The concept of symmetry in physics refers to the set of invariances of a system that is preserved when some operation is performed on the system. For example, a square rotated by 90aa is indistinguishable from the original and has symmetry under rotation. This is symmetry preservation or the maintenance of a particular invariance between the constituent parts of a system (i.e., to the maintenance of a particular invariance under all possible changes). J.J. Gibson, for example, assumes the preservation of perceptual symmetries under changing perspectives as one of the cardinal features of direct perception. Symmetry breaking occurs when the features of a system are no longer invariant under transformation. The constraints preserving the invariances in the system are broken and there follows the spontaneous emergence of a state of lower symmetry. Symmetry breaking is thus synonymous with the appearance of new properties
. See Constraints, Ecological psychology, Emergence, Pattern formation, Perception, Self-organization