In an controversial book published in 2000 (Rare Earth, Springer), two American authors, the paleontólogo PeterWard and astronomer Donald Brownlee, authors of the phrase above, they had considered the idea of that would be practically zero the possibility to exist similar intelligent life of the human being. In other words, we can be alone in the Universe.
It sees well, expensive reader, the controversy is not if it would exist any type of life in other points of the universe beyond the Land. The majority of the scientists agrees that it has an extremely high possibility of that it exists, and we will see below the argument in favor of this. The controversy most violent, and that it is crawled since the time of Giordano Bruno, is if beings could exist livings creature endowed with intelligence, that is, somebody similar to us, human beings.
The argument of Ward and Brownlee seems to strengthen what many religious ones affirm since the Average Age, that is, that the human being would be an only creation of God, made to its image and similarity, and that another place of the Universe would not exist in none. Had to this dogma, the Land it was placed in its center, and the celestial spheres had been considered abandoned, with exception of the angels and the good souls that they had deserved the redemption of the Sky.
For having affirmed (among others religious heresies for the time), that an infinite number of worlds would exist, and, therefore, of other intelligent races to the image of God, frade Italian Giordano Bruno was burnt alive by the Inquisition, for having defied the impositions of the “official knowledge” of the Church Catholic. Before dying, the Bruno rebel declared the judges: “Perhaps its fear in me to pass this judgment is bigger of what mine to receive it”, an excellent phrase of farewell, and until today it summarizes well what exists for backwards of the intolerância and the dogma: simply the fear.
Later, with the development and popularização of astronomy, we are knowing that the planets are other worlds as ours, and that they could theoretically have life (even so until today nothing he has been found). In the following centuries the Humanity took knowledge, shocked, that the Sun is only one star amongst more than the 100 billion the Way Láctea, and that this, in turn, is a galaxy of average size possibly enters some trillions of other dispersed galaxies in an unimaginably great space.
More recently, using new techniques, the astronomers had been capable to detect the existence of hundreds of new planets in other systems estelares. Almost all, for being giant, are similar Jupiter and other planets gaseous, incapable to shelter any type of life. However, in April of 2007 a planet was discovered for the first time, about 20 year-light of the Land, that seems to have water in liquid state and a temperature between 0 and 40 Celsius degrees, being capable, therefore, to this way shelter similar forms of life to the found ones.
Making some simple accounts, scientists as Frank Drake and Carl Sagan (authors of a famous equation developed in 1961 that she looked for to objective calculate this probability) soon had arrived at the conclusion who, enters the trillions of trillions of possible planets, would be a mathematical impossibility that in some of them, had not developed life, and, especially, intelligent life. The parameters of the such equation can be kicked to the will, then it is well little trustworthy, but a sufficiently pessimistic estimate gave, exactly thus, a result of at least 10 extraterrestrial civilizations in our galaxy.
The alive species had evolved, in some billions of years, from extremely simple organisms, as bacteria, seaweed or unicellular protozoários, adapted to the physical conditions of the Land. The cells, in turn, seem to have had its origin in organic molecular accumulations, but not carbon livings creature, composites, hydrogen, oxygen, nitrogen and other atoms, that exist in great amount for all part in the Universe, also in the interstellar dust. These atoms more weighed had been generated in the nuclear furnace inside of the stars, from hydrogen, and if they had spread for the sidereal space when these stars had blown up to the end of its life (new and super-new).