From ``Giant's Star'', by James P. Hogan.

``We can move objects from place to place instantaneously by means of artificially generated spinning black holes,'' Eesyan told them. ``As your own theories predict, a rapidly spinning black hole flattens out into a disk, and eventually becomes a toroid with the mass concentrated at the rim. In that situation the singularity exists across the central aperture and can be approached axially without catastrophic tidal effects. The aperture affords an `entry port' into a hyperrealm described by laws not subject to the conventional restrictions of ordinary space-time. Creating such an entry port also gives rise to a hypersymmetric effect that appears as a projection elsewhere in normal space, and which functions as a coupled exit port. By controlling the dimensions, spin, orientation, and certain other parameters of the initial hole, we can select with considerable accuracy the location of the exit up to distances in the order of several tens of light-years.''

With Eesyan between Vic and Lyn, they were walking along a broad, enclosed, brightly illuminated arcade of soaring lines, gleaming sculptures, and vast openings, which led into other spaces. There were more Escher-like distortions and inversions here and there in the scene, but nothing so overwhelming as the sight they had first seen from the perceptron. Apparently Ganymean gravitic engineering tricks came with the architecture on Thurien. For this was Thurien. They had emerged from the room and walked through a series of galleries and a huge domed space bustling with Ganymeans, eventually to this place, the illusory blending so smoothly into reality that Hunt had missed the point along the way at which the switch from one to the other had taken place. The meeting between the two worlds was about to take place, Eesyan had informed then, and he had been assigned to escort them there personally. No doubt VISAR could have transferred them there instantly, Hunt thought, but this seemed a more natural way while they were still ``acclimatizing.'' And having an opportunity to get to know at least one of the aliens informally in advance helped the process further. Probably that was the idea.

``That must be how you got the perceptron to Earth,'' Hunt said.

``Almost to Earth,'' Eesyan told him. ``A black hole large enough to take a sizable object creates a significant gravitational disturbance over a large distance. Therefore we don't project things like that into the middle of planetary systems; it would disrupt clocks and calendars and so on. We exited the perceptron outside the Solar System, and it had to make the last lap in a more conventional way.''

``So a round trip needs four conventional stages,'' Lyn commented. ``Two one way, and two the other?''

``Correct.''

``Which explains why it took something like a day to make it from Thurien to Earth,'' Hunt said.

``Yes. Instant planet-to-planet hopping is out. But communications is another matter entirely. We can send messages by beaming a gamma frequency microlaser into a microscopic black-hole toroid that can be generated in equipment capable of operating on planetary surfaces without undesirable side effects. So instant planet-to-planet datalinks are practicable. What's more, generating the microscopic black holes needed for them doesn't require the enormous amount of energy that holes big enough to send ships through do. So we don't do a lot of instantaneous people-moving unless we have to; we prefer moving information instead.''