When it comes to time travel human beings refuse to believe that it just can't be done, we personally love the idea of being able to literally control all of history and time and be limited by nothing, however it must be understood that although it is believed due to our recent technology wave that whatever one can imagine can be done, does not mean that it is true.
When it comes to time travel the only physically proven and conceivable way of traveling back in time is to use the space time continuum to your advantage by either moving faster then the speed of light or creating a hole in space with different aging ratios.
first off it must be understood that time and space interact, when one moves through space he consequently moves through less time, and under this rule if you were to achieve near the speed of light compared to everyone else you would age considerably slower, hardly at all for that matter. Two things must be understood about this concept, 1 this means that it is possible to change the rate at which you age to a specific point but this is not time travel, and 2 this means if it is physically possible to travel faster then the speed of light then you can go back in time. Through this it is believed that time travel can be achieved be either reaching past the speed of light by using the gravitational pull of a black hole, or to use a worn hole to create a passage through time by having the two ends a different aging ratios. The thing about these theories is that they are not possible practical and only hypothetical.
In the case of the black hole a few problems exist, one according to Einstein's theory of relativity it is impossible for matter to achieve the speed of light, let alone greater, as well as black holes pull in light there isn't much of a choice of getting close enough to speed up faster then the speed of light and get out. So if it was possible to achieve the speed of light, then it wouldn't be possible to go faster because the only means result in becoming a singularity.
Now when it comes to wormholes, there are many flaws in the idea of time travel through it, a few being that one they are only theoretical, two to create one a meter in a diameter you would have to have the negative gravity equivalent to that of Jupiter, and we don't have that kind of energy, and then perhaps the fact is that it is believed that if the ends of a wormhole were to exist in two different times the worm hole would collapse upon itself due to immense radiation created by the fluxuation in time, and boom, there it goes.
Now these are not the only problem with time travel, to go along with the mare all of the paradoxical challenges, the whole grandfather paradox for one, if you went back and killed your grandfather then you wouldn't be alive and wouldn't have gone back in time. As well as it has been said by many if time travel is possible then why don't we have visitors from the future right now?
The fact is that time travel is not possible not through physics not through nature, only through a few hypothetical theories that like much of science will eventually be revised.