  We study from a critical perspective several quantum-electrodynamic phenomena
commonly related to vacuum electromagnetic (EM) fluctuations in complex media.
We compute the resonance-shift, the spontaneous emission rate, the local
density of states and the van-der-Waals-Casimir pressure in a dielectric medium
using a microscopic diagrammatic approach. We find, in agreement with some
recent works, that these effects cannot be attributed to variations on the
energy of the EM vacuum but to variations of the dielectric self-energy. This
energy is the result of the interaction of the bare polarizability of the
dielectric constituents with the EM fluctuations of an actually polarized
vacuum. We have found an exact expression for the spectrum of these
fluctuations in a statistically homogeneous dielectric. Those fluctuations turn
out to be different to the ones of normal radiative modes. It is the latter
that carry the zero-point-energy (ZPE). Concerning spontaneous emission, we
clarify the nature of the radiation and the origin of the so-called local field
factors. Essential discrepancies are found with respect to previous works. We
perform a detailed analysis of the phenomenon of radiative and non-radiative
energy transfer. Analytical formulae are given for the decay rate of an
interstitial impurity in a Maxwell-Garnett dielectric and for the decay rate of
a substantial impurity sited in a large cavity. The construction of the
effective dielectric constant is found to be a self-consistency problem. The
van-der-Waals pressure in a complex medium is computed in terms of variations
of the dielectric self-energy at zero-temperature. An additional radiative
pressure appears associated to variations of the EM vacuum energy.
