Thursday, January 08, 2009

Casimir–Lifshitz Effect Causes Levitation

I suppose the big news making its round in the media this week is the work published in this week's Nature of the demonstration of the repulsive Casimir-Lifshitz effect[1] {the link is open for free only for a limited time}.

Casimir's original theoretical design and Capasso's group's experiment are different. Capasso's team replaced the vacuum with a liquid, bromobenzene, and, instead of metal plates, used a gold-coated polystyrene sphere attached to a cantilever, and a silica plate.

The key to the experiment is the dielectric permittivity of each of these materials. This property represents a material's ability to carry an electric field. To get a repulsive force out of the system, the dielectric permittivity of one plate must be higher than that of the surrounding liquid, and the dielectric permittivity of the second plate must be lower than that of the surrounding liquid. "We're talking about a repulsion that is controlled by the ordering of the dielectric properties of the materials, not the shape," says Capasso.

In the set-up used by Capasso's group, gold has the highest dielectric permittivity, followed by bromobenzene, followed by silica. The Casimir-Lifshitz force works so that the liquid is attracted into the gap between the two, forcing them apart.

Capasso used the cantilever attached to the gold-coated sphere to measure the size of the repulsive force. A change in a beam of light reflected off the top of the cantilever signalled movement in the system, and revealed that as the gold sphere was brought close to the silica plate it got pushed back. The results are published in Nature.

I suppose the reason why the media picked it up is the "sexiness" in the story involving "levitation".


[1] J.N. Munday et al., Nature v.457, p.170 (2009).


cometman said...

Does this pass the smell test for you? I saw an article earlier on ScienceDaily about this and it sounds reasonable, since I've read about the Casimir force before.

But they often just post press releases there and a week or two ago I caught one which was bogus about a couple of charlatans claiming they had decoded dolphin language and it was later deleted. Evidently someone didn't do the proper fact checking on it before posting.

Anonymous said...

It never to see if the physics journals/magazines pick it up.

Doug Natelson said...

Cometman - Capasso is a very serious scientist and engineer. He basically invented a fairly revolutionary type of semiconductor laser and is extremely clever. Yes, this is a published, peer-reviewed scientific result.