|MadSci Network: Physics|
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 firstname.lastname@example.org. I'd enjoy learning more about this! Your MadSci, -Matt email@example.com P.S. - Sorry to take so long answering. I had to think about this one a bit! :) Links: Paper Reference (See the Notes section & download .PDF files. Don't miss anything on the page. Good education here!) http://www.physi cs.lsa.umich.edu/bucksbaum/phys512/ 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.): http://www.sciam.com/129 7issue/1297yam.html Do you "hear", Casimir?: http://asa. aip.org/web2/asa/abstracts/search4/asa64.html Casimir Effect: http:// www.pcss.maps.susx.ac.uk/users/markh/RQF1/node33.html More: http:/ /www.worldscientific.com/journals/mpla/135/sitenko.html
Try the links in the MadSci Library for more information on Physics.