To begin with, there are reasons for believing that our decisions are determined. There are in fact several different arguments for determinism, and as a result several types of it. What they all have in common, however, is the idea that in some sense events are unavoidable. Basically, something is determined if it must occur. (The necessity here isn’t logical necessity; it refers to what is necessary in fact, given the way things are.) Thus, for example, if physical determinism is true, the current state of the universe combined with the laws of nature make it the case that only one future is possible for the universe as a whole. (Physical determinism is causal in nature, but in the next couple of posts I’ll mention non-causal types as well.)
Physical determinism, then, states that all of nature is causally deterministic. This is basically the view one finds in classical physics, and was made famous by Laplace’s thought experiment: if a demon knew every detail about the universe at a particular moment (the position, velocity, etc., of every particle, as well as all the laws of physics), he would be able to predict everything that will ever happen. If the laws of nature are such that everything that happens is a result of prior states, then there is only one possible course that history can take. It follows that Adam and Eve had no choice but to eat the fruit, and therefore that the standard Christian view is wrong.
Nowadays, physical determinism isn’t all that widely accepted because of quantum mechanics. But actually, quantum mechanics does not rule determinism out; it merely implies that determinism might not be true. It all depends on what the correct interpretation of quantum mechanics is. Whether physical determinism is true therefore remains an open question.
But even if natural laws are ultimately indeterministic, some problems remain for the proponent of free will. The world may contain a certain amount of randomness, but at the level of everyday objects, the randomness in the behavior of individual particles is almost entirely cancelled out, and things behave pretty much the way classical physics says they should. This is why Newtonian mechanics was thought of as the final word in physics for such a long time. We just don’t see billiard balls, for instance, move randomly (even if, like me, you’re really bad at pool). And human beings operate on this level. We and our brains are medium-sized objects, made up of trillions of subatomic particles, and therefore any quantum effects on our behavior should be completely negligible.
Even worse, if there were some noticeable randomness to our behavior, that wouldn’t mean we have free will. Free behavior isn’t random behavior. Eve wouldn’t be morally responsible for eating the fruit if her decision were the result of a chance event that she did not in any sense choose.
The only way that quantum indeterminacy might make free will possible is if it provides an “opening” for a non-physical mind to act on our brains. That is, if the firing of neurons isn’t completely determined, then a soul might, by taking advantage of the indeterminacy, be able to fire them one way rather than another. However, there are very good reasons for thinking that our minds are dependent on our brains, rather than residing in some non-physical substance (see my previous post).
Despite quantum mechanics, then, it is far more likely that the activity in our brains – and the behavior that results from it – is essentially deterministic. And that is inconsistent with free will.
[Originally published at Debunking Christianity]