As Jophiel looked further inwards, to the inner rim of the accretion disc, he saw that it glowed, hot and violent. There, infalling material was heated to billions of degrees. Most of it was hurled back into the wider disc – but a fraction fell into the hole, to be lost to the universe for ever.
And the black hole itself, a hemisphere rising up from the curdled light-sea of the accretion disc, had a kind of grand, sombre stillness, Jophiel thought.
The core of it was a shadow, in fact, deep and wide – three or four times the width of the event horizon, the ultimate inner surface from which not even light could escape – for the black hole deflected the light of the star fields behind it. A gravity shadow. Further out there was more evidence of the distortion of light. The spinning hole dragged at spacetime, a swirl that gathered and deflected the very starlight. So the black hole looked asymmetrical: its leading side was darker, as if shadowed, while the other was brightened by the collected light that the spinning hole hurled in Jophiel’s direction. Gravitational lensing, of an extreme kind.
There was a purity about this display. A clarity to the light cloaking the singularity. A perfection in the delineation of the arcs. It was angelic, almost.
And all of it nothing, at heart, but an artefact of spacetime.
‘I must remember this,’ he muttered. ‘All of it. For you, Michael. I saw this.’ To Lethe with depression, he thought. He might never have got to see all this. How depressing was that thought?
Nicola was smiling at him. Black-hole light reflecting from her silver skin. ‘Welcome back,’ she said.
‘Nearing closest approach,’ Asher said calmly. ‘I’m watching the innermost rim of the accretion disc.’
‘The caches,’ Nicola said now. ‘Look at the caches!’
Jophiel looked out, peering along the stream of pale boxes. Their neat cubical forms were an extraordinary element of symmetry in this howling chaos, he thought.
And now he saw them fission. Individual boxes growing, splitting, folding up into two copies, four . . . As more and more were produced the boxes collided with each other; some went tumbling out of the stream altogether.
He immediately saw the principle.
‘This is what it’s all about,’ he said. ‘The caches, I mean. The purpose of all this, for the Xeelee. The caches are made of hull plate, right? And hull plate turns radiant energy to mass. The more area it has to catch the light, the more it grows. An exponential process.’
‘Yes! That’s it,’ Nicola said, excited. ‘Remember the Cache on the surface of the Sun? In that light, it could double in size in a couple of hours. And in the intensity of the infall glow here—’
‘Seconds,’ Asher said, wondering. ‘A box a thousand kilometres across could double in size – or replicate – in seconds. Just by soaking up the mass-energy from the accretion disc.’
Jophiel thought it through. ‘A cache’s closest approach to the black hole will last only minutes. But that’s enough for many doublings – dozens, maybe. One box could become a thousand, more. And then all those boxes – all that frozen mass-energy – start the long haul back out to the Wheel again. Then, in fifteen hundred years or so, when they get there—’
‘And that is how the Xeelee made the Wheel,’ Asher said. ‘By turning black-hole energy into hull plate, and hurling that plate back out to the Wheel’s orbit. It would take millennia, but the Xeelee got here by hyperdrive, and it has had millennia. While we limped along after it at mere lightspeed.’
Jophiel grinned. ‘I love this—’
‘Ah,’ said Asher.
Nicola frowned. ‘What do you mean, “Ah”?’
‘Look ahead.’
Jophiel obeyed.
To see a cache, randomly deflected, wheeling out of the stream, spinning slowly.
Coming straight at them.
A thousand-kilometre wall.
‘We knew this was a hazardous environment,’ Nicola said softly. Her hands hovered over her control. ‘Trying to evade—’
Asher snapped, ‘Seconds to impact. Uploading last data dump back to the Cauchy.’
Nicola sighed. ‘That’s that, then.’
Jophiel Poole grabbed Nicola’s silver glove of a hand. He called, ‘Asher?’
‘I’m here.’
‘You know what?’
‘What?’
‘“Lucked out” my ass.’
Nicola laughed out loud.
And then—
40
Ship elapsed time since launch: 23 years 264 days
The last, compressed, heavily distorted neutrino-link message came through from the Chandra probe, just as the Cauchy prepared at last to leave its eyrie a half light year outside the perimeter of the Wheel, and begin its near-tangential journey towards the inner surface – a journey that would itself take over a year.
And as the last returned data were recorded and analysed, the principals, Jophiel, Nicola and Asher, finally integrated the memories of their partial copies into their own minds.
Or tried to. Jophiel found he struggled with conflicting memories, just as had his copy on the probe, it seemed. Nova dreams. Maybe casting off partials really was a dumb idea, in the long run.
He tried to lose himself in work. Medic Harris Kemp had no better remedy to recommend than that.
On the ninth day Nicola and Asher came to see him, in Poole’s apex office.
Jophiel greeted them with a grunt. ‘What’s this, the probe crew reunited?’
Nicola studied him, silver face unreadable. ‘Still feeling sorry for yourself? Get over it, Poole. We’ve got work to do.’
‘She’s right,’ Asher said. ‘It is pretty exciting. We’ve been able to figure it out from the data we returned.’
‘Figure out what?’
‘How the Xeelee built the Wheel.’
She conjured up a Virtual schematic of the Wheel. At the heart of the apex suite, it spun in mid-air.
‘Slowed down for effect,’ Asher said drily. ‘Given the Wheel is spinning at lightspeed. We’ve detected three decks, as we’ve called them – three levels above the c-floor, the structural level. You can see the upper decks are supported by these struts, rising up from the c-floor. The highest is over a thousand astronomical units above the base.
‘We think the essential construction material of all this is Xeelee hull plate.
‘Now, each deck is a ring a million kilometres wide and a light year in radius. That’s an area equivalent to a hundred billion Earth surfaces, peeled off and spread out flat. Look, you’re going to hear a lot of absurd numbers like this; just bear with me. But if it’s all made of hull plate, which is very fine stuff – and if it was stationary – the mass isn’t so big, actually. Less than one per cent that of Earth’s Moon, say.’
Nicola grimaced. ‘Only, she says.’
‘It’s going to get worse. Of course you have to multiply that up by a few factors to allow for the multiple decks and the support struts.
‘But what’s much more significant is the effects of motion. It’s all spinning at near lightspeed, remember. And the consequence of that is paradoxical. But Einstein figured it all out, back in the nineteenth century.’
‘The twentieth,’ Jophiel said automatically. ‘Actually, Einstein used spinning rings and discs as a thought experiment: a paradox to help him figure out relativity in the first place.’
Nicola was impassive. ‘Just imagine I don’t know what in Lethe you two are talking about.’
Asher grinned. ‘Look – we know that the radius of the Wheel is a light year. So its circumference ought to be two times pi times a light year – a bit more than six light years – if it were static. But it’s not. Imagine you had some giant pacing it out down there, with a measuring rod a light year long. She lays the rod down, over and over – six times and she’s nearly back where she started.
’
Jophiel knew where she was going with this. ‘If the Wheel were stationary.’
‘Yes. But it isn’t. We know what happens when objects approach lightspeed. Look at the Cauchy, at its peak velocity. As seen by observers on Earth, our clocks slowed to a crawl; they would have seen us take twenty-five thousand years to reach the Galaxy centre – whereas it seemed to us to take only twenty years. We were accelerated, they weren’t; acceleration changes the nature of the spacetime you inhabit.
‘And, if the Earth observers had been able to measure the apparent length of the Cauchy at its peak velocity, they’d have seen it squashed up lengthways. Space and time adjust to keep the speed of light constant for all observers . . .
‘So. Go back to the giant pacing out the Wheel. She’s moving at a speed close to that of light, compared to us. And so her clocks will slow down—’
‘And her measuring rod will contract, from our point of view,’ Nicola said.
‘That’s it. Her direction changes the whole time as she paces around the circle, but that makes no difference to the speed she’s moving at, and the relativistic distortion. We watch her lay down that shrunken rod, over and over, as she paces around a circumference that looks unchanged to us. And so she must put it down a lot more than six or seven times before she gets back to her starting point.’ She studied their faces. ‘You see where I’m going with this? Our surveyor down on the Wheel is in a spacetime distorted by the Wheel’s motion. She can measure that distortion, directly. Just by counting the number of times she lays down those sticks. She finds that the circumference of her circle is bigger than what Euclid said it should be . . . She would get the wrong answer for pi . . .’
‘How much bigger?’
‘Given our measure of how close the c-floor has approached the speed of light, the ultimate limit – we figure five million times.’
Nicola actually gasped. ‘So let me get this right. This two-light-year-diameter Wheel has a circumference that isn’t a mere six light years, a walk past Alpha Centauri, like you say. It’s more like thirty million light years.’
Asher grinned. ‘A walk that would take you out of the Galaxy. Out of the local group—’
‘All jammed into this diddly hoop?’
‘You got it.’
‘That’s outrageous.’
‘No, it’s not,’ Asher said calmly. ‘Einstein understood.’
But Jophiel was still puzzling at the numbers. ‘Five million times. OK, the distance expansion is one thing. But that factor would only deliver enough rest mass to complete the structure. Then there’s the kinetic energy to push it up to lightspeed in the first place.’
Asher smiled. ‘You’re right. Another factor of five million.’
Nicola said, ‘That’s got to mass a lot more than a slice of the Moon, then.’
‘You’re right. You’re looking at the mass-equivalent of several thousand stars.’ She glanced up at the spinning Wheel. ‘And most of the mass-energy delivered to this thing has had to be converted into kinetic energy.’
Jophiel laughed.
Nicola glared at him. ‘You can laugh at this. You are still a Poole, aren’t you? A little boy with another big dumb toy to play with.’
‘I’m just thinking how tricky such a thing would be to build. If you put together the Wheel, made it just long enough to close the six-light-year loop, and then spun it up – it would stretch, crack up, as space distorted. Conversely, once built, if somehow it slowed down, it could crumple, fold up. Not enough space to fit in its length. Einstein thought of that, in fact. He said that you’d have to build a spinning object of some kind of liquid – mercury, maybe – that would flow to fill the space as it distorts.’
Asher said, ‘We think the Xeelee has done something like that. As to how they built it—’
‘We saw the process, didn’t we?’ Nicola asked. ‘A stream of caches, grown at the black hole and spun back out here – incorporated into the structure somehow . . . Maybe starting with a single Xeelee flower.’
Asher nodded. ‘It all extrapolates from what Xeelee hull plate does. Put it in sunlight, in any strong radiation, it grows. Before long, it has doubled in size, and doubled again, growing faster and faster. You want to know how many doublings you’d need to get from a single Xeelee flower, with a few square centimetres of area, up to the Wheel – or its equivalent in hull plate, anyhow?’
Jophiel grinned. ‘Don’t guess, Nicola. I’ve fallen into these traps before. Always less than you think.’
‘Around a hundred and forty,’ Asher said with a kind of triumphant glee. ‘That’s all! As to how long a doubling would take – down at Chandra, you’re talking about seconds, no more. The radiant energy out of Chandra, from the infall from the accretion disc, is about two and a half thousand times that of the Sun . . .
‘So – you sit out here, a light year away from Chandra. You throw in one Xeelee flower. Just one. It takes over fifteen hundred years to sail in to the black hole, before whipping around in a few minutes, and beginning the long slow haul back out again. Still, we figure you could achieve twenty or thirty doublings, a quarter or a third of the total needed, in a single pass.
‘Then you sail the whole lot out again, and go back in for another pass. Do it again and again—’
‘We get the idea,’ Nicola said, holding her hands up. ‘The transfer across a light year each time is slow, though.’
‘Only if you don’t want to spend any energy on hauling the material out of the gravity well. To speed it up you could boost your climb out of the gravity well – for instance, sacrifice half the mass as reaction mass. There are other subtleties. The Wheel’s mass-energy is huge, equivalent to thousands of times the mass-energy of the Sun. Compared to that, even the total output of the natural radiation from the accretion disc is minuscule. We think the Xeelee is manipulating the replication process to adjust the accretion-disc infall, and so to extract more mass-energy from the system – ultimately from the black hole itself, and the knot of spacetime around it. Using the accretion disc as a kind of siphon, you see. And since Chandra masses several billion solar masses—’
Jophiel nodded. ‘The mass of a few thousand stars is small change. So it’s plausible. Barely.’
‘So that’s our model.’ Asher smiled. ‘Proof of principle anyhow. We’re sure the Xeelee has been smarter, more subtle.’
‘But it is elegant, isn’t it?’ Jophiel said. ‘I mean, the range of uses to which the Xeelee put the replicating hull plate, this single super-efficient technology. The Cache it used in the Solar System. We saw the forests of buildings down on Goober c. Now this.’
Asher nodded. ‘Maybe that’s the mark of a truly advanced technological culture.’
‘You two just love all this, don’t you?’ Nicola said. ‘So, Jophiel, you ready to come back to work yet?’
Jophiel grinned. ‘Is that all the sympathy I’m to get?’
‘You’re a Poole. And your ship is heading for a close encounter with the Wheel, however it was constructed. You’ve got work to do.’
41
Ship elapsed time since launch: 25 years 45 days
Twenty-five thousand light years from its home port, GUTdrive exhaust flaring, the crew of the lone ship Cauchy prepared to fly into the superstructure of the Xeelee Wheel.
The geometry was simple in principle, staggering in scale. The Cauchy, on arrival at the centre, had come to rest just above the plane of the Wheel, a half-radius outside its rim. The ship was, Nicola had remarked, like a fly cautiously inspecting the turning wheel of a tipped-over wagon. Now it was going further in – not towards the Wheel’s hub, but at an angle, cutting an arc across the Wheel’s open face. The plan was that it would pass through the plane of the Wheel, making a close approach to one deck, and then, heavily accelerating, rise up and make another pass back up through the plane, encountering another dec
k en routre.
It would use its main drive to achieve this; burning at a full gravity, it would still take more than a year to complete all this, to achieve a flyby.
It had felt like a long year.
Day by day the great structure swelled in the ship’s forward vision, a million-kilometre-wide belt hurtling through space. The Cauchy’s instruments peered intently at the surface that slowly grew before them, measuring velocities and dimensions, seeking details. Slowly grew, from a line across space, to a band, to a wall that covered the forward sky. From a distance it must look defiant, Jophiel thought, a single spark challenging that monstrous structure.
And then, at nine-tenths of lightspeed, the Cauchy flew within the outer arc of the Wheel, and swept low over the Wheel’s uppermost deck.
This deck – Deck Three – was thirteen hundred astronomical units above the lowest, Deck One, itself raised above the c-floor, the strange relativistic substrate. All Jophiel saw was a flat plane, soft grey Xeelee hull plate, infinite in all directions, fleeing below the lifedome. Jophiel had once walked on the surface of the Solar System Cache, when it had sailed past Mars. That had been a manufactured plain a mere thousand kilometres across. This great artefact was a million kilometres wide – as wide as eighty Earths, almost as wide as the Sun. He could repeat such statistics to himself as often as he liked, but it barely helped him grasp the reality.
Worse yet, the naked eye could make out no detail. After nearly five hundred days at a full gravity’s acceleration, the Cauchy had reached nearly ninety per cent of lightspeed, enough for some significant light aberration. Even so the mighty structure they were exploring was turning that much faster still, nearly a tenth of lightspeed more. As relative velocities went, that was a lot. The proximity of the spacecraft to such a whirling mass, at such speeds, was, he knew, making instinctive pilots, like Nicola, deeply anxious. Most of the crew were in their skinsuits, strapped into their crash couches.
Xeelee Redemption Page 24
