Scientists assume that there is "A Truth", lying in state, waiting to be discovered. That each step we take to uncover it takes us closer to The Truth one additional iota.
Every description of reality, be it by observation or physical model, is necessarily partial and incomplete. We all resemble the proverbial blind Indians describing an elephant they know by touch.
The attempt to explain the universe and human existence using physics and brain chemistry alone is necessarily a reductionist, "blind Indian" view.
This is where God comes in. It is the indescribable infinity that encompasses the universe, of which we can receive fleeting, partial, imperfect glimpses -- guided by the power of awareness.
And this is the explanation of free will. We all possess free will, whether or not we are aware of it. One cannot make the simplest moral choice without free will.
It is not the narcissistic, "New Age" free-will that purports to wield control over our entire existence; rather, it's the fleeting ability, guided by awareness, to navigate between constraints of reality and the free-will actions of our neighbors.
So if physics or biochemical models cannot describe free will, its source must come from the realm beyond them.
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