Tides of Light by Gregory Benford Page B

Abraham had known the value of simple
     times, of quiet days spent doing rough work with his hands, or just strolling through the ample green fields that ringed the
     Citadel.
    But Abraham had not been born into a simple time, and so he had come to be a master of the canny arts humans needed. Killeen
     had absorbed from him the savvy to survive when they raided mech larders, but that was not what he remembered best. The wry,
     weary face, with its perpetual promise of love and help, the look that fathers gave their sons when they glimpsed a fraction
     of themselves in their heirs—that had stayed with Killeen through years of blood and fear that had washed away most of the
     Citadel’s soft im-ages. He could not recall his mother nearly as well, perhaps because she had died when he was quite young.
    And what would Abraham say, now that his son had named a star for him that was a caldron of vast forces, beside which humanity
     was a mere fleck, a nuisance? Some promised land! Killeen grimaced.
    The hoop had finished its first revolution and begun the second, hastening. Its inner edge did not lie exactly along New Bishop’s
     axis but stood a tiny fraction out from it.
    As Killeen watched, the cosmic ring finished its second passage, revolving with ever-gathering speed. The hoop seemed like
     a part in some colossal engine, spinning to unknown purpose. It glowed with a high, prickly sheen as fresh impulses shot through
     it—amber, frosted blue, burnt orange—all smearing and thinning into the rich, brimming honey gold.
    —I’m picking up a whirring in the magnetic fields,—Shibo sent.
    His Arthur Aspect immediately observed:
    That is the inductive signal from the cosmic string’s revolution. It is acting like a coil of wire in a giant motor.
    “What
for?
” Killeen demanded, his throat tight. Without ever having set foot on it, he felt that New Bishop was
his
, the Family’s, and not some plaything in a grotesquely gargantuan contraption. He called up his Grey Aspect.
    I cannot…understand. Clearly it moves…to the beck…of some unseen hand…I have never heard…of mechs working on such a scale…nor
     of them using a cosmic string…To be sure…strings were supposed…in human theory…to be quite rare
.
They should move…at very near the speed of light. This one must have…collided with the many stars…and clouds…slowing it. Someone
     captured it…trapped with magnetic fields
.
    Arthur broke in:
    A truly difficult task, of course, beyond the scope of things human—but not, in principle, impossible. It merely demands the
     manipulation of magnetic field gradients on a scale unknown—
    “What’s your point?” Killeen demanded. Though the Aspect talk streamed through his mind blindingly fast, he had no patience
     for the smug, arched-eyebrow tone of Arthur’s little lectures. Equations fluttered in his left eye. They were leakage from
     Arthur; or maybe the Aspect thought much mumbo jumbo would impress him. Killeen grimaced. The Aspect had now assimilated Grey’s
     memories and was working with them. Grey’s dusty presence faded as Arthur continued crisply:
    Simply that the cosmic string is clearly employed here in some sort of civil-engineering sense. Shibo detects the strong inductive
     electromagnetic fields generated by its revolving, but surely this cannot be the purpose. No, it is a side effect.
    “Why slice in when the cut seals up right away?”
    Indeed. A puzzle, surely. Still, I can admire this object for its beauty alone. Grey tells me that they ascribed the very
     formation of the galaxies, and even whole clusters of galaxies, to immense cosmic strings, at the very dawnof our universe. Rings were once truly, cosmologically huge. Galaxies formed from the turbulence of their passing, like whorls
     behind a watercraft. As time waxed on, cosmic strings twisted on themselves, breaking where they intersected. Coiled strings
     did this repeatedly, proliferating into many lopped-off