Physics: the opening to complexity.

In the minds of the lay public, or even of scientists from unrelated fields, physics is mainly associated with extremes: big bangs and big bucks; the cosmic and the subnucleonic scales; matter in its most rarified form such as single trapped atoms; or measurements of extraordinary precision to detect phenomena-dark matter, proton decay, neutrino masses-which may well not be there at all. The intellectual basis for this kind of science has been expounded by Victor Weisskopf, Leon Lederman, Stephen Hawking, and particularly Steven Weinberg, in his book Dreams ofa Final Theory. The buzzword is "reductionism," the idea that the goal of physics is solely or mostly to discover the "fundamental" laws which all phenomena involving matter and energy must obey and that ignorance about these laws persists only on the extreme scales of the very small, the very cosmic, or the very weak and subtle. IThe glamorous image of physics that this preoccupation projects is not necessarily all good: with the end of the Cold War and of expansionist public spending, physics is seen by all too many policymakers as too expensive for its practical return or simply too big for its boots. Some pundits have called the past half-century "The Age of Physics" and suggested that this age is coming to an end. This pessimistic view may or may not be true even of Big Science physics. It seems to me that cosmic physics, at least, is in the midst of a very fertile period, not near collapse. But what it ignores is the fact that most physics and most physicists are not involved in this type of work at all. Eighty percent or so of research physicists do not classify themselves as cosmic or elementary particle physicists and are not much concerned with testing the fundamental laws. Admittedly, some portion of this 80% are concerned with applications of physics to various practical problems, as for example prospecting geophysicists or electronic device designers. But another large fraction are engaged in an entirely different type of fundamental research: research into phenomena that are too complex to be analyzed straightforwardly by simple application of the fundamental laws. These physicists are working at another frontier between the mysterious and the understood: the frontier of complexity. At this frontier, the watchword is not reductionism but emergence. Emergent complex phenomena are by no means in violation of the microscopic laws, but they do not appear as logically consequent on these laws. That this is the case can be illustrated by two examples which show that a complex phenomenon can follow laws independently of the detailed substrate in which it is expressed. (i) The "Bardeen-Cooper-Schrieffer (BCS)" phenomenon of broken gauge symmetry in dense Fermion liquids has at least three expressions: electrons in metals, of course, where it is called "superconductivity"; 3He atoms, which become a pair