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Conservation Laws
Conservation laws
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 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")
(This only applies to systems describable by a
Lagrangian).
There is an analogous theorem for
Hamiltonian mechanics. 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).
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,
the
invariants, 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 most solutions
of the equations of
physics.
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