  A Gedanken experiment is described to explore a counter-intuitive property of
quantum mechanics. A particle is placed in a one-dimensional infinite well. The
barrier on one side of the well is suddenly removed and the chamber
dramatically enlarged. At specific, periodically recurring, times the particle
can be found with probability one at the opposite end of the enlarged chamber
in an interval of the same size as the initial well. With the help of symmetry
considerations these times are calculated and shown to be dependent on the mass
of the particle and the size of the enlarged chamber. Parameter ranges are
given, where the non-relativistic nature of standard quantum mechanics becomes
particularly apparent.
