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The Allure of the Multiverse - Paul Halpern *****

What with multiverses and metaverses, you just can't move for verses at the moment (amusingly, the 'verse' part essentially refers to a turn, which makes no sense in either case). 'Multiverse' as a concept was always going to be a trifle confusing, as 'universe' is supposed to refer to everything in existence, but as we will see, there are plenty of different ways, both philosophically and physically, that the term is applied to something beyond the familiar, four dimensional universe.

Paul Halpern packs plenty into this book - in order to put the various kinds of multiverse concept into context he pretty much goes through quantum physics, Big Bang cosmology and string theory (plus a touch of loop quantum gravity) in a fair amount of detail. We see how the most straightforward multiverse concept of a series of bubble universes in the same normal spacetime has been used to explain the fine tuning of the universe or is put forward as a consequence of the contentious notion of eternal inflation. But we also get the quantum multiverse of the Many Worlds Interpretation, the potential for brane universes that collide, the multiverses that are effectively generated by adding extra dimensions to the familiar ones, and the statistical multiverses where a theory such as string/M-theory gives us inconceivably vast numbers of alternate possibilities for the state of a universe.

Halpern tries hard to be neutral, always pointing out that there is not a consensus acceptance of any one of these theories - they all have plenty of cosmologists and physicists who think they don't make sense. We get both sides of the argument, though you do get the feel that the author would rather like a multiverse theory to be true, if only for the fun of it. Many of these theories are considered by their detractors to be ascientific in the sense that while they (to some degree) fit what observe, there is no way of disproving them - they can feel like clever people playing with maths that will never be anything more than mathematical puzzles and diversions.

Although Halpern's writing style is approachable, he does pack in so much that you sometimes have to let statements go over your head and just get on with it in the hope it will eventually all make sense (on the whole, it does). I'm disappointed he doesn't mention the mathematical error in the strong anthropic principle argument that says fine tuning implies a multiverse. He also revivifies the Bruno myth, referring to the 'assertion by sixteenth-century Italian philosopher Giordano Bruno that there are myriad worlds in space - which led, in part, to him being burned at the stake.' Bruno was martyred for religious views - his cosmological speculations were suspiciously similar to those of Nicholas of Cusa from 100 years earlier, who suffered no such fate, instead being made a cardinal.

I am not a great fan of highly speculative 'science' that is never likely to have evidential claims that can be falsified. However, I surprised myself by very much enjoying this journey through the weird and wonderful speculations of some leading cosmologists and mathematicians. Recommended.

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Review by Brian Clegg - See all Brian's online articles or subscribe to a weekly email free here
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