TIME-REVERSAL SYMMETRY AND TIME-DEPENDENT PHYSICS

In this letter I study the concept of time-reversal invariance in both classical and quantum physics in the absence of time-translation invariance (explicit time dependence/external time-dependent fields). Accordingly I generalize the concept of time-reversed process when the time-origin of the process has physical significance. The cases of classical physics, standard quantum mechanics and time-neutral quantum mechanics with and without explicit time dependence are discussed.