Talk:Casimir effect
|
|
How big are theses forces ? Can they be sufficiant in order to enable to separate the two plates ?
- If you mean, to keep the plates apart from each other, overcoming gravity between the two? or overcoming the gravity of one on top? Hardly, since the force can only attract the two plates. If you mean, to oppose gravity enough to keep one on the bottom up against gravity (hardly what I'd call "separating", but just in case), it's hypothetically possible, for thin enough plates close enough together, but not in a useful, let's-use-this-for-antigravity kind of way. -- John Owens 04:45 Apr 9, 2003 (UTC)
- It says you can make them repulse as well. - Omegatron 20:24, Aug 16, 2004 (UTC)
- In certain configurations, not parallel plates. For example, it can be repulsive inside an enclosed sphere - but not enough to break apart spheres of almost any known composition. Even if some configuration were found where it was repulsive between two surfaces not bonded to one another, the separation would be fairly tiny: by the time the surfaces got a few microns apart, the force would drop to effectively zero.
Is this supposed to use permittivity or permeability for the first variable on the right side of the equation? Ever since the equation was introduced in the history, it's been <math>\eta<math>, eta, but the only use for that in electromagnetics is measuring the electromagnetic moment, which I really don't think is what belongs there. Permittivity uses <math>\epsilon<math>, epsilon, the other Greek 'e', so I suspect that's what was meant; permeability uses <math>\mu<math>, mu. -- John Owens 04:47 Apr 9, 2003 (UTC)
Here's a quote from The role of the Casimir effect in the static deflection and stiction of membrane strips in microelectromechanical systems (MEMS), Journal of Applied Physics, Volume 84, Number 5, September 1998:
- η depends on the dielectric permittivities of the plates and of the medium between them ( η = 1 for perfectly conducting plates with vacuum between them).
I found it at http://www.quantumfields.com/aip98.pdf. η appears to be a dimensionless quantity. -- Heron
| Contents |
Constants
Isn't <math>\hbar<math> the Dirac's constant, equals <math> \frac h{2 \pi}<math>?
- BW from it.wikipedia August, 3, 2004
Magnetic dipoles???
"Similarly, fluctuations in the electronic structure of molecules cause transient magnetic dipoles which lead to the Van der Waals force."
- The van der waals and london force articles do not mention magnetic dipoles. They seem to refer to electrostatic dipoles, which is what I was under the impression of as well. - Omegatron 20:24, Aug 16, 2004 (UTC)
Speed of light
Doesn't suppressing the vacuum fluctuations also increase the speed of light slightly? About how large is this effect? --Carnildo 06:27, 19 Jan 2005 (UTC)
ships
whoever wrote the bit about ships gets a big gold star. that's cool! - Omegatron 18:13, Apr 3, 2005 (UTC)
- Glad you like it :) Taken from a lecture (http://www.gresham.ac.uk/event.asp?PageId=4&EventId=258) by John Barrow at Gresham College earlier this year. -- ALoan (Talk) 10:27, 18 May 2005 (UTC)
application through technology
I would assume in the future that materials (plates) can be produced for a repulsive effect, it would be the to the benefit of these plates to be able to change in material structure dynamically to interact with different materials encountered over time during the repulsion phase of movement, and to increase or decrease repulsion energy strength.
- Parallel plates can't repulse. That's a fundamental property of the physics involved, which won't change with technology. A quick research seems to indicate it's only repulsive in enclosed spaces - hollow spheres or the like - but I'm not finding enough data to be sure that's the only case. It may simply be that no one's thoroughly investigated this yet. Even if there were an alternate geometry where plate-like structures repulse - say, if the plates were covered with hollow half-spheres - the need to keep them close to keep the repulsion going would mean this would mainly be useful for "reduced friction" systems, like magnetic levitation but with specially-shaped surfaces instead of magnets.
sum of positive integers
Can somebody fix the part where it's stated that the sum of positive integers is -1/12? This is of course not valid when renormalization is not used. AFAIK this is results from taken the difference of the sum of posivive integers and the integral from zero to infinity of x dx.
you could fix it yourself, click on edit
Hawking radiation "analogy"
What does Hawking radiation have to do with an analogy of the Casimir effect? This should be explained or removed from the article. -D. Estenson II 12:25, Jun 23, 2005 (UTC)