Time travel is one of the staple tropes in Science Fiction where the aim is to play around in the narrative with the various paradoxes produced by the phenomena. However the really weird thing is that some serious scientists are taking the whole idea seriously. It appears that the theory of relativity suggests a four-dimensional picture of the universe where travel back and forward across the forth dimension may be a genuine possibility.

The possibility of forward time travel has been irrefutably demonstrated by flying atomic clocks around the globe at hign speed. The time-dilation effect of speed causes time on the aircraft to slow-down relative to time of earth. Mind you the time-differences is merely a matter of nano-seconds so it make no practical difference. To travel years into the future you would need to push an aircraft up to a near-light-speed which requires a huge amount of energy.

To travel backwards in time would need the energy of the whole galaxy. That is, of course, assuming that the theory is correct. It could simply be that relativity and quantum theory are incomplete and will be replaced at a later date by a better theory which will resolve all the paradoxes. Pity is, we won't be around to find out unless a time traveller comes from the future to tell us and the current theory suggest that even if you could make a time machine it would not travel back before the time it was first constructed.

Paradoxes and problems in time-travel

How to travel in time safely