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Gerry Gilmore on Michio Kaku's pot-pourri of cosmology, Parallel Worlds
Parallel Worlds by Michio Kaku

Parallel Worlds: The Science of Alternative Universes and Our Future in the Cosmos
by Michio Kaku
432pp, Allen Lane, £20

Cosmology books, explaining the probable origins and possible futures of our universe, have become the latest little black number: everyone seems to have one, many are appealing, but few match the classics. Michio Kaku is the latest to enter the lists, with his version of the history of the discovery of modern cosmology, of the mind-stretching array of mathematically-based calculations and speculations about possible far futures, including travel outside our universe into other multi-verses, and of his speculations on what it all means. Longlisted for the Samuel Johnson award for non-fiction, this is not a classic, but does raise many interesting ideas.

It falls into three parts: the first reviews our discovery of modern cosmology, the second describes some of the more intellectually challenging and counter-intuitive aspects of modern physics, astrophysics and cosmology theories, the third considers possible long-term (very long-term) futures for existence, knowledge and the universe. Along the way the usual suspects are rounded up, with black holes, time travel, quantum entanglement, string theory, 11-dimensional M-branes, and the anthropic principle all getting a mention.

In the year AD 426 Augustine of Hippo reused what was already an old joke: "What was God doing before the Creation? Preparing Hell for those who ask that question." Hell is clearly the natural home of cosmologists. Which has not reduced their number at all.

At the beginning of the Renaissance, European man imagined himself at the peak of creation, comfortably located by God at the centre, on an Earth designed to support his life. That concept was the result of the accumulated wisdom of the greatest minds over millennia, and is indeed the most that can be deduced about the universe by pure thought — not very much, in fact, about what we have not observed, and even less about first causes.

The manifest limitations in the achievements of science without experiment and information began to be circumvented by the invention of precision scientific instruments, and the dedication of large amounts of money to "pure" research (the term "pure" making clear that scientists have never been short of public relations skills). Among the great here is Copernicus, whose scientific analyses of precision observations began the process by which first the Earth, then the solar system, then the milky way, and eventually matter as we know it, have become increasingly insignificant in the bigger picture. Our universe itself may even be an insignificant quantum fluctuation on a much grander "reality". The cosmological "Copernican principle" is now applied to cast aspersions on any result which implies that anything at all is special. Only the role of Man in all this has yet to be reassessed objectively, though much debate rages, some of it mentioned here.

This vast range of topics embraces modern cosmology, a subject increasingly replacing quantum mechanics and elementary particle physics at the head of the great race for knowledge and a theory of everything. Theoretical physicists, of whom Kaku is one, are moving into astrophysics and cosmology, enriching the breadth of approaches enormously, as well as library shelf loads. This process has strengths and weaknesses, both in evidence in this book.

The big weakness is in astrophysical history: new converts tend to know only post-enlightenment history, a restriction very evident here. The overview of the discovery of modern cosmology, occupying the first 100 pages of the book, is deeply flawed. Minor errors abound, many of fact, more of emphasis, some of understanding. A casual reader will, for example, develop a completely incorrect view of the importance of single experiments in a subject as complex and difficult as cosmology. Kaku gives the impression, for instance, that the satellite Wilkinson Microwave Anisotropy Probe (WMAP), currently in orbit and very soon to release its second set of results, wrote modern cosmology on a previously near-blank sheet. This is quite wrong. Progress in these subjects is incremental, technically challenging, and is always provisional without independent experimental confirmation. Even the WMAP results, splendid though they are, could be interpreted only when combined with the results of a huge many-year study of the distribution of galaxies in space carried out by a joint UK-Australian team.

Perhaps the most misleading statement of all is that the big bang was not big and was not a bang. This view, while common, is simply wrong: the sound waves from the bang are in fact the ripples in the cosmic microwave background which WMAP measured, and the same sound waves which grew over time to form the galaxies and large structures in the universe today. That noise made what we see and are. Deciding if the big bang was "big" of course depends on definition, though an event which encompasses the whole of our universe arguably merits the description.

The heart of the book is the exotic physics, which Kaku does know well. We are led along an intellectually challenging path, starting with black holes, and especially their much-debated possible implications for time-travel. No clear yes/no answer appears, since there is no agreed one. The continuing fascination of quantum mechanics is well-discussed. A foray into quantum entanglement is always a jolly way to spend some time, which Kaku does, and no serious cosmology book can avoid 11-dimensional theories for long. Overall, lots of intellectual challenge, a brief mention of most buzz-word topics, but I was left feeling it was a little too much of a pot-pourri.

And so on to the future, and the big open questions. Will all life, of any conceivable form, die, leaving the universe infinitely dead for infinitely long? Is there a special role for man in the universe? Does the fact that we are here to talk about it mean anything special? Cogito ergo sum, or Et in arcadia ego? These questions, the fate of existence and the anthropic principle, are becoming a staple of bar-room philosophy. The arguments, all well explained in popular books and TV programmes, are well reviewed here, though one can learn a great deal more by reading the originals.

It is interesting how people are frightened of extinction, while accepting death. We know that Ozymandias's fate befalls the greatest king, yet we clearly feel genuinely uncomfortable with the thought of a future for the universe in which the stars all burn out and everything cools and dies. That, though, is what our current cosmology predicts.

So, cosmologists speculate on other options: might there be some physics which allows a cosmological botox? A face-lift to avoid encroaching heat-death? No plausible prospects are known, but speculation abounds at several levels. Some, involving information transfer into conveniently accessible young universes, seem to meet more of a psychological than a physics need. The most common, sadly evident here, resorts to speculative metaphysics: I don't like the idea, so there must be some law of physics to prevent it, as the great scientist Eddington said in a different context. He was wrong, and white dwarfs, neutron stars and black holes do form. As our crude and preliminary intellectual enquiries become informed, and our understanding of the nature of the universe and existence slowly matures, I am sure the universe will prove itself to be more interesting than we have yet imagined. Perhaps, even, more interesting than we can imagine.

• Gerry Gilmore is professor of experimental philosophy at the Institute of Astronomy, Cambridge University.

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