Product Description

A synthesis of unifying ideas arising from quantum theory, the theory of computation, epistemology and the theory of evolution, this book explores the deep connections between the progress of knowledge of the world and the process of change in the world itself.

Product Details

• Amazon Sales Rank: #27402 in Books
• Published on: 1998-03-26
• Original language: German
• Binding: Paperback
• 400 pages

Review
One major school of quantum theory posits a multiplicity of universes; but what does that imply about the reality we live in? A simple experiment, familiar to every student of physics, involves light passing through slits in a barrier; its results, according to Oxford physicist Deutsch, lead inevitably to the idea that there are countless universes parallel to our own, through which some of the light must pass. This "many worlds" interpretation of quantum theory has gained advocates in recent years, and Deutsch argues that it is time for scientists to face the full implications of this idea. (After all, the entire point of science is to help us understand the world we live in - the "fabric of reality" of his title.) To that end, he outlines a new view of the multiverse (the total of all the parallel universes), combining ideas from four "strands" of science: quantum physics, epistemology, the theory of computation, and modern evolutionary theory. He argues that quantum computation, a discipline in which he is a pioneering thinker, has the potential for building computers that draw on their counterparts in parallel universes; this could make artificial intelligence a reality, despite Roger Penrose's objections (which Deutsch deals with in some detail). Likewise, time travel into both the future and the past should be possible, though not in quite the form envisioned by science fiction writers; the trips would almost certainly be one-way, and they would likely take the travelers into different universes from the one they began in. Deutsch takes particular pains to refute Thomas Kuhn's "paradigm" model of science, which essentially denies progress. A final chapter looks at the long-range implications of his views, including the place of esthetic and moral values (areas more scientists now seem willing to confront). Not easy going by any means, but worth the work for anyone interested in the thought processes of a scientist on the leading edge of his discipline. (Kirkus Reviews)

Synopsis
A synthesis of unifying ideas arising from quantum theory, the theory of computation, epistemology and the theory of evolution, this book explores the deep connections between the progress of knowledge of the world and the process of change in the world itself.

Customer Reviews

Quantum torture!
Life is far to short to waste on this excrutiatingly pompous, self-congratulatory and tedious (supposed) account of the theory of everything. If you ever decide self-flagellation is absolutely unavoidable this is just the thing for you! I ran screaming, pretty damn quickly, back to the sanctuary of Michio Kaku and Brian Greene!

Brilliant, but not perfect.
David Deutsch's aim in writing The Fabric of Reality is to present a theory that does not relate to one particular subject, but to all subjects: a `Theory of Everything'. To do so, he interrelates quantum mechanics, computation and virtual reality, Popperian scientific method, and Darwinian evolution. One of the unifying themes of the book is his view that science is concerned not with prediction but with explanation.

First, he discusses quantum physics and the existence, inferred from experiment and observation, of shadow photons. So far so good. But having done so, he goes on to deduce the existence of parallel universes - unobservable universes that are similar to but not the same as ours - in some ways connected to ours (how else would we guess their existence?) and yet in others not connected. These unobservable universes he refers to, collectively, as `the multiverse'. He then makes a speculation - unfounded apart from the inferred existence of unobservable shadow photons - that I find difficult to accept:

`While I was writing that, hosts of shadow Davids were writing it too. They too drew a distinction between tangible and shadow photons; but the photons they called `shadow' include the ones I call 'tangible', and the photons they called 'tangible' are among those I call 'shadow' [...] 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.'

Reading those words, I was reminded of Hume's assertion that while it is legitimate to infer a cause from an effect, it is not legitimate then to return and infer new effects from that same cause.

Deutsch's assumption is vulnerable to reductio ad absurdam. By his own argument for the existence of counterfactual or `might-have-been' worlds, a parallel universe could exist - and, if we are to believe the metaphysics of the philosopher David Lewis, really does exist - in which David Deutsch is a garbage operative and Mao Tse Tung is an evangelical Christian.

Having brought into being the multiverse, Deutsch continues throughout the book to refer to it as if its existence were an indisputable fact. Much later in the book, he claims, with little foundation as far as I can see, that the multiverse did not come into being until some time `after' the big bang - ignoring his earlier (and to my mind, well justified) agreement with presentism - that the past, the present and the future are all one, and terms like `before' and `after' are meaningless.

Having discussed problem-solving and criteria for reality, Deutsch goes on to discuss virtual reality with particular reference to the Turing Principle and logically possible experience. Here again, I feel that Deutsch makes an assumption that stretches the bounds of conceptual possibility to breaking point:

`Since we cannot hope to render all logically possible environments, let us consider a weaker (but ultimately more interesting) sort of universality. Let us define a universal virtual reality generator as one whose repertoire contains that of every other physically possible virtual reality generator. Can such a machine exist? It can. Thinking about futuristic devices based on computer-controlled nerve stimulation makes this obvious - in fact, almost too obvious. Such a machine could be programmed to have the characteristics of any rival machine. It could calculate how that machine would respond, under any given program, to any behaviour by the user and so could render those responses with perfect accuracy (from the point of view of any given user) [...] given the appropriate program and enough time and storage media, it could calculate the output of any computation performed by any other computer, including the one in the rival virtual reality generator. Thus the feasibility of a universal virtual reality generator depends on the existence of a universal computer - a single machine that can calculate anything that can be calculated.'

His reference to `perfect accuracy (from the point of view of any given user' I found particularly hard to swallow. Necessarily, accuracy cannot be perfect if it is from a point of view. That sort of accuracy is a relative. Besides, how can a given user testify to accuracy, even if they have experienced the environment? Perhaps Deutsch should read Wittgenstein's private language argument, in which the suggestion that it is possible to compare a pain I have today with a pain I had yesterday is reduced to absurdity.

Hume's scepticism with regard to reason is relevant: he points out that if we wish to make a judgment about the reliability of any proposition, we should first assess the reliability of that kind of proposition in general as well as the reliability of the author of the proposition. But we can't stop there. We must also apply the same rule to ourselves and assess our own ability to make assessments as to the reliability of propositions, and that of the authors of those propositions. Then there emerge further questions concerning our ability to assess our own ability to assess prior probabilities and so on ad infinitum so that `all the rules of logic require a continual diminution and, at last, a total extinction of belief and evidence.' (Basic Flying Instruction, p.105)

Deutsch is not only a physicist. He is a physicalist and a functionalist. Towards the end of the book he seems to get carried away by his functionalism, suggesting that human beings or their evolved descendants have the potential to control not only themselves, not only the planet, but the universe. I had the uncomfortable feeling, from time to time, that he was too ready to `pick and mix' worldviews to compile his explanation of reality. The universe is one, and then it is many. The multiverse is one, but it also could be many. Things are separate, but they could be joined. Time flows, then it doesn't.

Deutsch refers to photons travelling through a vacuum, presumably an absolute vacuum. This assumption sounds very much to me like Newton's supposition of `action at a distance', which was so brilliantly deflated by Faraday's metaphysical speculations, discarded by Einstein as a stepping stone to STR and GTR, and is denied by quantum field theory. Even in string theory, there has to be a length of string between the blobs. As Parmenides warned 2500 years ago, when we speak of `what is not' we get into serious trouble.

Deutsch relies heavily on the Cantor-Turing conjecture, which, following Roger Penrose, he states as the Turing principle:

`For abstract computers simulating physical objects, there exists an abstract universal computer whose repertoire includes any computation that any physically possible object can perform.'

From that principle, he concludes that it is possible to build a virtual reality generator whose repertoire includes every physically possible environment. In referring to `every physically possible environment' he assumes that that there are more than one physically possible environments, and that such environments are entirely separate. On page 291 he claims: `a virtual reality generator could [...] give one the experience of living in the age of the dinosaurs, or in the trenches of the First World War, and it could make the constellations, dates, newspapers or whatever appear correctly for those times.' My problem with this is that I believe that giving a `perfectly accurate' experience of the trenches in the First World War (or indeed any environment) is impossible, as every environment is joined to every other: there is only one environment.

Deutsch frequently refers to physical reality, and I am left wondering whether he distinguishes between reality and physical reality. Personally, I side with Spinoza's view that there is only one reality, that it is infinite in infinite ways, or aspects, or attributes, and that we human beings, being limited creatures, have access to reality - can conceive of it - in only two ways: through physics, and through logic or mathematics. (Descartes'`thought and extension'.)

Spinoza's view of energy as matter-in-motion and of Nature as one self-causing infinite reality conceived under infinite attributes, was influential on Einstein's development of space-time physics and his abandonment of the supposition of absolute simultaneity. Amazingly (to me, at any rate!), Spinoza's view seems to sit very well with David Deutsch's supposition of parallel universes, which seem to me to be nothing other than Spinoza's infinite aspects or attributes of reality, to which we have access only to thought and matter - maths and the physical sciences.

In spite of the above criticisms, this is a brilliant, exciting and stimulating book. I am not a professor of anything, only a miserable graduate in philosophy from the University of Durham. But as the mathematician Dodgson said, a cat may look at a king.

Five stars, but a warning...
...if you're going to read one book on quantum physics, don't read this one. I don't mean to say that the book is bad - in fact it's probably the most clearly written account available - just that it is a highly personal account with only one interpretation given. If you want to make your own mind up, go for something less exciting but more balanced like John Gribbin.

If you've done that, and want to see the consequences of taking a possible interpretation seriously, then this book is brilliant, and a lot easier to make headway with than, say, Penrose.