Inter-dimensional journey to the outer limits of science

Lisa Randall

Allen Lane, 20

THIS is an intelligent book about a very complicated subject. Randall, a leading American theoretical physicist, believes that the three dimensions of space we see around us are not the whole story. There are other, higher dimensions, which may explain why gravity is so much weaker than magnetism - making it possible, for example, for us to stick things on fridge doors.

She refers to these higher dimensions as "passages", and her explanation of them takes us through chapters such as 'Entryway Passages', 'Restricted Passages', 'Voluminous Passages' and even a 'Profound Passage' - all of which is apt to raise a snigger from any Julian Clary fans.

But laughs are in short supply here: the tone is earnest, lightened only occasionally by very dry wit. This book is not for softies. To be honest, it is hard work. Fridge doors may not sound like cutting-edge science, but the gap between gravity and other forces - the "hierarchy problem" - is a major concern for theorists, who have found many ways of potentially cracking it.

Randall takes us through "grand unified theories", which attempt to connect particles in a single model, but which have the snag of predicting that every atom in the universe will ultimately evaporate. She leads us on to superstring theory and "brane worlds", which picture particles as tiny vibrating filaments and the universe itself as a giant wobbly sheet.

Finally, she stakes out her own theory in detail. Imagine our universe being two-dimensional instead of three. Right next to our flat world is another flat world. Forces such as electricity and magnetism - the forces that make things solid and visible to us - are trapped on the flat sheets, but gravity can leak between them.

This would make gravity appear weaker than it really is - unable to pull a magnet off a fridge door. Other researchers have explored this, but Randall's twist is to make gravity weaken even further on its flight between the sheets. It means the universe might have different numbers of dimensions in different regions. Our three could be a local aberration.

The downside is the number of variations that are possible on the underlying theme. Faced with such a succession of subtly differing theories, the reader can easily be confused by the abundance.

The most appreciative audience for this book will be Randall's academic colleagues. Each chapter is laid out with the clarity of a well-delivered conference presentation: there is even a bullet-point summary of key features at the end of each. All that is missing is the equations.

But there are occasions when words are just as hard to understand: not even someone of Randall's intellect and talent can turn these very abstract ideas into reader-friendly form.

Nevertheless, there is a sizeable public appetite for challenging books such as this. Two decades after Stephen Hawking transformed the popular science market, we continue to see new books which are, if anything, even tougher going than his famously demanding one.

I enjoyed Warped Passages, but was left with a sense that theorists are still a long way from the final answer.

If you had asked Aristotle or Ptolemy to explain how planets move, you would have got a lecture on epicycles and equants. This book felt a little bit like that.