Paul sensed the bafflement of the woman, and anguish infiltrated his partial personalities. He had known that the initiation of the Xeelee hyperdrive would terrify the humans, but there was little he could do to protect them.

There was no time for this introspection. He must seek the Ring himself.

Paul’s focus of attention swept restlessly around the Solar System’s abandoned periphery. He found shipyards, weapons shops, blood-stained hospitals, the foundations of massive industrial complexes. Warships and fortresses, some as large as moons, circled the distant Sun.

Once two objects have been in contact they are forever linked by a thread of quantum wave functions. Once this had formed the basis of humanity’s inseparability communications net. Now the prowling Paul found tenuous quantum functions arcing from the warships to forgotten battlefields scattered across the Universe. Paul knew that the humans had attacked the site of the Ring, at least once; so among these haunted wrecks there must be relics of those great assaults, and a quantum link for him to follow.

At last he found it.

The Spline ship was a mile-wide corpse, its spherical form distorted by a single, vast wound a hundred yards across. Within the wound, organs and dried blood were still visible. Paul imagined the agony of the creature as it had returned from the battlefield, its guts open to the pain of hyperspace…

But this corpse-ship was embedded in a web of quantum functions which spun all the way to Bolder’s Ring; these sunken Spline eyes, hardened now, had once gazed upon the Ring itself.

Paul wrapped himself around a pencil of quantum functions. Absorbing them into his awareness was like being stretched, expanded, made unimaginably diffuse.

Cautiously at first, then with increasing confidence, he began to adjust the phases of the quantum threads, and the multiple foci of his awareness translated through spacetime.

Paul hauled himself along the quantum functions in search of Bolder’s Ring.

It was as if he were sliding down a long, vast slope in spacetime. At first the slope was all but imperceptible, but soon its steepness was unmistakable.

The Ring was the most massive single structure in the Universe. It was like a boulder dropped into a pool: across a region hundreds of millions of light years wide its monstrous gravity well drew in galaxies as effortlessly as a lamp attracts moths. Now Paul was crossing the lip of that well, with the shining ruins of the Universe sliding alongside him. Eventually he saw how the fragile structures — the filaments, loops and voids of galaxies which had emerged from the singularity itself — were distorted, smashed, broken by the fall into this great flaw in space.

The galaxies — all around the sky — were tinged blue, he realized now. Blue shift.

He had come, at last, to the place all the galaxies were falling into.

The Ring was a hoop woven from a billion-light-year length of cosmic string. Paul’s principal awareness focus was somewhere above the plane of the Ring. The near side of the artifact formed a tangled, impenetrable fence, 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.

Paul could study the Ring as Jim Bolder never had. With relish he sent sub-personalities skating along the tangled quantum functions that reached deep into the Ring’s stretched spacetime.

Cosmic strings were residual traces of the ultrahigh, symmetric vacuum of the primordial epoch — an era in which the forces of physics had yet to “freeze out” of a unified superforce — and the strings were now embedded in the “empty space” of the Universe, like residual lines of liquid water in solid ice. And the strings were superconducting; as they moved through the primordial magnetic fields, huge currents — of a hundred billion billion amps or more — were induced in the strings…

The strings writhed, like slow, interconnected snakes, across space. The strings were moving at close to lightspeed. They left behind them flat, glowing wakes — planes towards which matter was attracted, at several miles a second.

Paul looked into the center of the Ring. There he found a singularity. It was hoop-shaped, a circular flaw in space: a rip, caused by the rotation of the immense mass of the Ring. The singularity was about three hundred light years across — much smaller than the diameter of the Ring itself.

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 center — and, beyond them, by an ergosphere: a region in which gravitational drag would be so strong that nothing sublight could resist its current.

But the Ring was spinning… and too rapidly to permit the formation of an event horizon, or an ergosphere. And so, the singularity was naked.

Through the void at the heart of the Ring he could see blue-shifted starlight muddled, stirred. Here the wave functions were tangled, twisted, broken; here space was folded up like cheap cloth.

This distortion was the purpose of the Ring: this was the Kerr-metric Interface, a route to other universes — the gateway through which the Xeelee had made their escape.

…Ghostly flocks slid through the tangled cosmic string net that made up the Ring.

Paul widened his perception to embrace the entire Ring. Everywhere the photino birds soared, silent and purposeful. Somehow the great artifact seemed helpless, and Paul felt an absurd impulse to hurl himself forward, to try to protect the glorious baryonic monument.

At length the photino birds appeared to come to a decision. A knot of birds, billions of them, formed around one section of the toroid — perhaps some weak point — and from all around the Ring more bird flocks flickered in short hyperdrive hops to join the growing throng. Soon only a few scouts were left near outlying parts of the Ring, and around the weak point there was a swarm of shadow birds so thick they obscured the Ring itself.

Cautiously Paul slid his awareness focus closer to the stricken region. The photino birds, he realized, were now passing into the structure of the cosmic string itself.

If cosmic string self-intersected it cut itself. A new subloop formed, budding off the old. And perhaps that subloop, too, would self-intersect, and split into still smaller loops… and so on.

Paul understood. It would be an exponential decay process, once started. And so the birds, concentrating their mass, deflected the passage of string loops, causing them to self-intersect. Soon, threads — fragments of string thousands of miles long — drifted out of the structure, passing unimpeded through the ranks of birds.

Soon the ghost-gray birds were jostling in their eagerness to breach the threads; and, within minutes, a slice through the Ring — extremely thin, no more than a light year wide — began to turn a dull yellow.

The photino birds were cutting the Ring, Paul realized uneasily, and it didn’t appear that it would take them very long. And his little band of humans was still hours away.

He swept over the plain of the Ring and studied the turbulent space at its center. Thanks to the activities of the photino birds the Kerr-metric zone was like a pond into which gravel was being thrown. Star images rippled, and the inter-universal surface was awash with a milky blue light. Already the access paths through the zone must be disrupted—

— and a shock wave of gravitational radiation burst over him.

Rapidly he withdrew his attention foci from the Ring and rose to the roof of its star-walled chamber, so that it was as if he were an insect in some vast cathedral. Something monstrous had erupted into this region of space, mere light minutes away from him. He surveyed the space around the Ring, seeking the source of the gravitational radiation.