If Robinson Crusoe lived alone not on a desert island, but in a deserted metropolis, he would experience approximately the same feelings that scientists experience when trying to find an answer to the question: “Why are we alone in the Universe?”
In our Milky Way Galaxy alone there are between 100 and 400 billion stars. We know for sure that thousands of them have planetary systems, and several dozen planets have an atmosphere and temperature suitable for the development of terrestrial life forms. In reality, there are orders of magnitude more Earth twins (they are just not visible through our telescopes yet), but we do not observe signs of intelligent life in the Galaxy. What is the reason? Scientists have put forward several explanations for this phenomenon.
EARTH IS THE LATE CHILD OF THE UNIVERSE.
All representatives of extraterrestrial intelligence that have ever inhabited our Galaxy have already died – the Milky Way is a gigantic cemetery of civilizations. This is according to a study published in 2020 by a group of physicists at the California Institute of Technology. Using data from modern astronomy and statistical modeling, they mapped the rise and fall of intelligent life across time and space in the Milky Way. In fact, they improved the famous Drake Equation, with the help of which scientists tried to determine how many extraterrestrial civilizations are capable of coming into contact with us (according to calculations, there should be 20 such communities of green men). Caltech physicists have clarified an important factor: the tendency of intelligent beings to self-destruct.
Analyzing the rate of star formation and the formation of planetary systems, scientists came to the conclusion that the probability of the emergence of life in the vicinity of the Milky Way reached its maximum 8 billion years after the emergence of the Galaxy. And the epicenter of the appearance of intelligent beings was located at a distance of 13,000 light years from its center (the largest cluster of stars similar to the sun is located there).
By comparison, Earth is 25,000 light-years from the center of the Galaxy, and human civilization arose 13.5 billion years after the formation of the Milky Way.
If, from the point of view of probability theory, we evaluate the chances of self-destruction of a highly developed civilization as a result of a nuclear war or a climate catastrophe, then over the past 5.5 billion years we are guaranteed to have no fellow humans left in the Galaxy. In other words, humanity appeared on the theater stage when the performance in the Galaxy had already ended and the actors and the audience had already left.
THERE IS A GREAT FILTER IN THE PATH OF INTELLIGENT LIFE.
But what destroys intelligent life? There is a clear answer to this question: The Great Filter! It can work even at the initial stage. For example, preventing the emergence of multicellular organisms and complex life forms. From school biology courses, many remember the phrase “mitochondria are the powerhouse of the cell.” However, mitochondria were once a separate bacterium that lived on its own. But at some point on Earth, a single-celled organism tried to eat a mitochondrion, but the bacterium, instead of dutifully digesting it, for some reason merged with the cell. As a result of this alliance, the road to the emergence of higher forms of life was opened. Scientists believe that such an event is so unique that only a few civilizations in the Galaxy could have passed through this Great Filter.
Another Great Filter on Earth could be dinosaurs – giant creatures that dominated the planet for hundreds of millions of years. In the era of tyrannosaurs and brontosaurs, our mammalian ancestors were small, nocturnal, mouse-sized animals, eking out a miserable existence at the very bottom of the food chain. And only an accident, a collision with a giant asteroid that killed lizards 66 million years ago, cleared the way for mammals to hegemony on Earth. Without this, dinosaurs would still rule the planet. After all, in 250 million years they never became intelligent. But people only had 3 million years to do this.
Humanity has successfully passed several Great Filters, but scientists believe that there are deadly traps ahead that have destroyed more than one civilization. Some researchers believe that humanity initially carries the seeds of its future destruction within itself. The fact is that only a predator could become an intelligent creature on Earth, because its diet had enough protein for brain development. Throughout the history of civilization, our biological nature – aggressiveness and inability to negotiate – has led to bloody wars and the destruction of entire nations. But in the era of previous conflicts, people only owned bladed weapons and firearms. Today, a dozen countries have nuclear weapons at their disposal. Tomorrow, weapons of mass destruction will become even more accessible. And a miracle must happen so that religious fanatics or crazed dictators do not unleash a force that will destroy the Earth.
THE SUN GAVE US BIRTH – IT WILL KILL US.
American physicist Avi Loeb from Harvard University shares the opinion that the Milky Way is a huge cosmic graveyard where the mortal remains of extraterrestrial intelligent worlds rest. But he believes that the main Great Filter is the Sun and similar stars. Our star was formed 4.6 billion years ago. And by cosmic standards, the time of sunset has already come for the solar system. In the depths of our star, as a result of a thermonuclear reaction, millions of tons of hydrogen are converted into helium every second. This reaction increases the size of the Sun; in 1 billion years it will become so bright that the Earth will turn into Venus. Our oceans will boil, and as a result of the greenhouse effect, surface temperatures will reach 200-400 degrees Celsius. For some time, humanity will be able to hide from the deadly heat underground. But as hydrogen is depleted, the Sun will begin to expand and in its evolution will reach the “red giant” stage. Its luminosity will increase by about 2,700 times, and its size will increase by 250 times. As a result, the outer edge of the Sun will reach the current radius of the Earth’s orbit.
There are purely hypothetical ways to avoid this fate. Scientists are discussing the idea of creating huge space platforms that will allow humanity to leave the solar system. Some theorists believe that there is a chance to dislodge the Earth itself from orbit and tow it to a safe distance.
But according to Avi Loeb, the technical level of the vast majority of lost civilizations was only enough to send an SOS signal into interstellar space. Such a message can be carried by alien spacecraft, and sometimes they visit the boundaries of the solar system. Loeb believes that the strange cigar-shaped asteroid ‘Oumuamua could be such a reconnaissance ship. The only thing useful that humanity can do now for its salvation in the future is to look for such probes, in the hope that the lost civilizations managed to convey to us valuable information that will help us survive in the conditions of the collapse of the star.
