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Quantum Entanglement and retrocausality

  1. Aug 1, 2008 #1
    Recently, an experiment in the Canary Islands demonstrated that messages could be sent using Quantum Entanglement over a distance of 144km. Since I took courses in both Relativity and Quantum Mechanics, this confuses me, since the presence of distance between the two locals would cause retrocausality when looked at from different reference frames. Because Einstein states that all reference frames are equally pertinent and true, how is Quantum Entanglement even possible?
  2. jcsd
  3. Aug 1, 2008 #2
    Please cite your source.

    But rest assured, you will find the message was communicated slower than the speed of light.
  4. Aug 1, 2008 #3
    The second question is more troublesome. When you look at a quantum experiment and you ask *when* the wavefunction was collapsed for the two particles, if the two observers are in significantly different reference frames (moving very fast wrt one another) they will not agree on the sequence of events.

    The leads one to conclude, I think, that if there is non-local communication going on, it must be going on without regard to space *or* time. That is why I don't think any non-local theory will ever hold up in the end.
  5. Aug 4, 2008 #4
    It's 10 pages long, but the actual reading is pretty light. http://arxiv.org/abs/quant-ph/0607182
    And yes, I understand that this particular experiment was well within the speed of light. However, what disturbs me is that it's so easy to simply extend this thinking and imagine this experiment to be taking place over a much larger distance, say between two galaxies. I can only comprehend of this if the photons were in a correlation rather than a cause and effect relation.

    I'm having a hard time comprehending how it could be happening without obeying laws of space or time. How would you explain this?
  6. Aug 5, 2008 #5
    I can't.
  7. Aug 5, 2008 #6
    The abstract doesn't claim non-local communication. It claims only correlation via entanglement over 144 km. But the abstract in the final sentence is a rightous swindle, where they attempt to lead you into thinking that they somehow managed FLT.

    "The range achieved thereby demonstrates the feasibility of quantum communication in space, involving satellites or the International Space Station (ISS)."

    Enough so, that you might be enticed into reading about their wonderful distance record. But they claim no such thing as FLT. It's only a cheap jouralistic trick--a hook. If it were true it would be headline news, even in the NY times. The opponents in the pysics community would be running for cover--but no, they're sleeping soundly. I hear them snoring.

    Is arXiv peer reviewed?
    Last edited: Aug 6, 2008
  8. Aug 5, 2008 #7
    So? It would still work slower than light speed.

    Perhaps it would help you to express in detail how you imagine extending the experiment? And as for Phrak's "swindle", it seems no more than the old problem of people reading what they want to see rather than what is actually written.
  9. Aug 6, 2008 #8
    Good grief, man. People never intentionally deceive nor distort, do they.

    It's a given fact that authors are given some leeway or freedom in their abstracts. Would you like to talk about leeway or feedom in abstacts.

    What are they said to be free to do/
    Last edited: Aug 6, 2008
  10. Aug 6, 2008 #9


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    Well, Zeilinger's group DID demonstrate quantum communication from earth to space a few months ago so the authors were right when they claimed that it was feasible (and they are now also discussing putting an experiment on board ISS).

    Note that it does not say ANYTHING about FTL communication, what they are referring to is quantum cryptography. A practical QC setup that could be used to communicate between a satellite and earth would have some rather obvious applications.
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