Dyson sphere

From Wikipedia, the free encyclopedia

Dyson Sphere is a hypothetical megastructure that completely encompasses a star and hence captures most or all of its power output. It was first described by Freeman Dyson. Dyson speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization, and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life. Different types of Dyson spheres correlate with information on the Kardashev scale.

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). In May 2013, at the Starship Century Symposium in San Diego, Dyson repeated his comments that he wished the concept had not been named after him.^[1]

Origin of concept

The concept of the Dyson sphere was the result of a thought experiment 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.^[2] 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,^[3] by Olaf Stapledon, and possibly by the works of J. D. Bernal, Raymond Z. Gallun, and Edgar Rice Burroughs who seem to have explored similar concepts in their work.^[4]

Feasibility

While such megastructures may be theoretically possible, all plans to build a fixed-in-place Dyson sphere are currently far beyond humanity's engineering capacity. However, parts of the technology, like orbiting satellites and solar sails, have already been developed. Deployment of spacecraft and satellites using photovoltaics might be seen as the first small steps towards building a Dyson swarm.^[5] However, the number of craft required to obtain, transmit, and maintain a complete Dyson sphere far exceeds our present-day industrial capabilities.

Variants

In fictional accounts, the Dyson-sphere concept is often interpreted as an artificial hollow sphere of matter around a star. This perception is based on a literal interpretation of Dyson's original short paper introducing the concept. In response to letters prompted by this 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."^[6]

Dyson swarm

A Dyson ring — the simplest form of the Dyson swarm — to scale. Orbit is 1 AU in radius, collectors are 1.0×10⁷ km in diameter (~25× the Earth–Moon distance), spaced 3 degrees from center to center around the orbital circle.

A relatively simple arrangement of multiple Dyson rings of the type pictured above, to form a more complex Dyson swarm. Rings' orbital radii are spaced 1.5×10⁷ km with regard to one another, but average orbital radius is still 1 AU. Rings are rotated 15 degrees relative to one another, around a common axis of rotation.

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 habitats) orbiting in a dense formation around the star. This construction approach has advantages: components could be sized appropriately, and it can be constructed incrementally.^[5] Various forms of wireless energy transfer could be used to transfer energy between components and Earth.

Disadvantages: 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.^[7] 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 star's overall natural emitted spectrum would most likely be too small to be noticed on Earth.^[2]

Dyson bubble

A Dyson bubble: an arrangement of statites around a star, in a non-orbital pattern. As long as a statite has an unobstructed line-of-sight to its star, it can hover at any point in space near its star. This relatively simple arrangement is only one of an infinite number of possible statite configurations, and is meant as a contrast for a Dyson swarm only. Statites are pictured as the same size as the collectors pictured above, and arranged at a uniform 1 AU distance from the star.

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 habitats) 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 statites—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 is constant regardless of the distance (provided the statite has an unobstructed line-of-sight to the surface of its star^[8]), 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.^[9] 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 2.17×10²⁰ kg, which is about the same mass as the asteroid Pallas.^[10]

Such a material is currently beyond humanity's 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.^[11] A single sheet of graphene, the two-dimensional form of carbon, has a density of only 0.77 mg per square meter,^[12] but has not been fabricated in large sheets and has transparency of 97.7%, making such a single sheet of graphene very ineffective as a solar sail.

However, this could change thanks to the recent creation of ultra light carbon nanotubes meshed through molecular manufacturing techniques whose densities range from 1.3g/m² to 1.4g/m². By the time a civilization is ready to use this technology, the carbon nanotube's manufacturing might be optimised enough for them to have a density lower than the 0.7g/m² mark, and 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 3×10⁶ tons – could be supported by a circular light sail 3,000 km in diameter, with a combined sail/habitat mass of 5.4×10⁹ kg.^[13] 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).

Dyson shell

A cut-away diagram of an idealized Dyson shell, a variant on Dyson's original concept, with a radius of 1 AU.

The variant of the Dyson sphere most often depicted in fiction is the "Dyson shell": a uniform solid shell of matter around the star.^[14] 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 would be used for habitation, if the surface could be made habitable.

A spherical shell Dyson sphere in the 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 unit solid angle, would have a surface area of approximately 28.1 Eha (Exa Hectare), or about 550 million times the surface area of Earth. This would intercept the full 384.6 yottawatts (3.846 × 10²⁶ watts)^[15] of the Sun's output; other variant designs would intercept less, but the shell variant represents the maximum possible energy captured for the Solar System at this point of the Sun's evolution.^[14] This is approximately 33 trillion times the power consumption of humanity in 1998, which was 12 terawatts.^[16]

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 star (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.^[9]

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.^[17][18] 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.^[19]

If assuming a radius of one AU, then the compressive strength of the material forming the sphere would have to be immense to prevent implosion due to the star's gravity. 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.^[20] 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.^[21] Masses travelling in circular tracks on the inside of the sphere, at velocities significantly greater than orbital velocity, would press outwards on magnetic bearings 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.

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 1.82×10²⁶ 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 on average, depending on the density of the material. This includes the hard-to-access cores of the gas giants; the inner planets alone provide only 11.79×10²⁴ kg, enough for a 1-AU shell with a mass of just 42 kg/m².^[10]

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.

Other types

Dyson Net

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.

Bubbleworld

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?"^[22] 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.^[22] 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

Stellar engines are a class of hypothetical megastructures, whose purpose is to extract useful energy from a star, sometimes for specific purposes. For example, Matrioshka brains 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.^[23]

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.^[22]

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 civilization.^[24]

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.^[2] 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.^[2]

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.^[2]

SETI has adopted these assumptions in their search, looking for such "infrared heavy" spectra from solar analogs. As of 2005 Fermilab has an ongoing survey for such spectra by analyzing data from the Infrared Astronomical Satellite (IRAS).^[25][26] 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.^[27] Fermilab discovered 17 potential "ambiguous" candidates of which four have been named "amusing but still questionable".^[28] Other searches also resulted in several candidates, which are however unconfirmed.^[29]

Fiction

As noted above, the Dyson sphere originated in fiction,^[30][31] and it is a concept that has appeared often in science fiction since then. 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.^[14]

Freeman Dyson

From Wikipedia, the free encyclopedia

 

Freeman Dyson
Long Now Seminar in San Francisco, October 5, 2005
Born	Freeman John Dyson December 15, 1923 (age 90) Crowthorne, Berkshire, England
Nationality	American
Fields	Physics, Mathematics
Institutions	Royal Air Force Institute for Advanced Study University of Birmingham Duke University Cornell University
Alma mater	University of Cambridge, Cornell University[1]
Academic advisors	Hans Bethe
Known for	Dyson sphere Dyson operator Dyson series Schwinger-Dyson equation Circular ensemble Random Matrix Theory Advocacy against nuclear weapons Dyson conjecture Dyson's eternal intelligence Dyson number Dyson tree Dyson's transform Dyson Brownian Motion Project Orion TRIGA
Influences	Richard Feynman,[2][3][full citation needed] Abram Samoilovitch Besicovitch[4]
Notable awards	Heineman Prize (1965) Lorentz Medal (1966) Hughes Medal (1968) Harvey Prize (1977) Wolf Prize (1981) Oersted Medal (1991) Fermi Award (1993) Templeton Prize (2000) Pomeranchuk Prize (2003) Poincaré Prize (2012)
Notes He is notably the son of George Dyson, and father of Esther Dyson, Dorothy Dyson, Mia Dyson, Rebecca Dyson, Emily Dyson, and George Dyson.

Freeman John Dyson FRS (born December 15, 1923) is an English-born American^[5][6] theoretical physicist and mathematician, famous for his work in quantum electrodynamics, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists.^[7]

Biography

Early life

Born at Crowthorne in Berkshire, Dyson is the son of the English composer George Dyson, who was later knighted. His mother had a law degree, but after Dyson was born she worked as a social worker.^[8] Although not known to be related to the early 20th-century astronomer Frank Watson Dyson, as a small boy Dyson was aware of him and has credited the popularity of an astronomer sharing his surname as having helped to spark his own interest in science.^{[citation needed]} At the age of five he calculated the number of atoms in the sun.^[9] As a child, he showed an interest in large numbers and in the solar system, and was strongly influenced by the book Men of Mathematics by Eric Temple Bell.^[2]

From 1936 to 1941, Dyson was a Scholar at Winchester College, where his father was Director of Music. On July 25, 1943, he entered the Operational Research Section (ORS) of the Royal Air Force’s Bomber Command,^[10] where he developed analytical methods to help the RAF bomb German targets during World War II.^[11] After the war, Dyson enrolled in the University of Cambridge, where he obtained a Bachelor of Arts degree in mathematics.^[12] From 1946 to 1949 he was a Fellow of Trinity College, Cambridge, occupying rooms just below those of the philosopher Ludwig Wittgenstein, who would resign his professorship in 1947.^[13]

Career in the United States

In 1947 Dyson moved to the US, as Commonwealth Fellow at Cornell University (1947–1948) and the Institute for Advanced Study (1948–1949). Between 1949 and 1951, he was a teaching fellow at the University of Birmingham (UK).^[14]

In 1951 he joined the faculty at Cornell as a physics professor, although still lacking a doctorate, and in 1953 he received a permanent post at the Institute for Advanced Study in Princeton, New Jersey—where he has now lived for more than fifty years.^[15] In 1957 he became a naturalized citizen of the United States and renounced his British nationality. One reason he gave decades later is that his children born in the US had not been recognized as British subjects.^[5][6]

Dyson is best known for demonstrating in 1949 the equivalence of two then-current formulations of quantum electrodynamics—Richard Feynman's diagrams and the operator method developed by Julian Schwinger and Sin-Itiro Tomonaga.^[16] He was the first person (besides Feynman) to appreciate the power of Feynman diagrams, and his paper written in 1948 and published in 1949 was the first to make use of them. He said in that paper that Feynman diagrams were not just a computational tool, but a physical theory, and developed rules for the diagrams that completely solved the renormalization problem. Dyson's paper and also his lectures presented Feynman's theories of QED (quantum electrodynamics) in a form that other physicists could understand, facilitating the physics community's acceptance of Feynman's work. Robert Oppenheimer, in particular, was persuaded by Dyson that Feynman's new theory was as valid as Schwinger's and Tomonaga's. Oppenheimer rewarded Dyson with a lifetime appointment at the Institute for Advanced Study, "for proving me wrong", in Oppenheimer's words.^[17]

Also in 1949, in a related work, Dyson invented the Dyson series.^[18] It was this paper that inspired John Ward to derive his celebrated Ward identity.^[19]

Dyson also did work in a variety of topics in mathematics, such as topology, analysis, number theory and random matrices.^[20] There is an interesting story involving random matrices. In 1973 the number theorist Hugh Montgomery was visiting the Institute for Advanced Study and had just made his pair correlation conjecture concerning the distribution of the zeros of the Riemann zeta function. He showed his formula to the mathematician Atle Selberg who said it looked like something in mathematical physics and he should show it to Dyson, which he did. Dyson recognized the formula as the pair correlation function of the Gaussian unitary ensemble, which has been extensively studied by physicists. This suggested that there might be an unexpected connection between the distribution of primes 2,3,5,7,11, ... and the energy levels in the nuclei of heavy elements such as uranium.^[21]

From 1957 to 1961 he worked on the Orion Project, which proposed the possibility of space-flight using nuclear pulse propulsion. A prototype was demonstrated using conventional explosives, but the 1963 Partial Test Ban Treaty (which Dyson was involved in and supported) permitted only underground nuclear testing, so the project was abandoned.

In 1958 he led the design team for the TRIGA, a small, inherently safe nuclear reactor used throughout the world in hospitals and universities for the production of medical isotopes.

A seminal work by Dyson came in 1966 when, together with Andrew Lenard and independently of Elliott H. Lieb and Walter Thirring, he proved rigorously that the exclusion principle plays the main role in the stability of bulk matter.^[22][23][24] Hence, it is not the electromagnetic repulsion between outer-shell orbital electrons which prevents two wood blocks that are left on top of each other from coalescing into a single piece, but rather it is the exclusion principle applied to electrons and protons that generates the classical macroscopic normal force. In condensed matter physics, Dyson also did studies in the phase transition of the Ising model in 1 dimension and spin waves.^[20]

Around 1979, Dyson worked with the Institute for Energy Analysis on climate studies. This group, under the direction of Alvin Weinberg, pioneered multidisciplinary climate studies, including a strong biology group. Also during the 1970s, he worked on climate studies conducted by the JASON defense advisory group.^[15]

Dyson retired from the Institute for Advanced Study in 1994.^[25] In 1998, Dyson joined the board of the Solar Electric Light Fund. As of 2003 he was president of the Space Studies Institute, the space research organization founded by Gerard K. O'Neill; As of 2013 he is on its Board of Trustees.^[26] Dyson is a long-time member of the JASON group.

Dyson is a regular contributor to The New York Review of Books.

Dyson has won numerous scientific awards but never a Nobel Prize. Nobel physics laureate Steven Weinberg has said that the Nobel committee has "fleeced" Dyson, but Dyson himself remarked in 2009, "I think it's almost true without exception if you want to win a Nobel Prize, you should have a long attention span, get hold of some deep and important problem and stay with it for ten years. That wasn't my style."^[15]

In 2012, he published (with William H. Press) a fundamental new result about the Prisoners Dilemma in PNAS.^[27]

Marriages and children

With his first wife, the mathematician Verena Huber-Dyson, Dyson has two children, Esther and George. In 1958 he married Imme Jung, a masters runner, and they eventually had four more children, Dorothy, Mia, Rebecca, and Emily Dyson.^[15]

Dyson's eldest daughter, Esther, is a digital technology consultant and investor; she has been called "the most influential woman in all the computer world." ^[28] His son George is a historian of science,^[29] one of whose books is Project Orion: The Atomic Spaceship 1957–1965.

Character

Friends and colleagues describe Dyson as shy and self-effacing, with a contrarian streak that his friends find refreshing but his intellectual opponents find exasperating. "I have the sense that when consensus is forming like ice hardening on a lake, Dyson will do his best to chip at the ice", Steven Weinberg said of him. His friend, the neurologist and author Oliver Sacks, said: "A favorite word of Freeman's about doing science and being creative is the word 'subversive'. He feels it's rather important not only to be not orthodox, but to be subversive, and he's done that all his life."^{[15] [clarification needed]} In The God Delusion (2006), biologist Richard Dawkins criticized Dyson for accepting the religious Templeton Prize in 2000; "It would be taken as an endorsement of religion by one of the world's most distinguished physicists."^[30] However, Dyson declared in 2000 that he is a (non-denominational) Christian,^[31] and he has disagreed with Dawkins on several occasions, as when he criticized Dawkins' understanding of evolution.^[32]

Honors and awards

In 1952 he was elected a Fellow of the Royal Society.^[33]

Dyson was awarded the Lorentz Medal in 1966, Max Planck Medal in 1969 and the Harvey Prize in 1977.

In the 1984–85 academic year he gave the Gifford lectures at Aberdeen, which resulted in the book Infinite In All Directions.

In 1989, Dyson taught at Duke University as a Fritz London Memorial Lecturer. In the same year, he was elected as an Honorary Fellow of Trinity College, University of Cambridge.

Dyson has published a number of collections of speculations and observations about technology, science, and the future. In 1996 he was awarded the Lewis Thomas Prize for Writing about Science.

In 1993, Dyson was given the Enrico Fermi Award.

In 1995 he gave the Jerusalem-Harvard Lectures at the Hebrew University of Jerusalem, sponsored jointly by the Hebrew University and Harvard University Press that grew into the book Imagined Worlds.^[34]

In 2000, Dyson was awarded the Templeton Prize for Progress in Religion.

In 2003, Dyson was awarded the Telluride Tech Festival Award of Technology in Telluride, Colorado.

In 2011, Dyson was received as one of twenty distinguished Old Wykehamists at the Ad Portas celebration, the highest honour that Winchester College bestows.

Concepts

Biotechnology and genetic engineering

My book The Sun, the Genome, and the Internet (1999) describes a vision of green technology enriching villages all over the world and halting the migration from villages to megacities. The three components of the vision are all essential: the sun to provide energy where it is needed, the genome to provide plants that can convert sunlight into chemical fuels cheaply and efficiently, the Internet to end the intellectual and economic isolation of rural populations. With all three components in place, every village in Africa could enjoy its fair share of the blessings of civilization.^[35]

Dyson cheerfully admits his record as a prophet is mixed, but "it is better to be wrong than to be vague."^[36]

"To answer the world's material needs, technology has to be not only beautiful but also cheap."^[37]

Dyson sphere

Artist's concept of Dyson rings, forming a stable Dyson swarm, or "Dyson sphere".

One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.^[38]

In 1960 Dyson wrote a short paper for the journal Science, entitled "Search for Artificial Stellar Sources of Infrared Radiation".^[39] In it, he theorized that a technologically advanced extraterrestrial civilization might completely surround its native star with artificial structures in order to maximize the capture of the star's available energy. Eventually, the civilization would completely enclose the star, intercepting electromagnetic radiation with wavelengths from visible light downwards and radiating waste heat outwards as infrared radiation. Therefore, one method of searching for extraterrestrial civilizations would be to look for large objects radiating in the infrared range of the electromagnetic spectrum.

Dyson conceived that such structures would be clouds of asteroid-sized space habitats, though science fiction writers have preferred a solid structure: either way, such an artifact is often referred to as a Dyson sphere, although Dyson himself used the term "shell". Dyson says that he used the term "artificial biosphere" in the article meaning a habitat, not a shape.^[40] The general concept of such an energy-transferring shell had been advanced decades earlier by author Olaf Stapledon in his 1937 novel Star Maker, a source that Dyson has credited publicly.^[41][42]

Dyson tree

Dyson has also proposed the creation of a Dyson tree, a genetically-engineered plant capable of growing on a comet. He suggested that comets could be engineered to contain hollow spaces filled with a breathable atmosphere, thus providing self-sustaining habitats for humanity in the outer solar system.

Plants could grow greenhouses…just as turtles grow shells and polar bears grow fur and polyps build coral reefs in tropical seas. These plants could keep warm by the light from a distant Sun and conserve the oxygen that they produce by photosynthesis. The greenhouse would consist of a thick skin providing thermal insulation, with small transparent windows to admit sunlight. Outside the skin would be an array of simple lenses, focusing sunlight through the windows into the interior… Groups of greenhouses could grow together to form extended habitats for other species of plants and animals.^[43]

Space colonies

I've done some historical research on the costs of the Mayflower's voyage, and on the Mormons' emigration to Utah, and I think it's possible to go into space on a much smaller scale. A cost on the order of $40,000 per person [1978 dollars, $143,254 in 2013 dollars] would be the target to shoot for; in terms of real wages, that would make it comparable to the colonization of America. Unless it's brought down to that level it's not really interesting to me, because otherwise it would be a luxury that only governments could afford.^[38]

Dyson has been interested in space travel since he was a child, reading such science fiction classics as Olaf Stapledon's Star Maker. As a young man, he worked for General Atomics on the nuclear-powered Orion spacecraft. He hoped Project Orion would put men on Mars by 1965, Saturn by 1970.
He's been unhappy for a quarter-century on how the government conducts space travel:

The problem is, of course, that they can't afford to fail. The rules of the game are that you don't take a chance, because if you fail, then probably your whole program gets wiped out.^[38]

He still hopes for cheap space travel, but is resigned to waiting for private entrepreneurs to develop something new—and cheap.

No law of physics or biology forbids cheap travel and settlement all over the solar system and beyond. But it is impossible to predict how long this will take. Predictions of the dates of future achievements are notoriously fallible. My guess is that the era of cheap unmanned missions will be the next fifty years, and the era of cheap manned missions will start sometime late in the twenty-first century.

Any affordable program of manned exploration must be centered in biology, and its time frame tied to the time frame of biotechnology; a hundred years, roughly the time it will take us to learn to grow warm-blooded plants, is probably reasonable.^[43]

Dyson also has proposed the use of bioengineered space colonies to colonize the Kuiper Belt on the outer edge of our Solar System. He proposed that habitats could be grown from space hardened spores. The colonies could then be warmed by large reflector plant leaves that could focus the dim, distant sunlight back on the growing colony. This was illustrated by Pat Rawlings on the cover of the National Space Society's Ad Astra magazine.

Space exploration

A direct search for life in Europa's ocean would today be prohibitively expensive.

Impacts on Europa give us an easier way to look for evidence of life there. Every time a major impact occurs on Europa, a vast quantity of water is splashed from the ocean into the space around Jupiter. Some of the water evaporates, and some condenses into snow.

Creatures living in the water far enough from the impact have a chance of being splashed intact into space and quickly freeze-dried. Therefore, an easy way to look for evidence of life in Europa's ocean is to look for freeze-dried fish in the ring of space debris orbiting Jupiter.

Freeze-dried fish orbiting Jupiter is a fanciful notion, but nature in the biological realm has a tendency to be fanciful. Nature is usually more imaginative than we are. [...] To have the best chance of success, we should keep our eyes open for all possibilities.^[43]

Dyson's transform

Dyson also has some credits in pure mathematics. His concept "Dyson's transform" led to one of the most important lemmas of Olivier Ramaré's theorem that every even integer can be written as a sum of no more than six primes.

Dyson series

The Dyson series, the formal solution of an explicitly time-dependent Schrödinger equation by iteration, and the corresponding Dyson time-ordering operator an entity of basic importance in the mathematical formulation of quantum mechanics, are also named after Dyson.

Freeman Dyson in 2007 at the Institute for Advanced Study

Views

Metaphysics

Dyson has suggested a kind of cosmic metaphysics of mind. In his book Infinite in All Directions he writes about three levels of mind: "The universe shows evidence of the operations of mind on three levels. The first level is the level of elementary physical processes in quantum mechanics. Matter in quantum mechanics is [...] constantly making choices between alternative possibilities according to probabilistic laws. [...] The second level at which we detect the operations of mind is the level of direct human experience. [...] [I]t is reasonable to believe in the existence of a third level of mind, a mental component of the universe. If we believe in this mental component and call it God, then we can say that we are small pieces of God's mental apparatus" (p. 297).

Global warming

Dyson agrees that anthropogenic global warming exists, and has written that "[one] of the main causes of warming is the increase of carbon dioxide in the atmosphere resulting from our burning of fossil fuels such as oil and coal and natural gas."^[44] However, he believes that existing simulation models of climate fail to account for some important factors, and hence the results will contain too much error to reliably predict future trends:

The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world we live in ...^[44]

He is among signatories of a letter to the UN criticizing the IPCC^[45][46] and has also argued against ostracizing scientists whose views depart from the acknowledged mainstream of scientific opinion on climate change, stating that "heretics" have historically been an important force in driving scientific progress. "[H]eretics who question the dogmas are needed ... I am proud to be a heretic. The world always needs heretics to challenge the prevailing orthodoxies."^[44]

Dyson says his views on global warming have been strongly criticized. In reply, he notes that "[m]y objections to the global warming propaganda are not so much over the technical facts, about which I do not know much, but it’s rather against the way those people behave and the kind of intolerance to criticism that a lot of them have."^[47]

More recently, he has endorsed the now common usage of "global warming" as synonymous with global anthropogenic climate change, referring to "measurements that transformed global warming from a vague theoretical speculation into a precise observational science."^[48]

He has, however, argued that political efforts to reduce the causes of climate change distract from other global problems that should take priority:

I'm not saying the warming doesn't cause problems, obviously it does. Obviously we should be trying to understand it. I'm saying that the problems are being grossly exaggerated. They take away money and attention from other problems that are much more urgent and important. Poverty, infectious diseases, public education and public health. Not to mention the preservation of living creatures on land and in the oceans.^[49]

Since originally taking interest in climate studies in the 1970s, Dyson has suggested that carbon dioxide levels in the atmosphere could be controlled by planting fast-growing trees. He calculates that it would take a trillion trees to remove all carbon from the atmosphere.^[50][51]

In an interview at age 90, he said that "What I’m convinced of is that we don’t understand climate ... It will take a lot of very hard work before that question is settled." ^[2]

Nuclear winter

From his 1988 book Infinite in All Directions, he offered some criticism of then current models predicting a devastating nuclear winter in the event of a large-scale nuclear war:

As a scientist I want to rip the theory of nuclear winter apart, but as a human being I want to believe it. This is one of the rare instances of a genuine conflict between the demands of science and the demands of humanity. As a scientist, I judge the nuclear winter theory to be a sloppy piece of work, full of gaps and unjustified assumptions. As a human being, I hope fervently that it is right. Here is a real and uncomfortable dilemma. What does a scientist do when science and humanity pull in opposite directions?^[52]

Warfare and weapons

On hearing the news of the bombing of Hiroshima:

I agreed emphatically with Henry Stimson. Once we had got ourselves into the business of bombing cities, we might as well do the job competently and get it over with. I felt better that morning than I had felt for years… Those fellows who had built the atomic bombs obviously knew their stuff… Later, much later, I would remember [the downside].^[53]

I am convinced that to avoid nuclear war it is not sufficient to be afraid of it. It is necessary to be afraid, but it is equally necessary to understand. And the first step in understanding is to recognize that the problem of nuclear war is basically not technical but human and historical. If we are to avoid destruction we must first of all understand the human and historical context out of which destruction arises.^[54]

In his capacity as a military adviser Dyson wrote an influential paper on the issue of US use of nuclear weapons in the Vietnam War. When a general said in a meeting "We should throw in a nuke once in a while to keep the other side guessing," Dyson became alarmed and obtained permission to write an objective report discussing the pros and cons of using such weapons from a purely military point of view. His report, declassified from SECRET in 2002, was sufficiently objective that both sides in the debate based their arguments on the report. Dyson says that the report showed that even from a narrow military point of view the US was better off not using nuclear weapons. Dyson stated on the Dick Cavett show that the use of nuclear weaponry was a bad idea for the US at the time because "our targets were big and theirs were small."

At the British Bomber Command, Dyson and colleagues proposed ripping out two gun turrets from the RAF Lancaster bombers, to cut the catastrophic losses due to German fighters in the Battle of Berlin. A Lancaster without turrets could fly 50 mph (80 km/h) faster and be much more maneuverable.

All our advice to the commander in chief [went] through the chief of our section, who was a career civil servant. His guiding principle was to tell the commander in chief things that the commander in chief liked to hear… To push the idea of ripping out gun turrets, against the official mythology of the gallant gunner defending his crew mates…was not the kind of suggestion the commander in chief liked to hear.^[55]

Dyson opposed the Vietnam War, the Gulf War, and the invasion of Iraq. He supported Barack Obama in the 2008 US presidential election and The New York Times has described him as a political liberal.^[15]

The role of failure

You can't possibly get a good technology going without an enormous number of failures. It's a universal rule. If you look at bicycles, there were thousands of weird models built and tried before they found the one that really worked. You could never design a bicycle theoretically. Even now, after we've been building them for 100 years, it's very difficult to understand just why a bicycle works – it's even difficult to formulate it as a mathematical problem. But just by trial and error, we found out how to do it, and the error was essential.^[56]

On English academics

My view of the prevalence of doom-and-gloom in Cambridge is that it is a result of the English class system. In England there were always two sharply opposed middle classes, the academic middle class and the commercial middle class. In the nineteenth century, the academic middle class won the battle for power and status. As a child of the academic middle class, I learned to look on the commercial middle class with loathing and contempt. Then came the triumph of Margaret Thatcher, which was also the revenge of the commercial middle class. The academics lost their power and prestige and the business people took over. The academics never forgave Thatcher and have been gloomy ever since.^[57]

Science and religion

He is a non-denominational Christian and has attended various churches from Presbyterian to Roman Catholic. Regarding doctrinal or Christological issues, he has said, "I am neither a saint nor a theologian. To me, good works are more important than theology."^[58]

Science and religion are two windows that people look through, trying to understand the big universe outside, trying to understand why we are here. The two windows give different views, but they look out at the same universe. Both views are one-sided, neither is complete. Both leave out essential features of the real world. And both are worthy of respect.

Trouble arises when either science or religion claims universal jurisdiction, when either religious or scientific dogma claims to be infallible. Religious creationists and scientific materialists are equally dogmatic and insensitive. By their arrogance they bring both science and religion into disrepute. The media exaggerate their numbers and importance.

The media rarely mention the fact that the great majority of religious people belong to moderate denominations that treat science with respect, or the fact that the great majority of scientists treat religion with respect so long as religion does not claim jurisdiction over scientific questions.^[58]

Dyson partially disagrees with the famous remark by his fellow physicist Steven Weinberg that "With or without religion, good people can behave well and bad people can do evil; but for good people to do evil—that takes religion."^[59]

Weinberg's statement is true as far as it goes, but it is not the whole truth. To make it the whole truth, we must add an additional clause: "And for bad people to do good things—that [also] takes religion." The main point of Christianity is that it is a religion for sinners. Jesus made that very clear. When the Pharisees asked his disciples, "Why eateth your Master with publicans and sinners?" he said, "I come to call not the righteous but sinners to repentance." Only a small fraction of sinners repent and do good things but only a small fraction of good people are led by their religion to do bad things.^[59]

While Dyson has labeled himself a Christian, he identifies himself as agnostic about some of the specifics of his faith.^[60][61] For example, here is a passage from Dyson's review of The God of Hope and the End of the World from John Polkinghorne:

I am myself a Christian, a member of a community that preserves an ancient heritage of great literature and great music, provides help and counsel to young and old when they are in trouble, educates children in moral responsibility, and worships God in its own fashion. But I find Polkinghorne’s theology altogether too narrow for my taste. I have no use for a theology that claims to know the answers to deep questions but bases its arguments on the beliefs of a single tribe. I am a practicing Christian but not a believing Christian. To me, to worship God means to recognize that mind and intelligence are woven into the fabric of our universe in a way that altogether surpasses our comprehension.^[62]

Works

Freeman Dyson: Let's look for life in the outer solar system, TED Talks, February 2003.

Freeman Dyson 1 - My middle class upbringing, Web of Stories (1st of a series)

Big Ideas: Freeman Dyson on Living Through Four Revolutions, TVO, June 1, 2011 at Perimeter Institute, Waterloo, Canada.

• Symmetry Groups in Nuclear and Particle Physics, 1966 (Academic-oriented text)
• Interstellar Transport, Physics Today 1968
• Disturbing the Universe, 1979, ISBN 0-06-011108-9. Review
• Weapons and Hope, 1984 (Winner of the National Book Critics Circle Award).^[15] Review
• Origins of Life, 1986. Second edition, 1999. Review
• Infinite in All Directions, 1988, ISBN 0-14-014482-X. Review
• From Eros to Gaia, 1992
• Selected Papers of Freeman Dyson, 1996
• Imagined Worlds, Harvard University Press 1997, ISBN 978-0-674-53908-2. Review
• The Sun, the Genome and the Internet, 1999. Review
• L'mportanza di essere imprevedibile, Di Renzo Editore, 2003
• The Scientist as Rebel, 2006. Review
• Advanced Quantum Mechanics, World Scientific, 2007, ISBN 978-981-270-661-4. Freely available at: arXiv:quant-ph/0608140. (Dyson's 1951 Cornell lecture notes transcribed by David Derbes)
• A Many-Colored Glass: Reflections on the Place of Life in the Universe, University of Virginia Press, 2007. Review