  The pinch-off of an axisymmetric air bubble surrounded by an inviscid fluid
is compared in four physical realizations: (i) cavity collapse in the wake of
an impacting disc, (ii) gas bubbles injected through a small orifice, (iii)
bubble rupture in a straining flow, and (iv) a bubble with an initially necked
shape. Our boundary-integral simulations suggest that all systems eventually
follow the universal behavior characterized by slowly varying exponents
predicted in [Eggers et al., PRL 98, 094502 (2007)]. However, the time scale
for the onset of this final regime is found to vary by orders of magnitude
depending on the system in question: while for the impacting disc it is well in
the millisecond range, for the gas injection needle universal behavior sets in
only a few microseconds before pinch-off. These findings reconcile the
different views expressed in recent literature about the universal nature of
bubble pinch-off.
