1. The most commonly used method of time travel in science fiction is the instantaneous movement from one point in time to another, like using the controls on a CD player to skip to a previous or next song, though in most cases, there is a machine of some sort, and some energy expended in order to make this happen (like the time-traveling DeLorean in Back to the Future or the TARDIS (Time and Relative Dimension in Space) that travelled through time in Doctor Who). In some cases, there is not even the beginning of a scientific explanation for this kind of time travel; its popular probably because it is more spectacular and makes time travel simple. The Universal Remote used by Adam Sandler in the movie Click works in the same manner, although only in one direction, the future. While his character Michael Newman can travel back to a previous point it is merely a playback with which he cannot interact. 2. In The Time Machine, H.G. Wells explains that we are moving through time with a constant speed. Time travel then is, in Wells words, stopping or accelerating ones drift along the time-dimension, or even turning about and traveling the other way. George Pal, director of the 1960 adaptation based on Wellss classic, accordingly chose to depict time travel by employing time-lapse photography. To expand on the audio playback analogy used above, this would be like rewinding or fast forwarding an analogue audio cassette and playing the tape at a chosen point. Perhaps the oldest example of this method of time travel is in Lewis Carrolls Through the Looking-Glass (1871): the White Queen is living backwards, hence her memory is working both ways. Her kind of time travel is uncontrolled: she moves through time with a constant speed of −1 and she cannot change it. T.H. White, in the first part of his Arthurian novel The Once and Future King, The Sword in the Stone (1938) used the same idea: the wizard Merlyn lives backward in time, because he was born at the wrong end of time and has to live backwards from the front. Some people call it having second sight, he says. This method of gradual time travel is not as popular in modern science fiction, though a form of it does occur in the film Primer. Time travel or spacetime travel 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 the time machine departs and the date it returns. The idea that a traveler can go into a machine that sends him or her to 1865 and step out into the exact same spot on Earth might be said to ignore the issue that Earth is moving through space around the Sun, which is moving in the galaxy, and so on, so that advocates of this argument imagine that realistically the time machine should actually reappear in space far away from the Earths 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 different times[85] (such as an event on Earth today and an event on Earth in 1865), and thus no objective truth about which point in space at one time is at the same position that the Earth was at another time. In the theory of special relativity, which deals with situations where gravity is negligible, the laws of physics work the same way in every inertial frame of reference and therefore no frames perspective is physically better than any other frames, and different frames disagree about whether two events at different times happened at the same position or different positions. In the theory of general relativity, which incorporates the effects of gravity, all coordinate systems are on equal footing because of a feature known as diffeomorphism invariance.[86] Nevertheless, the idea that the Earth moves away from the time traveler when he takes a trip through time has been used in a few science fiction stories, such as the 2000 AD comic Strontium Dog, in which Johnny Alpha uses Time Bombs to propel an enemy several seconds into the future, during which time the movement of the Earth causes the unfortunate victim to re- appear in space. Much earlier, Clark Ashton Smith used this form of time travel in several stories such as The Letter from Mohaun Los (1932) where the protagonist ends up on a planet millions of years in the future which happened to occupy the same space through which Earth had passed. Other science fiction stories try to anticipate this objection and offer a rationale for the fact that the traveler remains on Earth, such as the 1957 Robert Heinlein novel The Door into Summer where Heinlein essentially handwaved the issue with a single sentence: You stay on the world line you were on. In his 1980 novel The Number of the Beast a continua device allows the protagonists to dial in the coordinates of space and time and it instantly moves them there—without explaining how such a device might work.
Posted on: Sat, 30 Nov 2013 08:13:09 +0000