CPT symmetry's a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity and time simultaneously. History Efforts in the late 1950s revealed the violation of P-symmetry by phenomena that involve the weak force, and there're well known violations of C-symmetry and T-symmetry as well. For a short time, the CP-symmetry was believed to be preserved by all physical phenomena, but that was later found to be false too. On the other hand, there's a theor… (More on Cpt-symmetry)