ADyson sphere is a hypotheticalmegastructure that encompasses astar and captures a large percentage of itspower output.[1][2][3] The concept is athought experiment that attempts to imagine how aspacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the homeplanet's resources alone. Because only a tiny fraction of a star's energy emissions reaches the surface of any orbiting planet, building structures encircling a star would enable a civilization to harvest far more energy.
The earliest modern imagining of such a structure was byOlaf Stapledon in his science fiction novelStar Maker (1937). The same concept was later used by physicistFreeman Dyson in his 1960 satirical[4][5] paper "Search for Artificial Stellar Sources ofInfrared Radiation".[6] Dyson speculated that such structures would be the logical consequence of the escalating energy needs of a technological civilization and would be a necessity for its long-term survival. A signature of such spheres detected in astronomical searches would be an indicator ofextraterrestrial intelligence.
Since Dyson's paper, many variant designs involving an artificial structure or series of structures to encompass a star have been proposed inexploratory engineering or described inscience fiction, often under the name "Dyson sphere". Fictional depictions often describe a solid shell of matter enclosing a star – an arrangement considered by Dyson himself to be impossible.
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Inspired by the 1937science fiction novelStar Maker byOlaf Stapledon,[7] the physicist and mathematicianFreeman Dyson was the first to formalize the concept of what became known as the "Dyson sphere" in his 1960Science paper "Search for Artificial Stellar Sources of Infra-Red Radiation". Dyson theorized that as the energy requirements of an advanced technological civilization increased, there would come a time when it would need to systematically harvest the energy from its local star on a large scale. He speculated that this could be done via a system of structures orbiting the star, designed to intercept and collect its energy. He argued that as the structure would result in the large-scale conversion of starlight intofar-infrared radiation, an earth-based search for sources of infrared radiation could identify stars supporting intelligent life.[6]
Dyson did not detail how such a system could be constructed, simply referring to it in the paper as a "shell" or "biosphere". He later clarified that he did not have in mind a solid structure, saying: "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."[8] Such a concept has often been referred to as aDyson swarm;[9] however, in 2013, Dyson said he had come to regret that the concept had been named after him.[10] In an interview withRobert Wright in 2003, Dyson referred to his paper on the search for Dyson spheres as "a little joke" and commented that "you get to be famous only for the things you don't think are serious",[11][5] later explaining that "And of course the joke is that the sky is crawling with infrared sources which look just the way a Type II civilization might look, so there is absolutely no reason to believe that they are artificial ... from our distance they would look the same".[12] However, in a later interview with students from The University of Edinburgh in 2018, he referred to the premise of the Dyson sphere as being "correct and uncontroversial".[13] In other interviews, while lamenting the naming of the object, Dyson commented that "the idea was a good one", and referred to his contribution to a paper on disassembling planets as a means of constructing one.[14]
Dyson-style energy collectors around a distant star would absorb and re-radiate energy from the star. The wavelengths of such re-radiated energy may be atypical for the star'sspectral type, due to the presence of heavy elements not naturally occurring within the star. If the percentage of such atypical wavelengths were to be significant, an alien megastructure could be detected at interstellar distances.[6] This could indicate the presence of what has been called a Type IIKardashev civilization.[15]
SETI has looked for such infrared-heavy spectra fromsolar analogs, as hasFermilab.[16][17] Fermilab discovered 17 potential "ambiguous" candidates, of which four were in 2006 called "amusing but still questionable".[16] Later searches also resulted in several candidates, all of which remain unconfirmed.[18][19][20]
On October 14, 2015,Planet Hunters' citizen scientists discovered unusual light fluctuations of the starKIC 8462852 raising press speculation that a Dyson sphere may have been discovered.[21][22] However, subsequent analysis showed that the results were consistent with the presence of dust.[23][24] A further campaign in 2024 identified seven possible candidates for Dyson-spheres, but further investigation was said to be required.[25][26]
In 2024 there was press speculation that potential signs of interstellar Dyson spheres had been discovered. The seven objects of interest – all located within a thousand light-years of Earth – wereM-dwarfs, a class of stars that are smaller and less luminous than the Sun. However, the authors of the findings were careful not to make any overblown claims.[27] Despite this, many media outlets picked up on the story. Less fantastical explanations included a suggestion that the detected infrared was caused by distant dust-obscured galaxies.[28][29][30]
Although Dyson sphere systems are theoretically possible, building a stable megastructure around the Sun is currently far beyond humanity's engineering capacity. The number of craft required to obtain, transmit, and maintain a complete Dyson sphere exceeds present-day industrial capabilities.George Dvorsky has advocated the use ofself-replicating robots to overcome this limitation in the relatively near term.[31] Some have suggested that Dyson sphere habitats could be built aroundwhite dwarfs[32] and evenpulsars.[33]
Stellar engines are hypothetical megastructures whose purpose is to extract useful energy from a star, sometimes for specific purposes. For example,Matrioshka brains have been proposed to use energy extracted by Dyson Spheres for computation, whileShkadov thrusters would extract energy for propulsion. Some proposed stellar engine designs are based on the Dyson sphere.[34][35]
A precursor to the concept of Dyson spheres was featured in the 1937 novelStar Maker byOlaf Stapledon,[1] in which he described "every solar system... surrounded by a gauze of light-traps, which focused the escaping solar energy for intelligent use";[36] Dyson got his inspiration from this book and suggested that "Stapledon sphere" would be a more apt name for the concept.[37] Fictional Dyson spheres are typically solid structures forming a continuous shell around the star in question, although Dyson himself considered that prospect to be mechanically implausible.[2][3] They are sometimes used as the type of plot device known as aBig Dumb Object.[38]
Dyson spheres appear as a background element in many works of fiction, including the 1964 novelThe Wanderer byFritz Leiber wherealiens enclose multiple stars in this way.[1][38][39] Dyson spheres are depicted in the 1975–1983 book seriesSaga of Cuckoo byFrederik Pohl andJack Williamson, and one functions as thesetting ofBob Shaw's 1975 novelOrbitsville and its sequels.[2][3] In the 1992 episode "Relics" of the TV showStar Trek: The Next Generation,[40] theUSS Enterprise finds itself trapped in an abandoned Dyson Sphere;[41][42] in a 2011 interview, Dyson said that he enjoyed the episode, although he considered the sphere depicted to be "nonsense".[43]Michael Jan Friedman who wrote the novelization observed that in the TV episode itself the Dyson sphere was effectively aMacGuffin, with "just nothing about it" in the story, and decided to flesh out the plot element in his novelization.[44]: ix
Other science-fiction story examples includeTony Rothman'sThe World Is Round,Somtow Sucharitkul's Inquestor series,Timothy Zahn'sSpinneret,James White'sFederation World,Stephen Baxter'sThe Time Ships, andPeter F. Hamilton'sPandora's Star.[1]: 133 Variations on the Dyson Sphere concept include a single circular band inLarry Niven's 1970 novelRingworld,[3][45][46] a half sphere in the 2012 novelBowl of Heaven byGregory Benford and Niven,[2][3] and nested spheres – also known as aMatrioshka brain – inColin Kapp's 1980sCageworld series andBrian Stableford's 1979–1990Asgard trilogy.[1][3]
Stableford himself observed that Dyson spheres are usually MacGuffins or largely deep in the backgrounds of stories, giving as examplesFritz Leiber'sThe Wanderer andLinda Nagata'sDeception Well, whereas stories involving space exploration tend to employ the variants like Niven'sRingworld.[1]: 133 He gives two reasons for this: firstly that Dyson spheres are simply too big to address, which Friedman also alluded to when pointing out that the reason his novelization of "Relics" did not go further into the sphere was that it was only four hundred pages and he had just shy of four weeks to write it; and secondly that, especially for hard science-fiction, Dyson spheres have certain engineering problems that complicate stories.[1]: 133 [44]: ix In particular, since gravitational attraction is in equilibrium inside such a sphere (per theshell theorem), other means such as rotating the sphere have to be employed in order to keep things attached to the interior surface, which then leads to the problem of a gravity gradient that goes to zero at the rotational poles.[1]: 133 Authors address this with various modifications of the idea such as the aforementionedCageworld nesting,Dan Alderson's double sphere idea, and Niven's reduced Ringworld (discussed in "Bigger Than Worlds" andRingworld § Influence).[1]: 133
Some science fiction writers have wrongly given me the credit of inventing the artificial biosphere. In fact, I took the idea from Olaf Stapledon, one of their own colleagues
Fifty [galaxies] were red enough to be hosting aliens gobbling up half or more of their starlight.
Wright: Did they actually use the phrase 'Dyson sphere' onStar Trek?
Freeman Dyson: Oh yes.
Wright: Did they really?
Freeman Dyson: One of my daughters sent me a tape of that program afterwards and so I watched it. Oh yes, it's very clearly labeled and actually it was sort of fun to watch it, but it's all nonsense. But it's quite a good piece of cinema. [punctuation supplied for unedited transcript]
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Notes: † Never inhabited due to launch or on-orbit failure, ‡ Part of theAlmaz military program, ° Never inhabited, lacks docking mechanism. | |||||||||
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