The God Equation - Michio Kaku ***

When physicist Leon Lederman wanted to  call his book on the elusive Higgs boson 'The Goddam Particle' his publisher objected and instead made it The God Particle. This usage has cropped up a couple of times since in popular science, notably The God Effect on quantum entanglement, and now Michio Kaku is applying it to the concept of a so-called Theory of Everything - a mechanism that pulls together the fundamental forces of nature including gravity. There is no certainty that such a theory is possible, but if it did exist, it would provide the foundation of physics. Even so, it seems unlikely that it would honour the claim in the book's publicity that it would 'fulfil that most ancient and basic of human desires - to understand the meaning of our lives'.

Kaku has worked on string theory - the theory he believes will give us that theory of everything - since the 1960s and is strongly invested in it. He promises us a 'balanced, objective analysis of string theory's breakthroughs and limitations' - but given this comes after him saying that it is the 'leading (and to my mind, only) candidate' for a theory of everything, it's not totally surprising that this feels quite a subjective view. For example, at one point we are told that a concern about string theory is the lack of evidence for the required 10 or 11 dimensions. Kaku points out that, if they exist, they should have a small impact on the force of gravity over small distances. He describes an experiment... where the results are negative. But rather than see this as more indication of the doubtful nature of the theory, he gives it the throwaway line 'But this means only that there are no added dimensions in Colorado.'

When Kaku gets onto what string theory actually is (which doesn't occur until page 141 out of 198), he gives a good high level overview before plunging into some very hand-waving attempts to show why it actually matters (certainly there is no suggestion it gives us a chance to understand the meaning of our lives). What I find disappointing is that there is no attempt to put string theory into context of rival approaches. I know loop quantum gravity, for example, is not a theory of everything, but they can't both hold - yet it never gets a mention. On the plus side, Kaku is honest about the problems of string theory and the lack of supporting evidence - but when, for example, he says that the discovery of supersymmetric particles would support it, but they haven't been found yet, he doesn't say that string theory enthusiasts had expected them to be found by the Large Hadron Collider.

It is also a shame how little detail there is of the development of string theory, what it says and why it, for instance, requires so many dimensions. For a book about a theory of everything, we seem to have almost everything but the theory itself. The reason we don't get into string theory until page 141 is that the majority of the book is pretty much a summary of the history of physics. In his usual flamboyant style, Kaku breezes through the history of science leading up to the development of string theory. Unfortunately, he adopts an approach that would worry historians of science, cherry picking and sometimes inaccurate.

We start with a very old fashioned presentation of the now-dismissed dark ages concept, when classical scientific 'philosophical discussions and debates were lost… Darkness spread over the Western world and scientific inquiry was largely replaced by belief in superstition, magic, and sorcery.' Kaku trots out the familiar myth that the 'chief crime' in Giordano Bruno's heresy trial was 'Declaring that life may exist on planets circling other stars', implies Galileo invented the telescope and blames 'the church' for standard Aristotelean theories such as the unchanging heavens and movement caused by natural tendencies.

When we get onto quantum physics, there are some real oddities. Kaku tells us that quantum effects are rarely seen directly 'because Planck's constant is a very small number and only affects the universe on the subatomic level' - but then trots out the Schrödinger's cat experiment as if it was significant. He gives unchallenged the idea that the Copenhagen interpretation involves 'observation (which requires consciousness)'. He also says Copenhagen has fallen in to disfavour, with the many worlds interpretation now 'more popular' - something that isn't borne out by surveys of physicists.

Overall, then, this is a book that gives a fast, light, readable, but somewhat limited, introduction to physics. As always, Kaku writes with energy, clear enthusiasm and a delight in the wonders that science uncovers. But the book fails to convince either that string theory is valid or that it can deliver anything of the sort of significance Kaku promises by comparing it to the innovation that arose from understanding Newtonian physics, electromagnetism and quantum theory. 

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Review by Brian Clegg