Have you ever wondered where you would go if you had a time machine?

A Chinese physicist says that the answer may be more frustrating than it seems: We can travel only to the future, not to the past.

Hongseng Zhang, a researcher at the University of Jinan, has shown that in a wide range of theoretical models of the universe, a return to the past can be impossible.

His argument is based on the way light and objects move into space-time.

According to him, if space-time can be divided into strands along which light travels, any object that moves slower than light should pass these layers in just one direction.

Zhang compares this to a ladder you can only climb up, but you can’t go down again to the ladder from which you started.

Two theoretical exceptions

However, the theory leaves two options that could at least mathematically allow for a return to the past.

The first is related to extreme areas, such as near the center of a rotating black hole. In such cases, space and time can be twisted so much that an object’s trajectory can form a snare.

A second option is related to the shape or topology of the universe. In theory, space can be built so that a journey always before it can lead you back to where you started.

These roads are known in physics as a timer.

The journey towards the future is real.

Unlike past travel, travel toward the future is supported by Albert Einstein’s theory of relativity.

When a person moves at very high speed or is in a very strong gravitational field, the time to spend more slowly compared with someone else.

Thus, astronauts who spend months at the International Space Station return to Earth several thousandths of a second younger than they would have been if they had stayed on Earth.

However, Zhang points out that his study does not prove that time travel is absolutely impossible.

It only shows that, in some types of space-time, the very geometry of the universe does not allow for a return to the past. /Telegraphy/