Time travel is the idea of going back in time to the past or forward to the future. Time travel is not known to be possible, but it is much used in fiction. The Time Machine (1895) by H. G. Wells was one of the first and most famous stories of time travel.
The popular British TV program Doctor Who is about an alien who has adventures by time travelling. Much later, the American movie "Back to the Future" tells a fictional story about a professor who builds a machine that can take people into the future or back in the past.