Phase Space

by Stephen Baxter

  But predators came too, sleek hyenas and cats stalking the vast herds. Though the antelopes were mighty runners – fuelled by high-density fat, able to race for days without a break – there were always outliers who could not keep up: the old, the very young, the injured, mothers gravid with infants. And it was on these weaker individuals that the predators feasted.

  Those predators included the people, who inhabited a neck of land between two continents, a funnel down which the migrant herds were forced to swarm.

  The antelope herd was huge. But it passed so rapidly that the great river of flesh was gone in a couple of days. And after another day, the predator packs that stalked it had gone too.

  The people ate their antelope meat and sucked rich marrow, and gathered their fruit and nuts and shoots, and waited for their next provision to come to them, delivered up by the tides of the world.

  But the next group of running animals to come by was small – everyone could sense that – and everybody knew what they were, from their distinctive, high-pitched cries.

  Everybody lost interest. Everybody but Nemoto.

  The Hams are aware of the coming and going of the herds of migrating herbivores on which they rely for much of their meat, and are even able to predict them by the passage of the seasons. But Hams do not plan. They seem to rely on the benison of the world to provision them, day to day. It means they sometimes go hungry, but not even that dents their deep, ancient faith in the world’s kindness.

  I remember a particular hunt. I followed a party of Hams along a trail through the forest.

  They stopped by a small tree, thick with hanging fibres, and with dark hollows showing beneath its prop roots. White lichen was plastered over its trunk, and a parasitic plant with narrow, dark-green leaves dangled from a hollow in its trunk. A Ham cut a sapling and pushed it into one deep dark hollow, just above the muddy mush of leaves and detritus at the base of the tree.

  A deep growling emerged from beneath the roots of the tree.

  Excited, the Hams gathered around the tree and began to haul at it, shaking it back and forth. To my amazement they pulled the tree over by brute force, just ripping the roots out of the ground. Out squirmed a crocodile, a metre long, jaws clamped at the end of the pole. It was dark brown with a red-tinged head, huge eyes, and startlingly white teeth.

  It was a forest crocodile. These creatures come out at night. They eat frogs, insects, flightless birds, anything they can find. They have barely changed in two hundred million years.

  This world is full of such archaisms and anachronisms – like the Hams themselves. Of course it is. For it is not my world, my Earth. It is not my universe.

  The Hams fell on the crocodile in their brutal, uncompromising way. They rolled it onto its back. One woman took a stone hand-axe and sliced off the right front leg, then the left. The animal, still alive, struggled feebly; its screams were low, like snoring. When the woman opened its chest it slumped at last.

  I confronted Abel. ‘Why didn’t you kill it before starting the butchering?’

  The big man just looked back at me, apparently bemused.

  These are not pet-owners. They aren’t even farmers. They are hunter-gatherers. They have no reason to be sentimental about the animals, to care about them. My ancestors were like this once.

  Not only that: the Hams do not anthropomorphize. They could not imagine how it would be to suffer like the animal, for it was a crocodile, not a person.

  I turned away from the blood, which was spreading over the ground.

  Sickly, gaunt, enfeebled, her clothing stained with her own shit and piss, her eyes so weak she had to wear slitted skins over her face, Nemoto seemed enraged by the approach of these new arrivals. She gathered up her tools of stone and metal, and hurried out of the cave towards the migrants.

  Mary followed Nemoto, catching her easily.

  Soon they saw the Running-folk.

  There were many of them, men, women, children. They had broken their lifelong trek at a river bank. They were splashing water into their mouths, and over their faces and necks. The children were paddling in the shallows. They were all naked, all hairless save for thatches on their scalps and in their groins and arm-pits.

  They would never have been considered beautiful by a human, for their legs were immensely long and their chests expanded behind huge rib cages, giving them something of the look of storks. But they had the faces of their Homo erectus ancestors, small and low-browed with wide, flat nostrils.

  And Nemoto was stalking towards this gathering, waving her arms and brandishing her weapons. ‘Get away! Get away from there, you brutes!’

  Some of the adults got to their feet, their legs unfolding, birdlike. Mary could hear their growls, though she and Nemoto were still distant.

  The first rock – crudely chipped, as if by a child – landed in the dirt at their feet.

  Mary grabbed Nemoto’s arm. Nemoto struggled and cursed, but Mary held her effortlessly. She dragged Nemoto back out of range of the stones.

  The Runners settled again to their bathing and drinking. They stayed where they were for most of that long day, and so did Nemoto, squatting in the dirt with scarcely a motion, staring at the Runners.

  Mary stayed with her, growing increasingly hot and thirsty.

  At last, as the evening drew in, the Runners got to their feet, one by one, picking up their long hinged legs. And then they began to move off along the river. They became lanky silhouettes against the setting sun, and the river gleamed gold.

  Nemoto stalked down towards the river.

  Here, just where the Runners had settled, there was a shell of white and black, cracked open. It was the thing Nemoto called a lander. Once, Nemoto had used it to bring the Hams here, to the Grey Earth, to home. Nemoto clambered inside the shattered hull. After so many cycles of the Grey Earth’s ferocious seasons, there was little left of the interior equipment now. Mary saw how birds and wasps and spiders had made their home here, and grass and herbs had colonized the remnants of the softer materials.

  Mary thought she understood. Though it had been broken open the moment it had fallen to the ground, Nemoto had done her best to protect and preserve the wreck of the lander. Perhaps she wanted it to take her home.

  But the lander remained resolutely smashed and broken, and Nemoto could not even persuade the people to get together to haul it away from the river.

  As the light seeped out of the sky, Nemoto, at last, came away from the wreck. Mary took her arm, and shepherded her quickly towards the security of the cave, for the predators hunted at sunset.

  It proved to be the last time Nemoto ever left the community.

  I do not know how this came to be, this manifold, this cosmic panoply, this proliferation of realities.

  There is a theory that our universe grew from a seed, a tiny piece of very high-density material that then inflated into a great volume of spacetime, with planets and stars and galaxies. This was the Big Bang. But perhaps that seed was not unique. Perhaps there is a sea of primordial high-density matter-energy – a sea where temperatures and densities and pressures exceed anything in our universe, where physics operates according to different laws – and within this sea universes inflate, one after another, like bubbles in foam. These bubble-universes would have no connection with each other. Their inhabitants would see only their own bubble, not the foam itself.

  That is my legend. The Hams’ legend is that the Old Ones created it all. Who is to say who is right? How could we ever know?

  Whatever the origin of the manifold, within it there could be an infinite number of universes. And in an infinite ensemble, everything which is logically possible must – somewhere, somehow – come to pass.

  Thus there must be a cluster of bubble-spaces with identical histories up to the moment of Earth’s formation, the Big Whack – and differing after that only in the details of the impact itself, and their consequences. I imagine the possible universes arrayed around me in phase space. And universes di
ffering only in the details of the Earth-Moon impact must somehow be close to ours in that graph of the possible.

  I know this from personal experience.

  For me it began when a new Moon appeared in Earth’s sky: a fat Moon, a Red Moon, replacing poor dead Luna. I travelled to that Moon on a quixotic jaunt with Reid Malenfant, ostensibly in search of his lost wife, Emma Stoney. There we encountered many hominid forms – some more or less human, some not – all refugees from different reality strands, swept away by that Red Moon, which slides in sideways knight’s moves between universes.

  Just as Malenfant and I were swept away, when my own Earth, Blue Earth, disappeared from the Moon’s sky. I knew immediately that I could never go home.

  To fulfil a pledge foolishly made to these Hams by Emma Stoney, I agreed to use our small Earth-Moon ferry spacecraft to carry the Hams back to their Grey Earth – when the opportunity presented itself, as our wandering Moon happened that way. Once I was off the Red Moon, with a spacecraft, I vaguely imagined that I would be able to go further, to get away from the deadening menticulture that rapidly emerged among the stranded on the Red Moon. But it was not to be; I crashed here, and when the Red Moon wandered away from the sky, I was left doubly stranded.

  The Red Moon is an agent of human evolution. That is why it wanders. Its interstitial meandering is a mixing device, an artefact of the Old Ones, who may even have manufactured this vast mesh of realities.

  So I believe.

  But whatever the purpose of that Moon’s wandering, it destroyed my own life.

  For the Hams, for Julia, the Grey Earth is home. For me, this entire universe is a vast prison.

  The air grew hotter yet, approaching its most violent peak of temperature, even though the sun still lingered beneath the horizon for part of its round, even though night still touched the Grey Earth. Soon the fast-growing grasses and herbs were dying back, and the migrant animals and birds had fled, seeking the temperate climes.

  The season’s last rain fell. Mary closed her eyes and raised her open mouth to the sky, for she knew it would be a long time before she felt rain on her face again.

  The ground became a plain of baked and cracked mud.

  The people retreated to their cave. Just as its thick rock walls had sheltered them from the most ferocious cold of the winter, so now the walls gave them coolness. And just as the people had drawn warmth from the sap of the blood-tree, pumped up from the ground, now the tree let its sap carry its excess heat down into the ground, and its tangle of roots cooled the cave further.

  The people ate the meat they had dried out and stored in the back of their cave, and they drank water from the drying rivers and lakes, and dug up hibernating frogs, fat sacks of water and meat that croaked resentfully as they were briskly killed.

  Nemoto could not leave the cave, of course. Long before the heat reached its height, her relentless illness had driven her to her pallet, where she remained, unable to rise, with a strip of skin tied across her eyes. But Mary brought her water and food.

  At length there came a day when the sun failed even to brush the horizon at its lowest point. From now on, for sixty-eight days, it would not rise or set, but would make meaningless circles in the sky, circles that would grow smaller and more elevated.

  The Long Day had begun.

  And still the great blood-tree grew, drinking in the endless light of the sun and the water it found deep beneath the ground, so that sometimes the roots that pierced the cave writhed like snakes.

  Here is how, or so I have come to believe, this Red Moon has played a key role in human evolution.

  Consider. How do new species arise, of hominids or any organism?

  Isolation is the key. If mutations arise in a large and freely mixing population, any new characteristic is diluted and will disappear within a few generations. But when a segment of the population becomes isolated from the rest, dilution through interbreeding is prevented. Thus the isolated group may, quite rapidly, diverge from the base population. And when those barriers to isolation are removed, the new species finds itself in competition with its predecessors. If it is more fit, in some sense, it will survive by out-competing the parent stock. If not, it declines.

  When our scientists believed there was only one Earth, they developed a theory of how the evolution of humanity occurred. The ape-like bipeds called Australopithecines gave rise to tool users, who in turn produced tall erect hairless creatures capable of walking on the open plain, who gave rise to various species of Homo sapiens – the genus that includes myself. It is believed that at some points in history there were many hominid species, all derived from the base Australopithecine stock, extant together on the Earth. But my kind – Homo sapiens sapiens – proved the fittest of them all. By out-competition, the variant species were removed.

  Presumably, each speciation episode was instigated by the isolation of a group of the parent stock. We assumed that the key isolating events were caused by climate changes: rising or falling sea levels, the birth or death of forests, the coming and going of glaciation. It was a plausible picture – before we knew of the Red Moon, of the Grey Earth, of other Moons and Earths.

  Assume that the base Australopithecine stock evolved on Earth – my Earth. Imagine that some mechanism scooped up handfuls of undifferentiated Australopithecines and, perhaps some generations later, deposited them on a variety of subtly different Earths.

  It is hard to imagine a more complete isolation. And the environments in which they were placed might have had no resemblance to those from which they were taken. In that case our Australopithecines would have had to adapt or die.

  And later, samples of those new populations were swept up in their turn, and handed on to other Earths, where they were shaped again. Thus the Hams, with their power and conservatism, have been shaped by the brutal conditions of this Grey Earth.

  This is my proposal: that hominid speciation has been driven by the transfer of populations between parallel Earths. It is fantastic, but logical.

  If this is true, then everything about us – everything about me – has been shaped by the meddling of the Old Ones, these engineers of worlds and hominids, for their own unrevealed, unfathomable purpose. Just as my own life story – too complicated to set out here – has become a scrawl across multiple realities.

  What remains unclear is why the Old Ones, if they exist, should wish to do this. Perhaps their motives were somehow malicious, or somehow benevolent; perhaps they wished to give the potential of humankind its fullest opportunity of expression.

  But their motive is scarcely material.

  What power for mortals to hold.

  What arrogance to wield it.

  Nemoto said she would not go into the ground until she saw another night. But she grew steadily weaker, until she could not raise her body from its pallet of moss, or clean herself, or even raise her hands to her mouth.

  Mary cared for her. She would give Nemoto water in sponges of mashed-up leaf, and when Nemoto fouled herself Mary cleaned her with bits of skin, and she bathed her body’s suppurating sores with blood-tree sap.

  But Nemoto’s skin continued to flake away, as the slow revenge of the bat disturbed from its hibernation took its gruesome course.

  There came a day when the sun rolled along the horizon, its light shimmering through the trees which flourished there. Mary knew that soon would come the first night, the first little night, since the spring. So she carried Nemoto to the mouth of the cave – she was light, like a thing of twigs and dried leaves – and propped her up on a bundle of skins, so that her face was bathed in the sunlight.

  But Nemoto screwed up her face. ‘I do not like the light,’ she said, her voice a peevish husk. ‘I can bear the dark. But not these endless days. I have always longed for tomorrow. For tomorrow I will understand a little more. I have always wanted to understand. Why I am here. Why the world is as it is. Why there is something, rather than nothing.’

  ‘Lon’ for tomorrow,’ Mary ech
oed, seeking to comfort her.

  ‘Yes. But you do not dream of the future, do you? For you there is only today. Here especially, with your Long Day and your Long Night, as if a whole year is made of one tremendous day.’

  Overhead, a single bright star appeared.

  Nemoto gasped. ‘The first star since the spring. How marvellous, how beautiful, how fragile.’ She settled back on her bundle of skins. ‘You know, the stars here are the same – I mean the same as those that surround the world where I grew up, the Blue Earth. But the way they swim around the sky is not the same.’ She was trying to raise her arm, perhaps to point, but could not. ‘You have a different pole star here. It is somewhere in Leo, near the sky’s equator. I cannot determine which … Your world is tipped over, you see, like Uranus, like a top lying on its side; that is how the Big Whack shaped it here. And so for six months, when your pole points at the sun, you have endless light; and for six months endless dark … Do you follow me? No, I am sure you do not.’ She coughed, and seemed to sink deeper into the skins. ‘All my life I have sought to understand. I believe I would have pursued the same course whichever of our splintered worlds I had been born into. And yet, and yet –’ She arched her back, and Mary laid her huge hands on Nemoto’s forehead, trying to soothe her. ‘And yet I die alone.’

  Mary took her hand. It was delicate, like a child’s. ‘Not alone,’ she said.

  ‘Ah. I have you, don’t I, Mary? I have a friend. That is something, isn’t it? That is an achievement …’ Nemoto tried to squeeze Mary’s hand; it was the gentlest of touches.