Casimir Repulsion between Metallic Objects in Vacuum
Abstract
The Casimir force between two parallel metal plates in vacuum is always attractive. A longstanding question is whether this is generally true for metallic or dielectric objects in vacuum, or whether the sign of the force can be changed by geometry alone. More precisely, can the force between noninterleaved metallic or dielectric bodies in vacuum--that is, bodies that lie on opposite sides of an imaginary separating plane--ever be repulsive? In this Letter, we answer this question in the affirmative by showing that a small elongated metal particle centered above a thin metal plate with a hole, depicted in Fig. 1(a), is repelled from the plate in vacuum when the particle is close to the plate. The particle is unstable to displacements away from the symmetry axis, so that the system does not support stable levitation, consistent with the theorem of Ref. [1]. We establish our result using a symmetry argument for an idealized case and by brute-force numerical calculations for more realistic geometries and materials. We also show that this geometry is closely related to an unusual electrostatic system in which a neutral metallic object repels an electric dipole (in fact, one can even obtain electrostatic repulsion for the case of a point charge [2]). Anisotropic particles are essential here; a spherical particle above a perforated plate is always attracted, although nonmonotonic effects in an isotropic case have been suggested for the null-energy condition rather than the Casimir energy [3].
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 27, 2010
- Accession Number
- ADA531517
Entities
People
- Alejandro W. Rodriguez
- Alexander P. Mccauley
- M. T. Reid
- Michael Levin
- Steven G. Johnson
Organizations
- Harvard University