I've explained on here before that, it's quite likely if time travel does exist until they develop faster than light travel or only jump in tiny moments with a space craft, time travelers probably ended up killing themselves simply because the earth moves.
The sun moves, the solar system moves, the galaxy moves, all rotating, spinning, and traveling. Even standing absolutely still you're still traveling at around 900km/s.
Stargate covered that during Children of The Gods. Dr Jackson said that the point of origin changes, so one had to compensate for the spatial movements.
This assumes that the universe has a unanimous frame of reference, doesn't it? Wouldn't that violate the idea that all motion is relative?
Surely a time machine would simply act in reference to the nearest most prevalent source of gravity. On Earth that would *be* the earth.
Indeed, the time machine itself would be moving at the same speed.
However, time might be disconnected from space, and by travelling through it you do not travel through space.
You don’t necessarily need a reference point.
In reference to @timebender25's comment That makes a pretty big assumption in and of itself. We barely have a grasp on how gravity affects matter and while it's postulated that gravity can affect time it's really only affecting the perception of time. Time itself is, at best guess, relative based on our observation of reality in conjunction with movement. That can't rule out a constant that may only be observable from outside our gravity well. If someone managed to figure out how to manipulate "time" and remove themselves or something from our perception time. And could then put themselves someplace else in that time stream, for lack of better word, there no way to know if gravity would act like an anchor. It's just as likely that you could experience all the gravity that would exist in a given area for the amount of time you jump and therefore exposing yourself to hundreds or thousands of g forces at once.
Or that gravity would cease to exist for you during the jump process and possibly flinging you out at the speed of your movement at the time of the jump. It's really all guess work at the moment since we really don't know enough to know what questions we should be asking. Let alone how to test for the answers.
The sun moves in the Milky Way too...
Surely a time machine would simply act in reference to the nearest most prevalent source of gravity. On Earth that would *be* the earth.
However, time might be disconnected from space, and by travelling through it you do not travel through space.
You don’t necessarily need a reference point.