'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.
-Exultant, Ch. 36