There is no objective reality in a reality that has no objectivity. That is unless you have defined your reality as being objective it cannot be considered, objective. In this sense we define the nature of our reality. Atheists define their reality as natural, meaning it is composed of those things they define as elements of the natural world. Anything that is not natural does not belong in their reality. That which is not natural is considered supernatural. We cannot prove supernatural elements are part of the natural world because that would contradict the nature of their reality.