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We study from a critical perspective several quantum-electrodynamic phenomenacommonly related to vacuum electromagnetic (EM) fluctuations in complex media.We compute the resonance-shift, the spontaneous emission rate, the localdensity of states and the van-der-Waals-Casimir pressure in a dielectric mediumusing a microscopic diagrammatic approach. We find, in agreement with somerecent works, that these effects cannot be attributed to variations on theenergy of the EM vacuum but to variations of the dielectric self-energy. Thisenergy is the result of the interaction of the bare polarizability of thedielectric constituents with the EM fluctuations of an actually polarizedvacuum. We have found an exact expression for the spectrum of thesefluctuations in a statistically homogeneous dielectric. Those fluctuations turnout to be different to the ones of normal radiative modes. It is the latterthat carry the zero-point-energy (ZPE). Concerning spontaneous emission, weclarify the nature of the radiation and the origin of the so-called local fieldfactors. Essential discrepancies are found with respect to previous works. Weperform a detailed analysis of the phenomenon of radiative and non-radiativeenergy transfer. Analytical formulae are given for the decay rate of aninterstitial impurity in a Maxwell-Garnett dielectric and for the decay rate ofa substantial impurity sited in a large cavity. The construction of theeffective dielectric constant is found to be a self-consistency problem. Thevan-der-Waals pressure in a complex medium is computed in terms of variationsof the dielectric self-energy at zero-temperature. An additional radiativepressure appears associated to variations of the EM vacuum energy.

The Quantum Vacuum of Complex Media. A Unified Approach to the  Dielectric Constant, the Spontaneous Emission and the Zero-Temperature  Electromagnetic Pressure