It is widely believed that quantum theory is nonlocal. A commonly used example that seems to prove this point is the EPR experiment: measuring one qubit of a Bell state seems to affect the Bell state’s second qubit instantaneously. Hidden-variable theories were invented to explain this paradoxical result and save locality, but they have since been ruled out by Bell’s theorem.
However, I will argue that quantum theory is a local theory—there is no 'spooky action at a distance.’ Despite Bell’s theorem, a pair of distant, entangled quantum-systems A and B cannot affect one another unless information from system A is carried to system B or vice versa. One can track the flow of information in such quantum systems explicitly and thus prove locality by analysing quantum computational networks in the Heisenberg picture.