Two Experiments Observe Explicit Violation of Time‐Reversal Symmetry

It is hard to imagine that nature might violate the CPT theorem. Its proof invokes only rock‐bottom assumptions of quantum field theory, and many of its consequences have been tested to very high precision. The theorem, independently discovered in the mid‐1950s by Gerhardt Lüders, Wolfgang Pauli and John Bell, asserts that any local field theory that is invariant under the “proper” Lorentz transformations must also be invariant under the combined operation of the three discrete (improper) transformations: time reversal (T), parity inversion (P) and charge conjugation (C).