Thermal Casimir Effect Observed For The First Time

I'm always astounded by these unbelievably delicate experiments that can detect such minuscule effects. It seems that for the first time since it was theorized by Landau, the thermal version of the Casimir effect has now been observed[1].

Whereas zero-point fluctuations occur at temperatures right down to absolute zero, an electromagnetic field also experiences an increasing number of thermal fluctuations at higher temperatures. In 1955 the Russian physicist Evgeny Lifshitz predicted that these fluctuations should have a similar effect on radiation pressure, leading to a thermal Casimir force.

Now at Yale University, Lamoreaux has teamed up with Alexander Sushkov and colleagues to measure the thermal Casimir force for the first time. Instead of using two parallel plates, the team looked for the force between a gold-coated plate and a sphere. This is the favoured method of measuring the Casimir force because aligning a sphere and plate is much easier than having to precisely line up two parallel plates.

A wonderful accomplishment!

Zz.

[1] A. O. Sushkov et al., "Observation of the thermal Casimir force", Nature Physics doi:10.1038/nphys1909. (full citation will be included once it is available)

High Heels, Physics, and Finance

While we have seen Physics and Finance being mixed, it isn't everyday that we see high heels and physics being mentioned in the same breath. But that's what is happening in this profile of a physicist who have made that jump into the world of finance, but still try to retain some feminine quality.

At work, Debbie Berebichez is a quantitative risk analyst. On her own time, she's the Science Babe. She's also an inspiration to young women interested in righted-brained careers, including finance.

It's good that, even though she has left the science world, she is still dedicating her effort towards encouraging more female into science. The timing of this article is also rather appropriate, because I'm in the middle of running the contest to find the most attractive physicist. Wonder if someone will nominate this "science babe"? :)

Zz.

Critical Casimir Effect

OK, so I didn't know that there's a thermodynamic analog of the Casimir effect, called the "critical Casimir effect". So this is definitely fascinating.

When two conducting plates are brought in close proximity to one another, vacuum fluctuations in the electromagnetic field between them create a pressure. This effective force, known as the Casimir effect, has a thermodynamic analog: the “critical Casimir effect.” In this case, thermal fluctuations of a local order parameter (such as density) near a continuous phase transition can attract or repel nearby objects when they are in confinement.

You can read more about it by getting the actual paper from the link given. I definitely will have to dig up the references in here to catch up on this.

Zz.

The Casimir Effect from a Condensed Matter Perspective

I didn't have time yet to read this paper carefully, but I thought I should still pass it along in case people missed it. It is a take on the Casimir effect but from the point of view of condensed matter physics.

Abstract: The Casimir effect, a key observable realization of vacuum fluctuations, is usually taught in graduate courses on quantum field theory. The growing importance of Casimir forces in microelectromechanical systems motivates this subject as a topic for graduate many-body physics courses. To this end, we revisit the Casimir effect using methods common in condensed matter physics. We recover previously derived results and explore the implications of the analogies implicit in this treatment.

It has been accepted for publication in AJP.

The first part is quite useful, because it covers the basics of the Casimir effect. And for those of you who can't find a use for all those complex calculus stuff you learned in math classes, such as contour integral, well here's the proof of one of their use now.

Zz.

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".

Zz.

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

Direct Measurement of Critical Casimir Forces

This is an amazing work. A group of physicists in Germany has made a "direct" measurement of the critical Casimir forces[1]. I suppose this is as direct as it can get, as of now.

There is a News and Views coverage of this paper in the same issue of Nature, and also on the Physics World website.

Zz.

[1] C. Hertlein et al, Nature v.451, p.172 (2008).