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Quantum Entanglement

  1. May 5, 2010 #1
    Hello I am new to this forum, and I may make a load of mistakes. I'm sorry.

    I was baffled by how quantum entanglement works… rather, the concept that distance does not play a roll in the synchronized actions. Why is that?
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  3. May 5, 2010 #2


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    Welcome to PhysicsForums, Fuji Katsuaki!

    I am not sure anyone truly knows the reason. It is a deduction (prediction) that is made from standard quantum mechanics. But the underlying mechanism itself is unknown.
  4. May 5, 2010 #3
    The short answer is that entangled particles have something in common, so that, for example, for certain combined settings of distant measuring devices, if the combined setting is known, then if the detection attribute of one of the particles is known, then the detection attribute of the other particle can be deduced. So, distance doesn't matter.

    The 'something in common' has to do with relationships between and among the motional properties of entangled particles that result from these particles' interaction with each other or with a common disturbance, or having a common origin, or being parts of an encompassing system.
  5. May 5, 2010 #4
    The concept of distance is exactly what scared Einstein into calling quantum entanglement, "spooky action at a distance". It is so strange to the man who discovered the cosmic speed limit of light to then have to say that instantaneous changes can occur between two entangled particles. This means that two entangled particles, once observed, will automatically react to the other particles change, even across distances of light years, without conforming to the ultimate speed of light. I can't answer your question very well either because it is still unknown in the world of science.
  6. May 7, 2010 #5
    Distance might matter. There are recent suggestions that Quantum Gravity imposes some limitations on how well entanglement can be maintained over large distances.

    However, entanglement doesn't involve any sort of communication at all. There isn't any interaction between the particles. It's just the quantum version of "there are 2 boxes, one with a red marble and one with a blue marble. you have 1 box, and your friend has the other". The quantum craziness comes in since properties like "marble A is red and marble B is blue" are not realized for some quantum systems until you actually do the measurement.
    To conclude what the other person has, you just have to open your box, but to actually make use of this information for computation purposes requires communication. That's where the effects of distance and time might come in.

    The Quantum Gravity limitations are being investigated by people whose work was being discussed here: https://www.physicsforums.com/showthread.php?t=381039
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