Theory time travel becomes possible. And Einsteins realitivity is correct and the closer you get to the speed of light the more time slows but the time everywhere else stays constant the farther you get from earth the older everyone gets on earth but the travelers don't change. incorporate a time travel engine with a space travel vessel so the travelers would be gone for years and travel to other star systems then when they're trip is through they come back to earth and travel back in time to not long after when they left there for they have actually traveled for what could be decades but as they traveled back in time they might only be perceived as being gone for days or weeks. as long as they do not go to far back to a point before they left the time continuum would not be effected.