What is a Dyson Sphere?

by Fraser Cain on September 19, 2013


As long as humans survive, we will likely be increasing our energy consumption. We want better transportation, faster computers, and stuff we just can’t imagine yet.

That’s going to take energy, and lots of it.

If you plot our overall use since the industrial era, you can see it’s a line that just goes up and up. There will come a time in the future when we’ve exhausted all the fossil and nuclear fuels. And once we’ve harvested as much wind, solar and geothermal energy as our planet can produce, we’re going to need to move out into space and collect energy directly from the Sun.

inSatellites in orbit collectg solar power.  Image: National Space Society.

Satellites in orbit collecting solar power. Image: National Space Society.

We will construct larger and larger solar arrays, beaming the energy back to Earth. Inevitably, we’ll enclose the entire Sun in a cloud of solar satellites, allowing us to make use of 100% of the radiation it’s emitting.

This is a Dyson sphere.

The concept was developed as part of a research paper in 1960 by the physicist Freeman Dyson. In a thought experiment, he assumed that the power needs for civilizations never stops increasing.

Dyson Sphere by Eburacum45

Dyson Sphere by Eburacum45

If our descendents could actually figure out how to enclose our star in a rigid shell, we’d have 550 million times more surface area than Earth has right now, and generate 384 yottawatts of energy.

Sounds great, lots of living space and free energy. But there are a host of problems.

There wouldn’t be any gravity to keep anything stuck to the surface of sphere – it would all drop down towards the star and be destroyed. The sphere would be free floating in space, and unless you could keep it balanced in relation to the star, it would eventually collide with it.

Finally, there might not be enough material to build a shell. This advanced civilization would need to make use of all our planets, asteroids and comets. In fact, even if you dismantled everything in the Solar System, you’d only have enough to build a shell about 15 cm-thick.

The physical strength of this material would have to be immense; otherwise the sphere itself would just implode and collapse into the star.

Dyson himself freely admitted that the idea of a rigid shell surrounding a star is unfeasible. Instead, he and others have proposed that civilizations would probably build a dense swarm of objects on independent orbits around their star – a Dyson cloud, or maybe a Dyson ring.

Each solar satellite would be stable on its own, and capable of beaming its energy back to some planet.

Artist's impression of a solar sail. Image credit: NASA

Artist’s impression of a solar sail. Image credit: NASA

You could also build a cloud of solar sails. These objects would be held in perfect balance between the gravity pulling them inward, and the light pressure from the Sun pushing them outward. They wouldn’t need to orbit at all to maintain a static distance from the Sun.

A full Dyson Sphere is probably impossible, but if we assume that alien civilization’s energy needs will continue to grow like ours, it makes sense to search the galaxy for megastructures. Just in case.

Even though the shell would absorb the light and high energy radiation from the star, it would still emit infrared radiation which would be detectable in our telescopes. Even a partial Dyson cloud would give off a telltale light signature as it obscured the light from a star.

This gives us yet another way we could search for extraterrestrial civilizations.

And if we did find a full Dyson sphere, out there in the Milky Way. Well, let’s just hope they’re nice aliens.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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