Theory on time travel and paradox's

My theory on time travel is that time can only move forward, so when someone goes back in time, they actually go to a parallel world/universe where the time they want to go back to is the present in that world but since time has passed in the world they left they cant go back so if they go foreword in time they go foreword in that worlds time line instead of the world they left. This theory helps solve a lot of the problems with time travel such as paradox's. Now if you don't know a paradox's are things that can not exist because it leads to contradictions and defies logic and reason such as the grandfather paradox where if you go back in time and become your own grandfather so therefore you can not be born so therefore you could not go back in time etc but there are some stories such as -all you zombies- which is a favorite of mine where a number a paradox's occur where a single girl becomes her own mother father daughter. now i love the concept of paradox's because they show that almost anything is possible if you are willing to risk everything such as the universe or your reality could change and you would not even know it and accept as reality.