According to US media reports, in 1950, a meaningful lunch session laid the groundwork for astronomical exploration in the next few decades. The physicist Enrico Fermi and his colleagues held some debate on the two main issues:
First, the galaxy is very old, very large, there are hundreds of billions of stars, and a large number of livable planets;
Second, this means that aliens in the galaxy has sufficient time to evolve and develop.
However, if aliens exist, humans have gone through decades of space exploration why they have not found them?
This simple and influential argument is called "Fermi Paradox", so far scientists have not given up on the exploration of aliens, they believe that aliens should be common in the universe, but now did not find any conclusive evidence.
SETI Institute uses the California Alan Telescope array to confirm the strange radio signals from the HD 164595 stars, HD 164595 stars from the Earth for 94 light years.
So far, mankind has not grasp the evidence of the existence of aliens, the United States, "Life Science Web site," the latest author lists the human beings did not find alien 12 reasons.
The following is a list of 12 possible reasons why scientists have not found aliens in humans:
1, the universe can not find aliens. In fact, a galaxy contains hundreds of billions of stars, and the livable zone may have 40 billion earth-like planets, the Earth is the only high intelligence civilization civilization seems unlikely.
2, in addition to the Earth human beings, the universe does not exist other high intelligence and civilization. Other planets in the universe may exist in the form of life, but they may be only microorganisms or other "quiet" creatures.
3, the wisdom of alien lack of advanced technology. At present, astronomers use the radio telescope to listen to the night sky, so if the aliens do not send any signal, we will never know their existence, perhaps aliens did not reach the Earth's human technology level.
4, the wisdom of life from the destruction. Whether it is weapons of mass destruction, planetary pollution or the manufacture of malignant diseases, may lead to the wisdom of life to self-destruction of the road, they may only exist for a short period of time, to self-destruction way to disappear.
5, the universe is a fatal place. The existence of the wisdom of life for billions of years of the universe is very short, asteroid collision, supernova explosion, gamma ray burst, flare and other phenomena may make a life planet completely destroyed, become alive.
6, the universe is too big. Only the diameter of the Milky Way has 100,000 light years, so we can imagine focusing on alien signals limited to the speed of light, it is difficult to survey the galaxy outside the more distant areas.
7, we did not observe for a long time. When people spend 80 years searching for alien signals through telescopes, we can actively search for aliens for 60 years. Maybe we spend less time on aliens and need more lasting observations and exploration in the future.
8, we did not find the right place. Scientists have mentioned the vastness of space, so there are many areas can listen to the alien signal, if we are not precisely towards the alien source, we will not hear.
9, alien technology may be too advanced. Radio technology has been widely used around the world, but for distant stars, extraterrestrial civilization may be more advanced, with more advanced communication technology, such as: neutrino signal. So far we still can not decode.
10, aliens do not send a signal. Researchers listen to the signals from aliens, but the signal is an inertial thinking of the Earth's human beings. In addition to some insignificant efforts, as well as the stars outside the solar system to send narrow band strong signal, we are difficult in the universe to prove the existence of human beings on Earth. In fact, if aliens like today's human beings to master similar radio telescope technology, our television and broadcast signals can only be detected within 0.3 light years, this distance can not even reach the most distant areas of the solar system.
11, aliens deliberately do not touch the earth mankind. Earth and we are in contact with the original indigenous people to follow certain rules, it is likely that the same thing will happen to humans. Like the episode described in the science fiction drama "Star Trek", higher intellectual civilization may limit contact with other extraterrestrial creatures and restrict exposure to species that acquire advanced technology.
12, aliens already exist, we just did not find. The conspirators like to discuss aliens with unusual explanations. Although the probability of finding aliens is very small, it is not impossible for the government to conceal the presence of aliens.