title: Opposites attract: a theorem about the Casimir Force.
abstract: We consider the Casimir interaction between (nonmagnetic) dielectric bodies or conductors. Our main result is a proof that the Casimir force between two bodies related by reflection is always attractive, independent of the exact form of the bodies or dielectric properties. Apart from being a fundamental property of fields, the theorem and its corollaries also rule out a class of suggestions to obtain repulsive forces, such as the two hemisphere repulsion suggestion and its relatives.
authors.affiliation: Department of Physics, Technion, Haifa, Israel.
authors.forename: Oded
authors.initials: O
authors.lastname: Kenneth
authors.forename: Israel
authors.initials: I
authors.lastname: Klich