Schild's Ladder (5 page)

Yet they would all be one person: awake, asleep. The dream she would not remember would be her own.

Here and now, though?

She would have to make do with whatever glimpses she could steal.

She turned to Yann. “Freeze me. One last time.”

Chapter 3

Cass looked around the simulated chamber. The display on the wall was densely inscribed with new data, but nothing else appeared to have changed. The Mimosans were the usual icons drawn by her Mediator; she still had no hope of perceiving them as they perceived themselves. The structures in her mind where sensory data was represented hadn't changed; they simply weren't coupled to genuine sense organs anymore. It was only the touch of Rainzi's nonexistent skin against her own—a translation interacting with a simulation—that proved she'd stepped from her world into his.

Or rather, they'd both stepped together into a new world, from which neither of them could hope to emerge.

Cass felt no anxiety, just a bittersweet sense of everything her newfound freedom did and didn't mean. If she'd abandoned embodiment a year or two earlier, she might have had some prospect of going further: finding a path of gradual change that led to new abilities, such as the power to interpret the Mimosans' language firsthand. As it was, she didn't even have time for the smallest act of self-indulgence: a simulated swim, a solid meal, a glass of cool water. After five years, all the pleasures she'd been pining for had become attainable at the very moment when they would be nothing but unwelcome distractions.

She slipped her hand free of Rainzi's and turned to examine the display. A faint spray of particles was radiating out from the center of the Quietener, the sign of an unstable boundary between old vacuum and new.

The data had only been coming in for a few hundredths of a picosecond, so the statistics were still ambiguous. As she watched, rows of figures were updated, the sprinkling of points on half a dozen charts grew denser, curves shifted slightly. Cass knew where every number and every curve was heading; it was like watching the face of a long-awaited friend materialize out of the darkness, having pictured the reunion a thousand times. And if the face might yet turn out to be a stranger's, that had nothing to do with the way she felt. There was pleasure enough in anticipation; she didn't need to conjure up traces of doubt just to savor the added suspense.

“What we're doing isn't all that unusual,” Darsono mused. “I think everyone lives in at least two time scales: one of them fast and immediate, and too detailed to retain in anything but outline; the other slow enough to be absorbed completely. We think our memory has no gaps, we think we carry our entire past inside us, because we're accustomed to looking back and seeing only sketches and highlights. But we all experience more than we remember.”

“That's not true of everyone,” Bakim countered. “There are people who record every thought they have.”

“Yes, but unless every part of that record has the potential to be triggered automatically by subsequent thoughts and perceptions—which no one ever allows, because the barrage of associations would drive them mad—it's not true memory. It's just a list of all the things they've forgotten.”

Bakim chortled. “‘True memory’? And I suppose if I perceive something with so much spatial resolution that I can't give immediate, conscious attention to every last detail simultaneously, it's not a ‘true’ perception—it's just a cruel taunt to drive home all the things I've failed to perceive?”

Cass smiled, but stayed out of the argument.
With certainty
? Probably not. But it was pointless dwelling on every potential branching; if and when she experienced something unpleasant, firsthand, or did something foolish herself, she could regret it. Anything else was both futile and a kind of masochistic doublecounting. (And she would not start wondering if
that
resolution was universal—a constant across histories, an act of inevitable good sense—or just the luck of one branch.)

Livia said, “I don't understand what's happening with the energy spectrum.” In the feigned weightlessness of the chamber, she appeared upside down, her face at the upper edge of Cass's vision. “Does that make sense to anyone?”

Cass examined the histogram showing the number of particles that had been detected in different energy ranges; it did not appear to be converging on the theoretically predicted curve. She'd noticed this earlier, but she'd assumed it was just an artifact of the small sample they'd collected. The histogram's rim was quite smooth, though, and its overall shape wasn't fluctuating much, so its failure to match the curve really didn't look like an accident of noise. Worse, all the high-powered statistics beneath the chart suggested that there was now enough data to give a reliable picture of the underlying spectrum.

“Could we have miscalculated the border geometry?” Rainzi wondered. The particles they were seeing reflected the way the novo-vacuum was collapsing. Cass had first modeled the process back on Earth, and her calculations had shown that, although the border's initial shape would be a product of both pure chance and some uncontrollable details of conditions in the Quietener, as it collapsed it would rapidly become spherical, all quirks and wrinkles smoothed out.

At least, that was true if some plausible assumptions held. She said, “If the converted region had a sufficiently pathological shape to start with, it might have retained that as it shrank. But I don't know what could have caused that in the first place.”

“Some minor contaminant that wasn't quite enough to wreck coherence?” Ilene suggested.

Cass made a noncommittal sound. It would be nice to have a view from several different angles, allowing them to pick up any asymmetry in the radiation. But they'd been woken by the arrival of data from the cluster of detectors closest to the femtomachine; information from the second-closest would take almost another microsecond to reach the same spot, by which time they'd be long gone. Her old embodied self would get to see the big picture, albeit more coarsely grained. Her own task—her own entire
raison d'être
—was to make what sense she could of the clues at hand.

The energy spectrum wasn't jagged and complicated, or even particularly broad. It didn't look
wrong enough
to be the product of a sausage- or pancake- or doughnut-shaped region of novo-vacuum, let alone some more exotic structure with a convoluted fractal border. The peak had about the same width, and the same kind of smooth symmetry as the predicted curve; it was merely displaced upward along the energy scale, and the shoulders on either side were reversed. It wasn't literally a mirror image of the expected result, but Cass felt sure it was the product of some fairly simple transformation. If you changed a single plus sign to a minus, somewhere deep in the underlying equations,
this
would be the outcome.

Zulkifli was one step ahead of her. “If you modify the operator that acts on the border, swapping the roles of the inside and outside of the region, you get a perfect match.”

Cass experienced a shiver of fear, all the more disturbing for evoking the phantom viscera of her Earth body.
If Zulkifli's claim was true, then the region was expanding, not collapsing
.

She said, “Are you sure that works?”

Zulkifli made his private calculations visible, and superimposed the results on the histogram. His curve ran straight through the tops of all the bars. He'd found the plus sign that had turned into a minus. Except—

“That can't be right,” she declared. The simple role reversal he'd suggested was elegant, but nonsensical: it was like claiming that they were seeing the light from a fire in which ashes were burning into wood. Conservation of energy was a subtle concept, even in classical general relativity, but in QGT it came down to the fact that the flat vacuum state remained completely unchanged from moment to moment. An awful lot of physics flowed from that simple requirement, and though it was remote from everyday notions of work, heat, and energy, a billion commonplace events that Cass had witnessed throughout her life would have been impossible, if the truth were so different that Zulkifli's border operator was the right choice.

There was silence. No one could contradict her, nor could they deny that Zulkifli's curve matched the data.

Then Livia spoke. “The Sarumpaet rules make our own vacuum perfectly stable; that's the touchstone Sarumpaet used from the start. But the novo-vacuum is
not
decaying in the way those rules predict. So what's the simplest way to reconcile the contradictions?” She paused for a moment, then offered her own solution. “Suppose
both
kinds of vacuum are perfectly stable, on their own. If there's a wider law that makes that true—with the Sarumpaet rules as a special case—we would never have stumbled on it in the staged experiments, because we never had the full set of virtual particles that constituted a viable alternative vacuum.”

Yann grinned appreciatively. “All states with the potential to be a vacuum must be treated equally? However exotic we might think they are, they're all eternal? Very democratic! But wouldn't that imply a stalemate? Wouldn't that freeze the novo-vacuum, leaving the border fixed?”

Ilene said, “No. The dynamics needn't be that evenhanded. One side could still convert the other at a boundary. The one with the fewest species of particles, I expect.”

By any count, the novo-vacuum was the more streamlined of the two
. Cass was more angry than afraid, though. Talk of a runaway vacuum conversion was intolerable; they'd spent five years ruling that out, validating the Sarumpaet rules for every related graph. They could not have been more cautious.

Rainzi said calmly, “Suppose the novo-vacuum is growing. What happens when it encounters some contamination? It's a coherent state that could only be created in perfect isolation, in the middle of the purest vacuum in the universe. It's fragility incarnate. Once it hits a few stray neutrinos and decoheres, it will be forty-eight flavors of ordinary vacuum—all of them in separate histories, all of them harmless.”

Livia glanced warily at Cass. It was as if she wanted Cass to be the bearer of bad news for a change, rather than always hearing it from her.

Cass obliged her. “I wish you were right, Rainzi, but that argument's biased. It's just as correct to say that our own vacuum is a superposition of different curved versions of the novo-vacuum. If there really is a new dynamic law at work here, and if it preserves the novo-vacuum precisely, then according to
that
law, it's
our
vacuum that's the delicate quantum object waiting to decohere.”

Rainzi pondered this. “You're right,” he conceded. “Though even that doesn't tell us much about the border. Neither of the specialized laws that apply on either side can hold there. We'll only understand the fate of the border if we can understand the general law.”

Cass laughed bitterly. “What difference does it make, what
we
understand? We won't be able to tell anyone! We won't be able to warn them!” The border wasn't traveling at lightspeed—or they wouldn't have been woken at all before it swept over the femtomachine—but it was unlikely to be spreading so slowly that their originals would see it coming, let alone have a chance to evacuate. In any case, what she and her fellow clones knew was worthless; they had no way to share their knowledge with the outside world. The femtomachine was designed to do no more than compute its inhabitants, for their own benefit. All it would leave behind was debris. Even if they could encode a message in the decay products, no one would be looking for it.

A lifetime's worth of defensive slogans about the perils of VR started clamoring in her head. She wanted to scrape this whole illusion off her face, like a poisonous, blinding cobweb; she wanted to see and touch reality again.
To have real skin, to breathe real air, would change everything
. If she could only see the world through her own eyes, and react with the instincts of her own body, she knew she could flee from any danger.

It was so perverse it was almost funny. She was perceiving the danger a billion times more clearly than she could ever have hoped to if she'd been embodied. She had all her reflexes at her disposal, and all her powers of reasoning, operating a billion times faster than usual.

It was just a shame that all of these advantages counted for nothing.

Zulkifli said, “The brightness is increasing.”

Cass examined the evidence as dispassionately as she could. A slow, steady rise in the rate of particle production was apparent now, clearly distinguishable from the background fluctuations that had initially masked it. That could only mean that the border was growing. Short of some freakishly benign explanation for this—a fractal crinkling that allowed the border to increase in area while the volume of novo-vacuum itself was shrinking—this left little room for doubt about which vacuum was being whittled away to produce the particles they were seeing. The thing she had always thought of as an elegant piece of whimsy—as charming and impractical as a mythical beast that might be bioengineered into existence, and kept alive briefly if it was pampered and protected, but which could never have lasted five minutes outside its glass cage—was now visibly devouring its ancient, wild cousin. She had summoned up, not a lone, defenseless exile from a world that could never have been, but the world itself—and it was proving to be every bit as autonomous and viable as her own.

Rainzi addressed her, gently but directly. “If the station is destroyed, we all have recent backups
en route
to Viro. What about you?”

She said, “I have my memories back on Earth. But nothing since I arrived here.” The five years she'd spent among the Mimosans would be lost.
It had still happened. She had still lived through it all. It would be amnesia, not death
. But if that argument had been enough to let her step willingly into the
cul-de-sac
she inhabited now, she wasn't sure she could push it far enough to reconcile herself to the greater loss. She had finally become someone new, at the station—someone different enough from her old self to be here now, beside the Mimosans. But the Cass who had steeled herself to leave the solar system for the very first time would wake from her frozen sleep unchanged, to learn that the emboldened traveler she'd hoped to become was dead.