Dyson sphere
Encyclopedia
A Dyson sphere is a hypothetical megastructure
originally described by Freeman Dyson
. Such a "sphere" would be a system of orbiting solar power satellites meant to completely encompass a star
and capture most or all of its energy output. Dyson speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization (regardless of the effects of planetary warming caused by the input of energy to the planet), and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life
.
Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering
or described in science fiction
under the name "Dyson sphere". These later proposals have not been limited to solar-power stations. Many involve habitation
or industrial
elements. Most fictional depictions describe a solid shell of matter enclosing a star, which is considered the least plausible variant of the idea (see below).
by physicist and mathematician Freeman Dyson
, when he theorized that all technological civilizations constantly increased their demand for energy. He reasoned that if our civilization expanded energy demands long enough, there would come a time when it demanded the total energy output of the Sun. He proposed a system of orbiting structures (which he referred to initially as a shell) designed to intercept and collect all energy produced by the Sun. Dyson's proposal did not detail how such a system would be constructed, but focused only on issues of energy collection.
Dyson is credited with being the first to formalize the concept of the Dyson sphere in his 1960 paper "Search for Artificial Stellar Sources of Infra-Red Radiation", published in the journal Science
. However, Dyson was not the first to advance this idea. He was inspired by the mention of the concept in the 1937 science fiction novel
Star Maker
, by Olaf Stapledon
, and possibly by the works of J. D. Bernal
and Raymond Z. Gallun
who seem to have explored similar concepts in their work.
and satellite
s using photovoltaics
might be seen as the first small steps towards building a Dyson swarm (see below for differences between these sub-types). However, the number of crafts required to obtain, transmit, and maintain a complete Dyson shell far exceeds our present-day industrial capabilities.
of matter
around a star. This perception is a misinterpretation of Dyson's original concept. In response to letters prompted by his original paper, Dyson replied, "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."
) orbiting in a dense formation around the star. This construction approach has advantages: components could be sized appropriately, and it can be constructed incrementally. Various forms of wireless energy transfer
could be used to transfer energy between components and earth.
Such a swarm is not without drawbacks. The nature of orbital mechanics
would make the arrangement of the orbits of the swarm extremely complex. The simplest such arrangement is the Dyson ring in which all such structures share the same orbit. More complex patterns with more rings would intercept more of the star's output, but would result in some constructs eclipsing others periodically when their orbits overlap. Another potential problem is the increasing loss of orbital stability when adding more elements increases the probability of orbital perturbations.
As noted below, such a cloud of collectors would alter the light emitted by the star system. However, the disruption compared to a stars overall natural emitted spectrum would most likely be too small to be noticed on earth.
A second type of Dyson sphere is the "Dyson bubble". It would be similar to a Dyson swarm, composed of many independent constructs (usually solar power satellites and space habitat
s) and likewise could be constructed incrementally.
Unlike the Dyson swarm, the constructs making it up are not in orbit around the star, but would be statite
s—satellites suspended by use of enormous light sails using radiation pressure
to counteract the star's pull of gravity. Such constructs would not be in danger of collision or of eclipsing one another; they would be totally stationary with regard to the star, and independent of one another. As the ratio of radiation pressure
and the force of gravity from a star are constant regardless of the distance (provided the statite has an unobstructed line-of-sight to the surface of its star), such statites could also vary their distance from their central star.
The practicality of this approach is questionable with modern material science, but cannot yet be ruled out. A statite deployed around our own sun would have to have an overall density
of 0.78 grams per square meter of sail. To illustrate the low mass of the required materials, consider that the total mass of a bubble of such material 1 AU in radius would be about 2.17 kg, which is about the same mass as the asteroid Pallas
.
Such a material is currently beyond our ability to produce; the lightest carbon-fiber light sail material currently produced has a density – without payload – of 3 g/m², or about four times as heavy as would be needed to construct a solar statite.
However, there has been some speculation about the creation of ultra light carbon nanotube
meshes through molecular manufacturing techniques whose density would be below 0.1 g/m². If production of such materials on an industrial scale is feasible, and such materials could be used in light sails, the average sail density with rigging
might be kept to 0.3 g/m² (a "spin stabilized" light sail requires minimal additional mass in rigging
). If such a sail could be constructed at this areal density, a space habitat
the size of the L5 Society
's proposed O'Neill cylinder – 500 km², with room for over 1 million inhabitants, massing 3 ton
s – could be supported by a circular light sail 3,000 km in diameter, with a combined sail/habitat mass of 5.4 kg. For comparison, this is just slightly smaller than the diameter of Jupiter
's moon Europa
(although the sail is a flat disc, not a sphere), or the distance between San Francisco and Kansas City
. Such a structure would, however, have a mass quite a lot less than many asteroids. While the construction of such a massive inhabitable statite would be a gigantic undertaking, and the required material science behind it is as yet uncertain, its technical challenges are negligible compared to other engineering feats and required materials proposed in other Dyson sphere variants.
In theory, if enough statites were created and deployed around their star, they would compose a non-rigid version of the Dyson shell mentioned below. Such a shell would not suffer from the drawbacks of massive compressive pressure, nor are the mass requirements of such a shell as high as the rigid form. Such a shell would, however, have the same optical and thermal properties as the rigid form, and would be detected by searchers in a similar fashion (see below).
The variant of the Dyson sphere most often depicted in fiction
is the "Dyson shell": a uniform solid shell of matter around the star. Such a structure would completely alter the emissions of the central star, and would intercept 100% of the star's energy output. Such a structure would also provide an immense surface which many envision being used for habitation, if the surface could be made habitable.
A spherical shell Dyson sphere in our solar system with a radius of one astronomical unit
, so that the interior surface would receive the same amount of sunlight as Earth does per solid angle
, would have a surface area of at least 272 quadrillion
km2, or about 550 million times the surface area of the Earth. This would intercept the full 384.6 yotta
watt
s (3.846 × 1026 watts) of the Sun's output; other variant designs would intercept less, but the shell variant represents the maximum possible energy captured for our solar system at this point of the Sun's evolution
. This is approximately 33 trillion
times the power consumption of humanity in 1998, which was 12 terawatts.
There are several serious theoretical difficulties with the solid shell variant of the Dyson sphere:
Such a shell would have no net gravitational interaction with its englobed sun (see Shell theorem
), and could drift in relation to the central star. If such movements went uncorrected, they could eventually result in a collision between the sphere and the star—most likely with disastrous results. Such structures would need either some form of propulsion to counteract any drift, or some way to repel the surface of the sphere away from the star.
For the same reason, such a shell would have no net gravitational interaction with anything else inside it. The contents of any biosphere placed on the inner surface of a Dyson shell would not be attracted to the sphere's surface and would simply fall into the star. It has been proposed that a biosphere could be contained between two concentric spheres, placed on the interior of a rotating sphere (in which case, the force of artificial "gravity" is perpendicular to the axis of rotation, causing all matter placed on the interior of the sphere to pool around the equator, effectively rendering the sphere a Niven ring for purposes of habitation, but still fully effective as a radiant-energy collector) or placed on the outside of the sphere where it would be held in place by the star's gravity. In such cases, some form of illumination would have to be devised, or the sphere made at least partly transparent, as the star's light would otherwise be completely hidden.
If assuming a radius of one AU
, then the compressive strength of the material forming the sphere would have to be immense. Any arbitrarily selected point on the surface of the sphere can be viewed as being under the pressure of the base of a dome 1 AU in height under the Sun's gravity at that distance. Indeed it can be viewed as being at the base of an infinite number of arbitrarily selected domes, but as much of the force from any one arbitrary dome is counteracted by those of another, the net force on that point is immense, but finite. No known or theorized material is strong enough to withstand this pressure, and form a rigid, static sphere around a star. It has been proposed by Paul Birch
(in relation to smaller "Supra-Jupiter" constructions around a large planet rather than a star) that it may be possible to support a Dyson shell by dynamic means similar to those used in a space fountain
. Masses travelling in circular tracks on the inside of the sphere, at velocities significantly greater than orbital velocity, would press outwards due to centrifugal force. For a Dyson shell of 1-AU radius around a star with the same mass as the Sun, a mass travelling ten times the orbital velocity (297.9 km/s) would support 99 (a=v2/r) times its own mass in additional shell structure. The arrangement of such tracks suffers from the same difficulties as arranging the orbits of a Dyson swarm, and it is unclear how much energy would be consumed ensuring the velocity of the masses was maintained.
Also if assuming a radius of one AU, then there may not be sufficient building material in the Solar System to construct a Dyson shell. Anders Sandberg
estimates that there is 1.82 kg of easily usable building material in the Solar System, enough for a 1-AU shell with a mass of 600 kg/m²—about 8–20 cm thick, depending on the density of the material. This includes the hard-to-access cores of the gas giants; the inner planets alone provide only 11.79 kg, enough for a 1-AU shell with a mass of just 42 kg/m².
The shell would be vulnerable to impacts from interstellar bodies, such as comets, meteoroids, and material in interstellar space that is currently being deflected by the Sun's bow shock
. The heliosphere
, and any protection it theoretically provides, would cease to exist.
A bubbleworld is an artificial construct that consists of a shell of living space around a sphere of hydrogen gas. The shell contains air, people, houses, furniture, etc. It was invented to answer the question, "What is the largest space colony that can be built?" However, most of the volume is not habitable and there is no power source.
Theoretically, any gas giant
could be enclosed in a solid shell; at a certain radius the surface gravity would be terrestrial, and energy could be provided by tapping the thermal energy of the planet. This concept is explored peripherally in the novel Accelerando (and the short story Curator which is incorporated into the novel as a chapter) by Charles Stross
, in which Saturn
is converted into a human-habitable world.
Stellar engine
s are a class of hypothetical megastructure
s, whose purpose is to extract useful energy from a star, sometimes for specific purposes. For example, Matrioshka brain
s extract energy for purposes of computation; Shkadov thrusters extract energy for purposes of propulsion. Some of the proposed stellar engine designs are based on the Dyson sphere.
A black hole
could be the power source instead of a star in order to increase energy-to-matter conversion efficiency. A black hole would also be smaller than a star. This would decrease communication distances which would be important for computer-based societies as those described above.
.
The existence of such a system of collectors would alter the light emitted from the star system. Collectors would absorb and reradiate energy from the star. The wavelength(s) of radiation emitted by the collectors would be determined by the emission spectra
of the substances making them up, and the temperature of the collectors. Since it seems most likely that these collectors would be made up of heavy elements not normally found in the emission spectra of their central star–or at least not radiating light at such relatively "low" energies as compared to that which they would be emitting as energetic free nuclei in the stellar atmosphere
–there would be atypical wavelengths of light for the star's spectral type in the light spectrum emitted by the star system. If the percentage of the star's output thus filtered or transformed by this absorption and reradiation was significant, it could be detected at interstellar distances.
Given the amount of energy available per square meter at a distance of 1 AU
from the Sun
, it is possible to calculate that most known substances would be reradiating energy in the infrared
part of the electromagnetic spectrum
. Thus, a Dyson Sphere, constructed by life forms not dissimilar to humans, who dwelled in proximity to a Sun-like star
, made with materials similar to those available to humans, would most likely cause an increase in the amount of infrared radiation in the star system's emitted spectrum. Hence, Dyson selected the title "Search for Artificial Stellar Sources of Infrared Radiation" for his published paper.
SETI
has adopted these assumptions in their search, looking for such "infrared heavy" spectra from solar analog
s. Fermilab
has an ongoing survey for such spectra by analyzing data from the Infrared Astronomical Satellite (IRAS)
. Identifying one of the many infra-red sources as a Dyson Sphere would require improved techniques for discriminating between a Dyson Sphere and natural sources.
since then (see Dyson spheres in popular culture for listed examples). In fictional accounts, Dyson spheres are most often depicted as a Dyson shell with the gravitational and engineering difficulties of this variant noted above largely ignored.
Megastructure
A megastructure is a very large manmade object, though the limits of precisely how large this is vary considerably. Some apply the term to any especially large or tall building....
originally described by Freeman Dyson
Freeman Dyson
Freeman John Dyson FRS is a British-born American theoretical physicist and mathematician, famous for his work in quantum field theory, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists...
. Such a "sphere" would be a system of orbiting solar power satellites meant to completely encompass a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
and capture most or all of its energy output. Dyson speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization (regardless of the effects of planetary warming caused by the input of energy to the planet), and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...
.
Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering
Exploratory engineering
Exploratory engineering is a term coined by K. Eric Drexler to describe the process of designing and analyzing detailed hypothetical models of systems that are not feasible with current technologies or methods, but do seem to be clearly within the bounds of what science considers to be possible...
or described in science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
under the name "Dyson sphere". These later proposals have not been limited to solar-power stations. Many involve habitation
Space habitat
A space habitat is a space station intended as a permanent settlement rather than as a simple waystation or other specialized facility...
or industrial
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
elements. Most fictional depictions describe a solid shell of matter enclosing a star, which is considered the least plausible variant of the idea (see below).
Origin of concept
The concept of the Dyson sphere was the result of a thought experimentThought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...
by physicist and mathematician Freeman Dyson
Freeman Dyson
Freeman John Dyson FRS is a British-born American theoretical physicist and mathematician, famous for his work in quantum field theory, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists...
, when he theorized that all technological civilizations constantly increased their demand for energy. He reasoned that if our civilization expanded energy demands long enough, there would come a time when it demanded the total energy output of the Sun. He proposed a system of orbiting structures (which he referred to initially as a shell) designed to intercept and collect all energy produced by the Sun. Dyson's proposal did not detail how such a system would be constructed, but focused only on issues of energy collection.
Dyson is credited with being the first to formalize the concept of the Dyson sphere in his 1960 paper "Search for Artificial Stellar Sources of Infra-Red Radiation", published in the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
. However, Dyson was not the first to advance this idea. He was inspired by the mention of the concept in the 1937 science fiction novel
Novel
A novel is a book of long narrative in literary prose. The genre has historical roots both in the fields of the medieval and early modern romance and in the tradition of the novella. The latter supplied the present generic term in the late 18th century....
Star Maker
Star Maker
-External links:*...
, by Olaf Stapledon
Olaf Stapledon
William Olaf Stapledon was a British philosopher and author of several influential works of science fiction.-Life:...
, and possibly by the works of J. D. Bernal
J. D. Bernal
John Desmond Bernal FRS was one of Britain’s best known and most controversial scientists, called "Sage" by his friends, and known for pioneering X-ray crystallography in molecular biology.-Origin and education:His family was Irish, of mixed Italian and Spanish/Portuguese Sephardic Jewish origin...
and Raymond Z. Gallun
Raymond Z. Gallun
Raymond Zinke Gallun was an American science fiction writer.Gallun was born in Beaver Dam, Wisconsin...
who seem to have explored similar concepts in their work.
Feasibility
Some ideas to build a fixed in place 'Dyson shell' are impractical. However, ideas to use orbiting satellites or solar sails employ technology largely already developed. Deployment of spacecraftSpacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
and satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s using photovoltaics
Photovoltaics
Photovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...
might be seen as the first small steps towards building a Dyson swarm (see below for differences between these sub-types). However, the number of crafts required to obtain, transmit, and maintain a complete Dyson shell far exceeds our present-day industrial capabilities.
Variants
In fictional accounts, the Dyson-sphere concept is often interpreted as an artificial hollow sphereSphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
of matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
around a star. This perception is a misinterpretation of Dyson's original concept. In response to letters prompted by his original paper, Dyson replied, "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."
Dyson swarm
The variant closest to Dyson's original conception is the "Dyson swarm". It consists of a large number of independent constructs (usually solar power satellites and space habitatsSpace colonization
Space colonization is the concept of permanent human habitation outside of Earth. Although hypothetical at the present time, there are many proposals and speculations about the first space colony...
) orbiting in a dense formation around the star. This construction approach has advantages: components could be sized appropriately, and it can be constructed incrementally. Various forms of wireless energy transfer
Wireless energy transfer
Wireless energy transfer or wireless power is the transmission of electrical energy from a power source to an electrical load without artificial interconnecting conductors. Wireless transmission is useful in cases where interconnecting wires are inconvenient, hazardous, or impossible...
could be used to transfer energy between components and earth.
Such a swarm is not without drawbacks. The nature of orbital mechanics
Astrodynamics
Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and Newton's law of universal gravitation. It...
would make the arrangement of the orbits of the swarm extremely complex. The simplest such arrangement is the Dyson ring in which all such structures share the same orbit. More complex patterns with more rings would intercept more of the star's output, but would result in some constructs eclipsing others periodically when their orbits overlap. Another potential problem is the increasing loss of orbital stability when adding more elements increases the probability of orbital perturbations.
As noted below, such a cloud of collectors would alter the light emitted by the star system. However, the disruption compared to a stars overall natural emitted spectrum would most likely be too small to be noticed on earth.
Dyson bubble
Space habitat
A space habitat is a space station intended as a permanent settlement rather than as a simple waystation or other specialized facility...
s) and likewise could be constructed incrementally.
Unlike the Dyson swarm, the constructs making it up are not in orbit around the star, but would be statite
Statite
A statite is a hypothetical type of artificial satellite that employs a solar sail to continuously modify its orbit in ways that gravity alone would not allow. Typically, a statite would use the solar sail to "hover" in a location that would not otherwise be available as a stable geosynchronous...
s—satellites suspended by use of enormous light sails using radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
to counteract the star's pull of gravity. Such constructs would not be in danger of collision or of eclipsing one another; they would be totally stationary with regard to the star, and independent of one another. As the ratio of radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
and the force of gravity from a star are constant regardless of the distance (provided the statite has an unobstructed line-of-sight to the surface of its star), such statites could also vary their distance from their central star.
The practicality of this approach is questionable with modern material science, but cannot yet be ruled out. A statite deployed around our own sun would have to have an overall density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of 0.78 grams per square meter of sail. To illustrate the low mass of the required materials, consider that the total mass of a bubble of such material 1 AU in radius would be about 2.17 kg, which is about the same mass as the asteroid Pallas
2 Pallas
Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...
.
Such a material is currently beyond our ability to produce; the lightest carbon-fiber light sail material currently produced has a density – without payload – of 3 g/m², or about four times as heavy as would be needed to construct a solar statite.
However, there has been some speculation about the creation of ultra light carbon nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
meshes through molecular manufacturing techniques whose density would be below 0.1 g/m². If production of such materials on an industrial scale is feasible, and such materials could be used in light sails, the average sail density with rigging
Rigging
Rigging is the apparatus through which the force of the wind is used to propel sailboats and sailing ships forward. This includes masts, yards, sails, and cordage.-Terms and classifications:...
might be kept to 0.3 g/m² (a "spin stabilized" light sail requires minimal additional mass in rigging
Rigging
Rigging is the apparatus through which the force of the wind is used to propel sailboats and sailing ships forward. This includes masts, yards, sails, and cordage.-Terms and classifications:...
). If such a sail could be constructed at this areal density, a space habitat
Space habitat
A space habitat is a space station intended as a permanent settlement rather than as a simple waystation or other specialized facility...
the size of the L5 Society
L5 Society
The L5 Society was founded in 1975 by Carolyn and Keith Henson to promote the space colony ideas of Dr Gerard K. O'Neill.The name comes from the and Lagrangian points in the Earth-Moon system proposed as locations for the huge rotating space habitats that Dr O'Neill envisioned...
's proposed O'Neill cylinder – 500 km², with room for over 1 million inhabitants, massing 3 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
s – could be supported by a circular light sail 3,000 km in diameter, with a combined sail/habitat mass of 5.4 kg. For comparison, this is just slightly smaller than the diameter of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's moon Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
(although the sail is a flat disc, not a sphere), or the distance between San Francisco and Kansas City
Kansas City, Missouri
Kansas City, Missouri is the largest city in the U.S. state of Missouri and is the anchor city of the Kansas City Metropolitan Area, the second largest metropolitan area in Missouri. It encompasses in parts of Jackson, Clay, Cass, and Platte counties...
. Such a structure would, however, have a mass quite a lot less than many asteroids. While the construction of such a massive inhabitable statite would be a gigantic undertaking, and the required material science behind it is as yet uncertain, its technical challenges are negligible compared to other engineering feats and required materials proposed in other Dyson sphere variants.
In theory, if enough statites were created and deployed around their star, they would compose a non-rigid version of the Dyson shell mentioned below. Such a shell would not suffer from the drawbacks of massive compressive pressure, nor are the mass requirements of such a shell as high as the rigid form. Such a shell would, however, have the same optical and thermal properties as the rigid form, and would be detected by searchers in a similar fashion (see below).
Dyson shell
Dyson spheres in fiction
This is a listing of the use of the Dyson sphere concept in popular fiction. For a discussion of the general concept and its history, see the main article....
is the "Dyson shell": a uniform solid shell of matter around the star. Such a structure would completely alter the emissions of the central star, and would intercept 100% of the star's energy output. Such a structure would also provide an immense surface which many envision being used for habitation, if the surface could be made habitable.
A spherical shell Dyson sphere in our solar system with a radius of one astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
, so that the interior surface would receive the same amount of sunlight as Earth does per solid angle
Solid angle
The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
, would have a surface area of at least 272 quadrillion
Quadrillion
Quadrillion may mean either of the two numbers :* 1,000,000,000,000,000 – for all short scale countries; increasingly common meaning in English language usage* 1,000,000,000,000,000,000,000,000 – for all...
km2, or about 550 million times the surface area of the Earth. This would intercept the full 384.6 yotta
Yotta
Yotta is the largest unit prefix in the International System of Units denoting a factor of 1024 or . It has the unit symbol Y.The prefix name is derived from the Greek , meaning eight, because it is equal to 10008...
watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s (3.846 × 1026 watts) of the Sun's output; other variant designs would intercept less, but the shell variant represents the maximum possible energy captured for our solar system at this point of the Sun's evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
. This is approximately 33 trillion
Trillion
-Numbers:Either of the two numbers :* 1,000,000,000,000 for all short scale countries...
times the power consumption of humanity in 1998, which was 12 terawatts.
There are several serious theoretical difficulties with the solid shell variant of the Dyson sphere:
Such a shell would have no net gravitational interaction with its englobed sun (see Shell theorem
Shell theorem
In classical mechanics, the shell theorem gives gravitational simplifications that can be applied to objects inside or outside a spherically symmetrical body...
), and could drift in relation to the central star. If such movements went uncorrected, they could eventually result in a collision between the sphere and the star—most likely with disastrous results. Such structures would need either some form of propulsion to counteract any drift, or some way to repel the surface of the sphere away from the star.
For the same reason, such a shell would have no net gravitational interaction with anything else inside it. The contents of any biosphere placed on the inner surface of a Dyson shell would not be attracted to the sphere's surface and would simply fall into the star. It has been proposed that a biosphere could be contained between two concentric spheres, placed on the interior of a rotating sphere (in which case, the force of artificial "gravity" is perpendicular to the axis of rotation, causing all matter placed on the interior of the sphere to pool around the equator, effectively rendering the sphere a Niven ring for purposes of habitation, but still fully effective as a radiant-energy collector) or placed on the outside of the sphere where it would be held in place by the star's gravity. In such cases, some form of illumination would have to be devised, or the sphere made at least partly transparent, as the star's light would otherwise be completely hidden.
If assuming a radius of one AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
, then the compressive strength of the material forming the sphere would have to be immense. Any arbitrarily selected point on the surface of the sphere can be viewed as being under the pressure of the base of a dome 1 AU in height under the Sun's gravity at that distance. Indeed it can be viewed as being at the base of an infinite number of arbitrarily selected domes, but as much of the force from any one arbitrary dome is counteracted by those of another, the net force on that point is immense, but finite. No known or theorized material is strong enough to withstand this pressure, and form a rigid, static sphere around a star. It has been proposed by Paul Birch
Paul Birch (writer)
Paul Birch is a British author, engineer and scientist, who has worked in radioastronomy and satellite communications, and now writes full time.He is a former Fellow of the British Interplanetary Society....
(in relation to smaller "Supra-Jupiter" constructions around a large planet rather than a star) that it may be possible to support a Dyson shell by dynamic means similar to those used in a space fountain
Space fountain
A space fountain is a proposed form of space elevator that does not require the structure to be in geostationary orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design , a space fountain is a tremendously tall tower extending up from the ground...
. Masses travelling in circular tracks on the inside of the sphere, at velocities significantly greater than orbital velocity, would press outwards due to centrifugal force. For a Dyson shell of 1-AU radius around a star with the same mass as the Sun, a mass travelling ten times the orbital velocity (297.9 km/s) would support 99 (a=v2/r) times its own mass in additional shell structure. The arrangement of such tracks suffers from the same difficulties as arranging the orbits of a Dyson swarm, and it is unclear how much energy would be consumed ensuring the velocity of the masses was maintained.
Also if assuming a radius of one AU, then there may not be sufficient building material in the Solar System to construct a Dyson shell. Anders Sandberg
Anders Sandberg
Anders Sandberg is a researcher, science debater, futurist, transhumanist, and author. He was born in Solna, Sweden. He holds a Ph.D...
estimates that there is 1.82 kg of easily usable building material in the Solar System, enough for a 1-AU shell with a mass of 600 kg/m²—about 8–20 cm thick, depending on the density of the material. This includes the hard-to-access cores of the gas giants; the inner planets alone provide only 11.79 kg, enough for a 1-AU shell with a mass of just 42 kg/m².
The shell would be vulnerable to impacts from interstellar bodies, such as comets, meteoroids, and material in interstellar space that is currently being deflected by the Sun's bow shock
Bow shock
A bow shock is the area between a magnetosphere and an ambient medium. For stars, this is typically the boundary between their stellar wind and the interstellar medium....
. The heliosphere
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
, and any protection it theoretically provides, would cease to exist.
Other types
Another possibility is the "Dyson net", a web of cables strung about the star which could have power or heat collection units strung between the cables. The Dyson net reduces to a special case of Dyson shell or bubble, however, depending on how the cables are supported against the sun's gravity.A bubbleworld is an artificial construct that consists of a shell of living space around a sphere of hydrogen gas. The shell contains air, people, houses, furniture, etc. It was invented to answer the question, "What is the largest space colony that can be built?" However, most of the volume is not habitable and there is no power source.
Theoretically, any gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
could be enclosed in a solid shell; at a certain radius the surface gravity would be terrestrial, and energy could be provided by tapping the thermal energy of the planet. This concept is explored peripherally in the novel Accelerando (and the short story Curator which is incorporated into the novel as a chapter) by Charles Stross
Charles Stross
Charles David George "Charlie" Stross is a British writer of science fiction, Lovecraftian horror and fantasy. He was born in Leeds.Stross specialises in hard science fiction and space opera...
, in which Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
is converted into a human-habitable world.
Stellar engine
Stellar engine
Stellar engines are a class of hypothetical megastructures which use a star's radiation to create usable energy. Some variants use this energy to produce thrust, and thus accelerate a star, and anything orbiting it, in a given direction...
s are a class of hypothetical megastructure
Megastructure
A megastructure is a very large manmade object, though the limits of precisely how large this is vary considerably. Some apply the term to any especially large or tall building....
s, whose purpose is to extract useful energy from a star, sometimes for specific purposes. For example, Matrioshka brain
Matrioshka brain
A matrioshka brain is a hypothetical megastructure proposed by Robert Bradbury, based on the Dyson sphere, of immense computational capacity. It is an example of a Class B stellar engine, employing the entire energy output of a star to drive computer systems...
s extract energy for purposes of computation; Shkadov thrusters extract energy for purposes of propulsion. Some of the proposed stellar engine designs are based on the Dyson sphere.
A black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
could be the power source instead of a star in order to increase energy-to-matter conversion efficiency. A black hole would also be smaller than a star. This would decrease communication distances which would be important for computer-based societies as those described above.
Search for extra-terrestrial intelligence
In Dyson's original paper, he speculated that sufficiently advanced extraterrestrial civilizations would likely follow a similar power consumption pattern as humans, and would eventually build their own sphere of collectors. Constructing such a system would make such a civilization a Type II Kardashev civilizationKardashev scale
The Kardashev scale is a method of measuring an advanced civilization's level of technological advancement. The scale is only theoretical and in terms of an actual civilization highly speculative; however, it puts energy consumption of an entire civilization in a cosmic perspective. It was first...
.
The existence of such a system of collectors would alter the light emitted from the star system. Collectors would absorb and reradiate energy from the star. The wavelength(s) of radiation emitted by the collectors would be determined by the emission spectra
Emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....
of the substances making them up, and the temperature of the collectors. Since it seems most likely that these collectors would be made up of heavy elements not normally found in the emission spectra of their central star–or at least not radiating light at such relatively "low" energies as compared to that which they would be emitting as energetic free nuclei in the stellar atmosphere
Stellar atmosphere
The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone. It is divided into several regions of distinct character:...
–there would be atypical wavelengths of light for the star's spectral type in the light spectrum emitted by the star system. If the percentage of the star's output thus filtered or transformed by this absorption and reradiation was significant, it could be detected at interstellar distances.
Given the amount of energy available per square meter at a distance of 1 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, it is possible to calculate that most known substances would be reradiating energy in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
part of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
. Thus, a Dyson Sphere, constructed by life forms not dissimilar to humans, who dwelled in proximity to a Sun-like star
Solar analog
Solar-type, solar analog, and solar twin stars are those stars that are particularly similar to the Sun. The classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type...
, made with materials similar to those available to humans, would most likely cause an increase in the amount of infrared radiation in the star system's emitted spectrum. Hence, Dyson selected the title "Search for Artificial Stellar Sources of Infrared Radiation" for his published paper.
SETI
SETI
The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...
has adopted these assumptions in their search, looking for such "infrared heavy" spectra from solar analog
Solar analog
Solar-type, solar analog, and solar twin stars are those stars that are particularly similar to the Sun. The classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type...
s. Fermilab
Fermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
has an ongoing survey for such spectra by analyzing data from the Infrared Astronomical Satellite (IRAS)
IRAS
The Infrared Astronomical Satellite was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths....
. Identifying one of the many infra-red sources as a Dyson Sphere would require improved techniques for discriminating between a Dyson Sphere and natural sources.
Fiction
As noted above, the Dyson sphere originated in fiction, and it is a concept that has appeared often in science fictionScience fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
since then (see Dyson spheres in popular culture for listed examples). In fictional accounts, Dyson spheres are most often depicted as a Dyson shell with the gravitational and engineering difficulties of this variant noted above largely ignored.
See also
- Alderson diskAlderson diskAn Alderson disk is an artificial astronomical megastructure, like Niven's Ringworld, or a Dyson sphere. The disk is a giant platter with a thickness of several thousand miles. The sun rests in the hole at the center of the disk. The outer radius of an Alderson disk would be roughly equivalent...
- Globus CassusGlobus CassusGlobus Cassus is an art project and book by Swiss architect and artist Christian Waldvogel presenting a conceptual transformation of Planet Earth into a much bigger, hollow, artificial world with an ecosphere on its inner surface...
- Klemperer rosetteKlemperer rosetteA Klemperer rosette is a gravitational system of heavier and lighter bodies orbiting in a regular repeating pattern around a common barycenter. It was first described by W. B...
- Matrioshka brainMatrioshka brainA matrioshka brain is a hypothetical megastructure proposed by Robert Bradbury, based on the Dyson sphere, of immense computational capacity. It is an example of a Class B stellar engine, employing the entire energy output of a star to drive computer systems...
- Megascale engineeringMegascale engineeringMegascale engineering is a form of exploratory engineering concerned with the construction of structures on an enormous scale. Typically these structures are at least 1,000 kilometers in length—in other words, at least 1 megameter, hence the name...
- RingworldRingworldRingworld is a Hugo, Nebula, and Locus award-winning 1970 science fiction novel by Larry Niven, set in his Known Space universe and considered a classic of science fiction literature. It is followed by three sequels, and preceded by four prequels, and ties into numerous other books set in Known Space...
- Star liftingStar liftingStar lifting is any of several hypothetical processes by which a highly advanced civilization could remove a substantial portion of a star's matter in a controlled manner for other uses. The term appears to have been coined by David Criswell.Stars already lose a small flow of mass via solar wind,...
- Stellar engineeringStellar engineeringStellar engineering is a type of engineering concerned with creating or modifying stars through artificial means....