  We address the problem of interference using the Heisenberg picture and
highlight some new aspects through the use of pre-selection, post-selection,
weak measurements, and modular variables, We present a physical explanation for
the different behaviors of a single particle when the distant slit is open or
closed: instead of having a quantum wave that passes through all slits, we have
a localized particle with non-local interactions with the other slit(s). We
introduce a Gedankenexperiment to measure this non-local exchange. While the
Heisenberg picture and the Schrodinger pictures are equivalent formulations of
quantum mechanics, nevertheless, the results discussed here support a new
approach which has led to new insights, new intuitions, new experiments, and
even the possibility of new devices that were missed from the old perspective.
