"[C]onsider the scalar ... the change in the electrons' interference pattern is a nonlocal effect of the electric field in the capacitor. This nonlocal effect is action at a distance! The electric field, acting at a distance on the electrons, yields a measurable effect (the change in the electrons' interference pattern). So quantum nonlocality does permit action at a distance. There is a constraint similar to the one we guessed. It is called (relativistic) causality. The principle of causality states that there is no way to send a message faster than light. We do not expect nonrelativistic quantum mechanics to obey this principle, because in nonrelativistic quantum mechanics there is no maximum speed. However... Nonlocal quantum correlations obey causality, because they are useless for sending messages. The Aharonov-Bohm effect, too, obeys causality: ...the change in the electrons' interference pattern - lies within the future light cone of the field. In each example we find that quantum nonlocality obeys causality."