some guy made this up back in 1961 and supposedly many scientists hold this equation to be second only to Einstein's E=mc^2 in the 20th century. check it out.
"The Drake Equation, as far as mathematical equations go, is quite simple. It consists of a string of unknowns multiplied by each other - that's it, no integration, no differentiation, nothing more difficult that multiplication. This means that the equation is accessible to pretty much everyone. Here it is:
N = R* fp ne f l fi fc L
R* is rate of formation of suitable stars (stars like the Sun) in the Milky Way galaxy
fp is the fraction of those stars that have planets
ne is the number of planets capable of sustaining life around each of those stars having planets
fl is the fraction of planets capable of sustaining life that actually evolve life
fi is the fraction of those planets where live has evolved that evolve intelligent life
fc is the fraction of planets with intelligent life that develop the capability to communicate
L is the fraction of the planet's life during which the intelligent life can communicate"
-interesting stuff, huh? another scientist i dont know who stated that there are other intellegent life forms out there, but that society will eventually destroy itself before they have the technology to contact eachother. it seems very plausible to me