Proponents of solar power know that only a tiny fraction of the sun’s total energy strikes the Earth. What if we, as a civilization, could collect all of the sun’s energy? If so, we would use some form of Dyson sphere, sometimes referred to as a Dyson shell or megastructure. Physicist and astronomer Freeman J. Dyson first explored this idea as a thought experiment in 1960. Dyson’s two-page paper in the journal Science was titled Search for Artificial Stellar Sources of Infrared Radiation because he was imagining a solar-system-sized solar power collection system not as a power source for us earthlings, but as a technology that other advanced civilizations in our galaxy would, inevitably, use. Dyson proposed that searching for evidence of the existence of such structures might lead to the discovery of advanced civilizations elsewhere in the galaxy, and indeed, in 2013, several groups of astronomers have begun a search for the telltale signs of Dyson spheres.
Originally, some envisioned a Dyson sphere as an artificial hollow sphere of matter around a star, and Dyson did originally use the word shell. But Dyson didn’t picture the energy-collectors in a solid shell. In an exchange of letters in Science with other scientists, following his 1960 Science article, Dyson wrote:
A solid shell or ring surrounding a star is mechanically impossible. The form of ‘biosphere’ which I envisaged consists of a loose collection or swarm of objects traveling on independent orbits around the star.
A Dyson sphere might be, say, the size of Earth’s orbit around the sun; we orbit at a distance of 93 million miles (about 150 million kilometers). The website SentientDevelopments describes the Dyson sphere this way:
It would consist of a shell of solar collectors (or habitats) around the star. With this model, all (or at least a significant amount) of the energy would hit a receiving surface where it can be used. [Dyson] speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization.
And of course science fiction writers have had a field day writing about Dyson spheres. In fact, Dyson admitted he borrowed from science fiction before he began his technical exploration of the idea of a megastructure gathering energy from its star. Olaf Stapledon first mentioned this idea in his 1937 science fiction novel Star Maker, which Dyson apparently read and used as inspiration.
As mentioned above, astronomers in 2013 are now seriously discussing the search for evidence of Dyson spheres in the space of our Milky Way galaxy. Frustrated by decades of seeking radio signals from intelligent civilizations beyond Earth – and not finding any – a few have begun to contemplate this new search strategy. What would they be looking for? Consider that if a system of solar power collectors – a megastructure – were put in place around a star, the star’s light, as seen from our perspective, would be altered. The solar collectors would absorb and reradiate energy from the star. It’s that reradiated energy that astronomers would need to seek.
Stephen Battersby at New Scientist wrote a great article about this search, released in April 2013. The article is available by subscription only, but if you search on the title (“Alien megaprojects: The hunt has begun”), you might find an alternative link.
There’s also a very cool diagram published in New Scientist that helps explain astronomers’ new search, which you can see
Bottom line: A Dyson sphere would consist of orbiting solar collectors in the space around the star of an advanced civilization. The goal would be to ensure a significant fraction of the star’s energy hit a receiving surface where it could be used to the civilization’s benefit. Freeman J. Dyson, who in 1960 became the first scientist to explore this concept, suggested that this method of energy collection be inevitable for advanced civilizations. In 2013, some groups of astronomers are seriously discussing the best ways to search for Dyson spheres in the space of our Milky Way galaxy.