In the 1950s, the famous physicist Enrico Fermi put forward a point of view: any civilization that masters interstellar travel will expand outward in the shortest possible time, and then occupy the large galaxy where they are located. , but why haven't we gotten in touch with this civilization yet? This problem is the so-called " Fermi paradox ".
Why haven't we found traces of alien civilization yet? For this extremely puzzling problem, scientists have put forward many explanations: maybe human beings are the only intelligent life, maybe interstellar travel will never be possible, or maybe civilization will never escape the end of "self-destruction" when it develops to the extreme.
However, with the successive discoveries of " habitable planets " in the universe, the Fermi paradox has become more difficult to explain, because in the Milky Way alone, there are at least hundreds of millions of planets suitable for the emergence and evolution of life. planet.
A few years ago, astronomers discovered a special planet and named it a "Mega-earth", also known as a "giant-earth".
It is a terrestrial planet with a mass about 17 times that of the earth, but the atmosphere is very thin. Earlier, some scientists pointed out that this type of planet has such a huge mass, and its atmosphere must be very thick, and humans simply cannot survive in this high temperature and high pressure environment.
However, if this view turns out to be wrong, then there will be another type of planet suitable for human existence in the universe, which will also make us more confused about the Fermi Paradox.
So why isn't the universe as bustling with advanced civilizations as it was originally envisioned? In this regard, the mainstream view is that climate is the root cause of this situation. In other words, most of the civilizations in the universe were killed by the overheated climate of the biosphere.
In the early stage of the formation of the star system, the lumin1 luminosity of the star is relatively low, and some planets close to the star can also have a comfortable ambient temperature.
However, as time goes on, stars will become brighter and their temperatures will gradually increase, the habitable zone of the star system will slowly shift outward, and the once comfortable and pleasant planetary environment will become hot and barren , and finally completely unfit for life.
Therefore, intelligent life may have become "impossible" before it can appear, so the universe is not as "lively" as imagined.
Although the sun's burning rate has become faster than when the earth was first formed, the climate of the earth for more than 4 billion years is still very suitable for human habitation.
However, the good days of human beings may already be able to see the "end", because according to climate models, the earth's environment will change significantly due to the aging of the sun in about 1 billion years. Drought, the liquid water on the surface will cease to exist, and the earth will no longer be suitable for human existence.
Of course, in addition to the conjecture of climate change, another conjecture has also been recognized by many people, that is, the number of intelligent civilizations in the universe itself is not large. Under the exaggerated distance scale of the universe, these civilizations are like falling into the sea. There is no way to really see each other, the only thing you can do is to "call" loudly.
This simple and crude way of communication brings a fact that is frustrating for : Humans may have missed the signal of many alien intelligent life.
Because human beings have the ability to " listen to ", it has only been a few hundred years, and the entire universe has been born for more than 13 billion years. During this period, there may be countless civilizations that have "screamed" to the outside world, but they are always rubbing against human beings. over the shoulder.
However, after SETI used the large radio telescope array and listened carefully to the extraterrestrial signal from the universe, still nothing was found, probably because we were listening in the wrong way.
At the very beginning, SETI assumed that alien civilizations would adopt the method of omnidirectional broadcasting, transmitting radio signals to all directions of the universe at the same time, but this method requires too much energy .
You must know that wireless radio waves decay very fast in the universe. If this method is really used to "call" in the universe, the energy required has far exceeded the energy output of a star. This kind of extravagance is very unbearable even for secondary civilizations capable of using stellar energy.
Therefore, whether it is energy consumption or economical, it is an unavoidable problem with radio omnidirectional calling.
In view of these two points, physicists James Benford and Gregory Benford have proposed a unique solution - the lighthouse mechanism.
is different from omnidirectional indiscriminate broadcasting, the lighthouse only transmits the signal in one direction, so its energy requirement is greatly reduced.
The alien civilization called by this method can point the lighthouse at an area or star where civilization may exist, then transmit a signal with high power, and then turn the lighthouse to the next area or star, and so on.
In fact, several previous signals sent by humans have used a similar method, such as the Arecibo message sent to the M13 star cluster in 1974.
It should be noted that although the lighthouse mechanism works very well in theory, it does not mean that humans can use this method to call alien civilizations in the galaxy, because it requires very low energy consumption. In terms of a first-level civilization, for humans who are not yet a first-level civilization, the energy it needs is beyond human beings.
The purpose of the lighthouse signal is to tell other civilizations their location, so behind the lighthouse signal, they can choose a lower power to transmit more information, if a civilization is attracted by the lighthouse signal, they can transmit high-precision radio The telescope is pointed in the direction it came from, and it takes longer to listen to the subsequent "sound".
From the current point of view, the lighthouse signal is only an idea of human beings, but it is obviously more accurate and reliable than the aimless search for broadcast signals, and it is a method worthy of in-depth research by human beings.
It is worth mentioning that the "Wow!" signal received by the astronomer Jerry R. Ehman with the "big ear" telescope in 1977 was most likely a beacon signal.
Compared to 1977, human technology has advanced a lot, but it still cannot explain the mystery of the "Wow!" signal, so it can only be regarded as the best candidate for alien signals. In fact, after
received the "Wow!" signal, scientists have been observing and searching for the source of the signal for decades, but they have not been able to find the same or similar signal.
Scientists have long expected this result, because if it is really a beacon signal, then it will send the signal in one direction for an extremely short time, and it is almost impossible to encounter it again in a short time.
For this reason, SETI pays relatively little attention to this area, and only spends a few hours a year for tracking and monitoring.
Finally, I want to say that maybe alien civilizations have been shouting at us in a way that humans can understand, but we are listening in the wrong direction.
Or when we master a new type of communication technology, we will instantly find that the entire universe is communicating all the time. Only at that moment can human beings officially enter the gate of the interstellar age and become a member of the Interstellar Club. a member.
