As in the tradition of physics, systems are described by their states, and the evolution in time of a system is described by a time-evolving state; a state for each moment. For instance, the current state of a ball may be ‘above the ground’ and it may be evolving towards ‘still above but closer to the ground’. All of this can be mathematicized in order to refer to system’s properties— like the position of the ball—more precisely. The elegance of physics lies in the existence of laws of motions, which permit to calculate the time-evolving state of a system from its state at a fixed time. In a way, the laws of motion permit reconstructing the full movie from a single snapshot.
