  The Casimir effect, which predicts the emergence of an attractive force
between two parallel, highly reflecting plates in vacuum, plays a vital role in
various fields of physics, from quantum field theory and cosmology to
nanophotonics and condensed matter physics. Nevertheless, Casimir forces still
lack an intuitive explanation and current derivations rely on regularisation
procedures to remove infinities. Starting from special relativity and treating
space and time coordinates equivalently, this paper overcomes no-go theorems of
quantum electrodynamics and obtains a local relativistic quantum description of
the electromagnetic field in free space. When extended to cavities, our
approach can be used to calculate Casimir forces directly in position space
without the introduction of cut-off frequencies.
