Some scientist had though that advanced civilizations would be able to build self replicating, automatic space probes, to send them everywhere in the galaxy to map all the existing planets, discovering the life everywhere it is.
OK, the idea is very plausible, aside that it is not necessary that these probes must be able to self replicate (self replication is another obsession of the Homo Sapiens, like the Creation and clonation).
It is likely that civilizations which are hundred millions years older than us, have already had enough time to build enough space probes to map periodically all the planets of the galaxy.
And right here comes again in focus the anthropocentrism of the Homo Sapiens. Some scientist say:
“If we don’t see these space probes, it means that probably we are alone, at least in the galaxy”
But damn! How can the Homo Sapiens be so idiot? If we are really alone in the Galaxy it is certainly not because we don’t see alien space probes flying above us right now!
The way of thinking of the Homo Sapiens is always distorted to fit his own needs! It is really so stupid and pathetic.
Very probably these probes already flew by our solar system, many thousands or millions of years ago. They mapped the planets, classified the Earth as a common ‘water-carbon’ biosphere and they proceeded with their journey. Maybe the probes visits periodically the same planetary systems to monitor the changes. Just watch and send simply the reports. It would be enough to know.
But no! The Homo Sapiens is so presumptuous to assume that these probes should fly above us exactly now in our narrow time frame, just to be sighted by us! A few decades of time frame in hundred of millions years. Maybe these probes will fly by again in thousands or millions of years in the future, but not right now, to be spotted by us!
And even if these probes would do a flyby right now with the Earth, maybe we can’t detect them, and very probably they are not programmed to get in contact with us, if they are intelligently programmed.
Finally, in the worst case, it could be that in the reality it is not possible to travel through the space so fast and comfortably as we would like, and maybe all the existing civilization, simply have no practical chances to meet them.