Manifold: Space

by Stephen Baxter

  She felt a pulse in her head, a pressure. "But," she said, "if we're just emulations in some toy starship, we're dead. I mean, we're no longer us. Are we? How can we be?"

  He eyed her. "The first time you stepped through a gateway you were no longer you. Every transition is a death, a rebirth. Why do you think it hurts so much?"

  She felt weak, her legs numb. Carefully, she lowered herself to the grass, dug her hands into the rich cool texture of the ground.

  He knelt beside her, took her hand. "Listen. I don't mean to be so tough on you. What do I know? I only have guesses too. I've had more time to get used to this stuff, is all." He went on with difficulty. "I know you came here to help me. I remember the way you fixed my suit, on the Cannonball. You were... kind."

  She said nothing.

  "I just don't think you can help," he said. His face was turning hard again. "Or will help."

  That chilled her, his harsh dismissal. "Help with what, Malenfant? Why did the Gaijin go to all this trouble – to train Neandertals to mine antimatter on Io, build a starship, hurl it across light-years?"

  He looked troubled at that. "I think – I have this awful feeling, a suspicion – that the purpose of it all was me. A huge alien conspiracy, all designed to give me a ride across the Galaxy." He studied her, face emptied by wonder. "Or is that paranoid, megalomaniacal? Do you think I'm crazy, Madeleine?"

  Beyond him, perhaps a half kilometer away, she made out a new shadow: angular, gaunt, crisp and precise before the cosmos light.

  It was a Gaijin.

  "Maybe we'll soon find out," she said.

  They approached the Gaijin. It just stood there impassively, silent. Madeleine saw how the pencil-thin cones that terminated its legs were stained green by crushed grass, and that a little quasi-African dust had settled on the surfaces of its upper carapace.

  Malenfant said he recognized it. It was the individual Gaijin he had come to know as Cassiopeia.

  "Oh, really? And how do you know that, Malenfant? The Gaijin are just spidery robots. Don't they all look alike?"

  He didn't try to answer.

  Madeleine found the Gaijin's calm mechanical silence infuriating. She bent down and picked up a handful of dirt. She threw it at the Gaijin; it pinged off that impassive hide, not making so much as a scratch. "You. Space robot. You've been playing with us since you showed up in our asteroid belt. I don't care how alien you are. No more fucking games."

  Malenfant seemed shocked by her swearing. A corner of her found amusement at that. Malenfant really was a man of his time: Here they were hurtling away from Earth at a tad less than light speed, shrunk to quark-sized copies or else trapped in some alien virtual reality, and he was shocked to hear a woman swear. But he just stood and let her rant her heart out. Therapy, for absorbing one shock after another.

  She ran out of energy, slumped back to the grass, numbed by tiredness.

  The Gaijin stirred, like a turret swiveling. Madeleine thought she heard something like hydraulics, perhaps a creak of metal scraping on metal. The Gaijin spoke, its booming voice a good emulation of a human's – a woman's voice, in fact, with a tinge of Malenfant's own accent.

  NO DOUBT YOU'RE WONDERING WHY I ASKED YOU HERE TODAY, Cassiopeia said.

  The silence stretched. Malenfant peered up at the Gaijin doubtfully.

  "She made a joke," Madeleine said slowly. "This ridiculous alien robot made a joke."

  Malenfant stared at Madeleine. Then he threw his hands in the air, slumped back on the grass, and laughed.

  Pretty soon, Madeleine caught the bug. The laugh seemed to start in her belly and burst out of her throat and mouth, despite her best efforts to contain it.

  So they laughed, and kept on laughing, while the Gaijin waited for them.

  And, cradling its precious cargo of mind and hope and fear, the ten-centimeters-long starship hurtled onward toward the core of the Galaxy, and its destiny.

  Chapter 33

  The Fermi Paradox

  They drank from a stream, and ate fruit, and lay on the grass, letting the tension drain out. Madeleine thought she slept for a while, curled up against Malenfant in the grass, like they were two exhausted kids.

  And then – when they were awake, sitting before Cassiopeia – the Gaijin waved a spidery metal limb, and the world dissolved. It melted like a defocusing image: grass and mud and trees and streams running together, everything but the three of them, two humans and a Gaijin, and that eerie universe-Sun, so that they seemed to be floating, bathed in a deeper darkness than Madeleine had ever known.

  She reached out and grabbed Malenfant's hand. It was warm, solid; she could see him, the folds on his jumpsuit picked out by the cosmic glow. She dug the fingers of her other hand into loamy soil beneath her. It was still there, cool and friable, invisible or not. She clung to its texture, to the pull of the fake world sticking her to the ground.

  But Malenfant was staring upward, past the Gaijin's metal shoulder. "Look at that. Holy shit."

  She looked up unwillingly, reluctant to face new wonders.

  Above them, a ceiling of curdled light spanned the sky. It was a galaxy.

  It was a disc of stars, flatter and thinner than she might have expected, in proportion to its width no thicker than a few sheets of paper. She thought she could see strata in that disc, layers of structure, a central sheet of swarming blue stars and dust lanes sandwiched between dimmer, older stars. The core, bulging out of the plane of the disc like an egg yolk, was a compact mass of yellowish light; but it was not spherical, rather markedly elliptical. The spiral arms were fragmented. They were a delicate blue laced with ruby-red nebulae and the blue-white blaze of individual stars – a granularity of light – and with dark lanes traced between each arm. She saw scattered flashes of light, blisters of gas. Perhaps those were supernova explosions, creating bubbles of hot plasma hundreds of light-years across.

  But the familiar disc – shining core, spiral arms – was actually embedded in a broader, spherical mass of dim red stars. The crimson fireflies were gathered in great clusters, each of which must contain millions of stars.

  The Gaijin hovered before the image, silhouetted, like the spidery projector cluster at the center of a planetarium.

  "So, a galaxy," said Madeleine. "Our Galaxy?"

  "I think so," Malenfant said. "It matches radio maps I've seen." He pointed, tracing patterns. "Look. That must be the Sagittarius Arm. The other big structure is called the Outer Arm." The two major arms, emerging from the elliptical core, defined the Galaxy, each of them wrapping right around the core before dispersing at the rim into a mist of shining stars and glowing nebulae and brooding black clouds. The other "arms" were really just scraps, she saw – the Galaxy's spiral structure was a lot messier than she had expected – but still, she thought, the Sun is in one of those scattered "fragments."

  The Galaxy image began to rotate, slowly.

  "A galactic day," Malenfant breathed. "Takes two hundred million years to complete a turn..."

  Madeleine could see the stars swarming, following individual orbits around the Galaxy core, like a school of sparkling fish. And the spiral arms were evolving too, ridges of light sparking with young stars, churning their way through the disc of the Galaxy. But the arms were just waves of compression, like the bunching of traffic jams, with individual stars swimming through the regions of high density.

  And now, Madeleine saw, a new kind of evolution was visible in the disc. Like the pulsing bubbles of supernovae, each was a ripple of change that began at an individual star before spreading across a small fraction of the disc. Within each wave front the stars went out, or turned red, or even green; or sometimes the stars would pop and flare, fizzing with light.

  "Life," she said. "Dyson spheres. Star Crackers – "

  "Yes," Malenfant said grimly. "Colonization bubbles. Just like the one we got caught up in."

  THIS IS WHAT WE HAVE LEARNED, the Gaijin said somberly.

  Life, Cassiopeia said, was emergent
everywhere. Planets were the crucible. Life curdled, took hold, evolved, in every nook and cranny it could find in the great nursery that was the Galaxy.

  Characteristically life took hundreds of millions of years to accrue the complexity it needed to start manipulating its environment on a major scale. On Earth, life had stuck at the single-celled stage for billions of years, most of its history. Still, on world after world, complexity emerged, mind dawned, civilizations arose.

  Most of these cultures were self-limiting.

  Some were sedentary. Some – for instance, aquatic creatures, like the Flips – lacked access to metals and fire. Some just destroyed themselves, one way or another, through wars, or accidents, or obscure philosophical crises, or just plain incompetence. The last, Madeleine suspected, might have been mankind's ultimate fate, left to its own devices.

  Maybe one in a thousand cultures made it through such bottlenecks.

  That fortunate few developed self-sustaining colonies off their home worlds, and – forever immune to the eggs-in-one-basket accidents that could afflict a race bound to a single world – they started spreading. Or else they made machines, robots that could change worlds and rebuild themselves, and sent them off into space, and they started spreading.

  Either way, from one in a thousand habitable worlds, a wave of colonization started to expand.

  There were many different strategies. Sometimes generations of colonists diffused slowly from star to star, like a pollutant spreading into a dense liquid. Sometimes the spread was much faster, like a gas into a vacuum. Sometimes there was a kind of percolation, a lacy, fractal structure of exploitation leaving great unspoiled voids within.

  It was a brutal business. Lesser species – even just a little behind in the race to evolve complexity and power – would simply be overrun, their worlds and stars consumed. And if a colonizing bubble from another species was encountered, there were often ferocious wars.

  "It's hard to believe that every damn species in the Galaxy behaves so badly," Madeleine said sourly.

  Malenfant grinned. "Why? This is how we are. And remember, the ones who expand across the stars are self-selecting. They grow, they consume, they aren't too good at restraining themselves, because that's the way they are. The ones who aren't ruthless predatory expansionists stay at home, or get eaten."

  Anyhow, the details of the expansion didn't seem to matter. In every case, after some generations of colonization, conflicts built up. Resource depletion within the settled bubble led to pressure on the colonies at the fringe. Or else the colonizers, their technological edge sharpened by the world-building frontier, would turn inward on their rich, sedentary cousins. Either way the cutting-edge colonizers were forced outward, farther and faster.

  Before long, the frontier of colonization was spreading out at near light speed, and the increasingly depleted region within, its inhabitants having nowhere to go, was riven by wars and economic crisis.

  So it would go on, over millennia, perhaps megayears.

  And then came the collapse.

  It happened over and over. None of the bubbles ever grew very large – no more than a few hundred light-years wide – before simply withering away, like a colony of bacteria frying under a sterilizing lamp. And one by one the stars would come out once more, shining cleanly out, as the red and green of technology and life dispersed.

  "The Polynesian syndrome," Madeleine said gloomily.

  "But," Malenfant growled, "it shouldn't always be like this. Sooner or later one of those races has got to win the local wars, beat out its own internal demons, and conquer the Galaxy. But we know that not one has made it, across the billions of years of the Galaxy's existence. And that is the Fermi paradox."

  YES, Cassiopeia said. BUT THE GALAXY IS NOT ALWAYS SO HOSPITABLE A PLACE.

  Now a new image was overlaid on the swiveling Galaxy: a spark that flared, a bloom of lurid blue light that originated close to the crowded core. It illuminated the nearby stars for perhaps an eighth of the galactic disc around it. And then, as the Galaxy slowly turned, there was another spark – and another, then another, and another still. Most of these events originated near the Galaxy core: something to do with the crowding of the stars, then. A few sparks, more rare, came from farther out – the disc, or even the dim halo of orbiting stars that surrounded the Galaxy proper.

  Each of these sparks caused devastation among any colonization bubbles nearby: a cessation of expansion, a restoring of starlight.

  Death, on an interstellar scale.

  Their virtual viewpoint changed, suddenly, swooping down into the plane of the Galaxy. As the spiral arms spread out above her, dissolving into individual stars that scattered over her head and out of sight, Madeleine cried out and clung to Malenfant. Now they swept inward, toward the Galaxy's core, and she glimpsed structure beyond the billowing stars, sculptures of gas and light and energy.

  Her attention came to rest, at last, on a pair of stars – small, fierce, angry. These stars were close, separated by no more than a few tens of their diameters. The two stars looped around each other on wild elliptical paths, taking just seconds to complete a revolution – like courting swallows, Madeleine thought – but the orbits changed rapidly, decaying as she watched, evolving into shallower ellipses, neat circles.

  A few wisps of gas circled the two stars. Each star seemed to glow blue, but the gas around them was reddish. Farther out she saw a lacy veil of color, filmy gas that billowed against the crowded background star clouds.

  "Neutron stars," Malenfant said. "A neutron star binary, in fact. That blue glow is synchrotron radiation, Madeleine. Electrons dragged at enormous speeds by the stars' powerful magnetic fields..."

  The Gaijin said, PERHAPS FIFTY PERCENT OF ALL THE STARS IN THE GALAXY ARE LOCKED IN BINARY SYSTEMS – SYSTEMS CONTAINING TWO STARS, OR PERHAPS MORE. AND SOME OF THESE STARS ARE GIANTS, DOOMED TO A RAPID EVOLUTION.

  Malenfant grunted. "Supernovae."

  MOST SUCH EXPLOSIONS SEPARATE THE RESULTANT REMNANT STARS. ONE IN A HUNDRED PAIRS REMAIN BOUND, EVEN AFTER A SUPERNOVA EXPLOSION. THE PAIRED NEUTRON STARS CIRCLE EACH OTHER RAPIDLY. THEY SHED ENERGY BY GRAVITATIONAL RADIATION – RIPPLES IN SPACETIME.

  The two stars were growing closer now, their energy ebbing away. The spinning became more rapid, the stars moving too fast for her to see. When the stars were no more than their own diameter apart, disruption began. Great gouts of shining material were torn from the surface of each star and thrown out into an immense glowing disc that obscured her view.

  At last the stars touched. They imploded in a flash of light.

  A shock wave pulsed through the debris disc, churning and scattering the material, a ferocious fount of energy. But the disc collapsed back on the impact site almost immediately, within seconds, save for a few wisps that dispersed slowly, cooling.

  "Has to form a black hole," Malenfant muttered. "Two neutron stars... too massive to form anything less. This is a gamma-ray burster. We've been observing them all over the sky since the 1960s. We sent up spacecraft to monitor illegal nuclear weapons tests beyond the atmosphere. Instead, we saw these."

  THERE IS INDEED A BURST OF GAMMA RAYS – VERY HIGH-ENERGY PHOTONS. THEN COMES A PULSE OF HIGH-ENERGY PARTICLES, COSMIC RAYS, HURLED OUT OF THE DISC OF COLLAPSING MATTER, FOLLOWING THE GAMMA RAYS AT A LITTLE LESS THAN LIGHT SPEED.

  THESE EVENTS ARE HIGHLY DESTRUCTIVE.

  A NEARBY PLANET WOULD RECEIVE – IN A FEW SECONDS, MOSTLY IN THE FORM OF GAMMA RAYS – SOME ONE-TENTH ITS ANNUAL ENERGY INPUT FROM ITS SUN. BUT THE GAMMA-RAY SHOWER IS ONLY THE PRECURSOR TO THE COSMIC RAY CASCADES, WHICH CAN LAST MONTHS. BATTERING INTO AN ATMOSPHERE, THE RAYS CREATE A SHOWER OF MUONS – HIGH-ENERGY SUBATOMIC PARTICLES. THE MUONS HAVE A GREAT DEAL OF PENETRATING POWER. EVEN HUNDREDS OF METERS OF WATER OR ROCK WOULD NOT BE A SUFFICIENT SHIELD AGAINST THEM.

  "I saw what these things can do, Madeleine," Malenfant said. "It would be like a nearby supernova going off. The ozone layer would be screwed by the gamma rays. Protein struct
ures would break down. Acid rain. Disruption of the biosphere – "

  A COLLAPSE IS OFTEN SUFFICIENT TO STERILIZE A REGION PERHAPS A THOUSAND LIGHT-YEARS WIDE. IN OUR OWN GALAXY, WE EXPECT ONE SUCH EVENT EVERY FEW TENS OF THOUSANDS OF YEARS – MOST OF THEM IN THE CROWDED GALAXY CORE.

  Madeleine watched as the Galaxy image was restored, and bursts erupted from the crowded core, over and over.

  Malenfant glared at the dangerous sky. "Cassiopeia, are you telling me that these collapses are the big secret – the cause of the reboot, the galactic extinction?"

  Madeleine shook her head. "How is that possible, if each of them is limited to a thousand light-years? The Galaxy is a hundred times as wide as that. It would be no fun to have one of these things go off in your backyard. But –"

  BUT, Cassiopeia said, SOME OF THESE EVENTS ARE... EXCEPTIONAL.

  They were shown a cascade, image after image, burst after burst.

  Some of the collapses involved particularly massive objects. Some of them were rare collisions involving three, four, even five objects simultaneously. Some of the bursts were damaging because of their orientation, with most of their founting, ferocious energy being delivered, by a chance of fate and collision dynamics, into the disc of the Galaxy, where the stars were crowded. And so on.

  Some of these events were very damaging indeed.

  FROM THE WORST OF THE EVENTS THE EXTINCTION PULSE PROCEEDS AT LIGHT SPEED, SPILLING OVER THE GALAXY AND ALL ITS INHABITANTS, ALL THE WAY TO THE RIM AND EVEN THE HALO CLUSTERS. NO SHIELDING IS POSSIBLE. NO COMPLEX ORGANISM, NO ORGANIZED DATA STORE, CAN SURVIVE. BIOSPHERES OF ALL KINDS ARE DESTROYED...

  So it finishes, Madeleine thought: the evolution and the colonizing and the wars and the groping toward understanding. All of it halted, obliterated in a flash, an accident of cosmological billiards. It was all a matter of chance, of bad luck. But there were enough neutron-star collisions that every few hundred million years there was an event powerful enough, or well-directed enough, to wipe the whole of the Galaxy clean.