There is growing recognition that progress in many scientific disciplines depends on an understanding of complexity. Complex systems play an important role in molecular biology, neurobiology and ecology as well as geology, engineering and economics. These systems consist of a large number of mutually interacting parts, often open to their environment, and the self-organization of these parts gives rise to novel macroscopic, or "emergent", properties. Put another way, in a complex system the whole turns out to be much more than the sum of its parts.
The response of the immune system to infectious organisms, for example, involves the cooperation of a body-wide network of cells and organs that has evolved to defend the body. Such cooperation allows the immune system to recognize many millions of distinctive foreign molecules, and to respond by producing matching antibodies. In physics, complexity can be found in condensed-matter systems, surfaces, fluids, polymers and astrophysical systems. At the dawn of the new millemium, complexity theory is set to be carried forward by the multidisciplinary integration of the physical sciences, artificial intelligence and soft computational techniques, and should continue to feed on analogies across the natural sciences. With time, this should lead to a better understanding of the limits of catastrophe prediction and help to provide us with adequate measures of risk in our complex world.
In the December issue of Physics World magazine, Didier Sornette from the Department of Earth and Space Sciences and the Institute of Geophysics and Planetary Physics, University of California, Los Angeles, and the CNRS at the University of Nice writes about the multidisciplinary field of complexity.