The Long Cosmos

by Terry Pratchett

  They seemed also to have clambered above most of the vertical wildlife that the tree nurtured. The few branches they passed were sparse and stubby, and in the crisp light the puddle-lakes like the one where they had spent the night were now scarce. Joshua supposed that they were above much of the weather here too; rainfall would be rare.

  But Sancho, without food and water almost since they had woken, seemed indifferent. He just climbed on and on.

  Joshua could only endure. He clung to Sancho’s back, his face buried in thick black troll hair.

  When Sancho next stopped, Joshua groggily saw that the sun was setting again. Below him were more layers of clouds – cirrus clouds this time, Joshua thought, a fine layer through which could be glimpsed deeper cloudscapes below, all of them threaded by the trunks of the trees – and above him, beyond the branches, only an astronaut’s sky, deep blue, specked by a handful of brilliant stars, empty of cloud save for only the palest icy streak.

  He was dimly aware that Sancho was untying the ropes. He gently unloaded Joshua and settled him in a crook of a branch. Beyond him the curious faces of other trolls hung like moons (what other trolls?). Joshua was confused, nauseous, breathless – and cold, and Sancho seemed to realize that, for with rough kindness he tucked the sleeping bag around Joshua’s inert body.

  Joshua lay back. Above him those branches combined in a canopy draped with huge leaves, like blankets spread out to dry in the sun. A second canopy, then. Why not? Up here in the clear cloudless air the conditions for photosynthesis must be ideal, he thought dimly, ideal for gathering the unending sunlight from a cloud-free sky – a harvest that nourished the growth of all he had seen below him, in the miles of their ascent.

  Miles?

  Could that really be true? How high were the highest cirrus clouds? Twenty, thirty thousand feet? Rod the pilot would know. He was maybe three, four miles high, then. At least. And he could see, leaning back, that the trunk of this vast tree went on even beyond this canopy layer, on up towards the blue-sky heaven. How tall could this tree grow? Five miles?

  Joshua laughed. ‘Sally, you should be here to see this.’

  And there were trolls up here.

  In the declining light he saw now the shadows of adults and cubs, big heavy trolls with big deep chests, moving cautiously. Maybe they lived up here permanently and their bodies had adapted to the thin air. There were whole families up here. They were eating fruit and grubs and what looked like haunches of meat, and they drank water from cupped leaves. As he watched them feed, he thought they were careful not to consume anything of the tree itself. He’d read somewhere that some trees, oaks for instance, evolved poisons against persistent herbivores.

  Silhouetted against the deepening purple of the sky, they looked like heavy fruit, hanging from these impossible branches, miles high. And he could clearly hear, floating on the still air, the trolls’ eternal song.

  ‘Yes, you should be here, Sally. You’d love it.’

  He pulled the blanket closer over him, tugged his hat down over his ears, and tried to sleep.

  He woke once in the night, growlingly thirsty. He tried to call for Sancho, but his voice was a scrape.

  He raised his head. All around him the trolls were visible in the light of the brilliant stars, huge mounds huddled together as they slept. When he called again for Sancho, a heavy hand touched his shoulder. He turned to see Sancho’s heavy, rather mournful face.

  ‘Water . . .’

  Joshua expected Sancho to go to the medical pack for one of Joshua’s flasks. Instead he held up a kind of greenish sac, an organic object, oddly streamlined – it was like a teardrop, Joshua thought, heavy with liquid within. Sancho expertly ripped a hole in this with thumb and forefinger, held it up over Joshua’s mouth, and clear, cold water trickled on to his tongue. When the sac was empty, Sancho just held it up and let it go.

  And the empty sac sailed up into the air, up over Sancho’s head, until it was lost against the details of the branches above.

  Somehow this didn’t seem at all surprising to Joshua, in this fantastical place. What else were things supposed to do but float off into the sky? He patted Sancho’s shoulder in thanks, and settled down to sleep again.

  43

  WHEN HE WOKE, in deep-blue daylight, his head felt much clearer, his thoughts sharper, the vague nausea that had plagued him receded. Evidently he was adapting to the altitude – adapting suspiciously well, in fact. Maybe this world was more oxygen-rich than the Datum. After all, a planet full of giant trees could well have a messed-up atmosphere. He hoped Maggie Kauffman would get somebody sent back here to study the place properly some day.

  In the meantime he badly needed a piss, more water, and food, in that order. He sat up – but too sharply, and his head swam briefly. A strong troll arm wrapped around his shoulders, to save him from falling back: Sancho, of course. And, looking beyond Sancho, Joshua saw that the rest of the trolls seemed to be congregated on one long, fat branch.

  Joshua grinned, and gently pushed Sancho’s arm away. ‘Thanks, buddy. Let me see if I can water this mule by myself.’ He made sure the rope around his waist was tied tight to the branch, then cautiously stood, bracing himself against the rough surface of the trunk wall. Then, facing away from Sancho, he unbuttoned and released the flow. His urine splashed against huge branches and fell in yellow droplets down into the deep air, and Joshua wondered vaguely how deep they would reach before evaporating, or maybe freezing out. Yellow hail!

  And how would it be if he did stumble, if his rope failed, if he fell from here? He would soon reach terminal velocity even in this thin air. It would surely take many minutes to reach the ground, sailing down past the trunk of this sky tree, crashing through layers of branches and startling the aerial fauna of this strange forest. Or maybe he wouldn’t fall at all. Perhaps he would just float up into the sky, like—

  The memory came back to him, clear and sharp. And as he stood here on one leg, before the wall of the trunk, he could swear he heard a kind of gurgle, as if from buried pipework, water rising through some kind of plumbing.

  He turned, almost falling in the process, grabbed Sancho’s shoulders, and reached for the troll-call in his pack. ‘Sancho. Water.’

  ‘Fire,’ said the troll gravely.

  ‘What? No, Sancho, water. Like the pod you fed me with last night.’

  Sancho pursed huge lips, then reached into the crook of a branchlet and produced a green sac, one of a stash, of the kind he’d given Joshua before.

  Joshua grabbed it. It was just as he remembered, and, given it was a sac of water the size of a grapefruit, it felt remarkably light. He ripped it open eagerly, dumped out the water – ‘Hoo!’ said a surprised Sancho – and then released the empty bag.

  Just as before, the sac sailed upwards, rising like a party balloon lost in the sky.

  Excited now, Joshua said to Sancho, ‘Show me.’

  ‘Hoo? Water?’

  ‘No, I don’t want the water. I want the bags. Show me where you get the water bags.’

  And Sancho, understanding what he wanted, but evidently puzzled by Joshua’s behaviour – he kept saying ‘Fire’, which puzzled Joshua in turn – led him to the tree’s trunk-face. Here a gash had been crudely cut, presumably by stone tools laboriously carried up from the ground. A gash wide enough for a troll hand to reach inside. Joshua could see nothing, but he could easily reach inside the cut and feel around.

  And he found more of the sacs, full of water, rising up through a smooth-walled channel deep within the tree.

  He sat with Sancho, Joshua chewing on compressed rations, the troll under his survival blanket, just as if they were back in their old codgers’ places at the bluff.

  With a little more thought – ‘By God I wish Lobsang was here! Or Sister Georgina!’ – Joshua believed he began to see the secret of the sky trees.

  ‘Here’s my theory, old buddy. Here’s how these impossible trees of yours aren’t impossible after all.’

&nb
sp; ‘Hoo?’

  ‘Those water sacs are like little balloons. Once they’ve lost their water ballast, they just float up into the air. So, just like a toy balloon, they have to be filled with something, some gas that’s lighter than air. Hot air? No, they weren’t even warm to the touch. What then? Helium or hydrogen, I figure – just like a twain. But where would a tree get helium from? That stuff’s pretty rare, as far as I know, on most worlds anyhow. Hydrogen, on the other hand, is everywhere.’ He remembered table-top chemistry experiments Sister Georgina had run with him in the Home. ‘You can get hydrogen from water. H-two-O. You pass an electrical current through water, and the water molecules are split into hydrogen and oxygen, and you just collect the hydrogen . . .’

  ‘Ha!’

  ‘Exactly.’ He looked up at the higher canopy, where vast leaves, suspended from vaster branches, bathed in the sunlight. ‘There’s all the energy you need to drive an electrical current, pouring down from the sky. Somehow, maybe through some kind of natural conductor, a fraction of that energy is passed all the way down to the trees’ roots. And I bet you’ll find a kind of natural electrolysis lab down there, where groundwater is split to give off hydrogen. The hydrogen is collected in vessels like your water pouches – the sacs. The mechanics of it must be fun.

  ‘And that’s how water is brought up from the ground, through a height of miles. Carried in natural hydrogen balloons, passing up through internal channels inside the tree itself. And that’s how come these beasts can grow seventy, eighty times taller than the tallest sequoia.’

  ‘Ha?’

  Joshua slapped his forehead. ‘And the reaching-wood! I saw it for myself. The whole substance of the wood is full of hydrogen. That’s what makes it so light, that’s what makes this damn tree able to stand up. Why, maybe it doesn’t support its own weight at all; maybe its upper layers are so light they are actually tethered to the ground by the trunk and the roots, like a twain on its cable. I love it!’

  ‘Fire!’

  ‘Yes, buddy! What about fire? Hydrogen is pretty inflammable. Sure, that’s why you didn’t want me building a campfire in the tree canopy the other night, right? And lightning strikes here must cause a hell of a mess. Although I imagine the trees must have evolved some way to resist fire. After all, they are full of bags of water . . . Loggers, though. Maybe that’s why something as obviously useful as reaching-wood, ultra-light, has never been brought back to the Low Earths. Because anybody who happened on this band of worlds – if anybody has made it out this far – has, on their first night, casually built a campfire . . . Ka-boom. Goodbye, loggers.’

  ‘Fire?’

  ‘I know, I know. What would Lobsang make of this? He’d try to figure out how it evolved, that’s what. I guess as soon as the hydrogen buoyancy trick emerges at all, there’d be a race to be tallest, strongest, the one to trap the light. No wonder the trees grow as high as they do, until the cold or the lack of oxygen limits them . . .’

  ‘Fire! Fire!’

  For the first time in long minutes Joshua paid attention to what the troll was actually trying to say to him. It wasn’t just the word; Sancho was pointing out to where the rest of the trolls were gathered, out at the end of that long limb, suspended in the sky. Joshua peered out that way, cursing aged eyes. And he thought he saw something at the very end of that branch, a stranger fruit yet – some kind of big heavy animal, bigger than a troll. Cornered, out on that branch, trapped by the trolls.

  And a splash of bright orange. Flight-suit orange.

  Joshua’s heart seemed to stop. He grabbed the troll-call again. ‘That’s my boy.’

  ‘Cub,’ Sancho agreed.

  ‘You found him. Shit. Sancho, I could kiss you. But now we have to go get him, right?’

  ‘Fire!’

  Joshua thought it over for one second. Then he dug in his pack and pulled out a box of matches. ‘This is what you want me to bring to the party?’

  ‘Fire, cub, fire!’

  ‘Somehow we’re going to use fire to get Rod back? OK, buddy, I’ll follow your lead . . . I have a feeling we won’t be coming back this way.’ Excited, bewildered, determined, Joshua tucked the matches into his jacket pocket, and hastily bundled up the rest of his gear into the med pack. Then, as he clambered on to the troll’s back, wrapping rope firmly around both their waists, Joshua muttered, ‘So, a tree-climbing croc has my son, and I’m crawling across a five-mile pillar of hydrogen, on the back of a troll, with a box of matches in my pocket. What can possibly go wrong?’

  44

  JOSHUA WAS SURPRISED to see how graceful the singer was, with that flexible, well-proportioned humanoid body, as it clambered around its branch. He’d first encountered the singer in a river, after all; but if it was a natural swimmer, it looked like it was just as good a tree-climber as any troll.

  Joshua didn’t know how Sancho had known the singer beast would come to this world, to this particular tree. He didn’t know how he and the local band of trolls had cornered this animal, out at the end of its branch. But if it was adapted to hunt trolls in the first place, maybe it used the same super-stepping passageways Sancho had used to bring him here. Once again it struck him that there was evidently a hell of a lot he’d yet to learn, along with the rest of humanity – even Lobsang – about trolls, and their lifestyles, and their capabilities, and their predators.

  Anyhow, right now that singer animal was backed up, close to the end of this branch that hung impossibly high and long in the sky – trapped by the massed trolls that had evidently driven it up there. And Joshua could see his son now, apparently unconscious, draped over the branch at the feet of the singer. Joshua couldn’t tell from this distance if Rod was dead or alive, or if he was injured, how badly.

  All that for later. Now he just had to get his son back.

  Sancho stood beside him, holding a chunk of reaching-wood, a section of branch – a rough tube. ‘Fire.’

  Joshua studied the log. ‘What are you thinking? Smoke him out somehow?’

  Sancho shoved the reaching-wood cylinder into Joshua’s arms, losing his usual phlegmatic patience. ‘Fire!’ With one finger he tapped Joshua’s pocket, where the matches were.

  Joshua studied the cylinder more closely. It was deceptively light, like all reaching-wood, and obviously organic, but peculiarly shaped. ‘This is a chunk of the tree, right? Hollow inside – the wood stuffed full of hydrogen – short and straight, almost streamlined. And these grooves on the outside surface are almost perfect spirals.’ Then he thought he had it. ‘Wow. Are you serious? I bet the troll-call has no translation of missile . . . But why would a tree grow natural hydrogen-fuelled missiles? . . .’

  ‘Fire!’

  ‘Right, right, I get it, I know. Don’t think, just do the job. You’re the boss, Sancho.’ He eyed the singer beast standing over his son, snarling with that big ape head at the trolls goading him. ‘OK, but let’s have a practice run first . . .’

  Joshua pointed the ‘missile’ out into the open air, away from the trolls and the singer. Then, improvising as he went along, he packed the base of the tube with dry leaf matter, and cut a stub off a candle to serve as a fuse. ‘Not having any ambition to blow myself up now I’m so close to Rod . . .’ Then he struck a match, lit the candle stub, and backed hastily away.

  The organic matter smouldered, sparked and flared, hydrogen vessels popping. It went briefly quiet, and Joshua thought maybe he’d created a dud. But then a bright white flame erupted from the base of the ‘missile’, and the tube soared away into the air, trailing a thread of billowing smoke. Joshua saw how it spun on its axis, those spiral flanges catching the air, and as a result it flew straight and true just where Joshua had aimed it – until, quite quickly, it ran out of gas, and, flaming, fell away into the open air.

  ‘Well, I’ll be,’ Joshua said, astonished. ‘I think this might actually work.’

  ‘Hoo!’

  ‘Let’s do this.’

  In the end it was a question of timing.
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  The trolls were hunters, used to cooperative operations. So the troll band kept up their barrage of cries and fist-waving at the singer, which snapped and snarled back, posturing over Rod’s prone body. All this was to distract the singer from Sancho, who silently, calmly, almost without a sense of threat, crept forward from the pack and edged a little closer to the animal, and to Rod.

  And Joshua forced himself to concentrate on setting up his second branch-missile: the first and last he’d ever fire in anger, he supposed, and he had to get it right. He tinkered with the aim, improvising a kind of launch rail with twigs and sticks, and sighted along the slim body of the branch, cursing his failing eyes.

  When he thought he had the alignment as right as it would ever be, he didn’t hesitate. Again the lit match applied to a candle stub, again the smoulder and pop of hydrogen-soaked leaf matter. He limped back out of the way, and got into cover.

  The fuse burned down.

  Again that flare of rocket power, again the flame and the smoke as the missile surged away – and it slammed straight into the belly of the singer beast. The animal fell away from its branch and went tumbling into the air. Joshua howled his triumph.

  But so massive was the singer’s body that the missile, still burning and spinning, was deflected, and began to soar back towards the tree, spiralling in the air, leaving behind a complex smoke trail.

  Even as the troll band yelled and whooped in exultation, Sancho dashed on all fours along the branch, and picked up the limp form of Rod as if he was no more than a bundle of rags. But Joshua was distracted by that flare of light far below. His missile, still burning, had shot back into the body of the tree – and, as Joshua watched, it slammed into the trunk at a junction with a thick branch. There was a deep, heavy explosion, and the whole tree shuddered.

  ‘Oops.’

  But here was Sancho, with Rod.

  Joshua helped the troll lay his son out on the surface of the branch. He checked Rod’s pulse at his neck, leaned over to hear his breath, felt its warmth on his cheek. Then he ran his hands quickly over Rod’s limbs. Joshua, eyes brimming with tears, working fast, forced himself to be methodical. ‘He seems intact,’ he told Sancho. ‘Pulse steady, breathing, no broken limbs. Any internal injuries – well, that’ll have to wait until he wakes up. Dehydrated, probably starving hungry. We’re lucky the singer didn’t just kill him – or maybe that’s an animal that likes to consume its prey warm.’