if or when time travel is invented it should be acceseble to anyone and no rules needed
you cannot change the past
what if you go to the past to change somthing but the actions you took turn out to be the reason that event you are trying to change happend
lets say i wanna go back to the past to prevent the titanic from sinking
i get myself on the titanic and try to wanr the captain but he s so shure nothing will happen that he decides to show you nothing is wrong by i dunno
speeding up or leaving the ruther unatended
no matter what you say to him he wont beleive you and make shure some guards or somthing make shure you cant get back into the control room (or bridge
whatever you call it) and bam beqouse you made him speed up or becouse they are to busy trying to contain you they dont notice the iceberg in time and
bam titanic goes down
anyway my point is you cannot change the past cous the past has already happend so also you going back in time trying to prevent it
it would give an interesting twist to the anciant astronout theory
instead of aliens comming to earth it could be time travelers that gave seartain civelisation writing and stuff

think about that