Casimir Forces and Boundary Conditions in One Dimension: Attraction, Repulsion, Planck Spectrum, and Entropy

Quantities associated with Casimir forces are calculated in a model wave system of one spatial dimension with Dirichlet or Neumann boundary conditions. 1)Due to zero-point fluctuations, a partition is attracted to the walls of a box if the wave boundary conditions are alike for the partition and the walls, but is repelled if the conditions are different. 2)The use of Casimir energies in the presence of zero-point radiation introduces a natural maximum-entropy principle which is satisfied only by the Planck spectrum for both like and unlike boundary conditions between the box and partition. 3)The Casimir forces are attractive and increasing with temperature for like boundary conditions, but are repulsive and decreasing with temperature for unlike conditions. 4)In the high-temperature limit, there is a temperature-independent Casimir entropy for like but not for unlike boundary conditions. These results have 3-dimensional electromagnetic counterparts.