The measure of free will and red herrings
Your actions affect whatever it is you initially ran from, and, however that thing reacts to your reaction affects you: two brains, each with multiple feedback/feedforward loops, interfering with each other.
Your move (photo by Ransom).
As I described in Measure of Chaos, complex, nonlinear systems like brains are unpredictable. To determine the behavior of a chaotic system, you have to know the initial conditions precisely; the entire state of the system at one time. The reason that these systems are called chaotic is that, even though they obey Newtonian physics—with no quantum voodoo—their behavior cannot be predicted through measurement. For linear systems, uncertainties in initial conditions lead to easily quantified variations in the predicted behavior, but that doesn’t hold for chaotic systems. In chaotic systems, the tiniest variations of initial conditions lead to widely disparate results.
The more complex the system, the greater the precision required to determine future behavior. For something as nonlinear as the human brain, the initial conditions—every sensory input, the state of every cell in the body, every neuron, synapse, and so forth—have to be known with perfect precision. If someone could make those measurements, then that someone could determine every move of that person from then onward and demonstrate that this person has no free will.
However, we cannot measure anything with perfect precision; in principle, we can make measurements with arbitrary accuracy, but there will always be uncertainty. It has nothing to do with quantum mechanics or Heisenberg's Uncertainty Principle, it is simply the reality of metrology.
Since a person’s response varies radically with even tiny differences in his or her initial state, and since we cannot measure that initial state with sufficient accuracy, no one can accurately, consistently predict how a person will respond to stimulus.
It's tempting to say something like "it is as if people have free will, but it's really deterministic." But this is an incorrect conclusion unless you believe in a supernatural deity.
A more accurate summary is “whether people have free will or not can’t be observed.”
It is impossible to discriminate between actions born of free will and actions of unobservable determinism. Without the ability to determine a person's actions with known uncertainty, we can only conclude from observation that people have free will.
Except for one possibility: if you believe that there is some perfect deity that can make perfect measurements, then that deity could determine how people respond to stimulus. That deity could distinguish between choice born of will and choice determined by circumstance. In a belief system incorporating such a deity, people have no free will.
Therefore, if you deny the existence of free will, you must necessarily invoke the existence of an all-perfect supernatural being or you’re left with a fundamentally unobservable belief.
Of course, most systems of thought that invoke the existence of deities require free will of the believer.
- Measure of Chaos: When Uncertainty Runs Amok
- Quantum wave functions come alive! May the Bohr Model rest in peace
- Measure of the mind: connectome
(The author of this article, Ransom Stephens, checked his horoscope before writing this.)