In theoretical physics, particularly string theory and M-theory, the notion of a flop-transition[1] is basically the shrinking of a sphere in a Calabi–Yau space to the point of tearing.
Based on typical spacetime topology, this is not possible due to mathematical technicalities.
If there is a given Calabi–Yau manifold (basically a space with 6 or more dimensions curled up in a special way) then a sphere in the center can shrink down to an infinitesimal point that resembles a singularity.
Theoretical physicist Edward Witten proposed that the reason no flop-transition has ever caused universally catastrophic results is because the world-sheet of the strings will surround the flop-transitioning sphere and virtually cancel out the effects.
The path integral formulation of quantum field theory says that the string (and therefore its world sheet) traverse virtually every possible path, and therefore for any flop-transition, a string world-sheet will be present to cancel out its effects.