Common Properties of Dispersion Forces
Casimir, Casimir–Polder and van der Waals forces are compared and related to each other. Examples show that forces between electric or magnetic objects are governed by simple power laws for retarded and nonretarded distances. They are a revealed to be a consequence of general scaling laws for dispersion interactions. Addressing the microscopic origin of dispersion forces, Casimir and Casimir–Polder forces are found to reduce to sums over van der Waals forces in the dilute-gas limit. This additivity breaks down for denser bodies due to many-atom interactions, as demonstrated for the Casimir–Polder potential. As an example, the Axilrod–Teller potential of three atoms is studied.