We've learned Q&M in modern physics but I need to make sure I'm getting this concept right... So the photoelectric effect demonstrated the fact that a photon (wave) can knock an electron out of a metal, which could only happen if a photon was a particle. So much for photons being waves. I get that part. I'm trying to think of this the other way around. So if an electron was shot at a photon (wave) and caused it to deflect, that would have to mean that an electron was a wave because the only way a wave can deflect is by some sort of wave interference. So much for electrons being particles??