Say we could map the interaction between every atom and molecule in the brain. Let's say we did that when a person was making a choice. Are you saying that at some points in time we could see that some atoms and molecules interacted in ways that violates the laws of physics?If you believe your choices are not completely predetermined (which you apparently do), then you must believe (for the sake of logical consistency) that something is happening in your decision-making that is "uncaused." (Atheistic or scientific materialism has trouble with "uncaused causes.")