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WE鈥橠 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. 鈥淭his should help
us exploit this fundamental force on a tiny scale,鈥� 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鈥檛
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鈥檛 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鈥檛 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鈥攄ramatically demonstrating that bizarre quantum goings-on really
can affect large-scale objects in the 鈥渞eal world鈥�. But pushing plates together
isn鈥檛 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鈥檛 get out any more energy than you put in, but it鈥檚 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 鈥渄ynamic Casimir effect鈥� that moves plates back and forth.

The team鈥檚 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 鈥渃urled up鈥� on a tiny scale. 鈥淲e should be able to place
limits on the size of these effects,鈥� says Mohideen.