In physics, the law of conservation of energy states that the total energy of an isolated system remains constant—it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another. For instance, chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite. In technical terms, conservation of energy can be rigorously proven by the Noether theorem to be a direct consequence of continuous time translation symmetry - wikipedia 
A consequence of the law of conservation of energy is that a perpetual motion machine of the first kind cannot exist. That is to say, no system without an external energy supply can deliver an unlimited amount of energy to its surroundings. For equations of motion which do not have time translation symmetry, the conservation of energy may not be able to be defined. Examples include curved spacetimes in general relativity or time crystals in condensed matter physics.
# See also * History * First law of thermodynamics * Noether's theorem * Relativity * Quantum theory * See also * References * Bibliography * External links