I believe it is possible to go forwards in time, but it is currently 'impossible' to go back in time.
Albert Einstein has developed a theory that says the faster you travel, the slower time goes around you. (It has been scientiically proven with accurate clocks and jet places) It is not a speed difference of just a few km per second, the changes in time around different speeds only vary greatly when you travel to around 87% of the speed of light or more. If you travel really fast, You are not necessarily travelling to a different dimension of another time, but because the time around you is going slower - the world around you is travelling relatively faster. In this way, it seems like you have gone to the future. Albert stated that there is no direct time or space. What you are seeing now is actually what has happened perhaps 1 millionth of a second before you saw the object.
The theory of relativity is also very intersting, Isaac Newton once said that everything around the universe travel at different speeds, however Einstein said that if everything travels at different speeds it is impossible to measure speed correctly because you can only calculate speed in relation to another object. Say for example, the Earth is moving 3 km/ second, but a tree on earth seems as if it is not moving 3 km/ second. Only because you are also travelling 3km/ second so it seems stationary.
However, Eintein also stated it is impossible to travel faster than the speed of light because to do that, your mass would be 0, and being 0 would mean you never existed. (black holes should also have mass because if black holes have such strong gravity - it must have mass. However everything that goes into a black hole collapses so I'm pretty unsure how it works - Sowwi, I don't specialise this area).
Nonetheless, physically I believe it is possible to see the past... if the universe is significantly cirucular, if there was a lend powerful enough to bend and capture light that revolves light around the universe once, what we see in the lens would have taken place many years before we saw it.
Another theory is that because the universe is expanding, (big bang theory) time is going forward... when the universe start to contract, time may go backwards. However I do not believe in this theory ( i believe in big bang, but not 'if the universe contract time goes backward') because it has many holes and is a sweeping statement.
Black holes and worm holes may also be a possibility of time travel, but I will cover those later and get you guys posting.

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i think time travel is definatly possible, as to how, i dont kno, but i kno one thing, we shouldnt be able to travel to the past, cause then someone could save hitler's life or worse or something, then the nazis would rule over us, so if we do figure out time travel, we should make sure nobody will use it for evil, like neo-nazis and ive heard of that big bang theory, its probably true, with the massive imploding