This paper takes part in the series essay competition of “great science” of Recordunkown.
We often say: the universe is so big that there are all kinds of strange things. In the vast space of the universe, there are only things that we have not seen, but none that do not exist. Any small probability event magnified into the whole universe will become an inevitable event.
Therefore, from the perspective of the universe, the existence of alien civilization is inevitable. If so, there should be a large number of alien civilizations in the universe theoretically, but why not contact us? I believe many friends have thought about such doubts, and scientists have put forward a variety of conjectures. In fact, there are two main reasons.
One reason is that the probability of civilization’s birth is very low. With the continuous improvement of human’s understanding of life, modern science believes that the origin of life does not require a high level of planet. As long as a planet has enough liquid water and geothermal energy, it is likely that life can be born.
There are many planets in the universe that meet this condition. Even in the solar system, there are many other planets that meet this condition besides the earth. For example, Europa has a lot of liquid water and geothermal besides its ice layer. Scientists have enough reason to suspect that Europa may have given birth to life, which shows that life may be universal in the universe.
Although life is very common in the universe, it is very difficult to form civilization through evolution. Let alone intelligent life, even complex life with preliminary consciousness is not so easy to be born.
If a planet wants to evolve intelligent life, it needs to meet very harsh conditions. According to the ecological situation of the earth, scientists have established a livable planet model. According to this model, scientists have found that the planet needs the following six factors for the birth of intelligent life.
1、 To be in the habitable zone of a galaxy is the most important external condition for a planet. Only when you are in the habitable zone can you get the appropriate light and heat demand, and there is a large amount of liquid water on the surface of the planet.
2、 There is a large amount of liquid water, which is the source of life. There are millions of organisms on the earth, most of which are composed of water. For example, 70% of human tissue is water.
Without water, life on earth would not be able to complete the following series of evolution, to evolve to a higher level of life, and to give birth to intelligent human life. Although the birth condition of life does not necessarily need the participation of water, but after the birth of life, if you want to continue to evolve into higher life, then the participation of a large number of liquid water is an inevitable condition. For example, the environment on Mars may give birth to life, but without a large amount of water, even if there is life, it can not continue to evolve and can only exist in the form of primitive microorganisms.
3、 The atmosphere is very important for life on a planet. As we all know, the universe is not peaceful and safe. There are many dangerous things that can threaten life, such as asteroid impact and all kinds of cosmic radiation.
Asteroid impact is very common in the solar system. We can see from a large number of craters on the moon, and the earth has encountered asteroid impact many times in its history. However, due to the existence of the atmosphere, these asteroids will rub and burn with the atmosphere before hitting the ground, and finally decompose and disappear.
Without the protection of the atmosphere, life on earth might have been destroyed many times, and there would not be the biological world now. The cosmic radiation is more destructive to life. Although many lives can survive in the harsh environment of the planet, few lives can resist the cosmic radiation. The atmosphere can effectively block and absorb most of the cosmic radiation and protect the planet’s ecological environment.
4、 There are two main functions of a strong magnetic field. One is to block all kinds of radiation from the universe. You should know that in a galactic environment, the radiation from stars is very strong. For example, the radiation of the sun, and can resist this radiation in addition to the atmosphere, another effective thing is the magnetic field.
Another function of magnetic field is to form a stable ecological cycle system. The earth is a world of magnetic field, and the existence of magnetic field makes the earth have a perfect and stable ecological system. Only a perfect and stable ecosystem can give life enough time for evolution, and there is hope for the birth of intelligent civilization.
5、 The guardian of a larger planet, we all know that in a stellar system, besides planets, there will be a large number of asteroids and other debris. The orbit of the planet is very stable, as long as the stars do not have major changes, there will be no chaos in the planetary system.
And a lot of asteroids and other debris are less stable, and they often go out of orbit and into the habitable zone. If a living planet is not guarded by a big planet in front of it, it will be hit by asteroids frequently, which will lead to the end of life evolution.
It is precisely because of the protection of the giant Jupiter that life can complete the evolution of 4 billion years, and finally the birth of human civilization. You know, in 1994, thousands of people witnessed a cosmic event never seen before in human history, that is, the collision between comet sumek levy 9 and Jupiter, the largest planet in the solar system.
Without the protection of Jupiter, this comet will collide with the earth, and the final result will be the complete end of the earth’s ecology and all life.
6、 There should be a satellite with a large mass nearby. A satellite with a large mass is very important for a living planet. The existence of a satellite with a large mass can change the rotation of the planet to a great extent and make it have a rotation speed more suitable for the evolution of life.
And the existence of massive satellites can also effectively stabilize the ecosystem on the planet’s surface, forming a very good ecosystem. It is precisely because of the existence of the moon that the earth has a stable and beautiful ecological environment and can complete the 4 billion year evolution of life.
These are the six factors that a planet needs to have in order to have an intelligent civilization. In the universe, there are very few planets that can satisfy these six difficulties at the same time, so the birth of intelligent civilization is not easy. Even so, the vast universe tells us that there should be a large number of alien civilizations.
But there is still no extraterrestrial civilization to contact us, here we have to think of another reason, that is distance. Distance hinders communication. This is what we all know. The vast universe is based on light years. The neighbor of the solar system is the beling galaxy. It’s 4.2 light years away from us. At the speed of human spaceships, it takes hundreds of thousands of years to reach.
It will take a long time for a civilization to realize this kind of interstellar shuttle. Before that, alien civilizations wanted to contact us only through radio signals, but we have not really received signals from alien civilizations until now. One reason for this may be that different civilizations use different signal modes.
For example, alien civilization uses gravitational waves to transmit signals, while human beings use electromagnetic waves. There are two different signal modes, so it is impossible to truly communicate. We can’t receive the signal from the alien civilization, and the alien civilization can’t receive the signal from the human. Only when the signal patterns of the two civilizations are the same or similar can they receive and communicate with each other.
Distance may be the main reason why we can’t contact with alien civilizations. From the cosmic scale and the harsh conditions required for the birth of civilizations, it’s very normal that there is only human civilization in the galaxy. If this is the case, then the alien civilization that we can communicate with needs to come from other galaxies outside the Milky way, such as Andromeda.
Andromeda is a neighbor of the Milky way, but it’s millions of light years away. If it is a radio wave signal with the speed of light, it will take at least millions of years for it to spread to the solar system, which is a very long time for a civilization. In addition, whether the wireless signal can spread so far without dissipating is also a problem.
In any case, the pace of human beings to explore extraterrestrial civilization will not stop. We can only expect that the signal of extraterrestrial civilization can be received by us. When human beings have the ability of interstellar navigation, we can take the initiative to explore other galaxies. At that time, we believe that it will not be too difficult to discover alien civilization.