Is there alien life in the vast universe and can it be synthesized?

The first reaction is "not necessarily? Because, if they really exist, why haven't we seen them? This response can be obtained from EnricoFermi, a famous physicist in the 20th century. 1950, when Fermi and his colleagues talked about the existence of aliens, Fermi's response was "Whereiseveryone? Where are the aliens? On the surface, Fermi's response can be interpreted as that I don't believe in the existence of aliens. But from the perspective of objective science, Fermi's response is: "Since you said that according to the analysis and estimation of scientific data, there should be aliens in the universe, and according to our scientific and technological achievements today, we can imagine that aliens will be able to explore and visit the earth. So how do we explain why we haven't seen aliens yet? So, this statement is called Fermi's sParadox, that is, aliens do not exist at all? Or are there really aliens, but we didn't see them?

Yes, do aliens exist? The second answer to this question is, "They may exist. Let's try to contact them and exchange information with them. 1959, two astrophysicists, GiuseppeCocconi and PhilipMorrison, put forward the possible idea of the existence of aliens, especially the way to detect the signals sent by aliens.

Yes, do aliens exist? The third answer to this question is "the universe is so big and the history is so long." According to the analysis and estimation of some data, aliens and alien civilizations should exist. The basic argument of this idea can be illustrated by an example. If a large group of monkeys are asked to knock on the computer, one monkey will always knock out a set of Shakespeare, and the other monkey will knock out a set of 300 Tang poems. The history of the universe is about 654.38+0.4 billion years. Our galaxy alone has nearly 1000 billion stars, while the universe has nearly 1000 billion galaxies. These are huge. 196 1 year, American astronomer FrankDrake proposed an equation to estimate the number of alien civilizations in our galaxy. This is the famous DrakeEquation.

I will discuss these three points one by one. In fact, when we ask, "Do aliens exist? When this question is asked, some people will ask, "Who cares if they exist or not? I don't care. This is a negative view. I will talk about some concerns about whether we should associate with them even if they exist.

Let me start with Fermi's dilemma. There are two possibilities to answer Fermi's dilemma. One is to find enough reasons to prove that aliens cannot exist. The other is the existence of aliens. First, maybe they left traces, but we didn't see them. Maybe we do, but we don't want to admit that they are traces left by aliens. Second, they haven't contacted us at all so far.

Let me have a closer look. Why can't aliens exist?

One explanation is that human beings are the most primitive life in the universe, and we have to wait for human beings to evolve gradually before aliens appear on other planets. However, in our galaxy alone, there are many stars much older than the sun. These stars existed one million years ago, so their technology and civilization should develop one million years earlier than ours.

One explanation is that the earth may be the only or very few places where there is an environment suitable for the reproduction and evolution of life. The relationship between the sun and the earth, the tides between the earth and the moon, and the existence of water and other chemical elements are quite unique conditions for the reproduction and evolution of life.

Another explanation is that the development of intelligence, language, science and technology is not necessarily an inevitable phenomenon in the process of life evolution. Therefore, perhaps human beings are the only intelligent creatures that have followed the development track of our present civilization.

However, when we discuss Derek's equation next week, Derek will say that these reasons are not sufficient.

Another possible solution to Fermi's dilemma is that aliens exist, but we can't see their traces, or we don't want to accept that they are traces left by aliens. Since ancient times, humans have seen UFOs in the sky, abbreviated as UFO(UnidentifiedFlyingObject). In the first chapter of Ezekiel in the Old Testament, it is described that Ezekiel heard the word of God and saw bright clouds around him, including four wheels and a car supported by four animals. Shen Kuo, a scientist and politician in the Song Dynasty in China, described in the 21st volume of Meng Qian's Bi Tan that in Yangzhou, he saw a shell as big as a half bed in the sky. When it is opened, there is a pearl in it. "The shell is as white as silver, but you can't face it, and your behavior is like flying; Floating on Apollo. /kloc-When Columbus crossed the Atlantic Ocean in the 5th century, he also saw an object glowing in the distance. In modern times, people all over the world often say that they have seen UFOs, such as UFOs. These can all be explained as alien means of transportation, and even the big characters written by aliens in the sky and corn fields are traces of alien existence. There is also a saying that human beings are descendants of aliens from other planets, but where are our ancestors? Also, another way of saying it is that aliens imprison us all on the earth, just like a zoo, and don't let us have contact with them.

Another possible solution to Fermi's dilemma is that aliens exist, but so far, they have not contacted us. Why didn't they contact us? Is it because of the distance between time and space, the signal they sent, or their tools for space exploration have not yet reached us? This seems unlikely, because the universe has a history of 65.438+0.4 billion years; Is it because they don't want to communicate with others? If there are millions of different civilizations in space, there will always be some who want to communicate with others. Is it because they want to keep a low profile as much as possible to avoid the danger of external invasion? So why don't these foreign invasions hurt us? Is it because we can't understand the signals they send? This brings us to the next paragraph I want to talk about, the idea of detecting alien radio signals put forward by Coconi and Morrison in 1959.

If alien Wen Mingzhen exists, how can we prove their existence and communicate with them? 1959, Coconi and Morrison published a paper called Classics. They think that aliens in a highly civilized society will send some signals, hoping to get in touch with other civilized societies through these signals. So what are these signals? Considering the speed and concentration of propagation, they will choose electromagnetic waves. Considering the attenuation of electromagnetic waves in space and the earth's surface, they will choose the frequency of electromagnetic waves not less than one million cycles per second (1 MHz) and not more than thirty billion cycles (3 1 MHz). However, in such a large range, which frequency will they choose? In astronomy, there is a very important frequency, which is 1420.4 MHz. This frequency is converted into wavelength, and the formula of wavelength divided by frequency is 2 1 cm. Where does this frequency come from? As we all know, a hydrogen atom has an electron rotating around a proton, and both electrons and protons have their own spins. When the spin directions of electrons and protons are the same, the energy of hydrogen atoms is relatively high, while when the spin directions of electrons and protons are opposite, the energy of hydrogen atoms is relatively low. If the hydrogen atom transitions from a high energy state to a low energy state, this energy difference will produce radiation with a frequency of 1420.4 MHz. It is possible for the hydrogen atom to transition between a higher and a lower energy state, but the probability is very, very low. 90% of substances in space are hydrogen atoms, so there are many hydrogen atoms. Taken together, we can indeed detect the radiation with the frequency of 1420.4 MHz on the earth. Astronomers discovered this phenomenon in the1940s, and it reached 65438+. Coconi and Morrison think this is the frequency that everyone in the universe knows. It is very likely that aliens use electromagnetic waves of this frequency to transmit signals! In addition, there is less background noise at this frequency in space.

However, there is still one question to answer. If we use a radio telescope to find the signal of 1420.4 MHz in space, which direction should the radio telescope point? Coconi and Morrison think that we should look for planets not far from the earth first, which are actually fifteen light-years away. Within this distance, they think that there are seven planets whose luminosity and life span are similar to that of the sun, and there may be life on them, including Tauceti (Tiancang 5 in China astronomy) and EtaEridani (Tianyuan 4 in Bojiang astronomy in China), which can be used as search targets.

In a word, Coconi and Morrison's paper not only pointed out the possibility of the existence of alien civilization, but also planned a specific action plan for the search. This paper also sets a precedent for the search for alien civilization in the next 50 years. At the end of their paper, they said: Our discussion may be considered as nonsense science fiction by some people, but our discussion is consistent with the current astronomical knowledge; Although, according to our statement, we can't know the probability of success in searching for signals from alien civilizations, we know that if we don't look for them, the probability of success is zero.

Let me add a footnote after finishing the paper of Coconut and Morrison. Also in 1959, Su Shuhuang, a China astronomer who is engaged in research in the United States, also published a paper, pointing out the possibility of life in the universe. He also believes that there are conditions and possibilities to support life in the four constellations of Whale and Tianyuan in Bojiang constellation near the earth. This result is the same as that of Coconut and Morrison. Huang is a famous astronomer. He and Yang Zhenning are classmates of The National SouthWest Associated University Physics Department. Like Yang Zhenning, they went to study in the United States at public expense from 65438 to 0947.

Starting from Coconi and Morrison's paper, in the past 50 years, the government, especially the military and private institutions, have invested a lot of money in finding aliens, built more powerful radio telescopes, and made more sophisticated test instruments in radio communication; Besides radio communication, the possibility of optical communication is also explored. Some people even suggested that why not just send a physical explorer into space? Of course, these efforts have not yet achieved obvious and concrete results.

Some people hold different opinions about the search for alien civilization. In addition to the possibility that alien civilization does not exist at all, there is another question: why do aliens send signals to the outside world? Is aimless communication a meaningful scientific act? Moreover, even if two civilizations successfully exchange signals with each other, the round-trip time will exceed 1000 years and 10000 years. In addition, in the past 50 years, our work on earth has focused on listening and searching. If we only receive and don't transmit, there is no way for aliens to know that we exist.

A deeper point of view, perhaps keeping silent, is a * * * mentality of cosmic civilization. Moreover, we can't know whether alien civilization is good or evil. If we contact them, what if they come to conquer and destroy us? Therefore, any information proposed to be sent to outer space must be approved by the United Nations General Assembly. As for the signals from outer space, they may contain computer viruses, which may destroy all our computers. Therefore, keeping silent is not necessarily a policy that should be followed.

20 10 On May 20th, an artificial life named "Synthia" was born in Craig Venter Institute, a private scientific research institution in the United States. Scientists artificially synthesized the artificially designed Mycoplasma fungoides DNA by chemical methods, and then implanted it into another hollowed-out Mycoplasma caprae, and the bacteria grew and propagated according to the instructions of the artificially designed genome. This is "Cynthia"

As soon as the news came out, it immediately attracted the attention of all parties around the world. "Cynthia" not only brought consternation and panic to the public, but also made synthetic biology quickly become the focus of media and public attention. In fact, Venter just synthesized a part of life-genetic material DNA, which is not a complete life as a cell. So, what is synthetic biology? Generally speaking, synthetic biology is to "design" and "transform" the existing natural biological system through artificial synthesis, or to create "artificial life" that does not exist in nature through artificial means.

The complexity of life phenomenon can only be glimpsed by human science so far. How can it be whimsical to "artificial life"? In fact, scientists also want to deepen their understanding of life in this way. In fact, human understanding of life is like facing a computer. The thinking of general biology is to analyze and synthesize natural life phenomena, just like disassembling a computer, trying to understand which parts it consists of, the network composed of these parts, and the control software that guides the network operation. Synthetic biology, on the other hand, tries to make a computer that runs according to human requirements with these components after human beings have known the basic components of life and their operating rules. In fact, it is still a great challenge to build a new life system with DNA and protein, even if we take out all the knowledge about life and use all the technologies that we can manipulate genes and protein.

The birth of "Cynthia" is to achieve this goal: under the guidance of known Mycoplasma fungoides gene sequence, design a new genome sequence, design a genome synthesis process, use "four chemicals" (two purines and two pyrimidines) to synthesize and splice their DNA fragments in the laboratory according to the design blueprint, and "glue" these fragments together by biochemical methods to form a complete genome and implant them into another bacterium. Although the experimental principle sounds simple, it took the researchers 15 years and 40 million dollars to succeed. Although Cynthia is only the smallest and simplest prokaryote, it has achieved the basic functions of metabolism and fission inheritance.

In fact, the term synthetic biology was first mentioned by French physical chemist Stephen Landouk in his book The Mechanism of Life as early as 19 1 year. However, limited by the understanding level of biology and life movement at that time, this concept is basically a formal simulation of life process, and there is almost no "scientific" basis. It was not until 1950s that the double helix model of DNA was put forward that nucleic acid was the material basis of heredity. Furthermore, under the guidance of DNA→RNA→ protein central rule and DNA recombination technology, molecular biology has flourished, which made Polish geneticist Vaclav Chivard base predict the arrival of synthetic biology many times in the mid-1970s. After the formation and maturity of genomics and genome technology in 1990s, E.Kool redefined the concept of synthetic biology by combining the achievements of systems biology and genetic engineering at the annual meeting of the American Chemical Society in 2000. This redefinition, to a certain extent, has become a symbol of the beginning of synthetic biology as a discipline.

From the appearance of the term synthetic biology to the beginning of this subject, synthetic biology has experienced a long period of 89 years, and its development is deeply rooted in molecular biology. With the maturity of large-scale genome sequencing technology and sequence analysis method, life science research began to enter the genome era, and a large amount of genome information and large-scale genome technology laid the foundation for the emergence of synthetic biology.