books and arts manifest themselves or how an ethologist could demonstrate their existence.However, UM/SPL the idea surely applies to the activity of BA J. scientific research, and perhaps even to the writing of a book. ■ Bernd Heinrich is in the Department of Biology, University of Vermont, Burlington, Vermont 05405, USA To infinity and beyond! Parallel Worlds: The Science of Alternative Universes and Our Future in the Cosmos by Michio Kaku Allen Lane/Doubleday: 2005. 448 pp. £20/$27.95 David Lindley Michio Kaku is an enthusiast. In the breath- less introductory chapters of Parallel Worlds, he speeds through the history of cosmology and fundamental physics to persuade us that science has never been as thrilling as Brane teaser: if parallel universes exist, they might take the form of bubbles in different dimensions. it is now. Edmund Halley may have been “shocked beyond belief” and “staggered” by physicists are drowning in branes, as Kaku civilization’s entire sum of information and Newton’s calculation of planetary orbits, puts it, and that they are beginning to think convey it down the wormhole in the memory but that’s small potatoes compared with the that M-theory itself must be part of some yet of a quantum nanobot. This is the big pay- staggering science that goes on nowadays. more basic theory that is awaiting discovery. off: by fully understanding physics, intelli- String theory is staggering; quantum com- This is progress,Kaku assures us. gence can escape its cosmic doom. puters are truly staggering; the recent dis- Although he has every confidence that Parallel Worlds slides from even-handed covery of accelerating cosmic expansion left the quest for a theory of everything will suc- discussion of what physicists and cosmol- scientists dumbfounded; their minds reel ceed, perhaps in just a few decades, Kaku is ogists are actually doing into areas that at the idea of parallel universes. And when vague about what success will look like. He are, shall we say, a touch speculative. Kaku they’re not reeling and staggering, they have describes how observations of gravitational mentions problems and difficulties along the to contend with the “insane conclusions of waves or of temperature fluctuations in the way,but he gives the distinct impression that quantum theory”. cosmic microwave background, or perhaps the prospects described in his final chapters Melodrama aside, Kaku’s book provides experiments at CERN’s upcoming Large are, if not exactly within our grasp, at least a sprightly and generally efficient account of Hadron Collider, might reveal tiny signs of reasonable extrapolations.Some readers will our present understanding of the Universe, M-theory seeping from higher dimensions no doubt be entranced by the grand vision, in which astronomical observation and ele- into our own poor world. Then again, they the great sweep of imagination. For me, the mentary physics combine to give a coherent, might not, in which case we have to fall parade of mind-boggling ideas breezily por- if rather bizarre, picture of the cosmos. Plain back on neopythagorean arguments of pure trayed here — the Big Bang as a collision of ordinary matter, such as we are made of, mathematical consistency to let us know branes, time travel around massive rotating is tame stuff. The Universe is mostly dark which is the right theory. If that theory is cylinders, matter as holographic projection matter and dark energy, both revealed by unique, we would “know the mind of God”, from higher to lower dimensions — created the dynamics of galaxies. As yet there is no says Kaku, borrowing a favourite phrase of a different cumulative impression. The great convincing explanation for either. Einstein’s. Or there could be lots of legit- enterprise of fundamental physics began to But string theory will take care of that. imate theories, so that our Universe would seem larky,whimsical and not quite serious. Beginning with the now familiar idea that all be merely one of many possible universes. String theory and its cosmological impli- particles are in fact little wiggly loops inhab- (I suppose this means that even God couldn’t cations embody, for the moment, a research iting extra dimensions, Kaku sketches how make his mind up.) programme much more than a genuine gravity may one day be unified with quan- Whatever universe we live in, it is bound theory of physics. Getting from one to the tum mechanics. Then we will understand to end badly. Stars die and cosmic expansion other demands detailed and diligent effort. space-time and all the matter and forces in it. can only lead to a cold, utterly attenuated There is no guarantee that it will all work out There was a time when string theory seemed emptiness. But we can escape this dreary as desired. But Kaku takes the truth of the unique: only one version of it could possibly fate, Kaku says. Once physicists have figured big ideas more or less for granted, and races work. But more versions appeared, to be out the theory of everything,they will be able ahead to the most far-reaching and literally subsumed some years later into M-theory, to manipulate space-time to create a worm- cosmic conclusions. This is intellectual which unifies string theories at the cost of hole through which we can pass to a new entertainment — brane candy, if you like — introducing fundamental surfaces of higher universe and start over again. Or maybe, if but will it ever be more than that? ■ dimensions (called ‘branes’). it is too difficult to send our physical selves David Lindley is a freelance science writer in It is a little unsettling now to learn that to another universe, we can capture our Alexandria, Virginia, USA. 274 NATURE | VOL 434 | 17 MARCH 2005 | www.nature.com/nature © 2005 Nature Publishing Group.