If parallel universes existed, would it possible that someone could go to their desired universe in the past or future.
Einstein's theory of relativity is still a hypothesis. This theory is too sci-fi now, let’s talk about something more realistic. It is now known that there is another Nikola Tesla theory of space and time called "The Dynamic Theory of Gravity"One could according to relativity theory build a machine that is sent near the event horizon of a black hole and kills you by electrocution each time your preferred future has not been met on earth according to your Twitter feed. You will only remember the future where you got what you wanted. The problems are: getting out of the black hole, futures already set in stone due to determinism, many failed electrocutions that you do remember, any afterlife, and that your space nemesis is spamming your feed with fake news to make the opposite things happen.
Going back in time to your own actual past would create a feedback loop and not work according to Stephen Hawking. You went there because you did not... Like stepping into a blender.
If parallel universes do exist, there might be an alternative universe where time moves slightly slower and looks almost like our past, but if you would somehow teleport there to a specific time and place, a centillion alternative versions of you from other universes might have the same idea and smash into each other, creating an instant black hole of human flesh destroying that entire alternative universe upon arrival.
All in all, time travel seems like a very dangerous hobby.
As a whole, yes. But the effect on time is still easily measurable and could be used to fast forward time. Earth itself is slightly like a time machine relative to the space around us.Einstein's theory of relativity is still a hypothesis.