True. The real, not main, problem, is that space and time are integrally related. You cannot travel through one without the other. Kip Thorne, who co-produced the movie Interstellar, had a particular way around that through the use of wormholes. Hypothetically, you can go back and forth through both time and space using one, which has two ends located at two different points in both. But even that results in unresolved paradoxes, like being able to produce infinite amounts of energy out of nothing. Or killing yourself before you were born. Anyway you look at it, travel into the past is impossible.
How come all those wormholes...gravity waves etc...are out there....why arent they here...or at least locally? Could there be nano or femto black holes on earth?