In the Aharonov-Bohm effect, proposed in 1959, quantum particles are
affected in measurable ways by the classical electromagnetic potential,
previously regarded as a purely mathematical construct. The
electromagnetic field is too far from the particles to have any direct
influence.
A 1959 Physical Review paper
claimed that an electric or magnetic field could influence quantum
particles even though the particles never experienced the field
directly. In classical electromagnetism there is no other way to
influence a particle besides direct contact with the fields. Even though
quantum mechanics was well-established by then, the idea met with
widespread skepticism.
Arguments over the theoretical analysis and attempts at experimental
verification continued for some years, but eventually the so-called
Aharonov-Bohm effect took its place as a legitimate demonstration of
unexpected physics in the quantum world.
In classical electromagnetism, electric and magnetic
fields are the fundamental entities responsible for all physical
effects. There is a compact formulation of electromagnetism that
expresses the fields in terms of another quantity known as the
electromagnetic potential, which can have a value everywhere in space.
The fields are easily derived theoretically from the potential, but the
potential itself was taken to be purely a mathematical device, with no
physical meaning...
Full article: http://physics.aps.org/story/v28/st4
