It is becoming increasingly obvious that the planet's natural resources are being used up at an unsustainable rate. An increasingly industrial East competes with a West built on air-conditioning units and the push rod V8 for the limited mineral energy contained in the Earth. Meanwhile, an almost infinite source of energy burns above our heads - the Sun. In 1959, physicist Freeman Dyson produced a paper on 'Search for Artificial Stellar Sources of Infra-Red Radiation' in which he stated that an advanced society could trap all the energy being produced by a star by constructing a vast structure that would encircle the star.
Your Basic Guide to a Dyson Sphere
A sphere of material that totally encompassed a star was first suggested by Olaf Stapledon in his novel Star Maker. There are a number of proposed types of Dyson sphere.
Type I1 Dyson Sphere - the Dyson Swarm
The structure that Dyson suggested would have been a large number of artificial satellites which would either be habitats or solar energy collectors. Dyson swarms are the easiest to contemplate constructing as they can be put together over a long period of time. The problem with swarms is orbital mechanics. Imagine millions of large lumps of rock orbiting a star at all conceivable angles; the gravity of each of the satellites and of the star would make trying to plot the orbital paths of each of the points in the system nearly impossible.
If all the rocks were arranged in a ring (like one of Saturn's rings) then the orbital paths would not overlap, but only a fraction of the star's energy would be harnessed. As more and more rings are introduced, more and more energy is harnessed. However, the system becomes more and more complex and the greater the chances of one satellite casting a shadow over another one.
A swarm is not too far beyond the technology of the human race.
Type II Dyson Sphere – the Dyson Shell
This is the real deal, a complete shell of material encompassing the star. The sphere can trap all the energy that a star gives out. The basic construction of a shell is incredibly difficult because until it is fully constructed it will be attracted to the star inside.
Once it is complete, it will need to have thrusters on the outside, otherwise any impact will cause the shell to drift towards the star, eventually striking it and melting. This is because the star's gravity is averaged out over the sphere and has no effect on its motion, so once it is moving, it will obey Newton's laws and carry on.
There is also the question of internal gravity. Inside the sphere the only gravity will be that of the star. To get artificial gravity one would have to spin the whole structure.
Construction of a shell is far beyond our present level of technology.
The Dyson Bubble
The bubble is a version of the swarm. Instead of the satellites orbiting the star, they are stationary statites2. They take the form of huge sails that use the pressure of the light coming out of the star to counteract the gravity. This version of the sphere would use less material than the other ones, but it would need a huge advance in material science to produce a solar collector that is light enough.
Larry Niven's concept of a ring stretching all the way around the star is featured in his Ringworld books. It can be thought of as a slice of a shell. This system was proposed as a solution to the problem of spinning a shell where only the middle is habitable. A ringworld, like a Type II shell, is not dynamically stable and needs station-keeping thrusters.
Dyson Sphere in a Vacuum - the Science Behind a Dyson Shell
This is a basic outline of some of the science behind the shell. We will assume that the star is an unregarded yellow Sun much like our own, and that the sphere will be built out to a distance of 1 AU (the average orbital distance of our utterly insignificant blue-green planet).
As stated above, inside a shell, the only gravity acting on a point will be the star's itself, the effect of which is about 1,000 times smaller than the gravity we feel on Earth. There is a set of equations to prove that the shell has no gravitational influence on a point inside it. So now we are left with the gravity of the Sun. Since the shell is spherical, the star acts on all points of it equally and the system is balanced. This equilibrium is knocked out of balance by any small impact by meteorites to the outside of the shell, which will cause the shell to drift towards the star. A Dyson shell would need some form of station-keeping thrusters to be able to keep the shell a constant distance from the star.
Constructing a spinning shell would seem to be the answer to keeping atmosphere and people on the inner surface of the shell, but to get the required effect, it would need to rotate roughly once every nine days. The stresses involved in getting 181,000,000,000,000,000,000,000 tonnes3 of shell to spin at this high speed would be immense and certainly beyond any foreseeable advances in engineering and material science.
Another failing of a spinning sphere would be that all the gases making up the atmosphere would be drawn into the equator, rendering most of the surface of the sphere uninhabitable.
Niven pointed out that if one wanted to make a spinning structure, it would be simpler to make it cylindrical. The structural engineering is less complex and you wouldn't have the problem of the atmosphere wandering off.
How much land area would a Dyson shell give?
The obvious answer is more than we could possibly use.
The surface of a sphere at 1 AU is about 500,000,000 times larger than the surface of the Earth, or somewhere in the region of 9,270,000,000,000 Belgiums.
How would we live on the shell?
There are two obvious ways that a shell could be populated. The first is that we live on it as we do on Earth, wandering free across the inner surface. Obviously for this we need some form of gravity to keep us and the atmosphere on the surface. If we used the spinning method mentioned above, this could mean that most of the sphere towards the poles would be uninhabitable because the gravity would drag everything to the equator; however, the polar areas could be fully utilised for energy collection. Also there would have to be some way of blocking out the star's light to create night and day. This would be vitally important if we were to bring other life forms with us.
The second way would be to live in domes or other sealed structures on the surface. It may be possible to live in domes without artificial gravity. It would mean that we could control night and day and be protected against the harmful effects of the Sun.
It would be likely that the inside surface of the sphere would be flat. Because of the amount of matter needed to build the shell, there would not be much left over to make into terrain.
How Much of the Star's Energy Would it Capture?
This is another easy question to answer: all of it.
A Dyson shell would collect about two thousand million times the solar energy as the Earth.
So Hang on, Won't it get Rather Hot?
Yes - even if most of the collected energy is stored, without active cooling, the interior of a Dyson shell would keep heating up. This leads to three rather major problems. The first is that a civilisation could not exist on the inside without a vast amount of protection. The second is that as the temperature in the interior heats up, it will affect the thermal equilibrium of the star, which would cause the star to expand. The third is that the materials that the shell is made from would probably give up the ghost with the heat when the temperature reaches a couple of thousand degrees.
The main reason the Dyson sphere heats up to such high temperatures and the Earth doesn't is that the star heats up all the space inside of the sphere, so it's not just the shell, but the interior that heats up. Also, Earth's rotation adds to the cooling effect, as the sunny side becomes the dark side 12 hours later and so can lose the heat it has gained. The inner surface of a Dyson shell cannot have a dark side, so the heat has to be transferred to the outside surface for radiative cooling into space. This has to be done using come kind of heat transfer system because natural conduction would mean that the inner surface would get far too hot.
Another, related problem is the solar wind, the stream of ions and radiation that the Sun sends out. If the engineers have managed to figure out a way for there to be an atmosphere, active cooling and gravity so that people can live on the surface, they would also have to conjure up a magnetic field to deflect the harmful radiation (in the same way the Earth's does) and also somewhere to send it. They would also find that the atmosphere would become increasingly hydrogen-rich because of the influx of ions.
So is there Enough Matter in the Solar System to Make a Shell?
Dyson said that there was enough matter in the planets and minor planets to make a 3m-thick shell around the sun at a distance of 1 AU. The problem with this reasoning is that Jupiter and Saturn are mainly unusable hydrogen and helium. It could be suggested that these elements can be changed to more usable elements through fusion, but if we had developed fusion on the scale required, there would be no need to make a Dyson shell as an energy-capturing device.
We know that all the inner planets are useable, as are the asteroids, Pluto and the moons of the gas giants. Jupiter and Saturn have iron cores and the other gas giants have a large amount of usable material.
If we could use all the usable matter to construct our Dyson shell, we would have a shell 8cm thick. It would be unlikely that this could withstand the structural forces of a stationary shell, let alone a spinning one.
Okay, so we can't Build one now, but has Anybody Else?
Believe it or not, there have been a number of searches to see if Dyson spheres can be detected. Not surprisingly, these searches have drawn a blank. What were they looking for?
Type I Dyson swarms should be easy enough to spot visually, as they do not completely cover the star, it should be possible to see them behind the satellites. But a Type II shell is not going to be visible. It should be possible to guess at the location of one by analysing the motions of nearby stars to detect the gravity of the enclosed star. The shell would be heated up due to having the star inside, and it is radiating away the waste heat. If we search the infrared spectrum we may be able to find signs of a sphere.
So How about Living on the Outside?
If we chose to live on the outside of a shell, we could use the gravitation of the star to hold an atmosphere to the surface. The problem is that we need to be much closer in than 1 AU. Of course, being further in means that you are closer to the surface of star and it will be hotter.
Because of this we can't consider building a sphere around a star like the Sun, but a small class M dwarf star4 could be the ideal combination of mass and luminosity. Class M stars are the most common type of star and a suitable candidate could probably be found. The sphere would be only a fraction of the size of a shell around a sun-like star, so it could be constructed much more solidly.
People living on the outside surface of a Dyson sphere would have to rely on artificial lighting as there is obviously no nearby star to light the surface.
Non-Stellar Dyson Spheres
A couple of other applications have been suggested for Dyson spheres.
The Gas Giant Sphere
The planet Jupiter produces a great deal of heat. If a shell is built at a distance around the planet that would give surface gravity equivalent to the Earth's, around 112,000km, then it could use the energy given out by the planet. This is the same principle as living on the surface of a shell around a Class M dwarf.
The Black Hole Sphere
Given the difficulty that members of the human race have in working together, it is difficult to picture the organisation needed to get different species from around a galaxy together to work on a much larger Dyson sphere. Basically, all the stars and matter in the galaxy are dragged into a dense core, only a few light months across. These are arranged around the super-black hole at the centre of the galaxy. All the matter that is sucked into the black hole is converted to Hawking Radiation5 and collected by a vast sphere.
This can be done on a smaller scale, with a smaller black hole and a stellar-sized shell, asteroids, moons and waste matter fed into the hole.
Dyson Spheres in Fiction
The Dyson sphere is a symbol in science fiction of the work that a truly united race can do. Ever since Olaf Stapledon's Star Maker hit the shelves, the sphere has appeared in every branch of science fiction. The first shell was seen in Robert Silverberg's novel Across a Billion Years, and has been the most common form of the sphere in science fiction. The USS Enterprise encountered a shell in the Star Trek - The Next Generation episode 'Relics', rescuing Scotty in the process. Star Trek - Voyager saw the USS Voyager encounter a Dyson web. A Dyson web is a network of stands that surround a star. The final level in the Microsoft game Freelancer involves flying into a Dyson shell to kick alien butt.
Other books that feature the spheres are the Cageworld series by Colin Kapp, the Orbitsville series by Bob Shaw, and Farthest Star and Wall Around a Star by Frederik Pohl & Jack Williamson. Larry Niven's Ringworld series are probably the best known books dealing with Dyson spheres. In Niven's books, he realised that if the world had to spin, it was better to make a cylindrical world, hence the title.
So Who was this Dyson Fellow Anyway?
Born in Berkshire on 15 December, 1923, Freeman Dyson is no relation to the Astronomer Royal, Frank Watson Dyson. However, having somebody with the same name as him being so prominent in the field, influenced Dyson to pursue the physical sciences. His father was the composer George Dyson.
After working for the RAF during the war, he obtained a degree in mathematics from Cambridge in 1945 and became a fellow at Trinity College. He moved to America to work at Cornell University in 1947 and gained American citizenship. He has been involved in fields as varied as quantum electrodynamics and Project Orion, the nuclear-powered spaceship6. Dyson has received numerous awards and has had many papers published.