Conservation law

In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. The following is a partial listing of conservation laws that have never been shown to be inexact.

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• conservation of energy
• conservation of momentum
• conservation of angular momentum
• conservation of electric charge
• conservation of color charge
• CPT symmetry

There are also approximate conservation laws. These are approximately true in particular situations, such as low speeds, short time scales, or certain interactions.

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• conservation of baryon number (See chiral anomaly)
• conservation of flavor (violated by the weak interaction)
• conservation of mass (only in nonrelativistic theories)
• conservation of parity
• CP symmetry.

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 systems which obey the Principle of least action and hence having a Lagrangian and a Hamiltonian (See Classical mechanics, Hamiltonian mechanics for details). 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.

Related Topics:
Noether's theorem - Invariance - Symmetries - Principle of least action - Lagrangian - Classical mechanics - Hamiltonian mechanics - Time invariance - Translation invariance - Rotation invariance

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Conservation law: Philosophy of conservation laws ►