How many intelligent civilizations must there be in our galaxy right now? In 1961, the American astrophysicist Frank Drake, who passed away on September 2 at the age of 92 came up with equation to estimate this (opens in a new tab). Drake’s equation, starting at a point in his career when he was “too naive to be nervous” (as he later put it), became famous and bears his name.
This puts Drake in the company of great physicists with equations named after them, including James Clerk Maxwell and Erwin Schrödinger. Unlike them, the Drake equation does not contain a law of nature. Instead, it combines some unknown probabilities into an informed estimate.
No matter how many reasonable values you put into the equation (see image below), it’s hard to avoid the conclusion that we must not be alone in the galaxy. Drake remained a fan and a fan the search for extraterrestrial life during his days, but did his equation teach us anything?
On the topic: The search for extraterrestrial life
The Drake equation may look complicated, but its principles are actually quite simple. It says that in a galaxy as old as ours, the number of civilizations that can be detected by broadcasting their presence should be equal to their rate of origin times their average lifetime.
Estimating the rate at which civilizations arose may seem like a guess, but Drake realized that it could be broken down into more understandable components.
He stated that the general rate is equal to the rate at which it is suitable stars are formed, multiplied by the fraction of those stars that have planets. This is then multiplied by the number of planets capable of supporting life in the system, multiplied by the fraction of planets where life originates, multiplied by the fraction of planets where life becomes intelligent, multiplied by the fraction of planets that make their presence known.
When Drake first formulated his equation, the only term that was known with certainty was the rate of star formation, about 30 per year.
As for the next term, back in the 1960s we had no evidence that other stars had planets, and one in 10 might have seemed like an optimistic guess. However, the observational findings of exoplanets (planets orbiting other stars), which began in the 1990s flourished in this century (opens in a new tab) now make us certain that most stars have planets.
Common sense dictates that most multi-planet systems will include one at the right distance from their star to be capable of supporting life. Earth it is a planet of our solar system. In addition, Mars might have been fit for a rich life in the past – and this may still cling (opens in a new tab).
Today we also understand that planets do not have to be warm enough for liquid water to exist on the surface and support life. It can happen in the inner ocean of a body covered with ice (opens in a new tab)sustained by heat generated either by radioactivity or tides rather than sunlight.
There are several likely candidates among the satellites Jupiter and Saturn, for example. In fact, if we add moons as capable of supporting life, the average number of habitable bodies per planetary system can easily exceed one.
The values of the terms on the right-hand side of the equation, however, remain more open to dispute. Some believe that if you play around a few million years, life will start anywhere.
This would mean that the fraction of suitable bodies that actually harbor life is pretty much unity. Others say that we still have no evidence that life originated anywhere other than Earth, so what the origin of life (opens in a new tab) can be an extremely rare event.
Or will the life that has begun eventually lead to the development of intelligence? It probably must first pass through the germ stage and become multicellular.
There is evidence of that multicellular life arose more than once (opens in a new tab) on Earth, so becoming multicellular cannot be an obstacle. Others, however, note that on Earth the “right kind” of multicellular lifewhich continued to evolve, appeared only once and may have been rare on a galactic scale.
Intelligence can provide a competitive advantage over other species, which means that its evolution can be quite likely. But we don’t know for sure.
And will intelligent life develop technology to the point where it (accidentally or intentionally) broadcasts its existence into space? Maybe for surface dwellers like us, but it could be a rarity for the inhabitants of inland oceans frozen worlds without atmosphere.
How long have civilizations existed?
What about the average lifespan of a discovered civilization, L? Our television broadcasts began to make the Earth visible from afar in the 1950s, giving minimal value to L about 70 years in our case.
in general L may be limited by the collapse of civilization (what are the chances that our own will last another 100 years?) or the near-total demise of radio broadcasting in favor of the Internet, or deliberate choice of “quiet” out of fear of hostile galactic inhabitants.
Play with the numbers yourself – it’s fun! You will see that when L over 1000 years, N (the number of discovered civilizations) will probably be more than a hundred. U interview recorded in 2010 (opens in a new tab)Drake said his best guess N there were about 10 thousand
Every year we learn more about exoplanets and enter an era when measuring the composition of their atmosphere (opens in a new tab) discovering evidence of life is becoming increasingly possible. Within the next decade or two, we can hope for a much more robust estimate of the fraction of Earth-like planets that host life.
It won’t tell us about life in the interior oceans, but we can hope to understand it with missions to icy moons Jupiter (opens in a new tab), Saturn (opens in a new tab) and Uranus (opens in a new tab). And we could certainly detect real signals from extraterrestrial intelligence.
Either way, Frank Drake’s equation, which has stimulated so many lines of research, will continue to give us a thought-provoking sense of perspective. We should be thankful for that.
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https://www.space.com/drake-equation-intelligent-alien-life-continuing-importance/ The Drake equation for alien intelligence is more important than ever