Can anybody be absolutely sure that we have free will? Maybe what we consider as free will is not as free as we think it to be. What if it's already destined what choices we are going to make, even as we believe we are doing so of our own volition.
There are some arguments that I have devised to go with the above statement. If everything is predestined (i.e., it's a deterministic world), then that means that "whatever" anybody does, what has to happen is not going to change even in the slightest details.
Before we proceed further, let's clear up a few things. The approach we are going to take here is that there are only two choices that we have here:
Either the world is completely deterministic or
It's non-deterministic.
This is so because there's no such thing as partial determinism. Even a trace amount of non-determinism will make the whole system non-deterministic. So if we can prove the existence of even one such instance that is non-deterministic, we can conclude that the whole system is non-deterministic.
Another approach that many people (especially religious people) prefer, is that certain things (e.g., small details) may be non-deterministic but the other things (e.g., the events on the whole) are deterministic. It means that we may have freedom to choose within a boundary. It may change a few things, but the overall picture is not going to change.
More compelling reasons for the above classification can be understood by closely looking at the way we are going to define determinism. Related to Chaos Theory there is a famous concept called "the butterfly effect". It propounds that even a small change can cause a major upheaval in the overall scheme of things. We see in our course of life that seemingly small decisions and events can cause a sea change in our lives. So if non-determinism is involved in a system even in very small ways, it has the capability to influence big events (the final state of the world). Hence as per our earlier arguments if we can show the existence of even one case of pure non-determinism, then we have to consider the entire world as non-deterministic.
But if something is deterministic, then there may exist a way of knowing it! So if we know it (or somehow find out), which is theoretically possible in a deterministic world (the reason it's called deterministic!), we may also be in a position to change it. Because if we have prior knowledge about something is going to happen (e.g., what we are going to eat at a give point of time) we may intentionally decide to change details, and may also succeed. And if we really succeed in our endeavour then the world will no longer remain deterministic.
This is a paradox. Hence if the above logic is correct then our world can't be deterministic!
P.S: These are random thoughts... I'm not putting them down for an audience, but mostly as a documentation of my thoughts. However I'll welcome any insights into these musings.