  We show that the vacuum permeability and permittivity may originate from the
magnetization and the polarization of continuously appearing and disappearing
fermion pairs. We then show that if we simply model the propagation of the
photon in vacuum as a series of transient captures within these ephemeral
pairs, we can derive a finite photon velocity. Requiring that this velocity is
equal to the speed of light constrains our model of vacuum. Within this
approach, the propagation of a photon is a statistical process at scales much
larger than the Planck scale. Therefore we expect its time of flight to
fluctuate. We propose an experimental test of this prediction.
