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In quantum field theory, the casuality is manifested as a requirement imposed on the Heisenberg fields $\varphi(x)$: they must be locally commutable:$$[\varphi(x),\varphi(y)]=0$$ when $x-y$ are spacelike. The aim is to make one measurement cannot affect the other which is outside the lightcone of the first one. The casuality can also give a condition for ...