For several decades now attempts have been made to "listen" to the Universe in search for signals from extraterrestrial rational beings. Although SETI programs are equipped with cutting edge optical and radiotelescopes, computers and other intricate instruments, no meaningful signals have so far been received from outer space. Now we have no shortage of sophisticated equipment to discover planets in remote constellations; up to 20 new planets are discovered every year. It has been calculated that the total number of stars in the Universe is roughly 1020. Therefore, the number of cold celestial objects, or planets, must be of the same order of magnitude. Not very long ago it was discovered that asteroid falling on our planet often contain fragments of organic molecules. This means that "seeds" of life can travel over the Universe (as postulated by the panspermia theory). Unless we stick to the opinion that our civilization is a unique phenomenon, it is reasonable to presume that evolution producing intelligent beings and, hence, civilizations could have occurred on other planets throughout the Universe at different times.
Studies indicate that development of life on our planet began at the moment when conditions (water, atmosphere, temperature) became suitable to support life. Organic molecules gradually "developed" under the influence of changing ambient conditions. As millions of generations came and gone, living organisms underwent fundamental changes. On a certain stage, it was about 550 million years ago, many forms of animal life had appeared.
Homo sapiens with their consciousness, speech and intelligence are the product of the struggle for survival and natural selection which, on a certain stage, stimulated growth of the brain. Next step was what we call a civilization, which was marked by development of sciences and taking many of the nature's mighty forces under control. "We are like a spark in the darkness; we appeared for a quick moment out of the black nonbeing of the unconscious existence of matter." (Andrei Sakharov).
Those who made it to the top of the evolution pyramid cannot but possess the qualities of best fighters, such as aggressiveness and brutality. The history of human civilization, filled heavily with bloody wars, only serves to confirm that. Driven by the need to withstand endless fighting, humans kept on inventing more and more sophisticated killer machines, and, finally, weapons powerful enough to destroy all life on the planet were created. As a result, it may happen that, following a not very long, but very spectacular, period – several thousand years of civilization and some more years of supercivilization – nature may return to its original, primitive state.
If we presume that similar processes might have taken place on other planets in the Universe, we must obviously acknowledge that the time interval when a civilization was enough developed to have equipment for receiving signals from other civilizations and the time interval when such signals arrived at a given planet may not coincide. Alternatively, these intervals may coincide on very rare occasions. For example, our civilization has been emitting such meaningful signals (bomb explosions, radio signals, etc.) for about 100 years now, i.e. 0.00001% of the total time of life evolution on the Earth. Roughly the same is the time we have been in possession of equipment for receiving meaningful signals from other planets.
The figure above illustrates the simplest case where two planets with similar conditions appeared simultaneously, and evolution of life took place there at similar tempos and within similar time frames (some segments on the figure are not to scale). As it can be seen, the time required for information (radio signals, etc.) to travel from one planet to another will be equal in years to the distance between the two planets expressed in light years. In this particular case, it will be equal to 300,000 years.
The main reason for such pessimistic scenario is rooted in the fact that those species which manage to make it to the top of the evolution pyramid and succeed in acquiring knowledge are those for whom struggle for survival, conflicts and wars occupy a significant part of life (at least, this conclusion follows from the experience of our planet). How can they survive, extend the period of their existence, with such a mentality? After all, having become "very intelligent" they keep on fighting, using more and more sophisticated and powerful weapons, weapons of mass destruction.
The only hope is that at a certain moment mankind will come to acknowledge the situation and chooses to radically change its pattern of behavior. Are there many civilizations in the Universe that manage to achieve that?
P.S. Possible instability and transience of highly intelligent civilizations (hence the silence of the Universe) provides one more reason for concern about the fate of our civilization. It is quite probable that on some planets the danger is acknowledged before it is too late and appropriate measures are taken, while on other planets the pessimistic scenario is realized. Hopefully, we will be among the lucky ones.
