  In this paper, we study the collapse of a superhorizon-sized void in the
early, radiation-dominated universe using an improved general relativistic
code. We find that in general a relativistic or nonrelativistic void collapses
via a shock at the speed of light. This is true even if the outward velocity of
the void wall is enormous. As the wall thickness decreases, the shock strength
increases and the collapse time decreases up to a limit set by the shock tube
solution. In addition, as the outward velocity of the wall increases, the
collapse time increases somewhat. When the collapse occurs in much less than a
Hubble time outside the void, gravitational forces contribute negligibly to the
solution at the collapse time; non-gravitational forces (caused by pressure and
velocity gradients) shape the solution almost entirely. This is true even if
the wall velocity is large enough that fluid in the peak shocks outward
substantially during this time. Gravitational forces are expected to be
dominant only {\it after} a void has collapsed.
