N = The number of communicative civilizations.
R* = The rate of formation of suitable stars.
fp = The fraction of those stars with planets.
ne = The number of Earth-like worlds per planetary system.
fl = The fraction of those Earth-like planets where life actually develops.
fi = The fraction of life sites where intelligence develops.
fc = The fraction of communicative planets (those on which electromagnetic communications technology develops).
L = The "lifetime" of communicating civilizations.
The number of intelligent civilizations currently exist in our galaxy could be between 50,000 and 1,000,000.
If you think that we are alone in the universe, you're crazy.
Alien voice from Saturn ring:
Alien bases on Moon:
Aliens in Area-51:
Liens & Sources :
commenter cet article