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The Uncertainty in QM

  1. Jun 2, 2004 #1
    I’ve been wondering about this question for some time. Is the uncertainty in QM due to simply being unable to measure with certainty? Or is the actual nature of the subatomic world uncertain?
  2. jcsd
  3. Jun 2, 2004 #2
    It's a fundamental property of nature, it has nothing to do with our technological abilities (which are already quite advanced).
  4. Jun 2, 2004 #3


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    This is certainly a valid question. So consider this. I'm sure you have seen (or maybe even done) the diffraction experiment, where light passes through a single thin slit, and you get the nice diffraction pattern on a screen. In fact, notice how the diffraction patterns get wider and wider as you make the slit narrower. Now, would you consider the observation of the diffraction pattern as being due to our inability to measure with certainty, or would you consider this to be an intrinsic property of the "light-slit" system? I vote for the latter, because the accuracy of my measurements does nothing to affect the nature of the diffraction.

    The phenomena of the diffraction pattern from a single-slit is, believe it or not, a DIRECT manifestation of the uncertainty principle.

  5. Jun 2, 2004 #4
    This is indeed a important question and one in which I have been struggling for sometime as well.

    Knowing full the question of momentum and position, and the difficulties involved here, two things became apparent to me. That as fuzzy as it may appear, uncertainty can be given structure in the form of orbitals?

    http://superstringtheory.com/forum/stringboard/messages25/52.html [Broken] and looking back to bell curve, things seem realistic to me if we can count on BEC graphed situations, in concert with the Bell curve.

    I would like to know if this thinking is wrong, as it has been the basis of my moves to the fifth dimension recognition of Kaluza and Klein ( the joining of electromagnetism to gravity ).


    These concepts are in line with wave theory, which, like all natural theories (for example, Darwin’s), pulls together many observations and experiments. Kaluza and Klein’s fifth dimension matches the properties of a magnetic loop


    What kind of Energy does it take to confine a particle?
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  6. Jun 2, 2004 #5
    I thought that the uncertainty principle comes about because when we try to measure the position of a particle, some kind of information has to be sent back and forth. This is usually done with particles like photons. When we do this, the velocity of the particle is then impossible to find with accuracy because we just hit it with a photon, thus changing its velocity. Please tell me anything questionable about what i've said.
  7. Jun 2, 2004 #6


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    Matrixman: that's an example of the uncertainty principle at work, not a description of the principle itself.

    - Warren
  8. Jun 2, 2004 #7


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    Photons exhibit the uncertainty too. It is not just that you do something that to affect the particle and that causes a physical change. For example: in EPR experiments, the 2 particles obey the uncertainty relations. If it were a question of the observation changing the physical situation, why is the other particle affected? Answer: the uncertainty is real and fundamental.
  9. Jun 3, 2004 #8
    Yes I’ve read about the slit experiment many times, that is that light can be either a particle or a wave, depending on whether one slit is open or two?
    It does seem to show the fundamental property of nature being rather unpredictable.
  10. Jun 3, 2004 #9
    I can’t quite put my finger on it but probabilistic determinations seem like it makes some sort of sense…

    I enjoyed reading those links btw.
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  11. Jun 3, 2004 #10
    Then you might enjoy the following.


    If we could see the overall effect like we see that "gif" in the previous links I gave, how would we measure this?

    Unification of gravity and electromagnetism needs a way in which to be described. I have elevated the discussion to include Kaluza and Klein, for this was the result? We are describing Gr with testable proceducres, but if you add quantum theory to the picture how on earth are we going to do this?

    We talk about supergravity and gravity and we know there are more complex points to consider here. What is the measure of the gravity then in that situation? There had to be a way to encapsulate everything? Bubbles can do that in M Theory? How shall we describe it in measure?

    http://www.physics.gla.ac.uk/gwg/geodynamics.html [Broken]
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  12. Jun 3, 2004 #11

    to understand the uncertanty principle, you have to understand the main quantum hypothesis. That energy is distributed in bundles called quanta. This means there is no middle area, it is either one or the other, in the quantum world, eveything is unditermined and had an approximate probability. A good example of that is electron tunneling.
  13. Jun 8, 2004 #12


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    No, what I described has nothing to do with "wave particle" thingy. Note that I was describing diffraction from a SINGLE SLIT, not a 2-slit or multi-slit experiment. So there isn't any ambiguity of which slit a photon passed through.

  14. Jun 21, 2004 #13
    I agree with chen. In fact it is the nature of the particles that make it imposible to measure some special quantities.
  15. Jul 3, 2004 #14
    Wow...are you guys are selling the standard Copenhagen interpretation today or what? Copenhagen would have us believe that not only is the theory complete, but that there is nothing else to know. It makes it all very convenient since then, as you say, the uncertainty is an intrinsic quality of nature and so 'determinism' can be buried in a deep hole as a poor-man's approximation of reality. Then we get to label things like 'free will' as meta-physical (because it certainly doesn't feel very 'causal') and believe it is because quantum mechanics obviously allows that sort of thing.

    But uncertainty and quantization occur with any system where we analyze the limit of what we can and can not know. But because the uncertainty seems to arise in the 'logic' (think 'mathematics) about the situation we convince ourselves the 'fuzziness' must be an aspect of nature and not an aspect of the 'looking at nature'. The uncertainty is tied up in the measurement, the measuring equipment and the 'things' we are measuring. How we may state the uncertainty is determined by our inability to separate (resolve) these components. So our eigen-states contain information about the limit of what we can know about the problem and not just information about the 'thing' we are trying to see.

    So, to resolve this we need new logic and and a new mathematics to go with it. Einstein said we can do this because we can theorize beyond what we can measure.
  16. Jul 3, 2004 #15


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    Yes, nickdanger, if quantum mechanics is wrong, then so are its predictions. We don't need a new logic or a new mathematics, however -- if quantum mechanics is wrong, what we need is experimental evidence that shows it to be wrong. So far, all experiments show it to be true, and it looks like we're stuck with its unsettling predictions.

    - Warren
  17. Jul 4, 2004 #16
    I think that this Quantum Mechanical principle has wrong interpretation. It is one of the Quantum-Mechanical axioms which is known as the Uncertain Complementation Principle by Bohr-Heisenberg. This Principle is consisting the philosophy basis of the absence the values of a coordinate and momentum of the microobjects at the same time before measurement. I think we can changing it by the well-known General Uncertain Inequalities as Quantum-Statistical Principle. The General Uncertain Inequalities been the form Δ(x)Δ(p)≥(h/2) in the Classical Statistical Physics where Δ(x), Δ(p) means the variance (dispersion) of measurement for the quantities x, p rather that uncertainly of its position. Than this theory we can name as Quantum Statistic but not Quantum Mechanic.
  18. Jul 5, 2004 #17
    Dear nickdanger:
    We can never see an electron so how can we improve our knoledge just by improvement of the device or mathematics???
    your answer will help me.
    Thanks in advanced.
  19. Jul 5, 2004 #18
    Warren -
    I don't say quantum mechanics is wrong...only partially right. It is incomplete. And don't quote me proofs that there are no hidden variables, we can't prove that anymore than we can prove that we have the theory of everything.

    I look at it this way. Every theory is incomplete, we just don't know where or we would fix it. We await the theorist that will give us the new idea (think variable) that we missed and that's not just unification, it will be simplification.

    Einstein said he didn't believe that QM was the 'real thing' yet. And as I said, 'Copenhagen' concluded the opposite and moreover that there is nothing more to know. But we have a similar mess in special relativity. Einstein suggested 4 dimensional space-time and that we are at the point where we should stop trying to 'physically' imagine it and simply accept the mathematics...that's exactly what QM finally concludes: We have gotten so much from it, so don't question its validity.

    So look at what we have. Two theories, QM and special relativity that are not reconciled and yet both of them have as their authors last postulate, 'don't question it'.

    Further, both theories have similar arguments in their defense: The correctness of their mathematical predictions when their theoretical basis is doesn't look so complete. You can't tell a technician on a synchrotron that special relativity is wrong, the math works everytime. Yet no one thinks when applied to cosmology that it is working theoretically. The same is true of QM, the predictions of the next particle is always correct. Yet anti-matter and QED are a mess. It's starting to look like correct predictions of 'easily' measureable, observable events doesn't correlate to a complete theory.

    Well anyway, I'm giving you rhetoric when I can't give you any new idea...sorry about that.
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  20. Jul 5, 2004 #19
    Cartuz -
    I think I agree with you. The variables have to be treated as though they are a statistic on a distribution. Of course, this can be interpreted exactly as it is now and we get no further since the probability interpretation already reflects the idea that the theory is "Quantum Statistical".

    But I think if we could take the idea further in some way, we might interpret the variables as representing a statistic on an ensemble, so that we then assume that the 'ensemble' that underlies the theory is a completely causal system, even if we don't know exactly what the ensemble is made of. It's no different in thermodynamics. Our statistic here is kT, we understand that the statistical parameter 'T' is an outcome of some 'velocity' statistic on an entire ensemble of particles even though we have limited ability to measure the velocity statistic directly. It's sufficient that we have made the connection between the statistic 'T' and the statistic 'velocity'. As long as we realize they both refer to an ensemble and not a single particle we we can advance a new theory just because we guessed it - which is what Boltzmann did.
  21. Jul 5, 2004 #20
    To Nickdanger,
    Thanks. Then more. I do not understand why peoples does not choice the way of concretized the hidden variables? Can I choice stochastic gravitation as nonlocal hidden variables? Of course, realization of this idea needs many. But I hope to success in future because I work.
    What do you think about? Thanks else.
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