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Question about Entanglement

  1. Oct 24, 2007 #1
    A friend asked me this question and I don't have an answer for him:

    So, we have two particles originating from a common source and travelling entangled in opposite directions and obeying conservation of momentum. After some time the two particles are a fair distance apart. We then make a measurement on one of the particles. At this moment, it is said that the wavefunction collapses and that the other particle immediately assumes a quantum state consistent with the measurement of the first particle. It is said that while this instantaneous collapse does not break relativity because classical information cannot be transferred by this mechanism, that some mechanism is responsible for this behavior.

    The way that scientists determine that this behavior is instantaneous is by recording the state of the other particle and then comparing it via a classical information channel, where they find consistency with the measurement and also find that the measurements were made in their corresponding local spaces at times that would've required faster-than-light communication.

    Now, I think that it is only at COMPARISON TIME, when these two individual measurements are brought together via a classical information channel that we see this consistency.

    Basically, we have two entangled particles. They are each measured independently by an observer which then becomes entangled with the particle they observe. Since each individual particle is also entangled with the other, the measuring devices are both entangled to each other. Both measuring devices then measure "every possible state" in a superstate of measurement. When they are brought together and the results are compared, this prior entanglement ensures the consistent histories of the measured values. So, there is never any instantaneous breakdown of the wavefunction, instead there are only consistencies in comparisons of entangled measuring devices that have both recorded every possible measurement in that when a particular and discrete measurement is discerned on one the consistent measurement is discerned on the other, even though the conscious observer could randomly observe any one discrete measurement from all possible measurements, thus implying that the observer is really in the superstate of observing all possible consistent measurements between the two measuring devices.

    The key here is comparison time consistency, not consistency of any discrete quantity through instantaneous wavefunction collapse.

    Any thoughts?
  2. jcsd
  3. Oct 24, 2007 #2
    It's good enough for now, but you can look at
    which briefly reviews Bell's argument of what constitutes a non-local theory.
    Even better, if you haven't already done so, you can look at the books by Roland Omnes (e.g. "Interpretation of Quantum mechanics") and Robert B. Griffiths' "Consistent quantum theory" involving consistent histories.
    Last edited: Oct 24, 2007
  4. Oct 25, 2007 #3
    I am familiar with Bell's inequality, and I don't believe that what I've put forward is inconsistent with his theorem. I do not postulate that my interpretation of the underlying mechanism responsible for the observed behavior of entangled states should have any effect on the measurements that are consistent with QM and Bell's inequality. Mine is not a local hidden variable theory and further I dismiss the notion of local hidden variables as a solution to the observed behavior of QM because of Bell's argument.

    What I've put forward is more of an interpretive framework similar in ways to Many Worlds and Consistent Histories. It seeks to eliminate the need for instantaneous collapse by explaining the observations in separate local spaces to be consistent only when one super-measurement is compared to another via a classical information channel.

    So, when one observer measures 'spin up' here, he expects the other observer to have measured spin down there, even when their observations are made 'instantaneously'.

    What I am saying is that the observer here does not measure 'spin up'. ObserverHere(a) measures spin up, ObserverHere(b) measures spin down, and ObserverHereĀ© gathers no information. Similarly, ObserverThere(a) measures spin down, ObserverThere(b) measures spin up, and ObserverThereĀ© gathers no information. Now, when 'they' compare their results classically later on, their results, whatever mechanism they are stored in, are entangled just as the original particles they measured were entangled.

    When ObserverHere(super) compares results with ObserverThere(super), they see consistency. 'Every possible comparison' is being made here:

    up/not measured
    down/not measured
    not measured/up
    not measured/down
    not measured/not measured

    My presumption is that when a given measurement of a truly random property is made, that property can be any number, and, due to random quantum perturbations in the subject and the measuring tool, the 'actual' measurement shows up as one particular and discrete value; whereas had the perturbations been slightly different, the 'actual' measurement might have been the other discrete value. Since the measuring tool and subject are really in a 'superstate' and not one exact quantum perturbation-set (if you will), the measuring tool *really* is in a superset of measuring *all possible* values.

    So, you have two measuring devices each having measured all possible states on the entangled state subject. The question you should pose, then, is "how is it then, that when I compare a particular discrete measurement from that superset on one measuring device, and compare it to whatever particular discrete measurement I happen to get from the other measuring device, I always see consistency?" Well, first, I want to be clear, when "you" do the compare "you" are really facilitating every possible comparison, so you yourself are in a superstate. For each discrete measurement you can discern on one measuring device there exists a subset of allowable and consistent discrete measurements that can be discerned on its partner.

    Why then do you never find two ups, or two downs? Why do you always find consistency? Because the two measuring devices are entangled with *each other* and the worlds where you would find two ups do not exist because they are logically impossible and mathematically their wavefunction has zero probability!

    So the point here is that there is no instantaneous collapse of the wavefunction - the consistency that supports 'spooky action at a distance' does not actually exist UNTIL comparison time!
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