I have read in many places that apparent faster-than-light transmission of information is made possible by quantum entanglement as measurements of an entangled system will always be random.

I recently came across this article which discusses (as I understand it) how in an experiment two particles 1 and 4 became entangled with each other by entangling particle 1 with another particle 2 and particle 4 with particle 3 and then finally entangling particles 2 and 3 with each other.

This got me wondering about the possibility of a larger experiment which involves $2n$ particles (where $n$ is large), where the one half of $n$ particles have been pairwise entangled to particles from the other half.

Say person-1 who is standing with one half of the particles, decided to entangle all their particles. Would this have the effect of entangling person 2’s $n$ other particles with each other simultaneously and if so, couldn’t this be used to send a message from one place to another faster than the speed of light? The idea being that person 2 could notice how measurements of one of their particles was correlated with measurements of another. If $n$ is a large number this is unlikely to happen by chance, thus he could conclude that their particles had become entangled


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  • $\begingroup$ May I ask why you've rolled back the edits I made? $\endgroup$ – Alex Robinson Oct 15 at 11:40
  • $\begingroup$ @Nikolai Stack Exchange is a community platform focused on creating quality Q&A resources for future visitors; as such community editing is the norm; please read that guidance carefully. Alex's edits are all helpful and positive and there is no reason to roll them back. If there are specific places within the edit where you feel that your meaning has been changed, then feel free to edit it further, but overall, Alex's improvements should stay. $\endgroup$ – Emilio Pisanty Oct 16 at 12:22
  • $\begingroup$ I only meant to change some of the edits. How do I undo the decision? $\endgroup$ – Nikolai riber skånstrøm Oct 16 at 21:17
  • $\begingroup$ @Nikolairiberskånstrøm You can edit your post using the edit link that is under the question. Rather than rolling back anything, just make further edits as you see fit. Please make sure edits are not trivial and serve to improve the quality of the post! $\endgroup$ – tpg2114 Oct 16 at 21:31

If it allows for faster-than-light travel, either the article, or your interpretation of it, or the scheme you build following from it, must be wrong.

More concretely, entanglement swapping (which is what the protocol you describe sounds like) requires classical communication before the entanglement between 1 and 4 is actually built up. Just as in teleportation, this limits the speed at which information can be transmitted.


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