# David Deutsch

David Deutsch (born 1953 in Haifa, Israel) is a British physicist at the University of Oxford. He is a non-stipendiary Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation, Clarendon Laboratory. He pioneered the field of quantum computers, and is a proponent of the many-worlds interpretation of quantum mechanics.

## Quotes

* A computation is a physical process in which physical objects like computers, or slide rules or brains are used to discover, or to demonstrate or to harness properties of abstract objects—like numbers and equations. How can they do that? The answer is that we use them only in situations where to the best of our understanding the laws of physics will cause physical variables like electric currents in computers (representing bits) faithfully to mimic the abstract entities that we’re interested in.
** What is computation? How Does Nature Compute? Lecture (November 1st, 2008)

### The Fabric of Reality (1997)

* Surely it is more interesting to argue about what the truth is, than about what some particular thinker, however great, did or did not think.
* Our best theories are not only truer than common sense, they make more sense than common sense...
* The truly privileged theories are not the ones referring to any particular scale of size or complexity, nor the ones situated at any particular level of the predictive hierarchy—but the ones that contain the deepest explanations.
* The overwhelming majority of theories are rejected because they contain bad explanations, not because they fail experimental tests.
* A prediction, or any assertion, that cannot be defended might still be true, but an explanation that cannot be defended is not an explanation.
* To say that prediction is the purpose of a scientific theory is to confuse means with ends. It is like saying that the purpose of a spaceship is to burn fuel. … Passing experimental tests is only one of many things a theory has to do to achieve the real purpose of science, which is to explain the world.
** Ch. 1
* The quantum theory of parallel universes is not the problem, it is the solution. It is not some troublesome, optional interpretation emerging from arcane theoretical considerations. It is the explanation—the only one that is tenable—of a remarkable and counter-intuitive reality.
** Ch. 2
* Reality contains not only evidence, but also the means (such as our minds, and our artefacts) of understanding it. There are mathematical symbols in physical reality. The fact that it is we who put them there does not make them any less physical.
** Ch.3
* Thus we can see that if we take solipsism seriously - if we assume that it is true and that all valid explanations must scrupulously conform to it - it self destructs. How exactly does solipsism, taken seriously, differ from its common-sense rival, realism? The difference is based on no more than a renaming scheme. Solipsism insists on referring to objectively different things (such as external reality and my unconscious mind, or introspection and scientific observation) by the same names. But then it has to introduce the distinction through explanations in terms of something like the 'outer part of myself'. But no such extra explanation would be necessary without its insistence on an inexplicable renaming scheme. Solipsism must also postulate the existence of an additional class of processes - invisible, inexplicable processes which give the mind the illusion of living in an external reality. The solipsist, who believes that nothing exists other than the contents of one mind, must also believe that that mind is a phenomenon of greater multiplicity than is normal supposed. It contains other-people-like thoughts, planet-like thoughts and laws-of-physics-like thoughts. These thoughts are real. They develop in a complex way (or pretend to), and they have enough autonomy to surprise, disappoint, enlighten or thwart other classes of thoughts which call themselves 'I'. Thus the solipsist's explanation of the world is in terms of interacting thoughts rather than interacting objects. But those thoughts are real, and interact according to the same rules that the realist says govern the interaction of objects. Thus solipsism, far from being a world view striped to its essentials, is actually just realism disguised and weighed down by additional baggage, introduced only to be explained away.
** Ch.4
* Think of all our knowledge-generating processes, our whole culture and civilization, and all the thought processes in the minds of every individual, and indeed the entire evolving biosphere as well, as being a gigantic computation. The whole thing is executing a self-motivated, self-generating computer program. More specifically it is, as I have mentioned, a virtual-reality program in the process of rendering, with ever-increasing accuracy, the whole of existence.
* It is possible to build a virtual-reality generator whose repertoire includes every possible environment.
** Ch. 6
* Since building a universal virtual-reality generator is physically possible, it must actually be built in some universes.
** Ch. 6
* Quantum computation is … nothing less than a distinctly new way of harnessing nature … It will be the first technology that allows useful tasks to be performed in collaboration between parallel universes, and then sharing the results.
** Ch. 9 : Quantum Computers
* The next chapter is likely to provoke many mathematicians. This can't be helped. Mathematics is not what they think it is.
** Ch. 10
* Mathematical knowledge may, just like our scientific knowledge, be deep and broad, it may be subtle and wonderfully explanatory, it may be uncontroversially accepted; but it cannot be certain.
** Ch. 10
* Necessary truth is merely the subject-matter of mathematics, not the reward we get for doing mathematics. The object of mathematics is not, and cannot be, mathematical certainty. It is not even mathematical truth, certain or otherwise. It is, and must be, mathematical explanation.
* Time travel may be achieved one day, or it may not. But if it is, it should not require any fundamental change in world-view, at least for those who broadly share the world view I am presenting in this book.
** Ch. 12
* Kuhn's theory suffers from a fatal flaw. It explains the succession from one paradigm to another in sociological or psychological terms, rather than as having primarily to do with the objective merit of the rival explanations. Yet unless one understands science as a quest for explanations, the fact that it does find successive explanations, each objectively better than the last, is inexplicable.
** Ch. 13; commentary on the ideas of Thomas Kuhn, as presented in the book The Structure of Scientific Revolutions

### The Beginning of Infinity (2011)

* Experience is indeed essential to science, but its role is different from that supposed by empiricism. It is not the source from which theories are derived. Its main use is to choose between theories that have already been guessed. That is what ‘learning from experience’ is.
** Ch. 1
* The misconception that knowledge needs authority to be genuine or reliable dates back to antiquity, and it still prevails. To this day, most courses in the philosophy of knowledge teach that knowledge is some form of justified, true belief, where ‘justified’ means designated as true (or at least ‘probable’) by reference to some authoritative source or touchstone of knowledge.
** Ch. 1
* That progress is both possible and desirable is perhaps the quintessential idea of the Enlightenment. It motivates all traditions of criticism, as well as the principle of seeking good explanations. But it can be interpreted in two almost opposite ways, both of which, confusingly, are known as ‘perfectibility’. One is that humans, or human societies, are capable of attaining a state of supposed perfection – such as the Buddhist or Hindu ‘nirvana’, or various political utopias. The other is that every attainable state can be indefinitely improved. Fallibilism rules out that first position in favour of the second.
** Ch. 3
* Any theory about improvement raises the question: how is the knowledge of how to make that improvement created? Was it already present at the outset? The theory that it was is creationism. Did it ‘just happen’? The theory that it did is spontaneous generation.
** Ch. 4
* If something is permitted by the laws of physics, then the only thing that can prevent it from being technologically possible is not knowing how.
** Ch. 9
* Let me define that [wealth] in a non-parochial way as the repertoire of physical transformations that they would be capable of causing.
** Ch. 9
* Could it be that the moral imperative not to destroy the means of correcting mistakes is the only moral imperative? That all other moral truths follow from it?
** Ch. 10

## Deutsch's Law

This was Deutsch's response to the 2004 Edge Annual Question: "What is Your Law?"
Deutsch's Law: Every problem that is interesting is also soluble.
    Corollary #1: Inherently insoluble problems are inherently boring.
    Corollary #2: In the long run, the distinction between what is interesting and what is boring is not a matter of subjective taste but an objective fact.
    Corollary #3: The problem of why every problem that is interesting is also soluble, is soluble.

## Weblog

* As I understand it, the claim is that the less you use Homeopathy, the better it works. Sounds plausible to me.

## TED Talks

* The rational thing for a layperson to do is to take seriously the prevailing scientific theory.

## Quotes about David Deutsch

* Native slipstream thinking, which has been around for millennia, anticipated recent cutting-edge physics, ironically suggesting that Natives have had things right all along. The closest approximation in quantum mechanics is the concept of the "multiverse," which posits that reality consists of a number of simultaneously existing alternate worlds and/or parallel worlds. Interested readers will enjoy John Gribbin's In Search of the Multiverse: Parallel Worlds, Hidden Dimensions, and the Quest for the Frontiers of Reality (2010) and David Deutsch's seminal The Fabric of Reality: The Science of Parallel Universes and Its Implications (1998). Deutsch's approach describes reality as "an infinite library full of copies of books that all start out the same way on page one, but in which the story in each book deviates more and more from the versions in the other books the farther into the book you read." The further twist of Deutsch's theory is that it "allows universes to merge back together... as if two of the books in the library have the same happy ending arrived at by different routes."
** Grace Dillon Walking the Clouds: An Anthology of Indigenous Science Fiction (2012)

## External links

* David Deutsch Old website (archival)
* David Deutsch New website (in progress)
* How are moral assertions connected with the world of facts?
* The Discrete and the Continuous