Can we ever create a time machine????:!!)
Travelling back in time, in theory, requires exotic inputs - like imaginary [mathematically speaking] matter and energy. Given evidence of their existence has not been observed, it appears to be an unphysical consequence of GR. From a more philosophical / logical persective, I think reverse time travel would eternally preclude a 'chrononaut' from returning to his/her original time line. This would be necessary to preserve causality, IMO.
Travelling forward in time, however, is sort of feasible based on Relativity. Just travel really fast for a while (like on a spaceship) and when you return, you'll see that time on Earth will have moved faster than it did for you. The faster you go, the farther into the future you can visit. No way to return though.
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