Sam Harris is well-known for believing in Determinism. I have thought about this topic since 2016 and been a firm believer since around the same year. Determinism states that everything that happens to us and around us is predetermined. For example you reading this post, couldn’t have happened in any other way. You might stop reading it now, to prove a point, but it was also set that you would do so anyway. It basically means that free-will doesn’t exist.
For example, that the choice between drinking a glass of water instead of juice doesn’t come from a magical place that cannot be determined. We could have picked water for many reasons. We might not like that particular juice brand, or we might want to reduce sugars, or we might dislike the orange flavour. We could also start to feel dehydrated and we know that juice won’t satiate the thirst. Although the feeling of dehydration is still a subconscious feeling, it’s already exerting its influence on the conscious realm. The idea that we have the freedom to pick either water or juice is an illusion. There’s an infinite number of variables influencing that decision. Because we can’t conceive, or single out, each one, we attribute this to free-will.
When I started thinking about this topic, the first hurdle was the amount of variables that surround every choice. Take the water versus juice situation. It’s an infinite number that falls in many categories. But what if we imagine a simpler universe? Let’s imagine a place where there’s only gravity and Earth. I mention only gravity, so we can remove things like wind resistance, humidity, Earth’s revolution, etc. So now we are hovering in the sky with a bowling ball. We know the exact dimensions and weight of the ball. Because we can conceive of every variable, it means that if we drop the ball, we know exactly where it will be after 5 seconds and exactly where it will hit on Earth and the precise moment. The function over time will tell me exactly where the ball will be, so I am free to change
t (as time) and see where it will be during the free fall. This is the sort of exercises we did at school in physics. Instead we would have a cannon and the teacher would ask us how far the cannonball would go, given the power, the angle and the weight. Because we can calculate all these things, we can predict the future. And if we know what will happen next there’s no free-will.
The trick when we expand the simpler universe to ours is: do we believe that everything that exists in the world is material? And by material I mean we can interact with it. Things like atoms, nerves, chemical reactions happening in our brains, genes, objects, gases (like oxygen) and everything we can see and touch. When we add immaterial concepts to the mix is when problems arise (e.g. soul). The question is then how do immaterial concepts interact with material ones? Descartes and Princess Elizabeth of Bohemia exchanged numerous letters about this problem. The latter argued that Descartes couldn’t reasonably explain how immaterial things could influence material ones. And she was right - Descartes didn’t have a good answer for this problem. If you believe that this can happen - e.g. that a soul can exert some force in the physical realm - then there isn’t anything in this post for you. However if you believe the opposite, then how can free-will exist if we could quantify all these material interactions?