The grandfather paradox is the name for when we create a situation in which we couldn't be born. The notion that there is some explainable reason as to why time only flows forwards and at the same speed for all of us, is because it's made up. Time is just a method we use to break our routines into managable and predictable increments. I think we got so far into the world of theory, so anal(istic), that we forgot about that little bit.
If we used gravity to form a time loop, the theoretical method of producing a time machine, then information stored in individual particles could be sent to the time when the device is switched on from any future time. This would cause a cascade of information, a chaotic download of everything until someone switches it off, likely within moments of the overload, thus stopping the future use of the machine and the overload to begin with, creating another pardox. What happens to all that information?
Heavy duty thinking, maybe I'm just not the type of person to fully grasp theortical physics.