We begin this discussion with the axiom that all known forces are the result of some form of energy, be it chemical, mechanical, molecular, nuclear, electromagnetic, or otherwise. It is therefore consistent and logical to conclude that gravitational force also results from some form of energy.
Many of the characteristics and effects of magnetic force are similar to the characteristics and effects of gravity. Both phenomena emanate from matter (mass) and appear to be energy related. Both forces are invisible to the eye and a priori extend to infinity. Both phenomena act at a distance through empty space, and both normally attract (pull) other matter rather than push it away.
There are, of course, dissimilarities. Magnetism only attracts certain types of matter, i.e. iron; whereas gravity attracts all types of matter, apparently equally. Magnetic attraction is not necessarily proportional to the quantity of matter attracted, nor to the quantity of matter of its source, and magnetic force can be increased or decreased. One magnet may repulse or push away another magnet with the same charge. Magnetic force appears to be much more intense than gravitational force, but “decreases almost as the cube of the distance,” rather than the square of the distance. Nevertheless, the similarities of the two phenomena indicate the possibility, or even the probability, of a common root cause.
In late 1905, Einstein reasoned that m=E/c2 (or E=mc2), and he concluded that “[T]he mass of a body is a measure of its energy content.” Then in 1911, Einstein also theorized that as energy is added to mass, both its inertial mass and its gravitational mass (its potential ability to attract other objects in space) are proportionally increased. If these two statements are true, then it follows that the energy content of mass must constitute its potential gravitational attracting capability or force. This conclusion is consistent with Einstein’s equation: E=mc2.
However, Einstein did not reach this conclusion in his late 1905 paper nor in his 1911 paper. In fact, his General Theory of Relativity specifically denied and negated the possibility that gravity is caused by the energy content of mass:
“[T]he concept of the [gravitational] force interaction, and with it the concept of energy [must be replaced by] a field theory of gravitation…the field takes the place of the force.”
This “field theory” then asserted that “gravity is nothing but the curvature of the four-dimensional spacetime continuum.”
Nevertheless, and despite Einstein’s General Theory, we empirically know that the mass of a body not only determines such body’s magnitude of potential attraction relative to another body (a phenomenon called “gravitational attraction”); but such mass also determines such body’s magnitude of resistance relative to the attraction or applied force of another body (a phenomenon called “inertial resistance” or “inertia”). The mass of a body also determines the magnitude of relative motion of two opposing gravitating objects—a phenomenon we call Relative Gravitational Acceleration. In other words, the mass of a body provides several, yet different, functions of equivalent magnitude: attraction, resistance to attraction, and gravitational acceleration.
The magnitude of attraction is equal to the energy content of the pulling mass. The magnitude of resistance is equal to the matter component (or energy content) of the pulled mass. And the magnitude of relative acceleration is determined by both of the above. These results are also consistent with the equation: E=mc2. In addition, they should be consistent with the aforementioned conclusions contained in Einstein’s 1905 paper and his 1911 paper.
Could it not be postulated from the above: a) that gravitational force of attraction is caused by the total energy content of matter, and the magnitude of the relevant opposing masses; b) that the energy content of one mass proportionally attracts the energy content of another mass, and vice versa; c) that the propagation or action of gravitational energy at a distance is undetectable because its intensity relative to the magnitude of its propagating mass is so minute; and d) that gravitational force is only a special case of the broader phenomenon of E=mc2?
Since the attracting force of a body (its total energy content) is proportional to its mass (Newton’s law of gravitational attraction), it follows that the energy content of one mass must attract the energy content of the opposing mass, and vice-versa. But, it must be left to future physicists and mathematicians to fill in the blanks as to specifically how the mechanism or process of these opposing energy contents and gravitational forces of attraction actually work.