It takes 400,000 years to encounter aliens? How did you calculate this?

Science fiction writer Liu Cixin said in his book "Cosmic Thoughts" that one day, humans will put their fragile bodies into metal seeds, fly across all desolate and prosperous worlds, and perceive things that gods cannot perceive. This may really be the purpose of their existence - to be witnesses to the beauty of the universe.

Will humans encounter alien civilizations in the process of witnessing the beauty of the universe? According to current scientific conclusions, the Earth is still that beautiful and lonely planet. No traces of alien civilizations have been found within the scope of exploration.

How long will it take us to find extraterrestrial civilizations? In a recent issue of The Astrophysical Journal, a research team from Beijing Normal University gave us a specific number: 400,000 years.

Assuming that there are extraterrestrial civilizations outside the Earth, it will take at least a few thousand years to have a chance to communicate with them. If we are optimistic, this process will take about 2,000 years. If we are pessimistic, it will take another 400,000 years to establish contact with aliens.

Human civilization is only a few thousand years old. Whether it is 2000 or 400,000 years, humans, who are tiny in time, probably have no chance to encounter aliens. After all, with the existence of threats such as nuclear explosions, extreme climate, deadly viruses, and planetary collisions, humans may become extinct before they can wait for thousands of years.

Although the conclusion is not so optimistic, what is more interesting in this study is that the researchers gave us a specific time of encounter: 2000 and 400,000 years. So what are these specific numbers based on?

Thought Experiment: The Drake Equation

To answer the question of when we will encounter alien civilizations, we first need to assume the probability and number of alien civilizations. The answer to this question is based on a thought experiment proposed by humans.

The search for communicative extraterrestrial civilizations began in 1960. Humans have tried various ways to explore extraterrestrial civilizations, including detectors, radio waves, and space exploration programs, but have not found any signs of life on other planets. Many astronomical and life scientists believe that the environment of extraterrestrial planets was very unstable in the early stages of their formation, and it was too difficult for extraterrestrial life to emerge. Astrobiologists Chopra and Linne Weaver also said that in the early days of their birth, the ecological environment of the planet was very harsh, with volcanic eruptions, the spread of poisonous gases, and frequent impacts of a large number of meteorites, making it difficult for life to germinate.

Although the conditions for the birth of life are harsh, in such a vast universe, there will always be planets as lucky as the Earth. Scientists believe in this fact and are trying to find ways to estimate the number of extraterrestrial civilizations that can communicate with the Earth.

Astronomer Frank Drake began a program to search for extraterrestrial civilizations in the radio band in 1961. At the same time, Drake proposed a formula to estimate the number of communicating civilizations in the Milky Way, which was named the Drake equation: N=R*×Fp×Ne×Fl×Fi×Fc×L, where N is the number of civilizations in the Milky Way that can detect electromagnetic radiation; R* is the star formation rate suitable for the development of intelligent life; Fp is the proportion of stars with planetary systems, Ne is the number of planets suitable for life in the Milky Way, and Fl is the proportion of planets suitable for life where life actually appears; Fi is the proportion of intelligent life on planets with life; Fc is the proportion of civilizations that have developed a technology to release detectable signs of their existence into space; L is the length of time (in years) that such a civilization releases detectable signals into space.

This formula is a thought experiment. There are many variables. The variables of the Drake equation are arranged in order from simplest to most difficult, and the exact values ​​of the variables themselves are difficult to determine. Not only are the number of conclusions drawn large, but they are also not so accurate. Because of its limitations, it has been criticized by many scientists.

Although the Drake equation itself has been criticized for many things, it also provides a fulcrum for the study of extraterrestrial civilizations. Many young scientists choose to make research estimates based on this equation when analyzing extraterrestrial research, and gradually add many variable factors in the process of exploration, such as the history of star formation in galaxies, the distribution of metallic abundance, and the possibility of stars having planets in the habitable zone.

The most famous study using the Drake equation to estimate extraterrestrial civilizations is a study by two researchers from the School of Physics and Astronomy at the University of Nottingham in 2020. The two scientists used the assumption that extraterrestrial life develops on exoplanets in a similar way to that on Earth to estimate the number of communicating extraterrestrial civilizations in the Milky Way. They calculated that there may be 36 active extraterrestrial civilizations in the Milky Way. The closest of these is a red dwarf star system 17,000 light-years away. Even this closest extraterrestrial civilization is too far away to be detected and communicated.

Back to the latest research from Beijing Normal University, the 400,000 years of data was also calculated based on the Drake equation.

Meeting aliens: 2000 years and 400,000 years

The study "The Possible Number of CETIs in the Milky Way and the Probability of Communication Between These CETIs" from Beijing Normal University went a step further based on previous research. Based on the Drake equation, the two scholars first explored the number of possible planets and the time it would take for life to evolve to the point where it could communicate with the outside world. By using these parameters as variables, they calculated data for 2,000 and 400,000 years.

Among them, the two authors of the study emphasized the numerical setting of Fc in the Drake equation. Because the probability of highly intelligent life being able to communicate cannot be determined, three different coefficients of 0.1%, 0.01% and 0.001% were artificially selected. The method of estimating this coefficient is not further explained in the paper, and in fact it cannot be explained. This value itself is difficult to estimate. After setting these key variables, the researchers simulated the time it would take for us to communicate with intelligent aliens under different initial conditions.

The study estimates that in an optimistic scenario, alien civilizations could emerge as early as 25% of a star's life cycle, with each planet having only a 0.1% chance of developing life forms into an alien civilization. In this scenario, there would be more than 42,000 alien civilizations at different stages of their evolution spread throughout the Milky Way. In theory, it would only take 2,000 years to achieve two-way communication with an alien civilization.

If we consider the more extreme case, where the star is much older and has probably exceeded 75% of its life cycle, the probability of an alien civilization appearing is only 0.001%. This would reduce the probability of an alien civilization appearing in the Milky Way to only 111, and two-way communication with an alien civilization would occur within 400,000 years.

Although a specific number of 400,000 years was calculated, in fact, this answer is also the result of a thought experiment, because the research is based on the time simulated by the Drake equation, and the key parameter Fc (the probability that highly intelligent life can communicate) is a completely artificial value, so the final calculation conclusion is still open to discussion. Therefore, strictly speaking, the answer to the question of how many years it will take to find aliens and communicate with them is still in chaos.

Of course, assuming that this conclusion has a probability of happening, then whether it is 2000 years or 400,000 years, it is too long for the scale of human life. In the face of threats such as extreme climate, nuclear explosion risks, deadly viruses, and planetary collisions, it is unknown whether humans can go that far. The survival of civilization is too small in the scale of cosmic space and eternal time.

However, the research still has its value. Some other scholars commented that scientists can still produce valuable models based on logical assumptions, or at least produce reasonable estimates of the occurrence rate of such civilizations.

There are many unknown situations in scientific research, but we cannot stop exploring just because they are unknown. Discussions on hypotheses and models are important links in the development of scientific research. The work done by predecessors will have continuing value for future research.

Actively calling alien civilization

In the journey of searching for extraterrestrial civilizations, humans have done many other things besides theoretical research. In the 1960s, humans began the "Ozma Project". This was the first time that humans organized and planned to search for extraterrestrial civilizations in the universe. In 1992, NASA launched a project called Search for Extraterrestrial Intelligence (SETI) and built two huge radio telescopes. They search the night sky for signals that may come from extraterrestrial civilizations and traces of technology used by extraterrestrial civilizations. Although the project was closed in the middle due to lack of progress, it was restarted in 2018, and the two radio telescopes are still working tirelessly.

China is also involved in the exploration of extraterrestrial civilizations. In 2001, China's FAST (500-meter Aperture Spherical Radio Telescope) was officially launched. After 15 years of hard work, FAST was officially completed in July 2016, becoming the world's most sensitive single-aperture radio telescope. Currently, the FAST telescope has also been put into use to observe extraterrestrial civilizations. However, although scientists are very active in searching for possible extraterrestrial civilizations in the universe, there has been no reliable progress so far. After much effort, radio wave information suspected of alien signals was collected, which was finally confirmed to be electromagnetic interference caused by human activities.

Although the results are not satisfactory, humans have been making rapid progress in deep space exploration. We will find that the development of the aerospace field in recent years has been visibly rapid. The successful launch of the Chang'e lunar probe series, the successful landing and operation of Mars probes such as Tianwen and Perseverance, the leap of the Xihe solar satellite, manned lunar landing and Mars immigration are all on the agenda. The landing of commercial aerospace has also brought several wealthy people to feast their eyes in space.

In the exploration of deep space, we are constantly making breakthroughs and opening up limited horizons bit by bit. The ancients said: Those who can reach the sky will be kings. Modern people have realized the ancients' wish to reach the sky, with interstellar probe roaming, manned space travel, and future interstellar immigration. These technologies are gradually spreading and radiating to the exploration of extraterrestrial civilizations.

In the process of exploring extraterrestrial civilizations, there are various voices. Opponents represented by Hawking advise humans not to expose information to extraterrestrial civilizations at will. If the universe is really like the law of the dark forest, it may be plundered and eroded if exposed. But scientists who advocate radical connections ignore these voices. In 1973, NASA's Pioneer probe flew into deep space with the location information of the earth and has now reached the planetary belt; the Arecibo Observatory in the United States also sent a string of information to the "M13 Globular Cluster" 25,000 light-years away from the earth to search for aliens. The International Astronomical Observatory also plans to use the Chinese radio telescope FAST in 2023 to send information about the earth to the central region of the Milky Way, where there are tens of billions of stars.

We are simultaneously conducting deep space exploration and sending messages to Earth to wait for contact from aliens. The vast nebula swallows up these inquiries, and humans have not yet received any response from civilization. Waiting for a response makes humans anxious. After all, no one knows whether the civilization that establishes contact with us is as fond of communication and peace as we are, or whether it wants to plunder resources and destroy us.

Whether it is for the purpose of searching for the origin of life or obtaining various resources from alien civilizations, we should satisfy our curiosity and be prepared for the worst. If the law of the universe is the dark forest, our civilization will come to an end.

As for the reality that our position has been exposed, there is no turning back. We are imminent to contact with alien civilizations. We are slow to find them, but if advanced civilizations exist, with these exposed earth coordinate information, it is hard to say when they will come to us. It may be an event in our lifetime. As for humans, we should rely on ourselves to develop honestly, consolidate aerospace technology, accumulate wisdom and scientific and technological power, and make various preparations. In case the shortcut we think is a detour or even destruction, at least we can resist.