Sound in sand

We have studied the vibrations in a granular material and have found that they are qualitatively different from those found in solids or liquids. In response to an external oscillation, the vibrations experienced by a single particle in the material are exceedingly noisy with a power spectrum S(f)∝${\mathit{f}}^{2.2}$ over more than 5 decades in frequency. The frequency response depends on the detailed packing of the beads, reminiscent of conductance fluctuations in mesoscopic metals.