A common misconception is that in a double slit experiment, the
electrons or the photons go through both slits at the same time
and interfere with themselves. Nothing of the sort ever happens
and that idea doesn’t come from quantum mechanics. It is just
meaningless to ask the question (from which slit did the
particle pass?) in the context of the particular experiment and
even more meaningless to say that it went through both. The
particle always passes from the one or the other slit if you
setup an experiment that asks the question and in the case that
you shoot the particles one at a time you always get one hit on
the screen and not an interference of portions of the particle.
I think that the misconception has its roots in the wave analogy
of the wave function description of quantum mechanics, where you
must have a wave passing from both slits in order to have
interference on the other side. Of course that picture doesn’t
translate to having a particle passing from both slits, but it
only states that there