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Quantum entanglement IS EVIL

  1. Mar 20, 2012 #1
    Physicist say "Quantum Entanglement is when you place 2 electrons together.
    They Vibrate in Unison.
    When you take them across the galaxy if you "jiggle" one, The other also "jiggles"

    Physicist say" however it does not transfer any meaningful information"


    This is a EVIL way of speaking.

    Why cant you Jiggle Once For YES
    Twice for NO

    10101010?

    That is to say you take one electron , go to the far side of the galaxy, spend trillions of years flying there
    you have a question that both sides already agreed upon for when you reach your destination
    say "is it raining?"
    Once you arrive they "jiggle" yes

    How is this not New and Meaningful FTL information

    FTL you now know that on the other side of the galaxy it is raining.
     
    Last edited: Mar 20, 2012
  2. jcsd
  3. Mar 20, 2012 #2
    If you "jiggle" the entanglement is broken. The next "jiggle" will not do anything.


    EVIL...?
     
  4. Mar 21, 2012 #3
    They say that if you alter the state of one, the state of the other is also altered and can be observed.
    but also claims that this is not meaningful information.

    But that's a false statement, as long as you can alter and observe the alteration, that is meaningful information.

    unless your saying that you cannot observe the alteration in any way.

    even if the entanglement breaks after 1 alteration, 1 bit of data is still meaningful information.
     
  5. Mar 21, 2012 #4

    Drakkith

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    Staff: Mentor

    Quantum entanglement does not work the way you are imagining it. You CANNOT tell whether the value you get upon measuring a particle is due to pure chance, or because someone altered the state. Shaking one electron does NOT cause the other one to move. What is meant is that when you measure the state of one particle the other particle must be in a different state. However neither one knows which state it is in until one of the particles is measured. At that point in time BOTH particles know which state to be in, no matter how far the distance is between them. No information can be transmitted using entanglement.
     
  6. Mar 21, 2012 #5

    DrChinese

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    Welcome to PhysicsForums, Causetic!

    When you interact with one member of the pair, let's say Alice, you cannot impart any specific action to it which will be transmitted to the other (who we will call Bob).

    The rule is: an observation about Alice tells you something about Bob. But that does NOT tell Bob anything specific. The reason is that the observation of Alice always produces a random result (otherwise Alice and Bob are not entangled). It is true that Bob will see that random result, but so what? All Bob sees is the equivalent of a random series of 0's and 1's. I.e. no useful information.

    Further, there is no experimental technique to even assure ourselves that it is Alice causing the collapse into a known state - it could be Bob. *Regardless of sequence*, there is no preference given to one's actions over the other. So who is to say that Alice collapses things; when Bob might see it the other way around.
     
  7. Mar 21, 2012 #6
    Sounds like another case of quantum misinformation!

    The easiest way to picture it in most cases is to imagine the entanglment as this;

    Take two socks, a red and a blue one.
    You take the socks and put them in boxes, you then randomize the boxes so you don't know what sock is in what box.
    We could describe the state of each box as 'red + blue' there's an equal probability that we have a red sock or a blue sock in our box.
    We then seperate the boxes by whatever distance you want. We then measure the box, just say we find red in our box, then the state of our box can then be described by just 'red' but in doing this we have changed the description of the state of the other box, it's state has gone from 'red + blue' to just 'blue'
    Can we convey information in this manner?

    No, we cannot.
     
  8. Mar 21, 2012 #7
    Thank you so much for your answers, I've been so frustrated with this issue ever since i was told my original statement.

    digging into my brain.

    i just wanted someone to dispute the bad description given to me but can't find anything on wiki /previous post specifically disputing it. (one that i can understand at least)

    thanks all

    :D
     
    Last edited: Mar 21, 2012
  9. Mar 22, 2012 #8

    Ken G

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    Your analogy serves to explain how two things can be entangled without sending signals, but be aware that this is the usual example used to distinguish classical entanglement (the socks) from quantum entanglement (which is quite a bit more subtle and doesn't happen with socks). Only the latter leads to Bell's theorem and "spooky action at a distance." To be clear, as it has been said, neither can be used to transmit information.
     
  10. Mar 22, 2012 #9
    Einstein, Podolsky, and Rosen thought that quantum entanglement is not any more mysterious than you socks example, but then Bell presented a powerful argument that a "socks" explanation does not suffice to understand the phenomenon. You can read about Bell's proof here.
     
  11. Mar 22, 2012 #10
    Hmm... I would say that the link you provided misses half the point of Bell's Theorem. Without getting too deep into it, you can read for instance here that the proof you presented misses the possibility of violation of counterfactual definiteness, which happens to be a property of the Many-Worlds interpretation, because of the basic postulate of multiple parallel universes due to superpositions at the macroscopical scale.

    The way I understand it, once the two photons are entangled, they are in a superposition of an infinity of polarisations, as good wavefunctions they are. And so, once you observe the photon, you become a part of the superposition, and all that.
    Now, the probability of mismatch described by the example given seems to be quite like the Born Probabilities which describe the pseudo-probabilistic nature of the evolution of the wavefunction.
    It seems, to me, that what happens is simply that the universe has entered a superposition of states, and so, according to the Born Probabilities, given that the two photons are entangled, and given that there is a 60º difference between the two SPOTs, it just so happens that in 75% of the universes the two bits will mismatch.
     
  12. Mar 22, 2012 #11
    No, Herbert doesn't miss this. His purpose is to disprove the hypothesis that "reality is local" AKA local realism or locality + counterfactual definiteness.
     
  13. Mar 22, 2012 #12

    BWV

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    The EPR example gives a good illustration of the impossibility of transmitting information. If you have two entangled electrons A and B then a measurement of the spin of A on a particular axis will lead to a measurement of the spin of B which will have a probability of an opposite spin equal to the square of the cosine of the angle between the two axis. So if A is measured along the x axis and B is later measured on the same axis then B will always have an opposite spin. If A and B are light years apart then the fact that A was first measured on a particular axis will immediately effect the probabilities of the measurement of B's spin, however there is no way for B to know what the spin of A is, all B knows is whether the spin is up or down on the axis he measured, and while A knows that once he measures spin along a given axis, then the probabilities for B will be determined by that, he has no way to know what axis B will chose to measure and is of course limited to the speed of light in attempting to communicate to B which axis was chosen.
     
  14. Mar 23, 2012 #13

    zonde

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    Where did you get that idea?
     
  15. Mar 23, 2012 #14
    I mean, they thought the only reason quantum entanglement seemed "spooky" was that quantum mechanics was an incomplete theory. But they thought a future, more complete theory would explain away "spooky action at a distance". so that quantum entanglement would be no more mysterious than the socks example.
     
  16. Mar 23, 2012 #15
    lol guys, the socks example is pretty much the best thing you can do without invoking maths, at least it's the best example I've seen so far that doesn't give people ideas of ftl stuff :shy:

    imo any explaination that doesn't use the maths directly will be insufficient in some way
     
  17. Mar 23, 2012 #16

    Ken G

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    It's not strictly necessary to invoke difficult maths to get the spirit of what is "spooky" about quantum entanglement, only if one wishes to actually verify that spookiness for one's self. At issue in EPR was not what is true about socks, it was expressly what is true in quantum mechanics that is not true about socks. Einstein and company understood socks just fine, indeed they felt that all matter had to act like socks. The whole point of EPR is that quantum mechanics does not act like socks, and EPR used that to try and conclude that therefore quantum mechanics was incomplete. Bell found a way to verify experimentally that quantum mechanics was actually right-- the reality of the particles was not like the reality of the socks, and thus quantum mechanics could still be a complete description. Of course how we interpret that completeness is still left wide open, and Bell favored the most "sock-like" of the interpretations, which is Bohm's. But even Bohm's allows behaviors that socks can't do, so it is still the crux of the matter as to how quantum particles don't act like socks.
     
  18. Mar 23, 2012 #17

    zonde

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    Well, yes, when it will be explained away it won't be mysterious. But then (and now) it was not explained away. Your statement kind of implies that they believed there was nothing to explain away.

    Actually Einstein said something like what you imply:
    "The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems."
    But considering that he does not say where he sees the difference between individual system and ensemble it can not be viewed as a way to explain entanglement away. IMHO
     
  19. Mar 23, 2012 #18
    OK, all I was trying to say is that Einstein et al. believed that ultimately quantum entanglement would be understood with a "socks" explanation, not anything "spooky".
     
  20. Mar 24, 2012 #19
    The analogy with socks is misleading, because it presupposes ignorance from the side of the observer. In QM entanglement is not about ignorance over the states of the two particles like in statistical mechanics. It is intrinsically inherent in the particle system itself. If we want to force the analogy between socks randomization and particles in QM we could say that when the blue and red socks come together they will form a red+blue=green physical 'entity'. And that 'entity' will remain green as long as it spreads throughout the universe and someone doesn't look at it. Then, when the measurement occurs, the green colored entity will collapse instantly to the red and blue socks (possibly light years apart). But which sock will have which color is a process that happens by pure chance, you can't force it to your advantage for encoding messages. We might say that entanglement is about a 'state of being', and not as a set of possible microstates as in statistical mechanics.
     
  21. Mar 25, 2012 #20
    So the entanglement is quite unstable [or should I say not verry stable]? If this is so, then does it mean that in the sub-atomic levels entanglements appearing [being build] and disapperaing [being destroyed] all the time?
     
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