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If that other thing didn't break a rule in relativity, how about this?

  1. Jan 26, 2012 #1
    So as far as evidence is concerned, entangled particles determined each other's state upon dis-entanglement instantaneously,
    so if we have one particle on Earth and another particle near a black hole, it wouldn't it still happen instantaneously? Would about inside a black hole?
     
  2. jcsd
  3. Jan 26, 2012 #2

    kith

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    I'd say it would happen instantly. But situations which require both QM and GR are difficult to predict, because there is no theory of quantum gravity.
     
  4. Jan 26, 2012 #3

    strangerep

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    It's misleading to think of it that way. There is no causation between them, only statistical correlation. The latter can only be calculated by a third party in their common future light cones.
     
  5. Jan 26, 2012 #4
    It makes sense that relativity would play a part in our measurement, but the problem with that is that we measure the photons that bounced off the entangled particles and it still happens too fast for light to make that distance.
     
  6. Jan 26, 2012 #5

    strangerep

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    You're still thinking in terms of one particle "causing" something to happen at the other,
    and vice-versa. Try to adjust your thinking to be in terms of ensembles of particles and statistical correlations only.
     
  7. Jan 26, 2012 #6
    I sort of see what your saying, but at the same time, doesn't entanglement only occur be-cause of an interaction and disentangle occurs be-cause of an interaction? Or at least, an interaction with a photon and your retina or whatever other force.
    Like if we measure it, then it has 0 probability of existing in an undefined state or something like that?
    Couldn't that statistic have only been gotten by observing interactions and causes and effects with entanglement though?

    Or wouldn't it have 0 probability of being in an undefined state be-cause of an interaction?
     
  8. Jan 26, 2012 #7

    strangerep

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    Hmm. Sounds like I'm pitching my answers at the wrong level.

    What's your background? How much quantum mechanics and special relativity have you studied, and from which textbooks?
     
  9. Jan 26, 2012 #8
    I haven't taken anything beyond a first year class for actual General Relativity and Quantum Mechanics but I know some of the mathematical properties described in QM. Most of my understanding comes from asking physicists questions in real life and I guess on forums.

    I get the point of view your talking about, where it's not just some interaction, it's just a sort of probability shift. Even while considering that though, things still interact in the real world, so I'd kind of like to know how an interaction itself changes probability and whether that breaks relativity.
    I suppose at this point if it's a probability shift it's not breaking relativity because information isn't traveling distance over time, kind of like how a sine wave on a graph doesn't actually necessarily represent position over time, those positions "just are" instantaneously equal to a point on a unit circle by the properties of math.

    Even still, how does that "instantaneousity" in the real world actually get like, recognized by the universe?
    Because a math equation itself it's anything to do with reality, it's just symbols.
     
    Last edited: Jan 26, 2012
  10. Jan 26, 2012 #9

    strangerep

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    You might need to read up a bit on probability, including stuff like probability distributions, expectation values, and correlations. The latter are certain quantities which are calculated from probability distributions.

    I usually recommend Ballentine as a QM textbook, but it's more upper-undergrad or graduate level. Maybe some of the other SAs here can recommended other books. Otherwise, try asking for recommendations over on the "academic guidance" forum.

    In general, time evolution is determined by Hamiltonian operator. If the Hamiltonian contains a term representing interaction, then states can evolve into new states.

    Probability distributions in QM are determined by (the square of) a product between states. So if you have an initial state, then allow it to evolve (interact), and then compare to all the possible other states, you get a probability distribution. (That's outrageously oversimplified of course.) Also remember that "initial state" should be thought of in terms of a large ensemble of identically prepared systems -- not a "one-off".

    Importantly, such interaction terms in the Hamiltonian never break the underlying principles of relativity. (If they did, they'd be unphysical rubbish.) Indeed, relativity is one of the guiding constraints when constructing mathematical models of interactions.


    If by "instantaneousity in the real world" you mean instantaneous causation of effects on one particle by another, well, there is no such thing in the real world. Interactions happen as part of time evolution, which respects relativity.

    (Sorry -- gotta go now.)
     
  11. Jan 27, 2012 #10
    So entanglement doesn't actually happen in the real world is what your saying, it's just how our math works?
     
  12. Jan 27, 2012 #11

    DaveC426913

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    No, he's saying entanglement is not a cause-effect relationship between particles; it is a correlation relationship.
     
  13. Jan 27, 2012 #12
    But doesn't the measurement of one particle "cause" a particle on one end to be determined and therefore "cause" the probability of existing in an undefined state to be 0?
     
  14. Jan 27, 2012 #13

    DaveC426913

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    No.
    [10 chars]
     
  15. Jan 27, 2012 #14
    Most working physicists would give up realism to retain locality in epr correlations. However, this is not something they know, it's something they chose to believe in(it happens quite often, whether they admit it or not). For newcomers it's always difficult to separate the philosophy from the physics.
     
  16. Jan 27, 2012 #15
    Care to expand in any way shape or form?
     
  17. Jan 27, 2012 #16

    DaveC426913

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    Well, I did, in post 11. You asked again if it's cause and effect. It isn't.

    Can I shed more light on it? Not really. It's a subtle subject requiring a book's worth of explanation.
     
  18. Jan 27, 2012 #17
    There's not really any room to interpret dis-entanglement other than "a photon hits an entangled particle and then hits something which measures it, thus causing the probability of atoms existing in an undefined state to be 0".
    unless of course you could care to elaborate on how exactly we aren't actually measuring something and thus leading it to its disentanglement.
     
  19. Jan 27, 2012 #18

    strangerep

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  20. Jan 27, 2012 #19
    Hmm, I see the point how it isn't a cause-and-effect by the notion that "a=b=c then a=c" is not information that is processed by means of distance over time such as with electrons and switches in a computer, although at this point I still can't completely give up the notion that "entanglement" and "disentanglement" still have real world meanings, especially considering that mathematics on it's own is utterly meaningless.
     
  21. Jan 27, 2012 #20

    strangerep

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    They do, but the "meaning" is in terms of "correlations", not instantaneous causation.
     
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