EQUATIONS OF MOTION
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We shall now consider the connection between the state of a system at one time and that at a subsequent time, provided that, in between, the state is not disturbed by an observation. It may be recalled that making an observation on a dynamical system will, in general, disturb the state of the system unless the state happens to be an eigenstate of the observable pertaining to the observation. If the state is not disturbed in between, the time evolution of the state of the system is governed by an equation of motion which would enable one to determine the state at a later time if the state at an earlier time is known. Such an equation of motion would enable one to get a complete dynamical picture of the system.