  Electromagnetic waves propagate in the Schwarzschild spacetime like in a
nonuniform medium with a varying refraction index. A fraction of the radiation
scatters off the curvature of the geometry. The energy of the backscattered
part of an initially outgoing pulse of electromagnetic radiation can be
estimated, in the case of dipole radiation, by a compact formula depending on
the initial energy, the Schwarzschild radius and the pulse location. The
magnitude of the backscattered energy depends on the frequency spectrum of the
initial configuration. This effect becomes negligible in the short wave limit,
but it can be significant in the long wave regime. Similar results hold for the
massless scalar fields and are expected to hold also for weak gravitational
waves.
