Is it possible for "time travel" to become a reality? Don't worry, the premise is...

What is time? It seems to be the greatest mystery in the universe.

Why can we move forward, backward, left, and right in space, but cannot freely travel through time and can only be pushed forward by time? In addition, we are all curious about what the future will be like after we leave this world. Although human life is limited, we are full of questions about what happens after death and have been looking for answers.

The science fiction novel "Janus Equation" describes a brilliant mathematician who is committed to exploring time travel. He meets a beautiful woman by chance and their relationship develops rapidly. Gradually, he becomes curious about her true identity and begins to actively explore. The mathematician later discovers that she has completely changed her appearance through plastic surgery and even had a sex change operation. The most unexpected thing is that this woman is actually a time traveler from the future.

At present, the mainstream scientific community still believes that time travel seems impossible, at least at the current level of technology and theory. There are several main reasons for this.

Albert Einstein's theory of special relativity tells us that time and space are closely linked. If a person travels at close to the speed of light, time will pass more slowly, and therefore they will appear younger relative to someone who remains stationary. But this doesn't give us any way to go back in time or travel to the future. According to special relativity, objects cannot move faster than the speed of light. So, to achieve time travel, we need to find a way around this limitation, but we don't seem to have found it yet.

Einstein's general theory of relativity tells us that the mass and gravity of an object will bend space-time. Although this theory has some strange space-time curves, such as black holes, it does not tell us how to travel through time.

The biggest problem here is the time paradox. If time travel is possible, it is possible to go back in time and change history, which will lead to logical confusion and paradox.

However, time travel into the future is actually possible, and such experiments have been proven millions of times. Suppose an astronaut flies at close to the speed of light and reaches the nearest star in one minute. Because the time inside the rocket slows down, only one minute has passed for the astronaut, but according to the time on Earth, it has jumped to four years in the future. In fact, every time an astronaut goes into space, he or she enters the future for a short time. When moving at a speed of 30,000 kilometers per hour above the Earth, their clocks run slightly slower than clocks on Earth.

Therefore, a time machine that can take us into the future would seem to fit in with Einstein's special theory of relativity.

Cosmologist Stephen Hawking has proven that time travel is possible by studying some theoretical physics concepts such as wormholes, space-time curvature, dark matter, etc. In 1990, Hawking read a colleague's paper that proposed a type of time machine, which aroused his doubts. He always believed that time travel was impossible because travelers from the future did not exist. If time travel was as common as having a picnic in the park on Sunday, travelers from the future should take pictures and interact with us, but this did not happen.

However, Hawking later changed his mind and said that "time travel may be possible, but it is not practical", which was widely reported in London newspapers. Hawking said that there is a time machine that involves wormholes. Einstein's equations describe that there may be a "bridge" in space that connects two distant points in space, allowing mathematical time travel, and traveling through a wormhole can travel to the past and even meet oneself. Hawking also said that matter can escape from a black hole and even lead to another universe. If you think you are in a black hole, remember that there is always a way out, but the wormhole through a black hole can only be a one-way trip.

As a result, time travel has become a field of study for theoretical physicists. Kip Thorne, a physicist at the California Institute of Technology and a scientific consultant for the Hollywood sci-fi blockbuster "Interstellar," wrote that scientists have realized that the nature of time is an important topic that should not be limited to science fiction writers.

Despite this, while there is still no direct evidence that time travel is possible, it is still often explored and depicted in science fiction literature and film, and time travel has become a common feature of science fiction works. The first novel to seriously attempt time travel was H.G. Wells' classic The Time Machine, in which the protagonist is transported 800,000 years into the future. In Superman 1, when Superman learns that Lois Lane is dead, he makes a desperate decision to turn back the clock, flying around the earth at high speeds, faster than the speed of light, until time itself turns back. The earth slows down, stops, and eventually spins in the opposite direction until all the clocks on the earth are running backwards. As the floodwaters quickly recede, the broken levees miraculously repair themselves, and Lois Lane returns from the realm of the dead.

In addition, there is another possibility, which is the concept of parallel universe or "many worlds", which at least solves the "grandmother paradox" of time travel: if the universe splits into two, on one of the timelines, the person you kill only looks like your relative, but is not your relative, because you are in a parallel universe, and this method seems to be the only one that conforms to quantum theory.

(The author Chen Sijin is a science fiction writer)