Traveling in the past in time

What would have changed if there had been an opportunity to carry out a traveling in the past in time with a subsequent return to the present. What would this lead to? Let us discuss the purely physical side of the question.

What would have changed if there had been an opportunity to carry out a traveling in the past in time with a subsequent return to the present

In one fantastic novel by renowned writer Ray Bradbury, the travel agency sends its customers, with the help of a time machine, to shoot a live dinosaur in the distant past!.. However, such journeys into the past in time are possible only on one condition: travelers should not interfere in the events of the ancient world, or change it. But one tourist violated the ban - he stepped on some butterfly and crushed it. Returning in our time, everyone saw with astonishment that much in the world around them has changed...

The fact is that all phenomena occurring in nature are continuous chains of causes and effects. When making journeys into the past in time, the heroes of the novel should not interfere during any events, changing them. This would inevitably cause certain changes in the whole subsequent causal chain of phenomena.

For example, if such travel to the past in time caused the death of some people, then all their descendants will not appear. But then tens of hundreds of people will disappear from the present, for whom the dead were direct ancestors... Similarly, not only people, but also works of art, buildings and even whole cities could disappear. That's what would happen if a time machine had appeared and irresponsible adventurers would have started to jump on it at different epochs...

On the other hand, travel to the past in time would not only destroy the individual cause-effect series, but also create new ones, and from this, in our reality suddenly unexpected objects could suddenly arise... But in this way one could be engaged in and "correction" or "improvement" of reality by discovering any negative events in the real history of mankind.

But back to physics, which simply travels to the past in time forbids. Any event occurring in a physical system can influence the evolution of this system only in the future and can not influence the behavior of the system in the past. This is the general principle of causality, which requires that every phenomenon has a natural cause. But if we imagine that somewhere in the universe there are areas in which time flows in the opposite direction compared to our time, then this could be used to travel to the past. For this it would be necessary to make a double transition - from our region to "here" and back.

The question of traveling back in time in time has not been fully explored, but it can be assumed that traveling to the past will someday become the norm.