Engineering the implausible? Paper explores stable Dyson spheres and ringworlds
- Matt von Hippel
- May 29
- 4 min read
Artificial structures surrounding an entire star were thought to be impossible. A new calculation shows that they could be supported by the gravity of a second star.
Since the earliest days of science fiction, writers have dreamed of awe-inspiring futures where civilizations harness the full energy output of a star. Olaf Stapledon imagined a sphere encompassing a star to harvest its energy—an idea later referred to as a Dyson sphere after the physicist Freeman Dyson analyzed the possibility. Meanwhile, Larry Niven envisioned a flat ring encircling a star at Earth’s orbital distance in his novel Ringworld, filling the orbit with space for people to live.
The instability of traditional ringworlds and Dyson spheres
These “megastructures” can be fascinating, but are not always realistic. It has long been known that both ringworlds and the spheres Stapledon imagined cannot orbit a star in the same way a planet can. A ringworld, for example, would require perfect balance. Even the slightest shift will cause it to drift inward, with increasing speed, until one side collides with its star. A rigid sphere fares better, but not much: a theorem by Isaac Newton shows that nothing holds such a sphere in place—the structure would slowly drift randomly out of position. For these reasons, Dyson proposed a more feasible alternative: not a solid shell, but a “swarm” of smaller objects orbiting the star.
Sometimes, though, even science fiction’s implausible dreams can be supported. In the February 2025 issue of the Monthly Notices of the Royal Astronomical Society, space engineering professor Colin McInnes demonstrated a new loophole: both ringworlds and Dyson spheres can be stable, provided they are built in the company of not one, but two stars. In these binary star systems, the gravitational tug-of-war creates a stability that can hold a ring or sphere in place as it encircles one of the paired stars.
Physics meets science fiction: The role of the three-body problem in megastructure engineering
As a student, McInnes was inspired by science fiction, including Niven’s work. He was also impressed at an early age by the power of physics to model the world.
“When I was a high school student, we studied projectile motion in physics class, and I remember being absolutely blown away,” said McInnes, “it was like some kind of magic that you could use symbols and a bit of paper to predict the future.”
Those interests led him to a PhD in Astrodynamics from the University of Glasgow, where he is currently the James Watt Chair, Professor of Engineering Science.
McInnes has spent his career studying the challenges of engineering in space, including pioneering work on solar sails. These days, he leads a research group investigating novel space technology, like swarms of extremely small satellites. A recurring interest of his is a core problem in work in space, called the restricted three-body problem.
The restricted three-body problem concerns how a small object moves under the influence of two much more massive bodies—say, a satellite interacting with Earth and the Moon. It’s a classic problem in orbital mechanics, but McInnes had a twist in mind: what if the object isn’t a point-like satellite, but an enormous ring?
“It was the usual Friday afternoon thing, just kind of kicking some ideas about,” said McInnes.
He had known that a ring around a single object was unstable. The problem had been investigated long ago by James Clark Maxwell in an 1856 essay. Maxwell was motivated not by science fiction or engineering but by astronomy. At the time, telescopes showed that Saturn had rings but could not establish what they were made of, and physicists argued about whether they could be solid. Maxwell put the argument to rest, showing that solid rings would be unstable and arguing for rings made of many small rocks, which we now know is the correct explanation.
Along the way, Maxwell considered another option. He imagined a solid circle with a moon attached on one side, like a diamond on an engagement ring. This could be stable, but only if the “diamond” was relatively large, too big to be plausible for Saturn. McInnes found a broader principle hiding in Maxwell’s sidenote. If there are two big objects, like a pair of binary stars, then a ring or sphere can be held stable in the pair’s gravitational field. Just as Maxwell found requirements on the mass of his “diamond”, McInnes found that only certain configurations could be stable for Dyson spheres and ringworlds. The megastructure would need to encircle the smaller of the two stars, and the two stars need to have the right relationship between their masses and the size of the ring. For a ringworld, the smaller star needs to be substantially smaller than the larger. For Dyson spheres, the smaller star can be up to 1/9 the mass of the larger—parameters that exist in real-world binary systems.
Dyson spheres, SETI, and the search for alien engineering
When Dyson originally investigated Dyson spheres, he thought the idea could be useful in the search for extraterrestrial intelligence, later pursued by organizations like SETI. If we spotted a star that was unusually dim, then it might be that some alien civilization had surrounded it with a sphere. McInnes sees his work as contributing to that tradition, helping narrow down where to look. A stable Dyson sphere might survive long enough for us to notice it, and McInnes’ work establishes the physical constraints it would have to satisfy.
“Engineers from some distant civilization are working to the same book of physics as us, the same recipes,” said McInnes, “So maybe there is something we can understand by using our own imagination.”
While we remain far from building a Dyson sphere ourselves, McInnes’ work opens a new frontier in thinking about what’s physically possible. With the right stellar setup, even ideas from classic science fiction may have a stable footing in reality.
Matt von Hippel is a science journalist based in Copenhagen with a background in particle physics. He blogs weekly at 4gravitons.com, and has written for Quanta Magazine, Scientific American, and Ars Technica.
