Casimir pressure is created by the Casimir force of virtual particles.
According to experiments, the Casimir force F {\displaystyle F} between two closely spaced neutral parallel plate conductors is directly proportional to their surface area A {\displaystyle A} :
F = P A . {\displaystyle F=PA.}
Therefore, dividing the magnitude of Casimir force by the area of each conductor, Casimir pressure P {\displaystyle P} can be found. Because the Casimir force between conductors is attractive, the Casimir pressure in space between the conductors is negative.