In physics, energy is subject to the law of conservation of energy. The use of the term “conservation” could be confusing as the idea of conserving energy by “saving gas” is a common phrase, but technically incorrect. According to this law, energy can neither be created (produced) nor destroyed. It can only be transformed. According to Conservation of energy the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. Given that understanding, the popular phrase “conserving energy by saving gas” really means: reducing the amount of energy that is transformed through combustion, from the potential energy stored in gasoline in to heat energy.
No one really knows what energy is, although it has been rigorously defined in theoretical physics. To this point, please consider the words of Richard Feynman, “It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.“
Despite this abstraction, scientists calculate energy, and after all of the calculations determine that energy is indestructible and immeasurably abundant. I understand this to be true, mathematically, for energy in all its various forms including: Thermal, Chemical, Mechanical, Sound, Elastic, Electric, Magnetic, Nuclear, Luminus, Mass and Radiant energies.
This fact, the indestructible and abundant nature of energy, is important to my thesis, which suggests that ordering our economy around the principal of scarcity is a logical fallacy.
 Richard Feynman, in The Feynman Lectures on Physics (1964) Volume I, 4-1