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Getting something out of nothing

New Scientist

WE'D all like to get something for nothing. But harnessing the energy of empty space?

It sounds crazy, but the idea is not so far-fetched, thanks to a strange force that comes out of nothing. Researchers have persuaded this force, called the Casimir effect, to slide tiny gold plates past each other. "This should help us exploit this fundamental force on a tiny scale," says Umar Mohideen, a physicist at the University of California, Riverside.

The Casimir effect depends on the fact that on tiny scales, empty space isn't empty at all. Even a total vacuum is filled with a quantum froth of virtual particles that pop in and out of existence. They don't last long enough for us to detect them directly, but in 1948 the Dutch physicist Hendrik Casimir predicted that if you put two parallel plates close enough together so that the largest particles can't squeeze into the gap, then the net pressure from the extra particles outside would push the plates together.

It took until 1996 for physicists to measure the effect directly-dramatically demonstrating that bizarre quantum goings-on really can affect large-scale objects in the "real world". But pushing plates together isn't much use to anyone, and the effect even threatens to jam up moving parts in micromachines (New Scientist, 17 February 2001, p 22).

Then, in 1997, MIT physicist Mehran Kardar worked out that the shape of the plates could have a startling effect. The Casimir force always acts perpendicular to the plane of the plate, so he reasoned that using corrugated plates should persuade the force to move them sideways past each other.

Last week, Mohideen and his team announced that they had measured this lateral force. They placed two corrugated gold plates a few hundred nanometres apart with their peaks and troughs aligned (see Diagram). When they moved the plates slightly out of alignment, they detected a force of a few piconewtons that pushed them back into position.

You don't get out any more energy than you put in, but it's the first time that virtual particles have been cajoled into doing work in this way. The researchers are now trying to generate other effects, such as a repulsive force and a "dynamic Casimir effect" that moves plates back and forth.

The team's measurements could also pick up signs of other as yet undiscovered fundamental forces, as well as evidence of extra spatial dimensions that some theorists predict are "curled up" on a tiny scale. "We should be able to place limits on the size of these effects," says Mohideen.

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Author: Justin Mullins

More at: http://arxiv.org/abs/quant-ph/0201087

New Scientist issue: 2nd February 2002

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