PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 300 December 20, 1996
by Phillip F. Schewe and Ben Stein
THE CASIMIR FORCE, a 1948 theoretical prediction in which
the seemingly desolate "vacuum" creates a tiny force between a
pair of conductors, has been precisely measured for the first time.
According to quantum mechanics, empty space (the "vacuum") is
not truly empty but instead contains fleeting electromagnetic
waves and particles that pop into and out of existence. However,
when the vacuum is bounded by a pair of conducting surfaces,
the only electromagnetic waves that can exist are those with
wavelengths shorter than the distance between the surfaces. The
exclusion of the longer wavelengths results in a tiny force
between the conductors. To measure the Casimir force, Steve
Lamoreaux, now at Los Alamos (505-667-5005), employs a
torsion pendulum, a twisting horizontal bar suspended by a
tungsten wire. The attraction between a gold-plated sphere and a
second gold plate causes a small twisting force in the bar. By
applying a voltage sufficient to keep the twisting angle of the bar
fixed, Lamoreaux determined the force caused by the attraction
of the plates. His results agree with theory to a 5% level.
(Upcoming paper in Physical Review Letters.) Researchers
previously measured the Casimir-Polder force (Update 122), a
different but related effect in which the vacuum creates an
attraction between a conducting plate and a neutral atom.
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