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A mental picture of entanglement?

  1. Jun 15, 2009 #1
    please do not laugh. i am only curious and want to learn.

    I read article about entanglement in scientific American for the first time just a few months ago. it was called "lights, camera, entanglement". then i read something about electron spin and how counterparts spin in exact opposite rotations. now for some reason when think i of these electrons and their counterparts i picture gears, wheels or spheres that have interlocking cogs with no space between them. when one gear spins the other immediately spins in the opposite direction. in this mental diagram i think of it as even and odd, all the odd spin one direction that is the same and all of the even spin in the exact opposite. you could line up and interlock as many gears as you wanted, the first odd gear will immediately effect the last even gear(which will spin in the opposite direction) in the sequence no matter how far apart they are from one another.

    of course this is oversimplified, but is it a good way to get a mental picture of how entanglement works?
  2. jcsd
  3. Jun 15, 2009 #2
    I don't think that interlocking gears are a very good analogy for spin, and it doesn't capture entanglement at all. Entanglement does not occur only for spin systems, the position measurments of entangled particles will also be effected in the appropriate experiments, and so on for anything else we can observe. The essence of entanglement is that the two particles become one, in a way. The physicist John Wheeler described entanglement as a "smoky dragon" with two heads which are sharply distinguished and a body made of smoke that is fuzzy all over. In my opinion this is as accurate of a picture as you can get without doing some (relatively simple) math.
  4. Jun 16, 2009 #3


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    No, it's a picture that has been proven false. Your model leads to correlations in measurement results called Bell inequalities. (If your model is correct, the Bell inequalities must hold). QM predicts that Bell inequalities are violated, and experiments have shown that they are.

    See e.g. pages 215-216 in Isham's book.
  5. Jun 16, 2009 #4
    alright, glad that you cleared that up for me. since i am new to the whole thing you do see how i could make that kind of mistake.
  6. Jun 16, 2009 #5
    Quantum mechanics is all about what happens in systems that are not interacting with the outside world (not interacting with the observer except to take measurements). Specifically, they are not transferring energy (trading particles, trading information) with the outside world.

    Every spooky (non-classical) thing there is about quantum mechanics occurs in a system when it is closed. And we also can see vestiges of spooky things in systems that interact just a few times with the outside world (between measurements). Systems interacting a lot with the outside world we call "classical".

    One way to look at it is this: The interaction of a particle with the rest of the universe is what actually ~defines~ a space-time event (and thus space-time intervals). So if two particles were not interacting with the outside, then no space-time interval between the particles was yet defined. When the particles are again measured, a space-time interval is defined between them by that measurement. Since there was no distance between the particles while they were in a closed system, they needn't obey causality--just as two local particles need not obey causality classically speaking, because information is transferred between local particles instantaneously (because they are local).
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