"If you're not relative to earth, then you haven't so much learned to teleport as you have learned to disappear into deep space never to be seen again."<br>You know, that never occurred to me, considering the fact that Earth orbits the SUN at 67,000 mph let alone how fast we're hurtling through space.,(reply>), That "disappear into space" thread was the sub-plot of the sci-fi show "Seven Days."  A person could go back in time seven days, but re-appeared in the void of space.  (The earth would have orbited 1/52 of its path around the sun.)  So the time-traveler would have had to "pilot" his time-capsule back onto the earth's surface.