  In this paper, we present a cluster algorithm for the simulation of hard
spheres and related systems. In this algorithm, a copy of the configuration is
rotated with respect to a randomly chosen pivot point. The two systems are then
superposed, and clusters of overlapping spheres in the joint system are
isolated. Each of these clusters can be ``flipped'' independently, a process
which generates non-local moves in the original configuration. A generalization
of this algorithm (which works perfectly well at small density) can be
successfully made to work at densities around the solid-liquid transition point
in the two-dimensional hard-sphere system.
