Photon dispersion in causal sets

This relation gives delays over astronomical distances of seconds (GeV energies) to hours (TeV energies). A motivation for this suggestion is the possibility that space-time may be lumpy, fuzzy, or even discrete, on small scales, and that this lumpiness may affect photon propagation in a dispersive way. We adopt the extreme viewpoint provided by causal set theory, an approach to quantum gravity pioneered by Rafael Sorkin [13], with the founding principle that spacetime is a partially ordered set of purely discrete points. The partial order nicely reflects the causal relationships between events fundamental to special relativity. We also adopt the Feynman sum-over-histories quantum electrodynamics, which is greatly simplified by the postulated discreteness: path integrals, and the difficulties associated with divergences and defining the measure on the space of all paths are replaced by discrete sums.