1.the phase factor in QM is invariant or symmetry all time but there is 2 kind of phases which is global phase and relative phase. Is global phase or relative phase related to open or close system?and both of it is still invariant? 2. If the phase do not have physical meaning then what about the phase factor in path integral? it used to describe the system, Exp[iS/h_bar] and S is the action. 3. bohm mechanics use S as the phase to interpret QM. what exactly difference between action and phase? is action use to describe phase or vice versa?