Symmetry breaking 1240378 221000398 2008-06-22T16:24:35Z DOI bot 6652755 Citation maintenance. Initiated by [[User:Fconaway|Fconaway]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. '''Symmetry breaking''' in [[physics]] describes a [[phenomenon]] where (infinitesimally) small [[fluctuation]]s acting on a [[system]] crossing a [[Critical point (physics)|critical point]] decide a system's fate, by determining which branch of a [[Bifurcation theory|bifurcation]] is taken. For an outside observer unaware of the fluctuations (the "[[Thermal noise|noise]]"), the choice will appear arbitrary. This process is called [[symmetry]] "breaking", because such transitions usually bring the system from a [[randomness|disorderly]] [[state (physics)|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#Quantum-mechanical_definition|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]]. * [[Biological symmetry breaking]] is the process by which a spatially uniform object (such as an undifferentiated [[oocyte]]) [[developmental biology|develops]] into an asymmetrical object. In 1972, [[Nobel prize in physics | Nobel laureate ]] [[Philip Warren Anderson | 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_%28journal%29 | Science]]<ref>{{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}}</ref>. ==See also== *[[Higgs mechanism]] *[[QCD vacuum]] *[[Goldstone boson]] [[Category:Symmetry]] ==References== {{reflist}} {{disambig}} [[zh:对称性破缺]]