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The Casimir Effect
HobbySpacer writes "A recent article in Physics World provides a lucid description of the the Casimir effect, which is an attractive force between two surfaces caused by electromagnetic fluctuations in the vacuum. The article discusses some practical application such as the nanotech machines mentioned here earlier."
Physicists are able to take into account all the forces interacting between two objects. It is exactly this precise accounting that led Casimir to investigate the experimental results that were contrary to their predictions.
Gravity is proportonal 1/d^2, while the Casimir force is proportional 1/d^4. Therefore, the Casimir force is much stronger at smaller distances, but practically non-existant at larger distances. As you halve the distance between two objects, the gravity increases by 4 times, but the Casimir force increases by 16 times.
The other force they mentioned is the Van der Waals force, which is really an electric force caused by the polarization of atoms and molecules at very small distances.
At the scale they were dealing with, the mass of the objects was so small and the distances so short that the Van der Waals force and the Casimir force was much much greater (>>) than the force of gravity.
The radical sect of Islam would either see you dead or "reverted" to Islam.
I'm pretty sure that the Casimir force was originally "discovered" as a natural consequence of quantum field theory. It was only recently (something like two years ago) that it was first measured by an experiment at Los Alamos. It was very exciting when it was measured because this aspect of quantum field theory predicts that the vacuum of space contains an infinite background energy and that the Casimir force is actually due to the charged plates restricting the wavelenghts of photons which could be created and anhillated by the vacuum. By imposing this boundary condition, the pressure from these photons on the inner surfaces of the plates is less that the pressure on the outer surfaces of the plates and thus the force pushing the plates together.
Yes. That is exactly what is happening. However gathering energy from such a source is going to be almost impossible. Just like thermodynamics breaks down on a very small level, so does quantum mechanics. You get to a point where nothing can be predicted, things are being created and destroyed, conservation of energy is violated constantly, and all the laws of physics are turned upside down and become meaningless traffic laws. But if you scoot back and look at the larger picture, you'll see that there is a pattern to this madness. You see how a photon was created and destroyed, but how it really was "moving" from one localized area to the next, and it really was a "real" photon, transferring energy from one spot to the next. It has a life beyond the small localized areas. While at this level, things aren't as predictable as you hope (which hole did the photon travel through?), it is still predictable to a large degree. Then you scoot back some more, and the probablities begin to add up, and things begin to become predictable with high accuracy. The laser beam doesn't change course, the people around you don't vanish and reappear, and you can be sure that there is going to be a sunrise tomorrow. The point is, even in thermodynamics, you can get violations of energy conservation -- or so it seems. The problem is that you were only looking too close at what was happening, and by looking to close, things don't make "sense" anymore. Things are truly random. However, the rolling of those millions and billions of dice end up with predictable results. Gathering energy from these statistical anomolies is going to be as possible as predicting with high accuracy the roll of a die. Until you can sit on the throne of Einstein's God who doesn't roll dice, it will be impossible.
The radical sect of Islam would either see you dead or "reverted" to Islam.
Confusion would be an excellent description. What in Heisenberg's name are you driving at here? The London force or dipole dispersion force varies as 1/r^6, where r is the separation radius.
The Casimir effect between two parallel uncharged plates in a vacuum at zero kelvin is given by:
pi^2 h-bar c
F = ----------- A
240 r^4
A = area of the plates and r is the separation distance.
The Van der Waals interaction can be considered and computed as a semi-classical electrostatic effect. The Casimir effect, although sometimes referred to as a "long-range Van der Waals effect" is fundamentally a quantum concept as shown by the appearance of h-bar in the equation above.
As you indicate, both forces follow a power law, but the Casimir effect will appear, again, between "neutral, conducting" plates at absolute zero, i.e. in a configuration where electrostatic forces due to charge distribution are not present, and the power relationship differs by an order of magnitude.
So the two forces are fundamentally different conceptually and similar in that they both describe attractive forces between objects. However the latter similarity would also allow you to say that casimir == ferromagnetism if that is the only metric.
Imagine a "vacuum" with two metallic (reflecting) plates in it, sitting near each other. The vacuum isn't pure. Photons could exist in it, momentarily, as governed by Heisenberg's Uncertainty Principle, wherein the energy of the photon is inversely proportional to the time it exists. Gamma rays would exist for a short period of time, radio waves much longer. Eventually, the Universe checks its books and corrects the accounting error, the photons go back to non-existence - conservation of mass-energy is upheld.
Here's where it gets weird. The photons kinda-sorta existed (virtually), so they kinda sorta could exert an influence. Whoa. Strange.
Next, only certain frequencies are allowed. The frequencies allowed to "kinda sorta exist" are modal, that is, they have to terminate with a node on one of the plates. So, clearly, you can't have gigantic radio waves between these two plates - radio waves are meters in length, they're too big to fit between the plates. You can have some blue photons, and all the gammas you can handle.
Meanwhile, on the OTHER side of the plate, you get all of the radio waves you want - you have an entire universe to stuff them in! And the blue photons, and all the gammas you can handle. So ... there's just a few more potential electromagnetic waves (virtual photons) on the OUTSIDES of the plates than there are on the INSIDE of the two plates - this leads to a net push of the plates together.
But that's not all - the force experienced by those two plates depends on a lot of things. In the symposium in question, it was demonstrated that, with the right geometry (concentric shells, weird flower-like arrangements) that the Casimir effect can be repulsive.
In short, it isn't always 1/r^4, and it isn't always attractive.
Now, for those of you who would like a free lunch out of this effect, it's not going to happen. Why? 'cause you have to push the plates back apart to complete a full cycle for any "free energy" machine you would like to devise. It's like a waterfall - you only get that energy from something falling down ONCE.
No, it doesn't have anything to do with the Higgs boson. No, it doesn't come from some folded-up dimension. No, it doesn't have to do anything with gravity at small ranges. C.E. results entirely from QM + EM.
On an aside, correcting other bits of non-information in these posts: no, photons are not influenced by charge. No, photons do not constantly form electron-positron pairs - most photons do not have enough energy to form an electron-positron pair - do the math if you don't believe me. The refractivity of materials comes from something entirely different. Photons don't have a non-zero rest mass - they never "rest" (discussion of the Bose-Einstein condensate usually ignores that the information about the photon was stored) - and many experiments have placed upper limits on the proper mass of a photon as being no greater than 10^-50 grams.
I'm aware that the Casimir effect can appear as a repulsive force, J. Ambjørn and Stephen Wolfram wrote a detailed paper that can be found at:
c le s/physics/83-properties1/
6 .p df
;-) So stating a bald equivalence between these two well known forces is a little misleading.
;)
http://www.stephenwolfram.com/publications/arti
Originally in Annals of Physics 147 (1983). I also came across an interesting paper in the June Physical Review Letters, by P. Bruno at the Max Planck Institute, available at:
http://www.mpi-halle.mpg.de/~bruno/publis/2002_
on calculating a magnetic Casimir effect for parallel ferromagnetic plates, which shows the resultant effect as antiferromagnetic.
As classical electromagnetism derives from an underlying quantum formulation, I concede that that Van Der Waals interactions are essentially classical manifestations of an underlying quantum explanation. However the "classical" vacuum parallel plate Casimir effect is one of those quantum manifestations, like superfluidity, that would not be expected or predicted from "common sense" physics. Van Der Waals forces, calculated without recourse to quantum effects, serve to explain all manner of chemical interactions and phase transitions, and, apparently, the adhesion of geckos to walls
(Note: I am not a physicist, I only play one on Slashdot