John Gribbin is a science writer who has written a large number of books explaining modern physics and cosmology to the non-mathematical reader and there is always the danger of repeating oneself when one is as prolific as this. This book is actually a sequel to an earlier one, called 'In Search of Schrödinger's Cat', published ten years previously, and this might lead one to suspect that it is a potboiler, but in fact it is better than this.
The reference to Schrödinger's notorious cat is a sound pointer to what we can expect from the book: it is about the paradoxes of quantum mechanics and the new theories that have been advanced since 1984 to account for them. The puzzle of wave-particle duality is summarized in a prologue, and then we go back in history to look at how earlier thinkers such as Huygens, Newton, Young, Faraday, and Maxwell thought about light. This part is done well; Gribbin gives just enough information but not too much. Coming to more modern times, we encounter Einstein and also Feynman, and with the historical background now taken care of we are equipped to contemplate the paradoxes inherent in what we know about light today. The quantum paradoxes are certainly mind-blowing, but their importance is not purely intellectual; as Gribbin explains, they may have practical implications as well, for they provide a possible basis for quantum cryptography and teleportation. I found I could believe in the cryptography but not, alas, in the teleportation.
In a chapter entitle 'Desperate Remedies', Gribbin takes up the theme of the different interpretations of quantum theory. Here he makes the interesting point that all the theories 'work', in the sense that they account for the behaviour of existing experiments and correctly predict the outcome of new experiments; this is unique in science. Choosing among the various possibilities on offer is thus a matter of personal taste. In a way, the multiplicity of intepretations mirrors the multiplicity of ways that a photon seems able to go through two slits at once. Gribbin himself thinks that none of the explanations is wholly satisfactory but that this does not matter too much because they are useful in practice. So perhaps, he thinks, we need all of them.
The final section of the book shifts our attention, rather briefly, from the very small (the world of photons) to the very large (cosmology), before concluding with some final reflections on the nature of reality. In an epilogue called 'The solution—myth for our times' Gribbin insists repeatedly that all interpretations are analogies, myths, or models. They are 'crutches to help us imagine what is going on at the quantum level and to make testable predictions'. This is true even of his own favourite, an interpretation advanced by John Cramer, which Gribbin explains in some detail. It requires one to picture 'a field which is a time-symmetric mixture of a retarded wave propagating into the future and an advanced wave propagating into the past'. Considerable intellectual agility is required to grasp this theory, I found, but this is only what should be expected, for, as Feynman said, 'nobody knows how it can be like that'.
This is an attractively written book which is well worth reading for anyone with a taste for grappling with the philosophical implications of modern physics. There is a useful bibliography.