This universe is based on Cause and Effect. That is why the flow of time is in one direction, meaning you cannot go back in time and change events.
According to Einstein’s theory of relativity you can go back in time, but there is a complication. In scientific terms, it is called the Grandfather Paradox.
Suppose you go to the past and kill your grandfather, will you be able to come back in the future and if you have killed your grandfather, then you cannot be born, then you go to the past and kill your grandfather. Came to kill?
So far the theory is that you can go back in time but not change anything. That is, you can only look at the past.
Another solution was to go past your own copy, not your own, and kill his grandfather, not yours. (It won’t hurt you). Your grandfather will live in your past.
But that is not the solution, because in a way you are ignoring the problem and making a new copy. The real problem is, if you kill your grandfather in the past, it is impossible for you to be, and if it is impossible for you to be, how can you kill your grandfather?
In quantum mechanics, atomic particles such as electrons, etc. are in superposition. That is, the rotation of an electron, both upside down and upside down, is possible at the same time. Unless it is observed, the electron is spinning upside down and upside down at the same time.
Something similar is possible in this case, as if you and your grandfather were both alive and dead at the same time.
In recent days, however, another interesting solution has emerged. That is, even if you kill your grandfather in the past, you will still live. The solution is that even if there is a disturbance in time or in the past, he fixes it on his own. That is, even if you kill your grandfather, the events will change or you will arrange yourself in such a way that you will be present in the future despite killing your grandfather. If one event has already happened and another event is to result, it will continue to happen. There is nothing that you can do about it. This is a very interesting but complex thing.