A phenomenon is said to be chiral if it is not identical to its mirror image (see Chirality (mathematics)).

The fundamental laws of physics may be chiral, as the weak charge is not invariant under a reflection unless particles are replaced by their antiparticles as well, and kaon decay appears to violate even that symmetry.

Chirality appears to be important in particle physics because the universe seems to be asymmetric as far as spin is concerned. Imagine a particle moving in the direction of one's thumb. The particle can be classified as left-handed if it is spinning in the direction of the fingers of the left-hand and right-handed if it is spinning in the direction of the fingers of the right-hand. Up to now, only left-handed neutrinos (and right-handed anti-neutrinos) have been observed.

Related topics

• explicit symmetry breaking