Example
The best physical example is a spherical ball balanced on a (symmetrical) hill. A slight disturbance of the ball's position will cause it to quickly roll down the hill into its lowest energy state. A perfectly symmetrical situation therefore collapses into an asymmetrical state.History of Symmetry Breaking
This property goes back for many years in physics. For example, Pierre Curie's work with ferromagnetic materials displays a symmetry breaking at the Curie temperature, where the symmetrical orientation of magnetic domains become asymmetric. (Though the principle was originally discovered by curie, it was explained in 1928 by Werner Heisenberg, since Curie died in 1906 and therefore had no knowledge of quantum theory or the atomic models necessary for such a detailed explanation.)Yoichiro Nambu discovered that spontaneous symmetry breaking in superconductors could be explained using field theories, which had an asymmetrical ground state but still possessed symmetry within the theory. In 1960, Nambu applied this principle to the quantum field theory for elementary particle physics, for which he was awarded half of the 2008 Nobel Prize in physics.
Nambu's work lead to spontaneous symmetry breaking being applied to solve some issues in developing the Standard Model of particle physics. Spontaneous symmetry breaking is seen as responsible for the existence of mass. In this model, the Higgs boson is the agent of this spontaneous symmetry breaking, which results in masses for the W and Z bosons that mediate the weak interaction.
