One of the great problems we have discussed when thinking of using man's known means to attempt contacts is the time in which it may take.
In fact, starting from the assumption that the laws of physics, as we have seen from our observations, are valid throughout the known universe, at some time in its evolution, an eventual civilization with carbon or silicon creatures must discover the waves of radio and learn how to use them in communication systems.
However, the distances in space are gigantic, and a simple radio signal takes 4 years to reach the nearest star, more than 100,000 years to cross our galaxy and over 1 million years to reach the nearest galaxy ( Andromeda).
This means that if we get a "smart" signal from the closest star which is empowered to live life through the studies, which is Tau Ceti, the signal left 9 years ago. If we send an invitation to a contact through the same way, it needs 9 years to go and 9 years to come back (if they respond immediately), that is, we will only have the answer after 18 years...
Obviously it is not an interesting solution to use this means of communications.
The other way explored is to simply let them know we exist and this is what Voyager is precisely about.
This ship carries a board "showing the existence of intelligent life" on the third planet of our system and giving some information which can be interpreted, since they consist of a logical language capable of being decoded by an alien intelligence. In Figure 2 we have this board.
But how long will it take for someone to discover this board and decide to contact us?
Another way to try to contact other civilizations is to not just be passive, trying to capture something from space, as it is done with the SETI project.
This form comes from the METI PROJECT (Messaging to ExtraTerrestrial Intelligence), which consists of making "noise" by sending signals, saying "Look! We're here! There is intelligent life on this planet!”
The idea is not new. It comes from the time when the possibility of life off the ground was boosted by the discovery of "channels" on Mars by the astronomer Percival Lowell.
At that time various means of saying that there was life on earth were suggested as to make a gigantic triangle in the Sahara, with dimensions that followed Pythagoras' theorem (thus showing that it would be artificial), projecting images with mirrors or laser on mars on the moon, and similar things.
Anyway, the problem still continues. How to make contact?
If every day we find more stars with planets similar to Earth around them increasing the possibility of sheltering an intelligent life, the way we will make contact is still problematic.
