Why have aliens never come into contact with humans?

This question lacks clues from outer space and seems to be unanswerable. However, as far as thinking movement is concerned, we can't be afraid that it is empty, we can guess and imagine. This is my guess and I think it's nonsense.

First, according to the principle of "absolute change", people on earth are unique. In the universe, there are no two identical quanta, countless quantum combinations and countless absolutely different celestial bodies. Only the earth can satisfy the ecological environment of the earth. So far, no celestial body with a body temperature of 37℃ has been found, and no celestial body with the proportion of oxygen in the earth's atmosphere has been found. All the evidence shows that there are no aliens. It seems that the earth is Olympia, and human beings are the gods of the whole universe, thinking, thinking, dominating and active, this lifeless universe. And the endless universe, the positive and negative lining of the human spirit, the power of human thinking is extremely powerful. Man is God!

Secondly, Murphy's law only holds for finite systems, but not for infinite systems in the universe, because it is very simple: the probability of1∞ is equal to zero! Ten thousand steps back, even if it is far enough away, suppose there is another "earth" near Sirius, which is closest to the earth, and the realistic possibility of human beings proving its existence is probably zero.

Voyager 2 was launched in 1977, and it is expected to reach Sirius 8.6 light years later after completing the task of studying four woody planets.

Sirius has an apparent magnitude of-1.47, which is the brightest star in the night sky, and its brightness is almost twice that of the second brightest old star. However, it is still not as bright as the moon, Venus or Jupiter. Mercury and Mars are occasionally brighter than Sirius. Sirius can be observed almost anywhere on earth except those who live north of 73 degrees north latitude. However, Sirius observed in some cities in the north of the earth will not rise very high, such as Sirius in St. Petersburg will only rise to 13 on the horizon. Because Sirius's declination is about-17, it is the arch star of 73 south latitude. At the beginning of July, Sirius can be seen from the place where the sun sets and rises before sunrise in the southern hemisphere. Under proper environmental conditions, Sirius can even be seen with the naked eye when there is the sun. Of course, the sky must be very clear, the altitude of the observation site must be very high, the sun should be low on the horizon, and Sirius should be overhead, which is very rare.

Based on the orbit of Sirius binary system, the minimum interval between two stars is 3 seconds, and the maximum interval is 1 1 second. When they are closest, it is difficult to separate the two stars when observing, because the white dwarf Sirius B is near Sirius A, which is much brighter than it. In order to distinguish them clearly, in addition to the ideal weather, an astronomical telescope with a diameter of at least 300 mm is needed. In 1994, two stars reached their arch point. After that, the two stars began to move away from each other, making it easier to separate them with astronomical telescopes. Sirius A and Sirius B are 2.6 parsec or 8.6 light years away from the Earth, occupying two of the eight closest stars in the solar system, and they are the fifth closest star system to the solar system. This closeness is one of the reasons why Sirius is so bright. Other similar stars are dim Nanmener, compared with distant but extremely bright Supergiant star such as Laoge, Betelgeuse or Betelgeuse. But Sirius is still 25 times brighter than the sun. The nearest large star to Sirius is Nanhesan, with an angular distance of 1.6 1 or 5.24 light years.

Third, I checked some information, and the following is still a bit reliable, even if it is an idea.

What is the possibility of the existence of extraterrestrial civilization? 1961110 In October, the National Radio Observatory of the United States, located near the town of Greenbank, West Virginia, held an academic seminar on exploring extraterrestrial intelligent life. American astrophysicist Drake put forward a famous equation, which was later called "Green Shore Formula", and tried to make a quantitative analysis of the exploration of extraterrestrial intelligent life for the first time. Drake's "Green Shore Formula" is as follows: n = r× Ne× fp× fl× fi× fe× l In the formula, n represents the number of scientific and technological civilization plaNets that can be detected in the galaxy, which depends on the product of seven numbers on the right side of the equation: r, ne, fp, fl, fi, fe and l, where r is the number of stars born in the galaxy every year and ne is the terrestrial planet in the planetary system. Fp is the number of stars with planets, fl is the number of planets with life in terrestrial planets, fe is the number of intelligent creatures capable of interstellar radio communication, and L is the average life span of communication civilization.

The importance of each factor in the formula is the same. If we substitute the lowest value of rough estimation for calculation, we can get that n = 40 is calculated according to the maximum possible value of each item, and n = 5000 million. In other words, there are at least 40 high-tech civilized planets in the Milky Way, as many as 50 million.

Asimov, a famous American popular science writer, put forward a formula similar to the Green Shore formula according to his own opinions. It is estimated that there are about 530,000 civilized planets in the Milky Way, that is, for every 1 10,000 stars in the Milky Way, there may be 18 high-tech civilized worlds on average.

In the past ten years, people have studied almost all the stars within 100 light years, and found about 100 planets around more than 1000 stars. If this ratio close to 10% is representative, then we can roughly estimate that 20 billion of the more than 200 billion stars in the Milky Way may have their own planetary systems, and it is entirely reasonable to guess that there are planets very similar to the Earth.

Earth-like planets that may have life.

We know that life can't exist on stars, and advanced life can only exist on planets. The nine planets in the solar system can be divided into terrestrial planets and woody planets. Because wooden planets are mainly composed of hydrogen, helium, ice, ammonia, methane and other substances, they are not suitable for life. Scientists believe that only a planet as big as the earth has the conditions for advanced life. Humans have conducted extensive investigations on two terrestrial planets (Venus and Mars) in the solar system. Unfortunately, Venus is too hot and Mars is too cold. Perhaps both Venus and Mars once had life, but the harsh climatic conditions and extreme temperatures make it impossible to keep evidence of life. Therefore, humans have turned their attention to terrestrial planets outside the solar system. Earthlike planets should have a solid surface, atmosphere and hydrosphere, so that life similar to that on earth can exist. This kind of life should evolve according to the law of biological origin; From low to high, from high to civilization, from civilization to technological civilization, from civilized society to technological society. Only when the other side has scientific and technological civilization can human beings on earth contact each other. More than 100 extrasolar planets have been discovered, but none of them are terrestrial planets, all of them are huge wooden planets, which are basically unsuitable for life because they are surrounded by helium and hydrogen.

How to find the companion star of the earth?

The biggest problem in finding distant planets is that people can't see them. The reason is that the planet itself does not emit light and can only reflect the light of the star. If the star is compared to a powerful searchlight, then the planet is just a small firefly standing on the edge of the searchlight. So, how can we "see" planets outside our solar system?

The easiest way is to aim the telescope at the star and look for images of nearby planets. Unfortunately, planets are always much darker than stars, and the angular distance between them is very small. This method is not feasible now.

At present, the most commonly used method to find extrasolar planets is the so-called "Doppler wobble". We usually say that "the planet revolves around the star under the action of universal gravitation", but in fact it should be a star-planet binary system revolving around their same center of mass. It's just that the mass of stars is much greater than that of planets, and their concentric centers are close to the stars and far away from the planets, so it's no problem for the planets to revolve around the stars. As the star itself moves around the center of mass along a tiny elliptical orbit, from the perspective of the earth, it is approaching and leaving the earth regularly. Due to the Doppler effect, when a star approaches the earth, its light reaching the earth will shift blue; In the process of moving away from the earth, the light will be redshifted. By observing the periodic small swing of the star spectrum, we can know that there must be an invisible celestial body pulling it nearby. Obviously, the greater the mass of a planet, the closer it is to its star, and the more obvious the effect of Doppler wobble. Therefore, it is natural that most extrasolar planets discovered by humans are very close to the stars and have huge mass.

The influence of a planet on the motion of its star can also be judged by directly observing the change of the position of the star without the help of spectrum, but the basic principle is basically the same as that of Doppler swing, which is suitable for planets with large mass. This method is to observe the periodic solar eclipse of the star through the planet: from the earth's point of view, when a planet passes through the surface of its star, although it cannot directly see the planet itself, the "solar eclipse" caused by it will weaken the light of the star, and the luminosity will return to normal after the eclipse. This method requires a little too much positioning of planets and stars, but it is the only feasible way to find small-mass planets, that is, planets about the size of the earth.

Listen to the voice of "alien"

Some scientists are so convinced of the existence of "aliens" that they skip the search for terrestrial planets and listen to the voice of "alien civilization" directly. Their reason is simple: if aliens do exist, they will definitely send a call to the people on earth. Thus, as early as 1960, astronomers began to use radio telescopes to look for aliens, that is, to scan interstellar waves emitted by other civilizations. As time goes on, the search for aliens is getting bigger and bigger. Finally, scientists designed a way to listen to thousands of radio frequencies at the same time. Although this tempting plan has not achieved any substantive results so far, the organizers and many participants of the plan still firmly believe that insufficient evidence does not mean that there is no evidence; If you give up your efforts now, you will never find the evidence.

Waiting for aliens to find us?

Some scientists hold another idea: waiting for aliens to find us. If alien civilizations can already reach the earth, their technology must be much more developed than ours, so why do they always avoid us? Why don't you openly associate with us? This leads to the second question: does a highly developed civilization have the desire to associate with a low-level civilization? This requires some speculation on the degree of development of civilization.

Soviet astrophysicist N.S. Kadashev once suggested that different civilizations in the universe can be classified according to the energy they use for communication. He divided the imaginary civilization into three types: I, II and III:

Type I civilization can mobilize energy equivalent to the overall output power of the earth for communication. Type II civilization can communicate with the output power equivalent to that of a typical star. The power used by type ⅲ civilization for communication is approximately equal to the power output of the whole galaxy. That is, I-class civilization can only develop on this planet; Class II civilization will expand its development to its own planetary system; Tertiary civilization should be active in all galaxies. The so-called search for extraterrestrial civilizations is to explore advanced creatures with these three civilizations. These advanced creatures should have the same understanding of the objective world of the universe, for example, mastering the ability of electromagnetic waves to transmit information, thus sending signals to outer space to show their existence and collecting signals of outer space civilization.

As early as 1960, Freeman Dyson put forward a theory called "dyson sphere". He believes that a planet like the earth has very limited energy, which is far from enough to support the development of its civilization to an advanced stage; At present, the planets in our solar system only receive1109 solar radiation energy. Dyson believes that a highly developed civilization must have the ability to surround the sun with a huge spherical structure, so that most of the radiation energy of the sun is intercepted. Only in this way can we support this civilization for a long time and make it develop to a sufficient height. Dyson's idea of a spherical structure around a star is called "dyson sphere". For the solar system, it is not enough to build such a huge dyson sphere with materials from the earth.

If the height of civilization can really be marked by Kadashev III, or if Dyson sphere has been built, will a III civilization be interested in interacting with I-type earth civilization? Astronauts on alien spacecraft use telescopes (if they also use telescopes) to observe our sun. When they see that it is still bright, they will know that the creatures on its planet have not yet built the Dyson sphere, and they will know what kind of "primary stage" these creatures are still in. It seems that there is no need to associate with us-just like we don't want to associate with ants.

Although so far, mankind has not found the companion star of the earth, scientists firmly believe that it is only a matter of time before finding planets similar to the earth outside the solar system. Finding more planets means that scientists can build a larger database, which will help scientists detect real terrestrial planets. The discovery of terrestrial planets outside our solar system will be one of the most important discoveries of mankind in the 2 1 century.