On the meaning of various mass definitions for asymptotically flat spacetimes

Abstract

In general relativity, the energy density of the gravitational field is not well defined. However, for asymptotically flat spacetimes, various definitions for total mass of the system have been proposed. In this paper, eight masses are considered and it is shown that some of them correspond to the active gravitational mass while the others correspond to the inertial mass. For example, the ADM mass corresponds to the inertial mass, while the Møller mass corresponds to the active gravitational mass. In general, the inertial and active gravitational masses are not equal. If the spacetime is vacuum at large r, the Einstein equations force the inertial and active gravitational masses to be the same. The Einstein equations also force these masses to be the same if any matter that extends out to large r satisfies the weak, strong, or dominant energy condition. The contributions of the inertial and active gravitational masses to the gravitational redshift, the deflection of light, the Shapiro time delay, the precession of perihelia, and the motion of test bodies in the spacetime are also examined.