Symmetry breaking

This article is about the concept in physics. For the concept in biology, see Symmetry breaking and cortical rotation.

Symmetry breaking in physics describes a phenomenon where (infinitesimally) small fluctuations acting on a system which is crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observer unaware of the fluctuations (or "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 definite states. Symmetry breaking is supposed to play a major role in pattern formation.

In particular, we distinguish between:

• Explicit symmetry breaking where the laws describing a system are themselves not invariant under the symmetry in question.
• Spontaneous symmetry breaking where the laws are invariant but the system isn't because the background of the system, its vacuum, is non-invariant. 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.

See also

• Higgs mechanism
• QCD vacuum
• Goldstone boson
• 1964 PRL symmetry breaking papers
• J. J. Sakurai Prize for Theoretical Particle Physics
• Spontaneous symmetry breaking