MAPPING SELF-ORGANIZED CRITICALITY ONTO CRITICALITY

We present a general conceptual framework for self-organized criticali ty (SOC), based on the recognition that it is nothing but the expressi on, ''unfolded'' in a suitable parameter space, of an underlying unsta ble dynamical critical point. More precisely, SOC is shown to result f rom the tuning of the order parameter to a vanishingly small, but posi tive value, thus ensuring that the corresponding control parameter Lie s exactly at its critical value for the underlying transition. This cl arifies the role and nature of the very slow driving rate common to al l systems exhibiting SOC. This mechanism is shown to apply to models o f sandpiles, earthquakes, depinning, fractal growth and forest fires, which have been proposed as examples of SOC.