## Drake Equation

The “Drake Equation” was composed by Frank Drake in 1960 as a means to predict the chances that there is intelligent life somewhere else in the universe. The equation includes a series of values that are estimated by common sense or logic or any other means available. Once the values are filled in, the equation is calculated to produce an output that represents a hypothetical number of intelligent civilizations in the universe. Here’s how it works.

The values:
N = the number of intelligent civilizations (capable of interstellar communication) in our galaxy

S = the number of stars in the Milky Way Galaxy
Current estimates are 200 to 400 billion.

P = the fraction of stars that have planets around them
Current estimates range from 20% to 50%.

A = number of planets per star that are able to sustain life
Common estimates range from 1 to 2.

L = the fraction of planets where life evolves
Current estimates are 100%

I = the fraction of life sustaining planets where life evolves to an intelligent level
Many estimates are around 50%

C = the fraction of planets with intelligent life that communicate
Estimates 10% to 20%

The equation then becomes: N = S x P x A x L x I x C

This version of the equation gives N = the number of intelligent civilizations (capable of interstellar communication) in our galaxy OVER ALL TIME. Most versions also include a factor that considers the lifetime of such an intelligent civilization. This is important because the span of time involved is so great that if the civilization lifetime is relatively small (such as 10,000 years or 100,000 years), the chances of two such civilizations being able to communicate with each other is slim.

New Angles on the Drake Equation – [centauri-dreams.org]

The Drake Equation in its various forms has been tormenting us for decades, raising the question of how to adjust variables that range from astronomical (the abundance of terrestrial planets) to biological (the probability of life’s emergence) and even sociological (the average lifetime of a technological civilization). Wildly optimistic estimates of the number of technological civilizations in our galaxy are now giving way to more sober reflection. Now Reginald Smith (Bouchet-Franklin Institute, Rochester NY) offers up a new analysis looking at how likely radio contact is given a civilization’s lifetime, and how widely that civilization’s signals can be clearly received. The key question: What if there is a reasonable horizon for the detection of a signal from an extraterrestrial sender?

The Drake Equation – [pbs.org]

There is no hard scientific evidence that intelligent life exists anywhere beyond Earth, yet when asked if there’s anyone else out there, most people have a strong opinion one way or the other. When astronomers answer the question—typically in the affirmative—they are playing a numbers game. There are hundreds of billions of galaxies, each bearing hundreds of billions of stars and perhaps billions of planets, so even if intelligent life is rare, we can’t be completely alone, the argument often goes.

The Drake Equation, named after its creator, radio astronomer Frank Drake, is an attempt to frame the question scientifically by assigning a value to all the relevant terms, from the number of stars born each year in our galaxy to the number of stars with planets, and so on. In this interactive version of the Drake Equation, see what Drake’s current estimates are, then play around with the numbers yourself to see what you come up with for the value N—the number of communicating civilizations in the Milky Way.