  In their recent "Mach's principle and higher-dimensional dynamics", Mashhoon
and Wesson argue that Mach's principle is not properly incorporated into
general relativity and that in Einstein's theory "the origin of inertia remains
essentially the same as in Newtonian physics." While it is true that the motion
of a single test particle in a Newtonian inertial frame of reference appears
essentially the same as in an Einsteinian local inertial frame, this misses the
point. The issue is not what motion looks like in an inertial frame of
reference but what is the origin of the inertial frame. Unlike Newtonian
dynamics, general relativity does implement Mach's principle when considered
from this correctly formulated point of view.
