How big is the vast universe? At present, no one can say clearly, with the current human observing capabilities, the observable range has reached 93 billion light-years. Within this wide observation range, there are approximately 2 trillion galaxies similar to the Milky Way, and there are 100-400 billion stars in each Milky Way.
In the cycle of each star, there are basically a varying number of planets orbiting around. In a suitable habitable zone, the conditions for the birth of life are theoretically available. Therefore, from the perspective of the vastness of the universe, there is a high probability that alien life and alien civilization exist, not to mention the 13.8 billion years since the birth of the universe, which makes us firmly believe that there should be a large number of alien civilizations.
Since there are a large number of alien civilizations, why have we been unable to find them? Scientists speculate: It may be affected by the large filter mechanism. For alien civilization, I believe that every friend has a strong curiosity, want to know what aliens look like? What kind of civilization is alien civilization?
Scientists are studying the process of exploring alien civilizations and put forward many famous conjectures. For example, in 1951, when Nobel Prize winner Fermi discussed the issue of aliens with others, he put forward the famous “Fermi Paradox”. “On”, Fermi believes that although the Milky Way is 100,000 light-years in diameter, from the perspective of the universe, the Milky Way can only be regarded as a particle of dust, it is very small.
The current scale of the Milky Way galaxy cannot be crossed by humans, but human science and technology have only been developed for more than 200 years. If we give us more than a million years of development time, we believe that humans can cross the galaxy. At that time, the Milky Way will be full of traces of human beings, and we will leave traces of human steps on various life planets, and alien civilization will naturally know the existence of humans based on these traces.
What human beings can do, maybe extraterrestrial civilization can also do it, and the age of the universe is 13.8 billion years old. In such a long period of time, in theory, there should be many millions of years and hundreds of millions of years earlier than human beings. Even a civilization of billions of years of wisdom.
If there is an intelligent civilization that has been developed for such a long time, then theoretically their technological strength is beyond our imagination, and there is a high probability that they will have the ability to navigate between stars. If the Milky Way has such a powerful advanced civilization, then they should have discovered the earth a long time ago, and may have been to it. But the reality is that we have not found any traces of aliens on the earth. What is going on?
There is a big difference between theory and reality, and this situation confuses many people. The power of science is infinite. In the 1960s, Soviet astronomer Nikolai Kardashev envisioned the level of cosmic civilization and divided the cosmic civilization into three levels. According to this classification standard, human beings are currently only 0.7 Level civilization.
In these three levels, as long as the technology is developed to the stage of second-level civilization, the galaxy can be crossed, or even initially out of the galaxy. If it reaches the third-level civilization, then the entire universe will be the back garden of civilization, and the universe will not have What secrets exist.
According to the age of the universe at 13.8 billion years, theoretically, there should be a technological civilization that has been developed for billions of years. Such a long technological development time can at least enter the stage of second-level civilization, and even hope to reach the field of third-level civilization. If so, the existence of the earth and human beings is not a secret at all. They will come to the earth to come into contact with humans or leave some traces on the solar system and the earth.
However, after more than half a century of exploration, scientists have not found anything definite about alien civilization in the solar system or on the earth. So where is the powerful alien civilization? In this regard, scientists have put forward many hypotheses and conjectures, the most famous of which is the “big filter” conjecture.
The “big filter” conjecture believes that the evolution and development of life in the universe must go through nine stages before it can develop step by step from the initial simple life to the stage of interstellar civilization. Each stage is a threshold, and only after crossing it can we enter the next stage.
According to the theory of planetary systems, as long as the terrestrial planets are in the habitable zone of stars, they have the conditions for the birth of life. It can be seen that life in the universe may be universal. It’s just that different life planets will go to different fates in the process of evolution and development. In some life planets, life may only evolve to the multi-cellular stage and then be destroyed by disasters. They did not cross this filter and were finally destroyed. eliminated.
Some life planets may have developed to the stage of intelligent life, but they have not yet stepped out of their mother planet, but they have also been destroyed due to cosmic disasters, and similarly they have not crossed the passer. On the countless life planets, due to the existence of the big filter, the countless life planets are reaching the end, and no civilization has passed through and eventually becomes an interstellar civilization.
Moreover, the nine stages of the Great Passer, the more difficult it becomes as they go to the back, some alien civilizations may be one step short of being able to become interstellar civilizations, but they will eventually be eliminated. Before becoming an interstellar civilization, no matter how much your technological strength develops, you will not be able to stop some cosmic disasters from destroying civilization.
We all know that the universe is not peaceful, and there are many disasters that can easily destroy a living planet, such as asteroid impacts, the transformation of stars into red giants, supernova explosions, and black holes engulfing. Among these disasters, supernova explosions have the greatest impact on life. Supernova explosions are a process that massive stars have to go through to their end.
In the process of supernova explosions, gamma-ray bursts will occur, which are the harvesters of life and can harvest carbon-based life within thousands of light-years. To escape the harvest of gamma rays, one must have the ability to navigate between stars.
The various terrible disasters in the universe may be the reason why life cannot completely cross the big filter. These disasters that occur all the time prevent civilizations from finally growing up to become interstellar civilizations. Before becoming an interstellar civilization, any intelligent civilization is in the universe. There are ants-like existences in front of them, and a disaster can easily end them.
Now that mankind has stepped out of the earth and began to develop into space, but even so, we have not reached the first-class civilization, and it may take at least 100 years before we can enter the first-class civilization. It is another important threshold to leap from the first-level civilization to the second-level civilization. Whether human beings can cross the past is still unknown.