  We review the possibility that quantum fluctuations in the structure of
space-time at the Planck scale might be subject to experimental probes. We
study the effects of space-time foam in an approach inspired by string theory,
in which solitonic D-brane excitations are taken into account when considering
the ground state. We model the properties of this medium by analyzing the
recoil of a D particle which is induced by the scattering of a closed-string
state. We find that this recoil causes an energy-dependent perturbation of the
background metric, which in turn induces an energy-dependent refractive index
in vacuo, and stochastic fluctuations of the light cone. We show how distant
astrophysical sources such as Gamma-Ray Bursters (GRBs) may be used to test
this possibility, making an illustrative analysis of GRBs whose redshifts have
been measured. Within this framework, we also discuss the propagation of
massive particles and the possible appearance of cosmological vacuum energy
that relaxes towards zero. We also discuss D-brane recoil in models with
`large' extra dimensions.

General Relativity and Quantum Cosmology;Astrophysics;High Energy Physics - Phenomenology;High Energy Physics - Theory