The observation that the law of Entropy does not apply at the sub-atomic level and the observation that processes occurring at the sub-atomic level are reversible, with no regard for "Time's Arrow" inevitably suggests that Entropy is an emergent process.
"Emergent" means that it comes into existence as a new phenomenon that characterizes a new function. It emerges coincident with, or as an expression of, integration of sub-atomic processes into atomic processes. With the appearance of atomic processes (i.e., chemistry and macroscopic physics), comes Time's Arrow and Entropy.
Whereas Time's Arrow is irreversible, Entropy is reversible (locally) by means of an irrefutably present process: Organization.
The tendency to Organization is the companion to Entropy.
Entropy is the tendency for the components of a functioning system to occupy an increasing number of states different from each other.
Organization is the tendency for "particles" in those different states to combine in stable ways to produce new, emergent, functional systems. Example: molecules combine to produce cells; cells behave in ways that molecules cannot.
Life is one such emergent function. Life is subject to Time's Arrow. The physical components that constitute life-forms -- atoms and molecules -- are subject to Time's Arrow, but the sub-atomic components of those atoms and molecules are NOT subject to Time's Arrow; the changes they undergo may go in either direction. Instead, they obey the law of Equilibrium.
Equilibrium is another word for, balance.
In the case of the sub-atomic realm, the balance is expressed by the axiom, "Matter (and energy) can be neither created nor destroyed, but only changed in form (or changed from one into the other)." This axiom is known as, "The Law of Conservation of Matter and Energy."
Thus, at the sub-atomic level, things are dynamically constant -- meaning that they change form, but in a way and at a rate that conserves "amount", in interchangeable form. Time's Arrow doesn't apply.
But at the level of atoms, molecules, and perception, Time's Arrow does apply. Things change in one direction, irreversibly -- meaning, they cannot go back exactly to the way they were.
The difference between the sub-atomic level and the atomic and higher levels of organization, is exactly that: organization.
So, to the four forces physicists have recognized -- the "strong" nuclear force, the "weak" nuclear force, electromagnetism, and gravity -- we must add a fifth: the tendency to Organization.
To me, it is interesting and noteworthy that one of the four forces -- gravity -- is insignificant at the sub-atomic and atomic levels. It becomes significant only at the scale size at which life-forms -- and organization -- appear. Gravity becomes significant only at the scale of size where Time's Arrow applies. Gravity becomes significant only at sufficiently large levels of material aggregation (things collecting at one location -- such as planets, organisms, and money).
A final word:
The fifth force, Organization, has a companion: Entropy.
Entropy creates the increasing variety of "particles" and states we see and hear about, everywhere; Organization combines members or units of this increasing variety into new, more complex patterns with new behaviors -- emergent behaviors that do not and cannot exist at simpler levels of complexity.
This description also describes the evolution of life-forms.