Bak, Tang, and Wiesenfeld proposed the idea of self-organized criticality in order to gain a general understanding of the behavior of extended dynamical systems driven in a nonequilibrium state. In particular this idea was intended to explain the ubiquitous scaling behavior and fractal structures that are observed in many different phenomena occurring spontaneously in nature. Recent experiments on the dynamics of a pile of sand, which had been expected to show self-organized criticality, are reviewed and it is shown that sand behaves in a manner more reminiscent of a first-order transition than of a second order (or critical) one.

DOI:https://doi.org/10.1103/RevModPhys.64.321