What do we mean when we say ‘energy’?
One of the most essential concepts for understanding physical reality is also one of the most difficult to define
Much like many other scientific concepts, the word “energy” permeates our lives and discourse in various ways and contexts. When we experience fatigue, we may lament a lack of energy, while healers often refer to providing an “energetic touch” or tapping into “cosmic energy,” among other common-language expressions of this concept. However, in the realm of science, energy is not synonymous with vitality or a mystical supernatural phenomenon.
Instead, it serves as a fundamental physical quantity that enables us to describe the behavior of phenomena across multiple disciplines and fields — from Newtonian mechanics and astronomy to relativity, quantum mechanics, chemistry, and biology.
So, what exactly is energy? The challenge lies in its definition. Although we have a basic intuition regarding the essence of this fundamental quantity, it’s hard to define it accurately. The challenge arises because energy manifests in numerous forms, yet the essence of energy transcends these manifestations.
Physicists have addressed this by defining energy not through intuitive, conceptual means, but rather by its fundamental properties—a purely mathematical concept. Energy, then, is defined as a quantity that remains conserved within closed systems. The significance of this statement will soon become apparent.
