Greg Egan - Schild's Ladder

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SCHILD'S LADDER
Greg Egan
Thanks to John Baez, Jennifer Brehl, Caroline Oakley, Anthony Cheetham, John Douglas, Simon
Spanton, Oisín Murphy-Lawless, Devi Pillai, Peter Robinson, Russell Galen, Carol Jackson, Emma
Bailey, Diana Mackay, Philip Patterson, Christodoulos Litharis, Nicola Fantini, Giancarlo Carlotti, Albert
Solé, Petr Kotrle, Makoto Yamagishi, Florin Pîtea, and Mihai-Dan Pavelescu.
Contents
Part One
Chapter 1
In the beginning was a graph, more like diamond than graphite.…
Chapter 2
Riding her ion scooter the million kilometers to the Quietener,…
Chapter 3
Cass looked around the simulated chamber. The display on…
Part Two
Chapter 4
By choice, Tchicaya's mind started running long before his…
Chapter 5
The shuttle separated from the Rindler, sending Tchicaya's…
Chapter 6
Something unseen stung Tchicaya's hand, a vibration like a…
Chapter 7
Sophus was far too tactful to ask Tchicaya how he and Mariama…
Chapter 8
Yann rolled off the bed and landed on the floor, laughing.…
Chapter 9
"Everyone complains about the laws of physics, but no one…
Chapter 10
"I've already designed the vehicle you're looking for," Yann…
Chapter 11
Tchicaya said, "We should tell them, now! Take them all the…
Chapter 12
"It looks as if the Colosseum is about to welcome us in,"…
Chapter 13
Tchicaya's Mediator woke him. It had just received a messenger…
Chapter 14
When the first, paralyzing wave of despair had left him, Tchicaya…
Chapter 15
Tchicaya looked out from the Sarumpaet into a lime-green sea.…
Chapter 16
Tchicaya looked down through the panes in the floor into a…
Chapter 17
The Sarumpaet circumnavigated the xennobe colony, reconnoitering,…
Chapter 18
Time was everything, and Tchicaya felt a streak of brutal…
References
About the Author
Other Books by Greg Egan
Cover
Credits
Copyright
About the Publisher
Part One
Chapter 1
In the beginning was a graph, more like diamond than graphite. Every node in this graph was tetravalent:
connected by four edges to four other nodes. By a count of edges, the shortest path from any node back
to itself was a loop six edges long. Every node belonged to twenty-four such loops, as well as forty-eight
loops eight edges long, and four hundred and eighty that were ten edges long. The edges had no length or
shape, the nodes no position; the graph consisted only of the fact that some nodes were connected to
others. This pattern of connections, repeated endlessly, was all there was.
In the beginning? Waking more fully, Cass corrected herself: that was the version she remembered from
childhood, but these days she preferred to be more cautious. The Sarumpaet rules let you trace the
history of the universe back to the vicnity of the Diamond Graph, and everything you could ask for in a
Big Bang was there: low entropy, particle creation, rapidly expanding space. Whether it made sense to
follow these signposts all the way back, though, was another question.
Cass let the graph's honeycomb pattern linger in the darkness of her skull. Having relinquished her
child's-eye view of the world, she was unable to decide which epoch of her life she actually inhabited. It
was one of the minor perils of longevity: waking could be like to trying to find your way home on a street
with ten thousand houses, all of which had once been your own. That the clues on the other side of her
eyelids might be more enlightening was beside the point; she had to follow the internal logic of her
memories back into the present before she could jolt herself awake.
The Sarumpaet rules assigned a quantum amplitude to the possibility of any one graph being followed by
another. Among other things, the rules predicted that if a graph contained a loop consisting of three
trivalent nodes alternating with three pentavalent ones, its most likely successors would share the same
pattern, but it would be shifted to an adjoining set of nodes. A loop like this was known as a photon. The
rules predicted that the photon would move. (Which way? All directions were equally likely. To aim the
photon took more work, superimposing a swarm of different versions that would interfere and cancel
each other out when they traveled in all but one favored direction.)
Other patterns could propagate in a similar fashion, and their symmetries and interactions matched up
perfectly with the known fundamental particles. Every graph was still just a graph, a collection of nodes
and their mutual connections, but the flaws in the diamond took on a life of their own.
The current state of the universe was a long way from the Diamond Graph. Even a patch of near-vacuum
in the middle of interstellar space owed its near-Euclidean geometry to the fact that it was an elaborate
superposition of a multitude of graphs, each one riddled with virtual particles. And while an ideal vacuum,
in all its complexity, was a known quantity, most real space departed from that ideal in an uncontrollable
manner: shot through with cosmic radiation, molecular contaminants, neutrinos, and the endless faint
ripple of gravitational waves.
So Cass had traveled to Mimosa Station, half a light-year from the blue subgiant for which it was named,
three hundred and seventy light-years from Earth. Here, Rainzi and his colleagues had built a shield
against the noise.
Cass opened her eyes. Lifting her head to peer through a portal, still strapped to the bed at the waist, she
could just make out the Quietener: a blue glint reflecting off the hull a million kilometers away. Mimosa
Station had so little room to spare that she'd had to settle for a body two millimeters high, which rendered
her vision less acute than usual. The combination of weightlessness, vacuum, and insectile dimensions did
make her feel pleasantly robust, though: her mass had shrunk a thousand times more than the cross
sections of her muscles and tendons, so the pressures and strains involved in any collision were
feather-light. Even if she charged straight into a ceramic wall, it felt like being stopped by a barricade of
petals.
It was a pity the same magical resilience couldn't apply to her encounters with less tangible obstacles.
She'd left Earth with no guarantee that the Mimosans would see any merit in her proposal, but it was only
in the last few days that she'd begun to face up to the possibility of a bruising rejection. She could have
presented her entire case from home, stoically accepting a sevenhundred-and-forty-year delay between
each stage of the argument. Or she could have sent a Surrogate, well briefed but nonsentient, to plead on
her behalf. But she'd succumbed to a mixture of impatience and a sense of proprietorship, and
transmitted herself blind.
Now the verdict was less than two hours away.
She unstrapped herself and drifted away from the bed. She didn't need to wash, or purge herself of
wastes. From the moment she'd arrived, as a stream of ultraviolet pulses with a header requesting
embodiment on almost any terms, the Mimosans had been polite and accommodating; Cass had been
careful not to abuse their hospitality by pleading for frivolous luxuries. A self-contained body and a safe
place to sleep were the only things she really needed in order to feel like herself. Being hermetically
sealed against the vacuum and feeding on nothing but light took some getting used to, but so did the
customs and climate of any unfamiliar region back on Earth. Demanding the right to eat and excrete, here,
would have been as crass as insisting on slavish recreations of her favorite childhood meals, while a guest
at some terrestrial facility.
A circular tunnel, slightly wider than her height, connected her spartan quarters to a chamber where she
could interact with the software she'd brought from Earth, and through it the Mimosans themselves. She
bounced down the borehole, slapping the wall with her hands and feet, bumping her head and elbows
deliberately.
As she entered the chamber, she seemed to emerge from the mouth of a burrow to float above a lush,
wide meadow beneath a cloud-dappled sky. The illusion was purely audiovisual--the sounds encoded in
radio waves--but with no weight to hold her against the ceramic hidden beneath the meadow, the force
of detail was eerily compelling. It only took a few blades of grass and some chirping insects to make her
half-believe that she could smell the late-summer air.
Would it really have been an act of self-betrayal, if this landscape had stretched all the way inside
her--right down to the sensations of inhabiting her old, two-meter body, gorging on a breakfast of fruit
and oats after swimming across Chalmers Lake? If she could drift in and out of this soothing work of art
without losing her grip on reality, why couldn't she take the process a few steps further?
She pushed the argument aside, though she was glad that it never stopped nagging at her. When the
means existed to transform yourself, instantly and effortlessly, into anything at all, the only way to maintain
an identity was to draw your own boundaries. But once you lost the urge to keep on asking whether or
not you'd drawn them in the right place, you might as well have been born Homo sapiens, with no real
choices at all.
A short distance from the burrow stood a marble statue of Rainzi, arms folded, smiling slightly. Cass
gestured at the messenger and it came to life, the white stone taking on the hue and texture of skin. Rainzi
himself was several generations removed from anyone who'd bothered to simulate a living dermis, let
alone possess one, but Cass was not equipped to make sense of the Mimosans' own communications
protocols, so she'd chosen to have everything translated into the visual dialect used back on Earth.
"We'll give you our decision at nine o'clock, as promised," the messenger assured her. "But we hope you
won't mind if we precede this with a final review session. Some of us feel that there are matters that have
yet to be entirely resolved. We'll begin at half past seven." The messenger bowed, then froze again,
expecting no reply.
Cass tried not to read too much into the sudden change of plan. It was unnerving to discover that her
hosts still hadn't been able to reach a verdict, but at least they weren't going to keep her waiting any
longer than she'd expected. The fact that she'd alread briefed them in detail on every aspect of the
experiment that had crossed her mind during three decades of preparation, and they now hoped to hear
something new and decisive from her in twenty minutes' time, was no reason to panic. Whatever loose
ends they'd found in her analysis, they were giving her the chance to put things right.
Her confidence was shaken, though, and she couldn't stop thinking about the prospect of failure. After a
month here, she still wasn't lonely, or homesick; that was the price she'd pay upon returning. Even at the
leisurely pace of the embodied, seven hundred and forty years cut a deep rift. It would be millennia
before the changes that her friends on Earth had lived through together would cease to set her apart from
them. Millennia, if ever.
She still believed that she could come to terms with that loss, so long as she had something to weigh
against it. Being a singleton meant accepting that every decision had its cost, but once you understood
that this state of affairs was a hard-won prize, not a plight to rail against, it gave some dignity to all but the
most foolish choices.
If the Mimosans turned her down, though? Maybe there was something daring and romantic in the mere
act of traveling hundreds of light-years, inhabiting the body of a vacuum-dwelling insect, and alienating
herself from the world where she belonged, all in the hope of seeing her ideas tested as rapidly as
possible. But for how long would she be able to take comfort from the sheer audacity of what she'd
done, once that hope had come to nothing?
She curled into a ball and tried to weep. She could not shed tears, and the sobs rebounding against her
membrance-sealed mouth were like the drone of a mosquito. But the shuddering as she worked her
vestigial lungs still provided some sense of release. She had not entirely erased the map of her Earthly
body from her mind; too much of the way she experienced emotions was bound up in its specific form.
So everything she'd amputated lingered as a kind of phantom--nowhere near as convincing as a true
simulation, but still compelling enough to make a difference.
When she was spent, Cass stretched out her limbs and drifted over the meadow like a dandelion seed, as
calm and lucid as she'd been at any time since her arrival.
She knew what she knew about Quantum Graph Theory, backward. Whatever insights she was capable
of extracting from that body of knowledge, she'd extracted long ago. But if the Mimosans had found a
question she couldn't answer, a doubt she couldn't assuage, that in itself would be a chance to learn
something more.
Even if they sent her home with nothing else, she would not be leaving empty-handed.
It was Livia who asked the first question, and it was far simpler than anything Cass had anticipated.
"Do you believe that the Sarumpaet rules are correct?"
Cass hesitated longer than she needed to, a calculated attempt to imbue her response with appropriate
gravity.
"I'm not certain that they are, but the likelihood seems overwhelming to me."
"Your experiment would test them more rigorously than anything that's been tried before," Livia
observed.
Cass nodded. "I do see that as a benefit, but only a minor one. I don't believe that merely testing the rules
one more time would justify the experiment. I'm more interested in what the rules imply, given that they're
almost certainly correct."
Where was this heading? She glanced around at the others, seated in a ring in the meadow: Yann,
Bakim, Darsono, Ilene, Zulkifli, and Rainzi. Her Mediator had chosen appearances for all of them, since
they offered none themselves, but at least their facial expressions and body language were modulated by
their own intentional signals. By choice, they all looked politely interested, but were giving nothing away.
"You have a lot of confidence in QGT?" Clearly, Livia did realize just how strange her questions
sounded; her tone was that of someone begging to be indulged until her purpose became apparent.
Cass said, "Yes, I do. It's simple, it's elegant, and it's consistent with all observations to date." That
handful of words sounded glib, but other people had quantified all of these criteria long ago. QGT as a
description of the dynamics of the universe with the minimum possible algorithmic complexity. QGT as a
topological redescription of some basic results in category theory--a mathematical setting in which the
Sarumpaet rules appeared as natural and inevitable as the rules of arithmetic. QGT as the most probable
underlying system of physical laws, given any substantial database of experimental results that spanned
both nuclear physics and cosmology.
Darsono leaned toward her and interjected, "But why, in your heart"--he thumped his chest with an
imaginary fist--"are you convinced that it's true?" Cass smiled. That was not a gesture in the staid
vocabulary her Mediator used by default; Darsono must have requested it explicitly.
"In part, it's the history," she admitted, relaxing slightly. "The lineage of the ideas. If some alien civilization
had handed us Quantum Graph Theory on a stone tablet--out of the blue, in the eighteenth or nineteenth
century--I might not feel the same way about it. But general relativity and quantum mechanics were
among the most beautiful things the ancients created, and they're still the best practical approximations we
have for most of the universe. QGT is their union. If general relativity is so close to the truth that only the
tiniest fragment can be missing, and quantum mechanics is the same...how much freedom can there be to
encompass all of the successes of both, and still be wrong?"
Kusnanto Sarumpaet had lived on Earth at the turn of the third millennium, when a group of physicists
and mathematicians scattered across the planet--now known universally as the Sultans of Spin--had
produced the first viable offspring of general relativity and quantum mechanics. To merge the two
descriptions of nature, you needed to replace the precise, unequivocal geometry of classical space-time
with a quantum state that assigned amplitudes to a whole range of possible geometries. One way to do
this was to imagine carrying a particle such as an electron around a loop, and computing the amplitude for
its direction of spin being the same at the end of the journey as when it first set out. In flat space, the spins
would always agree, but in curved space the result would depend on the detailed geometry of the region
through which the particle had traveled. Generalizing this idea, crisscrossing space with a whole network
of paths taken by particles of various spins, and comparing them all at the junctions where they met, led
to the notion of a spin network. Like the harmonics of a wave, these networks comprised a set of
building blocks from which all quantum states of geometry could be constructed.
Sarumpaet's quantum graphs were the children of spin networks, moving one step further away from
general relativity by taking their own parents' best qualities at face value. They abandoned the idea of any
preexisting space in which the network could be embedded, and defined everything--space, time,
geometry, and matter--entirely on their own terms. Particles were loops of altered valence woven into the
graph. The area of any surface was due to the number of edges of the graph that pierced it, the volume of
any region to the number of nodes it contained. And every measure of time, from planetary orbits to the
vibrations of nuclei, could ultimately be rephrased as a count of the changes between the graphs
describing space at two different moments.
Sarumpaet had struggled for decades to breathe life into this vision, by finding the correct laws that
governed the probability of any one graph evolving into another. In the end, he'd been blessed by a lack
of choices; there had only been one set of rules that could make everything work. The two grandparents
of his theory, imperfect as they were, could not be very far wrong: both had yielded predictions in their
respective domains that had been verified to hair's-breadth accuracy. Doing justice to both had left no
room for errors.
Livia said, "Conceptually, that argument is very appealing. But there could still be deviations from the
rules--far too small to have been detected so far--that would change the outcome of your experiment
completely."
"So it's a sensitive test," Cass agreed. "But that's not why I've proposed it." They were talking in circles.
"If the rules hold, the graph I've designed should be stable for almost six-trillionths of a second. That's
long enough to give us a wealth of observations of a space-time utterly different from our own. If it
doesn't last that long, I'll be disappointed. I'm not doing this in the hope of proving Sarumpaet wrong!"
Cass turned to Darsono, seeking some hint that he might share her exasperation, but before she could
gauge his mood, Livia spoke again.
"What if it lasts much longer?"
Finally, Cass understood. "This is about safety? I've addressed the potential risks, very thoroughly--"
"On the basis that the Sarumpaet rules are correct."
"Yes. What other basis should I have used?" Phoenician astrology? Californian lithomancy? Cass
resisted the urge to lapse into sarcasm; there was too much at stake. "I've admitted that there's no
certainty that the rules hold in every last untested circumstance. But I have nothing better to put in their
place."
"Nor do I," Livia said gently. "My point is, we mustn't over-interpret the success of the Sarumpaet rules.
General relativity and quantum field theory confessed from the start that they were just approximations:
pushed to extremes, they both yielded obvious nonsense. But the fact that QGT doesn't--the fact that
there is no fundamental reason why it can't be universally applicable--is no guarantee that it really does
stretch that far."
Cass gritted her teeth. "I concede that. But where does it leave us? Refusing to perform any experiment
that hasn't been tried before?"
Rainzi said, "Of course not. Livia is proposing a staged approach. Before attempting to construct your
graph, we'd move toward it in a series of experiments, gradually bridging the gap."
Cass fell silent. Compared to outright rejection this was a trivial obstacle, but it still stung: she'd worked
for thirty years to refine her own proposal, and she resented the implication that she'd been reckless.
"How many stages?"
"Fifteen," Livia replied. She swept a hand through the vacuum in front of her, and a sequence of target
graphs appeared. Cass studied them, taking her time.
They'd been well chosen. At first one by one, then in pairs, then triples, the features that conspired to
render her own target stable were introduced. If there was some undiscovered flaw in the rules that
would make the final graph dangerous, there could be no more systematic way to detect it in advance.
"It's your choice," Rainzi said. "We'll vote on whichever proposal you endorse."
Cass met his eyes. The openness of his face was an act of puppetry, but that didn't mean he was
insincere. This wasn't a threat, an attempt to bully her into agreeing. It was a mark of respect that they
were letting her decide, letting her weigh up her own costs, her own fears, before they voted.
She said, "Fifteen experiments. How long would that take?"
Ilene answered, "Perhaps three years. Perhaps five." Conditions varied, and the Quietener wasn't perfect.
Planning an experiment in QGT was like waiting for a stretch of ocean to grow sufficiently calm that a few
flimsy barriers could block the waves and keep out the wildlife long enough to let you test some subtle
principle of fluid dynamics. There was no equivalent of a laboratory water tank; space-time was all
ocean, indivisible.
In terms of separation from her friends, five years was nothing compared to the centuries she'd already
lost. Still, Cass found the prospect daunting. It must have shown on her face, because Bakim responded,
"You could always return to Earth immediately, and wait for the results there." Some of the Mimosans
had trouble understanding why anyone who found life in the station arduous would feel obliged to be here
in person at all.
Darsono, empathetic as ever, added quickly, "Or we could give you new quarters. There's a suitable
cavity on the other side of the station, almost twice as large; it's just a matter of rerouting some cables."
Cass laughed. "Thank you." Maybe they could build her a new body, too, four whole millimeters long. Or
she could abandon her scruples, melt into software, and wallow in whatever luxuries she desired. That
was the hazard she'd face every day, here: not just the risk that she'd give in to temptation, but the risk
that all the principles she'd chosen to define herself would come to seem like nothing but masochistic
nonsense.
She lowered her gaze toward the illusory meadow, laserpainted on her retinas like everything around her,
but her mind's eye conjured up another image just as strongly from within: the Diamond Graph, as she
saw it in her dreams. She could never reach it, never touch it, but she could learn to see it from a new
direction, understand it in a new way. She'd come here in the hope of being changed, by that knowledge
if by nothing else. To flee back to Earth out of fear that she might test her own boundaries more
rigorously here, in a mere five years of consciousness, than if she'd spent the same three-quarters of a
millennium at home, would be the greatest act of cowardice in her life.
"I'll accept the staged experiments," she declared. "I endorse Livia's proposal."
Rainzi said, "All in favor?"
There was silence. Cass could hear crickets chirping. No one? Not Livia herself? Not even Darsono?
She looked up.
All seven Mimosans had raised their hands.
Chapter 2
Riding her ion scooter the million kilometers to the Quietener, Cass found herself reveling in the view for
the first time in years. The scooter was doing one-and-a-quarter gees, but the couch pressed against her
back so gently that she might have been floating. Floating in dark water, beneath an alien sky. Even at
half a light-year, Mimosa punched a dazzling violet hole in the blackness, a pinprick ten times as bright as
a full moon. Away from its glare, the stars were far too plentiful to suggest constellations; any stick-figure
object that she began to sketch between them was soon undermined by an equally compelling alternative,
then a third, then a fourth--like a superposition of graphs, each with a different choice of edges between
the same nodes. When she'd first arrived, she'd homed in on her own star, watching with a mixture of
fear and exaltation as it hovered at the edge of visibility to her thousandth-scale eyes. Now, she'd
forgotten all the cues she'd need to find it, and she felt no urge to ask her navigation software to remind
her. The sun was no beacon of reassurance, and she'd be seeing it close-up again soon enough.
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 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.
摘要：

SCHILD'SLADDERGregEganThankstoJohnBaez,JenniferBrehl,CarolineOakley,AnthonyCheetham,JohnDouglas,SimonSpanton,OisínMurphy-Lawless,DeviPillai,PeterRobinson,RussellGalen,CarolJackson,EmmaBailey,DianaMackay,PhilipPatterson,ChristodoulosLitharis,NicolaFantini,GiancarloCarlotti,AlbertSolé,PetrKotrle,Makot...

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Greg Egan - Schild's Ladder.pdf

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