Physical mechanisms underpinning the vacuum permittivity.

Debate about the emptiness of the space goes back to the prehistory of science and is epitomized by the Aristotelian \emph{horror vacui}, which can be seen as the precursor of the ether, whose modern version is the dynamical quantum vacuum. Here, we change our view to \emph{gaudium vacui} and discuss how the vacuum fluctuations fix the value of the permittivity $\varepsilon_{0}$ and permeability $\mu_{0}$.