Ernst Mach is the physicist famous for his work in supersonics, and from whom the idea of a mach-number was derived (mach 1 being the speed of sound, mach 2, twice the speed of sound, and so forth). But Mach was also known to argue that the only way to explain the phenomenon of inertia was to assume that all of the masses in the universe were somehow connected. Albert Einstein later identified this argument as Mach’s Principle.
Mach’s Principle assumes, among other things, that “a particle’s inertia is due to some (unfortunately unspecified) interaction of that particle with all the other masses in the universe; the local standards of nonacceleration are determined by some average of the motions of all the masses in the universe, [and] all that matters in mechanics is the relative motion of all the masses.” Furthermore, “Mach’s Principle actually implies that not only gravity but all physics should be formulated without reference to preferred inertial frames. It advocates nothing less than the total relativity of physics. As a result, it even implies interactions between inertia and electromagnetism.” 
Mach’s Principle can be viewed as an entire universe being altered by changes in a single particle -- much in the same manner as hurricanes and tornadoes occurring in Florida because of an El Nino weather pattern in the Pacific Ocean, or perhaps more aptly, the flapping of a butterfly’s wings in Peru causing rains in Kansas.
Action at a Distance
The means by which such “actions-at-a-distance” can be interconnected (whether through the exchange of elementary particles, or some “unfortunately unspecified” means) has a long history in physics. In the Newtonian point of view, the equations of motion were based on an inertial frame of the “fixed stars”. But inasmuch as relativity -- the uniform motion of one inertial frame relative to another -- cannot be detected by internal mechanical experiments subject to Newton’s theory, Newton postulated the existence of Absolute Space.
Newton’s Absolute Space had many critics, from his near-contemporaries to those in modern times. Currently, the arguments against Newton’s concept of Absolute Space include: “It conflicts with one’s scientific understanding to conceive of a thing [AS] which acts but cannot be acted upon. The words are Einstein’s, but he attributes the thought to Mach. In any case, this is perhaps the most powerful objection of all.” At the same time, “it is clear that Einstein was led to General Relativity primarily by his philosophic desire to abolish totally the role of absolute space from physics.”  Mach’s Principle is thus an argument for relativity and against any idea of an Absolute Space.
D. W. Sciama in 1959 revived and extended a Maxwell-style gravitational theory of F. Tisserand and found that it encompasses Mach’s Principle, in effect saying that the inertial forces correspond to the universal gravitational radiation field and are proportional to the inverse first power of the distance. 
Maxwell’s ether might have provided an alternative answer to the objections to Absolute Space. In Maxwell’s theory we have a constant c with the dimensions of a speed and which was originally defined as a ratio between electrostatic and electrodynamic units of charge. But the theory also included the existence of electromagnetic waves, where the speed of propagation of disturbances in the electromagnetic field in a vacuum was this same constant. The fact that c coincided precisely with the known vacuum speed of light, led Maxwell to conjecture that light must be an electromagnetic wave phenomena.
Maxwell’s idea of a “luminiferous ether” was initiated to solve the problem that in electromagnetic theory one could apparently never alter the speed of light relative to itself no matter how one attempted to keep pace with a light wave. Because such behavior was totally absurd from the point of view of classical kinematics, it became necessary for the assumptions of length contraction and time dilation (Lorentz). Einstein then added his relativity principle which asserted that “all inertial frames are totally equivalent for the performance of all physical experiments.” As a generalization to the whole of physics of Newton’s purely mechanical relativity principle. Einstein declared Maxwell’s ether unobservable, and thus abolished the ether forever. 
Nevertheless, inertial frames seem quite real. In the case, for example, of two elastic spheres suspended on a common axis -- where one rotates and bulges while the other is at rest and undeformed -- it is not clear how the spheres “know” which of them rotates and which therefore must bulge. “Mach would have answered that the bulging sphere ‘felt’ the action of the cosmic masses rotating around it. To Newton, rotation with respect to Absolute Space produces centrifugal (inertial) forces, which are quite distinct from gravitational forces; to Mach, centrifugal forces are gravitational, i.e. caused by the action of mass upon mass.” 
Rindler  goes on to state: “Spacetime fully determines all free motions (i.e. motions under inertia and gravity); the question is whether the matter distribution, in turn, fully determines spacetime.” If we think of spacetime as both acting on mass (as a guiding field) and being acted upon by mass (i.e. suffering curvature), then we can counter the original argument against Newton’s Absolute Space as being something acting but unable to be acted upon. “Today’s quantum theoreticians (as well as many others) have little sympathy with Mach’s Principle. They point out that not only matter is the stuff of physics, but also fields, and that the whole of spacetime is occupied by the fields of the elementary particles.”
But what if “fields” are just the connecting links between matter? Do they make Mach’s Principle any less valid in that guise? “Even in the absence of matter, the fields of the virtual particles constitute an all-pervasive background which can in no way be eliminated. In fact, matter is only a small perturbation of it. This background, which possesses Lorentz invariance locally, can be looked upon as a modern ether. Since it possesses no net energy it makes no contribution to curvature, and hence it has no direct effect in general relativity. But it does suggest the a priori existence of spacetime, which matter merely modifies and does not create. According to Rindler , this says that “the fields of virtual particles constitute” “a modern ether”!
Ultimately, we are left with the idea that Mach’s Principle implies that the whole universe matters locally. This is thus in accord with Consciousness as the key element in Mind-Matter interactions, and that it is more related to David Bohm’s “implicate order” than mere matter. (Assuming that all of this actually matters.)
 Rindler, W., Essential Relativity, Springler-Verlag, New York, 1977.
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