Mass renormalization and runaway solutions

The relationship between negative mechanical mass and runaway solutions is studied using the model of a charged spherical shell. The model yields unexpected results: for example, for −I_el< I_mech<0 a runaway solution appears, but it disappears again for I_mech<−I_el, where I_el and I_mech are the electromagnetic and mechanical moments of inertia of the shell. The runaway solutions of this shell are contrasted with those of the quasi-stationary electron. The standard interpretation proposed by Wildermuth of how the negative mass causes runaway solutions is shown to be incorrect. However, an alternative interpretation, based on regarding mass renormalization as if it were an “external hidden force“ is capable of explaining the above runaway solutions.