# Flying out of the earth at the speed of light for one minute, can you still see your family and friends when you come back? There’s no hope

*This paper takes part in the series essay competition of “great science” of Recordunkown.*

*Time is something we touch all the time. For many people, time may not be mysterious, because it surrounds us all the time. We go to work, go to school, go to bed, get up and so on every day is determined by the time.*

The earth’s rotation cycle, day and night alternate, the four seasons of the year have time to participate in it. In our daily life, there is no intuitive feeling for time. It is too common for most people. But is time as common as we think?

In many people’s cognition, everyone, in different places, has the same time. When you have an appointment with your girlfriend to meet at a certain place at 8 p.m., when 8 p.m. arrives, normally you and your friends will meet at the appointed place.

One day, you arrive on time, but your girlfriend is an hour late or an hour early. At this time, if your friend thinks she arrived on time, what will you think? If both you and your friend didn’t lie and arrived at the prescribed time, it only means that your friend’s time is different from yours.

*This seemingly strange situation, in the eyes of many people, is impossible, because in our inherent cognition, the time is the same, impossible, your time is 8 o’clock, and your friend’s time is 7 o’clock.*

One reason why people have this kind of cognition is that the time we usually recognize is the same. Another reason is that Newton’s absolute view of time and space is deeply rooted in the hearts of the people, which affects our persistence in thinking.

So is time absolute? The answer is No. When Einstein put forward the theory of relativity, we have a more accurate definition and description of time and space. Under the theory of relativity, time is not an absolute thing. Space and time are distorted, so time naturally is distorted.

In special relativity: the passing speed of time is related to the moving speed of objects. The faster the moving speed of objects is, the slower the passing speed of time is. If an object moves infinitely close to the speed of light, then time infinitely close to static.

In general relativity: the speed of time passing is related to the gravitational field. The larger the gravity (the larger the curvature of space-time), the slower the speed of time passing. If there is a big space-time distortion in the space where you and your friends live, the time between you will be very different, and it’s normal to be late for an appointment.

In fact, time warping is everywhere. The time and space of the earth we live in are also warped, so there will be differences in time between different places. However, the difference is very small, and we can usually ignore it. But when we walk out of the earth, the time difference between the space-time outside the earth and the earth’s surface will become larger.

Many friends know the navigation system, it is the use of satellites to navigate things on the surface. The satellite navigation time we see is synchronized with us, and there seems to be no difference, but in fact, this time has been corrected.

There is a certain difference between the time on the navigation satellite and the time on the ground. If there is no correction, the navigation will deviate from the actual situation. Navigation is also an example of human’s initial application of time inflation.

The existence of time distortion and expansion has been a scientific theory, and the theory of relativity tells us that with the increasing speed of objects, time is also slowing down. When the time of an object is infinitely close to the speed of light, the time of the object itself will be infinitely close to rest.

Now that we know that time warps, let’s look back at this problem. If a spaceship flies out of the earth at the speed of light for one minute, for the people on the spaceship, the time is just a minute past, very short. But for the people on earth, it may be a very long time, it may be 100 years, 1000 years or even 10000 years.

In the process of flying, theoretically, the time of the spaceship itself will be at rest. No matter how long it flies, the time needle will be still. If so, then for the spacecraft itself, there is no one minute, because time has stopped.

However, according to Einstein’s theory of relativity, the speed of a mass object in this space-time can only be infinitely close to the speed of light, but can not reach, let alone exceed the speed of light. Therefore, the fastest speed of a spaceship can only be infinitely close to the speed of light for one minute, which is relative to that of a spaceship.

Due to the distortion of space-time, when a spaceship flies at sub light speed, the space it sails will expand in time, resulting in a huge difference between the spaceship’s own time and the outside time. In this way, people on earth will see the spaceship fly out of the earth, after a very long time to come back.

The people on the spaceship only experienced one minute, and in such a short time, they had little change. But when they returned to the earth, they saw earth shaking changes. The relatives and friends we met a minute ago may have long been dead, and they may even be ancient people in remote history.

This kind of situation is also relative to a kind of time travel, and you can travel to the future in a very short time by taking a spaceship that is infinitely close to the speed of light. This kind of travel is not acceptable to everyone. Imagine that when you are ready to fly at the speed of sublight in the universe, you may not be destined to see your relatives and friends on the earth again. Even if you only leave for one minute, the earth has gone through many vicissitudes.

Of course, the speed of sublight, which seems to us to be incredibly fast, is just a tortoise’s speed at the cosmic scale. At such a speed, it is difficult for human beings to get out of the galaxy, let alone explore the whole universe.

The speed that can make us realize the dream of exploring the universe is only faster than the speed of light, but under the theory of relativity, the speed of objects cannot exceed the speed of light. Does that mean that superluminal speed cannot exist? Of course not. In fact, the universe is faster than the speed of light. For example, the universe expands faster than the speed of light.

*Superluminal phenomena exist in the universe. Existence is reasonable, which is in line with scientific theory. But relativity tells us that the speed of an object cannot exceed the speed of light. What’s the matter?*

In fact, superluminal phenomena are not contrary to the theory of relativity. They are applicable to different areas. Relativity only says that the speed of an object cannot exceed the speed of light, but relativity tells us that space-time can be distorted. There is no upper limit on the speed of distorted space-time, which can exceed the speed of light.

Therefore, it is impossible for human beings to achieve superluminal flight in the future by relying on the power of objects. We can only put our hope on the research and exploration of space-time distortion. The spaceship itself cannot fly faster than the speed of light, but the space around the spaceship may exceed the speed of light under certain distortion.

Let the spaceship move forward in the twisted space with superluminal speed, then the object can fly at superluminal speed, which is similar to a kind of surfing on the earth. And this kind of interstellar voyage, we can often see in some science novels and movies, that is space jumping or wormhole shuttle.