Science fiction (sometimes shortened to sci-fi or SF) is a genre of speculative fiction that typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel universes, and extraterrestrial life. It has been called the 'literature of ideas', and it often explores the potential consequences of scientific, social, and technological innovations. Science fiction, when defined by a driving sense of wonder, can trace its roots back beyond the Bible and classical mythology, and is related to fantasy, horror, and superhero fiction, and contains many subgenres. Its exact definition has long been disputed among authors, critics, scholars, and readers. Science fiction literature, film, television, and other media have become popular and influential over much of the world. Besides providing entertainment, it can also criticize present-day society, and it is often said to inspire a 'sense of wonder'. Definitions American science fiction author and editor Lester del Rey wrote, 'Even the devoted aficionado or fanhas a hard time trying to explain what science fiction is, ' and the lack of a 'full satisfactory definition' is because 'there are no easily delineated limits to science fiction. ' Whereas, according to 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. ' Furthermore, 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. ' Damon Knight summed up the difficulty, saying 'science fiction is what we point to when we say it. 'Part of the reason that it is so difficult to pin down an agreed definition of science fiction is because there is a tendency among science fiction enthusiasts to act as their own arbiter in deciding what exactly constitutes science fiction. Ultimately, it may be more useful to talk around science fiction as the intersection of other, more concrete, genres and subgenres. = Alternative terms =Forrest J Ackerman is credited with first using the term 'sci-fi' (analogous to the then-trendy 'hi-fi') in 1954. As science fiction entered popular culture, writers and fans active in the field came to associate the term with low-budget, low-tech 'B-movies, ' and with low-quality pulp science fiction. By the 1970s, critics within the field, such as Damon Knight and Terry Carr, were using 'sci fi' to distinguish hack-work from serious science fiction.