You go back in time and create a new timeline (Back to the future, ...) so you can't go back to your timeline.
You go back in time and change the unique timeline (EG) so you memories change and whatever you changed it is now reality.

The difference is if the traveler is linked or not to the traveler's timeline. In the first case, the traveler is not linked and can change anything... But in the traveler's timeline nothing has changed and the travel didn't work.

In the second case, the traveler is linked and anything that changes because of the traveler is now that timeline reality and that can create a paradox. Imagine you go back and kill Trump when he was a kid. But you went back because you know the current Trump, the president. But of you kill him while he is a kid he won't become president and you won't know him so you won't travel back to kill him... so he will grow up and become the president and...

[–] Atomic@sh.itjust.works 5 points 1 day ago (1 children)

You forgot the third possible "outcome".

In short, you will never change anything in the present, because it already happened.

everything you've wanted to go back and change has already been changed by you, you going back doesn't change anything, because it already happened, you're just tying up and completing the paradox.

There wouldn't be anyone for you to go back and kill because if you did and succeeded they wouldn't even be alive when you decided to go back. E.g. let's say you wanted to kill Hitler (he's already dead) All you've done is one of the failed assasination attempts. And it's only now you realise that was you.

[–] meco03211@lemmy.world 4 points 1 day ago

Or you killed Klara Hitler's boy in the cradle whom she would have taught love and kindness to. Lost to recorded history, she adopts a new boy, because evidence of a random (at the time) woman adopting a kid can easily be lost. Now she's got a chip on her shoulder, and she raises her new son with one goal...

Congrats, you are the cause of Hitler.