I was recently studying Feynman's sum-over-histories approach to quantum probability. I also was reading an interesting paper on the double slit experiment. How do these two work together. Do some of the probability waves not have a out of phase partner to interfere with itself? On a related not, whats the difference between the proxy wave, and Feynman's probability waves. If the proxy wave is fictitious, how do atoms resist other atoms passing through it. I know this is a lengthy question but please try to answer.