I got sucked into a philosophical discussion on reddit.com, and two people effectively brought up the same issue regarding the lack of evidence for God. I was therefore inspired to write the following. Here it is for you to consider and tear apart.
We have the language to describe what we see, feel and experience; in other words, everything that we can tangibly define and share. I know my hand because I can see it, feel it, taste it, smell it (even if I'm not cognizant of its scent) and hear it as it interacts with other objects. I can relate these experiences with other people who come into contact with me and confirm with them that they have similar experience with their own hands and with mine. Thus we have the basis of common understanding.
It's possible to question our experiences even further, but such metaphysical discussions are pointless for this conversation to the degree that the question of God becomes meaningless.
Now we turn to the world around us. We can describe water and trees in such a way that everyone understands what we mean. Even if we don't share the same language, we can still make ourselves understood for simple concepts like that. We are sufficiently rooted in a common reality that communication becomes possible at high levels until abstract concepts become possible. This, then, gives us the foundation for establishing what satisfies the criteria for empirical data for our physical bodies.
Furthermore, every culture on earth has the foundation for mathematics to some degree, which is largely abstract, and all mathematical concepts thus discovered have been compatible. This means that our common reality is not restricted only to the physical world, but also the abstract.
Then we turn to the concept of God. Every culture on earth has some sort of supernatural creation myth, although not one of them shares common elements when developed in isolation. Thus, the common reality model fails. None of us share a common reality with regard to the supernatural, creating an impossible situation with regard to empirical data. In the millennia, probably eons of human experience with thousands of disparate cultures, we've discovered evidence of a multitude of common discoveries, but not one god or creation myth in common.
This is not proof of anything, nor does it disprove anything. It only suggests that we are a species that instinctively seeks patterns in the world around us, and we try to fill in the gaps when we have incomplete data. This is where the role of the supernatural enters our lives.
This lack of a common frame of reference for God or the supernatural creates severe problems when trying to justify our beliefs. Commonality only arises when we start indoctrinating cultures into our own beliefs; thus people become predisposed and any empirical evidence becomes tainted. Since we know that we have no problems with independently developed abstract concepts, there should be no reason for the human race to have developed such disparate concepts of God and creation. So we cannot compare the difficulties of establishing empirical evidence for physical bodies with empirical evidence for God. We are literally speaking of apples and oranges.