Particles and objects have gravitational interactions with universe (fixed) distant galaxies. Particles and objects resist accelerations because of these gravitational interactions. Accelerations are absolute (not relative) with respect to the fixed distant galaxies {Mach's principle} {Mach principle}. Universe distant galaxies make an absolute reference frame, and gravitational mass and inertial mass are equivalent because of these interactions.
However, general relativity does not use Mach's principle. In general relativity, gravitational mass and inertial mass are locally equivalent to observers, because they both curve space-time the same.
Physical Sciences>Physics>Relativity>General Relativity>Principles
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Date Modified: 2022.0224