Astrophysicist Ethan Siegel spoke about whether it is realistic to make a trip to the past. There are two scenarios for the consequences of such actions, one of which will lead to the destruction of the existing Universe.
Every second there is a huge number of quantum solutions in the world, and the chance to get an identical result once again under the same conditions and physical laws is equal to zero. Thus, a return in time and a change in the past cannot imply a return to the same Universe that we currently have. Events will inevitably develop differently, and they can turn out to be terrifying, the astrophysicist noted. He gave a well-known theoretical example: a person arrives in the past and kills his grandfather - in this case, he himself cannot be born. Such reasoning leads many scientists to the conclusion that time travel is impossible, since the past is "written" once and cannot be changed.
However, Ethan Siegel has suggested the parallel existence of several universes, and this idea can be combined with that of time travel. For example, a person learned about the impending death of his friend in a catastrophe. He invents a "time machine" and returns to the past in order to warn him of the danger. Everything goes according to plan, and the person safely returns to his present. But a problem arises - all this has already happened, and the friend would remember that he met with a friend in the past, received a warning and is ready for the inevitable. Thus, all actions in the past do not matter for the future, since they have already taken place.
An alternative way out is to assume that the past is not fixed, not written once and for all, and then it is possible to change it. However, in this case, any actions taken by the time traveler create a new, different history for the universe. Everything is possible here: killing your own grandfather before you were born, preventing parents from meeting and marrying, preventing World War II by Hitler's "re-education", and the like.
In other words, in this scenario, history can be changed. However, it should be remembered: the universe in which the time traveler lived will no longer exist after his return from the past. His actions changed the future - but at the cost of destroying his universe for him. In the new future, events will unfold differently - and, perhaps, the mentioned time traveler will not even be born in it, but will simply appear at the moment when he arrives on his time travel. That is, in this case, he would literally become a visitor from another universe.
Author: Vorobyova Alina