In one minute

Schoger, Spreng, Ingold, Lambrecht, Maia Neto and Reynaud study universal Casimir interactions between spheres in two configurations that turn out to be dual. One has Drude-model metal spheres in vacuum, the other dielectric spheres in salt water beyond the Debye screening length. In both, the long-distance or high-temperature limit is dominated by low-frequency transverse magnetic thermal fluctuations. The results do not depend on material details, because metals and salt water both have finite conductivity and so an infinite static dielectric constant. Their dependence on geometry is also universal, linked to an approximate conformal invariance of the reduced free energy.

Universal Casimir interactions in the sphere–sphere geometry