  Quantum mechanics asserts that a wave packet must inevitably spread as time
progresses since the dispersion relation for the quantum waves is assumed to be
quadratic in the momentum k. However, this assumption does not consider the
standard frequency Doppler shift formula of Galilean relativity. In this
article a non-dispersive wave packet is constructed by appropriately
considering the transformation rules between the laboratory and the
(particle's) rest inertial reference frames.
