Scalar Field Fluctuations between Parallel Plates

Quantum fluctuations of a scalar field and its derivatives are calculated when the field is confined between two parallel plates satisfying Dirichlet or Neumann boundary conditions. After regulation these fluctuations diverge in general when one approaches one of the plates. The energy density and the pressure between the plates is only consistent with the total Casimir energy when the canonical energy-momentum tensor is augmented by the Huggins term so to satisfy the requirement of conformal invariance for a massless, scalar field.