Time travel is just a theory and it will remain like that. The future is not pre-constructed. We create our future based on the decisions we make everyday. Suppose I have a gun in my hands trying to shot someone. The decision I will take at that point will be the beginning of other segments of future possibilities. And if we talk about the past. Changing one element can disturb the whole coarse of time line. What we have is today, past is for reference and future only shapes our dreams.