One of the more interesting panels I attended at Chicon was the one about Dyson spheres. (I know what you're thinking: how long is this guy going to keep gassing about some convention he went to last month?) I learned some new things and it made me think in some new directions. Let me share some of those thoughts with you.
First, are we all clear on what a Dyson sphere is? We're not talking about a vacuum cleaner. Back in 1960 the legendary physicist Freeman Dyson proposed that advanced civilizations might eventually surround their home star completely with energy-collecting devices, creating an object with the luminosity of a G-type star but with its emissions shifted into the deep infrared because all that would escape would be the civilization's waste heat.
Dyson may not have invented the idea -- a couple of science fiction writers may have anticipated him -- but he was the first person to treat the idea with scientific rigor, plus he was even then a well-known physicist, so it's named after him.
Anyway, the sphere as proposed by Dyson would not be a single giant object; rather, it would be a vast swarm of solar power collectors, space habitats, etc., circling the parent star in a variety of orbits to soak up every last photon. But for some reason, science fiction writers have always preferred to imagine a single giant ping-pong ball surrounding a star. The idea of something with a hundred quadrillion square miles of surface to live on is just incredibly appealing, I guess. (That's about equal to half a billion Earths!)
One of the first topics discussed on the panel is whether we could detect any Dyson spheres over interstellar distances, and whether the fact that we haven't indicates anything important. I believe it was Allen Steele who suggested maybe the Dyson spheres are all hidden. That prompted my first way-cool thought of the day: suppose we did discover signs of a Dyson sphere, hidden from view by a nebula or some other interstellar debris. The first question that would come to mind is: who are they hiding from? That's a pretty good story, right there. What's scary enough to frighten a civilization which controls the entire output of a star?
A second topic was one that G. David Nordley brought up: if you don't surround the star with habitats, but instead build a gigantic half-sphere, the thing can be balanced against the central star's gravity via the pressure of the solar wind. Now if you make the big hemisphere shiny on the inside (or even just paint it white), then the star's entire output is going in only one direction. As Mr. Newton can tell us, that means the star (and its associated planets) is going to move in the opposite direction. A half-Dyson sphere is a way to move entire solar systems around! Again, if you discover one, the question immediately becomes what are they running away from?
Finally, let's go back to the original Dyson sphere concept. Instead of a big ball, there's a vast swarm of space habitats surrounding the Sun. Each one can be quite large, with a population in the millions. There would be billions of these habitats, each as big and diverse as a modern nation. I can't really conceive of any government which could control them all, and no human could even begin to know all about each one -- any more than one person can personally know every human being on Earth today.
It seems to me that a far-future Dyson sphere swarm would look a lot like the old classic science fiction picture of the galaxy: lots of inhabited worlds, each with their own unique customs, but travel between them is not especially difficult. You can have down-at-heel space merchants, itinerant mercenary companies, aggressive empires, roguish adventurers, benevolent Federations, space princesses -- all the classic trops of Golden Age science fiction in a rock-hard realistic science fiction future.
I haven't written any of that yet, but I think I will. It's just too interesting. In the meantime, if you need a Dyson sphere fix, I suggest Allen Steele's Hex.