Since humans realized that they are just a tiny part of the vast universe, they have embarked on a journey to search for extraterrestrial life. The United States implemented the Operation Paperclip before and after the defeat of the Nazis, importing a large number of scientists from Nazi Germany, especially rocket and missile scientists, which directly contributed to the development of space technology, missiles, and rockets in the United States during the Cold War, and sent the first human to the moon. China, on the other hand, has made significant progress from sending humans into space for the first time to sending Mars probes today.
In recent years, there has been a lot of discussion about science fiction novels and TV shows in China, especially after Liu Cixin's novel "The Three-Body Problem" was adapted into a TV series. Combined with the recent release of some previously classified UFO sighting materials by the United States, many people have become obsessed with the idea of extraterrestrial life, whether it be the Trisolarans in the novel or the future humans who have invented time machines. One big question people have is why haven't aliens contacted humans?
We often see some mysterious bloggers on media platforms, including some short video websites, making mysterious claims. They either make up stories or use clickbait titles, but in the end, they don't provide any conclusive evidence or meaningful conclusions. It's important to give them the opportunity to speak and express their opinions, but we should approach these claims with rationality.
I believe that the main reason we haven't received any contact from aliens is that they simply don't exist. This is the fundamental reason, and all other reasons are secondary. The most likely possibility is that we are the only form of life in the universe, and there is no other life, even in parallel universes. No matter how much human civilization represents itself in the universe, there will be no aliens receiving our messages.
Some people may disagree with this conclusion and argue that if there are no aliens, then how did humans come into existence if we don't believe in gods or deities? The answer is simple: chance. If we choose to believe in the theory of natural selection, we should understand that our society is filled with many myths and theories. Religion has brought countless disasters and catastrophes to humanity over the past thousands of years, which is why we believe it needs to be abandoned. The origin of humans has already been explained by science, and while there may be some debate about the details, there is no need to rely on the existence of extraterrestrial life as the ultimate explanation. Human civilization is unique, and that is important to recognize.
Another possibility is that extraterrestrial civilizations are so advanced that they have no interest in communicating with us. If they have achieved communism and reached an extremely high level of civilization, they would have no need for communication or aggression towards other civilizations. Therefore, it is normal for us not to receive any messages from them. Even if extraterrestrial life exists, their advanced civilization would have the ability to remain invisible in the universe, making it impossible for lower civilizations to detect them. So, all we can see in the universe are countless stars, without any signs of life, even though many planets have water resources.
Many scientists have proposed theories such as wormholes and space folding, but we have yet to achieve short-distance and short-time travel between two different spacetimes. Our civilization is not advanced enough to reach such a high level, which is why even though we have theories, we lack the technology and scientific means to test and achieve them. In this state, higher civilizations that do not want to communicate with us can easily hide themselves. The solar system is just a small part of the entire Milky Way galaxy, and we are far from the center of the galaxy, let alone exploring the entire 13.8 billion light-years of the universe. Science has no limits.
Another possibility is that extraterrestrial civilizations are not as advanced as human civilization and are unable to communicate with us. This is another extreme. If an extraterrestrial civilization is just beginning to evolve, even if it has evolved for billions of years, it may have only evolved into primates and has not yet mastered basic radio technology. In this case, it would be impossible for them to send out messages to communicate with other civilizations, especially if the distance between multiple civilizations is vast.
Shouldn't we consider this possibility? Many people foolishly believe that human civilization is the most backward in the universe and that any extraterrestrial life is more advanced than humans. They often talk about discovering traces of life on Mars, Venus, or Saturn's moon Titan. But if we consider a different perspective, if extraterrestrial life is not animal-like but rather plant-like, without the ability to speak or even evolve into a civilization, how would they communicate with others?
Another possibility is that extraterrestrial civilizations are at a similar stage of development as humans and have not yet reached a level where they can communicate with others. This is similar to the previous point, but if we imagine that even extraterrestrial beings are trying to find other extraterrestrial beings, but their scientific and technological capabilities are similar to humans, and they cannot even leave their own star system, why would we assume that they can communicate with humans? When they are still struggling with global politics and religion, facing the problems caused by extreme nationalism and the criticism of developing space technology at the expense of the people, what ability do they have to find humans on another distant planet? There may be many planets in the universe that are similar to Earth, but the evolution of the human species is a result of many coincidences. This kind of evolution is often lengthy, and if they happen to evolve a civilization similar to humans, they would also have to deal with many internal issues. Therefore, it is unlikely that they would spend a lot of energy searching for humans who have very little chance of existence.
Another possibility is that extraterrestrial civilizations believe that humans do not exist. They consider themselves to be the only life forms in the universe and have no motivation to search for other life forms. In this mindset, they may not develop various space sciences or only apply these technologies to search for resources within their own star system (for non-advanced civilizations). Therefore, they may not be willing to venture beyond their own star system.
It is also possible that extraterrestrial civilizations have not yet discovered humans. The universe is vast, and even if aliens have advanced technology, it is still impossible for them to explore the entire universe in a short period of time, especially when the universe is still expanding. If there is a higher civilization beyond humans, there must be an even more advanced civilization after the Big Bang. In this case, it is understandable that these civilizations, with the belief of self-protection, would not make themselves known to other civilizations. However, if they want to search for other civilizations, it can only be a slow process. With so many planets in the universe, even if their environments are not as good as Earth's, it is still possible for life to evolve. Therefore, searching all the planets would be time-consuming and labor-intensive, and it is not surprising that extraterrestrial beings have not reached our Milky Way galaxy.
Another theory is that extraterrestrial civilizations see humans as experimental subjects. Similar to how humans experiment on white mice and monkeys, they observe the natural development of human civilization without actively intervening. This theory may explain the birth of humans. For example, the famous question of which came first, the chicken or the egg, if we answer that the chicken came first, we have to answer another question: how did the first chicken think of reproducing through eggs? And if we answer that the egg came first, we have to answer who incubated the egg. Unless there is a very stable environment, it is impossible for eggs to hatch into chickens without the incubation of a mother hen. This question has puzzled us for a long time.
If extraterrestrial beings see humans as experimental subjects, only observing the natural evolution of the highest intelligent species that has evolved in a suitable environment, would they make themselves known to us? Just like the Watchers in the Marvel Universe, they know that we are looking for them, but we don't know that they are observing us, observing our politics, economy, culture, and so on.
In conclusion, we have enough reasons to believe that we will not discover any extraterrestrial beings in the near future. Although I believe that within the known universe, there may not be any higher civilizations.