How many extraterrestrial intelligent civilizations are there and when will one of them send us a message?
The answers, according to a publication published in The Astrophysical Journal are 42,777 and somewhere in the next 2000 years. This is a decent explanation for the Fermi paradox, which asks why we have not yet received any messages from other civilizations, although they are very likely to exist.
It estimates the number of possible CETIs – communicating extraterrestrial intelligent civilizations – in our Milky Way galaxy. He also looks at how likely it is that one of them will contact us and when.
There are, of course, some huge unknowns behind these seemingly very accurate estimates, which, if known, would make a huge difference in the results:
- The possibility of life appearing on rocky planets and eventually evolving into a civilization advanced enough to connect with another.
- At what stage in the evolution of their host star will such advanced civilizations be born.
So the figure of 42,777, which has an error rate of a few hundred each country, is optimistic. It is based on the estimate that only 0.1% of civilizations can become advanced enough to connect with another. Here comes the Big Filter.
He also takes into account the idea that every civilization would have to survive for about three million years, giving or taking to reach that point.
Even if we are ever sent a message from an advanced civilization elsewhere in the Milky Way, the question remains whether humans can survive long enough to receive it. The authors suggest that we will only have to wait 2,000 years to receive an extraterrestrial signal.
These are the optimistic calculations. The authors’ pessimistic estimates are that only 0.001% of civilizations – about 111 – have become advanced enough to connect with another.
The result would be that people would have to wait 400,000 years to receive a message.
“The minimum value (0.001%) we accept can also be overestimated,” write the authors, Wenjie Song and He Gao of the Department of Astronomy at Beijing Normal University. “If so, the number of CETIs will become even smaller, and the opportunities for communication between CETIs will become extremely small.”
The only message ever received on Earth that could come from extraterrestrial intelligence is Wow! A signal received in 1977 from the Big Ear radio telescope, Ohio. It was heard for 72 seconds – the maximum possible at that time – and it never happened again.
The source of this signal remains unknown, although a recent publication found only one Sun-like star (called 2MASS 19281982- 2640123) in a sample of 66 in the night sky area, which Wow! came from. It is 18,000 light-years away.
In 2012, a document estimated that the closest civilization to the solar system could be 1933 light years away.
So let’s send an answer? Of course – and why not, given that the chances of an advanced alien civilization being malicious are really low – although there is one problem. Any radio or laser transmission will travel at the speed of light, so it will take 1,800 years to get there.
The authors note that astronomers sent the Arecibo message to the Great Spherical Cluster of Hercules (M13) in 1974, now using the Arecibo collapsing radio telescope. However, it was not very good. “If there really is a CETI in M13, their detection ability must be 21 orders of magnitude higher than ours to detect our signal,” the authors write. “Conversely, if they transmit such a signal, we need to improve the detection ability by 21 orders of magnitude to detect it.”
The space is large – really large – and even the messages in the galaxy are completely impractical. Even if we are not alone, it is doubtful that we will ever understand.
But that doesn’t stop us from looking for Earth-like exoplanets around 2MASS 19281982-2640123.
I wish you clear skies and open eyes.