Time travel ish complicated.... or so physicists think!
I remember I was on this forum one day and someone came on claiming to be a time traveler, I don't think he is, but one of the things he said was "People say 'If time travel is possible, why don't you see time tourists?' well, you do, you just don't notice. Hell, someone could come up and be like me and say 'Hey everyone I'm a time traveler!' and no one would believe him, like think about how many people reading this don't believe me." So I try not to seem close minded -.-
But he said that these things aren't so complicated.
Like with the grandfather paradox, he said many people before have traveled back and killed there grandfathers to see the effect, and nothing happened, they remained. They went back to the future and found out they never existed, but they did then.
And he took on other theories, I didn't read the whole thing.