Friday, October 06, 2006

Physics gets dirty

[This is my Materials Witness column for the November issue of Nature Materials.]

My copy of The New Physics, published in 1989 by Cambridge University Press, is much thumbed. Now regarded as something of a classic, it provides a peerless overview of key areas of modern physics, written by leading experts who achieve the rare combination of depth and clarity.

It’s reasonable, then, to regard the revised edition, just published as The New Physics for the 21st Century, as something of an authoritative statement on what’s in and what’s out in physics. And so it is striking to see materials, more or less entirely absent from the 1989 book, prominent on the new agenda.

Most noticeably, Robert Cahn of Cambridge University has contributed a chapter called ‘Physics and materials’, which covers topics ranging from dopant distributions in semiconductors to liquid crystal displays, photovoltaics and magnetic storage. In addition, Yoseph Imry of the Weizmann Institute in Israel contributes a chapter on ‘Small-scale structure and nanoscience’, a snapshot of one of the hottest areas of materials science.

All very well, but it begs the question of why materials science was, according to this measure, more or less absent from twentieth-century physics but central to that of the twenty-first. Indeed, one might have thought that the traditional image of materials science as an empirical engineering discipline with a theoretical framework based in classical mechanics looks far from cutting-edge, and would hardly rival the appeal of quantum field theory or cosmology.

Of course, topics such as inflationary theory and quantum gravity are still very much on the menu. But the new book drops topics that might be deemed the epitome of physicists’ reputed delight in abstraction: gone are the chapters on grand unified theories, gauge theories, and the conceptual foundations of quantum theory. Even Stephen Hawking’s contribution on ‘The edge of spacetime’ has been axed (a brave move by the publishers) in favour of down-to-earth biophysics and medical physics.

So what took physics so long to realize that it must acknowledge its material aspects? “Straight physicists alternate between the deep conviction that they could do materials science much better than trained materials scientists (they are apt to regards the latter as fictional) and a somewhat stand-offish refusal to take an interest”, claims Cahn.

One could also say that physics has sometimes tried to transcend material particularities. “There has been the thought that condensed matter and material physics is second-rate dirty, applied stuff”, Imry says. Even though condensed matter is fairly well served in the first edition, it tended to be rather dematerialized, couched in terms of critical points, dimensionality, theories of quantum phase transitions. But it is now clear that universality has its limits – high-temperature superconductors need their own theory, graphene is not like a copper monolayer nor poly(phenylene vinylene) like silicon.

“Nanoscience has both universal aspects, which has been much of the focus of modern physics, and variety due to the wealth of real materials”, says Imry. “That’s a part of the beauty of this field!”

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