“Nothing works but the inertial deflectors,” Torec said. That had to be true, or else the whole Rock, plummeting through the complicated geometry of Arches, would have been a hazard. She sighed. “Don’t they realize we are trying to save the Galaxy? How are we supposed to do that if the toilets don’t work?”
But there was nothing to be done about the strange internal politics of Arches, the Navy, the Coalition, and humankind in general. So they got to work.
For the next few days they wrestled with ancient air and water cyclers, balky nano-food systems, and hovering light globes that wouldn’t stay still. Even the machines didn’t seem to like them: they resisted being fixed, and developed faults and quirks that simply seemed perverse. Their social life didn’t get any better, either. If they had been outsiders in the Barracks Ball, they were definitely not wanted here, by engineers who clearly believed they had better things to do than labor over a lump of shit like Rock 492.
But in another way it was fun, Pirius thought. Getting immersed in the guts of a broken pump or a clogged air-filter system was dirty, hard work, but it was a job that was finite and understandable and something you could finish, unlike the diffuse politicking of Earth.
The systems came online one by one. As they heard the laboring of air pumps, and felt the shuddering of water pumping through the pipes, the place started to seem alive. And because they had worked so hard over it, Pirius and Torec thought of it as theirs. Before he had gone to Earth, the only homes Pirius had ever known had been one Barracks Ball after another. Now Rock 492 was starting to feel like home — though he and Torec only dared discuss such thoroughly non-Doctrinal matters in whispers, and they would never have mentioned it to Captain Seath.
The ensigns were summoned to regular meetings with Nilis.
These were always held in the Commissary’s room in Officer Country. Even though he had assimilated the experiences of his avatar Virtual who had ridden with Pirius Blue through the Cavity, Nilis seemed as scared of Arches’ daunting sky now as when he had first come here, and he tended to hide in his room. But he had quickly made this faceless little cabin his own, spreading his clutter of data desks, clothes and bric-a-brac over every surface, and filling the air with clustering Virtuals. Torec said he made every place he stayed into a nest, as rats made nests. Pirius thought a little wistfully of what it must mean to have a real home, and to miss it, as Nilis clearly missed his.
Torec complained about the state of Rock 492. Nilis said there was nothing he could do about it for now, they would have to wait for a meeting he had scheduled with Marshal Kimmer, the senior Navy officer on the base. After this “showdown,” as Nilis called it, he was sure their requests would be properly met, as the oversight committee had mandated.
Pirius wasn’t so sure. He knew that officers like Marshal Kimmer tended to regard their bases as their private domains. He wouldn’t take kindly to what he would surely see as interference from out- of-touch bureaucrats on far-off Earth, no matter what their formal authority.
Nilis had continued to analyze the data he had gathered on Chandra, the monstrous, enigmatic black hole at the center of the Galaxy, and hypothesized on its nature and what the Xeelee were doing with it.
He knew now that the Xeelee used Chandra to make nightfighters. Somehow, Nilis had deduced from remote images, they peeled spacetime-defect wings and other structures out of the distorted environment of the black hole. That much had long been suspected by Navy intelligence. But Nilis said he suspected the Xeelee had a more profound use for the black hole.
It was all to do with computing. There were fundamental limits to computing power, he said. The processing speed and memory of any computer were limited by the energy available to it.
He picked up a data desk and waved it around in the air. “This is a sophisticated gadget, the result of twenty-five thousand years of technological progress. But what does it weigh — around a kilogram? From the point of view of the gadget’s purpose, which is computation, almost all of this mass is wasted, just a framework. This desk would be able to achieve a lot more if all of its mass-energy were devoted to computing. In the form of photons, say, this kilogram of stuff could process at the rate of ten to power fifty-one operations per second. That’s a million billion billion billion billion…” Similarly, the memory capacity of a computer depended on how many distinguishable states its system could take. If Nilis’s inert kilogram were converted to a liter of light, the capacity would become some ten thousand billion billion billion bits.
“In fact, our most advanced computers have a design something like this,” he said. “Perhaps you know it. At the core of the ’nervous system’ of a greenship is a vat of radiant energy, much of it gamma-ray photons, but some of it more exotic higher-energy particles. Energy is bled off from the ship’s GUT generator, to keep the photon soup at around a billion degrees. Information is stored in the positions and trajectories of the photons, and is processed by collisions between the particles. To read it, you open up a hole in the side of the box and let some of the light out.”
There were limitations with such a design, because the rate at which information could be extracted, limited by lightspeed, was much less than the computer’s storage capacity. “You only get a glimpse of what’s going on in there,” said Nilis. “So our best computers are massively parallel, with subsections working virtually independently.” The input-output rate could be increased if the computer were made smaller, because it took less time for information to be moved around. But as the size was reduced, the energy density would increase. “You encounter more and more exotic high- energy particles,” said Nilis, “until you pass the point at which you can control them. Gamma-ray processing is the limit of our technological capabilities right now. But of course that’s not the physical limit. If you keep crushing down your computer, keep increasing its density, you finish up with—”
“A black hole,” said Torec.
“Yes.” He beamed, and plucked at a thread dangling from the sleeve of his battered robe. “And then the physics becomes simple again.”
Pirius began to see it. “And Chandra is a black hole — the biggest in the Galaxy.”
“Exactly,” Nilis whispered. “I thought the Xeelee were using Chandra to power their central computing facility. Now I believe that the Xeelee are using Chandra itself, a black hole with the mass of millions of suns, as a computer. The audacity!”
Torec asked, “How can you use a black hole as a computer?”
Nilis said that information could be “fed” to a black-hole computer during the hole’s formation, or by infalling matter later. “The data would be stored on the hole’s event horizon in the form of impressed strings.”
Pirius was becoming baffled. “Strings?”
All of reality could be looked on as an expression of vibrating strings. Invisibly small, these loops and knots shimmered and sang, and their vibration modes, the “notes” they sounded, were the particles of the universe humans could discern. Pirius took in little of this, but he liked the idea that the universe was a kind of symphony of invisible strings in harmony.
“A black hole’s event horizon is a terminus to our universe, though,” Nilis said. “Strings can’t extend beyond it. So they become embedded in the surface — like wet hair plastered over your head. The strings bear information about how the hole was formed, and how it grew.” To get at the information you had to let the hole evaporate, as all black holes did, by emitting a dribble of “Hawking radiation.” The smaller the hole the more rapidly it evaporated.