Portal:Physics/Selected article/August 2007

In physics, the Casimir effect or Casimir-Polder force is a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects. This is sometimes described in terms of virtual particles interacting with the objects, due to the mathematical form of one possible way of calculating the strength of the effect. Since the strength of the force falls off rapidly with distance it is only measurable when the distance between the objects is extremely small. On a submicrometre scale, this force becomes so strong that it becomes the dominant force between uncharged conductors. Indeed at separations of 10 nm - about a hundred times the typical size of an atom - the Casimir effect produces the equivalent of 1 atmosphere of pressure (101.3 kPa).

Dutch physicists Hendrik B. G. Casimir and Dirk Polder first proposed the existence of the force, and formulated an experiment to detect it in 1948 while participating in research at Philips Research Labs. The classic form of his experiment used a pair of uncharged parallel metal plates in a vacuum, and successfully demonstrated the force to within 15% of the value he had predicted according to his theory.

The van der Waals force between a pair of neutral atoms is a similar effect. In modern theoretical physics, the Casimir effect plays an important role in the chiral bag model of the nucleon; and in applied physics, it is becoming increasingly important in the development of the ever-smaller, miniaturised components of emerging micro- and nano-technologies.

Image: Casimir forces on parallel plates.