Why didn’t alien civilizations come to earth to contact with human beings? Scientists speculate that there may be five reasons

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

When human beings walk out of the earth with the help of science and technology and see the vast universe, they will think of the same question: is human the only civilization in the universe? Is there any alien civilization? Perhaps before human beings go out of the earth and see the vastness and mystery of the universe, they may have a very proud feeling that human beings are the only civilization in the universe.

However, when human beings really go out of the earth and realize the vastness and mystery of the universe, the previous pride no longer exists. In front of the universe, human beings are so small and terrible. It is the universe that is too big for us to imagine. Even if we analyze it with a very small probability, there can not be only human civilization in the universe. It is possible that the number of civilization in the universe exceeds our estimation and imagination.


If there are a lot of alien civilizations in the universe, why haven’t we found any? After walking out of the earth, human beings began the great “search for extraterrestrial civilization project”. Scientists launched Voyager spacecraft to explore the world outside the solar system, through astronomical telescopes to find earth like planets very similar to the earth, through radio telescopes to search for possible extraterrestrial civilization signals in the universe, and through observation to find the possible existence of the Dyson sphere.

Although scientists have taken various ways to find alien civilization, and it has been carried out for more than half a century, we still have not found any alien civilization. If we can’t find alien civilization because human science and technology are still very backward and have no ability to go out of the solar system to explore, then why don’t powerful alien civilizations come to contact us? Scientists speculate that there may be five reasons.

The first reason is that the alien civilization has not found us yet. As we all know, the vast universe is so big that we can’t imagine it. The observable range that can be achieved by human science and technology now is 92 billion light-years, and this range may only be the tip of the iceberg of the universe. In such a vast universe, there are so many stars, planets and galaxies that it is impossible to estimate. The distance in the universe is based on light years, and the distance between galaxies is more than a few light years.

It is precisely because the universe is too big, even if the science and technology of alien civilization is relatively advanced and there are more advanced observation means, it may be many times more difficult than looking for a needle in a haystack to observe the existence of the earth without the determination of the earth’s coordinates. And even if the alien civilization has observed the existence of the solar system and the earth, an unusual planet, it is impossible to determine whether the earth has civilization through remote observation equipment.


The second reason is that the distance of alien civilization is too far away. It’s easy to understand that the distance between galaxies can be as little as a few light years, as much as a few hundred or thousands of light years. If the alien civilization wants to come to the earth over such a long distance, the speed of the spaceship must at least achieve the speed of light. This is only relative to the galaxies close to the earth. If it is a galaxy very far away from the earth, it can’t be achieved before it can fly faster than light.

Some people may say that if the alien civilization is thousands of light-years away from the earth, and they also realize the speed of light, they can spend thousands of years to come to the earth. So is that possible? If so, alien civilization may be on its way to earth. But if we analyze it carefully, it seems that it is unlikely. Why?

As we all know, no life can live forever. In particular, the life span of intelligent life is not very long. The life span of human beings is about 70 years old now. Even if the life span of alien civilization is longer than that of human beings, it will not be too long. If the life span of alien intelligent life is as long as several hundred years, will it take them at least three generations to come to earth?


If we found out that there was an alien civilization in the biling galaxy, it would take us 3000 years to reach it at the speed of our spaceship. So will humans choose to send spaceships? I believe that the possibility is very rare, because the journey is too long. It takes more than ten generations for human beings to live a long life, and no one knows what will happen in the long journey.

There is only one situation in which alien civilization or human beings will spend thousands of years going to other galaxies. That is, when the galaxy where the parent star is located will be destroyed and unable to survive, for the sake of the continuation of civilization, we can only be forced to embark on a long and helpless interstellar journey. It’s better than that in wandering earth, when the sun is about to flash helium, human beings can only be forced to leave the solar system and spend more time It took thousands of years to go to the Bering system.

The third reason is that there is only one civilization in the Milky way. Some people may say, how can there be only one civilization in the Milky way with a diameter of 200000 light years? But if we know the vastness of the universe and the galaxy, when the universe is just a grain of dust, this possibility also exists.

We don’t know how many intelligent civilizations there are in the universe. Even if the number of civilizations in the universe is up to hundreds of millions, hundreds of billions or even more, they are extremely rare in the whole universe. We should know that within the scope of human observable universe, there may not be less than hundreds of billions of galaxies such as the Milky way. Even if there is only one civilization in each large galaxy, there will be hundreds of billions of civilizations within the scope of human observable universe.


Therefore, the possibility that there is only one civilization in the galaxy is very great. If there is only one civilization in the galaxy, then we can’t find the alien civilization, and the alien civilization can’t come to the earth, so we have a better answer. You know, even if a civilization wants to cross the Milky way, it needs to fly at the speed of light.

But if you want to reach Andromeda from the Milky way, you need millions of light-years of interstellar space, which is not the ordinary superluminal speed can achieve. So it’s very difficult for the intelligent civilization of other large galaxies to come to the galaxy.

The fourth reason is that human civilization is the most powerful civilization in the universe. Many people think it is even more impossible. How can human civilization be the most powerful civilization in the universe? If we say that human beings are the lower civilization in the universe, there is a great possibility. So can’t humans really be the most powerful civilization in the universe? If we analyze the history of the universe, we may find something new.


Our universe was born 13.8 billion years ago, and the newly born universe has only the most basic elements. It will take a long evolution to form a later rich universe, and this time may take 8 billion years. Scientists say that only after 8 billion years of the Big Bang can the whole universe be truly stable and have a relatively perfect environment and rules.

Only when the universe is stable can it have the foundation for the birth of life. Therefore, the birth time of life planet in the universe may be similar to that of life on earth. After the birth of life on a planet, it will take a long time for intelligent life and civilization to be born through evolution.

It took about 3.8 billion years for the earth from the birth of simple life 3.8 billion years ago to the birth of human beings. It is possible that this time is still a relatively short time in the evolution history of life to intelligent life. Therefore, the birth time of intelligent life on other living planets in the universe may be about the same as that of human beings, or even later than that of human beings.

Although it took millions of years for human beings to develop into the present scientific and technological civilization, it may also be a very short time for the evolution of a civilization. We need to know that human beings have only developed science and technology for hundreds of years, and then they have achieved their present achievements. This is a very extraordinary achievement. Alien civilization may not have such potential as human civilization. Therefore, most of the alien civilizations in the universe are still in the most primitive development time, and only a few of them may have just completed the feat of stepping out of the parent star.


The fifth reason is that the solar system is the experimental site of alien civilization. I believe many friends have heard of the “laboratory hypothesis”. This is a hypothesis put forward by scientists that the solar system is the experimental site of alien civilization, and the earth and human beings are the experimental products of alien civilization. For the laboratory, it is impossible for the alien civilization to contact with human beings. They just pay close attention to all the development of human civilization, from its birth to the present and the future.

Although the “laboratory hypothesis” sounds frightening to people, if a civilization develops to an advanced stage and has the technology to create life, it is entirely possible to carry out relevant life creation experiments in a galaxy or a planet in the universe. If human beings have mastered such technology in the future, maybe we will go to other galaxies to find a planet suitable for life, and then create life, constantly observe the various stages of life evolution, and the whole process from the birth to development of intelligent life.

The above five reasons are scientists’ conjectures about why alien civilizations did not come to earth. No one can give a definite answer to the truth. Only one day in the future, when human beings are really in contact with alien civilizations, will it be possible to know the answer. However, at that time, it was difficult to say whether human civilization was a blessing or a curse.


Guys, what do you think of this? Welcome to leave a message below to discuss and express your opinions.

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