I read a blog post here that reminded me of some thoughts I have had surrounding what evidence it would take regarding the existence of God that would be necessary for me to accept the existence of God.
For me this question is inseparable from the question of free will. The first question I would want an answer to is; Do we truly have free will and is the principle of free will one that is maintained absolutely for everyone?
To endeavor to answer this question, let's look first at the opposite of free will. The alternative to the concept of free will would be that our life outcome is the result of some form of predestination setup by an omnipotent (i.e all powerful) and omniscient (i.e. all knowing) being who really has no spontaneity because everything is already known and planned out exactly how it will happen (which sounds kind of boring). If God is, in fact, omniscient, does it mean He/She/It knows past, present and future? I would think so. If that is the case, then free will is an illusion and does not exist. If free will does, however, exist absolutely, then this same heavenly being is only omniscient to a point (could we really say God is omniscient then?) working really hard to react to every single stimulus and response to make sure that free will is maintained at all costs and is not really omniscient, but is omnipotent. A third possibility is that God is omniscient and omnipotent but is not all loving because He/She/It allows bad things to happen to good people (at least according to our traditional understanding of love - which could use further clarification as to what it means, I suppose).
Regarding predestination; I think most religious people reject the idea of predestination because the idea of us having absolute free will is the most encouraging possibility for us to be able to determine our life outcome and potential redemption/salvation in the hereafter. Otherwise, our eternal existence is already planned out, so this life becomes pretty irrelevant. In the religious context, what often follows the question of whether or not God is omniscient is an explanation that 1) He either knows what will happen in the future and does nothing about it (i.e. maintaining our illusion of free will that ultimately does not exist) or 2) He is only omniscient when it comes to expected outcomes, so He/She/It pretty much knows what will happen to you, based on a universal law of consequences, but again, chooses to do nothing about your/our consequences. In either case, the idea of an omnipotent AND loving God is just thrown out the window. Unless, the epitome of love is letting people learn through sad experience and pointless death, destruction and loss which, in many cases, does not appear to readily manifest its lesson or meaning/purpose.
Of course, an idea known as fore-ordination is one that creeps in every once in a while. I guess this would be the idea that we are given the potential to achieve a life outcome but the actual accomplishment of it is entirely up to us. This does not violate the concept of free will since we still can choose whether or not to live up to our potential in that scenario. So, based on the above, it would appear the idea of free will (i.e. our ability to choose our life outcome) exists absolutely as taught by the religious. I don't think I could find many that would dispute this conclusion.
If that is the case, then, there will never be anything that will happen to us that will violate our freedom of election to choose what we do (in response to stimuli) in any given situation. Based on my limited observations, this appears to be the case (Except where some people try to limit my choices by imposing rules that follow their whims instead of my desires).
So, if the question is asked, "What evidence would it take for you to accept that God exists?" I would have to respond by wondering, what evidence is a God who will not violate the principle of free will going to be willing to provide?
It seems to me that, if God appeared to me right now and said, now you see me, so you must believe. Then slapped me across the face for good measure to make sure I got the message and the sting would help me know that God was real. Would this not be a violation of my free will? In other words, wouldn't my freedom of choice not always be upheld? Would I retain the ability to choose whether or not to believe in God if He/She/It did that? I don't think so. Which leads me to the conclusion that God will never do something which takes away my freedom to choose. Since the act of appearing before me would take away my freedom to choose whether or not God exists, or not, it seems that God would not do that.
Why do believers insist on asking then, what evidence for God's existence would it take for you to believe? When no evidence can (or will ever) possibly be found if the principle of free will is maintained absolutely. Unless, of course, you believe in a deity that maintains free will except when it comes to subtly steering you towards a belief in He/She/It.
In any event, the concept of free will has been pronounced by religion to exist absolutely (at least as far as I am aware) in the context of powers granted to us and upheld by the divine creator that religion claims to receive direction and guidance from. So, if the religion is shown to be a man-made creation, the concept of free will (and any answers surrounding whether or not we have it absolutely) are pretty much null and void.
The only logical response to these questions is to utilize the scientific method to deduce what our present state of affairs is here on this planet and whether or not the concept of free will is even an important one. I would point out that if religion is man-made, the emphasis on free will comes out sounding more like an excuse to try and explain the state we find ourselves in (a.k.a. why bad things happen to good people) and not so much like a divine revelation from a being who either has everything already planned out that will happen (i.e. follows predestination) or is tip-toeing around making sure that there is not any overwhelming evidence on one side or the other (i.e. free will is maintained absolutely). The belief about how active a role God plays in our lives is one that usually serves to answer these questions.
See here for more discussion of this topic.
Sorry that Free Willy didn't make it into this post. I'm sure there are a whole bunch of Free Willy fans that are extremely disappointed now.