1. Action:
The fundamental constituent of physical reality. Basically composed of two quantities--energy times time, momentum times length, etc. Action is nonobservable; only changes in action are observed, and then only partially (in the linear case). The photon is the basic quantum of action, consisting of a piece of energy welded to a piece of time, with no seam in the middle, so to speak. All physical things are composed of rates of changes in action. Note that prior to observation, entities exist in 4-space (at least) and not as spatial "things". The observation process is a time-differentiating process applied to the 4-spatial (spacetime) entity as it actually exists in the flow of time. The "rate of flow of an object through time" is determined by the sum total of all its photon interactions. An absorbed photon adds time--e.g., to mass, converting it to masstime. The emission of a photon tears away that time component, reconverting masstime to mass. A myriad of photon interactions are ongoing, both in virtual and "observable" states. Hence the flow of time is "structured", and various parts of the object exist as a momentary frozen 3-space snapshot and then immediately afterward as a "smeared" 4-space entity, etc.