- In physics, parity is the quantum-mechanical
operation which reverses the signs of the coordinate axes being used
to describe a system; it has no significance in classical physics, but
essentially arises from the symmetry of space. Parity (P) is equivalent
to a mirror reflection followed by a rotation through 180°. The
parity is 1 (or even) if the wavefunction of the system is unchanged by an inversion (reflection in the origin)
of the coordinate system; it is -1 (or odd) if the wave function is
changed only in sign.
Parity is a constant in strong and electrodynamic interactions and does
not change with time because these interactions are governed by physical
laws which do not distinguish between a right- or a left-handed coordinate
system. Parity is, however, violated in the weak
interaction; that is, an object of positive parity can change with
time into an object of negative parity, and vice versa. See also CPT
theorem and CP violation.
- In mathematics, parity is:
(i) The sum of the digits in a binary representation of a number.
(ii) An indication of whether two numbers are both even or both odd
(same parity), or are such that one is even and one is odd (opposite
parity). This concept, of same or opposite polarity, can be applied
to any things that can have two different states – the sense
in which a knot is tied, the color of a chessboard square, and so