How many extraterrestrial intelligent civilizations are there and when will one of them send us a message?
The answers, according to an article published in The Astrophysical Journal are 42,777 and sometimes in the next 2,000 years. It’s a decent explanation of the Fermi Paradox, which asks why we still haven’t received messages from other civilizations when there is a high probability that they exist.
It estimates the number of possible CETIs – communicating extraterrestrial intelligent civilizations – in our Milky Way galaxy. It also looks at the likelihood that any of them will be able to contact us and when.
There are, of course, huge unknowns behind these seemingly very precise estimates which, if known, would make a huge difference in the results:
- The likelihood of life appearing on rocky planets and eventually evolving into a civilization advanced enough to contact another.
- At what stage in the evolution of their host star such advanced civilizations would have arisen.
So the figure of 42,777 – which has an error rate of a few hundred on either side – is rather optimistic. It is based on an estimate that only 0.1% of civilizations could become advanced enough to contact another. This is where the Great Filter comes in.
It also takes into account the idea that any civilization would need to survive for around three million years, more or less, to reach that point.
Even if a message is sent to us by 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 have to wait as little as 2,000 years to receive an extraterrestrial signal.
These are the optimistic calculations. According to the authors’ pessimistic estimates, only 0.001% of civilizations – about 111 – are advanced enough to contact another.
The result would be that humans would have to wait 400,000 years to receive a message.
“The minimum value (0.001%) we take may also be overestimated,” write the authors, Wenjie Song and He Gao from the Department of Astronomy at Beijing Normal University. “If this were the case, the number of CETIs would become even lower and the possibilities of communication between the CETIs would become extremely reduced.”
The only message ever received on Earth that could have come from an extraterrestrial intelligence is the Wow! Signal, which was received in 1977 at the Big Ear Radio Telescope, Ohio. It was heard for 72 seconds – the maximum possible at the time – and was never repeated.
The source of this signal remains unknown although a recent paper found only one Sun-like star (designated 2MASS 19281982-2640123) in a sample of 66 in the region of the night sky that Wow! came from. It’s 18,000 light years away.
In 2012, an article estimated that the closest civilization to the solar system could be 1,933 light years away.
So let’s send a response? Of course – and why not, given that the chances of an advanced alien civilization being malevolent are really slim – although there is a problem. Any radio or laser transmission will travel at the speed of light, so it would take 1,800 years to get there.
The authors note that astronomers sent the “Arecibo message” to the Greater Hercules globular cluster (M13) in 1974 using the now broken Arecibo radio telescope. However, it was not very good. “If there are indeed CETIs in M13, their detection capacity must be 21 orders of magnitude greater than ours to detect our signal,” the authors write. “Conversely, if they transmit a similar signal, we need to improve the detection capability by 21 orders of magnitude to detect it.”
Space is big – really big – and even messaging in the galaxy is completely impractical. Even if we are not alone, it is unlikely that we will ever know.
But that doesn’t stop us from looking for Earth-like exoplanets around 2MASS 19281982-2640123.
I wish you clear skies and big eyes.