Conservation law
In physics, a conservation law states that a particular measurable property of an isolated physical system doesn't change as the system evolves. The following list is a partial listing of conservation laws that have never been shown to be inexact:
- conservation of energy (including mass)
- conservation of mass
- conservation of momentum
- conservation of angular momentum
- conservation of electric charge
- conservation of color-charge
- conservation of magnetic flux
There are more subtle conservation laws in particle physics like those of spin, baryon number[?] and more recently strangeness[?].
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.
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