Editing Faster-than-light communication (section)

===Quantum nonlocality===
[[Quantum mechanics]] is non-local in the sense that distant systems can be [[quantum entanglement|entangled]]. Entangled states lead to correlations in the results of otherwise random measurements, even when the measurements are made nearly simultaneously and at far distant points. The impossibility of superluminal communication led Einstein, Podolsky, and Rosen to propose that quantum mechanics must be incomplete (see [[EPR paradox]]).

However, it is now well understood that quantum entanglement does not allow any influence or information to propagate superluminally.

Practically, any attempt to force one member of an entangled pair of particles into a particular quantum state, breaks the entanglement between the two particles. That is to say, the other member of the entangled pair is completely unaffected{{Dubious|Incorrect description using "completely unaffected" and "random"|date=October 2024}} by this "forcing" action, and its quantum state remains random;{{Dubious|Incorrect description using "completely unaffected" and "random"|date=October 2024}} a preferred outcome cannot be encoded into a quantum measurement.<ref>{{Cite web |last=Siegel |first=Ethan |title=No, We Still Can't Use Quantum Entanglement To Communicate Faster Than Light |url=https://www.forbes.com/sites/startswithabang/2020/01/02/no-we-still-cant-use-quantum-entanglement-to-communicate-faster-than-light/ |access-date=2024-05-28 |website=Forbes |language=en}}</ref>

Technically, the [[Wightman axioms#W3 .28local commutativity or microscopic causality.29|microscopic causality postulate]] of [[axiomatic quantum field theory]] implies the impossibility of superluminal communication using any phenomena whose behavior can be described by orthodox quantum field theory.<ref name="Eberhard" /> A special case of this is the [[no-communication theorem]], which prevents communication using the [[quantum entanglement]] of a composite system shared between two spacelike-separated observers.