and acknowledgments Self-organized criticality is a new way of viewing
nature. The basic picture is one where nature is perpetually out of
balance, but organized in a poised state-the critical state-where
anything can happen within well-defined statistical laws. The aim of the
science of self-organized criticality is to yield insight into the
fundamental question of why nature is complex, not simple, as the laws
of physics imply. Self-organized criticality explains some ubiquitous
patterns existing in nature that we view as complex. Fractal structure
and catastrophic events are among those regularities. Applications range
from the study of pulsars and black holes to earthquakes and the
evolution of life. One intriguing conse- quence of the theory is that
catastrophes can occur for no reason whatsoever. Mass extinctions may
take place without any external triggering mechanism such as a volcanic
eruption or a meteorite hitting the earth (although the the- ory of
course cannot rule out that this has in fact occurred). xu How Nature
Works Since we first proposed the idea in 1987, more than 2, ooo papers
have been written on self-organized criticality, making ours the most
cited paper in physics during that period. How Nature Works is the first
book to deal with the subject. The basic idea is simple, and most of the
mathematical models that have been used in the implementation of the
theory are not complicated.
