1.) Change is either the only thing we seek an explantion for, or at least the paradigm case of what we seek an explanation for.
Motion, change, kinesis, etc. is not just some feature of the world but the feature that makes us look for reasons and causes. The sciences that are most causal are those that are closes to explaining motion (meters, time, and mass are all defined though motions and all other units are complexes of these).
2.) But if change is your explanandum, your explanans can’t be something given as changing, since then it simply subsumed into the explanandum.
3.) It follows immediately that the unchanging cause is the explanans of what most of all needs explanation. Neither this explanans nor its activity can be described in meters, seconds, mass, or in any of the units built up from these. It cannot act by energy or by any other conserved quantity that transitions to cause change. It cannot begin to act at time t and so acts outside of any light cone and without needing to receive or convey information.
4.) The natural sciences are thus part of a larger project seeking the explanans of change, or the cause of what we most seek causes for. Any attempt to identify all causal explanations with natural science explains change only under some qualification and so as scattered into diverse causal domains.
5.) The unification of physical theory therefore cannot be affected by any physical theory, in spite of being the primary motivation in the development of the theories themselves. Natural sciences are therefore also a part of a larger project of unification of physical theories.
Because physical theory is a part of a larger explanatory picture that does not require the units, tools, or theories of physical theory, as these theories advance they will realize more and more that nothing in the science is entirely necessary and that even the most “self-evident” truth that is proper to their domain can be done without. If contact were absolutly necessary for motion then the immobile mover could not move anything, and so we discover (in Newton’s theory of inertia or gravity) that contact is not necessary for continued motion. If time were absolutely necessary for activity on the world then the unchanging explanans could not act upon it, and so we discover in the block universe or Barbour’s “Platonia” that a timeless world allows for physical theory.
As physical science advances it will allow the possibility and plausibility of more and more theories, not fewer, and these theories will become more and more radically different – allowing now for infinite and now for finite world, making time both fundamental and impossible, being both rigidly determinist and purely statistical, with all events given from the beginning and being absolutely unpredictable.
6.) The demand that the unchanging explanans be given in physical theory is a failure to understand both the unchanging and physical theory. Appeals to “brute facts” are obviously consistent with, and in fact arise from, the structure of physical theory, whose existence depends on principles giving it a trajectory outside of itself (i.e. seeking causes for change and seeking the unification of theories that do so.)