  We study asymptotic dynamics of photons propagating in the polarized vacuum
of a locally de Sitter Universe. The origin of the vacuum polarization is
fluctuations of a massless, minimally coupled, scalar, which we model by the
one-loop vacuum polarization tensor of scalar electrodynamics. We show that
late time dynamics of the electric field on superhorizon scales approaches that
of an Airy oscillator. The magentic field amplitude, on the other hand,
asymptotically approaches a nonvanishing constant (plus an exponentially small
oscillatory component), which is suppressed with respect to the initial
(vacuum) amplitude. This implies that the asymptotic photon dynamics is more
intricate than that of a massive photon obeying the local Proca equation.
