Freeman Dyson

Dyson was born on 15 December 1923, at Crowthorne in Berkshire, England. He was the son of Mildred Lucy (Atkey) and George Dyson. His father, a prominent composer, was later knighted. His mother had a law degree, and after Dyson was born she worked as a social worker.[17] Dyson had one sibling, his older sister, Alice, who remembered him as a boy surrounded by encyclopedias and always calculating on sheets of paper.[18] At the age of four he tried to calculate the number of atoms in the Sun.[19] 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.[4] Politically, Dyson said he was "brought up as a socialist".[20]

From 1936 to 1941 Dyson was a scholar at Winchester College, where his father was Director of Music. At the age of 17 he studied pure mathematics with A. S. Besicovitch as his tutor[21] at Trinity College, Cambridge (where he won a scholarship at age 15), and at age 19 he was assigned to war work in the Operational Research Section (ORS) of Royal Air Force Bomber Command, where he developed analytical methods for calculating the ideal density for bomber formations.[22][23] to help the Royal Air Force bomb German targets during World War II.[22] After the war, Dyson was readmitted to Trinity College, where he obtained a BA degree in mathematics.[24][5] From 1946 to 1949 he was a fellow of his college, occupying rooms just below those of the philosopher Ludwig Wittgenstein, who resigned his professorship in 1947.[25]

In 1947 Dyson published two papers in number theory.[26][27] Friends and colleagues described him as shy and self-effacing, with a contrarian streak that his friends found refreshing but intellectual opponents found 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 favourite 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."[13]

On G. I. Taylor's advice and recommendation, Dyson moved to the United States in 1947 as a Commonwealth Fellow for postgraduate study with Hans Bethe at Cornell University (1947–1948).[28][29] There he made the acquaintance of Richard Feynman. The budding English physicist recognized the brilliance of the flamboyant American and worked with him. He then moved to the Institute for Advanced Study (1948–1949), before returning to England (1949–51), where he was a research fellow at the University of Birmingham.[30] In 1949, Dyson demonstrated the equivalence of two formulations of quantum electrodynamics (QED): Richard Feynman's diagrams and the operator method developed by Julian Schwinger and Shin'ichirō Tomonaga. He was the first person after their creator 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 in a form that other physicists could understand, facilitating the physics community's acceptance of Feynman's work. J. Robert Oppenheimer, in particular, was persuaded by Dyson that Feynman's new theory was as valid as Schwinger's and Tomonaga's. Also in 1949, in related work, Dyson invented the Dyson series. It was this paper that inspired John Ward to derive his celebrated Ward–Takahashi identity.[31]

Dyson joined the faculty at Cornell as a physics professor in 1951, though he still had no doctorate. In December 1952, Oppenheimer, the director of the Institute for Advanced Study in Princeton, New Jersey, offered Dyson a lifetime appointment at the Institute, "for proving me wrong", in Oppenheimer's words.[32] Dyson remained at the Institute until the end of his career.[33][34] In 1957 he became a US citizen.[lower-alpha 1][5][35] From 1957 to 1961 Dyson worked on Project Orion,[36] 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, in which Dyson was involved and which he supported,[37] permitted only underground nuclear weapons testing,[38] and the project was abandoned in 1965.[39]

In 1958 Dyson was a member of the design team under Edward Teller for TRIGA, a small, inherently safe nuclear reactor used throughout the world in hospitals and universities for the production of medical isotopes.[40]

In 1966, independently of Elliott H. Lieb and Walter Thirring, Dyson and Andrew Lenard published a paper proving that the Pauli exclusion principle plays the main role in the stability of bulk matter.[41] Hence it is not the electromagnetic repulsion between outer-shell orbital electrons that prevents two stacked wood blocks from coalescing into a single piece, but the exclusion principle applied to electrons and protons that generates the classical macroscopic normal force. In condensed matter physics, Dyson also analysed the phase transition of the Ising model in one dimension and spin waves.[42]

Dyson also did work in a variety of topics in mathematics, such as topology, analysis, number theory and random matrices[43] In 1973 the number theorist Hugh Lowell 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 that it looked like something in mathematical physics and that Montgomery should show it to Dyson, which he did. Dyson recognized the formula as the pair correlation function of the Gaussian unitary ensemble, which physicists have studied extensively. 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.[44]

Around 1979 Dyson worked with the Institute for Energy Analysis on climate studies. This group, under Alvin Weinberg's direction, pioneered multidisciplinary climate studies, including a strong biology group. Also during the 1970s, Dyson worked on climate studies conducted by the JASON defense advisory group.[13]

Dyson retired from the Institute for Advanced Study in 1994.[45] In 1998 he 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 was on its board of trustees.[46] Dyson was a longtime member of the JASON group.[47]

Dyson won numerous scientific awards, but never a Nobel Prize. Nobel physics laureate Steven Weinberg said that the Nobel committee "fleeced" Dyson, but Dyson 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."[13] Dyson was a regular contributor to The New York Review of Books, and published a memoir, Maker of Patterns: An Autobiography Through Letters in 2018.[48]

In 2012 Dyson published (with William H. Press) a fundamental new result about the prisoner's dilemma in the Proceedings of the National Academy of Sciences of the United States of America.[49] He wrote a foreword to a treatise on psychic phenomena in which he concluded that "ESP is real... but cannot be tested with the clumsy tools of science".[50]

With his first wife, the Swiss mathematician Verena Huber-Dyson, Dyson had two children, Esther and George. In 1958 he married Imme Jung (born 1936) and they had four more children: Dorothy, Mia, Rebecca, and Emily Dyson.[13]

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".[51] His son George is a historian of science,[52] one of whose books is Project Orion: The Atomic Spaceship 1957–1965.[53]

Dyson died on 28 February 2020 at a hospital near Princeton, New Jersey, from complications following a fall. He was 96.[54][55][33]

Dyson admitted his record as a prophet was mixed, but thought it is better to be wrong than vague, and that in meeting the world's material needs, technology must be beautiful and cheap.

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.

— Dyson 2007

Dyson coined the term "green technologies", based on biology instead of physics or chemistry, to describe new species of microorganisms and plants designed to meet human needs. He argued that such technologies would be based on solar power rather than the fossil fuels whose use he saw as part of what he calls "gray technologies" of industry. He believed that genetically engineered crops, which he described as green, can help end rural poverty, with a movement based in ethics to end the inequitable distribution of wealth on the planet.[56]

Dyson favored the dual origin theory: that life first formed as cells, then enzymes, and finally, much later, genes. This was first propounded by the Russian Alexander Oparin.[57]J. B. S. Haldane developed the same theory independently.[58] In Dyson's version of the theory life evolved in two stages, widely separated in time. Because of the biochemistry he regards it as too unlikely that genes could have developed fully blown in one process. Current cells contain adenosine triphosphate or ATP and adenosine 5'-monophosphate or AMP, which greatly resemble each other but have completely different functions. ATP transports energy around the cell, and AMP is part of RNA and the genetic apparatus. Dyson proposed that in a primitive early cell containing ATP and AMP, RNA and replication came into existence only because of the similarity between AMP and RNA. He suggested that AMP was produced when ATP molecules lost two of their phosphate radicals, and then one cell somewhere performed Eigen's experiment and produced RNA.[59]

There is no direct evidence for the dual origin theory, because once genes developed, they took over, obliterating all traces of the earlier forms of life. In the first origin, the cells were probably just drops of water held together by surface tension, teeming with enzymes and chemical reactions, and having a primitive kind of growth or replication. When the liquid drop became too big, it split into two drops. Many complex molecules formed in these "little city economies" and the probability that genes would eventually develop in them was much greater than in the prebiotic environment.[60]

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

In 1960 Dyson wrote a short paper for the journal Science titled "Search for Artificial Stellar Sources of Infrared Radiation".[61] In it he speculated that a technologically advanced extraterrestrial civilization might surround its native star with artificial structures to maximize the capture of the star's energy. Eventually the civilization would enclose the star, intercepting electromagnetic radiation with wavelengths from visible light downward and radiating waste heat outward as infrared radiation. One method of searching for extraterrestrial civilizations would be to look for large objects radiating in the infrared range of the electromagnetic spectrum.

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 surrounds its parent star.

— Davis 1978

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 called a Dyson sphere, although Dyson used the term "shell". Dyson said that he used the term "artificial biosphere" in the article to mean a habitat, not a shape. 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 Dyson credited publicly.[62][lower-alpha 2]

Dyson 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.

— Dyson 1997

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.

— Davis 1978

Dyson was 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. For a quarter-century Dyson was unhappy about 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.

— Davis 1978

Dyson still hoped for cheap space travel, but was resigned to waiting for private entrepreneurs to develop something new and inexpensive.

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.

— Dyson 1997

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.

— Dyson 1997

Dyson proposed that an immortal group of intelligent beings could escape the prospect of heat death by extending time to infinity while expending only a finite amount of energy.[63] This is also known as the Dyson scenario.[64]

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.[65]

The Dyson series, the formal solution of an explicitly time-dependent Schrödinger equation by iteration, and the corresponding Dyson time-ordering operator ${\displaystyle {\mathcal {T}}\,,}$ an entity of basic importance in the mathematical formulation of quantum mechanics, are also named after Dyson.[66]

Freeman Dyson in 2007 at the Institute for Advanced Study

Dyson and Hugh Montgomery discovered an intriguing connection between quantum physics and Montgomery's pair correlation conjecture about the zeros of the zeta function. The primes 2, 3, 5, 7, 11, 13, 17, 19, ... are described by the Riemann zeta function, and Dyson had previously developed a description of quantum physics based on m by m arrays of totally random numbers.[67] Montgomery and Dyson discovered that the eigenvalues of these matrices are spaced apart in exactly the same manner as Montgomery conjectured for the nontrivial zeros of the zeta function. Andrew Odlyzko has verified the conjecture on a computer, using his Odlyzko–Schönhage algorithm to calculate many zeros.[68]

There are in nature one, two, and three dimensional quasicrystals. Mathematicians define a quasicrystal as a set of discrete points whose Fourier transform is also a set of discrete points. Odlyzko has done extensive computations of the Fourier transform of the nontrivial zeros of the zeta function, and they seem to form a one-dimensional quasicrystal. This would in fact follow from the Riemann hypothesis.[69]

The rank of a partition, shown as its Young diagram

In number theory and combinatorics rank of a partition of a positive integer is a certain integer associated with the partition. Dyson introduced the concept in a paper published in the journal Eureka. It was presented in the context of a study of certain congruence properties of the partition function discovered by the mathematician Srinivasa Ramanujan.[70]

In number theory, the crank of a partition is a certain integer associated with the partition in number theory. Dyson first introduced the term without a definition in a 1944 paper in a journal published by the Mathematics Society of Cambridge University.[71] He then gave a list of properties this yet-to-be-defined quantity should have. In 1988, George E. Andrews and Frank Garvan discovered a definition for the crank satisfying the properties Dyson had hypothesized.[72]

Astrochicken is the name given to a thought experiment Dyson expounded in his book Disturbing the Universe (1979). He contemplated how humanity could build a small, self-replicating automaton that could explore space more efficiently than a manned craft could. He attributed the general idea to John von Neumann, based on a lecture von Neumann gave in 1948 titled The General and Logical Theory of Automata. Dyson expanded on von Neumann's automata theories and added a biological component.[73]

John von Neumann

Dyson suggested that philosophers can be broadly, if simplistically, divided into lumpers and splitters. These roughly correspond to Platonists, who regard the world as made up of ideas, and as detailed by Gerard Cecil De Van Der Wall materialists, who imagine it divided into atoms.[74]

Dyson agreed that technically humans and additional CO₂ emissions contribute to warming. However, he felt that any such contribution was minor relative to natural effects and that the benefits of additional CO₂ outweighed any associated negative effects.[14] He said that in many ways increased atmospheric carbon dioxide is beneficial,[75] and that it is increasing biological growth, agricultural yields and forests.[14] He believed that existing simulation models of climate change fail to account for some important factors, and that the results thus contain too great a margin of error to reliably predict trends.[76][77]

Dyson's views on global warming were criticized.[13] Climate scientist James Hansen said that Dyson "doesn't know what he's talking about ... If he's going to wander into something with major consequences for humanity and other life on the planet, then he should first do his homework – which he obviously has not done on global warming."[78] Dyson replied 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."[79]

Dyson argued that political efforts to reduce the causes of climate change distract from other global problems that should take priority.[80]

Since originally taking interest in climate studies in the 1970s, Dyson suggested that carbon dioxide levels in the atmosphere could be controlled by planting fast-growing trees. He calculated that it would take a trillion trees to remove all carbon from the atmosphere.[81][13] In a 2014 interview he said, "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."[4]

Dyson was a member of the academic advisory council of the Global Warming Policy Foundation, a climate sceptic think tank chaired by Nigel Lawson.[82][83] He compared belief in climate change to religion.[14]

At the British Bomber Command, Dyson and colleagues proposed removing 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.

— Dyson 1979, The Children's Crusade

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].

— Dyson 1979, The Blood of a Poet

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.

— Dyson 1984

In 1967, in his capacity as a military adviser, Dyson wrote an influential paper on the issue of possible US use of tactical nuclear weapons in the Vietnam War. When a general said in a meeting, "I think it might be a good idea to throw in a nuke now and then, just to keep the other side guessing ..."[84] Dyson became alarmed and obtained permission to write a report on the pros and cons of using such weapons from a purely military point of view. (This report, Tactical Nuclear Weapons in Southeast Asia, published by the Institute for Defense Analyses, was obtained, with some redactions, by the Nautilus Institute for Security and Sustainability under the Freedom of Information act in 2002.)[85] It was sufficiently objective that both sides in the debate based their arguments on it. Dyson says that the report showed that, even from a narrow military point of view, the US was better off not using nuclear weapons.[86]

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 described him as a political liberal.[13] He was one of 29 leading US scientists who wrote Obama a strongly supportive letter about his administration's 2015 nuclear deal with Iran.[87]

Dyson was raised in what he described as a "watered-down Church of England Christianity".[13] He was a nondenominational Christian and attended various churches, from Presbyterian to Roman Catholic. Regarding doctrinal or Christological issues, he said, "I am neither a saint nor a theologian. To me, good works are more important than theology."[88]

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.[88]

Dyson partially disagreed 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."[89]

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.

— Dyson 2006c harvnb error: multiple targets (2×): CITEREFDyson2006c (help)

While Dyson called himself a Christian, he identified himself as agnostic about some of the specifics of his faith.[90][91] For example, in reviewing The God of Hope and the End of the World by John Polkinghorne, Dyson wrote:

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.

— Dyson 2002a

In The God Delusion (2006), evolutionary biologist and atheist activist Richard Dawkins singled out Dyson for accepting the Templeton Prize in 2000: "It would be taken as an endorsement of religion by one of the world's most distinguished physicists."[92] In 2000, Dyson declared that he was a (non-denominational) Christian,[88] and he disagreed with Dawkins on several occasions, as when he criticized Dawkins' understanding of evolution.[93]

• Freeman Dyson at The New York Review of Books (content for subscribers only)
• "Heretical thoughts about science & society", essay by Freeman Dyson [8.7.2007]
• Templeton Prize acceptance lecture 2000, by Freeman Dyson
• Imagined Worlds by Freeman Dyson, 1996: Chapter 1
• Video Interview of Freeman Dyson discussing Bogus Climate Models on YouTube
• A radio interview with Freeman Dyson Aired on the Lewis Burke Frumkes Radio Show in 2009.
• Suzan Mazur interviewing Dyson, 2012, CounterPunch
• "Pushing the Boundaries – A Conversation with Freeman Dyson", Ideas Roadshow, 2014
• Freeman Dyson and Gregory Benford: Forseeing the Next 35 Years – Where Will We Be in 2054? on YouTube, Arthur C. Clarke Center for Human Imagination, February 2019.

• "Freeman Dyson's Brain", interview by Stewart Brand at Wired, 1998
• 2008 Video Interview with Freeman Dyson by Atomic Heritage Foundation, Voices of the Manhattan Project
• Roberts, Russ (7 March 2011). "Dyson on Heresy, Climate Change, and Science". EconTalk. Library of Economics and Liberty.
• "Freeman Dyson: 'I kept quiet for thirty years, maybe it's time to speak'". 52 Insights. 15 June 2018. Retrieved 25 November 2019.
• "Three Mathematicians We Lost in 2020: John Conway, Ronald Graham, and Freeman Dyson all explored the world with their minds" Rockmore, Dan. (December 31, 2020) The New Yorker.
• Freeman Dyson at TED