In the double-slit experiment, without which-path information available, the diffraction pattern is usually shown as an even function with respect to the displacement from the midpoint of the slits: something like sin ay / y. (This is the case in Feynman's lectures, and many others.) The question was posed as to whether this result is valid for spin-aligned electrons. The most direct reply stated that it is indeed valid: This seems to contradict these UC Berkeley course notes, which state that if one of the paths is increased in length to make it out of phase from the other by 2∏ radians, then the interference pattern will go to zero, because the state function of the longer path will be multiplied by -1 (or exp i∏). It is stated in the notes that this effect was experimentally confirmed with neutrons (another fermion). This would not be the case for photons, which would constructively interfere. If this is indeed correct, then wouldn't it also be true that if the electron source were symmetrically placed between the two slits, that there would be places in the diffraction pattern that would be different with photons? So who's right? The Berkeley professor or Feynman? Note: It appears the Berkeley notes refer to a magnetic field, B0, which may have something to do with it.