Abstract
We study the response of a granular system at rest to an instantaneous input of energy in a localised region. We present scaling arguments that show that, in d dimensions, the radius of the resulting disturbance increases with time t as tα, and the energy decreases as t-αd, where the exponent α=1/(d+1) is independent of the coefficient of restitution. We support our arguments with an exact calculation in one dimension and event-driven molecular-dynamics simulations of hard-sphere particles in two and three dimensions.