The lifedome neatly detached itself from the ship"s drive section and swept smoothly down from orbit.

Hama watched the moon"s folded-over, crater-scarred landscape flatten out, the great circular ramparts of Valhalla marching over the close horizon.

The lifedome settled to the ice with the gentlest of crunches.

A walkway extended from a darkened building block, and nuzzled hesitantly against the ship. A hatch sighed open.

Hama stood in the hatchway. The walkway was a transparent, shimmering tube before him, concealing little of the silver-black morphology of the collapsed landscape beyond. The main feature was the big Valhalla ridge, of course. Seen this close it was merely a rise in the land, a scarp that marched to either horizon: it would have been impossible to tell from the ground that this was in fact part of a great circular rampart surrounding a continent-sized impact scar, and Hama felt insignificant, dwarfed.

He forced himself to take the first step along the walkway.

The gravity here was about an eighth of Earth"s, comparable to the Moon"s, and to walk through Callisto"s crystal stillness was enchanting; he floated between footsteps in great bounds.

Gemo mocked his pleasure. "We are like Armm-stron and All-dim."

Nomi growled, "More Gree-chs, pharaoh?"

Reth Cana was waiting to meet them at the end of the walkway.

He was short, squat, with a crisp scalp of white hair, and he wore a practical-looking coverall of some papery fabric. He was scowling at them, his face a round wrinkled mask.

Beyond him, Hama glimpsed extensive chambers, dug into the ice, dimly lit by a handful of floating globe lamps- extensive, but deserted.

But Kama"s gaze was drawn back to Reth. He looks like Gemo.

Gemo stepped forward now, and they faced each other, brother and sister separated for centuries. Stiffly, they em braced. They were like copies of each other, subtly morphed.

Sarfi hung back, watching, hands folded before her.

Hama felt excluded, almost envious of this piece of complex humanity. How must it be to be bound to another person by such strong ties-for life?

Reth stepped away from his sister and inspected Sarfi. Without warning he swept his clenched fist through the girl"s belly. He made a trail of disrupted pixels, like a fleshy comet. Sarfi crumpled over, crying out.

The sudden brutality shocked Hama.

Reth laughed. "A Virtual? I didn"t suspect you were so sentimental, Gemo."

Gemo stepped forward, her mouth working. "But I remember your cruelty."

Now Reth faced Hama. "And this is the one sent by Earth"s new junta of children."

Hama shrank before Reth"s arrogance and authority. His accent was exotic-antique, perhaps; there was a rustle of history about this man. Hama tried to keep his voice steady. "I have a specific a.s.signment here, sir-"

Reth snorted. "My work, a project of centuries, deals with the essence of reality itself. It is an achievement of which you have no understanding. If you had a glimmer of sensitivity you would leave now. Just as, if you and your mayfly friends had any true notion of duty, you would abandon your petty attempts at governing."

Nomi growled. "You think we got rid of the ax just to hand over our lives to the likes of you?"

Reth glared at her. "Can you really believe that we would have administered the withdrawal of the ax with more death and destruction than you have inflicted?"

Kama stood straight. "I"m not here to discuss hypotheticals with you, Reth Cana. We are pragmatic. If your work is in the interest of the species-"

Reth laughed out loud; Hama saw how his teeth were discolored, greenish. "The interest of the species."

He stalked about the echoing cavern, posturing.

"Gemo, I give you the future. If this young man has his way, science will be no more than a weapon! ...

And if I refuse to cooperate with his pragmatism?"

Nomi said smoothly, "Those who follow us will be a lot tougher. Believe it, jasoft."

Gemo listened, stony-faced.

"Tomorrow," Reth said to Hama. "Twelve hours from now. I will demonstrate my work, my results. But I will not justify it to the likes of you; make of it what you will." And he swept away into shadows beyond the fitful glow of the hovering globe lamps.

Nomi said quietly to Hama, "Reth is a man who has spent too long alone."

"We can deal with him," Hama said with more confidence than he felt.

"Perhaps. But why is he alone? Hama, we know that at least a dozen pharaohs came to this settlement before the Occupation was ended, and probably more during the collapse. Where are they?"

Hama frowned. "Find out."

Nomi nodded briskly.

The oily sea lapped even closer now. The beach was reduced to a thin strip, trapped between forest and sea.

She walked far along the beach. There was nothing different, just the same dense forest, the oily sea.

Here and there the sea had already covered the beach, encroaching into the forest, and she had to push into the vegetation to make further progress. Everywhere she found the tangle of roots and vine-like growths. Where the rising liquid had touched, the gra.s.ses and vines and trees crumbled and died, leaving bare, scattered dust.

The beach curved around on itself.

She was on an island. At least she had learned that much. Eventually, she supposed, that dark sea would rise so high it would cover everything. And they would all die.

There was no night. When she was tired, she rested on the beach, eyes closed.

There was no time here-not in the way she seemed to remember, on some deep level of herself: no days, no nights, no change. There was only the beach, the forest, that black oily sea, lapping ever closer, all of it under a shadowless gray-white sky.

She looked inward, seeking herself. She found only fragments of memory: an ice moon, a black sky-a face, a girl"s perhaps, delicate, troubled. She didn"t like to think about the face. It made her feel-complex.

Lonely. Guilty.

She asked Asgard about time.

Asgard, gnawing absently on a handful of bark chips, ran a casual finger through the reality dust, from grain to grain. "There," she said. "Time pa.s.sing.

From one moment to the next. For we, you see, are above time."

"I don"t understand."

"Of course you don"t. A blade of gra.s.s is a shard of story. Where the gra.s.s knits itself into vines and trees, that story deepens. And if / eat a gra.s.s blade I absorb its tiny story, and it becomes mine. So

Pharaoh said. And I don"t know who told him. Do you see?"

"No," said Callisto frankly.

Asgard just looked at her, apathetic, contemptuous.

There was a thin cry, from the ocean. Callisto shaded her eyes, looked that way.

It had been a newborn, thrust arbitrarily into the air, just as Callisto had been. But this newborn had fallen, not to the comparative safety of the dust, but direct into the sea. She- or he-made barely a ripple on that placid black surface. Callisto saw a hand raised briefly above the sluggish meniscus, the flesh already dissolving, white bones curling.

And then it was gone, the newborn lost.

Callisto felt a deep horror.

Now, as she looked along the beach, she saw dark ma.s.ses-a mound of flesh, the grisly articulation of fingers -fragments of the suddenly dead, washed up on this desolate beach. This had happened before, she realized. Over and over.

Asgard sat apathetically, chewing on her bark.

Is this it? Callisto wondered. Must I sit here like Asgard, waiting for the rising ocean of death to claim me?

She said, "We can"t stay here."

"No," Asgard agreed reluctantly. "No, we can"t."

Kama, with Reth and Gemo, rode a platform of metal deep into the rocky heart of Callisto.

The walls of the pressurized shaft, sliding slowly upward, were lined with slick transparent sheets, barring them from the ice. Hama reached out with a fingertip. The wall surface was cold and slippery, lubricated by a thin sheet of condensation from the chill air. There were no signs of structure, of strata in the ice; here and there small bores had been dug away from the shaft, perhaps as samples.

Callisto was a ball of dirty water ice. Save for surface impacts, nothing had happened to this moon since it accreted from the greater cloud that had formed the Jupiter system. The inner moons-lo, Europa, Ganymede-were heated, to one degree or another, by tidal pumping from Jupiter. So Europa, under a crust of ice, had a liquid ocean; and lo was driven by that perennial squeezing to spectacular volcanism.

But Callisto had been born too far from her huge parent for any of that gravitational succor. Here, the only heat was a relic of primordial radioactivity; here there had been no geology, no volcanism, no hidden ocean.

Nevertheless, it seemed, Reth Cana had found life here. And, as the platform descended, Reth"s cold excitement seemed to mount.

Nomi Ferrer was pursuing her own researches, in the settlement and out on the surface. But she had insisted that Kama be escorted by a squat, heavily-armed drone robot. Both Reth and Gemo ignored this silent companion, as if it were somehow impolite of Kama to have brought it along.

Nor did either of them mention Sarfi, who hadn"t accompanied them. To Kama it did not seem human to disregard one"s daughter, Virtual or otherwise. But then, what was human about a near-immortal traitor to the race? What was human about Reth, this man who had buried himself alone in the ice of Callisto, obsessively pursuing his obscure project, for decade after decade?

Even though the platform was small and cramped, Hama felt cold and alone; he suppressed a shiver.

The platform slowed, creaking, to a halt. He faced a chamber dug into the ice.

Reth said, "You are a kilometer beneath the surface. Go ahead. Take a look."

Kama saw that the seal between the lip of the circular platform and the roughly-cut ice was not perfect.

He felt a renewed dread at his reliance on ancient, patched-up technology. But, suppressing hesitation, he stepped off the platform and into the ice chamber. With a whir of aged bearings, the drone robot followed him. Hama stood in a rough cube perhaps twice his height. It had been cut out of the ice, its walls lined by some clear gla.s.sy substance; it was illuminated by two hovering light globes. There was a knot of instrumentation, none of it familiar to Hama, along with a heap of data slates, some emergency equipment, and scattered packets of food and water. This was a working place, impersonal. Reth stepped past him briskly. "Never mind the gadgetry; you wouldn"t understand it anyhow... Look" And he snapped his fingers, summoning one of the floating globes. It came to hover at Kama"s shoulder. Hama leaned close to inspect the cut-away ice. He could see texture: the ice was a pale, dirty gray, polluted by what looked like fine dust grains-and, here and there, it was stained by color, crimson and purple and brown. Reth had become animated. "I"d let you touch it," he breathed. "But the sheeting is there to protect it from us- not the other way around. The biota is much more ancient, unevolved, fragile than we are, the bugs on your breath might wipe it out in an instant. The prebiotic chemicals were probably delivered here by comet impacts during Callisto"s formation. There is carbon and hydrogen and nitrogen and oxygen. The biochemistry is a matter of carbon-carbon chains and water-like Earth"s, but not precisely so. Nothing exactly like our DNA structures ..." "Spell it out," Gemo said casually, prowling around the gadgetry. "Remember, Reth, the education of these young is woefully inadequate." "This is life," Hama said carefully. "Native to Callisto." "Life-yes," Reth said. "The highest forms are about equivalent to Earth"s bacteria. But-native? I believe the life forms here have a common ancestor, buried deep in time, with Earth rife-and with the more extravagant biota of Eu- ropa"s buried ocean, and probably the living things found elsewhere in the Solar System. Do you know me notion of panspermia? Life, you see, may have originated in one place, perhaps even outside the System, and then was spread through the worlds by the spraying of meteorite-impact debris. And everywhere it landed, life embarked on a different evolutionary path." "But here," Hama said slowly, fumbling to grasp these unfamiliar concepts, "it was unable to rise higher than the level of a bacterium?" "There is no room," said Reth. "There is liquid water here: just traces of it, soaked into the pores between the grains of rock and ice, kept from freezing by the radiogenic heat. But energy flows thin, and replication is very slow- spanning thousands of years." He shrugged. "Nevertheless there is a complete ecosystem ... Do you understand? My Callis...o...b..cteria are rather like the cryptoendoliths found in some inhospitable parts of the Earth. In Antarctica, for instance, you can crack open a rock and see layers of green life, leaching nutrients from the stone itself, sheltering from the wind and the desolating cold: communities of algae, cyan.o.bacteria, fungi, yeast-" "Not any more," Gemo murmured, running a finger over control panels. "Reth, the Extirpation was very thorough, an effective extinction event; I doubt if any of your cryptoendoliths can still survive." "Ah," said Reth. "A pity." Hama straightened up, frowning. He had come far from the cramped caverns of the Conurbations; he was confronting life from another world, half a billion kilometers from Earth. He ought to feel wonder. But these pale shadows evoked only a kind of pity. Perhaps this thin, cold, purposeless existence was a suitable object for the obsessive study of a lonely, half-mad immortal.

Reth"s eyes were on him, hard. Hama said carefully, "We know that before the Occupation the Solar System was extensively explored, by My-kal Puhl and those who followed him. The records of those times are lost-or hidden," he said with a glance at the impa.s.sive Gemo. "But we do know that everywhere the humans went, they found life. Life is commonplace. And in most places we reached, life has attained a much higher peak than this. Why not just catalog these sc.r.a.pings and abandon the station?" Reth threw up his arms theatrically. "I am wasting my time. Gemo, how can this mayfly mind possibly grasp the subtleties here?" She said dryly, "I think it would serve you to try to explain, brother!" She was studying a gadget that looked like a handgun mounted on a floating platform. "This, for example." When Hama approached this device, his weapon-laden drone whirred warningly. "What is it?" Reth stalked forward. "It is an experimental mechanism based on laser light, which ... It is a device for exploring the energy levels of an extended quantum structure!" He began to talk, rapidly, lacing his language with phrases like "spectral lines" and "electrostatic potential wells," none of which Hama understood. At length Gemo interpreted for Hama. "Imagine a very simple physical system-a hydrogen atom, for instance. I can raise its energy by bombarding it with laser light. But the atom is a quantum system, it can only a.s.sume energy levels at a series of specific steps. There are simple mathematical rules to describe the steps. This is called a "potential well."" As he endured this lecture, irritation slowly built in Hama; it was clear there was much knowledge to be reclaimed from these patronizing, arrogant pharaohs. "The potential well of a hydrogen atom is simple," said Reth rapidly. "The simplest quantum system of all. It follows an inverse-square rule. But I have found the potential wells of much more complex structures-" "Ah," said Gemo. "Structures embedded in the Callis...o...b..cteria." "Yes." Reth"s eyes gleamed. He s.n.a.t.c.hed a data slate from a pile at his feet. A series of numbers chattered over the slate, meaning little to Hama, a series of graphs that sloped sharply before dwindling to flatness: a portrait of the mysterious "potential wells," perhaps. Gemo seemed to understand immediately. "Let me." She took the slate, tapped its surface and quickly reconfigured the display. "Now, look, Hama: the energies of the photons M that are absorbed by the well are proportional to this series of numbers." .2.3.5.7.11.13... "Prime numbers," Kama said. "Exactly," snapped Reth. "Do you see?" Gemo put down the slate and walked to the ice wall; she ran her hand over the translucent cover, as if longing to touch the mystery that was embedded there. "So inside each of these bacteria," she said carefully, "there is a quantum potential well that encodes prime numbers." "And much more," said Reth. "The primes were just the key, the first hint of a continent of structures I have barely begun to explore." He paced back and forth, restless, animated. "Life is never content simply to subsist, to cling on. Life seeks rooms to spread. That is another commonplace, young man. But here, on Callisto, there was no room: not in the physical world; the energy and nutrients were simply too spa.r.s.e for that. And so-"

"Yes?"

"And so they grew sideways," he said. "And they reached orthogonal realms we never imagined existed."

Kama stared at the thin purple sc.r.a.pings and chattering primes, here at the bottom of a pit with these two immortals, and feared he had descended into madness.

...41.43.47.53.59...

In a suit no more substantial than a thialayer of cloth, Nomi Ferrer walked over Callisto"s raw surface, seeking evidence of crimes.

The sun was low on the horizon, evoking highlights from the curved ice plain all around her. From here, Jupiter was forever invisible, but Nomi saw two small discs, inner moons, following their endless dance of gravitational clockwork.

Gemo Cana had told her mayfly companions of how the Jovian system had once been. She told them of lo"s mineral mines, nestling in the shadow of the huge volcano Babbar Patera. She told them of Ganymede: larger than Mercury, heavily cratered and geologically rich-the most stable and heavily populated of all the Jovian moons. And Europa"s icy crust had sheltered an ocean hosting life, an ecosystem much more complex and rewarding than anybody had dreamed.

"They were worlds. Human worlds. All gone now, shut down by the ax. But remember ..."

Away from the sun"s glare, lesser stars glittered, surrounding Nomi with immensity.

But it was a crowded sky, despite that immensity. Crowded and dangerous. For-she had been warned by the Coalition-the Xeelee craft that had glowered over Earth was now coming here, hotly pursued by a Spline ship retrieved from the hands of jasoft rebels and manned by Green Army officers. What would happen when that miniature armada got here, Nomi couldn"t imagine.

The Xeelee were legends of a deep-buried, partly extirpated past. And perhaps they were monsters of the human future. The Xeelee were said to be G.o.dlike ent.i.ties so aloof that humans might never understand their goals. Some sc.r.a.ps of Xeelee technology, like starbreaker beams, had fallen into the hands of "lesser" species, like the ax, and transformed their fortunes. The Xeelee seemed to care little for this-but, on occasion, they intervened.

To devastating effect.

Some believed that by such interventions the Xeelee were maintaining their monopoly on power, controlling an empire which, perhaps, held sway across the Galaxy. Others said that, like the vengeful G.o.ds of humanity"s childhood, the Xeelee were protecting the "junior races" from themselves.

Either way, Nomi thought, it"s insulting. Claustrophobic. She felt an unexpected stab of resentment. We only just got rid of the ax, she thought. And now, this.

Gemo Cana had argued that in such a dangerous universe, humanity needed the pharaohs. "Everything humans know about the Xeelee today, every bit of intelligence we have, was preserved by the pharaohs.

I refuse to plead with you for my life. But I am concerned that you should understand. We pharaohs were not-dynastic tyrants. We fought, in our way, to survive the ax Occupation, and the Extirpation. For we are the wisdom and continuity of the race. Destroy us and you complete the work of the ax for them, finish the Extirpation. Destroy us and you destroy your own past-which we preserved for you, at great cost to ourselves."

Perhaps, Nomi thought. But in the end it was the bravery and ingenuity of one human-a mayfly-that had brought down the ax, not the supine compromising of the jasofts and pharaohs.

She looked up toward the sun, toward invisible Earth. I just want a sky clear of alien ships, she thought. And to achieve that, perhaps we will have to sacrifice much. Reth Cana began to describe where the Callis...o...b..gs had "gone." "There is no time," he whispered. "There is no s.p.a.ce. This is the resolution of an ancient debate-do we live in a universe of perpetual change, or a universe where neither time nor motion exists? Now we understand. Now we know we live in a universe of static shapes. Nothing exists but the particles that make up the universe-that make up us. Do you see? And we can measure nothing but the separation between those particles. "Imagine a universe consisting of a single elementary particle, an electron perhaps. Then there could be no s.p.a.ce. For s.p.a.ce is only the separation between particles. Time is only the measurement of changes in that separation. So there could be no time. "Imagine now a universe consisting of two particles ..." Gemo nodded. "Now you can have separation, and time." Reth bent and, with one finger, scattered a line of dark dust grains across the floor. "Let each dust grain represent a distance-a configuration of my miniature two-particle cosmos. Each grain is labeled with a single number: the separation between the two particles." He stabbed his finger into the line, picking out grains. "Here the particles are a meter apart; here a micron; here a light-year. There is one special grain, of course: the one that represents zero separation, the particles overlaid. This diagram of dust shows all that is important about the underlying universe-the separation between its two components. And every possible configuration is shown at once, from this G.o.d-like perspective." He let his finger wander back and forth along the line, tracing out a twisting path in the grains. "And here is a history: the two particles close and separate, close and separate. If they were conscious, the particles would think they were embedded in time, that they are coming near and far. But we can see that their universe is no more than dust grains, the lined-up configurations jostling against each other. It feels like time, inside. But from outside, it is just-sequence, a scattering of instants, of reality dust." Gemo said, "Yes. "It is utterly beyond our power to measure the change of things by time. uite the contrary, time is an abstraction at which we arrive by means of the changes of things."" She eyed Kama. "An ancient philosopher. Much, or Mar-que ..." "If the universe has three particles," said Reth, "you need three numbers. Three relative distances-the separation of the particles, one from the other determine the cosmos"s shape. And so the dust grains, mapping possible configurations, would fill up three-dimensional s.p.a.ce-though there is still a unique grain, representing the special instant where all the particles are joined. And with four particles-" "There would be six separation distances," Hama said. "And you would need a six-dimensional s.p.a.ce to map the possible configurations." Reth glared at him, eyes hard. "You are beginning to understand. Now. Imagine a s.p.a.ce of stupendously many dimensions." He held up a dust grain. "Each grain represents one configuration of all the particles in our universe, frozen in time. This is reality dust, a dust of the Nows. And the dust fills configuration s.p.a.ce, the realm of instants. Some of the dust grains may represent slices of our own history." He snapped his fingers, once, twice, three times. "There. There. There. Each moment, each juggling of the particles, a new grain, a new coordinate on the map. There is one grain that represents the coalescing of all the universe"s particles into a single point. There are many more grains representing chaos-darkness-a random, structureless shuffling of the atoms. "Configuration s.p.a.ce contains all the arrangements of matter there could ever be. It is an image of eternity." He waved a fingertip through the air. But if I trace out a path from point to point-" "You are tracing out a history," said Kama. "A sequence of configurations, the universe evolving from point to point." "Yes. But we know that time is an illusion. In configuration s.p.a.ce, all the moments that comprise our history exist simultaneously. And all the other configurations that are logically possible also exist, whether they lie along the track of that history or not." Kama frowned. "And the Callis...o...b..gs-" Reth smiled. "I believe that, constrained in this s.p.a.ce and time, the Callisto lifeforms have started to explore the wider realms of configuration s.p.a.ce. Seeking a place to play." Nomi turned away from the half-buried human township. She began to toil up the gentle slope of the ridge that loomed above the settlement. This was one of the great ring walls of the Valhalla system, curving away from this place for thousands of kilometers, rising nearly a kilometer above the surrounding plains. The land around her was silver and black, a midnight sculpture of ridges and craters. There were no mountains here, none at all; any created by primordial geology or the impacts since Callisto"s birth had long since subsided, slumping into formlessness. There was a thin smearing of black dust over the dirty white of the underlying ice; the dust was loose and fine-grained, and she disturbed it as she pa.s.sed, leaving bright footprints. "Do you understand what you"re looking at?" The sudden voice startled her; she looked up. It was Sarfi. She was dressed, as Nomi was, in a translucent protective suit, another nod to the laws of consistency that seemed to bind her Virtual existence. But she left no footprints, nor even cast a shadow. Sarfi kicked at the black dust, not disturbing a single grain. "The ice sublimes-did you know that? It shrivels away, a meter every ten million years-but it leaves the dust behind. That"s why the human settlements were established on the north side of the Valhalla ridges. There it is just a shade colder, and some of the sublimed ice condenses out. So there is a layer of purer ice, right at the surface. The humans lived off ten-million-year frost... You"re surprised I know so much. Nomi Ferrer, I was dead before you were born. Now I"m a ghost imprisoned in my mother"s head. But I"m conscious. And I am still curious." Nothing in Nomi"s life had prepared her for this conversation. "Do you love your mother, Sarfi?" Sarfi glared at her. "She preserved me. She gave up part of herself for me. It was a great sacrifice." Nomi thought, You resent her. You resent this cloying, possessive love. And all this resentment bubbles inside you, seeking release. "There was nothing else she could have done for you." "But I died anyway. I"m not me. I"m a download. I don"t exist for me, but for her. I"m a walking, talking construct of her guilt." She stalked away, climbing the slumped ice ridge. Gemo started to argue detail with her brother. How was it Possible for isolated bacteria-like creatures to form any kind of sophisticated sensorium?-but Reth believed there were slow pathways of chemical and electrical communication, etched into the ice and rock, tracks for great slow thoughts that pulsed through the substance of Callisto. Very well, but what of quantum mechanics? The universe was not made up of neat little particles, but was a mesh of quantum probability waves-Ah, but Reth imagined quantum probability lying like a mist over his reality dust, constrained by two things: the geometry of configuration s.p.a.ce, as acoustic echoes are determined by the geometry of a room; and something called a "static universal wave function," a mist of probability that governed the likelihood of a given Now being experienced ...

Hama closed his eyes, his mind whirling.