Theory and Phenomenology of Spacetime Defects
  Whether or not space-time is fundamentally discrete is of central importance for the development of the theory of quantum gravity. If the fundamental description of space-time is discrete, typically represented in terms of a graph or network, then the apparent smoothness of geometry on large scales should be imperfect -- it should have defects. Here, we review a model for space-time defects and summarize the constraints on the prevalence of these defects that can be derived from observation. 
Sabine Hossenfelder
hep-ph gr-qc