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Cassimir effect on a grand scale

  1. Jun 5, 2006 #1

    I had a question about the Cassimir effect. As I understand it the force is created by an Electromagnetic radiation vaccum created in between two closely spaced metal plates and since only non-half integer wavelengths can exist in this spacing, the plates are drawn slightly closer together...

    Anyhow my question is this: If some planets have iron cores (ie. mercury), would there be a cassimir effect between them even at such vast distances?

    I'm guessing that the effect would be very neglible since the unallowed wavelengths would be extremely long and therefore low energy.
  2. jcsd
  3. Jun 5, 2006 #2

    The force in between the two plates are essentially due to the radiation outside the plates. In fact, when the space in between the plates shrinks very much, there is less room for radiation in between the plates (long wavelengths are cut-off) while nothing changes outside the plates. Therefore, the radiation pressure in between the plates decreases, while the radiation pressure outside the plates remains unchanged. The net result is an -apparent- attraction of the plates.

    Note that the radiations I am talking about is the so-called "vacuum fluctuations". Its existence is a consequence of quantum mechanics. The fact that it has been observed is therefore one more verification of quantum mechanics. And this is why the Casimir effect is so famous, besides the Nobel price.

    Note also that this attration is extremely small. In addition, its increase when the distance decreases is limited by the space available in between atoms. This is why its observability is limited to several atomic distances.

    It is clear that it plays no role in most macroscopic systems, except for very specially prepared system, like plates.
    Last edited: Jun 5, 2006
  4. Jun 5, 2006 #3
    Ok thanks,

    So then would there be ANY effect between two planets with iron cores?
  5. Jul 28, 2009 #4
    Chaos' lil bro Order,

    Good question. I have wondered about this also. I do not know why, in your example, only planets with iron cores would be effected. Why not, say, any two material bodies?

    In fact, many years ago, I wondered if the gravitational force was actually a result of very, very long EM waves exerting a net force such that the two bodies appear to be attracted to each other. I know of no upper limit to the wavelength of EM waves and so there will be wavelengths greater than, say, the distance between those two bodies, for example the Sun and the Earth. Individually their energies will be small, but possibly numerous enough to produce the weak effect that we call gravity.

    However, I understand that The Theory of General Relativity correctly predicts the effect of curvature in time-space and the 'grand scale' Casimir effect I described does not (AFAIK).

    Maybe there is an effect but it's not gravity and presumably it's very small.

    I too, hope that someone will post and set me straight.
  6. Jul 29, 2009 #5
    like lalbatros said, the Casimir force is strongest when the distance between the two objects is incredibly small - like the micron level. Might be wrong, but I don't think you can measure it even if that distance is just a few feet.
  7. Jul 29, 2009 #6
    Interesting you should say that the gravitational force was a result of very long EM waves. Scientists are launching the Laser Interferometer Space Antenna LISA in 2014 to measure such an idea. LISA is an array of 3 crafts seperated by 500,000km which will try to detect the theoretical gravity wave. I know there are some experiements also being done to see if the gravitational constant 'g' veers from its constancy, as one looks at how gravity behaves on very large scales (see 'MOND'), and very small scales (as I recall a group in Washington showed that there was no deviation to 'g' on scales as small as 1/2 mm.)

    About your idea on gravity exerting force on two bodies and making them appear to be attracted to one another. Like you say, relativity has added benefit of including the fact that gravity curves space itself and that gravity on Earth can more properly be thought of as the Earth's gravity pulling space down on us, rather that Earth tugging at our heels.
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