# What happens when an astronaut flies at the speed of light for an hour and returns to earth?

Interstellar travel, in fact, refers to the travel across different stars. It is the dream of countless generations of human beings. In the future, it is also one of the important factors related to the survival of human race.

But for now, Star Trek is a huge challenge. Because of the vast space in the universe, the nearest star in our solar system is 4.3 light-years away from the neighboring star. The number of years of light is a unit of distance, that is, the number of years of light, which is about 946 million kilometers. This concept goes beyond everyday life experience. So even the nearest star is out of reach.

If we want to realize Star Trek, superluminal technology is a breakthrough. However, it is not easy for human beings to realize superluminal flight! So far, the fastest speed record created by artificial satellites is 17 kilometers per second, equivalent to 61000 kilometers per hour. How fast is that?

The circumference of our earth’s equator is 40075.02 km. It will take about 40 minutes for Voyager 1 to fly. The distance between the earth and the moon is about 384000 kilometers, and Voyager 1 will take about six hours to complete. The distance between the earth and the sun is 150 million kilometers, and Voyager 1 will take 1025 days to complete. Flying in the solar system takes such a long time and effort. It’s impossible to realize star trek.

But the speed of light is different. 300000 kilometers per second is equivalent to 1.08 billion kilometers per hour. It takes only 1.3 seconds, that is, 8 minutes, from the earth to the sun. How fast is the speed of visible light. Because the speed of light is very fast, people dream of having superluminal technology and want to experience the true meaning of light speed flight. In fact, Einstein explained the changes brought about by light speed flight in his theory of relativity.

When an object gets faster and faster, the time on it gets slower and slower. When it reaches the speed of light, it stops passing. When it goes faster than the speed of light, time goes back. But Einstein also poured cold water on human beings. He said that the speed of light is already the fastest in the universe, and human beings can’t surpass it in any case, which sounds frustrating.

If man can fly faster than light, when an astronaut flies at the speed of light for an hour and returns to earth in an hour, what will he see when he returns to earth?

If we refer to the time in the spaceship, according to Einstein’s general relative rate theory, the faster the speed is, the slower the time passes. When a person flies in the space at the speed of light for one hour, the time in the spaceship passes very slowly, but the time on the earth still passes at normal time. So when the spaceship flies at a very slow speed for one hour, the time on the earth will pass After thousands or even tens of thousands of years, when astronauts return to the earth, they may see that human civilization is more developed, or that human beings are extinct and dead.

If we take the time of the earth as a reference, this assumption also applies to Einstein’s conclusion in general relativity that the faster the speed, the slower the time. When astronauts return to earth from space, there is little change in the earth, because the earth is only one hour, while the time in the spacecraft is very slow, maybe only a few microseconds.

However, Xiaobian believes that according to the theory of relativity, if the speed reaches the speed of light, then time will be static. That is to say, for astronauts, the concept of time no longer exists, so whether it is a minute, a year or 10000 years, there is no difference in time for astronauts. So when he returns to the earth, the earth is likely to be the same as when he started It may be many years later, even the earth does not exist.

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