One of the more seriously bad-ass concepts in modern science fiction is the “Dyson Sphere.” The idea as generally portrayed (such as in the “Relics” episode of Star Trek: The Next Generation”) is a hollow spherical shell a hundred million miles or so in radius, with a star at the center. The purpose of this vast effort would be to capture all of the output of the sun, not just a small fraction, and to create a place to live with trillions of times the surface area of an Earth-like world.
A few small problems, not least of which being that it probably could not be made to work. For starters, gravity. No matter how massive the shell is, if it’s even remotely evenly thick and dense, there will be no net gravitational force inside the sphere. If a person (represented in the detailed schematic below by the little purple figure) happens to be near the wall of a hollow spherical shell, the mass in “Area 1” will obviously attract him. But subtending the same solid angle is “Area 2” on the opposite side of the shell. And while “Area 2” is vastly further away from the person than “Area 1” (say, 200,000,000 miles, as compared to six feet), “Area 2” compensates by being vastly more massive than “Area 1.” The end result is that the two areas cancel each other out. A consequence of this is that the only gravitational force felt within the sphere is that cause by the central sun. Typically, in science fiction hand-wavy “gravity generators” are built into the wall so that someone could stand on the inner surface.
Several alternatives to “gravity generators” have been dreamed up to counter this little problem:
1) Stand on the outside of the sphere. Duh. (but it’s cold and dark…)
2) Build a transparent sphere inside the larger opaque one, smaller in radius by a hundred miles or so. This will trap a hundred-mile-thick blanket of air, and will keep stuff from falling into the sun. The solar gravity, and the gravity felt by being on the *outside* of the transparent sphere would be minimal; for all intents and purposes, it’d be freefall. But it’s also be *weird,* and over time everything – dirt, trees, water, dead folk, bird crap – would cover the transparent sphere.
3) Spin the sphere to generate centrifugal force. But this will cause everything to fall downhill to the equator, leaving most of the surface area barren, uninhabitable and at an unfortunate slope. More, all the air will pool at the equator, so good luck with those climbs…
4) Build the Dyson Sphere not as a solid spherical shell, but as a stacked set of Ringworlds. Each Ringworld would be a ribbon of material a million miles or so wide, with rims several hundred miles high. Each would spin to create centrifugal force. Stack Ringworlds of various radii together to form a sphere. There would need to be frictionless (magnetic, most likely) bearings between the worlds, and the closer to the “poles” you get, the further down towards the horizon the sun would get. But this would seem to maximize the total livable area; plus you could have rings with different gravities. Below is a crude schematice of a cross-section of such a sphere. The individual rings are shown *way* bigger than in reality. Rather than a dozen or so, you’d probably want a hundred or two.
And… there’s:
5) Build the Dyson Sphere the way physicist Freeman Dyson actually wanted. Not as a solid sphere, but as a collection of separate, individual artificial space habitats. Instead of a solid wall intercepting all the energy of the sun, there’d simply be so many colonies that they would blot out the sun. This would seem to be not only the easiest way to make a sphere that traps all of a star’s energy, it would also seem to be damn near inevitable, assuming we can get off this rock.
There has been a long arguement over exactly what Dyson meant when he first described the concept, whether solid shell or cloud. Well, rather than hash that out, here are the letters (from Science magazine, all from 1960) where he first describes his concept. There are three letters of note: his letter of June 3, where he describes what seems to be a solid sphere, a rebuttal letter from July 22, where a reader takes him to task for the concept, and a reply from Dyson somewhat later where he clarifies his position to that of the “cloud.” The scans are made from crappy photocopies I made… yikes, about 18 years ago.
5 Responses to “The Dyson Sphere”
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I LOVE dyson sphere stuff in SF!
Most recently, I read a manga where the sphere was created mostly by accident (if you can imagine such a thing) by construction ‘bots over the course of tens of thousands of years. What started as some building projects on earth ended up engulfing the moon and (as some have postulated since the manga is pretty vague about some things) the sun as well. It’s called BLAME if the fancy strikes of checking it out.
Scott,
Just a couple of things, but first get a couple of aspirin (or your analgesic of choice) and take them.
First, envision a cross section of a solid Dyson Sphere (aka a Ringworld) with no spin. Got it? Okay, the number one way to give you surface gravity (other then gravity generators {talk about a Union Job!}, or one of the other things you mentioned) is to use high density unobtainium like Charles Sheffield did with MacAndrew’s ‘balanced drive’. So let’s use something like that that so you get 1 gravity about 20 feet from it’s surface (need somewhere for the dirt to support the trees, bury the cables and pipes).
Now, pull out the Physics 101 2D Rubber Sheet. Drop in the nominal Sun and add in the Dyson Sphere Cross Section and finally lay your first schematic down on it.
You’ll see that the Purple Guy, due to his proximity to Area A1, has his feet … well, is laying down, firmly on the ground and is not affected by the gravity of Area A2.
Okay, now make the Dyson Sphere Cross Section a whole Sphere and instead of the Rubber Sheet change it into a 3D wire matrix that contracts in correspondence to how the Rubber Sheet stretched.
I told you to take a couple of aspirin before we started.
You can blame David Gerrold for that last part, I got it from ‘Space Skimmer’.
Second, now to envision one the way Freeman Dyson wanted it (a bunch of space settlements) we turn to Howard Taylor … who also makes an interesting comment on what would happen to the language lexicon of any species that built one. http://www.schlockmercenary.com/d/20010702.html And later how it has more in common with a Solar Sail. http://www.schlockmercenary.com/d/20020309.html
I’m not seeing how the unobtanium is generating a useful gravity on the inner surface of the sphere. Unless the unobtanium generates gravity that dies off with distance in a way different than gravity does with regular matter (inverse square law), then it doesn’t matter how dense the material of the shell is… it’ll still be null-G on the inside of the shell.
For the more ‘obscure’ relating suggestion the book “The Millennial Project: Colonizing the Galaxy in 8 Easy Steps” by Marshall Savage
http://en.wikipedia.org/wiki/Living_Universe_Foundation
presents as “Step-7: Solaria” the idea that once people learn to really LIVE in-space (Step-4: Asgard where a VERY large Geosynchronus space station is built {actually Asgard consists of a number of inflatable “bubble” membrane spheres supported by multi-strand outer cable nets} as a developmental testing ground for the purposes using both mechanical and biological systems to make them as self supporting as possible) they will eventually build enough habitats to be intercepting a major portion of stellar output. Part of Solaria is the establishment of solar power generation statites (http://en.wikipedia.org/wiki/Statite) well within the orbit of Mercury that “hover” over the surface by the solar wind. Each Statite then beams power from there to users throughout the solar system.
Eventually the author notes that if enough of these habitats are built they will not only lower our suns apparent output as seen from oustide our solar system, but might even change our suns “color” as seen by an outside observer!
(He uses algae a lot as the basis of a lot of the biological processing systems and the bubble habitats are basically ‘clear’ but photo protective double-hull with water running between the skins to even out internal temperaturs, eventually our solar output light would look “green’ to any observers :o)
While Mr.Savage himself “moved-on” from the group created to help get “Step-1: Foundation” started, there are still many active members. Many of which are currently looking into updating and re-concepulizing the original ideas. See TMP2:
http://tmp2.wikia.com/wiki/Main_Page
Randy
Oh how could I have forgotten? Larry Niven also did an article on “Macro-Structures” for Analog where he mentioned another “Ring-Sphere” suggestion where the rings each inclined a bit and were slightly smaller to negate the low-solar angle issue. Not my favorite concept though as the accompanying illustration looked more like a fur-ball and would have been a nightmare of active station keeping :o)
Since you were having to mine nearby stars to get material for the additional ring-worlds I couldn’t actually see the point, but we’re talking “super-tech-advanced” abilities with probable boardom being a racial problem. Call it performance art and leave it for those who come later to figure it out :o)
Randy