What Is Physical Energy

(July 7, 2022) The core of any metaphysics is understanding causation. In physics causation is called a force but force is an instantaneous value so it usually has to be summed over space or time. Energy is a measure of force summed over space while momentum is a measure of force summed over time. If you are concerned with how deep a hole a metal ball makes when dropped in sand then you use energy. If instead you are concerned with how planets change speed over time you use momentum.

Force as applied to a mass can be summed across space in two ways: as potential energy and as kinetic energy. The two are convertible into each other (see image below). A system with a heavy rock high held high in the air has more potential energy than a rock held near the earth because the high rock can cause more things to happen as it falls. What gives a high rock its potential energy is the gravity (space curvature) field.

Causality also has a negative component. Anything which reduces causal potential summed through space is negative energy (not to be confused with positive energy moving in the opposite direction). The stretching of space due to the expansion of the universe is a negative energy  because it reduces potential energy by making the gravity field weaker (the space curvature more flat). This is exhibited by the light from distant galaxies being ​red shifted which means it has less kinetic energy when it reaches earth.

References

 Davies, P.C.W. (1979) The Forces of Nature. Cambridge University Press​

 French, A.P. (1968) Special Relativity. CRC Press

(July 7, 2022) The concept of physical energy as something conserved yet transformed has only been around for 170 years. It was developed intermittently during the early 1800’s out of the interaction of Scottish Universities, British marine engineering works, and British scientific societies. It combined previously independent domains into one unifying framework. The revolution was complete by 1851 when William Thomson (later Lord Kelvin) wrote this in his famous 1851 paper “On the Dynamical Theory of Heat.” Notice that heat was thought to be an immaterial fluid called caloric which flowed around and that the physics of the time had no problem working with the immaterial:

• 1. SIR HUMPHRY DAVY, by his experiment of melting two pieces of ice by rubbing them together, established the following proposition: “The phenomena of repulsion are not dependent on a peculiar elastic fluid for their existence, or caloric does not exist.” And he concludes that heat consists of a motion excited among the particles of bodies. “To distinguish this motion from others, and to signify the cause of our sensation of heat,” and of the expansion or expansive pressure produced in matter by heat, “the name repulsive motion has been adopted.” [1]
• 2. The dynamical theory of heat, thus established by Sir Humphry Davy, is extended to radiant heat by the discovery of phenomena, especially those of the polarization of radiant heat, which render it excessively probable that heat propagated through “vacant space,” or through diathermanic substances, consists of waves of transverse vibrations in an all-pervading medium.
• 3. The recent discoveries made by Mayer and Joule, [2] of the generation of heat through the friction of fluids in motion, and by the magneto-electric excitation of galvanic currents, would either of them be sufficient to demonstrate the immateriality of heat; and would so afford, if required, a perfect confirmation of Sir Humphry Davy’s views.

The next big advance merged the force field concept invented by Michael Faraday during the 1840’s with energy. The electromagnetic force field idea was invented to explain the connection between electricity and magnetism. Later, Scottish mathematician James Maxwell, was able to mathematically describe this force field concept in terms of energy in his famous equations that describe electrodynamics. He published these equations in a four part paper entitled “On Physical Lines of Force” between 1861 and 1862.

The energy concept was further extended in 1905 when Einstein showed energy could be converted into mass in the first linkage of what was then thought to be immaterial (energy) with the material (mass).​ 

References

Joules' precise experiments first showed that various forms of energy could be converted into each other.