What is a word or phrase that means the same thing as the law of conservation of energy

Energy remains constant is the answer you are looking for but it only applies, when no outside forces act on the object. 

Aform of energy that is reflected or emitted from objects in the form of electrical and magnetic waves that can travel through space. there are many forms of  electromagnetic  energy including gamma rays, x rays, ultraviolet radiation, visible light, infrared radiation, microwaves and radio waves.

Answer form flower;