Time TravelMain article: Time travel See also: Time travel in fiction, Wormhole, and Twin paradox
Time travel is the concept of moving backwards and/or forwards to different points in time, in a manner analogous to moving through space, and different from the normal "flow" of time to an earthbound observer. In this view, all points in time (including future times) "persist" in some way. Time travel has been a plot device in fiction since the 19th century. Traveling backwards in time has never been verified, presents many theoretic problems, and may be an impossibility. Any technological device, whether fictional or hypothetical, that is used to achieve time travel is known as a time machine.
A central problem with time travel to the past is the violation of causality; should an effect precede its cause, it would give rise to the possibility of a temporal paradox. Some interpretations of time travel resolve this by accepting the possibility of travel between branch points, parallel realities, or universes.
Another solution to the problem of causality-based temporal paradoxes is that such paradoxes cannot arise simply because they have not arisen. As illustrated in numerous works of fiction, free will either ceases to exist in the past or the outcomes of such decisions are predetermined. As such, it would not be possible to enact the grandfather paradox because it is a historical fact that your grandfather was not killed before his child (your parent) was conceived. This view doesn't simply hold that history is an unchangeable constant, but that any change made by a hypothetical future time traveler would already have happened in his or her past, resulting in the reality that the traveler moves from. More elaboration on this view can be found in the Novikov self-consistency principle.
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... into the path of an oncoming truck but saved his own life by traveling in time to before he left his home ... I made the decision instantly to turn back time," says the anonymous Scientologist, who then found himself "standing by the door I'd left not 10 seconds before - completely unscathed." The author ...
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... An objection that is sometimes raised against the concept of time machines in science fiction is that they ignore the motion of the Earth between the date ... of this argument imagine that "realistically" the time machine should actually reappear in space far away from the Earth's position at that date ... However, the theory of relativity rejects the idea of absolute time and space in relativity there can be no universal truth about the spatial distance between events which occur at ...
Famous quotes containing the words travel and/or time:
“Have we even so much as discovered and settled the shores? Let a man travel on foot along the coast ... and tell me if it looks like a discovered and settled country, and not rather, for the most part, like a desolate island, and No-Mans Land.”
—Henry David Thoreau (18171862)
“Ah, that Time could touch a form
That could show what Homers age
Bred to be a heros wage.”
—William Butler Yeats (18651939)