What is Science fiction ?

Science fiction is a genre of fiction dealing with imaginative content such as futuristic settings, futuristic science and technology,space travel, time travel, faster than light travel, parallel universes and extraterrestrial life. It usually eschews the supernatural, and unlike the related genre of fantasy, its imaginary elements are largely plausible within the scientifically established context of the story. Science fiction often explores the potential consequences of scientific and other innovations, and has been called a "literature of ideas.

Science fiction is difficult to define, as it includes a wide range of subgenres and themes. Author and editor Damon Knightsummed up the difficulty, saying "science fiction is what we point to when we say it", a definition echoed by author Mark C. Glassy, who argues that the definition of science fiction is like the definition of pornography: you do not know what it is, but you know it when you see it. Vladimir Nabokov argued that if we were rigorous with our definitions, Shakespeare's play The Tempest would have to be termed science fiction.

According to science fiction writer Robert A. Heinlein, "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." Rod Serling's definition is "fantasy is the impossible made probable. Science fiction is the improbable made possible." Lester del Rey wrote, "Even the devoted aficionado—or fan—has a hard time trying to explain what science fiction is", and that the reason for there not being a "full satisfactory definition" is that "there are no easily delineated limits to science fiction."

Science fiction is largely based on writing rationally about alternative possible worlds or futures. It is similar to, but differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically established or scientifically postulated physical laws (though some elements in a story might still be pure imaginative speculation).

The settings for science fiction are often contrary to those of consensus reality, but most science fiction relies on a considerable degree of suspension of disbelief, which is facilitated in the reader's mind by potential scientific explanations or solutions to various fictional elements. Science fiction elements include:

• A time setting in the future, in alternative timelines, or in a historical past that contradicts known facts of history or the archaeological record.
• A spatial setting or scenes in outer space (e.g. spaceflight), on other worlds, or on subterranean earth.
• Characters that include aliens, mutants, androids, or humanoid robots and other types of characters arising from a future human evolution.
• Futuristic or plausible technology such as ray guns, teleportation machines, and humanoid computers.
• Scientific principles that are new or that contradict accepted physical laws, for example time travel, wormholes, or faster-than-light travel or communication.
• New and different political or social systems, e.g. dystopian, post-scarcity, or post-apocalyptic.
• Paranormal abilities such as mind control, telepathy, telekinesis, and teleportation.
• Other universes or dimensions and travel between them.