Travelling is a very normal thing for us as we travel and move easily on the earth .We move up and down, left and right, forward and backward without thinking about it or even measuring the time in which it happens . We know the three spatial dimensions which are depth, width and length, but there is also a fourth dimension which is time and as a result of that came the idea of Time Travel . It is not a modern term and it means to move forward to the future or backward to the past .
Time travel has two types: forward time travel and backward time travel. Forward time travel or moving to the future was known long time ago as it was found in myths and ancient folk tales. For example, in a Hindu mythology which mentions the story of a king who travels to heaven to meet the god and when he comes back he finds that many ages have passed, although he had spent only few moments with god . This idea developed through ages till now as it is presented in movies.
The second type is backward time travel which means moving backward to the past . It is a modern term which is recently known . It is found in the stories by writers in which the hero or heroine returns back to the old past to meet a king or to experience some events which had been already experienced in reality.
Physicists and writers think that there are many ways for time travelling . It comes to be through the black hole or wormhole or the commonly known device which is time machine that appears in different shapes in movies and stories. Some of these ways are scientific and the others are imaginary.
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Some people and physicists think that the idea of forward time travel is true and real ,but they do not believe in the idea of backward time travel thinking that it is impossible . They say that the faster you move , the slower the time passes. In other words, the time passes more slowly when an object approaches or comes close to the speed of light . Time is relative as it is not always measured in seconds, minutes and hours ,but it differs according to the speed of the object in which it moves. For example , when someone who is about 30 years old leaves the earth to the space in a high speed which approaches the speed of light, leaving his brother who is about 20 years old and spending about ten years in space , he will return back to find himself younger than his brother who will be in forties or fifties depending on the speed of the rocket . Clocks on Mercury tick more slowly than those on Earth because Mercury circles the sun at a faster speed. Some people claim that forward time travel had already happened.
Other people also think that the idea of backward time travel is also might be real. They believe that as the time passes slowly when an object moves very fast , we can accelerate the speed of the object to exceed the speed of light and as a result of that the object will move to the past and the time will return backward.
To conclude , the idea of time travel whether it is forward or backward is still theoretical and hypothetical ,as it has not been experienced physically till now. No one knows if it can change our past or future or it will be just a déjà vu or re experiencing for what had already happened.