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EPR Experiment with Pool Balls

  1. Jan 9, 2004 #1
    ***EPR Experiment with Pool Balls***

    First of all sorry if what Im going to ask seems crazy stupid, but it is an idea that rounds my mind since I started reading about EPR subject.

    As far as Ive read, you can imagine EPR with photon polarization or with particle spin. So, I have imagined it with two complementary pool balls inside a bag. One is red, the other is black.
    I take one without looking at it. Then I travel, lets say, 1 lightyear distance.
    Now it is when I look at the ball to see its colour. 50% probability then. Obviously, if my ball is red, the remaining one in the bag is black.
    If we applicate the non locality principle, it will say that both balls were on a uncertain color until being looked. I know this is very stupid concept, because we certainly know that my ball was red all the time since my election, and the remaining one of course was black.

    The point of my question is why we cant apply the same logic to the EPR experiment. If I use two electrons with spin 1 and -1 to make the experiment, they were in that state all the time since the separation! Theres no any comunication nor information travel!

    Please dont be too hard with me in the answers
     
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  3. Jan 9, 2004 #2

    Doc Al

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    Re: ***EPR Experiment with Pool Balls***

    I assume you mean the usual kind of EPR experiment where you have two spin 1/2 particles in an entangled state where the total spin is zero.

    If we just measured the spin in one and the same direction for both particles, then your model would (seem to) work. If we measure spin along the x-axis, we will always get a matching pair of answers: if particle A says up, particle B says down. You could pretend that each particle had its x-axis spin assigned to it, just like the color of your pool balls.

    But things get more interesting when we measure the spin at different angles for each particle, say x-axis for one, y-axis for the other. It turns out that these spin measurements are incompatible, meaning that measuring one seems to "destroy" any value of the other. For any given measurement, you can only measure one direction of spin. You would have to extend your pool ball model to include a new variable to represent the y-axis measurement: let color be the spin in the x-direction, and (say) shape represent spin in the y-axis (round = up; cube = down). Things get even more complicated when you let the spin angle have any angle.

    A more sophisticated (but still unworkable) model would just assign an "instruction set" to each particle. The instructions would tell it what to do upon encountering a measuring device for any spin direction: essentially this is a list of spin values for any direction of measurement. All the spin information rides along with each particle, so no funny business about communication or information travel.

    But the bottom line is this. Nature doesn't seem to work that way! These kinds of model (your pool balls or the "instruction set" model) have been showed to lead to correlations that do not match the results of real experiments. (This is the essential content of Bell's theorem.) Quantum mechanics, on the other hand, predicts the results nicely.

    This may not seem like much of an answer, since I'm basically saying: It just doesn't work. To go deeper would involve describing the spin correlations and the details of Bell's theorem.
     
  4. Jan 9, 2004 #3
    But suppose particle A encounters a measuring device first. So it follows the instructions and 'becomes' a particle with spin Sa. So far so good.. but now particle B, as per its version of the instructions, must assume a definite spin Sb: it has no choice. However, Sb is corelated with Sa, which in turn is a function of the kind of measurement that A has encountered, and this could be light years away at that moment.. so the 'instruction set' model would have to be nonlocal anyway.

    The point being that a nonlocal "instruction set model" can be ruled out without delving into the details of Bell's theorm etc... no?
     
  5. Jan 9, 2004 #4
    Your answers are too focused on my error concerning spin version of the experiment, thanks for repliying and clarify that.

    The whole point of my question rests at the end: "Why we cant apply the same logic (of pool balls) to the EPR experiment".
    In other words, non locality exists or is the polarization of photons already decided from the start of the experiment?
     
    Last edited: Jan 9, 2004
  6. Jan 9, 2004 #5

    NateTG

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    The whole notion of 'instruction set' is what Bell's theorem is about. However, Bell's theorem does make some assumptions that aren't necessarily valid.

    I haven't studied QM, but I am fairily convinced that the non-locality is a quirk of the theory more than it is a contradiction -- Specifically, that it is possible to construct a model of the Electron that deals with the EPR paradox without nonlocality, but that behaves identically to other predictions made by the typical QM model otherwise.

    Proponents of the Consistent Histories approach to QM claim that the EPR paradox is actually like your pool ball example, but I don't know enought about it, or how it differs from the Copenhagen Interpretation to give you any further insight.
     
    Last edited: Jan 9, 2004
  7. Jan 9, 2004 #6

    Suppose you had a wierd kind of pool ball to which you could put the question : "Are you red or black?" and it would randomly reply either "red" or "black". If two balls were corelated, then getting a "red" reply from one would guarantee a "black" reply from the other.

    But now there is another question that you could ask: "Are you new or old?" (forget about the *meaning* of the answer :) If you get "new" from the first ball you are guaranteed to get "old" from the second.

    Finally, a ball that has replied "red" once will stick to this answer as long as you stick to the same question; but if you ask a "red" ball the old-new question, you will randomly get "old" or "new".

    If you ask "red or black" of a "new" ball you will get a random reply, either "red" or "black".


    If you alternate your questions successively, there is a fair chance that a ball that once said "red" will now say "black".

    NOW, in order to preserve the correlation between the two pool balls, it is clear that the second must know what question you asked the first one, so that it will know whether to randomize or not. As I understand it, it is this information that 'travels' nonlocally in the 'instruction set' model. Once this information is available, the second ball can follow the instructions to produce the corelated answer. If you discard the instruction set concept, then the answer itself must travel nonlocally.
    (Corrections welcome!)
     
    Last edited: Jan 9, 2004
  8. Jan 20, 2004 #7

    FZ+

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    Because that is what the EPR experiment invalidates.

    In essence, Einstein stated that it is nonsensical to say that observing at the end changes the other ball, and that the ball must have had a state (red or black) from your election. It is simply our knowledge that is lacking. Bell then analysed this and produced the Bell inequalities, which would be true if this sort of "local realistic", hidden variable logic is true.

    But experiments then carried out violated the Bell inequalities, showing this sort of thinking to be invalid. Simple as that.
     
  9. Jan 21, 2004 #8
    Not quite as simple. No experiment, despite three decades of trying, has invalidated local realism. Although the "Quantum Mystery Cult" euphemistically labels this failure as "loopholes" in the existent experiments, the simple fact is that only the "data" adjusted (cherry picked, for non-QMC members) using various convenient rationalizations (additional "assumptions" such as "fair" sampling, "accidental" coincidence subtractions, non-enhancement,... etc ) violate Bell inequalities.

    The unadjusted data not only has not violated the inequalities, but there are even plausible classical theories (such as "stochastic electrodynamics" for photons and Barut's self-field electrodynamics for fermions) which reproduce the actual data of all EPR experiments so far.
     
    Last edited: Jan 21, 2004
  10. Jan 21, 2004 #9

    DrChinese

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    Harsh words, and not really accurate. Following the standard Copenhagen Interpretation of QM does not qualify one as a member of the "Quantum Mystery Cult." Your spirit is misplaced.

    The fact is that decades of experiments have soundly supported the predictions of QM, and have failed to indicate the existence of a more complete specification of reality as discussed in EPR. To the vast majority of scientists in the area, the matter is reasonably settled by the experiments of Aspect et al. Local reality is rejected by experiment.

    What is true is that there have and will continue to be those to whom the experiements leave some amount of room for a "way out". For years, the criticism was leveled at Aspect that the observer and subject systems were in communication. He fixed that criticism. Lately, there has been a criticism on the grounds of counting inefficiency.

    I could certainly agree that further refinement of the experiments to answer such criticism is warranted. I don't expect anything radical or surprising to occur, but you never know.
     
  11. Jan 21, 2004 #10

    selfAdjoint

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    He is referring to criticisms of the Aspect and other experiments directed at showing the Bell inequality violation by quantum mechanics. There are some weaknesses that even quantum physicists recognize, and the "reality" partisans have chosen to make a stand on these.
     
  12. Jan 21, 2004 #11
    The fact is that decades of experiments have soundly supported the predictions of QM,

    No one is arguing against the QM statistical predictions. The argument is against the unsubstantiated claims that the experiments exclude local realism. To arrive at that "conclusion" the data has to be cherry picked based on metaphysical and unverified (or unverifiable) ad hoc rules.

    For example, in all the experiments there is a "fair sampling" assumption -- an assumption which implies that the local hidden variables do not affect the probability of detection. Under such assumption all that the experiment excludes are the local hidden variables which don't affect the probability of detector trigger.

    Check for example the paper by Emilio Santos which explains why "fair sampling" is an absurd assumption.

    To the vast majority of scientists in the area, the matter is reasonably settled by the experiments of Aspect et al. Local reality is rejected by experiment.

    The experiments still show only that certain absurdly restricted (as Santos explains in the paper above) types of local realism are excluded. Perfectly plausible local realistic theories, such as stochastic electrodynamics (e.g. check papers by Emilio Santos & Trevor Marshall for details) fit the actual data as well as QM.

    What is true is that there have and will continue to be those to whom the experiements leave some amount of room for a "way out".

    I suppose all the past inventors of "perpetuum mobile" machines could claim the same about the non-believers -- except for that little glitch with friction, which is entirely due to the present technological imperfections, and which we will fix in the near future, the machine runs for ever (even though it actually stops). The doubters are merely looking for "unimportant" loopholes and "wiggle room." Yeah, sure. It either works or it doesn't.

    For years, the criticism was leveled at Aspect that the observer and subject systems were in communication. He fixed that criticism.

    That was a fake "criticism" by the supporters of the QMC, not the opponents. No one was proposing models, much less theories, which would explain the optical experiments that way (via distant subluminal communication between the two far apart sides of the aparatus). The Aspect's "fix" was thus like a magician theatrically rolling up his coat sleeves, after a "neutral" voice from the public shouted about the card hiding in the sleeve.

    Lately, there has been a criticism on the grounds of counting inefficiency.

    The inefficiency problem better known under the euphemism "detection loophole" has been a known problem well before Aspect did his thesis. It hasn't been fixed.
     
    Last edited: Jan 21, 2004
  13. Jan 22, 2004 #12

    DrChinese

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    Nice paper by Santos, BUT...

    1. It is a new paper, and hardly the last word. Certainly would not be considered authoritative at this point. However, I will accord it the courtesy of addressing it on its merits.

    2. Bell's Inequalities: I did not take away from the Santos paper any real criticism of the Bell derivation. In a "perfect world", the Inequality could be used to rule out all LHV theories. I disagree with the notion that Bell's "second part" (per the paper) is confused in some way. All I can see is the criticism that an actual "loophole free" experimental setup was not described. Hardly a reasonable critique of Bell by any common standard. Bell did his job fully.

    3. The Aspect-type experimental setup and the "fair sampling" assumption:

    Santos states:

    "In the context of LHV theories the fair sampling assumption is, simply, absurd. In fact, the starting point of any hidden variables theory is the hypothesis that quantum mechanics is not complete, which essentially means that states which are considered identical in quantum theory may not be really identical. For instance if two atoms, whose excited states are represented by the same wave-function, decay at different times, in quantum mechanics this fact may be attributed to an ”essential indeterminacy”, meaning that identical causes (identical atoms) may produce different effects (different decay times). In contrast, the aim of introducing hidden variables would be to explain the different effects as due to the atomic states not being really identical, only our information (encapsuled in the wave-function) being the same for both atoms. That is, the essential purpose of hidden variables is to attribute differences to states which quantum mechanics may consider identical. Therefore it is absurd to use the fair sampling assumption -which rests upon the identity of all photon pairs- in the test of LHV theories, because that assumption excludes hidden variables a priori.

    "For similar arguments it is not allowed to subtract accidental coincidences, but the raw data of the experiments should be used. In fact, what is considered accidental in the quantum interpretation of an experiment might be essential in a hidden variables theory."

    There are some pretty big claims here, and I don't think they are warranted. Fair sampling is far from an absurd assumption. There has never been a single experimental test of a quantum variable which has even slightly hinted at the existence of a deeper level of reality than is currently predicted by QM. Hardly what I would call "absurd". You might as well call the notion that the sun will rise tomorrow as absurd.

    You might say that it is an unwarranted or burdensome requirement. But I don't even follow that line of reasoning. Clearly, the requirement is that a LHV theory otherwise provide identical predictions to QM. Fair sampling fits this naturally. In the view of Santos, not only are the Bell Inequalities not violated in the Aspect experiments, but a new and previously unknown hidden local quantum observable is rearing its head. And somehow this observable only shows itself during this type of experiment, and no others. That observable is one in which the photon detection is suppressed or enhanced just enough to appear to match the predictions of QM (i.e. outside of the Bell Inequality); while actually falling within the statistical range of the Inequality. That's a big step, one which I might reasonably expect to have been noticed previously.

    4. I have not had time to otherwise anaylze the formula logic of the paper. I will take a look at that.

    A degree of skepticism is good, and healthy. I don't see the point of insults.
     
    Last edited: Jan 22, 2004
  14. Jan 22, 2004 #13
    1. It is a new paper, and hardly the last word. Certainly would not be considered authoritative at this point. However, I will accord it the courtesy of addressing it on its merits.

    That particular paper is new, but Santos, Marshall, Jaynes and others have been criticizing the EPR-Bell experiment claims since the late 70s (check listings there, there are at least couple dozen papers by Marshall-Santos group). This wasn't merely a critique based on artificial narrow counterexamples for the particular experimental claims but a full fledged local realistic theory of quantum optics phenomena (stochastic electrodynamics; it falls short for the massive particles although the Barut's self-field electrodynamics covers fermions as well as QED to the orders it was computed).

    Regardless of the ultimate value of stochastic electrodynamics as an alternative theory (it is incomplete as it stands), the mere existence of a local fields model for the actual EPR-Bell experimental data plainly demonstrates that the claims that any local realistic mechanism is being excluded by the experiments is false.

    2. Bell's Inequalities: I did not take away from the Santos paper any real criticism of the Bell derivation.

    The Santos-Marshall group makes distinction between the QM dynamics, which they accept, and the "measurement theory" (the non-dynamical, mystical part - projection postulate) which they reject. The Bell's theorem needs a collapse of the remote state to achieve its locality violation. They reject such collapse and point out that it hasn't been demonstrated by the experiments.

    The problem nowdays with challenging the general state collapse hypothesis (projection postulate) is that it is a key ingredient necessary for Quantum Computing to work. If it is not true in the full generality, the QC won't work any better than a classical analog computer. Thus the challenge is not merely against ideas but against the funding draw QC has, a sure recipe to get yourself cut off from the leading journals and conferences. (Before the QC hype, there was a healthy debate and they were published in every major journal.)

    There are some pretty big claims here, and I don't think they are warranted. Fair sampling is far from an absurd assumption.

    In any deterministic hidden variable theory, the detection probability must by definition depend on some hidden variable value. The "fair sampling" hypothesis is thus an assumption that the hidden variable affecting the detection probability (the probability of triggering the avalanche and its timing when coincidence time-windows are used for pair detection) is independent from the hidden variables affecting the detected outcome (i.e. +/- choice).

    Therefore that is all that experiments exclude -- the local theories for which the two sets of hidden variables are independent of each other. That is not true even for the most simple minded classical electrodynamics models of polarization and detection (or for stochastic electrodynamics or for Barut's self-field ED).

    Thus the assumption is absurd since it helps experiments exclude something that isn't even included among the proposed alternatives. This is no different "exclusion" than the "refinements" of the experiments to use randomly varying polarizer direction (which you brought up earlier) -- it topples down its own strawman, not the actual theories being proposed by the opponents.

    There has never been a single experimental test of a quantum variable which has even slightly hinted at the existence of a deeper level of reality than is currently predicted by QM. Hardly what I would call "absurd".

    QM doesn't offer any "reality" deeper or otherwise. If you believe in any reality, local or not, the quantum phenomena require explanation beyond the prescriptions on how to calculate the probabilities.

    You might say that it is an unwarranted or burdensome requirement. But I don't even follow that line of reasoning. Clearly, the requirement is that a LHV theory otherwise provide identical predictions to QM. Fair sampling fits this naturally.

    There is no need for "unwarranted" or "burdensome" attributes in order to analyze what is it exactly that the "fair sampling" (purely mathematically) excludes -- it is an ad hoc constraint on hidden variables, which hand-waves off the table several proposed alternatives, leaving only the strawman local theories (that no one has proposed) for the experiments to refute.

    For more discussion on the "fair" sampling hypothesis and the proposed simple additional experiment to test it for the existent EPR-Bell setups check the paper by G. Adenier, A. Khrennikov. I haven't seen as yet any of the several active quantum optics groups, who are claiming to have established Bell inequality violations, checking the assumption on their setup. Since the additional tests proposed are quite simple on the existent setup, it is suprising that no one has yet picked the clear cut open challenge of the above paper, especially considering that the verification of the fair sampling as proposed would eliminate all known plausible LHV theories (they all rely on "unfair" sampling). Or maybe some have tried it and the data didn't come out the way they wished, and they didn't want to be the first with the "bad" news. We'll have to wait and see.

    PS: After writing the above, I contacted the authors of the cited paper and the status is that even though they had contacted all the groups which have done or plan to do EPR-Bell experiments, oddly no one was interested in testing the 'fair sampling' hypothesis.

    Clearly, the requirement is that a LHV theory otherwise provide identical predictions to QM. Fair sampling fits this naturally.

    As pointed out by Santos, the QM has two sharply divided components, dynamics and the measurement theory. They reject the measurement theory (in its full generality) and some of its implications. That is precisely what the Bell EPR tests were supposed to clarify - does the world behave that way. The result so far have not produced the type of distant collapse (projection of the composite state) as assumed by Bell for his inequalities.

    The "fair sampling" is an assumption outside of QM (or any other theory or any experiment). The actually proposed alternative theories do not satisfy fair sampling, i.e. the hidden variables do not decouple into independent sets which separately control the detection timing and probability from variables controlling the +/- outcome.
     
    Last edited: Jan 26, 2004
  15. Jan 27, 2004 #14
    epr without pool balls

    hi tachyon son!

    the problem with thinking the EPR problem wih pool balls is that there is a well defined colour for the pool ball, whether you measure it or not!

    but in q.m, a particle has a defenite value for an observable only when you measure it!

    in fact , this is what the original EPR paper is about! it doesn't talk anything about pool balls or about the usual thing about two particles with total spin zero sent in opposite directions(the usual stuff)
    what the actual epr paper says is this..

    in q.m, you can't have a particle in a state of defenite mamentum and position ...this is the position momentum uncertainity princple.
    now suppose you have an entangled pair(momentum entangled, ie total momentum is zero) of particles going off in the opposite directions , and you decide to measure. now, if you measure the position of particle A( let us call it particles A and B), particle B goes to a state(eigenstate) with a well defined position.
    ( particle A, on which you perform the measurement also goes to an eigenstate of position.)

    but suppose you decide to measure momentum instead, then particle B goes to a state with well defined momentum!

    so, in fact particle B goes to an eigenstate,which depends on what you decide to measure! suppose the particles are light years apart, then, your choice of whether to measure position or momentum influences( instantaneously) a a particle which is light years away to collapse it into an eigenstate(of what you measure)!
    until you make the measurement, you cannot say that the particles are in a state of position or momentum.

    you can do the EPR experiment with spin as well...that version is due to Bohm or somebody....and in fact the Aspect experiment which confirmed bell's theorem was performed with the polarizationof photons! so it doesn't depend on which variable(or, in the language of q.m,observable ) you use!

    that's all.[zz)]
     
  16. Jan 27, 2004 #15
    Re: epr without pool balls

    The Aspect's experiment, or any other attempt in over three decades of trying, have not confirmed Bell's inequality. See the above discussion of the "fair" sampling hypothesis (that all such experiments assume upfront) and what it means.
     
  17. Jan 27, 2004 #16

    DrChinese

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    Re: Re: epr without pool balls

    1. The predictions of QM are confirmed by Aspect's experiments, there is no question about this point. Period.

    2. The only question - as nightlight argues to the negative - is whether ALL Local Hidden Variable theories are excluded as a result of Aspect's experiments. The reference paper cited (Santos) asserts there ARE at least some LHV theories which would yield predictions in line with the results of the Aspect experiments. (Personally, I question the conclusion but am still reviewing this.)

    Nightlight is pushing a point of view which is not generally accepted. It may well be right, but remains to be seen.
     
  18. Jan 27, 2004 #17
    Re: Re: Re: epr without pool balls

    1. The predictions of QM are confirmed by Aspect's experiments, there is no question about this point. Period.

    The QM prediction which violates Bell's inequality has not been confirmed by the measured data, by Aspect or any other experiment. Only the adjusted data under:

    a) "fair" sampling hypothesis
    b) subtraction of "accidental" coincidences

    violate Bell's inequality. Both of these assumptions are outside of QM and even though there were proposals (for over a decade, see refs in Santos & Khrennikov) for experiments to verify them, no group has reported performing them.

    The theoretical prediction itself requires, among others, distant collapse of the composite state, a part of "measurement theory" of QM, which is not a generally accepted addition to the dynamical postulates of QM. The groups which reject assumptions (a) and (b), also question the "measurement theory," the distant instantaneous composite state collapse which Bell assumed. For them there is no such prediction (and everyone agrees that, so far, there is no _measured_ data confirming it).

    2. The only question - as nightlight argues to the negative - is whether ALL Local Hidden Variable theories are excluded as a result of Aspect's experiments. The reference paper cited (Santos) asserts there ARE at least some LHV theories which would yield predictions in line with the results of the Aspect experiments. (Personally, I question the conclusion but am still reviewing this.)

    All sides agree that not all LHV theories are excluded by the experiments. What Santos points out in the paper is that LHVs which are excluded are the most absurd subset of the conceivable LHV theories (there is no actual theory constructed, not even partial one, which satisfies "fair" sampling hypothesis), i.e. the experiment topples merely a strawman made up by the experimenter.

    The actual alternative LHV theories (or the QM extensions/completions) which exist (whether they are ultimately right or wrong in their full scope), such as stochastic electrodynamics (SED) and self-field electrodynamics, are not being addressed by these experiments -- these theories are waved off by hand upfront by an ad hoc "fair sampling" assumption, which is outside QM and which somehow no one wants to put to test. These LHV theories agree perfectly with the EPR-Bell experiments (as Marshall, Santos and their sudents have shown in numerous papers).

    Nightlight is pushing a point of view which is not generally accepted. It may well be right, but remains to be seen.

    Among the people doing the experiments and their critics, there is no dispute as what is being excluded by the experiments themselves. They all know what the assumptions (a) and (b) sweep away upfront and they know that the actual alternatives from the opposition are not being tested. They all know they could test assumption (a) and that no one wants to report whether they have done it and what was the result.

    The only disagreement on the experimental side is in the prediction what will happen as the technology improves -- the state collapse supporters believe Bell inequality will be ultimately violated as detectors improve (without "loopholes" i.e. without the need to adjust data via (a), (b) and such). The opponents believe it won't be violated.

    On the theoretical side, the contention is the "measurement theory", specifically the postulate on the composite system state collapse, and there is no generally accepted single view on that. Nothing in day to day use of QM/QED depends on that postulate, so the vast majority of physicists ignore the subject altogether -- it doesn't affect their work either way. If it turns out falsified, there won't be any experimental consequences in anything anyone has done so far (the only experiment which could confirm it, excluding alternatives, would be a loophole free EPR-Bell test). The main effect would be on the EPR-Bell storyline and on the so-called Quantum Computing (which would lose its non-classical "magic" powers attributed to it by the present state collapse proponents, as being right around the corner, as soon as the 'decoherence' is taken care of and the detectors improve).

    In summary, the only disagreement is in what will be measured/found in the future. What has actually been measured is known to those in the field and is not a matter of belief or taste. You only need to read carefully, bracket out the hype, euphemisms and the unspoken or footnoted limitations (which have been largely known since mid-1970s), to see that there is no actual disagreement between Santos/Marshall group and the EPR-Bell experimenters, as to what exactly has been excluded by the data and what by the additional assumptions. It is only in what will happen in the future that they can really disagree about, and the time is on the skeptics' side.
     
    Last edited: Jan 27, 2004
  19. Jan 27, 2004 #18

    DrChinese

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    Re: Re: Re: Re: epr without pool balls

    While I disagree with your characterization of the state of the current evidence, the above is just plain wrong.

    Bell's Inequality has little or nothing to do with testing the predictions of quantum theory, although Aspect's experiments do confirm the predictions of QM as a by-product. The Bell Inequality requires only the essential beliefs in local reality and follows classical reasoning. If you accept that the two emitted photons carry a crossed polarization, the inequality can be deduced.

    Quantum mechanics does not assume that the photons have definite polarization independent of their measurement. Classical reasoning requires this, and that is what leads to the Inequality, which is ultimately a reformulation of the idea that every measured permutation must have a likelihood of occurance between 0 and 100%. If this were true (which is the point being debated and which the Aspect experiments indicate are in fact false) then QM would not be a complete theory. Maybe. But it would not indicate that QM is "wrong". That could never happen, any more than you might consider Newton's gravitional laws "wrong".

    On the other hand, the reason some people are so emotional about the Aspect experiments is this: once all "objections" are dealt with, all LHV theories must be excluded from consideration. They would be rendered totally untenable, essentially "wrong". So the issue has different stakes depending on which side you are on.

    Aspect must be getting rather tired of hearing that his experiments have shown nothing. At any rate, I can agree that all voices are not in agreement on the interpretation of the results at this time. The most common conclusion I have heard is that locality has been violated, although that is not a strict conclusion from the results. And some, such as yourself, are not comfortable with the experimental procedure.

    Fine, perhaps there is a flaw. I don't see the angle of attack, but perhaps it is there.
     
  20. Jan 27, 2004 #19
    Re: Re: Re: Re: Re: epr without pool balls

    Bell's Inequality has little or nothing to do with testing the predictions of quantum theory, although Aspect's experiments do confirm the predictions of QM as a by-product. The Bell Inequality requires only the essential beliefs in local reality and follows classical reasoning. If you accept that the two emitted photons carry a crossed polarization, the inequality can be deduced.

    Of course it has to do -- the whole point was to produce a prediction of QM which no local deterministic theory would be able to. The QM predicition asserted by Bell was that QM would violate inequality that no local deterministic theory could violate. The whole excercise would have been pointless without the QM prediction falling on the opposite side of the Bell inequality from any LHV theory.

    Quantum mechanics does not assume that the photons have definite polarization independent of their measurement.

    That (the assumption of the lack of definite polarization) by itself doesn't imply violation of the Bell inequality. What does imply the violation is the projection postulate, part of the QM measurement theory, when applied to the entangled state.

    Classical reasoning requires this, and that is what leads to the Inequality,

    That alone, without also deducing a QM prediction which will violate inequality, would be pointless.

    On the other hand, the reason some people are so emotional about the Aspect experiments is this: once all "objections" are dealt with, all LHV theories must be excluded from consideration.

    Emotions have nothing to do with experimental facts. If you study this subject beyond the popular literature and hype, you can find out for yourself which class of LHV theories were excluded by the experimental data and which were excluded upfront (as not being the objective of the experiments). The status is as stated in my earlier posts (or as Santos states). If you find out that I have misclassified them (as described in previous posts), I would be glad to see the correction here.

    The most common conclusion I have heard is that locality has been violated, although that is not a strict conclusion from the results. And some, such as yourself, are not comfortable with the experimental procedure.

    Again, this is not a discussion of your or my inner "comfort". It is a simple straightforward question as to what has been excluded by the experimental data and what was taken out of consideration upfront. The plain fact, known to everyone in the field (since mid 1970s, although not emphasized equally by everyone) is that the "fair sampling" constraint on LHVs implies LHV theories in which the local variables determining the detection probabilities are independent of the variables determining the +/- outcome. It just happens that no such theories were constructed and that the actual LHV alternatives/extensions of QM (which can make predictions) do not satisfy the "fair sampling" constraint and their predictions agree with the experimental data.

    You seem to be confusing the LHVs excludied by the experiments with those excluded by the Bell's inequality -- indeed all LHVs are excluded by the Bell inequality, i.e. all LHVs satisfy the inequality. The only problem is that what Bell claimed to be a QM prediction violating the inequality (deduced via the projection postulate and measurement "theory") has not panned out in the experiments -- no experimental data has violated the inequality despite over three decades of trying. Only the data filtered through the additional ad hoc assumptions (always the "fair sampling" and often some others), which are outside the QM and are untested on their own, violate the inequalities.

    The point I brought up in this thread (along with Santos, Marshall, Barut, Jaynes, Khrenikov,... and other skeptics) is that if one looks closer at the experiments and the "fair sampling" assumption, it turns out that all the actual LHV alternatives (those actually constructed and developed, the theories making concrete predictions) are excluded by the "fair sampling" hypotheses all by itself, before any laser was turned on and before any detector counted a single count.

    If you wish to draw some other line among the LHVs excluded and those not excluded by the actual data, please, go ahead (without the mixup between the QM prediction asserted by Bell and the actual experimental data). Explain what kind of LHVs does the "fair sampling" hypothesis exclude all by itself?

    Lets hear your version and how does your separation line show that the experimental data (and not the "fair sampling" hypothesis) exclude the "pool ball logic" which started this thread.
     
    Last edited: Jan 28, 2004
  21. Jan 28, 2004 #20

    DrChinese

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    Nightflight:

    QM does not violate Bell's Inequality because the Inequality does not apply. QM makes predictions for actual experiments of photon beams with 2 polarizers. The QM prediction for a photon beam passing through both polarizers is a function only of the angle between the polarizers. The same formula applies whether you are talking about photons in an entangled state, such as the Aspect experiment measures, or a single beam passing through consecutive polarizers. In fact, the formula is the same in classical optics too, but only when light is treated like a wave.

    The problem from a LHV perspective is that if the beam is postulated to have a) an orientation which exists independently of the measurement apparatus which was b) determined at the time the photon was created. These 2 conditions are too severe to survive. You don't need the Aspect setup to see that something is wrong with that anyway. It follows from experiments anyone can do with 2, 3 and more polarizers in a single beam too. I will explain in a separate post.

    The Aspect experiments are simply the logical extension of the measurement process issues which were quickly evident as QM was being formulated, a la the double slit experiment. Clearly reality does not act as it does in the classical world, and I don't understand why this point is a topic of debate. Next you will be telling me that the double slit experiment does not prove anything, either. The fact is that any way you cut it, the Heisenberg Uncertainty Relations apply and there is no observable deeper level of local reality.
     
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