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Insights The Vacuum Fluctuation Myth - Comments

  1. Nov 7, 2016 #1

    A. Neumaier

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  2. jcsd
  3. Nov 7, 2016 #2

    A. Neumaier

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  4. Nov 7, 2016 #3
    Nice Insight Arnold!
     
  5. Nov 8, 2016 #4

    Drakkith

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    Nice article!
     
  6. Nov 18, 2016 #5
    But Hawking radiation itself is a myth. All we know about black holes is that there are things that match the description as deduced from billions of miles away.
     
  7. Nov 18, 2016 #6

    Nugatory

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    Only if you're willing to put Hawking's derivation (the real thing, not the heuristic upon which Professor Neumaier is heaping scorn) in the category of "myth".
     
  8. Nov 18, 2016 #7

    Drakkith

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    The same is true of stars, nebulas, exoplanets, galaxies, etc.
     
  9. Nov 19, 2016 #8
    I usually steer away from such insights because to me the specialists writing them assume too much prior knowledge in both the content and notation department.

    This insight I got a lot out of, thank you.
     
  10. Nov 19, 2016 #9
    Those are taken seriously as objects. If a physicist has a new idea about them, it's explored, refined, etc., and goes through an ordinary Kuhnian trial. Ideas about black holes, however, are argued on merely theoretical merit.

    What else would you call it? Already in just the abstract, the remarks about "entropy" are a huge red flag.
     
  11. Nov 19, 2016 #10
    Observed orbital motion around massive objects that appear as black holes of some sort kind of suggest black holes as predicted by GR.
     
  12. Nov 19, 2016 #11

    Vanadium 50

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    False.

    As an example, the "chirp" of GW150914 depends on the horizon radius of the merged black hole. If you don't have a horizon, or have it in another place, the chirp no longer matches the GR predictions.

    Now I will make a prediction - when confronted with the evidence, your reaction will not be "I was wrong". It will be some argument that somehow this doesn't count.
     
  13. Nov 21, 2016 #12


    Minute 48 and 49.
     
  14. Dec 12, 2016 #13
    It was a very strong description. I was curious about a few pieces in your explanation. In, the paper, Direct Observation of Quantum Phonon Fluctuations in a One-Dimensional Bose Gas[1] it is shown that quantum fluctuations result from 'acoustic vibrations'. Lending strong correlation with the analog of the fluctuation in very still and ice cold states. It is then repeated in 2016 [2] as "we prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions.". With analog vibrations having a seemingly strong subadvity for quantum fluctuations and the experiment involving analog hawking radiation of black holes using "dumb holes"[3], we could say the quantum fluctuation is relative to the energy of the black hole. Quantum fluctuations are also observed through the lamb shift [4].
    [1] http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.225306
    [2] http://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.041039
    [3] http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.85.4643
    [4]http://physics.aps.org/articles/v9/139
     
  15. Dec 12, 2016 #14

    bhobba

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    Gee - I always thought it was simply including higher orders and re-normalization.

    Its a total myth that quantum fluctuations, virtual particles yada, yada, yada exist. Its part of the pictorial language that has grown up with Feynman diagrams - but are really just terms in a Dyson series:
    https://en.wikipedia.org/wiki/Dyson_series

    Thanks
    Bill
     
    Last edited: Dec 12, 2016
  16. Dec 12, 2016 #15

    A. Neumaier

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    The paper [4] states: ''It arises because zero-point fluctuations of the electromagnetic field in vacuum perturb the position of the hydrogen atom’s single bound electron.'' The truth - shown by all sources that actually do the calculations - is that the electromagnetic field interacting with the hydrogen atom’s single bound electron introduces radiative corrections into the corresponding Dirac equation. According to standard quantum mechanical perturbation theory, these corrections result in the Lamb shift. Nothing with vacuum fluctuations or ''virtual photons popping in and out of existence'' as your source claims.

    I didn't check the other papers but it is unlikely that they provide harder evidence for what you want to imply.
     
    Last edited: Dec 12, 2016
  17. Dec 12, 2016 #16
    Of course you (and A. Neumaier) are right. However, it is interesting that respectable physicists (most recently, I saw a video lecture by Alan Guth where this happens) very often present their informal reasoning in terms of vacuum fluctuations. It seems like it's a useful heuristic for reasoning about what's possible, even though the mathematical details, when you actually try to calculate things, don't actually resemble the "fluctuation" reasoning much at all.

    For an example from Guth, http://web.mit.edu/physics/people/faculty/guth_alan.html
     
  18. Dec 12, 2016 #17
    They were virtual phonons, and I do not ascribe to the theory that phonons are particles, or even 'virtual particles'. though it is upsetting you didn't check the other papers. These fluctuations were not to be meant as a cohesive description upon one anothers papers. They do certainly outline quantum fluctuations. I don't see how your retort disproves acoustic quantum fluctuations. Considering you didn't take the time to read them nor cite any paper yourself, I find your assessment, illogical.
     
  19. Dec 12, 2016 #18

    A. Neumaier

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    It is a very useful (and historically sanctioned) tool to capture the imagination of an audience without presenting any formula, although it does not resemble at all what happens. The latter is discovered only if one wants to see what the talk means - and one discovers that it means nothing. ''vacuum fluctuations'' are just a buzzword for ''field theoretic effects'', nothing more.
     
  20. Dec 12, 2016 #19

    A. Neumaier

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    Quantum fluctuations are everywhere, but calling an unexcited crystal a quantum vacuum, as the authors of your source [4] do, is quite a misnomer. Analogies don't create truth.

    ''The authors measured an energy shift in the presence of the quantum vacuum, finding a value in good agreement with theoretical expectations. In addition to providing the first quantitative measurement of the phononic Lamb shift, the result confirms the validity of the theoretical framework that describes the effect. ''

    The author measured an energy shift in the presence of a crystal (producing of course an interaction that changes all energy levels), finding a value in good agreement with theoretical expectations. But this sounds too unexciting to be worth reporting.
     
  21. Dec 12, 2016 #20

    Haelfix

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    I'm a little uneasy by some of these discussions, b/c its a little difficult to know what the claim is, and whether its just a matter of terminology. I'm fine with saying the quantum vacuum is a subtle creature, and it's a little hard to define what a 'fluctuation' actually means considering that we are by assumption talking about stationary states (and then there are all the complicated renormalization scheme caveats associated with what we mean by this). However, i'm a little uneasy by the implication that the 'real' thing when properly understood is trivial or empty. That has definitely not been demonstrated.

    The only way you can measure the quantum vacuum, is by doing an experiment, and it's always an inferred counterfactual property (this is what we would measure if we thought the vacuum was trivial or empty). So when people talk about polarizing the vacuum like for the Lamb shift, its basically about feynman diagrams that sort of look like bonafide vacuum diagrams except that there are external legs present, and there is always a strong background field (as well as the presence of a hydrogen atom as a spectator). Of course real vacuum diagrams have no external legs, and there is no background field present, so it is technically true that the presence of a measured nonzero effect for the Lamb shift doesn't necessarily tell us about the nature of the real quantum vacuum.

    Then there is the temptation to think that the nonzero quantum vacuum is then only some sort of perturbative artifact. But this is also wrong. For instance, one can show that instantons can contribute to the QCD vacuum. Also, one of the virtues of supersymmetric theories, is that they are sometimes exactly solvable, and we can actually demonstrate that the vacuum is nonzero in certain cases.

    I guess I don't understand what the claim is specifically.
     
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