According to American writer and professor of biochemistry Isaac Asimov, "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology."[5] American science-fiction author and engineer Robert A. Heinlein wrote that "A handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the nature and significance of the scientific method."[6]