  A first step towards implementing a notion of coarse graining in an
intrinsically Lorentzian, discrete quantum- gravity approach, namely causal set
quantum gravity is taken. It makes use of an abstract notion of scale, based on
counting the number of discrete elements. To that end, the space of actions for
causal set quantum gravity is written in a matrix-model-like language, and a
flow equation for the effective action of the model is derived from the path
integral.
