Vacuum Diagrams

Moro approached her; he’d resumed the crude disembodied-head Virtual form Gage had first encountered. “Hi.” He grinned.

“I just died.”

Moro shrugged. “Tell me about it. We’re all stored inside the shelter now.” This was a hardened radiation shelter they’d built hurriedly into the heart of the ice world; it contained a solid-state datastore to support their new Virtual existence, what was left of their vegetation, their precious clutch of human zygotes embedded in ice. “Our bodies have been pulped, the raw material stored in a tank inside the shelter.”

“You’ve a way with words.”

“…We’re up to a thousand gee,” Moro said.

Gage’s Virtual reflexes hadn’t quite cut in, so she made her mouth drop open. “A thousand?”

“That’s what the missile is demanding of us. All our tunnels have collapsed.”

“I never liked them anyway.”

“And the drones are having to strengthen the structure of Chiron itself; the thing wasn’t built for this, and could collapse under the stress.”

At a thousand gee, the time-dilation factor they would pile up would be monstrous. Gage found herself contemplating that, her growing isolation from home in space and time, with no more than a mild detachment.

Gage rubbed Virtual hands over her arms. Her flesh felt rubbery, indistinct; it was like being mildly anesthetized. Perhaps she was, in some Virtual way.

“Come on,” she said. “Let’s see what the food is like here.”

The chase settled down to stalemate again.

Gage sat under (a Virtual image of) the sky, watching starlight bend itself into a bow around the ship. It was a beautiful sight; it reminded her of Saturn’s rings.

Their speed was already so close to that of light that time was passing a thousand times as quickly inside Chiron as beyond it. Everyone Gage knew in the Solar System must be long dead, despite AS treatment.

She wondered if the Squeem occupation still endured. Maybe not. Maybe humans had hyperdrive ships of their own by now.

This solitary drama might be the last, meaningless act of a historical tragedy, yet to play to its conclusion.

Most of the eighty had retreated to Virtual playgrounds, sinking into their own oceanic memories, oblivious of the Universe outside, isolated even from each other.

But Gage was still out here.

New problems were looming, she thought.

She sought out Maris Mackenzie.

“We’re going bloody fast,” she said.

“I know.” Maris Mackenzie looked lively, interested. “This is the way to travel between the stars, isn’t it? Carrying live, fragile humans through normal space across interstellar distances was always a pipedream. Humans are bags of water, unreasonably fragile. A starship is nothing but plumbing. Humans crap inordinate amounts, endless mountains of—”

“Yes,” said Gage patiently, “but we still can’t stop. Where are we going? Tau Ceti is long behind us. And we’re heading out of the plane of the ecliptic, remember; we’re soon going to pass out of the Galaxy altogether.”

“Um.” Mackenzie looked thoughtful. “What do you suggest?”

Gage set up a simulation of her old freighter’s pilot cocoon; for subjective days she reveled in the Virtual chamber, home again.

But she got impatient. Her control and speed of reaction were limited.

She dismissed the cocoon and found ways to interface directly with the sensors of Chiron, internal and external.

The GUTdrive felt like a fire in her belly; the sensor banks, fore and aft, were her eyes.

It was odd and at first she ached, over all her imaginary body; but gradually she grew accustomed to her new form. Sometimes it felt strange to return to a standard-human configuration. She found herself staring at Moro or Mackenzie, still seeing arrays of stars, the single, implacable spark of pursuing GUTlight superimposed on their faces.

Gage had been a good pilot. She was prepared to bet she was a better pilot than the Squeem missile. If she learned to pilot Chiron, maybe she could find a way to shake off the missile.

She searched ahead, through the thinning star-fields at the edge of the Galaxy. She had to find something, some opportunity to trick the Squeem missile, before they left the main disc.

The black hole and its companion star lay almost directly in the path of Chiron.

The hole was four miles across, with about the mass of the Sun. Its companion was a red giant, vast and cool, its outer layers so rarefied Gage could see stars beyond its bulk.

Gage had found her opportunity.

She summoned Maris Mackenzie. A pale Virtual of Mackenzie’s disembodied head floated over an image of the hole and its companion.

The hole raised tides of light in the giant. Material snaked out of the giant in a huge, unlikely vortex which marched around the giant’s equator. The vortex fueled an accretion disc around the hole, a glowing plane of rubble that spanned more than Earth’s orbit around its Sun.

Some of the giant’s matter fell directly into the hole. The infall was providing the hole with angular momentum — making it spin faster. Because of the infall the hole was rotating unusually fast, thirty times a second.

“Hear me out,” Gage said.

“Go on,” said Maris Mackenzie.

“If a black hole isn’t spinning — and it’s uncharged — then it has a spherical event horizon.”

“Right. That’s the Schwarzschild solution to Einstein’s equations. Spherically symmetric—”

“But if you spin the hole, things get more complicated.” It was called the Kerr-Newman solution. “The event horizon retreats in, a little way. And outside the event horizon there is another region, called the ergosphere.”

The ergosphere cloaked the event horizon. It touched the spherical horizon at its poles, but bulged out at the equator, forming a flattened spheroid.

“The greater the spin, the wider the ergosphere,” Gage said. “The hole ahead is four miles across. It’s spinning so fast that the depth of the ergosphere at the equator is a hundred and forty yards.”

Mackenzie looked thoughtful. “So?”

“We can’t enter the event horizon. But we could enter the ergosphere, or clip it, and get away safely.”

“Um. Inside the ergosphere we would be constrained to rotate with the hole.”

“That’s the plan. I want to flyby, clipping the ergosphere, and slingshot off the black hole.”

Mackenzie whistled. Pixels fluttered across her face, as she devoted processing power to checking out Gage’s proposal. “It could be done,” she said eventually. “But we would have a margin of error measured in yards. It would require damn fine piloting.”

“I’m a damn fine pilot. And we can take a lot of stress, remember.” It’s not as if we have to protect anyone living.

“Why do you want to do this?”

“Because,” Gage said, “the missile will follow me through the ergosphere. But after we’ve passed through, the hole will have been changed. The missile won’t be able to work out how…”

“We’ll have to get consent to this from the others. The eighty—”

“Come on,” Gage said. “Most of them have retreated into their own Virtual heads. There’s hardly anybody out here, still thinking, save you and me.”

Slowly, Mackenzie smiled.

For Gage’s scheme to work, the speed of Chiron would have to be raised much higher. When Chiron flew by the hole it would need an angular momentum comparable to that of the hole itself. So the drones ravaged Mackenzie’s frozen ocean, hurling the stuff of Chiron into the GUTdrives.

Chiron approached the lightspeed limit asymptotically.

By the time the hole approached, Chiron’s effective mass had reached about a tenth of the Sun’s. For every second passing in its interior, a hundred years wore away outside.

Ahead of her, the radiation from the black hole’s accretion disc was Doppler-shifted to a lethal sleet. Massive particles tore through the neural nets which comprised her awareness. She felt the nets reconfigure, healing themselves; it was painful and complex, like bone knitting.

Behind her the redshifted emptiness was broken only by the patient, glowering spark of the Squeem missile.

The black hole was only seconds away. She could make those seconds last a Virtual thousand years, if she wished.

In these last moments, she was assailed by doubt. Nobody had tried this maneuver before. Had she destroyed them all?

Gage let her enhanced awareness pan through the bulk of Chiron. Years of reaction-mass plundering had reduced the ice dwarf to a splinter, but it would survive to reach the lip of the black hole — and so would its precious cargo, the awareness of eighty downloaded humans, the canister containing their clutch of frozen zygotes. That canister felt like a child, inside her womb of ice.

Enough.

She reduced her clock-speed to human perception. The black hole flew at her face—

The misty giant companion star ballooned over Gage’s head, its thin gases battering at her face.

Chiron’s lower belly dipped fifty yards into the ergosphere. The gravitational pull of the hole gripped her. It felt like pliers in her gut. She was hurled around; she was a helpless child in the grip of some too-strong adult. The fabric of Chiron cracked; Solar System ice flaked into this black hole, here on the edge of the Galaxy, flaring X-radiation as it was crushed.

Then the gravity grip released. The hole system was behind her, receding. The pit dug in spacetime by the hole’s mass felt like a distant, fading ache.

She watched the patient GUTspark of the Squeem missile as it approached the hole. It matched her path almost exactly, she saw with grudging admiration.

The missile grazed the lip of the hole. There was a flare of X-radiation.

The GUTspark was gone.

It’s worked. By Lethe, after all these years, it’s worked.

Suddenly Gage felt utterly human. She wanted to cry, to sleep, to be held.

Cydonia, her home arcology, was an angular pyramid, huge before her, silhouetted against the light of the shrunken Sun. The ambient Martian light was like a late sunset, with the arcology drenched in a weak, deep pink color; against its surface its windows were rectangles of fluorescent light glowing a harsh pearl gray, startlingly alien.

Her boots had left crisp marks in the duricrust.

Gage wasn’t nostalgic, usually, but since the hole flyby she had felt the need to retreat into the scenes and motifs of her childhood.