How do scientists search for extraterrestrial life? What conditions are needed for life to develop into a first-level civilization?

Because life only exists on Earth now, the extraterrestrial life that people imagine also requires an environment similar to that of Earth. Therefore, the search for extraterrestrial life sets conditions similar to those required for Earth.

So far, no planet with the same environment as the Earth has been found. The most important condition set by the scientific community in the search for extraterrestrial life is to find a habitable planet. The so-called habitable planet is a planet suitable for human beings and other earth creatures to survive and live. According to the conditions for the growth and survival of life on Earth, life can only appear on a planet, and this planet must have a suitable temperature, liquid water, organic matter, an ideal atmosphere, etc.

Human unmanned probes have visited all the planets in the solar system and some dwarf planets and satellites, but have found no signs of life. As a result, the search for extraterrestrial life has shifted to the exoplanet (outside the solar system, the same below).

Through various telescopes, the scientific community has discovered more than 4,000 exoplanets. Among these numerous planets, there are not many habitable planets, only dozens of them have been discovered. The so-called Earth's big cousin, Earth 2.0, Earth's cousins, etc. refer to this type of planet. In other words, Earth's "real brothers" have not yet been found, let alone "twin brothers and sisters".

A habitable planet like the Earth is one that is within an appropriate range of star temperature and light, allowing the planet to maintain an appropriate temperature, which is the temperature that allows liquid water to exist. In this case, the daytime temperature must be above 0 degrees Celsius, which is the first factor.

Secondly, the existence of an atmosphere is also required, because the atmosphere has at least three important functions, such as activating the synthesis of organic matter through ultraviolet rays and lightning; the atmosphere can block stars and cosmic rays, protecting life from meteorites and radiation damage; the atmosphere can also diffuse and preserve the heat of the ground and regulate the temperature of the planet.

Thirdly, the elements on this planet have a reasonable structure and can synthesize organic matter through elements, mainly carbon, hydrogen, oxygen, nitrogen and other elements, because it is these elements that can give birth to the buds of life on Earth.

Humans cannot yet clearly see what exoplanets look like. Currently, human observation methods and capabilities are very limited. Telescopes cannot truly see exoplanets. To observe whether a star has a planet accompanying it, to study the size and mass of the planet, and how far it is from the star, we still mainly rely on the transit method and gravitational perturbation method.

The so-called transit method is to observe distant stars with a telescope. If a planet happens to move halfway between the human line of sight and the star, it will block part of the star's light, and the star's luminosity will change slightly. Based on the size and period of the star's luminosity change, we can roughly estimate whether it is a planet and how big the planet is.

The gravitational perturbation method is a method of observing the motion changes between stars and planets based on the law of universal gravitation to determine the relationship between celestial bodies and related parameters. The law of universal gravitation is expressed as F=GMm/R^2. Here F is the magnitude of gravity, G is the gravitational constant, M and m are the masses of the two celestial bodies that are gravitationally attracted to each other, and R is the distance between their centers of mass.

From the expression of the law of gravity, we can see that gravity affects each other. The magnitude of gravity caused by the two gravitational sources is proportional to the product of the masses of both parties and inversely proportional to the square of the distance between the two parties. In this way, after knowing that this star has planets through the transit method, the mass and distance of these planets can be obtained through the gravitational perturbation method. The two methods confirm each other and can obtain more accurate data.

Last year, scientists have observed two exoplanets through direct imaging, which is a huge breakthrough and can have a more intuitive understanding of exoplanets. However, the two planets directly imaged are extremely large gas planets, and it is impossible for life to exist. The two planets, named TYC 8998-760-1b and TYC 8998-760-1c, are about 300 light-years away from us. One is 16 times more massive than Jupiter, and the other is 6 times more massive than Jupiter. Even so large, they are still just a fuzzy point of light.

Therefore, there is still a long way to go to find out whether there is life on exoplanets.

The conditions for the existence of extraterrestrial life and civilization are quite controversial. Most scientists in the scientific community agree that extraterrestrial life and civilization may exist. There are certainly many reasons for this, but the simplest one is that the universe is too big. There are more than one trillion galaxies in the observable universe alone, and each galaxy has hundreds of billions or even trillions of stars. Most of these stars are accompanied by planets. Therefore, the possibility of life and civilization existing alone on Earth is too small.

But so far, humans have not found any evidence of extraterrestrial life and civilization. Why is this? The simplest explanation is that the conditions for the existence of extraterrestrial life and civilization are very harsh and too accidental, so they are extremely rare in the universe. This has also led to controversy over the conditions for the birth of life and the existence of civilization.

Many people believe that the conditions for the birth of life and the path of civilization development are not limited to the Earth. The universe is so large, and the environmental conditions vary greatly. The carbon-based life on Earth is not the only form of life. What is carbon-based life? It is an organism that uses carbon as the basis of organic matter. All organisms on our Earth are carbon-based organisms based on carbon and water.

Are there non-carbon-based organisms in the universe? For example, alkyl organisms do not need water and suitable temperatures to exist. People are very interested in Titan, because they believe that it is one of the planets in the solar system that is most likely to have life. The surface temperature of Titan is only -179℃, so it is impossible for liquid water to exist. However, there are liquid lakes and seas on its surface, and there are heavy rains. Are the "water" in these heavy rains and lakes and seas the common hydrogen compounds we see, but alkyl compounds such as liquid alkane or ethane?

Scientists believe that there may be a kind of creature that feeds on methane. They are deep in the hydroxyl lake (methane or ethane lake) and can withstand the cold of -179℃. Titan has a denser atmosphere than the Earth, and the surface atmospheric pressure is 1.5 times that of the Earth, but it is mainly nitrogen, with a nitrogen content of up to 98.44% in the atmosphere. There is almost no oxygen, only trace amounts of methane, ethane, butane, propane, carbon dioxide, etc. Therefore, if Titan creatures come to the Earth environment, there will be poisonous gas and water everywhere, and there is only one way to go.

Therefore, some scientists believe that the Earth's environment is not the only condition for the existence of life in the universe.

Many people also believe that extraterrestrial life or civilization may not even be organic matter. Some people have proposed that there may be a kind of "non-carbon-based life" with silicon or phosphorus, boron and other non-carbon elements as the core elements. The so-called silicon-based life or silicon-based civilization is life composed of biological molecules with silicon as the skeleton. The civilization nurtured by this kind of life is a silicon-based civilization.

Silicon ranks eighth in the universe in terms of reserves. It is everywhere. The main component of sand is silicon dioxide, and silicon is the second most abundant element in the earth's crust. Silicon Valley in the United States is the world's strongest and most concentrated place for high-tech products made of silicon as raw materials. Perhaps this is where the earth's silicon-based civilization was born? In the future, will artificial intelligence based on silicon replace humans as the master of civilization? This is another topic that this article will not discuss in depth.

The requirements of non-carbon-based life for the breeding and survival environment are completely different from those of Earth life. Therefore, many people believe that the way scientists are looking for habitable planets outside the solar system and trying to find extraterrestrial life and civilization is very narrow and may be wrong. But the problem is that so far, people have not found any evidence of the existence of these so-called non-carbon-based life and civilization, while Earth life does exist, so it is more practical to use this standard.

If we blindly search for extraterrestrial life and civilization without any conditions, wouldn't it be like a blind man touching an elephant without any logic or rules? Of course, this does not rule out the possibility of new discoveries in the future, and scientists will certainly improve their search methods to keep up with the times.

What conditions are needed for life to develop into civilization? The scientific community now has a standard for the level of cosmic civilization, called the Kardashev Level 3 civilization classification standard. Its main basis is the energy consumed by civilization for interstellar communication. The greater the energy consumed, the higher the level of civilization. I have talked about this standard many times in the past, so I will not repeat it this time.

According to the energy currently consumed by humans, some scientists estimate that the level of cosmic civilization has only reached level 0.73. If humans want to develop to level 1 civilization, they will need to work hard for another 200 years; to develop to level 2 civilization, they will need to work hard for another 5,000 years. Level 3 civilization is unimaginable now, so no one can predict how many billions of years it will take.

Taking human civilization as an example, to put it simply, the capabilities of each level of civilization are that when one reaches level one, one will be able to fully control the earth and will not be afraid of any disasters from the earth; when one develops to level two, one will be able to fully control the solar system and will not be afraid of any disasters from the solar system; when one develops to level three, one will be able to fully control the Milky Way and will not be afraid of any disasters from the entire galaxy.

The lowest level of civilization, that is, whether a group can be considered a civilization, is measured by whether it can conduct interstellar communication, or in layman's terms, whether it can use radio to send and receive radio waves into space. In this way, only technological civilization can be considered cosmic civilization, and the agricultural era before the development of modern science by humans is not even close to cosmic civilization.

There are hundreds of millions of species on Earth, all of which belong to life, but only humans have developed civilization. So what conditions does life need to have in order to develop a first-level civilization? I think the following are the most basic requirements:

1. This life group must produce wisdom, which presupposes that it has self-awareness and methods of communication between groups. For example, since humans have thoughts and language, they can form group wisdom and synergy through communication.

2. Be able to make and use tools to extend and increase one's ability to respond to and intervene in nature.

3. Have curiosity and a spirit of exploration, and be able to continuously gain insight into and deepen the exploration of the laws of nature. The laws of nature are not affected by region or subject of discovery, but are truths that can be applied to the universe and are the connection between the inner essence of things.

That’s all for today. Welcome to discuss and comment. Thank you for reading.

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