The London van der Waals force is approximatly given by F=-c *a^-7 where a is the distance between two neutral atoms and c is something like this: C=-23*hbar*c/4pi*(alpha1*alpha2) where alpha1 and alpha2 =(epsilon-1)/(4pi*N) and N is the atom number density and epsilon the permittivity. --> Question 1: Does that mean if I have a body with 10^30 atoms the moledule number density is 10^30? Now from the force between neutral atoms we can get to the Casimir-force. We can then just calclulate how much one atom of Plate A is attracted by the atoms of the other plates. Doing so with all atoms on Plate A we can sum over all the resulting forces and have the Casimir-Force. Question 2: is this correct?