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.
Rating: 
Summary: Rent fabric
Review: In the spectrum of quantum interpretations the parallel universe version has a beguiling science fiction charm, but seems to suffer the same fate as the intimations of 'platonic ideas': they seem to be there, but what is 'existence'? Til mathematicians decide, rogue physics can define no boundary to its abstractions and we find this phantom of the multiverse tricking us into borderline reality. Out in left field then, we suspect.
A very interesting book, which outstripped my competence, but which also struck me in another way, due to its fond wish for the higher coherence of physics, evolution, epistemology, and computation, taken into some unity.
I am often baffled by a genuine puzzle, why so many brilliant physicists can't see the flaws in Darwin's theory. This book unwittingly shows the reason, the projected 'consilience' of subjects, the ambition to complete the foundations for a Total World View, veil the transition of brilliant physics to Darwinian muddle, in the name of reductionism. It doesn't add up, and the wished for plug in unit in the ascent on complexity needs more than Dawkins' genetic 'evolutionary particle'. From genius to idiot. The funny thing is the brilliant intuition of parallel worlds, however that is to be taken. For we see in historical evolution a mysterious parallel effect, in the so-called 'Axial Age', as historical evolution branches into a synchronous phase. So maybe all this is onto something.
The big puzzle: why are all the world's best physicists confused about Darwinism?
Rating:
Summary: An Inspiring World View on The Four Strands ...
Review: This work, which I read about a year ago, presented an inspiring commentary on the interconnectedness of David Deutsch's "Four Strands": quantum physics and the Many-Worlds Interpretation (MWI); the theory of evolution as by Darwin/Dawkins; the theory of quantum computation; and the theory of knowledge (as per Karl Popper), explanation, and understanding (see David Deutsch's Web site at http://www.qubit.org/people/david/index.php?path=The%20Fabric%20of%20Reality).
Deutsch presents a convincing argument for MWI (see http://en.wikipedia.org/wiki/Everett_many-worlds_interpretation), as opposed to the Copenhagen Interpretation (CI) (see http://en.wikipedia.org/wiki/Copenhagen_interpretation). MWI and CI are opposing theories that seek to explain the observed results of the following "double-slit" light experiment (see http://en.wikipedia.org/wiki/Double-slit_experiment): When photons are passed through a double slit, they seem to behave as waves, yet when the photons are observed individually, they appear as particles, and not as waves. According to MWI, a phenomenon known as quantum interference, which assumes the existence of parallel universes, is responsible for this result; in contrast, according to CI, the act of measurement itself causes an instantaneous "collapse of the wave function," meaning that measuring the outcome causes a single outcome somehow to be picked nondeterministically from the collection of all possible outcomes.
Deutsch explains this experiment in a very clear and understandable manner, then argues that MWI is a superior explanation to CI. He presents a number of reasons for this (please correct me if my memory is wrong here, since I don't physically have the book with me right now): First, that MWI is intuitively far simpler than CI, and further, that MWI is also linked to theoretical results in quantum computation that show that a quantum computer would need to be able to make use of the order of 10^(500) atoms for some possible computations implementing Shor's Algorithm (see http://en.wikipedia.org/wiki/Shor's_algorithm) for factoring public keys for RSA encryption that are the products of very large primes in only polynomial time. Since there are only about 10^(80) atoms in the known universe, the atoms must come from somewhere outside the known universe. Deutsch argues that they, in fact, come from parallel universes. Hence, he argues, MWI provides an overall better explanation for these results than CI.
The style of the work reminded me distinctly of that of the late eminent British analytical philosopher, Bertrand Russell. The arguments were succinct and cohesive, yet added an element of David Deutsch's enthusiasm for the topic. I especially appreciated Deutsch's emphasis on understanding, as opposed to memorization, and his viewpoint that it was still theoretically possible to understand (although not to memorize) everything in the known universe.
Having come from an undergraduate background in theoretical computer science (algorithms, in particular, at Yale), I approached the book with an eye toward learning about quantum computation from an elementary, yet theoretical, perspective. This book further explained how quantum computation is only one strand among four that form Deutsch's comprehensive world view. The other three--quantum physics, the theory of evolution, and the theory of knowledge--are all interlinked. Further, he presents an argument as to why computation is a physical process, and not a purely abstract one, and hence that computation cannot be fully separated from physics--in fact, that computation properly belongs in the realm of physics.
Another aspect of the work that truly delighted me was his chapter on virtual reality, which I have yet to see in some other books on quantum computation so far. He explains the concept of a virtual reality generator, and explains why a such a generator could potentially simulate anything possible without violating the laws of logic, even if it would violate the known laws of physics. He further predicts that by approximately the year 2040 A.D., there will come to exist generators so sophisticated that they would be able to simulate reality to the extent that a person using such a generator would not be able to tell the difference between the generator-generated universe and the world outside. He adds that the key to designing such a generator would be direct manipulation of sensory input, since the brain interprets reality through the senses, and explains that it would even be possible to slow down natural brain processing in order to accomodate some potential calculations that could take too much computer time to keep up in real time with the brain.
This book enlighted me to the importance of learning physics for quantum computation. Further, the work was very lucidly written, and has motivated me to pursue self-study in quantum computation in the hope of entering this very exciting new field.
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Rating:
Summary: Good Ole Brain-Bending Material
Review: Warning: This book requires a strong foundation of physics knowledge. The author refers to relativity and skims over quantum mechanics pretty quickly in applying his thoughts.
As for the material itself, the book is great. Deutsch gives us a tour of leading theoretical physics and their applications to our understanding to the physical universe. For anyone interested in physics, epistemology, or philosophy, the narrative is engrossing as Deutsch meticulously develops ideas that really work your brain over.
My only issue with this book is the author's idea of the "four strands." Granted, Deutsch only claims that the future model of reality will include these four strands (evolution, computing, quantum mechanics, Popperian theory) in some way. Yet, I don't find his strands to intertwine with one another. His discourse on quantum mechanics is fascinating, but doesn't significantly tie-in to his overall philosophy. Deutsch does show wonderful similarities between Popperian epistemology, Godel's Incompleteness Theorem, and the Turing Principle. But again, he doesn't develop an overall encompassing philosophical model.
Regardless, the book is informative, a pleasure to read, and well-written. Definitely recommened.
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