Iossif Chklovski

There is then a possibility that contact with an extraterrestrial civilization has occurred within historic times.
There are no reliable reports of direct contact with an extraterrestrial civilization during the last few centuries, when critical scholarship and non-superstitious reasoning have been fairly widespread.
I do not claim that the following is necessarily an example of extraterrestrial contact, but it is the type of legend that deserves more careful study ... with the possibility of direct contact with an extraterrestrial civilization as one of the many possible alternative interpretations.

I think Shklovskii and I can be described as cautious optimists on this question. If it seemed likely that technical civilizations existed on planets only 10 or 20 light years away, or civilizations greatly in advance of our own, at larger distances, a serious effort to establish contact might be justified. On the other hand, if we can only reasonably expect civilizations at about our level of technical advance thousands of light years away, attempts at communication would not seem profitable, at least at the present time.
The number of extant civilizations substantially in advance of our own in the Galaxy today appears to be perhaps between 50 thousand and one million. The average distance between technical civilizations is between a few hundred light years and about 1,000 light years.
Because of the real possibility that such interstellar probes actually exist ... it is very important for us to investigate carefully all radio signals of cosmic origin.

Extrait de la préface:
When I received a copy of (Shklovskii's) book, I was struck by its broad scope and novel insights. I wrote to Shklovskii, asking him if we might translate it into English. Shklovskii readily consented, and invited me to add additional material as I saw fit.... I have added about as much material as there was in the work initially .... The result is a peculiar kind of cooperative endeavor. I have sent much of the entirely new material to Shklovskii for his comment, and he has sent much new material to me for inclusion