Energy cannot be created, according to the law of the conservation of energy, which was first published in an 1842 scientific article by the German Physicist Julius Mayer. Based on the same principle, energy cannot be destroyed either. In an isolated system, energy can be transformed from one form to another, but the total amount of energy within the system remains constant.
A system that is completely separated from its surroundings possesses unchanging mechanical properties, which are referred to as "constants of the motion." This fundamental observation is the basis for the conservation laws in physics, specifically in the field of mechanics. The most common among these conserved physical quantities is energy.
The invention of the steam engine in the early 1800s prompted scientists and engineers to study the rudiments of energy. Aside from Mayer, Hermann von Helmholtz, James Joule and William Thomson were also instrumental to the development of the energy conservation law. Through a series of experiments conducted by these prominent scientific figures, further evidence was provided to support the theory that energy is neither made nor destroyed in a closed system.
Any form of energy can only be converted to another form. However, it was Thomson, popularly known as Lord Kelvin, who first discovered that all energy transformations involve heat loss that cannot be regained, which is incorporated back into the material world.