Physics
In physics, the laws of motion of classical mechanics have the above property, if the operator π reverses the conjugate momenta of all the particles of the system, p -> -p . (T-symmetry).
In quantum mechanical systems, it turns out that the weak nuclear force is not invariant under T-symmetry alone. If weak interactions are present, reversible dynamics are still possible, but only if the operator π also reverses the signs of all the charges, and the parity of the spatial co-ordinates (C-symmetry and P-symmetry).
Read more about this topic: Reversible Dynamics
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