Sophus was far too tactful to ask Tchicaya how he and Mariama knew each other; it must have been obvious that the answer was long, complicated, and largely none of his business. Tchicaya volunteered the bare minimum that the situation seemed to require. "We grew up together, in the same town on Turaev," he explained. "It"s been a while since we last ran into each other."

When Mariama asked to hear what was happening on the Rindler, Tchicaya deferred to Sophus, who took up the task of outlining some seventeen decades' worth of advances and disappointments. Tchicaya listened politely, hoping Mariama was taking in more than he was. His thoughts were still so scattered by the shock of her arrival that he gave up trying to pay attention; he could replay the whole conversation later.

As Sophus talked, the three of them strolled around the ship. Mariama was unfazed by the view from the walkways; she might not have been this close to the border before, but apparently she"d become accustomed to space. Then again, it would not have surprised him if she had decided to choose equanimity in the new environment by fiat, even if this was her first time off-planet.

When Tchicaya tuned in to the discussion again, Mariama was saying, "So there"s no prospect of using universality-class arguments to design a generally effective Planck worm, before we pin down the detailed physics?"

Sophus said, "Tarek has looked into that, and even tried some experiments, but I believe it"s a dead end. For a start, we still don"t know what the bulk symmetries of this system are. I"ve more or less given up talking about the novo-vacuum; it"s too misleading. What vacuum? We don"t know that there"s state that lies in the null space of all annihilation operators for the Mimosan seed particles. And if there is such a state, we don"t know that it will obey anything remotely analogous to Lorentz invariance. Whatever"s behind the border might not even posses any kind of time-translation symmetry."

"You"re joking!"

"No. In fact, it"s looking more likely every day." Sophus glanced at Tchicaya meaningfully, as if he was waiting for the Preservationists' laudable openness to be acknowledged.

Tchicaya said, "That"s right. I watched one experiment myself, just a few hours ago." Mariama smiled at him, envious at this slight head start.

He smiled back at her, hoping his face wasn"t betraying his confusion. At the instant he"d seen her standing on the observation deck, he hadn"t consciously assumed anything about the faction she"d be joining; such ephemeral concerns had been swept from his thoughts entirely. Now that she"d casually revealed in passing that she"d come here to support the side that he would have sworn she"d be committed to opposing, the one part of his mind that resonated with this fact was the oldest, crudest model he had of her: someone whose only role in life was to confound and unsettle him. The original Mariama, who he had imagined would go to any lengths, not so much to spite him as to prove that he had no hope of pinning her down.

Tchicaya dragged his thoughts back to Sophus"s comments.

Kadir and Zyfete had been nowhere near as explicit, but then they"d not been in the friendliest of moods. Kadir"s despair made more sense now, though; it went beyond his growing fears for his home world, and one more ordinarily frustrating encounter with the border.

Time-translation symmetry was the key to all their hopes of predicting how the novo-vacuum would behave. In ordinary physics, if two people performed the same experiment, one starting work at midnight while the other began at noon, their separate versions could be compared, very easily: you merely added or subtracted half a day, and all their data could be superimposed. That sounded too obvious to be worth stating, but the fact that it was possible, and the fact that any laws of physics had to be compatible with this process of sliding the two sequences of events together, was a powerful constraint on the forms such laws could take.

Everything that happened in the universe was unique, on some level. If that were not true, there"d be no such thing as memory, or history; there"d be no meaningful chronology at all. At the same time, it was always possible to unpick some features of an event from the complicated tapestry of its context, and demand that this tiny patch of reality look the same as countless others, once you knew how to orient them all for the purpose of comparison. Taking a step north on Turaev on your eighteenth birthday could never be the same as taking a step west on Pachner four thousand years later, but in analyzing these two admittedly singular activities, you could safely abstract the relevant joints and muscles from the surrounding thicket of biographical and planetological detail, and declare that the applicable laws of mechanics were precisely the same in both cases.

It had been obvious since the accident that whatever the Mimosans had created in the Quietener did not possess the same symmetries as ordinary space-time, which allowed the unique location, time, orientation, and velocity of any physical system to be stripped away, revealing its essential nature. Still less had anyone expected the Mimosan vacuum to obey the "internal" symmetries that rendered an electron"s phase or a quark"s color as arbitrary as the choice of a planet"s prime meridian.

But everyone studying the novo-vacuum had been relying on the assumption that these familiar regularities had merely been replaced by more exotic ones. Mathematicians had long had a catalog of possibilities on offer that dwarfed those realized in nature: more or fewer dimensions, different invariant geometric structures, novel Lie groups for the transformations between particles. All of these things would be strange to encounter, but ultimately tractable. And at the very least, it had been taken for granted that there was some prospect of using the results of sufficiently simple experiments to deduce what would happen when those experiments were repeated. Once you lost that, prediction in the conventional sense became impossible. You might as well try to guess who you"d meet in a crowded theater on Quine by consulting the guest list for an opening night of Aeschylus.

Tchicaya said, "If you"re right, we"re wasting our time here."

Sophus laughed. "I wish all Yielders were so easily discouraged."

Tchicaya caught the change in Mariama"s demeanor as he was finally labeled for her. She did not appear surprised, or cooler toward him, but a look of resignation crossed her face, as if she was letting other possibilities slip away.

He replied, "I didn"t say I believed you. Now I know you"re just spreading misinformation."

Sophus said, "The data"s all public; you should judge for yourself. But I"m giving a presentation later today that might interest you."

"On why we should all give up and go home? Yielders first, of course."

"No. On why we shouldn"t, even if I"m right."

Tchicaya was intrigued. "Dishing out despair with one hand, taking it away with the other. You"re never going to drive us away like that."

"I"m really not interested in driving anyone away," Sophus protested. "The more people there are working on this, the sooner we"ll understand it. I"m happy to share my ideas with everyone - and if some Yielder beats me to the punch line because of it, and fails to show reciprocal generosity, what have I lost?"

"You"re not afraid we"ll get through the border first? And shore up what you hope to annihilate?"

Sophus smiled amiably. "There might come a point when that"s a real threat. If I"m ever convinced that we"ve reached it, I suppose I might change my strategy. For now, though, it"s like a game of Quantum Pass-the-Parcel: all the players work simultaneously to tear off the wrapping, and all the players share the benefits. Why convert to the classical version? This is faster, and much more enjoyable."

Tchicaya let the argument rest. It would have been impolite to state the obvious: when Sophus finally decided that sharing his insights had become too risky, it would not be to his advantage to announce the fact. At that point, the most logical strategy would be to continue displaying the same generosity as he"d shown in the past, but to replace the genuine, hard-won conjectures he"d revealed to his opponents in the past with equally well-crafted red herrings.

When they reached Mariama"s cabin, Sophus left them. Tchicaya hung back in the corridor, unsure whether she wanted him to stay or go.

She said, "Would you come in, if you"re coming in?"

He sat cross-legged on the bed while she moved around the cabin. She"d included some physical ornaments in her transmission - a handful of carved rocks and blown-glass objects that the Rindler's reception unit had obligingly re-created for her from spare materials - and now she couldn"t decide where to put them.

"I traveled light, myself," Tchicaya said teasingly. "It didn"t seem fair to ask them to cannibalize the ship to provide me with knickknacks."

Mariama narrowed her eyes. "Aren"t you the puritan? Not to the point of amnesia, I hope."

He laughed. "Not these days." In the past, he"d left some rarely used memories behind in the Qusps of his body trail. With fullsensory recall, the amount of data mounted up rapidly, and there"d come a point when knowing precisely what it had been like to shake water out of his ears in a river on Gupta or roll over and fart while camping in a desert on Peldan didn"t really strike him as a crucial part of his identity.

Yet he"d gathered up all the trivia again, before any of the Qusps were erased. And now that there was nowhere he could store his memories in the expectation that they"d remain secure - even if he archived them with a fleeing acorporeal community, their safety would come at the price of accessibility - they all seemed worth dragging around with him indefinitely.

Mariama finally settled on the shelf by the bed as the place for an elaborately braided variant of Klein"s bottle. "Holding on to your memories is one thing," she said. "It doesn"t stop you going over the horizon."

Tchicaya snorted. "Over the horizon? I"m four thousand and nine years old! Take out Slowdowns and travel insentience, and I"ve barely experienced half of that." Information theory put bounds on the kind of correlations anyone could sustain between their mental states at different times; the details depended on the structure of your mind, the nature of its hardware, and, ultimately, on the recently rather plasticized laws of physics. If there were unavoidable limits, though, they were eons away. "I think I can still lay claim to doing a far better job of resembling myself - at any prior age - than a randomly chosen stranger."

Mariama folded her arms, smiling slightly. "In the strict sense, obviously. But don"t you think people can cross another kind of horizon? The strict definition counts everything: every aspect of temperament, every minor taste, every trivial opinion. There are so many markers, it"s no wonder it takes an eternity for all of them to drift far enough to change someone beyond recognition. But they"re not the things that define us. They"re not the things that would make our younger selves accept us as their rightful successors, or recoil in horror."

Tchicaya gave her a warning look that he hoped would steer her away from the subject. With a stranger, he might have asked his Mediator to handle the subtext, but he didn"t believe either of them had changed so much that they couldn"t read each other"s faces.

He said, "Any more children?"

She nodded. "One. Emine. She"s six hundred and twelve."

Tchicaya smiled. "That"s very restrained. I"ve had six."

"Six! Are any of them with you here?"

"No." He took a moment to realize why she was asking; he"d always sworn that he"d never leave a child before a century had passed. "They"re all on Gleason; large families are common there. The youngest is four hundred and ninety."

"No travelers among them?"

"No. What about Emine?"

Mariama nodded happily. "She was born on Har"El. She left with me. We traveled together for a while."

"Where is she now?"

"I"m not certain." She admitted this without a trace of reticence, but Tchicaya still thought there was a hint of sadness in her voice.

He said, "One thing about being planet-bound is, once you"ve committed to the place, that"s it. Even if you wander off to the other side of the world, everyone else who"s chosen to stay is just a few hours away."

"But two travelers? What does that guarantee?" Mariama shrugged. "Chance meetings, every few hundred years. Or more often, if you make the effort. I don"t feel like I"ve lost Emine."

"Of course not. Nor the others. What"s to stop you visiting the ones who"ve stayed put?"

She shook her head. "You know the answer to that. You"re like a cross between a fairy-tale character and some kind of...rare climatic disaster."

"Oh, come on! It"s not that bad." Tchicaya knew there was a grain of truth in what she said, but it seemed perverse to complain about it. When he was made to feel welcome, it was as a visitor, a temporary novelty. When your child had lived with three or four generations of their own descendants, for centuries, you were not a missing piece of the puzzle. But he never expected to slot in, anywhere. Once he"d told the crib on Turaev that his birth flesh could be recycled, he"d given up the notion that somewhere there"d always be a room waiting for him.

He said, "So what about Emine"s other parent?"

Mariama smiled. "What about your partner back on Gleason? The one you raised six children with."

"I asked first."

"What is there to say? She stayed on Har"El. Not even Emine could drag her away." Mariama lowered here eyes and traced a fingertip over the edges of one of the abstract carvings.

Tchicaya said, "If you could drag everyone with you, what would be the point of leaving? There were cultures back on Earth that traveled across continents, whole extended families together - and they were usually more conservative than the ones that stayed put, or the ones that spawned diasporas."

Mariama scowled. "If two travelers happened to have a child, would that constitute a tribe?"

"No. But traveling is not about a change of scenery. It"s about breaking connections." Tchicaya felt a sudden sense of déjà vu, then realized that he was quoting her own words back at her. He"d got into the habit long ago of using them on other people. "I"m not saying that there"d be anything wrong if six whole generations uprooted themselves together, if that"s not a contradiction in terms. But they wouldn"t stay together for long - or at least, they wouldn"t without imposing rules on themselves a thousand times more restrictive than any they"d needed when they were planetbound."

Mariama said irritably, "You"re such a fucking ideologue sometimes! And before you call me a hypocrite: it"s always the converts who are the worst."

"Yeah? That"s not such a convenient axiom for you, if you remember that it cuts both ways." Tchicaya raised his hands in apology; he wasn"t really angry or offended yet, but he could see where they were heading. "Just...forget I said that. Can we change the subject? Please?"

"You can tell me what happened on Gleason."

Tchicaya thought for a while before replying. "Her name was Lesya. I was there for a hundred and sixty years. We were in love, all that time. We were like bedrock to each other. I was as happy as I"ve ever been." He spread his arms. "That"s it. That"s what happened on Gleason."

Mariama eyed him skeptically. "Nothing soured?"

"No."

"And you don"t wish you were still there?"

"No."

"Then you weren"t in love. You might have been happy, but you weren"t in love."

Tchicaya shook his head, amused. "Now who"s the ideologue?"

"You just woke up one morning and decided to leave? And there was no pain, and no rancor?"

"No, we woke up one morning, and we both knew I"d be gone within a year. Just because she wasn"t a traveler doesn"t mean it was all down to me. What do you think? I lied to her at the start?" He was becoming so animated he was messing up the bed; he stroked the sheet, and it tightened. "You know how I think she"ll feel, if the border reaches Gleason?"

Mariama resisted answering, knowing that she was being set up. After several seconds, she succumbed anyway.

"Terrified?"

"No. I think she"ll be grateful." Tchicaya smiled at Mariama"s expression of disgust. It was strange, but she"d probably given him more confidence in his stance, now that she"d turned out to be his opponent, than if they"d been allies willing to reassure each other endlessly.

He continued. "You don"t take a traveler for a partner if you hope that the world will always stay the same. You do it because you can"t quite break away, yourself, but you can"t live without the promise of change hanging over you every day.

"That"s what the border means, for a lot of people. The promise of change they"d never be able to make any other way."

Sophus"s presentation took place in a theater that the ship had improvised in the middle of one of the accommodation modules, folding up all the cabins that happened to be unoccupied to create a single large space. When Mariama realized that this included her own, she was not pleased.

"I have glass in there!" She pointed across the theater. "Right where that person"s sitting."

"It"ll be protected," Tchicaya reassured her, as if he were a veteran of the concertina effect. "Anyway, what"s there to lose? If anything"s broken, it can be reconstructed."

"They"ve never been broken," she complained.

Tchicaya said, "I hate to be the one to point this out, but - " He held up his thumb and forefinger and adjusted the spacing to atomic size.

Mariama glared at him until he dropped his hand. "It"s not the same thing. But I wouldn"t expect you to understand."

Tchicaya winced. "So now I"m an all-round philistine?"

Mariama"s face softened. She reached over and ran a hand affectionately across his stubbled scalp. "No. Your failings are much more specific than that."

Tchicaya spotted Yann coming through the entrance with a small group of people. He raised a hand and tentatively beckoned to him. Yann responded by bringing the whole group along to sit beside them.

Rasmah, Hayashi, Birago, and Suljan had been involved in designing the new spectrometer. Catching the tail end of the conversation they"d been having made it clear that all but Birago were Yielders; the other three were joking about his plans to sneak in a filter to conceal the telltale signature of Planck worms devouring the scenery. Birago seemed to be taking their teasing with equanimity, though it struck Tchicaya that he had the quietness of someone outnumbered, who had decided that there was no point in speaking his mind.

Perhaps Mariama felt outnumbered, too, but she appeared genuinely amiable toward the Yielders as introductions were made; she was certainly more than diplomatically polite. Tchicaya had been wondering whether their friendship had caused her to conceal the full measure of her distaste for his position, but whatever effort she was making for his benefit, she was nowhere near the point that Kadir and Zyfete had reached.

Yann said, "The new spectrometer looks good. We"ll be able to resolve a whole new band of gamma rays, and with twice the precision of the old machine."

Tchicaya nodded, unsure how much difference that would make. "Do you know what this is all about?" He gestured at the podium that was now growing before their eyes. His Mediator had explained that the timing was meant to encourage people to stop talking among themselves - like a change of lighting, or the raising of curtains - but apparently this was an aspect of the Rindler's local culture that had been documented without ever being practiced.

"Not really," Yann admitted. "There"s usually something on the grapevine about these talks, weeks in advance, but this one has come out of the blue. Sophus is always interesting, though. I"m sure he"ll be worth listening to."

"He said something to me earlier about time asymmetry."

"What, time-reversal asymmetry? He"s talking about an arrow of time in the novo-vacuum?"

"No, time-translation asymmetry."

Yann"s eyes widened. "Interesting might have been an understatement."

Sophus appeared and made his way to the podium, but then he stood to one side. People were still entering the theater, and it looked as if they"d keep on streaming in until it was completely full.

Mariama surveyed the latecomers irritably. "Why can"t they watch this in their heads?"

"It"s a flesh thing," Yann confided. "I don"t understand it either."

Tchicaya glanced up. People were sitting in chairs suspended from the ceiling, accessed via corridors through higher levels that would otherwise have come to a sudden end. The ship had made use of every square meter of available surface, even though there was no prospect of cramming every last passenger in. Rasmah caught Tchicaya"s eye and joked, "I always wanted to be at a performance where people were hanging from the rafters."

Sophus cleared his throat, and the audience fell silent almost immediately. Tchicaya was impressed; even if he"d known everyone on the ship personally, he would probably have asked his Mediator to plead on his behalf for their attention.

Sophus began. "We"ve been scribing probes and gathering data now for more than two hundred and fifty years, trying to understand what"s going on behind that wall." He motioned with a raised fist, as if pounding against the border. "The results are there for everyone to see. Theories come and go, and all we have gained is the ability to rule out ninety-nine percent of new models without performing a single new experiment, because we already have enough data to kill off most of our ideas at birth.

"To some people, it"s beginning to look hopeless. How can the laws we"ve failed to understand be so difficult to grasp? It only took three and a half centuries to get from Newton to Sarumpaet. What"s wrong with us? We have the mathematical tools to model systems far more arcane than anything nature has ever actually thrown at us, before. The acorporeals grew bored with physics ten thousand years ago; expecting them to live with such meager intellectual stimulation was like asking an adult to spend eternity playing with a child"s numbered blocks. But even their boundlessly flexible minds can"t make sense of the new toy they"ve come here to admire."

Tchicaya glanced at Yann, who whispered plaintively, "Maybe I should be grateful whenever it slips someone"s mind that acorporeals were running the Quietener."

"The Sarumpaet rules survived twenty thousand years of scrutiny!" Sophus marveled. "How flawed, how misguided, could they possibly be? So we began with the sensible, conservative approach: we"d find a new set of rules that extended the old ones, very slightly. The smallest change we could possibly make, the tiniest correction, or expansion, that would encompass all their past successes - but also explain what happened at Mimosa.

"Fine. That"s a simple enough piece of mathematics; people solved the equations within days of hearing the news. Then we built the Rindler...and that minimal extension didn"t quite fit what we found. So we tweaked the rules a little more. And a little more.

"In essence - and I know this is unfair to some of you, but I"m going to say it anyway - most of what"s been done here has consisted of repeating that process, over and over, for a quarter of a millennium. We"ve raised ever more elaborate theoretical towers on the same foundations, and most of them have been toppled by the very first prediction they made."

Sophus paused, frowning slightly. He looked almost apologetic, as if he"d been surprised by the tone of his own rhetoric. When he"d spoken to Tchicaya earlier, he"d appeared casually optimistic, but now his frustration was showing through. That sentiment was understandable, but it risked undermining the reception of whatever he said next: to claim any kind of fundamental new insight now would sound like arrogance, after so many people before him had struggled and failed. Still, if he honestly believed that they"d all been misguided, and that progress would come not from standing on their shoulders but from digging in the opposite direction entirely, there was a limit to how graciously that opinion could be expressed.

He collected himself and continued, loosening his posture, visibly striving to make light of his subject, however many worlds, and egos, were at stake.

"Sarumpaet was right about everything that happened before Mimosa. We have to hold on to that fact! And in one sense, we were right, to aim to tamper with his work as little as possible. But what we shouldn"t have done was paint ourselves into a corner where we just kept building ever more baroque and elaborate refinements of the original rules.

"What do the Sarumpaet rules really say?" Sophus looked around the theater, as if expecting volunteers, but he"d caught everyone off-balance, and there were no takers. "We can write them half a dozen ways, and they"re all equally elegant and compelling. A combinatorial recipe for transition amplitudes between quantum graphs. A Hamiltonian we exponentiate to compute the way a state vector evolves with time. There"s a Lagrangian formulation, a category-theoretic formulation, a qubit-processing formulation, and probably a hundred more versions cherished by various enthusiasts, who"ll never forgive me for leaving out their favorite one.

"But what do they all say, in the end? They say that our vacuum is stable. And why do they say that? Because Sarumpaet required them to do so! If they"d implied anything else, he would have considered them to be a failure. The stability of the vacuum is not a prediction that emerges from some deep principle that had to be satisfied, regardless; it was the number one design criterion for the whole theory. Sarumpaet certainly found some simple and beautiful axioms that met his goal, but mathematics is full of equally beautiful axioms that don"t get to govern everything that happens in the universe."

Sophus halted again, arms folded, head inclined. To Tchicaya he seemed to be pleading for forbearance; what he"d just stated was so obvious and uncontroversial that half the audience had probably found it baffling, if not downright offensive, that he"d wasted their time spelling it out for the thousandth time.

"Our vacuum is stable: that was the hook on which Sarumpaet hung everything. So why did he have such unprecedented success, despite basing his entire theory on something we now know to be false?"

Sophus let the question hang in the air for a moment, then changed tack completely.

"I wonder how many of you have heard of superselection rules? I only learned the phrase myself a month ago, while doing some historical research. They"re an arcane notion from the dawn of quantum mechanics, and they only persisted in the vocabulary for the first couple of centuries, before people finally got things straightened out.

"Everyone knows that it"s an axiom of quantum mechanics that you can form superpositions of any two state vectors: if V and W are possible physical states, then so is aV + bW, for any complex numbers a and b whose squared magnitudes sum to one. If that"s true, though, then why do we never see a quantum state with a fifty-percent probability of being negatively charged, and a fifty-percent probability of being positively charged? Conservation of charge is not the issue. Long after people could routinely prepare photons that were equally likely to be on opposite sides of a continent, why couldn"t they manage to prepare a system that was equally likely to be an electron here and a positron here" - Sophus held up his left hand, then his right - "or vice versa?

"For a hundred years or so, most people would have answered that question by saying: Oh, there"s a superselection rule for charge! You can usually combine state vectors...but not if they come from different superselection sectors of the Hilbert space! Apparently there were these strange ghettos that had been cordoned off from each other, and whose inhabitants were not allowed to mix. Cordoned off how? There was no mechanism, no system; it was just an inexplicable fact dressed up in some fancy terminology. But people went ahead and developed methods for doing quantum mechanics with these arbitrary borders thrown in, and the lines on the map became something to be memorized without too much scrutiny. If some innocent novice asked a jaded elder student, Why can"t you have a superposition of different charges? the reply would be, Because there"s a superselection rule forbidding it, you idiot!"

Sophus lowered his gaze slightly before adding acerbically, "We"re far more sophisticated now, of course. No one would tolerate mystification like that - and besides, every child knows the real reason. An electron and a positron in the same position would be correlated with vastly different states for the surrounding electric field, and unless you could track all the details of that field and incorporate them into your observations, you"d have no hope of recognizing the state as a superposition. Instead, the two different charge states would decohere, and you"d be split into two versions, one believing that you"d detected an electron, the other that you"d detected a positron. So although there are no superselection rules, the world still looks so much like the way it would look if there were that all the mathematics that revolved around the term lives on, in various guises."

Tchicaya sensed a sudden change in the atmosphere around him. When he"d glanced at people before, most had seemed puzzled that they were being offered such mundane observations. Tolerant, and prepared to go on listening for a while, thanks to Sophus"s reputation, but clearly not expecting much from yet another tortured reexamination of their field"s basic assumptions. Now there was a shifting of bodies, a creaking of seats, as people felt compelled to transform their postures of indifference or mild disappointment into something altogether more vigilant.

As this mood swept the room, Tchicaya felt gooseflesh rise along his spine. He couldn"t claim to have anticipated the words he heard next, but they thoroughly merited his body"s reaction.

"I believe there are no Sarumpaet rules," Sophus proclaimed. "Not the originals, and not some grander, more perfect version that will explain what happened at Mimosa. But the world still looks so much like the way it would look if there were that we couldn"t help but think such rules existed."

In the silence that followed, Tchicaya turned to Mariama, wondering if she"d picked up more from Sophus"s earlier remarks than he had, but she appeared to be equally stunned. Tchicaya was beaming with delight at the audacity of Sophus"s claim. Mariama looked dismayed, almost fearful.

Sophus continued. "How can the Sarumpaet rules seem to be true, when they"re false? How can our vacuum seem to be stable, when it isn"t? I believe that the right way to answer these questions is virtually identical to the resolution of another paradox, one that was dealt with almost twenty thousand years ago. How can the universe appear to obey classical mechanics, when it really obeys quantum mechanics?

"What creates the illusion of classical mechanics is our inability to keep track of every aspect of a quantum system. If we can"t observe the whole system - if it"s too large and complex in itself, or if it"s coupled to its surroundings, making them part of the system - we lose the information that distinguishes a genuine superposition, where alternatives coexist and interact, from a classical mixture of mutually exclusive possibilities.

"I believe the same effect is responsible for the Sarumpaet rules. How can that be? The Sarumpaet rules are quantum rules. They apply to systems that have not been rendered classical by decoherence. How can interaction with the environment explain anything wholly quantum-mechanical?"

Sophus smiled wearily. "It"s been staring us in the face for twenty thousand years. An electron - a charged particle, which transforms the ordinary vacuum around it into an entirely different state - still obeys quantum mechanics in all of its other degrees of freedom. Its position is quantum-mechanical, its charge is classical. Even when we do our best to isolate an electron from its surroundings, we actually fail miserably at half of the task, while succeeding at the other half. So decoherence hides superpositions of different charge states from us, but not different position states. Our failure looks classical, our success is quantum-mechanical.

"We thought the Sarumpaet rules were pure quantum mechanics: the final story, the lowest level, the rules that held for a system in perfect isolation. Of course, we accepted the fact that, in practice, we could never isolate anything from its surroundings completely, but that wasn"t the point. The universe itself, the total system, was assumed to be obeying the Sarumpaet rules - because whenever we did our best to examine any small part of it, separated out as scrupulously as possible, those were the laws that held.

"That was the wrong conclusion to reach. The electron shows how quantum and classical properties can coexist. The fact that you can demonstrate some quantum behavior in a system doesn"t mean you"ve uncovered all that there is to be found.

"I believe that the Sarumpaet rules are classical rules. Part of the total state vector of any system obeys them, but not the whole. The part that does follow the Sarumpaet rules interacts with the environment one way: transforming its surroundings into what we think of as our own vacuum. But there are other parts that interact differently, creating other states. Because we can"t begin to track what"s really happening to the environment on the Planck scale, what we see is a single, certain, classical outcome: the Sarumpaet rules hold absolutely true, and our vacuum is absolutely stable."

A member of the audience stood, and Sophus acknowledged the request. "Tarek?"

"You"re claiming that the vacuum has been stabilized by something like the quantum Zeno effect?"

Tchicaya craned his neck to observe the questioner more closely. Tarek was the Preservationist who"d been trying to scribe Planck worms to devour the novo-vacuum, without waiting to discover what it was, or what it might contain. There was nothing fanatical about his demeanor, though; he merely radiated an impatience that everyone in the audience shared.

"It"s similar to that," Sophus agreed. "The quantum Zeno effect stabilizes systems through constant measurement. I believe that part of the total graph in which everything"s embedded measures the part we see as the vacuum, which also determines the dynamic laws that govern matter moving through that vacuum. It"s like the vapor in a cloud chamber, condensing in droplets around the path of a subatomic particle. The particle only appears to follow a definite trajectory because each path is correlated with a particular pattern of droplets - and the droplets have too many hidden degrees of freedom to exhibit quantum effects themselves. But we know there are branches where the particle follows different paths, surrounded by different trails of droplets."

Tarek frowned. "So why can"t we discover the path, the rules, that are holding sway behind the border?"

Sophus said, "Because what lies behind the border is not another vacuum, another set of rules. It has no classical properties like that to discover. It"s not that it couldn"t be divided up - formally, mathematically - into a sum of components, each obeying a different analog of the Sarumpaet rules. But we"re not correlated with any particular component, the way we are with our own vacuum, so we can"t expect to uncover any particular set of rules."

Tchicaya was exhilarated. It was too soon to take Sophus"s idea seriously, but there was something deeply appealing in the simplicity of the notion. Behind the border was a superposition of every possible dynamic law.

Tarek said, "We can"t measure those properties? Make them definite, if only for different branches of ourselves? When we interact with the novo-vacuum - or whatever you now wish to call it - shouldn"t we end up as a superposition of observers who each find definite laws?"

Sophus shook his head firmly. "Not by dropping a few Planckscale probe graphs into a system six hundred light-years wide. If there were preexisting laws behind the border, we might hope to discover them that way, but that"s not what we"re dealing with. On our side of the border, there"s a tight correlation stretching across all of space-time: the dynamics being followed at different times and places has become a tangle of mutual interdependence. What lies behind the border isn"t correlated from place to place, or from moment to moment. What we"re sampling with our probe graphs might as well be random noise at every level."

Rasmah stood, just ahead of a dozen other people. The others resumed their seats, and Tarek begrudgingly followed.

She said, "This is wonderful speculation, Sophus, but how do you plan to test it? Do you have any solid predictions?"

Sophus gestured at the space behind him, and a set of graphs appeared.

"As you see, I can match the borderlight spectrum. That"s not claiming much. I can match the half-c velocity of the border, which is slightly harder. And I can match the pooled results of all the experiments performed here so far: namely, their complete failure to identify anything resembling a dynamic law.

"So much for retrodiction. I"m making the following prediction: when we repeat the old experiments, re-scribe the old probe graphs, and monitor the results with your new spectrometer...we"ll find exactly the same thing, all over again. No patterns will emerge, no symmetries, no invariants, no laws.

"We"ve already discovered that there"s nothing to be discovered. All I can predict is that however hard we look, that absence will be confirmed."

Yann rolled off the bed and landed on the floor, laughing.

Tchicaya peered over the edge. "Are you all right?"

Yann nodded, covering his mouth with a hand but unable to silence himself.

Tchicaya didn"t know whether to be annoyed or concerned. Acorporeals taking on bodies often mapped them in unusual ways. Perhaps laughter was Yann"s only available response to some terrible psychic affront that Tchicaya had unwittingly inflicted.

"You"re sure I haven"t hurt you?"

Yann shook his head, still laughing helplessly.

Tchicaya sat on the edge of the bed, struggling to regain his own sense of humor. "This is not a reaction I"m accustomed to. Rejection and hilarity are perfectly acceptable responses, but they"re supposed to occur much earlier in proceedings."

Yann managed to regain some composure. "I"m sorry. I didn"t mean to offend you."

"I take it you"re not interested in finishing what you started?"

"Umm." Yann grimaced. "I could try, if it"s important to you. But I think it would be very difficult to take seriously."

Tchicaya planted a foot on his chest. "Next time you want an authentic embodied experience...just simulate it." He still felt a pang of lust at the touch of skin on skin, but it was fading into a kind of exasperated affection.

He crouched down and kissed Yann on the mouth, meaning it as a gesture of finality. Yann smiled, puzzled. "That was nice."

"Forget it." Tchicaya stood and started dressing.

Yann lay on the floor, watching him. "I think I"m getting all the signals you talked about," he mused. "But they"re so crude, even now. And before, it was just a single message, repeating itself endlessly: Be happy, be happy, be happy! Do you think there"s something wrong with this body?"

"I doubt it." Tchicaya sat cross-legged on the floor beside him.

"You expected more?"

"I was already happy, so it was a bit redundant."

"How happy?"

"As happy as it"s possible to be, for no particular reason."

"I have no idea how to interpret that. What gets to count as a particular reason?"

Yann shrugged. "Something more than being told by my body: Be happy. Be happy...why?"

"Because you"re with someone you like. And you"re making them happy, too."

"Yes, but only if they accept the same reasoning. That"s circular."

Tchicaya groaned. "Now you"re being disingenuous. It"s a tradition, passed down from reproductive biology. Every tradition"s arbitrary. That doesn"t mean it"s empty."

"I know. But I still expected something more subtle."

"That takes time."

"What, hours?"

"Centuries."

Yann narrowed his eyes with suspicion.

Tchicaya laughed, but made a face protesting his honesty. "On Turaev, it takes six months of attraction before anything"s physically possible." Like most generic bodies, the Rindler's were promiscuous: any two of them could develop compatible sexual organs, more or less at will. You could wire in your own chosen restraints while you inhabited them, but since leaving home, Tchicaya had never felt the need to delegate the task. "The waiting was nice, in its own way," he admitted. "You might think it was risking an awful anticlimax, but I think the buildup improved the sex itself almost as much as it raised expectations. Acting on the spur of the moment is more likely to be disappointing."

Yann protested, "I"ve been contemplating this for almost six months."

"Since I arrived? I"m flattered. But then, who else would you dare to ask?"

Yann smiled abashedly. "How could I not be curious? It"s what flesh is famous for. However undeservedly." He watched Tchicaya carefully, serious for a moment. "Have I hurt you?"

Tchicaya shook his head. "That usually takes longer, too." He hesitated. "So what do acorporeals do, instead? When I was a child, I used to imagine that you"d all have simulated bodies. Sex would be just like embodied sex, but there"d be lots of colored lights, and cosmic bliss."

Yann guffawed. "Maybe twenty thousand years ago there were people that vacuous, but they must have all decayed into thermal noise before I was born." He added hastily, "I"m not saying you"re wrong to continue the tradition. You"ve mapped some stable mammalian neurobiology, and it"s not too pathological in its original form. I suppose it still serves some useful social functions, as well as being a mild existential placebo. But when you have a malleable mental structure, intensifying pleasure for its own sake is a very uninteresting cul-de-sac. We worked that out a long time ago."

"Fair enough. But what do you do instead?"

Yann sat up and leaned against the side of the bed. "All the other things the embodied do. Give gifts. Show affection. Be attentive. Sometimes we raise children together."

"What kind of gifts?"

"Art. Music. Theorems."

"Original theorems?"

"If you"re serious."

Tchicaya was impressed. Mathematics was a vast territory, far more challenging and intricate than physical space. Reaching a theorem no one had proved before was a remarkable feat. "That"s positively...chivalric," he said. "Like a knight riding off to the edge of the world, to bring back a dragon"s egg. And you"ve done that, yourself?"

"Yes."

"How often?"

"Nine times." Yann laughed at Tchicaya"s expression of astonishment, and added, "It"s not always that serious. If it was, it really would be as daunting as winning the hand of medieval royalty, and no one would bother."

"So you start with something easier?"

Yann nodded. "When I was ten years old, all I gave my sweet-heart was a pair of projections that turned the group of rotations in four dimensions into principal bundles over the three-sphere. Ancient constructions, though I did rediscover them for myself."

"How were they received?"

"She liked them so much, she extended them to larger spaces and gave me back the result."

"Can you show me?"

Yann sketched diagrams and equations with his hands; through their Mediators, Tchicaya saw them painted in the air. To make sense of the group of four-dimensional rotations, you could project it down to the three-dimensional sphere of directions in four dimensions, by mapping each rotation to the direction to which it took the x-axis. All the rotations that treated the x-axis in the same way then differed from each other by rotations of the other three directions. This effectively sliced the original group into copies of the group of three-dimensional rotations - which was just a solid sphere with opposite points on its boundary glued together, since any pair of rotations around opposite axes became equal once you reached one hundred and eighty degrees. Like an artful rendering of depth in a painting, these striations made the topology of the larger group much clearer.

"The other projection inverts all the rotations first, so it turns the whole construction inside out." Yann demonstrated, smiling nostalgically. "I know it"s sentimental, but the first time always stays with you."

"Yeah." The mathematics was simple, but it struck Tchicaya as having all the charm of an embodied child"s handmade gift.

"So what about you?"

"I"ve generally had more success with flowers."

Yann rolled his eyes. "Your own first love. What was that like?"

Tchicaya contemplated lying, but he usually did it badly. And what would he say? He wasn"t going to substitute someone else, writing Mariama out of his life.

He said, "I can"t tell you."

"Why not?" Yann was twice as eager for the details, now. "How embarrassing can it be, four thousand years later?"

"You"d be surprised." Tchicaya struggled to think of a way to deflect the inquiry without piquing Yann"s curiosity further. "There"s much better story I can tell you," he said. "About my father"s first love. Can I trade that instead?"

Yann agreed, reluctantly.

"When my father was fourteen," Tchicaya began, "he fell in love with Lajos. It started in winter, when they used to sneak into each other"s houses at night and sleep together."

Yann said, "Why did they have to sneak? Would their parents have stopped them?"

Tchicaya was momentarily at a loss for an answer; he"d never had to explain this before. "No. Their parents would have known. But it"s more enjoyable to pretend that it"s a secret."

Yann seemed slightly bemused by this claim, but willing to take his word for it. "Go on."

"By summer, they were giddy with it. They could touch and kiss, nothing more, but they knew it wouldn"t be much longer. They"d go swimming together, walking together, waiting for it to happen. Aching this wonderful ache." Tchicaya smiled, hiding a sudden upwelling of sadness. He doubted he"d ever return to Turaev, to talk to the stranger his father had become.

"At the height of summer, they were walking on the outskirts of town. And my father witnessed the strangest, most terrifying event that had happened on Turaev for a thousand years. A spaceship descended from the sky. An ancient engine, spouting flames, burning up crops, melting rocks."

Yann was outraged. "And Lajos - " He struggled with his emotions. "Your father saw Lajos - "

"No, no!" Tchicaya was amused at the preposterousness of this suggestion, but he still warmed to Yann"s response. He"d met bigots who would have assumed that an acorporeal would shrug off the notion that witnessing the local death of your first love would be of any consequence at all.

"Not even anachronauts land their spacecraft on top of people," he explained. "They do have instruments."

Yann relaxed. "So your father and Lajos got to meet the anachronauts. What were they like?"

"They"d left Earth fourteen thousand years before. Pre-Qusp. They used biological techniques to keep their flesh viable, but they spent a lot of time cryogenically suspended."

"Cryogenically suspended." Yann was mesmerized. "I always knew they were out there, but I"ve never met anyone before who"s spoken to someone who"s seen them in the flesh." He shuddered with vicarious otherworldliness. "What did they want?"

"When they left Earth, they knew they"d be overtaken by newer technologies; they knew they"d be traveling into the future. They knew there"d be established societies along their route. That was why they left. They wanted to witness what humanity would become."

"I see." Yann appeared to be on the verge of raising another objection, but then he let it pass.

"They had one particular interest, though," Tchicaya continued. "They told my father that they wanted to know what stage his people were in, in the eternal struggle between women and men. They wanted to hear about the wars, the truces. The victories, the compromises, the setbacks."

"Wait. How old is your father now?"

"About six millennia."

"So..." Yann rubbed his neck, perplexed. "Turaev was the very first planet they"d visited? After fourteen thousand years?"

"No, they"d made planet-fall six times before."

Yann spread his arms in surrender. "You"ve lost me, then."

"No one had had the heart to tell them," Tchicaya explained. "When they first made contact with a modern society, on Crane, it took a while before they were sufficiently at ease to reveal their purpose. But by the time they got around to asking questions, the locals had already gained a clear sense of the kind of preconceptions these travelers had. They"d been in cold storage for millennia, and now they were finally beginning the stage of their voyage that would justify the enormous sacrifices they"d made. Nobody could bring themselves to break the news that the sole surviving remnant of human sexual dimorphism was the retention, in some languages, of different inflections of various parts of speech associated with different proper names - and that expecting these grammatical fossils to be correlated with any aspect of a person"s anatomy would be like assuming from similar rules for inanimate objects that a cloud possessed a penis and a table contained a womb."

"So they lied to them?" Yann was horrified. "On Crane? And on all the other planets?"

"It must have seemed like the kindest thing to do," Tchicaya protested. "And when it started, no one seriously expected them to reach another planet. When they did, though, word had gone ahead of them, so people were much better prepared."

"And this happened six times? Even if they were fed the same story on every planet, by the time they"d had a few chances to compare it with reality - "

Tchicaya shook his head. "They weren"t fed the same story on every planet; that would have defeated the whole point. They"d traveled into the future in the hope of being entertained in a very specific way. On Crane, they"d revealed a lot about the kind of histories and practices they expected to encounter on their voyage, and so people played along with their expectations. The locals there told them that all the men had been wiped out by a virus shortly after settlement, and made a big song and dance about the struggle to adapt: one faction trying to reinvent the lost sex; another, bravely pursuing monosexuality, finally triumphant. The anachronauts lapped it up, oohing and aahing over all the profound things this told them about gender. They made notes, recorded images, observed a few fake ceremonies and historical re-enactments...then moved on."

Yann buried his face in his hands. "This is unforgivable!"

Tchicaya said, "No one lied to them about anything else. They had some equally bizarre notions about the future of physics, but the people on Crane gave them an honest account of all the latest work."

Yann looked up, slightly mollified. "What happened next?"

"After Crane? It became a kind of competition, to see who could Mead them the best: make up the most outlandish story, and get the anachronauts to swallow it. A plague wasn"t really barbaric enough. There had to be war between the sexes. There had to be oppression. There had to be slavery."

"Slavery?"

"Oh yes. And worse. On Krasnov, they said that for five thousand years, men had slaughtered their own firstborn child to gain access to a life-prolonging secretion in mother"s milk. The practice had only ended a century before."

Yann swayed against the bed. "That"s surreal on so many levels, I don"t know where to begin." He regarded Tchicaya forlornly. "This is really what the anachronauts expected? No progress, no happiness, no success, no harmony? Just the worst excesses of their own sordid history, repeated over and over for millennia?"

Tchicaya said, "On Mäkelä, the people insisted that their planet had been peaceful since settlement. The anachronauts were terribly suspicious, and kept digging for the awful secret that no one dared reveal. Finally, the locals reviewed the transmission from Crane describing the first contact, and they realized what was needed. They explained that their society had been stabilized by the invention of the Sacred Pentad, in which all family units were based around two males, two females, and one neuter." Tchicaya frowned. "There were rules about the sexual relationships between the members, something about equal numbers of heterosexual and homosexual pairings, but I could never get a clear description of that. But the anachronauts were thrilled by the great cultural richness they had finally uncovered. Apparently, their definition of cultural richness was the widespread enforcement of any social or sexual mores even more bizarre and arbitrary than the ones they"d left behind."

Yann said, "So what happened on Turaev?"

"The ship had been tracked for centuries, of course, so the mere fact of its arrival was no surprise to anyone. My father had known since early childhood that these strangers would be turning up, somewhere on the planet, at about this time. A variety of different hoaxes had been advocated by different groups, and though none of them had gained planet-wide support, the anachronauts rarely visited more than one place, so it would only require the people in one town to back each other up.

"My father wasn"t prepared at all, though. He hadn"t kept up with news of the precise timing of the ship"s arrival, and even though he"d been aware that it would happen soon, the chance of planet-fall outside his own town had been too microscopic to worry about. He"d had far more important things on his mind."

Yann smiled expectantly, despite himself. "So when the flames died down, and the dust settled, and your father"s Mediator dug up the visitors' ancient language from its files...he had to stand there and insist with a straight face that he knew nothing whatsoever about the subject of their inquiries?"

"Exactly. Neither he nor Lajos had the slightest idea what they were supposed to tell these strangers. If they"d read the reports on the anachronauts, they"d have realized that they could have claimed all manner of elaborate taboos on discussing the subject, but they weren"t in a position to know that and invoke some imaginary code of silence. So all they were left with was claiming ignorance: claiming to be both prepubescent, and stupid." Tchicaya laughed. "After six months of longing for each other? Within days, or even hours, of consumation? I don"t know how to translate that into terms you"re familiar with - "

Yann was offended. "I"m not an idiot. I understand how much pride they would have had to swallow. You don"t need to spoonfeed me similes."

Tchicaya bowed his head in apology, but he held out for precision. "Pride, yes, but it was more than that. Claiming anything but the truth would have felt like they were renouncing each other. Even if they"d known their lines, I"m not sure that they could have gone through with the charade." He held a fist against his chest. "It hurts, to lie about something like that. Other people might have been swept up in the excitement of the conspiracy. But to Lajos and my father, that was just noise. They were the center of the universe. Nothing else mattered."

"So they told them the truth?"

Tchicaya said, "Yes."

"About themselves?"

He nodded. "And more."

"About the whole planet? That this was the custom all over Turaev?"

"More."

Yann emitted an anguished groan. "They told them everything?"

Tchicaya said, "My father didn"t come right out and state that all their earlier informants had lied to them, but he explained that - apart from a few surviving contemporaries of the travelers themselves - there"d been nothing resembling sexual dimorphism in the descendants of humans, anywhere, for more than nineteen thousand years. Long before any extrasolar world was settled, it had gone the way of war, slavery, parasites, disease, and quantum indecisiveness. And apart from trivial local details, like the exact age of sexual maturity and the latency period between attraction and potency, he and his lover embodied a universal condition: they were both, simply, people. There were no other categories left to which they could belong."

Yann pondered this. "So did the intrepid gendographers believe him?"

Tchicaya held up a hand, gesturing for patience. "They were far too polite to call my father a liar to his face. So they went into town, and spoke to other people."

"Who, without exception, gave them the approved version?"

"Yes."

"So they left Turaev none the wiser. With an unlikely tale from two mischievous adolescents to add to their collection of sexual mythology."

Tchicaya said, "Perhaps. Except that since Turaev, they haven"t made planet-fall anywhere. They"ve been tracked, the ship"s still functioning, and they"ve had four or five opportunities to enter inhabited systems. But every time, they"ve flown on by."

Yann shivered. "You think it"s a ghost ship?"

Tchicaya said, "No. I think they"re in cold sleep, with their bodies frozen, and tiny currents flowing in their brains. Dreaming of all the horrors they"d wished upon us, in the name of some crude, masochistic notion of humanity that must have been dying right in front of them before they"d even left Earth."

As Tchicaya boarded the shuttle ahead of Yann, Mariama looked back and flashed him a brief smile. Her meaning was unmistakable, but he pretended not to notice. He didn"t mind her knowing what he and Yann had attempted, or even how it had ended, but it drove him to distraction that she could deduce at least half the story just by watching them together.

He could have instructed his Exoself to embargo whatever small gestures were giving him away. But that was not how he wanted to be: hermetically sealed, blank as a rock. For a moment, Tchicaya contemplated reaching over and putting his arm across Yann"s shoulders, just to devalue her powers of observation. On reflection that would have been petty, though, and likely to cause Yann all kinds of confusion.

Mariama sat beside Tarek. In the unlikely event that the two of them were lovers, Tchicaya would be the last to know. Behind him, the fifth passenger, Branco, strapped himself in place. Tchicaya turned to him and joked, "It doesn"t seem right that you"re outnumbered. You should at least have brought an observer along."

Branco said pleasantly, "Fuck that. The last thing I want to do is start mimicking all your paranoid games."

Branco had been part of the original coalition who"d designed and built both the Rindler and the Scribe. Yielders and Preservationists had arrived over the decades, exuding a kind of bureaucratic fog through which he was now forced to march, but as he"d explained to Tchicaya earlier, he"d become inured to the squatters and their demands. The Scribe was still available to its creators, occasionally, and with patience he could still get work done. The factions made a lot of noise, but in the long run, as far as Branco was concerned, they"d be about as significant as the vapid religious cults who"d once squabbled over contested shrines on Earth. "And you sad airheads can"t even slaughter each other," he"d observed gleefully. "How frustrating that must be."

As they fell away from the Rindler, Tchicaya barely noticed the weightlessness, or the strange doll"s-house/termite-colony view some of the modules offered as they shrank into the distance. The trip hadn"t quite become as unremarkable to him as air travel in a planetary atmosphere, but on a planet even repeated flights along the same route were never as unvarying as this.

Tarek said, "Actually, we"re outnumbered, three to two. If you"re neutral, you"re a Yielder. There is no difference."

"Oh, here we go!" Branco chuckled and settled back into his couch. "It"s a short trip, but please, entertain us."

"You"re not fooling anyone," Tarek insisted heatedly.

"It"s not important," Mariama said. Tchicaya watched her, wondering if she"d make eye contact with Tarek as she spoke. She didn"t. "There are observers here for both sides. It doesn"t matter how many there are." Her tone was calm, neither argumentative nor imploring.

Tarek dropped the subject. Tchicaya was impressed; she"d defused the situation without alienating Tarek, or incurring any debt to him. She hadn"t lost her touch, she"d only grown more subtle. When Tchicaya had trailed after her as a tortured, infatuated child, it must have perplexed and frustrated her to find that she couldn"t hone her skills on him. Anything above and beyond mere hormonal effects had been superfluous; she might as well have tried to learn martial arts by practicing on a rag doll.

Branco sighed with disappointment, then closed his eyes and appeared to doze off.

Most of the Rindler's passengers had watched with a mixture of denial and dismay as Sophus"s predictions had been borne out, and all their ingenious models had been dashed to pieces, once again, by the new spectrometer. Branco, however, had embraced the No Rules Theory wholeheartedly, and managed to extract predictions that went far beyond Sophus"s gloomy verdict. Just because there were no preexisting correlations between the dynamics on the far side of the border, that didn"t mean none could be created. Branco had designed an ingenious experiment that aimed to use the near side of the border as a kind of intermediary, to entangle different regions of the far side with each other. The dynamics revealed would still be a random choice from all the possibilities - or, strictly speaking, the near-side universe would split into decoherent branches, and in each, a different result would be observed - but at least the result would apply across more than a few square Planck lengths.

As they docked with the Scribe, Yann mused, "I think this is the first time I"ve come here with any possibility of being disappointed."

Tchicaya was taken aback. "You never had your hopes pinned on any of the old models? You never even had a favorite?"

"There were some esthetically pleasing ones," Yann conceded. "I certainly would have been happy if they"d survived testing. But I never had a good reason to expect it. Not until now."

"That"s very touching," Branco said dryly, "but I see no reason why you should abandon your earlier stance."

Tchicaya challenged him, "You have no emotional stake in the outcome at all?"

Branco regarded him with amusement. "You"ve been here how long?"

Tarek went through the tunnel first, then Mariama. Tchicaya followed her. "Do you remember that playground?" he whispered. "With all the pipes?" She glanced back at him, puzzled, and shook her head. Tchicaya felt a stab of disappointment; he"d assumed that the sight would have triggered the same memory in her.

In the control room, Branco instructed the stylus. With his gravelly voice and deliberate singsong intonation, he succeeded in making every word drip with contempt, like a kind of sardonic poetry. "The phase relationships between the twelve TeV and fifteen TeV beams will be as follows." They really are making me read this aloud.

Tchicaya looked out the window, down at the immutable plane of light. He"d had vivid dreams about the border, imagining as he slept that the wall of his cabin was the thing itself. He"d hold his ear against it, listening for sounds from the far side, straining with his whole body, urging the signal across.

Sometimes, the instant before he woke, he"d see an iridescent film blossoming on the wall, and his heart would race with joy and fear. Did this new infestation mean that he"d been found out? Or that his crime had never really happened?

Branco looked up and announced with mock astonishment, "Am I finished already? Is that all I have to do?"

Tarek said, "For now. But I"m invoking my right to a functional audit."

"Hooray," said Branco. He pushed himself away from the control panel and floated by the window with his hands on his head.

Tarek took his place, and instructed the stylus to rise from the border. Tchicaya had heard about functional audits, but he"d never witnessed one before. A package of detectors, verified by the faction invoking the audit, was placed under the tip of the stylus, and the particles emitted were scrutinized directly, to be sure that they conformed to the agreed sequence.

Tchicaya was tempted to say something derisive, but he held his tongue. Whatever made Tarek believe that this was necessary, complaining about the procedure would do nothing to lessen his suspicions.

He used the handholds beneath the windows to drag himself closer to Mariama. "Where have you been hiding? I haven"t seen you for weeks."

"I have a lot of meetings."

"I go to meetings, too."

"Not these ones," she said.

She didn"t need to spell it out. She"d come to the Rindler hoping to work with Tarek on Planck worm design, and apparently the notion still wasn"t dead.

The novo-vacuum was already the largest object in the galaxy, and it was growing so rapidly that its surface area would increase almost forty-fold while it was encircled at the speed of light. Even if the Preservationists discovered a potential method for dealing with it, there was no prospect whatsoever of surrounding the entire thing with conventional machinery to administer the cure. The only practical tool would be a self-replicating pattern embedded at the level of quantum graphs, able to "eat" novo-vacuum and excrete something more benign.

To supporters of the idea, these hypothetical Planck worms would do no more than reverse the disaster of Mimosa. To Tchicaya, the symmetry was false. The places lost to Mimosa - ordinary planets, unique as they were - had already been thoroughly understood. Learning just enough about the novo-vacuum to infect it with a kind of fungal rot struck him as a corruption of every impulse that made intelligence worthwhile. He had enough trouble forgiving that kind of cowardice in a child.

"So what do you think the prospects are?" He meant those for Branco"s experiment succeeding, though if she cared to disclose her thoughts on anything further down the line, so much the better.

Mariama thought carefully before replying. "I"m almost persuaded that Sophus is right, but I"m not certain that Branco"s ideas follow. When we have no access to any particular far-side dynamics, even plucking out a random correlated state seems like too much to ask."

Yann had been floating a polite distance away, but the room was too small for any real privacy, and now he gave up pretending that he couldn"t hear them. "You shouldn"t be so pessimistic," he said, approaching. "No Rules doesn"t mean no rules; there"s still some raw topology and quantum theory that has to hold. I"ve reanalyzed Branco"s work using qubit network theory, and it makes sense to me. It"s a lot like running an entanglement-creation experiment on a completely abstract quantum computer. That"s very nearly what Sophus is claiming lies behind the border: an enormous quantum computer that could perform any operation that falls under the general description of quantum physics - and in fact is in a superposition of states in which it"s doing all of them."

Mariama"s eyes widened, but then she protested, "Sophus never puts it like that."

"No, of course not," Yann agreed. "He"s much too careful to use overheated language like that. The universe is a Deutsch-Bennett-Turing machine"s is not a statement that goes down well with most physicists, since it has no empirically falsifiable content." He smiled mischievously. "It does remind me of something, though. If you ever want a good laugh, you should try some of the pre-Qusp anti-AI propaganda. I once read a glorious tract which asserted that as soon as there was intelligence without bodies, its 'unstoppable lust for processing power would drive it to convert the whole Earth, and then the whole universe, into a perfectly efficient Planck-scale computer. Self-restraint? Nah, we"d never show that. Morality? What, without livers and gonads? Needing some actual reason to want to do this? Well...who could ever have too much processing power?

"To which I can only reply: why haven"t you indolent fleshers transformed the whole galaxy into chocolate?"

Mariama said, "Give us time."

"The equipment seems to have passed inspection." Tarek pocketed the detector package and began lowering the stylus.

Branco folded his arms and pondered this announcement. "Seems? I"ll take that as a general statement of Cartesian skepticism, shall I?"

Tarek replied curtly, "You"re free to instruct it again."

Branco began repeating the sequence. Tchicaya was expecting him to rush through it this time, but instead he took pains to reproduce the same pacing and intonation as he"d employed originally.

Tchicaya caught Tarek"s eye and said, "You know, you have as much to gain from this experiment as anyone."

Tarek frowned, as if the implication was not merely unjust but completely surreal. "You"re right. That"s why I"m taking it seriously." He hesitated, then added defensively, "Don"t you think I"d prefer to believe that everyone was acting in good faith? I"d like to assume that. But I can"t; there"s too much at stake. If that makes me look petty to you, so be it. I"ll answer to my descendants."

Branco completed his second recitation. Yann said, "Approved."

Tarek said, "Yes, go ahead."

Branco addressed the Scribe. "Execute that."

The Scribe remained silent, but a heartbeat later there was a sharp hissing sound from under the floor. Tchicaya had no idea what this could be, until he saw the realization dawning on Branco"s face.

A fine crack appeared in one window, then another. Tchicaya turned to Mariama. "You"re backed up?"

She nodded. "While I slept. You?"

"The same." He smiled uncertainly, trying to reassure her that he was prepared for whatever happened, without discouraging her from expressing her own feelings. They"d been through a lot together, but neither of them had ever witnessed the other"s local death.

"Yann?"

"I"m covered, don"t worry."

Branco and Tarek were in the same position: no one risked losing more than a day"s memory. After his fourth local death, Tchicaya had ceased to feel genuine, gut-churning dread at his own fate - and he had some memories that led up to the moment itself - but in the company of others it was always more stressful. Wondering how much fear they felt, and how careful they"d been.

The hissing beneath them intensified, and the room began to creak. The windows had healed themselves, and the whole structure would be capable of a certain amount of self-repair, but if the border was lapping up against the Scribe, the wound it made would be reopened with every advance. The microjets were designed to compensate for the effects of bombardment with interstellar gas; shifts measured in microns were the crudest adjustments imaginable. The Scribe was not going to whisk them away to safety.

Tarek looked around nervously. "Shouldn"t we head for the shuttle?"

Branco said, "Yes."

The wall behind Tchicaya emitted a tortured groan. As he turned, it concertinaed visibly, the angle between two windows becoming impossibly acute. Tchicaya marveled at the sight. Air leaking from the Scribe couldn"t be producing shear forces of that magnitude; the border had to be tugging on the structure beneath them. Nothing of the kind had ever been witnessed before. Beams constructed from a variety of substances, poked through the border, had always behaved as if the far-side portion had simply ceased to exist; there were no forces exerted on the remainder. Whatever Branco had triggered, he"d done more than displace the border by a few centimeters.

The wall flexed again, and the pair of windows that had been squashed together separated. Instead of reversing their original motion, though, they parted at the seam, like doors swinging open.

Tchicaya bellowed with fright, and reached out for something to stop himself. He succeeded only in clutching Yann"s shoulder, and the two of them tumbled through the opening together.

For several seconds, Tchicaya remained rigid, preparing himself on some instinctive level for intense pain and a swift extinction. When neither arrived, his whole body began shaking with relief. He"d known that his suit would protect him, but the understanding hadn"t penetrated far. He"d skydived from altitudes where oxygen was needed, and swum at depths where the next free breath was hours away, but black and starry space had remained the quintessence of beautiful danger: pristine, indifferent to his needs, predating every form of life. Vacuum was not a word that offered hope. He should have been snuffed out in an eye blink.

He looked around. The push of the escaping air had been firm but brief, so it was unlikely that they were moving very rapidly, but he was facing the wrong way to catch sight of the Scribe, the only meaningful signpost. The border itself offered no cues as to their velocity in any direction.

He"d been holding his breath deliberately, as if he"d plunged into water, but he realized now that the urge to inhale had vanished as soon as the suit"s membrane had sealed off his mouth and nose. His body had shut down its lungs; the Rindler's model could operate for days on anaerobic metabolic pathways. His skin felt slightly chilly, but he could see the exposed film of the suit on the back of his hand, silvered to retain heat. He extended his arm shakily so he could examine Yann, whose face had turned entirely metallic except for two holes for his pupils.

"You should have known it was futile, Tin Man, trying to walk among us. Robot nature always shows through." Tchicaya"s teeth were chattering, but that made no difference; his Mediator grabbed his speech intentions and routed them away from his useless vocal cords, shunting them into a radio channel.

Yann said, "Believe me, the effect looks much stranger on you."

They were rotating slowly together, around an axis roughly perpendicular to the border. As they turned, the Scribe came into view over Yann"s shoulder. The lower half of the structure was buckled and twisted, but the control room was still safely clear of the border. As far as he could judge, he and Yann were still four or five meters from the border themselves, and their trajectory was virtually parallel to it. This freakish alignment was sure to prove inexact, though, one way or the other.

He spotted a shiny Mariama standing at the ruptured wall, watching him.

"We"re all right," he said. "Get in the shuttle."

She nodded and waved, as if he"d be unable to hear a reply.

Then she said, "Okay. We"ll come and pick you up." She vanished from sight.

Tchicaya instructed his Mediator to make his next words private. "Are we all right? I don"t have the skills to determine our velocity that accurately."

"We"re moving toward the border, but it would take hours before we"d hit it."

"Oh, good." Tchicaya shuddered. His right hand was still locked on to Yann"s shoulder, the fingers digging in as if his life depended on it. He knew that wasn"t true, but he couldn"t relax his grip.

"Am I hurting you?" he asked.

"No."

Yann"s metallic face brightened strangely, and Tchicaya glanced down. A patch of borderlight more intense than its surroundings drifted slowly by.

"What do you make of that?" Tchicaya asked. He was suddenly light-headed, from more than the shock of ejection. The Doppler-shift tints aside, he"d known the border as a featureless wall for centuries. The tiniest blemish was revolutionary; he felt like a child who"d just watched someone reach up and scratch a mark into the blue summer sky.

"I"d say Branco has succeeded in pinning something to the near side."

"We have physics? We have rules now?"

"Apparently."

Mariama said, "We"re in the shuttle. Everyone"s safe here."

"Good. No rush; the view is wonderful."

"I won"t hold you to that. We"ll be there in a few minutes."

The strange patch of brightness had moved out of sight, but after a few seconds another came into view. They were fuzzy-edged ellipses, traveling from the direction of the Scribe.

"They"re like the shadows of reef fish," Tchicaya suggested. "Swimming above us in the sunlight."

Yann said, "Do you think you might be coming slightly unhinged?"

As Tchicaya swung around him in their involuntary dance, he caught sight of the shuttle rising from the ruined Scribe. He smiled at the memory of Mariama"s voice, promising to rescue him. On Turaev, if they"d given in to their feelings, it would have ended badly, burning out in a year or two. When this was over, though -

Yann said, "That"s a bit ominous."

"What?"

"Can you turn your head back toward the Scribe? That might be quicker than me trying to put it into words."

Tchicaya twisted his neck. The border had formed a bellshaped hillock, forty or fifty meters high, that had completely swallowed the Scribe. As his rotation forced him to stretch even more, he stopped fighting it and twisted his neck the other way, hastening the sight"s return instead of trying to delay its departure.

The hillock was collapsing now, but as it did, a ring around it was rising up. Suddenly, Tchicaya noticed a whole series of lesser rings surrounding the first, like concentric ripples in water. They were undulating out from the center at great speed: the leading edge, the fastest component, in some kind of surface wave. The bulk of the wave was spreading more slowly. But it was still traveling faster than they were.

He searched for the shuttle, and found it, its exhaust a pale blue streamer against the stars. The thrust generated by the ion engine was very low; over time it could accumulate into a significant velocity, but the craft was about as maneuverable as a bathtub on ice. It might just reach them before the wave, and even accelerate away from the border again in time, but there"d be no margin left for any more surprises that might manifest themselves in the wake of Branco"s intervention.

Yann read his mind, and declared flatly, "They have to stay clear."

Tchicaya nodded. "Mariama?"

"No!" she hissed. "I know what you"re going to say!"

"It"s all right. We"re backed up, we"re calm. Don"t even think about it."

"It"s a wave. It"s a predictable phenomenon! I"ve computed a trajectory that meets all the constraints - "

"Predictable?"

"We can do it!"

"You"ve all voted on that, have you? Tarek? Branco?"

Branco replied laconically, "It"s all the same to me."

Tarek said nothing, and Tchicaya felt a pang of sympathy for him. No one could reasonably expect him to put himself at risk, merely to spare his two adversaries the loss of their replaceable bodies and a few hours' memories. Yet if he did, many people would respect him for it. You had to be a utilitarian zealot, rotted to the core by dogma, not to admire someone who was willing to jeopardize their own comfort and continuity to preserve another"s. Whether or not this required courage, at the very least it was an act of generosity.

Tchicaya said, "Stay clear! We can"t afford to lose the shuttle!" This argument made no sense - the Rindler's stock of raw materials had not been depleted, and there were parts of the ship itself that could be cannibalized anyway, if necessary - but he wanted to offer them an unselfish-sounding alibi. "You have to gather all the data you can," he added, a little more cogently. "With the Scribe gone, every observation you can make is invaluable." The Rindler itself had powerful instruments trained on the border, but some crucial detail might conceivably depend on the shuttle"s proximity.

Mariama did not reply immediately, but in the silence that followed Tchicaya knew that he"d swayed her.

"All right." Her voice was still strained, but there was a note Tchicaya recognized from their days on Turaev: a rare concession, not so much of defeat, as the realization that they"d been struggling over the wrong thing altogether. She understood the tradeoff, and she knew that he and Yann were resolved. "Peace, Tchicaya."

"Peace," he replied.

Yann said, "You handled that well."

"Thanks." Over Yann"s shoulder, Tchicaya could see the wave closing on them. It was dropping in height as it spread out from the point where the Scribe had been, but it wouldn"t fall far enough to miss them. Tchicaya wondered if Yann would want to be distracted, or to confront what was happening directly.

"So well that I almost hate to do this. How strong do you think your legs are?"

"What?" It took a moment for Tchicaya to understand what he was suggesting. "Oh, no. Please - "

"Don"t go squeamish on me; we don"t have time. It would be hard to decide who to save if we were from the same modes, but I can start from backup with no delay. You"d be out of the picture for months."

That was true. The Rindler had run out of bodies, and there were currently about twenty new arrivals waiting. Tchicaya would have to join the queue. Normally, a delay like that would mean nothing compared to the centuries he"d lost to transit insentience, but Branco"s experiment had just guaranteed that every day from now on would be unique.

"I"ve never killed anyone," he said. His stomach was knotted with revulsion at the thought.

Yann didn"t quibble over the hyperbole. "And I"ve never died, in a body. Sex and death, all in one day. What more could an acorporeal ask for?"

The wave came into view again; they"d have a minute or less. Tchicaya struggled to clear his head. Yann was demanding no more of him than he"d demanded of Mariama. The sense of shame and selfishness he felt, at the thought of indulging his own visceral urge to survive at Yann"s expense, was the right thing to feel, but that didn"t mean he had to elevate it above every other consideration. Nor, though, did he have to annihilate the emotion in order to act against it. He would do what the situation required, because it would be a foolish waste for both of them to lose their bodies, but he wasn"t going to pretend that he was happy, or indifferent about it.

He took hold of Yann"s left hand, then released his iron grip on his shoulder so they could join right hands as well. He folded his knees up against his chest, then froze. The crest of the wave was thirty meters away. This was too complicated. They"d never have time.

Yann said calmly, "Give me your body. I"ve worked out the steps."

Tchicaya surrendered motor control, and they began to move together in a perfect, symmetrical ballet. It was as if his limbs had been gripped by a dozen firm, invisible hands, manipulating him without resistance. His back arched, his arms stretched painfully, but their fingers stayed tangled in a monkey grip as their legs forced their bodies apart, until their feet met, sole to sole.

Tchicaya said, "You made me an isotopy."

Yann laughed. "Nothing original, I"m afraid."

"It"s the thought that counts."

Tchicaya had become disoriented, but as they swung around together his line of sight fell from the stars to the approaching wave. The muscles in his legs tensed, and the pressure against his feet grew until he felt as if his arms would be torn from his shoulders.

Yann said, "See you later."

Their fingers parted.

Tchicaya clutched at the emptiness between them, then stopped himself and wrapped his arms across his chest. He was ascending at a shallow angle, back toward the point where the Scribe had been. As the crest approached, he curled into a ball, and it raced past beneath him, a flash of silver licking at his heels as he tumbled.

An elaborate grid of colored lines scarred the inside of the retreating wave, like the map of some kind of convoluted maze. The pattern shifted as he watched. There was a tantalizing logic to the changes - the lines weren"t dancing about at random - but deciphering it on the spot was beyond him. All he could do was record the sight.

Drained for a moment of every other concern, Tchicaya locked his gaze on the retreating enigma.

Everything had changed, now. Whatever Branco had revealed, or created, the wall between the worlds had finally been breached.

"Everyone complains about the laws of physics, but no one does anything about them."

Tchicaya turned away from the control panel. He hadn"t heard Rasmah entering the Blue Room.

"It"s an old joke they used to tell, back on Maeder," she explained, crossing the wide, empty floor. "Which just goes to show how much work it takes to send a bad meme off to smallpox heaven."

"Don"t count on having done that," Tchicaya warned her. "I believe the original version was Everyone complains about human nature. When the second half became patently false, the meme just shifted context. You can tear the meaning right out of these one-liners, and they"ll still find a way to keep propagating."

"Damn." She sat beside him. "So what are the laws, right now?"

"As far as I can tell, we have a macroscopic SO(2,2) symmetry, and E7 as the gauge group." He gestured at the display. "Nothing we haven"t grabbed before, generically, though the details of the Lagrangian are unique." Tchicaya laughed. "Listen to me. I really am getting blasé about this."

"Seen one universe, seen them all." Rasmah leaned closer to examine the symmetry diagrams that the software had guessed from some partial results, and was now proceeding to test further with the Left Hand.

She glanced at the endurance clock. "Thirteen minutes? That"s close to the record. You think this might - " Tchicaya glowered at her, and she laughed. "Don"t tell me: I"m jinxing the result."

"Hardly. I"m just growing a little impatient with the idea that we keep grabbing dynamics, over and over, in the hope that one of them will turn out to be stable. It"s never going to happen."

"You think not?" Rasmah pursed her lips. "Okay. It"s no use just complaining, though. What do you want to do about it?"

Tchicaya made a gesture of helplessness.

She regarded him with disappointment. "Are you this lazy about everything?"

She was only teasing, but the accusation stung. Rasmah had been on the Rindler just six months longer than he had, but she"d already contributed substantially to several projects. Having helped to design the spectrometer that had been lost with the Scribe, she"d gone on to improve the design still further for the models used in both the Left and Right Hands. The Scribe"s replacement had been planned as a single machine, but when attempts to renegotiate the protocols for its shared use collapsed for the seventh time, even the most ecumenical researchers had lost patience, and agreed to the duplication.

Tchicaya stretched his arms. "I"ve certainly had enough of staring at this for one day. Are you here to take over?"

"Yes." She smiled and added, "But I"m early, so I"m afraid you can"t actually leave yet."

The destruction of the Scribe, and the end to cooperation between the factions, had delayed follow-ups to Branco"s experiment, but once the two Hands were in place and gathering data, everybody on the Rindler had been riveted by the results. For months, the Blue Room - where the Left Hand"s data was displayed, now that trips to the border were considered imprudent - had been packed with people twenty-four hours a day, and it was no secret that the Preservationists had reacted in the same way.

Branco"s technique appeared to have confirmed Sophus"s original assertion: the novo-vacuum did not obey any single analog or extension of the Sarumpaet rules. It was possible to correlate a macroscopic portion of the near side of the border with parts of the total far-side state that did obey specific rules, but each time the experiment was repeated, the rules were different. All of Sarumpaet"s carefully reasoned arguments about which patterns of nodes in a quantum graph could persist as particles had been revealed as utterly parochial; the larger truth was, the ordinary vacuum that dominated the near side was correlated with sequences of graphs that behaved in that particular fashion, so it hid the fact that they were really just part of a superposition of countless other possibilities. The quantum subtleties that could, in principle, render the whole superposition visible were buried in the sheer number of details that would have had to be tracked in order to observe it.

The far side lacked the means to conceal its quantum nature in the same fashion, but if the view was less misleading, it remained confusing. Interpreting the new experiments was like trying to make sense of a jungle by watching an endless parade of exotic creatures cling briefly to the windows of a vehicle, stunned by the light, curious, or angry, but always flying off a moment later, never to return.

At first, every new set of laws had had their fifteen minutes of fame, but since none of them could be pinned to the near side for much longer than that, the novelty had begun to wear thin. Exhilaration at the cornucopia had given way to frustration. The experiments continued, but it had become a struggle to maintain even the symbolic presence of one sentient observer around the clock. Tchicaya supposed that this was fair enough: all the theorists were drowning in data already, and they had better things to do than sit and watch more come pouring in. For a week or two, he"d hoped that patient observation might actually lead him to a worthwhile discovery himself, but that was beginning to sound as crazy as looking for patterns in any other set of random quantum results.

"Oh, there it goes!" Rasmah wailed, as if she"d seriously expected otherwise. The patch of the border they"d pinned to the latest set of laws had just reverted to the old inscrutable glow. "What do you think would happen," she mused, "if we scribed some device that could function under the far-side dynamics, before we lost the correlation?"

Tchicaya said, "Even if it survived, what good would that do us? We"ve never been able to grab the same dynamics twice."

"What if we scribed a Scribe?"

"Ha! Like that Escher drawing?"

"Yeah." Rasmah pulled a face, suddenly aghast. "Though...that"s a left hand drawing a right, and vice versa. We can"t have that, can we?"

"Are you serious, though? Do you think we could insert a machine that could signal back to us in some way?"

Rasmah didn"t reply immediately. "I don"t know. What does the border look like, from the other side? Does it always look as if our physics is happening behind it? Or is something more symmetrical going on, where someone on the far side would catch glimpses just as varied and transient as the ones we"re seeing?"

"I have no idea," Tchicaya admitted. "I don"t even see how you could pose that question, in Sophus"s model. You"d have to describe a specific observer on the far side, on whose terms you wanted to see things. But if the different far-side dynamics don"t form decoherent branches - except over the tiny patches where we"re forcing them to do so - what exactly are the laws the observer is supposed to obey?" The startled birds and butterflies fluttering against the window weren"t even real; it was no use asking what they saw, staring back. The slices of different "universes" pinned against the border were more like the patterns formed by splattered insects. If they hadn"t been dead, they would never have been seen side by side in quite the same way.

It was midnight, by the Rindler's arbitrary clock. The lighting of public spaces changed with the cycle, and though many people happily slept through the daytime and worked all night, Tchicaya had ended up in synch with the light.

He stood. "That"s it, I"ve had enough."

"You could stay and keep me company," Rasmah suggested.

"I wouldn"t want to distract you." He smiled and backed away, raising a hand good night. They"d been circling each other at a distance for weeks, and his body had begun to change for her, but Tchicaya had decided that he would not allow anything to happen between them. While it would have been unlikely to end as swiftly, or as comically, as his experiment with Yann, he wanted to keep his life free of complications.

Tchicaya made his way around the ship, slightly removed from everything around him. The corridors were nearly deserted; maybe the Preservationists were having some kind of conference. The ghost town ambience reminded him of a hundred provincial cities he"d trekked through at night; on the empty walkways, the blaze of stars was like the view when you left the brightest streets behind, and the sky came suddenly to life.

He recalled a night he"d spent in a small town on Quine, thirty-six subjective years after he"d left Turaev: the mirror image of his birth in the moment of his departure. Three centuries had passed, in real time. He"d sat in an alley and wept for hours, like an abandoned child. The next day, he"d made half a dozen new friends among the locals, and some of the friendships had lasted three times longer than all the years he"d spent on his home world.

He still missed those people. He still missed Lesya, and his children and grandchildren on Gleason. And yet, he could never entirely separate that from the realization that part of the joy he"d felt in their presence had come from the sense that they were lifting him out of his state of exile. They had never been substitutes for the home and family he"d left behind; it had never been that crude. But every kind of happiness bore some imprint in the shape of the pain it had assuaged.

He heard footsteps behind him, outpacing his own. He stopped and turned to face the wall of the walkway, as if admiring the view, wiping his eyes with his forearm, less embarrassed by his tears than the fact that he"d be at a loss to explain them. If he"d still been on Turaev after four thousand years, he would have gone mad. And if he"d traveled and returned in the approved way, to find that nothing had changed in his absence, he would have gone mad even faster. He did not regret leaving.

Mariama said, "You look like you"re about to jump off a bridge."

"I didn"t realize you were following me."

She laughed. "I wasn"t following you. What are we meant to do? Walk in opposite directions around the ship? All Preservationists must march clockwise? That would make for some long journeys."

"Forget it." He turned to look at her. It was unjust beyond belief, but right at this moment - having resolved for the thousandth time that he"d made the right decision - he wanted to rant in her face about the price she"d made him pay. After all her talk as a rebel child, after leading by example, after four thousand years as a traveler, she had now decided that her role in life was to fight to keep the planet-bound cultures - all the slaves she"d vowed to liberate, all the drones she"d promised to shake out of their stupor - safely marinating in their own inertia for another twenty thousand years.

He said, "Where are you heading?"

Mariama hesitated. "Do you know Kadir?"

"Only slightly. We didn"t exactly hit it off." Tchicaya was about to add something more acerbic, when he realized that today was the day Kadir"s home world, Zapata, would have fallen. That was only true in terms of a reference frame fixed to the local stars, not the Rindler's notion of simultaneity, and in any case no confirmation of the event would reach them for decades, but unless the border had magically altered its speed in distant regions, the planet"s loss was a certainty.

"He"s holding a kind of wake. That"s where I"m going."

"So you and he are close?"

Mariama said, "Not especially. But he"s invited everyone, not just his friends."

Tchicaya leaned back against the wall, unfazed by its transparency. He said, "Why did you come here?"

She shaded her eyes against the borderlight. "I thought you"d decided that we were never going to have this argument."

"If you think I"ve shut you up, now"s your chance."

"You know why I"m here," she said. "Don"t pretend it"s a mystery." The glare was too much; she turned to stand beside him. "Do you want to come with me, to this thing of Kadir"s?"

"You must be joking. Do you think I"m a provocateur, or just a masochist?"

"This isn"t factional. He"s invited everyone." She frowned. "Or are you afraid to spend ten minutes in the company of people who might disagree with you?"

"I spent ten years on Pachner."

"Keeping your mouth shut."

"No. I was honest with everyone I met."

"Everyone who asked. If the issue came up."

Tcicaya moved away from her angrily. "I wasn"t sure of my plans, when I first arrived. And when I was sure, I didn"t walk around with a banner that read I"m off to the Rindler, to make certain the same fate befalls as many other worlds as possible. Does that make me dishonest? Does that make me a coward?"

Mariama shook her head. "All right, forget Pachner. But if you"re so sure of your position now, why don"t you come with me? No one"s going to lynch you."

"It would be inflammatory. What makes you think Kadir wants the company of people who disagree with him?"

"There"s an open invitation," she protested. "Check with the ship if you don"t believe me."

She was right. Tchicaya"s Mediator had filtered it out automatically; he"d told it to classify general announcements by known factional allegiances, to keep him from being distracted, and depressed, by news of events where Yielders were unlikely to be welcome.

"I"m tired," he said. "It"s been a long day."

"You"re pathetic." Mariama walked away without another word.

Tchicaya called after her, "All right! I"ll come with you!" She didn"t stop. He ran to catch up with her.

They walked in silence for a while, then Tchicaya said, "This whole iron curtain thing is insane. Within a decade, we"ll find a way to pin some state to the border that will freeze it in place. If we worked on it together, it would take half as long."

Mariama regarded him coolly. "If we froze it, you think that would be enough?"

"Enough for what?"

"Enough to satisfy either side."

"Ideally, I still want to cross through," Tchicaya admitted. "We shouldn"t have to flee from this, or annihilate it. We should be able to adapt. If the ocean comes a few meters inshore, you retreat. A few kilometers, you build a dike. A few thousand...you learn to live in boats. But if freezing the border turns out to be possible, and it rules out exploration, I"d just have to accept that."

Mariama was skeptical. "And you"d take no risks at all, from that moment on? You"d do absolutely nothing that had a chance of unfreezing it? You"d let it sit there for a hundred thousand years, undisturbed, and you wouldn"t be tempted in the least?"

"Oh, I see. That"s the logic that dictates the use of Planck worms? If you don"t wipe the whole thing out of existence, some Yielder is certain to come along eventually, and unplug the dike."

Mariama didn"t reply. They entered the module where the wake was being held, and walked up the stairs.

On the map Tchicaya consulted, Kadir"s cabin had been merged with a dozen of his neighbors', producing a roughly circular room. Ahead of him, the entrance was wide open, and music wafted out into the corridor.

Mariama"s clothes changed as they approached the doorway, forming a pattern of woven bands broken up by ellipses, in earthen colors. "You look good in that," Tchicaya observed. The comment elicited a reluctant flicker of warmth in her eyes, and she knew him too well to mistake it for insincere flattery, but she walked on into the room without a word. He steeled himself, and followed her.

There was quite a crowd inside, talking, eating, a few people dancing. Tchicaya could see no other Yielders, but he resisted the urge to ask his Mediator to hunt for friendly signatures.

Images of Zapata shone from the walls. The planet from space; aerial views of towns, mountains, and rivers. Tchicaya had spent forty years on Zapata, moving from continent to continent, never really settling down long enough to make close friends.