How many intelligent alien civilizations do you think there are in the universe? 5? 4000? Just us? During the 1960s, while working as a radio astronomer at the National Radio Astronomy Observatory in West Virginia, Dr. Frank Drake pondered this very question. Determined to find an answer, he dove into the beautiful world of mathematics and, in 1961, emerged with the Drake Equation. It’s important to note that the equation doesn't estimate the number of primordial blobs, but the number of technological civilizations. This is because 'intelligent' life can probably communicate. The Drake equation uses a set of adjustable variables to estimate the number of these 'chatty-Cathy' civilizations.

Here's the full equation:

N = R* fp ne fl fi fc L

...Great, but what do all of those letters mean?

N is the number of civilizations in the Milky Way Galaxy (our galaxy) whose electromagnetic emissions are detectable.

So, the following letters (or variables) equal N:

R* - The rate of formation of stars suitable for the development of intelligent life.

Fp - The fraction of those stars with planetary systems.

Ne - The number of planets, per solar system, with an environment suitable for life.

Fl - The fraction of suitable planets on which life actually appears.

Fi - The fraction of life bearing planets on which intelligent life emerges.

Fc - The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

L - The length of time such civilizations release detectable signals into space.

Super simple to do in your head, right? Didn't think so. Check out this fun visual version - you can enter your own values and estimate how many phone calls ET might be making.

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Image by Pawel86