We can not get back to our original position?

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I was thinking about how the Earth moving all around the Sun, and the Sun moving around the galactic center of the Milky Way and having read that galaxies are moving away from one another at the speed of light, and If string theory is correct, the Universe is moving in a different vacuum, so it means we can never go back to the original position a second ago as we have just left it, even if we stand still. So could this be one of the reasons why time travel would be impossible?
 
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In relativity the notion of your "original position" doesn't have any objective meaning, different reference frames (coordinate systems) have different answers to whether an object is moving or at rest, and thus different answers about whether it's remaining at the same position or it's moved to a different position, and all these frames are considered equally valid in relativity. I don't understand your point about string theory, it's true that string theory does have many different possible vacuum states but if the theory is correct the observable universe that we live in has remained in the same vacuum state since shortly after the Big Bang.
 

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