Do We Have Free Will? This is What Physics Says.

30 Sep 2023

Did I write this out of my own free will? Or did the Big Bang make me write it?

The question of free will has been an active topic of discussion in Western philosophy. From ancient Greeks like Plato and Aristotle to enlightenment thinkers like René Decartes and Immanuel Kant, important philosophers of all eras had something to say about this question concerning the existence of an individual’s capacity to choose, without external interruption, between different courses of action.

If one cause leads to another and that causes our actions, where is the room for free will?

This was and still is a significant question to ask as it is closely related to the topic of moral responsibility. However, the age-old debate has largely relied on religion and philosophical logic with incomplete knowledge of natural laws for the majority of history. Then, what can modern science tell us about this important metaphysical question? In this article, I will attempt to answer that by discussing how fundamental theories of physics affect how we approach free will.

Hard Determinism

Everything in the universe is made up of a set of undividable particles. Setting aside the possibility of dark matter, as of today, physicists generally agree that there are seventeen of these elementary particles, and they are all described by the Standard Model of particle physics which developed during the 70s. Thus, any behavior of particles within the Standard Model can be described and be predicted with well-established mathematical equations.

Since humans are also a huge collection of these particles, our behavior can also be predicted with the mathematics of the Standard Model. Many scientists think that any advanced computer even in the future won’t be able to solve the equations for human behavior as they involve an uncountable amount of particles, but this doesn’t change the fact that these equations are deterministic, meaning any event is caused by past events therefore determined. This is the view of hard incompatibilists — people who believe that free will doesn’t exist because determinism is true and it is incompatible with free will.

However, traditional determinism ignores quantum mechanics, which states that the universe at the subatomic level is indeterministic in nature. Thus, hard determinism is unscientific, unless physicists prove superdeterminism — a theory that there are “hidden variables” behind the seemingly indeterministic theory — which is very controversial. Then, what are some alternative stances? One major alternative is libertarianism.

Libertarianism

No, this is not referring to the political ideology. Rather, libertarianism states that free will exists because the universe is indeterministic. However, this stance also has some significant flaws. To state that we have free will due to the indeterministic nature of quantum mechanics is essentially saying that elementary particles also have free will.

Let’s say we send a photon through a beam splitter. It will have a 50-50 chance to go through or reflect on the splitter. Thus, simply attributing free will to random quantum phenomena is basically believing in panpsychism (the view that everything in nature has a mind). The legitimacy of panpsychism, however, is untestable.

Another justification for libertarianism is agent causation, which is the view in philosophy that something not part of these events can cause an action. Agent causation requires a dualist view which states that the mind and body are separable. Obviously, this is a philosophical debate (on the mind-body problem)

Can Free Will and Determinism be Compatible?

Until now, we have discussed the two major incompatibilist views. However, can free will and determinism be both true? For compatibilists, the answer is yes.

A question could be raised here: “If compatibilists accept determinism like the hard determinists, does that mean they accept the hidden variable theory?” This is a legitimate question, but most compatibilists, by determinism, don’t mean that the universe is completely deterministic. In fact, they do accept the uncertain nature of quantum mechanics, but the behavior of quantum particles are still probabilistically predictable through their wavefunctions. Therefore, they call the universe “deterministic” when talking about free will.

How can it be that free will exists in a deterministic universe? Compatibilists try to find a more rigorous definition of free will. Defining this important term simply as “the ability to have done otherwise” has consequences as shown in the photon example. Therefore, compatibilists define free will in a way that is “practical,” emphasizing that traditionally-defined free will does not matter. Although the exact definition varies, most compatibilists view that the free will that matters is the ability to make decisions generally without any influence from outside of the brain.

Nevertheless, compatibilism has also received a lot of criticism. One prominent argument is that they reduce such a big problem like free will simply into a semantic issue. Thus, hard incompatibilism is another stance that many physicists take, stating that free will is both incompatible with determinism and indeterminism. However, this stance questions the rationale of moral responsibility and justice.

At this point, you might be desperate for exactly what physics says about free will. However, physics really says nothing. All of these views are neither provable nor disprovable through physics or any other sciences, although it can tell us which positions within the views are scientifically false. As previously mentioned, these debates are largely philosophical and are expected to remain so in the future.