Casimir force
= Casimir force
{c}
Two parallel ideal conducting plates at zero <temperature> have separation-dependent electromagnetic energy per area $-\pi^2\hbar c/(720d^3)$ and <pressure> $-\pi^2\hbar c/(240d^4)$. The negative sign denotes attraction in this geometry. Finite <temperature>, material response and boundary geometry change the ideal result; an absolute divergent vacuum energy is not the measured quantity.