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Quantum Entanglement (Essential Knowledge) - Jed Brody ****

An entry in MIT Press's pocket-sized Essential Knowledge series, this is an attempt to take on one of the strangest and most mind-bending aspects of physics - quantum entanglement - in a new way.

There are several books describing the historical development and implications of quantum entanglement, but what Jed Brody does is take an experimentalist's view and helps the reader understand what is involved in a Bell inequality and how a test of quantum entanglement in this fashion really works.

There are other bits as well - a very rapid introduction and a rather tagged-on feeling bit about quantum theory and relativity, plus a too-brief-to-understand trip into the unlikely world of quantum Bayesianism. But the crucial part of the book, and the reason it gets four stars, is that experimental bit. Specifically what Brody does, something that I have never seen before in any other book on the subject, is give an explanation of a specific Bell inequality that proves why the outcome of a particular measurement runs counter to local realism - that's a real achievement. Usually, the best that can be done is to tell the reader such an experiment will prove the outcome without explaining why.

There is one big proviso. I think this is a great book if you have already picked up the background to quantum entanglement (try The God Effect for this, rather than Brody's 'further reading' recommendations), but it really wouldn't be so useful if you haven't absorbed the context, history and meaning - so if the bits of the review above referring to a Bell inequality, say, don't mean a lot to you, do some background reading first.

Even with that background, some of the later examples that Brody gives involve just too much twisted logic to easily get your brain around - but I still think that the relatively small part of the book that involves working through a basic Bell inequality is well worth laying your hands on it, and make this title unique.

Definitely one of the better additions to this quirky series.

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Review by Brian Clegg

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