The MAIN problem with time travel is motion.
Nothing stands still.
Everything in the Universe is moving. Any given second, or microsecond, you, the Earth, the Sun, the Milky Way Galaxy and every other object in the universe is moving.
Let’s say that you just invented a ‘for real Time Machine’.
You step into it, set it for some particular time, forward or backward, it doesn’t matter which, and turn it on.
)Poof!( you disappear immediately from this ‘time’.
Suddenly you reappear at the designated time you set and immediately die.
You find that at the time you set, the Earth was not there, and you are in a vacuum of space and no chance to get back.............
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.
Good grief...youve destroyed the premise for countless scifi movies..books..tv shows...killjoy.