  Zitterbewegung, as it was originally described by Schr\"odinger, is an
unphysical, non-observable effect. We verify whether the effect can be observed
in non-inertial reference frames/curved spacetimes, where the ambiguity in
defining particle states results in a mixing of positive and negative frequency
modes. We explicitly demonstrate that such a mixing is in fact necessary to
obtain the correct classical value for a particle's velocity in a uniformly
accelerated reference frame, whereas in cosmological spacetime a particle does
indeed exhibit Zitterbewegung.

High Energy Physics - Theory;General Relativity and Quantum Cosmology;Quantum Physics