  Conventional textbook treatments on electromagnetic wave propagation consider
the induced charge and current densities as "bound", and therefore absorb them
into a refractive index. In principle it must also be possible to treat the
medium as vacuum, but with explicit charge and current densities. This gives a
more direct, physical description. However, since the induced waves propagate
in vacuum in this picture, it is not straightforward to realize that the
wavelength becomes different compared to that in vacuum. We provide an
explanation, and also associated time-domain simulations. As an extra bonus the
results turn out to illuminate the behavior of metamaterials.
