The Hidden Reality – Brian Greene *****

I hugely enjoyed Brian Greene’s previous books, The Elegant Universe and The Fabric of the Cosmos, so when I saw this title had been released I was looking forward to reading it. In The Hidden Reality, Greene explores the various possibilities of there being parallel universes beyond our own. He takes us through, in all, nine conceptions of the multiverse that seem to emerge naturally from the mathematics behind some of our most successful physical theories. The book turns out to be an absolute delight.

We start with the fascinating idea that, if the universe is infinite in extent, this implies the existence of an infinite number of places in the universe where physical conditions are identical to those we find around us, and therefore an unending number of worlds in which ‘you’ and ‘I’ are going about their lives in exactly the same way as we are doing, here. Later in the book, we look at, among other things, the ‘braneworlds’ scenario that comes out of string theory, and the idea that we live in one universe among many in a computer simulated multiverse.

For each variation on the multiverse theme, Greene first brings us up to speed on the physics we need in order to make sense of the ideas to be looked at, bringing in discussions of quantum mechanics, relativity, string theory and thermodynamics where necessary. This background information is incredibly useful in its own right – Greene’s explanation of the difficulties of merging quantum mechanics and general relativity, for instance, is better than I have seen anywhere else. Whilst good across the board, the best chapter is the one on the ‘Many Worlds’ interpretation of quantum mechanics – the summary here would be ideal to read before going on to look at a more full exploration of the subject.

Greene clearly appreciates the difficulties the layperson is likely to have in coming to grips with the tricky concepts being introduced, and he knows how to take the absolute beginner along with him, and to bring them to a good level of understanding. His analogies always get across the main ideas well, and when things get tough, the reader is warned.

Many of the ideas here do seem highly speculative, and some will argue that, because they appear not to be falsifiable, this is not good science. Greene anticipates this reaction, however, and devotes a chapter to it. He outlines the experiments and observations that could, in fact, give us an indication as to whether any of these ideas are on the right track. He sensibly emphasises that we shouldn’t consider sound any theory that cannot be verified by observation or experiment, and, ultimately, he is convincing that the ideas discussed in the book are at least worth considering for the time being.

If you have read Greene’s previous books, there will be occasions where you may want to skip a section or two, where the discussions overlap a little with those covered in the previous books. But whatever background you to come to this book with, you’re likely to be very impressed with the presentation of the science and hugely intrigued by the ideas themselves. I have no hesitation in giving this book five stars, and can easily see it being among the best popular science books of 2011. Highly recommended.

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Review by Matt Chorley