# Drake Equation (original)

Not Reviewed
N =
Drake Equation (original)
Variable Instructions Datatype
Rate Star Formation Enter the average rate per year at which stars are formed in our galaxy Decimal
Fraction Stars With Planets Enter the decimal fraction of those stars that have planets Decimal
Number Planets Supporting Life Enter the average number of planets that can potentially support life per star that has planets Decimal
Fraction Planets That Develop Life Enter the decimal fraction of planets that could support life that actually develop life at some point Decimal
Fraction With Intelligent Life Enter the decimal fraction of planets with life that actually develops intelligent life Decimal
Fraction Detectable Signals Enter the decimal fraction of civilizations that develop a technology that releases detectable signs of their existence into space Decimal
Duration Civilization Enter the length of time for which such an intelligent civilization releases detectable signals Decimal
Type
Equation
Category
vCommons
Contents
7 variables
Rating
ID
MichaelBartmess.Drake Equation (original)
UUID

This Drake Equation estimates the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. The equation was conceived in 1961 by Frank Drake not for purposes of quantifying the number of civilizations, but intended as a way to stimulate scientific dialogue at the world's first search for extraterrestrial intelligence (SETI) meeting, in Green Bank, West Virginia1. The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life. The Drake equation has proved controversial since several of its factors are currently unknown, and estimates of their values span a very wide range. This has led critics to label the equation a guesstimate, or even meaningless.

Contents

# Definition

The Drake Equation is
 N =  R_star * f_p * n_e * f_l * f_i * f_c * L
where

 N the number of civilizations in our galaxy with which radio-communication might be possible

and

 R_"*" the average rate of star formation in our galaxy f_p the fraction of those starts that have planets n_e the average number of planets that can potentially support life per star that has planets f_l the fraction of planets that could support life that actually develop life at some point f_i the fraction of planets with life that actually develops intelligent life f_c the fraction of civilizations that develop a technology that releases detectable signs of their existence into space L the length of time for which such an intelligent civilization releases detectable signals

There is considerable disagreement on the values of these parameters, but the 'educated guesses' used by Drake and his colleagues in 1961 were:

 R_"*" 1/year (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative) f_p 0.2-0.5 (one fifth to one half of all stars formed will have planets) n_e 1-5 (stars with planets will have between 1 and 5 planets capable of developing life) f_l 1 (100% of these planets will develop life) f_i 1 (100% of which will develop intelligent life) f_c 0.1-0.2 (10-20% of which will be able to communicate) L 1000-100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)

# History

In September 1959, physicists Giuseppe Cocconi and Philip Morrison published an article in the journal Nature with the provocative title "Searching for Interstellar Communications.23 Cocconi and Morrison argued that radio telescopes had become sensitive enough to pick up transmissions that might be broadcast into space by civilizations orbiting other stars. Such messages, they suggested, might be transmitted at a wavelength of 21 centimeters (1,420.4 megahertz). This is the wavelength of radio emission by neutral hydrogen, the most common element in the universe, and they reasoned that other intelligences might see this as a logical landmark in the radio spectrum.

Seven months later, radio astronomer Frank Drake became the first person to start a systematic search for intelligent signals from the cosmos. Using the 25 meter dish of the National Radio Astronomy Observatory in Green Bank, West Virginia, Drake listened in on two nearby Sun-like stars: Epsilon Eridani and Tau Ceti. In this project, which he called Project Ozma, he slowly scanned frequencies close to the 21 cm wavelength for six hours per day from April to July 1960.4  The project was well designed, cheap, simple by today's standards, and unsuccessful.

Soon thereafter, Drake hosted a "search for extraterrestrial intelligence" meeting on detecting their radio signals. The meeting was held at the Green Bank facility in 1961. The equation that bears Drake's name arose out of his preparations for the meeting.

The ten attendees were conference organiser Peter Pearman, Frank Drake, Philip Morrison, businessman and radio amateur Dana Atchley, chemist Melvin Calvin, astronomer Su-Shu Huang, neuroscientist John C. Lilly, inventor Barney Oliver, astronomer Carl Sagan and radio-astronomer Otto Struve.5These participants dubbed themselves "The Order of the Dolphin" (because of Lilly's work on dolphin communication), and commemorated their first meeting with a plaque at the observatory hall.67

# Usage

The defaults for this equation use the maximum values stated by Drake and his colleagues in 1961.

 R_"*" 1/year (1 star formed per year, on the average over the life of the galaxy) f_p 0.5 (one half of all stars formed will have planets) n_e 5 (stars with planets will have 5 planets capable of developing life) f_l 1 (100% of these planets will develop life) f_i 1 (100% of which will develop intelligent life) f_c 0.2 (20% of which will be able to communicate) L 100,000,000 years