Diaspora

"The system doesn't lose angular momentum." The worm placed an arrow at the center of the orbit, pointing up out of the plane. "Which is why the coupling strength doesn't fall, cutting off the interaction. But with each encounter, the direction of the angular momentum vector is changed slightly." As stars drifted by, the arrow began to wobble away from the vertical. Its height above the orbital plane represented its component in ordinary 3-space, and as it was jostled further and further from its original direction, the neutron stars began to spiral together. Their angular momentum wasn't being radiated away, by meson jets or anything else. It was being converted into extra-dimensional spin.

Karpal watched the animation with a dazed expression. Elena touched his arm. "Are you all right?"

He nodded. Paolo knew that this was what he'd joined the Diaspora to find, as much as any planet's refugee. He'd watched from the moon as Lacerta spiraled down, unable to make sense of the process, while thousands of fleshers died because no one could explain it, no one could convince them it was real.

Paolo was feeling disoriented himself. The Transmuters remained as elusive as ever, but this non-sentient tool of another civilization entirely had just casually answered the question that had driven the Diaspora across three universes.

Or half the question.

He summoned up a map of the Milky Way, every star labeled with gestalt tags indicating mass and velocity. "Can you read this?"

"Yes." The worm added candidly, "I know what you're going to ask. What's the fate of the core?"

Paolo was suddenly grateful that the thing was non-sentient. Their minds had all been read, they'd all been rendered as naked as they could be to any lover—but unless the worm was lying, it was churning through this information, blindly, to determine the answers they needed, with no more awareness than the polis library.

"So were the Transmuters right or wrong? Do you agree with their prediction?"

"Not quite. They were extrapolating a long way into the future, and a galaxy is a complex system. They couldn't be expected to get everything right."

Elena asked, "So how far out were they?"

The worm said, "As the core collapses, most of its energy will end up as extra-dimensional spin. Energy in that form can't interact with local gravitons, so the region won't seal itself off behind an event horizon as rapidly as it otherwise would. And before it does, the energy density will grow high enough to start creating new space-time."

"A mini Big Bang?" Karpal moved restlessly away from the girder, as if that could give him a head start in spreading the warning. "A center of creation, in the middle of the galaxy?"

"Yes."

Elena said, "But won't the new space-time be orthogonal to the old? A bubble perpendicular to the main universe, not intruding into it?" She sketched a rough diagram, a large sphere with a smaller one growing out of it, the two joined only at a narrow neck.

"That's correct. But that small, shared region at the galactic core will still reach extreme temperatures before it pinches off to form a black hole."

"How extreme?"

"Hot enough to break up nuclei within a radius of fifty thousand light years. Nothing in the galaxy will survive."

Elena fell silent. Paolo thought: There will he no sign of it, here. Not a pinprick of radiance, like a distant supernova, to mark the passing of a hundred billion worlds. The apocalypse would be invisible.

Paolo knew that the Contingency Handler could feel no compassion for their plight; it could only utter the formalities programmed into it long ago, translated as best it could. But the message it conveyed still managed to bridge time, and scale, and cultures.

It said, "Bring your people through. They're welcome here. There's room enough for everyone."

Part Eight

Yatima liked the way the concentric 3-spheres of color pricked out in the sky by stars of equal Doppler-shift converged on their destination; it seemed so much more emphatic than an ordinary star born of circular bands. Wrapping the image of Weyl so tightly, it seemed to promise that, this time, the Transmuters would not have slipped away.

Paolo said, "End of story, I suppose. From that point on, they'll know the territory better than we do."

"Maybe." Yatima hesitated. "They might still be curious about one thing, though."

"What?"

"You, Paolo. You had all the information you needed. You'd made the whole Diaspora worthwhile. So why did you choose to keep traveling?"

19

PURSUIT

Carter-Zimmerman polis, U**