why then can't electrons pass right through each other?
I like to think that there are a few universal facts impeding it. I can think of:
1) The sub-atomic particles are either close to or lightspeed accelerated. It should make a lot more difficult to observe an empty space at some given point of time. Since they are a giant quantity of particles, and they travel to the limit speed, it would be as if each orbit were solidly covered with an anular shaped body more than with a single ball travelling thru it.
2) Since at speeds close light speed mass is increased as soon you accelerate the particle another tiny bit, I like to think that since those sub-atomic particles are so much accelerated, they should be on rare (inflated?) state rendering more mass than the original for each particle.
3) If all the above fails, I think the sense of turn from each sub-atomic particle should have a lot to do with it. As you know the principles of electrostatic fields explain that equally polarized particles suffer repulsion and oppositely polarized particles suffer attraction. But I was never sure if the reason is the same than the dogmatically consignated one in the books of text. There is a lot more to it than what I could recall now, including Triboelectric Properties, and all the rest. Maybe it is just as easy as to think that particles with same angular momentum just keep appart one of each other... or maybe not!