Vacuum Diagrams

by Stephen Baxter

  Then the creatures within would unfold their limbs, and the long Project of the Xeelee would begin.

  Eventually the Project would lead to the development of the seed pods, the spawning of the antiXeelee itself; and so the circle would be closed. There was, of course, no paradox about this causal loop; although — for amusement — the antiXeelee had once studied a toy-creature, a human from whose viewpoint such events had seemed not merely paradoxical but impossible. Something like a smile reflex spread through its awareness. (... And, revived like an afterthought by the immense memory, the toy-creature whispered once more into being, a faint coherence in the vacuum.)

  So its work was done; the antiXeelee could let go. It spread wide and thin.

  Forgotten, the toy-creature stirred like an insect in its cocoon.

  Paul opened his eyes.

  The antiXeelee hovered over Paul.

  He was — discorporeal; it was as if the jewel of consciousness which had lain behind his eyes had been plucked out of his body and flung into space. He did not even have heartbeats to count. He remembered ruefully the casual contempt with which he had regarded Taft, Green and the rest on the Sugar Lump, how he had soared over their shambling, makeshift bodies, their limited awareness!

  ...And yet now, stranded, with no idea why he was here, he would have given a great deal to return to the comforting furniture of a human body.

  At least the antiXeelee was here with him. It was like a great ceiling under which he hovered and buzzed, insectlike. He sensed a vast, satisfied weariness in its mood, the contentment of the traveler at the end of a long and difficult road. For a long time he stayed within the glow of its protection.

  Then it began to dissolve.

  Paul wanted to cry out, like a child after its huge parent. He was buffeted, battered. It was as if a glacier of memories and emotions was calving into a hundred icebergs about him; and now those icebergs in turn burst into shards which melted into the surface of a waiting sea...

  With a brief, non-localized burst of selectrons and neutralinos the awareness of the antiXeelee multiplied, fragmented, shattered, sank into the vacuum.

  And Paul was left alone.

  It was impossible to measure time, other than by the slow evolution of his own emotions.

  He had lived among people no more than a few months, on the Xeelee seed pod they had called the Sugar Lump; but in that time he had been shown visions, sounds, scents, tactile images from all the worlds of the human empire, and he had formed an impression of the great storm of souls that constituted the human race. Each of those souls, he knew, was like a tiny line drawn in space-time, with a neat start, a thickening into self-awareness and a clean conclusion. The race was — had been — a vast, dynamic drawing of billions of such lifelines.

  He, Paul, spoiled the picture.

  His lifeline began in a tight, acausal knot wrapped around the Sugar Lump — and was then dragged across the face of the picture like a vandal's scribble — and finished here, a loose end beyond the conclusion of history.

  He felt no privilege to be here. His life was artificial, a construct, a random jotting of the Xeelee. He could see inside stars... but he had never looked into a human heart.

  He endured despair. Why had he been brought to this point in space-time and then so casually abandoned? Had he been correct in detecting a strain of amusement in the vast, crashing symphony of the antiXeelee's thoughts? Was he truly no more than a toy?

  The despair turned to anger, and lasted a long time.

  Later he became curious about the aging Universe around him. He had no senses, of course: no eyes, no ears, no fingers; nevertheless he tried to construct a simulacrum of a human awareness, to assign human labels to the objects and processes around him.

  There were still stars. He saw sheets of them, bands and rays, complex arrays.

  Evidently the Xeelee had remade the Universe.

  But there were anomalies. He found many supernova sites, swelling giants, wizened dwarfs: the stars were aged, more aged than he had expected. Clearly many millions of years had passed since his time on the Sugar Lump — enough time for the Xeelee to have completed their galactic engineering — yet this immense duration was insignificant on the cosmic scale.

  So why did the stars seem so old? He found no answer.

  Driven by curiosity he began to experiment with his awareness. Physically he was composed of a tight knot of quantum wave functions; now, cautiously, he began to unravel that knot, to allow the focus of his consciousness to slide over space-time. Soon it was as if he was flying over the arch of the cosmos, unbound by limits of space or time.

  He descended through the plane of the Galaxy, his sense-analogues spread wide.

  Much of the Milky Way, he found, had been rebuilt. Huge constructs, some light years across, had been assembled: there were rings, sheets, ribbons of stars, stars surrounded by vast artifacts — rings, spheres, polyhedra. In these celestial cities the component stars appeared to have been selected — or, perhaps, built — with great discrimination. Here, for example, was a ring of a dozen Sol-like yellow dwarfs surrounding a brooding red giant; the dwarfs circled their parent so closely that Paul could see how they dipped into the turbulent outer layers of the giant's red flesh. The dwarfs in that necklet must once have been utterly identical, but now time had taken its toll: one of the dwarfs even appeared to have suffered a minor nova explosion — the shrunken remnant was surrounded by a shell of expanding, cooling debris — and the rest were fading to dimness, their hydrogen fuel depleted and vast spots disfiguring their shining surfaces.

  Throughout the Galaxy Paul found evidence of such decay.

  He was saddened by what he saw... and puzzled. He had noted this star aging before; and the time scales still did not make sense.

  Something, some agency, had aged the stars.

  Paul soared beneath the plane of the Galaxy. The great disc was a ceiling of curdled gold above him. The spiral arms were devastated: made ragged, the spirals disrupted by the blisters of yellow-red light which swelled across the lanes of dust.

  Those blisters were supernova remnants. Enduring forced aging, a lot of the more spectacular, and beautiful, spiral arm stars would simply explode, tearing themselves apart... probably there had been chain reactions of supernovae, with the wreckage of one star destabilizing another.

  Paul stared up at the wreckage of the disc, the muddled spiral arms.

  Some things remained the same, though. Paul saw how the great star system rotated as one, as if solid. The Galaxy's visible matter was no more than a fraction of its total bulk; a vast, invisible halo of dark matter swathed the bright spiral, so that the light matter lay at the bottom of a deep gravity pit, turning like an oil drop in a puddle.

  Now Paul climbed out of that huge, deep gravity well and passed through the halo of dark matter. The ghostly stuff barely impinged on his awareness. Photinos — the dark matter particles — interacted with normal matter only through the gravitational force, so that even to Paul the halo was like the faintest mist.

  But he perceived odd hints of structure, too elusive to identify.

  Were there worlds here, he wondered, cold stars, perhaps even beings with their own goals and ambitions?

  Paul turned away from the Galaxy and faced the hostile Universe.

  The quantum functions connecting him to the site of man's original system stretched thin. Soon the human Galaxy shrank to a mote in the vast cathedral of space. He saw clusters and super clusters of galaxies, glowing softly, sprinkled over space in great filaments and sheets, so that it was as if the Universe were built of spiderweb.

  On the largest of scales space was a froth of baryonic matter, a chaotic structure of threads and sheets of shining starstuff, separated by voids a hundred million light years across.

  And everywhere, on both the small scale and the large, Paul found evidence of the work of intelligence, and in particular of the vast, unrestrained projects of the Xeelee. They had turned galaxies
into neat balls of stars, and in one place they had caused two galaxy clusters — whole clusters! — to collide, in order to create a region a million light years wide in which matter was nowhere less dense than in the outer layers of a red giant star.

  Paul wondered what manner of creatures moved through that vast sea...

  And everywhere he traveled Paul found the premature aging of stars.

  Paul's anger stirred, illogically.

  Cautiously, clinging to his wave-function ropes, Paul sank into the dark matter ocean.

  Currents of photinos swept past him. The moving masses distorted space-time, and the density was high enough for him to perceive vast structures gliding through his focus of awareness. Gradually he came to understand the structure of his Universe.

  Dark matter comprised most of the mass of the Universe. Baryons — protons and neutrons, the components of light, visible matter — and photinos — their dark matter analogues — existed largely independently of each other, interacting only through gravitational attraction.

  All matter, dark and light, had erupted from the singularity at the start of time which had forced space itself to unfurl like a torn sheet. The dark matter had spread like some viscous liquid into every corner of the young Universe and, seething, settled into a kind of equilibrium. The baryons had been sprinkled like a froth over this sea.

  At first the dark ocean was featureless, save only for variations in its smooth density. These glitches, representing mass concentrations on the order of millions of solar masses, formed gravitational wells, cosmic potholes into which fragments of light matter fell, pooled, and began to coalesce. Gravitational warming began, and — finally, fitfully — the first stars sputtered to brightness. A billion years after the singularity the galaxies formed, trapped like flies in the dark matter wrinkles.

  Slowly dark currents pushed the galaxies together, and large-scale structures — the vast, gaudy superstructure that would span the Universe — began to evolve.

  Most of this made no difference to the dark matter sea... but, here and there, the material of the shining stars began to exert an influence on its dark counterpart. Just as baryons had slithered into dark matter potholes, so — on a much smaller scale — photinos collected in the pinpoint gravity wells of the new stars.

  Even the human star, Sol, had contained a dark core the size of a moon. Human scientists had observed this dark parasite indirectly by its effect on the neutrino output of the Sun...

  And, in a slow explosion of insight, Paul began to see a connection between the dark matter canker at the hearts of the stars, and the aging of the baryonic Universe.

  Excited, he skimmed through the Universe, studying the cooling corpses of extinguished stars.

  And at last, datum by datum, he came to understand the secret history of the Universe.

  Thanks to the baryonic stars small-scale structure entered the dark matter Universe. Paul speculated that a chemistry must have begun, with varieties of the photinos combining to form some counterpart of molecules; strange rains had sleeted over the surfaces of the shadow worlds, still buried in the blazing cores of baryon stars.

  At last life had arisen.

  Paul had no way of knowing if the transition to life had occurred on one of the shadow planets or on several, perhaps in a variety of forms. Nor could he guess what form that life had taken, what technologies and philosophies it had evolved.

  But he could speculate how it had spread. Photino creatures like birds — photino birds — had fluttered out through the baryon stars as if they did not exist, colonizing shadow world after shadow world. Perhaps, Paul supposed, vast flocks had plied between the hearts of stars, with the humans and other baryonic races all unaware.

  Aeons had passed with the two grand families of life, dark and light, oblivious of each other...

  Then something had happened.

  Again Paul could only guess. Probably a supernova had ripped apart a baryon star, laying waste to its host shadow world in the process. Paul imagined the horror of the photino civilization as the irrelevant froth of baryons through which they moved turned into a source of deadly danger, perhaps threatening the ultimate survival of their civilization.

  Many courses of action must have been considered, including — Paul speculated with a kind of shudder — the total annihilation of the baryonic content of the Universe. But without baryon stars and their tiny gravity wells new shadow worlds could not form; therefore without the baryons there could be no replacement for the photino worlds as they grew stale and died: and so, in the end, the dark civilization itself would falter and fail.

  So the baryons had to stay. The photino birds needed the stars.

  But they didn't need the damn things exploding all over the place. And the Universe was full of these vast, gaudy stars, burning off energy and forever quivering on the brink of catastrophic explosions. Such extrovert monsters were simply unnecessary; all the dark races required from a star was a reasonably stable gravity well. The remnants of large stars — white dwarfs and neutron stars — were quite satisfactory, and so were immature stars: the brown dwarfs and Jovian gas planets which were warm but not quite large enough for fusion to be initiated.

  Cold, dull, and immensely stable. That was how a star should be.

  So the photino birds set out to transform the Universe.

  The photino birds set up two great programs. The first had been to shape the evolution of new stars. Paul imagined invisible flocks cruising through the vast gas clouds which served as the breeding grounds for new stars; the photino birds had used huge masses to skim layers off protostars and so condemn them to become brown dwarfs, little grander than Jupiter.

  The second program had been to rationalize existing stars.

  If the things were going to explode or swell up like balloons, the photino birds had reasoned, then they would prefer to accelerate the process and get it out of the way. Then the photino civilization could grow without limit or threat, basking in the long, stately twilight of the Universe.

  So the photino birds had settled into the hearts of stars. They infested the core of humanity's original Sun.

  For millions of years, unknown to humanity, the photino birds had fed off the Sun's hydrogen-fusing core. Each sip of energy, by each of the photino birds, had lowered the temperature of the core, minutely.

  In time, after billions of interactions, the core temperature dropped so far that hydrogen fusion was no longer possible. The core had become a ball of helium, dead, contracting. Meanwhile, a shell of fusing hydrogen burned its way out of the Sun, dropping a rain of helium ash onto the core...

  Five billion years early, the Sun left the Main Sequence, and ballooned into a red giant.

  With such cool calculation, such oceanic persistence, the photino birds made the stars old.

  Soon the first supernovae began. They spread like a plague from the photino birds' center of operation.

  And the Xeelee became troubled.

  By this time, Paul speculated, the Xeelee were already lords of the baryonic Universe. They had initiated many of their vast cosmic engineering projects, and a host of lesser races had begun to dog their gigantic footsteps.

  The Xeelee focused attention on the photino birds' activities, and rapidly came to understand the nature of the threat they faced. In peril was not just the future of the Xeelee themselves, but of all baryonic life.

  Perhaps they had tried to communicate with the birds, Paul speculated; perhaps they even succeeded. But the conflict with the photino birds was so fundamental that communication was meaningless. This was a dispute not between individuals, worlds, even species; it was a struggle for survival between two inimical life modes trapped in a single Universe.

  It was a struggle the Xeelee could not afford to lose. They abandoned their projects and mobilized.

  The final War must have started slowly. Paul imagined Xeelee nightfighters descending on stars known to harbor key photino bird flocks, cherry-red starbreaker beams shining
like swords. And there would be reciprocal action by the photino birds; their unimaginable weapons would slide all but unobserved past the best defenses of the Xeelee.

  And the Xeelee must, about the same time, have initiated the construction of the great causal loop controlled by the antiXeelee with its seed pods. At last Paul understood the antiXeelee's purpose: the Xeelee had, with awesome determination, decided to modify their own evolutionary history in order to equip themselves for the battle with the photino birds. Paul pictured a branching of the Universe as the antiXeelee changed the past. The Xeelee, modified and pre-warned, had time in this new history to prepare for the coming conflict, including the construction of the mighty artifact called Bolder's Ring — an escape route in case, despite all their preparation, the War were lost.

  And all the time humans and other races, oblivious to the great purpose of the Xeelee, had scrambled for abandoned Xeelee toys. Eventually humans had even had the audacity to attack the Xeelee themselves, unaware that the Xeelee were waging a total War against a common enemy far more deadly than the Qax, or the Squeem, or any of man's ancient foes.

  The Xeelee wars had been a ghastly, epochal error of mankind. Humans believed they must challenge the Xeelee: overthrow them, become petty kings of the baryonic cosmos.

  This absurd rivalry led, in the end, to the virtual destruction of the human species. And — worse, Paul reflected — it blinded humanity to the true nature of the Xeelee, and their goals: and to the threat of the dark matter realm.

  There was a fundamental conflict in the Universe, between the dark and light forms of matter — a conflict which had, at last, driven the stars to their extinction. Differences among baryonic species — the Xeelee and humanity, for instance — are as nothing compared to that great schism.