The phenomenon in physics that states energy cannot be created or destroyed is known as the law of conservation of energy. This fundamental principle asserts that the total energy in a closed system remains constant over time, although energy can change forms (e.g., from kinetic to potential energy). This concept is foundational in fields such as thermodynamics, mechanics, and electromagnetism. Understanding this principle is crucial for analyzing physical systems, energy efficiency, and the behavior of matter and energy in various contexts.