Stephen Baxter - Ring

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 traveling? Ten thousand light years with every lump… 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 toward 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.”

“A mirror?”

“The interstellar medium is opaque to the radio energy. So each radio photon gets reflected back into the cavity. The photon orbits the Ring — and on each pass it’s super-radiant amplified, as Lieserl described, and so sucks out a little more energy from the inertial drag of the Ring’s rotation. And then the photon heads out again… but it’s still trapped by the galaxy mirror. Back it goes again, to receive a little more amplification… Do you see? It’s a classic example of positive feedback. The trapped radio modes will grow endlessly, leaching energy from the Ring itself…”

“But the modes can’t grow indefinitely,” Morrow said.

“No,” Mark said. “The process is an inertial bomb, Morrow. All that electromagnetic pressure will build up in the cavity, until it can no longer be contained. And in the end — probably only a few tens of millennia from now — it will blow the cavity apart.”

Louise glanced around the sky, seeing again the smooth distribution of galaxies she’d noted earlier. “Right. And, in a hundred thousand years, the Northern will fly right into the middle of the debris from that huge explosion.”

Now the ship had sailed high above the plane of the Ring; Louise could see the whole structure, laid out before her like the rim of a glimmering mirror, with the sparkle of the singularity at its heart.

Lieserl said, “Louise, the hostile photino bird activity we’ve noted before — the direct assault on the Ring itself with lumps of matter — is spectacular, but Mark’s right: this radio bomb trick is what will truly bring down the Ring.” A subtle smile played on her lips. “It’s damn clever. The birds are draining the Ring itself, drawing energy out of the gravitational field using inertial drag. They’re going to use the Ring’s own mass-energy to wreck it.”

Subvocally, Louise checked her chronometer. Less than twenty minutes had elapsed since Mark and Lieserl had ordered Spinner to start moving the ship, but already they must have crossed eight million light-years — already they must be poised directly above the singularity.

“Mark. Where are we going?”

Poole, evidently trying to calm Spinner, told her what would happen to the nightfighter as it approached the disc singularity.

A timelike trajectory could reach the upper surface of the disc, Poole told her. A ship could reach the plane of the singularity. But — so said the equations of the Kerr metric — no timelike trajectory could pass through the singularity loop and emerge from the other side.

“So what happens? Will the ship be destroyed?”

No.

“But if the ship can’t travel through the loop — where does it go?”

There can be no discontinuity in the metric, you see, Spinner-of-Rope. Poole hesitated. Spinner-of-Rope, the singularity plane is a place where universes kiss.

“Lethe,” Louise said. “You’re planning to take us out of the Universe?”

Mark swiveled his head toward her, unnaturally stiffly; the degradation of the image of his face — the crawling pixel-defects, the garish color of his eyes — made him look utterly inhuman. “We’ve nowhere else to run, Louise. Unless you have a better idea…”

She stared up at the singularity. The AIs, working together at inhuman speed, had come up with a response to this scenario. But are they right? She felt the situation slipping away from her; she tried to plan, to come to terms with this.

Lieserl said drily, “Of course, timing is going to be critical. Or we might end up in the wrong universe…”

Morrow clung to his scooter, his eyes wide, his knuckles bloodless. “What in Lethe’s name are you talking about now?”

Mark hesitated. “The configuration of the string is changing constantly. It’s a dynamic system. And that’s changing the topology of the Kerr metric — it’s changing the basis of the analytical continuation of space through the singularity plane…”

“Damn you,” Morrow said. “I wish you’d stick to English.”

“The singularity plane is a point at which this Universe touches another smoothly. Okay? But because of the oscillations of the Ring, the contact point with the other universe isn’t a constant. It’s changing. Every few minutes sometimes more frequently — the interface changes to another continuation region — to another universe.”

Morrow frowned. “Is that significant for us?”

Mark ran a hand through his hair. “Only because the changes aren’t predictable, either in timing or scope. Maybe the changes cycle round, for all I know, so if we wait long enough we’ll get a second chance.”

“But we don’t have time to wait.”

“No. Well, we’re not exactly planning this… We won’t be able to choose which universe we end up in. And not every universe is habitable, of course…”

Louise pressed her knuckles to her temples. Good point, Mark. We’ve decided to commit ourselves to crashing out of our Universe, and we have half the Xeelee nightfighters in creation on our tails already… and now you bring me this. What am I supposed to do about it?