Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the need for the traveler to experience the intervening period (at least not at the normal rate). Any technological device, whether fictional or hypothetical, that would be used to achieve time travel is commonly known as a time machine.
Although time travel has been a common plot device in science fiction since the late 19th century, and the theories of special and general relativity suggest methods for forms of one-way travel into the future via time dilation, it is currently unknown whether the laws of physics would allow time travel into the past. Such backward time travel would have the potential to introduce paradoxes related tocausality, and a variety of hypotheses have been proposed to resolve them, as discussed in the sections Paradoxes and Rules of time travel below.
100 years ago in the journal Annalen der Physik, Germany, appeared an article entitled "Zur Elektrodynamik bewegter Kerper" or "On The Electrodynamics of Moving Bodies". Then this article is more known for proposing a new theory, namely Special Relativity. The author is Albert Einstein, who in 2005 the physics world celebrate it as the Year of Einstein. One hundred years ago it was a miracle year of Einstein. In addition to papers on Special Relativity Theory, he sent two other major papers to the same journal: the photoelectric effect that drove won the Nobel Prize in Physics 1921 and the study of Brownian motion.
Without disparage the other two papers, the work of Einstein's Special Theory of Relativity is the most controversial when it published. And until now, still remained as a subject of discussion. To some scientist, his theory is the strong foundation to allows the passage of time into the future. Ten years before Einstein came up with the idea, the idea of time travel as written by HG Wells novel : The Time Machine, is a science fiction as opposed to the Law of Physics.
According to the Special Theory of Relativity : space and time are not absolute, but relative. That is, space and time are different for each person. How someone experience thetime and space is depends on two things: where the person is watching and how fast he was moving when compared with the speed of light. Einstein observed that the speed of light is constant at 299 thousand kilometers per second. Speed of light would not be different, though observed by two people from two different observation points. In accordance with the formula, the velocity (v) is the distance (d) divided by time (t). If v is a constant, t and d was the one who should change. One consequence is that the clock is in that condition always moves slower than the clock ticking is still in place.
This leads to the famous "twin paradox". A pair of twins are separated, one of them was rocketed at high speed across the galaxy and come back to earth, the other one live on earth. Although the rocket velocity approaching the speed of light, it took 10 thousand years for the astronauts to explore the galaxy and back to a certain point on the earth. Because of relatively high mobility, the age of astronaut is longer than other his brother who live on earth. Astronauts will return to earth just a few years older than when he slid. Meanwhile, his twin brother had died long ago.
Predictions of a slowdown of time has also been confirmed by experiment atomic clocks flown around the earth with jet aircraft. "If you fly a plane around the earth to the east, you will be 59 nanoseconds younger than if you stay at home," Dr. J. Richard Gott said, an astrophysicist at Princeton University, in New Jersey, United States.
The record for this type of travel. He returned to Earth after living in the Russian space station Mir for 748 days. Age younger than the fifth of twelve seconds if he remains on earth.
In his 1905 paper, Einstein also predicted a slowing of time due to the speed of rotation of the earth. Thus, the clock at the Equator thick slower than the clock at the poles. However, this prediction turned out to be wrong.
Recently in an article in Physics Today, Dr Alex Harvey of Queens College in New York and Dr. Engelbert Schucking from New York University confirms that Einstein was not involved in the General Theory of Relativity, which came 10 years later. General Theory of Relativity states that the clocks run slowed more because the gravitational field in which he resides.
A cross between surfing at high speed and the effect of the gravitational field can be applied to future manned missions to the planet Mercury, for example. According to Gott, astronauts who go to the mission for 30 years would save 22 seconds of the life of an astronaut.
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