Discrete quantum gravity, covariant causal set
In this approach to discrete quantum gravity the basic structural element is a covariant causal set (c-causet). The geometry of a ccauset is described by a shell-sequence that determines the discrete gravity of a universe. In this growth model, universes evolve in discrete time by adding new vertices to their generating c-causet. We first describe an inflationary period that is common to all universes. After this very brief cycle, the model enters a multiverse period in which the system diverges in various ways forming paths of c-causets. At the beginning of the multiverse period, the structure of a four-dimensional discrete manifold emerges and quantum mechanics enters the picture. A natural Hilbert space is defined and a discrete, free Dirac operator is introduced. We determine the eigenvalues and eigenvectors of this operator. Finally, we propose values for coupling constants that determine multiverse probabilities. These probabilities predict the dominance of pulsating universes.
Gudder, S., "Inflation and Dirac in the Causal Set Approach to Discrete Quantum Gravity" (2015). Mathematics Preprint Series. 3.