  A recent theorem giving the initial behavior of very short-time fluctuations
of particle displacements in classical many-body systems is discussed. It has
applications to equilibrium and non-equilibrium systems, one of which is a
series expansion of the distribution of work fluctuations around a Gaussian
function. To determine the time-scale at which this series expansion is valid,
we present preliminary numerical results for a Lennard-Jones fluid. These
results suggest that the series expansion converges up to time scales on the
order of a picosecond, below which a simple Gaussian function for the
distribution of the displacements can be used.
