*For context you may need to read the previous post, if you haven’t already.*

Warning: This post will be very sciency. Proceed at your own risk.

Let’s do a little recap of where I left off. I decided that human actions can only be due to three things: reason, chemical reactions and randomness. The first two are inherently deterministic, the last is not. Therefore human actions can only be indeterministic if we are capable of randomness. Either way, this does not necessarily tell us anything about Free Will because of incompatibilism, so I will explore that possibility in a later post.

There are many everyday events which we normally call “random”. Examples may include the toss of a coin, or the roll of a die. When we say that these events are random, what we usually mean is that all possible outcomes are equally likely. In the case of the coin toss, this means it is equally likely to get heads or tails. We often consider this a good way to decide certain disputes, since the person that throws the coin cannot determine on which side the coin will fall.

This kind of “random” event is not the kind of random I’m talking about. Even in this case, if we had all possible data on the mass and velocity and position of the coin, we could easily determine what the outcome would be. That is, the event is not *causally* random. Repeating the **exact** same circumstances (which would certainly be impossible for a human) would yield the same result every single time. The process is still deterministic.

A causally random event will yield different results every time it happens. This is the only possible kind of indeterministic event. The only example of causally random events humans know about are quantum mechanical processes. According to Heisenberg’s uncertainty principle, it is not possible to know all the properties of a certain system at a given time. At very small scales the behaviour of particles is essentially random, although bound by the probabilities given by its wave-function.

But that’s “just a theory”, right? Isn’t it possible that we will eventually come up with a better theory that allows us to predict the behaviour of these systems with perfect accuracy? Not quite. According to Bell’s theorem, if a theory ever manages to describe all processes deterministically, it will have to violate the principle of locality. That is, quantum mechanics can only be deterministic if distant events can have an *instantaneous* effect on local events. If such a theory is correct, something that happens now in Mars (or even billions of light-years away in some distant galaxy) will have a direct effect on the particles we’re playing with here on Earth. If I want to know exactly what some particle is going to do, I would have to know the exact positions and velocities of **every particle in the universe.** Although it is conceivable this is the truth, it would be quite weird, and for now I’m just going to assume it isn’t, and that quantum mechanical processes are indeed random.

However, to show it is possible that humans are capable of making random decisions, it is not enough to show that there exist random processes in the universe, but I also need to show that these processes can have large-scale effects. But according to the correspondence principle, quantum events become more and more “classical” the more particles we involve. This makes sense, since it is clear that at most scales we encounter Newtonian mechanics gives deterministic results, and thus one would expect that quantum mechanics does not contradict it.

The nucleus of a neuron has a diameter of 3-18 micrometers. This puts it way out of the scale studied by quantum mechanics (for comparison you could fit about a billion protons side to side in that length), the scale at which random processes may exist. Even if we assume that a decision can be due to a single neuron (which I highly doubt), it does not seem plausible that such a neuron would be capable of producing a random result. In order for that to happen, its voltage would have to be somehow determined entirely by an extremely small subset of the particles that compose the neuron. Since small particles have correspondingly small charges, this is impossible.

In this way, we seem to have killed random choice. Without it, we are left only with the deterministic decision-making processes. This implies that every decision we make is causally connected to what is in our brains at any given time and to outside stimuli. A computer with all possible information about my brain, and which knew (or controlled) all stimuli that I receive through my senses, would know exactly what I will do for the rest of my life.

Does this necessarily mean we cannot have free will? I will discuss this question in the next post.