Time travel is a widely-recognized concept in philosophy and fiction. It is uncertain if time travel to the past is physically possible.

Forward time travel, outside the usual sense of the perception of time, is possible according to special relativity and general relativity.

Philosophers have discussed the nature of time since at least the time of ancient Greece; Parmenides presented the view that time is an illusion.

Centuries later, Newton supported the idea of absolute time, while his contemporary Leibniz maintained that time is only a relation between events and that it can not be expressed independently.

The latter approach eventually gave rise to the spacetime of relativity.

Time travel was popularized by H. G. Wells’ 1895 novel ‘The Time Machine’, which moved the concept of time travel into the public imagination.

The work is generally credited with the concept of time travel by using a vehicle that allows an operator to travel purposely and selectively forwards or backwards in time.

The term time machine is now almost universally used to refer to such a vehicle.