Official data show that the observable universe, estimated to be about 46.5 billion light years, in the entire universe, there may be 2 trillion galaxies, the universe is so vast that the probability of the absence of other intelligent life is almost zero, and the famous Fermi paradox also illustrates this. However, why has there never been any conclusive evidence of alien visits to human beings on Earth? Aliens do not come into contact with human beings on Earth, and there are probably the following theories:
First, the doctrine of legislative protection. This view holds that there is an interstellar organization in the universe similar to the United Nations on Earth, which is committed to protecting the diversity of planetary civilizations, supporting each planet to take the path of independent development, opposing the interference of higher civilizations in the internal affairs of lower civilizations, and establishing this principle in the form of legislation. It is under the protection of interstellar law that the Earth is in a relatively safe environment.
Second, pet ownership said. According to this view, human beings on Earth were created by aliens, and human beings are like canaries in a cage, just for the creator to watch and play, and will never be released from the cage, so that they are exposed to all kinds of dangers and uncertainties in the outside world. And the aliens who created the earthlings, for the purpose of protecting their pets, will not touch the bird today and scratch the bird tomorrow, precious things can always be viewed from a distance and cannot be desecrated, even the creator must keep a certain distance from the canary.
Third, the theory of covert contact. This view holds that aliens are not in contact with the earthlings, but in some way that is not easy to be noticed, they are fully involved in human history, firmly control the earth's politics, economy, and culture, greedily occupy the earth's abundant resources, and influence the development and evolution of human civilization all the time, in order to achieve their ulterior purposes. The reason why the aliens chose to do it in a stealthy way is because they are afraid that once they appear in public, they will provoke the revolt of the human race, and in order to protect their own interests, they will "hide".
Fourth, I am the only one. This view holds that before the birth of human beings, an interstellar war broke out between extraterrestrial civilizations that affected the whole universe, and because of the huge scale and tragedy of the war, the entire universe was ruined and became a barren land, and the serious environmental degradation made various aliens about to come to the end of their lives. At this critical juncture, the alien races put aside their prejudices, eliminated their estrangement, and agreed to inject the genes of their respective races into the human body, so that human beings can thrive on the only survivable earth in the whole universe.