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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."
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.