If God appeared, how many people would agree that, yes, that was really God? Conversely, how many would say, no, it really was not God? Unless we know what God is, we will never be able to determine whether or not he has appeared.
This dilemma, not being able to express what God is in a way others can agree on, is an on-going problem. Joeseph Smith said he heard from God and started the Mormon church. Pat Robertson recently said God told him who the Republican nominee is going to be. Because there is no agreed upon definition as to how God speaks to people, these claims can be neither comfirmed nor denied.
Some might scoff, “Anyone can claim they heard God speak. It’s only when we see God we will know.” But, there is no agreement as to what we will see when we see God.
There will be as many disagreements on whether or not someone has seen God as there are about hearing God speak. Will the God appear like it does in the movies, with choirs singing and special effects lighting? Or, will God be in a rabbit that runs across the road?
The Christian says he knows God and will know when he comes. The Hindu says exactly the same thing.
Neither of these people will recognize the god of the other. The concept of a god will remain an arbitrary one until someone can come up with a definition all can agree on.