Nonequivalence of Inertial Mass and Active Gravitational Mass

For the Kerr-Newman black hole, it is pointed out that the active gravitational mass equals twice the inertial mass. This remains valid when the solution is applied as a model for the electron. The factor 2 also occurs in a classical electrodynamics model for the electron proposed recently, where gravity is negligible. On the basis of this, one may assume that for all matter the active gravitational mass equals twice the inertial mass. Newtonian physics will remain unchanged provided the gravitational constant is reduced by a factor 2. In cosmology, effects will appear.