  We show that the uniform motion of a homogeneous distribution of electric
charge can be stable or unstable depending on its geometry. When the
electrodynamic body is perturbed from a state of rest, it starts to perform
fast oscillations, irrespective of the frequency of the perturbation. This
nonlinear oscillation is the result of the feedback interaction between
Coulombian and radiative fields. The resulting spontaneous symmetry breaking of
the Lorentz group implies that the principle of inertia only holds on average
and suggests that the default state of matter is not necessarily uniform
motion, but self-oscillation as well. We propose that the excitability of
electrodynamic bodies under external perturbations, which leads to limit cycle
oscillations, is at the basis of the wave particle duality and its related
quantum effects.
