Window Period Hypothesis
Seeing Yue Yuan walk to his side, Gan De turned his gaze back to the starry sky outside the porthole and said slowly, "In our previous discussions, there were many hypotheses about the Fermi Paradox, but now, many hypotheses such as the Planetarium Hypothesis, the Zoo Hypothesis, and conspiracy theories have been ruled out by us."
The remaining possibilities are the "Dark Forest" effect, the inability of Earth Era's technology to detect visiting aliens, and the filtering by a large filter.
Yue Yuan nodded. He knew all of the hypotheses that Gan De mentioned, and indeed many of them had been disproven by modern humans.
The Zoo Hypothesis and the Planetarium Hypothesis are similar. The former suggests that extraterrestrials use Earth as their zoo or nature reserve, so various Alien Civilization have reached an agreement not to interfere with or contact humanity. The latter suggests that humanity is being used as an experiment by an advanced civilization.
These two theories were debunked after the Solar System and the Alpha Centauri Triple Star System were reduced to ashes by an unknown civilization. As for the Dark Forest, based on humanity's experiences, scientists have reached a consensus: the Dark Forest exists within hostile civilizations that might attack any other civilization they encounter.
However, the purpose of the attack is not to destroy for the sake of destruction, but to target the opponent's technology, well, science and technology.
The large filter exists and has always existed. The three-stage filter summarized by mankind is only applicable to the process from the birth of life to the birth of intelligence. All intelligent races have already passed through this stage of the filter.
However, scientists believe that the large filter still exists. Although they do not know where or at what stage it is, they are certain that it still exists once they learned about the Technology Barrier.
Yue Yuan still remembers what the Awakeners told humanity about their purpose in coming to the Milky Way Galaxy. Perhaps the so-called limit of intelligence is one of the great filters.
It's unknown whether there are many other great filters that screen Cosmic Civilizations before reaching the limits of intelligence.
Oh, right, there's also the Brain in a Vat Hypothesis, but this hypothesis can neither be proven nor disproven, and it has the potential to be a contrarian argument. For example, the Brain in a Vat Hypothesis could have been disproven when humanity encountered other Alien Civilization, but those who support this hypothesis could argue that there is an even larger 'brain,' or even that the entire universe is a brain in a vat.
Discussing these things is meaningless for modern Human Civilization, so Yue Yuan naturally wouldn't use such rhetoric with Gan De at this time. He simply waited quietly for Gan De to continue.
Sure enough, after a short while, Gan De continued, "There was once a hypothesis called the Island Hypothesis, which said that most civilizations are trapped on isolated islands in the universe. Now it seems that this hypothesis is correct to some extent."
Each homeworld of an intelligent civilization is an isolated island compared to the homeworlds of other intelligent civilizations, and before a civilization reaches the Tier 1 Civilization, each Star System is an isolated island.
Even for those powerful Level Six Civilization, the galaxies are still isolated islands to them. This universe is simply too vast. Even for a powerful being like the Awakeners, traveling from one isolated island to another requires countless hardships and traversing vicissitudes of time.
Perhaps civilizations that reach a certain level lose interest in Primitive Civilization. They have their own goals, whether it's exploring the endless unknown, scaling higher scientific peaks, pursuing an ideal, or simply dedicating their lives to something for some reason.
Hearing Gan De's words, Yue Yuan first nodded in agreement, and then raised his own question, "Gan Boshi, that's true, but according to what you said, no matter which one it is, the probability of aliens visiting during the human Earth Era should not be zero."
"That's true. Logically speaking, with so many Cosmic Civilizations, no matter how low the probability, they should all have visited Earth." Gan De seemed to know that what he had just said couldn't truly answer the Fermi Paradox, so he continued:
"So in my opinion, there are only a few possibilities left. First, they came but humans didn't discover them, just like we did on the Dog-Headed People Planet. If we hadn't deliberately done that, the Dog-Headed People would never have been able to find us."
Therefore, extraterrestrials may have visited Earth in ancient times. Of course, discussing this now is meaningless; it only provides us with more unprovable hypotheses.
Upon hearing Gan De say this, Yue Yuan couldn't help but remind him, "Dr. Gan De, you seem to have forgotten something."
"Oh? Chief, please speak frankly." Gan De looked at Yue Yuan, his words revealing his true feelings, and he was not annoyed by Yue Yuan's comment about what he had looked at.
Yue Yuan didn't waste any words. "Life Planet are treasures of the universe!"
"Hmm," Gan De was taken aback, and his mind instantly conjured up various things he had seen and heard, such as 'Life Elixir', 'the Kun-Tai Civilization's home planet being taken away', and 'Biosphere Resources'.
"My mind... it was definitely my fault." Gan De suddenly came to his senses.
Indeed, Life Planet are treasures of the universe. If this is true, then in the 4 billion years since life first appeared on Earth, no advanced civilization should have visited it, otherwise they would have been taken away long ago.
Four billion years of natural evolution of life—how many treasures and cosmic secrets must be hidden within it? No civilization could resist that temptation.
Humans, naturally, could not resist this temptation either. Therefore, they had already marked the Life Planet that they had encountered on their star maps, especially Wolf Star with Levorotatory DNA biosphere. If they had the technology to pack it up and take it with them, they certainly would not have let it go.
At this moment, Gan De pondered for a moment, and then said, "With this condition added, there are only two possibilities left."
"Which two?" Yue Yuan pressed.
Gan De stroked his beard. "The first possibility is that the Solar System is incredibly lucky, and no Alien Civilization has been able to find it in the past 4 billion years."
After saying this, Gan De looked at Yue Yuan and saw that the latter was about to say something. So he quickly raised his hand to signal the latter to let him finish speaking first.
"Ahem," as if knowing what Yue Yuan wanted to say, Gan De pretended to clear his throat and continued, "Of course, the sun is just an ordinary star, and it doesn't have any ethereal luck to protect it. The fact that it was blown up along with Centaur Triad is the best proof of that."
Therefore, only the second possibility remains: the universe, or perhaps the Milky Way Galaxy. For some unknown reason, the Milky Way Galaxy experienced a Civilization Window Period. We cannot determine when this occurred—perhaps 2 billion years ago, perhaps 3 billion or 4 billion years ago. In any case, there must have been a period during which civilizations in the universe drastically decreased for some unknown reason, to the point that for a very long time, no civilization discovered Earth.
"Gan Boshi is talking about advanced civilizations, isn't he?" Yue Yuan pondered.
Gan De nodded. "Yes, it's Civilization Window Period. Although it's incredible, there may really have been such a period when advanced civilizations in the Milky Way Galaxy disappeared for some unknown reason, which is why life on Earth has progressed smoothly on its long evolutionary path."