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## Main Question or Discussion Point

Hello! I am a bit confused by the difference between T-odd and T-violation. For example, I read that the existence of a fundamental particle EDM is a violation of time symmetry. However, placing an electric dipole in an electric field, would produce a hamiltonian (non-relativistically, which is usually the region of interest for e.g. atomic experiments): ##H = -d\cdot E##, where d is the electric dipole and E is the electric field acting on the (say) electron. The dot product between d and E is odd under time reversal. But I am not sure I understand where the T-violation comes from. I thought that T-odd means just that the system changes sign under T operator, but it is still an eigenstate of it, which means that T and H commute. However, T-violation, I imagined, it means that T and H don't commute. Can someone help me clarify what odd and violation mean in this case? Thank you!