Dyson Spheres

24 10 2011

Dyson spheres are the product of a thought experiment on how an extremely advanced civilization could capture all of the energy given off by a star.  In its most extreme form, and the form that is most intriguing to science fiction writers, it consists of a shell completely surrounding a star with a radius of one Astronomical Unit (AU) or the mean distance that the Earth is from the Sun.

Presumably, this setup would allow people to live on the interior surface of the sphere providing 1/3 of a billion times the surface area of Earth on which to live.  Great idea for an expanding population who needs room to spread out.  Sounds like a necessity for a civilization that has cured most diseases and continues to grow at an exponential rate.  It would be quite a big space to grow into, however.  Consider what it would be like to transplant the current population of the earth into such an environment; every man, woman and child would be able to have 16 million square miles to themselves.  That’s a little bit smaller area than Asia.

There are many problems that said civilization would run into attempting such and engineering feat.  Let’s explore them.

1) The first problem would be where would you get all the materials to make such a large structure?  According to other people who felt like crunching numbers of that magnitude, using all of the iron in the solar system, you would end up with a shell that would be about 8 centimeters thick.  Doesn’t quite seem thick enough to handle the tremendous strain.  If you had enough energy to gather all of that material and were able to make something workable from it, why go through all the trouble of making a sphere in order to collect all of a star’s output.  Even building the thing seems iffy and that doesn’t take into account how hot the interior of the sphere would get even taking into account our ability to collect and store the solar energy.

2) The next problem I see is how to make that large of an area habitable to people.  If you wanted to say, make the entire interior of the planet into a landscape palatable to humans, where would you get all the organic material to make it possible.  There actually is a very sensible answer to this that also alleviates some of the problem with number 1 while increasing the population density from that ridiculous ‘everyone gets an Asia’ scenario.  You would only need to make parts of it habitats for humanity.  The rest can be filled with the equipment to gather and process all that energy your getting.  It also helps with our next problem a bit.

3) Gravity works funny inside a hollow sphere.  The gravity provided by the material in the sphere counteracts itself.  Let’s say you had a hollow Earth.  Would you be able to walk around on the interior of the surface?  No, you would float weightlessly.  Here is how it works: if you are near, lets say, North America inside the Earth, the gravity of the nearer smaller mass of North America pulls on you in equal amounts to the gravity of the further larger mass of the rest of the world.  Now let’s throw the sun into the center of our hollow Dyson Sphere.  The sun’s gravity would pull everything off the surface and into itself.  In fact, if you get any minor perturbation of the sphere, it will crash into the sun itself.  Sounds like a less than desirable situation to me.

I suppose if you have the technology to build one of these bad boys, you may have the technology to build artificial gravity generators to hold your population to the interior of the shell.  Since you are going to make only certain portions habitable anyway, you might as well dome those over to keep you and the air you breathe safe from falling up into the sun.

4) Now you are safely living on the interior surface of the Dyson Sphere.  Hope you like daylight, because that sun is never going to set.  It will always be high noon everywhere on the planet.  Not only will that make measuring time difficult, you will also probably end up with a lot of insomniacs.  Sure you can make the room you are sleeping in dark, but there will always be a little part of you whispering, “Hey, it’s noon, we should get up and do something.”  Maybe you could have multiple satellites orbiting between the outer surface and the star and count on eclipses to get the equivalent of night.  Sounds like a cool engineering project, but it’s nothing compared to what you accomplished to build the Dyson Sphere in the first place.

All of these problems are fixable if your technology has advanced to the point that the need for a Dyson Sphere becomes moot.  But I have an idea for how to mitigate some of these problems.

Find a binary star system with a lot of heavy metals or whatever materials you need to construct your Dyson Sphere.  Build a Dyson Sphere around the smaller of the two stars.  You can make this much smaller than the 1 AU radius sphere we were contemplating above.  Then have your people live on the outside of the sphere where gravity works for you and the larger sun rises and sets.  Problem solved.  Now all you have to do is figure out how to stop the cyclonic separation that the Dyson is known for and you’re all set.

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2 responses

25 10 2011
David Montgomery

It is always interesting to think about the theoretical. I am ready a book where they have habitats that are long cylinders. Instead of a sun, they have a sunline which is projected along the centerline of the cylinder producing just the rigth type of radiation but not too much heat for plant and animal life.

For the dyson sphere, could you limit habitation to a small band on the inside surface and have the sphere rotate fast enough for centripital force to counter act the sun’s gravity?

15 11 2011
Rey Sheedy

very interesting

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