In earlier posts I have explained the difference between exogenous and endogenous processes and why the equivalence principle only holds if and when gravitation (endogenous), acceleration and inertia share the same endogenous driver .
Consequently we have to make a distinction between inertia as the tendency to maintain momentum (exogenous) and inertia as the tendency to maintain mass (endogenous, see for instance post 17). Therefore I make the distinction between exo-inertia and endo-inertia.
Endo-inertia, how does it work, what are its properties, its relations to gravitation and acceleration?
As explained in post 21, the tendency of an electron to go nearer to the nucleus gets stronger the greater the distance from it, its mass increases, time delays. In lower orbits the opposite happens, a stronger tendency to get away from the nucleus through mass decrease and time-acceleration.
I suggest the possibility that electromagnetic interaction is in essence endo-inertia, the tendency to maintain mass. Gravitation (consequence of a continuous relation between mass and time), time-driven (de)-acceleration and emdo-inertia are equivalent (see post 15).