  We consider decay of an initial density or current perturbation at finite
temperature $T$ near a quantum critical point with emergent Lorentz invariance.
We argue that decay of perturbations with wavenumbers $k \gg T$ (in natural
units) is a good testing ground for holography---existence of a dual
gravitational description---in experimentally accessible systems. The reason is
that, computed holographically, the decay rate at large $k$ depends only on the
leading correction to the metric near the boundary, and that is quite
universal. In the limit of zero detuning (when the temperature is the only
dimensionful parameter), the result is a scaling law for the decay rate, with
the exponent that depends only on the dimensionality. We show that this follows
from an analytical argument and is borne out by a numerical study of
quasinormal modes.
