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Casimir effect

  1. Aug 12, 2008 #1
    I still do not understand the Casimir effect, more precisely what causes this. In the usual example of a parallel square plate kept very close to each other in vacuum, the plates feel an attractive force. This is a purely quantum field theoretic effect. My doubts are:

    1. It is said that in vacuum there is no photon in between the plates but all the possible vibrational modes are present. We build an expression out of the quantities h, c and a (plate separation) but the amplitude of any wave do not occur since we are dealing with vacuum. I am not able connect vacuum fluctuation and vacuum polarization with this effect. Can anyone explain.

    2. Why should only the electromagnetic field cause casimir effect? why not scalar/spinor/nonabelian gauge fields?
  2. jcsd
  3. Aug 12, 2008 #2
    The vacuum is awash with electromagnetic waves and various particles, from all sorts of sources, stars etc. In addition it has a high level of energy from the em and particle pairs that pop in and out from the vacuum energy, only constrained by the pairing of energy and time in the uncertainty relationship.
    If you put two plates close together it inhibits those waves and particles, both real and virtual, that need at least a half-wave space to exist. The closer you put them, the more waves etc are excluded.
    Thus there's more energy outside than inside. The difference shows as a force pushing the plates together.
  4. Aug 13, 2008 #3
    So can we apply casimir force to anything or is it a useless 'nice to know' thing?
  5. Aug 13, 2008 #4


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    by all means, they do! but the EM casimir is MUCH stronger, and therefore measurable.

    Well, one might say that everything is "useless" - so I'm not sure how to take that!

    We won't be building bridges with Casimir cranes anytime soon! Nor will we by flying to Mars in a Casimir-powered engine! But it is a physical effect, and it can be measured, and it might have something to do with things like the cosmological constant or stabilization of extra dimensions in string theory, or it might be important for nanotech devices, or who knows what else.

    So sure, it's "useful".

    Unless you couldn't care less about such things...
  6. Aug 13, 2008 #5
    We should consider how to get energy out of the vacuum in a usable form. Casimir plates are a 'one shot' source of energy - now, how to make that a continuous source.
  7. Aug 17, 2008 #6

    Vanadium 50

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    You can't. The energy you "get out" of the Casimir effect was put in when you configured the plates. It's ordinary potential energy, nothing more, nothing less. You can't get any more energy out than you put in.
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