  The long-standing controversy regarding the Aharonov-Bohm phase shift is
reviewed. The shifts of both optical and particle interference patterns are
summarized. It is pointed out that a line of electric dipoles and a line of
magnetic dipoles (a long solenoid) both produce experimentally observed phase
shifts similar to that produced by introducing a rectangular block of glass
behind one slit of a double-slit interference pattern; the double-slit pattern
is shifted while the single-slit envelope remains undisplaced. The quantum
explanation for the magnetic interference pattern shift introduced by Aharonov
and Bohm in 1959 involves completely different ideas from those suggested by a
semiclassical analysis. Experiments planned by Caprez, Barwick, and Batelaan
should clarify the connections between classical and quantum theories in
connection with the Ahronov-Bohm phase shift.
