Chapter III External Threat

Section IV Threat on Extraterrestrial Life

Extraterrestrial life means that, apart from people outside of our planet's intelligent life on other planets that is what we usually aliens. Alien invasion is keen to talk about the topic, many science fiction movies, by people's curiosity, but also play up to the danger of invasion of extraterrestrial life. So, if there is a genuine invasion of extraterrestrial life, no doubt for a devastating human catastrophe may be because in the eyes of extraterrestrial life, the earth is completely different organisms, may treat as ordinary human beings like animals, they will not be human to give any sympathy and human being, the brutal massacre of the Jews for even more than Hitler. Of course, extraterrestrial life may be very friendly towards the earth; they came to Earth not to occupy, but to tourism and friendship, or to out of curiosity. Nevertheless, in dealing with the attitude of extraterrestrial life, the guard against the invasion of extraterrestrial life and the killing, far more than hope that the friendly extraterrestrial life far more important, must not be wishful thinking to hope that things taken for granted in our lives friendly.

No doubt that so far we have not found the existence of extraterrestrial life of any evidence of the Earth in a variety of archaeological excavations and geological exploration, and there is no definitive evidence that extraterrestrial life has visited Earth, and all on the question of extraterrestrial life just stay in people's subjective thought.

Even so, we have every reason to request hundreds of millions of years the human standing on a long-term perspective, the threat of extraterrestrial life should be taken seriously.

Because so far, we know only the wisdom of life on Earth who, in addition to the earth from falling into the hands of individual meteorites found traces of micro-organisms in addition, there is no other way of clues to the existence of extraterrestrial life. Therefore, only through the study of our planet, and in order to infer the existence of extraterrestrial life may be; extraterrestrial life may exist in the universe, regional, and extraterrestrial life are likely to form on our threats.

I. Nurturing of Earth life

Through the solar system planets and their satellites to take close-up observations, as well as more in-depth and comprehensive scientific analysis can confirm, at least in the solar system, only Earth where we have the conditions for complex life to survive, and only have the complexity of life on Earth existence. So, what is given the power to create life on Earth then?

The formation of celestial bodies impacts the natural going through process of the earth. Many asteroids, meteorites and comets contain internal water molecules, when they hit each other and form larger objects; such water was taken corresponding to the Celestial Bodies. Impact caused by volcanoes and lava flows will be generated by high temperature evaporation and carbon dioxide along with喷向Sky, the Earth's early atmosphere of carbon dioxide is the main ingredient.

Carbon dioxide is the complexity of life can not be nurtured, but would also produce the greenhouse effect. Soon after the formation of the ocean, the ocean will have a micro-organisms, the first micro-organisms was born in about 38 million years ago, that is to say in just a few million years the Earth after the formation of a simple life with. After the emergence of a large number of biological species, and is the algae absorb carbon dioxide and biological oxygen release.

This absorption of oxygen in the process of release of carbon dioxide up to more than 30 million years, because the Earth needs a place too much oxygen, such as oxygen will have encountered most of the metal oxidation reaction, iron oxide, copper oxide and aluminum oxide, these elements are The combination of materials with oxygen, algae release oxygen biological must meet these consumer of oxygen.

5.3 billion years ago is the geological era known as the Precambrian era, the Earth appeared a large number of complex organisms, these organisms seem to appear in a vast ocean, the phenomenon known as the Cambrian explosion. We know that animals need oxygen to survive, therefore, must be a Precambrian oxygen production and consumption of surplus arising from the era. It is the birth of the extra oxygen Cambrian explosion prerequisite.

However, at this time has been only in the biological ocean, land is a dead silence in another 100 million years. About 4 billion years ago existed the only land-based organisms, as well as some animals and plants coming to land at the same time.

If the animal must have oxygen to survive, then it is the growth of plants to absorb carbon dioxide emitted oxygen, therefore, appear as early as shortly after the marine life, land plants should have, however, why the choice of plants and animals the same time from the Ocean to the land so slowly? Scientific research has shown that the ozone layer over the Earth's atmosphere is also in the 4 billion years ago, when formed, this time onto the land and biological time line exactly, this is a fortuitous coincidence?

The glorious sun of life has been described as the first element, if there is no sunlight and warmth, life will not happen, however, released from the sun, after all, is nuclear energy, it's glorious in not only the warmth we need, as well as A large part of highly destructive to life-ray, such as ultraviolet, X-ray, γ-rays, etc., if there is no protective device astronaut in space will soon be the face of the sun by the sun rays to kill.

Atmospheric absorption of harmful radiation is a protective coating, but the general atmosphere of oxygen absorption of the harmful rays is not enough, in the 4 billion years ago, due to harvest more than oxygen consumption, in the earth's ozone layer over the formed. Harmful for the ozone-ray absorption capacity particularly strong, although it is relatively small proportion of the atmosphere, but this has been enough to resist the harmful rays of the injury to life, there is no protection of the ozone layer, all life will forever be hiding in the sea; rely on water protection to survive.

We have a good life, "Shield", as a satellite operation of the moon around the earth; I do not know how many to decline to receive a guest from outside the Earth's celestial attacks. At the same time, the periphery of the earth have a series of planets like the Earth revolving around the sun, such as Jupiter, Saturn, Uranus, Neptune, and their quality is much greater than Earth, it is their enormous gravity of the inner solar system asteroids to attract out, and the Earth as a planet smaller, it could have been avoided by the impact of extraterrestrial objects trouble. Scientists had concluded that, if the solar system does not have a protector of the Earth, the Earth may never be the development of wisdom of life. Because the wisdom of life fostered by a very long time, if the wisdom of life whenever the fast breeding success on the impact of celestial bodies to a larger global disaster, all the efforts of the past will come to naught.

In recent years, the human exploration of the universe, the focus of our neighbor Mars and Venus have been studied, the human probe has landed this two planets, but also close to many of them in the air has been observed.

Observation results show that, although the distance of Mars from the sun than the Earth's distant third, but the average temperature of the surface of Mars is lower than -60 ℃, due to the diameter of Mars is only half of the Earth, it's the quality not only the Earth one-tenth of the quality of such a small planet is very difficult to seize the air outside, only the surface of Mars is extremely thin layer of air, the density of the Earth's surface is less than one percent of atmospheric density, mainly composed of carbon dioxide. Therefore, the Mars environment is not suitable for survival of life.

Venus and Earth are the most similar to a planet; its diameter is only slightly smaller than Earth that is the weight of 80% of the Earth, the distance from the sun than the Earth nearly a quarter. However, if as a paradise on Earth, then Venus is the real hell on earth, it is the surface temperature as high as 500 ℃, no water, a thick layer of carbon dioxide in the atmosphere than the Earth's atmospheric pressure is nine times higher in the surface of Venus, volcanic magma everywhere were signs of erosion than any life can not survive here. However, we have found in the surface of Venus have traces of the existence of shallow seas, the shallow water about 30 million years ago disappeared.

Why such as Venus and the Earth planet so similar conditions, can form a breeding life conditions? Moreover, the natural environment only in terms of simple, so similar to its environment, there were two different planets. After in-depth research and interpretation, two views were acceptable to all higher degrees. The first point of view, Venus from the sun than the Earth nearly a quarter of 30 million years ago, when the sun temperature, it will be Venus water to evaporate into space in the. In other words, precisely because of Venus and Earth from the sun is only a difference of a quarter of the distance, completely changed the fate of two planets.

Another view is that the two different from the fate of the planet does not lie primarily with the distance from the sun, but Venus's rotation is too slow, can not produce magnetic fields, and the metal center of the earth by the rapid rotation rate of magma of the earth have had a role magnetic field, which for the two planets was a foreshadowing of the fate of seeds. Because these scientists believe that the evolution of the magnetic field for the planet and the life to play a decisive role in breeding, it can prevent the solar wind and cosmic rays of the injury to life. Early Venus and the Earth have also gone through the same asteroid collisions, but also with the formation of the oceans, and the emergence of a carbon dioxide atmosphere. However, as Venus did not protect their own magnetic field, solar wind and cosmic rays of very strong anti-role, so that algae and even bacteria can not survive on Venus, so Venus's oceans like the Earth does not appear as algae biology, and thus there is no absorption of carbon dioxide and the release of oxygen systems. Thus, the accumulation of carbon dioxide in the atmosphere thicker, increasing the greenhouse effect, the surface temperature is getting higher and higher, so that all the water evaporated, until today, the temperature as high as 500 ℃, become a veritable hell planet.

There is no magnetic field on Mars, why is not the speed of its rotation, in fact, the rotation of Mars is also much faster than the Earth, but because of its size is too small, so there is no magmatic center, so there is no magnetic field of the protection of Mars. Thin air on the surface of Mars, the lack of sun block cosmic ray particles and the effective barrier would made life on Mars so complex.

Astronauts in space to observe the planet we live in when found on Earth is blue, very beautiful, it is different, stand out, like the desert in a small oasis. Over the past decades, many scientists in the detection and study of very complex form of life on the harsh conditions, when they are all the past results of observation and research into sorting out, and after a series of demonstration, many of Thinking people will return to the starting point for one of the most simple, that is, the earth is only an accidental universe, namely: in the vast universe of the galaxies a very fortuitous coincidence of a great star of a very casual around the planet, in the long the universe is not too long a time, a number of billion years, the occurrence of a series of very fortuitous events, the chance of this series is to create an extremely nurturing environment suitable for life, thereby creating a miracle in the lives of Genesis - mankind was born.

However, we are not ready to such an interpretation, because it is the scientific conclusion is yes, as long as there is sufficient time and sufficient conditions for the movement of material must be able to breed out of life, as well as the wisdom of human life this way, but such a long time, so that the requirements of the conditions too harsh, and we can not accurately predict, in the universe to a position if they would have created a miracle of life.

II. Required conditions for intelligent life nurturing

(1) Possible star system to nurture intelligent life

The wisdom of life needed to nurture extremely harsh conditions, first of all, must depend on stable, good and lasting burning stars. At the same time, the planet must have the required conditions for many, many, many, many times also need the chance, but also the needs of very, very long time Wild bred. According to our current ability to run, and it was not far from this series of conditions, one by one extra solar planet demonstration. However, we can open a list of prerequisites. It should be noted that these conditions are necessary but not sufficient condition, not sure that these conditions can not be bred out of the wisdom of life, and with these conditions are not necessarily on the wisdom of life to nurture. Because of the nurturing wisdom of life there are many we doing not fully understand the factors. Well, first of all, let us nurture the wisdom of life to analyze the necessary conditions for the stars.

Nurtured by the wisdom of relying on the lives of the stars must meet the following conditions:

1. It must be ongoing nuclear fusion of hydrogen in stars, the stars the only way to more stable combustion.

2. The system can not nurture the lives of stars. The quality of the larger star, its gravity caused by the more intense the internal thermonuclear reaction, the stars stay in the main sequence stars, the shorter the time. For example, a significant 1.2 times the solar mass stars in the main sequence stars only time more than 30 million years, according to the Earth's incubation period (i.e. 50 billion years), this star is only slightly larger than the sun is not up to standard.

3. A smaller stars around it is impossible the existence of intelligent life. The smaller star, issued by a corresponding smaller the light and heat, heat a small light-emitting stars, the planets must be able to rely on very close to the required access to the glorious life. However, when the planet is too close to the star, the star's gravity will be the planet's rotation will be slowed down greatly, so that the star of a face to face to receive long-term star baking, while the other side of the long-term cold in the dark, the In such a planet can not be complicated life.

In addition, when a star is only a small red dwarf star, its surface would be very unstable and often have enormous flares, a very destructive life-ray and such a star system is not suitable for the survival of life.

4. An entirely appropriate star must also be stable for billions of years gone through a history of burning, because the wisdom of life itself on the need for billions of years of breeding time.

5. The survival of life as a result of the wisdom of the planet must be a solid planet, there must be a carbon, nitrogen, oxygen, iron, silicon and other elements, and life itself can not be separated from carbon, oxygen, nitrogen and other heavy elements, because of heavy elements is by produced by the star, so only two or three generations after the life of stars can be bred.

6. In the universe there are many binary and triple stars, that is, two or three of the close proximity of the star, this star can not have a life around. In such a system, each star's gravity would interfere with the system of planets, resulting in a very volatile planet.

7. Can not be away from the big star of the close proximity. Because of the late star will be the evolution of supernova the end of the explosion of the form of his life, wisdom, life evolved in the absence of a high civilization, it is not able to prevent the explosion of supernova strong thermal radiation caused by cosmic rays and the hazards. In addition, the quality can not be near the middle near the close binary, because the quality of the dense medium will be formed in recent supernova binary explosion.

(2) Possible planet to nurture intelligent life

There is a suitable star, but with the wisdom of nurturing a condition of life, and then have a suitable planet, it is necessary to nurture the wisdom of the life of another condition, this condition requires more than the conditions of the star is very likely more difficult . To the solar system as an example, all the planets, only Earth has bred the conditions for intelligent life, and even the conditions very close to Earth are Venus and Mars simply can not meet the environment for survival of life, then what kind of planetary conditions that must be met in order to have bred the wisdom of life's needs?

1. The planet must be large enough, you can "seize" the atmosphere.

2. The planet's atmosphere is carbon dioxide and oxygen, and nitrogen should be there; they constitute an essential element of life. The existence of the universe is a large number of hydrogen and helium, with oxygen or carbon dioxide is rare planet.

3. The planet must be the main element is a metal planet. It appears in astronomy, in addition to hydrogen and heavy elements other than helium are considered to be metal elements, only the metal planet, it may be a solid base for the lives of rock stars, the universe, this planet is very minimal.

4. The planet must be the right distance from the star position. A little far from the star was not shining, too cold; little access to the stars near the light and heat and too much will kill the life of overheating.

5. The operation of a planet around the star can not be too large orbital eccentricity. If the eccentricity is too large into a flat oval track, the recent stellar distance too, very hot, and the aphelion distance of stars and too far away, very cold, life will not be able to survive such an environment.

6. Planets can not be too inclined to its rotation axis. If you are too inclined, lying as it will be like Uranus rotation, therefore, always have a face for six months during the day and night for six months, which is actually half of the winter half of the summer, in the summer sun baking straight up to six months, the temperature up to several hundred degrees Celsius, in winter, the six months there is no bit of light, temperature as low as minus 200 degrees Celsius, life in this environment is not suitable for survival.

7. A planet on the development of a complex life there are many other conditions, some are definitely necessary, while others may be necessary, based on the Earth and terrestrial planets in the solar system research, including many of these conditions. For example, is generally believed that planets have water that is necessary, there is no water in the planet of life will not be able to survive (but on this point there are different views of life on Earth is oxygen metabolism - water system, it was speculated that some life on the planet may be nitrogen - ammonia system, or any other material system).

Another example: with the right of the magnetic field may be necessary because the magnetic field can prevent the release of cosmic rays and the star of the harmful rays of the injury to life.

III. Location of extraterrestrial life

(1) Possible location of extraterrestrial life

Based on the above listed breeds need the wisdom of the life conditions of the stellar and planetary conditions (although they are not only a necessary condition for a sufficient condition), let us take a look at the situation of the universe surrounding the solar system. 15 light-years we may wish to analyze for the sector, because more than 15 light years away even if we have to fly the fastest aircraft of more than 10 years.

So, in this range, there are 30 star systems, including 10 Double Star, a San stars, so a total of 42 single stars. Conditions from the star, in full compliance with the nurturing wisdom of life, little, barely in line with the only light years away from our Cetus 11.68 τ. Cetus τ is a single star, and the sun is the same as G-type stars, is a yellow star, but the sun's spectral type G2, Cetus τ is the spectral type G8, coolish than the sun, and it stay in the main galaxy on the same time with the sun is about 4000 million -60 million years. These conditions seem to have very much in line with the conditions for nurturing stellar life, but, τ Cetus is a metal-poor stars, it is only the metal of the Sun's 30 percent, which indicates that it is hard around the planet rock solid.

This shows that even in the absence of indicators to consider the conditions of the planet, the only indicators of a star is almost entirely ruled out on around us the possibility of the existence of intelligent life.

Of course, today we can confirm that very few of the extra solar planets, the first time since 1995 found that since extra solar planets so far discovered only less than more than 350 stars, but the vast majority of similar quality are big as Jupiter with hydrogen and helium planets, and these planets we are still far from reach-depth observation and research level. April 2009, astronomers found that the "Gliese 581e" is considered the best of our knowledge so far the most similar to Earth's solar system, extra solar planets, only Earth-based twice the quality, but it is a hot, fiery red planet, because it is too close from the star, the public is only 3.15 days to cycle, can never be the existence of life.

We are almost impossible to indicators used to determine the planets in the universe where life outside position, but only to study the use of stellar targets. But one thing is sure, and this is the planet of indicators should be more stringent targets than the star.

(2) Extraterrestrial life searching actions

March 2, 1972, NASA launched the space probe "Pioneer 10" successful launch, and its task is to detect out of the solar system after Jupiter to find extraterrestrial life, the information transmission earth. June 13, 1983, it crossed Neptune in the history of mankind after the first man-made aircraft flying out of the solar system. "Pioneer 10" on a gold-plated with aluminum, gold-plated aluminum sheet on the use of neutron stars on the positioning of the solar system marked the universe with the Earth's orientation, as well as both a man and a woman on Earth, and that the two circle the most simple molecular substance is made up of two hydrogen atoms. This is an earth card; this card can be preserved for 10 million years, which with the "Pioneer 10" has been toward the Taurus, about 200 million years after the star arrived in Taurus Aldebaran.

One year after the April 6, 1973, "a pioneer on the 11th," then set foot on the journey, its destination is the Eagle, about 400 million years after the arrival of the stars of this constellation. August 20, 1977 and September 5, NASA has launched the "Voyager 2" and "Voyager 1" two detectors, their objectives are Sirius and Ophiuchus. These detectors have brought the Earth's information and our greetings.

Send detectors to the outer solar system are only part of our lives outside geotropism one of the ways to transmit information, and more through the radio waves to send information on extraterrestrial life geotropism.

July 2003, in the authority of NASA and other departments, with the support of 52 countries from around the world more than 90,000 "e-greetings" from the earth toward the sun similar to five stars.

As early as November 1962, the former Soviet Union leaves Vitoria Observatory on the first extraterrestrial life geotropism sent a greetings message; it uses ordinary telegraph code sent to the depths of the universe of "peace, the Soviet Union, Lenin" simple words.

In November 1974, is located in Puerto Rico currently the world's largest radio telescope completed, in order to celebrate that with the telescope to the Hercules globular cluster M13 fired up to three minutes greetings telegram. After the leaves were also Vitoria Observatory in 1999 and twice in 2001 geotropism sent greetings extraterrestrial life, but also play a concert organ was sent to the space, hope can be heard outside the life earth of music.

Of extraterrestrial life have been very interested in not only keen to bring our message to the aliens, but also want to do everything possible to obtain information on extraterrestrial life.

In March 2003, U.S. scientists from the universe, billions of radio signals in the selected 150 using the Space Telescope Observatory of these signal sources for three consecutive days of observation, but the result does not tell us extraterrestrial life, the exact information. May 1960, U.S. astronomers has implemented an observation plan, they used radio telescope at Cetus τ observed for three months, but to no avail.

Almost every Observatory will explore extraterrestrial life as one of their work, but so far have not been the existence of extraterrestrial life of any reliable evidence.

We know, UFO phenomenon has always been a mystery not yet solved. Since ancient times, we have the UFO records, many of these people think that UFO is extraterrestrial life visiting Earth's evidence, but no one there is sufficient evidence to prove his aliens really seen.

Of course, it was claimed that aliens have seen, and even aliens have been hijacked. However, careful analysis can be found in almost all the hijackers claimed to be alien or aliens to get along with those who are middle and lower income groups in society, or a relatively low level of knowledge of farmers and members of the public. Is it a high degree of wisdom, and can achieve interstellar travel Constant extraterrestrial life, in one hundred trillion kilometers across the vast expanse of space, the only place willing to work with only a single way to deal with it the earth? Rational analysis of events like this should be far more than the composition of false real ingredients.

IV. Further understanding of extraterrestrial life

Although we have not yet got the exact visit to the evidence of extraterrestrial life, although we know that the wisdom of life's harsh breeding conditions, but should be sure that the universe must be the existence of intelligent life, on the grounds that our universe is extremely vast, even if the probability of re - there will be a small miracle to happen.

Just imagine, according to modern astronomical observation and speculated that the Milky Way have about 200 billion stars, the universe also has a three hundred billion galaxies, then stars in the universe will be up to as much as trillion stars. 150 million years ago in the since the birth of the universe, stellar evolution has been at least four or five generations (the first generation of star system, life can not be bred), so long years, so many opportunities, even if the wisdom of life and then bred harsh conditions, but also We can not just only the birth of a human intelligent life on Earth.

However, even then, extraterrestrial life visiting Earth is not the possibility, the possibility of a threat to Earth's smaller. Their breeding grounds or conditions for intelligent life is too harsh, dozens of our planet in the distance, hundreds or even thousands of light years between the scope of the development of a planet on the possibility of intelligent life is very small. The wisdom of this life and they do appear, they travel to the possibility of the same small planet. Because the distance is so far, by means known to mankind today, many problems are solved.

Star Trek only need to solve the momentum is a big problem. Apollo spacecraft landing on the moon program, only more than 40 tons, but the rocket has a launch mass of more than 2000 tons, more are part of the basic propellant fuel, which means the need for more than 30 of the propellant section of the train in order to more than 40 tons of the spacecraft to the moon. But the moon away from us only 380,000 kilometers and from our recent stars than the stars next to it is far more than 100 million times.

At the same time must also consider the constant need for an interplanetary flight of hundreds of thousands, millions or even tens of millions of years of time travel in this, there are a series of technical, physiological, psychological problems to be resolved. Moreover, as a smart person to carry out this kind of travel is also a lack of sufficient motive, because, in this journey will be accompanied by the generation of tens of thousands or even millions of lives and re-generation reproduction, and evolution, the realization of such a visit, its meaning and have to pay a very difficult to match. I think that if these smart people who really exist, that is, most likely, like our Earth to Earth on a probe, or an e-mail made to satisfy their curiosity only.

Of course, it was suggested that the theory of relativity will be in that time and speed on the formula. So, if the Einstein's formula is completely correct, then to further prove that ultra-long-distance space travel is not possible, because according to this formula, we can see, time, speed and weight of the relationship between interrelated, when objects close to the speed of light, the time has become very slow, but the weight of objects will become great, when the velocity of light reached when the weight of objects to reach infinity. In other words, human beings want to do the travel, in terms of speed is still far from reaching the speed of light, they took the bones of his body crushed. At the same time, there is no driving force to accelerate the spacecraft so heavy, it has moved from high-energy particle accelerator to accelerate the elementary particles in the test to be confirmed. When the accelerator to speed up a very light quality of the elementary particles, the faster the increase of energy can increase the speed after the less, when close to the speed of light, then how to increase the speed of energy can not be raised further to achieve the speed of light.

We also often see in science fiction movies through the "wormhole" to achieve time travel story. Then we can really do this kind of travel?

Wormhole is based on general relativity and quantum theory as a corollary, in accordance with this inference, time and space can be curly, which can create distance between or very close to find a way; in the future or far away from each other today between the past, to create or find a fast reverse to reach or arrive at the time. Because of this, people made time travel, as well as manufacturers can change the distance and time the idea of the time machine.

In fact, the wormhole is still a very immature inference, based on the idea of wormhole, can not explain many of the issues, such as: wormhole to allow travel into the past, it was suggested that, if a person travel to the past, his mother also will not give birth to kill themselves, what kind of situation? Another example: wormhole to allow astronauts in the absence of the starting time has been returned to the Earth, which is obviously contrary to the logic of relations.

In this regard has been at the forefront of academic Hawking, in "A Brief History of Time (Illustrated)" a book also frankly admitted that the possibility of time travel is not a conclusion.

The past century, we have been committed in the Earth billions of years this has experienced the vicissitudes of life on the planet to look for extraterrestrial life traces left exact, the result is negative.

Since the Earth 38 million years ago will be able to nurture a simple life, then it means that the Earth has the basic conditions for survival of life, extraterrestrial life would like if the occupation of the Earth, the Earth would like to colonial, vacation travel or think of the Earth, but also as early as that came to Earth. Then, in a few billions of years past since there is no extraterrestrial life came to Earth, we have reason to believe that the future will not be billions of years aliens visit Earth. Of course, this is only a logical reasoning, but should be a reasonable guess.

We know that the universe was born in 150 million years ago, formed in the early universe, the first group of star systems can not be bred the conditions for life, then the wisdom of life bred conditional second-generation star systems no later than 10 billion years ago, there should also be to re-consider the wisdom of life 50 million years of breeding time, so the wisdom of the universe, life in the first 50 million years ago should have been born.

50 million years for the development of an intelligent life is an extremely long period of time, in such a long time, no matter what kind of technology should be able to create out why there is no extraterrestrial life has visited this planet? I would like to only two possible reasons:

First, the laws of nature inherent in the universe and decided to constant interstellar travel would have on the long-range needs of an extremely long period of time, and to overcome the extremely difficult conditions, that can not be any intelligent life beyond the law to carry out long-distance Star Trek constant. In addition, the birth of the wisdom of life is extremely harsh conditions, only very occasionally may be seen in the universe to the very small number of individual planets, which then determines the Earth from the alien planet the past, away from the earth is also far away enough so that any land extraterrestrial life can not have visited the Earth's conditions.

Second, when the naturally produced any kind of intellectual life at the same time, it is possible to give at the same time the wisdom of the defects inherent in life, the inherent defects, making any extraterrestrial life have not yet had time to achieve the long-distance constant of Star Trek when the self-destruction. Is also possible extraterrestrial life will be active for some reason to stop the development of space flight technology, and therefore it has not obtained the capacity of Constant Star Trek. In this regard, the back of this book there are chapters on.

Although the possibility of alien invasion of Earth is extremely small, almost certainly should be negligible, but it should not shy away from this problem, thinking there are two points of reference:

First, any major events that have taken place in advance signs of extraterrestrial life should have threatened invasion, we will have time to prepare accordingly. This is specifically targeted to the specific preparations for extraterrestrial life, soldiers to be blocked, water to soil cover, has always been the case. Wait and see changes, calmly deal with the situation on Earth to fight to the death to defend their homes, perhaps the only thing we can do everything.

Second, in today's real life, too many to study the alien invasion, or to prevent the invasion of extraterrestrial life to do too much preparation, is a very foolish thing. Because, should there be any invasion of extraterrestrial life, we are all ready to be without any objectives to waste effort. We know that 5 million years of human history, however, into the industrial community and is committed to the development of science and technology, only 200 years, and today's science and technology has reached a very advanced level of the real strength of the alien invasion of Earth, its civilization the level of lead than a few people on earth billions of years, the gap between the number of billions of years, and can be used for thousands of years or millions of years to catch up on years? ! And we have no idea what the other side, the use of what to do to catch up with the preparation and is completely pointless. Moreover, the Earth 38 million years ago lives on with the environment to survive, but 38 million years have not been to visit a precedent for extraterrestrial life, and tens of thousands of years of human very long time, in the face of a few billions of years are impossible to determine the threat to the preparation and the absence of such input is necessary.

In addition, would like to stress here is that we have been committed to observing extraterrestrial life, but also has been sending information to the space and the solar system a number of probes sent, brought human being  information, I believe that such actions is not rational. Should be said that the observation of extraterrestrial life, what information there is no problem, however, send a message geotropism extraterrestrial life is likely to be attracted to us big trouble.

According to previous analysis of extraterrestrial life the possibility of visiting the Earth is extremely small, this conclusion means that the two issues:

On the one hand, if we really can not contact extraterrestrial life, all our efforts are in vain, we all invested huge funds for this purpose are simply a waste, if that is merely to satisfy the curiosity of the case, such a price too high something. On the other hand, if extraterrestrial life is really able to receive our information, and I do not know than we do with the advanced science and technology, the number of times to visit the earth, waiting for our most likely will be the fate of the overall extinction.

It has been said that only allows us to detect alien information, and we do not send enough for them to do ethics. Those who hold this view is very naive and we observed extraterrestrial life information is only out of curiosity, or simply in good faith. However, we simply can not guarantee that extraterrestrial life is our attitude.

According to human and animal community can determine the survival of the law, and contempt of the strong will always prey upon the weak, the high civilization are always those who despise low civilization. Can visit a high civilization, the earth's biological reach the Earth, most of us will not "people" to see (and we have not the same species), free to kill us, even our food as they are most likely the If there one day, we humans will come by the end. Therefore, today's policy makers and scientists do not order a momentary curiosity, or for other purposes, to continue to do that may put an end to the matter of human being.

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