- While watching popular lectures from scientists such as Brian Greene, Sean Carroll and so many others the double slit experiment is often explained but exactly how the single electron or photon source gun chooses which slit to go through is not explained because the apparatus is not explained well enough.
So when explaining the results of quantum double slit experiments that have evolved from the classical wave double slit experiment, popular lecturers of quantum mechanics often show an animation of an electron gun or photon source shooting a lot of particles towards a double slit. The effect is like a shotgun blast where a lot of particles are shooting out from a source. Some particles hit the wall and bounce off, some go through one slit and others go through the other slit. The lecturers normally evolve the classical shotgun blast of tennis ball sized particles, then gradually make the particles smaller and smaller until the quantum effects begin to be seen; that is until the particles get to the size of electrons or photons. As I understand it once a particle leaves the source it travels in a straight line because it is in a vacuum and no other forces act on the particle. So how do the experimenters aim the gun towards the slit? Do they have to pick a slit to target? Do they first choose one slit then move the aim to go through the other slit? If there were no slits, would a single electron or photon always hit the exact same area of the blank wall where the slits should be? This question is especially important when I think about the exactly one particle at a time experiment. I know how physicists can generate a single particle at a time and still get the interference effects, but I do not know if they have to choose which slit to go through and if they do not know that, could they remove the slit and have the particle land on the same spot on the wall all the time.