Difficulty: Easy

A professor is giving a lecture to his students. He says, “Albert Einstein and Stephen Hawking are two of the smartest physicists of our time. In a historic meeting, they argued about Einstein's theory of relativity. Hawking said that it was too complicated and that it could be simplified. In spite of this, they remained friends.” A student raised his hand, “Professor, I'm sorry, but you are clearly making this up.” How did the student know?