When people say “Dyson sphere” they often picture a solid shell around a star. Freeman Dyson himself never meant that. In his 1960 paper in Science he wrote that a solid shell or ring surrounding a star is mechanically impossible, and instead described “a loose collection or swarm of objects traveling on independent orbits around the star”. That swarm is what is now called a Dyson swarm.
Why not a shell?
A rigid shell around a star has no stable position. Gravity does not hold it in place, so any small push would send it drifting until it struck the star, and no known material could bear the stresses. A swarm avoids both problems. Each collector is its own satellite on its own orbit, like the countless asteroids of the asteroid belt, and nothing has to hold the whole thing together.
What is at stake
The Sun puts out 3.828 × 10²⁶ watts. In 2021 all of humanity used about 18.87 terawatts, so the Sun gives off about 20 trillion times more power than our whole civilisation consumes. Earth intercepts less than a billionth of it. A swarm that caught most of it would put a civilisation at Type II on the Kardashev scale, the level of using the energy of an entire star.
The swarm would not need to be finished to be useful. It could start with a single collector and grow, with each new one adding power for building the next.
Variations
Engineers and writers have imagined several forms:
- A Dyson swarm: collectors and habitats on independent orbits, spread over many orbital planes.
- A Dyson bubble: collectors that do not orbit at all but hover, held up by the pressure of sunlight against their thin sails. Such a “statite” was named by the physicist Robert L. Forward, who patented a design in 1993.
- A Dyson ring: the simplest start, with all collectors sharing one orbit.
How we would see one
Whatever its shape, a swarm cannot destroy energy. Its collectors would warm up and radiate the waste as infrared heat, which is why Dyson suggested searching for stars with too much infrared light. Searches have found candidates, most recently seven red dwarfs flagged by Project Hephaistos II in 2024, but all have possible natural explanations and none is confirmed.