Stephen Hawking and co-author Leonard Mlodinow state in their book, The Grand Design, that it is reasonable to ask who or what created the universe, but if the answer is God, then the question has merely been deflected to that of who created God. Both authors claim however, that it is possible to answer these questions purely within the realm of science, and without invoking any divine beings. Neuroscientist Michael Nikoletseas has proposed that questions of the existence of God are no different from questions of natural sciences. Following a biological comparative approach, he concludes that it is highly probable that God exists, and, although not visible, it is possible that we know some of his attributes.