Which principle states that energy cannot be created or destroyed?

The principle of conservation of energy asserts that in a closed system, the total energy remains constant; energy can change forms or be transferred from one system to another, but it cannot be created from nothing or completely vanish. This principle is foundational in physical science, emphasizing that all energy transformations are governed by this constant. This means that for any energy transfer — such as in mechanical systems, electrical circuits, or even thermodynamic processes — the sum of energy before and after the process remains the same.

In contrast, the law of thermodynamics encompasses several overarching laws about energy and heat transfer, but it does not specify that energy cannot be created or destroyed in the same way the conservation principle does. The theory of relativity, while revolutionary in its view of mass-energy equivalence, does not address the conservation of energy in the traditional sense. The law of conservation of mass pertains to mass in chemical reactions, indicating that mass cannot be created or destroyed, but it is distinct from the energy conservation principle.