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 has
proposed (Aurel Bulgac, University of Washington, 206-685-2988,
bulgacphys.washington.edu). If experimentally confirmed, this
effect would constitute a new kind of force, akin to the traditional
"Casimir force," the slight attraction between two metallic plates in
a vacuum. The traditional 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 a
simple example, consider 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. (Bulgac and
Wirzba, Physical Review Letters, 17 September 2001)