MadSci Network: Physics

Re: Does the Casimir Effect only work in a vacuum?

Date: Wed Nov 17 22:14:33 1999
Posted By: Matthew B. Weyerich, Technical Coordinator,ES&R Dept., CPI Corp.
Area of science: Physics
ID: 941801416.Ph

Hi Brian!

I'm no expert on the Casimir Effect, but I'm pretty sure you have to have 
the vacuum.

(I'll paste links to support my thinking below my answer.)

To quote "Measurement of the Casimir-Polder Force" (Sukenik, Boshier, Cho, 
Sandoghar and Hinds) as printed in Physical Review Letters vol. 70, no.5, 1 
Feb., 1993: "The vacuum field in the vicinity of a …plate is different from 
that of free space".  (Ellipsis mine. The word I left out was "conducting". 
I left it out because other sources emphasize the plates should be 
non-conducting. Others say "charged", or, "uncharged". ) Seems to me, the 
vacuum is the "sine-qua-non" of the whole experiment.

The paper I quote above describes an experiment in which a beam of sodium 
atoms shoots through a V-shaped 1-micrometer cavity between two plates. 
(The experiment measured beam deflection vs. plate distance at the point 
the beam squirted through. See link below.) The authors note they were 
careful to use ground state sodium atoms, as excited atoms could eject 
resonant "real" photons, which would reflect back and perturb the sodium 
atoms in a manner so great as to obscure the Casimir effect.

If one PHOTON can do that, imagine what a rowdy gang of air molecules could 
do! The air you are breathing is composed of gas molecules, which zing 
around the room bumping into one another at a furious rate. They'd do that 
to your plates, too, but in unpredictable ways, even if the air were to be 
"still". If nothing else, air would make for a very noisy and unpredictable 
experiment. (I'm not saying you couldn't make it work. Air molecules move 
through a "vacuum" after all. I just think the introduction of air would 
outstrip our ability to confidently discern the effect in question. Too 
many variables.) 

I've found references to an acoustic Casimir Effect. (I'd think that would 
involve air, or something tangible.) Whether in air, solid, liquid, etc., 
the important thing to note is the people who propose it call it an 
"analogue" to the Casimir Effect. The "true" Casimir Effect is always 
associated with a vacuum, as far as I can tell.

One thing I should pass on: there's a lot of pseudo-science associated with 
"zero-point energy", the Casimir Effect, etc. It's often touted as a source 
of "free energy", but no one has yet made anything of it. You should 
probably keep that in mind as you research this. 

I hope this has helped answer your question in some way. If you have 
further questions, or, if you disagree with my answer, please e-mail me at I'd enjoy learning more about this!

Your MadSci,


P.S. - Sorry to take so long answering. I had to think about this one a 
bit! :)


Paper Reference (See the Notes section & download .PDF files. Don't miss 
anything on the page. Good education here!) http://www.physi

Except for the Casimir Effect, there is "Zero Point" to all of this… (SciAm 
link with good graphics, more links, and some things to think about.):

Do you "hear", Casimir?:  http://asa.

Casimir Effect:  http://

More: http:/

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