“Superet has pieced together some fragments of the history of the future, from the rubble the Crab left behind. We know about the Xeelee, for example. We even know — we think — the name of the Xeelee’s greatest project: the Ring. But — what happens to us? What happens to the human species? What destroys us, even as it extinguishes the stars?

“And — Superet asks — is there anything we can do to avert this, the final catastrophe?”

Louise looked up at the dying stars. “Ah. I think I understand why I’m here. Superet wants me to follow the Hermit Crab. To take the Great Northern — not to Tau Ceti — but on a circular trip, like Poole’s Cauchy, to establish a time bridge. Superet wants to set up a way — a stable way — of reaching this era: the end of time.

“I get it. We’ve long since taken responsibility for the management of our planets — for the survival of their ecologies. Why, now, should we not take responsibility for our own long term survival as a species?” She felt like laughing. “Superet really does think big, doesn’t it?”

Milpitas sat on the edge of her couch. “But what does survival mean, on such timescales? Surely even with AS treatments, survival of individuals — of us into the indefinite future is impossible. What, then? Survival of the genotype? Or of the culture of our species — the memes, the cultural elements, perhaps, preserved in some form — ”

Uvarov looked fascinated now, Louise thought; all his impatience and irritability gone, he stared up at the Virtual rendition of the future hungrily. “Either, or both, perhaps. Speaking as a flesh-and-blood human, I share a natural human bias to the survival of the actual genotype in some form. The preservation of mere information appears a sterile option to me.

“But, whatever survival means, it doesn’t matter. Look beyond the dome. In this time to which Michael Poole traveled, nothing of us has survived, in any form. And that’s the catastrophe Superet is determined — clearly — we must work to avert.”

Louise pulled her lip. “If this is such a compelling case, why is Superet a small, covert operation? Why shouldn’t Superet’s goals motivate the primary activity of the race?”

Poole sighed. “Because the case isn’t so compelling. Obviously. Louise, as a species we aren’t used to thinking on such timescales. Not yet. There is talk of hubris: of comparisons with the Friends of Wigner, who came back through time evidently — to manipulate history, to avert the Qax occupation.” He looked at Louise wearily. “There isn’t even agreement about what you’re seeing here. I’ve shown you just one scenario, reconstructed from the Interface incident evidence. Maybe, it’s argued, we’re addressing problems that don’t really exist.”

Louise folded her arms. “And what if that’s true?”

Uvarov said, “But if there’s even the smallest chance that this interpretation is correct — then isn’t it worth some investment, against the possibility?”

Mark frowned. “So we use the Northern to fly to the future. The flight to Tau Ceti is only supposed to take a century.”

Poole nodded. “With modem technology, the flight of the Northern into the future should last no more than a thousand subjective years — ”

Mark laughed. “Poole, that’s impossible. No ship could last that long, physically. No closed ecology could survive. A closed society would tear itself apart… We don’t even know if AS treatment can keep humans alive over such periods.”

Louise stared up at the simulated stars. A thousand years? Mark was right; it was inhumanly long — but she had the feeling it wasn’t long enough…

Uvarov nodded. “But that is clearly why you have been chosen: Louise, the best engineer of the day, and with will enough to sustain immense projects. You, Mark Wu, a good social engineer — ”

“There are better ones,” Mark said.

“Not married to Louise.”

“Formerly married.”

Poole turned to Milpitas. “The proposal is that you, Serena, will make the Great Northern herself viable for its unprecedented thousand-year flight. And you, Dr. Uvarov, have a deep understanding of the strengths and limitations of the engineering of the human form; you will help Mark Wu keep the people — the species — alive.”

Louise saw Uvarov’s eyes gleam.

“I’ve no intention of going on this flight,” Mark said. “And besides, the Northern already has a ship’s engineer. And a damn doctor, come to that.”

Poole smiled. “Not for this mission.”

“Hold it,” Louise said. “There’s something missing.” She thought over what she had to say: relativistic math, done in the head, was chancy. But still… “Poole, a thousand-year trip can’t be long enough.” She looked up at the decaying stars. “I’m no cosmologist. But I see no Main Sequence stars up there at all. I’d guess we’re looking at a sky from far into the future — tens of billions of years, at least.”

Poole shook his head. His Virtual face was difficult to see in the faded starlight. “No, Louise. You’re wrong. A thousand-subjective-year trip is quite sufficient.”

“How can it be?”

“Because the sky you’re seeing isn’t from tens of billions of years hence. It’s from five million years ahead. That’s all — five megayears, nothing in cosmological time…”

“But how — ”

“More than time will ruin the stars, Louise. If this reconstruction is anything like accurate, there’s an agency at large — which must be acting even now systematically destroying the stars…

“And, as a consequence, us.”

Uvarov turned his face, expressionless, up to the darkling sky.

Virtual-Poole said, “We have reason to believe that even our own Sun is subject to this mysterious assault.” He stood before Louise. “Look, Louise, you know I don’t advocate cosmic engineering — I was the one who opposed the Friends of Wigner, who did my damnedest to close my own bridge to the future. But this is different. Even I can sympathize with what Superet is attempting here. Now can you see why they want you to follow the Crab?”

The light show began to fade from the dome; evidently the display was over.

Poole still stood before Louise, but his definition was fading, his outlines growing blocky in clouds of pixels. She reached out a hand to him, but his face had already grown smooth, empty; long before the final pixels of his image dispersed, she realized, all trace of consciousness had fled.

Lieserl soared through her convective cavern, letting her sensory range expand and contract, almost at random.

She thought about the Sun.

For all its grandeur, the Sun, as a machine, was simple. When she looked down and opened her eyes she could see evidence of the fusing core, a glow of neutrino light beneath the radiative plasma ocean. If that core were ever extinguished, then the flood of energetic photons out of the core and into the radiative and convective layers would be staunched. The Sun was in hydrostatic equilibrium — the radiation pressure from the photons balanced the Sun’s tendency to collapse inwards, under gravity. And if the radiation pressure were removed the outer layers would implode, falling freely, within a few hours.

The Sun hadn’t always been as stable as this… and it wouldn’t always remain so.

The Sun had formed from a contracting cloud of gas — a protostar. At first the soft-edged, amorphous body had shone by the conversion of its gravitational energy alone.

When the central temperature had reached ten million degrees, hydrogen fusion had begun in the core.

The shrinkage had been halted, and stability reached rapidly. The fusion was restricted to an inner core, surrounded by the plasma sea and the convective “atmosphere”. The Sun, stable, burning tranquilly, had become a Main Sequence star; by the time Lieserl entered the convective zone, the Sun had burned for five billion years.