“I know, Lieserl. I’m sorry.” Louise had never found it easy to express affection. With a struggle, she said: “In fact, you’re one of the most human people I’ve ever met.”
Lieserl looked around at the makeshift hospital, following the soft cries of the wounded. “Louise,” she said slowly, “I have a long perspective. Think of the story of the race. Our timelines emerged from the oceans, and for millions of years circled the Sun with Earth. Then, in a brief, spectacular explosion of causality, the timelines erupted in wild scribbles, across the Universe. Humanity was everywhere.
“But now, our possibilities have reduced.
“Louise, all the potential paths of the race — all the time lines, running from those ancient oceans of the past, through millions of years to an unknown future — all of them have narrowed to a single event in spacetime: here, on this ship, now. And that event is under your control.”
Lieserl’s face loomed before Louise now, filling her vision; Louise looked into her soft, vulnerable eyes, and — for the first time, really she had a sudden, deep insight into Lieserl’s personality. This woman really is ancient — ancient, and wise.
“Louise, you are not a woman — or rather, you are more than a woman. You are a survival mechanism: the best to be found, for this crucial instant, by our genes, and our culture, and our minds. If you didn’t have the strength within you now, to deliver us through this causal gateway to the future, you would not have been chosen. But you do have the strength to continue,” Lieserl said. “To find a way through. Look within yourself, Louise. Tap into that strength…”
There was a deep, almost subsonic groan, all around Louise. It sounded like thunder, she thought.
It was the sound of metal, under immense stress.
She pulled away from Lieserl and twisted in the air. She looked across at the section of hull breached by the arc of string. The patch that had been applied across the string damage gleamed brightly, fresh and polished, at the center of the grass-coated hull surface. A stress failure — another breach of the lifedome — would kill them all. But the patch looked as if it was holding up okay… not that a visual inspection from this distance meant anything.
As if on cue, a projection of Mark’s head materialized before her. “Louise, I’m sorry.”
“What is it?”
“Come with me. We need to talk.”
“No,” she said. Suddenly, she felt enormously weary. “No more talk, Mark. I’ve done enough damage already.”
Behind her, Lieserl said warningly: “Louise…”
“I heard what you said, Lieserl.” Louise smiled. “But it’s all a little too mystical for a tired old engineer like me. I’m going to stay here. Help out in the hospital.”
Lieserl frowned at her. “Louise, you’re an engineer, not a doctor. Frankly, I wouldn’t want you treating me.”
Mark smiled. “Besides, we don’t have time for all this self pity, Louise. This is important.”
She sighed. “What is?”
He whispered, in a surprisingly unrealistic hiss, “Didn’t you hear the hull stress noise? Spinner is moving the ship again.”
Think of spacetime as a matrix, Michael Poole whispered. A four-dimensional grid, labeled by distance and duration. There are events: points in time and space, at nodes of the grid. These are the incidents that mark out our lives. And, connecting the events, there are trajectories.
The starbow across the sky broadened, now. That meant her speed had reduced, since the relativistic distortion was lessened. Spinner called up a faceplate display subvocally. Yes: the ship’s velocity had fallen to a fraction over half lightspeed.
Trajectories are paths through spacetime, Poole said. There are timelike trajectories, and there are spacelike trajectories. A ship going slower than light follows a timelike path. And, Spinner, we — all humans, since the beginning of history — work our snail-like way along timelike trajectories into the future. At last, our world lines will terminate at a place called timelike infinity at the infinitely remote, true end of time.
But “spacelike” means moving faster than light. A tachyon — a faster-than-light particle — follows a spacelike path, as does this nightfighter under hyperdrive.
She twisted in her seat. Already the neutron star system had vanished, into the red-shift distance. And directly ahead of her there was a cloud of cosmic string; space looked as if it were criss-crossed by fractures, around which blue shifted star images slid like oil drops.
Poole’s hands, invisible, tightened around hers as the ship threw itself into the cloud of string.
We know at least three ways to follow spacelike paths, Spinner-of-Rope: three ways to travel faster than light. We can use the Xeelee hyperdrive, of course. Or we can use spacetime wormholes. Or, Poole said slowly, we can use the conical spacetime around a length of cosmic string…
Think of the gravitational tensing effect that produces double images of stars around strings. A photon coming around one side of the string can take tens of thousands of years longer to reach our telescopes than a photon following a path on the other side of the string.
So, by passing through the string’s conical deficit, we could actually outrun a beam of light… There was string all around the ship, now, tangled, complex, an array of it receding to infinity. A pair of string lengths, so twisted around each other they were almost braided, swept over her head. She looked up. The strings trailed dazzling highways of refracting star images.
Behind her the huge wings spread wide, exultant.
This damn nightfighter was made for this, she thought.
Under Poole’s guidance, Spinner brought the craft to a dead halt; the discontinuity wings cupped as they tore at space. Then Spinner turned the craft around rapidly — impossibly rapidly — and sent it hurtling at the string pair once more. The nightfighter soared upwards, and this time the two strings passed underneath the ship’s bow.
…And if you can move along spacelike paths, Spinner-of Rope, you can construct closed timelike curves.
The neutron star system was old.
Once the system had been a spectacular binary pair, adorning some galaxy lost in the sky. Then one of the stars had suffered a supernova explosion, briefly and gloriously outshining its parent galaxy. The explosion had destroyed any planets, and damaged the companion star. After that, the remnant neutron star slowly cooled, glitching as it spun like some giant stirring in its sleep, while its companion star shed its life-blood hydrogen fuel over the neutron star’s wizened flesh. Slowly, too, the ring of lost gas formed, and the system’s strange, spectral second system of planets coalesced.
Then human beings had come here.
The humans soared about the system, surveying. They settled on the largest planet in the smoke ring. They threw microscopic wormhole mouths into the cooling corpse of the neutron star, and down through the wormholes they poured devices and — perhaps — human-analogues, made robust enough to survive in the neutron star’s impossibly rigorous environment.