simply bending space-time in bulk, like a slab of metal in a foundry, it had to be controlled with the same kind of precision as the particles in a two-slit interference experiment. But the “particles” of geometry were twenty-five orders of magnitude smaller than atoms, and they could never be vaporized, ionized, or otherwise coaxed apart to be handled one by one. So the same degree of delicacy had to be achieved with the equivalent of a ten-tonne lump of iron.
Refining the starting material helped, and the Quietener did its best to screen out every form of impurity. Ordinary matter and magnetic fields absorbed or deflected charged particles, while a shell of exotic nuclei, trapped by gamma-ray lasers in states from which they could not decay without absorbing neutrinos, mopped up a greater fraction of the billions wandering by than would have been stopped by a galaxy’s-worth of lead.
Gravitational waves passed through anything, so the only antidote was a second train of waves, tailored to cancel out the first. There was nothing to be done about sporadic cataclysms — supernovae, or black holes gorging on star clusters in the centers of distant galaxies — but the most persistent gravitational waves, coming from local binary stars, were cyclic, predictable, and faint. So the Quietener was ringed with countersources, their orbits timed to stretch space at the center of the device when the bodies they mimicked squeezed it, and vice versa.
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 farewelclass="underline" 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.”