In the year 1974 a digital message directed to the star cluster M13, containing 50.000 stars, has been sent from the huge Arecibo radio-telescope, located in the Porto Rico island.
M13 star cluster
M13 star cluster core (click on the full size image, to enlarge)
The hope was that among the 50.000 stars in the M13 cluster, some civilization could pick up the message and reply to us.
The idea is very nice and friendly, but it is rather improbable that it would work.
As first, the message will reach the M13 cluster only in 24.000 years, since the cluster is about 24.000 light years far from us.
Second, the transmission of the message took about only 2,5 minutes. Now, how can the homo Sapiens be so presumptuous to assume that in 24.000 years, someone in the cluster M13 will be listening the sky exactly in direction of Earth, and exactly during those infinitesimal 2,5 minutes, when the message will blink to them?? 2.5 minutes of hearing time in a time-window of 24.000 years! Or better millions of years, since the other existing civilizations are certainly many millions of years older than us.
To have a measurable chance of success, the transmission of the message should have been keep running for thousands of years, to have more wide time-windows for the receiving at the other side. But the electric bill would have been very salty. The transmission power of Arecibo was of 450 kW! So it would have been anyway not feasible keep it for a long time.
Yes, the hope is that someone in M13 is scanning the sky permanently in all directions and on all frequencies, but… who know which kind of technology, an advanced specie would use to communicate at interstellar distances?
The time frame between the appearing of an intelligent specie in a biosphere and the development of technology is very short, in relation to the life of a planed, and infinitesimal in the life of the universe.
Only 300.000 -500.000 years have passed since the coming of the first homo sapiens. Planets have a life of billions of years (without considering the possibility to migrate to another planet when it reaches the end of life).
Therefore in the practice, all the other existing civilization in the universe must be millions, hundred of millions, or billions of years more advanced than us. To discover a civilization in equal times to us or the ancient Egyptians or Greek, it would be like to win a lotto!
Then came the well known S.E.T.I. Project (Search for ExtraTerrestrial Intelligence). A network of radio-telescopes scans permanently the sky on a wide range of frequencies, in the hope to capture alien messages similar to our Arecibo message. A nice idea, but almost hopeless…
I don’t think that so highly advanced civilizations would use a primitive technology which requires centuries or millenniums to receive a reply, to communicate at interstellar distances. The people who sent a message will be died since thousands of years when the other part will receive it, on both directions.
How can the Homo Sapiens be so stupid to apply the limits of his primitive knowledge to such more older civilizations?
The radio waves are suitable to communicate only at local scale, inside of a planet on inside of a planetary system. But not at interstellar scale!
It is likely, that so much older civilizations have discovered other communication ways, other physical laws, which allow to communicate in more efficient way at interstellar distance. We don’t know yet all the laws of the universe. The Homo Sapiens can’t be so presumptuous to assume that such evolved civilizations are subjected to our same technological limits.
Furthermore, to give us the chance to capture their message right now, during our few years or SETI listening, the aliens should have aired their message continuously for millions of years, with huge power. While we aired our Arecibo message only for 2,5 minutes!
So, in conclusion, probably we will never capture an intentional message through the SETI. Moreover, very likely no civilization is interested at all in communicating with a specie like us. Therefore, please stop to say “If we hear nothing, it means that there is nobody there”, and stop to be surprised if the universe is “silent” in the radio wave spectrum, at interstellar scale.
All what the SETI project might hear someday, it could be some unintentional radio signal, sent for other purposes, but not to communicate at interstellar distances.