Physicists solve sticky problem with levitation


Aug 6, 2007

A WAY of making tiny objects levitate by reversing a mysterious force of nature has been proposed by two physicists at a Scottish university.

It centres on a phenomenon called the "Casimir force", which was predicted by quantum physicists in 1948 although it was first measured by scientists just ten years ago.

The force is caused by a quirk of nature which, at tiny scales, enables particles to pop into existence from nowhere.

This creates a force which will push together two objects placed very close to each other. It can also be demonstrated by a gecko's ability to stick to a surface with just one toe.

The Scottish pair's theory is now being examined by a leading American scientist, who may put the ideas into practice.

The theory will not enable people to fly like Peter Pan, but it could revolutionise nanotechnology and the design of micro-machines.

Generally, the Casimir force has no effect on everyday life and can be ignored. But it is extremely important when trying to develop tiny switches and micro-machines, since their components tend to stick to each other.

Professor Ulf Leonhardt and Dr Thomas Philbin, of St Andrews University, believe they have now worked out a way of reversing the Casimir force so that it repels instead of attracts.

Their discovery could ultimately lead to frictionless micro-machines with moving parts that levitate.

Prof Leonhardt said: "The Casimir force is the ultimate cause of friction in the nano-world, in particular in some micro-electromechanical systems.

"Such systems already play an important role - for example tiny mechanical devices which trigger a car airbag to inflate or those which power tiny 'lab on chip' devices used for drugs testing or chemical analysis.

"Micro or nano-machines could run smoother and with less or no friction at all if one can manipulate the force."

The solution to the Casimir problem is to sandwich a "perfect" lens between two objects. Such lenses, early versions of which have already been made, exhibit "negative refraction" and bend light in the opposite direction from a normal lens.

The peculiar properties of a perfect lens could lead to a reversal of the Casimir effect, say the theoretical physicists.

Other scientists are already sitting up and taking notice of their research, which is due to appear in this month's edition of the New Journal of Physics.

Dr Frederico Capasso, of Harvard University in the United States, has also been working on ways to manipulate the Casimir effect. Dr Philbin said: "We've shown him our work and he's very interested."

However, the St Andrews-based scientists say there is no likelihood in the foreseeable future of humans being able to levitate.

Prof Leonhardt said: "At the moment, in practice it is only going to be possible for micro-objects with the current technology, since this quantum force is small and acts only at short ranges.

"For now, human levitation remains the subject of cartoons, fairy tales and tales of the paranormal."