There is a theory that going back in time can make another universe. If you have heard about how electrons move, they basically “teleports” while sometimes scientists mean that they are two places at the same time. This has made a theory that we create new universes all the time!
If time travel really is possible, this could be the explanation why we haven’t seen anyone from the future. There is also a theory that all is already changed and that we are living in the “perfect” past.
Another theory states that if we in for example 2065 invent a time machine, we would only go back a few days, maximum 5 years because what would you do? Would you change history, or just some embarrassing moments in your life?
Or, there is few time travelers, they use some highly important rules before they can get on the journey (about how they look, how they talk, etc.) and they will act like normal citizens at that time and place to make sure they aren’t radically changing the past.
Anyway: If you go back to the past and kill your past self, then there is a 50/50 chance that you disappear or you didn’t kill your past self. This creates a mind bending paradox where if you killed your past self, you wouldn’t be alive when you went back in time to kill your past self, but if you are alive, you would kill your past self and so on…