[Belindanan]

http://www.daviddarling.info/encyclo...I_science.html

...According to the Drake Equation, the number of civilizations that might be sending us messages was the product of the rate of star formation, the percentage of stars that form planets, the percentage of those hospitable to life, the percentage of those on which life actually emerges, the percentage of those on which life evolves to become intelligent life, the percentage of those capable of interstellar communication, and the longevity of such civilizations. It is often written as follows:

N = R* fp ne fl fi fc L

Despite its central importance to SETI, the Drake Equation was not the product of studied reflection. As Drake recalled, "I thought we should organize the meeting, and that caused me simply to think about what we needed to discuss – there was not a great deal of profound thought or anything involved in putting it together."12 Even more striking than the casualness with which Drake constructed his equation was the boldness of the conferees' probability estimates for each of its seven variables....