About the existence of Alien being

The theoretical possibility that life could exist beyond Earth, is discussed for centuries. In the words for example, already Giordano Bruno in the 16th Century that the universe is infinite and that there are infinitely many creatures on other planets in the universe exist. Even Immanuel Kant in 1755 it employed in his work from the residents of the stars. The speculation increased especially in the second half of the 19th Century, as the theory of evolution gained more widespread, which says that life has on the Earth over periods of billions of natural mutation and selection processes from the simplest life forms to ever greater diversity, more complexity and eventually developed into intelligence. This idea, it was possible to appear that could have evolved on other planets in a similar way of life - especially after both the traditional biblical Christian worldview increasingly lost importance and pointed out the astronomy that our sun is a star similar to the billions star is.For the existence of intelligent life beyond Earth are particularly cited the fact that it alone in the Milky Way are 200-400 billion stars, and this in turn is only one of more than 100 billion galaxies. Furthermore, our sun has - if known - no special features, and even planetary systems seem to be widespread. Thus, it is assumed that there are many planets that offer similarly good conditions for life. Under this assumption, it seems extremely unlikely that would have evolved on this planet, no life. Thus, it is very likely that there are other life forms in the universe. This missing component, however, that the time window of intelligent life is possible only a few million years.The probability of the existence of such a life is estimated since 1961 with the Drake equation. However, many of the used in the Drake equation factors controversial. Even beyond the question of how the theoretical results of the Drake equation has practical relevance, or how it is to be interpreted at all, there are a lot of discussion.Another consideration is the possible spread of life on other planets. If technologically advanced life forms would be capable of interstellar colonization and also could maintain their civilization over millions of years, the galaxy would have to be fully colonized within a few million years. The fact that there are still no signs that speak for this fact is also known as Fermi's paradox.