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How Empty Spaces Can Exert Forces On Each Other

Empty spaces can exert forces on each other through the action of intervening matter, a US-German team of physicists has proposed.

The team is composed of Aurel Bulgac of the Department of Physics, University of Washington, Seattle, and Andreas Wirzba of the Institut für Kernphysik (Theorie) in Jülich, Germany.

If experimentally confirmed, the effect they propose would constitute a new kind of force, akin to the traditional "Casimir force," the slight attraction between two metallic plates in a vacuum.

Bulgac and Wirzba write: "In 1948 Casimir predicted the existence of a very peculiar effect, the attraction between two metallic parallel plates in vacuum. The existence of such an attraction has been confirmed experimentally with high accuracy only recently."

The Casimir attraction occurs because of the fleeting electromagnetic fields that exist in the vacuum. These fields exert forces on the plates.

In between the plates, however, certain electromagnetic waves cannot reside, namely those with wavelengths larger than the plate separation. This imbalance of electromagnetic forces serves to push the plates together.

In the newly proposed force, two or more cavities (empty regions of space) alter the waves associated with surrounding matter in the form of non-interacting fermions, such as a gas of electrons.

For instance, two hollow spheres separated by a sea of electrons which, according to quantum mechanics, can be considered as rippling waves. If the wavelengths of the electrons are comparable to the dimensions of the spheres, then forces between the empty spheres could result.

The spheres, even though they're separated, can effectively interact because the electron waves bounce back and forth between them. Whether the spheres attract or repel each other depends on the overall effect of all matter waves between them.

Demonstrating this effect is likely to be very challenging. One approach might be to immerse C60 molecules (buckyballs) in liquid mercury. The buckyballs, effectively hollow spheres, could bind to each other through the action of conducting electrons in the liquid mercury.

This new effect could act over an even longer range than the weakly attractive "van der Waals force" between molecules.

(Reference: Bulgac and Wirzba, Physical Review Letters, 17 September 2001)

(Editor's Note: This story is based on PHYSICS NEWS UPDATE, the American Institute of Physics Bulletin of Physics News Number 556, September 13, 2001, by Phillip F. Schewe, Ben Stein, and James Riordon.)

[Contact: Aurel Bulgac]






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