David Deutsch (born 1953) is a physicist at Oxford University. He is a non-stipendiary Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation, Clarendon Laboratory^[1]. He pioneered the field of quantum computers, and is a proponent of the many-worlds interpretation of quantum mechanics. 1953 (MCMLIII) was a common year starting on Thursday (link is to a full 1953 calendar). ... Physicists working in a government lab A physicist is a scientist who studies or practices physics. ... The University of Oxford (often called Oxford University), located in the city of Oxford, England, is the oldest university in the English-speaking world. ... The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers. ... The many-worlds interpretation (or MWI) is an interpretation of quantum mechanics, based on Hugh Everetts relative-state formulation. ... Fig. ...

The Fabric of Reality

In his 1997 book The Fabric of Reality this interpretation, or what he calls the multiverse hypothesis, is one strand of a four-strand theory of everything. The four strands are: A multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality. ...

1. Hugh Everett's many-worlds interpretation of quantum physics, "the first and most important of the four strands".
2. Karl Popper's epistemology, especially its anti-inductivism and its requiring a realist (non-instrumental) interpretation of scientific theories, and its emphasis on taking seriously those bold conjectures that resist falsification.
3. Alan Turing's theory of computation especially as developed in Deutsch's "Turing principle", Turing's universal Turing machine being replaced by Deutsch's universal quantum computer. ("The theory of computation is now the quantum theory of computation.")
4. Richard Dawkins's refinement of Darwinian evolutionary theory, especially the ideas of replicator and meme as they integrate with Popperian problem-solving (the epistemological strand).

His theory of everything is emergentist rather than reductive. It aims not at the reduction of everything to particle physics, but rather mutual support among multiverse, computational, epistemological, and evolutionary principles. Hugh Everett III (November 11, 1930 – July 19, 1982) was an American physicist who first proposed the many-worlds interpretation of quantum physics, which he called his relative state formulation. ... This article may be too technical for most readers to understand. ... Fig. ... Sir Karl Raimund Popper, CH, MA, Ph. ... Epistemology or theory of knowledge is the branch of philosophy that studies the nature and scope of knowledge. ... Scientific realism is a view in the philosophy of science about the nature of scientific success, an answer to the question what does the success of science involve? The debate over what the success of science involves centers primarily on the status of unobservable entities (objects, process and events) apparently... Alan Turing is often considered the father of modern computer science. ... An artistic representation of a Turing Machine . ... Clinton Richard Dawkins (born March 26, 1941) is an eminent British ethologist, evolutionary theorist, and popular science writer who holds the Charles Simonyi Chair in the Public Understanding of Science at Oxford University. ... The name Darwin may refer to various places, things, and people, including: Charles Darwin (1809–1882), renowned naturalist and thinker associated with the theory of Natural Selection Darwin, Northern Territory, Australian city and the capital of the Northern Territory Darwin (operating system), a computer operating system used in Apples... The term meme (IPA: ), coined in 1976 by Richard Dawkins, refers to a replicator of cultural information that one mind transmits (verbally or by demonstration) to another mind. ... This article or section should include material from Episteme Epistemology (from the Greek words episteme=science and logos=word/speech) is the branch of philosophy that deals with the nature, origin and scope of knowledge. ...

The Turing principle

This emergentist posture allows computing theory's Turing principle to do serious work in Deutsch's world-view. In the strong form he favors it implies that a universal quantum computer, capable of rendering any physically possible environment, actually exists near the end of spacetime in every universe and is maintained by sentient beings with the knowledge required to increase its memory, computing cycles, and energy supply. In this he follows Frank Tipler in The Physics of Immortality, though he emphasizes the scientific component of Tipler's Omega Point hypothesis, the component that is justified by Popperian epistemology as implied by our best science. He is much less sympathetic to the non-scientific component, which provides rational reconstructions for traditional theological categories such as God, omniscience, omnipresence, benevolence, creation, and so on. The strong form of the Turing principle rests on a delicate mathematical argument favoring a universal quantum computer in all universes over such a computer in one universe, and either of these over such a computer in, say, 17 universes. So a weaker form of the Turing principle would commit to one universe. Also the reasoning for 'either one or all' presupposes a Big Crunch cosmology in order to generate the energy for the required computing cycles. If the universe instead expands forever, the Turing principle would have to take a weaker form, implying the existence of a more or less remote approximation to a universal quantum computer. Frank J. Tipler is a professor of mathematical physics at Tulane University, New Orleans, physicist, theologian and cornucopian philosopher. ... Omega point is a term invented by Pierre Teilhard de Chardin to describe the ultimate maximum level of complexity-consciousness, considered by him the aim towards which consciousness evolves. ... Epistemology or theory of knowledge is the branch of philosophy that studies the nature and scope of knowledge. ... This article discusses the term God in the context of monotheism and henotheism. ... Omniscience is the capacity to know everything, or at least everything that can be known about a character/s including thoughts, feelings, etc. ... Omnipresence is the ability to be present in every place at any, and/or every, time; unbounded or universal presence. ... In physical cosmology, the Big Crunch is a hypothesized collapse of the universe upon itself after its expansion eventually stops — a counterpart to the Big Bang. ...

The Turing principle is also sometimes called the Deutsch principle by those who question whether Turing's work on the foundations of computing was aiming to disclose what could be computed tractably "in nature". More conservative readings of Turing view him as concerned with what could be computed "by human computers", i.e. human mathematicians. On this reading Turing didn't aim at foundations for computing that provided tractability, because an algorithm might be calculable "by human computers" but without the speed to compute tractably what happens "in nature". There are tractability issues when, for instance, factoring and decryption problems are attacked with Turing-machine or classical-computation methods, problems that seem to be resolved by quantum-computing techniques such as Shor's algorithm, which takes advantage of the superposition of states in qubits to calculate "all at once" what a Turing machine would calculate serially. Turing universality isn't universality enough, Deutsch thinks. Turing's abstract computer needs to be replaced by the actual, physical, universal quantum computer derived from the Turing/Deutsch principle. In computer science, computational complexity theory is the branch of the theory of computation that studies the resources, or cost, of the computation required to solve a given computational problem. ... In math, see Factorization. ... This article is about algorithms for encryption and decryption. ... An artistic representation of a Turing Machine . ... Shors algorithm is a quantum algorithm for factoring a number N in O((log N)3) time and O(log N) space, named after Peter Shor. ... To meet Wikipedias quality standards and make it more accessible, this article needs a better explanation of technical details or more context regarding applications or importance to make it more accessible to a general audience, or at least to technical readers outside this specialty. ...

That principle is also sometimes called the Matrix principle, because Deutsch's conception of virtual reality figures in its statement: "It is possible to build a virtual reality generator whose repertoire includes every physically possible environment." Some cognitive psychologists think that Deutsch's view of the brain as a virtual-reality generating computer, adequate to rendering a humanly experienced environment, affords a sufficiently robust account of subjective experience or qualia, one consistent with a view of the mind/brain as a computer, to break down the impasse between qualia-phobes and qualia-freaks. A virtual-reality generator consists of an image generator to provide the subject with perceptual content from the several sensory modalities, perhaps in the forms of transducers connected directly to afferent nerves by use of neural implants, and a program to handle interaction between the subject's choices and the virtual environment. Nearer to the omega point this transhuman enhanced-biology scenario gives way to a posthuman condition, because biology becomes untenable. Gravitational shearing and other extreme forces call for more durable substrates for human psychology. The brain is replaced by sturdy computational equivalents in virtual realities, protected from the Big Crunch and pushed in the final moments by unlimited computational cycles affording their posthuman residents the subjective experience of immortality. The Matrix is a science fiction/action film written and directed by Larry and Andy Wachowski and starring Keanu Reeves, Laurence Fishburne, Carrie-Anne Moss and Hugo Weaving. ... Virtual reality (VR) is a technology which allows a user to interact with a computer-simulated environment, be it a real or imagined one. ... Cognitive Psychology is the school of psychology that examines internal mental processes such as problem solving, memory, and language. ... Redness is the canonical quale. ... Omega point is a term invented by Pierre Teilhard de Chardin to describe the ultimate maximum level of complexity-consciousness, considered by him the aim towards which consciousness evolves. ... Natasha Vita-Mores Primo is an artistic depiction of a hypothetical posthuman of transhumanist speculation. ... In literary and critical theory, posthumanism, meaning beyond humanism, is a European emergent philosophy and is the dominant secular, rational humanist philosophy. ... In physical cosmology, the Big Crunch is a hypothesized collapse of the universe upon itself after its expansion eventually stops — a counterpart to the Big Bang. ...

Quantum Computers and Proof Theory

A quantum computer farms out computing problems to other universes in order to achieve tractability for solutions that otherwise get bogged down by exponentially increasing demands for more time and other computational resources. The apparent need on a realist conception of science to posit such collaboration inspires a pugnacious comment from Deutsch: "To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor's algorithm works." The challenge is meant to imply that a Turing machine is incapable in principle of doing what a quantum computer can do, since the latter's operations in executing Shor's algorithm require computational resources from other worlds. And generally, a quantum computer's operations include computational steps in other worlds that are not present in any Turing-machine's tape (in this world). Deutsch thinks this has implications for proof theory, which must abandon the Cartesian model of an inspectable list of premises leading to a conclusion, in favor of a model of a process in which the relationship between premises and conclusion may be mediated by computations that are not inspectable (in this world). The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers. ... Scientific realism is a view in the philosophy of science about the nature of scientific success, an answer to the question what does the success of science involve? The debate over what the success of science involves centers primarily on the status of unobservable entities (objects, process and events) apparently... Shors algorithm is a quantum algorithm for factoring a number N in O((log N)3) time and O(log N) space, named after Peter Shor. ... Proof theory, studied as a branch of mathematical logic, represents proofs as formal mathematical objects, facilitating their analysis by mathematical techniques. ... René Descartes René Descartes (IPA: , March 31, 1596 – February 11, 1650), also known as Cartesius, worked as a philosopher and mathematician. ...

Counterfactual Inferences and Modal Realism

Another important theme in the book is that basic ideas about the universe are either vindicated or undermined by the multiverse hypothesis. For instance, counterfactual conditionals refer to nearby parallel worlds when they stipulate what a thing would do under conditions that do not actually obtain; one-worlders implicitly collapse what things can do into what they actually do. Consider a coin toss. The identical worlds in which I (copies of me) see it spinning become branched; in fifty-percent of those worlds versions of me see 'heads', and in fifty percent they see 'tails'. This actual distribution of worlds is what licenses the inference, about this world, that if the coin hadn't turned up 'heads' it would have turned up 'tails'. Instead of its being a basic fact that my observing 'heads' collapses probabilities into an actual outcome of the coin toss, those probabilites are grounded in actual universes in which both outcomes are represented. This is sometimes referred to as the difference between "collapse theories" (e.g., the Copenhagen interpretation) and no-collapse theories (e.g., many-worlds or the multiverse interpretation).[1] A counterfactual conditional (sometimes called a subjunctive conditional) is a logical conditional statement whose antecedent is (ordinarily) taken to be contrary to fact by those who utter it. ...

Deutsch acknowledges a kindred spirit in the philosopher David Lewis, whose modal realism handles counterfactuals in a similar fashion. He takes Lewis to have "postulated the existence of a multiverse for philosophical reasons alone." This is a contentious claim, since Lewis's realism about parallel worlds extends to worlds that are not physically possible, such as the world where Harry Potter was schooled at Hogwarts, whereas the parallel worlds in Deutsch's multiverse comprise all and only physically possible worlds. The worlds of the multiverse are governed by the same natural laws. Also Lewis's possible worlds are disjoint, whereas Deutsch's parallel worlds interact through interference. On the other hand, Lewis recognizes overlapping worlds as a theoretical possibility, and Deutsch's universal quantum computer can render Harry Potter worlds to any desired degree of accuracy. David K. Lewis David Kellogg Lewis (September 28, 1941 – October 14, 2001) is considered to have been one of the leading analytic philosophers of the latter half of the 20th century. ... A counterfactual conditional (sometimes called a subjunctive conditional) is a logical conditional statement whose antecedent is (ordinarily) taken to be contrary to fact by those who utter it. ... Parallel universe or alternate reality in science fiction and fantasy is a self-contained separate reality coexisting with our own. ... The Harry Potter books are an extremely popular series of fantasy novels by British writer J. K. Rowling. ... Hogwarts School of Witchcraft and Wizardry is a fictional school of magic that is the main setting of the Harry Potter series. ...

Knowledge and Life

Knowledge is a trans-universe structure, as one might expect because knowledge supports counterfactual implications, as revealed for instance in Robert Nozick's tracking account of knowledge. Nearby parallel worlds are united by a common history of knowledge acquisition, spelled out in broadly Popperian terms. The resulting epistemological niche lends stability and reliability to knowledge in each universe. Life is a similar trans-universe structure, molded by natural selection rather than rational criticism. What distinguishes genuine replicating DNA from junk DNA is that the former but not the latter is representative of a niche of replicators that extends across worlds. Indeed personal identity is inseparable from such a niche, which Deutsch picks out with the word "copies". A person is a set of copies in nearby parallel worlds. This comes out in his analysis of free will: I could have chosen otherwise is analysed as Other copies of me chose otherwise. And in the denouement to a dramatic chapter that rehearses interference experiments from a multiverse viewpoint, he writes of his copies, "Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone for a cup of tea." Knowledge is information of which a person, organization or other entity is aware. ... Robert Nozick (November 16, 1938 – January 23, 2002) was an American philosopher and Pellegrino University Professor at Harvard University. ... For other uses, see Life (disambiguation), Lives (disambiguation) or Living (disambiguation), Living Things (disambiguation) Look up life, living in Wiktionary, the free dictionary. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ... In philosophy, the issue of personal identity concerns the conditions under which a person at one time is the same person at another time. ... Free will is the philosophical doctrine that holds that our choices are ultimately up to ourselves. ...

Time, Causation, and Free Will

Not only are persons spread out through worlds, but they, like everything else, are quantized through time in any given world. Time is a series of moments, and a person who exists at a moment exists there forever in four-dimensional spacetime, rather than being transformed continuously through the flow of time. Such change and flow are mythical, Deutsch argues. The argument doesn't strictly require the multiverse hypothesis, but rather spacetime physics since Newton has implied that the openness of the future is an illusion, and consequently causation and free will are illusions. What the multiverse adds is a reduced account of common sense's ideas of causation and free will. Although an effect can't be changed by its cause, the counterfactuals that causal statements support are true. If the cause hadn't occurred, the effect would not have occurred. For the multiverse, which is "to a first approximation" a very large number of co-existing and slightly interacting spacetimes, includes universes in which the cause doesn't occur and its effect doesn't occur. And although the "me-copy" in this spacetime could not have done otherwise, there are me-copies in other worlds that actually do otherwise. There is a branching of these me-copies that validates my sense that my future is open, in contrast to spacetime physics. However, the open future of common sense is a myth. There is no flow of time dividing the actualities of the past from the unactualized potentialities of the future.

An intellectual descendant of David Hume via the paternity of Popper, Deutsch is not only a critic of induction but also a Humean about causation, to the degree that he rejects the idea of a causal power effecting a change, in favor of construing it as a multiverse regularity. So A causes B means something like After A-copies occur in many nearby parallel worlds, including the one in this world, B-copies occur. This regularity supports counterfactuals that accompany true causal claims, such as If A hadn't happened, B would not have taken place. There are affinities to Hume's constant-conjunction understanding of causation and Popper's deductive-nomological account. David Hume (April 26, 1711 – August 25, 1776)[1] was a Scottish philosopher, economist, and historian, as well as an important figure of Western philosophy and of the Scottish Enlightenment. ... Induction or inductive reasoning, sometimes called inductive logic, is the process of reasoning in which the premises of an argument support the conclusion, but do not ensure it. ... The philosophical concept of causality, the principles of causes, or causation, the working of causes, refers to the set of all particular causal or cause-and-effect relations. ... The D-N model is a formalisation of natural language scientific explanations. ...

Time and Personal Identity

Since "other times are just special cases of other universes", the temporal granularity of personhood through time is a special case of being spread out through worlds. In addition to one's identically time-stamped copies at a moment across parallel worlds transversely, there are the differently time-stamped copies across parallel worlds longitudinally, linked by natural law so as to give the individual's experience of one world and a continuous self. The implications for the theory of personal identity are not yet clear, but Derek Parfit's Reductionist view seems to be favored: The concept of personal identity ceases to apply when branching is taken into account, but branching maintains what's important about personal identity, such as psychological continuities having to do with memory, desire, character, and so forth.[2] Another possibility is that Robert Nozick's Closest-Continuer theory could be modified so as to track closeness transversely as well as longitudinally. The tracked slices of "me-copies" would be the continuing person. Deutsch would seem to favor some such approach. There are "multiple identical copies" of me in the multiverse. Which one am I? Deutsch answers, "I am, of course, all of them." (The Parfitian answer would be, "The concept of personal identity doesn't apply.") Copies need not be strictly identical in the sense of the identity of indiscernibles relativized to universes: All of my copies see a coin spinning in a coin toss, but an instant later half my copies see 'heads' come up, the other half see 'tails'. A distinction between copies, versions, and variants is at work here. Variants of me need not see the spinning coin. Versions of me see it though some of them see 'heads' and some 'tails'. The multiple identical copies of me all see the spinning coin. Derek Parfit (born December 11, 1942) is a British philosopher who specializes in problems of personal identity, rationality and ethics, and the relations between them. ... Robert Nozick (November 16, 1938 – January 23, 2002) was an American philosopher and Pellegrino University Professor at Harvard University. ... The identity of indiscernibles is an ontological principle that states that if there is no way of telling two entities apart then they are one and the same entity. ...

Time Travel

The possibility of future-directed time travel is assured by Einstein's special theory of relativity, which says that an observer who accelerates or decelerates will experience less time than an observer who is at rest or in uniform motion. This time dilation could make an astronaut's flight very short and the duration on Earth very long, but such a trip to Earth's future would be irreversible. as "no amount of time dilation can allow a spaceship to return from a flight before it took off". As for past-directed time travel, it is possible as a sort of sidestep from one universe to another, requiring a path between the two universes that is "hard-wired" into the structure of the multiverse. Whether such paths exist or not is an unresolved empirical question. If they were to exist and were to allow macro-objects like human beings to traverse them, time travel could occur without the grandfather paradox, because the time traveller would go to a point prior to the branching between his "home" universe and the universe in which he (the copy of him in the "away" universe) kills his grandfather (grandfather-copy). The grandfather paradox is a paradox of time travel, first conceived by the science fiction writer René Barjavel in his 1943 book Le voyageur imprudent (The imprudent traveller) [1]. The paradox, stated in the second person, is this: Suppose you travelled back in time and killed your biological grandfather before...

The multiverse hypothesis alone doesn't avoid the knowledge paradox, in which the time traveller goes to a point where he gives the collected works of Shakespeare to a hack writer, who seems to get "knowledge for free" that he uses to become the celebrated Shakespeare in that world. The Popperian epistemological strand of Deutsch's four-strand theory is invoked at this point. Just as life is understood as a trans-universe structure that is physically possible only through processes of natural selection, so too knowledge is understood as such a structure that is physically possible only through processes of rational problem-solving. Knowledge for free isn't possible in the multiverse when the multiverse is understood through Deutsch's emergentist Theory of Everything.

Summary of views

Politically, Deutsch is known to be sympathetic to libertarianism, and was a founder, along with Sarah Fitz-Claridge and Kolya Wolfe, of the Taking Children Seriously movement. He is also an atheist. See also Libertarianism and Libertarian Party Libertarian,is a term for person who has made a conscious and principled commitment, evidenced by a statement or Pledge, to forswear violating others rights and usually living in voluntary communities: thus in law no longer subject to government supervision. ... Taking Children Seriously is an educational philosophy founded by the libertarians Sarah Fitz-Claridge and David Deutsch. ... For information about the band, see Atheist (band). ...

Awards

He was awarded the Dirac Prize of the Institute of Physics in 1998, and the Edge of Computation Science Prize in 2005. Confusingly, there are two prominent awards in the field of theoretical physics and mathematics commonly known as the Dirac Prize, awarded by different organizations. ... The Institute of Physics (IOP) is the United Kingdoms professional body for physicists. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

Popular publications

• The Fabric of Reality, ISBN 0-14-014690-3

External links

• David Deutsch's homepage
• "It's much bigger than it looks" -- Edge
• David Deutsch's 20 min Talk at TED Conference (2005) Oxford, UK

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