Degree to which nature abhors a vacuum measured

17 Jun 2002

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 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, Los Alamos National Laboratory, 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, published in an upcoming paper in Physical Review Letters agree with theory to a 5% level. Researchers previously measured the Casimir-Polder force, a different but related effect in which the vacuum creates an attraction between a conducting plate and a neutral atom.