Hierarchically related processes and macroscopic emergence of fluctuations in weakly perturbed granular media

We report an experiment where a torsion oscillator is forced to penetrate a granular system over a small distance as, and the angular deflection is continuously detected. From angular deflections time series we deduce the granular noise and obtain insights on the grain-level mechanisms. In particular, we identify a control parameter, , on which the granular noise depends exponentially. At very low as, the granular noise follows a Vogel–Fulcher–Tammann glass-like law. We explain this dependence with the idea that the macroscopic granular dynamics, seen by the oscillator, is governed by the emergence of extreme mesoscopic fluctuations.