Beyond the clear dome, string filled the Universe.
Here, a hundred thousand years into the past, the galaxies still fell, fragmenting and blue-shifted, into the deepest gravity well in the Universe. And the Northern had emerged from its jaunts through the string loop’s spacetime defects to find itself once more inside a star-walled cavity, at the bottom of this Universal well.
There the similarity ended, though, Louise thought. The cavity walls were much smoother than in the future, containing rather fewer of the ragged holes she’d noted… The walls looked almost artificially smooth here, she thought uneasily.
And, of course, there was the Ring, whole and magnificent.
The Ring was a hoop woven from a billion-light-year length of cosmic string. The Northern was positioned somewhere above the plane of the Ring. The near side of the artifact formed a tangled, impenetrable fence over the lifedome, twisted exuberantly into arcs and cusps, with shards of galaxy images glittering through the morass of spacetime defects. And the far side of the object was visible as a pale, hard band, remote across the blue-shifted sky.
The rough disc of space enclosed by the Ring — a disc no less than ten million light-years across, Louise reminded herself — seemed virtually empty. Perhaps, she mused, in this era the Xeelee were actively working to keep that central region clear.
…Clear, Louise saw as she looked more carefully, save for a single, glowing point of light, right at the geometric center of the Ring. She saw how Lieserl was staring into that point of light, her mouth half-open.
Spinner-of-Rope’s precipitate action had delivered them, back through time, to another snapshot-timeslice of this war in Heaven… and this was, it seemed, an era not far removed from the Ring’s final fall.
She was aware of their eyes — Mark’s, Lieserl’s, Morrow’s resting on her, expectantly. On her.
Remember what Lieserl said, she told herself. I’m a survival mechanism. That’s all. I have to keep functioning, for just a little while longer… She reached deep inside her.
She clapped her hands. “All right, people — Mark, Lieserl. Let’s do some work. I think it’s obvious we’ve delivered ourselves right into the middle of a war zone. We know that, at this moment, the photino birds must be hitting this Ring from all sides — because, within a hundred thousand years, we know that the Ring is going to be destroyed. That gives me the feeling that we don’t have much time, before one side or other notices we’re here…”
“I think you’re right, Louise,” Mark said. Both the Virtuals, on high-capacity data links to the central processors, were working on different aspects of the situation. “I don’t think we should be fooled by the fact that most of the action in this incredible war seems to be occurring at sublight velocities, so that — on this scale it has all the pace of an ant column crossing the Sahara. Let’s not forget the Xeelee have a hyperdrive — which we’ve stolen — and, for all we know, so do the photino birds. We could be discovered at any time.”
“So give me a summary of the environment.”
Mark nodded. “First of all, our position in time: Spinner-of-Rope constructed enough closed timelike paths for us to have traveled a hundred thousand years into the past, back from the era to which our first journey brought us.” He raised his face to the skydome and rose into the air by a few feet, absently forgetting to take his Virtual-scooter with him. “The Ring is complete in this era, as far as we can tell. Its mass is immense — in fact we’re suffering inertial drag from it. Kind of a lot of drag, in fact… We’re being hauled around, through space, by the Ring. Spinner-of-Rope seems to be compensating…”
“Lieserl. Tell me what you have.”
Lieserl seemed to have to tear her eyes away from that tantalizing point of light at the heart of the Ring. She looked down at Louise.
“I have the Ring, Louise. We have been restored to an era before its destruction. Bolder’s Ring is a single loop of cosmic string… but an immense one, no less than ten million light-years across and with the mass of tens of thousands of galaxies, united into one seamless whole. The string is twisted over on itself like wool wrapped around a skein; the Ring’s topography is made up of string arcs moving at close to lightspeed, and cusps which actually reach light speed. The motion is complex, but — as far as I can tell it’s non-intersecting. The Ring could persist forever.
“Louise, there is no way this monster could have formed naturally. Our best theories say that any natural string loops should be a mere thousand light-years across.” She looked up, and the blue false color of the string images caught her profile, picking out the lines around her eyes. “Somehow — ” she laughed briefly ” — somehow the Xeelee found a way to drag cosmic string across space — or else to manufacture it on a truly heroic scale — and then to knit it up into this immense artifact.”
Louise stared up at the Ring, tracing the tangle of string around the sky, letting Lieserl’s statistics pour through her head. And I might have died without seeing this. Thank you. Oh, thank you…
“The cosmology here is… spectacular,” Lieserl said, smiling. “We have, essentially, an extremely massive torus, rotating very rapidly. And it’s devastating the structure of spacetime. The sheer mass of the Ring has generated a gravity well so deep that matter — galaxies — is being drawn in, toward this point, across hundreds of millions of light years. Even our original Galaxy, the Galaxy of mankind, was drawn by the Ring’s mass. So we know that the Ring was indeed the ‘Great Attractor’ identified by human astronomers.
“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 toward its center, 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.”