Science fiction (or sci-fi) is a film genre that uses speculative, fictional science-based depictions of phenomena that are not fully accepted by mainstream science, such as extraterrestrial lifeforms, alien worlds, extrasensory perception and time travel, along with futuristic elements such as spacecraft, robots, cyborgs, interstellar travel or other technologies. Science fiction films have often been used to focus on political or social issues, and to explore philosophical issues like the human condition.