  Motivated by the long-debated question about the internal stability of the
electron, the force densities acting on the charge density of the 1s electron
in the H atom are investigated. The problem is mapped onto the canonical
formalism for a classical Dirac field coupled to the electric field of an
external point charge. An explicit calculation shows that the attractive
Coulomb force density is balanced exactly at every point in space by the
repulsive confinement force density. The latter requires evaluating the
divergence of the stress tensor for the 1s solution of the Dirac equation. Such
a local force balance goes beyond the global stability criteria that are
usually given for the H atom. This concept is extended to the internal
stability of any charged particle by investigating the force densities acting
on its surrounding vacuum polarization. At large distances one has to consider
only the charge density of virtual electrons and positrons, induced by a point
charge in the vacuum of quantum electrodynamics.
