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"Not married to Louise."
"Formerly married."
Poole turned to Milpitas. "The proposal is that you, Serena, will make theGreat 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 thehuman 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, theNorthern 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."
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"How can it be?"
"Because the sky you're seeing isn't from tens of billions of years hence. It's fromfive 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 actingeven 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 theCrab?"
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 andopened 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 aprotostar. 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 aMain Sequence star; by the time Lieserl entered the convective zone, the Sun had burned for
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five billion years.
But the Sun would not remain on the Main Sequence forever.
The mass converted to energy was millions of tons per second. The Sun's bulk was so huge that this was
a tiny fraction; in all its five-billion-year history so far the Sun had burned only five percent of its hydrogen
fuel...
But, relentlessly, the fuel in the core would be exhausted. Gradually an ash of helium would accumulate
in the core, and the central temperature would drop. The delicate balance between gravity and radiation
pressure would be lost, and the core would implode under the weight of the surrounding, cooler layers.
Paradoxically, the implosion would cause the core temperature torise once more so much so that new
fusion processes would become possible and the star's overall energy output would rise.
The outer layers would expand enormously, driven out by the new-burning core. The Sun would engulf
Mercury, and perhaps more of the inner planets, before reaching a new gravity-pressure equilibrium as [ Pobierz całość w formacie PDF ]