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Thread: how real is ZPE (for quantum fields)

  1. #1 how real is ZPE (for quantum fields) 
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    As an autodidact i always though that the Casimir effect showed the existence for zero point energy in empty space without doubt.
    But then i read more about it and it looked like the existence the ZPE for quantum fields is not without doubt!

    The best article i could find about this is: http://www.astrophys-neunhof.de/mtlg/se08011.pdf

    So, the Casimir effect can also be predicted using "oscillation modes of material systems with a finite number of degrees of freedom" and does not proof the existence of the ZPE for quantum fields.

    I do find this a very interesting subject so i wondered if anybody knows if there are experiments possible to prove or disprove the existence of the ZPE for quantum fields.
    Last edited by physpruts; 04-16-2014 at 07:03 AM.
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    I don't think vacuum energy is in doubt. The cosmological constant is "the value of the energy density of the vacuum of space". But as far as I know the Casimir effect doesn't demonstrate it. Think of an ocean. Vacuum energy is represented by the depth of this ocean. But the Casimir effect is merely detecting the tiny ripplets on its surface.
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  3. #3  
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    Interesting question. In my opinion it is actually central to the understanding of QM. See this article about how the Shrodinger equation can be derived from these random fluctuations.
    https://www.researchgate.net/profile...&inViewer=true
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    Quote Originally Posted by Farsight View Post
    I don't think vacuum energy is in doubt. The cosmological constant is "the value of the energy density of the vacuum of space". But as far as I know the Casimir effect doesn't demonstrate it. Think of an ocean. Vacuum energy is represented by the depth of this ocean. But the Casimir effect is merely detecting the tiny ripplets on its surface.
    I understood that there is a huge difference between the measured value of the cosmological constant (almost zero) and the quantum field energy (when cut-off at planck length: about 1E120 difference). So, when ZPE is real, it seems logical that the detected cosmological constant only represents the energy of the ripples on its surface.

    On the other hand, the casimir effect shows a force/energy curve more or less consistent with the absolute value of the (absurd high?) ZPE level! (at least for frequencies for which the plates are more or less perfect conductors)

    This leaves the question whether the casimir effect shows interaction with the QFE or if it is only a quantum electro dynamic effect. Perhaps the quantum electrodynamic effects for calculating the casimir force without the ZPE are just a manifestation of interaction with the ZPE?
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  5. #5  
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    Quote Originally Posted by Jilan View Post
    Interesting question. In my opinion it is actually central to the understanding of QM. See this article about how the Shrodinger equation can be derived from these random fluctuations.
    https://www.researchgate.net/profile...&inViewer=true
    Unfortunately i can not read that link.
    I also thought that the existence of ZPE was without doubt. But than i read that it could also be seen as a mathematical bookkeeping trick for explaining other effects and that the casimir effect could also be explained without reference to ZPE.
    Last edited by physpruts; 04-18-2014 at 08:11 AM. Reason: typo
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  6. #6  
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    This article is along similar lines, but not quite so good.
    http://www.ptep-online.com/index_fil...1/PP-27-06.PDF

    The original idea belongs to a guy called Nelson, here is his paper from 1966
    http://dieumsnh.qfb.umich.mx/archivo...Nelson%20a.pdf

    Of course back then there was no talk of zero point energy to explain the random fluctuations!
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  7. #7  
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    Quote Originally Posted by physpruts View Post
    I understood that there is a huge difference between the measured value of the cosmological constant (almost zero) and the quantum field energy (when cut-off at planck length: about 1E120 difference). So, when ZPE is real, it seems logical that the detected cosmological constant only represents the energy of the ripples on its surface.
    I wondered when the vacuum catastrophe would come up! The point I was trying to make was that vacuum energy is not in doubt. Even though the amount of it is. There's another problem here in that the cosmological constant is totally at odds with conservation of energy.

    Quote Originally Posted by physpruts View Post
    On the other hand, the casimir effect shows a force/energy curve more or less consistent with the absolute value of the (absurd high?) ZPE level! (at least for frequencies for which the plates are more or less perfect conductors)
    The Casimir effect is rather weak. There's some confusion with all this. To get across what I mean, have a look at wikipedia. See this:

    "In a simplified view, a 'field' in physics may be envisioned as if space were filled with interconnected vibrating balls and springs, and the strength of the field can be visualized as the displacement of a ball from its rest position".

    Imagine space filled with balls and springs, but compressed springs. If all springs are compressed by some huge degree there's a lot of vacuum energy present. But if all the balls are motionless, it looks like there's none. Then if some of the balls are being displaced, that doesn't tell you how compressed those springs are.

    Quote Originally Posted by physpruts View Post
    This leaves the question whether the casimir effect shows interaction with the QFE or if it is only a quantum electro dynamic effect. Perhaps the quantum electrodynamic effects for calculating the casimir force without the ZPE are just a manifestation of interaction with the ZPE?
    IMHO the Casimir effect is just the tip of the iceberg. The ripplets on the sea.
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  8. #8  
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    Quote Originally Posted by Farsight View Post
    IMHO the Casimir effect is just the tip of the iceberg. The ripplets on the sea.
    The casimir force is about 8 mN/m for a plate distance of 1m, and about 5N/m for a distance of 200nm.
    This does not seem much, but it results in a energy density of 8mJ/m (for 1m, actually negative and relative to when d).
    This is already quite a lot more than than the measured value of the cosmological constant: 7.3x10-⁷kg/m=6.6x10⁻⁰J/m.

    So i made the conclusion that the casimir force can not be related to the ZPE as measured for the cosmological constant because the energy of ripplets can not be negative.
    But then, according Lifshitz, the casimir force is not related to vacuum quantum fluctuations at all...
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  9. #9  
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    How so? Gravitational energy is negative.
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    On Casimir Force - Scholarpedia i did find the following:

    Thus we are still left with the question of whether the vacuum of free space contains electromagnetic zero point energy. Results from observational cosmology suggest that it does not, due to the enormous amount of energy of the zero point. We might reformulate this question as to one of whether space is simply a map or is an object in its own right? Modern observation implies the existence of a cosmological constant that imbibes space with an intrinsic property. However, given the enormous energy associated with the electromagnetic zero point, we should probably conclude that it does not contribute to the cosmological constant, but is an artifact of the way electromagnetic fields interact with matter; the interaction is such that the field can be treated as having a zero point energy. Of course, this argument is not entirely satisfactory, and the question remains open.
    So i guess nobody knows how real ZPE is.
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    Quote Originally Posted by physpruts View Post
    So i made the conclusion that the casimir force can not be related to the ZPE as measured for the cosmological constant because the energy of ripplets can not be negative.
    I think your conclusion is correct but for the wrong reason. There is no negative energy or negative energy density. Go back to the analogy of the springs and balls. Imagine you compress all the springs to half their length. You expended energy to do that. That's your ZPE. Now imagine I flick the structure and make it ripple. The ripples are your vacuum fluctuations. There is energy to them, but it isn't the energy of the ZPE.

    Quote Originally Posted by physpruts View Post
    So i made the conclusion that the casimir force can not be related to the ZPE...
    Of course not.

    Quote Originally Posted by physpruts
    So I guess nobody knows how real ZPE is.
    Not for sure. But think about where the energy goes when you compress a spring. Not into the atoms. Into the bonds. The space.
    Last edited by Farsight; 04-25-2014 at 09:21 AM. Reason: quoted the wrong sentence before "of course not"
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  12. #12  
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    Good point, you will only be ever to detect energy differences. Who knows how much energy there is there coiled up so to speak!
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