Noether's theorem expresses the equivalence which exists between conservation laws and the invariance of physical laws with respect to certain transformations (typically called "symmetries"). For instance, time-invariance[?] implies that energy is conserved, translation-invariance[?] implies that momentum is conserved, and rotation-invariance[?] implies that angular momentum is conserved.
Some conservation laws hold in many circumstances, but exceptions to them have been observed. Such is the violation of parity conservation; apparently the universe has "handedness" (right versus left).
Philosophy of Conservation Laws The idea that some things remain unchanging throughout the evolution of the universe has been motivating philosophers and scientists alike for a long time.
In fact, quantities that are conserved, in some sense, seem to preserve what one would like to call some kind of a 'physical reality' and seem to have a more meaningful existence than many other physical quantities. These laws bring a great deal of simplicity into the structure of a physical theory. They are the ultimate basis for solving most physical variables.