Time travel science

Fun fact. If time travel exists, you could technically see a time traveler anywhere in the timeline, technically.

It's also technically possible that the time that's already passed and the time that the time traveler arrives in could be different. The timeline would split just from that person being there, no matter how careful they are, they would affect the future. If we haven't seen any time travelers its probably just because they are in a different reality of sorts.
That's my theory.

The way that i see it, each second of every minute is lost forever once it passes, a good example would Stephen Kings 'The Langoliers' where the plane travels backwards in time to a hollow second which has already passed and is decaying into nothing. So i don't think travelling back in time to a point that has already passed is possible, because that implies that time is a tangible thing, which it isn't.