Spooky or not spooky, that is the question.

Discussion in 'Physics & Math' started by quantum_wave, Jan 27, 2016.

  1. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Here is an article I came across today.

    https://www.sciencenews.org/blog/context/entanglement-spooky-not-action-distance

    These two paragraphs contain the part that I am fuzzy on.

    "Suppose you prepared entangled photons and sent them to Alice and Bob in such a way that if Alice measured hers to be vertically polarized, she instantly knows that Bob’s will be horizontally polarized. In this scenario, Alice oriented her filter vertically, and the photon passed through and the detector behind the filter recorded its arrival with a click. If Bob oriented his filter horizontally, his detector would click as well (left-handed glove). If Bob’s filter was oriented vertically, no click (mitten).

    But the tricky thing is, Alice’s vertical photon might just as well have been horizontal. It doesn’t “decide” what to do until it’s measured. Suppose Alice always chooses the vertical orientation for her detector. If you repeated the experiment over and over, sending out entangled photons in exactly the same quantum state every time, Alice’s detector would not always click. Sometimes the photon would be vertical, pass through the filter and strike the detector, but sometimes not. The photon does not have an orientation until Alice detects it. Same for Bob’s. But once Alice makes a measurement, the outcome of Bob’s measurement is certain."

    Let me start my question with this sentence, "But the tricky thing is, Alice’s vertical photon might just as well have been horizontal."

    This is simply true; no one doubts this, right?

    Then come this, "It doesn’t “decide” what to do until it’s measured."

    First, I hope everyone knows that they don't mean that the photon has the ability to decide anything, so it seems clear that could have been left out, and the sentence would mean the same thing if it said, "We don't know what the orientation of Alice's photon is if we don't measure it; it could be vertical or horizontally or in between."

    Then the paragraph goes on, "Suppose Alice always chooses the vertical orientation for her detector. If you repeated the experiment over and over, sending out entangled photons in exactly the same quantum state every time, Alice’s detector would not always click. Sometimes the photon would be vertical, pass through the filter and strike the detector, but sometimes not."

    This is also true, and is what I implied with the rewording of the previous sentence. So far, what we know is that if Alice always uses the vertical orientation, and it the photon passes through the vertical filter it has vertically polarized. If it doesn't pass, we don't know what it's orientation is, we just know it isn't vertical.

    Here is where I cannot quite agree: "The photon does not have an orientation until Alice detects it. Same for Bob’s."

    All we know if it doesn't pass through the vertical filter, is that it isn't vertically orientated. It could be horizontal or in between, and so the statement is false. Further, it seems clear that it goes beyond the facts to say "the photon does not have an orientation", when all that is determined at that point is that we don't know what it's orientation is until we measure it. There is no evidence that it doesn't have some other orientation.

    And the last sentence is, "But once Alice makes a measurement, the outcome of Bob’s measurement is certain."

    This is true, but I get the feeling that it isn't proper to imply that there has to be something "spooky" about that? Not if Alice's photon has some other orientation besides vertical when she determines that it isn't vertically oriented. It is likely to be horizontal or in between. And it is also factual that every time Alice determines what the orientation of her photon actually is, Bob confirms it. Nothing spooky has happened.
     
    Last edited: Jan 27, 2016
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  3. Fednis48 Registered Senior Member

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    Like most pop science articles, that blog post doesn't do the subject matter justice if you examine it closely. You're right that if Alice just uses a vertical polarizer over and over, everything can be explained by treating the photon's polarization as a classical, random variable. In the early years of quantum mechanics, a lot of physicists thought that something similar was underlying all of the apparent randomness - that quantum mechanics was just an incomplete description of some underlying "hidden variable" theory. In 1964, John Bell showed that no hidden variable theory can account for all the predictions of quantum mechanics, a result known as Bell's theorem. Let's go back to the example of Alice and Bob with their photons, but instead of measuring at fixed polarizations, they randomly and independently rotate their polarizers before each photon measurement. Since the polarizers aren't locked at 90 degrees to each other, Alice's measurement no longer tells her for sure whether Bob's detector will click, but it does give her some information (enough to predict the results of Bob's measurements with greater than 50% accuracy). After measuring many pairs of entangled photons, Alice and Bob compute the correlation strength between their measurements, effectively quantifying how good Alice's predictions were. Surprisingly, quantum mechanics predicts stronger correlations than any hidden variable theory; Alice's measurement is doing more than just telling her about the state in which the photons were prepared. Many experiments have verified the stronger prediction, so we know that something "spooky" is going on that cannot be explained away with hidden variables. Of course, the exact nature of the spooky events is still very much up for debate, but that's another can of worms.
     
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  5. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    The thing about Bell's theorem is that any hidden variables theory that invokes local realism as defined below, cannot reproduce all the predictions of quantum mechanical theory." Wiki.

    Many experiments show differences between correlations that could not be explained by any such local hidden variables.

    The experimental results have been taken by many as refuting the concept of local realism as an explanation of the physical phenomena under test. For a hidden variable theory, if Bell's conditions are correct, the results that agree with quantum mechanical theory appear to indicate superluminal effects, in contradiction to the principle of locality." Wiki.

    (Paraphrased from Wiki) Three concepts stand out as requirements for any hidden variables theory, locality, realism, and freedom. They are technical and much debated. In particular, the concept of realism is now somewhat different from what it was in discussions in the 1930s. It is more precisely called counterfactual definiteness; it means that we may think of outcomes of measurements that were not actually performed as being just as much part of reality as those that were made. Locality is short for local relativistic causality, [which just means that the cause precedes the effect]. Freedom refers to the physical possibility of determining settings on measurement devices independently of the internal state of the physical system being measured.

    No only are classical theories eliminated under those conditions, but only hidden variables theories that are consistent with the three key concepts mentioned are considered sufficient to qualify any proposed hidden variables theory. There are none, given the requirements.

    Local realism: https://en.m.wikipedia.org/wiki/Principle_of_locality#Local_realism

    In physics, the principle of locality states that an object is only directly influenced by its immediate surroundings. A physical theory is said to be a local theory if it is consistent with the principle of locality. An alternative to the earlier concept of instantaneous "action at a distance", locality evolved as a property of the field theories of classical physics. The concept of locality is that, for an action at one point to have an influence at another point, something in the space between the points, such as a field, must mediate the action. To exert an influence, something, such as a wave or particle, must travel through the space between the two points, to carry the influence.

    "Bell's theorem, derived in his seminal 1964 paper titled On the Einstein Podolsky Rosen paradox,[4] has been called, on the assumption that the theory is correct, "the most profound in science".[12] " "Perhaps of equal importance is Bell's deliberate effort to encourage and bring legitimacy to work on the completeness issues, which had fallen into disrepute."

    I'm a bit of a contrarian on that point, and I like to make a distinction between a Hidden Variables Theory (HVT), and the Hidden Variables Interpretation (HVI) of QM. Those of the HVI persuasion still leave open the possibility that QM is incomplete.

    Wiki again: [13] Later in his life, Bell expressed his hope that such work would "continue to inspire those who suspect that what is proved by the impossibility proofs is lack of imagination."[13]

    I agree, and believe that there are many invariant natural laws that are as yet unknown, or unexplained, and that there are natural mechanistic explanations that make everything work together without anything that is supernatural or inexplicable in the end.
     
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  7. Bruinthor Registered Member

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    Ok two indistinguishable things with different conditions are mixed into a single thing. The mixed thing cannot not be said to be in one condition or the other. Split the mixed thing back into its components and subsequently test them. We find that condition of the things is correlated, great. How is it we presume that our ignorance of their respective condition of the things between their separation and measurement controls their actual condition.
    IMHO we performed the measurement when we separated the things. Subsequent manipulation may or may not have preserved the correlation imposed by initial mixing. Our final measurement confirms that and only that.
     
    Last edited: Jan 28, 2016
  8. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    If the initial event, the emission of two photons that will have opposite polarity, or two elections with spin that equals 1, for example, actually represents the measurement, like you say, then the glove analogy applies. All of the quantum explanations say that isn't it. The wave function is said to defeat local reality because of the belief that the polarity or the spin is not present as part of that function until a measurement of the particle is made after entanglement.

    However, if we are to hang our hat on the "incompleteness" of QM, the HVI as I call it, hidden variables interpretation of QM, then there would have to be some fundamental natural law at work that reconciles the classical leaning toward handedness at the outset, with the postulates of QM; entanglement and superposition. I don't know what that would be, but I'm sure that the professional community will not consider it "the end" when they come up with "loophole free" experiments.
     
  9. Bruinthor Registered Member

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    quantum_wave, It seems to me that you are presuming what you intend to prove. The believe the problem is with the term measurement, we seem to confuse human perception with measurement.
    I seems to me it would be better to define measurement as a metastable change from the previous condition.
     
  10. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    I think you are right, but I don't intend to prove it. I will just be watching to see what unfolds.
    That would rule out the "freedom" stipulation required for a sufficient HVT, meaning human intervention to set up the experimental procedures, like measurement orientations, wouldn't it? But heck, in for a penny, in for a pound, lol.
     
  11. Fednis48 Registered Senior Member

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    That's entirely fair. There are plenty of perfectly legitimate hidden variable interpretations of quantum mechanics, and you're right to emphasize that they are different in kind from the hidden variables that Bell's theorem eliminates. The real import of Bell's theorem is that if such a hidden variable interpretation is correct, the variables must behave very differently from the kinds of classical properties we see day to day.
    This is exactly the kind of intuition that Bell's theorem is meant to disprove. When you say "we performed the measurement when we separated the things", I assume you mean that the final measured quantity (polarization, spin, or whatever) is set when the particles separate, and we only think the measurements are uncertain because we don't yet know what that quantity is. But the correlations we see are too strong to be explained by such a mechanism. The correlations act as though Bob's result depends to some extent on what measurement Alice chose to perform; if the outcomes were determined beforehand, this could not be the case. Of course, the problem can be sidestepped if we allow Alice's choice of measurement to depend on the state of the particle. This is sometimes called the superdeterminism loophole, and it's why freedom is one of the three requirements quantum_wave listed for Bell's theorem. But physicists being predetermined to choose measurements that match quantum mechanics goes well beyond simply incomplete information.
     
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  12. CptBork Valued Senior Member

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    Exactly- whatever "hidden variable interpretation" one chooses to invoke while correctly predicting the results of Bell tests, it can't be a purely deterministic interpretation without necessarily invoking superluminal behaviour and violating the timelike cause-and-effect structuring required by Special Relativity. Insisting on determinism is basically an arrogant dead end.
     
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  13. Bruinthor Registered Member

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    While the equations we use to predict the probabilities of the out come must include all possible states I don't see that it the actual states of the must be so confused. I disagree with your contention that this is excluded by the premises of Bell's argument. But that is just my opinion.
     
  14. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Agreed, and by pursuing "behave very differently", we go firmly into Alternative Theories territory, and you can't get the right time of day out there, lol.

    But I believe that it is sound and practical science to go forward on the premise that there are natural invariant laws that govern the way everything works together, including ways that the laws of quantum mechanics might be incomplete. As long as discussions stay within that narrow objective, it seems that it may be acceptably "on topic" here.

    There are several teams working on experiments that will close all of the loopholes in Bell type experiments, and they probably will be successful some time soon. However, that will not make the question of the completeness of QM go away.
     
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  15. PhysBang Valued Senior Member

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    Last edited: Jan 28, 2016
  16. CptBork Valued Senior Member

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    It won't make the possibility of QM incompleteness go away, but it will most definitely deal a death blow to classical determinism.
     
  17. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Yes it will.
    Thanks. I was aware of part two, and will check out your other link.

    Let me ask a question in regard to conducting a discussion about incompleteness, and a joint venture into some thinking about what a particle could be like that would behave very differently from anything currently envisioned in QM. Is that OK with everyone?

    One of my valued reference books is Atomic Physics, by Max Born, a reprint of the 1969 edition, printed in 1989. If any of you have it, go to page 27. It reads, "With regard to the measurement of e/m, exact experiments have shown that this, the specific charge, is not precisely constant, but depends to some extent on the velocity of the electrons. ... According to Einstein, the value of the charge e is invariable; the mass, however, is variable, it's magnitude in fact depending upon the velocity which it has, relative to the observer who happens to measure it. The electron may have the "rest mass" m sub o, i.e. this is its mass for the case when it is at rest relative to the observer; but if it moves relative to the observer with a velocity v, it behaves as if it possessed the mass, m sub o / sqrt of 1- (v2/c2)." A slightly higher mass.

    This is just a starting point at describing a particle that would behave very differently from anything currently envisioned in QM. What structure of an electron, or any particle, when accelerated relative to our rest position, would accommodate its ability to contain more mass?

    It would be one that gains energy from relative motion, and my thinking is that it would have some internal composition that represents its rest energy, and which changes when accelerated. This is about an internal structure of the electron. Any comments?
     
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  18. CptBork Valued Senior Member

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    Paul Dirac explained Relativistic electrons in terms of the quantum framework back in the early 1920's. Special Relativity and Quantum Mechanics go together just fine, it's gravity that screws the picture up.
     
  19. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    So are you thinking that there are things about particles at the fundamental level that are defined just fine, but that progress toward a quantum theory of gravity might lead to describing a particle that would behave very differently from the structure currently envisioned by QM?
     
  20. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    The question, spooky or not spooky, in the context of the OP, and recognizing subsequent contributions from other members, can be characterized in the different interpretations of Quantum Mechanics. The Hidden Variables Interpretation promotes the "incompleteness" of the laws of quantum mechanics, and there is content form several members in this thread pointing to how fundamentally different the underlying foundational nature of things would have to be in order for there to be a reconciliation between the existing postulates, and the underlying forces of nature that we do not yet understand, and cannot directly observe.

    On that point, I'm coming from the perspective that nature, at the foundational level is quantum. The mention of gravity is on point, in that there will be a quantum solution to gravity, if there is to be any reconciliation. Further, the observed oscillations that are evident in electric and magnetic action within and among particles, molecules, and objects must have a quantum level origin, pointing to something in nature that oscillates in the background. That foundational oscillation must be something that makes sense and ties into the way everything must work together.

    So tell me what the mechanics are of the foundational occillations of nature?
     
    Last edited: Jan 30, 2016
  21. QuarkHead Remedial Math Student Valued Senior Member

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    The following argument is somewhat pot hoc , but see if it helps....

    Let's define a pair of quantum entities as entangled if there exists a single state function - a wave function recall - that uniquely describes their "joint" state.

    Now recall that Max Born postulated that the prior probability of finding a particular measurement outcome for any operator acting on this state is given by the square of this wave function (a postulate that has been widely accepted ever since - a remarkable insight since it was prior to P.A.M Dirac's formalization of QM as an operator theory on an Hilbert space).

    Clearly this probability has values in the interval [0,1]. Equally clearly, the sum of all such prior probabilities must be 1.

    For simplicity, consider an entangled pair, with only 2 possible measurement outcomes - + or -.

    Then obviously, after a measurement on one element of the pair that yields the answer + the posterior probability of this measurement is 1. But since sums of posterior probabilities must also be 1, then it follows that the posterior probability of the measurement + on the other element of the pair must be 0.

    And since there are only 2 possible outcomes, this second measurement must yield -.

    The only thing is, a 2-element quantum system can remain in a single state even after (possible) infinite spacetime separation. But from the above above, I see no reason why not.
     
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  22. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Pot hoc? Tell me if you think the same thing tomorrow, lol. But anyway, it is a good, on-topic response.

    It defines a "joint state", an entanglement, where, in superposition, each state can be faithfully recalled when the time comes for measurement. If there is no measurement, the superposition of each entangled particle retains the ability to have one or the other of its entangled states recalled when measured.

    When measurement takes place, it will be either + or -. The nature of superposition assumes some connection between the particles over space and time, and so if one measures +, then the other particle in the pair will not be +, and in fact will be -. Did I understand you correctly?

    If all that is said, we have introduced some important parts of the quantum postulates. Uncertainty, the wave function, entanglement, superposition, determination of the state of one particle by measurement, and then identifying the state of the second particle by deduction, and expressing a "spooky" confidence that the other particle's state is determined at the moment that the first particle is measured.

    Where the Hidden Variables Interpretation goes though, is that there might be something fundamentally wrong with that scenario. Exactly what, we don't know. Maybe instead of there being such a thing as entanglement of two states into a state of superposition, the "wave function recall", as you phrase it, does not occur. Just talking here, but maybe because at all times, the particle's internal composition was able to faithful retain both of the two states, not in a joint superposition state.

    It would be like the wave-particle nature of a photon existing at all times as the photon traverses space. Then it would be the method of measurement that determines which state we detect. If we see a wave interference pattern, we are detecting the wave state, and if we see a point on a screen, we are detecting the particle state.

    I know there is a lot of territory not covered by such a "maybe", but your scenario has that spooky aspect, and work still needs to done to reconcile QM with the idea that everything is governed by invariant natural laws with mechanistic explanations.
     
    Last edited: Jan 30, 2016
  23. Cheezle Hab SoSlI' Quch! Registered Senior Member

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    I would suggest you watch this lecture about quantum superposition. The entire lecture series is excellent.

     

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