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Re: Question on Repulsive Casimir Force.



The Casimir effect is a well known Physical phenomenon. Basically if we have
two highly flat plates separated by a small distance we can measure an
attractive force between the plates. This is due to the fact that virtual
particles whose wavelengths exceed the distance between the plates are
excluded from existing between them causing the vacuum energy to be lower
between the plates than outside the plates. Since we define the vacuum as a
zero point energy we can say we have negative energy density in the region
between the plates.
However it turns out that if we replace the plates with objects with a
highly curved surfaces we actually observe repulsive forces when these two
objects are brought close together. It would seem curved surfaces enhance the
number of virtual particles possible between the objects as compared to the
vacuum. Can anyone explain how this could be?
Also we also get repulsive Casimir effects if the dielectric constant of
the space separating the plates has a value greater than the dielectric
constant of one plate and less than the other plate. What could be the
explanation for this? Any help would be appreciated.

Bob Zannelli

Hi, Bob,

It turns out that the Casimir force is quite complicated and
it is difficult to come up with a simple explanation which determines
the sign of the force, even for perfectly conducting bodies. The
situation is even worse for dielectric bodies and media which require
the Lifshitz theory.
Here are some good references to check out:

"Essentials of the Casimir Effect and its Computation," E.
Elizalde and A. Romeo, Am. J. Phys., Vol. 59, 711 (1991).

"Resource Letter CF-1: Casimir Force," S. K. Lamoreaux, Am.
J. Phys., Vol. 67, 850 (1999).

"Repulsive Casimir force as a Result of Vacuum Radiation
Pressure," V. Hushwater, Am. J. Phys., Vol. 65, 381 (1997).

"Casimir Forces," P. W. Milonni and M.-L. Shih, Contemporary
Physics, Vol. 33, 313 (1992).

"The Quantum Vacuum," P. W. Milonni (Academic Press, 1994).


Dennis

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