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slice is closed up so that the spacetime is like a cone. Still flat, but with a missing piece.
"If you were to draw a circle around a string, you would find its circumference shorter than you would
expect from its radius it's just like drawing a circle around the apex of a cone."
"And this small spacetime defect is sufficient to cause the double images you speak of?"
"Yes," Mark said.
A cosmic string wasn't visible directly. But its pathcould be made visible, by a track of double images of
remote objects, separated by about six arc seconds, along the length of the string.
Louise said, "Uvarov, imagine two photons setting off toward us from a remote galaxy, beyond a string.
One of them comes to us directly. The second, passing on the far side of the string, travels through the
conical defect. The second photon actually has less distance to travel to reach us, thanks to the defect; its
journey time is less than the first's by around ten thousand years. Hence, the double images."
Uvarov grunted. "Louise, you have explained to me how the network of strings was the web around
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which the galaxies coalesced. I do not understand how this can be, if the gravitational effects of these
strings are so slight."
Louise sighed. "The strings are primeval objects: they were formed within an invisible fraction of a
second after the Big Bang itself, during the symmetry loss caused by the decomposition of the unified
superforce. Since then, the expansion of the Universe hasstretched the strings. So the strings are under
great tension a tension caused by the expansion of the Universe itself... The strings whip through space,
at close to the speed of light.
"Where the strings pass, their conical defects cause them to leave awake. Matter falls in toward the
two-dimensional, sheet-like path swept out by the string. And it's this infalling that caused the formation
of the baryonic matter structures we observe now: clusters of galaxies, in threads and sheets."
"In fact," Mark said, "the wake is itself observable. Or should be. It imposes a slight Doppler shift on the
microwave background radiation. I should be able to see a slightly brighter sky on one side of the
invisible string than on the other..."
"And have you seen this?" Uvarov snapped.
"No," Mark admitted. "Damn it. TheNorthern couldn't be a much worse platform for this kind of
measurement; the microwave Doppler is below my level of resolution."
"But do you think you've found some image pairs," Uvarov persisted.
"Yes," Mark said, sounding excited again. "Two pairs so far, and a few other candidates. The two pairs
are aligned, just as you'd expect them to be if a string is the cause..."
"Enough," Uvarov snapped. He raised his chair into the air above them and prowled across the
underside of the sky-dome, his ravaged profile silhouetted against the false colors of the galaxies. "Now
tell me what this means. Let us accept, Louise, that your Virtual lover has found a fragment of this
string.So what? Why should we care?"
"We're in avoid, Uvarov," Louise said patiently. "We'd expect to find string at the heart of huge baryonic
structures like the Great Wall, for instance, a sheet of clusters half a billion light-years long, which "
"But we arenot at the heart of such a huge baryonic structure. Is that your point, Louise?"
"Yes. That's the point. There's no reason why we should find stringhere, in this void, away from any
concentrations of matter."
"I see. There is nothing out there but dark matter," Uvarov growled quietly. "Nothing but the photino
birds, and their even more exotic cousins and whatever they've chosen to build, here at the heart of
their dark empire, far from any baryonic structure."
Uvarov wheeled to face Louise, his scooters spurting puffs of reaction gas. "If it exists, will the string
have any effect on the photino birds?"
"Possibly," Mark said. "Strings are gravitational defects. Dark matter is influenced by gravity..."
Uvarov nodded. "So perhaps the string is here to do damage to the photino birds. Is that possible?
Perhaps the string has been moved heredeliberately."
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"I hadn't thought of that, but I guess it's possible." Mark peered up into the dome, his eerie, disembodied
head looking bizarre. "Yes. If someone is waging war on the photino birds, then maybe they are using
lengths of cosmic string as weapons. Think of that. And more: who in this Universe is capable of such an
act, but the Xeelee themselves?
"Lethe fighting wars with bits of cosmic string. How have they the audacity to evenimagine such
weapons?"
Louise looked up into the dome's sketchy, gaudy rendering of the Universe. Suddenly these scraps of
data seemed pathetic, their understanding hopelessly limited. Were the final wars for the destiny of the
Universe being played out between Xeelee and photino birds, somewhere in this huge void, even now, as
she stared up in her blindness and ignorance? [ Pobierz całość w formacie PDF ]