On the origin of inertial accelerations

And therefore, all external impediments removed, a heavy body on a spherical surface concentric with the earth will be indifferent to rest and to movements toward any part of the horizon. And it will maintain itself in that state in which it has once been placed; that is if placed in a state of rest, it will conserve that; and if placed in movement toward the west (for example), it will maintain itself in that movement. Thus a ship, for instance, having once received some impetus through the tranquil sea, would move continually around our globe without ever stopping; and placed at rest it would perpetually remain at rest, if in the first case all extrinsic impediments could be removed, and in the second case no external cause of motion were added. Galileo Galilei (**) (1613)

Summary

Are inertial forces of gravitational origin? The standard geometric interpretation of the general theory of relativity may be employed to show that inertial effects cannot be caused by the gravitational influence of distant masses. The same would hold in any metric theory of gravity that combines local Lorentz invariance with Newtonian gravitation as in general relativity. In fact, the status of the origin of translational inertial accelerations in the relativistic theory of gravitation is similar to that in Newtonian mechanics.