the truth of the matter is that we don't know.we know that the universe gives intelligent life appeared a lot of probability, such as 1022 such volume.however, from species to the wisdom of life evolution, from technology development to advanced civilization, only a small possibility.we don't know is that the opportunity is 10-3, 10-20, 10 to 50, or any other number.we know that, like human life, at least, at the universe in which they appear, so the probability must be zero.but beyond that?we need the data.and don't have much speculation or declaration can instead of this information, we have to find it can know.any other, although a variety of prophet may claim, but that's just a guess.
in the entire history of the universe, may never have another clever, advanced technology of alien species.however, it seems that intelligent life is inevitable.considering there may be 400 billion stars in the milky way galaxy, in as many as three of these star system might be habitable planet, there are about two trillion galaxies in the universe.but our intuition often can bring us astray, we feel unable to instead of science.the origin of life, evolution, long-term sex and other unknown factors, we doubt many assumptions of life.high intelligence and high technology has a lot to the possibility of life forms does exist, but huge uncertainty makes humans become knowable only exists in reality.
(nasa astronaut bruce mccandless the longest space walk(sts-41-b))
as early as 1961 years, scientists have proposed the first frank drake formula to predict how much space in the universe civilization.he relies on a series of an unknown quantity, he can estimate, finally it is concluded that the current in the milky way and how many of the observable universe technology advanced alien creatures.with the progress of the past 55 years, we have only by speculation to estimate the number of now with amazing accuracy is known.
in the first place, we has deepened understanding of size and scale of the universe.due to space and earth observatory observations(cover the full spectrum of electromagnetic spectrum), we now know how big is the universe, how many galaxies.our operation mode for the formation of stars and star have a better understanding, so when we explore the universe to the outer space the deep, we can calculate how many stars in the universe, whether now or the whole history of the universe(since the big bang).the number is huge-nearly 1024-it represents the past 13.8 billion years the number of the universe to create the opportunity to be of life.
(from nasa's kepler space telescope illustration)
once we want to know, how many stars have planets around, how many planets have the ability to have the atmosphere, how many planets distance stars suitable surface of liquid water.generation after generation, it was the only thing we want to know.however, due to the tremendous progress in the study of exoplanets, particularly the united states nasa's kepler space telescope, we have seen a lot of information about alien creatures, including:
1.80-100% of the stars have planets or planetary systems around them running,
2.about 20%-25% of the planetary systems in the"habitable zone"have a planet, which is formed on the surface of liquid water appropriate location,
3.about 10%-10% of the planet is similar to earth in size and quality.
in conclusion, there are more than 1022 earth-like planets in the universe, which the conditions can be favorable to life.
situation is even better than this, because in addition to the first generation of stars in the first few generations, almost all the stars are rich in heavy elements and ingredients for life.when we observe the interstellar medium, the molecular gas clouds, in the center of the distant galaxy, in the effluent of high-mass stars or even our own galaxy, we found that the elements of the periodic table of elements, carbon, nitrogen, oxygen, silicon, sulfur, phosphorus, copper, iron, etc.(the essential element to life as we know).when we watch meteor and asteroids in our solar system, we not only found these elements, also found that they are configured to organic molecules, such as sugar, carbon ring and amino acids.this means that the universe is not only more than 1022 potential earth-like planets, and it contains the life constitute appropriate composition.
there should be a lot of the world are in earth-like conditions, in our own galaxy and the universe, and we have almost can quantify the world to the point of accurate and reliable.based on the scientific honesty and caution, however, it seems a bit too optimistic.because in order to get a similar human civilization, there are three important steps need to happen:
1.the origin of life needs to happen.is related to the process of organic raw materials, actually turned out to be what we think of"life".
2.life must be in the billions of years to survive, and thrive on a planet, we evolved to cells, more complex, differentiation, and finally, we call it"wisdom".
3.finally, the intelligent life must become a technological civilization, or gain the ability to announced that it exists in the universe, or extending outward, the exploration of the universe, or reach can listen to other forms of cosmic intelligence.
(or, more optimistic, the three are.)
when carl sagan proposed that the universe for the first time in 1980, he claimed that the three steps of each with a 10% success rate is reasonable.if this is correct, then there will be more than 10 million intelligent alien civilization exists in the milky way!
there are some people think that the three steps in the probability of less than 10 to 22, it is not realistic, so came to the conclusion that there must be aliens exist in the universe.but this itself is a ridiculous idea, don't have any evidence.natural origin may be very common, it may occur alone on earth many times, or on mars, dione, europa, venus, moon or elsewhere, even outside our own solar system.but it could also be a rare process, even if we created one hundred young earth(or one thousand, or one million, or even more), our world may be the only one have a life of the planet.
(alh84001 meteorite structure, some people think that early life on mars may be shown here)
even if life really produced, how lucky, can let its survive billions of years?a catastrophic like venus warming will become the norm?or be disastrous frozen, such as on mars?or, life in most of the time, eventually poison myself, as happened on earth almost two billion years ago?although life for billions of years, how long can wait until the cambrian explosion, where huge, multicellular, macroscopic plants, animals and fungi dominate a planet?
this is likely to be relatively common, has a 10% chance of success;and may be very rare, have a 1000000 or even 100000000 the possibility of becoming a reality.
(at the san diego zoo bonobos"fishing"is for the sake of termites)
even if possible, like people to use tools and development technology, such as the rocket how rare species?complex reptiles, birds and mammals, according to many indices can be considered to be intelligent, they have been around for tens to hundreds of millions of years, but modern humans emerged in less than about one million years ago, and we only in the last century or two decades as we think of"advanced technology".if there is a 10% chance to can accomplish the previous step, civilization will enter space?chance or is more like one over one thousand, one over one million, one over one million, or worse?