Extraterrestrial Life - The Drake Equation

The Drake Equation

In 1961, University of California, Santa Cruz astronomer and astrophysicist Dr. Frank Drake devised the Drake equation. This controversial equation multiplied estimates of the following terms together:

• The rate of formation of suitable stars.
• The fraction of those stars which are orbited by planets.
• The number of Earth-like worlds per planetary system.
• The fraction of planets where intelligent life develops.
• The fraction of possible communicative planets.
• The "lifetime" of possible communicative civilizations.

Criticism of the Drake equation follows mostly from the observation that the terms in the equation are entirely based on conjecture. Thus the equation cannot be used to draw firm conclusions of any kind. Although the Drake equation currently involves speculation about unmeasured parameters, it was not meant to be science, but intended as a way to stimulate dialogue on these topics. Then the focus becomes how to proceed experimentally. Indeed, Drake originally formulated the equation merely as an agenda for discussion at the Green Bank conference.

Drake used the equation to estimate that there are approximately 10,000 planets in the Milky Way galaxy containing intelligent life with the possible capability of communicating with Earth.

Based on observations from the Hubble Space Telescope, there are at least 125 billion galaxies in the observable Universe. It is estimated that at least ten percent of all sun-like stars have a system of planets, i.e. there are 6.25×1018 stars with planets orbiting them in the observable Universe. Even if we assume that only one out of a billion of these stars have planets supporting life, there would be some 6.25×109 (billion) life-supporting planetary systems in the observable Universe.

The apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations is known as the Fermi paradox.