Without loss of generality, consider our universe to be of 0‽
Things that are constant (e.g., "Gravity draws things with mass together") seem to posses 0‽ over time
But what about things that are likely but not constant, for example, someone visiting reddit (event r). r appears to have a fluctuating cuil over time (t) such that Cuil(r,t) is in (-1‽,1‽). In this case, its always very close to 0. I believe the function is tangent to 0‽ each time someone logs onto reddit, although it could cross… this is where the d‽/dt would be interesting to look at.