In space, Yang Liwei once heard a mysterious "knock on the door", but fortunately it was only a false alarm.

It has been a long time since mankind first looked up at the stars and successfully flew into space. During this period, we were arrogant and thought that we were the creator who ruled the earth.

However, with awareness, we found that this "heaven and earth" is far broader than what we saw. Gradually, we have a fear of the universe, but we still have the courage to explore. The more things we explore, the more awe we feel.

Of course, China people also have space dreams. After all, it was China who first created the "ancient simple rocket". It is said that he tied explosives under the chair and tried to blow himself up. It seems ridiculous now, but it represents our people's longing for the universe.

So, after everything was ready, Yang Liwei, as the first person in China's space flight, successfully took off in Shenzhou 5, and a small space capsule floated in the vast universe, and he really realized the feeling of "flying on earth, a drop in the ocean" written by Su Shi.

To know where the mysterious knock on the door in space comes from, we need to review how the sound is generated and how it spreads.

The junior high school physics textbook introduces the generation and propagation of sound in detail, pointing out that sound comes from the vibration of objects, so this kind of vibration is also called sound wave, and the sound wave that humans can hear is generally between 20 Hz and 20000Hz.

The fastest light in the universe can travel without medium, but not sound. It must spread through the media to be heard by everyone. In contrast, the voice is really much weaker.

It travels at different speeds in different media. Generally speaking, solids are greater than liquids, and liquids are greater than gases. For example, the propagation speed in air is 33 1m/s, and it can reach 153 1m/s in seawater. At this rate, Poseidon, the god of the sea, speaks at the bottom of the sea, and it must be faster than Zeus in the sky.

The transmission of sound belongs to machinery, in short, machinery produces fluctuations and then transmits energy through related media. Accordingly, we often see electromagnetic waves, which can spread easily even in the vacuum environment of the universe without medium. As for the common water waves and seismic waves in our lives, they all belong to the category of mechanical waves.

The principle of sound propagation is very simple, that is, the object vibrates, then propagates through the medium (solid, liquid, gas) and finally reaches our eardrums. Take air-borne sound as an example. This vibration collides with molecules in the air.

At the same time, sound has many characteristics, such as loudness, tone, frequency, timbre and so on. In the choir, the voices will be divided according to these characteristics, such as the common tenor and alto.

As for timbre, it's a matter of talent. Although they are both men, but their timbres are very similar to those of girls, the difference in appearance and voice between Charlie and Li Yugang has aroused heated discussion among the public.

One day in June 65438+1October 65438+May, 2003, Yang Liwei, the first man in China's space, boarded the Shenzhou 5 at Jiuquan Launch Center and successfully took off. He completed 14 laps in orbit and stayed in space for 2 1 hour for 23 minutes. Afterwards, Yang Liwei successfully returned to China under the eyes of the public, realizing the Chinese nation's desire to travel in space for many years and representing a new chapter in China's space industry.

After successfully returning to the ground, major media rushed to interview Yang Liwei, hoping to learn more about his magical and short space trip. After patiently answering many questions, Yang Liwei mentioned a very strange thing he met.

He said that after flying into space, he had heard strange sounds, like someone knocking on the door of a spaceship, which kept ringing. Strangely, the ship didn't give any alarm, which means that all the equipment is all right. Yang Liwei immediately told himself to stay calm, listen to the sound quietly through the porthole and observe the movement around him.

However, Yang Liwei finally failed to find the source of the sound, and as an astronaut with long-term training and rich physical knowledge, he did not think that any sound could be transmitted through the space capsule in a "vacuum" space environment, let alone a "mysterious man" knocking at the door outside the capsule.

After returning to the ground, he immediately told the engineer about it, but in the end he didn't find out the reason, and it became a mystery.

When people heard about it, they all expressed their guesses. Some people think that pebbles in space hit the cabin, some people think that small robots sent by aliens tried to knock on the hatch to communicate with us, but more people think that this sound is the sound made by the spacecraft itself when flying at high speed. Everyone stuck to their words and felt that what they said was more reasonable. The "mysterious knock on the door" once caused heated public opinion.

Compared with folk speculation, experts will start from a more rational and scientific perspective. Experts in space engineering at the National University of Singapore pointed out that the propagation of sound depends on the medium, and there is no medium in the space vacuum environment. Therefore, this knocking sound can only be caused by something hitting the spacecraft, but it can make such a loud sound, and the frequency is very high, which is unlikely to be an object collision.

It was not until 13 years later that another experimental device "Gong Yue No.1" was established in China based on the Chang 'e Project, in which volunteers also heard the same knocking sound. After repeated records and research, Liu Hong, the chief designer of Gong Yue No.1, gave the answer.

Gong Yue-1 is actually a small ecological cabin, in which the ecosystem can create conditions for human survival. It can be regarded as an ultra-small "immigration base", with a planting area of 69 square meters and a comprehensive cabin area of 42 square meters.

According to the volunteers in the hut,

Unlike Yang Liwei's inability to leave the cabin for inspection, everyone immediately left the cabin for inspection, but the source of the sound was not found. Finally, the technicians carefully examined the cabin body of the closed cabin and found that the material of the cabin body was deformed under the action of internal and external pressure difference, and it was this deformation that made a banging sound.

Experts say that this is actually when the temperature changes, the pressure inside and outside the cabin is also affected, and the change of pressure difference affects the shape of the cabin material, making it change.

Therefore, the mysterious knock on the door that Yang Liwei heard that year came from this change. It is conceivable that the space capsule exercises muscles like a human. After all, when we stretch our muscles, we sometimes click.

Fortunately, the so-called mysterious "knock on the door in space" is just a false alarm. Sure enough, we still have to stick to the scientific concept and find the answer to the puzzle.

The principle of sound propagation introduces the conditions of sound propagation, but apart from mechanical waves that can only propagate through media, another electromagnetic wave can completely propagate in a vacuum environment. However, many people believe that in order to be worthy of the mystery and vastness of space, the environment of "telling more in silence than they tell in sound" is better.

Although there is no medium for mechanical wave propagation such as water molecules and air molecules in space, there are countless particles controlled by electromagnetic fields. These particles are surrounded by moving electromagnetic waves and fly around. We can hear these sounds when we listen with professional equipment. Now astronauts also use electromagnetic waves to communicate in space, which is also called radio communication.

Generally, there will be a radio communication device in the spacesuit, and you can hear the sound after receiving the signal from your companion.

Of course, the sound here belongs to the category of mechanical waves. After all, there is air in the ecological cabin of the spacesuit. Moreover, with human hearing and understanding, it is impossible to directly hear and analyze the contents of electromagnetic waves.

It is worth mentioning that one of the most important ways for us to find extraterrestrial civilization is to use the method of receiving and analyzing radio waves to try to find and crack the laws behind this pile of chaotic sounds. This may be the only way for us to communicate with alien civilizations in the future, provided that we find them.

You can imagine how you would react if you were Yang Liwei and you were sitting alone in the spaceship and suddenly heard a knock at the door. I believe that most people will feel panic.

Looking out through the small porthole, my eyes are full of darkness. The whole spaceship is like a small drifting bottle in the middle of the vast sea, and I don't know where to go.

Humans are naturally afraid of darkness and loneliness. Fire helps us to light up the darkness, and living in groups eliminates loneliness for us. However, the darkness and loneliness of astronauts in space will be infinitely magnified. So how to overcome psychological problems and spend a long space journey? In addition to daily training, the companionship of peers is also very important.

Fortunately, China's space technology has developed to a higher level. The recently launched Shenzhou XIII will take astronauts to travel in space for six months, even after the first "China Year in Space".

Fortunately, the astronauts traveled together this time. Even if the journey is long and you are in boundless darkness, everything will not be so bad once you have company.

According to the video reported by the media, the three astronauts are in good spirits and will help each other get haircuts. It is reported that when the China New Year comes, they also plan to package "Space jiaozi" and spend a happy China Year in space with the people all over the country on the ground.

Looking forward to the continuous development of science and technology in the future, one day we can travel in space together. At this time, if you hear a knock at the door in the cabin, you don't have to panic and wonder. After all, we already know the real answer.

Human cognition of the world has always been tortuous. In those days, the inexplicable mysterious knock on the door turned out to be just a false alarm, and those horrible thoughts just scared themselves. With the development of science, many past puzzles have been solved by us, which is a necessary process for our cognition to become clearer.

I don't know what new experiences people who immigrated there for the first time will have after establishing other planetary bases for decades or a hundred years.

Whether it's a knock on the door in space or the mysterious "gibberish" of aliens, we can't stop exploring. "Science" has always been fearless, calm and rational. With the tenacious will of mankind, it will surely climb higher and further.