They say that when you are moving then time slows down for you. If you go in an airplane then time slows down for you, if you go faster than that then it slows down even more. The closer you travel at the speed of light the more time slows down. In theory if you travel at the speed of light then you simply don’t age at all. That part is only a theory because nothing with mass can travel that fast.
Physicists say that to think this way would be throwing the laws of nature out the window. I learned this stuff in high school in my physics class, and the teacher didn’t once say that it was impossible, they said it was theoretical and cannot be proven or disproven just yet. The consensus is if you travel fast than the speed of light that you could turn around and see yourself going backwards, essentially seeing yourself go back to the point in which you started traveling that fast.
Thinking about this today lead me to question that, seeing as how if you are moving at faster than the speed of light, then light cannot wrap around you and therefore your presence would be unknown. Einstein thought that traveling faster than the speed of light was possible. Just by proving that the faster you move, the more time slows down, showed him that time could be manipulated with movement, so why wouldn’t time be manipulated in such a way that we travel back or forward in time?
Many people believe that time travel is impossible because we have yet to see any futuristic tourists. Of course this might be because time travel is too dangerous and we wouldn’t want to see them fall into the wrong hands, so we simply do not use it in the future. Another possibility would be that people do travel here but are careful enough to know what they change and how it will affect the future, so as to avoid a grandfather paradox. Another idea is that anything a time traveler does is already done and is part of history. There is yet another possibility, going back in time creates an alternate timeline in which the traveler can do anything he wishes and not affect the current one.
We may never know if it is possible to time travel, until the day comes in which we invent a way to do it. I think one thing is safe to say though, a delorean will not be doing the time traveling, even though that would be pretty cool.