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Instantaneous Communications Using Entangled States

  1. Feb 27, 2006 #1
    Hey all. I know it's been a long time since I have posted, but I just finished reading Entanglement: The Greatest Mystery in Physics, by Amir D. Aczel and I had a question concerning the conclusion of the work.

    He made the claim that GR was not violated by entanglement since messages could not be transmitted due to the impossibility of predicting the spin of an entangled particle before measurement, and that after spin was detected you had to transmit the message of it's state via a conventional channel.

    My question was if instantaneous communication could be achieved by using time-shifted measurement of states.

    Let's say that Bill is on the Earth and Alice is traveling to Mars in a manned space capsule. Before launch sophisticated as-yet unrealized equipment to quickly measure the spin of entangled particles was installed with a few hundred or thousand entangled particles mated between matching equipment at Houston and in the spacecraft. Before launch, Bill measured the states of his particles, communicated the states to Alice, and Alice mesured her states and verified pairs of opposites. The equipment then continuously monitors the states of the pairs in both Bill and Alice's equpment. After Alice leaves Earth, bill needs to send her a message and does so by altering the states of his particles in a predertimined ordered fassion. Wouldn't Alice's mated pairs also alter states in a predictable fassion, or would the possible states to which they are altered not be deterministic? Obviously if this is possible QE could be used to transmit messages at infinite speed, eliminating the need for time delay in communications, interferrance, etc...
     
  2. jcsd
  3. Feb 27, 2006 #2
    No as the book indicates entanglement ends with the ‘first’ measurement by A or B, there is no changing of a state that remains entangled. Just one measure that ends that entanglement.
     
  4. Feb 27, 2006 #3
    what about teleportation of states? The book also said that when two particles are entangled they are always entangled.
     
  5. Feb 27, 2006 #4
    Until one measure ends that entanglement.(even if you don't see or record the measurement, if it hits something unlike a mirror - like the side of a container)
     
  6. Feb 27, 2006 #5

    DrChinese

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    The state is essentially the relationship of the particles... not the individual values themselves. So you can know the states are identical or orthogonal (as the case may be) but since the values themselves are random, it won't do much for you.
     
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