Editing Order and disorder (section)

{{Short description|Presence/absence of symmetry or correlation in a many-particle system}}
{{More citations needed|date=February 2024}}

In [[physics]], the terms '''order''' and '''disorder''' designate the presence or absence of some [[symmetry]] or [[correlation]] in a many-particle system.{{citation needed|date=February 2024}}

In [[condensed matter physics]], systems typically are ordered at low [[temperature]]s; upon heating, they undergo one or several [[phase transition]]s into less ordered states.
Examples for such an '''order-disorder transition''' are:
* the [[melting]] of [[ice]]: solid–liquid transition, loss of [[Crystallinity|crystalline order]];
* the [[demagnetization]] of [[iron]] by heating above the [[Curie temperature]]: [[ferromagnetic]]–[[paramagnetic]] transition, loss of magnetic order.

The [[degree of freedom]] that is ordered or disordered can be translational ([[crystal]]line ordering), rotational ([[ferroelectricity|ferroelectric]] ordering), or a spin state ([[magnetism|magnetic]] ordering).

The order can consist either in a full crystalline [[space group]] symmetry, or in a correlation. Depending on how the correlations decay with distance, one speaks of [[long range order]] or [[short range order]].

If a disordered state is not in [[thermodynamic equilibrium]], one speaks of '''quenched disorder'''. For instance, a [[glass]] is obtained by quenching ([[supercooling]]) a liquid. By extension, other quenched states are called [[spin glass]], [[orientational glass]]. In some contexts, the opposite of quenched disorder is '''annealed disorder'''.