After the current state of science (so far as it is known to me) it is not possible to say if there exist extraterrestrial civilisations. I wonder if already microorganism from the Earth are on the Moon or on the planet Mars, terrestrial space vehicles have already landed there.
After my experiences it is not clear how life comes from dead matter. I don't have heard yet that the the chemists are able to create it. So it is not clear where lifes comes from and it is only possible to speculate. Is life coming from the outer space? It could be embedded in meteorites falling down to the earth. Meteorites could be parts of former planets.
The special thing of life is that it comes from life.
Scientifics conclude from observations that a lot of matter outsite the earth is similar than the matter we know. This insigth is concluded from the analysis of radiation coming from outsite the earth, consisting of matter (elementary particles) and of energy quants (photons), or of neutrinos, or ... ?
The insights about the structure of the universe comes from observation, mainly from the analysis of radiation coming from shining matter, like stars, galaxies, or from second radiation coming from dust clouds. Founded on the analysis of the movement of galaxies (depending from their gravitation potential) one concludes that the biggest part of the matter in the universe is completely unknown to us, the so called dark matter. It could be concentrated in big black holes or in radiation around the galaxies, maybe in neutrinos, but currently one can not say what it may be, only the gravity effect on the movement of galaxies can be observed, and there is not enough shining matter to justify the observations.
Besite this unknown matter there is an experimental evidence that also in great distances (1,000,000,000 light years or even more) exist matter who is similar than the one we have on earth.
There exists thousands of 1,000,000 of galaxies consisting of thousands of 1,000,000 of stars (stars, similar like our sun). One has already discovered planet around stars in the neighborhood of the earth. Therefore the probability that a lot of planet systems exist is very great. Also the probablity that a lot of this planets have a similar distance from their sun as the earth from it's own sun is great. If the evolution in our planet system is not very special then the existence of extraterrestrial civilisations can be assumed.
The question is how can this civilisations communicate with each other?
After Einstein there exist a maximum velocity a system in movement can have relative to another system. As an example the velocity of an airplane relative to the surface of the earth can reach some 1000 kilometer/hour. The velocity of light is 300000 kilometer/second.
To reach a foreign planet system a space shuttle has to travel lightyears. A lightyear is the distance the light travels during a year. Currently earth vehicles only reach a very little part of this velocity, so they would need thousands of years to reach the next planet system. The nearest stars are in a distance about 4 lightyears, the diameter of our galaxy is about 100000 lightyears and the next galaxy is about 2000000 lightyears away, and there exist thousands of 1,000,000 of galaxies until a distance of 10,000,000,000 of lightyears (the horizon of the Universe).
So it seems impossible for earth people to reach big parts of the universe.
But after A. Einstein the time insite a space ship with a velocity near to the velocity of light relative to the Earth goes "slower" then the time for the people remaining on the Earth. It is important that this space ship startet sometimes from the Earth (for the theoretical considerations), otherwise the thoughts about relativity can give a lot of confusion. I have analysed this in more detail in the chapters about Special Relativity. An example is given which shows how different the clocks are measuring time.
The question is why should extraterrestrial civilisations communicate with us, although many humen beings are not friendly against foreigners of their own race? I think if we can not overcome this social behaviour we are not usuable for extraterrestrial communication.
On the other site the fictions of Perry Rhodan tell us that terrestrial wars will be continued to extraterrestrial ones. The galactic civilisations fight against each other to improve their sphere of influence. An additional factor are the cosmological entities using the "lower level" civilisations for their own interests. It is similar as if the Greek mythology has been transformed to the outer space.
I hope that this is not the continuation of our current life.
It can give a lot of pleasure to explore scientific questions, to come to new insights and to play with them. This is a chance to overcome a lot of social dependencies and to look for more reasonable ways of living, to make more people happy. After my opinion this would also be the best way to improve creativity of individuals and of groups, and to use the potential that the totallity of the human race gives, otherwise I see the danger that sometimes androids or robots are constructed that replace the human race. But I know that it is impossible to reach this goals only through scientific insights.