Science has answered many questions and illuminated many truths. As our understanding of nature expands it becomes clearer that our existence is explainable by the physical properties of our universe. Taking this further, our existence is actually defined by these properties. Being fully defined, how can a rational mind believe in choice?
At my will, I can think to bend my arm, and then I bend my arm, and it bends. Surely this is proof of choice? Did I not just choose to do and execute that choice? Well actually my brain state interacted with my muscles by firing electrical currents. This current was triggered by a chemical process, driven by physical molecules. Those interactions all colluded to result in my arm moving. What part did I play in it? The event happened, I precipitated the event. Or did I just observe it? All these questions are turning away from choice and focusing on understanding what the "I" label means.
As we chase the cause and effect trying to determine what originated the choice we soon run out of sources within our own body. The event was influenced by our environment, which was a result of our upbringing, and before that our genes. Everything leading to the event of me bending my arm was a beautiful, logarithmically complex chain of events from the big bang, expansion of the cosmos, formation of RNA, formation of life, evolution, on a scale of time that is incomprehensible. It was all inevitable. There is only one outcome. What appears to be random is just our lack of understanding. An understanding that can never be reached because its only manifestation is its entirely.
When you watch a river flow, you can spot eddies and patterns in the water. You are looking at completely different water but the shape of the bank causes these patterns to persist. Complex shapes and dances form. We ourselves are similar. We appear as an entity in full self control, but actually we are entirely a result of a universal history. Our bodies are just cells which have developed in a symbiosis which allowed them to grow. Our thoughts occurring in the neural network of our chemical brain. Most of the molecules are transients from eating, drinking and breathing which get absorbed transformed and ejected continuously. Even our digestion is governed by bacterial processes which come from entirely external sources. Everything about us is governed by causes and effects that we cannot fully measure, but which are bound by the laws of physics like some giant game of dominoes.
So we are observers it seems. Conscious enough to watch the movie but even our own actions are the result of processes that cannot be controlled. The script is unknown to us, but is already fully determined and unchangeable.
Pick a religion and it comes up empty on the question of choice also. It is possible to conceptualize ourselves as some kind of supernatural dice machine with a mystical link to the physical world. Even so, that would remove all possibility of the rationality required to make a choice and reduce it to a random event.
So how can a rational mind believe in choice?