Dyson Sphere: Difference between revisions
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{{trope}}
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The technologies and resources needed to do it raise the [[Awesome but Impractical|question of whether a race that could build one would still need it]]. It has been estimated that constructing the sphere would require the energy equivalent of the lifetimes of ''several'' stars AND the raw materials of more than the entire solar system, which rather defeats the purpose of the initial construction.
For a real-life example: there is absolutely ''nothing'' stopping the human race from building a bridge across the Pacific Ocean. Humanity has all the engineering know-how and resources needed. So why haven't we? Well, we already have ships and airplanes, not to mention things like
The [[Ringworld]] concept was created by science fiction author [[Larry Niven]] as a mid-point between this and a true planet because, as Niven put it in his essay ''Bigger Than Worlds'' (a discussion of [[Ringworld Planet|Ring World Planets]], Dyson Spheres, and other possible macrostructures), "I like being able to see the stars at night". Something that a Dyson Sphere prevents.
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=== Some useful notes on the [[Real Life]] physics of objects this size
* In response to letters prompted by his original paper, Freeman Dyson replied: "A solid shell or ring surrounding a star is mechanically impossible. The form of 'biosphere' which I envisaged consists of a loose collection or swarm of objects travelling on independent orbits around the star." The evolution of the term "Dyson Sphere" is an example of [[Memetic Mutation]]. Dyson himself referred to his idea as a "shell" or "swarm", and his use of [[wikipedia:Biosphere|"biosphere"]] was in the ''ecological'', rather than any ''geometric'' sense. But then [[Rule of Cool]] caught up with him.
* The surface gravity of the outside of a stereotypical 1-AU solid shell is likely to be negligible. Gravitational acceleration due to the Sun out there is less than 1/1000 g. Calculus and physics (the [[wikipedia:Shell theorem|Shell Theorem]]) tell us that the gravitational effect of any spherical shell we're outside of is equivalent to that of the same mass as a point source at the shell's center; we can assume that the sphere doesn't have mass orders of magnitude more than the Sun, considering that it has to be made of locally available materials and the Sun weighs much more than everything else nearby combined, so don't expect much.
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* The title object in ''Wall Around a Star''.
* ''Second Genesis'' by Donald Moffitt is mostly set on a Dyson Sphere composed of planet-orbit sized disks, used to power a massive interstellar transmitter (The rest of the story is set on another of Dyson's conceptual objects, a [[wikipedia:Dyson tree|Dyson Tree]] that has been converted into a [[Living Ship]]).
* William Forstchen's Gamester Wars universe has a Dyson Sphere setting that's still being
* Half of ''[[Alastair Reynolds|Century Rain]]'' is set in one of these, but it wasn't built for the normal reasons. The inside of the sphere is patterned with stars that match the stars in our own solar system, and by some pseudo-scientific method they shift as our own stars would, so that those inside the sphere don't know that they're not really on Earth.
* In Robert Silverberg's ''Across a Billion Years'', some archaeologists discover an artifact left behind by a billion-year-old vanished civilization that leads them to the Dyson Sphere that the civilization disappeared into.
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