CPT theorem

The CPT theorem is a result that binds together parity, charge conjugation and time reversal.

Basically, this says that regardless of system, subsequent application of parity, charge conjugation and time reversal always leads to a system that exhibits identical behavior. Effectively, applying all three "does nothing". It is nevertheless possible to violate each one individually (e.g. C violation) or even in pairs (e.g. CP violation).

This theorem has three consequences:

1. Mass and mean lifetime must be the same for any particle and its antiparticle.
2. Antiparticles must have opposite quantum numbers compared to their particles.
3. Violating CPT means violating the inherent structure of spacetime.