Zima Blue and Other Stories

  A double helix writhed in the sky, luminous and serpentlike against Plenitude's perpetual pink twilight.

  Releasing Gallinule's hand, Sayaca lifted a finger and the DNA coil swelled to godlike size, until the individual base pairs were themselves too large to discern as anything other than blurred assemblages of atoms, huger than mountains. But atoms were only the beginning of the descent into the world of the vanishingly small. Atoms were assembled from even tinier components: electrons, protons and neutrons, bound together by the electroweak and -strong forces. But even those fundamental particles held deeper layers of structure. All matter in the universe was woven from quarks or leptons; all force mediated by bosons.

  Even that was not the end.

  In the deepest of deep symmetries, the fermions - the quarks and leptons - and the bosons - the messengers of force - blurred into one kind of entity. Particle was no longer the right word for it. What everything in the universe seemed to boil down to, at the very fundamental level, was a series of loops vibrating at different frequencies, embedded in a multidimensional space.

  What, Sayaca said, scientists had once termed superstrings.

  It was elegant beyond words, and it explained seemingly everything. But the trouble with superstring theory, Sayaca added, was that it was extraordinarily difficult to test. It was likely that the theory had been reinvented and discarded dozens or hundreds of times in human history, during each brief phase of enlightenment. Undoubtedly the Waymakers must have come to some final wisdom as to the ultimate nature of reality . . . but if they had, they had not left that verdict in any form now remembered. So from Sayaca's viewpoint, superstring theory was at least as viable as any other model for unifying the fundamental particles and forces.

  'But I don't see how any of this helps us understand Pauraque's storm,' Merlin said.

  'Wait,' said Sayaca's semblance. 'I haven't finished. There's more than one type of superstring theory, understand? And some of those theories make a special prediction about the existence of something called shadow matter. It's not the same thing as antimatter. Shadow matter's like normal matter in every respect, except it's invisible and insubstantial. Objects made of normal and shadow matter just slip through each other like ghosts. There's only one way in which they sense each other.'

  'Gravity,' Merlin said.

  'Yes. As far as gravity's concerned, there's nothing to distinguish them.'

  'So what are you saying, that there could be whole universes made of shadow matter coexisting with our own?'

  'Exactly that.' She went on to tell them there was every reason to suppose that the shadow universe was just as complex as the normal one, with exactly analogous particle types, atoms and chemistry. There would be shadow galaxies, shadow stars and shadow worlds - perhaps even shadow life.

  Merlin absorbed that. 'Why haven't we encountered anything like shadow matter before?'

  'There must be strong segregation between the two types across the plane of the galaxy. For one reason or another, that segregation has broken down around Bright Boy. There seems to be about half a solar mass of shadow matter gravitationally bound to this system - most of it sitting in Bright Boy's core.'

  Merlin tightened his grip on the balustrade. 'Tell me this answers all our riddles, Sayaca.'

  Sayaca told them the rest, reminding Merlin how they had probed Cinder's interior via sound waves, each sonic pulse generated by the impact of an in-falling meteorite; the sound waves tracked as they swept through Cinder, gathered by a network of listening posts sprinkled across the surface. It was these seismic images that had first elucidated the fine structure of the Digger tunnels. But - unwittingly - Sayaca had learned much more than that.

  'We measured Cinder's mass twice. The first time was when we put our own mapping satellites into orbit. That gave us one figure. The seismic data should have given us a second estimate that agreed to within a few per cent. But the seismic data said there was only two-thirds as much mass as there should have been, compared with the gravitational mass estimate.' Sayaca's semblance paused, perhaps giving the two of them time to make the connection themselves. When neither spoke, she permitted herself to continue. 'If there's a large chunk of shadow matter inside Cinder, it explains everything. The seismic waves only travel through normal matter, so they don't see one-third of Cinder's composition at all. But the gravitational signature of normal and shadow matter is identical. Our satellites felt the pull of the normal and shadow matter, just as we did when we were walking around inside Cinder.'

  'All right,' he said. 'Tell me about Bright Boy too.'

  'It makes just as much sense. Most of the shadow matter in this system must be inside the star. Half a solar mass would be enough for Bright Boy's shadow counterpart to become a star in its own right - burning its own shadow hydrogen to shadow helium, giving off shadow photons and shadow neutrinos, none of which we can see. Except just like Bright Boy it would be an astrophysical anomaly - too bright and small to make any kind of sense, because its structure is being affected by the presence of an equal amount of normal matter from our universe. Both stars end up with hotter cores, since the nuclear reactions have to work harder to hold up the weight of overlying stellar atmosphere.'

  Sayaca thought that the two halves of Bright Boy - the normal and shadow-matter suns - had once been spatially separated, so that they formed the two stars of a close binary system. That, she said, would have been something so strange that no passing culture could have missed it, for the visible counterpart of Bright Boy would have appeared locked in orbital embrace with an invisible partner, signalling its oddity across half the galaxy. Over the ensuing billions of years, the two stars had whirled closer and closer together, their orbital motions damped by tidal dissipation, until they had merged and settled into the same spatial volume. Whoever comes after us, Merlin thought, we won't be the last to study this cosmic mystery.

  'Then tell me about Pauraque's storm,' he said, flinching at the memory of her crushed survival egg.

  Gallinule nodded. 'Go on. I want to know what killed her.'

  Sayaca spoke now with less ease. 'It must be another chunk of shadow matter - about the mass of a large moon, squashed into a volume no more than a few tens of kilometres across. Of course, it wasn't the shadow matter itself that killed her. Just the storm it caused by its passage through the atmosphere.'

  And not even that, Merlin thought. It was his decision that killed her; his conviction that it was more vital to save the first egg, the one falling into the storm's eye. Afterwards, discovering that there was no gamma-ray point there, he had realised that he could have saved both of them if he had saved Pauraque first.

  'Something that massive, and that small . . .' Gallinule paused. 'It can't be a moon, can it?'

  Sayaca turned away from the sunset. 'No. It's no moon. Whatever it is, it was made by someone. Not the Huskers, I think, but someone else. And I think we have to work out what they had in mind.'

  Nervously, Merlin watched seniors populate the auditorium - walking in or simply popping into holographic existence, like card figures dropped into a toy theatre. Sayaca had bided her time before announcing her discovery to the rest of the expedition, but eventually the three of them had gathered enough data to refute any argument. When it became clear that her news would be momentous, seniors had flown in from across the system, leaving the putative hideaways they were investigating. A few of them even sent their semblances, for the simulacra were now sophisticated enough to make many physical journeys unnecessary.

  The announcement would take place in the auditorium of the largest orbiting station, poised above Ghost's cloud-tops. An auroral storm was lashing Ghost's northern pole, appropriately dramatic for the event. He wondered if Sayaca had scheduled the meeting with that display in mind.

  'Go easy on the superstring physics,' Gallinule whispered in Sayaca's ear, as she sat between the two men. 'You don't want to lose them before you've begun. Some of these relics don't even know what a quark is, let
alone a baryon-to-entropy ratio.'

  Gallinule was right to warn Sayaca. It would be like her to begin her announcement by projecting a forest of equations on the display wall.

  'Don't worry,' Sayaca said. 'I'll keep it nice and simple; throw in a few jokes to wake them up.'

  Gallinule kept his voice low. 'They won't need waking up once they realise what the implications are. Straightforward hiding's no longer an option, not with something as strange as the Ghost anomaly sitting in our neighbourhood. When the Huskers arrive they're bound to start investigating. They're also bound to find any hideaway we construct, no matter how well camouflaged.'

  'Not if we dig deep enough,' Merlin said.

  'Forget it. There's no way we can hide now. Not the way it was planned, anyway. Unless--'

  'Don't tell me: we'd be perfectly safe if we could store ourselves as patterns in some machine memory?'

  'Don't sound so nauseated. You can't argue with the logic. We'd be nearly invulnerable. The storage media could be physically tiny, distributed in many locations. Impossible for the Huskers to find them all.'

  'The Council can decide,' Sayaca said, raising a hand to shut the two of them up. 'Let's see how they take my discovery, first.'

  'It was Pauraque's discovery,' Merlin said quietly.

  'Whatever.'

  She was already walking away from them, crossing the auditorium's floor towards the podium where she would address the congregation. Sayaca walked on air, striding across the clouds. It was a trick, of course: the real view outside the station was constantly changing because of the structure's rotation, but the illusion was flawless.

  'It may have been Pauraque who discovered the storm,' Gallinule said, 'but it was Sayaca who interpreted it.'

  'I wasn't trying to take anything away from her.'

  'Good.'

  Now she stepped up to the podium, the hem of her electric-blue gown floating above the clouds. She stood pridefully, surveying the people who had gathered here to hear her speak. Her expression was one of complete calm and self-assurance, but Merlin saw how tightly she grasped the edges of the podium. He sensed that beneath that shell of control she was acutely nervous, knowing that this was the most important moment in her life, the one that would make her reputation amongst the seniors and perhaps shape all of their destinies.

  'Seniors . . .' Sayaca said. 'Thank you for coming here. I hope that by the time I've finished speaking, you'll feel that your time wasn't wasted.' Then she extended a hand towards the middle of the room and an image of Ghost sprang into being. 'Ever since we identified this system as our only chance of concealment, we've had to ignore the troubling aspects of the place. Bright Boy's anomalous mass-luminosity relationship, for instance. The seismic discrepancies in Cinder. Pauraque's deep-atmospheric phenomenon in Ghost. Now the time has come to deal with these puzzles. I'm afraid that what they tell us may not be entirely to our liking.'

  Promising start, Merlin thought. She had spoken for more than half a minute without using a single mathematical expression.

  Sayaca began to speak again, but she was cut off abruptly by another speaker. 'Sayaca, there's something we should discuss first.' Everyone's attention moved to the interjector. Merlin recognised him immediately: Weaver. Cruelly handsome, the boy had outgrown his adolescent awkwardness in the years since Merlin had first known him as one of Sayaca's class.

  'What is it?' she said, only the tiniest hint of suspicion in her voice.

  'Some news we've just obtained.' Weaver looked around the room, clearly enjoying his moment in the limelight while attempting to maintain the appropriate air of solemnity. 'We've been looking along the Way, as a matter of routine, monitoring the swarm that lies ahead of us. Sometimes off the line of the Way too - just in case we find anything. We've also been following the Bluethroat.'

  It was so long since anyone had mentioned that name that it took Merlin an instant to place it. Of course, the Bluethroat. The part of the original ship that Crombec had flown onward, while the rest of them piled into Starling and slowed down around Bright Boy. It was not that anyone hated Crombec or wished to excise him and his followers from history, simply that there had been more than enough to focus on in the new system.

  'Go on . . .' Sayaca said.

  'There was a flash. A tiny burst of energy light-years from here, but in the direction we know Crombec was headed. I think the implications are clear enough. They met Huskers, even in interstellar space.'

  'Force and wisdom,' said Shikra, the archivist in charge of the Cohort's most precious data troves. 'They can't have survived.'

  Merlin raised his voice above the sudden murmur of debate. 'When did you find this out, Weaver?'

  'A few days ago.'

  'And you waited until now to let us know?'

  Weaver shifted uncomfortably, beginning to sweat. 'There were questions of interpretation. We couldn't release the news until we were sure of it.' Then he nodded towards Sayaca. 'You know what I mean, don't you?'

  'Believe me, I know exactly what you mean,' she said, shaking her head. She must have known that the moment was no longer hers; that even if she held the attention of the audience again, their minds would not be fully on what she had to say.

  She handled it well, Merlin thought.

  But irrespective of what she had found in Ghost, the news was very bad. The deaths of Crombec and his followers could only mean that the immediate volume of space was much thicker with Husker assets than anyone had dared fear. Forget the two swarms they had already known about; there might be dozens more, lurking quietly only one or two light-years from the system. And perhaps they had learned enough from Crombec's trajectory to guess that there must be other humans nearby. It would not take them long to arrive.

  In a handful of years they might be here.

  'This is gravely serious,' one of the other seniors said, raising her voice above the others. 'But it must not be allowed to overshadow the news Sayaca has for us.' She nodded at Sayaca expectantly. 'Continue, won't you?'

  Months later, Merlin and Gallinule were alone in the Palace, standing on the balcony. Gallinule was toying with a white mouse, letting it run along the balustrade's narrow top before picking it up and placing it at the start again. They had put Weaver's spiteful sabotage long behind them, once it became clear that it had barely dented the impact of Sayaca's announcement. Even the most conservative seniors had accepted the shadow-matter hypothesis, even if the precise nature of what the shadow matter represented was not yet clear.

  Which was not to say that Weaver's own announcement had been ignored, either. The Huskers were no longer a remote threat, decades away from Bright Boy. The fact that they were almost certainly converging on the system brought an air of apocalyptic gloom to the whole hideaway enterprise. They were living in end times, certain that no actions they now took would really make much difference.

  It's been centuries since we made contact with another human faction, another element of the Cohort, Merlin thought. For all we know, there are no more humans anywhere in the galaxy. We are all that remains; the last niche the Huskers haven't yet sterilised. And in a few years we might all be dead as well.

  'I almost envy Sayaca,' Gallinule said. 'She's completely absorbed in her work in Cinder again. As if nothing else will ever affect her. Don't you admire that kind of dedication?'

  'She thinks she'll find something in Cinder that will save us all.'

  'At least she's still optimistic. Or desperate, depending on your point of view. She sends her regards, incidentally.'

  'Thanks,' Merlin said, biting his tongue.

  Gallinule had just returned from Cinder, his third and longest trip there since Sayaca had left Ghost. Once the shadow-matter hypothesis had been accepted, Sayaca had seen no reason to stay here. Other gifted people could handle this line of enquiry while she returned to her beloved tunnels. Merlin had visited her once, but the reception she had given him had been no more than cordial. He had not gone back.

  'Wel
l, what do you think?' Gallinule said.

  Suspended far out to sea was a representation of what they now knew to be lurking inside Ghost. It was the sharpest view Merlin had seen yet, gleaned by swarms of gravitational-mapping drones swimming through the atmosphere. What the thing looked like, to Merlin's eye, was a sphere wrapped around with dense, branching circuitry. The closer they looked, the sharper their focus, the more circuitry appeared, on steadily smaller scales, down to the current limiting resolution of about ten metres. Anything smaller than that was simply blurred away. But what they saw was enough. They had been right, all those months ago: this was nothing natural. And it was not quite a sphere, either: resolution was good enough now to see a teardrop shape, with the sharp end pointed more or less parallel to the surface of the liquid hydrogen ocean.

  'I think it scares me,' Merlin said. 'I think it shows that this is the worst possible place we could ever have picked to hide.'