Rating: 
Summary: Quantum Theory at last well explained!
Review: As I am very interested in all modern theories, I have read several books trying to go deep into the Quantum Theory. Up till this one, none had satisfied me.
To be able to explain a difficult subject, and Quantum Theory is a very difficult one, one needs to really understand it and David Deutsch really knows what he is talking about!
Unhappily, most of the well known scientists know and believe little about what they talk.
Read this book, follow David explanations step by step, and you will arrive into places and conclusions your mind never thought possible they exist.
The book takes you into unsuspected areas, and opens fantastic horizons to your mind!
A mandatory book to any one that is trying to understand the world in which we live, as well as all the other possible worlds!
Rating: 
Summary: An awesome book with an optimistic world view
Review: Combining quantum physics, the theory of knowledge
(Karl Popper), computation and evolution
David Deutsch arrives at a world view that is
optimistic and points the way to things to come
in the next century. A time were one person can
once again understand everything that is known,
according to Deutsch.Surely, We might not experience reality but rather
some elaborate
Virtual Reality show in our minds, still we can construct
impressive models of the universe. By looking at photons David Deutsch arrives at the remarkable
theory of the multiverse.
I guess most people wouldn't agree that the existence
of parallel universes can be detected
from experiments like the two-slit light experiment.
Also, I guess that most people would think that the
multiverse theory should be consigned
to the room of scientific oddities.
Still, I rather enjoy the theory and how Deutsch plays
around with it! In the multiverse other times are just special
cases of other universes. So, travelling "back" in time
doesn't create a paradox. One might meet historical persons
and interact with them (in another universe),
but such universe will not evolve into the universe we
know - so no paradox.
Out there in the mindblowing array of parallel universes,
that make up the multiverse, Virtual Reality generators
of increasing sophistication exists. Including some that
can mimic any part of the multiverse.
If reality was not slippery before, certainly
it is after reading this book!
The grand finale is Frank Tiplers Omega Point Theory,
where extreme cosmological scenarios makes settings
possible where one can perform unlimited computations
in a limited time. Beings here might resurrect the dead (us)
in Virtual Reality renderings for their own amusement -
Or they might embark upon the solution of tremendous
problems creating still more awesome scenarios. The book seems to be saying, that somewhere out
there in the multiverse, someone will necessarily
succeed in making a Omega Point spacetime.
Awesome perspectives in an awesome book.
And a fun read. -Simon
Rating: 
Summary: Mind-bending analysis that falls short in places
Review: Deutsch's presentation is fascinating, mind-expanding, challenging, provocative, and--at times--riveting. It is also infuriating, perplexing, reductive, and--at times--vague. (Please note: I am not convinced that the multiverse as Deutsch describes it exists, nor am I threatened by the possibility that it might. As a result, I do not mean to quarrel with--or support--the idea itself. Instead, I am reviewing Deutsch's book from the point of view of a lay reader.) I do recommend this book to anyone interested in reading a summary of the pursuit of a "theory of everything" and a defense of the science of parallel universes. Deutsch's theory of everything depends on four theories: quantum (as espoused by Everett), epistemology (Popper), evolution (Dawkins), and computation (Turing). Even if one does not ultimately agree with Deutsch's ideas, his book offers some interesting thought experiments (the chapter on "time travel" is especially fun) and a concise overview of several scientific trends. In addition, his book provides a decent defense of why the theory of the multiverse should be considered a reasonable explanation for the interference results obtained the infamous two-slit experiment. That said, I do think Deutsch's book contains many shortcomings. First, although the multiverse may be a valid explanation for interference phenomenon, Deutsch fails to convince that it is THE explanation. In one short paragraph, he dismisses David Bohm's theory of wave-particle duality. "Working out what Bohm's invisible wave will do requires the same computations as working out what trillions of shadow photons will do." One could easily reverse this sentence as a criticism of Everett and Deutsch: that the trillions of unseen photons requires the same computations as working out what Bohm's single invisible wave will do. Deutsch does not explain (in this book, anyway) why trillions of photons are simpler than one wave, and he does his readers a disservice by pretending that Bohm's work does not deserve a full refutation. Second, and similarly, Deutsch dismisses with an even shorter paragraph the charge that his "theory of everything" is anthropocentric. (He pretty much admits it is, but tries--unconvincingly, to this reader--to turn it into an argument in his favor.) Third, his discussion of evolution (one of the four "equal" strands of his theory of everything) is a mere 25 pages and, unlike the rest of the book, is at times incomprehensible and seems completely indebted to Dawkins. (Not that there is anything wrong with Dawkins's work; rather, Deutsch just seems in over his head during this part of the book.) Fourth, he rejects Kuhn's belief in the rigidity of scientific paradigms (for example, the inability of thinkers in Galileo's time to accept the full implications of the Copernican system because they were so used to thinking of the world in Ptolemaic and Judeo-Christian terms), but then he describes a modern scientific establishment that refuses to accept the multiverse implications of quantum theory because they are rooted to the concept of a single universe. (Just because modern scientific discourse is more civil does not mean that Kuhn's argument is incorrect. Deutsch's opponents are still mocking him behind his back, in book reviews, and anonymously on this Web site. Or, even more effectively, they are ignoring him altogether.) And, finally, his discussion of Tipler's omega-point theory is hurried and unfortunately nebulous: at one point, Deutsch seems to be saying that knowledge in the universe will become omniscient and omnipresent--which is practically the same as saying that the universe will become itself. Nevertheless, regardless of what you think of its implications, Deutsch's views deserve serious consideration and, as necessary, rebuttal--not mockery and scorn. In the same way that we read Lucretius even though we know him to be wrong (or, for that matter, Einstein because we believe he is mostly right), we should read Deutsch's work because he challenges the way we look at our world.
Rating: 
Summary: Waste of time & money. BADLY written. Better books elsewhere
Review: Hello! I actually slogged my way all the way through this EXCEPTIONALLY BADLY written book, because of my large interest in the subject matter. David Deutsch should have used a ghost writer for this, as he obviously was not up to the task. He is in love with page long paragraphs, as this book is filled with them. This, of course, reduces readability and comprehension. He couldn't write a clearly written sentence, if his life depended on it. He also (out of 3,000+ books I have read) is the most arrogant writer I have ever read. He dismisses, cavalierly, and without much explanation, ANYONE who doesn't agree with him, and, though not saying this directly, certainly hinting strongly that he thinks that anyone disagreeing with him is an idiot. I found this attitude repulsive. I expected to see a lot of experimental research to be quoted in this book, but it is almost totally lacking in any. He wanders around in this book, in bizarre philosophical mumbo-jumbo, that I don't think that he really understands properly, acting as if this proves some cosmic points. The few facts that he actually provides in this book, are better described in any number of other books. If I had not read previously on related topics, his writing is so bad, that this book would have been incomprehensible to me. To sum up in a much clearer way, than Deutsch could ever manage, the main point of his book, he basically says that a finite (but very large), number of parallel universes exist, that cover everything that every could, or might have happened; and that this in essence, happened at the moment of the big bang, or within 10 to the -43 seconds after. Time is discrete, not continuous (like a string of pearls looks continuous, but if you break the thread, it is actually shown to be discrete). Time doesn't "flow", but our conciousnesses are only aware of one discrete moment of time, at a time. (Think, motion picture here. There are 30 static, non-moving picture frames per second, but your mind "fuses" them, into an apparent continuous whole, of an illusion of motion. This is how Deutsch views the universe. ALL the "movies" (universes), that can, could, or might, ever exist; and all possible events of "time", were created simultaneously at the moment of the big bang. Our conciousness, though, is only aware of one, discrete, "movie frame" (discrete bit of time), at a time, within only one "movie" (universe). So, continuous time DOESN'T really exist. It just appears that way because of limitations in our conciousness. Another way to think of it, is that the multiverse is like a video tape store. Each video tape, represents a different universe. Each static frame on the video tape, represents a discrete moment of time. Though all video tapes (universes), and all static frames (discrete moments of time), exist simultaneously, your consciousness can only derive meaning from it, from experiencing the frames sequencially, NOT simultaneously. So, only discret time exists, not continuous time.) There, now you don't have to bother buying this book. Since he gives almost NO experimental evidence for this point of view, anyway, you don't need to worry about the fact that I didn't offer "proof", either! For those people whose reviews I read, that seem to think that this book was a stunning revelation; I can only conclude that you haven't read much about this topic, before. Stuff along these lines, existed in science fiction probably since the thirties, and in hard science, for decades. Whether or not some of what Deutsch believes, is ultimately proven to be correct or not, I don't know. For people in the field pushing parallel universes, though, it might have been better if this book had never been written, as it was such a HUGE turn-off for me. My 2 cents worth. Karl
Rating: 
Summary: I cannot recommend this book
Review: I expected far more from the author in substance and style. I was disappointed! David Deutsch is a brilliant mathematician and Quantum Physicist and a pioneer in Quantum Computation. I have seen his lectures and read some of his publications on the subject, and those were indeed brilliant. However, I could not finish this book and I was bored to my teeth. I think this book can be reduced to one fifth its size without losing much substance. The first chapter was not a good start; the author presented his views about categories of physicists and their approachs to science and experimentations. I thought this subject, if it had any place in the book, it would be the last chapter or possibly an appendix. Certainly, if the author expends time to explain that a beam of light is made of photons, he should not expect novice readers to be interested in the inner politics of the modern physics community. Probably the most interesting theme in this book is the discussion on shadow particles from others universes and their interaction with tangible particles in our real universe (the one I am writing this review in). The author is an avid proponent of the multi-universe theory (Multiverse), and I think his passion comes through on this subject.
Rating:
Summary: Complicated - fluffed up and poorly written
Review: I found this book to be extremely hard to follow as it was more of a fluffed up marshmellow than actually fact or theory based. What I found much easier to follow was one by M. R. Franks titled The Universe and Multiple Reality.
Rating:
Summary: Thoroughly enjoyable albeit disjointed.
Review: I read this once about 5 years ago. It was a vertigo-inducing experience. The author's writing context-switched between way too many subjects to do justice to any of them. On many topics, the author's reach clearly exceeded his grasp; and certainly, he fails to communication just exactly how all of these supposedly complementary theories interlock into a coherent, multifaceted whole. Despite all this, I found the book very enjoyable. What really caught my attention was his highly conversant treatment of Popperian philosophy of science. Many scientists and mathematicians are unaware of some of the weirder turns taken by 20th century philosophers of science (analytic not to mention continental). The author does a good job of refuting what still today is the prevailing view of epistemology. Where he errs is in his categorical claim that knowledge obtained by "Popperian" selection & criticism is justified (in the philosophical sense of the word). Popper never, ever would have claimed this for his theory. What Popper did was to propose a way out of the the Wittgensteinian cul-de-sac of all-or-nothing knowledge. Readers interested in this subject would do well to check out "Evolutionary Epistemology" Radnitzky & Bartley, ed.
Rating:
Summary: A scientist does not a philosopher make
Review: I really cannot find any redeeming value in this book. I had hoped to find some insights from a world famous quantum physicist, and a founder of Quantum Computation, however what I received was a hodge-podge of loosely related themes, the only connection I could find was "Physics is the most important thing in the multiverse, and quantum physics is even more important." Some of the outlandish claims that Deutsch makes in this book are the following: the mind-body problem is solved; P=NP is solved (it's false); the Church-Turing Thesis is a fact; everything that Deutsch dislikes is a form of solipsism. Of course, no details are given to the solutions, as these are just trivial facts, I guess, according to Deutsch. But after reading the book, probably the one claim that I abhorred the most was never explicitly stated, but a simple corrollary are statements that he makes again and again: every human endeavour is just quantum physics. The reason for this is because human beings are (at the base level) just quantum-mechanical things, everything we do is a result of physics, and therefore while mathematicians (I happen to be a PhD student in mathematics, set-theory in particular) may think that they are dealing with abstract concepts, they are actually dealing with nothing more that quantum effects in their brains (which Deutsch equates with minds). A simple extension of this principle tells us that philosophy is just a quantum-mechanical process, ditto with art, politics, friendships, love, etc. Of course, something that is hidden in the above idea is a reductionist claim --- that everything can be reduced to quantum effects. Not surprisingly, it turns out that Deutsch thinks that reductionism is wrong. There are several places in the text where Deutsch ends up contradicting himself, or appeals to claims that he thinks are incorrect. (He grants that criticism of scientific theories does not rest on experimental evidence alone, but while claiming that in fact experimental evidence is very low on the scale, for the most part the only criticisms he ends up making are through experimental evidence.) My advice for anyone interested in the metaphysical or epistemological issues raised in this book --- read the works of a meta-physicist, not a quantum-physicist.
Rating:
Summary: A scientist does not a philosopher make
Review: I really cannot find any redeeming value in this book. I had hoped to find some insights from a world famous quantum physicist, and a founder of Quantum Computation, however what I received was a hodge-podge of loosely related themes, the only connection I could find was "Physics is the most important thing in the multiverse, and quantum physics is even more important." Some of the outlandish claims that Deutsch makes in this book are the following: the mind-body problem is solved; P=NP is solved (it's false); the Church-Turing Thesis is a fact; everything that Deutsch dislikes is a form of solipsism. Of course, no details are given to the solutions, as these are just trivial facts, I guess, according to Deutsch. But after reading the book, probably the one claim that I abhorred the most was never explicitly stated, but a simple corrollary are statements that he makes again and again: every human endeavour is just quantum physics. The reason for this is because human beings are (at the base level) just quantum-mechanical things, everything we do is a result of physics, and therefore while mathematicians (I happen to be a PhD student in mathematics, set-theory in particular) may think that they are dealing with abstract concepts, they are actually dealing with nothing more that quantum effects in their brains (which Deutsch equates with minds). A simple extension of this principle tells us that philosophy is just a quantum-mechanical process, ditto with art, politics, friendships, love, etc. Of course, something that is hidden in the above idea is a reductionist claim --- that everything can be reduced to quantum effects. Not surprisingly, it turns out that Deutsch thinks that reductionism is wrong. There are several places in the text where Deutsch ends up contradicting himself, or appeals to claims that he thinks are incorrect. (He grants that criticism of scientific theories does not rest on experimental evidence alone, but while claiming that in fact experimental evidence is very low on the scale, for the most part the only criticisms he ends up making are through experimental evidence.) My advice for anyone interested in the metaphysical or epistemological issues raised in this book --- read the works of a meta-physicist, not a quantum-physicist.
Rating:
Summary: Should compare with best alternatives, no evidence, limited
Review: I would love to see many-worlds shown superior to all available alternatives, but this book did not make the case. The chapter on epistemology is excellent. He concludes that a successful theory must have explanatory power and must satisfy evidence that refutes all prior theories. He does a good but incomplete job of illustrating the explanatory power of many-worlds, failing to show how many-worlds explains the EPR results. Unfortunately he ignores all competent existing theories. Indeterminism and wavefunction collapse are not required by QM. They are merely interpretations. Wavefunction collapse in particular is not required to explain the double-slit results because the virtual particles (another interpretation) that constitute the wavefunction are not observable and have no relation to the new entity that results from a "measurement" interaction. The EPR experiments assert that "hidden variables" havc been eliminated, but indeterminacy is still not proven. Deutsch rightfully proclaims many-worlds superior to one interpretation of QM, based solely on the double-slit results, but he fails to mention alternatives. The most compelling evidence is the idea that a quantum computer could make computations requiring >10^500 parallel universes. IF such a computation is performed, it may be difficult to explain in any other way, but it has not been done and the obstacles may be fundamental. He asserts that all worlds in the multiverse must follow the same physical laws. There are many more worlds out there that fit in his philosophy. We know our particular laws result from post-Big-Bang broken symmetries and that event itself was not a pristine Perfect Form. What does Deutsch mean by "laws of physics"? Is his interpretation that there are many multiverses? I had great hopes for the chapter on time, but his writing style is sometimes impenetrable and it came across as hand-waving. If Richard Feynman liked many-worlds, it must be right. Deutsch should try again, in collaboration with a scientifically literate writer.
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