parityArticle Free Pass parity, in physics, property important
in the quantum-mechanical description of a physical system. In
most cases it relates to the symmetry of the wave function
representing a system of fundamental particles. A parity
transformation replaces such a system with a type of mirror
image. Stated mathematically, the spatial coordinates describing
the system are inverted through the point at the origin; that
is, the coordinates x, y, and z are replaced with −x, −y, and
−z. In general, if a system is identical to the original system
after a parity transformation, the system is said to have even
parity. If the final formulation is the negative of the
original, its parity is odd. For either parity the physical
observables, which depend on the square of the wave function,
are unchanged. A complex system has an overall parity that is
the product of the parities of its components. Until 1956 it was
assumed that, when an isolated system of fundamental particles
interacts, the overall parity remains