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Scale Models Can "Compute" Casimir Forces
KentuckyFC writes "Place two conducting parallel plates a few nanometres apart and the well-known but difficult-to-measure Casimir force will push them together. The force depends crucially on the shape of the plates but nobody is exactly sure how. That's because calculations with anything other than flat plates are fiendishly difficult and measurements are even harder. Now a group at MIT has come up with an ingenious new way to investigate Casimir forces. What the team has noticed is a mathematical analogy between the Casimir force acting on microscopic bodies in a vacuum and the electromagnetic behavior of macroscopic bodies floating in a conducting fluid. Their idea is to build a centimeter-scale metal model of the system they want to investigate, place it in salt water, and bombard it with microwaves and see what happens. The team says the experiment does not measure the force on the scale model but instead a quantity that is mathematically related to the force. So the experiment is not a simulator but actually an analog computer that calculates the force (abstract). What's exciting is that the method should for the first time give researchers a way of testing nano-machines designed to exploit the Casimir force."
The way the Casimir force works is that when you put smooth plates very very close together, they are pulled closer.
This is posited to be caused by pairs of virtual photons which spring into existence and annihilate constantly.
When you put the plates close enough together, there's not enough room for photons to appear between them. Therefore there is theoretically more of a vacuum between the plates than outside. As we all know, vacuum's suck so we get a force pulling the plates together.
Except that it is somewhat inaccurate. The correct explanation is that only photons of certain frequencies can exist in the space between the plates, while elsewhere you can have photons of any frequency.
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