Fawen Wollay put down the screen from which he had been reading and stared at nothing in particular, deep in thought. The screen turned itself off quietly and furled itself neatly back into his pen-shaped terminal. Wollay was taking his ease in a comfortable suite which looked out through open patio doors over a sun-drenched terrace and onto a lush and carefully tended tropical garden filled with rare blooms and exotic plants which would have seemed entirely at home in the equatorial regions of any of hundreds of planets.
Wollay's home and garden was not on any planet, nor in any kind of enclosed habitat or Rock, or even on one of the great ships, the General Service Vehicles which plied the greater galaxy representing the Culture to other, usually less sophisticated civilizations. In fact, his house and grounds occupied some infinitesimal fraction of the surface of K'oothla Orbital in the Thalanth system; just another of millions of orbitals which provided the trillions of Culture citizens with all the room they might desire.
Orbitals provided the maximum amount of living space coupled with elegantly-minimal usage of material, a situation which appealed mightily to the Minds and AIs which ran the Culture and even those humans who chose to take an interest. For a society which prided itself on providing huge variety and choice for its citizens, Culture orbitals were curiously uniform in size, and in appearance - at least on the outside.
An orbital was a fine bracelet about three million kilometres across but only a few thousand kilometres wide, placed in orbit around a suitable star and tilted just off the ecliptic. Orbitals span on their own axis to produce one Culture-standard gravity and a Culture-standard day-night cycle. Orbitals were made from superdense exotic materials and held together almost entirely by force-fields; the outsides were a uniform coal-black colour, interspersed with occasional deep dark caverns and undulations representing the features on the other side.
The inside surface of an orbital was a completely different matter, of course. It was a work of art: a fabulous complexity and variety of landscapes and panoramas, created with inventiveness and imagination for the enjoyment of all, and spread over hundreds of times the surface area of the kind of rocky planet humans would find acceptably comfortable. Edge walls - many kilometres high - and Bulkhead ranges between individual Plates kept the air in - or other atmospheres, sometimes; the latter also allowed an orbital to be constructed piecemeal, a Plate at a time.
Such a vast area had space for as many different ecosystems as could be imagined, not all of them necessarily suitable for the unprotected human form. There were beautiful places for people to enjoy: sandy beaches and manicured gardens and shady parks. There were also large areas of apparently unmanaged wildness: rainforests, tundra, deserts and badlands, ravine-haunted mountain ranges and rolling hills, all for different and more energetic enjoyment. There was also a lot of water: rivers and lakes and seas and oceans of every description, full of sea-adapted creatures of all kinds and more than a few sea-adapted humans, too.
Wollay looked up suddenly, as if coming to a decision.
"Hub?" he said to the air.
"Here," a deep voice said, the sound emerging from nowhere in particular, "How can I help?"
Managing all the different environments on an orbital, and running the weather controls, the transport networks, the communication grids and all the other multitudinous systems was a frightening complex affair - even with the aid of a huge amount of automation - and overall coordination required a very smart machine indeed. Culture convention was that very smart machines were also personally sentient, with their own personality and peccadillos. Such Culture Minds, as they were called, basically ran everything; every orbital had at least one Mind, generally installed at the centre point of the ring and therefore generally known as Hub by the locals.
"I've been studying histories," Wollay went on, "Of this orbital, and of you, Hub."
"I can see that," the deep voice replied, "I profess myself flattered."
"It's a long and distinguished career," Wollay said, "But there do seem to be some gaps in the records."
"That might be true," Hub agreed, "I can see you want to talk about it. Shall I send one of my Avatars?"
An equally important part of the role of an orbital Hub was to make sure all the people - humans, drones and assorted aliens - were happy and healthy. A Hub Mind existed almost entirely in hyperspace and operated at the speed of HS light; it was perfectly capable of holding a simultaneous real-time conversation with every one of the many billions which inhabited an orbital with every evidence of effortlessness and with a thoughtful regard to the preferences and dislikes of each individual.
Still, some people found it easier to talk directly to a person, or at least something which looked like one, rather than converse into thin air or at one remove using a terminal. For this reason, orbital Hub Minds tended to have Avatars, generally humanoid in shape but carefully designed to be very difficult to confuse with a real human.
Still deep in thought, Wollay picked up his terminal and sent a single short message.
A few moments later, a tall slender silver-skinned being appeared on the terrace, exactly as if it was out for a casual afternoon stroll and knocked politely on the frame of the patio doors.
"Hello," it said, in the same smooth deep voice Wollay had heard before, "May I come in?"