Where are they?
In the middle of the last century, the famous physicist Fermi suddenly came up with five words by chance, which became the essence of Fermi's paradox. Although it is only a simple five words, it contains too much content. In the decades that followed, the "Fermi Paradox" became one of the problems that plagued astronomers.
According to the interpretation of the "Fermi Paradox", the Milky Way has more than 200 billion stars, and the observable universe has hundreds of billions of galaxies such as the Milky Way. Each star has almost its own star system, with more than one planet. This means that there are trillions of planets in the observable universe.
Among the large number of planets, even if the probability of intelligent life appearing is very small, in absolute numbers, there will be a large number of alien civilizations. This probabilistic analysis is derived from the idea that the Earth is not special, and the Drake formula illustrates this well.
This is also more in line with the "mediocrity theory" view, that is, our earth is not special, nor rare, but just an ordinary planet in the vast universe.
The emergence of human civilization is only a million years, and the emergence of modern civilization is only a few hundred years, which is only a moment in the long history of cosmic evolution. The universe has a history of 13.7 billion years, and if there are a large number of alien civilizations in the universe, theoretical analysis, the possibility of one or more alien civilizations with a history of more than 10,000 or even millions of years is very large.
Imagine how high an alien civilization that has developed for millions of years would reach, or the entire universe would see them. But why hasn't humanity found any clues to an alien civilization?
For the whole problem, it is not only the universe lovers and melon-eating masses who are confused, but also the astronomers who feel headaches. Based on existing relevant theories and the evolutionary history of life on Earth, scientists have given the following speculations.
1. Human beings are really lonely, and the vast universe is really only ourselves.
Don't rush to refute it, it's just a guess, a theoretical possibility. At least until we actually find aliens, this possibility does exist in theory. But I believe that no one would think that humans are really the only intelligent species in the universe, and if so, how conceited would that be?
2. Human technological civilization is still quite low-level, and there is no way to find aliens.
Human civilization has developed by leaps and bounds in recent centuries, especially in recent decades. As rulers of the planet, we have the capital to be proud of it. But looking at the entire universe, human achievements are insignificant, just as the earth is as small as a grain of sand in the vast universe.
A fact that is so simple that it is almost desperate illustrates this point very well. The Voyager I spacecraft, which has flown for half a century, is currently the farthest artificial vehicle to fly away from the earth to the vast space, flying more than 20 billion kilometers.
But at the current speed of Voyager One, it will take more than 10,000 years to fly out of the solar system. Flying to the closest star system to the Sun, Proxima Centauri, takes 70,000 years!
Speed is the basic factor that restricts human flight out of outer space. But if humans want to fly farther, it's not just about speed. Safety, diet and many other aspects of the problem must be solved. Once off earth, the fragile side of humanity is fully exposed!
3. Aliens do exist, but before they developed the technology of interstellar travel, they went extinct for various reasons.
This is also the legendary "Big Filter" theory. A barren planet develops an intelligent civilization with interstellar colonization, divided into nine stages, each of which acts like a "filter" to filter out countless life forms that may develop civilizations.
And even if life passes through the "Great Filter" to the stage of interstellar civilization in the process of evolution, it does not mean that it is smooth sailing, and there are many "filters" testing interstellar civilization.
For example, violent cosmic events, fierce conflicts within civilizations (such as nuclear wars, biological and chemical weapons, etc.), and technical barriers that are difficult to break through in key technologies of interstellar travel may block an intelligent civilization from the ranks of real cosmic civilizations.
The current human civilization can only be regarded as just entering the ranks of interstellar civilizations, our exploration of outer space has just begun, and it is still a long time before we can truly travel through the space of the universe.
Perhaps, in the process of development of countless alien civilizations, most of them have been filtered out by the "big filter", and the very few who can make breakthroughs are difficult to be discovered.
4. The direction of human exploration of extraterrestrial civilizations has gone wrong.
For a long time, humans basically relied on electromagnetic wave signals to find clues to alien civilizations, but there was almost nothing to gain for decades.
Humans use electromagnetic wave signals to transmit all kinds of information, and it is taken for granted that extraterrestrial civilizations will do the same. But who can be sure? What if extraterrestrial civilizations had long ago abandoned electromagnetic waves, the "old" way of disseminating information? In that case, we will never find the existence of an alien civilization.
Electromagnetic waves travel at the speed of light. The speed of light is very fast in the eyes of human beings, but it is as slow as a snail in the face of the vast universe. It is hard to imagine that a highly developed alien civilization is still using electromagnetic waves to transmit signals!
In the past decade, more and more mysteries of the universe have been discovered by scientists, such as dark matter and dark energy. Unfortunately, scientists know almost nothing about them at the moment. And dark matter, dark energy fills every corner of the universe, they occupy 95% of the universe, and only 5% of the matter we are familiar with. It wouldn't be surprising if a highly developed alien civilization could master the manipulation of dark energy and dark matter!
5. Aliens have long discovered the earth and humans, and even come to you and me long ago, but humans just can't find it.
The possibility exists. In recent decades, the rapid development of human technology, especially biotechnology, artificial intelligence and other cutting-edge technologies, let us see more possibilities in the future, some technologies that used to appear only in science fiction movies have now slowly begun to appear in our daily lives.
Think about what kind of technology would be acquired millions of years later, if humanity were lucky enough to still exist? If the humans of that time had traveled to this day, they would have been able to easily appear with you and me without being discovered.
6. The "Zoo Hypothesis". The highly developed alien civilization does not care to establish any connection with human civilization, but only wants to protect the earth as a "nature reserve", quietly observe, and not disturb human development.
Human beings have established various large and small "nature reserves" on the earth to protect the ecological balance and species diversity on the earth. Highly developed alien civilizations may have Earth-like "nature reserves" in many galaxies, and they do so to ensure the diversity of life development in the universe.
7. The universe we live in is virtual and simulated.
Modern computer technology is advancing rapidly, enabling more and more real-world scenarios to be simulated. Theoretically, one day, humans will be able to simulate the scenario of the solar system, the Milky Way, and even the entire universe.
So the question is, if one day human beings can simulate the entire universe, how can we be sure that our own universe is not simulated by a more developed alien civilization?
Through the above analysis, it can be seen that no matter what the reason, the possibility of human beings discovering alien civilizations is very small, and this cruel fact is also very much in line with the current reality of human exploration of outer space: let alone alien civilizations, even the most basic extraterrestrial life has not been discovered!
Perhaps, human beings are so obsessed with searching for aliens that they are a mistake in themselves. In our eyes, alien civilizations are usually highly developed, which is why we are so curious about aliens.
Perhaps, what we should do more is to strive to develop human civilization and strive to make ourselves highly developed "aliens" in our eyes. This possibility is even greater than the possibility of finding an alien civilization. Because human beings have goals, directions, and more wisdom to seek greater space for development!