  Casimir forces are a manifestation of the change in the zero-point energy of
the vacuum caused by the insertion of boundaries. We show how the Casimir force
can be computed by consideration of the vacuum fluctuations that are suppressed
by the boundaries, and rederive the scalar Casimir effects for a series of
geometries. For the planar case a finite universal force is automatically
found. For curved geometries formally divergent expressions are encountered
which we argue are largely due to the divergent self-energy of the boundary
contributing to the force. This idea is supported by computing the effect for a
fixed perimeter wedge-arc geometry in two dimensions.
