Symmetry breaking

Symmetry breaking in physics describes a phenomenon where (infinitesimally) small fluctuations acting on a system crossing a critical point decide a system's fate, by determining which branch of a bifurcation is taken. For an outside observer unaware of the fluctuations (the "noise"), the choice will appear arbitrary. This process is called symmetry "breaking", because such transitions usually bring the system from a disorderly state into one of two more ordered, less probable states. Since disorder is more symmetric in the sense that small variations to it don't change its overall appearance, the symmetry gets "broken".

Symmetry breaking is supposed to play a major role in pattern formation.

In particular, we can distinguish between:
* An explicit symmetry breaking happens when the laws describing a system are themselves not invariant under the symmetry in question.
* Spontaneous symmetry breaking describes the case where the laws are invariant but it appears the system isn't because the background of the system, its vacuum, is noninvariant. Such a symmetry breaking is parametrized by an order parameter. A special case of this type of symmetry breaking is dynamical symmetry breaking.

In 1972, Nobel laureate P.W.Anderson used the idea of Symmetry breaking to show some of the drawbacks of Reductionism in his paper titled "More is different" in Science [cite journal | last=Anderson | first=P.W. | title=More is Different | journal=Science | volume=177 | issue=4047| pages=393–396 | year=1972 | url=http://www.cmp.caltech.edu/~motrunch/Teaching/Phy135b_Winter07/MoreIsDifferent.pdf | doi=10.1126/science.177.4047.393 | pmid=17796623] .

ee also

*Higgs mechanism
*QCD vacuum
*Goldstone boson

References