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James A. Putnam
Theory Introduction Page
Website Homepage Table of Contents
ã 2003
It is believed by relativists that because a person in free fall
experiences no sense of being under the influence of a force, there is, for him,
no force of gravity. He is merely doing a very natural thing as explained by
the general theory of relativity. In general relativity the force of gravity
does not need to be explained any more than does the experience of moving at a
constant velocity with no resistance.
This claim, if correct, gives gravity a different nature from all
other forces. If physical unity exists at the true fundamental level, then it
requires that gravity actually have the same nature as all other forces. For
this kind of unity, Einstein's claim must be wrong. This claim is his
Equivalence Principle. The error he made was to ascribe something to gravity
belonging to all acceleration. In principle, any body undergoing pure
acceleration will feel nothing. The cause of the acceleration is not a factor
if the acceleration is pure and complete in its application.
There is certainly something felt from most accelerations, so what
is it? What is felt is distortion and compression. These effects are the result
of uneven acceleration. If a body is pushed on one side only, it will undergo
compression. If a body is pushed at one small part only, it will undergo both
compression and distortion. We feel the effects of changes in the distance
between our molecules and atoms. We feel nothing if all particles in our body
suddenly accelerate in perfect unison. During free fall due to gravity this
situation is very closely approximated.
What then is to be said of the principle of equivalence? Let us
examine a common example cited in support of this principle. The example is of
a sequestered scientist inside a windowless room. The point stressed is that there
is no way for the scientist to determine the difference between the effects of
gravity or the effect of acceleration. Since the scientist cannot devise a test
to determine why he remains standing on the floor, the conclusion is made that
gravity and acceleration are the same phenomenon. In other words, if we can't
tell the difference then there is no difference.
There is a revealing connection between this example and the importance of first properly understanding force. The connection is: An analysis of force tells us there is a difference for the scientist between the gravity situation and the acceleration situation. In the case of gravity, we know that there are two forces at work on the scientist. Gravity exerts a force on him trying to pull him downward. The floor of the room is exerting a second and separate force pushing upward against him. There are two equal but opposite forces at work. These two forces cause compression and distortion. In the case of acceleration there is only one force at work on the scientist. This force is the floor pushing him upward. It also causes compression and distortion. Therefore, the difference between the two situations is a difference in the number of forces at work.
The fact that the scientist cannot distinguish between the two cases does not prove that gravity and acceleration are equivalent. All he needs is a window to prove they are different. The available decisive empirical evidence is hidden from him due to the lack of a window or, better yet, a glass room. This is a scientific experiment and must be properly set up. It must enable the scientist to gather the necessary empirical evidence in order to properly interpret the phenomenon. There is either a material source of gravity which is stationary with respect to him or there is not. This is the decisive evidence that the windowless room makes unavailable to him. If he finds there is no source of gravity present, then he must be experiencing acceleration.
What the scientist does learn in the windowless room is: We cannot distinguish between different
combinations of force so long as they add up to the same effect. In these two
cases the effect felt is not acceleration. It is almost identical compression
and distortion to the scientist's body. Therefore, it is all force that should
be investigated as having a common nature. The equivalence principle belongs to
all force.