Every people in every time made this question when they see the majesty of night sky. The answer is No. Our Galaxy (Milky Way) has 200.000.000.000 stars and is sure that exist more planets as our where there are life. Other thing is if these planets have intelligent life, if these intelligent lives have a technological civilization, and technological civilizations have technologies compatible with ours.
We aren’t alone that is sure, but has our neighbors anytime visited us? More people believe that is true and this is happening now. They think to have conclusive proves of this fact, but science community say these aren’t valid and today officially there aren’t evidence of extraterrestrial are coming now or they were coming before.
We would like that a more intelligent people than us, come to earth to solve our problems. ET is the new god who is different than traditional in it lives in the same dimension to us. Today society is finding new referents and new transcendence which could grab. ET never will be a god, they only would be other travelers with the same questions that we had make from the beginning of time: Who we are? and Where we go?
But extraterrestrial visit is extremely improbable, because advanced technology doesn’t mean to be able make miracles. Distances between stars are unimaginable with our minds; Alpha-centauri is from 4.5 light years (45,000,000,000,000,000 Km; 27,000,000,000,000 miles) and there aren’t planets in Alpha-centauri. The first star found where could be life is 500 ly and it will be more luckily that it has technological life. We can think: distances is making short with increase velocity; unfortunately physics says that exist a limit of velocity that is light and one thing worse energy to increase velocity rises exponential with tendency to infinite in light speed. Fortunately Relativity gives us the possibility to circumvent the time, because in high speed time slows down. Travel to center galaxy is possible yes, even in a generation but when travelers will return Earth will not find anybody of their friends; in fact they will not find humans surely because time passed in Earth will be millions years and human will extinct. To us and ET this travel is with never returning and their discoveries never will give to the society that paid it.
The more powerful argue to discard the visit is the silence of our visitors. We never fish any communication extraterrestrial. SETI is a project to capture messages that become of starts, from seventies years until today only few signals have been candidates to be extraterrestrial communications but less concluding and without repeat. SETI isn’t thinking to capture local communications but it doesn’t matter locally we have more and more antennas which are listen all electromagnetic spectrum. Unbelievably ET doesn’t call to home.
Why can’t we hear any communication of extraterrestrial intelligences? The easy answer is that it doesn’t exist. If we take the natural history of Earth, we can see that life Intelligent species is around 200.000 years while life is in planet more than 3,500 to 3,800 million years; even if we take only the last 750 million years when the main multicellular domains are consolidates, and animals are comparable as current, we can see that is a 0.000026% of time. The possibility of coincidence with other smart specie in cosmos is very little. We are born now but in other planet intelligence it was born and death time before, with the great quantities of time that universe play one million year is nothing.
Energy can play in this equation also. Radiation only to propagate is attenuating as square of distance. It means that signal of relative near stars we couldn’t listen. Our radiotelescopes hear explosion of supernova (a star several times bigger than Sun that explodes) in center of our galaxy as a whisper. Our signal has traveled only about 100 light years distance, more near to us for to be listened by other planet habitable) but its current intensity isn’t detectable by standard engines. If we must send messages to stars, as it was sending in seventies, we need more energy and use resonant canals (for example 21 cm) and never expect to arrive more than 10.000 ly (Milky Way have diameter 120.000.000 ly).
But what does it mean simultaneity when distances are greatest? Relativity proved that time and space are relative to observer, and simultaneity is only a local phenomenon. In other hand light needs time to arrive us; distances are enormous even in solar system, light of Sun needs eight minutes to arrive Earth and light of Uranus eleven hours; Alpha-centaruri needs 4.5 years. When we see Alpha-centauri we see really Alpha-centauri to 4.5 years ago; Betelgeuse is a star that is at time to become a Supernova, is at only 650 yl; Betelgeuse could be explode yet but us and our son never will know because explosion will arrive us in 650 years.
We aren’t alone in universe that is sure but it doesn’t want to means that we can contact with them. But I want to be optimistic and I prefer to think that one day our specie will travel to stars, and our technology and knowledge can save obstacles today unsafely. Yes to contact with other species of other planets and sure other kind of biology will be the greatest achievements never do it for mankind. However we must forget to find ours saviors, because while we wait some messiahs which will arrive to stars, it means that we aren’t ready to know other intelligent specie.