Abstract

We have carried out an experiment in which sandpiles are built up to a critical size and then perturbed by the dropping of individual grains of sand onto the pile. After each grain is added, the size of the resulting avalanche, if any, is recorded. For sufficiently small sandpiles, the observed mass fluctuations are scale invariant and the probability distribution of avalanches shows finite-size scaling. This demonstrates that real, finite-size sandpiles may be described by models of self-organized criticality. However, we also find that this description breaks down in the limit of large sandpiles.