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I Can you help me understand this core principle?

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  1. Feb 20, 2017 #1

    RTT

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    "As all good textbooks of quantum mechanics have to emphasize and clarify in one way or another, it is critically important that one avoids the assumption that even before the measurement, any of the quantities that may be observed later already have some objective, particular values."

    Imagine I encountered a forest and decided to count its trees. Is there or isn't there a certain, predetermined number of trees already there? If you say that the number of trees is unknown before they are counted - how do you know someone didn't count them before me? More importantly, to me - how can that be true? Trees grow over many years - they are not a figment of my imagination, right? I feel that I am in danger of totally misinterpreting this basic aspect of quantum theory.

    Does this example work any differently?: I draw a line segment on a piece of paper. Does it or does it not have a predetermined length that could be measured? Classical physics says it does, provided you know the velocity of my hand, the resistance of the surface, etc. But does QM disagree? How so? I feel intuitively that I am off track with my questioning - that QM aren't meant to be extrapolated to this type of scenario - but if that's the case, can someone help me get back on track?
     
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  3. Feb 20, 2017 #2

    DrClaude

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    Quantum theory itself doesn't say anything about the reality of some quantities when they are not measured. What you can say about those quantities is basically a question of interpretation.

    See Mermin's Is the Moon there when nobody looks?
     
  4. Feb 20, 2017 #3

    RTT

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    Thanks very much for your reply. I ... think ... you're saying that right now, there is no conclusive answer, and presumably not even a widely-accepted view of the matter. The Aspect experiment was confusing to me, but that's just to say that I am likely hopeless in the face of quantum theory itself. Instead of understand it, I'd like to understand more about it - how it is shaping perspective and what it can mean in terms of practical philosophy. So far, I have it boiled down to:

    I) quantum theory is infallible as a math
    II) it's nonsensical to argue it's predictive capabilities - they are actualized in many forms already, like the internet I'm using now
    III) so far, it doesn't offer much in the way of instruction for practical philosophy, other than to say that the more you are convinced of something, the more likely you are to be wrong, echoing the sentiment of Marcus Aurelius when he said that "all you hear is opinion, not fact, and all you see is perspective, not truth"
     
  5. Feb 20, 2017 #4

    DrClaude

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    We don't discuss philosophy at PhysicsForum.
     
  6. Feb 20, 2017 #5

    RTT

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    Ha! I assume you are not joking, but your position makes you very difficult to take seriously. Philosophy is not a "thing" that you can choose to discuss or not to discuss. It is many things, all implicit and inherent in any discussion of science, but especially, particularly in a discussion of quantum physics. Everyone has philosophy, and it is inseparable from the way we present ideas when using words. If "Physics Forums" did not discuss philosophy, it would not use words - only math. Please see the definition below - and try to understand what I am saying - there is not a possible way for this forum to exist and simultaneously exclude all of the following:

    noun, plural philosophies.
    1.
    the rational investigation of the truths and principles of being,knowledge, or conduct.
    2.
    any of the three branches, namely natural philosophy, moral philosophy, and metaphysical philosophy, that are accepted ascomposing this study.
    3.
    a particular system of thought based on such study or investigation:
    the philosophy of Spinoza.
    4.
    the critical study of the basic principles and concepts of a particularbranch of knowledge, especially with a view to improving orreconstituting them:
    the philosophy of science.
    5.
    a system of principles for guidance in practical affairs.
    6.
    an attitude of rationality, patience, composure, and calm in the presence of troubles or annoyances

    Good luck trying to "actualize" that version of reality. Meanwhile, I'll be deleting my membership and looking for information anywhere but here, because quantum physics without philosophy is the most arbitrary and pointless "science" I've ever heard of.
     
  7. Feb 20, 2017 #6

    DrClaude

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    You are being pedantic. I guess you understand the difference between discussing science (what is measurable and can be theorized in the form of equations) and the philosophical implications. The latter discussions are difficult to moderate (they easily drift towards speculation and unsubstantiated personal opinions) and rarely lead to anything productive. Therefore, here at PF we stick to the scientific discussions.

    I personally have nothing against philosophy (which is rather a minority opinion among physicists in general), but I think it is rather the other way around: there are too many pointless discussions of the philosophy of QM. At least make sure you have a very firm grasp of the physics before you delve into the philosophy of QM.

    Thread closed.
     
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