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.

“You won’t be surprised that the Silver Ghosts once dabbled with this kind of technology,” Nilis said ruefully. “They created microscopic black holes, with information and processing instructions encoded in the formative collapse. Small enough holes evaporate very quickly—they explode, in fact. The computation’s output is encoded in the radiation they emit in the process. You can solve some spectacularly hard problems that way.” He sniffed. “The Ghosts did get it to work. But each micro-hole computer was a one-off; you could only run one program, because it blew itself up in the process! Even the Ghosts couldn’t find a way to make the technology practical.”

“And,” Torec prompted, “this is what the Xeelee are doing?”

“Yes. But they don’t restrict themselves to mere microscopic holes.”

He showed them data extracted from Pirius Blue’s jaunt into the Cavity. They still had no good close-up images of Chandra, but somehow the Xeelee were controlling the inflow of matter to the event horizon. And through that control, they were “programming” the monstrous black hole. They allowed the Planck scale dynamics of the event horizon to process the input information, and were “reading” the results by analyzing the Hawking radiation the black hole gave off.

“At least that’s what I think they are doing,” Nilis said. “There is still a great deal we don’t know about black holes. For instance, there must be structure in the deep interior, close to the singularity. There the strings and membranes that underlie subatomic particles must be torn and stretched, perhaps reaching dimensions comparable to the black hole itself. Can this ‘fuzzball’ be used for computing purposes? I don’t know—I can’t rule it out. Or perhaps the Xeelee work on some other principle entirely . . .