Time travel is easy to understand. Just read this **** :
“People assume that time is a strict progression of cause to effect, but *actually* from a non-linear, non-subjective viewpoint - it's more like a big ball of wibbly wobbly... time-y wimey... stuff.”
― Steven Moffat
“If the Universe came to an end every time there was some uncertainty about what had happened in it, it would never have got beyond the first picosecond. And many of course don't. It's like a human body, you see. A few cuts and bruises here and there don't hurt it. Not even major surgery if it's done properly. Paradoxes are just the scar tissue. Time and space heal themselves up around them and people simply remember a version of events which makes as much sense as they require it to make.”
― Douglas Adams, Dirk Gently's Holistic Detective Agency
“Yeah, but what if you went back and killed your own grandfather?"
He stared at me, baffled. "Why the **** would you do that?”
― Stephen King, 11/22/63
“His older self had taught his younger self a language which the older self knew because the younger self, after being taught, grew up to be the older self and was, therefore, capable of teaching.”
― Robert A. Heinlein
“This is what I say: I've got good news and bad news.
The good news is, you don't have to worry, you can't change the past.
The bad news is, you don't have to worry, no matter how hard you try, you can't change the past.
The universe just doesn't put up with that. We aren't important enough. No one is. Even in our own lives. We're not strong enough, willful enough, skilled enough in chronodiegetic manipulation to be able to just accidentally change the entire course of anything, even ourselves.”
― Charles Yu, How to Live Safely in a Science Fictional Universe
“Nothing could go wrong because nothing had...I meant "nothing would." No - Then I quit trying to phrase it, realizing that if time travel ever became widespread, English grammar was going to have to add a whole new set of tenses to describe reflexive situations - conjugations that would make the French literary tenses and the Latin historical tenses look simple.”
― Robert A. Heinlein, The Door Into Summer