The Jennin seemed oblivious to their reaction. “I have many responsibilities here, which I am reluctant to shed. I am undecided. But failing that, if I am not there—”

  LuSi felt as if she was groping towards an understanding of all this. “Me? You want me to spend the next fifty Years arguing with my mother, about Sim theory and theology?”

  He grinned. “That’s the idea. Somebody has to. And I think you have it in you, LuSi, even if you don’t see it yet yourself. Look—I don’t mean to impose on you, in this time you two have left together. Or to order you around. I want to inspire you, and I know I’m not always good at that, am I? A Jennin I may be, but not always a great teacher.”

  “Inspire me? How?”

  “I’ve secured you a ride on a torchship. You too, JaEm, if you must. We’re going into space! I know our journey will be dwarfed by your jaunt to the stars, but the scenery will be a lot more fun.”

  JaEm gaped, evidently delighted.

  “Why?” LuSi asked, more sceptical. “What’s the point? What are we going to be talking about?”

  “The Backstory,” Jennin PiRo said simply.

  The torchship was called the Holy Water. Owned by PiRo’s university, it was a practical, basic design meant for scientists, surveyors, explorers, a small, highly manoeuvrable, all but automated craft, capable of transporting a dozen passengers in comfort between the worlds of the Ember system in a matter of Days. LuSi and JaEm had travelled in such ships many times before; the Holy Water was a trivial achievement for a civilisation capable of routine interstellar travel.

  But as they boarded, as the ship leapt out of another gigantic port facility and into the sky, the Jennin made them think about how the ship worked, the miracle of physics that powered it.

  “You are riding a fusion torch,” he said. “And, generous as the Ember is to give us its warmth and light, the Ember is a failed star, it never achieved the mass it needed to allow fusion to spark in its core. Until humanity arose here—”

  “Or came here,” LuSi said automatically, correcting JaEm’s father’s mild multi-origin heresy.

  “Before us, fusion had never happened here, in this system, not since the birth of the universe itself. Think what a wonder that is—what power we have!…”

  The first few days of the voyage were a jaunt. The Jennin took them on a looping tour of the Ember’s planetary system. LuSi knew that compared to some systems out among the stars of the Bubble, this was an impoverished place, with only two large planets, Urthen and Bigmars, a handful of smaller, scattered worldlets, and more distant belts of asteroids, comets and sparse ice moons. Both Urthen and Bigmars orbited so close to the Ember that they were tidally locked, each holding one face permanently to the sub-star’s dim glow—the price they paid for the meagre warmth of the Ember. But that warmth had not been enough to save Bigmars from an endless age of ice; unlike Urthen, which too had its chilly regions, no liquid water could persist on Bigmars’s surface.

  It was towards Bigmars that Jennin at last pointed the ship’s prow. And as that cold, glittering world approached, he ordered the youngsters to tell him the Backstory.

  The Backstory was the history of the universe and of mankind in it, and every child on Urthen learned it at first school. “The Ark was built, by the giants Nimrod, Seba and Halivah, so that their children could flee Denva when the oceans rose,” LuSi said. “The Crew struggled to survive, until the Son extracted the Ship’s Law from the Will. And the Ship’s Law remains the basis of our system of justice to this day.”

  Jennin waved a hand. “Yes, yes. And then?”

  JaEm went on, “And then the Ark split in two, when some of the Crew fell upon the poison ground of a world of false promise. Then there was the Blow-Out, when rebel children challenged the parameters of the Sim itself and caused a lethal rupture of the remnant Ark.”

  “Which is commonly interpreted as a metaphor for a Sim systems crash,” said LuSi. “According to an analysis by—”

  “Don’t analyse!” the Jennin snapped. “Don’t interpret! Just tell me the story.”

  JaEm went on uncertainly, “The Ark split in two at one more false world. Then finally its mighty journey was over, the sacred engines were shut down for the last time—”

  “Yes, yes. And humans fell to the ground of Urthen all those Years ago, ten thousand Years. Then what?”

  “Then we prospered, and spread, and cultivated our farms,” LuSi said. “Cities rose. Learning spread. At last we built new ships, not as mighty as the Ark but capable of reaching the stars. And we sent out emissaries to the false worlds, and their peoples, and we found new false worlds and we populated them, until the Bubble was filled with worlds—”

  “And then the Xaians of Windru got hold of starship technology,” the Jennin said.

  LuSi suppressed a smile. It sounded to her as if PiRo was becoming enthralled by the familiar story, despite his intellectual scepticism. “The Xaians,” she said, “seeking to cut mankind free of the burden of history, scoured the worlds of the Bubble and destroyed all traces of the human past, on world after world—”

  “Or tried to,” PiRo said. “All they succeeded in doing was making the job of the archaeologists and historians and other Jennins a lot more difficult.”

  “On Urthen, even starship technology was lost. But eventually it was recovered…”

  Bigmars was looming close now. Through the transparent hull of the habitable compartment the planet bellied before them, its surface rust-red and wrinkled under splashes of ice. Awed or intimidated by the sight, they fell silent.

  The Jennin was the first to speak. “The Backstory,” he said. “The whole tangle of it. LuSi, think. Of course it has a storytelling unity. But doesn’t it all sound too complicated? If you were a Sim Designer and you were going to invent a history for mankind, why make it so complex and unlikely? All these ships flying around an empty universe … And what about the elements of the Backstory that have nothing to do with mankind at all? What are they for?”

  JaEm frowned. “What do you mean, father?”

  The Jennin snorted. “Tell him, LuSi.”

  LuSi, embarrassed for JaEm, just said: “Look down.”

  They were in orbit now, swooping low over the northern hemisphere of Bigmars. Close to what looked unmistakeably like the shore of a sea, vanished save for glinting salt flats, were rows of dimples in the ground, like craters, small features seen from space but huge if you were down there among them. But they were not craters.

  “You know what they are,” Jennin PiRo said. “Even you, JaEm—”

  “Evidence of starships.”

  “Yes. Construction yards, like on Urthen—maybe. Or at least the marks of the launch of starships. Interstellar technology is always going to be hugely energetic; it is always going to mark any planet on which it takes root. And we know this isn’t evidence of human activity because—”

  LuSi said, “It’s all too old. Sealed under water ice and frozen air.”

  “More air than water, but yes. What do we think happened to the people who built this?”

  “They left in their starships. Or else they died out here, so long ago that their tombs have eroded away…”

  “The Ember got too cool,” said JaEm.

  “That’s it,” said the Jennin. “That’s the story—or the Backstory. The Ember is cooling, slowly, but inexorably. At any point in time there is a location in space around the Ember where a planet is warm enough for life—life like ours, life that needs liquid water. Once Bigmars was warm enough. But the habitable radius moved in towards the Ember, and Bigmars froze. Much of its water is probably still there, but locked underground in big aquifers. Useless for life. All this took a long time, billions of Years, but it was inexorable. And, yes, LuSi, the inhabitants of Bigmars must have fled, or died out. Just as we, one day, will have to flee, when Urthen starts to freeze in its turn.”

  LuSi said carefully, “Some people think that adds to the authenticity of the Backstory. I mean, the story of the Ark. The crew must have come far; maybe they could go no further, and had to stop here, however imperfect the world is, however inadequate the Ember.”

  The Jennin snorted dismissively. “That’s not what I brought you here to see.”

  “I know,” LuSi said. “It’s just like the starship yards at home. You argue that there is no need for a human Backstory to include evidence of a vanished alien civilisation.”

  “Well, why should it?”

  She faced him. “You say you want me to argue with my mother over her interpretation. But she has evidence on her side. At least for the consistency of the Backstory, the logic of the Sim. For instance, the very existence of mankind on the many worlds of the Bubble. How could we have got there if a ship didn’t deliver us?”

  “Oh, there are plenty of secondary colonies. We know that. But the primary worlds, including Airtree, Windru, Urthen—mankind arose separately on all these worlds. Convergent evolution. Our form is in some sense optimal for sentient, tool-wielding creatures.”

  “But it’s not just mankind. What about the Human Suite? That’s what the ecologists call it, isn’t it?”

  “Go on. What is the Human Suite?”

  “The creatures on which we rely, the grasses, the animals. Things we eat, or that can eat us. They are always to be found on human worlds—even though we have to share every world with other forms of life. Some quite unlike ours.”

  “So what? So on each world there has been a multiple origin of life—more than one tree of life. Why not? Why should the initiation of life be unique? And as for the Human Suite—convergent evolution, once again. What else?”

  “There’s the fact that the human worlds share elements of culture. Similarities of language, we all speak something like Anglish. We even use time measures like Years and Days that have nothing to do with the turn and spin periods of a world like ours—”

  “All probably imposed by the Xaians in their ideological fervour, much more recently than the flight of any Ark from a proto-world. Certainly that’s a much simpler explanation, and one based on an event we know happened, from the surviving records.” The Jennin leaned forward. “Look, child. I’m not expecting you to swallow my arguments today. Or ever, even. I just believe that your mother needs a countering voice.

  “Her pet theory, and the theological orthodoxy on this world and many others— that we are all trapped in some artificial reality—is deadening for the human spirit. The Backstory reinforces the idea. On the other hand the notion that the universe is just as it seems, that humanity evolved independently on all these habitable worlds, is actually simpler; we don’t need an elaborate secret history to explain it all … If the Backstory is confirmed by your mother, the whole Sim hypothesis is strengthened too. Your mother is never going to be convinced by the likes of me, but at least she needs a counter-voice. She must be made to work hard to convince others, no matter what she finds out there among the stars. And that’s what I want of you, LuSi—to be that counter-voice…”

  “Or,” JaEm said, reading a note scrolling on a comms screen, “you could do that job yourself, father.”

  “What do you mean?”

  “The university has just made an announcement. It is a big project, after all; the journey will take at least a century, there and back. They want a presence on board. And the College of Zaens is apparently going to mandate it.”

  “Mandate what?… Oh. My presence on the ship.”

  “You’re going to the stars too.” JaEm grinned at LuSi. “And so are we.”

  They couldn’t resist it. They flung themselves at each other and embraced.

  The Jennin groaned and rubbed his face. “Serves me right. Be careful what you wish for, in case you get it. I bet that saying is as old as mankind itself…”

  It took another year before the great starship Reality Dreams was ready to cross the interstellar gulf.

  It took fourteen more years to achieve that crossing.

  LuSi and JaEm were together on the ship; in the course of the journey they were even married. Thanks to their advanced anti-senescence science, the people of Urthen were long-lived; only a fraction of their potential lifetimes was expended.

  But still, by the time the ship reached Airtree, its first destination, their youth was gone.

  II

  After the battle was done, the Speaker of Speakers paused by the small field hospital that tended to the wounded, and reassured the dying that death was not an end, merely a return to the frozen patterns of thoughts in the greater Memory of the Sim …

  * * *

  The starship Reality Dreams settled into orbit around Airtree.

  Shuttles, approved by the local authority, came up from the ground to transport down the passengers. Blocky winged craft powered by fission rockets for the ascent, and essentially gliders for the re-entry and landing, these were all elderly, well-worn craft, beaten up by multiple flights to the edge of space. JaEm, who had devoted his life aboard the Reality Dreams to space engineering, looked faintly appalled at the sight of them.

  But LuSi knew this was what they had to expect. Airtree was ruled by a single government, as it had been through most of its history: a theocracy built around the cult of the Sim Controllers. The theocracy was rich, but its world was technologically backward, relatively.

  Even the slightly grander craft that was to transport Zaen SheLu, the Jennin PiRo, and their children LuSi and JaEm, plastered with heat-resistant tiles and holy symbols, was old and shabby and smelled faintly of urine. LuSi settled in grimly beside JaEm; nearly thirty years old now, and after fourteen years in the cavernous interior of the starship, she felt a twinge of apprehension as the shuttle parted from its lock with a rattle of opening latches.

  Before making their descent they completed a high-inclination orbital loop around the planet, and LuSi was able to make out the main features of this world, fixing them against the maps she had studied in the years before their arrival. Like Urthen, Airtree orbited close in to its sun, so that a single hemisphere faced the light. The illuminated face was a muddle of ocean and land, and LuSi could make out great concentric bands of vegetation types surrounding the subsolar point, green fading to brown or grey, swathes of forest or grasslands or crops, or even surviving scraps of native life, she supposed, adapted to the particular conditions of light and climate dictated by the unchanging altitude of the sun in the sky.

  And above all this, LuSi saw Reality Dreams, patiently following its own orbit. The starship was an engineered asteroid, a bubble of glass and ice that shone green from within, like a tremendous jewel; it looked more like a small moon than a ship. It was a miracle of the ancient warp technology that had driven the ship between the stars that in flight this huge bulk was folded away out of spacetime into a higher dimension, so that only a warp bubble the size of a sand grain protruded into the mundane cosmic stratum. LuSi longed with all her heart to be back aboard the ship, with JaEm, in the home they had built together, with their work, their slates and models, their friends. But she knew, too, that that was a symptom of her long interstellar confinement; she was like a released prisoner longing to be locked up again.

  At Airtree’s subsolar point was an island, the largest of a chain, a speck of land directly under the suspended star. The shuttle dipped low over this, heading north towards the shore of a continent called Seba, where they would make landfall. Light flared beyond the cabin windows, and the ride grew briefly bumpier, the air thickening, turbulent. When the plasma glow faded, the starry sky had been replaced by a violet blue, the stars were obscured, and the starship was lost to LuSi’s view. She reached out for JaEm’s hand.

  Speaker Tanz Vlov, sitting opposite them, observed this. This Airtree native, compact, shaven-headed, had been sent up in the shuttle to be their escort to the ground. Like many of his people, from a world of sterner gravity than Urthen, he was short by the standards LuSi was used to, but not exceptionally so. Despite his drab clerical garb he was a cheery, irreverent man who appeared about forty, but since anti-ageing treatments were available on this world, at least to the ruling elite, that was no real guide. Now Vlov smiled. “You look nostalgic.” He spoke the Urthen tongue—or their particular Anglish dialect depending on how you classified it—well but with a heavy accent. “You miss your ship.”

  “It is our home,” LuSi said. “Has been since we were both teenagers.”

  “Your home? You are married, yes? You have children?”

  “Not yet,” JaEm said. “Perhaps in the next phase of the journey. Which will take another thirty years, nearly, to Windru.”

  Vlov whistled. “Thirty more years, in a big enclosed machine. Strange to think of it.”

  Jennin PiRo leaned forward, past his son. “It shouldn’t be strange. Not to you. This world is the capital of the Creed of the Sim! You’re a Speaker, senior in the faith. You believe that everything is an artefact—even the physical world, even the stars, all a dream stored in some vast machine’s frozen Memory. What is life in a starship but a metaphor for that? It should seem familiar to you…”

  LuSi was used to this kind of goading from the Jennin. Vlov’s reaction seemed to be a commonsense one; he winked at her, and grinned. “Of course nothing is real. But the Sim Controllers created us for a purpose, a purpose expressed through how we live our lives. And we must live those lives as if it were all real. What else is there to do?”

  LuSi’s mother, meanwhile, was entirely uninterested in the conversation. SheLu was dressed in her own world’s version of clerical garb, the plain steel-grey robe of a Zaen, a priest of the Sim, and her hair, while not shaven close, was cut short and neat. She was in her sixties now but her ageing treatments had preserved her at around thirty; seeing her in the unfamiliar light of this new world, LuSi saw how her skin was just a little too taut, her eyes a little too clear. She peered out of the small window beside her seat, as the shuttle banked and turned in the air. “And that is the island you call the Navel?”