Time travel

There are many ways to travel in future. But traveling in past is somewhat practically impossible.
            These are some of the ways that we can travel in future but some are still hypothetical and theortical:-

1) By approaching speed of light:--

           Time slows down for objects traveling close to the speed of light and the time stops for objects traveling at the speed of light so if we travel faster then the speed of light then time must go backwards. But according to Einsteins mass-energy relationship that is E=mc² no object can travel faster then the light because on approaching the speed of light, objects starts increasing in mass rather than speed and it would take an infinite time and amount of energy for an object to achieve speed of light. This is why we can't travel back in time( that is in past). So therefore if we try to approach close to speed of light then we can experience time dilation and hence we travel future. 

       This is a thoroughly a practical concept and it has also proved and measured practically. Using twin atomic clocks.( One clock stationary on earth and other flown around in a jet aircraft). Scientist found that a flying clock ticks slower because of it's speed. Another practically tested example is of
Cosmonaut Sergei Krikalev technically lives in the future due to his extended period on the International Space Station.

Cosmonaut Sergei krikalev

After spending almost 804 days in space arrived back in Earth 0.02 seconds in the future thanks to a process known as time dilation.

Under accepted theories of time travel engineers would have to build a space ship which could travel at the speed of light (186,000 miles-per-SECOND), and head out into space.

Theoretical physicist and string theorist Brian Greene, of Columbia University, said: “You can build a spaceship, go out into space [and travel] near the speed of light, turn around and come back.

Imagine you go out for six months and you turn around and you come back for six months.”

While you are travelling at the speed of light, time stays slow relative to the people who are standing still back on Earth.

As a result, you would be going fast while your clock would still be going slow.

Prof Greene: “When you step out of your ship, you’re one year older but Earth has gone through many, many years.

“It can have gone through 10,000, 100,000 or a million years depending on how close to the speed of light you traveled.”

However, the only problem is that a machine travelling at such speed would require an “unimaginable” amount of energy, while the stress from the centrifugal force on the body would likely prove fatal.

2) Black hole:--

           According to Einsteins general relativity, the stronger the gravity you feel, the slower the time will move. 

            So therefore all we have to do is to go near a region having extremely high gravity such as a  Black hole. Black holes has such a strong gravity that not even a light can escape. Since black holes have such a huge mass its gravitational force will also be tremendous. 

           So imagine hypothetically going near the event horizon with a powerful rocket with enough fuel. We have to go on accelerating around event horizon for some time and we can experience time dilation because of the warping of time space due to strong gravity of black hole.
          Therefore if you go very close to a black hole, time slows down and you will effectively travel into the future from the near observer who is looking far from it.

3) Worm holes:--

            Worm holes are a thin hypothetical tube of space that connects two distant parts of the space. It is the shortcut to travel millions light years away. It is created by space-time bending. Due to continuous bending of light, space time fabric gets bended and thus a worm hole is formed.

 
   For example:Now think of a 2D sheet of paper, fold it over so that two regions of paper are very close. Now by connecting the two parts of paper by essentially cutting circular holes on both parts and then connect them by two edges. Same way if we bend the space time and connect two different points, it becomes a shortcut to travel millions light years away. But still it is a hypothetical concept.