Hello! I read some books on QM and QFT but I didn't really noticed (or I missed it?) a proof for the canonical quantization. For example, for energy and momentum it makes sense to have opposite signs, due to Minkowski metric, be related to the variation of space and time, due to Noether theorem or have an ##i## in order to be hermitian, but this is not a proof. Can someone explain to me how can you derive this or point me towards a derivation (not only energy and momentum, but all this theory in general)? And as a side note, why isn't this proved (or at least given some rough clues) in the physics books (at least not in all of them)? Thank you!