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In short, time travel means nothing without space travel. Earth is rotating around the Sun (Sol star), Sol rotates around the galaxy and the galaxy is also moving. So say you want to prevent the assassination of JFK, you’re not just talking about going back 66-67 years, but say you don’t even care where on Earth you end up, where was Earth then? What’s your point of reference? Your point of reference moved.
Not just travel, but faster-than-light travel. Either one implies the other.
And there's absolutely nothing to suggest if you time travel, you will be a fixed point in space.
There's nothing to suggest that won't be the case, but until we know more about the universe, this argument will never hold water for me.
Of course since it's all theoretical and will never be relevant in our lifetimes, it holds as much water as any other argument...
Well, if you assume that going back in time means you also go back along the position of the earth, then sure. But to simply go back in time doesn’t imply that. You’re right in that it’s all fantasy, I’m just saying it’s two different movements, and us understanding one (movement in space, like walking) and not the other (time) tells me they aren’t necessarily connected.
Isn't space travel based on speed?
Time travel isn't based on anything, since it's currently theoretically impossible.
It's practically impossible. Theoretically there doesn't seem to be anything stopping one from changing their flow of time. Physics technically allows for time travel. Reality and practical application don't.