The life of an individual, of humanity as a whole, of all living nature on planet Earth, of the Solar System, the cosmos, and perhaps the universe as a whole can be understood as dynamic systems. What makes a system dynamic? Essentially, changes in its state and the rules that govern those changes. A dynamic system can be studied discretely as a sequence of successive “cross-sections”: a series of static states containing certain variables and connected by a temporal scale.
The evolution of a system over time can be represented as a trajectory through its state space, and its entire history as a collection of “cross-sections” of the same system together with the relations between them. (In another model, time itself could also be incorporated into the structure being described rather than treated merely as an external parameter. But we will deliberately leave that model aside for now.) One important property of time is the resolution of its scale: it allows us to determine how frequently to take “snapshots of reality” for different systems, distinguishing relatively stable parameters from variables that change at different characteristic rates.