Models on Event Symmetric Space-Time
  In the event symmetric approach to quantum gravity it is assumed that the fundamental laws of physics must be invariant under exchange of any two space-time events. The fact that this symmetry if obviously not observed is attributed to the possibility of a spontaneous symmetry breaking mechanism in which the residual symmetry is diffeomorphism invariance on a continuum. The approach has a discrete nature while dimensionality, continuity of space-time and causality are abandoned as fundamental principles. Consequently space-time is a dynamical object which may undergo changes of topology or dimension. A number of different types of Event Symmetric model are described. The most interesting models are event symmetric superstring models based on discrete string supergroups. 
P. E. Gibbs