Is it possible to go back in time?

Going back in time cannot be realized.

Back in time generally refers to a closed time-like curve in relativity. Given a four-dimensional space, the distance between two points in the coordinate system is 0. In Euclidean space, two points with a distance of 0 coincide, but it is generally believed that there is a time axis in four-dimensional space, that is, two points overlap in space, but there is still a time distance.

That is, at two different time points at the same point, a new cone-like space will be formed in the coordinate system, commonly known as "light cone", that is, the overlapping points in space can transmit light in time. If we are in the "light cone", it is called "time-like" and vice versa.

The time machine is to construct a closed time-like curve and realize the reverse transmission on the time axis. Theoretically, it exists, but according to the calculation, all the coordinates at this time are unreasonable, that is, there is a strong spatio-temporal oscillation, which leads to the instability of spatio-temporal, and the transmission cannot be completed, so it is impossible to turn back the clock.

Related influence

If many technical problems are overcome, the production of time machine will open Pandora's box full of paradoxes. There is one last paradox about cross-time travel, which no one can solve so far.

For example, if a person really "goes back to the past" and kills his grandmother before his mother is pregnant with him, will the time traveler himself still exist? The most popular solution to the "grandma fallacy" in physics today is the "multiverse" theory-there is not only one world, but also many parallel worlds.

Refer to the above? Baidu encyclopedia-it's time to go back