Gravitational Potential Energy
Potential energy is always a negative, absolute quantity, the value of which can never be physically measured except as a linear dimension between the centers of two particular bodies. A valid analogy can he made between potential energy and an automobile fuel tank. The gasoline in the tank represents kinetic energy and the empty portion of the tank represents potential energy. When the tank is empty potential gasoline is its maximum and when the tank is full potential gasoline is zero. We never consider the empty portion of our fuel tank to be equivalent to real gasoline, nor when we fill our fuel tank, do we consider it to be a process of converting empty space into gasoline.
We know that any body at rest will attain a velocity of 11,179 m/s if it falls to Earth from deep space. The energy inherent in this velocity (E=MV2/2) is the maximum potential energy of this body when it was sitting at rest in deep space. Potential energy is always a negative quantity and can never be represented as real energy. Its value is always absolute in quantity, negative in quality, and strictly relative to the Earths center. For example, a one kilogram clock is said to have 62,485,020 joules (J) of potential energy when it sits at rest out in deep space a significant distance from Earth. (In the moons orbit at 58R it would have 61,946,322 J).
This maximum value of about 62 megajoules (MJ), however, is insignificant when compared to the clocks potential energies relative to other bodies. The clocks potential energy to Jupiter is 608 MJ, 190,000 MJ to the sun and millions more to Sirius. If the clock was sitting at rest, half way between two stars of equal mass, is its gravitational potential energy double or nothing? If a small amount of energy is used to set this clock in motion toward one of these stars, its potential energy relative to that star will decrease more rapidly than its potential energy relative to the other star increases. Therefore potential energy is neither equivalent between bodies nor to the kinetic energy used to initiate its change in value. If we consider and total the potential energy relative to every other body in the universe, we see that a bodys potential energy is nearly infinite when viewed from this absolute, but meaningless perspective.
The same clock sitting at rest at the center of the earth would have zero potential energy. The only way that kinetic energy can be measured and represented is by the motion of mass. The only way that potential energy can be measured and represented is at an at-rest position on a linear scale extending between the center of the earth and infinity. Potential energy is only a position on this scale and has no direct link to the kinetic energy of the clock. Two identical bodies can have identical potential energies but greatly different kinetic energies. The extreme example is the orbit. Potential energy can not be converted to, nor is it equivalent to kinetic energy. Kinetic energy is always a relative quantity that can be either negative or positive and is always measured as an acceleration or deceleration of mass. Positive kinetic energy increases the absolute velocity of a body and slows its clock, and negative kinetic energy decreases the absolute velocity of a body and speeds its clock.
To illustrate the relative nature of kinetic energy and the absolute nature of momentum lets consider the following thought experiment. Bob and Alice are situated a certain distance apart in the same inertial reference frame. Alice throws a one kilogram lump of clay towards Bob with a velocity of 10 m/s and a kinetic energy of 50 joules. Bob then takes another lump of clay and throws it at the first so that when the two lumps collide they stick together and are stopped completely. How much energy did Bob have to impart to his lump of clay so that Alices lump could be completely stopped?
(A) 1 joule (B) 10 joules (C) 100 joules (D) none of above (E) all of above
Many people quickly jump to the conclusion that the answer is (D) because they assume that since Alices lump of clay had 50 joules of energy he would have to exert 50 joules to stop its motion. Actually the answer is (E) because the quantity of energy to accelerate a body to a given velocity can vary greatly depending on the method used. Energy also is completely irrelevant when it comes to bringing it to a stop. The energy that Bob needs to impart to his lump of clay depends entirely on the mass of the lump he decides to throw because it is an equal amount of momentum that is needed to stop the ball and not an equal amount energy. If Bob chose a .5 kg lump he would have to give it 100 J and if he chose a 50 kg lump he would only need 1 J. Had he used the Titanic to stop the lump it would only take 1.25x10-8 joules of energy. Had he used photons to stop it, the energy requirements would be equivalent to about 500 kg of TNT (3x109 J).
The precise determination of the absolute motion of a body is very difficult because it must be measured against the motion of the universe as a whole. Seemingly, the most reliable marker for the inertial reference frame of all photons and thus the universe itself is the Doppler shifts measurements made by the COBE satellite of the dipole anisotropy within the 2.7 degree cosmic background radiation (CBR). These measurements revealed a CBR wind blowing from the direction of Leo and toward Aquarius at about 370 km/s (.002 C). This means that the absolute velocity of Earth relative to the photons inertial reference frame is approximately 370 km/s in the direction of the constellation Leo (a=11.2h , d=-7o (l=264.7o, b=48.2o). This velocity changes slightly over time because of the motion of Earth in its orbit around the sun (30 km/s) and the motion of the sun at the present position of its orbit around the Milky Way. The velocity of our local group of galaxies relative to the CBR Rest is about 600 km/s in the direction of a=10.5h , d=-26o (l=268o, b=27o).
For our one kg clock this velocity of 370 km/s represents a kinetic energy of 6.8x1010 J and slows its rate so that the duration of its intervals increases by 1.00000076 and any =1 photons it emits at right angles to either Aquarius or Leo will have an absolute wavelength of =1.00000076 and any =1 photons that it emits toward Aquarius will have an absolute wavelength of =1.001234 and any =1 photons emitted toward Leo will have an absolute wavelength of =.99877.
For all practical purposes it is meaningless to try and determine whether kinetic energy is positive or negative in absolute terms. It is usually only useful to measure kinetic energy relative to the surface of the earth. However, with the kinetic energy associated with gravitational motion there is never any ambiguity as to whether it is positive or negative. Any energy that decreases potential energy is positive and any energy that increases potential energy is negative. The true upward acceleration of Earths gravity is measured as an acceleration relative to the changing values of gravitational time. However, when this same acceleration is measured with the unchanging values of Absolute Time it becomes a constant velocity. In effect, the earths upward motion is slowing down at the same rate that it is speeding up. It is this upward motion that is the real force of gravity.
When a body falls to Earth, all of the kinetic energy released in the collision comes from the upward velocity of Earths surface, not from the body falling. This upward velocity is the same as the escape velocity for any given point at or above Earths surface. The energy inherent in this upward surface velocity provides all of the kinetic energy released when the Earth collides with a falling body. It is this easily measured upward change in motion of Earths surface that is the source of gravitational energy. The only evidence that has ever been offered for the idea that a falling body undergoes a constant downward change in motion is that universal human function called intuition. Ask anyone if falling objects move and you wont find anyone who will say they dont. If you ask if the earth moves, the best responses youll receive will acknowledge the motion of Earths rotation, its orbit, solar motion, galactic motion, and background radiation motion. If you then ask if they can feel the earth move they will say only during earthquakes. Then ask if anyone can feel the changing accelerations that their body experiences when they ride on a roller coaster and they will say of course they can.
The widely held belief that falling bodies move downward is just that, a belief. This idea is supported only by intuition and pure faith and no experimental evidence has ever been offered in its support. All accelerometers and other measuring instruments show Earths surface to be accelerating upward and falling bodies to be motionless, except for the upward force of air resistance.