In
quantum mechanics, a
parity transformation (also called
parity inversion) is the flip in the sign of
one spatial coordinate. In three dimensions, it is also often described by the simultaneous flip in the sign of all three spatial coordinates (a
point reflection):
It can also be thought of as a test for
chirality of a physical phenomenon, in that a parity inversion transforms a phenomenon into its mirror image. A parity transformation on something
achiral, on the other hand, can be viewed as an identity transformation. All fundamental interactions of
elementary particles, with the exception of the
weak interaction, are symmetric under parity. The weak interaction is chiral and thus provides a means for probing chirality in physics. In interactions that are symmetric under parity, such as electromagnetism in atomic and molecular physics, parity serves as a powerful controlling principle underlying quantum transitions.
