‘And the
rotation
has significant effects. Louise, we’re on the fringe of a Kerr metric - the classic relativistic solution to the gravitational field of a rotating mass. In fact, this is what’s called a
maximal
Kerr metric: because the torus is spinning so fast the angular momentum far exceeds the mass, in gravitational units . . .
‘As Mark said, the Ring’s rotation is exerting a large torque on the ship. This is
inertial drag:
the twisting of spacetime around the rotating Ring.’
Morrow frowned. ‘Inertial drag?’
Lieserl said, ‘Morrow, naive ideas of gravity predicted that the
spin
of an object wouldn’t affect its gravitational field. No matter how fast a star rotated, you’d be attracted simply towards its centre, just as if it wasn’t rotating at all.
‘But relativity tells us that isn’t true. There are nonlinear terms in the equations which couple the rotating mass to the external field. In other words, a spinning object drags space around with it,’ she said. ‘
Inertial drag
. And that’s the torque the
Northern
is experiencing now.’
‘What else?’ Louise asked. ‘Mark?’
He nodded. ‘The first point is, we’re
drowning
in radio-wavelength photons—’
That was unexpected. ‘What are you talking about?’
‘I mean it,’ he said seriously, turning to face her. ‘That’s the single most significant difference in our gross physical environment, compared to the era we came from: we’re now immersed in a dense mush of radio waves.’ He looked absent for a moment. ‘And the intensity of it is increasing. There’s an
amplification
going on, slow, but significant on the timescales of this war; the doubling time is around a thousand years. Louise, none of this shows up in the future era. By then, the radio photons will be gone.’
Louise shook her head. ‘I can’t make sense of this. What’s causing the amplification?’
He shrugged, theatrically. ‘Beats me.’ He glanced around the sky. ‘But look around. The Ring is contained in a shell of galactic material, Louise. The frequencies of the radio waves are below the plasma frequency of the interstellar medium. So the waves are
trapped
in this galaxy-walled box. We’re inside an immense resonant cavity, ten million light-years across, with reflecting walls.’
Morrow looked beyond the skydome uncertainly. ‘Trapped? But what happens when—’
Lieserl cut in, ‘Mark, I think I’ve figured it out. The cause of the radio-wave amplification.’
He glanced at her. ‘What?’
‘It’s the inertial drag. We’re seeing superradiant scattering from the gravitational field. A photon, falling into the Ring’s gravity well, is coupled to the Ring by the inertial drag, and is then thrown out with additional energy—’
‘
Ah
. Right.’ Mark nodded, looking distant. ‘That would give an amplification of a few tenths of one per cent each traverse . . . just about fitting my observations.’
Morrow frowned. ‘Did I understand that? It sounds as if the photons are doing gravitational slingshots around this Ring.’
Louise smiled at him, sensing his fear. ‘That’s right. The inertial drag is letting each photon extract a little energy from the Ring; the radiation is amplified, and the Ring is left spinning just a fraction slower . . .
‘Lieserl. Tell us more about the spacetime metric.’ She looked up, at the point of light at the heart of the Ring. ‘What do we see, there, at the centre?’
Lieserl looked up, her face composed. ‘I think you know, Louise. It is a
singularity
, at the centre of the Ring itself. The singularity is hoop-shaped, a circular flaw in space: a rip, caused by the rotation of the immense mass of the Ring. The singularity is about three hundred light-years across - obviously a lot smaller than the diameter of the material Ring . . .
‘If the Ring were spinning more slowly, the Kerr metric would be quite well-behaved. The singularity would be cloaked in
two
event horizons - one-way membranes into the centre - and, beyond them, by an
ergosphere:
a region in which the inertial drag is so strong that
nothing
sublight can resist it. If we were in an ergosphere, we’d have no choice but to rotate with the Ring. In fact, if it weren’t rotating at all, the Kerr field would collapse into a simple, stationary black hole, with a point singularity, a single event horizon and no ergosphere.
‘But the Ring
is
spinning . . . and too rapidly to permit the formation of an event horizon, or an ergosphere. And so . . .’
Louise prompted, ‘Yes, Lieserl?’
‘And so, the singularity is
naked
.’
Michael Poole sat with his legs crossed comfortably on the shoulder of the nightfighter. His gaze was on Spinner’s face, steady, direct.
The Ring is a machine, whose sole purpose is to manufacture that naked singularity. Don’t you see? The Xeelee constructed this huge Ring and set it spinning in order to tear a hole in the Universe.
Spinner-of-Rope enhanced the false-colour of the central singularity in her faceplate imager. The flaw looked like a solid disc - a coin, perhaps - almost on edge towards her, but tipped slightly so that she could see its upper surface.
In that surface, white starlight swam. (
White?
)
She said to Poole, ‘The Xeelee built all of this - they modified history, disrupted spacetime, drew in galaxies to their destruction across hundreds of millions of light-years - just for
this
?’
Poole lifted his eyebrows.
It is the greatest baryonic artifact, Spinner-of-Rope. The greatest achievement of the Xeelee . . .
The singularity was like a jewel, surrounded by the undisciplined string-scribble of the Ring itself.
‘It’s very beautiful,’ she conceded.
Poole smiled.
Ah, but its beauty lies in what it does
. . .
He turned his gaunt, tired face up to the singularity.
Spinner-of-Rope, humans have imputed many purposes to this artifact. But the Ring is not a fortress, or a last redoubt, or a battleship, or a base from which the Xeelee can reclaim their baryonic Universe
, he said sadly.
Spinner, the Xeelee know they have lost this war in Heaven. Perhaps they have always known that, even from the dawn of their history.
‘I don’t understand.’
Spinner, the singularity is an escape hatch
.
Lieserl and Mark turned to each other, inhumanly quickly. They stared into each other’s eyes, as if exchanging data by some means invisible to humans, their blank expressions like mirror images.
‘What is it?’ Louise asked. ‘What’s happened?’
Pixels, defects in the Virtual projection, crawled across Mark’s cheek. ‘We need Spinner-of-Rope,’ he snapped. ‘We can’t wait for the repairs to the data links. We’re trying to find bypasses - working quickly—’
Louise frowned. ‘Why?’
Mark turned to her, his face expressionless. ‘We’re in trouble, Louise. The cops are here.’
Spinner-of-Rope asked, ‘How do you
destroy
a loop of cosmic string ten million light-years across?’
It isn’t so difficult . . . if you have the resources of a universe, and a billion years, to play with, Spinner-of-Rope
. Poole, perched on the shoulder of the nightfighter, pointed at a hail of infalling galaxies swamping a nearby section of the Ring.
If the Ring tangles - if cosmic string self-intersects - it cuts itself
, he said.
It intercommutes. And a new subloop is formed, budding off the old. And perhaps that subloop, too, will self-intersect, and split into still smaller loops . . . and so on.
Spinner nodded. ‘I think I understand. It would be an exponential process, once started. Pretty soon, the Ring would decay into the torus of debris we found - will find - a hundred thousand years from now . . .’
Yes. No doubt the motion of the Ring has been designed by the Xeelee so that it does not cut itself. But all one need do is start the process, by disrupting the Ring’s periodic behaviour. And that is evidently what the photino birds are endeavouring to do, by hurling galaxies - like thrown rocks - at the Ring.
Spinner sniffed. ‘Seems kind of a crude technique.’
Poole laughed.
Baryonic chauvinism, Spinner-of-Rope? Besides, the birds have other mechanisms. I—
‘ . . . Spinner.
Spinner-of-Rope
. Can you hear me?’
Spinner sat bolt upright in her couch and clutched at her helmet. ‘Lieserl? Is that you?’
‘Listen to me. We don’t have much time.’
‘Oh, Lieserl, I was beginning to think I’d never—’
‘
Spinner
! Shut up, damn you, and
listen
.’
Spinner subsided. She’d never heard Lieserl use a tone like that before.
‘Use the waldoes, Spinner. You have to get us out of here. Take us straight up, with the hyperdrive, over the plane of the Ring. Have you got that? Use the longest jump distance you can find. We’ll try to patch subroutines into the waldoes, but—’
‘Lieserl, you’re scaring the pants off me. Can’t you tell me what’s wrong?’
‘No time, Spinner. Please. Just do it . . .’
The Universe
darkened
.
For a bleak, heart-stopping instant Spinner thought she was going blind. But the telltales on the waldoes still gleamed at her, as brightly as ever.
She looked up. There was something before the ship, occluding the blue-shifted galaxy fragments, hiding the Ring.
She saw night-dark wings, spread to their fullest extent, looming over the
Northern
.
Nightfighters
.
She twisted in her seat. There were
hundreds
of them - impossibly many, dark lanterns hanging in the sky.
They were Xeelee. The
Northern
was surrounded.
Spinner screamed, and slammed her fists against the hyperdrive waldo.
The ‘fighters moved through electric-blue cosmic string like birds through the branches of a forest. There were so many of them in this era. They were cool and magnificent, their night-dark forms arrayed deep into space all around her. Lieserl stared at the swooping, gliding forms, willing herself to see them more clearly. Had any humans ever been closer to Xeelee than this?
The Xeelee moved in tight formation, like bird-flocks, or schools of fish; they executed sudden changes of direction, their domain wall wings beating, in squads spanning millions of miles - absolutely in unison. Now Lieserl saw how ‘fighters
should
be handled, in contrast to Spinner’s earnest, clumsy work. The nightfighters were sculptures of spacetime, with a sleek beauty that made her shiver: this was baryonic technology raised to perfection, to a supreme art, she thought.
She was struck by the contrast between this era and the age of devastation - of victory for the photino birds - to which the
Northern
had first brought them. Here, the Ring was complete and magnificent, and the Xeelee, in their pomp, filled space. Already, she knew, the final defeat was inevitable, and the Xeelee were, in truth, huddling inside their final retreat. But still, her heart beat harder inside her as she looked out over this, the supremacy of baryonic life.
The overlapping lengths of string slid down, smoothly, past the lifedome, as the
Northern
climbed. The nightfighters swooped like starlings through the string, and around the
Northern -
no, Spinner realized suddenly; the nightfighters were
flickering
across space.
‘They’re using their hyperdrive,’ she breathed.
Yes
. Poole stared up at the nightfighters, his lined face translucent.
And we’re hyperdriving too. You’re pushing it, Spinner; we’ve never tried jumps of this scale, even in test. Do you know how fast you’re travelling? Ten thousand light-years with every jump . . . But even so, the Xeelee are easily keeping pace with us.
Of course they are
, Spinner thought.
They are Xeelee.
These ‘fighters could have stopped the
Northern
at any time - even destroyed it. But they hadn’t.
Why not?
The ship was rising high above the plane of the Ring. The tangle of string fell away from the foreground, and she could see easily now the million-light-year curve of the structure’s limb. And at the heart of the Ring, the singularity seemed to be unfolding towards her, almost welcoming.
The Xeelee ‘fighters rose all around her, like leaves in a storm.
They can’t believe we’re a threat. I guess humans never were a threat, in truth. Now, it’s almost as if the Xeelee are escorting us
, she thought.
‘Lieserl,’ she said.
‘I hear you, Spinner-of-Rope.’
‘Tell me what in
Lethe’s
name we’re doing.’
‘You’re taking us out of the plane of the Ring . . .’
‘And then?’
‘
Down
. . . ’ Lieserl hesitated. ‘Look, Spinner, we’ve got to get away from the Xeelee, before they change their mind about us. And we’ve nowhere else to run, not in all of the Universe.’
‘And this is your plan?’ Spinner was aware of the hysteria in her own voice; she felt fear spread through her stomach and chest, like a cold fluid. ‘
To fly into a singularity
?’
Mark punched his thigh. ‘I was right, damn it,’ he said. ‘I was right all along.’
The tension was a painful presence, clamped around Louise’s throat. ‘Damn it, Mark, be specific.’
He turned to her. ‘About the significance of the radio energy flux. Don’t you see? The photino birds have
manufactured
this immense cavity, of stars and smashed-up galaxies, to imprison the Ring.’ He glanced around the skydome. ‘Lethe. It must have taken them a billion years, but they’ve done it. They’ve built a huge mirror of star-stuff, all around the Ring. It’s a feat of cosmic engineering almost on a par with the construction of the Ring itself.’