paritychange

Paritychange is a term used to describe the alteration of a system’s parity, a property that characterizes how a state responds to a symmetry operation such as spatial inversion. In physics and chemistry, parity refers to whether a state is even (unchanged) or odd (maps to a negative) under inversion of spatial coordinates. A parity change occurs when a process connects states of opposite parity.

In physics, parity is a useful quantum number for classifying states. Strong and electromagnetic interactions conserve parity, so transitions that would require a parity change are forbidden under those forces. The weak interaction, by contrast, violates parity, allowing certain parity-changing transitions. Experimental demonstrations of parity violation in the 1950s revealed that nature does not always treat left and right symmetrically, which has deep implications for particle physics and the formulation of fundamental theories.

In molecular spectroscopy and chemistry, parity plays a role in the selection rules for transitions. For centrosymmetric molecules, electronic states are labeled as gerade (g) or ungerade (u). Electric dipole transitions typically require a change in parity, so a g→u transition is allowed while a g→g transition is forbidden. Parity changes can also influence vibronic coupling and the interpretation of spectra in symmetric molecules.

In computing and information theory, parity changes relate to error-detecting schemes. A parity bit is added to data to provide a simple test for errors; if a single bit flips during transmission, the overall parity changes, signaling a potential error. Parity change operations, such as flipping a bit, are used in parity checks and error-correction protocols.

See also parity operator, parity violation, and parity bit.