Extraterrestrial enthusiasts have forever hoped to determine if and how many alien societies are out there for our discovery.  The fundamental question in searching for life has been whether or not intelligent life exists.  In 1961, Frank Drake created an equation to take an educated stab at an answer.  Estimating each of the numerous factors in the Drake’s namesake equation is a fascinating thought exercise that can get us closer a conclusion to the fundamental question.

The SETi institute defines the Drake equation as follows:

N = R  * fp * ne * fl  * fi * fc * L

Here N represents the number of civilizations in the Milky Way Galaxy that would communicate with us.  The first two factors have had extensive experimental evidence to narrow their range of error.  R is the rate of formation of stars that would promote the development of intelligent life and fp is the fraction of those stars with planets.  

Per Cambridge University, the rate of star formation is around 2 stars a year.  Contrary to Drake’s initial guess, BBC found that the average star had 1 planet in orbit.  From here however, the estimates become much more difficult.

ne, or the number of planets in each solar system that could support life, is open to some debate.  Astronomers using data from the Kepler space mission estimate a value of three, while disagreeing members believe it could be as low as 0.4.  The next factor, fl, is the fraction of of planets which will develop life.  The current consensus in the scientific community is that this factor is close to 1, but not quite.

The final three factors are highly contested.  fi  denotes the fraction of planets which will develop intelligent life.  fc represents the fraction of civilizations that will develop a means to communicate with other extrasolar civilizations and L is the length of time such civilizations release detectable signals into space.  

To find the true range of values for N one approach would be to use all the lowest estimates to determine the smallest possible value, and the same method for all the high estimates.  The most conservative estimates, for those who support the rare Earth hypothesis is a value for  fi  of one in a billion.  Even pessimists give fc at least a 0.2, however thought leaders including Carl Sagan argued that L could be as small as 300, given conflicts and self destructive tendencies.  

Similarly, optimists believe fi to be nearly 1, as over billions of years intelligent life will develop by random chance.  With this train of thought, it is incredibly likely that said life would choose to communicate, making  fc around 0.9.  Finally, if that life is able to overcome its obstacles, it could be a successful civilization for potentially billions of years.  

Therefore, the most pessimistic and optimistic calculations are as follows:

N = 2 * 1 * 0.4 * 0.9 * (1*10^-9) * 0.2 * 300 = 2.16 * 10^-7

N = 2 * 1 * 0.4 * 0.9 * 1 * 0.9 * (1*10^9)  = 648 * 10^6

It’s obvious that this is an enormous range.  However, the results are telling.  A value of 2.16 * 10^-7 indicates that there is virtually no chance of life in our galaxy communicating with us.  According to the New York Times, there are approximately 500 billion galaxies in the universe, which means there are likely few hundred intelligent civilizations out there we will never hear from.  On the other hand, 648 * 10^6 is indicative of a plethora of life outside our solar system.  There is even a distinct possibility we could communicate with them.  

Whether an optimist or pessimist, this range changes a fundamental approach to searching for life.  The new basis question should not be whether intelligent life exists outside of of us, but whether it will communicate with us.






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Replies to This Discussion

Wow I liked this post a lot. Great analysis of the drake equation. I would have liked to see where the numbers actually came from with some references, but it was all present well and organized. Its very interesting to try to put numbers to this and see how even with our best guesses it doesn't clear anything up! it is a cool concept though and hopefully we can start to narrow down the numbers as we continue to do research. Great post!

I enjoyed the format of the post itself, was quite clear and concise in terms of describing what each term in the equation means. It was also good to see that there were some "optimistic calculations" as you put it, which are quite broad but just exemplifies how refined each of our variables need to be in order to determine a more succinct value for N.

I maybe would have liked to have seen an estimate with variables that correlate closely to what we know currently, in that N ~ 1 (as we are the only known things so far), just as a comparison value to supplement your other values.

Intriguing and well written really makes you think hmm. Though if I had one piece of criticism I would say would be maybe not put numbers in? I mean it helps but the equation itself is a fluid equation that has a lot of flavor and variety though the numbers help it could be argued how and where did they come from and could give detractors more fire fuel.


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