A two-dimensional rough surface: Experiments on a pile of rice

Dynamical roughening of interfaces has received much attention in recent years. However, experiments have been restricted to one dimensional (1d) systems. Moreover, theoretical studies of the two dimensional (2d) case have been highly inconclusive. Here we introduce an experimental 2d system, with which the theories can be tested. As is shown, the surface of a 2d pile of rice shows roughening behaviour in both space and time, with a roughness exponent $\alpha_{2d}$ = 0.39(3) and a growth exponent $\beta_{2d}$ = 0.27(3).