In trying to learn about Quantum mechanics (QM) from popular science books and Stack Exchange (I of course expect my knowledge to be anything but complete) I regularly come up with seemingly childish questions where I wish I could interrupt the author or visit them during office hours.
I'd prefer low level answers (beginning undergrad in maths with no formal physics whatsoever).
Regarding the double slit experiment (DSE):
Q1: I've heard about Feynman's view that the electron somehow takes every possible route from start to finish. For example, in Brian Greene's "The Elegant Universe" (TEU): "Feynman argued that in traveling from the source to a given point on the phosphorescent screen each individual electron actually traverses every possible trajectory simultaneously."
How can this argument be made without violating FTL?
Q2: When does the interference pattern result of DSE disappear as you increase the size of the "chunks" fired? E.g. if you fire protons or even larger ensambles. And, does it happen for all discovered particles? Is there a sharp point at when this happens or does rather the interference pattern disappear gradually?