 |
There are currently, 330 guest(s) and 0 member(s) that are online.
You are Anonymous user. You can register for free by clicking here
| |
| |
THE CASIMIR EFFECT HEATS UP
Posted on Wednesday, February 07, 2007 @ 23:08:39 UTC by vlad
|
|
For the first time, a group led by Nobel laureate Eric Cornell at the National Institute of Standards and Technology and the University of Colorado in Boulder has confirmed a 1955 prediction, by physicist Evgeny Lifschitz, that temperature affects the Casimir force, the attraction between two objects when they come to within 5 millionths of a meter (approximately 1/5000 of an inch) of each other or less.
These efforts heighten the understanding of the force and enable future experiments to better account for its effects. Tiny as it is, the Casimir effect causes parts in nano- and microelectromechanical systems (NEMS and MEMS) to stick together. It confounds tabletop experimental efforts to detect exotic new forces beyond those predicted by Newtonian gravity and the Standard Model of particle physics.
In their work, the researchers investigated the Casimir-Polder force, the attraction between a neutral atom and a nearby surface.
The Colorado group sent ultracold rubidium atoms to within a few microns of a glass surface. Doubling the temperature of the glass to 600 degrees Kelvin while keeping the surroundings near room temperature caused the glass to increase its attractive force threefold, confirming theoretical predictions recently made by the group's theorist co-authors in Trento, Italy.
What was happening here? The Casimir force arises from effects of the vacuum (empty space). According to quantum mechanics, the vacuum contains fleeting electromagnetic waves, in turn consisting of electric and magnetic fields. The electric fields can slightly rearrange the charge in atoms. Such "polarized" atoms can then feel a force from an electric field. The vacuum's electric fields are altered by the presence of the glass, creating a region of maximum electric field that attracts the atoms. In addition, heat inside the glass also drives the fleeting electromagnetic waves, some of which leak onto the surface as "evanescent waves." These evanescent waves have a maximum electric field on the surface and further attract the atoms. Electromagnetic waves from heat in the rest of the environment would usually cancel out the thermal attraction from the glass surface. However, dialing up the temperature on the glass tilts the playing field in favor of glass's thermal force and heightens the attraction between the wall and the atoms.
(Obrecht et al., Physical Review Letters, 9 February 2007)
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics
News
Number 811 7 February 2007 by Phillip F. Schewe, Ben
Stein,
Turner Brinton,and Davide Castelvecchi www.aip.org/pnu
|
| |
|
Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.
| |
|
|
No Comments Allowed for Anonymous, please register |
|
Casimir Force Gets Hot And Sticky (Score: 1)
by vlad on Wednesday, February 21, 2007 @ 19:17:04 UTC
(User Info | Send a Message) http://www.zpenergy.com | Anonymous writes: from: http://www.scienceagogo.com/news/20070107225851data_trunc_sys.shtml
Physicists
at JILA (a joint initiative of the National Institute of Standards and
Technology (NIST) and the University of Colorado at Boulder) have shown
that when a surface is warmed, the Casimir-Polder force it exerts
becomes stronger.
The Casimir-Polder force, one of the stranger
effects of quantum mechanics, arises from the ever-present random
fluctuation of microscopic electric fields in empty space. The
fluctuations get stronger near a surface, and an isolated neutral atom
nearby will feel them as a subtle pull - much like gravitation.
Understanding the Casimir force is of great importance to
nanotechnology researchers as it influences the design of devices that
rely on small-scale interactions, such as atom chips, nanomachines, and
microelectromechanical systems.
Writing in Physical Review
Letters, the JILA team describe the first measurement of the
temperature dependence of this force. By using a combination of
temperatures at opposite extremes - making a glass surface very hot
while keeping the environment neutral and using ultracold atoms as a
measurement tool - the new research underscores the power of surfaces
to influence the Casimir-Polder force. That is, electric fields within
the glass mostly reflect inside the surface but also leak out a little
bit to greatly strengthen the fluctuations in neighboring space. As a
result, says JILA researcher Eric Cornell, "warm glass is stickier than
cold glass."
The experiments also demonstrate the practical use
of a Bose-Einstein Condensate (BEC), a form of matter first created a
decade ago. In a BEC, thousands of ultracold atoms coalesce into a
"superatom" in a single quantum state. The purity and sensitivity of a
BEC make it uniquely useful as a tool for measuring very slight forces
and changes.
In the JILA experiments, a BEC of about 250,000
rubidium atoms in a magnetic trap was placed a few micrometers from a
glass plate. As the BEC was brought closer to the surface, the
"wiggling" of the condensate was observed over time and the changes in
the oscillation frequency allowed the researchers to calculate the
force. The measurements were made as a laser beam was used to heat the
glass plate to about 330 degrees Celsius, while the surrounding
environment was kept near room temperature. The strength of the force
was shown to be nearly three times larger when the glass was heated.
|
|
|
|
|
