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Time Travel
Perhaps one of the Doctor's most
impressive abilities is that he can explore
not only space but time as well. The idea of
time travel has been a point of great
fascination for many decades, inspiring
countless works of fiction including The Time Machine
by H.G. Wells and Star Trek. In reality, time
travel is not only allowed for by the laws of
physics, it has been achieved on many
occasions.
Moving Forward in Time: Special Relativity Einstein's theory of special relativity describes a phenomenon called time dilation. When two individuals are moving relative to one another, they will perceive one another to be moving more slowly. For example, if a clock is sent into space in a rocket, an observer on Earth will perceive the clock to be ticking more slowly. However, from the perspective of an astronaut accompanying the clock, time is moving normally. As an object approaches the speed of light (3.0x108 m/s) a relatively stationary observer will perceive that object to freeze in time. Time dilation allows for time travel in that, an individual may move forward in time relative to others (1). While "long distance" time travel may be currently out of our reach, small scale time travel occurs on a daily basis. In any situation where an individual travels more quickly (or slowly) relative to a stationary observer on the earths surface, that individual will have experienced the effects of time dilation. While these effects are not normally perceivable, they have been experimentally quantified. In Hafele and Keating's groundbreaking 1971 experiment, four cesium beam atomic clocks were placed on commercial jets and flown around the world twice. One jet traveled east while the other traveled west. When the clocks were reunited with the ground, they were compared to two clocks which had been left stationary (3). They found that the clocks traveling east (with Earth's rotation) lost 59 ± 10 nanoseconds while the clocks traveling west (against Earth's rotation) gained 273 ± 7 nanoseconds (4). The kind of time travel measured by the Hafele-Keating experiment is miniscule compared to the Doctor's. Rather than traveling forward by nanoseconds, the Doctor has been known to leap thousands of years into the future, even visiting the end of the universe as portrayed in Utopia. |