Symmetry breaking

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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 order parameter, is noninvariant.
• Biological symmetry breaking is the process by which a spatially uniform object (such as an undifferentiated oocyte) develops into an asymmetrical object.