GR and QM relation is work in progress. The "quantum of action" was discovered and according to science this granularity is just there. It's hard not to accept it. If we do then the logical step is determining the Planck's length and time. Well, Planck time is the time that it would take a photon travelling at light speed to cross a distance of Planck's length. Since this would represent crossing the shortest possible distance at the fastest possible speed, this gives us the smallest meaningful unit of time. As of now it seems a photon can not travel faster than light in a vacuum. It means that Planck's length and time are the smallest meaningful limits and it's very hard to imagine and come up with theories below them. Therefore, I'll repeat, it seems to me that under normal circumstances the lowest meaningful time slice is the Planck time. Please, show me how you describe the universe below Planck's constants.
