For generations, the Dyson Sphere has fired the imaginations of scientists. However, a growing body of research indicates that megastructures are impractical. This could have implications for the Search for Extraterrestrial Intelligence (SETI). In 1960, famed British-American theoretical physicist Freeman Dyson made a radical proposal that shook up the search for extraterrestrial intelligence (SETI). In short, Dyson hypothesized that advanced civilizations (driven by population pressures and the growing need for energy) might eventually be forced to create massive structures capable of enclosing their entire star. This structure became known as a " " in Freeman's honor. According to Dyson, a structure of this kind could harness all the energy of a star while increasing the habitable volume of an advanced civilization by orders of magnitude. Moreover, Dyson proposed a way for SETI researchers to search for these structures by looking for their infrared (heat) signatures. Since he first made this proposal, scientists have considered many other possible types of megastructures. While some, like the Niven Ring (or Ringworld), , and , are variations on Dyson's original idea, other ideas have been a bit more exotic - like the , the , and the . These concepts are often collectively called “Dyson Structures” in recognition of Dyson’s original idea. There was even speculation that humanity had found possible evidence of a back in 2017 when astronomers began noticing periodic dips in the brightness of KIC 8462852 (aka. ). While subsequent research found other plausible explanations for the phenomenon, the incident piqued interest in the subject of " ." However, some scientists disagreed with many of the arguments put forth in Dyson’s paper. For instance, many engineers have criticized his proposal from a structural standpoint, claiming that such a sphere would be extremely difficult to build, impractical, and subject to all kinds of hazards and challenges. After more than sixty years of debate, is it time to reconsider Dyson Spheres and megastructures as a possibility? The answer to this question could have significant implications for SETI as scientists continue to probe the depths of space, looking for the technosignatures that indicate the presence of advanced civilizations. Origins of the Concept Dyson’s proposal first appeared in a paper titled " ,” published in the journal on June 3, 1960. At the time, the search for extraterrestrial intelligence (SETI) was very much in its infancy. In fact, the very first SETI experiment — , led by Cornell Professor — was taking place at the Greenbank Observatory when Dyson’s paper came out. In response to proposals that radio antennas be directed toward nearby stars to listen for extraterrestrial transmissions, Dyson offered another possibility. Dyson theorized that extraterrestrial civilizations would likely be older and thus more advanced than humanity, given the age of the Universe (13.8 billion years) and the fact that Earth and the Solar System had only formed within the last 4.5 billion years. Therefore, Dyson argued, it was necessary to consider how an advanced civilization might ensure it had enough space to expand. Dyson surmised that the material factors that limit the expansion of a technically advanced species are “the supply of matter and the supply of energy.” In that same vein, he posited that the quantities of matter and energy accessible to humanity in the Solar System were 2 x 10 grams (the mass of Jupiter) and 4 x 10 ergs per second (the total energy output of the Sun). Based on these two figures, the concept of the Dyson Sphere was born. As he : The idea had an immediate impact on astronomers and SETI researchers, including well-known astronomers and science communicators Carl Sagan and Russel Walker. In 1966, they published a paper titled “ ,” arguing that existing infrared space telescopes could detect Dyson structures within the local arm of our galaxy. They also recommended that IR signatures be paired with other technosignatures like “monochromatic radio-frequency emissions” to distinguish Dyson structures from “naturally occurring low-temperature objects” like Y-type (brown dwarf) or M-type (red dwarf) stellar objects. A Question of Scale Dyson’s groundbreaking idea predicted another major contribution to the field of SETI. In 1964, famed Soviet and
Russian astrophysicist and radio astronomer published a paper titled “ .” Kardashev’s goal with this paper was to suggest what types of radio frequencies (and at what energies) SETI researchers should look for. Kardashev theorized that these civilizations, older and more advanced than humanity, could harness levels of energy inaccessible to humans. To characterize the potential level of a civilization’s development, Kardashev proposed a three-level scale based on the amount of energy they could harness. This Scale included: Type I – Planetary Civilizations: This refers to those that have developed the means to harness and store all of their home planet’s energy. According to Kardashev, this would amount to the consumption of 4 x 10 erg/sec, which would likely be in the forms of fusion power, antimatter, and renewable energy on a global scale. Type II – Stellar Civilizations: These civilizations have evolved to the point where they can harvest all the energy emitted by their star. In this case, this would work out to a consumption of 4×10³³ erg/sec. Type III – Galactic Civilizations: These civilizations could harness the energy of an entire galaxy, which would work out to energy consumption on the order of 4 x 10 erg/sec. Regarding Type II Civilizations, Kardashev mentioned Dyson’s concept and cited his original paper. Feasibility Over time, Dyson’s proposals have been met with a combination of criticism and endorsement. On the one hand, some scientists agree that there is sufficient material in the Solar System to build it. After looking at the mathematics of building a Dyson Sphere, theoretical cosmologist and science communicator, concluded that building the shell itself (based on the specifications) was : On the other end of things, critics challenge Dyson’s central claim that Jupiter possesses enough material to build a shell. For example, in his proposal paper, Dyson did not acknowledge that only a fraction of the planet’s mass would be suitable for construction purposes. This includes the rocky interior and metallic core, which comprise just 13% of the planet’s mass fraction. Meanwhile, hydrogen and helium make up 87 percent of the planet’s mass. Between Jupiter’s atmosphere and its rocky/metallic core is a mantle composed of “metallic hydrogen,” where the gravitational pressure condenses hydrogen until it forms a solid. Whether or not this hydrogen can remain in its metallic state (metastable) once the pressure is removed remains a contentious issue. In 2016, a team of Harvard scientists announced that they had using a diamond vice and that the sample was metastable. However, these claims were met with skepticism, and the team did not attempt to repeat the experiment. In 2022, another Harvard team and found that the hydrogen became unstable once pressure was removed. In short, once Jupiter is dismantled, 87 percent of its mass would revert to its gaseous state and be lost to space. While the remaining 13 percent would still be abundant, more planets would likely need to be demolished to provide sufficient building materials. Smashing planets?! Another point raised by critics is the ethics of dismantling planets to create an artificial megastructure. Would a species really be willing to destroy the planets in its own solar system and change the nature of that system forever? This was discussed In a by Narasimha et al., a team of scientists from the : Moreover, Dyson’s idea was based partly on , which states that population growth will invariably outstrip a species’ resource base. This theory, originally proposed in 1798, has been criticized for centuries by scientists and scholars for its failure to account for technological advancement and other factors influencing population dynamics. For example, periods of rapid population growth have stimulated technological innovation that has allowed humans to make their resources go further. A by the U.S. Geological Survey (USGS) addressed the persistent fear that population growth would outstrip mineral resources. However, using specific examples, the paper concluded that historically, technology has helped to ease resource constraints. A similar study produced by the Ifo Institute for Economic Research considered Malthusian principles alongside Boserup's Theory, which posits that population growth drives technological innovation (especially concerning food production). Their conclusions stated that: Lastly, there is a well-established connection between development and birth rates, where increased living standards and access to medical care stabilize population growth. According to the report compiled by the UN Department of Economic and Social Affairs, the continued rise of populations worldwide in this century will be mirrored by declining fertility rates, eventually leading to a state of equilibrium by 2100. Protections! But the most compelling argument for why a Dyson Sphere would not work is how it would expose its inhabitants to natural hazards. As Narasimha et al. indicated in a , this would include hazards from within: What’s more, enclosing our star would mean that the solar wind that usually reaches the edge of our system would be trapped inside the shell. Where these charged particles meet the interstellar medium (ISM), the is formed. This giant bubble protects the Solar System from galactic cosmic radiation. Ergo, enclosing the Sun would mean that the resulting shell would be exposed to very high doses of harmful radiation. Furthermore, there’s also the argument that the vast resources of the Solar System would have better uses than as simple building material. For example, the vast amounts of hydrogen and helium-3 could provide abundant energy for fusion reactors and nuclear
spacecraft. The abundant ice in the Main Asteroid Belt, Kuiper Belt, and elsewhere could provide abundant drinking water and drought relief. Meanwhile, all the silicate minerals and metals could be harvested as building materials, which could be fashioned into many smaller “islands” in space like rotating space stations (aka. Stanford Toruses and ). Implications for SETI? Considering the downsides and expense, why would an advanced species build a Dyson Sphere? Is it inevitable that Malthusian pressures and the need for energy would force a species to destroy the very worlds it came from and rely on just to increase the amount of living space available? Wouldn't developing more advanced technologies — like fusion power, nanotechnology, and massive space stations — meet their needs sufficiently? Dyson was clear in his original paper that this was merely a thought experiment. And while he was a bit scant on details in the original paper, he later clarified what he meant by “shell” and “biosphere,” : "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." Nevertheless, these considerations could have implications for future . Should our telescopes be looking for sources of infrared radiation that indicate the presence of “swarms" of artificial structures? Or should they concentrate on other potential technosignatures, such as spillover from optical transmissions and directed energy, bands of satellites around a planet, and good old-fashioned radio waves? All that we know for certain is that the search will continue! And whatever we find, once we find it, will be a total game-changer. As famed scientist and futurist Arthur C. Clarke said in the Foreward to his novel , “This is only a work of fiction. The truth, as always, will be far stranger.”