# Repulsive Casimir Forces

## Main Question or Discussion Point

I need to do a basic talk for a few minutes on Casimir forces and their effects on nanotechnology.

I kind of understand the basic concept of Casimir forces intuitively, as less virtual particles can exist in the standing wave state between the plates than can exist outside of the plates and hence the two plates are driven together. This has a classical analogue in the motion of two ships at sea that are arranged like the two plates, as it was known that the ships would approach one another.

I also understand that it is possible to create a repulsive Casimir force by controlling the optical properties of the plates and the mediums they are in. Is there any intuitive way to understand these repulsive Casimir forces or any way of easily explaining the mathematical description? If so, this would be greatly appreciated as I would like to mention how such repulsive forces would help to reduce static friction in nanotechnology.

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Has the force caused by the Casimir effect been measured experimentally? If so, does it give us a value for the vacuum density?

I also understand that it is possible to create a repulsive Casimir force by controlling the optical properties of the plates and the mediums they are in.
No way. Really? Do you have a reference?

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Born2bwire
Gold Member
I need to do a basic talk for a few minutes on Casimir forces and their effects on nanotechnology.

I kind of understand the basic concept of Casimir forces intuitively, as less virtual particles can exist in the standing wave state between the plates than can exist outside of the plates and hence the two plates are driven together. This has a classical analogue in the motion of two ships at sea that are arranged like the two plates, as it was known that the ships would approach one another.

I also understand that it is possible to create a repulsive Casimir force by controlling the optical properties of the plates and the mediums they are in. Is there any intuitive way to understand these repulsive Casimir forces or any way of easily explaining the mathematical description? If so, this would be greatly appreciated as I would like to mention how such repulsive forces would help to reduce static friction in nanotechnology.
The description using virtual photon radiation pressure is the most intuitive I have found for basic explanations. There are many ways of calculating the Casimir force but I feel they are conceptually more diffcult to understand.

Has the force caused by the Casimir effect been measured experimentally? If so, does it give us a value for the vacuum density?
Yeah, there have been several experimental measurements and verifications of the Casimir force, starting in the 1990's. I recall though that the dielectric Casimir force was experimentally described using gases back in the 1950's or so, which prompted Lifgarbagez to develop his theory for dielectrics.

S. K. Lamoreaux, "Demonstration of the Casimir Force in the 0.6 to 6 µm Range", Phys. Rev. Lett. 78, 5–8 (1997)

The above is typically the paper cited as one of the first measurements of the force. By vacuum density, do you mean the electromagnetic vacuum energy spectrum? Casimir force doesn't provide a means of measuring the energy spectrum because it only reacts to changes in the energy. We can always renormalize the vacuum energy to be zero and we will still have the same vacuum fluctuation behavior that gives rise to the Casimir force.

No way. Really? Do you have a reference?
Yeah, it's been discussed in papers before though it requires dielectrics for it to occur from what I have read and the geometries can be a bit unusual. I think I recall one configuration being spherical dielectric inside another spherical dielectric shell.