the above situation is like a source of light located at $x_L$, which is suddenly “turned on” at $t=0$. It takes time for the wavefront to propagate to the reflecting surface, and additional time for the reflected wavefront to make its way back to $x=x_L$. Prior to the latter point in time, the evolution of the truncated electromagnetic wave is decidedly [*non*]{}-stationary; afterwards however, a stationary wave is achieved, at least within the region of interest, $x_L\le x \le 0$, as the wavefront has by this stage propagated beyond this region. The same qualitative comments apply to the bipolar quantum case, although of course the evolution equations are different.

A similar prescription may be used to achieve rudimentary “wavepacket dynamics,” even in the context of purely stationary states. Instead of retaining [*all*]{} initial trajectories that lie to the left of $x_L$, one retains only those that lie within some finite interval. The resulting time evolution is analogous to a light source that is turned on at $t=0$, and then turned off at some later time (prior to when the wavefront arrives at the reflecting surface). The initial “wavepacket” has uniform density, and moves with uniform speed towards the hard wall. 