Here's something I have never understood about Feynman diagrams, and I hope someone can explain it to me.

A Feynman diagram represents one possible way that two particles can interact, and from a single diagram you can work out the probability of that event occuring. But wouldn't there be an infinite number of ways an interaction could play out, and therefore an infinite number of diagrams? How do you know which one to draw?

According to Feynman's QED, there's no such thing as "wave-particle duality", it's just all particles. The behavior of the particles, however, is very strange, and that's what accounts for their wave-like characteristics. QED came after Dirac and Schrodinger (it was a refinement of their theories), so I'm not sure why it doesn't get acknowledged in these kinds of discussions.

QED also predicts exactly the results of things like the double slit experiment without ever resorting to the "well the wave collapses into a particle when we observer it" kind of thing.