Being engaged in science myself, I'm never content to let one side dominate the discussion without providing other sides the chance to test its predictions. Thus, while riding my bike today, I traipsed upon an architecture for experiments that could potentially reveal evidence for the soul or whatever transcendental entity theists' believe supplies free will.
But first, some background on the inspiration.
In 1867, James Clerk Maxwell described a thought experiment about a "demon" that could violate the second law of thermodynamics, which we should remember states that a closed system of two bodies in contact and with equal temperatures will never reach a state where one body has a significantly higher temperature. This is the law that gave us the concept of entropy: over time differences in temperature, density, and pressure become diminished across an isolated system.
Here's Maxwell's description of the demon, taken from the Wikipedia page.
... if we conceive of a being whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us. For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics.If you've ever read The Calling of Lot 49, then the description will sound familiar (its occurring to me now that the section may have been Pynchon self-correcting his previous amateurish obsession with entropy documented in Slow Learner).
Maxwell's demon is, of course, an impossible entity in the physical world. The Second Law only applies to an isolated system, and Maxwell's conclusion to the thought-experiment fails to include the demon itself within the system. To perform its actions, the demon - as a physical entity - would be as much involved in the system's sliding toward a state of equilibrium as the molecules in A and B.
Yet if the demon, like its namesake, is not a physical entity and not subject to the physical laws that apply to the molecules or the vessels, then the Second Law could be violated. An observer from within the system could identify that some supernatural effect was taking place by the evidence available to them without needing to describe the specific mechanisms that allow the demon to sustain itself and interact with the physical world. The observer couldn't describe the the demon but only its effect on the material world.
If the soul allows humans to have wills that are free (at least to some degree) from material causality, then our souls must act like Maxwell's demon in some sense. The soul must allow neural impulses to proceed unhindered in some instances but not others, but being separate from the physical world, there's no physical requirement for the soul to balance the energy consumed and the energy expended. The purpose of the soul is less specific than Maxwell's demon, but we might expect to see that energy is added to the system extra-physically when the brain makes moral decision and that the energy added may be proportional to the complexity of the dilemma or to the desire of the individual to do the immoral act.
Directly observing the brain and the circular system interact at this level of detail is still a difficult task, but our methods for studying the body are improving all the time. Given a specific hypothesis and the funding, I'm sure the next decade could see at least early trials performed and the methodology refined until the real experiments can be done.
Regardless of how soon the work is done, these experiments could provide solid evidence for a concept that is now currently sustained through faith alone. Current material evidence and prevailing scientific attitudes suggest that our minds are purely the product of our physical brain. If Christians and other theists wish to assert otherwise, it might be beneficial for them to close the empirical gap rather than continue to assert their position by appealing only to faith, ancient writing, and fear that a material universe provides no absolute morality.