Searching for Aliens: Unveiling the Scientific Logic and Clues

　　I believe many people have already seen the “alien remains” displayed in the Mexican Congress on September 12, 2023. Facing two shriveled bodies covered in white, although the congressmen in the video looked serious, the audience obviously did not believe in this “performance”. This news got us thinking: are there really aliens in the world? How should we search for aliens scientifically?
scientific logic

　　In fact, finding aliens is not just a “patent” for the United States and Mexico. After entering the 20th century, influenced by various factors such as technological development, superhero comics, and the Cold War, people around the world became even more enthusiastic about finding aliens. Reports of “Close Encounters of the Third Kind” are becoming more and more bizarre. Although the search for aliens has a low threshold for practice and a high level of bragging, it has attracted a large number of civil scientists and conspiracy theorists to participate, but there are indeed some people who take the topic of extraterrestrial life seriously. For example, former U.S. Presidents Ford and Carter both claimed that they had seen aliens. For this reason, Ford convened some Air Force officials and scientists to hold a hearing and developed a “Blue Book” plan specifically to search for extraterrestrial life.
　　So where does the logic of searching for aliens come from? During the Mars opposition in 1877, Italian astronomer Giovanni Schiaparelli observed a large, slender straight-line network distributed between 60° south and north of the equator of Mars. Giorni believed that these straight-line networks were Mars. network of water on the planet and named them “Mars Canals”. The American astronomer Lowell of the same period believed that these “canals” were evidence of the existence of intelligent life on Mars, and was generally recognized by the academic community. The reason why Lowell’s view was accepted by mainstream academic circles is that humans were building canals on the earth at that time, and these dense water networks represented the possibility of advanced productivity on Mars. On the other hand, it was because people at that time had realized the importance of water to life to a certain extent.
　　Lowell’s unscientific hypothesis actually reveals the logic that runs throughout the search for extraterrestrial life: wherever there are aliens, there must be conditions for the production of life, and there must be traces of the activities of intelligent creatures. Taking the earth we live on as a reference, the threshold for the birth of life is actually quite high. First of all, a planet capable of producing life must be located in a “feng shui treasure place” in the universe: the distance from the star must be moderate, not too far or too close. Only in this way can sufficient and stable illumination and relatively suitable temperature be guaranteed. We also need a relatively stable and safe environment and relatively stable climate change. Planets that meet all the above conditions are called habitable planets.
　　Secondly, not all habitable planets may be inhabited by aliens. The planets also need to have the basic elements for building life. In 1950, chemist Stanley Lloyd Miller and his teacher Harold Urie poured methane, ammonia, hydrogen and liquid water into a round-bottomed flask in the experiment, and obtained it after electrifying Amino acids symbolizing life were found in the reddish-brown residue. Miller and Urey’s experiments showed that life could be formed from chemical reactions of inorganic substances, and that water and carbon were necessary to create life. Therefore, people speculate that on a planet that can produce life, there must be carbon, nitrogen and other basic elements that constitute organic matter, as well as abundant and easily available liquid water. In other words, as long as we examine the elemental composition of a habitable zone planet, we can make a preliminary judgment on whether there may be life on this planet.
scientific clues

　　So how do scientists examine elements on these planets? At present, the most commonly used idea is to judge by spectrum. We all know that atoms are composed of nuclei and electrons. These electrons are distributed at different energy levels and move around the nucleus. When electrons are excited by photons, they can jump to a higher energy level. When a photon is absorbed, it leaves a dark line on the otherwise complete spectrum. Different elements require different energy to make transitions, and the wavelengths corresponding to the absorbed photons are different, so the positions of the black lines are also different. Then let the light pass through the coronagraph first, filter out the star light, and then input the obtained planetary light through the optical fiber into the spectrometer for analysis, and you can distinguish those planets that contain water vapor, carbon dioxide, methane, etc. that “may have life”.
　　But even the Keck Telescope in Hawaii, the largest in the world today, is not big enough or sensitive enough. It is currently difficult to conduct compositional analysis of known terrestrial planets directly on Earth. It was not until the breakthrough of extraterrestrial aviation technology during the Cold War that longer-distance detection became possible. On October 4, 1957, the R7 rocket designed by Soviet missile expert Korolev successfully launched into space, sending Sputnik 1, the first artificial satellite in human history. This news in the Soviet Union’s “Pravda” deeply stimulated the United States, which was experiencing successive failures in satellite launches.
　　In order to catch up with the Soviet Union, under the call of then-President Eisenhower of the United States, a large amount of money was spent to combine talents from all over the country to establish the “National Aeronautics and Space Administration (NASA)”. Finally, in 1965, the Mariner 4 probe was successfully sent to Mars, and photos were used to confirm that there was no surface water on Mars. In 1996, the United States’ Mars Global Surveyor spacecraft went a step further and transmitted detailed geological conditions of Mars to the earth through a laser spectrometer, which completely put an end to the debate about whether there is life on Mars. Human beings have gone to such great lengths to find aliens, so can we let aliens come to us on their own initiative?
Space “drift bottle” and huge “telescope”

　　Yes, such as the gold-plated records carried on the Voyager 1 launched by the United States in 1977. The gold-plated record, which can be preserved for a billion years, is filled with 115 images, various natural sounds such as waves, thunder, whales and human greetings in 55 languages. In order for aliens to be able to read this information and find people on Earth, an “abstract painting”-like instruction manual was engraved on the surface of the record. The spider web-like diagram records the 14 pulsar cycles near the solar system in binary form. These pulsars that constantly flash periodically are equivalent to lighthouses in the universe. Intelligent creatures can mark other planets and their relative distances by observing their flashing cycles.
　　As long as the aliens correctly understand this information, they can lock the coordinates of the earth through these 14 lines.

　　This is actually the prototype of the deterrent broadcast idea in “The Three-Body Problem”, but we don’t have to worry about the possibility of “two-way foil (a weapon of aliens in the novel)” threatening human beings, because the scientific theory is that – within 40,000 Years later, Voyager 1 will have the opportunity to approach the nearest star to Earth that may harbor life. Regardless of the probability that aliens will find this drift bottle and correctly understand the information contained in it, whether Voyager 1 can survive safely until then is also a question.
　　Is there a more feasible way for humans to directly connect with space civilization? This requires radio telescopes. Electromagnetic waves are currently the most suitable carrier for interstellar communication. Electromagnetic waves travel at the speed of light at 300,000 kilometers per second, and it only takes four years to reach Proxima Centauri, the nearest star to us. Moreover, the cost of emitting electromagnetic waves is very small. Every time we make a phone call or send a WeChat message, it is a segment of electromagnetic waves. Whether it is us or aliens, it is the best choice after the development of civilization.
　　If aliens emit strong enough electromagnetic waves into space, they can be received by antenna equipment on Earth – this is a radio telescope. Not only that, in addition to being able to receive information, the Arecibo telescope in the United States has also been equipped with a transmitter to send an “Arecibo message” containing human DNA information and the location of the solar system into distant space. In order to find aliens, humans have built many such large antennas since the last century.
　　Of course, this search is not aimless. Because scientists believe that generally speaking, after excluding natural signals in the universe, some signals with frequencies lower than 500GHz bandwidth or narrower bandwidth are likely to be “man-made”, so the target of radio telescope search is such narrow-band signals . In 1977, astronomer Eyman received such a narrow-band signal at Ohio State University. This signal with a frequency of 1.4204556GHz lasted for about 72 seconds. After realizing the special nature of this signal, Aiman ​​could not hide his excitement and excitedly wrote a big “Wow!” on the data paper. This signal also Therefore it is called Wow! Signal.
　　The largest existing radio telescope is the FAST telescope, the “China Sky Eye” located in Guizhou, my country. It has also discovered narrow-band signals. However, the discovery of narrowband signals is not the same as the discovery of extraterrestrial civilization. Similar signals have been discovered many times over the past few decades, but the vast majority of narrowband signals have been shown to be the result of interference. The few remaining narrowband signals, including Wow! signal, it is still impossible to give a conclusion based on the current technical level.
　　In fact, so far, all human explorations of extraterrestrial life have not yet obtained definite results. Even our methods for searching for extraterrestrial life are only based on our understanding of the earth and humans. In 1950, physicist Enrico Fermi casually raised a question while chatting with several colleagues: “If there are really aliens, why can’t humans find them?” Today, we generally think of this The problem is called the Fermi Paradox. The universe that humans face is actually an adventure that is both unknown and certain, and the only answer we can give is to keep moving forward.