Cut the strings and glimpse the way the universe might unravel

The New Physics for the 21st Century is described by its editor, Gordon Fraser, as "an authoritative anthology of frontier science". It is certainly wide ranging, consisting of some 19 articles written by 23 distinguished authors. For me, the delight of such a book is to gain insight into how true experts in a field think about their subject. Let me warn the reader now that this is often quite a different experience from having the subject explained in an easily understandable way, however, but perhaps this book is not really about that. How could recent progress in string theory or superconductivity be simultaneously reviewed and explained at a relatively high level in 20 pages? Indeed, the decision not to write "popular accounts" but articles whose primary purpose is to describe the frontier of research in 2005 is bold and to be applauded, although it must limit the potential readership. What these articles do is to reward (very) careful and thoughtful reading and rereading.

For the above reasons, The New Physics is quite a daunting prospect to review, and to begin with I intended not to attempt to describe each of the 19 relatively stand-alone articles. But on reflection I realised that this is probably a book readers will dip into rather than read cover to cover, and the chapters people choose to read will depend on their interests or needs. One could well imagine using this book as a source for interesting and up-to-date material to insert into undergraduate lecture courses, for example. With this in mind, I will try, in this limited space, to give at least a glimpse of the sheer breadth of knowledge and information contained within, while not allowing the review to degenerate into a list.

The book is split into five sections. The first is titled "Matter and the universe", and covers the latest theoretical and experimental advances in astronomy, cosmology and particle physics. In the past decade, cosmology has entered a new golden age, fuelled by precision data from the COBE and WMAP satellites and ever-more detailed observations across the electromagnetic spectrum, summarised by Arnon Dar, Wendy Freedman and Edward Kolb. These precision data have led cosmologists to believe that the universe is made primarily out of something we cannot see; about 25 per cent is dark matter and 75 per cent dark energy, with only 5 per cent in the rare form that we understand, the constituents of stars, planets and people. This challenging new problem for 21st-century science permeates all the articles in this section and demonstrates the value of a multidisciplinary review such as this. If everyone writing about cosmology, gravity, particle physics and string theory spends time talking about dark energy, you know it is important.

Chris Quigg points out that attempts to calculate the amount of dark energy based on the otherwise tremendously successful standard model of particle physics gives an answer at least 54 orders of magnitude too large. For this and many other reasons, the standard model will soon be confronted with new and precise data from the km-long Large Hadron Collider at Cern. I hope that, come 2010, the cultural impact of this machine will be so great that the words hadron and collider will be in included in every dictionary and my spellchecker will no longer attempt to rename this machine the Large Hard-on Colluder.

While the LHC will lead at the very least to a profound revision of the standard model, it is possible that an answer to the dark energy problem will have to await a unification of gravity and the quantum field theories of particle physics. General relativity, which provides our current best understanding of gravity, has consistently resisted all attempts at such a marriage. Ronald Adler gives an excellent review of general relativity, the experimental tests of the theory and its limitations at ultrahigh energies or when confronted with exotic astrophysical phenomena such as black holes.

At present, the most popular game in town for resolving these problems is superstring theory, which describes a universe of extra, curled up dimensions populated by exquisitely tiny one-dimensional strings and other higher dimensional exotica. Michael Green gives one of the most readable short overviews I have seen of this extremely abstract, difficult and fascinating subject.

The second section, "Quantum matter", covers the rapidly evolving field of ultra-cold atoms and the manipulation of atoms with photons. Henry Hall's review of superfluids matches my own entertaining and challenging experience of attending his undergraduate lectures at Manchester University in the early 1990s. Careful reading and thought are rewarded, while a cursory read brings only bafflement. I enjoyed this article immensely, but only after spending a long time with it. Claude Cohen-Tannoudji and Jean Dalibard review the techniques used to manipulate atoms with light. These techniques are most often used to produce ultra-cold atoms in the laboratory and, increasingly, in devices such as high-precision atomic clocks and (future) quantum computers. William Phillips and Christopher Foot give an overview of the techniques used to cool down and trap atoms at temperatures of only a ten-billionth of a degree above absolute zero. I found it particularly fascinating to see experimental images in which the differences between bosons and fermions are clearly visible; quantum behaviour taking place before our very eyes.

The section is rounded off by Subir Sachdev's chapter on quantum phase transitions, which gives a glimpse at the very edge of the current understanding of what he calls "quantum matter", including the fast-evolving world of high-temperature superconductivity.

"Quanta in action" focuses on quantum computing and nano-science. Anton Zeilinger is one of the world experts in the field and he gives a short introduction to quantum entanglement, cryptography and teleportation. It will come as a surprise to many who see quantum behaviour as a subatomic phenomenon that entangled pairs of photons have been separated in free space across the River Danube. Artur Ekert gives an overview of quantum computing, including one of the most readable descriptions I have seen of quantum logic gates. Articles about quantum computing tend to focus on two possible uses: the factorising of very large numbers, which would render public-key encryption completely useless, and the solution in terms of quantum cryptography. If all quantum computing can do is to create a problem and then solve it, perhaps we should stop now.

Of course there is much more to it, and another few pages here to cover more applications would not have gone amiss. Yoseph Imry writes about small-scale structures and nanoscience, focusing on what the latest experimental techniques such as scanning electron microscopy can teach us about the interface between classical and quantum behaviour by allowing us to observe the behaviour of materials at the scale of single atoms.

"Calculation and computation" covers chaos, complex systems and Grid computing. In his article on chaotic systems, Henry Abarbanels raises the issue that, were the 1/r classical gravitational potential is not unusually symmetric, planetary motion would itself be chaotic, and ancient astronomers might have found it difficult to interpret celestial phenomena.

If the Earth's orbit were chaotic, I found myself thinking, this may be the least of civilisation's problems. But the point is well made - the physics we all take for granted, ie, the physics of systems that exhibit behaviour stable to small changes in the initial conditions, is the exception rather than the rule.

There follows an often challenging overview of the chaotic motion of a fluid between two flat, two-dimensional plates, the famous Lorentz system, and then onwards to the use of synchronised chaotic systems to allow robust transmission of data. Antonio Politi describes the physics of complex systems, with difficult but ultimately understandable descriptions of non-equilibrium phenomena, the emergence of scaling laws in earthquakes and many other phenomena. Tony Hey and Anne Trefethen round off the section with an article on the Grid. This computing infrastructure will be crucial for future big science projects in many fields (the Large Hadron Collider being a good example) that will require multipetabyte data storage and huge processing resources spread out across the world, while remaining transparently accessible to everyone authorised to use it.

"Science in Action" ends the book with a collection of articles on real-world applications of cutting-edge physics. Cyrus Safinya describes the latest research into the structure and function of proteins and membranes, the manipulation of DNA to allow cheap and rapid sequencing, and, fascinatingly, the beginnings of research into the decay and repair of nerve cells. One of the highlights of the book in terms of readability is the review of medical physics by Nikolaj Pavel, which describes the use of radiation therapy, SPECT and PET scans and Compton cameras. NMR scanning techniques are discussed in some detail. I also learnt that the bio-magnetic field of the heart is as weak as that of an electric screwdriver at 5m. Robert Cahn gives an equally readable overview of the physics of materials, covering subjects as diverse as solar cells, liquid crystal and flat-panel displays, optical fibres and nanotubes. And did you know that more transistors are produced every year than grains of rice? If, like me, you want to know how your flat-screen TV works, you will enjoy this article. The book concludes with a contribution from Ugo Amaldi on physics and society. This is a wonderful manifesto for investment in research, and I urge any of the politicians or accountants many of us deal with every day to read this before they come to argue with us about funding.

This book is a reasonable attempt at a landmark publication. It is beautifully presented and, given the contributor list, authoritative, but it is not for any but the most committed general science reader. However, I wholeheartedly recommend it to researchers, postgraduate students and perhaps advanced undergraduates in the sciences.

Brian Cox is a Royal Society fellow, Manchester University.