Erico Fermi’s paradox was simple: if there are trillions of galaxies with billions of civilizations that have been around for millions of years … where are they? Astrophysicist Frank Drake developed a controversial scientific equation to give a better idea of how many of these civilizations there might be. The Search for Extraterrestrial Intelligence (SETI) became controversial recently with one group switching from searching to sending – broadcasting messages that will notify other civilizations of our existence. As a result, two scientists promoting Communicating Extraterrestrial Intelligent Civilizations (CETI) took the Drake approach and developed an equation to calculate when we might get a response – either by communications or by aliens physically on our doorstep.
“Based on the latest astrophysical information, we carry out Monte Carlo simulations to estimate the number of possible CETIs within our Galaxy and the communication probability among them.”
In a new study published in The Astrophysical Journal, Wenjie Song and He Gao, astronomers at Beijing Normal University, carried out simulations on CETI in the Milky Way galaxy using the Monte Carlo method, which is suited for modeling the probability of different outcomes in a process with many random variables, making it better for this estimation than the Drake equation. In this case, Song and Gao chose two variables -- how many terrestrial planets are habitable and how often life on these planets evolves into a communicating species. They then ran Monte Carlo simulations manipulating the variables and plotted the results to show optimistic and pessimistic scenarios. (Universe Today has charts showing the results.)
Which one are you?
If you’re an optimist, the calculations say a star has to have lived one-quarter of its total lifetime for a CETI to evolve, but there’s only a 0.1 percent chance of a CETI appearing on each planet. That still calculates to 42,777 CETI planets in the Milky Way, although that’s also over the length of the existence of the galaxy.
We thought you said this was the optimistic result!
It is. For pessimists, the Monte Carlo calculations say a star needs to live 75% of its total lifetime before a CETI appears, and there’s only a 0.001 percent chance of that happening per planet. That puts the total CETIs in the lifespan of the Milky Way at 111. If you still like those odds (Monte Carlo casinos would LOVE you) and you want to wait for a civilization to respond to your message letting them know we’re here, you will need to wait 400,000 years. If that convinces you to look for a glass half full, optimistically you will still need to wait about 2,000 years for a response.
If you’re a super-pessimist, Song and Gao have some calculations for you too.
“However, it has been proposed that the lifetime of civilizations is very likely self-limiting (known as the Doomsday argument), due to many potential disruptions, such as population issues, nuclear annihilation, sudden climate change, rogue comets, ecological changes, etc.. If the Doomsday argument is correct, for some pessimistic situations, humans may not receive any signals from other CETIs before extinction.”
The same technology that facilitates space communication and transportation can also cause annihilation … successful CETI depends on which comes first. Then there’s the possibility that two CETIs are sending messages but in the wrong directions and never pick up a response.
So, what do Song and Gao think? Are they optimists, pessimists or super-pessimists?
“According to our simulations, for the tail value of some optimistic situations, human beings still have hope of detecting a CETI signal.”
What about an alien ringing our doorbell and announcing – verbally or telepathically – “We’re he-ee-re!”? It appears the Song-Gao Calculation doesn’t even bother with that scenario.
Is anyone working on a Las Vegas simulation?