The laws of physics dictate the processes that go on, have gone on and are going to go on in the universe. They dictate the state of our universe. Until the quantum mechanics arrived, it was believed that every state of any given natural system could be predicted if the adequate natural laws and the history of the system are known.
This is called determinism. Everything that will be is predetermined. It is not written in paper as a prediction or a prophecy. It is dictated by a natural law. If there exists an exact physical law, an equation to describe the behavior of each element of the system and its interactions to all other elements of the system, any state of the system, in any given point in time could be determined.
If there is empty space, with only two particles, and positions, velocities and other properties of these particles are known, then we can conclude that the behavior of these two particles can be easily determined by their equations. Similarly, if the system comprises of three, four or more particles, the same calculation can be applied, but the symbolic interpretation of the equations would be more complicated as the number of particles in our system increases. Nevertheless, the equations would exist, and it would be possible to predict the behavior of the system. This conclusion can be derived by mathematical induction, which is a form of deduction.
If an equation exists to describe the behavior of each particle in the system and the interactions of all the particles in the system, than the behavior of the system is predictable. Here, the term ‘particle’ is used, but it could as well be replaced with the term ‘element’. If we look at human beings and their surroundings as matter, which is made out of particles, we can deduce that the behavior of the humans and their surroundings is predictable by an extremely complex, but finite, equation.
This equation would give the state of society as a system in any point in time and thus could, given a point in time, yield a future state of the society, thereby determining its future from the given point in time. This means that any choice made by anyone is determined by the natural laws. Stating that it is predetermined is irrelevant from the perspective of the equation, as it is true and holds for any point in time. For the equation, time is irrelevant. What is, was, and will be.
Of course, this is true only if our premises are true, and the behavior of each particle is modelable by a deterministic equation. If it is not, then the above deduction does not hold.
Quantum mechanics introduced the possibility of particles taking random movements that could not be determined precisely, which could go in favor of the indeterministic future. However, the problem with that is that there could be an underlying physical law that cannot be observed, yet exists, and can determine the exact behavior of the particle.
For the sake of argument, let us assume that the behavior of a particle cannot be predicted by a deterministic equation. Would the human beings and other animals have the freedom of choice?
We can approach this in a similar manner to the above-mentioned deterministic one. Let us model a complex behavior based on an elementary choice. If in any given point in time, a particle can choose what path to take between two options that exist (it can easily be shown the same would hold if there were multiple paths, but to make things simpler, we will use a choice of two), its behavior could not be determined and it would be free. However, this would pose the problem of multiple particles. If each particle, individually, has a choice, than what we see is not coherent with that possibility. On the macroscopic level, events are predictable by the laws of classical mechanics, which contradicts the premise of the elementary choice. If each particle has an independent choice, it would be very unlikely for them to make the choices in such a way to create the behavior seen on the macroscopic level. This could indicate that there is an underlying law that determines or offers the choice to the elementary particles, which would imply determinism.
On the other hand, we could use the top-down approach to try to explain free will. If a human being can choose what to do (how to move, how to act and what choices to make), then they could, in a way, bend the laws on the macroscopic level. If a person moves their arm by their choice, this would imply that all the particles that make up their arm consolidated to make that choice and to behave differently than the rest of the body whose behavior is determined by the laws both on microscopic and macroscopic level. This poses a different problem: if random particles consolidate to make a choice, than why does this not happen on other objects in nature (trees, stones, etc.)? Falling stones do not change their mind.
We can assume that free will originates in the brain, and then propagates through the body in accordance to the laws of nature to produce an effect that is a result of a choice. This would imply that there exist particles that do have a choice and those that do not, and that the behavior of these free-will particles can produce a larger effect on a macroscopic level. There is also the problem of why do these particles only influence the human body and not its surroundings. If there are enough of these particles, or a single particle has enough potential to achieve an effect on the macroscopic level, why the effect is only concentrated on the body. We could argue that the existence of such a particle would determine whether something is alive. This and the origin of such a particle is a whole other subject.
Whether we have a freedom of choice or not might be irrelevant. If we sit and wait for the events to simply unfold as they should, we will see them do. We will likely end up sitting with nothing happening but our waiting, and realize that this waiting was the unfolding of the events as they should have happened. On the other hand, if we accept the freedom or illusion of choice and act as if we have a choice, the events will likely unfold in such a way as if the choices we made had to have been made. However, the two scenarios would likely have very different outcomes. It might be best for us to believe we have a choice, and accept their inevitability after we have made them. After all, “we have all made the choice; we are here to understand why we made that choice”.