Time travel

Time travel is the concept of moving forward and backward to different points in time, much as we do through space. It also includes traveling sideways in time between parallel realities or universes.

Related Topics:
Space - Parallel realities

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Humans are in fact always travelling in time — in a linear fashion, from the present to the immediate future, inexorably, until death. Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime, or certain types of motion in space, may allow time travel into the past and future if these geometries or motions are possible. It has been confirmed that the effects of relativistic and gravitational time dilation can cause a traveller who starts at and returns to a point of origin that remains stationary, to arrive at a time farther in the future in that reference frame than their subjective elapsed time would indicate (a constrained form of time travel into the future).

Related Topics:
Special - General relativity - Spacetime - Space - Time dilation

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In physics, the concept of time travel has been often used to examine the consequences of physical theories such as special relativity, general relativity and quantum mechanics. There is no experimental evidence of time travel, and it is not even well understood whether (let alone how) the current physical theories permit any kind of time travel. However, theories do exist about the possibility of folding time to hop from one point to another.

Related Topics:
Physics - Special relativity - General relativity - Quantum mechanics

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In science fiction it is a recurring plot device, used to set a character in a particular time not their own, and explore the character's interaction with the people and technology of that time—as a kind of culture shock. Other ramifications explored are change and reactions to it, such as alternate histories.

Related Topics:
Science fiction - Plot device - Time - Alternate histories

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