I have found that many people do not believe that time travel is possible. They feel that since time is a constant that is always moving forward that you can not go back. I feel they are viewing it too much as a string theory. I tend to think of it as something that can be bent or folded thus allowing one to step ahead or behind in time. Just got to figure out how to do that. IF I can I will be rich.
When I said that I didn't think it would be possible I meant that it wouldn't be possible for a human being, in order to actually time travel you have to move faster than the speed of light which is technically impossible so there you go.
According to General Relativity, the closer you get to the speed of light, the more time slows down from your perspective. While tachyons are theorized to actually travel FTL, no proof has been found ... Yet. One thing that does seem to travel FTL is communication at the quantum level using entanglement. Two entangled quanta, separated by any distance, still have an effect on each other that seems instantaneous. This means that we will be able to communicate instantly across space, possibly even teleportation with energy to matter, matter to energy conversions.
I believe it is possible in a broad since. If you think about those who go into space and come back after a while, the differences in our bodies and their bodies are evident. The length of time is different, and I consider that time travel. When you look at the stars and other things in the sky, you are looking into the past, and that is time travel in a since.
Do I believe that you can be in one time one moment and then go three years in the future or the past? No, I don't.