I MASS-ENERGY ACCELERATION
With an abstract notion originally called "impetus", Galileo discovered that all objects tend to maintain a uniform motion forever until acted on by some external force. Conversely, all objects at rest will remain at rest forever until acted on by some force. This mysterious cosmic laziness became our law of inertia.
Galileo also discovered that if air friction could be removed, all objects, regardless of their mass, would fall at the exact same rate. This means that a feather and a hammer will fall equally in a vacuum. This baffling truth, a major mystery for its time, confounded everyone until it was discovered that it could be explained by the other mystery, inertia. What a coincidence. Two bodies of unequal weight fell at the same rate because their different weights were offset by their different tendencies to remain inert. That is, the unexplained tendency to attract a heavier body was equalized by a stronger tendency to remain at rest. An object with more weight would also have more cosmic laziness, thus two bodies with different weights fell equally.
This meant that a body must have two kinds of masses that must be equal: gravitational mass and inertial mass. And the supposition that these two masses were always precisely equal and offsetting was--and still is--considered a remarkable coincidence of nature; a coincidence that has baffled philosophers and scientists for centuries.
Einstein, however, didn't buy it. It was just a little too coincidental. He noticed that "the same quality of a body manifests itself according to circumstances as 'inertia' or as 'weight'".1 That is, Einstein made the bold assumption that there was only one quality with two separate names: "Gravity and inertia are two different words for exactly the same thing" (Gardner). "Thus the concept of gravity as an independent force completely disappears from our reasoning" (Gamow). Said another way, "...gravity hasn't really been united with inertia, it's been dispensed with altogether" (Jones).
The irony of all this is that in the textbooks and classrooms (the same ones teaching relativity), the mystery of falling bodies is still explained away by the coincidence of an "attractive" force offset by an inertial tendency. And this is in spite of the fact that general relativity has withstood the test of time. Unlike quantum theory which adds a "supplementary term" whenever it's faced with inconsistencies or contradictions, general relativity has been found flawless. "In the sixty four years since [Eddington's confirmation – now over 80 years)...general relativity has met every experimental test to which it has been subjected."2
Now inertial mass is defined as the resistance to acceleration, or non-uniform motion (deceleration is also non-uniform motion). Gravitational mass is weight. Einstein's theory begins with and rests squarely on "the principle of equivalence", the unification of these two masses. There can only be one. Gravity is no longer a force, but an effect. And inertia is only a tendency. Einstein didn't clear up the falling bodies dilemma, as some claim, but took away the one and only fictional explanation there was. And even he didn't clarify what weight was except to prove its equivalence to the resistance of acceleration. That is, that we could think of ourselves as being on the floor of a continuously accelerating elevator!
I'm not sure how one can square with calling something “precisely equivalent” on the one hand, yet not be willing to admit they're the same thing on the other. Nevertheless, this still has profound implications.
One of the compounding effects of the mystery of gravity is the fact that a body not only falls to the earth – which is mystery enough – but that it accelerates, and will continue to accelerate forever (until, of course, it makes contact with a frictional force such as air or some surface). Since we live in a dense atmosphere which limits this acceleration, it is not immediately apparent. This illustrates the genius of Galileo's discovery and the ability to overcome the fallacy of some of our initial, common-sense observations.
But why would a body forever accelerate directly towards the center of another body as Newton's theory and countless experiments clearly demonstrate? Given the context of what has passed in subsequent chapters, the reader may begin to realize how easily this question could herein be answered. For we've just learned that weight is somehow related to the resistance to acceleration, that it is "precisely equivalent" to the ground accelerating up! And that two unequal bodies continue to fall at the same rate defying all attempts to explain it. And that a body in the fourth dimension must necessarily grow or diminish in relative size. And that the psi-function predicts what atomic experiments show consistently and some physicists reluctantly admit; that "unobserved" matter spreads out and extends omni-directionally throughout space. And that if observed matter were spreading, the spreading couldn't be observed. Therefore, allowing the consistency of the argument, the ground must be "accelerating up". Or, more precisely, the surface of both bodies must be accelerating towards each other. As ridiculous as this may sound and as psychologically unacceptable as it may sound, there is just no other consistent explanation.
Einstein provided no answer as to what accelerates. What he did provide was the startling notion that both acceleration and matter (or, if you like, accelerated matter) curves or warps the space surrounding it. And that this curved space in turn effects the motion of a body contained within. Or as Wheeler said many times, “Matter tells space how to curve and space tells matter how to move.” What this means is that there are two separate but related ways to look at the cause of this totality we call gravitation. While we've shown how a body can accelerate, we have not explained why. Nor have we shown how or why bodies "fall" in the first place. And since mass-energy acceleration by no means explains all of the vicissitudes of gravity, it is to the arena of space that we must now turn.