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Observed superposition states

  1. Jul 23, 2010 #1
    Since there have now been directly observed superpositions in laboratory experiments, meaning of course that superposition is not an interpretative issue but an observed aspect of nature, does this have any consequences for certain interpretations of QM? I particurlarly had in mind hidden variables theories such as Bohm's. I am not knowledgeable enough on the field of QM to know for sure.
     
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  3. Jul 23, 2010 #2
    Directly observed? What exactly does the 'directly' mean there? If you explain that, I'll probably better understand the question.
     
  4. Jul 23, 2010 #3
    Strictly speaking the superpostition wasn't directly observed, since that would be impossible. What i am referring to is the more recent experiments which have demonstrated (albeit without direct observation) superposition states, such as the oscillation/non-oscillation of tiny strips of metal that are large enough to be seen with the naked eye. I can't be that specific about the details of such experiments so can't be sure of their exact significance, but i was under the impression that demonstration of superposition for larger and larger objects was to some degree confirming the reality of superposition, elevating it from theoretical conjecture to experimentally confirmed fact. I may however be wrong. Is there any real doubt now as to whether superposition actually happens, and if there isn't then what are the implications of this for various of interpretations of QM.
     
  5. Jul 23, 2010 #4
    Oh. It doesn't seem to have any real implications. People seem to have the false, but totally understandable assumption that if somethign can be seen with our eyes (or other senses) it somehow is more real. This isn't the case. The fact that it's big means nothing. Our eyes and other senses are measurement devices like any other. I don't tihnk the tihng with that oscillating strips (ive seen the article by the way) changes anythign.
     
  6. Jul 24, 2010 #5
    My turn
    Whats about neutral kaons - Kl and Ks, how are they interpreted in BM?
     
  7. Jul 24, 2010 #6

    alxm

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    Quantum-mechanical superpositions aren't a theoretical conjecture. They were in fact observed half a century before quantum mechanics was invented. In 1872 Kekulé suggested that the double bonds of a benzene molecule 'oscillated' back and forth (as seen http://www.chemvc.com/~tim/Benzene Resonance Structures.jpg"). This was necessary to explain the fact that all six bonds were found to be equivalent experimentally. In 1928, using the brand-new quantum mechanics, Linus Pauling showed that this (and all such 'resonance structures') were in fact a quantum-mechanical superposition of states.

    ("Quantum mechanics: Explaining stuff chemists already know, since June 30, 1927." )
     
    Last edited by a moderator: Apr 25, 2017
  8. Jul 24, 2010 #7
    When you say observed do you mean directly observed rather than inferred from the behaviour in the experiments. I was under the impression from the reply from my original post that superpositions were never directly observed. Is this in fact the case and if so my original query still stands. How does directly observed superposition states square with interpretations of QM?
     
  9. Jul 24, 2010 #8

    alxm

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    Again, what does 'directly' supposedly mean? Everything is inferred to some extent.

    You're quite able to observe a superposition. What you cannot do, is perform an experiment to determine whether or not its in state A or B (when it's in a superposition of these two states) and get the result that it's in both. If you 'observe' A or B, you will 'collapse the wave function' and get A or B. That doesn't stop you from measuring any other property, which will not cause such a 'collapse' and getting a result that indicates a superposition. For instance, you can 'directly' observe the charge density on a benzene ring (resulting in something that looks like http://newton.ex.ac.uk/research/qsystems/jones/projects/STM/chden.gif" [Broken]).

    This new experiment doesn't change any fundamental QM, it's just a larger-scale superposition than typically exists.
     
    Last edited by a moderator: May 4, 2017
  10. Jul 24, 2010 #9
    What i am getting at is whether there is any real dispute that superposition, rather than being an issue of interpretation is regarded as an experimenally confirmed fact. For instance violation of bells inequality transcends any specific interpretation, and disregarding an extreme minority of fringe scientists is regarded as how nature behaves. It is impossible in principle that local reality can exist based on the results of confirmed and repeated observations. Is quantum superposition the same in this regards? Is it a matter of logical necessity that any future version or interpretation of QM must incorporate superposition in the same way that it would have to incorporate non-local reality (or local non-reality).
     
  11. Jul 24, 2010 #10

    alxm

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    No, superposition is an experimentally confirmed fact that has never been in question.
    Only what the wave function 'is' and how this gives rise to the superposition (either being e.g. a genuinely indeterminate state as in 'mainstream' QM, or a statistical ensemble as in the de Broglie-Bohm interpretation)
     
  12. Jul 24, 2010 #11
    Thanks for your reply alxm. Thats exactly what i was trying to verify. Sorry for my very basic questions. I'm not an expert in this field and still trying to get around the very basic features of QM. It is made more difficult sometimes because it seems that in a minority of articles and resources on QM the strangeness of the theory seems to be played down. I am currently seeking to distinguish between aspects of QM that are realistically beyond question and aspects that could potentially be subject to alteration from future interpretations and insights into QM.
     
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